JP7538845B2 - LAMINATE AND POWER MODULE - Google Patents

Description

This disclosure relates to a laminate, a manufacturing method thereof, and a power module.

Power modules that control large currents are used in fields such as automobiles, electric railways, industrial equipment, and power generation. Ceramic substrates are used as insulating substrates mounted on power modules. Ceramic substrates have a ceramic plate and a metal circuit layer provided on the ceramic plate.

In recent years, there has been a trend to increase the thickness of the metal circuit layer in order to increase the current density. This has resulted in increased thermal stress caused by the difference in thermal expansion between the ceramic plate and the metal circuit layer. Therefore, ceramic substrates are required to have even greater durability against heat cycles. From the perspective of improving the durability of ceramic substrates against heat cycles, it is considered effective to provide an intermediate layer that reduces thermal stress caused by the difference in thermal expansion between the ceramic plate and the metal circuit layer.

In addition, from the viewpoint of improving the productivity and reliability of ceramic substrates, methods are being considered for manufacturing ceramic substrates that enable circuit formation without the necessity of etching processes and suppress the oxidation of materials that occurs with heating. As one example, a method for forming a metal circuit layer by cold spraying is being considered (for example, Patent Documents 1 and 2, etc.).

JP 2013-018190 A International Publication No. WO 2018/135490

One advantage of the method for manufacturing a ceramic substrate using the cold spray method is that it allows a metal circuit to be formed on the ceramic substrate without using brazing material. However, on the other hand, forming a metal circuit layer without using brazing material may result in weaker bonding between the ceramic substrate and the metal circuit layer compared to ceramic substrates obtained using conventional manufacturing methods. It would be useful if the method for manufacturing a ceramic substrate using the cold spray method could suppress the deterioration of bonding between the ceramic substrate and the metal circuit layer and produce a ceramic substrate with excellent durability against heat cycles.

The present disclosure aims to provide a laminate with excellent durability against heat cycles and a manufacturing method thereof. The present disclosure also aims to provide a power module with excellent reliability.

One aspect of the present disclosure provides a laminate comprising a ceramic plate, a stress relief layer formed on the ceramic plate, and a metal circuit layer formed on the stress relief layer, the stress relief layer having an alloy layer in contact with the ceramic plate, the alloy layer having a magnesium content of 7.5 mass% or less and an average thickness of less than 0.2 mm, and a metal layer in contact with the metal circuit layer, the alloy layer having a lower magnesium content than the alloy layer.

The laminate has a stress relief layer that has an alloy layer and a metal layer, and the alloy layer in contact with the ceramic plate contains magnesium, which provides strong adhesion between the ceramic plate and the metal circuit. The laminate also has a low magnesium content in the metal layer in contact with the metal circuit layer, and the alloy layer is provided to be less than a predetermined thickness, which prevents the stress relief layer from becoming too hard and allows the metal layer side of the stress relief layer to thermally expand appropriately, resulting in excellent durability against heat cycles overall.

The average thickness of the alloy layer may be 0.02 mm or more and less than 0.2 mm.

The thermal expansion coefficient of the stress relaxation layer may be greater than that of the ceramic plate and greater than that of the metal circuit layer. When the thermal expansion coefficient of the stress relaxation layer satisfies the above-mentioned conditions, the thermal stress from the metal circuit layer, which has a greater thermal expansion coefficient than the ceramic plate, can be more sufficiently relieved, and durability against heat cycles can be further improved.

The metal layer may contain aluminum.

The average thickness of the metal layer may be greater than 0.1 mm.

The ceramic plate may be a silicon nitride plate, an aluminum nitride plate, or an aluminum oxide plate.

One aspect of the present disclosure provides a power module comprising a circuit board, a semiconductor element electrically connected to one main surface of the circuit board, and a heat dissipation member connected to the other main surface of the circuit board, the circuit board being the laminate described above.

The power module has excellent reliability because the circuit board is the laminate described above.

One aspect of the present disclosure provides a method for manufacturing a laminate, comprising the steps of: spraying a first metal powder containing magnesium from a nozzle together with an inert gas against the surface of a ceramic plate to form a first deposition layer in contact with the ceramic plate; heat-treating the first deposition layer under an inert gas atmosphere to form an alloy layer; spraying a second metal powder having a lower magnesium content than the first metal powder together with an inert gas against the surface of the alloy layer to form a second deposition layer in contact with the alloy layer; heat-treating the second deposition layer under an inert gas atmosphere to form a metal layer; spraying a third metal powder containing metal particles from a nozzle together with an inert gas against the surface of the metal layer to form a third deposition layer in contact with the metal layer; and heat-treating the third deposition layer under an inert gas atmosphere to form a metal circuit layer.

The above-mentioned method for manufacturing a laminate can produce a laminate having an alloy layer, a metal layer, and a metal circuit layer on a ceramic plate by spraying metal powder. This manufacturing method makes it possible to form the alloy layer and the metal layer so that the magnesium content gradually decreases from the ceramic plate side, and can produce a laminate with excellent durability against heat cycles.

The first metal powder may be a gas atomized powder containing aluminum-magnesium alloy particles.

According to the present disclosure, it is possible to provide a laminate having excellent durability against heat cycles and a manufacturing method thereof. According to the present disclosure, it is also possible to provide a power module having excellent reliability.

FIG. 1 is a schematic cross-sectional view showing an example of a laminate. FIG. 2 is a schematic cross-sectional view showing an example of a laminate. FIG. 3 is a schematic diagram showing an example of a process for forming an alloy layer on a ceramic plate. FIG. 4 is a schematic cross-sectional view showing an example of a power module.

An embodiment of the present disclosure will be described below, with reference to the drawings where appropriate. However, the following embodiment is an example for explaining the present disclosure, and is not intended to limit the present disclosure to the following content. In the description, the same reference numerals will be used for the same elements or elements having the same functions, and duplicated descriptions will be omitted where appropriate. Furthermore, unless otherwise specified, positional relationships such as up, down, left, and right will be based on the positional relationships shown in the drawings. Furthermore, the dimensional ratios of each element are not limited to those shown in the drawings.

One embodiment of the laminate includes a ceramic plate, a stress relief layer formed on the ceramic plate, and a metal circuit layer formed on the stress relief layer. Here, the stress relief layer has an alloy layer in contact with the ceramic plate, the alloy layer having a magnesium content of 7.5 mass% or less and an average thickness of less than 0.2 mm, and a metal layer in contact with the metal circuit layer, the alloy layer having a lower magnesium content than the alloy layer.

Figure 1 is a schematic cross-sectional view showing an example of a laminate. The laminate 100 shown in Figure 1 has a ceramic plate 1 and metal circuits 2a and 2b provided on both sides thereof. The metal circuit 2a is composed of a stress relaxation layer 20a and a metal circuit layer 23a. The metal circuit layer 23a is bonded to the ceramic plate 1 via the stress relaxation layer 20a. The stress relaxation layer 20a is composed of an alloy layer 21a in contact with the ceramic plate 1 and a metal layer 22a provided on the alloy layer 21a and in contact with the metal circuit layer 23a. The metal circuit 2b is composed of a stress relaxation layer 20b and a metal circuit layer 23b. The metal circuit layer 23b is bonded to the ceramic plate 1 via the stress relaxation layer 20b. The stress relaxation layer 20b is composed of an alloy layer 21b in contact with the ceramic plate 1 and a metal layer 22b provided on the alloy layer 21b and in contact with the metal circuit layer 23b. The metal circuit layers 23a and 23b shown in FIG. 1 are both described as uniform layers, but may have patterns such as wiring. The metal circuit 2a and the metal circuit 2b are electrically insulated by the ceramic plate 1. As described above, the metal circuit layer and the stress relief layer or the metal circuit layer are in direct contact, and the laminate 100 does not have a brazing material layer.

The type of ceramic component constituting the ceramic plate 1 may be, for example, carbide, oxide, nitride, etc. The type of ceramic component may be, specifically, silicon carbide (SiC), aluminum oxide (Al ₂ O ₃ ), silicon nitride (Si ₃ N ₄ ), aluminum nitride (AlN ₃ ), etc. The ceramic plate 1 may be, for example, an aluminum oxide plate, a silicon nitride plate, or an aluminum nitride plate. Since the silicon nitride plate has a small oxide layer on the surface, the effect of the present disclosure is more remarkable when the ceramic plate 1 is a silicon nitride plate. The oxide layer improves the adhesive strength with other layers. The laminate according to the present disclosure improves the adhesive strength by containing a predetermined amount of magnesium in the alloy layer. As a result, sufficient adhesive strength can be exhibited even when a ceramic plate with a small oxide layer is used.

The average thickness of the ceramic plate 1 may be, for example, 0.2 to 1.5 mm, or 0.25 to 1.0 mm.

The average thickness of the plate and layer in this specification means the average thickness measured by a micrometer. The average value is the arithmetic mean value of the values obtained by measuring 10 locations.

The stress relaxation layers 20a and 20b are layers that relieve stress caused by the difference in thermal expansion between the ceramic plate 1 and the metal circuit layers 23a and 23b during heat cycles. The thermal expansion coefficient of the stress relaxation layers 20a and 20b may be greater than that of the ceramic plate 1 and greater than that of the metal circuit layers 23a and 23b.

The stress relaxation layers 20a and 20b are shown as being composed of two layers, the alloy layers 21a and 21b, and the metal layers 22a and 22b, respectively, but may be composed of, for example, three or more layers. The magnesium content in the stress relaxation layers 20a and 20b is set so that it is greater on the ceramic plate 1 side and smaller on the metal circuit layers 23a and 23b side. The metal layers 22a and 22b in contact with the metal circuit layers 23a and 23b do not need to contain magnesium. By not containing magnesium, the metal layers 22a and 22b are softer than the alloy layers 21a and 21b, and the stress relaxation performance can be further improved.

The alloy layers 21a and 21b contain magnesium. The inclusion of magnesium, which has excellent oxygen affinity, makes the bond between the alloy layers 21a and 21b and the ceramic plate 1 stronger. This effect is more pronounced when there is a small oxide layer on the surface of the ceramic plate. Here, the alloy layers 21a and 21b may be an alloy containing magnesium and aluminum. The composition of the alloy layers 21a and 21b can be selected to match the metal composition of the metal layers 22a and 22b. The alloy layers 21a and 21b may be an aluminum-magnesium alloy or an aluminum-magnesium alloy.

The alloy layers 21a and 21b may contain other components other than aluminum and magnesium, as long as the effect of the present invention is not impaired. The total content of the other components may be, for example, 5 mass% or less, 4 mass% or less, 3 mass% or less, 2 mass% or less, 1 mass% or less, 0.5 mass% or less, 0.1 mass% or less, 0.05 mass% or less, or 0.01 mass% or less. Here, the term "other components" includes impurities that are unintentionally contained in addition to the components that are optionally added. Examples of other components include O, C, Si, Mn, P, S, N, Ca, Cr, Ti, Nb, V, B, Mo, Cu, Ni, Sb, Sn, Ta, Mg, Zn, Co, Zr, REM (rare-earth elements), and compounds thereof (e.g., oxides, nitrides, sulfides, etc.).

The upper limit of the magnesium content in the alloy layer 21a is 7.5% by mass or less based on the total amount of the alloy layer 21a, but may be, for example, 7.0% by mass or less, 6.5% by mass or less, or 6.0% by mass or less. By having the upper limit of the magnesium content within the above range, the stress relaxation layer 20a is more sufficiently prevented from becoming too hard, and the overall durability against heat cycles is superior. The lower limit of the magnesium content in the alloy layer 21a may be, for example, more than 0% by mass based on the total amount of the alloy layer 21a, and may be, for example, 0.001% by mass or more, 0.01% by mass or more, 0.05% by mass or more, 0.1% by mass or more, or 0.3% by mass or more. By having the lower limit of the magnesium content within the above range, chemical bonds are generated via oxygen atoms, and the bond between the stress relaxation layer 20a and the ceramic plate 1 can be made stronger. The magnesium content in the alloy layer 21a may be adjusted within the above range, and may be, for example, 0.001 to 7.5 mass% based on the total amount of the alloy layer 21a.

The magnesium content in this specification refers to the value measured by inductively coupled plasma (ICP) optical emission spectrometry.

The upper limit of the average thickness of the alloy layer 21a is less than 0.2 mm, but may be, for example, 0.1 mm or less. Since the alloy layer 21a contains magnesium and is a relatively hard layer, if the upper limit of the average thickness of the alloy layer 21a is within the above range, the stress relaxation layer 20a is more sufficiently prevented from becoming too hard, and the durability against heat cycles is more excellent. The lower limit of the average thickness of the alloy layer 21a may be, for example, 0.02 mm or more, 0.03 mm or more, 0.04 mm or more, or 0.05 mm or more. If the lower limit of the average thickness of the alloy layer 21a is within the above range, the bond between the stress relaxation layer 20a and the ceramic plate 1 can be made stronger. The average thickness of the alloy layer 21a may be adjusted within the above range, and may be, for example, 0.02 mm or more but less than 0.2 mm, 0.02 mm to 0.1 mm, or 0.03 mm to 0.1 mm.

The magnesium content in alloy layer 21b may be the same as that described above for alloy layer 21a. The magnesium content in alloy layer 21b and the magnesium content in alloy layer 21a may be the same or different. It may be adjusted according to the type and thickness of the metal circuit layers 23a and 23b.

The average thickness of the alloy layer 21b may be the same as that described above for the alloy layer 21a. The average thickness of the alloy layer 21b may be the same as or different from the average thickness of the alloy layer 21a. The average thicknesses of the alloy layers 21a and 21b can be adjusted depending on the composition of the alloy layer and the difference in the thermal expansion coefficient between the ceramic plate 1 and the metal circuit layers 23a and 23b.

The metal layers 22a and 22b are layers with a lower magnesium content than the alloy layers 21a and 21b, and may not contain magnesium. The metal layers 22a and 22b may contain at least one selected from the group consisting of aluminum and aluminum alloys, and may be made of aluminum or an aluminum alloy, or may be made of aluminum. The metal layers 22a and 22b preferably do not contain magnesium, and more preferably consist of only aluminum and the metal constituting the metal circuit layers 23a and 23b. When the metal layers 22a and 22b contain a metal constituting the metal circuit layers 23a and 23b, the metal may form an alloy with aluminum, and in this case, the alloy may be scattered on the surface of the metal layers 22a and 22b on the metal circuit layers 23a and 23b side.

The metal layers 22a and 22b may contain other components other than aluminum and magnesium, as long as the effect of the present invention is not impaired. The total content of the other components may be, for example, 5 mass% or less, 4 mass% or less, 3 mass% or less, 2 mass% or less, 1 mass% or less, 0.5 mass% or less, 0.1 mass% or less, 0.05 mass% or less, or 0.01 mass% or less. Here, the term "other components" includes impurities unintentionally contained in addition to the components optionally added. Examples of other components include O, C, Si, Mn, P, S, N, Ca, Cr, Ti, Nb, V, B, Mo, Cu, Ni, Sb, Sn, Ta, Mg, Zn, Co, Zr, REM, and compounds thereof (e.g., oxides, nitrides, sulfides, etc.).

The average thickness of the metal layer 22a is greater than the average thickness of the alloy layer 21a, and may be, for example, 1.0 times or more, 1.5 times or more, or 2 times or more based on the average thickness of the alloy layer 21a. The above relationship between the average thickness of the metal layer 22a and the average thickness of the alloy layer 21a more sufficiently prevents the stress relaxation layer 20a from becoming too hard, and the durability against heat cycles is more excellent. The average thickness of the metal layer 22a may be, for example, 20 times or less, 17 times or less, or 15 times or less based on the average thickness of the alloy layer 21a. The above relationship between the average thickness of the metal layer 22a and the average thickness of the alloy layer 21a can reduce the thermal resistance of the ceramic substrate. The average thickness of the metal layer 22a may be adjusted within the above range, and may be, for example, 1.0 to 20 times based on the average thickness of the alloy layer 21a.

The lower limit of the average thickness of the metal layer 22a may be, for example, more than 0.1 mm, 0.15 mm or more, or 0.2 mm or more. When the lower limit of the average thickness of the metal layer 22a is within the above range, the durability against heat cycles is superior. The upper limit of the average thickness of the metal layer 22a may be, for example, 0.4 mm or less, 0.35 mm or less, or 0.3 mm or less. When the upper limit of the average thickness of the metal layer 22a is within the above range, the thermal resistance of the ceramic substrate can be reduced.

The average thickness of metal layer 22b may be the same as that described above for metal layer 22a. The average thickness of metal layer 22b may be the same as or different from the average thickness of metal layer 22a. The average thickness of metal layers 22a and 22b can be adjusted according to differences in the thermal expansion coefficients, etc. between ceramic plate 1 and metal circuit layers 23a and 23b.

The metal circuit layers 23a and 23b may include metals such as gold, platinum, silver, copper, nickel, and chromium, or may include gold, silver, copper, or may be made of copper. The metal circuit layers 23a and 23b may be, for example, a wiring pattern made of copper, or a wiring pattern made of a copper alloy.

The lower limit of the average thickness of the metal circuit layers 23a and 23b may be, for example, 0.3 mm or more, 0.35 mm or more, or 0.4 mm or more. The upper limit of the average thickness of the metal circuit layers 23a and 23b may be, for example, 4 mm or less, 3 mm or less, or 2 mm or less.

The laminate 100 in FIG. 1 is shown as an example in which the end face 21E of the alloy layer 21a, the end face 22E of the metal layer 22a, and the end face 23E of the metal circuit layer 23a are on the same plane, but the face formed by the end face 21E of the alloy layer 21a and the end face 22E of the metal layer 22a and the face formed by the end face 23E of the metal circuit layer 23a do not necessarily have to be on the same plane. The laminate 101 shown in FIG. 2 shows an example in which the face formed by the end face 21E of the alloy layer 21a and the end face 22E of the metal layer 22a and the face formed by the end face 23E of the metal circuit layer 23a are different faces. By setting the width of the stress relaxation layers 20a, 20b to be larger than the width of the metal circuit layers 23a, 23b as in the laminate 101, the laminate can have better durability against heat cycles. The difference between the width of the metal circuit layers 23a, 23b and the width of the stress relief layers 20a, 20b may be, for example, 1 to 1000 μm, or 10 to 100 μm.

The above-mentioned laminates 100, 101 can be manufactured by a method of sequentially forming an alloy layer, a stress relief layer including a metal layer, and a metal circuit layer on a ceramic plate using a so-called cold spray method. When a stress relief layer having an alloy layer and a metal layer, and a metal circuit layer are formed on a ceramic plate by a spraying operation such as cold spraying or thermal spraying, unevenness due to the spraying operation may be formed at the interface between the layers. Therefore, the above-mentioned laminates 100, 101 have characteristics different from those manufactured by sequentially laminating thin metal films formed in advance in layers.

One embodiment of the method for manufacturing a laminate includes the steps of forming a first deposition layer in contact with the ceramic plate by spraying a first metal powder containing magnesium together with an inert gas from a nozzle onto the surface of the ceramic plate, heat-treating the first deposition layer under an inert gas atmosphere to form an alloy layer, spraying a second metal powder having a lower magnesium content than the first metal powder together with an inert gas onto the surface of the alloy layer to form a second deposition layer in contact with the alloy layer, heat-treating the second deposition layer under an inert gas atmosphere to form a metal layer, spraying a third metal powder containing metal particles together with an inert gas onto the surface of the metal layer from a nozzle to form a third deposition layer in contact with the metal layer, and heat-treating the third deposition layer under an inert gas atmosphere to form a metal circuit layer.

Figure 3 is a schematic diagram showing an example of a process for forming an alloy layer on a ceramic plate. In the method shown in Figure 3, a first deposition layer is formed on the ceramic plate 1 by spraying metal powder onto the surface of the ceramic plate 1 using a powder spray device 3. The first deposition layer is heat-treated to form an alloy layer 21a. After forming the alloy layer 21a, an alloy layer 21b may be formed on the back side thereof.

The powder spray device 3 shown in Figure 3 is mainly composed of a high-pressure gas cylinder 4, a heater 6, a powder supply device 7, a tapered spray gun nozzle 10, and piping connecting these. A first pressure regulator 5a is provided downstream of the multiple high-pressure gas cylinders 4, and the piping branches into two circuits downstream of the first pressure regulator 5a. A second pressure regulator 5b and a heater 6, and a third pressure regulator 5c and a powder supply device 7 are connected to each of the two branched piping circuits. The piping from the heater 6 and the powder supply device 7 is connected to the nozzle 10.

In the powder spray device 3, the high-pressure gas cylinder 4 is filled with an inert gas used as a working gas, for example, at a pressure of 1 MPa or more. The inert gas may be, for example, a single gas such as helium or nitrogen, or a mixture of these gases. The working gas OG supplied from the high-pressure gas cylinder 4 is heated by a heater 6 after the pressure is adjusted on one circuit by a second pressure regulator 5b, and then supplied to the nozzle 10 of the spray gun. The working gas OG is also supplied to the powder supply device 7 after the pressure is adjusted by a third pressure regulator 5c on the other circuit. Metal powder for film formation is supplied from the powder supply device 7 to the nozzle 10 of the spray gun together with the working gas OG.

The gauge pressure of the working gas OG at the inlet 10a of the nozzle 10 is adjusted to, for example, 1.5 to 5.0 MPa, or 2.0 to 4.0 MPa. By keeping the gauge pressure of the working gas OG within the above range, a deposition layer (a layer that will later be heat-treated to become an alloy layer) and the like can be efficiently formed. The gauge pressure of the working gas OG at the nozzle inlet can be measured at the connection between the nozzle and the piping.

The heating temperature by the heater 6 is usually set lower than the melting point or softening point of the metal powder to be deposited. The heater 6 can be selected from any ordinary heating device.

The working gas supplied to the nozzle 10 of the spray gun is compressed as it passes through the convergent section, and then rapidly expands and accelerates in the divergent section downstream. The metal powder is heated to a predetermined temperature and accelerated to a predetermined speed, and then ejected from the outlet of the nozzle 10. The metal powder ejected from the nozzle 10 is sprayed onto the surface of the ceramic plate 1. As a result, the metal powder collides in a solid phase on the surface of the ceramic plate 1 and accumulates, forming a first deposition layer. The first deposition layer is then heat-treated to form an alloy layer 21a. The thickness of the alloy layer that is formed later can be controlled by adjusting the amount of the first metal powder sprayed.

The first metal powder may be, for example, magnesium alloy particles containing magnesium and another metal element, or may be aluminum-magnesium alloy particles. The aluminum-magnesium alloy particles may be a gas atomized powder in which magnesium is dissolved in aluminum. Since the composition of the first metal powder (e.g., magnesium content) is reflected in the composition of the alloy layer formed later (e.g., magnesium content), the composition of the alloy layer can be controlled by adjusting the composition of the first metal powder.

In forming the first deposition layer, the first metal powder may be heated to, for example, 10 to 270°C, or 20 to 260°C. By setting the heating temperature of the first metal powder within this range, the first laminated body can be formed efficiently. In this specification, the temperature to which the metal powder is heated means the maximum temperature that the metal powder reaches. The temperature of the inert gas at the outlet of the nozzle 10 can also be considered to be the temperature to which the metal powder is heated. Here, in this specification, the term "heat" is used to include adjusting the temperature to a predetermined temperature below room temperature.

A first deposition layer or the like having a pattern (circuit pattern) may be formed on the ceramic substrate by disposing a mask material on the ceramic plate 1 so as to cover a portion of the surface of the ceramic plate 1. According to this method, a metal circuit having a desired pattern can be easily formed without performing additional processing such as etching after forming an alloy layer or the like. The method according to this embodiment simplifies the process and is advantageous over conventional molten metal methods and brazing methods that require etching to form a pattern, from the viewpoint of quality control of the resulting product, etc.

The first metal powder may be accelerated to 250 to 1050 m/s in the nozzle 10. In this specification, the speed at which the metal powder is accelerated means the maximum speed that the accelerated metal powder reaches. If the speed at which the accelerated metal powder reaches is less than 250 m/s, the metal powder is unlikely to undergo sufficient plastic deformation at the moment it collides with the ceramic substrate, etc., making it difficult to form a deposition layer or tending to reduce the adhesion of the formed deposition layer. If the speed at which the accelerated metal powder reaches exceeds 1050 m/s, the metal powder tends to be crushed and scattered when it collides with the ceramic substrate, etc., making it difficult to form a deposition layer.

The first laminate formed on the ceramic plate is heat-treated under an inert gas atmosphere. The temperature of the heat treatment may be, for example, 400 to 600°C. By heating the first laminate at a temperature of 400°C or higher, the reaction between the magnesium and the oxide layer on the surface of the ceramic plate can be promoted, resulting in a strong bond. In addition, by heating the first laminate at a temperature of 600°C or lower, the effect of the first laminate softening can be reduced.

After the alloy layer is formed, a second metal powder is sprayed onto the surface of the alloy layer in the same manner as in the formation of the alloy layer described above to form a second deposition layer, followed by a heat treatment to form a metal layer. When the stress relaxation layer is composed of three or more layers, the layers can be formed sequentially, for example, by repeating the same means as in the formation of the alloy layer described above. The composition and thickness of the metal layer can be controlled by the composition and spray amount of the second metal powder, respectively. In this case, the composition of the alloy or metal constituting each layer can be changed by adjusting the composition of the metal powder sprayed onto the surface of each layer. For example, the magnesium content in the metal powder may be adjusted to gradually decrease. It is preferable that the metal powder sprayed finally to form a layer to be bonded to the metal circuit layer formed later does not contain magnesium, and from the viewpoint of improving stress relaxation performance, it is preferable that it is, for example, aluminum powder.

After the metal layer is formed, a third metal powder containing copper or other metals as its main component is sprayed onto the surface of the metal layer from a nozzle together with an inert gas to form a third deposition layer, and then a metal circuit layer is formed by a heat treatment.

In forming the third deposition layer, the third metal powder may be heated to, for example, 10 to 650°C or 20 to 640°C. By setting the heating temperature of the third metal powder within the above range, the third deposition layer can be formed efficiently. By setting the heating temperature of the third metal powder to 650°C or less, it is possible to prevent softened metal particles such as copper from adhering to the inner wall of the nozzle or to prevent the nozzle from clogging, making it easier to form the metal circuit layer. By setting the heating temperature of the third metal powder to 10°C or more, it is possible to make the plastic deformation of metal particles such as copper easier, making it easier to form the third deposition layer.

In forming the third deposition layer, the gauge pressure of the working gas OG at the inlet 10a of the nozzle 10 may be, for example, 1.5 to 5.0 MPa, or 2.0 to 4.0 MPa. By setting the gauge pressure of the working gas OG within the above range, the third deposition layer can be formed efficiently. By setting the gauge pressure of the working gas at the inlet of the nozzle to 1.5 MPa or more, it is possible to suppress the third metal powder from being difficult to adhere to the metal layer, making it easier to form the third deposition layer. By setting the gauge pressure of the working gas at the inlet of the nozzle to 5.0 MPa or less, it is possible to further suppress the third metal powder sprayed onto the metal layer together with the inert gas from being crushed, which reduces the efficiency of forming the third deposition layer.

In addition, the conditions for forming the third deposition layer by spraying the third metal powder may be adjusted in the same manner as for the formation of the alloy layer and metal layer described above. When forming the third deposition layer, similar to the formation of the alloy layer and metal layer, a mask material may be placed on the ceramic plate 1 to form a third deposition layer having a pattern, and this may be heat-treated to form a metal circuit layer having a pattern.

The third deposition layer is heat-treated under an inert gas atmosphere. The temperature for this heat treatment may be, for example, 250 to 350°C. By heating the third deposition layer at a temperature of 250°C or higher, it is possible to reduce distortion in the alloy layer and metal layer due to work hardening. By heating the third deposition layer at a relatively low temperature of 350°C or lower, it is possible to suppress the generation of intermetallic compounds due to the reaction between the metal layer and the third deposition layer, and the diffusion of metal components.

To suppress the formation of pores in the alloy layer, the metal layer, and the metal circuit layer, the first metal powder, the second metal powder, and/or the third metal powder may each be composed of spherical particles. The first metal powder, the second metal powder, and/or the third metal powder may each have a small variation in particle size. The average particle size of the metal powder may be, for example, 10 to 70 μm, or 20 to 60 μm. By making the average particle size of the metal powder 10 μm or more, clogging of the tapered portion of the nozzle can be further suppressed. By making the average particle size of the metal powder 70 μm or less, the speed of the metal powder can be sufficiently increased.

The average particle size in this specification refers to the particle size (D50) when the cumulative value from the smallest particle size reaches 50% of the total in the volume-based particle size distribution curve measured by the laser diffraction/scattering method. D50 is also called the median size and is known as the average particle size of the target particles.

The laminate described above has excellent durability against heat cycles, and can therefore be suitably used, for example, as a component (e.g., a circuit board) constituting a power module or the like. One embodiment of the power module comprises a circuit board, a semiconductor element electrically connected to one main surface of the circuit board, and a heat dissipation member connected to the other main surface of the circuit board. The circuit board is the laminate described above.

Figure 4 is a schematic cross-sectional view showing an example of a power module. The power module 300 includes a base plate 70 and a circuit board 102 joined to one side of the base plate 70 via solder 32. The metal circuit 2b (alloy layer, metal layer, and metal circuit layer) of the circuit board 102 is joined to the solder 32. The circuit board 102 may be the laminate 100, 101, etc. described above.

A semiconductor element 60 is attached to the metal circuit 2a of the circuit board 102 via solder 31. The semiconductor element 60 is connected to a predetermined location of the metal circuit 2a with a metal wire 34 such as an aluminum wire. To electrically connect the outside of the housing 36 to the metal circuit 2a, a predetermined portion of the metal circuit 2a is connected to an electrode 33 that penetrates the housing 36 via solder 35.

A housing 36 is disposed on one side of the base plate 70 to house the circuit board 102. The housing space formed by the one side of the base plate 70 and the housing 36 is filled with a resin 30 such as silicone gel.

A cooling fin 72, which serves as a heat dissipation member, is joined to the other side of the base plate 70 via grease 74. A screw 73 is attached to the end of the base plate 70 to fix the cooling fin 72 to the base plate 70. The base plate 70 and the cooling fin 72 may be made of aluminum. The base plate 70 and the cooling fin 72 function well as heat dissipation parts due to their high thermal conductivity.

The power module 300 includes metal circuits 2a and 2b on the circuit board 102 and a semiconductor element 60 electrically connected to the metal circuit 2a. The semiconductor element 60 is sealed together with the circuit board 102 by resin 30. Such a power module 300 can maintain adhesion between the resin 30 and the ceramic plate 1 even if the semiconductor element 60 generates heat.

Although several embodiments have been described above, the present disclosure is in no way limited to the above-mentioned embodiments. Furthermore, the contents of the descriptions of the above-mentioned embodiments can be mutually applied.

The contents of this disclosure will be described in more detail below with reference to examples and comparative examples. However, this disclosure is not limited to the following examples.

<Preparation of Aluminum Nitride Plate (AlN)>
A commercially available aluminum nitride plate (manufactured by Maruwa Corporation) was used as the ceramic plate.

<Preparation of silicon nitride plate (Si ₃ N ₄ plate)>
Silicon nitride powder, _{magnesium oxide powder as a sintering aid, and yttrium oxide powder were prepared. These were mixed in a ratio of Si3N4:Y2O3 : MgO =} 94.0:3.0:3.0 (mass ratio) to obtain a raw material powder. This raw material powder was uniaxially pressed to produce a molded body. This molded body was placed in an electric furnace equipped with a carbon heater and fired at 1800°C for 12 hours in a nitrogen gas atmosphere to obtain a flat silicon nitride plate. The obtained silicon nitride plate was used as a ceramic plate.

<Preparation of Aluminum Oxide Plate (Al ₂ O ₃ )>
A commercially available aluminum oxide plate (manufactured by Maruwa Co., Ltd.) was used as the ceramic plate.

Example 1
<Formation of alloy layer (layer made of aluminum-magnesium alloy)>
Using aluminum-magnesium alloy powder (manufactured by Kojundo Chemical Laboratory Co., Ltd., gas atomized powder, median diameter: 24 μm), a deposition layer (first deposition layer) of aluminum-magnesium alloy powder having a length of 56 mm, width of 46 mm, and thickness of 0.1 mm was formed in a range 2 mm inward from the end face of the substrate on both sides of the aluminum nitride plate by using a powder spray device having a configuration similar to that of FIG. The first deposition layer was formed using nitrogen as the working gas under conditions of a temperature of the aluminum-magnesium alloy powder (gas atomized powder) of 260° C. and a pressure of the working gas at the nozzle inlet of 3 MPa. The first deposition layer was heat-treated by holding it at a temperature of 550° C. for 3 hours in a nitrogen atmosphere to form an aluminum-magnesium alloy layer (alloy layer).

<Formation of Metal Layer (Layer Made of Aluminum)>
Next, aluminum powder (manufactured by Kojundo Kagaku Kenkyusho Co., Ltd., gas atomized powder, median diameter: 24 μm) was used, and a powder spray device having a configuration similar to that of FIG. 3 was used to form a deposition layer (second deposition layer) of aluminum powder having a length of 56 mm, a width of 46 mm, and a thickness of 0.2 mm on each surface of the two alloy layers formed as described above, so that the deposition layer had a length of 56 mm and a width of 46 mm, the same as the alloy layer. The second deposition layer was formed using nitrogen as the working gas under conditions of a temperature of the aluminum powder of 260° C. and a pressure of the working gas at the nozzle inlet of 3 MPa. The second deposition layer was heat-treated by holding it at a temperature of 550° C. for 3 hours under a nitrogen atmosphere to form an aluminum layer (metal layer).

<Formation of Metal Circuit Layer (Copper Layer)>
Further, a part of the aluminum layer was masked with an iron mask material, and a copper powder (manufactured by Fukuda Metal Foil and Powder Co., Ltd., water atomized powder, median diameter: 17 μm) was used to form a copper powder deposition layer (third deposition layer) in a range 50 μm inside from the end face of the aluminum layer by a powder spray device having a configuration similar to that of FIG. 3, so that the deposition layer had a length of 55.9 mm, a width of 45.9 mm, and a thickness of 0.4 mm. The third deposition layer was formed under conditions of using nitrogen as the working gas, a temperature of the copper powder of 640° C., and a pressure of the working gas at the nozzle inlet of 3 MPa. The end face of the aluminum layer protruded outward by a width of 50 μm from the end face of the copper layer. The third deposition layer was heat-treated by holding it at a temperature of 300° C. for 1 hour under a nitrogen atmosphere to form a copper layer (metal circuit layer).

By following these steps, a laminate was obtained in which metal circuits consisting of an aluminum-magnesium alloy layer, an aluminum layer, and a copper layer were formed on both sides of the silicon nitride plate.

(Examples 2 to 9)
A laminate was prepared in the same manner as in Example 1, except that the type and thickness of the ceramic plate, the magnesium content in the alloy layer and the thickness of the alloy layer, and the thickness of the metal layer were changed as shown in Table 1.

(Comparative Examples 1 to 3)
A laminate was prepared in the same manner as in Example 1, except that no metal layer was provided, and the type and thickness of the ceramic plate and the magnesium content in the alloy layer were changed as shown in Table 2.

(Comparative Examples 4 to 5)
A laminate was prepared in the same manner as in Example 1, except that no alloy layer was provided, and the type and thickness of the ceramic plate and the thickness of the metal layer were changed as shown in Table 2.

(Comparative Examples 7 to 14)
A laminate was prepared in the same manner as in Example 2, except that the type and thickness of the ceramic plate, the magnesium content in the alloy layer and the thickness of the alloy layer, and the thickness of the metal layer were changed as shown in Table 1.

<Evaluation of durability against heat cycle: heat cycle test>
A heat cycle test was carried out on each of the laminates prepared in Examples 1 to 9 and Comparative Examples 1 to 17 to evaluate durability against heat cycles. Specifically, the heat cycle test was carried out by carrying out 3,000 cycles of "leaving the laminate in an environment of 180°C for 30 minutes and then in an environment of -55°C for 30 minutes" as one cycle. The laminates after the test were observed in cross section and evaluated according to the following criteria. The results are shown in Tables 1 and 2.
A: No abnormality such as peeling was observed even after 3000 cycles.
B: Peeling was observed after more than 1,500 cycles and less than 3,000 cycles.
C: Peeling was observed at more than 1,000 cycles and up to 1,500 cycles.
D: Peeling was observed within 1000 cycles or less.

According to the present disclosure, it is possible to provide a laminate having excellent durability against heat cycles. According to the present disclosure, it is also possible to provide a power module having excellent reliability.

1...ceramic plate, 2a, 2b...metal circuit, 3...powder spray device, 4...high pressure gas cylinder, 5a...first pressure regulator, 5b...second pressure regulator, 5c...third pressure regulator, 6...heater, 7...powder supply device, 10...nozzle, 10a...inlet, 20a, 20b...stress relaxation layer, 21a, 21b...alloy layer, 22a, 22b...metal layer, 23a, 23b...metal circuit layer, 30...resin, 31, 32, 35...solder, 33...electrode, 34...metal wire, 36...housing, 60...semiconductor element, 70...base plate, 72...cooling fin, 73...screw, 74...grease, 100, 101...laminated body, 102...circuit board, 300...power module.

Claims (4)

Ceramic plate and
a stress relief layer formed on the ceramic plate;
a metal circuit layer including at least one of copper and a copper alloy formed on the stress relaxation layer;
the thermal expansion coefficient of the stress relaxation layer is larger than that of the ceramic board and is larger than that of the metal circuit layer;
The stress relief layer is
an alloy layer in contact with the ceramic plate, the alloy layer being an alloy containing magnesium and aluminum, the magnesium content being 0.001 to 7.5 mass % and the average thickness being less than 0.2 mm;
A laminate comprising: a metal layer containing at least one selected from the group consisting of aluminum and an aluminum alloy, the metal layer having a lower magnesium content than the alloy layer, and in contact with the metal circuit layer. The laminate according to claim 1, wherein the average thickness of the alloy layer is 0.02 mm or more and less than 0.2 mm. 3. The laminate according to claim 1 or 2 , wherein the average thickness of the metal layer is greater than 0.1 mm. A circuit board;
a semiconductor element electrically connected to one main surface of the circuit board;
a heat dissipation member connected to the other main surface of the circuit board,
A power module, wherein the circuit board is the laminate according to any one of claims 1 to 3 .

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