WO2024202729A1 - Silicon nitride powder and resin composition using same - Google Patents

Abstract

This silicon nitride powder contains a plurality of silicon nitride particles, and has a crystallite diameter of more than 70.2 nm as measured by the Scherrer method.

Description

Silicon nitride powder and resin composition using same

This disclosure relates to silicon nitride powder and a resin composition using the same.

Heat generated by passing current through an electronic component is dissipated via a heat sink. In order to improve the efficiency of heat dissipation, a technique is known in which a heat dissipation material is filled between the electronic component and the heat sink.
One type of heat dissipation material is a resin composition containing a resin and inorganic particles, and it is known that silicon nitride powder can be used as the inorganic particles (for example, Patent Document 1).

Patent document 1 discloses a low-aluminum spherical β silicon nitride powder used as a filler in electronic packaging materials. The silicon nitride powder is characterized by a sphericity of 0.5 to 0.99, an Al impurity content of less than 500 ppm, and a particle size range of 0.5 μm to 50 μm.

Patent Document 2 discloses a method for producing silicon nitride powder suitable for producing silicon nitride sintered bodies and silicon nitride powder obtained by said method. The silicon nitride powder has an average particle size of 1-50 μm, a metal oxide content of 0-10 wt%, and an impurity content of less than 1 wt%, preferably a metal oxide content of less than 1 wt%, and the sintered body has a thermal conductivity of 90 W/mK or more and a bending strength of 700 MPa or more, and preferably the sintering conditions for the sintered body are to mix the silicon nitride powder with MgO and Y ₂ O ₃ , polish, dry press mold the base, and gas pressure sinter the base at 1900° C. and 1 MPa nitrogen gas pressure for 8 hours.

Patent Document 3 discloses silicon nitride powder suitable for producing highly thermally conductive silicon nitride sintered bodies. The silicon nitride powder is characterized by having a β fraction of 30-100%, an oxygen content of less than 0.5 wt%, an average particle size of 0.2-10 μm, an aspect ratio of 10 or less, and containing columnar particles with grooves formed in the long axis direction of the particle.

Special Publication No. 2022-522814 Special Publication No. 2022-541208 JP 2004-262756 A

Resin compositions used as heat dissipation members are desirably placed in the vicinity of electronic components and therefore desirably have low dielectric loss, and therefore there is a demand for silicon nitride powder capable of forming resin compositions with low dielectric loss.
However, the silicon nitride powders described in Patent Documents 1 to 3 have not been considered for forming a resin composition with low dielectric loss.

In view of this situation, one embodiment of the present invention aims to provide a silicon nitride powder that is used as a filler for resin compositions and that can form a resin composition with low dielectric loss. Furthermore, another embodiment of the present invention aims to provide a resin composition that uses the silicon nitride powder.

Aspect 1 of the present invention is
The silicon nitride powder comprises a plurality of silicon nitride particles, the crystallite size being greater than 70.2 nm as measured by the Scherrer method.

Aspect 2 of the present invention is
2. The silicon nitride powder according to claim 1, having an apparent density of greater than 3.17 g/ ^cm3 .

Aspect 3 of the present invention is
3. The silicon nitride powder according to aspect 1 or 2, having a specific surface area of 3.50 m ² /g or less.

Aspect 4 of the present invention is
The silicon nitride powder according to any one of Aspects 1 to 3, wherein the β-formation rate is 65% or more.

Aspect 5 of the present invention is
The silicon nitride powder according to any one of Aspects 1 to 4, wherein the ratio (L2/L1) of the total length L2 of the internal boundary line to the length L1 of the outer edge is 1% or less, and the maximum particle size of the silicon nitride particles is 6.8 μm or more.

Aspect 6 of the present invention is
A resin composition comprising a resin and the silicon nitride powder according to any one of Aspects 1 to 5.

By using the silicon nitride powder according to one embodiment of the present invention as a filler, a resin composition with low dielectric loss can be obtained.

[Silicon nitride powder]
The present inventors have studied silicon nitride powder used as a filler for resin compositions from various viewpoints in order to realize a resin composition with low dielectric loss. As a result, they have found for the first time that it is important to control the crystallite size of silicon nitride powder measured by the Scherrer method to a predetermined value or more, and have completed the present invention. The details of each requirement stipulated in the embodiment of the present invention are shown below.

(Crystallite size)
The silicon nitride powder according to the embodiment of the present invention comprises a plurality of silicon nitride particles, and has a crystallite diameter of more than 70.2 nm as measured by the Scherrer method. In silicon nitride powder, since there are no defects in the crystallites, the larger the crystallite diameter, the lower the dielectric loss. Therefore, by using silicon nitride powder with a large crystallite diameter, a resin composition with low dielectric loss can be obtained. Preferably, the crystallite diameter is 70.5 nm or more, more preferably 72.0 nm or more, even more preferably 76.0 nm or more, even more preferably 80.0 nm or more, and particularly preferably 85.0 nm or more. The upper limit is not particularly limited, but may be less than 300 nm, may be 200 nm or less, or may be 150 nm or less.
In this specification, the term "crystallite" refers to the smallest unit of crystal that contributes to X-ray diffraction. Meanwhile, in this specification, the term "single crystal particle" described later refers to a relatively large crystal in which, when a boundary (also called a high-angle boundary) with a crystal orientation difference (oblique angle) exceeding 15° is taken as a crystal grain boundary as a result of EBSD analysis, the crystal grain boundary does not exist (i.e., a boundary with a crystal orientation difference of 15° or less may exist). In this specification, the term "single crystal particle" may include, for example, multiple "crystallites".

As described above, the crystallite size of the silicon nitride powder according to the embodiment of the present invention is measured by the Scherrer method. Specifically, the diffraction pattern of the silicon nitride powder is obtained by powder X-ray diffraction (X-ray source: CuKα ray). From the diffraction pattern, the diffraction angle θ and half-width β of the peak of each plane are obtained for the (110) plane, (200) plane, (101) plane, and (210) plane (or (120) plane) of β-type silicon nitride, and are substituted into the following Scherrer formula (1) to obtain the crystallite size D. The average value of the crystallite size calculated for each plane is taken as the crystallite size of the silicon nitride powder.

D=Kλ/βcosθ...(1)

In the above formula (1), K is the Scherrer constant (=0.94), β is the half-width of the peak (rad.), θ is the diffraction angle (rad.), and λ is 0.15418 nm.

(Apparent density)
The apparent density of the silicon nitride powder according to the embodiment of the present invention is preferably more than 3.17 g/cm ³ , more preferably more than 3.18 g/cm ^3. This allows the silicon nitride powder to contain a large number of silicon nitride particles with a small amount of internal voids, making it easier to obtain a resin composition with lower dielectric loss. The upper limit of the apparent density is, for example, 3.44 g/cm ^3. In addition, since the apparent density is not too high, it is expected that the silicon nitride powder will not easily settle when mixed with a resin and will be easily dispersed. In order to exert such an effect, the apparent density of the silicon nitride powder is preferably 3.30 g/cm ³ or less, more preferably 3.25 g/cm ³ or less.

The apparent density of silicon nitride powder is measured by the pycnometer method in accordance with JIS R 1620:1995. Measurements should be taken at least five times, and the average value is taken as the apparent density of the silicon nitride powder. For example, an Accupyc 1330 (Micromeritics) can be used for the measurement.

(Specific surface area)
The specific surface area of the silicon nitride powder according to the embodiment of the present invention is a BET specific surface area measured by a krypton adsorption method based on JIS Z 8830:2013, and is preferably 3.50 m ² /g or less, more preferably less than 2.66 m ² /g, even more preferably 2.00 m ² /g or less, even more preferably 1.50 m ² /g or less, and particularly preferably less than 1.36 ^{m 2} /g. This reduces the interface with the resin, and as a result, it is expected that the dielectric loss of the resin composition can be reduced. The lower limit of the specific surface area is not particularly limited, but may be, for example, 0.01 m ² /g or more, 0.05 m ² /g or more, 0.10 m ² /g or more, or 0.50 m ² /g or more.

(Beta rate)
The β-phase ratio of the silicon nitride powder is preferably 65% or more. When the β-phase ratio is 65% or more, a resin composition having a lower dielectric loss can be easily obtained.
The β-formation rate is more preferably 70% or more, further preferably 80% or more, even more preferably 85% or more, and particularly preferably 90% or more.

In this specification, the "β-type rate" refers to the content (volume %) of β-type silicon nitride relative to the total silicon nitride contained in the silicon nitride powder.

In calculating the β-phase ratio, a diffraction pattern of the silicon nitride powder is obtained by powder X-ray diffraction (X-ray source: CuKα radiation), and the diffraction pattern is analyzed by the Gazzara & Messier method (G.P. Gazzara and D.P. Messier, “Determination of Phase Content _{of Si3N4} by X-ray Diffraction Analysis”, Am. Ceram. Soc. Bull., 56[9]777-80 (1977)) to calculate the β-phase ratio.

(The maximum particle size of silicon nitride particles having a ratio (L2/L1) of the total length L2 of the internal boundary lines to the length L1 of the outer edge of 1% or less is 6.8 μm or more)
The fewer the grain boundaries and cavities inside the silicon nitride particle, the lower the dielectric loss of the silicon nitride particle. Therefore, the ratio of the total length L2 of the boundary line to the length L1 of the outer edge (L2/L1) is introduced as an index of the content of grain boundaries inside the silicon nitride particle. L1 and L2 are obtained by observing the cross section of the silicon nitride particle. Here, "grain boundary" and "boundary line" refer to a boundary (also called a high-angle grain boundary) whose crystal orientation difference (oblique angle) exceeds 15° as a result of EBSD analysis.

When the length of the outer edge of one silicon nitride particle is L1 and the total length of the boundary lines that the silicon nitride particle has is L2, silicon nitride particles with a small value of L2/L1 can be said to have a low content of boundary lines. In this embodiment, silicon nitride particles with an L2/L1 of 1% or less are considered to be silicon nitride particles made of a single crystal (these are referred to as "single crystal particles"). Single crystal particles can be said to be silicon nitride particles with low dielectric loss.

In this embodiment, the maximum particle size of silicon nitride particles with L2/L1 of 1% or less (i.e., single crystal) is preferably 6.8 μm or more, more preferably 10.0 μm or more, even more preferably 15.0 μm or more, and particularly preferably 20.0 μm or more. This makes it easier to obtain a resin composition with low dielectric loss.

(Average aspect ratio of silicon nitride particles)
The silicon nitride particles contained in the silicon nitride powder preferably have an average aspect ratio of the minor axis to the major axis of more than 0.50, more preferably more than 0.60, even more preferably 0.70 or more, and even more preferably 0.72 or more. On the other hand, the average aspect ratio of the silicon nitride particles is preferably less than 0.87, more preferably 0.85 or less, and even more preferably 0.80 or less.
When the average aspect ratio of the silicon nitride particles is within an appropriate range, the filling rate in the resin composition can be further improved.

The average aspect ratio of the silicon nitride particles is measured as follows.
SEM images of silicon nitride particles contained in the silicon nitride powder are analyzed using image processing software (e.g., Image J (manufactured by the National Institute of Health)). The maximum particle size of the silicon nitride particles (referred to as the "major axis") is identified, and the particle size in the direction perpendicular to the major axis is regarded as the "minor axis". The major and minor axes are measured for 20 random silicon nitride particles, and the ratio of the minor axis to the major axis (minor axis/major axis) is determined for each particle. The arithmetic mean value of these ratios is regarded as the average aspect ratio of the silicon nitride particles.

(Surface roughness Ra)
The surface roughness Ra (arithmetic mean roughness) of the silicon nitride powder is preferably less than 0.97 nm. If the surface roughness Ra is less than 0.97 nm, the interface with the resin will be reduced when the powder is used as a filler for a resin composition, and as a result, it is expected that the dielectric loss of the resin composition can be reduced.
The surface roughness Ra is preferably less than 0.97 nm, more preferably 0.95 nm or less, even more preferably less than 0.93 nm, still more preferably 0.90 nm or less, and even more preferably 0.80 nm or less.

To measure surface roughness Ra, a measurement area of 100 nm x 100 nm is observed on the surface of any silicon nitride particle using a scanning probe microscope (SPM). The surface roughness Ra is calculated from the obtained shape image. The surface roughness Ra is measured for four silicon nitride particles, and the average value is taken as the surface roughness Ra of the silicon nitride powder.

[Method for producing silicon nitride particles]
The silicon nitride powder according to the embodiment of the present invention is
(1) synthesizing a silicon nitride composite crystal by a combustion synthesis method under a nitrogen atmosphere using a raw material containing Si;
(2) crushing the silicon nitride composite crystals to obtain a coarsely pulverized silicon nitride powder;
(3) finely pulverizing the coarsely pulverized silicon nitride powder to obtain a finely pulverized silicon nitride powder; and (4) heat-treating the finely pulverized silicon nitride powder to obtain a silicon nitride powder.
Each step will be described in detail below.

Step (1): Step of synthesizing silicon nitride synthetic crystal As the raw material containing Si, for example, Si powder is used.
The average particle diameter D50 of the raw material is, for example, within the range of 2 to 10 μm. This makes it possible to suppress the amount of oxygen impurities and increase the combustion speed to raise the synthesis temperature, thereby obtaining good crystal growth. As an example, the average particle diameter D50 of Si is 5 μm.

The diluent is used to adjust the amount of Si in the raw materials. Separately prepared silicon nitride powder is used as the diluent. The diluent may be either α-type silicon nitride powder or β-type silicon nitride powder, or a mixture of these may be used. The average particle diameter D50 of the diluent is preferably in the range of 0.5 to 2.0 μm. As an example, the average particle diameter D50 of the diluent is 1.0 μm. The amount of diluent added is less than 10 mass% of the total raw materials (including the diluent). As an example, the diluent is added in an amount of 5 to 8 mass% of the total raw materials. By adding the amount of diluent within the above range, it becomes easier to obtain silicon nitride powder with a specified crystallite size.

In this embodiment, a diluent is mixed into the raw materials and filled into an insulating heat-resistant container. The insulating heat-resistant container has a thermal conductivity of 1 W/mK or less, and can be made of alumina or zirconia, but carbon is preferred in consideration of the risk of impurities being mixed in. After filling with the raw materials, the container is covered with a lid made of the same material as the insulating heat-resistant container. Furthermore, in order to increase the temperature inside the synthesis body during combustion, the thickness of the mixed raw materials is made to be more than 100 mm, preferably more than 100 mm and not more than 150 mm. Combustion synthesis is performed under a nitrogen atmosphere in the range of 0.5 to 1 MPa (for example, 0.9 MPa). By adjusting the pressure range within the above range, efficient synthesis can be achieved while suppressing increases in equipment costs.

When filling the crucible with the mixed raw materials, a layer of powder (silicon nitride) with a thickness of 1 mm to 80 mm is laid on the bottom and sides of the crucible, the mixed raw materials are then filled, and the top surface is covered with a layer of powder with a thickness of 1 mm to 80 mm. The thickness of the powder is 100 mm or less, and preferably 1 mm to 80 mm. Covering the powder keeps the mixed raw materials warm, making it easier to obtain silicon nitride powder with the specified crystallite size.

To promote crystal growth more effectively, a catalyst may be used, for example, about 0.01 to 0.1 mass % of Y ₂ O ₃ , Fe ₂ O ₃ , CaO, Ni, Co, C, etc. is added. In addition, external auxiliary heating in the range of 500° C. to 1700° C. (for example, 1500° C.) is performed to increase the combustion temperature in the combustion synthesis method by self-ignition.

Step (2): Obtaining a coarsely pulverized silicon nitride powder The silicon nitride composite crystal is in the form of an aggregate of multiple silicon nitride particles. In step (2), the silicon nitride composite crystal is crushed to obtain a coarsely pulverized silicon nitride powder. For example, the composite is crushed using a general crushing device such as a hammer mill or a disk mill until it passes through a sieve with a predetermined mesh size (for example, a sieve with a mesh size in the range of 400 μm to 500 μm).

Step (3): Step of obtaining finely pulverized silicon nitride powder The coarsely pulverized silicon nitride powder is further pulverized to obtain finely pulverized silicon nitride powder. The pulverization is carried out using a pulverizing device such as a jet mill or a ball mill. If necessary, the obtained finely pulverized powder may be classified. The classification may be carried out by sieving, wet classification, or the like.

Step (4): Step of Obtaining Silicon Nitride Powder The finely pulverized powder of silicon nitride is heat-treated to obtain silicon nitride powder. By the heat treatment, an oxide film is formed on the surface of the silicon nitride particles, so that the silicon nitride particles can be chemically stabilized. The heat treatment is performed in air at 500°C or more and 1200°C or less, preferably more than 800°C and 1100°C or less. The heat treatment time can be appropriately adjusted according to the heat treatment temperature. The heat treatment time is, for example, 5 hours.

In the method for producing silicon nitride powder, the heat generated by the combustion synthesis method is used to synthesize silicon nitride composite crystals, which are then crushed, classified, and finely pulverized to produce the silicon nitride powder according to this embodiment.

[Resin composition]
By using the silicon nitride powder according to the embodiment of the present invention as a filler for a resin composition, a resin composition having low dielectric loss can be obtained. The resin composition contains a resin and the silicon nitride powder according to the embodiment of the present invention.

The blending ratio of the resin/silicon nitride powder in the resin composition according to the embodiment of the present invention can be appropriately determined depending on the purpose and/or application. As an example, the ratio of the resin to the silicon nitride powder may be 5 to 75 volume % and 95 to 25 volume % relative to the resin composition (composite).
The filling rate of the silicon nitride powder in the resin composition refers to the content (volume %) of the silicon nitride powder when the volume of the resin composition (including the silicon nitride powder) is taken as 100 volume %.

A method for producing the resin composition will be described.
A resin composition can be obtained by mixing silicon nitride powder and a resin using a commonly used known method. For example, when the resin is liquid (such as liquid epoxy resin), the resin composition can be obtained by mixing the liquid resin, silicon nitride powder, and a curing agent, and then curing with heat or ultraviolet light. Known curing agents, mixing methods, and curing methods can be used. On the other hand, when the resin is solid, the silicon nitride powder and the resin are mixed, and then kneaded by a known method such as melt kneading to obtain the desired resin composition.

　The resin used in the resin composition may be a known resin such as an epoxy resin. The type of resin may be selected from thermoplastic resins, thermoplastic elastomers, and thermosetting resins. The resin may be used alone or in combination of two or more types.

Furthermore, these resin compositions may contain, as necessary, one or more of known additives such as plasticizers, curing accelerators, coupling agents, fillers, pigments, flame retardants, antioxidants, surfactants, compatibilizers, weather resistance agents, antiblocking agents, antistatic agents, leveling agents, and release agents, within the scope of the invention that does not impair the effects of the invention.

The silicon nitride powder according to the embodiment and the resin composition containing the silicon nitride powder are particularly suitable for use as a heat dissipating material with low dielectric loss. Thus, in one aspect of the present disclosure, it is possible to provide a heat dissipating silicon nitride powder with low dielectric loss and a heat dissipating resin composition with low dielectric loss.

Below, the embodiments of the present invention will be described in detail with reference to examples carried out to clarify the effects of the embodiments of the present invention. Note that the embodiments of the present invention are not limited in any way by the following examples.

<Preparation of silicon nitride powder>
Si powder (particle size = 5 μm) and silicon nitride powder (particle size = 1 μm) prepared separately as a diluent were mixed in a rolling ball mill. The amount of diluent added was 5 to 8 mass% with respect to the entire raw material (including diluent). The mixed powder was filled in a carbonaceous heat-insulating heat-resistant container with a layer of powder having a thickness of 1 mm to 80 mm on the bottom and sides so that the raw material layer thickness was more than 100 mm and 150 mm or less, and the raw material layer was further covered with a layer of powder having a thickness of 1 mm to 80 mm or less. Then, a lid made of a carbonaceous heat-insulating heat-resistant material was placed, and synthesis was performed under a nitrogen atmosphere of 0.9 MPa. After synthesis, coarse pulverization (disintegration) was performed in a mortar until it passed through a sieve with a predetermined opening. The openings of the sieve used are shown in Table 1.

(Samples No. 1, 3 and 4)
The obtained coarsely pulverized powder was further pulverized by a nano jetmizer (manufactured by Aisin Nano Technologies Co., Ltd.). A nano jetmizer with the model number shown in Table 1 was used for pulverization. The obtained finely pulverized powder was classified by the method shown in Table 1. The D50 of the classified powder of the obtained sample No. 3 was 12.0 μm, and the D50 of the classified powder of the obtained sample No. 4 was 14.0 μm. The obtained classified powder was then placed in an alumina crucible and heat-treated in an air atmosphere using a small powder programmable electric furnace (MMF series manufactured by AS ONE Co., Ltd.) under the conditions (heat treatment temperature, heat treatment time) shown in Table 1 to obtain silicon nitride powders (samples No. 1, 3 and 4).

(Sample No. 5)
Coarsely pulverized powders were prepared in the same manner as in the above-mentioned "Samples No. 1, 3, and 4." Note that the sieve used in the coarse pulverization (disintegration) had an opening of 500 μm.
The resulting coarsely pulverized powder was finely pulverized in a ball mill. The resulting finely pulverized powder was sieved using a vibrating sieve in the following manner, and then further wet-classified to obtain a silicon nitride powder having a desired D50.
The powder that remained under the sieve when sieving with a 63 μm mesh sieve was further sieved with a 10 μm mesh sieve. The silicon nitride powder obtained was then placed in an alumina crucible and heat-treated in an air atmosphere at a heat treatment temperature of 1100° C. for 5 hours using a small powder programmable electric furnace (MMF series manufactured by AS ONE) to obtain silicon nitride powder (sample No. 5). The D50 of sample No. 5 was 3.5 μm.

Various measurements were performed on the obtained samples No. 1 and 3 to 5 (Examples) and, as a comparative example, a commercially available silicon nitride powder (manufactured by Aldrich, silicon nitride (predominantly β-phase, ≦10 micron primary particle size, product code 248622); hereafter referred to as "Sample No. 2")

(1) Crystallite diameter The crystallite diameter of the sample (silicon nitride powder) was measured by the Scherrer method. Specifically, the diffraction pattern of the sample was obtained by powder X-ray diffraction (X-ray source: CuKα ray). From the diffraction pattern, the diffraction angle θ and half-width β of the peak of each plane were obtained for the (110) plane, (200) plane, (101) plane, and (210) plane (or (120) plane) of β-type silicon nitride, and substituted into the following Scherrer formula (1) to obtain the crystallite diameter D. The average value of the crystallite diameter values calculated for each plane was taken as the crystallite diameter of the silicon nitride powder.

D=Kλ/βcosθ...(1)

In the above formula (1), K is the Scherrer constant (=0.94), β is the half-width of the peak (rad.), θ is the diffraction angle (rad.), and λ is 0.15418 nm.

(2) Apparent Density The apparent density of the sample (silicon nitride powder) was measured in accordance with JIS R 1620: 1995. The measurement method and conditions were as follows:
Measurement method: Gas replacement method Sample drying: 200°C, 8 hours or more Equipment used: Accupic 1330 (Micromeritics)
Measurement conditions: Purge 10 times Purge filling pressure: 15.0 psig
Number of measurements: 5 Measurement filling pressure: 15.0 psig
Equilibrium pressure: 0.005 psig/min Measurement with precision setting: Yes
Variation tolerance: 0.05%
Sample cell size: 10 ^cm3

(3) Specific Surface Area The specific surface area of the sample (silicon nitride powder) was measured.
The specific surface area of a powder (solid) was measured by gas adsorption in accordance with JIS Z 8830: 2013, using krypton as the adsorption gas. In the measurement, 1 g of silicon nitride powder was placed in a sample tube, an adsorption/desorption isotherm was obtained, and the specific surface area ( ^m2 /g) was calculated by the multipoint plot method.

(4) β-Proportion The diffraction pattern of a sample (silicon nitride powder) was obtained using a powder X-ray diffractometer (manufactured by Rigaku Denki Co., Ltd.) under the following measurement conditions:
・X-ray source: CuKα rays ・X-ray output: 45kV, 200mA
・Graphite monochromator ・Diffraction angle (2θ): Step scan in the range of 2 to 90° in 0.02° increments ・Scanning speed: 21.7 deg/min

When a sample contained components other than silicon nitride, the peaks of those components were compared with the corresponding peaks of standard samples of those components to determine the proportions of those components. For Samples No. 1 and 2, the powder X-ray diffraction patterns obtained confirmed that the samples were composed only of alpha-type silicon nitride and beta-type silicon nitride. The proportion of beta-type silicon nitride in the sample (beta ratio) was then calculated using the Gazzara & Messier method.

(5) The maximum particle size of silicon nitride particles having an L2/L1 ratio of 1% or less (the maximum particle size of single crystal particles)
A sample for cross-sectional observation was prepared using the sample (silicon nitride particles). In preparing the sample for cross-sectional observation, the silicon nitride particles were embedded in resin, and then the resin and silicon nitride particles were cut with a diamond cutter. Thereafter, Pt was vapor-deposited on the cross-section as a protective film, the cross-section was prepared by Ar ion milling, and the sample was fixed to the SEM sample stage with Cu double-sided tape, and SEM-EBSD measurement was performed without vapor deposition. The observation position was determined so that two or more silicon nitride particles were completely contained within the observation area (i.e., two or more silicon nitride particles were not in contact with the frame of the observation area). The measurement was performed with β-type silicon nitride particles.

The following equipment was used for sample pretreatment and EBSD measurement.
・Equipment used: Ion milling device: E-3500 (manufactured by Hitachi High-Tech Corporation)
Ion sputtering device: E-1030 (manufactured by Hitachi, Ltd.)
Schottky scanning electron microscope: SU5000 (Hitachi High-Tech Corporation)
Backscattered electron diffraction device: Velocity (manufactured by METEK Corporation)

The conditions for the EBSD measurement were as follows:
・Measurement area: 500.0μm x 400.0μm
Acceleration voltage: 15.0 kV
Magnification: x500
Vacuum degree: 30 Pa

In the obtained EBSD image, two or more silicon nitride particles that were not in contact with the frame of the observation area were selected, and the length L1 of the outer edge of each silicon nitride particle was averaged using image processing software Image J (manufactured by the National Institute of Health). The total length L2 of the boundary lines was also calculated. The "total length L2 of the boundary lines" is the sum of the boundary lines contained inside the silicon nitride particle, and does not include the outer edge of the silicon nitride particle. The total length L2 of the boundary lines was calculated by adding the total length of the grain boundaries inside the silicon nitride particle and the total length of the inner wall of the cavity (if there is a cavity inside the silicon nitride particle). Note that "grain boundary" and "boundary line" here refer to a boundary (also called a high-angle grain boundary) where the crystal orientation difference (oblique angle) exceeds 15° as a result of EBSD analysis.

Such measurements were carried out once for 20 random silicon nitride particles, and silicon nitride particles with an L2/L1 ratio of 1% or less were regarded as single crystal particles, and the length of their major axis was measured and recorded as the "maximum particle size of the single crystal particle." If the 20 silicon nitride particles measured contained multiple single crystal particles, the arithmetic average of their maximum particle sizes was calculated.

(6) Average aspect ratio of silicon nitride particles SEM images of the sample (silicon nitride powder) were taken using the following equipment.
・Equipment used: Scanning electron microscope: JSM-IT200 (manufactured by JEOL Ltd.)
The photographing conditions were as follows:
Acceleration voltage: 5.0 kV
Signal: SED
Irradiation current: Std. -PC55
Magnification: 1000x

The SEM images were processed using the image processing software Image J (manufactured by the National Institute of Health) to determine the aspect ratio of 20 randomly selected silicon nitride particles in the SEM images. The maximum diameter of the silicon nitride particle was taken as the major axis, and the particle size in the direction perpendicular to the major axis was taken as the minor axis. The major and minor axes were measured for 20 randomly selected silicon nitride particles, and the ratio of the minor axis to the major axis (minor axis/major axis) was determined for each particle. The arithmetic mean value of these ratios was taken as the average aspect ratio of the silicon nitride particles (referred to as "aspect ratio" in Table 2).

(7) Surface roughness Ra
The surface roughness Ra was measured using a scanning probe microscope SPA300HV manufactured by Seiko Instruments Inc. The measurement conditions were as follows.
Probe station/unit SPI4000/SPA300HV
Cantilever: SI-DF20
Scanner: 20 μm
Data type: Shape image Observation mode: DFM (Dynamic Force Mode Microscope)
Scanning area: 100 nm x 100 nm
Scanning frequency: 0.25Hz
Analysis software: (included with the measuring device)

Five random silicon nitride particles were selected from the image, and a measurement area of 100 nm x 100 nm on the surface of each particle was observed using a scanning probe microscope (SPM). The surface roughness Ra of each particle was calculated from the obtained shape image, and the average value was taken as the surface roughness Ra of the silicon nitride powder.

(8) Dielectric loss of resin composition (composite) Polypropylene resin (J105G manufactured by Prime Polymer Co., Ltd.) and a sample (silicon nitride powder) were mixed in a volume ratio of 60:40. Using a press molding machine, vacuum press molding was performed under the following conditions to produce a silicon nitride powder-resin composite with a thickness of 600 μm.

The dielectric loss (tan δ) of the composite was measured under the following measurement conditions.
Measurement equipment: Network analyzer 8720ES (Agilent Technologies)
・Test piece dimensions: 50mm x 50mm
・Measurement frequency: 12GHz
Test environment: 22°C/59% RH

The measurement results are summarized in Tables 2 and 3.

The measurement results are discussed below.
The composites using silicon nitride powder of Samples No. 1 and 3 to 5, which satisfied the requirements of this embodiment, exhibited low dielectric loss. On the other hand, the composite using silicon nitride powder of Sample No. 2, which did not satisfy the requirements of this embodiment, exhibited high dielectric loss.

This application claims priority from Japanese Patent Application No. 2023-058622, filed on March 31, 2023. Japanese Patent Application No. 2023-058622 is incorporated herein by reference.

Claims (6)

Silicon nitride powder comprising multiple silicon nitride particles, the crystallite diameter of which, as measured by the Scherrer method, is greater than 70.2 nm. 2. The silicon nitride powder of claim 1, having an apparent density greater than 3.17 g/ ^cm3 . 2. The silicon nitride powder according to claim 1, having a specific surface area of 3.50 m ² /g or less. The silicon nitride powder according to claim 1, in which the beta conversion rate is 65% or more. The silicon nitride powder according to claim 1, wherein the ratio (L2/L1) of the total length L2 of the internal boundary lines to the length L1 of the outer edge is 1% or less and the maximum particle size of the silicon nitride particles is 6.8 μm or more. A resin composition comprising a resin and the silicon nitride powder according to any one of claims 1 to 5.