Composite material having high thermal conductivity and low thermal expansion coefficient, and heat-dissipating substrate, and their production methods
A composite material having a high thermal conductivity and a small thermal expansion coefficient, which is obtained by impregnating a porous graphitized extrudate with a metal; the composite material having such anisotropy that the thermal conductivity and the thermal expansion coefficient are 250 W/mK or more and less than 4×10 −6 /K, respectively, in an extrusion direction; and that the thermal conductivity and the thermal expansion coefficient are 150 W/mK or more and 10×10 −6 /K or less, respectively, in a direction perpendicular to the extrusion direction.
1. A composite material having a high thermal conductivity and a small thermal expansion coefficient, which is obtained by impregnating a porous graphitized extrudate with a metal; a dimensional change ratio due to thermal hysteresis being within ±0.1% in an extrusion direction and in a direction perpendicular to said extrusion direction after a heat treatment.
2. The composite material having a high thermal conductivity and a small thermal expansion coefficient according to claim 1 , wherein the composite material has a bulk density of 1.9 g/cm 3 or more; and wherein the amount of said metal is 10 to 30% by volume.
3. The composite material having a high thermal conductivity and a small thermal expansion coefficient according to claim 1 , wherein a resistivity of the composite material is 4 μΩm or less in said extrusion direction and 7 μΩm or less in said perpendicular direction.
4. The composite material having a high thermal conductivity and a small thermal expansion coefficient according to claim 1 , wherein said metal is at least one metal selected from the group consisting of aluminum, copper, chromium, silver, magnesium and zinc, or an alloy comprising one or more of said metals.
5. The composite material having a high thermal conductivity and a small thermal expansion coefficient according to claim 4 , wherein said metal is an aluminum alloy comprising 11 to 14% by mass of silicon, the balance being substantially aluminum and inevitable impurities, and wherein a percentage of a needle-shaped structure having a length of 30 μm or less and an aspect ratio (length/diameter) of 10 or more is 10% or less among a silicon (Si)-rich phase precipitated in said metal.
6. The composite material having a high thermal conductivity and a small thermal expansion coefficient according to claim 4 , wherein said metal is copper or its alloy; and wherein the amount of oxygen in said metal is 400 ppm or less.
7. A heat-dissipating substrate comprising the composite material having a high thermal conductivity and a small thermal expansion coefficient recited in claim 1 , wherein a thickness direction of said substrate is substantially in alignment with the extrusion direction of said porous graphitized extrudate; and wherein said composite material has a surface perpendicular to said extrusion direction, onto which a heat-generating body is going to be bonded.
8. The heat-dissipating substrate according to claim 7 , wherein a metal layer having such sealability that an amount of a helium gas leaked is 1×10 −2 Pa·cm 3 /s or less is formed on at least on a surface, onto which a heat-generating body is going to be bonded.
9. The heat-dissipating substrate according to claim 8 , wherein said metal layer comprises a Ni—B plating layer and/or a Ni—P plating layer each having a thickness of 0.5 to 20 μm.
10. The heat-dissipating substrate according to claim 7 , wherein said substrate has throughholes, in each of which a reinforcing pipe member is fitted.