JP2010024077A - Aluminum-silicon carbide composite and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aluminum-silicon carbide composite suitable as a base plate for a power module. <P>SOLUTION: A method for producing the plate-shaped aluminum-silicon carbide composite having 2-6 mm thickness includes the steps of: mixing 20-40 vol.% metal powder containing 77-94.5 mass% aluminum, 5-20 mass% silicon and 0.5-3 mass% magnesium with 60-80 vol.% silicon carbide powder having 50-300 μm average particle size; packing the obtained mixture in a mold which is subjected to mold-release treatment; heating the packed mixture to 600-750°C; and subjecting the heated mixture to hot press molding under ≥10 MPa. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to an aluminum-silicon carbide composite suitable as a base plate for a power module and a heat dissipation component using the same.

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 substrate such as an aluminum nitride substrate or a silicon nitride substrate having high insulation and high thermal conductivity, and a metal heat sink made of copper or aluminum is formed on the back surface. This circuit board 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 caused by a difference in thermal expansion coefficient between the base plate and the circuit board occurs in the solder layer, and as a result, heat radiation becomes insufficient and the semiconductor element is 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, the aluminum-silicon carbide composite by the powder metallurgy method has a problem that the thermal conductivity and the like are lower than those of the melt forging method.
Japanese Patent No. 3468358 JP-T-5-507030. JP-A-9-157773 JP-A-10-335538

The base plate is often used by being joined to a heat radiating fin, and the shape and warpage of the joined part are also important characteristics. For example, when joining the base plate to the heat radiating fins, it is common to apply heat radiating grease with high thermal conductivity and screw it to the heat radiating fins or heat radiating unit using the holes provided in the peripheral edge of the base plate. If there are a lot of minute irregularities on the plate, a gap will be created between the base plate and the heat radiating fins, and even if high heat conductive heat radiating grease is applied, the heat transfer will be significantly reduced. As a result, the ceramic circuit board and base There existed a subject that the heat dissipation of the whole module comprised with a board, a radiation fin, etc. will fall remarkably.

Therefore, in order to prevent a gap as much as possible between the base plate and the heat radiating fin, a base plate with a convex warp is used in advance. A technique has been proposed in which a warp is imparted by applying a pressure to the base plate under heating, using a jig having a predetermined shape (Patent Document 5). The warp obtained by this method has a problem that when the surface of the base plate has waviness, the shape is not constant and the quality is not stable. In addition, there is a problem in that a large gap is generated between the heat dissipating fins due to variations in the warp shape and surface irregularities.
Patent 3792180

There is also a method of warping by cutting the surface of the base plate by machining, but since the aluminum-silicon carbide composite is very hard, it requires a lot of grinding using a tool such as diamond, which increases the cost. There was a problem.

The present invention has been made in view of the above situation, and an object thereof is to provide an aluminum-silicon carbide composite suitable as a base plate for a power module.

  As a result of intensive studies to achieve the above object, the present inventor has optimized the particle size and content of silicon carbide powder in an aluminum-silicon carbide composite, and pressurizes it in a temperature range near the melting point of aluminum. The present invention was completed by obtaining the knowledge that the thermal conductivity can be improved by molding. Furthermore, the present invention has been completed by obtaining the knowledge that the warp shape of the plate-like aluminum-silicon carbide composite can be controlled by adjusting the mold shape at the time of heat forming or creep deformation by a hot press.

That is, the present invention has a metal powder content of 20 to 40% by volume containing 77 to 94.5% by mass of aluminum, 5 to 20% by mass of silicon and 0.5 to 3% by mass of magnesium, and an average particle size of 50 to 300 μm. A plate characterized by mixing 60 to 80% by volume of silicon carbide powder, filling a mold subjected to a release treatment, heating to a temperature of 600 to 750 ° C., and performing hot press molding at a pressure of 10 MPa or more. This is a method for producing a plate-like aluminum-silicon carbide composite having a thickness of 2 to 6 mm.

Moreover, this invention is 20-40 volume% of metal powder containing 77-94.5 mass% of aluminum, 5-20 mass% of silicon, and 0.5-3 mass% of magnesium, and an average particle diameter is 50-300 micrometers. After mixing 60 to 80% by volume of silicon carbide powder, ceramic fibers having a thickness of 0.1 to 0.5 mm and a Vf of 3 to 20% by volume are disposed on both main surfaces in a mold subjected to a release treatment. An aluminum-ceramic fiber composite having a thickness of 0.1 to 0.3 mm on both main surfaces, wherein the mixed powder is filled, heated to a temperature of 600 to 750 ° C., and heated and pressed at a pressure of 10 MPa or more. This is a method for producing a plate-like aluminum-silicon carbide composite having a body thickness of 2 to 6 mm.

Furthermore, the present invention uses a mold having a concave warp of 50 to 500 μm per 200 mm at the time of hot press molding, and imparts a convex warp of 50 to 500 μm per 200 mm to one main surface. A method for producing a plate-like aluminum-silicon carbide composite.

In addition, the present invention is such that the plate-like aluminum-silicon carbide composite is heat-treated at a temperature of 400 to 550 ° C. for 30 seconds or more in a state where a stress of 10 kPa or more is applied so as to bend to a certain curvature. It is a method for producing a plate-like aluminum-silicon carbide composite material, which is subjected to creep deformation to give a convex warp of 50 to 500 μm per 200 mm.

In the present invention, the porosity is 2 to 10% by volume, the coefficient of thermal expansion at a temperature of 25 ° C. to 150 ° C. is 5 × 10 ^{−6 to} 9 × 10 ⁻⁶ / K, and the heat conduction at a temperature of 25 ° C. A plate-like aluminum-silicon carbide composite having a rate of 150 to 300 W / mK and a three-point bending strength of 100 to 350 MPa.

Furthermore, in the present invention, a plate-like aluminum-silicon carbide composite is processed with a mounting hole and then plated, and one principal surface is soldered or brazed to a ceramic circuit board, and the other principal surface Is a power module base plate used as a heat dissipation surface.

  The aluminum-silicon carbide composite of the present invention has characteristics of low thermal expansion and high thermal conductivity. The present invention relates to an aluminum-silicon carbide composite obtained by heat-molding metal powder such as aluminum powder and silicon carbide powder, by optimizing the particle size and content of the silicon carbide powder. Characteristics such as thermal conductivity can be remarkably improved, and an aluminum-silicon carbide composite suitable as a base plate of a power module on which a semiconductor element requiring high reliability is mounted is supplied at low cost.

The aluminum-silicon carbide composite of the present invention comprises a first component made of an aluminum alloy whose main component is aluminum and a second component whose main component is silicon carbide. In the composite body in which different kinds of materials are combined as in the present invention, heat can be exchanged with each other because the interfaces of the different kinds of materials are firmly connected. For this reason, when the adhesion at the interface is poor, the thermal conductivity of the composite is governed by the matrix material (in the present invention, an aluminum alloy), and how high the thermal conductivity of the reinforcing material (in the present invention, silicon carbide) itself is. Even so, the thermal conductivity characteristics of the entire composite are less than the matrix material. The basic idea of the present invention is how to firmly adhere the metal component and the reinforcing material in the composite, and as a technique thereof, the metal component is pressure-molded in a molten state to strengthen the interface between the two. And achieve the desired properties.

  Particularly important characteristics of the aluminum-silicon carbide composite of the present invention are thermal conductivity and coefficient of thermal expansion. For this reason, as a reinforcing material to be used, it is necessary that the raw material itself has a high thermal conductivity and a low thermal expansion coefficient, and silicon carbide is preferable. Furthermore, the heat transfer mechanism differs between silicon carbide and aluminum. For this reason, the heat transfer loss at the interface between the two materials greatly affects the thermal conductivity of the composite, and reducing the area of this interface (using silicon carbide powder having a large particle diameter) results in a composite It is effective in improving the thermal conductivity of

The reinforcing material used for the aluminum-silicon carbide composite of the present invention is 60 to 80% by volume of silicon carbide powder having an average particle diameter of 50 to 300 μm. Regarding the particle size of the silicon carbide powder, the average particle size is 50 μm or more from the viewpoint of the thermal conductivity of the aluminum-silicon carbide composite. On the other hand, an average particle diameter exceeding 300 μm is not preferable because the surface roughness of the aluminum-silicon carbide composite decreases and strength characteristics decrease. If the content of the silicon carbide powder is less than 60% by volume, the thermal conductivity of the aluminum-silicon carbide composite is lowered, and the thermal expansion coefficient is increased, which is not preferable. On the other hand, if the content of the silicon carbide powder exceeds 80% by volume, the aluminum-silicon carbide composite is insufficiently densified, and the strength and thermal conductivity are undesirably lowered. In order to increase the content of silicon carbide powder and achieve densification, it is preferable to mix silicon carbide powders having different average particle sizes. In this case, the average particle diameter of the silicon carbide powder is calculated from the average particle diameter and content of each silicon carbide powder. For this reason, when carrying out particle size blending, a powder having an average particle size of less than 50 μm and / or more than 300 μm can also be used. Furthermore, using a silicon carbide powder close to a spherical shape is effective for increasing the content.

The metal powder used in the present invention is a metal powder containing 77 to 94.5% by mass of aluminum, 5 to 20% by mass of silicon, and 0.5 to 3% by mass of magnesium. As this metal powder, (1) a mixed metal powder is used, (2) a mixed metal powder and an alloy powder are used (for example, an aluminum powder, a silicon powder and an aluminum-magnesium alloy powder are used), (3 ) It is possible to use an alloy powder containing a predetermined amount of the three components. If the silicon component is less than 5% by mass or exceeds 20% by mass, the melting point of the alloy composed of the three components is increased, and the densification may not proceed. On the other hand, when the silicon component is less than 5% by mass, the thermal expansion coefficient of the obtained alloy is increased, and as a result, the thermal expansion coefficient of the obtained aluminum-silicon carbide composite is increased. 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 aluminum-silicon carbide composite is lowered, which is not preferable. The magnesium component has an effect of improving the wettability of the obtained alloy and silicon carbide. If the content is less than 0.5% by mass, the effect is insufficient, and characteristics such as thermal conductivity and strength are unfavorable. On the other hand, when the magnesium component exceeds 3% by mass, aluminum carbide (Al ₄ C ₃ ) is likely to be generated at the time of compounding, which is not preferable in terms of thermal conductivity and strength.

The content of these metal powders is 20 to 40% by volume with respect to the obtained aluminum-silicon carbide composite. Here, the content (volume%) of the metal powder defines the content (volume%) with the average density of the metal powder being 2.7 g / cm ³ . If it is less than 20% by volume, the amount of molten alloy at the time of hot press molding is insufficient, and the densification of the aluminum-silicon carbide composite is insufficient. On the other hand, if it exceeds 40% by volume, a dense aluminum-silicon carbide based composite can be obtained, but this is not preferable because the thermal expansion coefficient of the aluminum-silicon carbide based composite becomes too large. Regarding the particle size of these metal powders, an average particle size of about 10 to 200 μm is preferable. If the average particle size is less than 10 μm, the densification is inhibited by oxidation of the metal particle surface, which is not preferable. On the other hand, when the average particle size exceeds 200 μm, the homogenization of mixing is hindered and the characteristics may be deteriorated.

The mixing method of the raw material powder of the present invention is not particularly limited as long as the individual raw materials are uniformly mixed. Ball mill mixing, mixing with a mixer, and the like are possible. Regarding the mixing time, a time that does not allow oxidation and pulverization of the raw material powder is preferable, and depending on the mixing method and the filling amount, it is generally about 15 minutes to 5 hours. If the mixing time is short, insufficient densification of the aluminum-silicon carbide composite or non-uniformity of the composite structure will occur. On the other hand, if the mixing time is too long, the raw material powder is pulverized by oxidation and pulverization, and as a result, the thermal conductivity of the aluminum-silicon carbide composite may be lowered. Moreover, if it can be removed at the heating stage at the time of hot press molding, a shape-retaining binder or the like can be used as necessary.

The mold used in the hot press molding of the present invention is suitably made of an iron material such as cast iron or stainless steel from the viewpoint of strength, and although expensive, ceramics such as silicon nitride can also be used. Furthermore, a graphite mold can also be used. The mold is used by applying a release agent on the surface from the surface of the mold release property with the composite obtained by hot press molding. As the mold release agent, a mold release agent such as graphite, alumina, boron nitride or the like is suitable. In addition, by forming a thin film such as alumina on the mold and then applying a release agent, it is possible to obtain excellent mold release properties and extend the life of the mold. In addition, a release plate such as a graphite sheet can be used between the mold and the product as necessary.

In the present invention, a mixed powder of metal powder and silicon carbide powder is filled in a mold and heated and press-molded to obtain a dense plate-like aluminum-silicon carbide composite having a thickness of 2 to 6 mm. In this case, the plate thickness of the obtained plate-like aluminum-silicon carbide composite is adjusted by the amount of mixed powder filled in the mold. When the plate thickness is less than 2 mm, when used as a base plate for a power module, heat transfer in the surface direction is insufficient, and the heat dissipation characteristics of the entire power module are deteriorated. On the other hand, if the plate thickness exceeds 6 mm, the thermal resistance of the base plate itself increases due to the increase in the plate thickness, and as a result, the temperature of the semiconductor element increases excessively, which is not preferable. A more preferable plate thickness of the plate-like aluminum-silicon carbide composite is 3 to 5 mm.

In the present invention, the mixed powder is filled in a mold subjected to a release treatment and heated to a temperature of 600 to 750 ° C. This heating temperature is preferably equal to or higher than the melting point of the metal powder used. If the temperature is less than 600 ° C., depending on the alloy composition to be used, it becomes unmelted, and the densification of the aluminum-silicon carbide composite is insufficient. On the other hand, when the heating temperature exceeds 750 ° C., aluminum and silicon carbide react to easily produce aluminum carbide (Al ₄ C ₃ ), which is not preferable in terms of thermal conductivity and strength.

The molding pressure at the time of hot press molding is 10 MPa or more. When the pressure at the time of hot press molding is less than 10 MPa, densification is insufficient, and the metal component and the reinforcing material cannot be firmly adhered at the time of hot press molding, and characteristics such as thermal conductivity and strength are reduced. It is not preferable. Further, the upper limit of the press pressure is not limited in terms of characteristics, but 300 MPa or less is appropriate from the strength of the mold and the strength of the apparatus. The aluminum-silicon carbide composite 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, annealing treatment of the aluminum-silicon carbide composite may be performed.

The annealing treatment performed for the purpose of removing strain at the time of compounding is preferably performed at a temperature of 400 ° C. to 550 ° C. for 10 minutes or more. If the annealing temperature is less than 400 ° C., the distortion inside the composite may not be sufficiently released, and the shape may change due to heat treatment after machining. On the other hand, when the annealing temperature exceeds 550 ° C., the aluminum alloy in the composite may be melted. When the annealing time is less than 10 minutes, even if the annealing temperature is 400 ° C. to 550 ° C., the distortion inside the composite is not sufficiently released, and the shape may be changed by the heat treatment after machining.

  The aluminum-silicon carbide based composite of the present invention has a surface covered with a metal layer mainly composed of aluminum, and is suitable for plating the aluminum-silicon carbide based composite. Furthermore, this surface layer is formed on a mold that has been subjected to a mold release treatment at the time of lamination, and ceramic fibers having a thickness of 0.1 to 0.5 mm and a Vf (ceramic content) of 3 to 20% by volume on both main surfaces. It can be prepared by placing, filling a mixed powder of metal powder and silicon carbide powder, and hot pressing. In the aluminum-silicon carbide composite obtained by the above production method, a surface layer made of an aluminum-ceramic fiber composite having a thickness of 0.1 to 0.3 mm is formed on both main surfaces.

  In the aluminum-ceramic fiber composite layer, the content other than the aluminum alloy is preferably less than 30% by volume because of the plating property. For this reason, as ceramic fiber arrange | positioned in a metal mold | die, thickness is 0.1-0.5 mm and Vf shall be 3-20 volume%. When the thickness of the ceramic fiber exceeds 0.5 mm, a sufficiently densified aluminum-ceramic fiber composite layer cannot be obtained by hot press molding, which is not preferable. The lower limit of the thickness of the ceramic fiber is not limited by characteristics, but is preferably 0.1 mm or more from the viewpoint of handling properties. Moreover, when Vf of ceramic fiber exceeds 20 volume%, content other than the aluminum alloy of the aluminum-ceramic fiber composite layer obtained exceeds 30 volume%, and plating property falls and it is not preferable. The lower limit of Vf is not limited by characteristics, but is preferably 3% by volume or more from the viewpoint of handling properties. Although it does not specifically limit as a ceramic fiber, Ceramic fibers, such as an alumina fiber, a silica fiber, and a mullite fiber, can use preferably from a heat resistant surface.

  Moreover, it is preferable that the thickness of the aluminum-silicon carbide based composite layer formed on both main surfaces of the aluminum-silicon carbide based composite is 0.1 to 0.3 mm. If the thickness of the aluminum-silicon carbide composite layer is 0.1 mm or more, the plating property can be ensured. On the other hand, when the thickness of the aluminum-silicon carbide composite layer exceeds 0.3 mm, the thermal conductivity is lowered and the thermal expansion coefficient is increased, which is not preferable.

In the present invention, at the time of hot press molding, a convex warp of 50 to 500 μm per 200 mm is formed on one main surface by hot press molding using a mold having a concave warp of 50 to 500 μm per 200 mm. Can be granted. In this case, the plate-like aluminum-silicon carbide composite can be obtained with an ideal spherical heat dissipation surface by machining the die surface into a concave shape with a warpage of 50 to 500 μm. This is possible and good heat dissipation characteristics can be obtained. When the plate-like aluminum-silicon carbide composite of the present invention is used as a base plate for a power module, if the amount of warpage is less than 50 μm per 200 mm in length, it is between the base plate and the heat radiating fin in the subsequent module assembly process. Even if high thermal conductivity heat dissipation grease is applied, the heat transfer performance is significantly reduced, resulting in a significant decrease in the heat dissipation performance of the module composed of ceramic circuit board, base plate, heat dissipation fins, etc. May end up. On the other hand, if the amount of warpage exceeds 500 μm, a crack may occur in the base plate or the ceramic circuit board at the time of screwing at the time of joining to the heat radiating fin, which is not preferable.

  As a method of forming the warp of the plate-like aluminum-silicon carbide composite of the present invention, the stress of 10 kPa or more is applied so that the plate-like aluminum-silicon carbide composite is bent to a curvature of 100 to 1000 μm per 200 mm. In this state, the film can be creep-deformed by heat treatment at a temperature of 400 to 550 ° C. for 30 seconds or more to give a convex warp of 50 to 500 μm per 200 mm. When the stress applied during the heat treatment is less than 10 kPa, the amount of warpage is insufficient and the desired amount of warpage cannot be obtained. Further, even if the processing temperature is less than 400 ° C. or the processing temperature is 400 to 550 ° C., if the processing time is less than 30 seconds, sufficient creep deformation cannot be caused, and the desired amount of warpage cannot be obtained. When the treatment temperature exceeds 550 ° C., problems such as a decrease in density due to the movement of the metal component in the composite occur, which is not preferable.

Next, the example of the processing method of the aluminum-silicon carbide composite of this invention is demonstrated. Although the aluminum-silicon carbide composite is a very hard and difficult-to-work material, the outer peripheral portion and / or the hole portion can be processed by a water jet processing machine. As a result, the obtained aluminum-silicon carbide composite has a structure in which the aluminum-silicon carbide composite is exposed at the outer peripheral portion and / or the hole. Here, the said hole part should just be provided so that an up-and-down surface may be penetrated so that it can be screwed to another heat radiating component. In addition, the processing cost can be reduced by processing into a shape like a U-shape connected to the outer peripheral portion.

  Since the aluminum-silicon carbide composite of the present invention is a conductive material, the outer peripheral portion and / or the hole portion can be processed using an electric discharge machine. The obtained aluminum-silicon carbide composite has a structure in which the aluminum-silicon carbide composite is exposed at the outer peripheral portion and / or the hole. Although the aluminum-silicon carbide composite of the present invention can be processed using a normal diamond tool or the like, it is a very hard and difficult-to-process material, so from the viewpoint of tool durability and processing cost. Processing by a water jet machine or an electric discharge machine is preferable. Furthermore, the main surface of the aluminum-silicon carbide based composite of the present invention can be polished or ground as necessary.

When the aluminum-silicon carbide composite of the present invention is used as a base plate for a power module, particularly important characteristics are thermal conductivity and thermal expansion coefficient. For this reason, as the reinforcing material to be used, silicon carbide having a high thermal conductivity and a low thermal expansion coefficient is selected. Further, since the heat transfer mechanism is different between silicon carbide and aluminum, at the interface between the two materials. In order to suppress heat transfer loss, the area of this interface is reduced (use of silicon carbide powder having a large particle diameter) and the mixing ratio is optimized, thereby improving the thermal conductivity and reducing the thermal expansion coefficient. I have control. In the present invention, the silicon carbide powder, which is a reinforcing material, and an aluminum alloy are firmly adhered at the interface by hot press molding at a molding pressure of 10 MPa or more at a temperature equal to or higher than the melting point of the metal powder to be used. It controls the porosity of the porous composite and improves the strength characteristics.

  The thermal conductivity in the thickness direction of the aluminum-silicon carbide composite of the present invention at a temperature of 25 ° C. is 150 to 300 W / mK. A thermal conductivity of less than 150 W / mK is not preferable because sufficient heat dissipation characteristics cannot be obtained when used as a heat dissipation component such as a base plate for a power module. The upper limit of the thermal conductivity is not limited in terms of characteristics, but is 300 W / mK or less due to the characteristics of silicon carbide itself.

In the present invention, since the aluminum-silicon carbide composite is produced by hot press molding, the resulting aluminum-silicon carbide composite inevitably has anisotropy in characteristics due to the orientation of the raw material powder. . In the composite of the present invention, due to the orientation of silicon carbide having a high thermal conductivity, the thermal conductivity in the main surface direction is larger than the thermal conductivity in the plate thickness direction, and the thermal conductivity in the plate thickness direction is higher than that in the main surface direction. It is preferable that it is 80% or more of the rate.

The thermal expansion coefficient of the aluminum-silicon carbide composite of the present invention at a temperature of 25 ° C. to 150 ° C. is 5 × 10 ^{−6 to} 9 × 10 ⁻⁶ / K. When used as a heat dissipation component such as a base plate for a power module, matching of the thermal expansion coefficient with the ceramic circuit board to be joined is very important. If the coefficient of thermal expansion is less than 5 × 10 ⁻⁶ / K or more than 9 × 10 ⁻⁶ / K, the thermal load during operation of the semiconductor element causes destruction of the bonding layer (solder layer, etc.) and ceramics. May decrease, which is not preferable.

The porosity of the aluminum-silicon carbide composite of the present invention is 2 to 10% by volume. When the porosity exceeds 10% by volume, the thermal conductivity and other characteristics deteriorate, and when used as a heat dissipation component such as a base plate for a power module, the corrosion resistance of the module itself due to the permeation of moisture from the usage environment. Problems occur and are not preferred. About the lower limit of the porosity, in order to obtain an aluminum-silicon carbide composite with high thermal conductivity and low thermal expansion that is the object of the present invention, it is 2% by volume or more from the relationship between the particle size and blending ratio of the silicon carbide powder that is a reinforcing material. However, from the viewpoint of characteristics, the content is preferably 2% by volume or less.

The three-point bending strength of the aluminum-silicon carbide composite of the present invention is 100 to 350 MPa. When the aluminum-silicon carbide composite is used as a heat dissipation part such as a base plate for a power module, if the three-point bending strength is less than 100 MPa, cracking due to screwing, or chipping due to vibration during use, etc. There is a problem and it is not preferable. There is no restriction on the upper limit of the three-point bending strength, but in order to extremely improve the three-point bending strength, it is necessary to increase the amount of silicon carbide added and to pulverize. As a result, the resulting aluminum -It is preferable that it is 350 MPa or less because the thermal conductivity of the silicon carbide composite decreases.

  When the aluminum-silicon carbide composite according to the present invention is used as a base plate for a power module, it is generally used after processing a mounting hole or the like and then joining to a ceramic circuit board by soldering. For this reason, it is necessary to apply Ni plating to the surface of the aluminum-silicon carbide composite. The plating method is not particularly limited, and any of electroless plating and electroplating may be used. The thickness of the Ni plating is preferably 1 to 20 μm. If the plating thickness is less than 1 μm, plating pinholes are partially generated, solder voids (voids) are generated during soldering, and the heat dissipation characteristics from the circuit board may be deteriorated. On the other hand, when the thickness of the Ni plating exceeds 20 μm, plating peeling may occur due to a difference in thermal expansion between the Ni plating film and the surface aluminum alloy. The purity of the Ni plating film is not particularly limited as long as it does not hinder solder wettability, and may contain phosphorus, boron, or the like. Furthermore, it is also possible to apply gold plating to the Ni plating surface.

The joining of the aluminum-silicon carbide composite and the ceramic circuit board according to the present invention can be brazed via an active metal brazing material. The active metal brazing material may be a paste, but an alloy foil is preferred for handling. In this case, the active metal brazing material preferably has a lower melting point than the alloy as the metal component of the aluminum-silicon carbide composite. For example, Cu 1-6 mass% Al—Cu alloy foil, 2018 alloy foil containing 4 mass% Cu and 0.5 mass% Mg, 2017 alloy foil containing 0.5 mass% Mn, and JIS alloy 2001, Alloy foils such as 2003, 2005, 2007, 2011, 2014, 2024, 2025, 2030, 2034, 2036, 2048, 2090, 2117, 2124, 2218, 2224, 2324, 7050, and 7075 can be used. Further, it is possible to use a material containing up to 5% by mass of a third component such as Mg, Zn, In, Mn, Cr, Ti, Bi and the like.

Example 1
Silicon carbide powder A (manufactured by Taiyo Random Company / average particle size: 150 μm, density: 3.2 g / cm ³ ): 102 g (35% by volume), silicon carbide powder B (manufactured by Taiyo Random Company / average particle size: 50 μm) , Density: 2.2 g / cm ³ ): 102 g (35% by volume), aluminum powder (manufactured by Alcoa / average particle size: 25 μm): 64.2 g, silicon powder (manufactured by Elchem / average particle size: 20 μm): 8.9 g and magnesium powder (average particle size: 50 μm) 0.7 g were mixed for 1 hour in a ball mill. Next, a cast iron mold 1 (outer shape: 200 × 200 × 50 mm, inner diameter: 140 × 130 × 50 mm) and a mold 2 (lower portion: 200 × 200 × 20 mm, upper portion: 139.9 × 129 shown in FIG. (9 × 10 mm) was coated with graphite and boron nitride as a release agent, laminated, and a graphite sheet was placed on the upper surface of the mold 2 and filled with the mixed powder. Further, a graphite sheet is arranged on the upper part of the mixed powder, and a mold 3 (139.9 × 129.9 × 60 mm) coated with a release agent is laminated in the same manner, and preformed at a surface pressure of 10 MPa with a hydraulic press. Carried out.

  Next, this laminated body was heated to a temperature of 650 ° C. in an electric furnace in an air atmosphere and held for 15 minutes, so that the temperature of the laminated body was set to 650 ° C. The heated laminate was subjected to hot press molding at a surface pressure of 50 MPa for 5 minutes with a hydraulic press through a 5 mm thick heat insulating material, and then the pressure was released and the laminate was cooled to room temperature. Next, the mold 2 is removed, the mold 3 is pushed in with a hydraulic press, the molded body is taken out, and then the graphite sheet disposed for mold release is peeled off, and a 140 × 130 × 5 mmt aluminum-silicon carbide composite Got.

The obtained aluminum-silicon carbide composite uses 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 50 mm / min by a water jet processing machine (Abrasive Jet Cutter NC manufactured by Sugino Machine). Then, after processing through-holes with a diameter of 7 mm at six edge peripheral portions, the outer peripheral portion was processed into a shape of 127 mm × 137 mm × 5 mm.

Next, in order to give a warp to the aluminum-silicon carbide composite, an uneven mold provided with a spherical surface made of carbon and having a curvature radius of 15 m was prepared. This concavo-convex mold was mounted on a hot press and heated to set the mold surface temperature at 510 ° C. The composite was placed between the concave and convex molds and pressed at 40 KPa. At this time, a thermocouple was brought into contact with the side surface of the composite to measure temperature. After maintaining the temperature of the composite at 500 ° C. for 3 minutes, the pressure was released and the product was naturally cooled to 50 ° C. Next, the obtained composite was annealed in an electric furnace at a temperature of 350 ° C. for 30 minutes in order to remove residual strain at the time of warping. Result of measuring the shape of the heat radiating surface of the obtained aluminum-silicon carbide composite with a contact-type two-dimensional contour measuring machine (manufactured by Tokyo Seimitsu Co., Ltd .; contour record 1600D-22) and measuring the amount of warpage per 200 mm. The amount of warpage per 200 mm was 190 μm.

Next, after blasting with alumina abrasive grains under conditions of a pressure of 0.4 MPa and a conveying speed of 1.0 m / min to clean, electroless Ni—P and Ni—B plating are performed, and the composite surface is 8 μm thick. A plating layer (Ni—P: 6 μm + Ni—B: 2 μm) was formed. The obtained plated product was good with no pinholes confirmed with the naked eye.

From the aluminum-silicon carbide composite obtained by hot press molding, a specimen for measuring thermal conductivity in the plate thickness direction (diameter 11 mm, thickness 3 mm) and a specimen for measuring thermal expansion coefficient (3 × 3 ×) by grinding. 10 mm) and. Using each test piece, the thermal expansion coefficient at a temperature of 25 ° C. to 150 ° C. was measured with a thermal dilatometer (manufactured by Seiko Denshi Kogyo; TMA300), and the thermal conductivity at 25 ° C. was measured with a laser flash method (manufactured by Rigaku Corporation); LF / TCM-8510B). As a result, the thermal conductivity in the plate thickness direction at a temperature of 25 ° C. was 230 W / mK, and the thermal expansion coefficient at a temperature of 25 ° C. to 150 ° C. was 6.5 × 10 ⁻⁶ / K. Further, the amount of the mixed powder of Example 1 was tripled, and a 140 × 130 × 15 mmt aluminum-silicon carbide composite was produced in the same manner, and a specimen for measuring thermal conductivity in the principal surface direction by grinding ( 11 mm in diameter and 3 mm in thickness) and the thermal conductivity was measured. As a result, the thermal conductivity in the principal surface direction at a temperature of 25 ° C. was 250 W / mK.

A three-point bending strength measurement specimen (3 × 4 × 40 mm) was produced from the aluminum-silicon carbide composite by grinding, and the three-point bending strength was measured with a bending strength tester. As a result, it was 240 MPa. . Furthermore, the density of the aluminum-silicon carbide composite was measured by the Archimedes method, and the porosity was calculated. As a result, the porosity was 3.5% by volume.

(Example 2)
In the same manner as in Example 1, a mixed powder of silicon carbide powder A, silicon carbide powder B, aluminum powder, silicon powder and magnesium powder was produced. Next, a cast iron mold 1 (outer shape: 200 × 200 × 50 mm, inner diameter: 140 × 130 × 50 mm) and a mold 2 (lower portion: 200 × 200 × 20 mm, upper portion: 139.9 × 129 shown in FIG. 9 × 10 mm), graphite and boron nitride as a release agent are applied, laminated, and an alumina fiber sheet having a Vf of 10% by volume and a thickness of 0.2 mm is disposed on the upper surface of the mold 2, and the mixing is performed. The powder was filled and an alumina fiber sheet was placed on top of the mixed powder. Furthermore, a mold release agent is applied to the mold 3 (139.9 × 129.9 × 60 mm) machined with a certain curvature so that the surface in contact with the mixed powder has a concave curvature of 200 μm per 200 mm. Were applied and laminated, and preformed with a hydraulic press at a surface pressure of 10 MPa.

The laminated body was hot press-molded by the same method as in Example 1, and then the pressure was released to cool to room temperature to obtain a 140 × 130 × 5 mmt aluminum-silicon carbide composite. The obtained aluminum-silicon carbide composite was subjected to an annealing treatment of holding at a temperature of 500 ° C. for 1 hour and gradually cooling to room temperature. Next, the aluminum-silicon carbide based composite was processed with through holes having a diameter of 7 mm at six edge peripheral portions at a processing speed of 10 mm / min using an electric discharge machine, and then the outer peripheral portion was processed to 127 mm × 137 mm. The shape was × 5 mm. Result of measuring the shape of the heat radiating surface of the obtained aluminum-silicon carbide composite with a contact-type two-dimensional contour measuring machine (manufactured by Tokyo Seimitsu Co., Ltd .; contour record 1600D-22) and measuring the amount of warpage per 200 mm. The amount of warpage per 200 mm was 210 μm.

Next, after blasting with alumina abrasive grains under conditions of a pressure of 0.4 MPa and a conveying speed of 1.0 m / min to clean, electroless Ni—P and Ni—B plating are performed, and the composite surface is 8 μm thick. A plating layer (Ni—P: 6 μm + Ni—B: 2 μm) was formed. The obtained plated product was good with no pinholes confirmed with the naked eye.

From the aluminum-silicon carbide composite obtained by hot press molding, a specimen for measuring thermal conductivity in the plate thickness direction (diameter 11 mm, thickness 3 mm) and a specimen for measuring thermal expansion coefficient (3 × 3 ×) by grinding. 10 mm). Using each test piece, the thermal expansion coefficient at a temperature of 25 ° C. to 150 ° C. was measured with a thermal dilatometer (manufactured by Seiko Denshi Kogyo; TMA300), and the thermal conductivity at 25 ° C. was measured with a laser flash method (manufactured by Rigaku Corporation); LF / TCM-8510B). As a result, the thermal conductivity in the plate thickness direction at a temperature of 25 ° C. was 210 W / mK, and the thermal expansion coefficient at a temperature of 25 ° C. to 150 ° C. was 6.4 × 10 ⁻⁶ / K.

Further, a three-point bending strength test specimen (3 × 4 × 40 mm) was prepared from the aluminum-silicon carbide composite by grinding. As a result of measuring the three-point bending strength with a bending strength tester, it was 220 MPa. As a result of measuring the density of the aluminum-silicon carbide composite by Archimedes method and calculating the porosity, the porosity was 3.3% by volume.

(Examples 3-8, Comparative Examples 1-3)
Silicon carbide powder A (manufactured by Taiyo Random Company / average particle size: 150 μm, density: 3.2 g / cm ³ ): 102 g (35% by volume), silicon carbide powder B (manufactured by Taiyo Random Company / average particle size: 50 μm) , Density: 2.2 g / cm ³ ): 102 g (35% by volume), aluminum powder (manufactured by Alcoa / average particle size: 25 μm), silicon powder (manufactured by Elchem / average particle size: 20 μm), magnesium powder ( Average particle size: 50 μm), aluminum-magnesium alloy powder (average particle size: 80 μm), magnesium-silicon powder / Mg ₂ Si (average particle size: 70 μm), aluminum-silicon-magnesium alloy powder (average particle size: 40 μm) Were mixed for 1 hour in a ball mill with the formulation shown in Table 1. Next, a cast iron mold 1 (outside: 200 × 200 × 50 mm, inner diameter: 140 × 130 × 50 mm) and a mold 2 (lower part: 200 × 200 × 20 mm, upper part) in the same manner as in Example 1 139.9 × 129.9 × 10 mm) was coated with graphite and boron nitride as a release agent, laminated, and a graphite sheet was placed on the upper surface of the mold 2 and filled with the mixed powder. Further, a graphite sheet is arranged on the upper part of the mixed powder, and a mold 3 (139.9 × 129.9 × 60 mm) coated with a release agent is laminated in the same manner, and preformed at a surface pressure of 10 MPa with a hydraulic press. Carried out.

  Next, this laminate was subjected to hot press molding in the same manner as in Example 1, and then the pressure was released to cool to room temperature to obtain a 140 × 130 × 5 mmt aluminum-silicon carbide composite. . The obtained aluminum-silicon carbide composite was prepared by grinding to produce a specimen for measuring thermal conductivity in the plate thickness direction (diameter 11 mm, thickness 3 mm) and thermal expansion coefficient measuring specimen (3 × 3 × 10 mm). did. Using each test piece, the thermal expansion coefficient at a temperature of 25 ° C. to 150 ° C. was measured with a thermal dilatometer (manufactured by Seiko Denshi Kogyo; TMA300), and the thermal conductivity at 25 ° C. was measured with a laser flash method (manufactured by Rigaku Corporation); LF / TCM-8510B). Further, a three-point bending strength measurement specimen (3 × 4 × 40 mm) was prepared from the aluminum-silicon carbide composite by grinding, and the three-point bending strength was measured with a bending strength tester. Furthermore, the density of the aluminum-silicon carbide composite was measured by the Archimedes method, and the porosity was calculated. The results are shown in Table 2.

The aluminum-silicon carbide composite obtained by the hot press molding in Examples 3 to 8 was subjected to a water jet processing machine (Abrasive Jet Cutter NC manufactured by Sugino Machine) under the conditions of a pressure of 250 MPa and a processing speed of 50 mm / min. Using a garnet having a particle size of 100 μm as abrasive grains, through holes with a diameter of 7 mm were processed at six locations on the peripheral edge, and then the outer peripheral portion was processed. Then, using a diamond tool at a machining center, countersunk holes of φ10-4 mm were processed at four locations to form a 127 mm × 137 mm × 5 mm shape.

Next, after cleaning by blasting with alumina abrasive grains under conditions of pressure 0.4 MPa and transport speed 1.0 m / min, electroless Ni—P plating is performed, and a 6 μm thick plating layer is formed on the composite surface. After the formation, electroless Au plating was performed to form a 0.2 μm Au plating layer. The obtained plated product was good with no pinholes confirmed with the naked eye.

(Examples 9-13, Comparative Examples 4-7)
Aluminum powder (manufactured by Alcoa / average particle size: 25 μm): 435 g, silicon powder (manufactured by Elchem / average particle size: 20 μm): 60 g, 5 g of magnesium powder (average particle size: 50 μm) are mixed in a ball mill for 10 minutes. Thus, a mixed powder of metal powder was produced. This metal powder, silicon carbide powder A (manufactured by Taiyo Random Company / average particle size: 150 μm), silicon carbide powder B (manufactured by Taiyo Random Company / average particle size: 50 μm), silicon carbide powder C (manufactured by Taiyo Random Company) Manufactured / average particle size: 1000 μm), silicon carbide powder D (manufactured by Taiyo Random Corporation / average particle size: 300 μm), silicon carbide powder E (manufactured by Yakushima Electric Works / average particle size: 15 μm) shown in Table 3 The mixture was mixed in a ball mill for 1 hour. Here, the mixed powder of the metal powder was calculated as an average density of 2.7 g / cm ³ . Next, a cast iron mold 1 (outer shape: 200 × 200 × 50 mm, inner diameter: 140 × 130 × 50 mm) and a mold 2 (lower portion: 200 × 200 × 20 mm, upper portion: 139.9 × 129 shown in FIG. (9 × 10 mm) was coated with graphite and boron nitride as a release agent, laminated, and a graphite sheet was placed on the upper surface of the mold 2 and filled with the mixed powder. Further, a graphite sheet is arranged on the upper part of the mixed powder, and a mold 3 (139.9 × 129.9 × 60 mm) coated with a release agent is laminated in the same manner, and preformed at a surface pressure of 10 MPa with a hydraulic press. Carried out.

  Next, this laminate was subjected to hot press molding in the same manner as in Example 1, and then the pressure was released to cool to room temperature to obtain a 140 × 130 × 5 mmt aluminum-silicon carbide composite. . The obtained aluminum-silicon carbide composite was prepared by grinding to produce a specimen for measuring thermal conductivity in the plate thickness direction (diameter 11 mm, thickness 3 mm) and thermal expansion coefficient measuring specimen (3 × 3 × 10 mm). did. Using each test piece, the thermal expansion coefficient at a temperature of 25 ° C. to 150 ° C. was measured with a thermal dilatometer (manufactured by Seiko Denshi Kogyo; TMA300), and the thermal conductivity at 25 ° C. was measured with a laser flash method (manufactured by Rigaku Corporation); LF / TCM-8510B). Further, a three-point bending strength measurement specimen (3 × 4 × 40 mm) was prepared from the aluminum-silicon carbide composite by grinding, and the three-point bending strength was measured with a bending strength tester. Furthermore, the density of the aluminum-silicon carbide composite was measured by the Archimedes method, and the porosity was calculated. The results are shown in Table 4.

The aluminum-silicon carbide composite obtained by hot press molding was subjected to a pressure of 250 MPa and a processing speed of 50 mm / min by a water jet processing machine (Abrasive Jet Cutter NC manufactured by Sugino Machine), with a particle size of 100 μm as abrasive grains. Using a garnet, through holes with a diameter of 7 mm were processed at six locations on the peripheral edge, and the outer peripheral portion was processed into a 127 mm × 137 mm × 5 mm shape.

Next, after blasting with alumina abrasive grains under conditions of a pressure of 0.4 MPa and a conveying speed of 1.0 m / min to clean, electroless Ni—P and Ni—B plating are performed, and the composite surface is 8 μm thick. A plating layer (Ni—P: 6 μm + Ni—B: 2 μm) was formed. The plated products of Examples 9 to 13 and Comparative Examples 4 and 6 were good with no pinholes confirmed with the naked eye. In Comparative Example 5, the surface irregularities were severe, and plating pinholes that could be confirmed with the naked eye were observed. Further, in Comparative Example 7, a stain of the chemical solution due to insufficient densification was observed.

(Examples 17-20, Comparative Examples 9-11)
Silicon carbide powder A (manufactured by Taiyo Random Company / average particle size: 150 μm, density: 3.2 g / cm ³ ): 102 g (35% by volume), silicon carbide powder B (manufactured by Taiyo Random Company / average particle size: 50 μm) , Density: 2.2 g / cm ³ ): 102 g (35% by volume), aluminum powder (manufactured by Alcoa / average particle size: 25 μm): 64.2 g, silicon powder (manufactured by Elchem / average particle size: 20 μm): 8.9 g and magnesium powder (average particle size: 50 μm) 0.7 g were mixed for 1 hour in a ball mill. Next, a cast iron mold 1 (outside: 200 × 200 × 50 mm, inner diameter: 140 × 130 × 50 mm) and a mold 2 (lower part: 200 × 200 × 20 mm, upper part) in the same manner as in Example 1 : 139.9 × 129.9 × 10 mm) and graphite and boron nitride as a release agent, and then laminated to form an alumina fiber sheet having a Vf of 5% by volume and a thickness of 0.2 mm on the upper surface of the mold 2. Placed and filled with the mixed powder. Further, an alumina fiber sheet is placed on top of the mixed powder, and a mold 3 (139.9 × 129.9 × 60 mm) coated with a release agent is laminated in the same manner, and the surface pressure is 10 MPa by a hydraulic press. Pre-forming was performed.

  Next, this laminate was heated in an electric furnace to the temperature shown in Table 5 in an air atmosphere and held for 15 minutes, so that the temperature of the laminate was set to the temperature shown in Table 5. The heated laminate was subjected to hot press molding for 5 minutes at a surface pressure shown in Table 5 with a hydraulic press through a 5 mm thick heat insulating material, and then the pressure was released and the mixture was cooled to room temperature. Next, the mold 2 is removed, the mold 3 is pushed in with a hydraulic press, the molded product is taken out, and then the graphite sheet disposed for mold release is peeled off to obtain a 140 × 130 × 21 mmt aluminum-silicon carbide composite. Got.

From the obtained aluminum-silicon carbide composite, a specimen for thermal conductivity measurement in the plate thickness direction (diameter 11 mm, thickness 3 mm) and a specimen for thermal expansion coefficient measurement (3 × 3 × 10 mm) are produced by grinding. did. Using each test piece, the thermal expansion coefficient at a temperature of 25 ° C. to 150 ° C. was measured with a thermal dilatometer (manufactured by Seiko Denshi Kogyo; TMA300), and the thermal conductivity at 25 ° C. was measured with a laser flash method (manufactured by Rigaku Corporation); LF / TCM-8510B). Further, a three-point bending strength measurement specimen (3 × 4 × 40 mm) was prepared from the aluminum-silicon carbide composite by grinding, and the three-point bending strength was measured with a bending strength tester. Furthermore, the density of the aluminum-silicon carbide composite was measured by the Archimedes method, and the porosity was calculated. The results are shown in Table 6.

Explanatory drawing which shows the preparation methods of an aluminum-silicon carbide composite (Example 1, laminated state before compounding) Explanatory drawing which shows the preparation methods of an aluminum-silicon carbide composite (Example 2, lamination state before compounding)

Explanation of symbols

1 Mold 1
2 Mold 2
3 Mold 3
4 Mixed powder of metal powder, silicon carbide powder and graphite powder 5 Graphite sheet 6 Ceramic fiber

Claims (6)

20 to 40% by volume of metal powder containing 77 to 94.5% by mass of aluminum, 5 to 20% by mass of silicon and 0.5 to 3% by mass of magnesium, and silicon carbide powder 60 to 80 having an average particle size of 50 to 300 μm A plate having a thickness of 2 to 6 mm, which is obtained by mixing volume%, filling a mold subjected to a release treatment, heating to a temperature of 600 to 750 ° C., and hot press molding at a pressure of 10 MPa or more. Method for producing aluminum-silicon carbide composite. 20 to 40% by volume of metal powder containing 77 to 94.5% by mass of aluminum, 5 to 20% by mass of silicon and 0.5 to 3% by mass of magnesium, and silicon carbide powder 60 to 80 having an average particle size of 50 to 300 μm After mixing the volume%, the mixed powder is filled with ceramic fibers having a thickness of 0.1 to 0.5 mm and Vf of 3 to 20 volume% on both main surfaces in a mold subjected to a release treatment. And heating and press-molding at a pressure of 10 MPa or higher, and having an aluminum-ceramic fiber composite layer having a thickness of 0.1 to 0.3 mm on both main surfaces. A method for producing a plate-like aluminum-silicon carbide composite having a thickness of 2 to 6 mm. 2. A convex warp of 50 to 500 μm per 200 mm is imparted to one main surface using a mold comprising a concave warp of 50 to 500 μm per 200 mm at the time of hot press molding. 3. A method for producing a plate-like aluminum-silicon carbide composite according to 2. The plate-like aluminum-silicon carbide composite is creep-deformed by heating at a temperature of 400 to 550 ° C. for 30 seconds or more in a state where a stress of 10 kPa or more is applied so as to bend to a constant curvature, and is about 200 mm. The method for producing a plate-like aluminum-silicon carbide composite according to claim 1 or 2, wherein a convex warp of 50 to 500 µm is imparted. The porosity is 2 to 10% by volume, the thermal expansion coefficient at a temperature of 25 ° C. to 150 ° C. is 5 × 10 ^{−6 to} 9 × 10 ⁻⁶ / K, and the thermal conductivity at a temperature of 25 ° C. is 150 to 300 W / 5. The plate-like aluminum-silicon carbide composite obtained by the production method according to claim 1, wherein the plate-like aluminum-silicon carbide composite has a three-point bending strength of 100 to 350 MPa. The plate-like aluminum-silicon carbide composite according to claim 5 is processed with a mounting hole and then plated, and one principal surface is soldered or brazed to the ceramic circuit board, and the other principal surface is Power module base plate used as a heat dissipation surface.

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