JPH0964254A - Heat radiating member for semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To raise time thermal conductivity by using metal compound material containing carbon fibers of a specific length in a specific range of volume, and having a thermal expansion coefficient being in a specific range by their reaction with a metal component. SOLUTION: Metal compound material contains fibers of lengths of 40μm or less and a metal component composed of either Cu or Al, and has a thermal expansion coefficient of 5×10<-6> -10×10<-6> . Especially, reactivity of the metal component with the carbon fibers can be enhanced, by adding 0.3-5wt.% of at least one kind of metal out of Ti, Zr, Cr, and Si to the metal compound material. Besides, sinterability can be enhanced by adding 0.3-8wt.% of at least one kind of metal different from the metal component out of Si, Ag, Sn, P, Al, and Cu to the metal compound material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat dissipation member for a semiconductor device to be mounted on a substrate on which various semiconductor elements are mounted.

[0002]

2. Description of the Related Art One of the major problems of electronic equipment-related products is how to dissipate heat. LS for that purpose
A semiconductor device such as an I package or an optical semiconductor package is provided with a heat dissipation member called a heat spreader or a heat sink (FIGS. 2A and 2B).
FIG. 2C). The characteristic required for this member is that it has a high thermal conductivity in order to dissipate heat (100 to 20).
0 W / m · k), and the coefficient of thermal expansion is the same as that of the substrate because it is bonded to the ceramics or glass substrate (5 to 5)
10 × 10 ⁻⁶ / k). At present, an alloy of copper and tungsten (hereinafter abbreviated as Cu-W alloy) is often used as a material satisfying these characteristics. In reference,
Table 1 shows a characteristic example of a commercially available Cu-W alloy.

[0003]

[Table 1]

[0004]

C currently in widespread use
The u-W alloy is an alloy selected so as to have the same coefficient of thermal expansion for bonding with the ceramic of the substrate material and to have high thermal conductivity. However, since this material uses tungsten, the raw material cost is high,
There is a problem that the specific gravity is large. Further, there is a problem that workability is generally poor, and development of alternative materials has been desired.

Further, Japanese Utility Model Application Laid-Open No. 55-141953 and Japanese Utility Model Application Laid-Open No. 58-11254 disclose heat-dissipating materials in which carbon fiber is contained in copper. Therefore, it is three-dimensionally anisotropic. Therefore, there is a problem that the thermal conductivity and the thermal expansion coefficient are directional, and the handling thereof is difficult.

An object of the present invention is to provide a heat dissipation member for a semiconductor device, which has a performance equivalent to that of a Cu-W alloy at low cost.

[0007]

The present invention has been made in view of the problems of the prior art as described above, and its main purpose is to provide carbon fibers having a length of 40 μm or less in an amount of 65% by volume to 90% by volume. And a metal component made of either Cu or Al, and having a coefficient of thermal expansion of 5 × 10 ⁻⁶ to 10 ×.
^Another object of the present invention is to provide a heat dissipation member for a semiconductor device, which is made of a metal composite material of 10 ⁻⁶ or less. In particular, 0.3 wt% to 5 wt% of at least one metal selected from Ti, Zr, Cr and Si is added to the metal composite material in order to improve the reactivity between the metal component and the carbon fiber. In addition, in order to improve sinterability, at least one metal different from the metal component of Si, Ag, Sn, P, Al and Cu is added to the metal composite material by 0.3.
It is advisable to add from 8% to 8% by weight.

As the inorganic material, graphite powder and carbon fiber, which have high thermal conductivity, small thermal expansion coefficient, and low cost, are suitable, but the elastic modulus of graphite powder and carbon fiber is 20 GP.
a is significantly different from 400 GPa, and short fibers of carbon fibers or powder thereof having a large elastic modulus are more effective in achieving the desired low thermal expansion. Regarding carbon fibers, long fibers have anisotropy when compounded with a metal, and thus it is desirable to use short fibers (length 40 μm or less) or pulverize to obtain powder. Short fibers or pulverized powder eliminates the anisotropy peculiar to fibers, and a three-dimensional isotropic composite material can be obtained. In addition, the coefficient of thermal expansion of a composite material can be simply calculated by the following formula in an ideal state (reference document: Composite material dictionary Asakura Shoten).

Α _c = (α ₁ K ₁ X ₁ + α ₂ K ₂ X ₂ ) / (K ₁ X ₁ + K ₂ X ₂ ) α _c : thermal expansion coefficient of composite material α _i : thermal expansion coefficient of i component K _i : bulk modulus of the i component X _i : volume fraction of the i component

Although copper and carbon fibers do not react with each other, it is difficult to sinter them. However, by hot-pressing (hereinafter abbreviated as H / P) carbon powder and copper powder by pulverizing and mixing (mechanical alloying). ) Can be sintered. Further, by pulverizing the carbon fiber to 40 μm or less, the sinterability is increased, and a three-dimensional isotropic sintered body that does not cause the anisotropy peculiar to the fiber is obtained.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

Table 2 shows the results of various combinations of composite materials composed of an inorganic material and a metal material.

[0013]

[Table 2]

The sinterability was expressed in the following three stages. △: Pressurized with H / P to sinter to some extent (sintered density 85%
~ 90%) ○: Can be completely sintered by pressing with H / P (sintered density 90% ~
99%) ◎: Pressureless sintering is possible after molding

The above composite material is manufactured by a ball mill mixing method (mechanical alloying method) using steel balls, and H /
Sintered with P. The sintering conditions were held in vacuum (1030 ° C. when the metal component was Cu, 600 ° C. when Al was used) for 10 hours, and a load of 4 kgf / mm ^{2 was} applied.

According to Table 2, when graphite powder is used, the sinterability is poor because 92 vol% or more of graphite is required to obtain the desired coefficient of thermal expansion. However, when the carbon fiber is used, it can be seen that the effect of lowering the coefficient of thermal expansion is great even with a small amount because the elastic modulus of the carbon fiber is high.

Further, in the metal component (Al, Cu) and the carbon fiber-based metal composite material, since the metal component and the carbon fiber do not actually react with each other, the thermal conductivity tends to be lower than the predicted value, and the carbon If the fiber content increases, the sinterability deteriorates. When the third element was added to improve reactivity and sinterability, the following effects were obtained.

An element (Ti,
The thermal conductivity was improved by adding 0.3 wt% to 5 wt% of Zr, Cr, Si). If it is less than 0.3 wt%, there is almost no effect, and if it exceeds 5 wt%, the reaction layer becomes too thick and the whole becomes brittle, and the reaction layer lowers the thermal conductivity. Elements that form a liquid layer in the metal component during sintering (Si, Ag,
The sinterability was improved by adding 0.3 wt% to 8 wt% of Sn, P, Al, Cu). If it is less than 0.3% by weight, there is no effect of improving sinterability, and if it is added in excess of 8% by weight, too much liquid phase appears to improve sinterability,
There is a risk of melting the whole.

In order to obtain the desired coefficient of thermal expansion,
Table 3 shows the results of the examination conducted by changing the compounding ratio of the carbon fibers.
If the carbon fiber content is 65% by volume or more, a coefficient of thermal expansion capable of joining with ceramics is given, and the thermal conductivity also satisfies the required value.
When the carbon fiber content is less than 65% by volume, the thermal conductivity is good,
The coefficient of thermal expansion gives a value that cannot be joined to ceramics.

[0020]

[Table 3]

FIG. 1 shows a micrograph of the metal structure of an example of a sintered body of the copper-carbon fiber composite material of this example. This sintered body has a thermal conductivity of 203 W / m · K (at R.
T. ), Thermal expansion coefficient 10 × 10 ⁻⁶ / K (50 ° C. to 200 ° C.)
C)), which satisfies the characteristics required for the heat spreader. As a result, when the heat spreader and the ceramics substrate are joined together during manufacturing of the package, the ceramics substrate is not destroyed, and thermal stress due to the heating / cooling cycle is not generated during the operation of the package.

[0022]

According to the heat dissipating member for a semiconductor device made of the composite material of the present invention, the heat conductivity is improved by using copper or aluminum as a matrix, and the carbon fiber having a length of 40 μm or less is 65% by volume to 90% by volume. By blending in a volume percentage, the coefficient of thermal expansion can be lowered within a target range, and a three-dimensional isotropic sintered body can be obtained. Here, the coefficient of thermal expansion can be adjusted by changing the compounding ratio of the carbon fibers depending on the substrates to be joined. Moreover, the raw material cost is reduced by using the inexpensive carbon fiber.

[Brief description of drawings]

FIG. 1 is a micrograph showing a metal structure of a sintered body of a copper-carbon fiber-based metal composite material as a heat dissipation member for a semiconductor device to which the present invention is applied.

FIG. 2 is a perspective view showing a package structure of a general semiconductor device.

Claims (3)

[Claims] 1. A carbon fiber containing 65% by volume to 90% by volume of carbon fiber having a length of 40 μm or less and a metal component made of either Cu or Al, and having a coefficient of thermal expansion of 5 × 10 ^−6.
A heat dissipation member for a semiconductor device, which is made of a metal composite material of 10 to 10 ^-6 or less. 2. The metal composite material is provided with Ti, Zr, in order to improve the reactivity between the metal component and the carbon fiber.
The heat dissipation member for a semiconductor device according to claim 1, wherein at least one kind of metal selected from the group consisting of Cr and Si is added in an amount of 0.3% by weight to 5% by weight. 3. The metal composite material contains at least one kind of metal different from the metal component of Si, Ag, Sn, P, Al and Cu for improving sinterability.
The heat dissipating member for a semiconductor device according to claim 1 or 2, wherein 3 wt% to 8 wt% is added.