JPH11140560A - Production of composite body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suitably use the composite body for a heat sink for a semiconductor device, such as a IC package and wiring board, by impregnating metal into a porous ceramic structure under pressure, at a temp. in a specific range, at a specific rate of temperature decrease. SOLUTION: Cooling velocity, within the region between the solidification point of the metal to be impregnated into the porous ceramic structure and a temp. higher by 50 deg.C than the solidification point, is regulated to a temp.-fall rate of (1 to 20) deg.C/hr. By this procedure, the microstructure of the resultant composite body can be stabilized and reproducibility can be provided, and as a result, the composite body having stable physical properties can be obtained with superior reproducibility in high yield. When silicon carbide, aluminum nitride, silicon nitride, alumina, etc., having high thermal conductivity and low coefficient of thermal expansion, are used for the above ceramic structure, the composite body suitable for a heat sink for semiconductor circuit board can be obtained. Further, it is preferable to use, as the metal to be impregnated, light metal, such as Al and Mg, or alloys thereof for the purpose of attaining high thermal conductivity and lightweight characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat sink for a semiconductor device such as an IC package or a multilayer wiring board.
A composite composed of a metal or alloy and ceramic (hereinafter, “metal-ceramic composite” or simply “composite”
).

[0002]

2. Description of the Related Art In the field of semiconductors, the amount of heat generated by silicon chips is increasing steadily, as LSIs are being integrated and operated at higher speeds, and in recent years, the use of power devices such as GTOs and IGBTs is expanding. . At the same time, circuit boards for dissipating heat generated from silicon chips and heat sinks are required to have higher performance.

More specifically, ceramic circuit boards such as alumina, aluminum nitride, and silicon nitride having good heat conductivity are used for the circuit boards, and the heat conductivity of the heat sink itself that is used by joining the ceramic circuit boards is high. Higher ones are used. Furthermore, when both are combined to form a module, it is desired that the circuit board and the heat sink have similar thermal expansion coefficients. This is due to the heat generated from the semiconductor element during actual use, the generated thermal stress destroys the circuit board, deteriorating the electrical insulation and thermal conductivity of the circuit board, and lowering the reliability as a module This is because it may cause them to do so.

[0004] Under the circumstances described above, in fields where high reliability is important such as electric or vehicle applications such as automobiles, a metal-ceramic composite (hereinafter, referred to as a composite).
Has been applied to heat sinks because the coefficient of thermal expansion is close to that of ceramic circuit boards.
No. 83634, JP-A-9-209058).

[0005] The composite is generally composed of ceramic powder,
A ceramic fiber or the like is formed and, if necessary, fired to produce a porous ceramic structure, which is then impregnated with a molten metal and then cooled.
As a method for impregnating a molten metal, a method based on a powder metallurgy method, for example, a die casting method (Japanese Patent Laid-Open No.
No. Gazette) and molten metal forging (Materia, Vol. 36, No. 1,
1997, pp. 40-46) and various methods such as a method by spontaneous infiltration (JP-A-2-197368).

[0006]

However, in the metal-ceramic composite obtained by the above-mentioned conventionally known method, the molten metal and the ceramic are hardly wet and the pore shape in the ceramic structure is not stable. In addition, the microstructure of the resulting metal-ceramic composite is unstable, possibly due to unstable cooling conditions of the molten metal, and as a result, there is a problem that it is difficult to obtain a composite having stable characteristics.

The present inventors have solved the above problems, and when applied to a ceramic circuit board on which a semiconductor element is mounted, there is no problem that the ceramic circuit board is damaged by a thermal shock in actual use. Further, the present inventors have studied to provide a highly reliable heat sink which has sufficiently high thermal conductivity and hardly malfunctions a semiconductor element, and as a result, the present invention has been accomplished.

[0008]

SUMMARY OF THE INVENTION The present invention relates to a method for producing a composite in which a porous ceramic structure is impregnated with a metal, the method comprising the steps of:
Within the range of high temperature, 1-20 ° C / H under pressure
A method for producing a composite, characterized by impregnating at a temperature decreasing rate of r. In addition, the present invention provides a composite obtained by impregnating a porous ceramic structure with a metal, in a range of a freezing point temperature of the metal and a temperature 50 ° C. higher than the freezing point temperature, from 1 to 20 ° C. This is a method for producing a composite, wherein the treatment is performed at a temperature lowering rate of Hr.

The present invention is the above-mentioned method for producing a composite, wherein the porous ceramic structure comprises at least one selected from the group consisting of silicon carbide, aluminum nitride, silicon nitride, alumina and silica. ,Preferably,
The above-described method for producing a composite, wherein the metal contains aluminum or magnesium as a main component. More preferably, the porous ceramic structure is made of silicon carbide having a porosity of 20 to 50%. Wherein the metal is mainly composed of aluminum.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have studied the manufacturing conditions for obtaining a metal-ceramic composite having a low coefficient of thermal expansion and a high thermal conductivity in a stable manner. The cooling conditions in a specific temperature range when the molten metal solidifies are important, and by sufficiently slowing the cooling rate in the specific temperature range, a reproducible microstructure can be achieved, and as a result, the characteristic The present invention has been completed based on the finding that a stable metal-ceramic composite can be obtained.

The above-mentioned specific temperature range is based on the results of experimental studies by the present inventors, with the lower limit being the freezing point temperature of the metal (or alloy) impregnated in the porous ceramic structure,
The upper limit is a temperature range from the freezing point temperature to 50 ° C.
Here, the freezing point temperature is a temperature at which a molten metal in a liquid phase completely becomes a solid phase. For example, in the case of pure aluminum, the melting point is 660 ° C., and in the case of an aluminum-silicon alloy, the eutectic temperature is 577 ° C. The temperature control may be started at a temperature exceeding 50 ° C. from the freezing point temperature, or the control may be continued at a temperature lower than the freezing point temperature, but the effect of further stabilizing the characteristics cannot be expected, and the productivity is rather lowered. Not so effective.

In the present invention, the cooling rate in the specific range, that is, in the range between the freezing point temperature of the metal and the temperature 50 ° C. higher than the freezing point temperature, is set to a cooling rate of 1 to 20 ° C./Hr. . When controlling the temperature within the temperature range at a specific cooling rate, the microstructure of the obtained composite is stable and has reproducibility, and as a result, the composite having a stable physical property value has good reproducibility and high yield. Therefore, it can be obtained with high productivity. As for the control condition of the temperature decreasing rate, 20 ° C./H
At a temperature lowering rate exceeding r, the effect of characteristic stabilization may not be obtained. The lower limit of the cooling rate is not particularly limited. However, if the cooling rate is lower than 1 ° C./Hr, the effect of further stabilizing the characteristics will not be obtained, but rather the productivity will be reduced, which is not effective.

With respect to the pressure conditions in the above-mentioned specific temperature range, it is sufficient that the pressure is increased, and it is not necessary to set an upper limit on the pressure in order to achieve the object of the present invention. However, if it exceeds 200 MPa, cracks and cracks may occur in the porous ceramic composite, which is not preferable. Even if it is less than 0.5 MPa, the stability of the properties may not be sufficient, and 0.5 MPa to 200 MPa is a preferable range. Is selected as More practically, 1 to 100 MPa is selected as the best range.

It is not always necessary to cool and solidify the molten metal in the porous ceramic structure at a specific cooling rate under pressure and at a specific cooling rate in the above-mentioned specific temperature range to stably exhibit a low coefficient of thermal expansion and a high coefficient of thermal conductivity. The present invention is not limited to the impregnation operation, and may be applied to a metal-ceramic composite obtained through the impregnation operation once. However, from the viewpoint of productivity, it is preferable to apply the treatment of setting a specific cooling rate under a specific temperature range under pressure in the present invention to a specific cooling rate subsequent to the impregnation operation.
Furthermore, in the case of a high-pressure casting method such as a die casting method or a molten metal forging method in which the impregnation operation is performed under pressure, it is only necessary to control the temperature conditions, and the operability is excellent, which is preferable. In addition, when the above operation is applied to the metal-ceramic composite obtained through the impregnation operation, the above operation is performed by using an atmosphere pressurizing device or the like to remove a rare gas such as argon or helium or a non-reactive gas phase such as nitrogen. The above processing can also be performed in the presence.

The porous ceramic structure of the present invention has open pores that can be impregnated with a metal or an alloy,
Moreover, any structure may be used as long as it has mechanical strength that does not break during the impregnation operation. However, when the metal-ceramic composite is applied to a heat sink for a semiconductor circuit board, the thermal conductivity of the metal-ceramic composite is high, and it is difficult to decrease with increasing temperature, and the thermal expansion coefficient is alumina, aluminum nitride. Since it is necessary to be as small as a ceramic circuit board such as silicon nitride or the like, silicon carbide, aluminum nitride, silicon nitride, alumina and the like, which have high thermal conductivity and a low coefficient of thermal expansion, are preferable.

Although silica has a lower thermal conductivity than the ceramics described above, it has a small coefficient of thermal expansion. Therefore, it is possible to bring the coefficient of thermal expansion of the metal-silica composite closer to that of the ceramic substrate with a small amount of addition. There is a feature that can be. Generally, for a metal-ceramic composite,
Regarding the temperature dependence of the thermal conductivity, as the ceramic content in the composite increases, the temperature significantly decreases. However, from the above-described characteristics, the composite obtained using silica exhibits a decrease in the thermal conductivity when the temperature increases. This is also preferable because the same effect as when using the ceramics can be obtained.

Among the above-mentioned ceramics, silicon carbide has a higher thermal conductivity than that of aluminum, which is a metal having a high thermal conductivity, and when silicon carbide is used, the thermal conductivity of a single metal is high. It is particularly preferably selected because a metal-ceramic composite having higher thermal conductivity can be obtained.

The metal used in the present invention may be any metal as long as the object of the present invention can be achieved. However, in order to achieve high thermal conductivity and light weight, aluminum and magnesium are used. And their alloys or alloys thereof are preferred. In the case of an aluminum alloy, AC2A, AC2B, AC4A, AC4 having a Si content of 4 to 10% from the viewpoint of ease of casting and development of high thermal conductivity.
B, AC4C, AC8B, AC4D, AC8C, ADC
Alloys such as 10, ADC12 are particularly preferred.

Regarding the above-mentioned combination of ceramic and metal, an aluminum-silicon carbide composite using aluminum or an aluminum-based alloy as the metal and silicon carbide as the ceramic is lightweight, has a high thermal conductivity, and is compatible with the coefficient of thermal expansion with the ceramic substrate. This is a particularly excellent combination in terms of the above.
The present inventors have conducted various studies on this aluminum-silicon carbide composite, and as a result, have found that the silicon carbide content has a range suitable for achieving the object of the present invention, which has led to the present invention. Things. That is, the silicon carbide content in the aluminum-silicon carbide composite is 50% by volume.
If it is less than 7, the coefficient of thermal expansion may be high, and in this case, the above-described problem due to the difference in the coefficient of thermal expansion from the ceramic substrate tends to occur. Further, when the ceramic has a silicon carbide content of more than 80% by volume due to a decrease in thermal conductivity at a high temperature, when used as a heat sink of a circuit board for mounting a semiconductor, a semiconductor element or the like in actual use is used. The problem that the decrease in thermal conductivity becomes remarkable due to a rise in temperature due to heat generated from the substrate becomes significant. For the above reasons, the silicon carbide content in the aluminum-silicon carbide composite is preferably 50 to 80% by volume, and in order to achieve the above conditions, the porosity of the porous silicon carbide structure is 50%.
-20% by volume is preferred.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

[0021]

[Example 1] Silica sol as a binder was mixed at 5 wt% as a binder with silicon carbide having an average particle diameter of 50 µm at a solid content of 5 wt%. 3mm, porosity 40%
Was produced.

Next, a mold having an inner diameter of 50 mm and a thickness of 25 mm is prepared, and a hole having a depth of 20 mm is provided from the outer surface of the mold.
A thermocouple for measuring the inner surface temperature of the mold was set in the hole. The mold was heated with a burner, and it was confirmed that there was no difference between the measured value of the inner surface temperature of the mold with a contact thermometer and the measured value of the thermocouple for measuring the inner surface temperature of the mold at that time.

After the porous silicon carbide structure is preheated at 800 ° C., it is put into the mold having an inner surface temperature maintained at 710 ° C. by a burner heating, and pure aluminum melted at 900 ° C. is poured into the mold and pressed. Set the stick and 100MP
Pressurized at the pressure of a.

Cooling is performed while maintaining the pressurized state, the strength of the burner is adjusted while observing the measured value of the thermocouple for measuring the inner surface temperature of the mold, and the rate of temperature decrease from 710 ° C. to 660 ° C. is 10 ° C./H.
The pressure was stopped when the burner was turned off at 660 ° C. and cooled to 100 ° C.

Three samples of an aluminum-silicon carbide composite were prepared by the same method, and the thermal conductivity, thermal expansion coefficient and strength of the obtained composite were measured. Table 1 shows the results.

[0026]

[Table 1]

Example 2 The inner surface temperature of the mold at the time of pouring the molten metal was 627 ° C., the temperature range in which the cooling rate was controlled was 627 to 577 ° C., the metal was aluminum-6 wt% silicon alloy, and the melting temperature of the alloy In the same manner as in Example 1, three samples of an aluminum alloy-silicon carbide composite were prepared, and the thermal conductivity, the coefficient of thermal expansion, and the strength of the obtained composite were measured. Are shown in Table 2.

[0028]

[Table 2]

Example 3 Three samples of an aluminum alloy-silicon carbide composite were prepared in the same manner as in Example 2 except that the cooling rate was 20 ° C./Hr, and the thermal conductivity of the obtained composite was , Thermal expansion coefficient and strength were measured, and the results are shown in Table 3.

[0030]

[Table 3]

Example 4 Three samples of an aluminum alloy-silicon carbide composite were prepared in the same manner as in Example 2 except that the pressure was 200 MPa, and the thermal conductivity and thermal expansion coefficient of the obtained composite were And the strength were measured, and the results shown in Table 4 were obtained.

[0032]

[Table 4]

Example 5 Three samples of an aluminum alloy-silicon carbide composite were prepared in the same manner as in Example 2 except that the pressure was 0.5 MPa, and the thermal conductivity and heat of the obtained composite were measured. The expansion coefficient and strength were measured, and the results shown in Table 5 were obtained.

[0034]

[Table 5]

Example 6 Three samples of an aluminum alloy-silicon carbide composite were prepared in the same manner as in Example 4 except that the pressure was 220 MPa, and the thermal conductivity and thermal expansion coefficient of the obtained composite were measured. And the strength were measured, and the results shown in Table 6 were obtained.

[0036]

[Table 6]

[Comparative Example 1] The cooling rate from 650 ° C to 600 ° C was 10 ° C / Hr, and the cooling rate below 600 ° C was 25.
Three samples of an aluminum alloy-silicon carbide composite were prepared in the same manner as in Example 2 except that the temperature was not less than ° C / Hr, and the thermal conductivity, thermal expansion coefficient, and strength of the obtained composite were measured. 7 were obtained. As compared with Example 2,
It became clear that the thermal conductivity, coefficient of thermal expansion and strength were not stable.

[0038]

[Table 7]

[Comparative Example 2] The cooling rate from 600 ° C to 550 ° C was 10 ° C / Hr, and the cooling rate at 550 ° C or less was 25.
Three samples of an aluminum alloy-silicon carbide composite were prepared in the same manner as in Example 2 except that the temperature was not less than ° C / Hr, and the thermal conductivity, thermal expansion coefficient, and strength of the obtained composite were measured. 8 were obtained. As compared with Example 2,
It became clear that the thermal conductivity, coefficient of thermal expansion and strength were not stable.

[0040]

[Table 8]

Comparative Example 3 Three samples of an aluminum alloy-silicon carbide composite were prepared in the same manner as in Example 3 except that the temperature drop rate was 25 ° C./Hr, and the thermal conductivity of the obtained composite was , Thermal expansion coefficient and strength were measured, and the results shown in Table 9 were obtained. Compared with Example 3, it became clear that the thermal conductivity, the coefficient of thermal expansion, and the strength were not stable.

[0042]

[Table 9]

[Comparative Example 4] Normal pressure (0.1 MPa)
In the same manner as in Example 5, three samples of an aluminum alloy-silicon carbide composite were prepared, and the thermal conductivity, the coefficient of thermal expansion, and the strength of the obtained composite were measured.
Were obtained. It became clear that the thermal conductivity, the coefficient of thermal expansion and the strength were not stable as compared with Example 5.

[0044]

[Table 10]

[0045]

According to the present invention, a metal-ceramic composite having stable characteristics such as thermal conductivity, thermal expansion coefficient and strength can be manufactured with a high yield, and a highly reliable metal-ceramic composite can be obtained. Since it can be provided stably at low cost, it is extremely useful in industry.

The metal-ceramic composite produced by the method of the present invention is particularly suitable as a heat-radiating component for electronic components and a heat-sink material for ceramic circuit boards because of its high thermal conductivity, low thermal expansion and light weight. is there.

The metal-ceramic composite of the present invention has a light weight and a mechanical property, and therefore is not intended for heat sink use.
For example, it is also useful for metal replacement materials in the transportation and aviation fields.

Claims (5)

[Claims] 1. A method for producing a composite in which a porous ceramic structure is impregnated with a metal, wherein a temperature within a range between a freezing point temperature of the metal and a temperature 50 ° C. higher than the freezing point temperature is 1 to 20 under pressure. A method for producing a composite, comprising impregnating at a temperature lowering rate of ° C./Hr. 2. A method comprising impregnating a composite obtained by impregnating a porous ceramic structure with a metal in a range between a freezing point temperature of the metal and a temperature 50 ° C. higher than the freezing point temperature by 1 to 2 under pressure.
A method for producing a composite, comprising treating at a temperature lowering rate of 0 ° C./Hr. 3. The porous ceramic structure is silicon carbide,
The method for producing a composite according to claim 1, wherein the composite comprises at least one selected from the group consisting of aluminum nitride, silicon nitride, alumina, and silica. 4. The method for producing a composite according to claim 1, wherein the metal contains aluminum or magnesium as a main component. 5. The porous ceramic structure according to claim 1, wherein the porous ceramic structure is made of silicon carbide having a porosity of 20 to 50%, and the metal is mainly aluminum. A method for producing the composite according to claim 4.