JP4344934B2 - High thermal conductivity / low thermal expansion composite material, heat dissipation substrate and manufacturing method thereof - Google Patents

Description

  The present invention relates to a high thermal conductivity / low thermal expansion composite material, a heat dissipation substrate comprising the same, and a method for producing the same, and in particular, a composite material of a porous graphitized extruded product and aluminum or copper, and has a high thermal conductivity and a low thermal expansion coefficient. High thermal conductivity / low thermal expansion composite material having low specific resistance and substantially no thermal history, heat dissipation substrate such as heat sink made of such composite material, and method for manufacturing the same About.

  The amount of heat generation is increasing as electronic parts become highly integrated, have a large capacity, and have a high output, and a material having a high thermal conductivity and a low coefficient of thermal expansion is required. Since semiconductor elements such as CPUs and light emitting diodes generate a large amount of heat, a heat sink is usually attached. The heat transmitted from the semiconductor element to the heat sink is forcibly dissipated by a fan, a cooling medium, or the like. As the heat sink, aluminum, copper, or an alloy thereof, which is usually excellent in thermal conductivity, is used.

  For example, since the CPU is much smaller than the heat sink, a high heat conductor called a heat spreader is usually interposed between the two. As a material of the heat spreader, a material having not only high thermal conductivity but also a low thermal expansion coefficient comparable to that of a CPU made of silicon is desired. The same applies to light-emitting diodes made of compound semiconductors (GaAs, GaN, etc.). For this purpose, many substrates made of a composite material of silicon carbide, alumina, silicon nitride, or aluminum nitride and aluminum or copper, which are ceramics having a low coefficient of thermal expansion, have been proposed. Since ceramics are included, there is a difficulty that processing is difficult. A composite material substrate made of tungsten or molybdenum, which is a metal having a small coefficient of thermal expansion, and copper has also been proposed. However, these composite material substrates also have a problem that processing is difficult.

  In view of the above circumstances, many attempts have recently been made to use a composite material of carbon particles or carbon fibers and metal as a heat dissipation substrate. For example, JP-A-10-168502 (Patent Document 1) discloses that 1 to 200 parts by weight of a crystalline carbon material selected from graphite, carbon fiber, carbon black, fullerene or carbon nanotube, Fe, Cu, High thermal conductivity obtained by mixing 100 parts by weight of a metal powder selected from the group consisting of Al, Ag, Be, Mg, W, Ni, Mo, Si, Zn, and alloys thereof, and hot pressing. Rate composites are disclosed. However, this composite material has a structure in which a crystalline carbon material is dispersed in a metal matrix and has a high thermal conductivity, but has a problem that the thermal expansion coefficient is as high as that of the metal matrix.

  Japanese Patent Application Laid-Open No. 2000-203973 (Patent Document 2) discloses that at least one metal selected from the group consisting of aluminum, magnesium, tin, zinc, copper, silver, iron, nickel and alloys thereof is contained in a carbonaceous matrix. A carbon-based metal composite material impregnated, wherein 90% by volume or more of the pores of the carbonaceous matrix is impregnated with the metal, and the content of the metal is 35% by volume or less of the total carbon-based metal composite material. A carbon-based metal composite is disclosed.

Japanese Patent Laid-Open No. 2001-58255 (Patent Document 3) discloses a method in which aluminum, copper, silver, or an alloy thereof is pressure impregnated by a molten metal forging method into a carbon molded body including carbon particles including carbon crystals or carbon fibers. a carbon base metal composite material produced, and a thermal conductivity of the thickness direction at room temperature of 0.99 W / mK or more, the thermal expansion coefficient in the ^{4 × 10 -6 / K~12 × 10} -6 / K A carbon-based metal composite is disclosed. These carbon-based metal composites have a structure in which a graphite matrix having high rigidity, high thermal conductivity, and low thermal expansion coefficient is used as a skeleton, and the pores are impregnated with metal. Therefore, the low thermal expansion coefficient of graphite and the high thermal conductivity of metal Combined.

Japanese Patent Laid-Open No. 10-168502 JP 2000-203973 A Japanese Patent Laid-Open No. 2001-58255

  Despite the above advantages, these carbon-based metal composites have the disadvantage of having a much larger coefficient of thermal expansion than silicon and compound semiconductors. If the difference in coefficient of thermal expansion from silicon or compound semiconductor is large, not only the CPU or light emitting diode is subjected to large thermal stress during soldering or brazing work to join the heat dissipation board to the CPU or light emitting diode, but also the CPU Further, it is not preferable because the CPU and the light emitting diode are subjected to a large thermal stress during the operation of the light emitting diode. Therefore, a stress relaxation material is usually interposed between the CPU or light emitting diode and the heat dissipation substrate. However, since the thermal conductivity of the stress relaxation material is not necessarily sufficiently high, there is a problem that even if a carbon-based metal composite material having a high thermal conductivity is used for the heat dissipation substrate, the effect is not sufficiently exhibited.

  Furthermore, when joining a heat dissipation board to a CPU or light emitting diode, for example, in the case of an aluminum-impregnated graphite board, soldering (usually about 200-300 ° C) is performed, and in the case of a copper-impregnated graphite board, brazing (usually 700-- 800 ° C). However, it has been found that when exposed to such a high temperature, the composite substrate impregnated with aluminum or copper has a significant difference between the dimension before heating and the dimension after heating due to residual stress. If there is such a thermal history, the heat sink board joined to the CPU or light emitting diode may be warped, eventually resulting in destruction, and the CPU or laser diode may be damaged by thermal stress. .

  Accordingly, an object of the present invention is to provide a high thermal conductivity / low thermal expansion composite material having a high thermal conductivity, a small thermal expansion coefficient comparable to that of silicon or a compound semiconductor, and substantially no thermal history. is there.

  Another object of the present invention is to provide a heat dissipation substrate made of a high thermal conductivity / low thermal expansion composite material having such characteristics.

  Still another object of the present invention is to provide a method for manufacturing such a high thermal conductivity / low thermal expansion composite material and a heat dissipation substrate.

  As a result of diligent research in view of the above object, the present inventor found that the porous graphitized extrudate was impregnated with molten metal and then heat-treated to increase (a) the thermal conductivity and the thermal expansion coefficient of silicon. Alternatively, the thermal expansion coefficient can be reduced to the same level as that of the compound semiconductor, and (b) the thermal history of the thermal expansion coefficient can be substantially removed, so that good dimensional stability can be obtained during heating. Discovered and came up with the present invention.

That is, the high thermal conductivity / low thermal expansion composite material of the present invention is a high thermal conductivity / low thermal expansion composite material obtained by impregnating a porous graphitized extruded body with a metal, wherein the metal is aluminum or an alloy thereof, and the composite material Is heat-treated at a temperature of 200 ° C. or more after impregnating the metal (melting point of the metal −10 ° C.), and depending on the heat history in the extrusion direction after the heat treatment and in the direction perpendicular to the extrusion direction The dimensional change rate is within ± 0.1%.
The heat treatment is preferably performed under conditions of a heating rate of 30 ° C./min or less and a cooling rate of 20 ° C./min or less. More preferably, the heating rate is 10 ° C./min or less and the cooling rate is 10 ° C./min or less.
The metal is an aluminum alloy composed of 11 to 14% by mass of silicon, the balance being aluminum and inevitable impurities. Of the silicon (Si) -rich phases precipitated in the metal structure, the major axis is 30 μm or less and the aspect ratio (major axis / It is preferable that the ratio (area ratio in the micrograph) of the acicular structure having a minor axis) of 10 or more is 10% or less. More preferably, it is 5% or less. The amount of oxygen in the aluminum alloy is preferably 400 ppm or less.

Another high thermal conductivity / low thermal expansion composite material of the present invention is a high thermal conductivity / low thermal expansion composite material obtained by impregnating a porous graphitized extruded body with a metal, wherein the metal is copper or an alloy thereof. The material is heat-treated at a temperature of 300 ° C. or higher after impregnating the metal (melting point of the metal −10 ° C.), and heat history in the extrusion direction after the heat treatment and in the direction perpendicular to the extrusion direction. It is characterized in that the dimensional change rate due to is within ± 0.1%.
The heat treatment is preferably performed under conditions of a heating rate of 30 ° C./min or less and a cooling rate of 20 ° C./min or less. More preferably, the heating rate is 10 ° C./min or less and the cooling rate is 10 ° C./min or less.
When the metal is copper or an alloy thereof, the amount of oxygen in the metal is preferably 400 ppm or less, more preferably 250 ppm or less.

The high thermal conductivity / low thermal expansion composite material has anisotropy in thermal conductivity and thermal expansion coefficient, thermal conductivity in the extrusion direction is 250 W / mK or more, and thermal expansion coefficient is less than 4 × 10 ⁻⁶ / K. It is preferable that the thermal conductivity in the direction orthogonal to the extrusion direction is 150 W / mK or more and the thermal expansion coefficient is 10 × 10 ⁻⁶ / K or less .

In a preferred embodiment of the present invention, the thermal conductivity in the extrusion direction is 250 W / mK or more and the thermal expansion coefficient is 0.1 × 10 ⁻⁶ / K or more and less than 4 × 10 ⁻⁶ / K, and is orthogonal to the extrusion direction. The thermal conductivity in the direction of the flow is 150 W / mK or more, and the thermal expansion coefficient is 4 × 10 ⁻⁶ / K or more and 10 × 10 ⁻⁶ / K or less.

Heat sink substrate of the present invention consists of the high thermal conductivity and low thermal expansion composite material, the thickness direction of the substrate coincides with the direction of extrusion of the multi-porous graphitized extrudate, heating element on a surface perpendicular to the extrusion direction It is characterized by joining.

The method for producing a high thermal conductivity / low thermal expansion composite material of the present invention includes: (1) graphitization by firing an extruded product of carbon particles and / or carbon fibers and tar pitch; and (2) the obtained porous graphite. the reduction extruded body, the molten metal of aluminum or its alloys, the impregnated at a pressure of 10 ° C. or higher high temperature and 10 MPa or more than the melting point of the molten metal, (3) the obtained graphite / metal composite material (the It is characterized in that the heat treatment is performed at a temperature not higher than the melting point of the metal −10 ° C.) and not lower than 200 ° C.
Another method for producing a high thermal conductivity / low thermal expansion composite material of the present invention is (1) graphitized by firing an extruded product of carbon particles and / or carbon fibers and tar pitch, and (2) obtained. (3) Obtained graphite / metal composite material by impregnating a porous graphitized extrudate with a molten metal of copper or an alloy thereof at a temperature of 10 ° C. or higher and a pressure of 10 MPa or higher than the melting point of the molten metal. (The melting point of the metal is −10 ° C.) or less, and heat treatment is performed at a temperature of 300 ° C. or more.
The heat treatment is preferably performed under conditions of a heating rate of 30 ° C./min or less and a cooling rate of 20 ° C./min or less. More preferably, the heating rate is 10 ° C./min or less and the cooling rate is 10 ° C./min or less.

Method for manufacturing a heat sink substrate of the present invention is characterized in that cut out after producing a high thermal conductivity and low thermal expansion composite by the above methods, along the extrusion direction and vertical surface of the porous graphitized extrudate . The vertical surface is preferably used as a surface for joining the heating elements.

  The thus obtained high thermal conductivity / low thermal expansion composite material is preferably cut into a plate shape having a thickness of about 0.1 to 100 mm and used as a heat sink or the like. After the metal-impregnated composite is heat-treated, it is usually cut into a plate shape. However, if an ultra-high precision shape is required, the metal-impregnated composite is cut into a plate shape. It is preferable to heat-treat and process into the desired shape again. In any case, the heat dissipation substrate made of a porous graphitized extruded product has a dimensional change rate within ± 0.1% due to thermal history in the extrusion direction and in the orthogonal direction, so even if thermal stress is applied during brazing, etc. There are no problems such as warping or peeling at the bonding interface after cooling.

The high thermal conductivity / low thermal expansion composite material of the present invention has anisotropy in thermal conductivity and thermal expansion coefficient. Specifically, in the extrusion direction, the thermal conductivity is 250 W / mK or more and the thermal expansion coefficient is 4 ×. less than 10 ^-6 / K, and the thermal conductivity in the direction perpendicular to the extrusion direction is the thermal expansion coefficient at 0.99 W / mK or more and less 10 × 10 ^-6 / K. Therefore, when used in a heat sink or heat spreader for semiconductor elements, the influence of thermal stress is suppressed, heat spreads in the lateral direction and conducts well in the thickness direction, and can efficiently dissipate heat. . Further, since the coefficient of thermal expansion in the thickness direction is low, the dimensional accuracy in the thickness direction is good when assembled into a package, and a highly airtight package can be obtained.

Hereinafter, a preferable configuration of the high thermal conductivity / low thermal expansion composite material of the present invention will be described. The high thermal conductivity / low thermal expansion composite of the present invention preferably has a bulk density of 1.9 g / cm ³ or more, and the metal content is preferably 10 to 30% by volume.

  The specific resistance in the extrusion direction of the high thermal conductivity / low thermal expansion composite material is preferably 4 μΩm or less, and the specific resistance in the orthogonal direction is preferably 7 μΩm or less. More preferably, the specific resistance in the extrusion direction is 2 μΩm or less, and the specific resistance in the orthogonal direction is 3.5 μΩm or less.

  The porous graphitized extruded product used in the present invention comprises carbon particles such as coke and tar pitch, and the carbon particles preferably have an average particle size of 50 μm or more. The ash content of the extruded product is preferably 0.5% by mass or less, and more preferably 0.3% by mass.

  The specific resistance of the porous graphitized extruded product used in the present invention is less than 7 μΩm in the extrusion direction, 7 μΩm or more in the direction orthogonal to the extrusion direction, and the extrusion direction / orthogonal direction ratio of the specific resistance is 0.9 or less. Is preferred. More preferably, the specific resistance of the porous graphitized extrudate is 6 μΩm or less in the extrusion direction, 8 μΩm or more in the direction orthogonal to the extrusion direction, and the extrusion direction / orthogonal direction ratio of the specific resistance is 0.6 or less.

The thermal expansion coefficient of the porous graphitized extrudate used in the present invention is 3 × 10 ⁻⁶ / K or less in the extrusion direction, and 4 × 10 ⁻⁶ / K or less in the direction orthogonal to the extrusion direction. The ratio of the thermal expansion coefficient in the extrusion direction / orthogonal direction is preferably 0.8 or less. More preferably, the porous graphitized extrudate has a thermal expansion coefficient of 1 × 10 ⁻⁶ / K or less in the extrusion direction and 3 × 10 ⁻⁶ / K or less in the direction orthogonal to the extrusion direction. The direction / orthogonal ratio is 0.5 or less.

  The thermal conductivity of the porous graphitized extrudate used in the present invention is 150 W / mK or more in the extrusion direction, 80 W / mK or more in the direction orthogonal to the extrusion direction, and more preferably 100 W / mK. mK or more. The extrusion direction / orthogonal direction ratio of the thermal conductivity is 1.3 or more, more preferably 1.5 or more.

When aluminum or an alloy thereof is used as the metal, it is preferable to impregnate the porous graphitized extrudate with the molten metal at a temperature higher than its melting point by 10 ° C. or higher and a pressure of 10 MPa or higher.

When copper or an alloy thereof is used as the metal, it is preferable to impregnate the porous graphitized extrudate with the molten metal at a temperature higher than its melting point by 10 ° C. or higher and a pressure of 10 MPa or higher.

  From the above, the graphite / metal composite material of the present invention is composed of (a) a skeleton made of graphite and a metal having a high thermal conductivity impregnated in the pores. (B) The heat conductivity is somewhat improved by the heat treatment, and the coefficient of thermal expansion is remarkably reduced. Moreover, since the graphite / metal composite material of the present invention has a graphitized extruded product as a skeleton, there is a difference in characteristic values between the extrusion direction and the orthogonal direction. Therefore, a heat dissipation substrate having a desired thermal conductivity and thermal expansion coefficient can be obtained by making the cutting direction parallel to the extrusion direction or the orthogonal direction according to the application. Furthermore, the graphite / metal composite material of the present invention has an advantage that the dimensional accuracy is good even after soldering or brazing because the thermal history of thermal expansion is substantially eliminated by heat treatment.

[1] High thermal conductivity / low thermal expansion composite
(A) Configuration
(1) Porous graphitized extrudate The porous graphitized extrudate used in the present invention preferably has a bulk density of 2 g / cm ³ or less, particularly 1.6 to 1.95 g / cm ³ . When the bulk density is more than 2 g / cm ³ , the impregnation with the molten metal is insufficient, and the effect of sufficiently improving the thermal conductivity cannot be obtained. If it is less than 1.6 g / cm ³ , the strength of the graphite skeleton is insufficient, and the thermal expansion coefficient of the entire composite material is greatly influenced by the thermal expansion coefficient of the metal and increases. A more preferable bulk density of the porous graphitized extruded product is 1.65 to 1.85 g / cm ³ .

(2) Impregnated metal The molten metal impregnated into the porous graphitized extrudate is aluminum or an alloy thereof , or copper or an alloy thereof . In particular, the aluminum alloy is preferably an aluminum-silicon alloy containing 11 to 14% by mass of silicon. The reason is considered to be that the melting point of the molten metal is lowered by containing 11 to 14% by mass of silicon, and as a result, the formation of aluminum carbide is suppressed, and the decrease in thermal conductivity is prevented. Furthermore, it is considered that the needle-like silicon particles contained in the alloy were granulated by heat treatment, so that the thermal resistance was lowered, and as a result, the thermal conductivity was improved.

  Moreover, as a copper alloy, a chromium copper alloy is preferable. The reason for this is considered that chromium contained in the alloy has an effect of improving the strength of the interface between graphite and copper, and as a result, the strength of the composite material is improved. The chromium content is 0.1 to 10% by mass, preferably 0.1 to 5% by mass, and more preferably 0.1 to 2% by mass.

The proportion of metal in the composite is preferably 10-30% by volume. When the metal impregnated into the porous graphitized extruded product is less than 10% by volume of the composite material, the bulk density becomes less than 1.9 g / cm ^3, and the effect of improving the thermal conductivity by the metal impregnation is insufficient. If the metal content exceeds 30% by volume, the amount of impregnation of the metal with the graphite skeleton is too large, so the thermal expansion coefficient of the entire composite material is greatly influenced by the thermal expansion coefficient of the metal, and the thermal expansion of silicon and compound semiconductors. The difference from the rate is too large. A more desirable ratio of the metal in the composite material is 15 to 25% by volume.

Since it is preferable that the pores of the porous graphitized extruded product are filled with the metal as densely as possible, the bulk density of the composite material is preferably 1.9 g / cm ³ or more. When the bulk density is less than 1.9 g / cm ³ , the porosity of the composite material is too high, so that the thermal conductivity cannot be sufficiently increased. On the other hand, if the bulk density exceeds 5 g / cm ³ , the temperature / pressure conditions in the pressure impregnation step become too severe, which not only makes the production difficult but also increases the cost. A more preferable bulk density of the composite material is 1.9 to 4 g / cm ³ .

(B) Manufacturing method
(1) Production of porous graphitized extruded product The porous graphitized extruded product itself can be produced by a known method. Typically, a carbon raw material such as coke is pulverized and classified to an appropriate particle size, and then pitch is added as a binder and melt-kneaded. The kneaded product is extruded from a die having an extrusion port having a predetermined shape, cut into a predetermined length, fired, and graphitized. Carbon fiber may be used instead of carbon powder, or a mixture of carbon powder and carbon fiber may be used.

  The average particle size of carbon powder such as coke powder is preferably 50 μm or more. When the average particle size of the carbon powder is less than 50 μm, the heat conductivity of the obtained porous graphitized extruded product is insufficient. Further, if the average particle size of the carbon powder is more than 3 mm, there is a problem that the mechanical strength is insufficient. A more preferable average particle size of the carbon powder is about 50 μm to 3 mm. In the case of carbon fibers, pitch-based carbon fibers are preferable, and the average length is preferably about 50 μm to 5 mm.

  The mixing ratio (weight basis) of carbon powder and / or carbon fiber and pitch is preferably 10: 1 to 10: 4, and more preferably 10: 2 to 10: 3. If the mixing ratio is less than 10: 1 or more than 10: 4, the viscosity of the kneaded product becomes inappropriate and extrusion molding becomes difficult.

  The melt-kneaded product of carbon powder and / or carbon fiber and tar pitch is preferably extruded from an extrusion die at a temperature of 100 to 140 ° C.

In order to obtain a graphite / metal composite material having excellent thermal conductivity and coefficient of thermal expansion, the porous graphitized extrudate is preferably made of high-purity graphite. Specifically, the ash content in the porous graphitized extruded product is preferably 0.5% by mass or less, and more preferably 0.3% by mass or less. First, the porous graphitized extrudate is fired at 700 to 1000 ° C. after extrusion. Since the fired compact has a large number of pores, pitch is impregnated into the pores of the fired compact and refired in order to obtain a bulk density of 1.65 g / cm ³ or more. Thereafter, heat treatment is performed at a temperature of 2600 to 3000 ° C. to obtain a graphitized molded body, whereby the carbonaceous material is changed to a graphite material to obtain a porous graphitized extruded product. In order to obtain a graphite / metal composite material having high thermal conductivity and low thermal expansion coefficient, the non-combustible mineral (ash) remaining after burning the porous graphitized extruded product should be 0.5% by mass or less, and the purity It is important to make it high in graphite.

(2) Impregnation of metal Impregnation of the molten metal into the porous graphitized extrudate can be performed by a molten metal forging method. An example of a mold apparatus preferable for performing the molten metal forging method is shown in FIG. As shown in FIG. 1 (a), a mold apparatus 1 includes an upper mold 11 having a cavity 11a at the center, a lower mold 12 disposed below the upper mold 11 and having an opening 12a at the center, and an upper mold. A lower punch 13 disposed in the cavity 11a of the eleventh shaft, a shaft 14 connected to the bottom of the lower punch 13 and penetrating through the opening 12a of the lower mold 12, and an upper punch 15 entering the cavity 11a of the upper mold 11 And a plunger shaft 16 connected to the upper surface of the upper punch 15.

  As shown in FIG. 1 (a), the upper punch 15 is first removed, and the lower punch 13 on which the porous graphitized extruded product 20 is placed is lowered to the lowermost part in the cavity 11a of the upper die 11. The molten metal M is poured into the cavity 11a from the ladle 2. At this time, it is preferable that the upper and lower molds 11 and 12 and the porous graphitized extruded product are heated to a predetermined temperature and a sufficient amount of molten metal M is injected into the cavity 11a so as not to solidify during the impregnation. . In order to prevent the porous graphitized extruded product 20 from floating when the molten metal is injected, it is more preferable to weight the iron material or the like.

  As shown in FIG. 1 (b), when the upper punch 15 enters the cavity 11a and presses the upper punch 15 at a high pressure via the plunger shaft 16, the molten metal M at a high pressure becomes porous graphitized extrusion. It penetrates into the pores of the molded body 20. After the molten metal M that has entered the porous graphitized extrudate 20 has solidified, as shown in FIG. 1 (c), the upper punch 15 is removed, and then the lower punch 13 is raised to obtain the resulting metal impregnation. The porous graphitized extruded product 21 is taken out. Finally, as shown in FIG. 1 (d), the metal-impregnated porous graphitized extrudate 21 is cut out from the solidified metal M '. In order to prevent the molten metal M from solidifying before sufficiently intruding into the pores of the porous graphitized extrudate 20, the upper and lower molds 11 and 12 and the punches 13 and 15 during the forging of the molten metal. Is preferably heated to a predetermined temperature.

The molten metal forging temperature varies depending on the type of the molten metal, but is generally preferably a temperature that is 10 ° C. or higher than the melting point of the molten metal. Specifically, the melt forging temperature of each metal or its alloy is as shown in Table 1 below. In any case of molten metal, if the molten metal forging temperature is lower than the lower limit temperature, the molten metal does not sufficiently penetrate into the pores of the porous graphitized extruded product. Further, the effect obtained by raising the molten metal forging temperature is almost saturated at the upper limit temperature, and even if the temperature is higher than that, the effect associated therewith cannot be obtained. Further, in any case of the molten metal, before impregnation, if the temperature of the porous graphitized extruded molded body is preheated to the melting point of the molten metal, preferably higher than the melting point of the molten metal, the molded body This is preferable because sufficient penetration of the molten metal into the pores is achieved.

  The forging pressure of molten metal must be 10 MPa or more regardless of the type of molten metal. More preferably, it is 50 MPa or more. In any case of the molten metal, if the molten metal forging pressure is less than the lower limit temperature, the molten metal does not sufficiently enter the pores of the porous graphitized extruded product. Further, the effect obtained by increasing the melt forging pressure is almost saturated at the upper limit pressure, and even if it is higher than that, the improvement of the effect cannot be obtained.

  The pressurization time is generally from 1 minute to 30 minutes regardless of the type of molten metal, temperature and pressure. When the pressurization time is less than 1 minute, the porous graphitized extrudate is not sufficiently impregnated with the molten metal, and when it exceeds 30 minutes, the temperature of the molten metal is lowered and the impregnation does not proceed further.

(3) Heat treatment FIG. 2 shows a heat treatment pattern of the graphite / metal composite material preferred in the present invention. The temperature rising rate of the graphite / metal composite is preferably 30 ° C./min or less, and more preferably 10 ° C./min or less. If the rate of temperature rise exceeds 30 ° C./min, there is a problem that the temperature of the composite material does not become uniform. The lower limit of the heating rate may be about 0.5 ° C./min in consideration of the heat treatment efficiency.

The holding temperature of the graphite / metal composite is generally (melting point of each metal −10 ° C.) or lower and preferably 200 ° C. or higher. If the holding temperature is higher than (melting point of each metal −10 ° C.) , the metal may be softened or melted and ooze out from the porous graphitized extruded product. If the holding temperature is less than 200 ° C., the heat treatment effect cannot be obtained sufficiently. The holding time may be about 1 to 120 minutes.

  Since the graphite / metal composite maintained at the above temperature is preferably slowly cooled, the cooling rate is preferably 20 ° C./min or less, more preferably 10 ° C./min or less. When the cooling rate exceeds 20 ° C./min, the heat history of the impregnated metal remains. The lower limit of the cooling rate may be about 0.5 ° C./min in consideration of the heat treatment efficiency.

  These heat treatments may be performed in the state of the metal-impregnated porous graphitized extrudate 21 or the metal-impregnated graphite / metal composite material cut out along a plane perpendicular to the extrusion direction may be heat-treated. The former is preferable in the manufacturing process.

The preferable heat treatment conditions for each metal-impregnated graphite / metal composite are summarized in Table 2 below.

(C) Characteristics
(1) Thermal conductivity The graphite / metal composite of the present invention has a structure in which a metal with high thermal conductivity is pressed into the pores of the porous graphitized extruded product, and therefore has a significantly higher thermal conductivity than graphite. Have. Further, the graphite skeleton itself is made of an extruded product and has anisotropy, so that there is a difference in thermal conductivity between the extrusion direction and the orthogonal direction. The thermal conductivity of the porous graphitized extruded product itself is 150 W / mK or more in the extrusion direction and 80 W / mK or more in the orthogonal direction. Therefore, regardless of the type of metal to be impregnated, the thermal conductivity of the composite material is 250 W / mK or more in the extrusion direction, and can exhibit a thermal conductivity of 150 W / mK or more in the orthogonal direction. Furthermore, as a feature of the present invention, the thermal conductivity of the graphite / metal composite is further improved by heat treatment.

The thermal conductivity of each graphite / metal composite before and after heat treatment is summarized in Table 3 below.

(2) Coefficient of thermal expansion The graphite / metal composite of the present invention has a coefficient of thermal expansion generally close to that of graphite because the skeleton is made of a porous graphitized extruded product. Further, since the graphite skeleton is made of an extruded product, there is a difference in the coefficient of thermal expansion between the extrusion direction and the orthogonal direction. The thermal expansion coefficient of the porous graphitized extrudate itself is less 3.0 × 10 ^-6 / K in the extrusion direction is less that in the orthogonal direction 4.0 × 10 ^-6 / K. Therefore, although it varies somewhat depending on the type of metal to be impregnated, the thermal expansion coefficient of the composite material is less than 4.0 × 10 ⁻⁶ / K in the extrusion direction, and low thermal expansion of 10 × 10 ⁻⁶ / K or less in the orthogonal direction. The rate can be demonstrated. Further, as a feature of the present invention, the thermal expansion coefficient of the graphite / metal composite material is further lowered by performing a heat treatment.

The thermal expansion coefficient and the dimensional change rate of each graphite / metal composite before and after heat treatment are summarized in Table 4 below.

(3) Thermal history of thermal expansion The thermal expansion of the graphite / metal composite before heat treatment has a thermal history. That is, when the graphite / metal composite material before heat treatment is heated, the graphite / metal composite material thermally expands, but after heating and cooling, it does not return to its original size at room temperature and has a disadvantage of poor dimensional stability. However, it has been found that when the heat treatment of the present invention is applied, the dimensional change rate is significantly reduced. Excellent dimensional stability means that when a graphite / metal composite is used as a heat dissipation board, even if it receives heat from soldering or brazing, there is virtually no change in dimensions, and the heat dissipation board warps, Alternatively, unnecessary stress is not applied to the heating element such as a laser element.

(4) Other properties The specific resistance of graphite / metal composites is slightly reduced by heat treatment. The decrease in specific resistance is particularly remarkable in the extrusion direction. In general, the specific resistance of the graphite / metal composite material is preferably 4 μΩm or less in the extrusion direction, and preferably 7 μΩm or less in the orthogonal direction. The specific resistance before and after heat treatment of each graphite / metal composite is summarized in Table 5 below.

  It is presumed that the specific resistance of the graphite / metal composite is lowered by the heat treatment because the oxygen content in the impregnated metal is lowered by the heat treatment, so that the purification is advanced. The amount of oxygen in the impregnated metal varies depending on the type of metal. In general, the graphite / metal composite before heat treatment is 200 to 400 ppm in the case of aluminum or its alloy, 500 to 1000 ppm in the case of copper or its alloy, and 200 in the case of silver or its alloy. ~ 600 ppm, in the case of magnesium or its alloys 200-600 ppm, and in the case of zinc or its alloys 500-2000 ppm. In particular, in the case of copper or an alloy thereof, the oxygen content is significantly reduced by heat treatment. Specifically, the oxygen content of the graphite / copper composite after the heat treatment is reduced to 400 ppm or less.

  The Young's modulus of the graphite / metal composite material hardly changes before and after the heat treatment and is 5 GPa or more in the plane direction necessary for use as a heat dissipation substrate. Further, the bending strength of the graphite / metal composite material is almost the same before and after the heat treatment, and is 10 MPa or more, which is a required level when used as a heat dissipation substrate. It is considered that the increase in thermal conductivity, lower thermal expansion coefficient and improvement in dimensional stability by heat treatment are mainly due to the disappearance of residual strain during molten forging. In particular, when an Al—Si alloy is used, it is considered that the acicular structure that increases the thermal resistance is granulated by heat treatment, which contributes to the improvement of the thermal conductivity. Moreover, when copper or copper alloy is used, it is thought that the oxygen amount that increases the thermal resistance is reduced by the heat treatment, which contributes to the improvement of the thermal conductivity.

[2] Heat dissipation substrate The heat dissipation substrate is obtained by cutting a heat-treated graphite / metal composite material into a predetermined size. The heat dissipating substrate is preferably used as a heat sink or a heat spreader, but it is also possible to have a structure in which the heat dissipating fin and the heat spreader are integrated due to the excellent workability of the graphite / metal composite material. A surface to which a heating element such as a semiconductor element or a laser element is bonded is preferably a plane orthogonal to the extrusion direction of the graphite / metal composite material, but may be a plane parallel to the extrusion direction.

  For example, as shown in FIG. 3, when the surface to which the semiconductor element 3 is joined is a heat dissipation substrate 4 perpendicular to the extrusion direction, the heat conductivity of the heat dissipation substrate 4 is greater in the thickness direction than in the surface direction. The heat of the element 3 is quickly transmitted to the heat sink 5 bonded to the other surface of the heat dissipation substrate 4. On the other hand, the thermal expansion coefficient of the heat dissipation substrate 4 is larger in the thickness direction in the surface direction, and therefore, the thermal expansion coefficient in the surface direction of the heat dissipation substrate 4 is close to both the thermal expansion coefficient of the semiconductor element 3 and the heat expansion coefficient of the heat sink. . Therefore, a large thermal stress is not applied to both the bonding surface with the heat dissipation substrate 4 and the bonding surface of the heat sink during the operation of the semiconductor element 3.

Further, even when solder for joining the semiconductor element 3 to the heat dissipation substrate 4 or heating during brazing, the semiconductor element 3 is not subjected to a large thermal stress.
Furthermore, since the thermal expansion coefficient of the heat dissipation substrate is less than half in the thickness direction than in the surface direction, the expansion coefficient in the height direction is small during heating during package fabrication, and positioning is easy in the assembly process.

  The manufacturing method of the heat dissipation substrate is characterized by cutting out the graphite / metal composite material after the heat treatment. If the graphite / metal composite material is cut before the heat treatment, the dimensional stability is inferior. Therefore, the dimensions of the heat dissipation substrate change due to heating during soldering or brazing or temperature rise during operation. For this reason, there is a problem that finishing is required to obtain dimensional accuracy, and the reliability of the heat dissipation substrate joint is lowered.

It is preferable to provide a metal layer on the surface of the heat dissipation board that has been cut into a predetermined dimension in order to ensure the hermeticity of the package. In general, it is preferable to provide a metal layer on the entire surface of the heat dissipation substrate, but it may be provided at least on the surface (and the back surface) on which a semiconductor element or the like is mounted for the purpose of ensuring the airtightness of the package. As the airtightness, any leakage amount of 1 × 10 ⁻² Pa · cm ³ / s or less may be used.

  Examples of the method for forming the metal layer include a CVD method, a vapor deposition method, a sputtering method, a metal paste printing / firing method, and a plating method. In order to ensure airtightness, the thickness of the metal layer is preferably 0.5 μm to 10 μm. In the case of plating, electroless plating is preferable to electroplating because a metal layer can be uniformly formed on the outer periphery of the heat dissipation substrate.

  As the plating layer, Ni-P, Ni-B, Cu plating or the like is preferable. When the impregnated metal is copper or an alloy thereof and heat resistance of 700 ° C. or higher is required, Ni—B plating that is difficult to diffuse and react with the metal is particularly preferable because it is stable. These metal layers can be used not only for airtightness but also as a base for bonding with other components. Providing such a metal layer is desirable because adhesion to a heating element such as a semiconductor element or a package is improved.

  In particular, a heat dissipation board in which the impregnated metal is aluminum or an alloy thereof has a large thermal conductivity, a thermal expansion coefficient close to that of silicon or a compound semiconductor, and good solderability. It is suitable for a heat spreader for semiconductor elements using Further, the graphite / aluminum composite material has an advantage that the manufacturing cost is low because the melt forging temperature and the heat treatment temperature are low. Furthermore, since it has a coefficient of thermal expansion closer to that of a semiconductor element than a conventional heat spreader made of copper or aluminum and is lightweight, it is also preferable for a heat spreader via grease.

  Moreover, the heat dissipation board | substrate whose impregnation metal is copper or its alloy has a small thermal expansion coefficient while having a large thermal conductivity, and its dimensional stability is favorable. In addition, since it is impregnated with a relatively high melting point copper, it has high heat resistance and does not change even at a brazing temperature. Therefore, it is suitable for uses such as an optical communication package including heat radiation of a laser element that is brazed using silver brazing.

  In addition, in the case of a heat dissipation board having a fastening through-hole, when a metal pipe member is fitted into the through-hole, it works as a reinforcing member and can prevent damage such as cracks even when a high fastening torque is applied. High tightening torque can be obtained. Further, the metal pipe member also functions as a heat conduction member that disperses the thermal stress concentrated around the through hole, and the effect as a heat dissipation substrate is enhanced.

  The heat dissipation substrate whose impregnated metal is silver or an alloy thereof is impregnated with silver having a large thermal conductivity and a melting point between aluminum and copper, so that the heat resistance of about 900 ° C. is required. Is preferred.

  The heat dissipation substrate in which the impregnated metal is magnesium or an alloy thereof is impregnated with magnesium having a melting point between aluminum and silver, and thus is suitable for a component that requires higher heat resistance than aluminum.

  A heat dissipation substrate whose impregnated metal is zinc or an alloy thereof has a larger coefficient of thermal expansion than a substrate impregnated with aluminum, copper, silver, magnesium, etc., so that it is joined with a heat sink such as aluminum or copper. It is suitable for use in joining to a member having a large coefficient of thermal expansion. Further, since the impregnation temperature is low, it is advantageous in terms of cost.

  The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

Example 1
A porous graphitized extruded product obtained by extruding and graphitizing a melt-kneaded product of coke particles having an average particle diameter of 500 μm and pitch (bulk specific gravity: 1.70, ash content of 0.3% by mass, direction of extrusion and direction orthogonal to the direction of extrusion) Specific resistance is 5.0 μΩm and 8.5 μΩm, respectively, and thermal expansion coefficients in the extrusion direction and the direction orthogonal to the extrusion direction are 0.6 × 10 ⁻⁶ / K and 2.0 × 10 ⁻⁶ / K, respectively, and are orthogonal to the extrusion direction and the extrusion direction. The graphite / Al-Si composite was manufactured under the following conditions using an Al-Si alloy having a thermal conductivity in the direction of 230 W / mK and 120 W / mK, respectively, and 12 mass% of Si. .

First, after placing the porous graphitized extrudate in the cavity of the mold apparatus (held at 750 ° C) shown in Fig. 1 (a) and pouring the molten Al-Si alloy (750 ° C). The upper punch was pushed down, and the molten metal was forged at 100 MPa for 5 minutes. Excess Al-Si alloy was removed by cutting to obtain a graphite / Al-Si composite. The graphite / Al—Si composite material was heat-treated under the following conditions.
Temperature rising rate: 2 ° C / min Holding condition: 500 ° C x 60 minutes Cooling rate: 2 ° C / min

  The heat-treated graphite / Al-Si composite material was cut into a size of 40.0 mm x 20.0 mm x 2.0 mm, and used as a heat dissipation substrate sample. The thickness direction of the heat radiating substrate was matched with the extrusion direction of the composite material.

  For graphite / Al-Si composite samples before and after heat treatment, the content of Al-Si alloy, the content of needle-like structure in the Si-rich phase of Al-Si alloy, bulk density, thermal conductivity, heat The expansion coefficient, specific resistance, elastic modulus (Young's modulus), bending strength, and dimensional change rate were measured by the following methods. The measurement results are shown in Table 6 below.

(1) The bulk density was the weight per apparent unit volume.
(2) The thermal conductivity was measured with a TC-7000H laser flash method thermal constant measuring device manufactured by ULVAC-RIKO, based on JIS R 1611.
(3) The coefficient of thermal expansion and the rate of dimensional change were measured by a thermomechanical analyzer using an EXSTAR6000 thermal analysis system manufactured by Seiko Instruments Inc.
(4) The specific resistance was measured by the 4-terminal method using ZEM-2 manufactured by ULVAC-RIKO.
(5) Young's modulus was measured by a two-probe method using a sink-around unit UVM-2 and a digital oscilloscope to receive ultrasonic transmitted waves.
(6) The bending strength was measured by a three-point bending test method using an autograph AG-G type manufactured by Shimadzu Corporation based on JIS R 1601.

Comparative Example 1
A graphite / Al—Si composite was prepared and evaluated in the same manner as in Example 1 except that heat treatment was performed under the following conditions. The results are shown in Table 6 below.
Temperature rising rate: 2 ° C / min Holding conditions: 150 ° C x 60 minutes Cooling rate: 2 ° C / min

  As is clear from Table 6, the thermal conductivity of the graphite / Al—Si composite increased with the heat treatment, and the thermal expansion coefficient and dimensional change rate decreased significantly. Further, the resistance, Young's modulus and bending strength were almost unchanged before and after the heat treatment. From the above results, it can be said that the graphite / Al—Si composite material has achieved desirable performance as a heat dissipation substrate by heat treatment. On the other hand, in Comparative Example 1, the thermal conductivity, thermal expansion coefficient, and dimensional change rate were almost the same as before heat treatment.

  About the sample which consists of a graphite / Al-Si composite material before and behind heat processing, the structure | tissue of the Al-Si part was observed using the Hitachi, Ltd. scanning ion microscope (SIM) FB-2000A. A SIM photograph is shown in FIG. As apparent from FIG. 4 (a), in the sample made of the graphite / Al—Si composite material before the heat treatment, an acicular structure made of the Si-rich phase was precipitated. On the other hand, as apparent from FIG. 4B, in the sample made of the graphite / Al—Si composite material after the heat treatment, the acicular structure was spheroidized. In this example, the ratio (area ratio in the micrograph) of the acicular structure having a major axis of 30 μm or less and an aspect ratio (major axis / minor axis) of 10 or more in the silicon-rich phase was reduced to 5%. Since the Si-rich phase has low thermal conductivity, it is estimated that spheroidizing reduces thermal resistance and contributes to improvement in thermal conductivity. It has been found that the thermal conductivity increases remarkably when the area ratio of a needle-like structure having a major axis of 30 μm or less and an aspect ratio of 10 or more in the silicon-rich phase is 10% or less, particularly 5% or less.

  About the sample which consists of a graphite / Al-Si composite material before and behind heat processing, after heating from room temperature to 500 degreeC, it stood to cool, and the log | history of the thermal expansion in an extrusion direction and an orthogonal direction was measured, respectively. The results are shown in FIGS. As is clear from FIGS. 5 (a) and 6 (a), the graphite / Al—Si composite material before heat treatment exhibited a dimensional change rate of 0.18% in the extrusion direction and 0.32% in the orthogonal direction after the heat history. . On the other hand, as is clear from FIGS. 5 (b) and 6 (b), the heat-treated graphite / Al-Si composite has a dimensional change rate of only 0.01% in both the extrusion direction and the orthogonal direction after the thermal history. It can be seen that there was virtually no dimensional change. From the above results, it can be seen that the graphite / Al—Si composite material of the present invention, which is heat-treated after metal impregnation, has little dimensional change even after heat history and is excellent in dimensional stability.

Example 2
Using the same porous graphitized extrudate as used in Example 1 and pure copper (purity 99.9% or more), a graphite / copper composite was produced as follows. First, the porous graphitized extrudate is placed in the cavity of the mold apparatus (maintained at 1000 ° C.) shown in FIG. 1 (a), and the above-described pure copper molten metal (1350 ° C.) is poured into the upper punch. Was pushed down and forged for 5 minutes at 100 MPa. Excess pure copper was removed by cutting to obtain a graphite / copper composite. This graphite / copper composite was heat-treated under the following conditions.
Temperature increase rate: 5 ° C / min Holding conditions: 900 ° C x 120 minutes Cooling rate: 5 ° C / min

  The heat-treated graphite / copper composite material was cut into a size of 40.0 mm × 20.0 mm × 2.0 mm, and used as a heat dissipation substrate sample. The thickness direction of the heat radiating substrate coincided with the extrusion direction of the composite material. For each sample, in the same manner as in Example 1, the copper content, bulk density, thermal conductivity, thermal expansion coefficient, dimensional change rate (dimensional change rate after heating / cooling), specific resistance, elasticity The rate (Young's modulus), bending strength, and oxygen content in copper were measured. The measurement results are shown in Table 7 below.

Reference example 1
Porous graphitized extrudate (bulk specific gravity: 1.58, ash content 0.7% by mass, specific resistance in extrusion direction and direction orthogonal to extrusion direction is 9.0μΩm and 9.5μΩm, respectively, thermal expansion in extrusion direction and direction orthogonal to extrusion direction Examples except that the coefficients are 4.0 × 10 ⁻⁶ / K and 4.2 × 10 ⁻⁶ / K, respectively, and the thermal conductivities in the extrusion direction and the direction orthogonal to the extrusion direction are 130 W / mK and 80 W / mK, respectively. In the same manner as in Example 2, a graphite / copper composite material was produced, and the same measurement as in Example 2 was performed. The measurement results are shown in Table 7 below.

As is apparent from Table 7, the heat conductivity of the graphite / copper composite slightly increased and the coefficient of thermal expansion significantly decreased by the heat treatment. Further, the resistance, Young's modulus and bending strength were almost unchanged before and after the heat treatment. From the above results, it can be said that the graphite / copper composite has obtained desirable performance as a heat dissipation substrate by heat treatment. On the other hand, in Reference Example 1 , the dimensional change rate was reduced by the heat treatment, but even after the heat treatment, the thermal conductivity was low and the thermal expansion coefficient was large.

  About the sample which consists of a graphite / copper composite material before and behind heat processing, the copper part was observed with the scanning ion microscope (SIM). A SIM photograph is shown in FIG. As apparent from FIG. 7 (a), in the sample made of the graphite / copper composite material before the heat treatment, the copper phase exhibited a typical cast structure. On the other hand, as apparent from FIG. 7 (b), in the sample made of the graphite / copper composite material after the heat treatment, the copper phase was changed to equiaxed crystals. In addition, the amount of oxygen was significantly reduced. It is estimated that the reduction in the amount of oxygen that increases the thermal resistance resulted in an improvement in thermal conductivity.

  About the sample which consists of a graphite / copper composite material before and behind heat processing, after heating from room temperature to 900 degreeC, it stood to cool, and the log | history of the thermal expansion in an extrusion direction and an orthogonal direction was measured, respectively. The results are shown in FIGS. As is clear from FIGS. 8 (a) and 9 (a), the graphite / copper composite before heat treatment had dimensional change rates of 0.35% and 0.40% in the extrusion direction and the orthogonal direction after cooling, respectively. As is clear from FIG. 8 (b) and FIG. 9 (b), the graphite / copper composite after the heat treatment had a dimensional change rate of 0.02% and 0.01% in the extrusion direction and the orthogonal direction, respectively, and there was substantially no dimensional change. . From this, it can be seen that the graphite / copper composite of the present invention has a small dimensional change even when heated, and is excellent in dimensional stability.

Example 3
The same porous graphitized extruded product used in Example 1 (bulk specific gravity: 1.70, ash content 0.3% by mass, specific resistance in the extrusion direction and direction orthogonal to the extrusion direction is 5.0 μΩm and 8.5 μΩm, respectively, The thermal expansion coefficients in the direction orthogonal to the extrusion direction are 0.6 × 10 ⁻⁶ / K and 2.0 × 10 ⁻⁶ / K, respectively, and the thermal conductivities in the extrusion direction and the direction orthogonal to the extrusion direction are 230 W / mK and 120 W, respectively. / mK), and a brass made of 70% by mass of Cu and 30% by mass of Zn, a graphite / brass composite material was manufactured under the following conditions.

First, the graphite is placed in the cavity of the mold apparatus (maintained at 1000 ° C) shown in Fig. 1 (a), the molten brass (1350 ° C) is injected, and the upper punch is pushed down to 100 MPa. And forged the melt for 5 minutes. Excess pure copper was removed by cutting to obtain a graphite / brass composite material. This graphite / brass composite material was heat-treated under the following conditions.
Temperature increase rate: 5 ° C / min Holding conditions: 900 ° C x 120 minutes Cooling rate: 5 ° C / min

  For the obtained graphite / brass composite sample, the brass content, bulk density, thermal conductivity, thermal expansion coefficient, dimensional change rate (dimensions after heating / cooling) in the same manner as in Example 1. Change rate), specific resistance, Young's modulus, bending strength, and oxygen content in brass. The measurement results are shown in Table 8 below.

Comparative Example 2
A graphite / brass composite material was prepared and measured in the same manner as in Example 3 except that heat treatment was performed under the following conditions. The results are shown in Table 8.
Temperature increase rate: 5 ° C / min Holding conditions: 250 ° C x 120 minutes

Example 4
Electroless Ni-P plating after zincate treatment was applied to the surface of a 40.0 mm x 20.0 mm x 2.0 mm heat dissipation board cut out from the graphite / Al-Si alloy composite of Example 1 shown in Table 6 (after heat treatment). did. Further, electroless Ni—B plating was applied to the surface of a 40.0 mm × 20.0 mm × 2.0 mm heat dissipation substrate cut out from the graphite / Cu composite (after heat treatment) of Example 2 shown in Table 7. In order to evaluate the correlation between the presence of the plating layer and airtightness for each plated heat dissipation board,
Based on JIS C 7021 A-6, a helium leak detector model DLMS-33 made by Nippon Vacuum was used to measure the amount of helium gas penetrating the plated heat dissipation substrate. The amount of helium gas penetrating through the plated heat dissipation substrate was taken as the leak amount and used as an airtight parameter. The results are shown in Table 9 below.

  It was found that the airtightness of graphite / Al-12Si and graphite / Cu was remarkably improved by plating. If the plating thickness is less than 0.5 μm, sufficient airtightness cannot be obtained. On the other hand, if the thickness exceeds 20 μm, the plating film peels off due to an increase in residual stress. In addition, graphite / Al-12Si composite is preferable because the Al deposited film also has high adhesion. The graphite / Cu composite or the like may form a film fired at 900 ° C. after printing an Ag paste. In this case, since the film stress is low, the film thickness may be about 30 μm.

Example 5
An example in which the graphite / metal composite material (Cu) of the present invention is used in a module for mounting a semiconductor element is shown in FIG. The module for mounting a semiconductor device shown in the figure is a heat dissipation substrate 4a made of graphite / Cu composite of length 100 mm x width 100 mm x thickness 2 mm, and silicon nitride substrate 30 mm long x 30 mm wide x 0.8 mm thick The insulating substrate 6 is made of a heat sink 5.

  The heat radiating substrate 4a and the insulating substrate 6 were brazed, and the insulating substrate 6 was plated with Ni, and then the 10 mm × 10 mm semiconductor chip 3 was soldered to the insulating substrate 6. Further, the heat radiating board 4a and the heat sink 5 were mechanically fastened with bolts or the like via high thermal conductive grease to form a module.

The heat dissipation substrate 4a is made of a graphite / Cu composite. Here, a chromium copper alloy containing 1.0% by mass of Cr is impregnated, the thermal conductivity in the thickness direction of the substrate is 250 W / mK or more, and the thermal expansion coefficient is 0.1 × 10. ^Greater than ⁻⁶ / K and less than 4 × 10 ⁻⁶ / K, thermal conductivity in the direction perpendicular to the thickness direction (element mounting surface side) is 150 W / mK or more, thermal expansion coefficient is 4 × 10 ⁻⁶ / K or more, The heat dissipation board 4a was 10 × 10 ⁻⁶ / K or less.

  The heat dissipation characteristics of the semiconductor module of this example were evaluated. For the heat dissipation characteristics, the surface temperature of the semiconductor chip during energization and the thermal resistance (° C / W) between the semiconductor chip 3 and the back surface of the heat sink 5 were measured, and a temperature increase / decrease test from -40 ° C to 125 ° C was measured. The thermal resistance between the semiconductor chip 3 after cycling and the back surface of the heat sink 5 was measured. The thermal resistance after the 3000-cycle temperature cycle test is shown by the rate of increase from the thermal resistance before the temperature cycle test.

  As a result, the surface temperature of the semiconductor element was 52.1 ° C, the thermal resistance was 0.23 ° C / W, and the rate of increase after the cycle test was 2.5%. The surface temperature and thermal resistance of the semiconductor element were generally lower than before. The rate of increase after the cycle test was also reduced.

  Further, when the graphite / metal composite material of the present invention is used for the heat dissipation substrate 4a, a through hole 40 may be provided in the heat dissipation substrate 4a for fastening with the heat sink 5 as in the above embodiment. At this time, it is desirable to fit the metal pipe member 7 to the inner peripheral portion of the through hole 40. The shape of the pipe member 7 is not particularly limited as long as it can be fitted to the inner peripheral surface of the through hole 40. The shape shown in FIGS. 12 (a) and 12 (b), or FIG. ) As in). It is preferable that there are ridges 70 at both ends because cracks starting from the through hole 40 can be further suppressed. When the collar 70 is formed only on one end, it is formed on the side where the bolt head contacts.

  Furthermore, the pipe member 7 can be made into the slit 71 as shown in FIG. 12 (d) and the notch 72 as shown in FIG. 12 (e). When such slits 71 and notches 72 are included, elastic deformation is possible in the circumferential direction, so that the pipe member 7 can be easily fitted into the through hole 40. Further, the slit 71 and the notch 72 also have a role of buffering a load on the substrate due to expansion of the pipe member 7 accompanying heating of the substrate. Such a pipe member 7 has sufficient durability against a cooling / heating cycle and a solder reflow process. In addition, it is preferable to perform metal bonding at the interface between the pipe member 7 and the substrate using a brazing material or the like because adhesion can be improved and heat dissipation can be further improved.

It is a schematic sectional drawing which shows the metal mold | die apparatus for implementing a molten metal forging with respect to a porous graphitized extrusion molded object, (a) is a molten metal in the mold cavity which mounted the porous graphitized extrusion molded object. (B) shows a state in which molten forging is performed with the porous graphitized extruded body surrounded by molten metal, (c) shows a state in which the molten forged product is taken out from the mold, (d) shows a state in which a porous graphitized extrusion-molded body impregnated with metal is cut out from a molten forged product. It is a graph which shows roughly the pattern of the heat processing performed with respect to the graphite / metal composite material of this invention. It is a schematic sectional drawing which shows the thermal radiation board | substrate of this invention joined to the semiconductor element. It is a SIM photograph of the graphite / Al-Si composite material in Example 1, (a) is before heat treatment, and (b) is after heat treatment. It is a graph which shows the log | history of the thermal expansion in the extrusion direction of the graphite / Al-Si composite material in Example 1, (a) is before heat processing, (b) is after heat processing. It is a graph which shows the log | history of the thermal expansion in the orthogonal direction of the graphite / Al-Si composite material in Example 1, (a) is before heat processing, (b) is after heat processing. It is a SIM photograph of the graphite / copper composite material in Example 2, (a) is before heat treatment, and (b) is after heat treatment. It is a graph which shows the log | history of the thermal expansion in the extrusion direction of the graphite / copper composite material in Example 2, (a) is before heat processing, (b) is after heat processing. It is a graph which shows the log | history of the thermal expansion in the orthogonal direction of the graphite / copper composite material in Example 2, (a) is before heat processing, (b) is after heat processing. It is sectional drawing which shows the Example which used the graphite / metal composite material of this invention for the semiconductor module. It is a perspective view which shows the example of the pipe member used for a board | substrate with a through-hole. 11A is a cross-sectional view taken along the line AA in FIG. 11, FIG. 11B is a cross-sectional view illustrating a state where the metal pipe member is fitted into the through hole of the heat dissipation board shown in FIG. 11, and FIG. It is sectional drawing which shows another example of the metal pipe member fitted by the through-hole of this, (d) is a perspective view which shows another example of the metal pipe member fitted by the through-hole of a thermal radiation board | substrate. (E) is a perspective view showing still another example of the metal pipe member fitted into the through hole of the heat dissipation board.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Mold apparatus 2 for molten metal forging ... Ladle 3 ... Semiconductor element 4 ... Heat dissipation board (heat spreader)
4a ... heat dissipation substrate 5 ... heat sink 6 ... insulating substrate (silicon nitride substrate)
7 ... Pipe member
11 ... Upper mold
12 ... Lower mold
13 ... Bottom punch
14, 16 ... Plunger
15 ... Upper punch
20 ... Porous graphitized extruded product
21 ... Graphite / metal composite
M ... Molten metal
40 ... through hole
71 ... Slit
72 ... Notch

Claims (21)

A high thermal conductivity / low thermal expansion composite material in which a porous graphitized extruded product is impregnated with a metal , wherein the metal is aluminum or an alloy thereof, and the composite material is impregnated with the metal (the melting point of the metal− 10 ° C.) or less and at a temperature of 200 ° C. or more, and the dimensional change rate due to thermal history in the extrusion direction after the heat treatment and the direction perpendicular to the extrusion direction is within ± 0.1%. High thermal conductivity and low thermal expansion composite material. 2. The high thermal conductivity / low thermal expansion composite material according to claim 1 , wherein the metal is an aluminum alloy composed of 11 to 14% by mass of silicon, the balance being aluminum and inevitable impurities, and silicon (Si) precipitated in the metal structure thereof. Of the rich phase, the proportion of needle-like tissue with a major axis of 30 μm or less and an aspect ratio (major axis / minor axis) of 10 or more (area ratio in the micrograph) is 10% or less. Composite material. A high thermal conductivity / low thermal expansion composite material in which a porous graphitized extruded product is impregnated with metal, wherein the metal is copper or an alloy thereof, and the composite material is impregnated with the metal (the melting point of the metal− 10 ° C.) or less and at a temperature of 300 ° C. or more, and the dimensional change rate due to the thermal history in the extrusion direction after the heat treatment and the direction perpendicular to the extrusion direction is within ± 0.1%. High thermal conductivity and low thermal expansion composite material. 4. The high thermal conductivity / low thermal expansion composite material according to claim 3 , wherein the amount of oxygen in the metal is 400 ppm or less. 5. The high thermal conductivity / low thermal expansion composite material according to claim 1, wherein the heat treatment is performed under conditions of a heating rate of 30 ° C./min or less and a cooling rate of 20 ° C./min or less. High thermal conductivity and low thermal expansion composite material. The high thermal conductivity / low thermal expansion composite material according to any one of claims 1 to 5, wherein a bulk density is 1.9 g / cm ³ or more, and a content of the metal is 10 to 30% by volume. High thermal conductivity and low thermal expansion composite material. The high thermal conductivity / low thermal expansion composite material according to claim 1 , wherein a specific resistance in the extrusion direction is 4 μΩm or less and a specific resistance in the orthogonal direction is 7 μΩm or less.・ Low thermal expansion composite. A method for producing a composite material with high thermal conductivity and low thermal expansion, comprising: (1) graphitization by firing an extruded product of carbon particles and / or carbon fibers and tar pitch; and (2) the resulting porous graphitization. The extrudate is impregnated with a molten metal of aluminum or an alloy thereof at a temperature of 10 ° C. or higher than the melting point of the molten metal and a pressure of 10 MPa or more . (3) The obtained graphite / metal composite (the metal The melting point of which is −10 ° C.) or lower and at a temperature of 200 ° C. or higher . A method for producing a composite material with high thermal conductivity and low thermal expansion, comprising: (1) graphitization by firing an extruded product of carbon particles and / or carbon fibers and tar pitch; and (2) the resulting porous graphitization. The extrudate is impregnated with a molten metal of copper or an alloy thereof at a temperature of 10 ° C. or higher than the melting point of the molten metal and a pressure of 10 MPa or more . (3) The obtained graphite / metal composite (the metal The melting point of which is −10 ° C.) or lower and at a temperature of 300 ° C. or higher . 10. The method for producing a high thermal conductivity / low thermal expansion composite material according to claim 8 or 9, wherein the heat treatment is performed under conditions of a heating rate of 30 ° C./min or less and a cooling rate of 20 ° C./min or less. 11. The method for producing a high thermal conductivity / low thermal expansion composite material according to claim 8 , wherein the extrusion-molded body is composed of carbon particles and tar pitch, and the carbon particles have an average particle diameter of 50 μm or more and an ash content. The method characterized by being 0.5 mass% or less. 12. The method for producing a high thermal conductivity / low thermal expansion composite material according to claim 8, wherein the specific resistance is less than 7 μΩm in the extrusion direction, and is 7 μΩm or more in the direction orthogonal to the extrusion direction. A method comprising impregnating a porous graphitized extruded product having an extrusion direction / orthogonal direction ratio of 0.9 or less with the molten metal . The method for producing a high thermal conductivity / low thermal expansion composite material according to any one of claims 8 to 12 , wherein a coefficient of thermal expansion is 3 x ^10-6 / K or less in an extrusion direction and is perpendicular to the extrusion direction. A method characterized by impregnating the molten metal with a porous graphitized extruded product having a ratio of extrusion direction / orthogonal direction of the thermal expansion coefficient of 0.8 × 4 × 10 ⁻⁶ / K or less. The method for producing a high thermal conductivity / low thermal expansion composite material according to any one of claims 8 to 13 , wherein the thermal conductivity is 150 W / mK or more in the extrusion direction, and 80 W / m in a direction orthogonal to the extrusion direction. A method comprising impregnating the molten metal with a porous graphitized extrudate having a mK or more and an extruding direction / orthogonal ratio of the heat conductivity of 1.3 or more. A heat dissipation substrate comprising the high thermal conductivity / low thermal expansion composite material according to any one of claims 1 to 7 , wherein a thickness direction of the substrate coincides with an extrusion direction of the porous graphitized extrusion molded body, A heat dissipation board characterized in that a heating element is joined to a surface orthogonal to the direction. 16. The heat dissipation board according to claim 15 , wherein a metal layer having an air tightness with a leak amount of 1 × 10 ⁻² Pa · cm ³ / s or less is formed at least on a heating element joint surface. . 17. The heat dissipation board according to claim 16 , wherein the metal layer is a Ni—B plating layer and / or a Ni—P plating layer having a thickness of 0.5 to 20 μm. The heat dissipation board according to any one of claims 15 to 17 , wherein the board has a through hole, and a pipe-shaped reinforcing member is fitted to an inner peripheral portion of the through hole. substrate. A method for producing a heat dissipation substrate having high thermal conductivity and low thermal expansion, wherein after producing a high thermal conductivity / low thermal expansion composite material by the method according to any one of claims 8 to 14 , wherein the cutting out along the extrusion direction and vertical plane. 20. The method for manufacturing a heat dissipation board according to claim 19 , wherein the vertical surface is used as a surface to which a heating element is joined. 21. The method for manufacturing a heat dissipation board according to claim 19 or 20 , wherein after the heat dissipation board is cut out, a metal layer is formed at least on a surface to which the heating element is joined.