JP2000022055A - Carbon fabric composite radiator plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a good thermal conductivity in the direction parallel to a surface for excellent heat dissipation efficiency by coating a carbon fabric composite plate, composed in an array in one direction, with a metal member layer of specific thickness or less through a metal base material layer. SOLUTION: Related to a heat radiator plate 1, the surface of a carbon fabric composite plate 2 is sequentially coated with a metal base material layer 3 and a metal member layer 4. Related to the carbon fabric composite plate 2, a carbon fabric 6 is composed with a matrix 5 in parallel to the surface of the composite plate 2 while arrayed in one direction. The thickness is about 0.5-4 mm. Since the carbon fabric composed with the matrix 5 is of high thermal conductivity in longitudinal direction, the thermal conductivity in the direction parallel to the surface of the composite plate 2 may be larger than a metal material such as a silver. The metal member layer 4 is entirely coated over the entire surface of the carbon fabric composite plate as usual. At least both sides surface and beakside, are coated. The thickness of the metal member layer is 100 μm or less. With excellent thermal conductivity in the direction parallel to a surface, the accumulated heat of a semiconductor is dissipated well while the semiconductor element is hard to cause distortion since the elastic modulus in surface direction is small.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon fiber composite heat radiating plate for dissipating heat generated by a semiconductor element used for a computer integrated circuit (MPU, CPU, DRAM, etc.) or a power transistor.

[0002]

2. Description of the Related Art In recent years, the performance of computers, especially the speed thereof, has been remarkable. The higher speed has been realized by increasing the frequency of the semiconductor integrated circuit. However, the amount of heat generated by the semiconductor element and the like has increased, and heat dissipation has become an important issue. For example, as shown in FIG. 3, the heat dissipation of the semiconductor element is performed by forming a part of the outer periphery of the semiconductor package 8 with the heat sink 1 and bonding the semiconductor element 10 to the inner surface of the heat sink 1 with an adhesive. ing. In FIG. 3, 9 is a semiconductor element 10 and a circuit board 11.
Are electrically connected to each other, 12 is a ceramic sealing body, and 13 is an input / output terminal.

When a metal plate made of copper or aluminum is used for the heat radiating plate, thermal stress is generated between the metal plate and a semiconductor element (such as a silicon element) having a small coefficient of thermal expansion since the metal plate has a large coefficient of thermal expansion. The semiconductor element may be peeled off or a performance defect may occur. On the other hand, materials having a low coefficient of thermal expansion include a copper / tungsten composite material, a metal-coated CBN sintered body, aluminum nitride, and diamond, all of which are expensive. Among them, the copper / tungsten composite material is used in some cases, but has a problem that it is heavy and has insufficient heat dissipation. For this reason, a heat radiating plate has been proposed in which carbon fibers having high thermal conductivity are arranged and compounded in the thickness direction of the carbon mother plate, and a metal member layer is coated on the surface to provide airtightness.

[0004]

However, the heat sink has excellent heat dissipation in the thickness direction, but is inferior in the direction parallel to the surface, so that the area of the heat sink is large compared to the size of the semiconductor element. Sometimes the heat dissipation efficiency is poor and its use is limited to places where the area of the heat sink cannot be made large. Further, since the carbon fibers are arranged in the thickness direction, there is a problem that cracks are easily generated in a direction parallel to the surface. INDUSTRIAL APPLICABILITY The present invention has a low coefficient of thermal expansion, is low in cost, and is excellent in heat conductivity (heat spreader property) in a direction parallel to the surface, and in particular, can have a large area of a heat sink compared to the size of a semiconductor element. It is an object of the present invention to provide a carbon fiber composite heat sink suitable for use in a location.

[0005]

According to the first aspect of the present invention,
A metal member layer having a thickness of 100 μm or less is coated on a carbon fiber composite plate in which carbon fibers are compositely arranged in a direction parallel to the surface (that is, a plane perpendicular to the thickness direction) and a metal base layer. It is a carbon fiber composite radiator plate characterized by the following.

According to a second aspect of the present invention, there is provided the carbon fiber composite heat radiating plate according to the first aspect, wherein the entire surface of the carbon fiber composite plate is covered with a metal member layer via a metal base layer.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings. FIG. 1 is a longitudinal sectional view showing a first embodiment of a heat sink of the present invention. The heat radiating plate 1 of the present invention comprises a carbon fiber composite plate 2 having a surface coated with a metal base layer 3 and a metal member layer 4 in this order. The composite is arranged parallel to the surface of the plate 2 (the bonding surface of the semiconductor element) and in one direction. The thickness is about 0.5 to 4 mm.

As the base material, various materials such as carbon, ceramics such as silicon carbide, metallic silicon, Al, and Al alloy are used. In particular, carbon is preferably inexpensive in terms of processing cost until cutting into a thin plate. .

Since the carbon fibers to be composited with the base material have high thermal conductivity in the longitudinal direction, the thermal conductivity in the direction parallel to the surface of the composite plate (the direction in which the carbon fibers are arranged) is silver, copper, aluminum or the like. It can be larger than the metal material. For example, a pitch-based carbon fiber heat-treated at 3000 ° C. using a liquid crystal pitch as a raw material has a thermal conductivity in the length direction of 1000 W / m · k or more, and a carbon fiber of a composite plate obtained by compounding the carbon fiber in one direction by 60% by volume. The thermal conductivity in the arrangement direction is 500 W / m · k or more regardless of the type of the base material.

In the present invention, the metal base layer functions to join the composite plate and the metal member layer. Metal brazing such as silver brazing, Ni brazing or copper brazing is used for the metal base layer. The metal braze adheres well even when the base material of the composite plate is carbon. In particular, the active braze of an Ag-Ti alloy has excellent adhesion. The active wax (melting temperature 800 ° C. or less)
For example, it is formed by evaporating Ti on the composite plate, evaporating Ag thereon, and then performing heat treatment. The active solder is brazed in a non-oxidizing atmosphere such as vacuum or argon gas because Ti is easily oxidized. Ni brazing or copper brazing (both melting temperatures of 800 ° C. or higher) can be brazed in a hydrogen atmosphere, so that continuous processing is possible.

In the present invention, the metal member layer prevents the composite plate from being damaged or warped during assembling or using the semiconductor package, and penetrates in the thickness direction when the base material is carbon. This has the effect of sealing the micropores to be formed, preventing contamination by the exfoliated carbon powder, and preventing gas adsorption when heating and cooling are repeated. The metal member layer usually covers the entire surface of the carbon fiber composite plate. Cover at least both sides. Otherwise, warpage occurs due to the difference in thermal expansion coefficient between the base material and the metal member layer. In addition, in order to prevent warpage, it is desirable that the metal member is simultaneously coated on both the front and back surfaces of the composite plate, and that the same kind of metal member layer is coated on both the front and back surfaces.

The metal member layer has a good wettability with the metal base layer, a higher melting temperature than the metal base layer, and a material having excellent thermal conductivity, for example, Ag, Ag-Ti alloy, copper, molybdenum, stainless steel, and the like. , Nickel alloy, chromium alloy, Kovar, 42 alloy, and other foils, plates, and radiating fins. Of these, Ag and Ag-T
An i-based alloy is preferable, and molybdenum,
Kovar, 42 alloy and the like are desirable. Since the metal member layer has a large coefficient of thermal expansion and elasticity, if it is too thick, a joint portion with a semiconductor element or a ceramic sealing material may peel off due to thermal stress when the temperature changes. Therefore, in the present invention, the thickness of the metal member layer is specified to be 100 μm or less.
In particular, it is preferably 60 μm or less. The lower limit is desirably 5 μm or more in order to obtain the effect. It is difficult to make the carbon fiber composite plate thinner than 0.8 mm, and when the thickness of the entire heat sink is reduced, the metal member layer must be formed as thin as possible.

Since the heat sink of the present invention has carbon fibers having high thermal conductivity arranged in parallel to the surface, the heat sink has excellent heat conductivity in a direction parallel to the surface, so that heat generated by the semiconductor element is radiated well. Since the elastic modulus in the direction is small, the semiconductor element is hardly distorted. In addition, a high-temperature solder (melting temperature 800
℃ or more), high-temperature solder can be used for bonding with a ceramic sealing material or the like. For example, if Ni brazing or Cu brazing is used for the metal base layer, silver brazing can be used for joining with the ceramic sealing material. In this case, silver braze can be used for a power transistor through which a large current flows because of its low electric resistance.

The carbon fiber composite board used in the present invention is manufactured as follows. When the base material is carbon, a thermosetting resin solution (such as a phenol resin dissolved in furfuryl alcohol) in which fine powder such as solid pitch or coke is dispersed in a bundle of carbon fibers arranged in one direction. Impregnated and then the solvent is removed by drying to form a sheet material (prepreg) in which carbon fibers are arranged in one direction in the carbon matrix precursor, and a large number of such sheets are laminated so that the carbon fibers face in one direction. Then, the laminate is heated under pressure to cure the thermosetting resin, and then calcined at a high temperature in an inert atmosphere to carbonize the phenol resin and the fine powder of pitch or coke to form a carbon-carbon fiber composite block. And cut it out into a plate parallel to the direction of arrangement of the carbon fibers. According to this method, a base material having a sufficiently dense structure can be obtained by one firing carbonization treatment. Densification treatment such as re-impregnation and re-firing becomes unnecessary. When the base material is Al, a bundle of carbon fibers arranged in one direction is fixed with an inorganic binder, and dried to form a preform. The preform is preheated, and the molten aluminum is impregnated with pressure. To produce an Al-carbon fiber composite block, which is cut out in a plate shape in parallel with the arrangement direction of the carbon fibers.

In the method of forming a heat sink by coating the composite plate with a metal member layer, for example, as shown in FIG. 2A, a metal base layer (such as an Ag-Ti layer) 3 is formed on the entire surface of the carbon fiber composite plate 2. Then, as shown in FIG. 2B, the two metal member layers 4 (Ni foil or the like) are coated by pressing and pressing the hot press mold 7 from above and below, respectively.

[0016]

The present invention will be described below in detail with reference to examples. (Example 1) A carbon / carbon fiber composite block is described in paragraph 001.
4 and cut in parallel with the carbon fiber arrangement direction using a multi-wire saw
(25.4 mm square, thickness 1.0 mm), and Ni
-P alloy (metal underlayer) is plated to a thickness of 30 µm, and a copper foil (metal member layer) having a thickness of 35 µm is laminated thereon, and heated to 950 ° C in a hydrogen continuous annealing furnace (no pressure). Then, a heat sink having the same structure as that shown in FIG. 1 was manufactured. Table 1 shows the physical properties of the composite plate.

[0017]

[Table 1]

(Example 2) A Ti-Ag alloy (metal underlayer) having a thickness of 10 μm was formed on the entire surface of the same composite plate as used in Example 1.
It was vapor-deposited to a thickness, and a 35 μm-thick Ni foil (metal member layer) was coated thereon by a vacuum hot press (see FIGS. 2A and 2B) at 850 ° C. and 5 MPa to produce a heat sink.

Comparative Example 1 A radiator plate was manufactured in the same manner as in Example 1 except that a composite plate was cut from a carbon / carbon fiber composite block at a right angle to the direction in which carbon fibers were arranged.

Comparative Example 2 A copper foil having a thickness of 35 μm was adhered to both surfaces of the same composite board as used in Example 1 with an epoxy resin adhesive (about 40 μm thick), and 50 kg / cm ^2.
While applying the pressure and holding at 150 ° C. for 2 hours to form a heat sink.

The cross section of each of the heat sinks obtained in Examples 1 and 2 and Comparative Examples 1 and 2 was observed, and it was confirmed that each layer was well bonded.

Each of the heat sinks (thickness: about 1 mm) obtained in Examples 1 and 2 and Comparative Examples 1 and 2 was provided with a silicon plate having a thickness of 0.5 mm on one side and an alumina plate having a thickness of 1 mm on the other side. Each of the test pieces was solder-joined to form a test piece, and the heat distortion rate of a connection portion generated when the test piece was heated to 150 ° C. was measured on both sides of each heat sink. As the solder, a solder containing 60% of tin and 40% of lead was used. Further, the heat resistance temperature of each test piece was measured. Table 2 shows the results
Shown in Table 2 also shows physical properties such as thermal conductivity, electrical resistance, thermal expansion coefficient, and elastic modulus of each heat sink. The measurement results and physical properties of the conventional heat sink are also shown.

[0023]

[Table 2] (Note) * No.1 is Example 1, No.2 is Example 2, No.3 is Comparative Example 1, No.4 is Comparative Example 2, and grades of No.5-8 are described in the remarks column. No. 9 is a copper / tungsten plate.

As is clear from Table 2, the product of the present invention is
High thermal conductivity in the direction parallel to the surface, which is advantageous when used in places where a large area can be taken with respect to the size of the semiconductor element. Also, since the coefficient of thermal expansion and the elastic modulus are low, the thermal strain coefficient of the joint is low. And the heat resistance was high, so that it was suitable for a heat sink. On the other hand, the comparative example product is inferior in any of the characteristics required as a heat sink, and the silver plate, the tungsten plate, and the copper / tungsten plate are expensive and lack practicality.

Next, the test pieces were subjected to 0 ° C. and 150 ° C.
The heat cycle test was repeated 1000 times between the temperatures of
In the example of the present invention, peeling or breakage of the silicon plate or the alumina plate was not recognized at all. On the other hand, in Comparative Example 1, cracks occurred in the carbon base material, and in Comparative Example 2, the electric resistance in the thickness direction of the heat sink increased to 10 mΩ, which was not applicable to power devices and the like. When the silicon plate was joined by high-temperature solder (350 ° C.), the adhesive turned black, melted, and the copper foil peeled off.

Next, a radiator plate A was prepared by removing the metal member layer and the metal base layer on the side surface S of the radiator plate of Example 1 perpendicular to the carbon fiber arrangement direction. The semiconductor elements were bonded to the inner surface of the heat sink B, and the semiconductor packages shown in FIG. 3 were assembled using these heat sinks, left in the air for three days, and then their bonding properties were examined. Although the heat radiating plate B (Example 1) was excellent in bonding, the heat radiating plate A had no practical problem, but the bonding property was slightly lowered, and the metal member layer near the side surface S was slightly discolored. Admitted.
It is considered that the decrease in the bonding property is caused by the occurrence of distortion due to the partial lack of the metal member layer.

[0027]

As described above, according to the heat sink of the present invention, the metal member layer is provided with the metal base layer on the composite plate in which the carbon fibers having high thermal conductivity are arranged in parallel and unidirectionally on the surface. Since it has good thermal conductivity in the direction parallel to the surface, it is used as a heat radiating plate having a large area compared to the size of the semiconductor element, and has excellent heat dissipation efficiency. In addition, since the carbon fiber has a coefficient of thermal expansion as small as that of a semiconductor element, peeling of the semiconductor element and poor performance are unlikely to occur. In addition, the airtightness and the sealing property are improved by coating the metal member layer. Set the thickness of the metal member layer to 10
Since the thickness is specified to be 0 μm or less, the influence of the metal member layer on the semiconductor element is small, and peeling of the semiconductor element hardly occurs. By covering the entire surface of the heat sink with the metal member layer, the bonding property and the like are improved. Therefore, an industrially remarkable effect is achieved.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing an embodiment of a heat sink of the present invention.

FIGS. 2A and 2B are process explanatory views showing an embodiment of the method for manufacturing a heat sink according to the present invention.

FIG. 3 is an explanatory view of a semiconductor package provided with a heat sink.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heat sink 2 Composite board 3 Metal underlayer 4 Metal member layer 5 Base material of composite board 6 Carbon fiber 7 Hot press type 8 Semiconductor package 9 Semiconductor element 10 Ceramic sealing body 11 Bonding wire 12 I / O terminal 13 Circuit board

Claims (2)

[Claims] 1. A carbon fiber composite plate in which carbon fibers are arrayed in parallel and unidirectionally on a surface, and a metal member layer having a thickness of 100 μm or less is coated via a metal base layer. Carbon fiber composite heat sink. 2. The carbon fiber composite heat radiating plate according to claim 1, wherein a metal member layer is coated on the entire surface of the carbon fiber composite plate via a metal base layer.