JP2000192168A - Silicon carbide composite material and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the thermal conductivity of the composite material by controlling the asepect ractio of particles essentially consisting of silicon carbide to the value above the specified one and allowing the thermal conductivity in the 1st direction and that in the 2nd direction orthogonal to the 1st direction to satisfy specified relation. SOLUTION: This material is the one in which the aspect ratio of silicon carbide particles is controlled to >1, and there is anisotropy in thermal conductivity. Namely, the relation of 0.7Kx<=Ky<=0.9Kx is valid between the thermal conductivity Kx in the 1st direction of the material and the thermal conductivity Ky in the 2nd direction orthogonal to the 1st direction. In the case a planar radiating substrate is formed by using this material, ordinarily, the 1st direction is applied as the main plane direction, and the 2nd direction is applied as the thickness direction. In the case of being increasing the thermal conductivity in the main face direction, in the producing process of the material, the main planes of the powder particles are orientated to the main plane of the substrate as much as possible. The degree of the anisotropy is remarkable, mainly, as the aspect ratio is made higher, but, it is influenced also by the amt. of the silicon carbide particles, and the amt. is preferably controlled to 50 to 80 wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat dissipation substrate used for various devices and equipment, and particularly to a silicon carbide composite material having high thermal conductivity used for a heat dissipation substrate of a semiconductor device and a semiconductor device using the same.

[0002]

2. Description of the Related Art In recent years, market demands for high-speed operation and high integration of semiconductor devices have been rapidly increasing. At the same time, the heat dissipation board for mounting the semiconductor element of the device has been required to further improve the thermal conductivity in order to more efficiently release the heat generated from the element. Furthermore, other elements in the same device and the same device arranged adjacent to the same substrate
In order to further reduce the thermal strain between them and (peripheral members), it has been required to have a thermal expansion coefficient much closer to them. Specifically, Si usually used as the semiconductor element, the thermal expansion coefficient of GaAs are each ^{4.2 × 10 -6 /℃,6.5×10 -6 / ℃} , usually as an envelope material of a semiconductor device Since the alumina ceramic used is about 6.5 × 10 ⁻⁶ / ° C., it is desired that the thermal expansion coefficient of the substrate be close to these values.

[0003] Further, with the remarkable expansion of the application range of electronic equipment in recent years, the use range of semiconductor devices has been further diversified. Among them, applications to so-called semiconductor power device devices such as high-output AC converters and frequency converters are increasing. In these devices, the heat generated by the semiconductor elements is several times to several tens times (typically, for example, several tens of watts) compared to semiconductor memories and microprocessors.
Extend to For this reason, it is important for the heat radiation board used in these devices to remarkably improve the thermal conductivity and to improve the matching of the thermal expansion coefficient with that of the peripheral members. Therefore, the basic structure is usually as follows, for example. First, the Si semiconductor element is mounted on a high thermal conductive aluminum nitride (hereinafter, also simply referred to as AlN) ceramic substrate which is a first heat dissipation substrate. Next, a second heat radiating substrate made of a metal having higher thermal conductivity such as copper is arranged under the first heat radiating substrate. Further, a heat dissipating mechanism capable of water-cooling or air-cooling this is disposed below the second substrate. The above structure allows heat to escape to the outside without delay. Therefore, a complicated heat dissipation structure is inevitable.
In this structure, assuming that AlN ceramics, which is the first radiating substrate, is about 170 W / m · K, the second radiating substrate uses the heat transmitted from the first substrate to radiate heat thereunder. It is necessary to escape to the mechanism without delay. For this reason, the second substrate should be at least 200 W at room temperature.
/ M · K or higher and 10 × 10 ^-6 / ° C or lower, especially 8 × 10
A material having a low thermal expansion coefficient of ^-6 / ° C or less is required.

[0004] In particular, among power devices having a large heat value in practical use, the temperature of the heat radiation substrate itself may rise to 100 ° C or more, so that a high thermal conductivity at such a temperature is required. In some cases. Therefore, a material having a thermal conductivity of 150 W / m · K or more is required even at such a temperature. Also, the larger the capacity, the more S
The size of the i semiconductor element also increases. Therefore, the heat radiation board on which it is mounted must be large. For example, while a substrate for a personal computer has a size of at most about 20 to 40 mm square, a power device having a large capacity is required to have a size exceeding 200 mm square. In such a large substrate, it is required that not only the dimensional accuracy at the time of mounting but also the accuracy does not decrease at high temperatures. That is, when the substrate is warped or deformed at a high temperature, a gap is formed at an interface with a heat radiation mechanism (such as a radiator or a fin) disposed below the substrate, thereby lowering the heat radiation efficiency. In the worst case, the semiconductor element may be destroyed. Therefore, ensuring excellent thermal conductivity of the heat dissipation board at high temperatures is an important issue.

For such a substrate, a substrate made of, for example, a Cu-W or Cu-Mo composite alloy has been used. These substrates have a problem that the cost is high and the weight is large because the raw material is expensive. Accordingly, recently, various aluminum (hereinafter, also simply referred to as Al) composite alloys have been attracting attention as inexpensive and lightweight materials. Above all, Al-SiC-based composite alloys containing Al and silicon carbide (hereinafter also simply referred to as SiC) as main components are relatively inexpensive, lightweight, and have high thermal conductivity. In addition, pure Al, S which is usually commercially available
The density of iC alone is about 2.7 g / cm ³ ,
About 3.2 g / cm ³ , each having a thermal conductivity of 240 W
/ M · K, up to about 200 to 300 W / m · K, but it is expected that the level of thermal conductivity will be further improved by further adjusting its purity and defect concentration. Therefore, it is a material that has received special attention. Also pure Si
The thermal expansion coefficients of C alone and Al alone are 4.2 × 10
^-6 / ° C. and 24 × 10 ^-6 / ° C., and by combining them, the thermal expansion coefficient can be controlled in a wide range. Therefore, this point is also advantageous.

[0006] The Al-SiC-based composite alloy and the method for producing the same are described in (1) JP-A-1-501489, (2) JP-A-2-343729, and (3) JP-A-Sho-6.
1-222668 and (4) JP-A-9-1577.
No. 73 is disclosed. (1) relates to a method in which Al in a mixture of SiC and Al is melted and solidified by a casting method. (2) and (3) are both SiC
The present invention relates to a method for infiltrating Al into voids of a porous body. Of these, (3) relates to a so-called pressure infiltration method in which Al is infiltrated under pressure. Further, (4) relates to a method of sintering a compact of a mixed powder of SiC and Al or a hot-pressed compact thereof in a mold and subjecting the compact to a liquid phase sintering at a temperature equal to or higher than the melting point of Al in a vacuum. It is.

The present inventors have disclosed in Japanese Patent Application No. Hei 9-136164 (5) an aluminum-silicon carbide composite material obtained by (5) a liquid phase sintering method and having a thermal conductivity of 180 W / m · K or more. Is presented. This composite material is, for example, 10-7
After molding a mixed powder of 0 wt% of particulate SiC powder and Al powder, it contains 99% by volume of nitrogen and has an oxygen concentration of 20%.
It is obtained by a step of sintering at 600 to 750 ° C in a non-oxidizing atmosphere having 0 ppm or less and a dew point of -20 ° C or less. Further, the present inventors have filed Japanese Patent Application No. 9-93467.
(6) A so-called net-shaped aluminum-silicon carbide having a coefficient of thermal expansion of 18 × 10 ⁻⁶ / ° C. or less, a thermal conductivity of 230 W / m · K or more, and a dimension after sintering close to a practical dimension. Based composites are also presented. Further, the present inventors have proposed in Japanese Patent Application No. 10-41447 a method (7) for producing the same composite material by combining the normal pressure sintering method and the HIP method. According to this, for example, particulate SiC
The Al-SiC-based mixed powder compact of about 70% by weight was mixed in a non-oxidizing atmosphere containing 99% or more of nitrogen gas for 60 days.
Normal pressure sintering in a temperature range of 0 ° C. or higher and Al melting temperature or lower, then sealing in a metal container and H 2 at a temperature of 700 ° C. or higher
By IP, it is homogeneous and its thermal conductivity is 200W
/ M · K or more is obtained.

Further, (8) Japanese Patent Application Laid-Open No. 9-157773 discloses a method in which a mixture of an Al powder and a SiC powder is hot-pressed to simultaneously perform molding and sintering.
The method is to form a mixed powder of 10 to 80% by volume of Al and the balance of SiC, and to form 500 kg /
Hot pressing is performed at a pressure of ² cm ² or more. According to this method, an aluminum-silicon carbide composite material having a thermal conductivity of 150 to 280 W / m · K is obtained.

[0009] Although there are few documents about copper-silicon carbide based composite materials in which the main component metal is replaced by copper instead of aluminum, according to the findings of the present inventors, this composite material is obtained by replacing aluminum with copper. (Hereinafter simply referred to as Cu), it can be obtained by a method substantially similar to the manufacturing method described above. The density of pure Cu is 8.9 g.
/ Cm ³ , its thermal conductivity is about 395 W / m · K,
Its thermal expansion coefficient is about 17 × 10 ⁻⁶ / ° C. Therefore, the density of the composite material obtained is higher than that of an aluminum-based composite material, and the effect of weight reduction is small. Copper, on the other hand, has a thermal conductivity that is about 60% greater than that of aluminum and a coefficient of thermal expansion that is about 40% smaller than that of aluminum. Therefore, it is an advantageous material for manufacturing a substrate material that requires a high thermal conductivity and a low thermal expansion coefficient as compared with aluminum-based materials. Since copper has a much higher melting temperature and a higher weight than aluminum, it is somewhat disadvantageous in terms of manufacturing cost as compared with aluminum.

[0010]

The composite material as described above is used as a substrate which requires a large amount of heat radiation, particularly a heat radiation substrate having a relatively large practical size and a large amount of heat radiation, such as a substrate for a semiconductor power device. In order to do so, there remain some issues to be solved as described below. In particular, when the peripheral members of the substrate have relatively small coefficients of thermal expansion, it is necessary to consider their matching with these members. On the other hand, a material having a higher thermal conductivity than before is required. For example, it is considered that a high thermal conductivity level of a substrate for a semiconductor power device exceeding 280 W / m · K will be required in the future. However,
The silicon carbide-based composite material obtained by the conventional method described above has a thermal conductivity of at most about 260 W / m · K,
In addition, each of the levels decreases with an increase in the amount of SiC. Therefore, it may not be used for a substrate having a low coefficient of thermal expansion.

For example, Japanese Patent Application Laid-Open No. 9-157773 described in the above (8)
No. intended for Al-SiC system described in JP, when you try to its thermal expansion coefficient 10 × 10 ^-6 / ℃ below, the S
iC amount must be 80% by volume or more. As a result, only those having a thermal conductivity of 157 W / m · K or less can be obtained. Further, in the case of the above-mentioned (5) Al-SiC-based material described in Japanese Patent Application No. 9-136164, in order to obtain the same thermal expansion coefficient, the SiC amount must be 60% by volume or more. As a result, only those having a thermal conductivity of about 200 W / m · K can be obtained. Further, even in the case of the one manufactured by the method (7) in which the normal pressure sintering method and the HIP method are combined, if the same thermal expansion coefficient is to be obtained, the SiC amount is 6%.
It must be at least 0% by weight. Therefore 200
Only those having a thermal conductivity of about W / m · K or less can be obtained.

In the method for producing an Al—SiC composite material according to the above (1), the molten Al is poured into a mold,
A casting method in which C particles are dispersed and solidified is used. Therefore, due to the density difference between Al and SiC, Si
Segregation of C particles occurs, and the composition of the solidified body tends to be non-uniform. Therefore, it is inevitable that the surface of the solidified body is covered with a coating layer made of Al or an Al alloy (hereinafter, this layer is also referred to as an Al coating layer). Usually, the thickness of the coating layer varies considerably depending on the location on the surface of the solidified body. Furthermore, since there is a considerable difference in the thermal expansion coefficient between the surface of the solidified body composed of the coating layer and the inside thereof, when heat is transmitted to the interface between them, thermal stress is generated there. Therefore, if this material is used as a heat dissipation board for mounting semiconductor devices while leaving this coating layer, the substrate will be warped or deformed by the generated thermal stress, and as a result, cracks will occur between the semiconductor device and peripheral members and the substrate. Or a semiconductor element or a peripheral member is deformed or broken. Therefore, it is necessary to completely remove this coating layer in advance. In addition, since the thickness of the coating layer varies as described above, the removal is processing of a portion where a soft ductile phase mainly composed of Al and a phase containing SiC having high rigidity coexist. Therefore, it becomes difficult to process.

In the above-mentioned methods (2) and (3) for producing an Al—SiC composite material, Al is infiltrated into the voids of the porous SiC material. In this case, the melting A which is generated during the casting of steel
It is necessary to obtain a dense composite alloy by preventing shrinkage cavities of 1 and completely filling Al in the voids of SiC. For this reason, excess Al is usually disposed as an infiltrant on the outer periphery of the porous SiC body. After the infiltration, the excess Al is eluted and fixed on the outer periphery of the infiltrated body, and it takes a lot of trouble to remove it. In addition, a mixed powder mainly composed of Al and SiC is previously molded and sintered.
In the method described in (5), when the sintering is performed at a temperature exceeding the melting point of Al, the same phenomenon occurs, albeit mildly.

Therefore, in order to prevent such elution and fixation of Al on the outer periphery, as described in (6) above,
Before infiltration, a thin layer made of a mixture of the anti-elution agent and an infiltration accelerator that promotes the infiltration is also applied and formed on the outer periphery of the porous SiC body. However, applying these layers and removing them after infiltration is troublesome.

In the pressure infiltration method (3), a porous SiC body is placed in a mold that can be uniaxially pressed, and Al or an Al alloy is placed on the porous body. This is subjected to a step of forcibly filling the SiC porous body by applying uniaxial pressure from the outside. In this case, finally, the infiltration body is gradually cooled from the lower part with a temperature gradient. At this time, since the difference in thermal expansion coefficient between the SiC skeleton portion inside the infiltrated body and the portion filled with Al is large, Al is pulled into the infiltrated body during cooling and Al is not infiltrated (the above-described shrinkage cavity). (Equivalent to). Therefore, a complicated control mechanism that can simultaneously and accurately control the temperature gradient during cooling and the pressurization / heating program is required. The device is therefore quite expensive.

Further, the method using hot pressing in a mold described in the above (4) has problems in production and quality as described below. For example, when a continuous type hot press device is used, a vacuum atmosphere is set and the temperature is set to A.
In order to increase the melting point to 1 or more, it is necessary to suppress the outflow of the melt out of the mold. Therefore, in order to suppress variations in the component amounts and obtain a target having a uniform composition, an extremely expensive manufacturing apparatus is required. On the other hand, when the apparatus is of a batch type, the outflow of the melt out of the mold can be somewhat suppressed as compared with the continuous type. However, on the other hand, a series of steps of loading the molded body into the mold, holding at a predetermined temperature program and cooling are intermittently repeated,
This method lacks productivity.

As described in detail above, the conventional Al-SiC
There are several quality and production issues associated with the production of composite materials. Therefore, Al-SiC-based composite materials have been used as one of the substrates requiring high heat dissipation, such as semiconductor power modules, despite their recent promising performance. The casting method, the infiltration method, the sintering method, the hot pressing method, or any combination thereof have not been able to obtain satisfactory original performance levels. The following can be considered as one of the reasons. That is, the wettability between Al and SiC is improved to promote spontaneous infiltration of the Al melt between the SiC particles, or a minor component such as Si is added to Al to suppress generation of vacancies. In some cases, Al containing these subcomponents as impurities is used. For this reason, a decrease in the thermal conductivity of the composite material was unavoidable due to the presence of these auxiliary components. In particular, while the SiC itself has a high thermal conductivity comparable or superior to Al, the conventional Al-SiC-based composite material has low thermal conductivity in a composition region where the amount is large.

In general, the thermal conductivity of a substance is a function of the density, specific heat, and thermal diffusivity of the substance as shown in the following equation. Thermal conductivity = Density x Specific heat x Thermal diffusivity Equation (1) Here, in the case of a composite material, the specific heat is determined by the composition ratio of the components. Therefore, if the composition is the same, it is necessary to increase the density and the thermal diffusivity in order to improve the thermal conductivity. In the above-mentioned conventional Al-SiC-based composite material, even if its density is 99% or more, its thermal conductivity is about 200 W / m · K.
In particular, it is necessary to improve the thermal diffusivity.

It is considered that the thermal diffusivity of an Al-SiC-based composite material is determined by the thermal diffusivity of Al and SiC and the state of close contact between the two phases. The degree of adhesion at the interface between the two phases basically improves as the density increases. Therefore, it is considered that the most important point for increasing the thermal diffusivity of the Al-SiC-based composite material is to increase the thermal diffusivity of both component phases, particularly that of the SiC phase.

[0020]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to improve the quality of the conventional silicon carbide composite material described above.
An object of the present invention is to provide an aluminum-silicon carbide-based material and a copper-silicon carbide-based composite material having excellent heat conductivity and a low-cost production method thereof. In order to solve the above-mentioned conventional problems, the present inventors have repeated studies with an emphasis on improving thermal conductivity particularly in a composition region having a large amount of SiC. As a result, Japanese Patent Application No. 10-26003 has already proposed a means that can substantially overcome this problem. However, when such a composite material is used for a heat dissipation board of a power module, particularly for a high output power,
It is expected that a broader main surface will be required in the future. For this reason, it seems that high heat dissipation in the main surface direction is particularly required. The present inventors have continued research to overcome this problem, and as a result, the use of silicon carbide powder composed of specific crystal grains has anisotropy in heat conduction, and extremely high heat conduction in a certain direction. It has been found that a silicon carbide-based composite material exhibiting properties can be obtained.

The thermal conductivity and the anisotropy of a hexagonal SiC single crystal having a plate-like crystal shape are described in, for example, "High Temperature-Hi".
ghPressures "Vol. 29 (1997) No. 7
It is described in a paper by OveNilsson et al. On pages 3-79. Table 1 and Fi on page 78
According to Gure5, the thermal conductivity of the hexagonal 6H single crystal synthesized by vapor phase is 330 W / m · K at room temperature, and decreases with increasing temperature. The table also contains values from other documents, but some data exceed 400 W / m · K. The values in the table are values in the C-axis direction of the crystal, that is, the thickness direction of the sample. The same page also cited other documents and stated that the thermal conductivity in the C-axis direction was 30% lower than that in the direction perpendicular thereto, and they stated, "Assuming that,
The thermal conductivity of the synthesized crystal in the principal plane direction is 470 W / m · K, which is close to that of the highest purity. ” The present inventor has developed a material having excellent thermal conductivity in the main surface direction by using the same hexagonal particles also in the case of polycrystalline powder and combining this with aluminum and copper. Has been advanced.

That is, the silicon carbide-based composite material provided by the present invention is a silicon carbide-based composite material containing a metal mainly composed of aluminum or copper as a first component and particles mainly composed of silicon carbide as a second component. The particles having the aspect ratio of more than 1 and having a thermal conductivity of Kx in a first direction and a thermal conductivity in a second direction orthogonal to the same direction in the particles having the silicon carbide as a main component. Ky, 0.7Kx ≦ Ky ≦ 0.
It is a silicon carbide based composite material satisfying the relationship of 9Kx. The preferable range of the silicon carbide particle amount of this material is 50 to 80% by weight. The present invention also includes the silicon carbide particles having a plate shape, particularly a hexagonal plate shape, and having a thickness in the C-axis direction. In addition, those having an aspect ratio of 1.25 or more are included.

The material of the present invention contains silicon carbide particles,
The oxygen content is 1% by weight or less, the content of the component containing iron is 0.01% by weight or less in terms of iron element, and the content of the component containing aluminum is 0.01% by weight or less in terms of aluminum element. Includes those with high purity and low defects.

When the first component is a metal containing aluminum as a main component, Kx is 300 W / m · K or more, and when the first component is a metal containing copper as a main component, Kx is 330 W / m · K.
The above are preferred. Furthermore, the present invention also includes various semiconductor devices such as power modules using these silicon carbide composite materials.

The method for producing a silicon carbide-based composite material according to the present invention comprises the steps of: preparing a first component composed of a metal containing aluminum or copper as a main component; and a silicon carbide powder composed of plate-like crystal grains having an aspect ratio of more than 1. A step of preparing a raw material containing a second component as a main component, a step of mixing these raw materials to form a mixture, a step of molding the mixture to form a molded body, and forming the molded body into aluminum or copper. And heating to a sintered body at a temperature equal to or higher than the melting point of the metal containing as a main component. This method includes a method in which the mixing amount of the silicon carbide powder is 50 to 80% by weight. Also included are those in which the main surfaces of the crystal grains of the second component powder have a hexagonal plate shape. Also included are those having an aspect ratio of the crystal grains of 1.25 or more. The aspect ratio in this case is a ratio of the maximum diameter (usually the length of a diagonal line) of the main surface of the crystal grain to the thickness. That is, the larger the ratio, the flatter the particles.

The step of forming the sintered body includes a step of heating the formed body at the above-mentioned temperature and further forging it under pressure. In the present invention, this method is also called a forging method. Further, this step includes a step of sintering by heating to the above temperature under normal pressure or mechanical pressure. In the present invention, this method is also called a sintering method. In particular, a method of sintering under mechanical pressure is also called a hot press method. The present invention also includes a heat treatment step of further heating the sintered body obtained by the various methods described above at a temperature Th lower than the melting point Tm of a metal containing aluminum or copper as a main component.

In the above method, in the step of preparing the raw material, the amount of oxygen is 1% by weight or less, the amount of the component containing iron is 0.01% by weight or less in terms of iron element, and the amount of the component containing aluminum is 0.01% by weight or less. May use a silicon carbide powder of 0.01% by weight or less in terms of aluminum element. Such a powder is prepared by mixing silicon carbide powder in an inert gas atmosphere at 1600 to
It can also be obtained through a preheating step of heating in a temperature range of 2400 ° C. Further, such a powder can be obtained by immersing the silicon carbide powder in an aqueous solution containing at least one acid selected from hydrofluoric acid, nitric acid and hydrochloric acid. Such a powder can also be obtained by performing a preliminary heating treatment after the preliminary acid treatment.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION The silicon carbide-based composite material provided by the present invention roughly includes a first component composed of a metal mainly composed of aluminum and a second component mainly composed of silicon carbide. Includes a composite material (hereinafter also referred to as an Al-SiC-based composite material or simply an Al-SiC-based or Al-based material), a first component composed of a metal mainly containing copper, and a second component mainly composed of silicon carbide. Composite material (hereinafter also referred to as Cu-SiC-based composite material or simply Cu-SiC-based, Cu-based)
There is. The present invention focuses on these materials,
(Heat sink), in particular, to improve the thermal conductivity of a heat dissipation substrate for a semiconductor device.

The silicon carbide composite material of the present invention has an aspect ratio of silicon carbide particles exceeding 1, and has anisotropy in heat conduction. That is, the thermal conductivity of the composite material of the present invention in the first direction is Kx, and the thermal conductivity in the second direction orthogonal to the same direction is Ky.
Satisfies the relationship 0.7Kx ≦ Ky ≦ 0.9Kx. In the case of using a composite material to form a plate-shaped heat radiation substrate, the first direction is usually applied to the main surface direction, and the second direction is applied to the thickness direction. Note that both Kx and Ky change substantially according to the compositional rules of the composite material. The same applies to the coefficient of thermal expansion. Some of the composite materials of the present invention have silicon carbide particles having a hexagonal plate shape and a thickness in the C-axis direction. Further, there are particles having the aspect ratio of 1.25 or more.

In the case where the material of the present invention is used for a plate-shaped heat radiation substrate and the thermal conductivity in the main surface direction is to be enhanced, this anisotropy is utilized to the maximum. Therefore, in the production process of the material of the present invention, the main surface of the powder particles is oriented as much as possible in the main surface direction of the substrate. The ratio of Ky and Kx, that is, the degree of anisotropy of heat conduction is mainly affected by this aspect ratio. The greater the ratio, the greater the degree. It is also somewhat affected by the amount of SiC particles. That is, the higher the amount, the higher it. When used as a plate-like substrate as described above, the anisotropy of heat conduction due to this orientation appears remarkably when the amount of SiC is 50% by weight or more. On the other hand, if the amount exceeds 80% by weight, the hard particles are increased, so that molding and sintering become difficult, and finishing after sintering becomes difficult. Therefore, the SiC content of the material of the present invention is in the range of 50 to 80% by weight.

In the material of the present invention, the silicon carbide particles have an oxygen content of 1% by weight or less, an iron-containing component has a content of 0.01% by weight or less in terms of iron element, and an aluminum-containing component. Includes those having a high purity of 0.01% by weight or less in terms of aluminum element and low defects.

The composite material of the present invention described above has a
Although depending on the amount, aspect ratio and purity of the C particles, when the first component is a metal containing aluminum as a main component, the thermal conductivity Kx can be 300 W / m · K or more. Similarly, when the first component is a metal mainly composed of copper, its thermal conductivity Kx can be set to 330 W / m · K or more. Note that the level of the thermal conductivity Kx is affected by the aspect ratio if the amount and purity of the SiC particles are the same. For example, the present invention having an aspect ratio close to 1 and having the same or higher thermal conductivity of 1.25 or more than that of the prior art having an isotropic heat conductivity has a higher Kx. Therefore, if a SiC particle having a high aspect ratio is selected and the main surface of the particle is oriented in the main surface direction of the heat radiation substrate, a material having a high thermal conductivity (in this case, Kx) in the main surface direction can be obtained. Can be In addition, if the material is oriented in the thickness direction, a material having a high thermal conductivity (in this case, Kx) in the thickness direction can be obtained, which is higher than ever before. Similarly, when the main surface is a rectangular substrate, the lengthwise direction of the rectangular substrate can be reduced by taking into account the feeding means during molding and the molding means after feeding.
The main surface of the particles in the width direction can also be oriented.

Next, a method for producing the silicon carbide composite material of the present invention will be described. The method includes, as described above, a first component composed of a metal mainly composed of aluminum or copper and a second component mainly composed of silicon carbide powder composed of crystal grains having an aspect ratio exceeding 1. A step of preparing a raw material, a step of mixing a raw material containing the first component and the second component to form a mixture, a step of molding the mixture to form a molded body, and forming the molded body into aluminum or copper. Heating at a temperature equal to or higher than the melting point of the metal as the main component to form a sintered body. That is, it is characterized in that the above-mentioned material is used as the silicon carbide raw material powder. The mixing amount of the silicon carbide powder is preferably in the range of 50 to 80% by weight. The reason for setting the same amount in this range is as described above. In addition, pressurization at the time of sintering in the above method promotes anisotropy of heat conduction. The same effect can also be obtained by giving anisotropy to the direction of pressing and the direction of molding during powder molding. This is because the main surface of the SiC particles is easily oriented in a direction perpendicular to the pressing direction. It is also effective to apply vibration to the mold after emphasizing powder supply and powder during molding. Hereinafter, the correlation between this method and the level of the thermal conductivity anisotropy and thermal conductivity will be described.

As described above, the anisotropy of heat conduction is promoted by using silicon carbide powder composed of crystal grains having an aspect ratio of more than 1, especially 1.25 or more. The larger the aspect ratio, the better. In particular, it is desirable to be 5 or more. Although there is no upper limit, it is usually up to about 50. If the degree of flatness or the maximum diameter of the main surface becomes too large, the uniform distribution of the particles in the material is impaired. As a result, it is difficult to obtain a homogeneous product. The particles having such a shape may be obtained and used, but may be prepared by applying a high load to the individual particles at the time of pulverization and mixing in a ball mill or the like. Further, as described above, in order to increase the anisotropy of heat conduction of the final material, when the mixed powder is formed, the main surface of the plate-like particles is oriented in a specific direction. For example, suitable molding methods include extrusion molding, injection molding, and doctor blade molding. In the case of sintering the compact as described above, the same effect can be obtained by applying pressure at the same time. For example, a hot press method or a forging method under pressure is suitable for this.
If the pressing direction during sintering is selected so as to further promote the orientation of the particles oriented at the time of molding, the effect is further enhanced.

The means for improving the thermal conductivity level of the composite material of the present invention will be described below. The first is oxygen,
It is to use a silicon carbide raw material powder having a small amount of cationic impurities, particularly impurities containing iron and aluminum. Thereby, the amount of impurities and defects in the obtained silicon carbide crystal particles can be reduced. As a result, although the anisotropy of the thermal conductivity of the composite material has little relation, the level can be increased. In particular, the oxygen content in the crystal particles is 1% by weight or less, and the content of the component containing iron is 0.01% in terms of iron element.
A high-purity silicon carbide powder having a content of a component containing aluminum of 0.01% by weight or less in terms of aluminum element is used, and silicon carbide crystal particles having the same amount of impurities and defects are used. Is desirable. If the amount of oxygen or the amount of impurities including iron and aluminum exceeds this amount, the thermal conductivity may be significantly reduced. As described above, the silicon carbide powder at the impurity level can also be obtained through a preheating step of heating the silicon carbide powder in an inert gas atmosphere in a temperature range of 1600 to 2400 ° C. In this case, it is important that the atmosphere gas does not contain a nitrogen or carbon component which tends to form a lattice defect in the crystal by forming a solid solution in the SiC particles. It is desirable that the pressure of the atmosphere gas be higher. For example, HIP (hot isostatic pressing) treatment may be performed under high pressure. When the temperature is lower than 1600 ° C., the effect of reducing defects in the heat treatment tends to be small. On the other hand, when the temperature exceeds 2400 ° C., sublimation / decomposition of SiC is likely to occur, and the yield may decrease.

Further, such a powder can be obtained by immersing the silicon carbide powder in an aqueous solution containing at least one of hydrofluoric acid, nitric acid and hydrochloric acid. By this treatment, cationic impurities present on the surface of the particles in the powder, impurities containing transition metals such as iron (Fe), chromium (Cr), vanadium (V), nickel (Ni), especially iron (F)
e), oxygen and carbon can be dissolved and removed. This reduces the amount of impurities that cause phonon scattering in the SiC crystal particles, and improves the thermal conductivity of the obtained composite material. That is, these components diffuse from the particle surface to the inside at a high temperature to form defects and easily cause a decrease in thermal conductivity. By performing a pre-heating treatment after the pre-acid treatment, SiC with higher purity and lower defects can be obtained.
A powder is obtained.

It is considered that the carrier concentration in the SiC crystal also affects its thermal diffusivity. Generally, SiC is
It is a material that can be an n-type semiconductor having excess electrons or a p-type semiconductor having excess vacancies. Therefore, as these excess electron and vacancy (carrier) concentrations increase,
This contributes to scattering of phonons in the C crystal particles. Therefore, it is considered that the thermal conductivity of SiC is reduced. S
In iC, there are polymorphs having different crystal forms such as 6H, 4H, 3C, and 15R. As described above, among these, the 6H or 4H type has a high thermal conductivity.
Type SiC is an n-type semiconductor and has a lower carrier concentration than those of other crystal types if the amount of impurities in the crystal is of the same level. Therefore, the SiC raw material used for the silicon carbide based composite material of the present invention is desirably a 6H type. Also in this regard, the SiC powder of the present invention is particularly hexagonal and plate-like,
That is, those made of hexagonal plate-like flat particles are desirable.
The carrier concentration is desirably 1 × 10 ¹⁹ / cm ³ or less. The SiC raw material used for producing the silicon carbide-based composite material of the present invention is desirably of the 6H type in its entirety, but may be partially mixed with another crystal type.

The amount of the impurities present on the surface of the SiC particles can be confirmed by an acid extraction method. The procedure is
The SiC powder is immersed in a mixed acid aqueous solution of nitric acid and hydrofluoric acid maintained at 100 ° C. for about 2 hours to elute impurities present on the surface, and the eluted substance is quantified by IPC emission spectroscopy. When it is desired to check the amount of impurities present inside the SiC particles, the impurities are eluted by the acid decomposition under pressure. In this case, the SiC powder is 190 to 2
It is immersed in a mixed acid aqueous solution of nitric acid and hydrofluoric acid maintained at 30 ° C. for about 40 hours. As a result, impurities not only on the surface of the SiC particles but also inside can be extracted, and the eluate is similarly quantified by IPC emission spectroscopy. Si
The amount of stacking faults of the C particles can be confirmed by directly observing the target SiC particles with a transmission electron microscope.
When confirming the amount of impurities and stacking faults of the SiC particles in the silicon carbide composite material after the compounding, first, the first component is separated and removed with an acid or the like, and the remaining SiC particles are analyzed in a similar procedure. ·evaluate. Note that it is difficult to confirm the carrier concentration of the SiC particles, but it can be confirmed by Raman spectroscopy if the powder is an aggregate of the particles.

The raw material of the first component containing aluminum or copper as a main component may be a commercially available one. However, in order not to lower the thermal conductivity of the produced composite material, it is desirable that its purity is high. For example, it is desirable to use one having 99% or more. The raw material of the first component used in the present invention may be in any form such as a lump, a powder, or the like, but usually a powder is used. As the impurity species interposed in the raw material powder, it is desirable that a component containing a transition metal element particularly easily soluble in aluminum, particularly a component containing a Group 8a element, be as small as possible. Therefore, when a commercially available aluminum alloy powder is used, it is desirable to select a powder having few components for producing these alloys.
In order to further increase the aluminum purity of the raw material powder of aluminum or aluminum alloy, in order to increase the purity of commercially available powder, prepare a powder prepared by melting the powder, a physical or chemical treatment method. There is a need.

As described above, the raw materials used in the present invention are those having the largest possible aspect ratio, high purity and low defect as SiC powder of the second component, and aluminum and copper of the first component. It is desirable to use a high-purity material as a main component. The method of mixing the raw materials may be any existing method as long as the raw material purity does not decrease according to the form and properties of the raw materials. Further, in order to enhance the formability of the mixture, it is preferable to reduce the bulk by, for example, granulating the mixture into granules. The method for molding the mixture may be any ordinary method.

In the method for producing a material according to the present invention, it is desirable to employ a forging method for sintering and solidifying. That is, the above-mentioned forging method promotes not only anisotropy of heat conduction but also an improvement in the level. In particular, as the prior heating method, a method capable of rapid and uniform short-time heating is desirable. For example, the heating during forging is soaked within 15 minutes by an electromagnetic induction method or a plasma induction heating method. Silicon carbide particles are crushed by forging, and penetration into the gaps becomes easy. The interface reactant between the first component and silicon carbide has low thermal conductivity, but generates less. Further, it is better to use a first component having high purity with high thermal conductivity, but a high purity component has poor wettability with silicon carbide. Therefore, in the conventional method, in order to improve the wet adhesion, alloy components are added at the expense of thermal conductivity. However, according to forging, even if a high purity material is used as the first component, it adheres sufficiently by rapid compression and has a relative density of 1%.
00% is easily obtained. Furthermore, the productivity is higher than the conventional method. For the above reasons, when solidified by forging, a dense composite material having high thermal conductivity can be obtained at low cost.

In the manufacturing method of the present invention, as described above, the material obtained in the sintering step may be further heat-treated at a temperature Th lower than the melting point Tm of the first component metal. This means can also increase the thermal conductivity. The reason is that the alloy component solidified in the first component metal is discharged out of the particles by this heat treatment. In this case, it is desirable that the temperature Th of the heat treatment step be a temperature that satisfies the relationship of Th> Tm-100.

[0043]

Examples (Example 1) As raw materials, all had an average particle diameter (in this case, an average of the maximum diameter) of 50 μm.
Table 2 shows the SiC raw material powders subjected to various pretreatments described in Table 2.
And the Cu-based material described in Table 3 were prepared. The carrier concentration of the SiC raw material powder confirmed by Raman spectroscopy was 1 × 10 ¹⁷ /
cm ³ . Note that "None" is displayed in the preliminary processing column of Table 1.
In the description, the corresponding preliminary processing has not been performed. The preliminary acid treatment was performed by a procedure of immersing in an aqueous acid solution having the concentration and temperature shown in the table for the time shown in the table, followed by washing with pure water three times, and drying it with warm air. Therefore, for example, in the case of the raw material S2, the SiC powder of the raw material S1 is first immersed in a 10% hydrofluoric acid aqueous solution at room temperature for 30 minutes, then washed with pure water, and this series of operations is repeated three times. Dehydrated and dried by wind. The preheating treatment is a method in which the powder is charged into a silicon carbide case, the heater is set in a furnace made of tungsten, and is held in an argon gas atmosphere under the same gas pressure and at the described temperature for 1 hour. went. The amount of impurities in each SiC powder described in the same table is a value obtained by dissolving and extracting an impurity-containing component from the powder by the pressurized acid decomposition method under the conditions described above, and analyzing the extract by IPC emission spectroscopy. Is the amount present not only on the particle surface but also on the entire particle including the inside. Table 1
Does not describe the amount of the cation element (transition metal element) other than Fe (iron) according to the present invention, but the amount of each of them was at most 500 ppm in the raw materials of any numbers. Further, the amount of C (carbon) was at most 500 ppm in the raw materials of any numbers. The aspect ratio of the SiC powder particles was determined by dividing the maximum diameter of all the plate-like particles in the field of view of the scanning electron microscope at a magnification of 1000 (the average value in this example is 50 μm) by the thickness of the plate-like particles. Was determined by dividing the aspect ratio by the number of weighed particles. The same applies to that of the sintered body.

[0044]

[Table 1]

[0045]

[Table 2]

[0046]

[Table 3]

Each of the SiC raw material powders shown in Table 1 as the second component, and the Al-based raw material powder A1 shown in Table 2 as the first component
1 or a Cu-based raw material powder C11 described in Table 3 was selected, and a silicon carbide-based composite material specimen containing 50% by weight of SiC was produced by the hot forging method of the present invention in each combination. The raw material column in Table 4 shows combinations of the 28 types of raw materials produced. First, 50% by weight of each SiC raw material powder shown in Table 1 and the remaining 50% by weight were weighed so as to become the raw material powder of A11 or C11, and 3% by weight of paraffin was added as a binder and mixed in ethanol for 3 hours. did. The obtained slurry was spray-dried to obtain a granulated powder. This was pressed by a dry powder molding press at a molding pressure of 7
After molding to a diameter of 100 mm and a thickness of 10 mm at ton / cm ² , the binder was removed at 400 ° C. in the atmosphere to obtain a molded body. Each of these compacts was set in a heating furnace of an electromagnetic induction heating system and heated in the atmosphere. The heating conditions were as follows: the temperature rising rate was 600 ° C./min, and the holding temperature was 6 in the case of Al—SiC system.
70 ° C., 1090 ° C. in the case of Cu—SiC, and a holding time of 10 seconds. Thereafter, these compacts were immediately placed in a separately heated forging die and forged at a pressure of 9 ton / cm ² . The forging die is made of Al-SiC, Cu-S
In each case of iC type, a die steel was used, and the heating temperature of the mold was 450 ° C. in all cases. The final thickness of the forged body was approximately 10 mm for each sample. Thereafter, the sample was finished by grinding. In addition, when the fracture surface in the thickness direction and the surface in the radial direction of the sample forged body using a hexagonal plate-shaped SiC particle having an aspect ratio exceeding 1 were observed with a scanning electron microscope, the SiC plate-like particles in the sample showed that It was confirmed that the main surfaces were arranged substantially along the radial direction of the main surface of the sample. In addition, * mark in a table | surface is a comparative example.

[0048]

[Table 4]

From the apparent density calculated from the actually measured unit weight and volume of each forged body sample, and from the theoretical density calculated from the density of the main component and its composition ratio according to the compound rule, the porosity and relative density (hereinafter referred to as the respective tables) Is simply expressed as “density” in units of%), and the thermal conductivity Kx in the radial direction and the thermal conductivity Ky in the thickness direction of the forged body by the laser flash method.
The coefficient of thermal expansion was determined by a differential transformer type thermal expansion coefficient measuring apparatus, and the amount of impurities in the SiC crystal particles was determined by a combination of the above-mentioned pressurized acid decomposition method and emission spectroscopy. Table 4 shows the results. In addition, using the SiC raw material powder S1 which was separately performed by switching the atmosphere gas of the preheating treatment to a gas containing nitrogen or carbon,
The forged body produced by the same composition / combination with the first component as shown in Table 4 and the same molding / forging procedure has a thermal conductivity that has been subjected to a prior acid treatment, and has an Al—SiC system in the Kx direction. And about 11 in Table 4 and about Cu-SiC sample 2 in Table 4
In the case where the preliminary acid treatment was not performed, the value was lower than that of the pre-acid treatment.
The effect of the preliminary heat treatment was reduced by about m · K and about 250 W / m · K in the case of Cu—SiC.

Separately, SiC powders of S1, S4 to S9 of Table 1 having different aspect ratios were selected as the second component, and Al-SiC samples having SiC contents of 48, 70 and 80% by weight were prepared. The used first component powder, the steps from mixing to finishing, and the contents of evaluation were the same as described above. Although the amount of impurities in the SiC particles of the sintered sample is not shown,
It was the same as that of the same SiC raw material in Table 4. In addition, * mark in a table | surface is a comparative example.

[0051]

[Table 5]

From the above results, the following can be understood.
(1) In a forged body manufactured by the first manufacturing method of the present invention using SiC raw material powder composed of hexagonal plate-like particles having an aspect ratio exceeding 1, the main surface of the SiC particles is oriented in the main surface direction. Then, the thermal conductivity Kx in the same direction becomes larger than that in the thickness direction Ky. The Ky / Kx value decreases as the aspect ratio of the SiC particles increases. That is, the anisotropy of heat conduction increases. If the aspect ratio exceeds 1 and remains the same, the anisotropy increases with the amount of SiC particles. In particular, Table 5
In the embodiment of the present invention, when the amount of SiC is less than 50% by weight, Ky
The aspect ratio at which the / Kx value is 0.9 or less is 2 or more. When the SiC amount is 70% by weight or more, the aspect ratio becomes a value close to 0.7 at an aspect ratio of 10 or more. (2) In the first manufacturing method of forging a molded body of a mixture of the SiC raw material powder and the first component, when the SiC raw material powder is subjected to a preliminary treatment (a preliminary acid treatment or a preliminary heating treatment), the same treatment is not performed. Si compared to
Impurities in the C particles are reduced, and as a result, a material having higher thermal conductivity is obtained. In particular, when a preliminary heating treatment is performed after the preliminary acid treatment, the effect is remarkable. The reason for this is that the amount of impurities in the SiC particles was reduced, and high-speed densification by forging resulted in a material with less occurrence of defects and strains in the particles and high adhesion between the main components. It is thought to be due to.

Example 2 SiC powder of S12 of Table 1, A11 aluminum powder of Table 2 and C11 of Table 3
Using the copper powder, the Al-SiC-based and Cu-SiC-based forged body samples having the SiC amount shown in Table 6 were prepared by the same manufacturing method as in Example 1 (the method of passing through the steps of powder preparation or hot forging). Then, the same evaluation as in Example 1 was performed. Table 5 shows the results. As in Example 1, it was confirmed that the main surfaces of the SiC plate-like particles in the sample were arranged substantially along the main surface direction of the sample.

[0054]

[Table 6]

From the above results, it can be understood that when the amount of SiC composed of plate-like particles having the same aspect ratio is changed to prepare a composite material, the anisotropy of heat conduction increases as the amount increases.

Example 3 The SiC powder of S14 in Table 1 (with an aspect ratio of 5 after pre-acid treatment and pre-heating treatment)
Hex flat plate), A12 aluminum powder in Table 2 and C12 copper powder in Table 3 were used to produce and evaluate Al-SiC-based and Cu-SiC-based composite materials mainly by the second production method of the present invention. Table 7 shows the results. In each sample, the amount of SiC was set to 70% by weight. In the same table, the samples described as dry and extruded in the column of "manufacturing method" are those in which the mixed powder was formed by the dry molding method and the extrusion molding method, respectively. In the same column, the samples described as sintering, HP, and forging were sintered under normal pressure in a nitrogen atmosphere, hot press sintering in a nitrogen atmosphere, and in the air under the same conditions as in Example 1. It was performed by hot forging. For comparison, a sample having the same composition and the same production procedure as in Example 1 was also prepared by a first manufacturing method (forming was performed by dry forming and sintering was performed by hot forging). The procedure for preparing a molded body by dry molding is as follows.
A molded article having the same shape was obtained in the same manner as in Example 1. A molded article by the extrusion molding method was prepared as follows. First, the above raw material powder was weighed at a composition ratio of 70% by weight of SiC, and then methylcellulose as an organic binder was added at 3% by weight based on the total weight of the powder, water and a small amount of a plasticizer were added, and the mixture was kneaded with a kneader for 3 hours. The obtained mixture has a cross section of 120 mm.
An extruded sheet having a width of 12 mm was prepared. This sheet was punched into a disk having a diameter of 110 mm, placed on a metal tray, and dried with hot air to obtain a molded body. Thereafter, the compact is mounted on a smooth silicon carbide tray, and
The organic binder was removed at 00 ° C. In addition, this compact was formed into a disk shape having a size similar to that of Example 1 by sintering.

The hot forging described above was performed under the same conditions as in Example 1. In the normal pressure sintering, each compact is heated at 670 ° C. in an Al—SiC system in a nitrogen stream and 1 ° C. in a Cu—SiC system.
Heating was performed at 090 ° C. for 30 minutes each.
The hot press puts each compact in a silicon carbide mold and raises the temperature.
In the case of the iC type, the procedure was such that a mechanical pressure of 1 MPa was applied at 1090 ° C. in a nitrogen atmosphere. A sample that had undergone a process combining these molding methods and sintering methods was finished to a size of 100 mm in diameter and 10 mm in thickness as in Example 1, and was evaluated in the same procedure as in Example 1. In each case, as in Example 1, the SiC plate-like particles in the sample were:
It was confirmed that the main surfaces were arranged substantially along the main surface direction of the sample. From the results in the table, the extrusion method is more effective for heat conduction anisotropy than the dry molding method.
(Eg, from comparison of samples 60 and 42 in Table 7). In addition, the sintering method is more effective in heat conduction anisotropy when performed under mechanical pressure than under normal pressure (for example, from the comparison of samples 63 and 65 in Table 7).

[0058]

[Table 7]

Example 4 The samples obtained in Examples 1 to 3 and described in the material column of Table 8 below were placed in a nitrogen stream.
Heat treatment was performed for 3 hours at each temperature described in the processing temperature column in the same table.
The results are shown in the same table. The temperature in the melting point column in the table is
The temperature of each material at which the liquid layer of the first component starts to be formed, which was confirmed by differential thermal analysis (DTA). In the table, the thermal conductivity after the heat treatment was obtained in the same manner as in Example 1, and the value was shown. Although the porosity, the relative density, the coefficient of thermal expansion, and the amount of impurities in the SiC particles after the heat treatment were not shown in the same table, they were at substantially the same level as the starting material. The following points can be seen from the results in the table. That is, the heat conductivity of the raw materials produced by the first and second production methods of the present invention is improved by further performing a heat treatment at a temperature lower than the melting point of the metal of the first component of each raw material. The reason for this is that part of the alloy component dissolved in the crystal phase of the first component by this treatment is discharged out of the same phase, so that the lattice distortion of the same phase itself is reduced, and the high thermal conductivity This is considered to be due to being close to the component. The preferable range of the processing temperature Th is less than the melting point Tm of the first component and Tm.
It can also be seen that it is desirable to set the temperature range over -100.

[0060]

[Table 8]

(Example 5) Sample Nos. 1, 4, 14, 15, 18, 28, 48, 55, and 6 of the examples described above.
The silicon carbide-based composite materials obtained by the same method as those of the samples 0, 64, 66, 70, 82, and 84 were each subjected to finish processing into 50 base materials each having a length of 200 mm, a width of 200 mm, and a thickness of 3 mm. This was mounted on a power module as schematically shown in FIG. 1 as a heat radiating substrate, and a temperature cycle test was performed including each mounting step. In FIG. 1, 1
Is a second heat radiation substrate made of the composite material of the present invention, 2 is disposed on the same substrate, on the upper surface thereof (not shown) an electrically insulating first substrate made of ceramics formed with a copper circuit, Reference numeral 3 denotes a Si semiconductor element, and reference numeral 4 denotes a heat dissipation structure disposed below the second heat dissipation board. This jacket,
In this embodiment, a water-cooled jacket is used, but there are also air-cooled fins and the like. It should be noted that wiring and the like around the semiconductor element are omitted in FIG. In the present embodiment, a module in which six Si semiconductor elements are mounted via the first ceramic substrate is used.

Since the first substrate cannot be directly soldered to the second substrate prior to mounting, an electroless nickel plating layer having an average thickness of 10 μm and an average thickness of 5 μm are formed on the main surface of the second substrate in advance.
m of electrolytic nickel plating layer was formed. Each of the four specimens is a 5 mm diameter hemispherical Ag on nickel plating.
A copper wire having a diameter of 1 mm was attached by a Sn-based solder in a direction perpendicular to the plating surface. The substrate body of this sample was fixed to a jig, a copper wire was grasped and pulled in a direction perpendicular to the plating surface, and the adhesion strength of the plating layer to the substrate was confirmed. As a result, the plating layers on any of the substrates were not peeled off even with a tensile force of 1 kg / mm ² or more. Also, 10 samples were taken out of another sample on which the plating layer was formed, and held at −60 ° C. for 30 minutes.
A heat cycle test was performed by repeating 1000 cycles of raising and lowering the temperature at 150 ° C. for 30 minutes, and after the test, the same adhesion strength as above was confirmed. Obtained. From the above results, it was found that the adhesion of the plating to the substrate made of the composite material of the present invention was at a level having no practical problem.

Next, the first ceramic substrate mounted on the second substrate has a thermal conductivity of 150 W / m · K,
Coefficient of thermal expansion 4.5 × 10 ^-6 / ° C, 3-point bending strength 450
A substrate made of aluminum nitride ceramics of MPa, thermal conductivity of 120 W / m · K, and thermal expansion coefficient of 3.7 ×
Eighteen first substrates on which two types of copper circuits were formed, each of which was a substrate B made of silicon nitride ceramic having a ^10-6 / ° C and a three-point bending strength of 1300 MPa, were prepared. Each of these substrates has a length of 90 mm, a width of 60 mm, and a thickness of 1 m.
m. These substrates were arranged at equal intervals in two rows and three columns on a 200 mm square main surface of the second substrate, and were fixed on the surface of the same substrate on which the nickel plating layer was formed by Ag-Sn solder. Next, the back surface side of the second substrate of this assembly and the water-cooled jacket were fixed with bolts closed by applying a silicone oil compound to the contact surface thereof. In this case, the mounting holes of the first substrate were formed by irradiating a carbon dioxide laser to the prepared holes previously formed in the four corners at the material stage and expanding the holes to a diameter of 3 mm. This processing is performed with other ceramic materials, Cu-W, Cu
-Higher accuracy and higher speed than in the case of Mo. This tendency was particularly remarkable as the thermal conductivity increased.

From each of these test pieces, 15 first substrates A and B were selected and subjected to a heat cycle test of 3000 cycles under the same single cycle conditions as described above. The change in output was confirmed. As a result, the output of all modules did not decrease until 1000 cycles, which is considered to be practically no problem. However, regardless of the material type of the first substrate, 1
After 1100 cycles after 000 cycles, it was confirmed that the second substrate had a thermal expansion coefficient of 10 × 10 ⁻⁶ / ° C. or more and a thermal conductivity Kx in the main surface direction of 250 W / m · K or less.
In the case of using the plates Nos. 4 and 4, a slight decrease in the output of the module due to the heat cycle was observed. In particular, one plate having a thermal conductivity Ky of 180 W / m · K and 183 W / m · K
In the case of using a plate No. 4 of K, one out of 15 samples whose output slightly decreased after the completion of 1100 cycles was observed. In the sample in which the output was reduced, generation of a fine crack was observed on the first substrate side of the soldered joint interface between the first and second substrates. The expansion coefficient is 11.0 × 10 ^-6
In the module using 48 at a temperature of / ° C, a slight decrease in output due to the same cause was observed after 15 cycles of 2000 cycles.
One of them was observed. 3000 other than the above
There were no such abnormalities until the end of the cycle.

From the above results, the power module using the first substrate made of the silicon carbide-based composite material of the present invention is:
It can be seen that the level is practically no problem. Among them, the thermal conductivity is 250 W / m · K or more,
In SiC, Kx is 300 W / m · K or more, Cu-SiC
It can be seen that in the system, a material using Kx of 330 W / m · K or more for the first substrate can be used as a large module substrate as described above even under severe thermal cycling conditions.

The material of the present invention was also mounted and evaluated as a heat dissipation board on a semiconductor device mounting device such as a personal computer having a low output and a low heat (cycle) load and a high capacity compared to this type of module. -There was no problem in practical performance.

[0067]

As described in detail above, according to the present invention, as silicon carbide (SiC), powder composed of crystal grains having an aspect ratio exceeding 1 is used to perform directional molding or sintering. By applying pressure, Al-SiC having anisotropic heat conduction is promoted in one direction of the particles.
-Based or Cu-SiC-based silicon carbide based composite material can be provided. This material has a thermal conductivity in the first direction of Kx and a thermal conductivity in a direction orthogonal to the same direction as Ky.
Some have a Ky / Kx ratio in the range of 0.7 to 0.9.
In particular, by setting the amount of SiC particles to 50 to 80% by weight and the aspect ratio of the particles to 1.25 or more, the particles having this ratio can be obtained stably. As a result, by aligning the heat dissipation main surface with the first direction having particularly high thermal conductivity, a heat dissipation board having high heat dissipation efficiency in the main surface direction can be provided. In addition, by preliminarily immersing in an acid or performing a preliminary treatment of heating, using a purified silicon carbide powder material to reduce the amount of impurities including components including transition metals, and performing forging or final solidification by forging, An unprecedented composite material having extremely high thermal conductivity can be obtained. In addition, the step of purifying silicon carbide by the preliminary treatment and / or the step of heating at a temperature lower than the melting point of the Al-based component or Cu-based component after solidification are applied to a conventional sintering method, hot pressing method, or the like. Thereby, the thermal conductivity can be further increased. Therefore, the silicon carbide composite material of the present invention is useful as a heat radiation substrate on which a semiconductor element is mounted, particularly as a highly reliable heat radiation substrate for a high-output power module.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a semiconductor device (power module) using a material of the present invention for a substrate.

[Explanation of symbols]

 1. 1. First substrate made of silicon carbide composite material Second substrate 3. Semiconductor element 4. Heat dissipation structure

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C22C 9/00 C22C 29/06 Z 29/06 32/00 F 32/00 U C22F 1/04 Z C22F 1 / 04 1/00 603 // C22F 1/00 603 627 627 628 628 650F 650 661Z 661 687 687 691B 691 1/08 F 1/08 B22F 3/02 101C H01L 23/373 H01L 23/36 MF term (reference 4K018 AA04 AA15 AB02 AC01 BB01 BC01 BC09 DA18 EA44 FA11 KA32 KA62 4K020 AA22 AC01 AC04 BB26 BB29 BC02 5F036 AA01 BA23 BB01 BD01 BD03 BD14

Claims (17)

[Claims] 1. A silicon carbide-based composite material containing a metal containing aluminum or copper as a main component as a first component and particles containing silicon carbide as a main component as a second component. The particles having an aspect ratio exceeding 1 and having a thermal conductivity in the first direction of the composite material of Kx and a thermal conductivity in the second direction orthogonal to the direction of Ky are 0.7 Kx.
A silicon carbide-based composite material that satisfies the relationship of ≤ Ky ≤ 0.9 Kx. 2. The silicon carbide composite material according to claim 1, wherein the amount of the particles containing silicon carbide as a main component is 50 to 80% by weight. 3. The silicon carbide-based composite material according to claim 1, wherein the silicon carbide particles have a hexagonal plate shape and a thickness in a C-axis direction. 4. The silicon carbide particles have an aspect ratio of:
The silicon carbide-based composite material according to any one of claims 1 to 3, which is 1.25 or more. 5. The silicon carbide particles have an oxygen content of 1% by weight or less, an iron-containing component content of 0.01% by weight or less in terms of iron element, and an aluminum-containing component content of aluminum. The silicon carbide composite material according to any one of claims 1 to 4, which has a high purity of 0.01% by weight or less and a low defect in terms of an element. 6. The first component is a metal containing aluminum as a main component, and the thermal conductivity Kx in the first direction is 3%.
The silicon carbide-based composite material according to any one of claims 1 to 5, which is at least 00 W / mK. 7. The first component is a metal containing copper as a main component, and the thermal conductivity Kx in the first direction is 330 W / m.
The silicon carbide composite material according to any one of claims 1 to 5, which has a K of not less than K. 8. A semiconductor device using the silicon carbide based composite material according to claim 1. 9. A method for producing a silicon carbide composite material comprising a metal mainly composed of aluminum or copper as a first component and particles mainly composed of silicon carbide as a second component. A step of preparing a raw material including a first component composed of a metal as a main component and a second component composed mainly of a silicon carbide powder composed of plate-like crystal grains having an aspect ratio of more than 1; Mixing the mixture to form a mixture, forming the mixture to form a molded body, and heating the molded body at a temperature equal to or higher than the melting point of a metal containing aluminum or copper as a main component to form a sintered body. A method for producing a silicon carbide-based composite material containing: 10. The method for producing a silicon carbide-based composite material according to claim 9, wherein a mixing amount of the silicon carbide powder in the step of forming the mixture is 50 to 80% by weight. 11. The method for producing a silicon carbide-based composite material according to claim 9, wherein said silicon carbide crystal particles are silicon carbide powder having a hexagonal plate shape and a thickness in a C-axis direction. 12. The crystal particles of the silicon carbide powder have an aspect ratio of 1.25 or more.
The method for producing a silicon carbide-based composite material according to any one of the above. 13. The step of forming the sintered body includes a step of heating the formed body at a temperature equal to or higher than the melting point of a metal containing aluminum or copper as a main component and then forging it under pressure. 13. The method for producing a silicon carbide-based composite material according to any one of 12. 14. A heat treatment step of heating the sintered body at a temperature Th lower than the melting point Tm of a metal containing aluminum or copper as a main component after the step of forming the sintered body. The method for producing a silicon carbide-based composite material according to any one of the above. 15. In the step of preparing the raw material, the silicon carbide powder has an oxygen content of 1% by weight or less, an iron-containing component in an amount of 0.01% by weight or less in terms of iron element, and aluminum. The method for producing a silicon carbide-based composite material according to any one of claims 9 to 14, wherein the amount of the component is 0.01% by weight or less in terms of aluminum element. 16. In the step of preparing the raw material, the silicon carbide powder is a powder that has been subjected to a preheating step of heating the silicon carbide powder in an inert gas atmosphere in a temperature range of 1600 to 2400 ° C. Item 16. The method for producing a silicon carbide composite material according to Item 15. 17. A pre-acid treatment step in which the silicon carbide powder is immersed in an aqueous solution containing at least one of hydrofluoric acid, nitric acid and hydrochloric acid in the step of preparing the raw material. The method for producing a silicon carbide-based composite material according to claim 15, which is a powder that has passed through.