JP2011139000A - Power module structure and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive power module structure that is superior in heat dissipation of a ceramics circuit board and a metal base plate, and to provide a method of manufacturing the same. <P>SOLUTION: The power module structure has such a thermal expansion coefficient that satisfies an inequality of (α+γ)/2-4<β<(α+γ)/2+4 when the thermal expansion coefficient of a ceramics circuit board 1 is α(×10<SP>-6</SP>/K), the thermal expansion coefficient of a stress relaxation plate 2 is β(×10<SP>-6</SP>/K), and the thermal expansion of a metal base plate 3 is γ(×10<SP>-6</SP>/K), and a metal layer is formed on the surface of the stress relaxation plate 2 wherein the thermal conductivity is 100 W/(m K) or more at 25°C with a plate thickness of 0.5-3.0 mm and a 3-point flexural strength of 50 MPa or more, and then it is soldered and brazed between the ceramics circuit board 1 and the metal base plate 3. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a heat dissipation material and a manufacturing method thereof, and more particularly to a heat dissipation material suitable as a heat dissipation substrate for a power module.

Today, as the integration and size of semiconductor elements increase, the amount of generated heat continues to increase, and the issue is how to efficiently dissipate heat. A copper or aluminum metal circuit is formed on the surface of a ceramic circuit board such as an aluminum nitride substrate or a silicon nitride substrate having high insulation and high thermal conductivity, and a copper or aluminum metal heat sink is formed on the back surface. The ceramic circuit board thus formed is used as a power module circuit board.

A typical heat dissipation structure of a conventional circuit board is formed by soldering a base plate via a metal plate, for example, a copper plate, on the back surface (heat dissipation surface) of the circuit board, and copper is generally used as the base plate. there were. However, in this structure, when a thermal load is applied to the semiconductor device, a crack due to the difference in thermal expansion coefficient between the base plate and the circuit board occurs in the solder layer, resulting in insufficient heat dissipation and the semiconductor element. There was a problem of malfunction or damage.

Therefore, an aluminum-silicon carbide composite has been proposed as a base plate having a thermal expansion coefficient close to that of a circuit board. As a method for producing the aluminum-silicon carbide composite for the base plate, a molten forging method (Patent Document 1) in which a silicon carbide porous body is impregnated with a molten aluminum alloy (Patent Document 1), an aluminum alloy porous silicon body is made of aluminum alloy. A non-pressure impregnation method (Patent Document 2) in which molten metal permeates without pressure has been put into practical use. On the other hand, in terms of cost, a powder metallurgy method in which aluminum powder and silicon carbide powder are mixed and heat-molded is advantageous, and an aluminum-silicon carbide composite by the same production method is also being studied (Patent Document 3). 4). However, since aluminum-silicon carbide composites of any manufacturing method have a problem in cost, inexpensive copper base plates are often used in fields where cost reduction is required. There was a problem in reliability between copper base plates.
Japanese Patent No. 3468358 JP-T-5-507030. JP-A-9-157773 JP-A-10-335538

Metals such as copper and aluminum used for the base plate have a large thermal expansion coefficient of about 17 to 23 × 10 ⁻⁶ / K and a thermal expansion coefficient with a ceramic circuit board having a thermal expansion coefficient of about 5 × 10 ⁻⁶ / K. Since the difference is large, solder cracks occur in the solder layer of the bonding layer.

This invention is made | formed in view of said situation, The objective is by mounting the stress relaxation board which has a thermal expansion coefficient between a ceramic circuit board and a copper base board as a power module structure. An object of the present invention is to provide a stress relieving plate that can relieve stress generated by a difference in thermal expansion coefficient and achieve improved reliability, and a method of manufacturing the same.

In the present invention, the thermal expansion coefficient of the ceramic circuit board is α (× 10 ⁻⁶ / K), the thermal expansion coefficient of the stress relaxation plate is β (× 10 ⁻⁶ / K), and the thermal expansion coefficient of the metal base plate is γ ( × 10 ⁻⁶ / K), it has a thermal expansion coefficient satisfying (α + γ) / 2-4 <β <(α + γ) / 2 + 4, a plate thickness of 0.5 to 3.0 mm, and a temperature of 25 ° C. After forming a metal layer on the surface of a stress relaxation plate with a thermal conductivity of 100 W / (m · K) or more and a three-point bending strength of 50 MPa or more, soldering or brazing between the ceramic circuit board and the metal base plate A power module structure is proposed.

In the present invention, the stress relaxation plate is a porous body composed of one or more ceramic powders selected from silicon carbide, aluminum nitride, silicon nitride, boron nitride, and graphite, or a powder compact and aluminum or aluminum alloy. A plate-shaped metal-impregnated ceramic substrate obtained by compounding, or a metal plate selected from Cu, Ni, Mo, W, Co and Fe, an alloy plate containing at least one of the metal components, or the metal plate and the alloy It is preferable that the power module structure is a laminated plate composed of two or more selected from the plates.

Furthermore, the present invention provides Ni, Co having a thickness of 0.5 to 20 μm on the surface of a plate-like metal-impregnated ceramic substrate obtained by any of the following steps (1) to (4). , Pd, Cu, Ag, Au, Pt, and Sn. A method for producing a stress relaxation plate used in a power module structure formed by plating at least one metal selected from plating.
(1) A block-like porous body having a porosity of 10 to 60% by volume, or a powder molded body and aluminum made of one or more ceramic powders selected from silicon carbide, aluminum nitride, silicon nitride, boron nitride, and graphite Alternatively, a step of producing a plate-shaped metal-impregnated ceramic substrate by compounding an aluminum alloy by a molten forging method at a pressure of 30 MPa or more and cutting and / or shaping a block-shaped metal-impregnated ceramic body.
(2) A plate-shaped porous body having a porosity of 10 to 60% by volume or a powder molded body made of one or more ceramic powders selected from silicon carbide, aluminum nitride, silicon nitride, boron nitride, and graphite is separated. A step of laminating through a mold plate and impregnating aluminum or aluminum alloy with a molten metal forging method at a pressure of 30 MPa or more to produce a plate-like metal-impregnated ceramic body, and then processing the shape to produce a metal-impregnated ceramic substrate.
(3) Separate a powder obtained by mixing 40 to 90% by volume of one or more ceramic powders selected from silicon carbide, aluminum nitride, silicon nitride, boron nitride, and graphite and 10 to 60% by volume of aluminum or an aluminum alloy. Filled with a mold that has been subjected to mold treatment, heated to a temperature higher than the melting point of aluminum or aluminum alloy, heated and pressed at a pressure of 30 MPa or more to be combined into a block shape, and plate-like by cutting and / or peripheral processing A step of obtaining a metal-impregnated ceramic substrate.
(4) Separate from 40 to 90% by volume of one or more ceramic powders selected from silicon carbide, aluminum nitride, silicon nitride, boron nitride, and graphite and 10 to 60% by volume of aluminum or aluminum alloy. A step of filling a mold subjected to mold treatment, heating to a temperature equal to or higher than the melting point of aluminum or an aluminum alloy, and heating and pressing at a pressure of 30 MPa or more to form a composite in a plate-like metal-impregnated ceramic substrate.

According to the present invention, by optimizing the particle size, type, and content of the ceramic powder used for the stress relaxation plate, and by optimizing the metal component, the obtained stress relaxation plate is placed between the ceramic circuit board and the copper base plate. Since the thermal expansion coefficient can be controlled, it is possible to provide a power module structure in which good matching is obtained for both the ceramic circuit board side and the copper base plate side, and the reliability is remarkably improved.

Furthermore, since the thermal conductivity is 100 W / (m · K) or more, the heat from the ceramic circuit board can be transferred well to the copper base plate, and it can be suitably used as a power module structure.

FIG. 1 is an explanatory view showing an example of a power module structure according to the present invention. FIG. 2 is a schematic cross-sectional view of the metal-impregnated ceramic body of the present invention.

  The stress relaxation plate used for the power module structure of the present invention has a plate thickness of 0.5 to 3.0 mmt, preferably 0.5 to 2.0 mm, and a three-point bending strength of 50 MPa or more. A power module structure that is soldered or brazed between the ceramic circuit board and the metal base board after the metal layer is formed on the surface of the stress relaxation board, so heat from the ceramic circuit board is good for the base board And a highly reliable power module structure can be realized.

If the thickness of the stress relaxation plate is less than 0.5 mm, the stress relaxation layer is too thin to relieve stress and reliability is lowered. On the other hand, if it exceeds 3.0 mm, the thermal resistance of the stress relaxation plate increases.

The thermal conductivity of the stress relaxation plate at a temperature of 25 ° C. is 100 W / (m · K) or more, preferably 200 W / (m · K) or more. The semiconductor may malfunction or be damaged without sufficiently transferring heat to the metal base plate.

Further, the thermal expansion coefficient of the ceramic circuit board is α (× 10 ⁻⁶ / K), the thermal expansion coefficient of the stress relaxation plate is β (× 10 ⁻⁶ / K), and the thermal expansion coefficient of the metal base plate is γ (× 10 ⁻⁶ / K), it preferably has a thermal expansion coefficient satisfying (α + γ) / 2-4 <β <(α + γ) / 2 + 4, and the thermal expansion coefficient is a stress relaxation plate between the ceramic circuit board and the metal base plate. By using, high reliability can be realized.
When the thermal expansion coefficient of the stress relaxation plate is out of the above range, the thermal stress during the operation of the semiconductor element may cause destruction of the bonding layer (solder layer, etc.) and the ceramic circuit board, resulting in deterioration of heat dissipation characteristics. When the stress relaxation plate is made of a metal-impregnated ceramic body, the thermal conductivity and the thermal expansion coefficient can be increased or decreased depending on the impregnation rate of the metal to be combined and the ceramic material.

The three-point bending strength of the stress relaxation plate is preferably 50 MPa or more. When used as a heat dissipation component for a power module, if the three-point bending strength is less than 50 MPa, there is a problem of chipping due to the influence of vibration or the like during use, which is not preferable. The upper limit of the three-point bending strength is not limited by characteristics, but in order to extremely improve the three-point bending strength, it is necessary to increase the amount of silicon carbide added and to make the powder fine. As a result, the resulting metal Since the thermal conductivity of the impregnated ceramic body is lowered, it is preferably 350 MPa or less.

The stress relaxation plate made of a metal-impregnated ceramic body contains 40 to 90% by volume of one or more ceramic powders, and the balance (10 to 60% by volume) is aluminum or an aluminum alloy, preferably the aluminum content is 80 to 100% by mass. It is preferable that the aluminum-silicon alloy is compounded.
As a method for compounding ceramics and aluminum or an aluminum alloy, it is preferable that the ceramic is produced by a molten forging method impregnated by a method such as the example of Japanese Patent No. 3468358.

Also, instead of the molten metal forging method, a mixed powder of ceramic powder and aluminum or aluminum alloy powder is filled into a mold that has been subjected to a release treatment, and heated to a temperature equal to or higher than the melting point of aluminum or aluminum alloy, and then pressed to be combined. Even those produced by the method can be used.

The pressure required for combining ceramic powder and aluminum or aluminum alloy is preferably 30 MPa or more. If the pressure at the time of hot press molding is less than 30 MPa, the adhesiveness between the ceramic powder and aluminum or aluminum alloy is insufficient, and characteristics such as thermal conductivity and strength are deteriorated. Further, the upper limit of the press pressure is not limited in terms of characteristics, but 200 MPa or less is appropriate from the strength of the mold and the strength of the apparatus. The metal-impregnated ceramic body is depressurized at a temperature below the melting point and then cooled to room temperature. For the purpose of removing the strain at the time of compounding, the metal-impregnated ceramic body may be annealed.

The material of the ceramic powder is preferably at least one inorganic component selected from silicon carbide, aluminum nitride, silicon nitride, boron nitride, and graphite. The filling amount of the ceramic is preferably 40 to 90% by volume, particularly 50 to 80% by volume. When the filling amount of the ceramic is less than 40% by volume, the coefficient of thermal expansion of the metal-impregnated ceramic body becomes too large. On the other hand, if it exceeds 90% by volume, the metal cannot be sufficiently impregnated and the thermal conductivity may be too small. Further, the ceramic filling state is not particularly limited, and a ceramic porous body or a ceramic powder molded body can be used. The amount of ceramics to be filled can be adjusted by adjusting the particle size of ceramic components, shaping pressure, sintering conditions, and the like.

Moreover, the metal component compounded with ceramics is preferably aluminum or aluminum alloy containing 80 to 100% by mass of aluminum and 0 to 20% by mass of silicon. If the silicon component exceeds 20% by mass, the melting point of the alloy increases, and an unimpregnated portion may occur. On the other hand, when the silicon component exceeds 20% by mass, the thermal conductivity of the obtained alloy is lowered, and as a result, the thermal conductivity of the obtained metal-impregnated ceramic substrate is lowered, which is not preferable. The component other than the silicon component is not particularly limited as long as it does not affect the characteristics, but magnesium has an effect of improving the wettability of the obtained alloy and ceramic, and within 3% by mass, the production of aluminum carbide adversely affecting the strength and thermal conductivity (Al 4 _{C 3)} may contain can be suppressed.

The ceramic powder compact can be produced by molding only a ceramic component powder, or can be produced using an inorganic binder such as silica sol or alumina sol. For forming, a general ceramic powder forming method such as press forming or cast forming is employed. The ceramic porous body can be produced, for example, by subjecting the ceramic powder compact to a sintering treatment. There is no restriction | limiting in the shape of a ceramic porous body and a ceramic powder molded object, It uses by flat form, a column shape, etc.

In order to form a metal-impregnated ceramic substrate from a ceramic porous body or a ceramic powder molded body impregnated with metal, cutting and surface processing are usually performed. When the shape of the ceramic porous body or ceramic powder molded body impregnated with metal is a rectangular parallelepiped shape, the final shape is processed with a multi-wire saw, inner peripheral edge cutter, etc. It is preferable to cut to a thickness of about 0.1 to 0.5 mm thicker. There is no limitation on the cutting method, but a multi-wire saw having a small cutting margin and suitable for mass production is preferable. In the cutting of a multi-wire saw, a wire to which an abrasive such as a loose abrasive type and diamond is attached is used. In the surface processing, a plate thickness is processed to 0.5 to 3 mm using a processing machine such as a double-side grinding machine, a rotary grinding machine, a surface grinding machine, or a lapping machine.

When the shape of the ceramic porous body or ceramic powder molded body impregnated with metal is plate-like, using a processing machine such as a double-sided grinder, rotary grinder, surface grinder, lapping machine, Surface processing is performed to 3 mm and the surface roughness (Ra) is 1.0 μm or less, and then outer periphery processing is performed into a predetermined shape by a water jet processing machine, an electric discharge processing machine, a laser processing machine, a dicing machine, a cylindrical grinding machine or the like. In this case, surface processing may be performed after the outer periphery processing is performed first.

On the other hand, the stress relaxation plate made of metal is a metal plate selected from copper (Cu), nickel (Ni), molybdenum (Mo), tungsten (W), cobalt (Co) and iron (Fe), It is preferable that it is comprised from the laminated plate comprised by the alloy plate containing at least 1 type, or 2 or more types chosen from the said metal plate and the said alloy plate. As the shape, a flat plate shape, a cylindrical shape, or the like is used.

It is particularly preferable that at least one metal selected from Ni, Co, Pd, Cu, Ag, Au, Pt and Sn is formed on the surface of any of the stress relaxation plates of the metal-impregnated ceramic substrate or the metal substrate. Preferably has a metal layer with a thickness of 0.5 to 20 μm made of Ni or Au. A particularly preferable thickness of the metal layer is 2 to 10 μm. Thereby, the adhesion state of the ceramic circuit board, the stress relaxation plate and the metal base plate is improved. When the thickness of the metal layer is less than 0.5 μm, the adhesion state is deteriorated, and when it exceeds 20 μm, there is a possibility that peeling due to a difference in thermal expansion between the metal layer and the stress relaxation plate may occur. The metal layer can be formed by performing electroless plating or electrolytic plating with the above metal species after washing the stress relaxation plate. It can also be formed by metal vapor deposition or metal coating.

The ceramic circuit board, the stress relaxation plate, and the metal base plate are joined using soldering or brazing. As the solder, cream solder, eutectic solder, lead-free solder or the like may be used. Bonding by a brazing method is preferable, and since the bonding layer can be made thin and uniform, thermal resistance can be reduced.

[Example 1]
Silicon carbide powder A (commercial product: average particle size 150 μm) 3250 g, silicon carbide powder B (commercial product:
An average particle size of 10 μm (1750 g) and silica sol (Nissan Chemical Co., Ltd .: Snowtex) 750 g were weighed and mixed for 30 minutes with a stirrer and then pressed into a shape of 70 mm × 70 mm × 100 mm in a surface pressure of 10 MPa. Thus, a molded body was produced. The obtained molded body was dried at a temperature of 120 ° C. for 1 hour and then fired in a nitrogen atmosphere at a temperature of 1000 ° C. for 2 hours to produce a sintered body having a porosity of 35%. Using a surface grinder, External dimensions are 56mm x 47mm x 100mm
The SiC porous body was manufactured by processing into the shape. After applying a boron nitride release agent to the obtained SiC porous body, it is inserted into a cylindrical graphite jig (outer dimensions: 80 mm × 80 mm × 100 mm, inner dimensions: 56.5 mm × 47.5 × 100 mm). Structure.

4 pieces of the above structure are assembled (160.8 mm x 160.8 mm x 100 mm) with a release plate (80 mm x 100 mm x 0.8 mm) made of a stainless steel plate coated with graphite mold release agent, and iron plates on both sides (Thickness 12 mm) was placed and connected with 8 bolts to form a single laminate.
This laminate is preheated to a temperature of 700 ° C. in an electric furnace and then placed in a preheated press mold (inner diameter: 400 mm × height: 300 mm), and contains 12% by mass of silicon and 1% by mass of magnesium. A molten aluminum alloy (temperature: 800 ° C.) was poured, and the aluminum alloy was impregnated by applying pressure of 100 MPa for 25 minutes. After cooling to room temperature, it is cut along the shape of the release plate with a wet band saw, and the release plate is peeled off. Then, the graphite jig portion is removed with a lathe, and four composites (56 × 47 × 100 mm) are obtained. Manufactured. This was annealed at a temperature of 530 ° C. for 3 hours to remove distortion during impregnation.

From the obtained composite, a thermal expansion coefficient measurement specimen (diameter 4 mm, length 20 mm), thermal conductivity measurement specimen (25 mm × 25 mm × 1 mm), strength measurement specimen (40 mm × 4 mm ×) by grinding. 3 mm), the coefficient of thermal expansion at a temperature of 25 ° C. to 150 ° C. is measured with a thermal dilatometer (manufactured by Seiko Denshi Kogyo; TMA300), and the thermal conductivity at a temperature of 25 ° C. is measured with a laser flash method (manufactured by ULVAC; TC3000). The three-point bending strength was measured with a bending strength tester (manufactured by Imada Seisakusho; SV301). As a result, the thermal expansion coefficient was 7.5 × 10 ⁻⁶ / K, the thermal conductivity was 200 W / (m · K), and the three-point bending strength was 400 MPa.

Next, the outer periphery of the composite was processed into a shape of 54 mm × 45 mm × 100 mm and then cut into a plate having a thickness of 1.5 mm at a cutting speed of 0.2 mm / min using diamond abrasive grains with a multi-wire saw. Further, it was ground to a thickness of 1.2 mm using a # 600 diamond grindstone with a double-side grinder. Then, after polishing to a plate thickness of 1.0 mm using diamond abrasive grains on a lapping machine, electroless Ni-P plating is performed to form a metal layer (6 μm thickness) to produce a stress relaxation plate A did.
<Power module structure>
The power module structure shown in FIG. 1 was produced using the following constituent materials. That is, a power module structure was produced by laminating the stress relaxation plate 2 between the ceramic circuit board 1 and the metal base plate 3 via the bonding layer 4.

<Constituent materials>
Ceramic circuit board 1: Silicon nitride substrate: 58 mm x 49 mm x 0.635 mm
(Copper circuit: 54mm x 45mm x 0.2mm)
Stress relaxation plate 2: Stress relaxation plate A manufactured above: 54 mm × 45 mm × 1.0 mm
Base plate 3: Copper plate: 100 mm x 80 mm x 4 mm
Bonding layer 4: Cream solder (0.2 mm thickness)

<Evaluation of reliability of power module structure>
After holding the power module structure in a thermostatic bath at −40 ° C. and 125 ° C. for 30 minutes and performing a heat cycle treatment (1000 times), the appearance and the joining state were confirmed by ultrasonic flaw detection. The problem was not confirmed.

[Example 2]
Silicon carbide powder A (commercial product: average particle size 150 μm) 3250 g, silicon carbide powder B (commercial product: average particle size 10 μm) 1750 g, silica sol (Nissan Chemical Co., Ltd .: Snowtex) 750 g were weighed and stirred and mixed. After mixing for 30 minutes, it was press-molded into a plate having dimensions of 70 mm × 70 mm × 100 mm at a surface pressure of 10 MPa to produce a molded body. The obtained molded body was dried at a temperature of 120 ° C. for 1 hour and then fired in a nitrogen atmosphere at a temperature of 1000 ° C. for 2 hours to produce a sintered body having a porosity of 35%. Using a surface grinder, A SiC porous body was manufactured by processing into an external dimension of 56 mm × 47 mm × 100 mm. The obtained SiC porous body was processed into a shape having an outer dimension of 56 mm × 47 × 2 mm by a slicer and a lapping grinder.

32 pieces of porous ceramics with outer dimensions of 56 mm x 47 x 2 mm are laminated with a release plate (160 mm x 160 mm x 0.8 mm) coated with a graphite release agent applied to every 4 sheets for characteristic evaluation There is no structure body (170 mm x 170 mm x 30 mm) sandwiched by 4 pieces of 56 x 47 x 5 mm together, and an iron plate (plate thickness 12 mm) is arranged on both sides and connected with 8 bolts to form a single laminate. did. Hereinafter, a composite (56 mm × 47 mm × 2 mm) was produced in the same manner as the stress relaxation plate A of Example 1, the thermal expansion coefficient at a temperature of 25 ° C. to 150 ° C., the thermal conductivity at a temperature of 25 ° C., and three-point bending. When the strength was measured, they were 7.5 × 10 ⁻⁶ / K, 200 W / (m · K), and 400 MPa, respectively.

The obtained composite was surface-processed into a plate having a thickness of 1.0 mm using a diamond grindstone with a surface grinder, and subsequently, with a water jet processing machine (Abrasive Jet Cutter NC manufactured by Sugino Machine). Using a garnet having a particle size of 100 μm as abrasive grains under the conditions of a pressure of 250 MPa and a processing speed of 100 mm / min, it was cut into a shape of 54 mm × 45 mm × 1.0 mm. Thereafter, a metal layer similar to that of the stress relaxation plate A is applied to form a stress relaxation plate B, and then the obtained stress relaxation plate B is bonded using the same technique as the ceramic circuit board and metal base plate of Example 1. Then, a power module structure was manufactured, and the same reliability evaluation as in Example 1 was performed. As a result, problems such as peeling of the bonding layer were not confirmed.

[Examples 3 and 4]
Silicon carbide powder C (commercial product: average particle size 10 μm) 818 g of powder (Example 3), or graphite powder A (commercial product: average particle size 300 μm) 245 g and silicon carbide powder D (commercial product: average particle size 20 μm) 358 g of the mixed powder (Example 4) was filled into a cylindrical graphite jig (inside dimensions: 70 mm × 70 mm × 100 mm) and press-molded to have a porosity of 48% (Example 3) or a porosity of 35%. A powder molded body of (Example 4) was produced. The powder compact was filled in a jig to form a laminate using the same method as in Example 1 to produce a composite. Except for using them and using an aluminum nitride substrate: 61 mm × 54 mm × 0.635 mm (Cu circuit: 59 mm × 52 mm × 0.2 mm) as the ceramic circuit substrate, the same as in the case of the stress relaxation plate A of Example 1 Stress relief plate C: 59 mm × 52 mm × 1.0 mm (Example 3), stress relief plate D: 59 mm × 52 mm × 2.0 mm (Example 4), power module structure manufactured, Evaluation was performed. As a result, no peeling of the bonding layer was confirmed.
Moreover, when the thermal expansion coefficient at a temperature of 25 ° C. to 150 ° C., the thermal conductivity at a temperature of 25 ° C., and the three-point bending strength were measured in the same manner as in Example 1, the thermal expansion coefficient of the stress relaxation plate C was 11.5. × 10 ^-6 / K, thermal conductivity is 120 W / (m · K), three-point bending strength is 510 MPa, thermal expansion coefficient of stress relaxation plate D is 8.5 × 10 ^-6 / K, thermal conductivity is 250 W / (M · K), the three-point bending strength was 110 MPa.

[Examples 5 to 11, Comparative Example 1]
Example except that instead of the plating layer of (Ni-P: 6 μm), a metal layer having the metal species and metal layer thickness shown in Table 2 was formed, the plate thickness was changed, and the joining method was changed. The stress relaxation plate and the power module structure were manufactured in the same manner as in the case of using the stress relaxation plate A of 1, and the reliability was evaluated. As a result, in Examples 5 to 11, problems such as peeling of the bonding layer were not confirmed, but in Comparative Example 1, cracks in the stress relaxation plate were confirmed.

[Examples 12 to 14, Comparative Examples 2 and 3]
Isotropic graphite compact A (commercial product, porosity: 22% by volume, dimensions: 70 mm × 70 mm × 100 mm) (Example 12) and isotropic graphite compact B (commercial product, porosity) : 21 volume%, dimensions: 70 mm x 70 mm x 100 mm) (Example 13), isotropic graphite compact C (commercial product, porosity: 40 volume%, dimensions: 70 mm x 70 mm x 100 mm) (Example) 14) Extruded graphite molded body A (commercial product, porosity: 20% by volume, dimensions: 70 mm × 70 mm × 100 mm) (Comparative Example 2), isotropic graphite molded body D (commercial product, porosity: 18 volume) %, Dimensions: 70 mm × 70 mm × 100 mm) (Comparative Example 3), except that pure Al was used instead of the aluminum alloy, a composite was produced in the same manner as in Example 1, and the shape processing was 59 mm × 52 mm. X 2.0 mm. Thereafter, the production of the stress relaxation plate A, except that the aluminum nitride substrate used in Example 3 was used as the ceramic circuit substrate and that the aluminum plate (100 mm × 80 mm × 4 mm) was used as the base plate (Example 14). In accordance with the above, stress relaxation plates L, M, N, Z, AA and a power module structure were manufactured and evaluated for reliability. As a result, although problems such as peeling of the bonding layer were not confirmed in Examples 12 to 14, cracks of the stress relaxation plate were confirmed in Comparative Example 2, and peeling of the solder bonding layer (solder crack) was observed in Comparative Example 3. Was confirmed.

Further, in the same manner as in Example 1, when the thermal expansion coefficient at a temperature of 25 ° C. to 150 ° C., the thermal conductivity at a temperature of 25 ° C., and the three-point bending strength were measured, the thermal expansion coefficient of the stress relaxation plate L was 9. 2 × 10 ⁻⁶ / K, thermal conductivity is 170 W / (m · K), the strength is 105 MPa, the thermal expansion coefficient of the stress relaxation plate M is 8.2 × 10 ⁻⁶ / K, and the thermal conductivity is 250 W / ( m · K), the three-point bending strength is 65 MPa, the thermal expansion coefficient of the stress relaxation plate N is 13.2 × 10 ⁻⁶ / K, the thermal conductivity is 210 W / (m · K), the three-point bending strength is 75 MPa, The thermal expansion coefficient of the stress relaxation plate Z is 7.5 × 10 ⁻⁶ / K, the thermal conductivity is 350 W / (m · K), the three-point bending strength is 25 MPa, and the thermal expansion coefficient of the stress relaxation plate AA is 5. 0 × 10 ^-6 / K, the thermal conductivity of 200W / (m · K), 3 -point bending strength was 80 MPa.

[Example 15]
A mixed powder of aluminum nitride powder (commercial product: average particle size 2 μm) 2300 g, yttria powder (commercial product: average particle size 1 μm) 96 g, molding binder (methylcellulose) 120 g, and pure water 120 g was press-molded at a surface pressure of 10 MPa. Thereafter, CIP molding was further performed at a molding pressure of 50 MPa to produce a cylindrical body (diameter 110 mm × 110 mm). This was degreased for 2 hours at a temperature of 600 ° C. in an air atmosphere, and then fired at a temperature of 1780 ° C. for 4 hours in a nitrogen atmosphere to produce a sintered body. Then, the porosity was 30 using a diamond grindstone at a machining center. % Inorganic porous material (70 mm × 70 mm × 100 mm) was produced.

Stress relaxation plate O (59 mm × 52 mm × 1.0 mm) and power module structure in the same manner as the stress relaxation plate L of Example 12, except that this inorganic porous material was combined in the same manner as in Example 12. The body was manufactured and the reliability was evaluated. As a result, problems such as peeling of the joint portion were not confirmed. Further, when the thermal expansion coefficient at a temperature of 25 ° C. to 150 ° C., the thermal conductivity at a temperature of 25 ° C., and the three-point bending strength were measured in the same manner as in Example 1, the thermal expansion coefficient of the stress relaxation plate O was 7. 6 × 10 ⁻⁶ / K, thermal conductivity was 170 W / (m · K), and three-point bending strength was 360 MPa.

[Example 16]
Except for using a mixture of 2760 g of silicon nitride powder (commercial product: average particle size 1 μm), 150 g of yttria powder (commercial product: average particle size 1 μm), and 90 g of magnesium oxide powder (commercial product: average particle size 1 μm), A cylindrical body (diameter: 110 mm × 110 mm) was produced in the same manner as in Example 15. This was fired at a temperature of 1600 ° C. for 4 hours under a nitrogen pressure atmosphere of 0.01 MPa to produce a sintered body, and then an inorganic porous body having a porosity of 22% (70 mm × 70 mm) using a diamond grindstone at a machining center. 70 mm × 100 mm).

The stress relaxation plate P (59 mm × 52 mm × 1.0 mm) and the power module structure are the same as the stress relaxation plate L of Example 12, except that the ceramic porous body is combined by the same method as in Example 12. The body was manufactured and the reliability was evaluated. As a result, problems such as peeling of the bonding layer were not confirmed. Further, in the same manner as in Example 1, when the thermal expansion coefficient at a temperature of 25 ° C. to 150 ° C., the thermal conductivity at a temperature of 25 ° C., and the three-point bending strength were measured, the thermal expansion coefficient of the stress relaxation plate P was 7. 3 × 10 ⁻⁶ / K, the thermal conductivity was 100 W / (m · K), and the three-point bending strength was 520 MPa.

[Example 17]
Graphite powder A (commercial product: average particle size 300 μm) 377 g, silicon carbide powder D (commercial product: average particle size 20 μm) 550 g ceramic powder, and aluminum powder (commercial product: average particle size 20 μm) 343 g, silicon powder ( Commercially available product: 47 g of metal powder with an average particle size of 7 μm) was mixed for 15 minutes with a ball mill, and a cylindrical iron mold (inner dimensions: 70 mm × 70 mm × 150 mm) was subjected to mold release treatment of 26 g of mixed powder and graphite. 8mmt release plates (SUS plates) are alternately filled, heated to a temperature equal to or higher than the melting point of the aluminum alloy (600 ° C), and then solidified from one direction in a state of being pressurized at 50MPa, and 70% by volume of ceramic powder. A composite (70 mm × 70 mm × 2 mm) was prepared. The composite was processed by the same method as the composite of Example 2 to produce a stress relaxation plate Q (57 mm × 50 mm × 1.0 mm). Similarly to Example 1, the thermal expansion coefficient at a temperature of 25 ° C. to 150 ° C., the thermal conductivity at a temperature of 25 ° C., and the three-point bending strength were measured. 0 × 10 ⁻⁶ / K, thermal conductivity was 200 W / (m · K), and three-point bending strength was 100 MPa.

Example 1 except that this stress relaxation plate Q was used and an aluminum nitride substrate: 61 × 54 × 0.635 mmt (Al circuit: 57 × 50 × 0.2 mmt) was used as the ceramic circuit substrate. Thus, a power module structure was manufactured and evaluated for reliability. As a result, problems such as peeling of the joint portion were not confirmed.

[Example 18]
Graphite powder A (commercial product: average particle size 300 μm) 296 g, silicon carbide powder D (commercial product: average particle size 20 μm) 433 g ceramic powder, and aluminum powder (commercial product: average particle size 20 μm) 515 g, silicon powder ( Commercially available product: 70 g of metal powder with an average particle size of 7 μm) is mixed for 15 minutes with a ball mill and filled into a cylindrical iron mold (inner dimensions: 70 mm × 70 mm × 150 mm), at a temperature (600 ° C.) above the melting point of the aluminum alloy. A composite (70 mm × 70 mm × 100 mm) containing 55% by volume of ceramic powder was produced by solidifying from one direction in a state of being pressurized at 50 MPa after heating. Using the same method as in Example 1, a stress relaxation plate R (57 mm × 50 mm × 1.0 mm) is manufactured from this composite, and a power module structure is manufactured in the same method as in Example 17, and the reliability is improved. Sex evaluation was performed. As a result, problems such as peeling of the joint portion were not confirmed. Further, in the same manner as in Example 1, when the thermal expansion coefficient at a temperature of 25 ° C. to 150 ° C., the thermal conductivity at a temperature of 25 ° C., and the three-point bending strength were measured, the thermal expansion coefficient of the stress relaxation plate R was 11. 9 × 10 ⁻⁶ / K, the thermal conductivity was 190 W / (m · K), and the three-point bending strength was 130 MPa.

[Example 19]
Graphite powder A (commercial product: average particle size 300 μm) 216 g, silicon carbide powder D (commercial product: average particle size 20 μm) 315 g ceramic powder, and aluminum powder (commercial product: average particle size 20 μm) 687 g, silicon powder ( Commercial product: average particle size 7 μm) 94 g of metal powder is mixed for 15 minutes with a ball mill and filled into a cylindrical iron mold (inner dimensions: 70 mm × 70 mm × 150 mm), and the temperature is higher than the melting point of the aluminum alloy (600 ° C.). A composite (70 mm × 70 mm × 100 mm) containing 40% by volume of ceramic powder was produced by solidifying from one direction in a state of being pressurized at 50 MPa after heating. A stress relaxation plate S (57 mm × 50 mm × 1.0 mm) is manufactured from this composite using the same method as in Example 1, a ceramic circuit board similar to Example 17, and a base plate similar to Example 14 Was used to manufacture a power module structure, and the reliability was evaluated. As a result, problems such as peeling of the joint portion were not confirmed. Further, in the same manner as in Example 1, when the thermal expansion coefficient at a temperature of 25 ° C. to 150 ° C., the thermal conductivity at a temperature of 25 ° C., and the three-point bending strength were measured, the linear expansion coefficient of the stress relaxation plate S was 14. 5 × 10 ⁻⁶ / K, the thermal conductivity was 180 W / (m · K), and the three-point bending strength was 140 MPa.

[Comparative Example 4]
162 g of graphite powder A (commercial product: average particle size 300 μm), 236 g of ceramic powder of silicon carbide powder D (commercial product: average particle size 20 μm), and 802 g of aluminum powder (commercial product: average particle size 20 μm), silicon powder ( Commercially available product: 109 g of metal powder with an average particle size of 7 μm) is mixed for 15 minutes by a ball mill and filled into a cylindrical iron mold (inner dimensions: 70 mm × 70 mm × 150 mm), at a temperature (600 ° C.) above the melting point of the aluminum alloy. A composite (70 mm × 70 mm × 100 mm) containing 30% by volume of ceramic powder was produced by solidifying from one direction in a state where the pressure was increased to 50 MPa after heating. Using a method similar to that of Example 18, a stress relaxation plate AB (57 mm × 50 mm × 1.0 mm) and a power module structure were manufactured from this composite, and reliability evaluation was performed. As a result, peeling (solder crack) of the solder joint portion was confirmed at the joint portion. Further, in the same manner as in Example 1, when the thermal expansion coefficient at a temperature of 25 ° C. to 150 ° C., the thermal conductivity at a temperature of 25 ° C., and the three-point bending strength were measured, the thermal expansion coefficient of the stress relaxation plate Q was 17. 0 × 10 ⁻⁶ / K, thermal conductivity was 150 W / (m · K), and three-point bending strength was 135 MPa.

[Examples 20 to 22]
Copper-tungsten (composition (mass%)) having a thermal expansion coefficient of 8.5 × 10 ⁻⁶ / K at a temperature of 25 ° C. to 150 ° C. and a thermal conductivity of 230 W / (m · K) at a temperature of 25 ° C. : Cu / W = 20/80) Various stress relaxation plates made of a metal substrate having a thickness changed as shown in Table 2 were prepared. A power module structure was manufactured in the same manner as the stress relaxation plate Q of Example 17 except that these stress relaxation plates were used, and reliability evaluation was performed. As a result, problems such as peeling of the joint portion were not confirmed.

[Examples 23 and 24]
Instead of a metal plate made of Cu / W, a metal substrate of copper-molybdenum (composition (mass%): Cu / Mo = 50/50) having a thermal conductivity of 240 W / (m · K) at a temperature of 25 ° C. Example 23) is a copper-molybdenum-copper (Cu / Mo / Cu) three-layer laminate having a thermal conductivity of 200 W / (m · K) (a metal substrate having a thickness of 0.2 mm for each layer) Except that Example 24) was used as a stress relaxation plate, a power module structure was produced and evaluated for reliability in the same manner as in Example 17. As a result, problems such as peeling of the joint portion were not confirmed. It was.

The main conditions and results of Examples and Comparative Examples are shown in Tables 1 to 3.

1. Ceramic circuit board2. 2. Stress relaxation plate Metal base plate4. Metal circuit
5. Bonding layer 6. Metal 7. Ceramic powder

Claims (6)

The thermal expansion coefficient of the ceramic circuit board is α (× 10 ⁻⁶ / K), the thermal expansion coefficient of the stress relaxation plate is β (× 10 ⁻⁶ / K), and the thermal expansion coefficient of the metal base plate is γ (× 10 ^−6). / K), it has a thermal expansion coefficient satisfying (α + γ) / 2-4 <β <(α + γ) / 2 + 4, and has a plate thickness of 0.5 to 3.0 mm and a thermal conductivity of 25 ° C. Power formed by soldering or brazing between a ceramic circuit board and a metal base plate after forming a metal layer on the surface of a stress relaxation plate with a three-point bending strength of 50 MPa or more at 100 W / (m · K) or more Module structure. The stress relaxation plate is a porous body composed of one or more ceramic powders selected from silicon carbide, aluminum nitride, silicon nitride, boron nitride, and graphite, or a plate-shaped composite of a powder compact and aluminum or an aluminum alloy. The power module structure according to claim 1, wherein the power module structure is a metal-impregnated ceramic substrate. The stress relaxation plate is a metal plate selected from Cu, Ni, Mo, W, Co and Fe, an alloy plate containing at least one of the metal components, or two or more selected from the metal plate and the alloy plate. The power module structure according to claim 1, wherein the power module structure is formed of 3. The power module structure according to claim 1, wherein a metal layer is formed on a surface of a plate-like metal-impregnated ceramic substrate obtained through the following step (1) or (2). A method of manufacturing a stress relaxation plate.
(1) A block-like porous body having a porosity of 10 to 60% by volume, or a powder molded body and aluminum made of one or more ceramic powders selected from silicon carbide, aluminum nitride, silicon nitride, boron nitride, and graphite Alternatively, a step of producing a plate-shaped metal-impregnated ceramic substrate by compounding an aluminum alloy by a molten forging method at a pressure of 30 MPa or more and cutting and / or shaping a block-shaped metal-impregnated ceramic body.
(2) A plate-shaped porous body having a porosity of 10 to 60% by volume or a powder molded body made of one or more ceramic powders selected from silicon carbide, aluminum nitride, silicon nitride, boron nitride, and graphite is separated. A step of laminating through a mold plate and impregnating aluminum or aluminum alloy with a molten metal forging method at a pressure of 30 MPa or more to produce a plate-like metal-impregnated ceramic body, and then processing the shape to produce a metal-impregnated ceramic substrate. 3. The power module structure according to claim 1, wherein a metal layer is formed on a surface of a plate-like metal-impregnated ceramic substrate obtained through the following step (3) or (4). A method of manufacturing a stress relaxation plate.
(3) Separate a powder obtained by mixing 40 to 90% by volume of one or more ceramic powders selected from silicon carbide, aluminum nitride, silicon nitride, boron nitride, and graphite and 10 to 60% by volume of aluminum or an aluminum alloy. Filled with a mold that has been subjected to mold treatment, heated to a temperature higher than the melting point of aluminum or aluminum alloy, heated and pressed at a pressure of 30 MPa or more to be combined into a block shape, and plate-like by cutting and / or peripheral processing A step of obtaining a metal-impregnated ceramic substrate.
(4) Separate from 40 to 90% by volume of one or more ceramic powders selected from silicon carbide, aluminum nitride, silicon nitride, boron nitride, and graphite and 10 to 60% by volume of aluminum or aluminum alloy. A step of filling a mold subjected to mold treatment, heating to a temperature equal to or higher than the melting point of aluminum or an aluminum alloy, and heating and pressing at a pressure of 30 MPa or more to form a composite in a plate-like metal-impregnated ceramic substrate. The metal layer on the surface of the stress relaxation plate is formed by plating at least one metal selected from Ni, Co, Pd, Cu, Ag, Au, Pt, and Sn having a thickness of 0.5 to 20 μm. The manufacturing method of the stress relaxation board used for the power module structure in any one of Claims 1-5 characterized by the above-mentioned.