JP3855583B2 - Composite - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a composite material of carbon fiber and metal, for example, a composite material suitable as a heat radiating member of a semiconductor device or an electronic component mounting substrate.
[0002]
[Prior art]
Conventionally, JP-A-4-147654 has proposed a composite material in which carbon fiber is contained in aluminum or an aluminum alloy as this type of electronic component mounting base material. This composite material is manufactured by impregnating aluminum at high pressure into a carbon fiber preform that is obtained by dispersing pitch-based carbon fibers in a solvent and stirring and filtering them.
[0003]
Japanese Patent Laid-Open No. 11-49578 discloses a graphitized carbon matrix as a heat radiating member for a semiconductor device, and graphitized carbon long fibers parallel to an electronic component mounting surface at a right angle or at a predetermined angle in a two-dimensional plane. There has been proposed a graphitized carbon fiber / graphitized carbon composite having a group of fibers arranged in a pseudo-isotropic manner and oriented in a direction perpendicular to the electronic component mounting surface. This composite is produced by repeating a graphitization process of impregnation with a pitch resin, carbonization, and graphitization multiple times on graphitized carbon fibers woven in three dimensions.
[0004]
[Problems to be solved by the invention]
The composite material disclosed in Japanese Patent Application Laid-Open No. 11-49578 has thermal characteristics suitable for a heat radiating member for a semiconductor device, both in terms of thermal conductivity and thermal expansion coefficient. However, in order to produce this composite material, it is necessary to repeat the graphitization process steps of impregnation with the pitch resin, carbonization, and graphitization several times on the three-dimensional woven fabric of graphitized carbon fiber, which reduces the production cost. Get higher.
[0005]
In addition, graphitized carbon fiber is weak in bending because of its small fracture strain, and is easily cut by rubbing yarns (fibers) when manufacturing a three-dimensional woven fabric, and in particular, the yarn for bonding the fiber layers is easily cut. Therefore, there is also a problem that productivity is poor.
[0006]
In the composite material disclosed in Japanese Patent Laid-Open No. 4-147654, the thermal expansion coefficient of the pitch-based carbon fiber constituting the reinforcing fiber is small, so that the thermal expansion coefficient of the entire composite material is smaller than that of aluminum. However, because the short fibers are randomly dispersed in the matrix, the thermal expansion coefficient of the composite material is simply determined by the ratio of aluminum and carbon fibers, and the carbon fibers have a function of actively suppressing the expansion of aluminum. Therefore, it is difficult to reduce the amount of expansion of the composite material.
[0007]
The present invention has been made in view of the above-described conventional problems, and has an object of having thermal conductivity necessary when used as a heat dissipation member or an electronic component mounting substrate of a semiconductor device, and at least An object of the present invention is to provide a composite material that has a low coefficient of thermal expansion on the side facing the semiconductor device and can be manufactured at low cost.
[0008]
[Means for Solving the Problems]
In the invention described in claim 1 for achieving the above object, the metal member formed in a predetermined shape by metal having excellent thermal conductivity, on at least two sides including the electronic component mounting surface side, the carbon consisting of long fibers predetermined rate for the fiber to suppress expansion of the metal to or below a predetermined amount, and array in a predetermined direction an embedded state.
[0009]
In the composite material of the present invention, sufficient heat dissipation is ensured by the metal member having good thermal conductivity in the entire composite material. Further, on the side on which the electronic component is mounted, the thermal expansion of the metal is suppressed by the long carbon fibers arranged in a predetermined direction. Therefore, even when used as a heat dissipation member of a semiconductor device having a small coefficient of thermal expansion, it is possible to suppress an excessive thermal stress from acting on the semiconductor device. Further, the productivity is high and the cost is low as compared with a case where the whole is a composite of a three-dimensional carbon fiber structure and graphitized carbon. Furthermore, in this invention, the expansion rate of the entire composite material is reduced and the composite material is less likely to warp as compared with the carbon fibers arranged on one side.
[0010]
According to a second aspect of the present invention, in the first aspect of the present invention, the carbon fibers are arranged in the X and Y2 directions. Therefore, in this invention, expansion of the composite material in the two directions X and Y is uniformly suppressed.
[0012]
In invention of Claim 3 , in the invention of Claim 1 or Claim 2 , the said metal is copper. Therefore, according to the present invention, a composite having a high thermal conductivity can be produced at a low cost, and since the wettability with the carbon fiber is better than that with aluminum, the effect of suppressing the thermal expansion of the metal by the carbon fiber is improved.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
As shown in FIG. 1, the composite material 1 is configured by embedding carbon fibers 3 on one side of a square plate-like metal member 2. Copper having a good thermal conductivity is used for the metal member 2. The carbon fiber 3 is composed of a woven fabric (plain woven fabric) 4 arranged in two directions perpendicular to each other, and a part of the woven fabric 4 is exposed on the surface of the metal member 2 and the arrangement direction of the carbon fibers 3 is It is embedded along the X and Y directions of the composite material.
[0014]
As the carbon fiber 3, a relatively inexpensive PAN-based carbon fiber (polyacrylonitrile-based carbon fiber) is used. Each carbon fiber 3 is used in a roving (tow) state. Roving (tow) means a substantially untwisted fiber bundle in which a large number of thin filaments (long fibers) are bundled. The texture of the fabric 4 is set so that the carbon fiber 3 has a predetermined ratio for suppressing the expansion of the metal member 2 in the portion where the carbon fiber 3 is embedded to a predetermined amount or less. The roughness of the eyes is set so that the volume ratio of carbon fiber 3 is in the range of 30% to 50% in the portion where carbon fiber 3 is embedded. That is, in FIG. 2, the volume ratio of the carbon fibers 3 included in the portion of the thickness t in which the carbon fibers 3 are embedded is set to be 30% to 50%. Accordingly, the fabric 4 having a mesh size that is approximately the same as the thickness of the carbon fiber 3 to about twice that of the carbon fiber 3 is used. In FIGS. 1 and 2, the roughness of the eyes is shown to be coarser than the actual.
[0015]
The range of the carbon fiber content was determined from the relationship between the volume content (%) of carbon fiber and the linear expansion coefficient and thermal conductivity of the composite material when carbon fiber and copper were combined. As shown in FIG. 3, the thermal conductivity of the carbon fiber and copper composite material (CF / Cu composite material) decreases in proportion to the volume content of the carbon fiber, and the linear expansion coefficient becomes the volume content of the carbon fiber. Decreases almost proportionally. The linear expansion coefficient is close to the value of silicon, and even when thermal expansion occurs when the composite material 1 of the present invention is used as a heat radiating member, no excessive stress is generated on the member that requires heat radiation. The volume content of the carbon fiber is set so as to be in the range A shown. With the volume content in this range A, the thermal conductivity is about 200 W / (mK) or more, which is larger than 150 W / (mK) of the thermal conductivity of the heat dissipation member currently used for semiconductor chips.
[0016]
The composite material 1 having the above-described structure is a fabric in which a carbon fiber fabric 4 is placed in a mold with a predetermined tension applied or without tension, and molten copper is poured under high temperature and high pressure. 4 is embedded in copper and impregnated with copper in the voids of carbon fibers constituting the fabric 4.
[0017]
When the composite material 1 configured as described above is used as, for example, a heat dissipation member for a semiconductor device, the composite material 1 is cut into a predetermined size. Then, the carbon fiber 3 side surface is bonded to the semiconductor chip via silver paste or solder, and the heat sink is bonded to the side opposite to the bonding surface with the semiconductor chip as necessary.
[0018]
This embodiment has the following effects.
(1) In the composite material 1, since the carbon fibers 3 made of long fibers arranged in an embedded state on the semiconductor device mounting surface side suppress the expansion of copper, at least the expansion rate on the mounting surface side becomes the expansion rate of the semiconductor device. A close value. Therefore, when used as a heat radiating member of a semiconductor device, an excessive stress is prevented from acting on the semiconductor device, and it can be suitably used as a heat radiating member utilizing the properties of copper having good thermal conductivity.
[0019]
(2) The carbon fibers 3 are provided in a predetermined ratio and in an embedded state in order to suppress metal expansion to a predetermined amount or less. Therefore, the amount of the carbon fiber 3 can be minimized, the raw material cost can be reduced, and the manufacturing cost of the composite material can be reduced.
[0020]
(3) Since the carbon fibers 3 are arranged in the X and Y2 directions, expansion of the composite material in the X and Y directions is evenly suppressed.
(4) Since the carbon fiber 3 is composed of the plain woven fabric 4, the volume content of the carbon fiber 3 can be easily adjusted by adjusting the roughness of the woven fabric 4 when the volume content is adjusted to a desired value. Moreover, when manufacturing the composite material 1, it becomes easy to arrange the carbon fibers 3 in the X and Y2 directions, and the manufacturing becomes easy.
[0021]
(5) Since copper is used as the material of the metal member 2, a composite with high thermal conductivity can be produced at low cost, and the impregnation process is easy because the wettability with carbon fiber is better than aluminum. Become.
[0022]
(6) A PAN-based carbon fiber that is relatively inexpensive and is superior to the pitch-based carbon fiber with respect to bending and rubbing is used for the carbon fiber 3. Therefore, when manufacturing the fabric 4, it can be manufactured in a state in which the fluff and thread breakage of the carbon fiber are suppressed, and the manufacturing cost can be reduced.
[0023]
The embodiment is not limited to the above, and may be embodied as follows, for example.
The carbon fibers 3 may be provided not only on one side of the composite material 1 but also on both surfaces of the composite material 1 as shown in FIG. 4, or evenly provided on the entire composite material 1 as shown in FIG. When carbon fibers are arranged only on one side of the composite material 1, the composite material 1 may be warped at a high temperature, but by arranging the carbon fibers on both sides or the whole, the composite material 1 is warped at a high temperature. Can be prevented.
[0024]
A pitch-based carbon fiber may be used as the carbon fiber 3 instead of the PAN-based carbon fiber. The pitch-based carbon fiber has a higher tensile elastic modulus and has the same expansion suppressing effect with a small amount, and the copper content can be increased to increase the thermal conductivity.
[0025]
O The metal which comprises a matrix is not restricted to Cu, What is necessary is just to have the thermal conductivity equivalent to or more than aluminum. For example, in a composite material used as a heat radiating member that does not require much thermal conductivity, aluminum is used for the metal. FIG. 6 shows the relationship between the carbon fiber volume content, the thermal conductivity, and the linear expansion coefficient in the carbon fiber and aluminum composite material (CF / Al composite material). In order for the linear expansion coefficient of the CF / Al composite material to have a value in the same range as that of the CF / Cu composite material, the volume content of the carbon fiber is approximately 35% to 55%. It becomes. Aluminum has a thermal conductivity of about 60% of Cu, but its density is almost 1/3, which contributes to weight reduction. Further, since the melting point of aluminum is 660 ° C. and 400 ° C. lower than the melting point of Cu, the temperature during impregnation can be lowered, and the energy required for melting is reduced.
[0026]
When the composite material 1 is used as a heat radiating material for a semiconductor device, as shown in FIG. 7, it may be used by cutting into a shape having a large number of heat radiating fins 5 on the side opposite to the side attached to the semiconductor device. Good. Even when carbon fibers are arranged on both sides or the whole of the composite material 1, fins may be formed on one side. In the case of graphitized carbon fiber / graphitized carbon composite, such processing is difficult, but processing using a metal as a matrix is relatively easy. In this case, the number of parts and the number of assembling steps are reduced as compared with the case where a heat sink of another part is used.
[0027]
The arrangement direction of the carbon fibers 3 is not necessarily limited to the two axes X and Y, but a set of two layers arranged so as to be inclined at a predetermined angle (for example, ± 45 °) with respect to the two axes X and Y A bias yarn may be included. In this case, the shape stability of the composite material 1 is improved.
[0028]
In the configuration in which the woven fabric 4 is arranged on one side or both sides of the metal member 2, the number of the woven fabric 4 is not limited to one and may be a plurality.
○ Instead of arranging the carbon fibers 3 in the form of the woven fabric 4 in which the carbon fibers 3 are arranged in two directions, the roving of the carbon fibers may be arranged alternately in two layers or three or more layers in the X direction and the Y direction. . In this case, compared with the fabric 4, it becomes possible to arrange the carbon fibers arranged in a predetermined direction in a straight state, and the function of the carbon fibers to suppress the thermal expansion of the metal is enhanced.
[0029]
About technique Sube思virtual that can be grasped from the above embodiment will be described in conjunction with the effects below.
(1) Before Symbol composite is used as a heat radiating member, a plurality of heat radiation fins are formed on the opposite side with its mounting surface. In this case, the number of parts and the number of assembly steps can be reduced as compared with the case where a heat sink of another part is used.
[0030]
(2) pre-SL carbon fiber is composed of fabrics that are arranged in two directions in which the fibers are orthogonal. In this case, the arrangement of the carbon fibers is simplified, and the volume content of the carbon fibers can be easily adjusted by the roughness of the fabric.
[0031]
(3) PAN-based carbon fibers are used as a pre-SL carbon fibers. In this case, since the PAN-based carbon fiber is cheaper than the pitch-based carbon fiber and excellent in bending and rubbing, the manufacturing cost is reduced and the carbon fibers can be easily arranged in a woven state. Become.
[0032]
【The invention's effect】
As described above in detail, the invention according to claims 1 to 3 has a thermal conductivity required when used as a heat dissipation member or an electronic component mounting substrate of a semiconductor device, and at least faces the semiconductor device. The coefficient of thermal expansion on the side to be used is low and can be manufactured at low cost.
[Brief description of the drawings]
FIG. 1 is a schematic perspective view of a composite material according to an embodiment.
FIG. 2 is a schematic sectional view of the same.
FIG. 3 is a graph showing the relationship between the CF volume content, the linear expansion coefficient, and the thermal conductivity of a CF / Cu composite material.
FIG. 4 is a schematic cross-sectional view of a composite material according to another embodiment.
FIG. 5 is a schematic cross-sectional view of a composite material according to another embodiment.
FIG. 6 is a graph showing the relationship between the CF volume content, the linear expansion coefficient, and the thermal conductivity of a CF / Al composite material.
FIG. 7 is a schematic cross-sectional view of a composite material according to another embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Composite material, 2 ... Metal member, 3 ... Carbon fiber, 4 ... Woven fabric.

Claims (3)

Metal member formed in a predetermined shape by metal having excellent thermal conductivity, on at least two sides including the electronic component mounting surface side, a predetermined ratio for suppressing carbon fiber having a length fibers expansion of the metal to or below a predetermined amount the composite material in which an array in a predetermined direction an embedded state.   The composite material according to claim 1, wherein the carbon fibers are arranged in the X and Y2 directions. The composite material according to claim 1 , wherein the metal is copper .

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