JP6108389B2 - Interlayer thermal connection member and interlayer thermal connection method - Google Patents

Description

The present invention relates to an interlayer thermal connection member and an interlayer thermal connection method for quickly transferring heat from a heat generation source to a cooling / radiating member.

In recent years, heat generation in electronic devices such as mobile phones, personal computers, PDAs, game machines, and LED lighting has been solved in the electronics field due to an increase in the amount of heat generated due to high-speed microprocessors and high-performance LED chips. It has become a big challenge.

There are methods using heat conduction, heat radiation, and heat convection for heat dissipation and cooling, heat sinks and air cooling fins as cooling methods using heat convection, ceramic plates etc. as those using heat radiation, Examples of those utilizing thermal conduction include various thermal conduction (diffusion) sheets, thermal conductive resins, and the like. In order to effectively dissipate and cool the heat of the heat source, it is necessary to efficiently transfer the heat of the heat generating part to a circuit board, cooling fin, heat sink, heat diffusion sheet, or a member having a heat radiation / cooling role such as ceramic. For this purpose, it is important to reduce the thermal resistance between the layers.

As shown in FIG. 1, even if members of solids (metals or metals and ceramics) are simply connected, they are basically in point contact due to the unevenness of the surface, and the thermal conductivity is low between the layers. Since there is an air layer (thermal conductivity: 0.02 W / mK), the thermal resistance increases. An interlayer thermal connection member (Thermal Interface Material: hereinafter abbreviated as TIM) is used to lower the thermal resistance between such layers, and is used by being sandwiched between the members. In this case, it is an important requirement that the TIM itself has high thermal conductivity and that the thermal resistance at the interface (between the member and the TIM) is small. In order to reduce the thermal resistance at the interface, it is necessary to increase the contact area of the interface (that is, to make surface contact), and usually TIM requires flexibility.

Conventionally, as TIM, a composite of a flexible polymer material for bringing the interface into surface contact and a high thermal conductive inorganic filler for achieving high thermal conductivity has been used (hereinafter referred to as polymer / inorganic). Abbreviated filler composite). FIG. 2 shows a connection state between the layers. The interface is in surface contact with the polymer / inorganic filler composite, and the air layer is removed from the interlayer. As a result, the thermal resistance between the layers can be reduced. However, when the amount of the high thermal conductive inorganic filler added is increased in order to achieve high thermal conductivity, there is a problem that flexibility is impaired and thermal resistance at the interface increases. Therefore, at present, only a polymer / inorganic filler composite having a thermal conductivity of about 1 to 2 W / mK and a high thermal conductivity product having a thermal conductivity of about 5 W / mK has been commercialized. The thickness of the polymer / inorganic filler composite is about 0.5 to 5 mm.

Since it is difficult for a solid TIM to make the interface completely in surface contact, the magnitude of the thermal resistance at the interface is a problem. Therefore, it is necessary to evaluate the practical characteristics of the TIM not by the thermal conductivity of the TIM itself but by the thermal resistance characteristics between the layers. The thermal resistance value (unit: K · cm ² / W) means how much temperature difference occurs between the layers when there is a heat flow rate of 1 W / cm ² between the layers. The thermal resistance value between the layers is the sum of the thermal resistance of the TIM itself and the thermal resistance at the interface. In the case of a polymer / inorganic filler composite, the value is about 0.4 to 3.0 K · cm ² / W. There are often. Since this thermal resistance value also varies depending on the value of pressure applied during characteristic measurement, it is necessary to write the pressure value during measurement in order to display the thermal resistance value.

In the case of a polymer / inorganic filler composite, the polymer material that is a matrix resin for softening is limited to several types of polymers such as acrylic resin or silicone resin. Has a problem in heat resistance, and in the case of a silicone resin, although the heat resistance characteristics are slightly improved, there is a problem that a silicone monomer generated by high temperature heating causes a contact failure of an electronic device circuit.

On the other hand, a graphite film as a thermal diffusion film is known, although it is not used for TIM. Because of its excellent heat resistance, chemical resistance, high thermal conductivity, and high electrical conductivity, graphite is used in a wide range of fields such as energy, space, and medicine as structural materials, reinforcing materials, sliding materials, conductive materials, etc. It has an important position as an industrial material.

The basic structure of graphite crystal is a layered structure in which the basal planes of carbon atoms connected in a hexagonal network are regularly stacked (the stacking direction is called the c-axis direction, and the carbon atoms connected in a hexagonal network are formed The direction in which the basal plane spreads is referred to as the ab plane direction). The carbon atoms in the basal plane are strongly bonded by a covalent bond, while the stacked basal plane interplane bond is due to a weak Van der Walls force, and the plane spacing is 3.354 A °.
Reflecting such anisotropy, the electrical conductivity and thermal conductivity of graphite are large in the ab plane direction, and the electrical conductivity and thermal conductivity in this direction are good indicators for determining the quality of graphite. The thermal conductivity in the ab plane direction of the highest quality graphite known in the past is 1800 W / mK, and the thermal conductivity in the c-axis direction is 5 W / mK (Non-Patent Documents 1 and 2).

As a method for obtaining a film-like high-quality, high-heat-conductive graphite, a method of directly heat-treating a special polymer to carbonize / graphite (hereinafter abbreviated as a polymer firing method) has been developed. Examples of the polymer used include polyoxadiazole, polyimides, and polyphenylene vinylene (Non-Patent Documents 3 and 4). Patent Documents 1 and 2 and Non-Patent Document 5 disclose films prepared by carbonizing polyimide, polyamide and polybenzimidazole films at 1000 to 2500 ° C. As shown in FIG. 3, the film produced by these methods is oriented so that the c-axis of the graphite crystal is perpendicular to the film plane (orientated so that the ab plane is parallel to the film plane). Film.

High thermal conductivity graphite films obtained by such a method are widely used as thermal diffusion sheets (for example, Patent Documents 3 to 5). The thermal diffusion sheet is used for the purpose of improving cooling and heat dissipation efficiency by spreading the heat of a heat source such as a CPU or LED over a wide range. The graphite sheet is used for such a purpose as described above. The thermal conductivity in the ab plane direction is very large as described above, and the heat generated when a thermal problem occurs in a small electronic device such as a cellular phone. This is because it is optimal as a diffusion material. These graphite thermal diffusion sheets are usually often combined with various polymer films and metals in order to impart adhesion, improve mechanical strength, or impart insulation (patents). References 6-8).

However, the application of such graphite as a heat conduction (diffusion) sheet is completely different from the TIM application, and at present, a graphite TIM has not been put into practical use. The reason is that the heat conduction in the thickness direction of the graphite film is at most about 5 W / mK because the c-axis of the graphite crystal is oriented perpendicular to the film surface, and the graphite is solid. For this reason, the interface is not in perfect surface contact, and the thermal resistance at the interface increases.

As a countermeasure, it is conceivable that the ab plane of the highly thermal conductive graphite crystal is oriented in a direction perpendicular to the graphite film plane, and such graphite is used as the TIM. If such an orientation can be realized, in principle, high thermal conductivity (1800 W / mK) in the ab plane direction of the graphite crystal can be used for interlayer thermal connection (Patent Documents 9 to 11). However, this method is such that the c-axis of the graphite crystal is parallel to the film surface (the ab surface is perpendicular to the film surface) by mechanically cutting laminated or cylindrical graphite blocks. Therefore, it is impossible to increase the area or reduce the thickness to 1 mm or less, and it is possible to obtain a film that is practically a block shape or a plate shape but cannot be regarded as a film. Therefore, it cannot be said that it is a practical method.

In addition, as a method of reducing the thermal resistance between the graphite film and the interface, the graphite film, which has been improved in flexibility by inserting an air layer into the graphite film (that is, reducing the density), is compressed and used to connect the interface. A method for reducing the thermal resistance of the interface by bringing the surface closer to surface connection has been reported (Patent Document 12). However, even if a graphite film subjected to such treatment is used, complete surface connection cannot be realized, and further, there is a problem that the thermal resistance of the graphite film itself is increased by an air layer inserted into the graphite film.

JP 2007-177024 A JP 2008-24571 A JP 2003-158393 A JP 2005-314168 A JP 2006-044999 A JP 2008-171030 A JP 2010-001191 A JP 2011-023670 A JP 2009-295921 A JP 2010-189244 A JP 2011-23670 A JP 2007-217206 A

L. Spain, A. R. Ubbelohde, and D. A. Young. "Electronic properties of oriented graphite" PHILOSOPHICAL TRANSACTIONS OF THE ROYALSOCIETY T. C. Chieu, M. S. Dresselhaus and M. Endo, Phys. Rev. B26, 5867 (1982) M. Murakami, N. Nishiki, K. Nakamura, J. Ehara, H. Okada, T. Kouzaki, K. Watanabe, T. Hoshi, and S. Yoshimura, Carbon, vol. 30, 2, 255 (1992) M. Inagaki, T. Takechi, Y. Hishiyama, and A. Oberin, Chem. Phys. Carbon, 26, 245 (1999) TANSO, No.245, p196-199 (2010)

An object of the present invention is to solve the problems of conventional polymer / inorganic filler composites and to provide a high-performance, high heat-resistant graphite TIM.

As a result of intensive studies, the present inventors have found that a graphite film in which the ab surface of the graphite crystal is oriented perpendicularly to the film surface has interlayer heat connection characteristics far exceeding that of the conventional polymer / inorganic filler composite. In addition, the inventors have found that this interlayer thermal connection member can be produced by a polymer firing method, and have completed the present invention.

That is, the present invention provides a graphite film characterized in that carbon atoms form a graphite crystal in the film, and the angle formed between the ab plane of the graphite crystal and the film plane is 45 ° to 90 °. It has an interlayer thermal connection member.

The graphite film preferably has a thermal conductivity in a direction perpendicular to the film surface that is greater than a thermal conductivity in a direction parallel to the film surface.

The graphite film is preferably 10 μm or less in thickness.

The graphite film is preferably prepared by heat treatment of a polymer film having a thickness of 5 μm or less.

The polymer film preferably contains a condensed aromatic polymer.

The heat treatment is preferably performed in an inert gas atmosphere or in a vacuum, and the treatment temperature is preferably 800 ° C to 3200 ° C.

The condensed aromatic polymer is polyamide, polyazomethine, polyimide, polyquinoxaline, polyoxadiazole, polybenzimidazole, polybenzoxazole, polybenzthiazole, polyquinazolinedione, polybenzoxazinone, polyquinazolone, benzimidazolobenzo It is preferably at least one selected from phenanthroline ladder polymers and derivatives thereof.

The polymer film is formed by applying a solution of a condensed aromatic polymer on a substrate and then drying a coagulated product obtained by bringing the condensed aromatic polymer into contact with a poor solvent. Preferably there is.

It is preferable that the interlayer heat connection member includes a fluid substance having fluidity at room temperature or higher.

It is preferable to contain 1 to 200% by weight of the fluid substance with respect to the weight of the graphite film.

The fluid material is preferably oil having a boiling point of 200 ° C. or higher.

The present invention also includes a step of applying a condensed aromatic polymer solution on a substrate,
Contacting the condensed aromatic polymer with a poor solvent;
Drying the produced coagulum to form a polymer film, and
The present invention relates to a method for producing an interlayer thermal connection member including a step of heat-treating the polymer film to form a graphite film.

The present invention also relates to an interlayer thermal connection method including a step of installing the interlayer thermal connection member of the present invention between members to be thermally connected.

According to the present invention, it is possible to obtain a high-performance interlayer thermal connection member that uses the high thermal conductivity characteristics of the ab plane of the graphite crystal for interlayer thermal connection and is very excellent in flexibility. Furthermore, an interlayer heat connection member having excellent durability and heat resistance can be realized.

It is a conceptual diagram between layers when not using TIM. It is a conceptual diagram of the interlayer connection state at the time of using a polymer / inorganic filler composite. Black circles (●) in the figure are high thermal conductive inorganic fillers. It is a schematic diagram of the graphite film by a prior art. It is the figure which showed the definition of the "film" in this invention. It is a schematic diagram of the graphite film which the interlayer heat connection member of this invention has. It is a conceptual diagram of the interlayer connection state using the graphite film TIM of this invention. 2 is a scanning electron microscope (SEM) photograph of a graphite film included in the interlayer thermal connection member of Example 1. FIG. 2 is a transmission electron microscope (TEM) photograph of a graphite film included in an interlayer thermal connection member of Example 1. FIG.

The interlayer thermal connection member of the present invention is characterized in that carbon atoms form a graphite crystal in the film, and the angle formed by the ab plane of the graphite crystal and the film surface is 45 ° to 90 °. Has a graphite film.
The orientation of the graphite crystal is completely different from the orientation in which the ab plane of the conventional graphite crystal is parallel to the graphite film surface.

As described above, in the graphite film obtained by the conventional polymer baking method, the ab plane of the graphite crystal is parallel (FIG. 3) or randomly oriented with respect to the film plane. It was impossible to align them in parallel.

The carbon hexagonal mesh surfaces generated by the thermal decomposition of the polymer are laminated with each other in a high temperature heat treatment process to form a carbon hexagonal mesh area layer body. The carbon hexagonal network area layer body grows into a graphite crystal having three-dimensional regularity by reducing the stacking interval and simultaneously shifting adjacent network surfaces in the plane direction. When the carbon hexagonal network area layer grows into a graphite crystal, the carbon hexagonal network area layer extends in the plane direction and contracts in the stacking direction. Since such deformation inside the graphite film is constrained by the outer periphery of the graphite film, a biaxial compressive stress is generated in the plane direction and a uniaxial tensile stress is generated in the laminating direction in the carbon hexagonal net layer. Since the elastic modulus of the carbon hexagonal mesh area layer has an overwhelmingly larger value in the plane direction than the laminating direction, the compressive stress is overwhelmingly larger than the tensile stress. Thus, it is considered that the carbon hexagonal network plane is oriented in the direction in which the compressive stress is reduced when growing into a graphite crystal.

For example, when a polymer solution is spread on a substrate in a planar shape, and the polymer chains are oriented parallel to the film surface in the film, such as a polymer film prepared by evaporating and removing the solvent. In addition, the carbon hexagonal mesh surface generated by thermal decomposition is also oriented parallel to the film surface. Usually, such a phenomenon does not occur because rotation of the carbon hexagonal mesh plane oriented parallel to the film surface causes a large internal stress to occur perpendicular to the film surface. Therefore, even when this film is further heat-treated at a high temperature to grow a graphite crystal, the carbon hexagonal network surface in the graphite film remains parallel to the film surface, and the c-axis of the graphite crystal is relative to the film surface. Orient to be vertical. That is, the angle formed by the average ab plane and the film plane is 0 °.

When the c-axis of the graphite crystal is randomly oriented with respect to the film surface, the angle formed by the ab surface of the graphite crystal and the film surface is less than 45 ° on average and 45 ° or more. There is no. This is because the ab plane of the graphite crystal as a whole has the property of being oriented parallel to the film plane, so even though random orientation is not completely random, the average ab plane and film plane This is because the angle formed by is in the range of greater than 0 ° and less than 45 ° and never greater than 45 °.

In this specification, a member between members that can cause a temperature difference is defined as an interlayer.

Further, a member for performing heat transfer from one member to another member is defined as an interlayer thermal connection member (TIM).
A connection interface between the TIM and the member is defined as an interface.

Also, it is a single flat plate shape, where l / t ≧ 1000 and w / t ≧ 1000 and t ≦ 250 μm, where l is length, width is w, and thickness is t Is defined as film. FIG. 4 shows the definition of the film in this specification. Two surfaces whose lengths are 1 and w are defined as film surfaces. In addition, two surfaces whose lengths of two sides are t and l and two surfaces whose lengths are t and w are defined as edge surfaces.

Further, the state in which the angle formed between the ab plane of the graphite crystal and the film plane observed in the transmission electron microscope (TEM) measurement is within the range of 45 ° to 90 ° on average is the ab of the graphite crystal. The angle formed by the surface and the film surface is defined to be 45 ° to 90 °.
The angle formed between the ab plane of the graphite crystal and the film plane can be measured by a method such as a transmission electron microscope (TEM) or X-ray diffraction.

(Graphite film)
In the graphite film, the angle formed by the ab plane of the graphite crystal and the film plane is 45 ° to 90 °, preferably 50 ° to 90 °, and more preferably 60 ° to 90 °. .

FIG. 6 is a conceptual diagram of an interlayer connection state using the graphite film TIM of the present invention. The vertical line in the graphite film indicates the ab plane of the graphite crystal.

The thickness of the graphite film is 250 μm or less, preferably 10 μm or less, more preferably 5 μm or less, and most preferably 3 μm or less. Further, it is preferably 10 nm or more, more preferably 20 nm or more, and most preferably 50 nm or more. When the thickness exceeds 250 μm, there is a problem that the ab plane of the graphite crystal is difficult to be perpendicular to the film plane. On the other hand, if it is less than 10 nm, the thermal resistance of the film itself becomes small, but it may be extremely difficult to handle as a self-supporting film.

Area of the graphite film is preferably at 0.25 cm ² or more, and more preferably 1 cm ² or more. Further, it is preferably 40000Cm ² or less, more preferably 10000 cm ² or less. If it is less than 0.25 cm ² , the range of use may be limited, and if it is greater than 40000 cm ² , it may be difficult to produce a graphite film having a uniform thickness.

Further, when the ab plane of the graphite crystal is oriented perpendicular to the film plane, the thermal conductivity in the direction perpendicular to the film plane is greater than the thermal conductivity in the film plane direction. Actually, according to the present invention, for example, it is possible to produce a graphite film having a high thermal conductivity of 50 W / mK or more in the direction perpendicular to the film surface and larger than the heat conductivity in the film surface direction. I can do it. Incidentally, the thermal conductivity in the direction perpendicular to the film surface is 10 times the thermal conductivity (5 W / mK) in the c-axis direction of the graphite crystal, that is, in the film surface direction.

Therefore, when the thermal conductivity in the direction perpendicular to the film surface is greater than the thermal conductivity in the film surface direction, the ab surface of the graphite crystal is a graphite film oriented perpendicular to the film surface. Can think.

In a randomly oriented graphite film, not only is it difficult to achieve a thermal conductivity of 50 W / mK or more in a direction perpendicular to the film surface, but as described above, the ab plane of the graphite crystal as a whole Needless to say, the thermal conductivity in the direction perpendicular to the film surface does not exceed the thermal conductivity in the direction of the film surface.

The thermal conductivity in the direction perpendicular to the film surface of the graphite film is preferably 50 W / mK or more, and preferably 10 times or more the thermal conductivity in the direction parallel to the film surface. It is more preferable that the thermal conductivity in the direction perpendicular to the film surface is 100 W / mK or more and 20 times or more the thermal conductivity in the direction parallel to the film surface.

The conditions for the thermal conductivity and the anisotropy are conditions for the graphite film of the present invention to have flexibility and compressibility that are preferable as a TIM. A graphite film with a thermal conductivity in the direction perpendicular to the film surface of 50 W / mK or more must have a sufficiently grown graphite crystal and is basically soft and compressible in the film thickness direction to realize a high-performance TIM. I can do it. When the thermal conductivity in the direction perpendicular to the film surface is less than 10 times the thermal conductivity in the direction parallel to the film surface and the thermal conductivity in the direction perpendicular to the film surface is 50 W / mK or less, graphite crystals Insufficient growth of the film tends to make the film itself hard and brittle.

According to the present invention, in principle, the thermal conductivity in the ab plane direction of the graphite single crystal becomes the thermal conductivity in the direction perpendicular to the film plane, and it is expected that a high thermal conductivity of 1800 W / mK can be realized. . Actually, it is extremely difficult to realize a thermal conductivity of 1800 W / mK, but as described above, a high thermal conductivity of 50 W / mK or more can be realized. This value is an extremely excellent value that is 10 times or more that of the highest quality polymer / inorganic filler composite.

(Method for producing graphite film)
The manufacturing method of a graphite film is not specifically limited, For example, it can obtain by the method of heat-processing a polymer film. The polymer film preferably contains a condensed aromatic polymer from the viewpoint of a high carbon content and a carbocyclic structure similar to the ab plane of graphite. Among them, polyamide, polyazomethine, polyoxadiazole, polyimide, polybenzimidazole, polybenzoxazole, polybenzthiazole, polyquinazolinedione, polybenzoxazinone, polyquinazolone, polyquinoxaline, benzimidazobenzophenanthroline ladder polymer, and these It is preferably at least one selected from derivatives. Among these, a benzimidazobenzophenanthroline ladder polymer and derivatives thereof are particularly preferable because they have a high carbon content and a graphite film can be obtained in a high yield.

Further, in order to align the angle between the ab plane of the graphite crystal and the film plane to be 45 ° to 90 °, the thickness of the polymer film is more preferably 5 μm or less, and 2 μm or less. Even more preferably, it is most preferably 1 μm or less.

When the planar polymer chains are randomly oriented in the polymer film, the orientation of the carbon hexagonal network surface generated by thermal decomposition is also random. When this film is further heat-treated at a high temperature to grow a graphite crystal, the ab surface of the graphite crystal tends to be oriented parallel to the film surface, so that even in this case, the orientation is not completely random. It is as follows.

However, the present inventors have found that, in a polymer film in which planar polymer chains are randomly oriented, particularly when the thickness of the film is 5 μm or less, when a graphite crystal is grown by heating at a high temperature, It has been found that the ab plane of the crystal is oriented perpendicular to the film plane. This is considered to be because when the film thickness is sufficiently small with respect to the area of the film surface, the force for restraining deformation in the thickness direction of the film becomes smaller than the force for restraining deformation in the film surface direction. It can also be considered that it is deformed so as to reduce the generated internal stress. As a result, it is considered that the ab plane of the graphite crystal can be oriented perpendicular to the film plane as shown in FIG.

When producing a graphite film of the present invention using a polymer film having a thickness of 5 μm or less, the thickness of the obtained film is often 10 μm or less. That is, the thickness of the resulting graphite film tends to be within twice the thickness of the starting polymer film. The thickness varies depending on the type of the starting polymer film and the disorder of the orientation of the graphite crystal during film formation. The area of the resulting graphite film is often smaller than the area of the starting polymer film. In addition, the thickness of the graphite film obtained may be thinner than the thickness of the starting polymer film.

The polymer film is formed by drying a coagulated product obtained by contacting a condensed aromatic polymer with a poor solvent after applying a solution of the condensed aromatic polymer on a substrate. It is preferable. The substrate on which the condensed aromatic polymer solution is applied is not particularly limited as long as it does not chemically react with the condensed aromatic polymer solution, and is a PET substrate, PBT substrate, glass substrate, quartz substrate, SiC substrate. A known substrate such as a Si substrate, a sapphire substrate, a glassy carbon substrate, or a diamond substrate can be used. Among these, a PET substrate and a glass substrate are preferable because the polymer film can be easily peeled off.

The solvent for dissolving the condensed aromatic polymer is not particularly limited, and for example, methanesulfonic acid, trifluoromethanesulfonic acid, N, N-dimethylformamide and the like can be used.

The method for applying the condensed aromatic polymer solution is not particularly limited, and known methods such as a bar coating method, a doctor blade method, a spin coating method, a printing method, an ink jet method, a spray coating method, and a dip coating method can be used. . In addition, a condensed aromatic polymer film may be formed on the substrate by vapor deposition polymerization.

The molecular orientation of the polymer film is preferably random. As a method for disturbing the molecular orientation, it is preferable to bring the condensed aromatic polymer coated on the substrate into contact with a poor solvent. The type of the poor solvent is not particularly limited, and may be appropriately selected from distilled water, methanol, ethanol, acetone, THF, a mixed solvent thereof, and the like according to the polymer to be used. The method for contacting is not particularly limited, and examples thereof include dipping, coating, spraying, dropping, and dipping.

The condensed aromatic polymer is brought into contact with a poor solvent and solidified into a film on the substrate, and then the solidified product is dried to form a polymer film. The method for drying the polymer film is not particularly limited as long as the method does not change the polymer film chemically and physically, and a known drying method can be used. Among these, vacuum drying, vacuum drying, and freeze drying are particularly preferable.

Thereafter, it is preferable to peel the polymer film from the substrate. The method of peeling is not particularly limited, and the substrate may be removed with a chemical or a solvent. In addition, for example, a solution of a polymer soluble in water or an organic solvent is applied to a condensed aromatic polymer on a substrate and dried to form a laminated film, and then the laminated film is peeled off from the substrate. A method of removing a polymer soluble in water or an organic solvent with a solvent can also be mentioned. The polymer that is soluble in water or an organic solvent is not particularly limited. For example, polymers such as polyvinyl butyral, polyvinyl pyrrolidone, polyvinyl alcohol, and polymethyl methacrylate can be preferably used. The organic solvent is not particularly limited as long as the organic solvent dissolves the polymer and does not dissolve the condensed aromatic polymer film.

As an example, the case where polymethyl methacrylate is used as a polymer soluble in water or an organic solvent will be described in detail. A solution prepared by dissolving polymethyl methacrylate in a solvent is applied onto a condensation aromatic polymer film, and then dried to form a laminated film of the condensation aromatic polymer and polymethyl methacrylate on the substrate. . After peeling off the laminated film from the substrate, polymethyl methacrylate is dissolved and removed with an organic solvent and dried to prepare a condensed aromatic polymer film. The organic solvent is not particularly limited, but acetone, tetrahydrofuran, or N, N-dimethylformamide is preferably used.

As a method for heat-treating the condensed aromatic polymer film, a known method using a tubular electric furnace, a Tamman furnace, a muffle furnace, an induction heating furnace or the like can be used, and it is not particularly limited. The polymer film is preferably heat-treated in an inert gas atmosphere such as nitrogen, argon or helium, or in a vacuum, but the method is not particularly limited.

The temperature for heat-treating the polymer film is not particularly limited as long as it is a temperature at which graphite crystals can be generated, but is preferably 800 ° C. or higher and 3200 ° C. or lower, and particularly preferably 1500 ° C. or higher. If it is less than 800 ° C., the graphite crystal may be difficult to grow. Further, if it is higher than 3200 ° C., it is preferable for the growth of the graphite crystal, but it is not preferable from the economical viewpoint because the consumption of the heater of the furnace used for the heat treatment becomes severe.

It is preferable to heat-treat the condensed aromatic polymer film between plates. The material used for the heat treatment is not particularly limited as long as it does not chemically react with the condensed aromatic polymer film and can withstand heat treatment in an inert gas atmosphere. The material of the material can be adopted. Among them, a glassy carbon plate or a graphite plate is preferable as a substrate that can withstand temperatures of 1500 ° C. or more and 3200 ° C. or less.

(Fluid material)
It is preferable that the interlayer thermal connection member further includes a fluid substance having fluidity at room temperature or higher. By wetting the surface of the graphite film with a fluid substance such as oil, the thermal resistance at the interface can be lowered, the thermal resistance between the layers can be reduced, and excellent interlayer thermal connection can be realized.

The content of the fluid substance is preferably 1 to 200% by weight, more preferably 2 to 100% by weight, and most preferably 5 to 50% by weight based on the weight of the graphite film. If it is less than 1% by weight, the effect of adding tends to be hardly obtained. When it exceeds 200% by weight, the thermal connection resistance of the composite tends to increase due to the thermal resistance of the flowable substance. Here, “fluidity” means a liquid state that easily flows at room temperature, or a paste that is highly viscous and does not flow easily, but can be deformed or spread by applying pressure. Means state.

The fluid substance is not particularly limited, and examples thereof include an oil substance (oil) and a fluid polymer. As the oily substance, mineral oil, vegetable oil, synthetic oil, essential oil, edible oil, animal oil, and mixtures thereof are preferable. Moreover, as the fluid polymer, a silicone resin is preferable. Above all, in order not to lose the high heat resistance and high durability, which are one of the characteristics of TIM, a substance having a low vapor pressure is desirable. The oily substance preferably has a boiling point of 200 ° C. or higher, more preferably 300 ° C. or higher. As a silicone resin, what has fluidity | liquidity between 20 to 100 degreeC is preferable.

(Interlayer thermal connection member)
The interlayer thermal connection member of the present invention may be composed only of a graphite film, and may further include the above-described fluid substance, a metal thin film, an inorganic thin film, a plurality of graphite films, and the like.

The method for producing an interlayer thermal connection member according to the present invention includes a step of applying a condensed aromatic polymer solution on a substrate, a step of bringing the condensed aromatic polymer into contact with a poor solvent, and drying the produced coagulum. Forming a polymer film, and heat-treating the polymer film to form a graphite film.
Specific examples of each process are as described above.

(Interlayer thermal connection method)
The interlayer thermal connection method of the present invention includes a step of installing the interlayer thermal connection member between members to be thermally connected. By sandwiching between the layers, the heat generation source or a member thermally connected to the heat generation source can perform interlayer heat connection for transferring heat to the second member having a temperature lower than that. Each member and the graphite film are in direct contact. In order to realize excellent heat resistance and excellent thermal connection, it is preferable to connect the layers only with a graphite film without using various adhesive layers. As a method for realizing interlayer thermal connection without using an adhesive layer, it may be simply fixed by mechanical pressure. Mechanically caulking with screws, screws, springs or the like is effective and preferable for direct thermal connection.

The layer for sandwiching the graphite film is not particularly limited, but aluminum (thermal conductivity: 237 W / mK), copper (thermal conductivity: 398 W / mK), silver (thermal conductivity: 428 W / mK), nickel ( Metal materials with excellent thermal conductivity such as thermal conductivity: 90 W / mK, silica (thermal conductivity: 1.5 W / mK), alumina (thermal conductivity: 20 W / mK), magnesium oxide (MgO) (heat Conductivity: 40 W / mK), boron nitride (BN) (thermal conductivity: 60 W / mK), aluminum nitride (AlN) (thermal conductivity: 70-270 W / mK), silicon carbide (SiC) (thermal conductivity: A ceramic material such as 88 to 128 W / mK (depending on the crystal system), various polymer materials, or a member in which these are combined can be used.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not restrict | limited at all to description of these Examples.

The physical properties of the graphite film were measured by the following methods.
<Thermal conductivity>
The thermal diffusivity of the graphite film was measured at 23 ° C. under vacuum at 10 Hz using a thermal diffusivity measuring device (“LaserPit” manufactured by ULVAC-RIKO). The thermal conductivity was calculated using the measured thermal diffusivity and the density and specific heat values of the graphite film.

<Interlayer thermal resistance>
A graphite model heater (simulating a CPU as a heating element) and a copper block (15 cm x 15 cm in length and width), each having a shape of 10 mm x 10 mm in length and width of 1.8 mm, cut into a 10 mm x 10 mm size graphite film. A pressure of 1.0 kgf / cm ^{2 to} 4.5 kgf / cm ² was applied. Next, 2.0 W of electric power was supplied to the model heater, and the temperature of the model heater and the temperature of the copper block after 5 minutes were measured using thermocouples embedded therein. The thermal resistance value R (K · cm ² / W) between the model heater and the copper block was calculated using the following equation, where the temperature of the model heater was T ₁ and the temperature of the copper block was T ₂ .
R = (T ₁ −T ₂ ) / 2

[Example 1]
Benzimidazobenzophenanthroline ladder by polycondensation of 1,4,5,8-naphthalenetetracarboxylic acid (1 mol) and 1,2,4,5-benzenetetraamine tetrahydrochloride (1 mol) in polyphosphoric acid A polymer (hereinafter abbreviated as BBL polymer) was synthesized. 0.25 g of BBL polymer was dissolved in 25 ml of methanesulfonic acid (Wako Pure Chemical Industries, manufacturer code No. 138-01576) to prepare coating solution A. Similarly, 1.25 g of polymethyl methacrylate (hereinafter abbreviated as PMMA) (Aldrich, manufacturer code No. 19-3760) is dissolved in 25 ml of ethyl acetate (Wako Pure Chemical Industries, manufacturer code No. 051-00356). A coating liquid B was prepared.

The coating liquid A is spin-coated on a glass substrate, the whole substrate is immersed in distilled water, the BBL polymer is solidified on the glass substrate in a film shape, and dried under reduced pressure overnight to form a BBL polymer film on the glass substrate shape. Formed. The coating liquid B was spin-coated on the BBL polymer film formed on the glass substrate and dried to form a two-layer laminated film composed of the BBL polymer and PMMA on the glass substrate. The two-layer laminated film was peeled off from the glass substrate and transferred onto a filter paper, and PMMA was dissolved and removed using acetone and freeze-dried to obtain a BBL polymer film. The thickness of the obtained BBL polymer film was 120 nm.

This BBL polymer film was sandwiched between graphite plates and heat-treated at 1500 ° C. for 1 hour under a nitrogen atmosphere, and subsequently heat-treated at 2800 ° C. for 1 hour under an argon atmosphere to obtain a graphite film. The obtained film was a self-supporting structure and had optical transparency. The photograph which observed the cross section of the film obtained in FIG. 7 with the scanning electron microscope (SEM) is shown. The film thickness determined from this photographic image was 100 nm.

FIG. 8 shows an image observed by a transmission electron microscope (TEM) with an electron beam incident perpendicular to the edge surface of the obtained film. In FIG. 8, it can be seen that a plurality of elongated images extending in the vertical direction, which is the thickness direction, are each a graphite crystal, and the carbon hexagonal mesh surface of the graphite crystal is oriented perpendicular to the film surface. Thus, although the carbon hexagonal network surface in this film has a slight distribution, it is oriented almost uniformly perpendicular to the film surface over the entire observation region, and the ab surface and the film surface of the graphite crystal It is clear that the angle formed by is 45 ° or more. From the above results, it was found that the graphite crystal was oriented so that the angle formed by the ab plane and the film plane was 45 ° to 90 °. Further, the thermal conductivity in the direction perpendicular to the film surface of this graphite film was 200 W / mK, and the thermal conductivity in the film surface direction was 20 W / mK.

When the graphite film was used, the thermal resistance value between the layers was 0.09 to 0.18 K · cm ² / W as shown in Table 1. Considering that the heat resistance value when using a polymer / inorganic filler composite generally used is about 0.4 to 3.0 K · cm ² / W, the graphite film of the present invention is extremely useful as a TIM. I found it excellent.

[Comparative Example 1]
5 g of the BBL polymer synthesized in the same manner as in Example 1 was dissolved in 100 ml of methanesulfonic acid to prepare a BBL polymer solution. This BBL polymer solution was developed in a petri dish and heated under reduced pressure to evaporate and remove the solvent. The BBL polymer film formed on the bottom of the petri dish was peeled off, washed sequentially with a methanol solution of triethylamine and methanol, and then dried under reduced pressure at room temperature to obtain a BBL polymer film. The resulting BBL polymer film had a thickness of 320 nm. The obtained BBL polymer film was heat-treated in the same manner as in Example 1 to obtain a graphite film having a thickness of 120 nm. In the obtained graphite film, it was confirmed that the ab surface of the graphite crystal was oriented so as to be parallel to the film surface. The thermal conductivity in the direction perpendicular to the film surface was 5 W / mK, and the thermal conductivity in the film surface direction was 1200 W / mK.

When this graphite film is used, the thermal resistance value between the layers is 0.14 to 0.34 K · cm ² / W as shown in Table 1, and when the conventional polymer / inorganic filler composite is used. Although it was excellent in heat resistance characteristics by comparison, it was found to be inferior to the graphite film of Example 1.

[Example 2]
20 g of acetic anhydride and 10 g of isoquinoline are added to 100 g of an 18 wt% DMF solution of polyamic acid synthesized from pyromellitic dianhydride, 4,4′-diaminodiphenyl ether and p-phenylenediamine (4/3/1 in molar ratio). The hardener consisting of was mixed, stirred, defoamed by centrifugation, and cast onto an aluminum foil. The process from stirring to defoaming was performed while cooling to 0 ° C. This laminate of aluminum foil and polyamic acid solution was heated at 120 ° C. for 150 seconds, and further heated at 300 ° C. for 30 seconds. Next, it was immersed in distilled water to solidify the polymer into a film and dried overnight under reduced pressure to form a polymer film. The aluminum foil was removed by etching to obtain a self-supporting polyimide film. The thickness of the polyimide film was 300 nm.

This polyimide film was sandwiched between graphite plates and heat treated at 1500 ° C. for 1 hour in a nitrogen atmosphere, and then heat treated at 2800 ° C. for 1 hour in an argon atmosphere to obtain a graphite film. The cross section of the obtained graphite film was observed with SEM, and the thickness of the film was determined to be 230 nm. The thermal conductivity in the direction perpendicular to the film surface of this graphite film is 100 W / mK, the thermal conductivity in the film surface direction is 40 W / mK, and the thermal conductivity in the direction perpendicular to the film surface is the heat conductivity in the film surface direction. It was concluded that this film was a graphite film oriented so that the ab plane of the graphite crystal was mainly perpendicular to the film plane.

As shown in Table 1, the thermal resistance value between the layers when the above graphite film was used was 0.11 to 0.20 K · cm ² / W. Considering that the heat resistance value between layers when using a generally used polymer / inorganic filler composite is about 0.4 to 3.0 K · cm ² / W, the graphite film of the present invention is extremely It turned out to be an excellent TIM.

[Comparative Examples 2-1 and 2-2]
20 g of acetic anhydride and 10 g of isoquinoline are added to 100 g of an 18 wt% DMF solution of polyamic acid synthesized from pyromellitic dianhydride, 4,4′-diaminodiphenyl ether and p-phenylenediamine (4/3/1 in molar ratio). The hardener consisting of was mixed, stirred, defoamed by centrifugation, and cast onto aluminum foil at different thicknesses. The process from stirring to defoaming was performed while cooling to 0 ° C. The laminate of the aluminum foil and the polyamic acid solution was heated at 120 ° C. for 150 seconds to obtain a gel film having self-supporting properties. This gel film was peeled off from the aluminum foil and fixed to the frame. This gel film was heated at 300 ° C., 400 ° C., and 500 ° C. for 30 seconds in sequence to obtain polyimide films having different thicknesses. The film thickness was 1.0 μm and 600 nm, respectively.

The obtained polyimide film was pretreated using an electric furnace in nitrogen gas at 1000 ° C. for 1 hour. The obtained carbonized film surface was sandwiched between surface-polished graphite blocks, set inside a cylindrical graphite heater, heated to 2800 ° C., and held for 10 minutes. This heat treatment was performed in an argon atmosphere. The thickness of the obtained graphite film was 300 nm and 74 nm, respectively. They are referred to as Comparative Example 2-1 and Comparative Example 2-2, respectively. From the results of the cross-sectional TEM measurement, it was confirmed that the ab planes of the graphite crystals were aligned so as to be parallel to the film plane. In the graphite film of Comparative Example 2-1, the thermal conductivity in the direction perpendicular to the film surface was 4.8 W / mK, and the thermal conductivity in the direction parallel to the film surface was 1700 W / mK. In the graphite film of Comparative Example 2-2, the thermal conductivity in the direction perpendicular to the film surface was 5.0 W / mK, and the thermal conductivity in the direction parallel to the film surface was 1850 W / mK.

As shown in Table 1, the thermal resistance value between the layers when the above two types of graphite films are used is 0.14 to 0.34 K · cm ² / W in Comparative Example 2-1, and in Comparative Example 2-2. Although it is 0.18-0.33 K * cm < ² > / W and it is the heat resistance characteristic excellent compared with the case where the conventional polymer / inorganic filler composite_body | complex is used, the graphite film of Example 1, 2 is shown. It turned out to be inferior compared to the case.

[Examples 3-1, 3-2, 3-3]
The graphite film of Example 1 (thickness 100 nm) was immersed in a commercially available canola oil (smoke point 204 ° C.), and then placed on oil-absorbing paper to absorb the canola oil. Different graphite films were made. The amount of impregnation was measured by weight measurement. The thermal resistance between the layers when these graphite films were used was measured by the same method as in Example 1. The experimental results are shown in Table 2. Compared to the thermal resistance without impregnation of canola oil, the thermal resistance between layers could be reduced when 3 to 75% by weight of canola oil was impregnated. This is probably because the canola oil on the graphite surface increased the substantial contact area of the interface and decreased the thermal resistance of the interface.

Comparing the above examples, comparative examples, and conventionally used polymer / inorganic filler composites, it is clear that the graphite film of the present invention is a TIM having very excellent characteristics.

This is because the ab surface of the graphite crystal is oriented so that it is perpendicular to the film surface, so that the flexibility of the graphite film is sufficiently large, so that the substantial contact area of the interface is reduced. This is thought to be because it grows.

Such a graphite film does not deteriorate even at a high temperature of 600 ° C. and has extremely excellent heat resistance. Furthermore, it has been clarified that the thermal resistance of the interface can be lowered by wetting the surface of the graphite film with a fluid substance such as oil. Of course, when a fluid material such as oil is used, the heat resistance of the TIM is somewhat sacrificed, but by selecting a fluid material with a high boiling point, the heat resistance surpasses that of conventional polymer / inorganic filler composites. Realization of characteristics becomes possible.

Claims (13)

An interlayer heat connection member having a graphite film, wherein carbon atoms form a graphite crystal in the film, and an angle between the ab plane of the graphite crystal and the film surface is 45 ° to 90 °. The interlayer thermal connection member according to claim 1, wherein the graphite film has a thermal conductivity in a direction perpendicular to the film surface larger than a thermal conductivity in a direction parallel to the film surface. The interlayer thermal connection member according to claim 1, wherein the graphite film has a thickness of 10 μm or less. The interlayer thermal connection member according to any one of claims 1 to 3, wherein the graphite film is produced by heat treatment of a polymer film having a thickness of 5 µm or less. The interlayer heat connecting member according to claim 4, wherein the polymer film contains a condensed aromatic polymer. The interlayer heat connection member according to claim 4 or 5, wherein the heat treatment is performed in an inert gas atmosphere or in a vacuum, and the treatment temperature is 800 ° C to 3200 ° C. The condensed aromatic polymer is polyamide, polyazomethine, polyimide, polyquinoxaline, polyoxadiazole, polybenzimidazole, polybenzoxazole, polybenzthiazole, polyquinazolinedione, polybenzoxazinone, polyquinazolone, benzimidazobenzo The interlayer thermal connection member according to claim 5 or 6, wherein the interlayer thermal connection member is at least one selected from phenanthroline ladder polymers and derivatives thereof. The polymer film is formed by applying a solution of a condensed aromatic polymer onto a substrate and then drying a coagulum obtained by contacting the condensed aromatic polymer with a poor solvent. The interlayer thermal connection member according to claim 5, wherein the interlayer thermal connection member is provided. The interlayer thermal connection member according to claim 1, comprising a fluid substance having fluidity at room temperature or higher. The interlaminar thermal connection member according to claim 9, wherein the fluid substance is included in an amount of 1 to 200% by weight based on the weight of the graphite film. The interlayer heat connecting member according to claim 9, wherein the fluid substance is an oil having a boiling point of 200 ° C. or more. Applying a solution of a condensed aromatic polymer onto a substrate;
Contacting the condensed aromatic polymer with a poor solvent;
Drying the produced coagulum to form a polymer film, and
A method for producing an interlayer thermal connection member, comprising a step of heat-treating the polymer film to form a graphite film. The interlayer thermal connection method including the process of installing the interlayer thermal connection member in any one of Claims 1-11 between the members to thermally connect.