JP2000141022A - Silicon carbide composite body and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silicon carbide composite body having a high thermal conductivity, which is suitably used for a heat sink such as a power module. SOLUTION: Relating to a silicon carbide composite body wherein aluminum or an alloy mainly consisting of aluminum is impregnated in a porous silicon carbide molding, it has thermal conductivity of >=200 W/mK, concretely the content of oxygen is <=1.1 weight %, and a volume ratio of silicon carbide in the silicon carbide composite body is >=50%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION In recent years, the present invention has been mainly used in power modules for power modules because of its excellent properties such as high thermal conductivity, low thermal expansion and low specific gravity.
The present invention relates to a composite mainly containing aluminum and silicon carbide, which is being used for tosinks and the like.

[0002]

2. Description of the Related Art Conventionally, copper has been used as a heat sink material in power modules. However, when copper is used as the heat sink material, its high thermal expansion coefficient (17 ppm / K) causes a problem in reliability such as cracks occurring between the heat sink material and the substrate mounted thereon. There has been a demand for a heat sink material having low thermal expansion and high thermal conductivity that does not cause such a phenomenon.

[0003] Under the above circumstances, the aluminum-silicon carbide-based composite can suppress the thermal expansion coefficient to 10 ppm / K or less by increasing the content of silicon carbide, and can exhibit high thermal conductivity. Has recently attracted attention as a heat sink material because of its low specific gravity.

[0004]

However, the thermal conductivity of the aluminum-silicon carbide composites developed so far is at most about 170 W / mK at room temperature, and that of copper (400 W / mK). Development of an aluminum-silicon carbide composite having even higher thermal conductivity than mK) has been desired. The present invention has been made to meet this demand, and has achieved an unprecedented 200 W / m.
It is an object of the present invention to obtain the composite having a thermal conductivity of not less than K, in particular, a thermal expansion coefficient of 9 ppm / K or less close to that of copper and a thermal conductivity of 200 W / mK or more.

[0005]

The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, have found that
The thermal conductivity of a silicon carbide-based composite (hereinafter, referred to as a silicon carbide-based composite) largely depends not only on the content of silicon carbide but also on the oxygen content of the composite itself. In the composite having the above, a thermal conductivity of 200 W / mK or more is exhibited, and the oxygen content of the composite mainly depends on the oxygen content of the preform before the impregnation of the alloy containing silicon carbide as a main component. The use of a preform having an oxygen content of not more than a specific amount, and further limiting the oxygen content of aluminum or an alloy containing aluminum as a main component to be impregnated, whereby the aluminum having a thermal conductivity of 200 W / mK or more. -It has been found that a silicon carbide composite can be easily obtained, and the present invention has been completed.

That is, the present invention relates to a silicon carbide composite obtained by impregnating a porous silicon carbide compact with aluminum or an alloy containing aluminum as a main component.
A silicon carbide composite having the above thermal conductivity, specifically, the silicon carbide composite having an oxygen content of 1.1% by weight or less. The silicon carbide composite according to the above, wherein the volume ratio of silicon carbide in the silicon carbide composite is 50% or more. Further, the present invention is the above-mentioned silicon carbide composite, wherein a thermal expansion coefficient from room temperature to 150 ° C. is 9 ppm / K or less.

In addition, the present invention relates to a method for producing a silicon carbide composite in which a porous silicon carbide molded body is impregnated with aluminum or an alloy containing aluminum as a main component. A method for producing a silicon carbide-based composite, wherein the density is 50% by volume or more and the oxygen content is 1.4% by weight or less. A plurality of types of silicon carbide powders having different particle size distributions are mixed to obtain a raw material powder, and an inorganic binder to be fired to be silicon oxide is added to the raw material powder. Drying, followed by firing at a temperature in the range of 750 ° C. to 900 ° C., wherein the method comprises the steps of: ~ 1 And the percent by weight of silicon, 0.5 to 2.5
The method for producing a silicon carbide-based composite according to the above, comprising magnesium by weight.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

The present inventors have conducted various studies on a silicon carbide composite obtained by impregnating a porous silicon carbide compact with aluminum or an alloy containing aluminum as a main component. And the oxygen content is greatly related to the thermal conductivity. In the conventional silicon carbide composite, oxygen derived from the raw material or its production history is mixed, and the thermal conductivity is at most 170 W / mK.
It has been found that they are limited to a certain extent, and has led to the present invention.

That is, the silicon carbide composite of the present invention has 20
It is characterized by having a thermal conductivity of 0 W / mK or more, and in a preferable case, has a thermal expansion coefficient of 9 ppm / K or less, and is a heat sink material in a power module in which copper has been conventionally used. And the like.

The silicon carbide composite of the present invention has an oxygen content of 1.1% by weight or less in order to achieve the above high thermal conductivity. Preferably, it is at most 0.9% by weight. When the amount of oxygen exceeds 1.1% by weight, 200 W /
In some cases, a thermal conductivity of mK or more cannot be obtained. It is not clear why the high thermal conductivity is achieved when the oxygen content is low, but the present inventors have found that oxygen is present at the interface between aluminum and silicon carbide particles or at the contact surface between silicon carbide particles and silicon carbide particles. This is presumed to be due to agglomeration and heat transfer at these interfaces.

In the silicon carbide composite of the present invention, the space ratio occupied by the silicon carbide (hereinafter referred to as silicon carbide content) is preferably at least 50% by volume. There are many unclear points as to how various factors affect the thermal conductivity of the silicon carbide composite. When the content of silicon carbide is less than 50% by volume, the thermal conductivity is 200 W / mK or more. May not always be available.

In the silicon carbide composite of the present invention,
When the content of silicon carbide is 60% by volume or more, the coefficient of thermal expansion from room temperature to 150 ° C. is 9 ppm /
It can be controlled to K or less. And the coefficient of thermal expansion is 9
By controlling to less than ppm / K, as described above, the silicon carbide composite of the present invention can be used as a heat sink material for power modules due to its high thermal conductivity. It has the feature that it can be preferably applied to applications requiring low thermal expansion properties, such as a plate.

Next, as a method for obtaining the silicon carbide composite of the present invention, a method using a molten metal forging method will be exemplified, but the silicon carbide composite of the present invention is not limited thereto. The molten metal forging method is a method in which a preform is placed in a mold, an aluminum alloy is charged, and then pressurized by a mechanical pressure. This is because, when it is performed, the aluminum alloy can be impregnated under such a temperature condition that the residual heat does not cause large oxidation of the preform. In such a molten metal forging method, the conditions for impregnating the above aluminum alloy are as follows: the temperature of the molten aluminum alloy is 700 to 850.
° C and the pressure at the time of impregnation are 30 MPa or more.

As the raw material for the porous silicon carbide molded body (hereinafter, referred to as a preform) used in the present invention, powder or whisker is usually used as a raw material. Preferably, the silicon carbide content in the silicon carbide composite is 50% by volume.
As described above, more preferably, those achieving 60% by volume or more are selected.

In producing the preform, known molding methods such as a press molding method, a casting molding method, and an extrusion molding method can be adopted as the molding method, and a molding method such as methylcellulose, PVA or the like can be employed. There is no problem in using water, an organic solvent, or the like as a solvent, as well as an ordinary inorganic binder such as an organic binder or colloidal silica, and the amount of oxygen in the preform before impregnation is 1.4 wt%. The following should be possible. When the oxygen content of the preform immediately before the impregnation exceeds 1.4% by weight, the oxygen content in the obtained silicon carbide composite is adjusted together with the oxygen content mixed from the metal or the like to be impregnated in the impregnation step. Exceeds 1.1% by weight, and as a result, 200 W /
In some cases, a silicon carbide composite having a thermal conductivity of mK or more cannot be obtained.

In order to obtain a preform having an oxygen content of 1.4% by weight or less, the raw material silicon carbide powder or whisker
In consideration of the amount of oxygen, oxidation of these during firing, and oxygen contamination from inorganic binders such as colloidal silica,
Achieved by optimizing. In particular, when preparing a preform from silicon carbide powder, it is preferable to use a large amount of low-oxygen-content silicon carbide coarse powder, but using a fine powder having a high oxygen content to reduce in a subsequent heat treatment. It is needless to say that a preform of 1.4% by weight or less can be obtained.

In the present invention, not only the amount of oxygen but also the filling degree of silicon carbide in the preform (that is, the filling rate of silicon carbide in the silicon carbide composite) is set to 50% by volume or more. preferable. If it is less than 50% by volume, 2
This is because a silicon carbide composite having a thermal conductivity of 00 W / mK or more may not be obtained.

In order to prepare a preform that achieves a silicon carbide content of 50% by volume or more, it is necessary to adjust the particle size and length / diameter ratio of the silicon carbide powder and whisker to be used, and to add an organic binder and This can be achieved by adjusting the type and amount of the inorganic binder and the type and amount of the solvent for adjusting the fluidity during molding. In particular, when forming a preform using silicon carbide powder, generally only coarse powder is used.
It is not easy to achieve a content of 0% by volume or more. Therefore, it is more effective to combine so-called particle sizes, that is, combine appropriate amounts of coarse powder and fine powder in appropriate sizes.

Here, an example of the particle size mixing ratio of the silicon carbide powder is as follows.
75 parts by weight of silicon carbide powder having an average particle size of 7 μm
Combination of 25 parts by weight or average particle size of 90μ
m silicon carbide powder, 65 parts by weight, average particle diameter of 30 μm, 15 parts by weight, and average particle diameter of 10 μm
Of silicon carbide powder of 20 parts by weight.

In forming a preform using the silicon carbide raw material powder having the above-mentioned particle size composition, no matter which molding method is adopted, the preform strength after firing must be exhibited. In general, an inorganic binder such as colloidal silica and alumina sol is added. Of these, colloidal silica becomes silica by firing and binds silicon carbide particles to develop sufficient preform strength. However, the addition of these inorganic binders increases the amount of oxygen derived from the inorganic binder in the preform. May occur. Any inorganic binder may be used as long as it becomes silicon oxide or aluminum oxide by firing. For example, a silicon-containing compound such as silicon or silicon nitride or an aluminum-containing compound such as aluminum or aluminum nitride can be used.

The preform containing an inorganic binder is dried and fired as necessary to develop strength. Firing is often performed in an oxidizing atmosphere such as in the air, and at this time, an increase in oxygen due to oxidation of the silicon carbide powder may also occur. For this reason, although it depends on the holding time, baking in the air is preferably performed at a temperature lower than 950 ° C. to reduce the increase in oxygen. A temperature range of 750 ° C. to 900 ° C. is a preferable temperature range in view of the balance between the developed strength and the increase in oxygen.

As a method for impregnating the preform with aluminum or an alloy containing aluminum as a main component (hereinafter, both are collectively referred to as an aluminum alloy), there are known methods such as a molten metal forging method, a die casting method and a method of improving them. Can be used. During the impregnation, it is usually preferable to carry out a pre-heating of the preform as a preliminary step so that the aluminum alloy can easily penetrate. In the present invention, it is necessary that the pre-heat treatment conditions such as temperature, time, atmosphere, etc., are such that the oxygen amount of the preform falls within a predetermined amount range.

As the alloy containing aluminum as a main component in the present invention, an aluminum-silicon-based alloy used for producing a usual aluminum-silicon carbide composite is used.
Aluminum-silicon-magnesium alloys and aluminum-magnesium alloys may be mentioned. Among these, an aluminum-silicon-magnesium alloy capable of lowering the melting point of the aluminum alloy is preferable from the viewpoint of workability, and an aluminum-magnesium alloy is preferable from the viewpoint of improving thermal conductivity. In particular, in the former case, since silicon causes a decrease in thermal conductivity, its amount is preferably 18 wt% or less. Further, regarding the amount of magnesium, it is considered that if the amount is small, the melting point of the alloy is not lowered and the workability is deteriorated, and if the amount is large, the thermal conductivity is reduced. 5-2.5w
It is good to be t%.

Hereinafter, the present invention will be described in more detail with reference to examples.

[0026]

EXAMPLES Example 1 65 parts by weight of silicon carbide powder having an average particle diameter of 110 μm, 35 parts by weight of silicon carbide powder having an average particle diameter of 7 μm, and colloidal silica (silica equivalent was 20 parts by weight)
6% by weight) and 12 parts by weight of water were weighed and mixed to prepare a slurry. The slurry was poured into a gypsum mold and allowed to stand, then removed from the mold and dried to obtain a plurality of molded products. Each of the compacts was fired in air at 850 ° C. for 2 hours to obtain a preform. The silicon carbide powder used had an average particle size of 7 μm and was manufactured by Yakushima Denko Co., Ltd., and the other silicon carbide powders were manufactured by Taiheiyo Random Co., Ltd., and colloidal silica was manufactured by Nissan Chemical Co., Ltd. It is made.

A part of the preform is LEC
Using a nitrogen / oxygen analyzer TC-436 manufactured by Company O, the preform was processed to have a diameter of 20 mm and a thickness of 3 mm for measuring the density while measuring the density. The silicon carbide filling degree of the preform was defined as a percentage by dividing the density of the processed product by the theoretical density of silicon carbide of 3.21 g / cm ³ . As a result, the filling degree of silicon carbide in the preform was 65% by volume, and the oxygen content was 0.92% by weight.
Met. The remaining preform was impregnated with an aluminum alloy by the aforementioned melt forging method.

The method of impregnation is as follows. First, the preform was fired in air at 650 ° C. for 1 hour, and a pre-heat treatment was performed. Immediately after preheating, the preform was placed in the mold, and an aluminum alloy containing 12 wt% of silicon and 1 wt% of magnesium and melted at 850 ° C. was molded so that the front surface of the preform was sufficiently hidden. I put it in.
Then, it was quickly pressed by a punch at a pressure of 70 MPa for 5 minutes, and after cooling, an aluminum alloy lump containing the aluminum-silicon carbide composite was taken out of the mold.
An aluminum-silicon carbide-based composite portion was cut out from this lump by a machining method.

The composite obtained by the above operation was partially measured to have a diameter of 10 mm and a thickness of 3 to measure the thermal conductivity at room temperature.
mm and used as a sample. The specific gravity, thermal diffusivity, and specific heat of the sample were measured, and the thermal conductivity was calculated. As a result, the thermal conductivity was 218 W / mK. The thermal diffusivity was measured by a laser flash method ("LF / TCM" manufactured by Rigaku Corporation).
-FA8510B "), the specific heat is measured by DSC (" DSC200 "manufactured by Seiko Instruments Inc.).

Further, regarding the sample after the measurement of the thermal conductivity,
The oxygen content was measured by the method described above, and the oxygen content of the composite was determined. As a result, the oxygen content of the composite was 0.7
It was 8% by weight. Further, a sample for measuring thermal expansion coefficient was newly cut out from the above composite, and the thermal expansion coefficient from room temperature to 150 ° C. was measured (“TMA30” manufactured by Seiko Instruments Inc.).
0 "), however, it was 7.9 ppm / K. Also, using the chips at the time of machining of the aluminum alloy ingot,
The oxygen content in the aluminum alloy was also measured. Tables 1 and 2 show the above various conditions and results.

[0031]

[Table 1]

[0032]

[Table 2]

Example 2 Silicon Carbide Powder was Prepared with an Average Particle Size of 20
70 parts by weight of 0 μm, 30 with an average particle size of 30 μm
A preform was prepared in the same manner as in Example 1 except that the
And composites were made. The results are shown in Tables 1 and 2.

Example 3 Silicon Carbide Powder was Prepared with an Average Particle Size of 60
A preform and a composite were prepared in the same manner as in Example 1 except that the composition was 45 parts by weight and the average particle size was 55 parts by weight. The results are shown in Tables 1 and 2.

Example 4 Silicon Carbide Powder was Prepared with an Average Particle Size of 90
The same method as in Example 1 except that 65 parts by weight of μm, 15 parts by weight of 30 μm in average particle diameter, and 20 parts by weight of 10 μm in average diameter, and the firing temperature of the molded body was 800 ° C. To form a preform and a composite. The results are shown in Tables 1 and 2.

[Example 5] Silicon carbide powder was prepared with an average particle size of 90.
A preform and a composite were prepared in the same manner as in Example 1 except that 50 parts by weight of 50 μm, 50 parts by weight of average particle diameter of 60 μm, and the amount of colloidal silica were 3 parts. The results are shown in Tables 1 and 2.

Example 6 Silicon Carbide Powder was Prepared with an Average Particle Size of 60
Example 1 was the same as Example 1 except that the amount was 60 parts by weight for μm, 40 parts by weight for an average particle diameter of 7 μm, the amount of colloidal silica was 4 parts by weight, and the firing temperature of the molded body was 800 ° C. Preforms and composites were prepared in the same manner. The results are shown in Tables 1 and 2.

[Example 7] Silicon carbide powder was prepared with an average particle size of 20.
65 parts by weight of 0 μm, 35 with an average particle size of 30 μm
A preform and a composite were produced in the same manner as in Example 1 except that the amount was changed to parts by weight and the firing temperature of the molded body was set to 800 ° C. The results are shown in Tables 1 and 2.

Example 8 A preform and a composite were prepared in the same manner as in Example 1 except that the aluminum alloy was an aluminum alloy containing 1% by weight of magnesium.
The results are shown in Tables 1 and 2.

Example 9 A preform and a composite were prepared in the same manner as in Example 2 except that the aluminum alloy was an aluminum alloy containing 1% by weight of magnesium. The results are shown in Tables 1 and 2.

Example 10 A preform and a composite were prepared in the same manner as in Example 4 except that the aluminum alloy was an aluminum alloy containing 1% by weight of magnesium and 18% by weight of silicon. The results are shown in Tables 1 and 2.

Example 11 A preform and a composite were produced in the same manner as in Example 6, except that the aluminum alloy was an aluminum alloy containing 1% by weight of magnesium and 18% by weight of silicon. The results are shown in Tables 1 and 2.

Example 12 A preform and a composite were produced in the same manner as in Example 3, except that the aluminum alloy was an aluminum alloy containing 0.5% by weight of magnesium. The results are shown in Tables 1 and 2.

Example 13 A preform and a composite were produced in the same manner as in Example 5, except that the aluminum alloy was an aluminum alloy containing 2.5% by weight of magnesium. The results are shown in Tables 1 and 2.

Example 14 The impregnation of the aluminum alloy was carried out by a so-called die casting method in which the preform was placed in a mold having a space slightly larger than the preform, and then the molten aluminum alloy was rapidly injected. A preform and a composite were prepared in the same manner as in Example 3.
The results are shown in Tables 1 and 2.

Example 15 A preform and a composite were produced in the same manner as in Example 6, except that the same die casting method as in Example 14 was employed. The results are shown in Tables 1 and 2.

Example 16 To the silicon carbide powder and colloidal silica of Example 5, 10 parts by weight of a 30% by weight aqueous solution of PVA was added, mixed well, and the mixture was dried appropriately. Filling mold and pressure 1000kg / c
A preform and a composite were produced in the same manner as in Example 5 except that the molding was performed at m ² . The results are shown in Tables 1 and 2.

Example 17 To the silicon carbide powder and colloidal silica of Example 6, 10 parts by weight of an aqueous PVA solution having a concentration of 30% by weight was added and thoroughly mixed. And pressure 1000kg / cm
^A preform and a composite were prepared in the same manner as in Example 6, except that the press molding was performed in Step 2. Tables 1 and 2 show the results.
Shown in

Example 18 A preform and a composite were prepared in the same manner as in Example 5, except that alumina sol having an alumina content of 20% by weight was used instead of colloidal silica. The results are shown in Tables 1 and 2.

Example 19 A preform and a composite were prepared in the same manner as in Example 6 except that alumina sol having an alumina content of 20% by weight was used instead of colloidal silica. The results are shown in Tables 1 and 2.

[Comparative Example 1] Silicon carbide powder having an average particle size of 6
A preform and a composite were produced in the same manner as in Example 3 except that 35 parts by weight of 0 μm and 65 parts by weight of an average particle diameter of 7 μm were used. The results are shown in Tables 1 and 2.

[Comparative Example 2] Silicon carbide powder having an average particle size of 2
80 parts by weight of 00 μm, 2 with an average particle size of 30 μm
A preform and a composite were prepared in the same manner as in Example 2 except that the amount was 0 parts by weight. The results are shown in Tables 1 and 2.

Comparative Example 3 The firing temperature of the compact was 1050
A preform and a composite were prepared in the same manner as in Example 1 except that the temperature was changed to ° C. The results are shown in Tables 1 and 2.

[Comparative Example 4] The firing temperature of the compact was 950 ° C.
A preform and a composite were prepared in the same manner as in Example 3, except that The results are shown in Tables 1 and 2.

Comparative Example 5 A preform and a composite were prepared in the same manner as in Example 4 except that the amount of colloidal silica was changed to 15 parts by weight. The results are shown in Tables 1 and 2.

Comparative Example 6 A preform and a composite were produced in the same manner as in Example 2 except that the amount of colloidal silica was changed to 20 parts by weight. The results are shown in Tables 1 and 2.

[0057]

The silicon carbide composite of the present invention has a capacity of 200 W
/ MK or higher, and preferably 9 ppm / K or lower, as a heat dissipating member for a circuit board for mounting a semiconductor, particularly for a heat sink for a power module. It is suitable.

Claims (7)

[Claims] 1. A silicon carbide composite obtained by impregnating a porous silicon carbide compact with aluminum or an alloy containing aluminum as a main component, having a thermal conductivity of 200 W / mK or more. Silicon carbide composite. 2. The silicon carbide composite according to claim 1, wherein the oxygen content is 1.1% by weight or less. 3. The silicon carbide composite according to claim 1, wherein the volume ratio of silicon carbide in the silicon carbide composite is 50% or more. 4. A thermal expansion coefficient at room temperature to 150 ° C. of 9
The silicon carbide composite according to claim 1, wherein the content is at most ppm / K. 5. 5. A method for producing a silicon carbide composite in which a porous silicon carbide molded body is impregnated with aluminum or an alloy containing aluminum as a main component, wherein the relative density of the porous silicon carbide molded body is 50% by volume. A method for producing a silicon carbide-based composite, characterized by having an oxygen content of 1.4% by weight or less. 6. A raw material powder is obtained by mixing a plurality of silicon carbide powders having two or more different particle size distributions in the silicon carbide-based molded body to obtain a raw material powder, and the raw material powder is fired to form silicon oxide. The method for producing a silicon carbide-based composite according to claim 5, wherein an inorganic binder is added, and after molding, drying is performed as necessary, and then firing is performed at a temperature in the range of 750C to 900C. . 7. An aluminum or aluminum-based alloy comprising 0 to 18% by weight of silicon and 0.5 to 2.5% by weight.
The method for producing a silicon carbide-based composite according to claim 5, comprising magnesium by weight.