WO2022203031A1 - Thermally conductive resin composition, thermally conductive resin sheet, multilayer heat dissipation sheet, heat-dissipating circuit board, and power semiconductor device - Google Patents

Abstract

The present invention provides a thermally conductive resin sheet which has good withstand voltage performance and good thermal conductivity coefficient, while exhibiting excellent reflow resistance after moisture absorption. A thermally conductive resin composition according to one embodiment of the present invention contains a thermoplastic resin and boron nitride agglomerated particles; and if A1 is the intraparticle pore volume of the boron nitride agglomerated particles and B1 is the interparticle volume, both determined by means of a mercury intrusion method, B1/(A1 + B1) is 0.60 or more. A thermally conductive resin sheet is obtained from this composition. A thermally conductive resin sheet according to another embodiment of the present invention is formed from a resin composition that contains a thermoplastic resin and boron nitride agglomerated particles; with respect to the pore size distribution curve as determined by measurement of the residual ash, which is obtained by heating the thermally conductive resin sheet at 700°C for 5 hours, by means of a mercury intrusion method, if a peak that has the maximum value at a pore diameter of less than 5 μm is taken as the first peak, and a peak that has the maximum value at a pore diameter of not less than 5 μm is taken as the second peak, the second peak top height is 1.0 mL/g or more and the second peak top diameter is 15 μm or more.

Description

THERMALLY CONDUCTIVE RESIN COMPOSITION, THERMAL CONDUCTIVE RESIN SHEET, LAMINATED HEAT DISPERSION SHEET, HEAT DISPERSION CIRCUIT BOARD, AND POWER SEMICONDUCTOR DEVICE

The present invention provides a thermally conductive resin composition, a thermally conductive resin sheet, a laminated heat-dissipating sheet having a configuration in which a heat-dissipating metal layer is laminated on the surface of the heat-conductive resin sheet, and further a conductive circuit is formed. The present invention relates to a heat dissipating circuit board having such a configuration.

In recent years, power semiconductor devices, which are used in various fields such as railways, automobiles, industrial applications, and general home appliances, are shifting from conventional Si power semiconductors to further miniaturization, cost reduction, and higher efficiency. , SiC, AlN, GaN, etc. are shifting to power semiconductors.
A power semiconductor device is generally used as a power semiconductor module in which a plurality of semiconductor devices are arranged on a common heat sink and packaged.

Various issues have been pointed out for the practical use of such power semiconductor devices. One of them is the problem of heat generation from the device. Power semiconductor devices can be operated at high temperatures to achieve high output and high density. On the other hand, there is concern that the heat generated due to switching of the device may reduce the reliability of the power semiconductor device.

In recent years, especially in the electrical and electronic fields, heat generation due to the increasing density of integrated circuits has become a major problem, and how to dissipate heat has become an urgent issue. As one method for solving this problem, a ceramic substrate with high thermal conductivity, such as an alumina substrate or an aluminum nitride substrate, is used as a heat dissipation substrate on which power semiconductor devices are mounted. However, ceramic substrates have problems such as being susceptible to cracking due to impact, and being difficult to thin and miniaturize.

Therefore, a thermally conductive resin sheet containing a resin and an inorganic filler has been studied as a substitute for the ceramic substrate.
Among them, as an inorganic filler, attention is paid to hexagonal boron nitride from the viewpoint of thermal conductivity and the like.
However, since the hexagonal boron nitride particles are tabular, they have high thermal conductivity in the plane direction (ab-axis direction) but low thermal conductivity in the thickness direction (c-axis direction). When this hexagonal boron nitride is mixed with a resin and molded into a sheet, the hexagonal boron nitride tends to be oriented in the flow direction of the resin composition, that is, in the plane direction of the sheet. The thermal conductivity in the direction is high, but the thermal conductivity in the thickness direction is low.

In order to improve the anisotropy of the thermal conductivity of the thermally conductive resin sheet, it has been investigated to reduce the orientation of the particles by using aggregated boron nitride particles obtained by aggregating boron nitride particles.
For example, Patent Documents 1 and 2 propose spherical agglomerates obtained by binding boron nitride particles with a binder and then spray-drying them.
Further, Patent Document 3 proposes hexagonal boron nitride particles in which primary particles of hexagonal boron nitride are aggregated in a pinecone shape.
Furthermore, Patent Document 4 includes spherical secondary particles formed by aggregating scale-like boron nitride, and the density of the primary particles in the core portion of the secondary particles is the density of the primary particles in the shell portion. Granulated flours lower than
Patent Document 5 proposes boron nitride aggregated particles in which primary particles of hexagonal boron nitride are aggregated, and the primary particles in the boron nitride aggregated particles have a card house structure. ing.

JP 2006-257392 A Japanese Patent Publication No. 2008-510878 JP-A-09-202663 JP 2016-044098 A JP 2015-006985 A

With conventional thermally conductive resin sheets, there were cases where the withstand voltage performance and thermal conductivity were not sufficient.

In addition, thermally conductive resin sheets for use in power semiconductor devices are required to have resistance to reflow processes.
A reflow process is one of the processes for assembling a power semiconductor module. In the reflow process, the members are rapidly heated to melt the solder and join the metal members together. In recent years, as the operating temperature of power semiconductor devices has increased with the increase in output and density, heat resistance is required for the solder used in the above reflow process. It is becoming common to use Therefore, in the reflow process, the process of raising the temperature to about 290° C. at which the high-temperature solder flows and then cooling is repeated.
Furthermore, if the member absorbs moisture before performing the reflow process, deterioration of the member is greatly accelerated during the reflow process, and the withstand voltage performance may be greatly reduced.

Accordingly, an object of the present invention is to provide a thermally conductive resin sheet that has good withstand voltage performance and thermal conductivity, and is excellent in moisture absorption reflow resistance.
In this specification, the term "moisture absorption reflow resistance" means that a thermally conductive resin sheet is laminated with a metal plate and stored under high temperature and high humidity conditions (for example, 85 ° C., 85% RH for 3 days). Even after performing a moisture absorption reflow test (for example, 290 ° C), it has high withstand voltage and does not cause deformation due to interfacial peeling from the metal plate and foaming of the thermally conductive resin sheet. Say.

A thermally conductive resin composition according to one aspect of the present invention is a resin composition containing a thermoplastic resin and aggregated boron nitride particles, and the intra-particle pores of the aggregated boron nitride particles are measured by a mercury intrusion method. When the volume is A ₁ and the interparticle volume is B ₁ , B ₁ /(A ₁ +B ₁ ) is 0.60 or more.
Further, a thermally conductive resin sheet according to another aspect of the present invention is a thermally conductive resin sheet made of a resin composition containing a thermoplastic resin and boron nitride aggregated particles, and the thermally conductive resin sheet is heated at 700°C. In the pore size distribution curve obtained by measuring the residual ash content when heated for 5 hours by mercury porosimetry, the first peak is the peak having a maximum value at a pore size of less than 5 μm, and the maximum value at a pore size of 5 μm or more. The second peak has a top height of 1.0 mL/g or more and a second peak top diameter of 15 μm or more.

A thermally conductive resin sheet obtained from the thermally conductive resin composition according to one aspect of the present invention has excellent withstand voltage performance and thermal conductivity, and excellent moisture absorption reflow resistance.
Further, the thermally conductive resin sheet according to another aspect of the present invention also has good withstand voltage performance and thermal conductivity, and is excellent in moisture absorption reflow resistance.

FIG. 2 is a diagram showing the principle of measurement of intra-particle pore volume, inter-particle volume, peak top diameter and peak top height of aggregated boron nitride particles by mercury porosimetry. FIG. 2 is a conceptual diagram of intraparticle pore volume. FIG. 2 is a conceptual diagram of interparticle volume; 1 is a conceptual diagram of a cross-sectional view of a particle according to an example of aggregated boron nitride particles having a small inter-particle volume. FIG. 4 is a SEM photograph (a photograph substituting for a drawing) of a particle surface according to an example of aggregated boron nitride particles having a small inter-particle volume. 1 is a conceptual diagram of a cross-sectional view of a particle according to an example of aggregated boron nitride particles having a large inter-particle volume. FIG. 4 is an SEM photograph (photograph substituting for a drawing) of a particle surface according to an example of aggregated boron nitride particles having a large interparticle volume. It is a schematic diagram of a card house structure. 1 shows an example of a SEM photograph of aggregated boron nitride particles contained in residual ash when the thermally conductive resin sheet of Example 2 was heated at 700° C. for 5 hours.

An example of an embodiment of the present invention will be described in detail below. However, the present invention is not limited to the following embodiments, and various modifications can be made within the scope of the gist of the present invention.

<First embodiment>
1. Resin composition The thermally conductive resin sheet according to the first embodiment of the present invention is a resin composition containing a thermoplastic resin and aggregated boron nitride particles, and the aggregated boron nitride particles are measured by a mercury intrusion method. A thermally conductive resin composition in which B ₁ /(A ₁ +B ₁ ) is 0.60 or more, where A ₁ is the intra-particle pore volume and B ₁ is the inter-particle interstitial volume.
Each component will be described in detail below.

(1) Thermoplastic resin The thermoplastic resin used in the thermally conductive resin composition of the present embodiment has a reduced elastic modulus even under reflow conditions for heat-dissipating circuit boards, such as 290°C for 5 minutes. It is preferable that recovery of flow, plastic deformation, and thermal recovery strain hardly occur. In order to satisfy it, it is preferable that the thermoplastic resin has a glass transition temperature (Tg) of 300° C. or higher or a melting point (Tm) of 300° C. or higher.

When the thermoplastic resin is a resin composition composed of a combination of two or more thermoplastic resins that are compatible with each other, the glass transition temperature (Tg) of the resin composition is 300 ° C. or higher. or the melting point (Tm) of the resin composition is preferably 300° C. or higher.
On the other hand, when the thermoplastic resin is a combination of two or more thermoplastic resins and is a resin composition composed of resins that are not compatible with each other, the glass of the thermoplastic resin that is the main component of the resin composition It is preferable that the transition temperature (Tg) is 300° C. or higher, or the melting point (Tm) of the thermoplastic resin that is the main component of the resin composition is 300° C. or higher.
Here, the “main component” means a resin having the highest content by mass in the resin composition, and is 50% by mass or more, especially 60% by mass or more, especially 70% by mass or more, of the resin composition. A resin that accounts for 80 mass % or more, especially 90 mass % or more, especially 95 mass % or more (including 100 mass %).

From the above viewpoint, the thermoplastic resin may contain an amorphous thermoplastic resin having a glass transition temperature (Tg) of 300°C or higher and/or a crystalline thermoplastic resin having a melting point (Tm) of 300°C or higher. preferable.
Among them, an amorphous thermoplastic resin having a glass transition temperature (Tg) of 300°C or higher and/or a crystalline thermoplastic resin having a melting point (Tm) of 300°C or higher is the main component of the thermoplastic resin, i.e. , preferably accounts for 50% by mass or more of the entire thermoplastic resin. Among them, it is more preferably 60% by mass or more, 70% by mass or more, 80% by mass or more, and 90% by mass or more (including 100% by mass).

In the present invention, "amorphous thermoplastic resin" refers to a thermoplastic resin that does not have a melting point. On the other hand, a "crystalline thermoplastic resin" refers to a thermoplastic resin having a melting point.

Examples of heat-resistant amorphous thermoplastic resins available as commercially available raw materials include polycarbonate resin (Tg: 152°C), modified polyphenylene ether resin (Tg: 211°C), polysulfone resin (Tg: 190°C), polyphenylene ether resin (Tg: 190°C), sulfone resin (Tg: 220°C), polyethersulfone resin (Tg: 225°C), polyetherimide resin (Tg: 217°C), and the like.
However, none of these commercially available heat-resistant non-crystalline thermoplastic resins has a glass transition temperature of 300° C. or higher.
Thermoplastic polyimide resins having a glass transition temperature of 300° C. or higher are also commercially available. However, since the thermoplastic polyimide resin has a very high moldable temperature and a very high melt viscosity at the moldable temperature, it is difficult to fill a large amount of aggregated boron nitride particles. Furthermore, since it contains an imide group in its molecular structure, it is not preferable to be used as the main component of the thermoplastic resin of the present embodiment because of its high hygroscopicity.

From the above, it is preferable that the thermoplastic resin used in the thermally conductive resin composition of the present embodiment is a resin mainly composed of a crystalline thermoplastic resin having a melting point of 300°C or higher. By using a crystalline thermoplastic resin having a melting point of 300° C. or higher as a main component, it is possible to obtain sufficient heat resistance and durability as a substrate for power semiconductor devices. In addition, the moldability is good even when a large amount of boron nitride aggregated particles are filled, and voids inside the sheet generated due to the shape of the aggregated particles and internal voids, and voids inside the sheet generated due to moisture absorption of the resin component or aggregated particles. Since the voids can be sufficiently reduced, the insulating properties are improved. In addition, a crystalline thermoplastic resin having a melting point of 300° C. or higher is resistant to resin flow, plastic deformation, and thermal recovery strain recovery due to a decrease in elastic modulus under reflow conditions. .

The melting point of a thermoplastic resin can be measured by the method specified in JIS K-7121 "Method for measuring transition temperature of plastics-method for determining melting temperature". Specifically, the thermoplastic resin composition is measured using a differential scanning calorimeter (DSC: for example, "DSC-7" manufactured by PerkinElmer Inc.), 10 mg of a sample is used as a test piece, and the heating rate is 10 ° C. The temperature was raised from −40° C. to 380° C. at a rate of 10° C./min, held at 380° C. for 1 minute, then cooled to −40° C. at a cooling rate of 10° C./min, held at the same temperature for 1 minute, and then again 10° C./min. The melting point (Tm) is obtained by reading the temperature (Tpm) at the top of the melting peak when the temperature is raised in minutes.
As the crystalline thermoplastic resin in the present embodiment, at least an endothermic peak due to crystal melting can be clearly confirmed, and the temperature at the top of the main peak among the peaks is 300 ° C. or higher. can be used.
In addition, even when the resin composition to which the boron nitride aggregated particles are added is measured by a differential scanning calorimeter (DSC), the addition of the boron nitride aggregated particles does not accelerate the deterioration of the matrix resin during heat molding. There is no significant difference in melting point between

From the viewpoint of moisture absorption reflow resistance at 290°C, the melting point of the crystalline thermoplastic resin is more preferably 310°C or higher, more preferably 320°C or higher, and even more preferably 330°C or higher. On the other hand, the upper limit of the melting point is not particularly limited. Above all, from the viewpoint of moldability and productivity, the temperature is preferably 380° C. or lower, more preferably 370° C. or lower, and even more preferably 360° C. or lower.

When the melting point of the thermoplastic resin is 300° C. or higher, the elastic modulus of the resin material is less likely to decrease even at 290° C. which is the reflow condition. Therefore, it is possible to suppress the flow deformation of the resin even in the reflow process, and it is difficult to restore the elastic strain of the resin layer. It is possible to obtain a thermally conductive resin sheet having sufficient strength.
In addition, since the elastic modulus of the resin raw material is difficult to decrease at 290 ° C., the resin composition absorbs moisture in a moist heat environment, and even if moisture is present in the resin composition, the reflow process or mounting to the module Since the moisture in the resin composition is less likely to expand during the process and the thermally conductive resin sheet is less likely to foam, the withstand voltage performance and thermal conductivity are improved.

In addition, it is considered that the foaming in the thermally conductive resin sheet in the reflow process, the withstand voltage performance, and the thermal conductivity are related, for example, as follows.
When the moisture in the resin composition expands due to the reflow process or the mounting process to the module, the inside of the thermally conductive resin sheet, the vicinity of the interface between the metal layer for heat radiation and the thermally conductive resin sheet, or the conductive circuit pattern and the thermally conductive resin Foaming may occur near the interface with the sheet.
For example, if foaming occurs inside the thermally conductive resin sheet, there is a risk that the withstand voltage performance will drop significantly.
When a heat-dissipating metal material is laminated on one surface of a thermally conductive resin sheet, if foaming occurs in the vicinity of the interface between the heat-dissipating metal material and the heat-conductive resin sheet, the heat-dissipating metal material There is a risk that it will peel off and the thermal conductivity will drop significantly.
In addition, when a conductive circuit pattern is formed on the other surface of the thermally conductive resin sheet, if foaming occurs near the interface between the conductive circuit pattern and the thermally conductive resin sheet, the conductive circuit pattern will peel off. There is a possibility that the heat conductive resin sheet may drop or come off, causing an abnormality in the electric circuit or significantly lowering the heat conductivity of the heat conductive resin sheet.

Specific examples of heat-resistant crystalline thermoplastic resins include polybutylene terephthalate resin (PBT, melting point: 224°C), polyamide 6 (nylon 6, melting point: 225°C), polyamide 66 (nylon 66, melting point: 265°C). ), liquid crystal polymer (LCP, melting point: 320°C to 344°C), polyetherketone resin (melting point: 303°C to 400°C), polytetrafluoroethylene resin (PTFE, melting point: 327°C), tetrafluoroethylene Perfluoroalkoxyethylene copolymer resin (PFA, melting point: 302° C. to 310° C.), ethylene tetrafluoride/propylene hexafluoride copolymer resin (FEP, melting point: 250° C. to 290° C.), and the like.

As the crystalline thermoplastic resin used in the present embodiment, liquid crystal polymer, polyetherketone resin, PTFE, and PFA are preferable because they have a melting point of 300° C. or higher.
Among these crystalline thermoplastic resins having a melting point of 300° C. or higher, liquid crystal polymers and/or polyetherketone resins are particularly preferable from the viewpoint of moldability. Among them, polyetherketone-based resins are preferable from the viewpoint of adhesiveness to heat-dissipating metal layers such as copper plates.

The polyetherketone-based resin that can be used in the present embodiment is a general term for thermoplastic resins having a repeating unit represented by the following formula (1) (in which m and n are 1 or 2).

Polyetherketone resins include polyetherketone (PEK; m = 1, n = 1, melting point 373°C), polyetheretherketone (PEEK; m = 2, n = 1, melting point 343°C), polyetherketone Ketone (PEKK; m = 1, n = 2, melting point 303°C to 400°C), polyetheretherketoneketone (PEEKK; m = 2, n = 2, melting point 358°C), polyetherketoneetherketoneketone (PEKEKK; A copolymer containing both a structural unit of m=1, n=1 and a structural unit of m=1, n=2, melting point of 387° C.) can be exemplified. Both are available as commercial raw materials.

Among polyetherketone resins, it has a sufficiently high melting point and a relatively low molding temperature, which shortens the molding cycle. It has the most chemically stable structure among polyetherketone-based resins, and has excellent hot water resistance and chemical resistance. Polyether ether ketone (PEEK) can be particularly preferably used in consideration of the points and the point that the price has come down due to its use in a wide range of applications.

When polyetheretherketone (PEEK) is used as the crystalline thermoplastic resin of this embodiment, it may be blended with other thermoplastic resins.
The type of other thermoplastic resin is not particularly limited. Among others, as the other thermoplastic resin, a compatible resin having an effect of compensating for insufficient performance when only polyetheretherketone is used for the application of the present embodiment is preferable.

Polyetherimide (PEI) is more preferable as the compatible resin.
By combining PEEK and PEI, it is possible not only to adjust the crystallinity of PEEK (the amount of heat of crystal fusion), but also to adjust the crystallization rate of PEEK together with glass when the resin composition is in an amorphous state. The transition temperature can be increased (PEEK has a Tg of 143° C. vs. PEI of 217° C.).
Since PEI is an amorphous resin, even if PEEK and PEI are combined, the melting point of the resin does not change.
In addition, in this embodiment, by using PEI that has an imide group and is amorphous, it is possible to improve the adhesiveness to a metal material for heat dissipation such as a copper plate.

The amount of PEI added is preferably 50% by mass or less when the total amount of the resin composition is 100% by mass. When the amount of PEI added is 50% by mass or less, the heat resistance in the moisture absorption reflow test can be maintained by the crystallinity of PEEK, and the adhesiveness to the metal material for heat dissipation can be improved.

Various commercial products can be used for PEEK. For example, "KetaSpire (registered trademark)" manufactured by Solvay, "Vestakeep (registered trademark)" manufactured by Daicel-Evonik, "Victrex PEEK" manufactured by Victrex, etc. can be obtained from various companies with various melt viscosities. I can.
A single grade may be used for these PEEK raw materials, and multiple grades having different melt viscosities may be blended and used.

The melt viscosity of the crystalline thermoplastic resin in this embodiment is not particularly limited. Above all, the melt viscosity of the crystalline thermoplastic resin is preferably 0.60 kPa·s or less, and 0.60 kPa. 30 kPa·s or less is more preferable. When the melt viscosity is within the above range, it is not necessary to set the temperature of the molding machine excessively high, and deterioration of the raw material can be suppressed. On the other hand, the lower limit of the melt viscosity is not particularly limited. Among them, 0.01 kPa·s or more is preferable.
The melt viscosity is based on ASTM D3835 and is a value measured under conditions of a shear rate of 1000 s ^-1 and a temperature of 400°C.

The mass average molecular weight (Mw) of the crystalline thermoplastic resin is preferably 48,000 or more, more preferably 49,000 or more, and more preferably 50,000 or more, from the viewpoint of long-term durability in a heated environment. On the other hand, from the viewpoint of moldability, it is preferably 120,000 or less, more preferably 110,000 or less, and more preferably 100,000 or less.

The MFR of the crystalline thermoplastic resin is preferably 8 g/10 min or more, especially 9 g/10 min or more, from the viewpoint of moldability and difficulty in forming voids between the added boron nitride aggregate particles. Among them, it is more preferably 10 g/10 minutes or more. On the other hand, from the viewpoint of long-term durability in a heated environment, it is preferably 180 g/10 minutes or less, more preferably 170 g/10 minutes or less, and more preferably 160 g/10 minutes or less.
The MFR is a value measured at 380°C and 5 kgf according to JIS K7210:2014.

(2) Aggregated boron nitride particles In the aggregated boron nitride particles of the present embodiment, when the intra-particle pore volume of the boron nitride aggregated particles is measured by a mercury intrusion method and the inter _- particle volume is B ₁ , B ₁ /(A ₁ +B ₁ ) is preferably 0.60 or more.
In the present invention, the intra-particle pore volume and the inter-particle volume of the aggregated boron nitride particles are determined according to JIS R1655:2003 by the method described in the Examples.
Specifically, first, 200 mg of aggregated boron nitride particles are prepared, and a mercury intrusion exit curve is measured by a mercury intrusion method. Next, as exemplified in FIG. 1, a pore size distribution curve is created with the pore size on the horizontal axis and the logarithmic differential pore volume on the vertical axis. Usually less than 5 μm, preferably in the range of 0.1 μm or more and less than 5 μm, peak a derived from intraparticle pores is observed, and usually 5 μm or more, preferably in the range of 5 μm or more and 100 μm or less, peak b derived from interparticle pores is seen. Between these peaks a and b, the diameter (division diameter, X in FIG. 1) at which the logarithmic differential pore volume takes the minimum value with respect to the pore diameter is read. The interparticle volume is the integrated value of the mercury intrusion withdrawal curve in the region (broken line arrow in FIG. 1) where the pore diameter is larger than the division diameter.
In addition, the integrated value of the mercury intrusion exit curve in the entire measurement region is the total pore volume, and the intraparticle pore volume is obtained by subtracting the interparticle volume from the total pore volume.

In FIG. 2, the intraparticle pore volume is obtained by excluding closed pores into which mercury is not injected among the pores α existing inside the aggregated particles. This intraparticle pore volume is a numerical value determined by the denseness of the boron nitride primary particles that constitute the aggregated particles, the average aspect ratio, the particle thickness, etc., and the mechanical properties of the boron nitride aggregated particles and the heat conduction inside the aggregated particles Involved in sexuality, etc.
When the intraparticle pore volume is moderately reduced, there are not too many voids that increase the thermal resistance in the aggregated particles, so there is a tendency that the heat conduction inside the aggregated particles can be efficiently enhanced. Furthermore, the strength of the aggregated particles can be increased. For example, even when a sheet is produced by press molding, the aggregated particles themselves do not crush or undergo excessive deformation, and the isotropy of the aggregated particles is maintained. Therefore, it is possible to effectively prevent a decrease in thermal conductivity in the thickness direction of the thermally conductive resin sheet.
On the other hand, when the intra-particle pore volume is moderately increased, it is possible to sufficiently ensure the penetration of the resin into the internal pores of the aggregated particles, and it is possible to suppress the generation of voids in the thermally conductive resin sheet. tend to be better.

From the above viewpoints, the intraparticle pore volume A1 is preferably 0.30 mL _/ g or more, more preferably 0.35 mL/g or more, still more preferably 0.40 mL/g or more, and more preferably 0.42 mL/g or more. More preferred. In addition, the intra _- particle pore volume A1 is preferably 0.80 mL/g or less, more preferably 0.70 mL/g or less, still more preferably 0.60 mL/g or less, even more preferably 0.55 mL/g or less, 0.50 mL/g or less is particularly preferred.

The particle interstitial volume is the pores β existing between a plurality of agglomerated particles in FIG. However, with respect to the boron nitride aggregated particles, in addition to the above, the orientation state of the primary particles on the surface of the aggregated particles (the primary particle surface is oriented in the radial direction of the aggregated particles, or the primary particle (whether the surface is oriented, etc.), the denseness of the surface primary particles, the average aspect ratio, the particle thickness, etc., and the denseness and average aspect ratio of the primary particles that make up the entire aggregated particles. and particle thickness. This is because if the size of the primary particles is too large and lacks denseness, etc., the strength of the aggregated particles themselves will be insufficient, and during various operations before blending with the resin, the particles will be broken, or , The surface primary particles fall off, and the crushed pieces of the particles generated by the crushing and the isolated primary particles fill the gaps between the aggregated particles during the mercury porosimetry measurement.

Here, the interparticle volume will be described in more detail with reference to FIGS. 4 to 7. FIG.
For example, as shown in FIGS. 4 and 5, when the thickness direction (c-axis direction) of the primary particles near the outermost surface of the aggregated particles has a structure in which the radial direction of the aggregated particles coincides, the interparticle volume is small. tend to become Such agglomerated particles have good coatability when a thermally conductive resin sheet is produced by a wet coating method, and have the advantage that it is easy to obtain a sheet with few residual voids. Since the particles lie so as to cover the aggregated particles, the thermal resistance at the interface between the surface of the aggregated particles and the resin or at the contact interface between a plurality of aggregated particles may increase.
Also. When a plurality of aggregated particles are filled in the thermally conductive resin sheet so as to be in contact with each other, the aggregated particles shown in FIGS. ) to conduct heat. Since the thermal conductivity in the thickness direction of the primary particles is low, there is a limit to the thermal conductivity in the thickness direction of the thermally conductive resin sheet.
Further, for example, when the primary particles constituting the aggregated particles are excessively large and lack denseness, the interparticle volume becomes small. Since such agglomerated particles lack strength, for example, when a sheet is produced by press molding, the agglomerated particles may break or surface primary particles may fall off. Since the isolated primary particles are tabular or scale-like, the thickness direction (c-axis direction) of the particles is oriented in the surface direction of the sheet, and the thermal conductivity in the thickness direction of the thermally conductive resin sheet is reduced. Sometimes.

On the other hand, for example, as shown in FIGS. 6 and 7, the aggregated particles have a structure in which the plane direction (ab-axis direction) of the primary particles near the outermost surface coincides with the radial direction of the aggregated particles. When the surface primary particles are densely present, the inter-particle volume tends to be large.
When such agglomerated particles are packed so that a plurality of agglomerated particles are in contact with each other in the thermally conductive resin sheet, compared to the agglomerated particles in which the primary particles near the outermost surface lie so as to cover the agglomerated particles, the particles The contact area between them increases. Therefore, the thermal resistance between particles is reduced, so that the thermal conductivity in the thickness direction of the thermally conductive resin sheet is increased. In addition, when the inter-particle volume is large, if the intra-particle pore volume, average particle size and particle size distribution are the same, the contact surface of a plurality of agglomerated particles will be as shown in FIG. , the contact area increases so that the polyhedrons come into contact with each other, forming a surface contact-like state, further reducing the thermal resistance between the particles.
Further, for example, when the primary particles constituting the aggregated particles are appropriately small and dense, the interparticle volume also increases. Since such aggregated particles have good strength, it is possible to prevent breakage of the aggregated particles during molding and falling off of surface primary particles. Therefore, since isolation of the primary particles can be suppressed, the thermal conductivity in the thickness direction of the thermally conductive resin sheet can be improved.

From the above viewpoints, the particle interstitial volume _B1 is preferably 0.50 mL/g or more, more preferably 0.55 mL/g or more, still more preferably 0.60 mL/g or more, and even more preferably 0.65 mL/g or more. . Furthermore, it is preferably 0.70 mL/g or more, more preferably 0.75 mL/g or more, still more preferably 0.80 mL/g or more, and even more preferably 0.85 mL/g or more. Also, the interparticle volume _B1 is preferably 1.0 mL/g or less, more preferably 0.95 mL/g or less, and even more preferably 0.90 mL/g or less.

B ₁ /(A ₁ +B ₁ ) in this embodiment indicates the ratio of interparticle volume to total pore volume. B ₁ /(A ₁ +B ₁ ) is preferably 0.60 or more, more preferably 0.62 or more, still more preferably 0.64 or more, and even more preferably 0.66 or more. In addition, B ₁ /(A ₁ +B ₁ ) is preferably less than 1.00, more preferably 0.90 or less, still more preferably 0.80 or less, even more preferably 0.75 or less, especially 0.70 or less preferable.
As described above, the strength of agglomerated particles represented by the intra-particle pore volume and inter-particle volume, the orientation state of primary particles, and the like affect the withstand voltage performance and thermal conductivity. The inventors have found that the balance between intraparticle pore volume and interparticle volume affects these.
More specifically, when B ₁ /(A ₁ +B ₁ ) is within the above range, the aggregated particles have sufficient strength, so that the aggregated particles can be prevented from collapsing during molding, etc. Since the primary particles on the surface of the particles are radially oriented, sufficient heat conduction paths can be formed between the aggregated particles. In addition, when B ₁ /(A ₁ +B ₁ ) is within the above range, the interior of the aggregated particles is dense and the structure with isotropic thermal conductivity is maintained, while the primary particles on the surface of the aggregated particles The radially oriented region deforms moderately during molding, so to speak, so to speak, has a structure of "internally hard and externally soft", so that the contact area between adjacent aggregated particles increases, and the thermally conductive resin sheet The thermal conductivity in the thickness direction can be further increased.
In addition, when B ₁ /(A ₁ +B ₁ ) is within the above range, the inside of the aggregated particles is dense, and the resin sufficiently penetrates into the particles, so that the generation of voids during molding can be suppressed. It is also possible to further improve the withstand voltage performance.

Examples of aggregated particles of boron nitride having B ₁ /(A ₁ +B ₁ ) of 0.60 or more include aggregated particles having a card house structure. Further, after obtaining aggregated boron nitride particles by a known method, physical or chemical surface roughening treatment is performed so that B ₁ /(A ₁ +B ₁ ) is 0.60 or more. good too.
Agglomerated boron nitride particles commercially available from various companies use primary particles of boron nitride that are relatively crystallized during granulation, so stable primary particle planes (ab planes) are preferentially stacked. Therefore, many of them have a “cabbage structure” in which the thickness direction of the primary particles near the outermost surface of the aggregated particles coincides with the radial direction of the aggregated particles. Aggregated particles having a “cabbage structure” lie so that the primary particles near the outermost surface cover the aggregated particles, so B ₁ /(A ₁ +B ₁ ) is unlikely to be 0.60 or more. Therefore, when using agglomerated particles having a “cabbage structure”, it is preferable to perform the above-described roughening treatment for adjustment.

The shape of the aggregated boron nitride particles of the present embodiment is preferably spherical.
"Spherical" means that the aspect ratio (ratio of major axis to minor axis) is usually 1 or more and 2 or less, preferably 1 or more and 1.75 or less, more preferably 1 or more and 1.5 or less, further preferably 1 or more and 1.4 or less. It means that:
The aspect ratio is obtained by arbitrarily selecting 200 or more particles from an image of the cross section of the thermally conductive resin sheet taken with a scanning electron microscope (SEM), calculating the ratio of the major axis to the minor axis of each, and calculating the average value. It can be obtained by calculating.

In addition, the “circularity” measured using a particle image analyzer (Mofologi G3S, manufactured by Malvern) may be used as an index of “spherical”. In this measurement, a projection plane image (two-dimensional image) of particles is observed. By increasing the number of measurements and averaging them, it is possible to evaluate the "sphericity" degree.
The circularity is preferably 0.90 or more, more preferably 0.92 or more, still more preferably 0.94 or more, and even more preferably 0.96 or more, with 1 being the upper limit.

The aggregated structure of the boron nitride aggregated particles is preferably a card house structure from the viewpoint of improving thermal conductivity.
The aggregate structure of the aggregated boron nitride particles can be confirmed with a scanning electron microscope (SEM).

The card house structure is a structure in which tabular particles are not oriented and are intricately laminated, and is described in "Ceramics 43 No. 2" (published by the Ceramic Society of Japan, 2008). More specifically, the plane portion of the primary particle forming the aggregated particle and the end surface portion of the other primary particle present in the aggregated particle are firmly bonded or joined, and the scaly or flat plate-like It refers to a structure in which each primary particle is present in aggregated particles in random directions. A schematic diagram of the card house structure is shown in FIG.
Aggregated particles having a card house structure have a very high breaking strength due to having the above structure and having a relatively high degree of sphericity as aggregated particles. It does not collapse even in the pressurizing process. Therefore, the primary particles, which are normally oriented in the longitudinal direction of the thermally conductive resin sheet, can be present in random directions. Therefore, the use of agglomerated particles having a card house structure can increase the proportion of the ab planes of the primary particles oriented in the thickness direction of the thermally conductive resin sheet, thereby effectively conducting heat in the thickness direction of the sheet. It is possible to further increase the thermal conductivity in the thickness direction.

The aggregated boron nitride particles having a card house structure can be produced, for example, by the method described in International Publication No. 2015/119198. It is preferable that the boron nitride agglomerated particles in the present embodiment are not subjected to a treatment such as a ball mill that applies a force to the surface.

When using aggregated boron nitride particles having a card house structure, the particles may be surface-treated with a surface-treating agent.
As the surface treatment agent, for example, a known surface treatment agent such as silane coupling treatment can be used. In general, there is often no direct affinity or adhesion between the boron nitride aggregated particles and the thermoplastic resin, and this is also the case when the boron nitride aggregated particles having a card house structure are used. is. It is believed that the attenuation of thermal conductivity at the interface can be further reduced by increasing the adhesion at the interface between the aggregated boron nitride particles and the matrix resin by chemical treatment.

The aggregated boron nitride particles of the present embodiment can have a larger particle size than when the primary particles are used as they are.
By increasing the particle size of the aggregated boron nitride particles, the heat transfer paths between the aggregated boron nitride particles via the thermoplastic resin with low thermal conductivity can be reduced, and the heat resistance in the heat transfer paths in the thickness direction can be reduced. Increase can be reduced.

From the above viewpoint, the lower limit of the volume-based maximum particle diameter Dmax (hereinafter also referred to as “maximum particle diameter”) of the boron nitride aggregated particles is preferably 20 μm or more, more preferably 30 μm or more, and still more preferably 50 μm. That's it. On the other hand, the upper limit of the maximum particle size Dmax is preferably 300 µm or less, more preferably 200 µm or less, still more preferably 100 µm or less, and even more preferably 90 µm or less.

In addition, the lower limit of the volume-based average particle diameter D50 of the aggregated boron nitride particles is preferably 10 μm or more, more preferably 20 μm or more, and still more preferably 30 μm or more. On the other hand, the upper limit of the average particle diameter D50 is preferably 200 µm or less, more preferably 100 µm or less, still more preferably 80 µm or less, and even more preferably 60 µm or less.

Since the maximum particle size of the boron nitride aggregated particles is equal to or less than the above upper limit, when the boron nitride aggregated particles are contained in the matrix resin, the interface between the matrix resin and the boron nitride aggregated particles is reduced, resulting in a small thermal resistance. As a result, it is possible to achieve high thermal conductivity and to form a high-quality film free from surface roughness. When the maximum particle size is equal to or greater than the above lower limit, a sufficient effect of improving thermal conductivity as boron nitride aggregated particles required for power semiconductor devices can be obtained.

In addition, the effect of the thermal resistance at the interface between the matrix resin and the aggregated boron nitride particles on the thickness of the thermally conductive resin sheet becomes significant because the size of the aggregated boron nitride particles relative to the thickness of the thermally conductive resin sheet is 1. /10 or less. Especially for power semiconductor devices, thermally conductive resin sheets with a thickness of 100 μm to 300 μm are often applied. It is preferably larger than the above lower limit.
Further, when the maximum particle diameter Dmax of the aggregated boron nitride particles is at least the above lower limit, not only is the increase in thermal resistance caused by the interface between the aggregated boron nitride particles and the matrix resin suppressed, but also the required inter-particle The number of thermally conductive paths decreases, and the probability of connecting from one surface to the other surface in the thickness direction of the thermally conductive resin sheet increases.
Furthermore, since the maximum particle diameter Dmax of the aggregated boron nitride particles is equal to or greater than the above lower limit, the interface area between the matrix resin and the aggregated boron nitride particles is smaller than when the same mass of particles having Dmax smaller than the above lower limit is used. Therefore, it is possible to reduce the occurrence of voids that are likely to occur at the interface between the matrix resin and the aggregated boron nitride particles in the thermally conductive resin sheet, and it is easy to obtain excellent withstand voltage characteristics.
On the other hand, when the volume-based maximum particle diameter Dmax of the boron nitride aggregated particles is equal to or less than the above upper limit, protrusion of the boron nitride aggregated particles to the surface of the thermally conductive resin sheet is suppressed, and a good surface without surface roughness is obtained. Since the shape can be obtained, when producing a sheet bonded to a copper substrate, it has sufficient adhesion and excellent withstand voltage characteristics can be obtained.

The ratio (Dmax/thickness) of the size (Dmax) of the aggregated boron nitride particles to the thickness of the thermally conductive resin sheet is preferably 0.3 or more and 1.0 or less, more preferably 0.35 or more or 0.35 or more. 95 or less, more preferably 0.4 or more or 0.9 or less.

The maximum particle size Dmax and average particle size D50 of the aggregated boron nitride particles can be measured, for example, by the following methods.
A sample obtained by dispersing aggregated boron nitride particles in a solvent, specifically, a sample obtained by dispersing aggregated boron nitride particles in a pure water medium containing sodium hexametaphosphate as a dispersion stabilizer, was analyzed using a laser diffraction/scattering formula. The particle size distribution is measured with a particle size distribution analyzer LA-920 (manufactured by HORIBA, Ltd.), and the maximum particle size Dmax and average particle size D50 of the aggregated boron nitride particles can be obtained from the obtained particle size distribution.
The maximum particle size and average particle size can also be obtained with a dry particle size distribution analyzer such as Morphologi G3S (manufactured by Malvern).
Regarding the maximum particle diameter Dmax and the average particle diameter D50 of the boron nitride aggregated particles added to the thermoplastic resin, the thermoplastic resin is dissolved and removed in a solvent (including a heated solvent), or the boron nitride aggregated particles are swollen. It is possible to measure by the same method as described above by physically removing after reducing the adhesion strength with the resin component, and further removing by heating the resin component in the atmosphere to incinerate it.

(3) Content of Each Component The lower limit of the content of the thermoplastic resin in 100% by mass of the resin composition of the present embodiment is preferably 15% by mass or more, more preferably 20% by mass or more. On the other hand, the upper limit of the thermoplastic resin content is preferably 40% by mass or less, more preferably 35% by mass or less.
Moreover, the lower limit of the content of the aggregated boron nitride particles in 100% by mass of the resin composition of the present embodiment is preferably 60% by mass or more, more preferably 65% by mass or more. On the other hand, the upper limit of the content of aggregated boron nitride particles is preferably 85% by mass or less, more preferably 80% by mass or less.
When the content of the aggregated boron nitride particles is at least the above lower limit, the effect of improving the thermal conductivity and the effect of controlling the coefficient of linear expansion by the aggregated boron nitride particles are exhibited satisfactorily. On the other hand, when the content of the aggregated boron nitride particles is equal to or less than the upper limit, moldability of the resin composition and interfacial adhesiveness with different materials are improved.

In general, the mixing ratio of the thermally conductive resin composition is often defined by the volume fractions of the matrix resin and the aggregated boron nitride particles (therefore, the area ratio in the cross section of the thermally conductive resin sheet). . Regarding the thermal conductivity in the thickness direction of the thermally conductive resin sheet, it is not determined only by the volume fraction, but various factors such as the above-mentioned preferable particle size, particle orientation state, particle shape, etc. are involved. Therefore, in the present invention, the mass fraction is used for the convenience of actual formulation.
In particular, when aggregated particles of boron nitride having a house-of-cards structure are used, the internal structure of the particles exhibits a house-of-cards structure, and on the surfaces of the particles, plate-like primary particles of boron nitride oriented in the radial direction are formed in a so-called burr-like shape. Alternatively, a large number of protrusions called confetti are formed, and the protrusions of adjacent card house structure particles come into physical contact with each other, forming a heat transfer path with low thermal resistance in the thickness direction. will do. Therefore, it may not be easy to determine the respective volume fractions of the matrix resin and the aggregated boron nitride particles by observation with a normal scanning electron microscope (SEM). Furthermore, when the addition amount of the boron nitride agglomerated particles having a house-of-cards structure having the characteristics of the present invention is increased, the particles come into contact with each other as spherical particles due to the pressure applied during hot press molding of the resin composition. It is observed that the portions where the particles are in contact with each other are deformed instead of the point contact, and the contact portions are in linear, that is, planar contact. In such a contact state, the addition of boron nitride having a card house structure enables efficient formation of a thermal conduction path. However, even in such a case, it is not easy to determine the volume fractions of the matrix resin and the aggregated boron nitride particles by SEM observation.

The resin composition of the present embodiment may contain other components in addition to the thermoplastic resin and the aggregated boron nitride particles. However, from the viewpoint of enhancing thermal conductivity, it is preferable not to contain other components.
Other ingredients include phosphorus-based, phenol-based and other antioxidants, phenol-acrylate-based process stabilizers, heat stabilizers, hindered amine-based radical scavengers (HAAS), impact modifiers, processing aids, and metal inerts. Additives such as activators, copper damage inhibitors, antistatic agents, flame retardants, and silane coupling agents that improve the affinity of the interface between boron nitride aggregate particles and thermoplastic resins, as well as resins such as silane coupling agents. Additives, extenders, and the like, which can be expected to have the effect of increasing the adhesion strength between the sheet and the metal plate material, can be mentioned. When these additives are used, the amount to be added may be within the range of amounts normally used for these purposes.

2. Thermally Conductive Resin Sheet The thermally conductive resin sheet of the present embodiment is made of the resin composition described above, has excellent moisture absorption reflow resistance, and is less prone to interfacial peeling due to thermal expansion and thermal contraction when formed into a laminate with a metal plate. It has the characteristics of

The thermal conductivity in the thickness direction of the thermally conductive resin sheet at 25° C. is preferably 16 W/m·K or more, more preferably 18 W/m·K or more, and 19 W/m·K or more. It is more preferably 20 W/m·K or more. Since the thermal conductivity in the thickness direction is equal to or higher than the above lower limit, it can be suitably used for power semiconductor devices and the like that operate at high temperatures.
The thermal conductivity is the type and melt viscosity of the thermoplastic resin, the value of B ₁ / (A ₁ + B ₁ ) of the boron nitride aggregated particles, the structure and content, the thermoplastic resin and the boron nitride aggregated particles It can be adjusted by the mixing method, the conditions in the heating and kneading step described later, and the like.

Incidentally, the thermal conductivity can be measured by the following method.
First, the thermal diffusivity a (mm ² /sec) in the thickness direction of the resin sheet at a measurement temperature of 25° C. is measured by the laser flash method. Since there is no JIS standard for thermal diffusivity and thermal conductivity in resin materials, measure in accordance with JIS R1611:2010 (Method for measuring thermal diffusivity, specific heat capacity, and thermal conductivity of fine ceramics by flash method). .
Since JIS R1611:2010 specifies that "the thickness of the sample is 0.5 mm or more and 5 mm or less", the thickness of the resin sheet is adjusted to 0.5 mm or more for measurement. When the thickness of the resin sheet is less than 0.5 mm, a plurality of sheets may be stacked to adjust the total thickness to 0.5 mm or more for measurement.
Next, according to JIS K6268, the density ρ (g/m ³ ) of the resin sheet is determined by the Archimedes method.
Furthermore, according to JIS K7123, the specific heat capacity c (J/(g·K)) at 25° C. is measured using a DSC measuring device.
From these measured values, the thermal conductivity in the thickness direction of the sheet at 25° C. can be obtained as "H=a×ρ×c".

The lower limit of the thickness of the thermally conductive resin sheet is preferably 50 µm or more, more preferably 60 µm or more, and even more preferably 70 µm or more. On the other hand, the upper limit of the thickness is preferably 300 µm or less, more preferably 200 µm or less, and even more preferably 160 µm or less.
By setting the thickness of the thermally conductive resin sheet to 50 μm or more, sufficient withstand voltage characteristics can be ensured. On the other hand, by making it 300 μm or less, it is possible to achieve miniaturization and thinning, especially when the thermally conductive resin sheet is used for a power semiconductor device, etc., and compared to an insulating thermally conductive layer made of a ceramic material. , the effect of reducing thermal resistance in the thickness direction by thinning can be obtained.

In the thermally conductive resin sheet of the present embodiment, in order to reduce the anisotropy of thermal conductivity and increase the thermal conductivity in the thickness direction, it is possible to reduce the orientation of the primary particles of the aggregated boron nitride particles. preferable.
Regarding the orientation of the primary particles, the diffraction peak intensity of the (002) plane is I (002), and the diffraction peak intensity of the (100) plane is I (100 ), the evaluation can be performed by obtaining the ratio “I(002)/I(100)”.
The ratio "I(002)/I(100)" is preferably 20 or less, more preferably 17 or less, even more preferably 15 or less. When the above ratio exceeds 20, the boron nitride aggregated particles are collapsed in the melt-kneading process, or the boron nitride aggregated particles are excessively crushed in the press molding process, parallel to the surface direction of the thermally conductive resin sheet, Alternatively, the number of primary particles having small angles is increased. In this case, even if the content of the aggregated boron nitride particles is increased, it is difficult to increase the thermal conductivity in the thickness direction.
The lower limit of the ratio "I(002)/I(100)" is not particularly limited. For example, when using boron nitride agglomerated particles having a card house structure in which the boron nitride primary particles are highly isotropic and therefore have very little orientation in a specific direction, the ratio "I (002) / I (100)” is about 4.5 to 6.6, so 4.5 is considered to be the lower limit except for the case of intentional alignment operation.

In the thermally conductive resin sheet of the present embodiment, regarding the boron nitride aggregated particles contained in the residual ash when heated at 700 ° C. for 5 hours, the intra-particle pore volume measured by mercury porosimetry is defined as _A2 , and the inter-particle volume is B ₂ , A ₂ /A ₁ is preferably 0.70 or more and B ₂ /B ₁ is preferably 0.85 or less.
The fact that A ₂ /A ₁ is 0.70 or more indicates that the state of the primary particles inside the aggregated particles does not change significantly before and after sheet molding, and therefore the strength of the aggregated particles is relatively high. . Therefore, the fact that A ₂ /A ₁ is 0.70 or more means that the structure that forms a thermally conductive path inside the original boron nitride aggregated particles is sufficiently maintained even after sheet molding. be. In addition, it can be said that the generation of isolated primary particles due to crushing of aggregated particles is small even though deformation due to pressurization is applied during molding. The reduced generation of isolated primary particles has the effect of reducing the heat resistance in the thickness direction of the sheet. The reason why the isolated primary particles hinder efficient heat conduction in the thickness direction is that the primary particles are tabular or scaly particles. This is for orientation in the plane direction of the sheet.
On the other hand, the fact that B ₂ /B ₁ is 0.85 or less indicates that relatively large deformation occurs on the surface of the aggregated particles before and after sheet formation. As shown in FIG. 9, this deformation is due to the fact that the contact surfaces of a plurality of agglomerated particles increase in contact area such that polyhedrons are in contact with each other, forming a surface contact-like state.
Therefore, when the aggregated boron nitride particles are present in the sheet with both A ₂ /A ₁ and B ₂ /B ₁ satisfying the above numerical ranges, high thermal conductivity can be obtained.

From the above viewpoint, A ₂ /A ₁ is preferably 0.70 or more, more preferably 0.72 or more, still more preferably 0.75 or more, and even more preferably 0.80 or more. Also, A ₂ /A ₁ is preferably 1.0 or less, more preferably 0.90 or less, and even more preferably 0.88 or less.
On the other hand, B ₂ /B ₁ is preferably 0.85 or less, more preferably 0.80 or less, still more preferably 0.75 or less, and even more preferably 0.70 or less. Furthermore, it is preferably 0.65 or less, more preferably 0.60 or less, and even more preferably 0.50 or less. Also, B ₂ /B ₁ is preferably 0.40 or more, more preferably 0.45 or more.

The intra-particle pore volume _A2 of the boron nitride aggregated particles contained in the residual ash is preferably 0.20 mL/g or more, more preferably 0.25 mL/g or more, further preferably 0.30 mL/g or more, and 0.32 mL /g or more is more preferable, and 0.34 mL/g or more is particularly preferable. In addition, the intraparticle pore volume _A2 is preferably 0.60 mL/g or less, more preferably 0.50 mL/g or less, even more preferably 0.45 mL/g or less, and even more preferably 0.40 mL/g or less.

_The interparticle volume B2 of the boron nitride aggregated particles contained in the residual ash is preferably 0.35 mL/g or more, more preferably 0.40 mL/g or more, still more preferably 0.45 mL/g or more, and 0.50 mL/g. The above is even more preferable. In addition, the interparticle _volume B2 is preferably 0.80 mL/g or less, more preferably 0.70 mL/g or less, and even more preferably 0.65 mL/g or less.

In addition, the circularity of the aggregated boron nitride particles contained in the residual ash is preferably 0.85 or more, more preferably 0.90 or more, even more preferably 0.92 or more, and even more preferably 0.94 or more.

3. Method for Producing Thermally Conductive Resin Sheet An example of the method for producing the thermally conductive resin sheet of the present embodiment will be described below.
As an example of the method for producing the thermally conductive resin sheet of the present embodiment, for example, a method including a mixing step and a press molding step can be given.

As a conventional manufacturing method, there is a method (wet coating method) of obtaining a thermally conductive resin film by coating a substrate with a slurry in which a matrix resin and aggregated boron nitride particles are dispersed in a solvent. However, the withstand voltage performance deteriorates due to the inclusion of air bubbles during coating on the substrate, and the foaming caused by the residual solvent in the coating film if the solvent is not dried sufficiently. there was a case. In particular, when the intra _- particle pore volume of the boron nitride aggregated particles is A1 and the particle interstitial volume is _B1 , _{B1 /} (A1+ _B1 ) is 0.60 or more. Boron nitride aggregated particles were used. In this case, since the primary particles on the surface of the aggregated particles are radial, the surface of the aggregated particles becomes uneven, and the slurry tends to increase in viscosity, and more air bubbles are contained during kneading with the resin or coating on the substrate. Therefore, air bubbles tend to remain in the resin film, and this deterioration in withstand voltage performance tends to occur.
In addition, in the wet coating method, if the addition amount of the aggregated boron nitride particles is increased in order to increase the thermal conductivity, streaks may occur during coating, resulting in poor productivity. In particular, the streaks are likely to occur when the boron nitride agglomerated particles having B ₁ /(A ₁ +B ₁ ) of 0.60 or more are used.

In the production method of the present embodiment, the thermoplastic resin is pressurized at a temperature at which the thermoplastic resin exhibits fluidity to form a sheet, whereby the thermoplastic resin is pressed into the voids in the aggregated boron nitride particles, so air bubbles are formed in the sheet. difficult to contain. In addition, since the sheet can be obtained without using a solvent in the present embodiment, foaming due to residual solvent does not occur. Therefore, according to the manufacturing method of the present embodiment, it is possible to improve the withstand voltage performance of the thermally conductive resin sheet.
In addition, since the manufacturing method of the present embodiment does not include a coating step, even if the above-mentioned B ₁ /(A ₁ + B ₁ ) is 0.60 or more, even if the boron nitride aggregated particles are used, coating such as generation of streaks Productivity is good without any problems due to

As described in the examples of Patent Documents 4 and 5, conventionally, thermosetting resins have been mainly used as matrix resins, so wet coating methods are often used as methods for producing thermally conductive resin sheets. was used. _In this wet coating method, if the surface of the aggregated particles has _a lot of unevenness, the above _- mentioned problems often occur. is less than 0.60) are considered preferred.
On the other hand, from the viewpoint of thermal conductivity, the primary particles on the surface of the aggregated particles are preferably radial, and such particles have a ratio of B ₁ /(A ₁ +B ₁ ) greater than 0.60. often become.
Thus, in the case of using a conventional manufacturing method, the improvement of voltage resistance performance and productivity and the improvement of thermal conductivity are the intra-particle pore volume A ₁ and the inter-particle volume B ₁ of the boron nitride aggregated particles. , that is, a trade-off relationship in B ₁ /(A ₁ +B ₁ ).
According to the production method of the present embodiment, aggregated particles having a ratio of B ₁ / (A ₁ + B ₁ ) of 0.60 or more can be used without considering problems in the wet coating method. It is possible to increase the thermal conductivity while improving the productivity.

(1) Mixing step In the mixing step, when the intra-particle pore volume of the powder made of the thermoplastic resin and the boron nitride aggregated particles is A ₁ and the inter-particle volume is B ₁ , B ₁ / (A ₁ + B ₁ ) is 0.60 or more, and stirred and mixed at room temperature.
As a conventional production method, there is a method of heat-melting and kneading a matrix resin and aggregated boron nitride particles. However, this melt-kneading may cause shear fracture of the aggregated boron nitride particles. In particular, when boron nitride agglomerated particles having a B ₁ /(A ₁ +B ₁ ) ratio of 0.60 or more are used, shear fracture is likely to occur due to the large amount of irregularities on the surface.
Therefore, in the present embodiment, a powder made of a thermoplastic resin and boron nitride aggregated particles having a ratio of B ₁ /(A ₁ +B ₁ ) of 0.60 or more are stirred and mixed at room temperature without performing heat melt kneading. By doing so, it is possible to make the aggregated particles less susceptible to shear failure and to increase the thermal conductivity of the resulting sheet.

(2) Press-molding step In the press-molding step, the mixture obtained in the mixing step is heated and pressed to form a sheet.

As the press molding method, various known press machines for molding thermoplastic resins can be used.
From the viewpoint of preventing deterioration of the resin during hot pressing, it is particularly preferable to use a vacuum pressing device capable of reducing the amount of oxygen in the pressing machine during heating, or a pressing device equipped with a nitrogen replacement device.

In the press molding step, in addition to the purpose of forming the melt-kneaded product into a sheet body with a uniform thickness, the added boron nitride aggregated particles are joined together, and a heat path is formed by deforming the particle surface of the joining portion. It is preferable to set the applied pressure for the purpose of eliminating voids and gaps in the sheet.
From this point of view, the actual pressure applied to the sample in the press molding step is usually 8 MPa or higher, preferably 9 MPa or higher, and more preferably 10 MPa or higher. Also, it is preferably 50 MPa or less, more preferably 40 MPa or less, and still more preferably 30 MPa or less.
By setting the pressure at the time of pressurization to the above upper limit or less, crushing of the aggregated boron nitride particles can be prevented, and a thermally conductive resin sheet having high thermal conductivity can be obtained. In addition, by setting the pressing pressure to the above lower limit or more, the contact between the boron nitride aggregated particles becomes good, it becomes easy to form a thermal conduction path, and a sheet having high thermal conductivity can be obtained.In addition, the resin sheet Since the internal voids can be reduced, the thermally conductive resin sheet can have a high dielectric breakdown voltage even after the moisture absorption reflow test.

The set temperature of the press device in the press molding step is preferably a temperature at which the thermoplastic resin exhibits fluidity, for example, the melting point of the thermoplastic resin as the main component +30° C. or higher. For example, when a polyetherketone-based resin is used as the main component, the set temperature of the press is preferably 370° C. to 440° C., more preferably 380° C. or higher or 420° C. or lower.
By performing press molding at a temperature within this range, the resulting thermally conductive resin sheet can be provided with good thickness uniformity and high thermal conductivity due to good contact between the added boron nitride aggregate particles. When the molding temperature is 370° C. or higher, the resin viscosity is lowered to a level sufficient for shaping processing, and sufficient thickness uniformity can be imparted to the thermally conductive resin sheet to be molded. On the other hand, if the set temperature of the press is 440° C. or less, deterioration of the resin itself and deterioration of physical properties of the molded thermally conductive resin sheet can be suppressed.

The pressurization time is usually 30 seconds or longer, preferably 1 minute or longer, more preferably 3 minutes or longer, and still more preferably 5 minutes or longer. Also, it is preferably 1 hour or less, more preferably 30 minutes or less, still more preferably 15 minutes or less.
By keeping the value below the above upper limit, the manufacturing process time of the thermally conductive resin sheet can be reduced, the cycle time can be shortened compared to the thermally conductive resin sheet using a heat-resistant thermosetting resin, and the production cost can be suppressed. tend to be able. In addition, when the thickness is at least the above lower limit, the thickness of the thermally conductive resin sheet can be sufficiently uniform, the internal voids and voids can be sufficiently removed, and the thermal conductivity performance and withstand voltage characteristics can be uneven. can be prevented.

4. Laminated Heat Dissipating Sheet The laminated heat dissipating sheet of the present embodiment is obtained by laminating a heat dissipating metal layer containing a heat dissipating material on one surface of the thermally conductive resin sheet of the present embodiment.
The heat dissipating material is not particularly limited as long as it is made of a material having good thermal conductivity. Among them, in order to increase the thermal conductivity in the laminated structure, it is preferable to use a metal material for heat radiation, and among them, it is more preferable to use a flat metal material.
The material of the metal material is not particularly limited. Among them, a copper plate, an aluminum plate, an aluminum alloy plate, and the like are preferable because they have good thermal conductivity and are relatively inexpensive.

When a flat metal material is used as the metal material for heat dissipation in the laminated heat dissipation sheet, the thickness of the metal material is preferably 0.03 to 6 mm, especially 0.03 to 6 mm, in order to ensure sufficient heat dissipation. It is more preferably 1 mm or more or 5 mm or less.

Regarding adhesion to metal materials for heat dissipation, the surface of the metal material laminated with the thermally conductive resin sheet is roughened by soft etching, burn plating, oxidation-reduction treatment, etc., and various treatments are performed to ensure adhesion durability. Surface treatments such as plating of metals and metal alloys, organic surface treatments including silane coupling treatments such as amino-based and mercapto-based treatments, and surface treatments using organic/inorganic composite materials may be applied. By performing these surface treatments, it is possible to further improve the initial adhesive strength, the durability of the adhesive strength, and the effect of suppressing interfacial peeling after the moisture absorption reflow test.

On the other hand, the surface of the metal material for heat radiation opposite to the side laminated with the thermally conductive resin sheet does not have to be a simple flat plate. may be subjected to processing or the like to increase the
Examples of processing for increasing the surface area include roughening the surface by blasting or the like to increase the surface area; In the method of forming directly on the material, the heat-dissipating metal layer made of a flat metal material is further processed to increase the surface area by casting, diffusion bonding, bolting, soldering, brazing, etc. Other examples include joining another metal material, embedding a metal pin, and the like. Furthermore, it is also conceivable to directly press-laminate a heat-conducting resin sheet on a heat-dissipating metal layer having a cavity for passing a cooling medium. However, since the pressing pressure between the thermally conductive resin sheet and the heat dissipating metal plate is relatively high, in these cases, the flat metal material and the thermally conductive resin sheet are laminated and integrated in a post-process. It is preferable to integrate it with a grooved metal plate or a metal layer having a cavity for flowing a coolant by soldering, brazing, bolting, or the like.

Regarding the lamination and integration of the heat-dissipating metal material and the thermally conductive resin sheet in the laminated heat-dissipating sheet, press molding, which is a batch process, can be preferably used. The press equipment, press conditions, etc. in this case are the same as the range of the press molding conditions for obtaining the above-mentioned thermally conductive resin sheet.

5. Heat Dissipating Circuit Board The heat dissipating circuit board of the present embodiment has the laminated heat dissipating sheet. That is, the heat-dissipating metal layer is laminated on one surface of the thermally conductive resin sheet of the present embodiment, and the other surface of the heat-dissipating metal layer of the heat-conductive resin sheet is coated with a circuit board by, for example, etching treatment. It has a configuration formed by forming

As for the configuration of the heat-dissipating circuit board, it is more preferable to integrate "heat-dissipating metal layer/thermally-conductive resin sheet/conductive circuit". The state before circuit etching is, for example, an integrated structure of "metal layer for heat radiation/thermally conductive resin sheet/metal layer for conductive circuit formation", in which the metal layer for conductive circuit formation is in the form of a plate, and a thermal conductive resin is used. Examples include those formed on the entire surface of one side of the sheet and those formed on a partial area.

The material of the conductive circuit forming metal layer is not particularly limited. Above all, it is generally preferable to use a copper thin plate having a thickness of 0.05 mm or more and 1.2 mm or less from the viewpoint of good electrical conductivity, etching properties, and cost.

The dielectric breakdown voltage of the heat-dissipating circuit board is preferably 40 kV/mm or higher, more preferably 50 kV/mm or higher, even more preferably 60 kV/mm or higher, and even more preferably 80 kV/mm or higher. With a dielectric breakdown voltage of 40 kV/mm or more, for example, even with a thermally conductive resin sheet having a thickness of 100 μm, a dielectric breakdown voltage of 4 kV or more can be obtained, and if the dielectric breakdown voltage is 80 kV/mm or more , Since a dielectric breakdown voltage of 4 kV or more can be obtained even with a thickness of 50 μm, while using a thin thermally conductive resin layer that is advantageous in terms of thermal resistance, it has sufficient withstand voltage performance and dielectric breakdown occurs when high voltage is applied. can be suppressed.

6. Power Semiconductor Device The thermally conductive resin sheet of the present embodiment or the laminated heat dissipation sheet of the present embodiment can be suitably used as a heat dissipation sheet for power semiconductor devices, and a highly reliable power semiconductor module can be realized. .
The power semiconductor device is a power semiconductor device using the thermally conductive resin sheet or the laminated heat dissipation sheet, and the thermally conductive resin sheet or the laminated heat dissipation sheet is mounted on a power semiconductor device as a heat dissipation circuit board. It is a thing.
The power semiconductor device has a heat radiation effect due to its high thermal conductivity, and can achieve high output and high density with high reliability.
In the power semiconductor device device, conventionally known members such as aluminum wiring, sealing material, packaging material, heat sink, thermal paste, and solder other than the thermally conductive resin sheet or the laminated heat dissipation sheet can be appropriately employed.

<Second embodiment>
1. Resin Composition The thermally conductive resin sheet according to the second embodiment of the present invention is made of a resin composition containing a thermoplastic resin and aggregated boron nitride particles.

(1) Thermoplastic resin The thermoplastic resin according to the present embodiment is the same as the thermoplastic resin described in the first embodiment. It is the same as the first embodiment.

(2) Boron nitride aggregated particles The boron nitride aggregated particles according to this embodiment are the same as the boron nitride aggregated particles described in the first embodiment, and the physical properties and structure of the boron nitride aggregated particles suitable for this embodiment are also , are the same as those of the first embodiment.
In the present embodiment, the circularity of the aggregated boron nitride particles in the resin composition is preferably greater than 0.945, more preferably 0.95 or more, and even more preferably 0.96 or more, with an upper limit of 1. .

(3) Content of Each Component The contents of the thermoplastic resin and the aggregated boron nitride particles in the resin composition of the present embodiment are the same as those of the first embodiment.
Moreover, the resin composition of the present embodiment may contain other components in addition to the thermoplastic resin and the aggregated boron nitride particles. However, from the viewpoint of enhancing thermal conductivity, it is preferable not to contain other components. The other components are those exemplified in the first embodiment.

2. Thermally conductive resin sheet The thermally conductive resin sheet of the present embodiment is made of the above resin composition, has high thermal conductivity in the thickness direction, has excellent moisture absorption reflow resistance, and is a laminate with a metal plate. It has the characteristic that interfacial peeling due to thermal expansion and thermal contraction is difficult to occur in some cases.

A thermally conductive resin sheet made of a resin composition containing boron nitride aggregated particles is heated at 700 ° C. for 5 hours to remove the resin component, and the ash content is measured for mercury intrusion exit curve by a mercury intrusion method. When a pore size distribution curve is created with the horizontal axis as the logarithmic differential pore volume and the vertical axis as the logarithmic differential pore volume, the range is usually less than 5 μm, preferably 0.1 μm or more and less than 5 μm, and the range is usually 5 μm or more, preferably 5 μm or more and 100 μm or less. A peak is seen in . In the present invention, a peak having a maximum value in the range of less than 5 μm, preferably 0.1 μm or more and less than 5 μm is defined as the first peak, and a peak having a maximum value in the range of 5 μm or more, preferably 5 μm or more and 100 μm or less is defined as the second peak. be the peak of The range of less than 5 μm includes a peak a due to intra-particle pores of the aggregated boron nitride particles, and the range of 5 μm or more includes a peak b due to inter-particle gaps of the aggregated boron nitride particles.

In the present invention, the maximum values of the first peak and the second peak are referred to as the first peak top height and the second peak top height, respectively. Also, the pore diameters at which the first peak and the second peak show their maximum values are referred to as the first peak top diameter and the second peak top diameter, respectively.

As for the case where there are multiple peaks in the range of 5 μm or more, when the residual ash is mixed with boron nitride aggregated particles having two types of particle size distribution, in addition to the boron nitride aggregated particles, nitriding It is conceivable that a filler other than boron is contained, or a peak due to primary particles detached from the crushed pieces or aggregated particles generated by the collapse of the boron nitride aggregated particles during the molding process appears. In these cases, the second peak top height is often smaller than in the present embodiment, and it is considered difficult to obtain a high thermal conductivity.

In order to increase the thermal conductivity of the thermally conductive resin sheet, aggregated particles having a structure in which the primary particles in the vicinity of the outermost surface of the aggregated particles are aligned with the radial direction of the aggregated particles are used. It is preferable that the vicinity of the surface is deformed into a contacting state, that the aggregated particles themselves are less likely to disintegrate and primary particles are less likely to fall off, and that the contact area between the aggregated particles is larger. From this point of view, it is preferable that the second peak top diameter is large.

The second peak top diameter is preferably 15 μm or more, more preferably 16 μm or more, and even more preferably 17 μm or more. On the other hand, the second peak top diameter is preferably 30 μm or less, more preferably 25 μm or less, from the viewpoint of reducing the thermal resistance between the agglomerated particles by increasing the contact area so that the agglomerated particles are in surface contact with each other. preferable.
When the second peak top diameter is large, a portion where only resin exists between a plurality of aggregated particles, and therefore a portion with high thermal resistance when viewed partially exists in a relatively large volume. gives the heat dissipation sheet a high thermal conductivity.
However, when the boron nitride aggregated particles are used as the thermally conductive filler, particularly in the card house type boron nitride aggregated particles formed by strongly bonding the primary particles constituting the aggregated particles, the primary particles inside the aggregated particles It is important to maintain the strong bond between the sheets even after the sheet is formed. To maintain efficient heat transfer between primary particles within the aggregate, it is preferred to avoid excessive deformation or crushing of the aggregate in the sheet. A single primary particle or several primary particles bound together may be detached from aggregated particles that have been excessively deformed or crushed. When these particles are generated, the height of the second peak top tends to decrease, the diameter of the second peak top tends to decrease, and the shape of the second peak tends to broaden.

The second peak top height is preferably 1.0 mL/g or more, more preferably 1.2 mL/g or more, and even more preferably 1.5 mL/g or more. The upper limit of the second peak top height is not particularly limited. , preferably 3.2 mL/g or less, more preferably 3.0 mL/g or less, even more preferably 2.7 mL/g or less, and even more preferably 2.5 mL/g or less.
The second peak top height is an index showing the uniformity of surface contact state between aggregated particles in the sheet.
As described above, the aggregated particles in the sheet are preferably deformed in the vicinity of the surface thereof so that the aggregated particles are in surface contact with each other, but the degree of deformation differs greatly for each aggregated particle. If a portion of the sheet is in a state close to point contact, high thermal conductivity cannot be obtained as a whole sheet. In such cases, the second peak top height is reduced.
The fact that the second peak top height is at least the above lower limit value means that the aggregated particles in the sheet are accompanied by relatively uniform deformation and are in a relatively uniform surface contact state, and the interparticle volume is compared. It shows that it is uniform.

In addition, the thermally conductive resin sheet of the present embodiment preferably has a small first peak top diameter, that is, a structure in which the particle gaps are small and the aggregated particles are dense.
When the first peak top diameter is small, it is considered that the particle gaps of the raw material boron nitride aggregated particles themselves are small, and as a result, the small particle gaps derived from the raw material are maintained even after sheet formation. Aggregated boron nitride particles with small interparticle gaps are considered to have a structure in which the primary particles form a dense bond, and high thermal conductivity is easily obtained inside the aggregated particles. The fact that the first peak top diameter is small reflects that the aggregated particles as described above do not cause excessive deformation, crushing, falling off of primary particles, etc. even after undergoing pressurization during sheet processing. Therefore, it is considered that when the first peak top diameter is small, the thermal conductivity tends to be good.
It is conceivable that the aggregated particles may be excessively deformed or collapsed due to pressurization or the like during sheet molding, resulting in a decrease in the first peak top diameter, but in this case, the second peak top height and the second peak top diameter are outside the above range.
From the above viewpoints, the first peak top diameter is preferably 0.4 μm or less, more preferably 0.38 μm or less. On the other hand, from the viewpoint of ensuring sufficient penetration of the resin into the internal pores of the agglomerated particles, suppressing the generation of voids in the thermally conductive resin sheet, and enhancing the withstand voltage performance, the first peak top diameter is 0.5. 1 μm or more is preferable, 0.15 μm or more is more preferable, and 0.2 μm or more is even more preferable.

The first peak top height is preferably 0.25 mL/g or more, more preferably 0.3 mL/g or more, and even more preferably 0.4 mL/g or more. Although the upper limit of the first peak top height is not particularly limited, it is preferably 0.7 mL/g or less, more preferably 0.65 mL/g or less, and even more preferably 0.6 mL/g or less.
When the first peak top height is equal to or less than the above upper limit, the pore volume inside the aggregated particles does not become too large, and the primary particles capable of efficiently conducting heat are present appropriately inside the aggregated particles. Become.
On the other hand, the fact that the first peak top height is equal to or higher than the above lower limit indicates that the aggregated particles themselves used as the raw material have an appropriate amount of internal voids. With such aggregated particles, it is considered that the vicinity of the surface of the aggregated particles in the sheet is moderately deformed, and surface contact is likely to occur.
Further, as a case where the first peak top height is below the above lower limit, it is conceivable that the first peak is observed as a broad peak. In this case, the three-dimensional structure of the primary particles that make up the aggregated particles used as the raw material varies from place to place, or the interior of the aggregated particles is deformed or destroyed due to pressure during sheet molding. It is conceivable that there are

As described above, depending on the first peak top height, first peak top diameter, second peak top height and second peak top diameter, the strength of aggregated particles, the orientation state of primary particles after sheeting, etc. is represented.
The inventors have found that, among these factors, the second peak top height and the second peak top diameter affect the withstand voltage performance and thermal conductivity.
The fact that the second peak top height and the second peak top diameter are within the above range indicates that aggregated particles having sufficient strength are used, and such a thermally conductive resin sheet The use of card house-type boron nitride aggregated particles, in which the aggregated particles are less likely to collapse during molding, etc., and the primary particles on the surface of the aggregated particles are radially oriented, is used as a raw material to improve the heat conduction path between the aggregated particles. fully formed.
The inventors also found that among these factors, the first peak top diameter and the second peak top diameter affect the withstand voltage performance and thermal conductivity.
When the first peak top diameter and the second peak top diameter are within the above range, the interior of the aggregated particles is dense and the structure with isotropic thermal conductivity is maintained, while the surface of the aggregated particles has a primary The area where the particles are oriented radially deforms appropriately during molding, etc., so to speak, so to speak, it has a structure of "hard inner and outer soft", so that the contact area between adjacent aggregated particles increases, and the thermally conductive resin sheet It is possible to further increase the thermal conductivity in the thickness direction.

As the boron nitride aggregated particles having the first peak top height, the first peak top diameter, the second peak top height and the second peak top diameter within the above ranges, for example, aggregated particles having a card house structure are mentioned. Further, after obtaining aggregated boron nitride particles by a known method, the surface may be adjusted by performing a physical or chemical roughening treatment.
Generally commercially available boron nitride agglomerated particles use boron nitride primary particles that are relatively crystallized during granulation, so stable primary particle planes (ab planes) are preferentially stacked. As a result, many aggregated particles have a "cabbage structure" in which the thickness direction of the primary particles near the outermost surface of the aggregated particles coincides with the radial direction of the aggregated particles. Agglomerated particles with a “cabbage structure” lie so that the primary particles near the outermost surface cover the aggregated particles, and the strength of the aggregated particles itself is often low, so in the measurement of the heated ash content of the sheet, the second peak The top height and the second peak top diameter tend to be small. Therefore, when using agglomerated particles having a “cabbage structure”, the surface roughening treatment may be performed for adjustment.

The thermal conductivity in the thickness direction of the thermally conductive resin sheet of the present embodiment at 25° C. is preferably 18 W/m·K or more, more preferably 19 W/m·K or more, and even more preferably 20 W/m·K or more. Since the thermal conductivity in the thickness direction is equal to or higher than the above lower limit, it can be suitably used for power semiconductor devices and the like that operate at high temperatures.
The thermal conductivity is the type of thermoplastic resin and physical properties such as melt viscosity, the first peak top height, the first peak top diameter, the second peak top height and the second peak top height in the thermally conductive resin sheet. , the structure and content of the aggregated boron nitride particles, the method of mixing the thermoplastic resin and the aggregated boron nitride particles, the conditions in the heating and kneading step described later, and the like.

In addition, the circularity of the aggregated boron nitride particles contained in the residual ash of the present embodiment is preferably more than 0.945 from the viewpoint of suppressing excessive deformation of the aggregated particles and improving the thermal conductivity of the sheet. 0.95 or more is more preferable. Further, when the aggregated particles come into surface contact with each other, the thermal conductivity of the sheet is improved.

3. Method for Producing Thermally Conductive Resin Sheet As an example of the method for producing the thermally conductive resin sheet of the present embodiment, for example, a method including a mixing step and a press molding step can be given.

As the boron nitride agglomerated particles that increase the second peak top diameter measured for the heated ash of the sheet, the primary particles on the agglomerated particle surface are radial and the agglomerated particle surface is highly uneven. can be done.
When such boron nitride aggregated particles are used in a conventional manufacturing method (wet coating method), it is possible to obtain the effect of reducing the interfacial thermal resistance when the aggregated particles come into contact with each other due to pressing during press molding of the sheet. Since the slurry tends to increase in viscosity and contain air bubbles more easily during kneading with the resin or coating on the substrate, the air bubbles tend to remain in the resin film, and the withstand voltage performance tends to decrease. Moreover, when such aggregated boron nitride particles are used, streaks are likely to occur when applied, and productivity may deteriorate.

In the production method of the present embodiment, the thermoplastic resin is pressurized at a temperature at which the thermoplastic resin exhibits fluidity to form a sheet, whereby the thermoplastic resin is pressed into the voids in the aggregated boron nitride particles, so air bubbles are formed in the sheet. difficult to contain. In addition, since the sheet can be obtained without using a solvent in the present embodiment, foaming due to residual solvent does not occur. Therefore, according to the manufacturing method of the present embodiment, it is possible to improve the withstand voltage performance of the thermally conductive resin sheet.
In addition, since the manufacturing method of the present embodiment does not include a coating step, even if boron nitride aggregated particles that increase the second peak top diameter measured for the heated ash of the sheet are used as a raw material, streaks and the like are generated. The productivity is good without causing any problems due to the coating of .

As described above, conventionally, thermosetting resins have mainly been used as matrix resins, and thus wet coating methods have been widely used as methods for producing thermally conductive resin sheets. In this wet coating method, if there are many irregularities on the surface of the aggregated particles, the above-mentioned problems often occur. Agglomerated particles of smaller diameter) are believed to be preferred.
On the other hand, from the viewpoint of thermal conductivity, it is preferable that the primary particles on the surface of the aggregated particles are radial, and when such particles are used to produce a sheet, the second peak top diameter often becomes large.
As described above, in the case of using the conventional manufacturing method, there is a trade-off relationship between the improvement of withstand voltage performance and productivity and the improvement of thermal conductivity in the second peak top diameter.
According to the production method of the present embodiment, it is possible to use aggregated particles that increase the second peak top diameter measured for the heated ash content of the sheet without considering problems in the wet coating method. Thermal conductivity can be increased while improving performance and productivity.

(1) Mixing Step In the mixing step, the thermoplastic resin powder and the aggregated boron nitride particles are stirred and mixed at room temperature.
As a conventional production method, there is a method of heat-melting and kneading a matrix resin and aggregated boron nitride particles. However, when boron nitride agglomerated particles that increase the second peak top diameter measured for the heated ash content of the sheet are used, shear failure is likely to occur because the surface has many irregularities.
Therefore, in the present embodiment, a powder made of a thermoplastic resin and agglomerated boron nitride particles that increase the second peak top diameter measured for the heated ash content of the sheet are mixed at room temperature without performing heat melt kneading. Stirring and mixing makes it difficult for the agglomerated particles to be shear-broken and increases the thermal conductivity of the resulting sheet.

(2) Press-molding step In the press-molding step, the mixture obtained in the mixing step is heated and pressed to form a sheet.
A preferred press molding method in this embodiment is the same as in the first embodiment.

4. Laminated Heat Dissipating Sheet, Heat Dissipating Circuit Board, and Power Semiconductor Device The thermally conductive resin sheet of the present embodiment can be suitably used as a laminated heat dissipating sheet, a heat dissipating circuit board, and a power semiconductor device, as in the first embodiment. can be done.

<Explanation of terms>
In the present invention, when expressing "X to Y" (X and Y are arbitrary numbers), unless otherwise specified, "X or more and Y or less" and "preferably larger than X" or "preferably larger than Y" It also includes the meaning of "small".
In addition, when expressing “X or more” (X is an arbitrary number) or “Y or less” (Y is an arbitrary number), it is necessary to express “preferably larger than X” or “preferably less than Y”. It also includes intent.
In the present invention, the term "sheet" conceptually includes sheets, films and tapes.

The present invention will be further described in detail below with reference to examples. However, the present invention is not limited to the following examples as long as the gist thereof is not exceeded.

<Examples 1 to 3 and Comparative Examples 1 to 4>
Materials used, production methods, measurement conditions and evaluation methods of the thermally conductive resin sheets in Examples 1 to 3 and Comparative Examples 1 to 4 are as follows.

[Materials used]
(Thermoplastic resin)
Thermoplastic resin 1: Polyether ether ketone "KetaSpire KT-880FP" (manufactured by Solvay, melting point: 343 ° C., melt viscosity: 0.15 kPa s (400 ° C.), average particle size (D50): 30.0 to 45 0 μm, MFR: 86 g/10 min, weight average molecular weight (Mw): 58,000.

(Thermosetting resin)
Thermosetting resin 1: Epoxy resin composition (bisphenol F type epoxy resin (manufactured by Mitsubishi Chemical Corporation, weight average molecular weight in terms of polystyrene: 60000) 8.74 parts by mass, hydrogenated bisphenol A type liquid epoxy resin (Mitsubishi Chemical Corporation ) 10.93 parts by mass, p-aminophenol type liquid epoxy resin (manufactured by Mitsubishi Chemical Corporation) 2.62 parts by mass, phenolic resin curing agent "MEH-8000H" (manufactured by Meiwa Kasei Co., Ltd.) 5.73 parts by mass, 1-Cyanoethyl-2-undecylimidazole “C11Z-CN” (manufactured by Shikoku Kasei Co., Ltd., molecular weight 275) 0.48 parts by mass) was used as a curing catalyst.

Boron Nitride Agglomerated Particles (Thermal Conductive Filler)
The thermally conductive fillers used as the aggregated boron nitride particles are as follows.
Thermally conductive filler 1: Aggregated boron nitride particles having a card house structure (B ₁ /(A ₁ +B ₁ ) = 0.664, average particle size (D50): 35 µm, maximum particle size Dmax: 90 µm)
Thermally conductive filler 2: Aggregated boron nitride particles having a card house structure (B ₁ /(A ₁ +B ₁ ) = 0.662, average particle size (D50): 35 µm, maximum particle size Dmax: 90 µm)
Thermally conductive filler 3: Aggregated boron nitride particles having a card house structure (B ₁ /(A ₁ +B ₁ ) = 0.648, average particle size (D50): 35 µm, maximum particle size Dmax: 90 µm)
Thermally conductive filler 4: Aggregated boron nitride particles having a card house structure (B ₁ /(A ₁ +B ₁ ) = 0.516, average particle size (D50): 34 µm, maximum particle size Dmax: 90 µm)
Thermally conductive filler 5: Aggregated boron nitride particles having a card house structure (B ₁ /(A ₁ +B ₁ ) = 0.556, average particle size (D50): 40 µm, maximum particle size Dmax: 90 µm)
Thermally conductive filler 6: Boron nitride aggregated particles ("PTX25" (manufactured by Momentive, _B1 /(A ₁ +B ₁ )=0.441, average particle diameter (D50) 25 μm, specific surface area 7 m ² /g)

Thermally conductive fillers 1 and 2 were produced by the method described below.
Note that the thermally conductive fillers 1 and 2 were performed as the same lot until (raw materials), (preparation of slurry), (granulation), and (thermal decomposition) described below, and (preparation of aggregated boron nitride particles). Only the in-furnace treatment at 2000° C. in section 1 was carried out successively as separate batches.

(material)
As a raw material, hexagonal boron nitride (hereinafter referred to as "raw material h-BN powder"): 10000 g, binder (Taki Chemical Co., Ltd. "Taxeram M160L", solid content concentration 21% by mass): 11496 g, surfactant (Kao Corporation surfactant " Ammonium lauryl sulfate": solid content concentration 14% by mass): 250 g was used.

(Preparation of slurry)
The raw material h-BN powder was weighed into a resin bottle in the above amount, and then the binder was added in the above amount. Further, after adding the surfactant in the above amount, zirconia ceramic balls were added, and the mixture was stirred for 1 hour on a rotary table of a pot mill to obtain a BN slurry. The viscosity of this slurry was 810 mPa·s.

(granulation)
The BN slurry was spray-dried using a spray dryer (FOC-20 manufactured by Okawara Kakoki Co., Ltd.) at a disk rotation speed of 20000 to 23000 rpm and a drying temperature of 80 ° C. to obtain spherical BN granulated particles. .

(Thermal decomposition)
The BN granulated particles were heat-treated at 700° C. for 5 hours in an air atmosphere to obtain precursor particles.

(Production of aggregated boron nitride particles)
The above precursor particles are filled in a disk shape in a circular graphite crucible with a lid, and the inside of the furnace is replaced with nitrogen gas flowing at room temperature and normal pressure, and the temperature is increased to 2000 ° C. at 83 ° C./hour while nitrogen gas is flowing. After the temperature was raised and reached 2000° C., the temperature was maintained for 5 hours while nitrogen gas was circulated, and then the temperature was cooled to room temperature. The material to be fired was taken out from the crucible, and the part in contact with the graphite was removed. The material was manually pulverized using a mortar and pestle, and then treated with a roll mill to obtain spherical boron nitride agglomerated particles having a card house structure. rice field.
The obtained aggregated boron nitride particles were sieved using a sieve with openings of 90 μm, and only the particles that passed through the sieve were used as the thermally conductive filler.
For the thermally conductive fillers 1 and 2, after the furnace treatment at 2000° C., manual crushing and roll mill treatment were separately performed. The sequential implementation resulted in no difference in the measurement results of the mercury intrusion method.

The thermally conductive filler 3 is made by mixing 5000 g each of hexagonal boron nitride with an oxygen concentration of 5% by mass and hexagonal boron nitride with an oxygen concentration of 7.5% by mass as raw materials. It was prepared in the same manner as the synthetic filler 1.
The thermally conductive filler 4 is formed by subjecting the thermally conductive filler 2 to dry treatment for 30 minutes in a bead mill using nylon balls with a diameter of 10 mm. Spherical agglomerated particles were used. As shown in FIG. 5, from the SEM observation image of the aggregated particles alone, it is judged that the aggregated particles themselves do not collapse or break, and the internal card house structure is maintained.
In addition, the thermally conductive filler 5 is prepared in the same manner as the thermally conductive filler 1 except that 10000 g of hexagonal boron nitride having an oxygen concentration of 7.5% by mass is used as a raw material. By performing a dry process for 30 minutes in a bead mill using balls, the primary particles on the surface of the aggregated particles were bent and used as spherical aggregated particles having a folded structure covering the aggregated particles. From the SEM observation image of the aggregated particles alone, it was determined that the aggregated particles themselves did not collapse or break, and the internal card house structure was maintained in the filler 5 as well.

[Preparation of Thermally Conductive Resin Sheets of Examples 1 to 3 and Comparative Examples 1 to 3]
The matrix resin powder and the thermally conductive filler powder are mixed at room temperature, and the resulting powder mixture is pressed with a high-temperature vacuum press (manufactured by Kitagawa Seiki Co., Ltd.) at a press temperature of 395 ° C. and a press surface pressure of 10 MPa for 10 minutes. Pressing was performed to obtain a thermally conductive resin sheet having a size of 15 cm square and a thickness of 150 μm and a thermally conductive resin sheet having a size of 15 cm square and a thickness of 500 μm. At this time, the thickness of the sheet was adjusted by adjusting the amount of powder. However, only Example 2 was pressed for 10 minutes at a press temperature of 395° C. and a press surface pressure of 20 MPa.
The thermally conductive resin sheet with a thickness of 150 μm was used as a specimen for a moisture absorption reflow test, which will be described later, and the thermally conductive resin sheet with a thickness of 500 μm was used as a specimen for thermal conductivity measurement, which will be described later.

Here, the above 10 minutes means that the inside of the vacuum press is preheated to 150° C., the powder mixture is put in there as a component to be pressed, and the vacuum pump is operated while the powder mixture is A light pressurization of several MPa was applied, the internal temperature of the press machine was set to 395° C., and after the temperature was raised for 40 minutes, the press surface pressure was set to 10 MPa, and 10 minutes. After 10 minutes had passed, the internal temperature of the press was raised to 150°C again, and when the internal temperature approached 150°C, the vacuum was released and the thermally conductive resin sheet was taken out.

The above-mentioned press preparation structure is a frame-shaped spacer having a thickness of 6 mm, an outer edge of 20 cm in length and width, and an opening of 15 cm in length and width x 15 cm in length and width. Inside, a powdery mixture of a mass necessary to obtain a press sheet with a thickness of 150 μm or a press sheet with a thickness of 500 μm is dispersed, and a sample with a thickness of 5.85 mm (a sample thickness of 150 μm) is collected in the opening of 15 cm × 15 cm. ), or 5.50 mm thick (when collecting a sample with a thickness of 500 μm), fitted with a drop lid measuring 14.6 cm x 14.6 cm in length and width, and placed on an upper plated plate. It is a construct.

[Preparation of Thermally Conductive Resin Sheet of Comparative Example 4]
A thermally conductive filler is added so that the total amount of the epoxy resin composition and the thermally conductive filler is 100% by mass, and the total solid content of the epoxy resin composition and the thermally conductive filler is 62. 37.2% by mass of a mixed solution of methyl ethyl ketone and cyclohexanone (mixing ratio (volume ratio) 1:1) was added and mixed to obtain a coating slurry (coating solution for sheet) so as to obtain a .8% by mass. At the time of mixing these, after stirring by hand, stirring was performed for 2 minutes using a rotating and revolving stirrer “Awatori Rentaro AR-250”.
The coating slurry obtained above was applied onto a 38 μm thick polyethylene terephthalate film (hereinafter also referred to as “PET film”) by a doctor blade method, dried by heating at 60° C. for 120 minutes, and then pressed at a temperature of 42° C. Pressing was performed for 10 minutes at a pressing surface pressure of 15 MPa to obtain an uncured epoxy resin sheet-like molding. This epoxy resin sheet-like molding was used as a specimen for a moisture absorption reflow test, which will be described later.

In addition, a thermally conductive resin sheet with a thickness of 500 μm used for measuring thermal conductivity, which will be described later, was produced by the following method. The above uncured epoxy resin sheet-like molded body was cut into 10 cm × 10 cm pieces, and four sheets of the molded body were laminated to form a press-fed structure. Using the same spacer and drop lid as in the case of obtaining, pressing was performed at a pressing temperature of 175° C. and a pressing surface pressure of 10 MPa for 1 hour to obtain a thermally conductive resin sheet with a thickness of 500 μm. The excess thickness of the laminated uncured epoxy resin sheet-like molding is absorbed in the empty volume portion between the sheet size of 10 cm×10 cm and the spacer size of 15 cm×15 cm.

<Measurement conditions, evaluation method>
The thermally conductive fillers 1 to 6 and the thermally conductive resin sheets of Examples 1 to 3 and Comparative Examples 1 to 4 were measured and evaluated by the following methods.

[Physical properties of aggregated particles (raw material powder)]
(Dmax and D50)
The maximum particle size Dmax and average particle size D50 of the aggregated boron nitride particles were measured by the following methods.
A sample obtained by ultrasonically dispersing 20 mg of aggregated boron nitride particles in 10 mL of a pure water medium containing sodium hexametaphosphate was measured using a laser diffraction/scattering particle size distribution analyzer LA-920 (manufactured by Horiba Ltd.). The particle size distribution was measured using a mortar, and the maximum particle size Dmax and the average particle size D50 of the aggregated boron nitride particles were determined from the resulting particle size distribution.

(Intraparticle Pore Volume A ₁ , Interparticle Volume B ₁ and B ₁ /(A ₁ +B ₁ ))
The intra-particle pore volume A ₁ (mL/g) and the inter-particle volume B ₁ (mL/g) of the boron nitride aggregated particles are respectively determined according to JIS R1655: 2003 "Method for testing fine ceramics compact pore size distribution by mercury intrusion method. ”.
Specifically, as a mercury porosimeter, Autopore IV manufactured by Micromeritex Co., Ltd. is used, 200 mg of a sample is filled in a measurement cell, and after vacuum treatment for 10 minutes under reduced pressure (50 μmHg or less), the total pore volume is measured. and the mercury intrusion exit curve was measured. A pore size distribution curve is created with the pore size on the horizontal axis and the logarithmic differential pore volume on the vertical axis. The diameter (division diameter) at which the logarithmic differential pore volume takes the minimum value with respect to the pore diameter between peak b was read. The particle interstitial volume B ₁ (mL/g) was obtained from the integrated value of the mercury intrusion exit curve in the region where the pore diameter was larger than the division diameter.
Further, the intra-particle pore volume A ₁ (mL/g) was obtained by subtracting the interparticle volume B ₁ from the total pore volume. From this measurement result, "B ₁ /(A ₁ +B ₁ )" was obtained.
When filling the sample into the cell of the mercury porosimeter, no special operations such as tapping are performed. Measurement results that depend only on the properties of the aggregated boron nitride particles can be obtained.
Boron nitride agglomerated particles may also exist that are subject to fracture by mercury intrusion, but such particles do not satisfy the conditions of the present invention.

(Circularity)
For thermally conductive fillers 2 to 5, the circularity was measured using a particle image analyzer (Mofologi G3S, manufactured by Malvern). Regarding any of the above boron nitride aggregated particles, the boron nitride particles remain as primary particles without forming aggregates, or the aggregated particles are once formed, but are dropped from the aggregated particles in subsequent handling to form primary boron nitride particles. Since it is conceivable that there may be particles that have turned into particles, the particles were classified by air flow dispersion at 1 Bar, and then image analysis was performed to measure the degree of circularity. The measurement of the circularity in Morphologi is obtained by measuring and calculating the perimeter of a particle and the perimeter of a circle having an area equal to the area of the particle, using the former as the denominator and the latter as the numerator. Measurements were taken for 10,000 pieces, and the average value was taken as the degree of circularity.
Since no measurement was performed for Filler 1, it is indicated as "-" in Table 1.

[Physical properties of aggregated particles (sheet ash)]
(Intraparticle Pore Volume A ₂ , Interparticle Volume B ₂ , A ₂ /A ₁ and B ₂ /B ₁ )
Intra-particle pore volume A ₂ (mL/g) and particle interstitial volume B ₂ (mL/ g) was measured as follows.
First, a heat conductive resin layer with a thickness of 150 μm prepared for a moisture absorption reflow test described later is laminated with a copper plate “metal plate material for heat dissipation (copper plate, thickness 2 mm) / heat conductive resin sheet (thickness 0.15 mm) /Copper plate for conductive circuit formation (thickness: 0.5 mm)”, all the copper plate was removed by etching treatment, and only the resin sheet was isolated to obtain a sample. 400 mg of the sample (approximately 3.6 cm x 3.6 cm in terms of resin sheet area) was collected and heated in a heating furnace in the air at 700°C for 5 hours to decompose and remove the resin to obtain heated ash. .
The sheet before heating and the ash content after heating were each weighed, and it was confirmed that the mass of the ash content approximately coincided with the calculated value of the mass of the mixed boron nitride agglomerated particles.
Next, using Autopore IV manufactured by Micromeritex as a mercury porosimeter, 200 mg of the sample was filled in the measurement cell, and a pore size distribution curve was created in the same manner as the above-mentioned A ₁ and B ₁ measurements, and the sheet ash content was measured. Inter-particle volume B ₂ (ml/g) and intra-particle pore volume A ₂ (ml/g) of boron nitride aggregated particles were determined.
Intra-particle pore volume A ₁ and inter-particle interstitial volume B ₁ of the fillers used in Examples 1-3 and Comparative Examples 1-4, respectively, and inter-particle pore volume A ₂ and inter-particle interstices in the ash content of the thermally conductive resin sheet The residual ratios A ₂ /A ₁ and B ₂ /B ₁ were obtained from the volume B ₂ .

(Peak top height and peak top diameter)
A first peak top height, a first peak top diameter, a second peak top height and a second peak top diameter were obtained from the pore size distribution curve in the sheet ash obtained above.

(Circularity)
For Examples 2 to 3 and Comparative Examples 1 to 3, the circularity of the ash content of the thermally conductive resin sheets was measured using a particle image analyzer (Mofologi G3S, manufactured by Malvern). In any of the sheet ash, the boron nitride particles remain as primary particles without forming aggregates, or once aggregated particles are formed, but the aggregated particles are separated from the aggregated particles in the subsequent handling or pressurization process for sheet molding. Since it is conceivable that there may be particles that have fallen off and become primary particles of boron nitride, classification was carried out by air flow dispersion at 1 Bar, and then image analysis was carried out to measure the degree of circularity. The measurement of the circularity in Morphologi is obtained by measuring and calculating the perimeter of a particle and the perimeter of a circle having an area equal to the area of the particle, using the former as the denominator and the latter as the numerator. Measurements were taken for 10,000 pieces, and the average value was taken as the degree of circularity.
Since the thermally conductive resin sheet of Example 1 was not measured, it is indicated as "-" in Table 1. The circularity of the thermally conductive resin sheet of Comparative Example 3 could not be measured because the aggregated particles had collapsed.

[Thermal conductivity at 25°C]
From the thermally conductive resin sheet (specimen) having a thickness of 500 μm obtained in Examples 1 to 3 and Comparative Examples 1 to 4, a measurement sample cut into a size of 10 mm square was used, and a “laser light absorption spray ( After thinly applying "Black Guard Spray FC-153" manufactured by Fine Chemical Japan Co., Ltd. on both sides and drying it, a xenon flash analyzer ("LFA447/NanoFlash300" manufactured by NETZSCH) was measured by the laser flash method at a measurement temperature of 25 ° C. The thermal diffusivity a (mm ² /sec) in the thickness direction of the resin sheet was measured. Five points cut out from the same sheet were measured, and the arithmetic average was obtained.

Next, according to JIS K6268, the density ρ (g/m ³ ) of the resin sheet was determined by the Archimedes method using a specific gravity meter (manufactured by A&D). Further, the specific heat capacity c (J/(g·K)) at 25° C. was measured using a DSC measuring device (ThermoPlusEvo DSC8230, manufactured by Rigaku Corporation) in accordance with JIS K7123.
From these measured values, the thermal conductivity in the sheet thickness direction at 25° C. was determined as "H=a×ρ×c".

The thermal diffusivity a (mm ² /sec) does not exist in the JIS standard regarding the thermal diffusivity and thermal conductivity of resin materials, so JIS R1611: 2010 (Thermal diffusivity by flash method of fine ceramics・Measurement method of specific heat capacity and thermal conductivity), and since the same standard stipulates that "the thickness of the sample is 0.5 mm or more and 5 mm or less", only the sample used for thermal conductivity measurement The thickness was adjusted to 0.5 mm and measured.

[Dielectric breakdown voltage (BDV) before moisture absorption reflow test]
(Production of circuit board for heat dissipation)
The thermally conductive resin sheets having a thickness of 150 μm produced in Examples 1 to 3 and Comparative Examples 1 to 4 were cut into a size of 40 mm×80 mm to obtain thermally conductive resin sheets for circuit boards.
On the other hand, a copper plate with a size of 40 mm × 80 mm and a thickness of 2000 µm, which is a metal plate material for heat dissipation, and a copper plate with a thickness of 40 mm × 80 mm, which is a copper plate for forming a conductive circuit and a thickness of 500 µm, are used as the heat conductive material for the circuit board. One sheet of each was prepared for one sheet of the resin sheet.
One side of a copper plate with a thickness of 2000 μm and one side of a copper plate with a thickness of 500 μm are each polished in advance with #100 sandpaper to roughen the surface, and the roughened surface of each copper plate with a different thickness is the circuit board. The heat conductive resin sheet for circuit boards is sandwiched so as to face the heat conductive resin sheet for heat dissipation, and the press temperature is 390 ° C. and the press surface pressure is 13 MPa for 10 minutes. )/thermal conductive resin sheet/copper plate for forming a conductive circuit” was obtained.

On the other hand, for Comparative Example 4, which is a thermally conductive resin sheet made of a thermosetting resin, an epoxy resin sheet-like molding having a thickness of 150 μm, which is uncured or has undergone only a slight curing reaction, is subjected to the above roughening treatment. It is sandwiched between a metal plate material for heat dissipation (copper plate) and a copper plate for forming a conductive circuit, and vacuum pressed for 30 minutes at a press temperature of 175 ° C. and a press surface pressure of 10 MPa to complete the curing reaction of the thermosetting resin. A laminated heat-dissipating sheet consisting of a metal plate material (copper plate)/thermal conductive resin sheet/copper plate for forming a conductive circuit was obtained.

Further, the conductive circuit forming copper plate of each laminated heat dissipation sheet was etched and patterned to obtain a heat dissipation circuit board. The pattern was such that two copper plates for a conductive circuit with a circular pattern of φ25 mm remained on a thermally conductive resin sheet of 40 mm×80 mm.

(Measurement of dielectric breakdown voltage (BDV))
The heat-dissipating circuit boards prepared using the thermally conductive resin sheets obtained in Examples 1 to 3 and Comparative Examples 1 to 4 by the above method were immersed in Fluorinert FC-40 (manufactured by 3M) and subjected to ultra-high voltage. Using a withstand voltage tester 7470 (manufactured by Keisoku Giken Co., Ltd.), a φ25 mm electrode is placed on a φ25 mm copper plate patterned by etching on the heat dissipation circuit board, and a voltage of 0.5 kV is applied at intervals of 60 seconds. The voltage was increased by 0.5 kV each time, and the measurement was performed until dielectric breakdown occurred. The measurement was performed at a frequency of 60 Hz and a boost rate of 1000 V/sec.

If the dielectric breakdown voltage per unit thickness (converted value for a thickness of 1 mm) is 60 kV / mm or more, "○ (good)", if it is 40 kV / mm or more and less than 60 kV / mm, "△ (not good) )”, and when less than 40 kV/mm, “× (poor)”. These measurement results are shown in Table 1.
The evaluation of the dielectric breakdown voltage (BDV) before the moisture absorption reflow test can be used as the evaluation of the withstand voltage performance.

[Dielectric breakdown voltage (BDV) after moisture absorption reflow test]
(Measurement of dielectric breakdown voltage (BDV))
Using the thermally conductive resin sheets obtained in Examples 1 to 3 and Comparative Examples 1 to 4, a heat dissipating circuit board was prepared in the same manner as in the above [Breakdown voltage (BDV) before moisture absorption reflow test]. After storing for 3 days in an environment of 85 ° C. and 85% RH using a constant humidity machine SH-221 (manufactured by Espec Co., Ltd.), the temperature was raised from room temperature to 290 ° C. in 12 minutes in a nitrogen atmosphere within 30 minutes. C. for 10 minutes, and then cooled to room temperature (moisture absorption reflow test). After that, the heat dissipating circuit board was immersed in Fluorinert FC-40 (manufactured by 3M), and an ultra-high voltage withstand voltage tester 7470 (manufactured by Keisoku Giken Co., Ltd.) was used to pattern the heat dissipating circuit board by etching. A φ25 mm electrode was placed on the copper plate, a voltage of 0.5 kV was applied, and the voltage was increased by 0.5 kV every 60 seconds, and the measurement was carried out until dielectric breakdown occurred. The measurement was performed at a frequency of 60 Hz and a boost rate of 1000 V/sec.

If the dielectric breakdown voltage per unit thickness (converted value for a thickness of 1 mm) is 60 kV / mm or more, "○ (good)", if it is 40 kV / mm or more and less than 60 kV / mm, "△ (not good) )”, and when less than 40 kV/mm, “× (poor)”. These measurement results are shown in Table 1.
The evaluation of the dielectric breakdown voltage (BDV) after the moisture absorption reflow test can be the evaluation of the moisture absorption reflow resistance.

[Observation of sample state after moisture absorption reflow test]
The heat-dissipating circuit boards prepared in Examples 1-3 and Comparative Examples 1-4 were subjected to a moisture absorption reflow test in the same manner as above, and then patterned by the above etching using an ultrasonic imaging device FinSAT (FS300III) (manufactured by Hitachi Power Solutions). The interface between the φ25 mm copper electrode and the thermally conductive resin sheet was observed. A probe with a frequency of 50 MHz was used for the measurement, a gain of 30 dB and a pitch of 0.2 mm were used, and the sample was placed in water. A case where no peeling, floating, or void generation was observed at the interface was indicated as "Good", and a case where peeling, floating, or void generation was observed at the interface, was indicated as "X (poor)". This evaluation result is also shown in Table 1.
Evaluation of interfacial detachment after moisture absorption reflow test is performed by laminating a thermally conductive resin sheet to a metal plate and performing a reflow process. It can be evaluated whether or not it is likely to occur.

Comparing Examples 1 to 3 with Comparative Examples 1 to 3, by using aggregated boron nitride particles having B ₁ /(A ₁ +B ₁ ) of 0.60 or more, the thermal conductivity is remarkably high. was found to be obtained. It was also found that a heat-dissipating sheet having remarkably high thermal conductivity can be obtained by setting the second peak top height and the second peak top diameter in the sheet ash content within the ranges of the present invention.
In Examples 1 to 3, A ₂ /A ₁ before and after sheet molding was 0.70 or more and B ₂ /B ₁ was 0.85 or less, and the first From the peak, the second peak, and the degree of circularity, the boron nitride agglomerated particles used for these maintain the internal structure of the agglomerated particles themselves even after sheet molding, thereby maintaining high thermal conductivity inside the agglomerated particles. At the same time, it is thought that the thermal resistance between particles is kept low by appropriately deforming the surface of the contact portion between adjacent particles. From the SEM photograph of the boron nitride aggregated particles contained in the ash of the thermally conductive resin sheet of Example 2 shown in FIG. It can be confirmed that is moderately deformed.
In addition, when comparing Examples 1 to 3 and Comparative Example 4 with respect to the value of the dielectric breakdown voltage before and after the moisture absorption reflow test, it was found that by using a thermoplastic resin having a melting point of 300 ° C. or higher as the matrix resin, the withstand voltage It was found that performance and moisture absorption reflow resistance were improved.
Furthermore, in Examples 1 to 3, the manufacturing method includes a mixing step of mixing a powder made of a thermoplastic resin and aggregated boron nitride particles, and a press molding step of pressing the mixture to form a sheet. Therefore, without impairing the original characteristics of the boron nitride aggregated particles with high thermal conductivity, voids remaining in the sheet during molding are suppressed, so that both withstand voltage performance and thermal conductivity can be compatible. I found out.
In Comparative Example 4, an epoxy resin and the aggregated boron nitride particles of Example 1 were used to form a sheet by a conventional wet coating method. It is estimated that the inter-particle volume of the aggregated boron nitride particles is too large for use in the wet coating method. presumably decreased. Due to the effect of air bubbles in the sheet, the thermal conductivity was also inferior to that of Example 1 in which the same amount of the same aggregated boron nitride particles was blended.

In addition, the present invention can also take the following configurations.
[1] A resin composition containing a thermoplastic resin and boron nitride aggregated particles,
B ₁ /(A ₁ +B ₁ ) is 0.60 or more, where A ₁ is the intra-particle pore volume and B ₁ is the inter-particle volume of the boron nitride aggregated particles measured by mercury porosimetry. , a thermally conductive resin composition.
[2] The resin composition according to [1] above, wherein the main component of the thermoplastic resin is a crystalline thermoplastic resin having a melting point of 300°C or higher.
[3] The resin composition according to [2] above, wherein the crystalline thermoplastic resin having a melting point of 300° C. or higher is a polyetherketone-based resin.
[4] The resin composition according to [3] above, wherein the polyether ketone-based resin is polyether ether ketone.
[5] The resin composition according to any one of [1] to [4] above, wherein the aggregated boron nitride particles have a card house structure.
[6] The resin composition according to any one of [1] to [5] above, wherein the volume-based average particle diameter D50 of the aggregated boron nitride particles is 10 μm or more and 200 μm or less.
[7] 100% by mass of the resin composition contains 15% by mass or more and 40% by mass or less of the thermoplastic resin, and 60% by mass or more and 85% by mass or less of the boron nitride aggregate particles, above [1] to [ 6], the resin composition according to any one of the above.
[8] A thermally conductive resin sheet made of the resin composition according to any one of [1] to [7] above.
[9] Regarding the boron nitride aggregated particles contained in the residual ash when the thermally conductive resin sheet was heated at 700°C for 5 hours, the intraparticle pore volume measured by mercury porosimetry was defined as _A2 , and the interparticle volume was defined as The thermally conductive resin sheet according to [8] above, wherein A ₂ /A ₁ is 0.70 or more and B ₂ /B ₁ is 0.85 or less when B ₂ .
[10] The heat conduction according to [8] or [9] above, wherein the boron nitride aggregated particles contained in the residual ash after heating the thermally conductive resin sheet at 700 ° C. for 5 hours have a circularity of 0.85 or more. flexible resin sheet.
[11] The thermally conductive resin sheet according to any one of [8] to [10] above, which has a thickness of 50 μm or more and 300 μm or less.
[12] The thermally conductive resin sheet according to any one of [8] to [11] above, which has a thermal conductivity in the thickness direction at 25° C. of 16 W/m·K or more.
[13] A laminated heat-dissipating sheet comprising a heat-dissipating metal layer laminated on one surface of the heat-conducting resin sheet according to any one of [8] to [12] above.
[14] A heat-dissipating circuit board having the laminated heat-dissipating sheet according to [13] above.
[15] The heat dissipating circuit board according to [14] above, which has a structure in which a conductive circuit is formed on the other surface of the heat conductive resin sheet.
[16] A power semiconductor device comprising the heat dissipation circuit board according to [14] or [15] above.
[17] A mixing step of obtaining a mixture of a powder made of a thermoplastic resin and aggregated boron nitride particles;
A press molding step of pressing the mixture to form a sheet,
B ₁ /(A ₁ +B ₁ ) is 0.60 or more, where A ₁ is the intra-particle pore volume of the boron nitride aggregated particle raw material and B ₁ is the inter-particle volume measured by the mercury intrusion method. A method for producing a thermally conductive resin sheet.
[18] A thermally conductive resin sheet made of a resin composition containing a thermoplastic resin and aggregated particles of boron nitride,
In the pore size distribution curve obtained by measuring the residual ash content when the thermally conductive resin sheet is heated at 700° C. for 5 hours by a mercury intrusion method, the peak having a maximum value at a pore size of less than 5 μm is defined as the first peak. , when the peak having a maximum value at a pore diameter of 5 μm or more is the second peak,
A thermally conductive resin sheet having a second peak top height of 1.0 mL/g or more and a second peak top diameter of 15 μm or more.
[19] The thermally conductive resin sheet according to [18] above, wherein the main component of the thermoplastic resin is a crystalline thermoplastic resin having a melting point of 300°C or higher.
[20] The thermally conductive resin sheet according to [19] above, wherein the crystalline thermoplastic resin having a melting point of 300°C or higher is a polyetherketone-based resin.
[21] The thermally conductive resin sheet according to [20] above, wherein the polyetherketone-based resin is polyetheretherketone.
[22] The thermally conductive resin sheet according to any one of [18] to [21] above, wherein the aggregated boron nitride particles have a card house structure.
[23] The thermally conductive resin sheet according to any one of [18] to [22] above, wherein the volume-based average particle diameter D50 of the aggregated boron nitride particles is 10 μm or more and 200 μm or less.
[24] 100% by mass of the resin composition contains 15% by mass or more and 40% by mass or less of the thermoplastic resin, and 60% by mass or more and 85% by mass or less of the boron nitride aggregate particles, above [18] to [ 23], the thermally conductive resin sheet according to any one of the above.
[25] The thermally conductive resin sheet according to any one of [18] to [24] above, wherein the first peak top diameter is 0.4 μm or less.
[26] The thermally conductive resin sheet according to any one of [18] to [25] above, wherein the first peak top height is 0.25 mL/g or more and 0.7 mL/g or less.
[27] Any one of the above [18] to [26], wherein the circularity of the aggregated boron nitride particles contained in the residual ash after heating the thermally conductive resin sheet at 700° C. for 5 hours exceeds 0.945. The thermally conductive resin sheet described.
[28] The thermally conductive resin sheet according to any one of [18] to [27] above, which has a thickness of 50 μm or more and 300 μm or less.
[29] The thermally conductive resin sheet according to any one of the above [18] to [28], which has a thickness direction thermal conductivity of 18 W/m·K or more at 25°C.
[30] A laminated heat-dissipating sheet comprising a heat-dissipating metal layer laminated on one surface of the heat-conducting resin sheet according to any one of [18] to [29] above.
[31] A heat-dissipating circuit board having the laminated heat-dissipating sheet according to [30] above.
[32] The heat dissipating circuit board according to [31] above, which has a structure in which a conductive circuit is formed on the other surface of the heat conductive resin sheet.
[33] A power semiconductor device having the heat dissipation circuit board according to [31] or [32] above.
[34] A mixing step of obtaining a mixture of a powder made of a thermoplastic resin and aggregated boron nitride particles;
A press molding step of heating and pressurizing the mixture to form a sheet,
In the pore size distribution curve obtained by measuring the residual ash content when the sheet is heated at 700 ° C. for 5 hours by mercury porosimetry, the peak having a maximum value at a pore size of less than 5 µm is defined as the first peak, and the pore size is 5 µm. When the peak having the maximum value above is the second peak,
A method for producing a thermally conductive resin sheet, wherein the second peak top height is 1.0 mL/g or more and the second peak top diameter is 15 μm or more.
[35] A thermally conductive resin sheet made of a resin composition containing a thermoplastic resin and aggregated particles of boron nitride,
In the pore size distribution curve obtained by measuring the residual ash content when the thermally conductive resin sheet is heated at 700° C. for 5 hours by a mercury intrusion method, the peak having a maximum value at a pore size of less than 5 μm is defined as the first peak. , when the peak having a maximum value at a pore diameter of 5 μm or more is the second peak,
A thermally conductive resin sheet having a first peak top diameter of 0.4 μm or less and a second peak top diameter of 15 μm or more.
[36] The thermally conductive resin sheet according to [35] above, wherein the main component of the thermoplastic resin is a crystalline thermoplastic resin having a melting point of 300°C or higher.
[37] The thermally conductive resin sheet according to [36] above, wherein the crystalline thermoplastic resin having a melting point of 300°C or higher is a polyetherketone-based resin.
[38] The thermally conductive resin sheet according to the above [37], wherein the polyetherketone-based resin is polyetheretherketone.
[39] The thermally conductive resin sheet according to any one of [35] to [38] above, wherein the aggregated boron nitride particles have a card house structure.
[40] The thermally conductive resin sheet according to any one of [35] to [39] above, wherein the volume-based average particle diameter D50 of the aggregated boron nitride particles is 10 μm or more and 200 μm or less.
[41] 100% by mass of the resin composition contains 15% by mass or more and 40% by mass or less of the thermoplastic resin, and 60% by mass or more and 85% by mass or less of the boron nitride aggregate particles, above [35] to [ 40], the thermally conductive resin sheet according to any one of the above.
[42] The thermally conductive resin sheet according to any one of [35] to [41] above, wherein the second peak top height is 1.0 mL/g or more.
[43] The thermally conductive resin sheet according to any one of [35] to [42] above, wherein the first peak top height is 0.25 mL/g or more and 0.7 mL/g or less.
[44] Any one of the above [35] to [43], wherein the circularity of the aggregated boron nitride particles contained in the residual ash after heating the thermally conductive resin sheet at 700° C. for 5 hours exceeds 0.945. The thermally conductive resin sheet described.
[45] The thermally conductive resin sheet according to any one of [35] to [44] above, which has a thickness of 50 μm or more and 300 μm or less.
[46] The thermally conductive resin sheet according to any one of the above [35] to [45], which has a thickness direction thermal conductivity of 18 W/m·K or more at 25°C.
[47] A laminated heat-dissipating sheet comprising a heat-dissipating metal layer laminated on one surface of the heat-conducting resin sheet according to any one of [35] to [46] above.
[48] A heat-dissipating circuit board having the laminated heat-dissipating sheet described in [47] above.
[49] The heat dissipating circuit board according to [48] above, which has a configuration in which a conductive circuit is formed on the other surface of the heat conductive resin sheet.
[50] A power semiconductor device having the heat dissipation circuit board according to [48] or [49] above.
[51] A mixing step of obtaining a mixture of a powder made of a thermoplastic resin and aggregated boron nitride particles;
A press molding step of heating and pressurizing the mixture to form a sheet,
In the pore size distribution curve obtained by measuring the residual ash content when the sheet is heated at 700 ° C. for 5 hours by mercury porosimetry, the peak having a maximum value at a pore size of less than 5 µm is defined as the first peak, and the pore size is 5 µm. When the peak having the maximum value above is the second peak,
A method for producing a thermally conductive resin sheet, wherein the first peak top diameter is 0.4 μm or less and the second peak top diameter is 15 μm or more.

Claims (29)

A resin composition containing a thermoplastic resin and boron nitride aggregated particles,
B ₁ /(A ₁ +B ₁ ) is 0.60 or more, where A ₁ is the intra-particle pore volume and B ₁ is the inter-particle volume of the boron nitride aggregated particles measured by mercury porosimetry. , a thermally conductive resin composition. The resin composition according to claim 1, wherein the main component of the thermoplastic resin is a crystalline thermoplastic resin having a melting point of 300°C or higher. The resin composition according to claim 2, wherein the crystalline thermoplastic resin having a melting point of 300°C or higher is a polyetherketone-based resin. The resin composition according to claim 3, wherein the polyetherketone-based resin is polyetheretherketone. The resin composition according to any one of claims 1 to 4, wherein the aggregated boron nitride particles have a card house structure. The resin composition according to any one of claims 1 to 5, wherein the volume-based average particle diameter D50 of the boron nitride aggregated particles is 10 µm or more and 200 µm or less. Any one of claims 1 to 6, wherein 100% by mass of the resin composition contains 15% by mass or more and 40% by mass or less of the thermoplastic resin, and 60% by mass or more and 85% by mass or less of the boron nitride aggregate particles. The resin composition according to Item. A thermally conductive resin sheet made of the resin composition according to any one of claims 1 to 7. Regarding the boron nitride agglomerated particles contained in the residual ash when the thermally conductive resin sheet was heated at 700° C. for 5 hours, the intra-particle pore volume measured by the mercury intrusion method was defined as A ₂ , and the inter-particle volume was defined as B ₂ . 9 . The thermally conductive resin sheet according to claim 8 , wherein A ₂ /A ₁ is 0.70 or more and B ₂ /B ₁ is 0.85 or less. The thermally conductive resin sheet according to claim 8 or 9, wherein the boron nitride aggregated particles contained in the residual ash after heating the thermally conductive resin sheet at 700°C for 5 hours have a circularity of 0.85 or more. A thermally conductive resin sheet made of a resin composition containing a thermoplastic resin and boron nitride aggregated particles,
In the pore size distribution curve obtained by measuring the residual ash content when the thermally conductive resin sheet is heated at 700° C. for 5 hours by a mercury intrusion method, the peak having a maximum value at a pore size of less than 5 μm is defined as the first peak. , when the second peak is a peak having a maximum value at a pore diameter of 5 μm or more,
A thermally conductive resin sheet having a second peak top height of 1.0 mL/g or more and a second peak top diameter of 15 μm or more. The thermally conductive resin sheet according to claim 11, wherein the main component of said thermoplastic resin is a crystalline thermoplastic resin having a melting point of 300°C or higher. The thermally conductive resin sheet according to claim 12, wherein the crystalline thermoplastic resin having a melting point of 300°C or higher is a polyetherketone-based resin. The thermally conductive resin sheet according to claim 13, wherein the polyetherketone-based resin is polyetheretherketone. The thermally conductive resin sheet according to any one of claims 11 to 14, wherein the aggregated boron nitride particles have a card house structure. The thermally conductive resin sheet according to any one of claims 11 to 15, wherein the volume-based average particle diameter D50 of the boron nitride aggregated particles is 10 µm or more and 200 µm or less. Any one of claims 11 to 16, wherein 100% by mass of the resin composition contains 15% by mass or more and 40% by mass or less of the thermoplastic resin, and 60% by mass or more and 85% by mass or less of the boron nitride aggregate particles. The thermally conductive resin sheet according to Item. The thermally conductive resin sheet according to any one of claims 11 to 17, wherein the first peak top diameter is 0.4 μm or less. The thermally conductive resin sheet according to any one of claims 11 to 18, wherein the first peak top height is 0.25 mL/g or more and 0.7 mL/g or less. The thermally conductive resin according to any one of claims 11 to 19, wherein the circularity of the aggregated boron nitride particles contained in the residual ash after heating the thermally conductive resin sheet at 700°C for 5 hours exceeds 0.945. sheet. The thermally conductive resin sheet according to any one of claims 8 to 20, having a thickness of 50 µm or more and 300 µm or less. The thermally conductive resin sheet according to any one of claims 8 to 21, which has a thermal conductivity of 16 W/m·K or more in the thickness direction at 25°C. The thermally conductive resin sheet according to any one of claims 8 to 21, which has a thermal conductivity of 18 W/m·K or more in the thickness direction at 25°C. A laminated heat-dissipating sheet having a configuration in which a heat-dissipating metal layer is laminated on one surface of the thermally conductive resin sheet according to any one of claims 8 to 23. A heat-dissipating circuit board having the laminated heat-dissipating sheet according to claim 24. 26. The heat dissipating circuit board according to claim 25, comprising a configuration in which a conductive circuit is formed on the other surface of the heat conductive resin sheet. A power semiconductor device having the heat dissipation circuit board according to claim 25 or 26. A mixing step of obtaining a mixture of a powder made of a thermoplastic resin and aggregated particles of boron nitride;
A press molding step of heating and pressurizing the mixture to form a sheet,
B ₁ /(A ₁ +B ₁ ) is 0.60 or more, where A ₁ is the intra-particle pore volume of the boron nitride aggregated particle raw material and B ₁ is the inter-particle volume measured by the mercury intrusion method. A method for producing a thermally conductive resin sheet. A mixing step of obtaining a mixture of a powder made of a thermoplastic resin and aggregated particles of boron nitride;
A press molding step of heating and pressurizing the mixture to form a sheet,
In the pore size distribution curve obtained by measuring the residual ash content when the sheet is heated at 700 ° C. for 5 hours by mercury porosimetry, the peak having a maximum value at a pore size of less than 5 µm is defined as the first peak, and the pore size is 5 µm. When the peak having a maximum value less than the second peak,
A method for producing a thermally conductive resin sheet, wherein the second peak top height is 1.0 mL/g or more and the second peak top diameter is 15 μm or more.

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