SILICON CARBIDE COMPLEX, METHOD FOR MANUFACTURING SAME, AND HEAT DISSIPATION COMPONENT USING SAME

Abstract

[Problem] To inexpensively provide a heat dissipating component that has thermal conductivity, as well as a low specific gravity, and a coefficient of thermal expansion close to that of a ceramic substrate, and furthermore having warpage so as to be able to be joined with good closeness of contact to a heat dissipating component or the like. [Solution] A silicon carbide composite which is a plate-shaped composite formed by impregnation of a porous silicon carbide molded article by a metal having aluminum as a main component, wherein the amount of warpage with respect to 10 cm of length of the main surface of the composite is 250 m or less, and the amount of warpage of a power module using the plate-shaped composite is 250 m or less; and a heat dissipating component using the same.

Claims

1. A silicon carbide composite which is a plate-shaped composite formed by pressure impregnation of a porous silicon carbide molded article with a metal containing aluminum, the silicon carbide composite having a plate thickness t of 2 mm to 6 mm and an in-plane thickness variation within t0.3 mm, having four or more hole portions for screw-fastening another heat dissipating component in the plane of the plate-shaped composite so as to face a convex surface of the plate-shaped composite, wherein an amount of warpage (Cx; m) with respect to 10 cm of length in an inter-hole direction (X direction) and an amount of warpage (Cy; m) with respect to 10 cm of length in a direction (Y direction) perpendicular thereto have the relationships 50Cx250 and 0Cy200, and the amounts of warpage of the composite main surface in a power module using the plate-shaped composite is 50Cx250 and 0Cy200.

2. The silicon carbide composite according to claim 1, wherein front and back surfaces are both covered by a metal layer containing aluminum having an average thickness of 10 to 110 m, and the difference in average thickness between the front and back metal layers is 100 m or less.

3. The silicon carbide composite according to claim 1, comprising a composite portion (A), and a metal layer (B) containing aluminum provided on at least one surface of the composite, wherein the ratio (TA/TB) between the average value (TA; m) of the thickness of the plate-shaped composite (A) and the sum (TB; m) of the average values of the thicknesses of the metal layers (B) on both surfaces is 10 to 30.

4. The silicon carbide composite according to claim 1, wherein the product of the maximum length (L; cm) of the composite and the absolute value (|TB1TB2|) of the difference between the average value (TB1; m) of the thickness of the metal layer (B) on the front surface and the average value (TB2; m) of the thickness thereof on the back surface is at least 500 and at most 2000.

5. The silicon carbide composite according to claim 1, wherein the thermal conductivity at a temperature of 25 C. is at least 150 W/mK, the coefficient of linear thermal expansion from a temperature of 25 C. to 300 C. is 510.sup.6 to 1010.sup.6/K, the three-point bending strength at a temperature of 25 C. is 150 MPa to 500 MPa, the elasticity at a temperature of 25 C. is 150 GPa to 350 GPa, and the density is 2.8 to 3.1 g/cm.sup.3.

6. A method for manufacturing the silicon carbide composite according to claim 1, wherein the silicon carbide composite is warped by plastic deformation by applying stress at a temperature of at least 350 C.

7. A heat dissipating component obtained by joining, to the plate-shaped silicon carbide composite according to claim 1, a ceramic substrate for mounting a semiconductor.

8. The heat dissipating component according to claim 7, wherein the ceramic substrate is aluminum nitride or silicon nitride.

9. The heat dissipating component according to claim 7, wherein when the surface that is not joined to the ceramic substrate for mounting a semiconductor is attached to a flat plate with a heat dissipating grease provided therebetween, at least 90% of the surface closely contacts the flat plate under conditions of a tightening torque of at least 2 N.

Description

MODES FOR CARRYING OUT THE INVENTION

[0026] The coefficient of thermal expansion of a metal-ceramic composite is normally determined by the content ratio between the ceramic which is the reinforcing material and the metal which is the base material. The coefficients of thermal expansion of ceramics are much lower than the coefficients of thermal expansion of metals, so increasing the proportion of ceramics is effective in lowering the coefficient of thermal expansion of composites. On the other hand, the thermal conductivity of a metal-ceramic composite is basically also determined by the content ratio between the ceramic which is the reinforcing material and the metal which is the base material, but in the case of thermal conductivity, the bonding state at the interface between the reinforcing material and the base material contributes significantly. Between ceramics and metals, the thermal conductivity of metals is generally higher, but silicon carbide (SiC), aluminum nitride (AlN), boron nitride (BN) and the like have a theoretical thermal conductivity equivalent to or greater than that of metals (300 W/mK or more), so they are extremely promising as reinforcing materials for raising the thermal conductivity. However, when actually producing a composite, AlN and BN are expensive, which makes the resulting composite expensive as well. Additionally, AlN and BN easily oxidize in an air atmosphere, and when used to form composites, tend to form a glass phase with extremely low thermal conductivity between the ceramic which is the reinforcing material and the metal which is the base material, and as a result, the thermal conductivity of the obtained composite is lowered.

[0027] As a result of various studies regarding reinforcing materials, the present inventors discovered that ceramics that have silicon carbides as their main component are suitable for producing metal-ceramic composites having both high thermal conductivity and a low coefficient of thermal expansion.

[0028] On the other hand, when producing such a composite, the wettability between the reinforcing material and the metal becomes important in order to obtain a dense composite. If the melting point of the impregnated metal is high, the temperature will be high at the time of impregnation, and this can cause the ceramic to oxidize, or the ceramic and metal to react and form compounds with undesirable properties. Furthermore, if the melting point of the metal which is the base material is high, the impregnation temperature becomes high, limiting the materials that can be used for the mold elements or the like, and also increasing the casting cost, making the obtained composite expensive.

[0029] As a result of various studies regarding the metal which is the base material, the present inventors discovered that a good composite can be produced by using an alloy having aluminum as the main component. In other words, the composite of the present invention is obtained by impregnating a silicon carbide powder or a silicon carbide porous body with a metal having aluminum as the main component.

[0030] The properties such as the coefficient of thermal expansion and thermal conductivity of the metal-ceramic composite are determined by the properties of the ceramic which is the reinforcing material and the metal which is the base material, and their content ratio. The silicon carbide content in the composite of the present invention is preferably 50 to 80 vol %, and more preferably 60 to 70 vol %. If the silicon carbide content is less than 50 vol %, the coefficient of thermal expansion of the composite becomes high and the highly reliable heat dissipating component which is the objective of the present invention cannot be obtained. Additionally, while a high silicon carbide content is effective for obtaining high thermal conductivity and a low coefficient of thermal expansion in the composite, if filled in excess of 80 vol %, there are problems such as the need for an extremely high molding pressure, and the cost of the resulting metal-ceramic composite becomes extremely high.

[0031] On the other hand, the metal in the silicon carbide composite of the present invention is an alloy having aluminum as the main component, preferably containing at most 20 mass % of silicon and at most 5 mass % of magnesium. Regarding metal components other than aluminum, silicon or magnesium in the alloy, copper or the like can also be included if within a range that does not extremely change the properties of the alloy. By adjusting the components other than the aluminum in the alloy, the thermal conductivity and coefficient of thermal expansion of the alloy itself can be changed, and the coefficient of thermal expansion and thermal conductivity of the resulting composite may also be adjusted. Additionally, due to the formation of an alloy of an aluminum metal with silicon or magnesium, the melting point of the alloy is lowered and the viscosity of the molten metal at high temperatures is reduced, making it easier to obtain a dense composite with a high-temperature casting method or the like. Furthermore, by forming an alloy of aluminum metal, the hardness of the metal itself is increased, as a result of which the mechanical properties such as the strength of the resulting composite are also improved.

[0032] Additionally, the silicon carbide composite of the present invention is characterized by having a plate thickness t of 2 mm to 6 mm, and an in-plane thickness variation within t0.3 mm. If the plate thickness is less than 2 mm, when used as a heat dissipating component, the heat dissipating ability in the planar direction of the silicon carbide composite is lowered, and the heat dissipating ability of the heat dissipating component is undesirably lowered. On the other hand, if the plate thickness exceeds 6 mm, the thermal resistance of the silicon carbide composite itself becomes large, and the heat dissipating ability of the heat dissipating component is undesirably lowered. Additionally, if the in-plane thickness variation lies outside the range of t0.3 mm, when components such as power modules incorporating heat dissipating components comprising the silicon carbide composite are used by screwing them onto heat dissipating fins or the like, air gaps will be formed at the joint surfaces between the components such as power modules and the heat dissipating fins, thereby undesirably reducing the heat dissipating ability. The expression an in-plane thickness variation within t0.3 mm means that if the thickness of the composite is measured at multiple locations and the average thickness of the composite is calculated from the average value thereof and set as 0, then the maximum value and minimum value will fall within 0.3 mm.

[0033] Additionally, essential to the present invention is that the warpage amount is 250 m or less with respect to 10 cm of length of the main surface of the composite. If the warpage amount exceeds 250 m with respect to 10 cm of length of the main surface of the composite, when using the composite of the present invention as a heat dissipating component, there are problems such as joining defects occurring with circuit boards or the like, or excessive bending stress being applied when screw-fastening heat dissipating fins or the like, resulting in damage to the composite. On the other hand, components such as power modules incorporating heat dissipating components comprising such composites are used by screw-fastening them to heat dissipating fins or the like. In that case, in order for stress to act on the joint surface between the components such as power modules and heat dissipating fins, it is preferable in terms of heat dissipation for the joint surface to be convex, so that the clamping force after screw-fastening is large. The convex surface may be formed by making use of the warpage that occurs when producing the composite, or formed by forcibly warpage using a jig as shown in FIG. 3.

[0034] The second invention of the present invention has four or more hole portions so as to allow other heat dissipating components to be screw-fastened within the main surface of the plate-shaped composite. Regarding the shapes of the holes, they may be appropriately chosen depending on the size of the heat dissipating component or the like, but a size allowing penetration of an M6 to M10 screw will generally be satisfactory. Regarding the number of holes, many may be provided such as four or more depending on the heat dissipating plate, but if there are three or less, the entire surface of the heat dissipating plate may not be able to be made to closely contact the other heat dissipating components. While the hole formation locations may be chosen on a discretionary basis, they could, for example, be formed at the four corners of the plate-shaped composite.

[0035] Essential to the present invention is that the amount of warpage (Cx; m) with respect to 10 cm of length in the inter-hole direction (X direction) and the amount of warpage (Cy; m) with respect to 10 cm of length in the direction (Y direction) perpendicular to the X direction have the relationships 0Cx250 and also 0Cy300. Additionally, when the warpage amounts (Cx; m and Cy; m) are within the specific ranges mentioned above, the amount of warpage of a power module using the plate-shaped composite becomes 50Cx250 and 0Cy200. In general, the inter-hole direction (X direction) refers to one direction on the surface of the heat dissipating plate as shown in FIG. 1(a) to (d), and the Y direction refers to the direction within the surface perpendicular to the X direction.

[0036] The present inventors experimentally considered many possibilities in an attempt to solve the aforementioned problems in the conventional art, as a result of which they discovered that a heat dissipating plate composed of a composite can be screw-fastened to another heat dissipating component with good closeness of contact when the amounts of warpage (Cx; m and Cy; m) are within the aforementioned specific ranges, thereby arriving at the present invention. When screw-fastening a heat dissipating plate composed of the composite of the present invention to another heat dissipating component with good closeness of contact, they will generally be fastened by providing heat dissipating grease or the like between the heat dissipating plate and the heat dissipating component. For this reason, the absolute value of the warpage amount (Cy) in the Y direction is preferably smaller than the thickness of the heat dissipating grease. Additionally, when considering the deformation of the heat dissipating plate during tightening, the warpage amount (Cy) in the Y direction should preferably smaller than the warpage amount (Cx) in the X direction. When the aforementioned warpage amounts cannot satisfy the aforementioned specific ranges, the heat dissipating plate may not always be able to be screw-fastened to other heat dissipating components with good closeness of contact.

[0037] Additionally, the third invention of the present invention is a plate-shaped composite formed by joining an alloy layer (B) having aluminum as the main component on both surfaces of a plate-shaped composite (A). Due to the surface portion being covered by an alloy layer having aluminum as the main component, when processing the surface portion, it is sufficient to process this metal portion, and the load at the time of processing can be significantly reduced. This is because, if there is a metal-ceramic composite at the surface portion, just that part will be hard, and the processing will be uneven, or expensive processing tools such as diamonds or the like will be needed. Additionally, due to the surface portion being a metal layer, the uniformity is improved when performing a plating process. For the above reasons, the average thickness of the metal layer is chosen to be at least 10 m.

[0038] On the other hand, since the metal layer consists of a metal having aluminum as the main component, the coefficient of thermal expansion is high compared to the metal-ceramic composite portions. Therefore, if the thickness of the metal layer increases, the coefficient of thermal expansion of the composite overall becomes large, and the average thickness of the metal layer is chosen to be 110 m or less.

[0039] Additionally, if there is a difference in the average thicknesses of the front and back metal surfaces, then differences in the coefficient of thermal expansion between the metal layer and the metal-ceramic composite may cause differences in the thermal expansion of the front and back surfaces of the composite itself, as a result of which the composite can be warped. Such warpage, if not controlled, can cause joint defects with circuit boards or the like when using the composite as a heat dissipating component or the like. There is a close relationship between the warpage amount and the thickness difference between the front and back metal layers, such that if the thickness difference exceeds 110 m, the warpage of the composite becomes too large, and is no longer suitable for use as a heat dissipating component or the like. Additionally, when the main surface of the plate-shaped composite has hole portions so as to allow screw-fastening to other heat dissipating components, if the distance between holes is compact, i.e. 10 cm or less, then in order to screw-fasten the heat dissipating plate to other heat dissipating components with good closeness of contact, the warpage amount should preferably be 100 m or less with respect to 10 cm of length of the main surface of the composite.

[0040] Furthermore, the fourth invention of the present invention is a composite wherein the ratio (TA/TB) between the average value (TA) of the thickness of the plate-shaped composite (A) and the sum (TB) of the average values of the thicknesses of the front and back alloy layers is 5 to 30, preferably 10 to 30. If TA/TB is less than 5, the alloy layers on the surfaces become too thick, and the properties such as the coefficient of thermal expansion and the thermal conductivity are reduced. On the other hand, if TA/TB exceeds 30, the alloy layers on the surface become too thin, so that when performing mechanical processing or the like of the surface portion, the plate-shaped composite may be partially exposed, causing problems such as damaging processing tools, or reducing the plating properties. Additionally, the alloy layer must have a certain thickness when adjusting the thickness of the surface alloy layers in order to adjust the shape, specifically the warpage amount, of the composite, so TA/TB must be 30 or less.

[0041] Additionally, the warpage amount with respect to 10 cm of length of the main surface of the composite should be 50 to 250 m, and the maximum length (L; cm) of the composite and the difference between the average value (TB1; m) of the thickness of the alloy layer (B) on the front side and the average value (TB2; m) of the thickness on the back side should satisfy the relationship 500<(TB1TB2)L<2500, preferably 500<(TB1TB2)L2000. If the amount of warpage with respect to 10 cm of length in the main surface of the composite exceeds 250 m, when using the composite of the present invention as a heat dissipating component, problems tend to occur, such as joint defects occurring with circuit boards or the like, and excessive bending stress being applied when screw-fastening heat dissipating fins or the like and causing damage to the composite. On the other hand, components such as power modules incorporating heat dissipating components composed of such a composite can be used by screw-fastening them to heat dissipating fins or the like. In that case, in order for stress to act on the joint surfaces between components such as power modules and heat dissipating fins, it is preferable, for purposes of heat dissipation, for the joint surface to be convex so that the clamping force after screw-fastening is large. For this reason, if the warpage amount with respect to 10 cm of length in the main surface of the composite is less than 50 m, the amount of warpage when used as a heat dissipating component or the like can be insufficient, and problems in the heat dissipation properties may occur.

[0042] In a composite of this structure, if there are differences in the thickness of the front and back alloy layers due to differences in the coefficient of thermal expansion between the alloy layer and the plate-shaped composite (metal-ceramic composite), there will be differences in thermal expansion between the front and back of the composite itself, as a result of which warpage will occur in the composite. Such warpage is closely related to the thickness difference between the front and back alloy layers and the size of the plate-shaped composite, and it becomes greater as the thickness difference between the front and back alloy layers increases, and as the size of the plate-shaped composite becomes larger. If (TB1TB2)L exceeds 2500, the warpage amount of the composite becomes too large, and if (TB1TB2)L is less than 500, the warpage amount of the composite becomes too small, and undesirably, problems such as described above will occur when used as a heat dissipating component.

[0043] As the amount of warpage of the composite, a warpage amount of 50 to 250 m with respect to 10 cm of length in the main surface of the composite is preferable. If the warpage amount exceeds 250 m with respect to 10 cm of length in the main surface of the composite, when the composite of the present invention is used as a heat dissipating component, problems may occur, such as joint defects with circuit boards or the like, and excessive bending stress being applied when screw-fastening to heat dissipating fins or the like, causing damage to the composite. On the other hand, components such as power modules incorporating heat dissipating components composed of such a composite can be used by screw-fastening to heat dissipating fins or the like. In that case, in order for stress to act on the joint surface between components such as power modules and heat dissipating fins, it is preferable, for purposes of heat dissipation, for the joint surface to be convex so that the clamping force after screw-fastening is large. For this reason, if the warpage amount with respect to 10 cm of length in the main surface of the composite is less than 50 m, the amount of warpage when used as a heat dissipating component or the like can be insufficient, and the purposes of the present invention may not be able to be achieved.

[0044] Additionally, the present invention relates to a method for producing a silicon carbide composite, wherein the aforementioned plate-shaped composite is plastically deformed by applying a stress perpendicular to the main surface at a temperature of at least 350 C., thereby applying warpage. Due to this operation, a plate-shaped composite having the desired amount of warpage can be easily obtained. In this case, a method of pressing the composite into a mold having internal surfaces preformed in a desired shape is highly reproducible and preferred. At a temperature less than 350 C., the metal having aluminum as the main component in the composite will substantially not undergo plastic deformation, so the purpose of the invention will be difficult to achieve. Regarding the upper limit of the temperature, if the temperature exceeds 600 C., a portion of the aluminum alloy may form a liquid phase and begin to flow, but when heated to a temperature at which flow occurs, deformation may undesirably occur together with solidification when cooled.

[0045] Furthermore, the thermal conductivity of the composite of the present invention at room temperature (25 C.) is at least 150 W/mK. When the thermal conductivity is less than 150 W/mK, there are problems in that sufficient heat dissipation properties are not obtained when used as a heat dissipating component or the like, and the possible applications are limited.

[0046] Additionally, the composite of the present invention has an average coefficient of thermal expansion of 910.sup.6/K or less when heated from room temperature (25 C.) to 150 C. If the average coefficient of thermal expansion when heated from room temperature (25 C.) to 150 C. exceeds 910.sup.6/K, when used as a heat dissipating component in a power module or the like, the difference in the coefficient of thermal expansion with respect to the ceramic substrate becomes too large, and problems such as cracking or breaking of the ceramic substrate may occur due to the load from thermal cycling and thermal joining, and the possible applications are limited when used as a heat dissipating component requiring reliability.

[0047] Additionally, the composite of the present invention has a density of about 3 g/cm.sup.3, which is light compared to metals such as copper, and when used as a heat dissipating component or the like, is effective in reducing the weight of components. On the other hand, the composite of the present invention has a high bending strength of at least 300 MPa, and has sufficient mechanical properties for use as a heat dissipating component or the like.

[0048] Furthermore, the present invention relates to a heat dissipating component using the above-mentioned composite. The heat dissipating component of the present invention has excellent thermal conductivity properties and sufficient mechanical properties, and is suitable for use in heat sinks or the like. Additionally, the heat dissipating component of the present invention is lightweight with a density of about 3 g/cm.sup.3, and is suitable as a heat dissipating component for use in mobile equipment. The heat dissipating component of the present invention has excellent thermal conductivity properties, and has a low average coefficient of thermal expansion of 910.sup.6/K or less, so when used as a heat dissipating component such as a heat sink or the like, the thermal expansion difference with ceramic substrates joined to the heat dissipating component is smaller than in the case of using conventional copper or the like, and cracking or breaking of the ceramic substrate due to thermal cycling or the like that occurs when operating a semiconductor device on the substrate can be suppressed. Due thereto, the invention is suitable as a heat dissipating component for use in mobile equipment such as electric automobiles or the like requiring high reliability.

[0049] Additionally, with the integration and increased size of semiconductor devices, the ceramic substrates on which they are mounted are required to have high heat dissipating properties. Aluminum nitride and silicon carbide substrates have excellent insulation properties and excellent heat dissipation properties, so that by using them by joining them to the heat dissipating component of the present invention, high reliability can be obtained with extremely little cracking or breaking due to thermal cycling or the like.

[0050] Additionally, the heat dissipating plate of the present invention has the characteristic that at least 90% of the surface is in close contact when a surface to which a ceramic substrate is not joined is mounted on a flat plate with a heat dissipation grease therebetween, under conditions of at least 2 N of tightening torque, and this provides the advantage of allowing heat generated when operating semiconductor devices on a ceramic substrate to be quickly dissipated, and allowing a highly reliable module to be formed.

[0051] The method for manufacturing the composite of the present invention involves adding and mixing a predetermined amount of a silica sol and/or an alumina sol or the like as a binding agent in a silicon carbide powder, and molding to a desired shape. The molding method may be dry press molding, wet press molding, extrusion molding, cast molding or the like, and a shape-retaining binder may be added as needed. Additionally, regarding the silicon carbide powder, one type of powder may be used, but it is even more preferable to blend a plurality of powders of appropriate grain size, since this allows a high density molded article to be easily obtained. Next, the resulting molded article is calcined at a temperature of 700 to 1600 C. in air or in an inert gas atmosphere such as nitrogen to produce a silicon carbide porous body. On the other hand, a similar production method may be used by adding and mixing a silicon powder as a binder to the silicon carbide powder. Furthermore, with regard to the production method of the silicon carbide porous body, it can be produced by baking a silicon carbide powder or a mixed powder of silicon powder and carbon powder at a temperature of 1600 to 2200 C. in an inert gas atmosphere.

[0052] The resulting silicon carbide porous body, after processing to a predetermined shape, is preheated in order to prevent cracking or the like due to thermal shock, and impregnated at a high pressure with molten metal having aluminum as the main component, heated to a temperature of at least the melting point, to form a composite. In order to adjust the thickness of the metal layer on the surface of the composite, when processing the silicon carbide porous body, grooves or the like may be added to the surface portion so as to adjust the thickness of the alloy layer on the surface of the composite obtained by impregnation. Additionally, it can be adjusted by laminating a thin plate of Al alloy onto the surface of the silicon carbide porous body and impregnating. In this case, not only a porous body, but also a silicon carbide powder may be used. Furthermore, the thickness of the metal layer on the surface of the composite can be adjusted by mechanically processing the metal layer on the surface of the composite. Furthermore, by making use of a die or the like, a preform of a slightly smaller size than the size of a cavity in the die can be provided inside the cavity, and the molten metal injected into the cavity inside the die.

[0053] Regarding the impregnation method of the metal component, there are no particular limitations, and high-pressure casting, die casting or the like may be used.

EXAMPLES

[0054] Herebelow, the present invention will be explained in further detail by providing examples and comparative examples, but the present invention is not to be construed as being limited thereto.

Examples 1-8, Comparative Examples 1-4

[0055] Silicon carbide powder A (manufactured by Pacific Rundum: NG-150, average particle size 100 m), silicon carbide powder B (manufactured by Yakushima Denko: GC-1000F, average particle size 10 m) and a silica sol (manufactured by Nissan Chemical Industries: Snowtex) were blended in a composition at a mass ratio of 60:40:10, mixed for 1 hour in a stirrer/mixer, then molded at a pressure of 10 MPa to a shape of 187 mm137 mm7 mm. Thereafter, the molded article was heated for 2 hours at 960 C. in air to produce a silicon carbide porous body. The resulting silicon carbide porous body was processed to a shape of 20 mm7 mm, and upon calculating the relative density based on the dimensions and the mass, a value of 65% was obtained.

[0056] Next, the resulting silicon carbide porous body was processed to a desired thickness using a diamond processing tool, twelve of the samples were separated by 0.8 mm thick SUS plates coated with a mold release agent, and 12 mm thick iron plates were provided on both ends, after which they were fastened using 10 mm bolts and nuts to form a single block.

[0057] Next, two of the aforementioned blocks were used as one block which was preheated to a temperature of 650 C. in an electric furnace, and placed inside a preheated press mold having a cavity with internal dimensions of 320 mm260 mm440 mm, after which a melt of an aluminum alloy (ADC-12) heated to a temperature of 810 C. was poured in and pressed for at least 13 minutes at a pressure of 500 MPa to impregnate the silicon carbide porous body with the aluminum metal. The resulting metal ingot containing the composite was cooled to room temperature and cut with a wet band saw to release the silicon carbide composite.

[0058] For the resulting composite, the top and bottom positions in the thickness direction of the composite were sensed by a laser using a laser thickness measuring device (manufactured by Keyence; VT2-10SB) to measure the thickness at the five points shown in FIG. 2, the average thickness of the composite was calculated from the average value thereof, and the thickness variation was determined from the maximum value and the minimum value. Additionally, after the surface of the composite was polished using a roll polisher to remove altered layers of the composite surface, a laser three-dimensional shape measuring device (manufactured by Keyence: LK-GD500) was used to illuminate the object with a laser beam, the light that was diffused and reflected from the object was received to calculate the amount of displacement, and the amount of warpage of the main surface of the composite was measured. The warpage amounts (Cx, Cy) of the main surface of the composite were measured for power modules using each of the composites, by means of a laser three-dimensional shape measuring device. The results are shown in Table 1.

TABLE-US-00001 TABLE 1 Thickness of Thickness Composite Variation of Composite Power Module (t) Composite Cx Cy Cx Cy Type (mm) (mm) (m) (m) (m) (m) Example 1 2.0 0.1 60 60 50 60 Example 2 3.0 0.1 100 100 90 70 Example 3 4.0 0.2 170 130 160 110 Example 4 5.0 0.2 130 70 90 60 Example 5 5.0 0.3 100 70 100 60 Example 6 5.0 0.2 120 130 110 100 Example 7 5.0 0.3 160 160 150 150 Example 8 6.0 0.3 140 130 90 90 Comparative 1.0 0.2 30 270 0 260 Example 1 Comparative 7.0 0.2 100 0 0 20 Example 2 Comparative 4.0 0.4 100 100 50 50 Example 3 Comparative 5.0 0.5 100 20 50 0 Example 4 Cx, Cy: Warpage amount with respect to 10 cm sample length

[0059] Additionally, from the resulting composite, a diamond processing tool was used to grind a test sample for measurement of coefficient of thermal expansion (4420 mm), a test sample for measurement of thermal conductivity at room temperature (25 mm25 mm1 mm), and a test sample for measurement of three-point bending strength (3 mm30 mmthickness). Additionally, using a portion of the test sample for measurement of three-point bending strength, the cross section was observed under a microscope, and the thicknesses of the front and back metal layers of the composite were measured at nine locations and the average thickness was calculated. The results are shown in Table 2.

TABLE-US-00002 TABLE 2 Average Thickness (m) of Metal Layer Type Front Back Difference Example 1 90 80 10 Example 2 30 60 30 Example 3 50 40 10 Example 4 50 40 10 Example 5 60 30 30 Example 6 70 80 10 Example 7 50 50 0 Example 8 40 20 20 Comparative 150 100 50 Example 1 Comparative 10 5 5 Example 2 Comparative 200 80 120 Example 3 Comparative 350 50 300 Example 4

[0060] Next, using each of the test samples, the coefficient of thermal expansion from room temperature to 250 C. was measured using a thermal expansion meter, the thermal conductivity at room temperature was measured by a laser flash method, and the three-point bending strength was measured using a bend testing machine. Furthermore, the densities of the composites were calculated from the dimensions and weights of the samples for measurement of thermal conductivity. The results are shown in Table 3.

TABLE-US-00003 TABLE 3 Coefficient Three-point of Thermal Thermal Bending Expansion Conductivity Strength Density Type (10.sup.6/K) (W/mK) (MPa) (g/cm.sup.3) Example 1 6.4 190 410 2.98 Example 2 6.9 225 350 2.98 Example 3 7.4 210 420 2.99 Example 4 7.2 220 400 2.98 Example 5 7.7 225 410 2.98 Example 6 7.4 230 400 2.98 Example 7 7.5 230 360 2.98 Example 8 7.3 205 400 2.97 Comparative 11.0 140 100 2.75 Example 1 Comparative 10.5 210 400 2.98 Example 2 Comparative 10.3 200 410 2.99 Example 3 Comparative 10.2 205 390 2.98 Example 4

[0061] Additionally, for various composites obtained by the aforementioned operations, one side was coated with silicon grease (manufactured by Shin-etsu Chemical) weighed to have a thickness of 50 m, then attached to an acrylic plate with a thickness of 30 mm using 6M screws with a tightening torque of 3 N. After letting stand for 1 minute, the screws were removed and the rate of close contact (proportional area) of the silicon grease-coated surface was measured. The results are shown in Table 4.

TABLE-US-00004 TABLE 4 Close Contact Rate Type (%) Example 1 99 Example 2 99 Example 3 98 Example 4 98 Example 5 93 Example 6 97 Example 7 99 Example 8 99 Comparative 55 Example 1 Comparative 60 Example 2 Comparative 75 Example 3 Comparative 45 Example 4

Examples 9 to 11

[0062] The silicon carbide composite produced in Comparative Example 1 was set in a jig composed of SUS-304 as shown in FIG. 3, a stress perpendicular to the main surface was applied as a load using an M10 screw, after which the composite was heated for 30 minutes in an electric furnace at a temperature of 500 C., then cooled to room temperature and freed from the load. The amount of warpage of the resulting composite is shown in Table 5. Next, the results of evaluation of the obtained composite using the same method as in Examples 1-8 are shown in Table 5. As shown in Table 5, the rate of close contact was able to be raised by forming a convex surface using a jig.

TABLE-US-00005 TABLE 5 Close Contact Type Cx (m) Cy (m) Rate (%) Example 9 120 50 99 Example 10 150 70 99 Example 11 180 90 99

BRIEF DESCRIPTION OF THE DRAWINGS

[0063] FIG. 1 Plan view showing an example of a composite according to the present invention.

[0064] FIG. 2 Representative diagram of thickness measurement points of a composite according to the present invention.

[0065] FIG. 3 Explanatory diagram of a jig used in an embodiment of the present invention.