JP2016153356A - High heat-conductive heat radiation substrate and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a soft, smooth, and lightweight high heat-conductive heat radiation substrate that can be used as a substrate for electronics.SOLUTION: In a high heat-conductive heat radiation substrate, a graphite sheet has a thickness of 0.5 μm or more and 9.6 μm or less, an arithmetic surface roughness of 1.5 μm or less, and a thermal conductivity in the plane direction of 1,800 W/mK or more. When the high heat-conductive heat radiation substrate is manufactured, it is preferable that the substrate is manufactured via a surface polishing process.SELECTED DRAWING: None

Description

  The present invention relates to a highly thermally conductive heat dissipation substrate (for example, a flattened graphite sheet) having excellent surface smoothness, flexibility, and high thermal conductivity in the surface direction, and a method for producing the same.

  In recent years, flexible electronics having features such as light weight, flexibility, thinness, and the like that have not existed in electronics have attracted attention (Non-Patent Document 1). Such flexible electronic devices can be directly attached to places, clothes, and skin, which are difficult to install with conventional devices, and their application development to video communication equipment, sports, medical fields, etc. is accelerating. In order to give flexibility, flexible electronics are often made of a plastic substrate or a rubber substrate. Furthermore, in actual devices, there are many layers of plastic layers such as gas barrier films, insulating films, and protective films for protection, so heat is likely to accumulate in the device and heat dissipation is not possible. There is a problem that the reduction is likely to occur. Particularly in the case of using an organic semiconductor material, deterioration of characteristics due to heat is an important problem (Non-Patent Documents 2 and 3).

In general electronic devices, a heat sink and a fan such as copper (density 8.94 g / cm ³ , thermal conductivity 398 W / mK), aluminum (density 2.70 g / cm ³ , thermal conductivity 237 W / mK) are used in combination. Heat dissipation is performed (Non-Patent Document 4). However, in the field of flexible electronics, where light weight is important, there is no place to install a fan, etc., and the cooling method used in smartphones etc. is mainly radiating heat to the entire housing, so heat from the heat source is efficiently In order to disperse, a material that is lighter than copper and higher in thermal conductivity than aluminum is required.

  Graphite has high thermal conductivity and is already used in tablets, PCs, mobile phones and the like because of its lightness of about 25% of copper, and is expected as a heat dissipation substrate for flexible electronics in the future (Non-patent Document 5). A highly oriented graphite block (HOPG) or an isotropic graphite substrate has been reported as a heat dissipation graphite substrate, but this substrate has surface irregularities that occur during fabrication, and these surfaces can be smoothed by various polishing methods. However, it is extremely difficult to cut out these materials into a film having a thickness of 50 μm or less, and there is a problem that the flexibility of the sheet is poor even when cut out (Non-Patent Document 6). In addition, it is necessary to add an insulator for the planarization, but it is difficult to completely planarize the original substrate because of the large unevenness of the original substrate. Further, since this unevenness affects the characteristics of the device, it is as flat as possible. (Non-patent Document 7).

  Examples of natural graphite sheets have been reported, but since natural graphite is rolled and used, it is necessary to increase the thickness of the graphite sheet to some extent in order to ensure physical strength, and its thermal conductivity Tends to be low (Patent Document 1). In particular, a natural graphite sheet having a thickness of 50 μm or less has poor mechanical strength and flexibility, and there is a problem that flattening such as polishing is difficult due to the soft and brittle characteristics even if the surface is made flat.

  As described above, a substrate for producing a flexible electronic device is required to have flexibility, light weight, high heat dissipation, and flatness, and development of a highly thermally conductive material having these features is eagerly desired.

Japanese Patent No. 3691836

Nikkei Electronics November 24, 2014 issue, page 26 Chen, J.A. et al. J. Polym. Sci. Part B: Polym. Phys. , Vol. 44,3631-3641 (2006) Ebata, H .; et al. , J .; Am. Chem. Soc. , 129, 15732 (2007) Heat control, heat dissipation / cooling technology in the electronics field, volume 2 (Technical Information Association) Production and Technology 66,84, (2014) Industrial Chemical Journal 65 (4), 463-466, (1962) (The Chemical Society of Japan) Sekitani, T .; et al. , Nature Materials 9, 1015, (2010)

  An object of the present invention is to provide a flexible, smooth, lightweight high thermal conductive heat dissipation substrate that can be used as a substrate for electronics, and a method for manufacturing the same.

  From the above background, the present inventors have high flexibility that can be used as a substrate for electronics, flatness, and smoothness, while being able to instantaneously diffuse heat generated from an integrated circuit or the like. Conducted research on conductive heat dissipation substrates.

  As a result, using a graphite sheet produced by heat-treating a polymer film at an ultra-high temperature of 2800 ° C. or higher, and polishing the surface by various methods, a highly thermally conductive heat dissipation substrate having flexibility and surface smoothness is produced. It was discovered that it was possible to achieve the present invention.

  Substrates having such flexibility, flatness, lightness, and high thermal conductivity are very rare, and therefore the range of application is considered to be very wide.

That is, the present invention is as follows.
1) The thickness of the graphite sheet is 9.6 μm or less, 0.5 μm or more, the arithmetic surface roughness of the graphite sheet is 1.5 μm or less, and the thermal conductivity in the surface direction of the graphite sheet is 1800 W / mK or more. A highly heat-conductive heat dissipation board.
2) The thickness of the graphite sheet is 9.6 μm or more and 50 μm or less, the arithmetic surface roughness of the graphite sheet is 2.0 μm or less, and the thermal conductivity in the surface direction of the graphite sheet is 1300 W / mK or more. High heat conductive heat dissipation board.
3) The highly heat-conductive heat dissipation substrate according to 1) or 2), wherein the graphite sheet is not damaged even in a bending test using a mandrel having a diameter of 10 mm.
4) The graphite sheet density is 1.8 g / cm ³ or more, 2.26 g / cm ³ high thermal conductivity heat dissipation substrate according to any one of features 1) to 3) that less.
5) The highly heat-conductive heat dissipation substrate according to any one of 1) to 4), comprising the graphite sheet and an insulating layer having a thickness of more than 1 μm and not more than 100 μm.
6) The high thermal conductive heat dissipation substrate according to 5), wherein the insulating layer is a polymer film or an insulating inorganic compound.
7) The polymer film is made of polystyrene resin, polyethylene resin, polyimide resin, polymethyl methacrylate resin, polycarbonate resin, silicone resin, epoxy resin, polyamide resin, polyethylene terephthalate resin, polyethylene naphthalate resin, fluorine resin, cycloolefin polymer. The high thermal conductive heat dissipation substrate according to 6), which is made of any one of resins.
8) The insulating inorganic compound comprises a single layer or a laminate of aluminum nitride, aluminum oxide, aluminum nitride oxide, magnesium oxide, crystalline silica, aluminum hydroxide, boron nitride, silicon nitride, silicon carbide, or beryllium oxide. A highly heat-conductive heat dissipation substrate as described in 6), which is characterized in that
9) The method for producing a highly heat-conductive heat dissipation substrate according to any one of 1) to 8), comprising a step of polishing a graphite sheet.
10) The method of polishing a graphite sheet is selected from the group consisting of blast polishing, belt polishing, lapping polishing, buff polishing, shot polishing, electrolytic polishing, ion milling, and focused ion beam (FIB). 9) The method for producing a high thermal conductive heat dissipation substrate according to 9).
11) The method for producing a highly heat-conductive heat dissipation substrate according to 10), wherein the method for polishing the graphite sheet is lapping or buffing.
12) Polishing using one or more abrasives selected from the group consisting of alumina, diamond slurry, colloidal silica, and cerium oxide, according to any one of 9) to 11) A method for producing a high thermal conductive heat dissipation substrate.
13) The method for producing a high thermal conductive heat dissipation substrate according to any one of 9) to 12), wherein, when the polishing apparatus is used, the graphite sheet is bonded to a graphite block and then polished. .
14) Buffing, ion milling, or focused ion beam (FIB) of a graphite sheet having a film thickness of 5 μm or less is performed, and the high thermal conductive heat dissipation substrate according to any one of 9) to 13) Manufacturing method.
15) The method for producing a high thermal conductivity heat dissipation substrate according to 14), wherein ion milling is performed.

  ADVANTAGE OF THE INVENTION According to this invention, it can be used as a board | substrate for electronics, and a flexible, smooth, lightweight highly heat conductive heat dissipation board | substrate and its manufacturing method can be provided. In addition, according to the present invention, it is also possible to provide a high thermal conductive heat dissipation substrate that can adjust the width setting and positioning of the electrode with high accuracy when a device is manufactured by patterning, vapor deposition, or the like.

FIG. 1 shows an SEM photograph of the graphite sheet obtained in Example 13 before buffing (FIG. 1 (a)) or after buffing (FIG. 1 (b)) (the magnification of the SEM photograph is 1000 times). .)

Details of the present invention will be described below, but the present invention is not limited to the following description.
In the present specification, the high thermal conductive heat dissipation substrate may be referred to as a graphite sheet, a graphite film, graphite, or a graphite sheet.

  The high thermal conductive heat dissipation board of the present invention has a thermal conductivity corresponding to a predetermined thickness and a predetermined arithmetic surface roughness. Even if the conventional graphite sheet is thin and has a high thermal conductivity, undulation is likely to occur due to the thinness of the film and static electricity, making it difficult to perform surface treatment. The high thermal conductivity heat dissipation substrate of the present invention polishes the surface of the graphite sheet in a predetermined manner while maintaining a predetermined thickness and thermal conductivity, thereby simultaneously providing heat dissipation, flexibility (for example, flexibility), and smoothness. Can be achieved.

  The high thermal conductive heat dissipation substrate of the present invention is preferably a film obtained by baking a polymer, and more preferably an aromatic polymer. The aromatic polymer is preferably at least one selected from polyamide, polyimide, polyquinoxaline, polyoxadiazole, polybenzimidazole, polybenzoxazole, polybenzthiazole, and derivatives thereof. What is necessary is just to manufacture these films with a well-known manufacturing method.

  A particularly preferred aromatic polymer is an aromatic polyimide. Above all, the aromatic polyimide prepared from polyamic acid from acid dianhydride (especially aromatic dianhydride) and diamine (especially aromatic diamine) described below is used as a raw material polymer for preparing graphite of the present invention. Particularly preferred.

<Polyimide synthesis and film formation>
Examples of the acid dianhydride include pyromellitic acid anhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 1,2 , 5,6-naphthalenetetracarboxylic dianhydride, p-phenylenebis (trimellitic acid monoester acid anhydride), ethylene bis (trimellitic acid monoester acid anhydride), bisphenol A bis (trimellitic acid monoester) Acid anhydrides), and the like, which can be used alone or in any proportion of the mixture. In particular, as the polymer structure has a linear and rigid structure, the orientation of the polyimide film increases, and from the viewpoint of availability, pyromellitic anhydride, 3,3 ′, 4,4 ′ -Biphenyltetracarboxylic dianhydride is preferred.

  Examples of the diamine include 4,4′-diaminodiphenyl ether, p-phenylenediamine, 4,4′-diaminodiphenylpropane, 4,4′-diaminodiphenylmethane, benzidine, 1,4-diaminobenzene (p-phenylenediamine), 1,3-diaminobenzene, 1,2-diaminobenzene and the like can be used. These can be used alone or in a mixture in any proportion. Further, from the viewpoint of increasing the orientation of the polyimide film and availability, it is preferable to synthesize using 4,4'-diaminodiphenyl ether and p-phenylenediamine as raw materials.

  The polyimide production method includes a heat curing method in which the precursor polyamic acid is converted to imide by heating, a polyhydric acid such as acetic anhydride and other dehydrating agents, picoline, quinoline, isoquinoline, pyridine, etc. There is a chemical cure method in which both or one of the tertiary amines is used as an imidization accelerator and imide conversion is performed, and any of them may be used. The resulting film has a small coefficient of linear expansion, a high elastic modulus, and a high birefringence, which can be easily damaged without being damaged even when a tension is applied during the baking of the film, and a high-quality graphite can be obtained. Therefore, the chemical cure method is preferable.

  The polymer film can be produced from the polymer raw material or its synthetic raw material by various known methods. For example, a polyimide film is produced by casting an organic solvent solution of polyamic acid, which is the polyimide precursor, on a support such as an endless belt or a stainless drum, followed by drying and imidization. Specifically, the method for producing a film by chemical curing is as follows. First, a stoichiometric or higher stoichiometric dehydrating agent and a catalytic amount of an imidization accelerator are added to the above polyamic acid solution, and cast or coated on a support such as a support plate, an organic film such as PET, a drum or an endless belt, etc. And a film having self-supporting properties is obtained by evaporating the organic solvent. Then, this is further heated and dried to imidize to obtain a polyimide film. The temperature during heating is preferably in the range of 150 ° C to 550 ° C. Furthermore, it is preferable to include a step of fixing or stretching the film in order to prevent shrinkage during the polyimide manufacturing process. This is because the conversion to graphite proceeds more easily by using a film having a controlled molecular structure and higher order structure. In other words, in order for the graphitization reaction to proceed smoothly, the carbon molecules in the carbon precursor need to be rearranged. However, since polyimides with excellent orientation require minimal rearrangement, they can be converted to graphite even at low temperatures. It is presumed that the conversion of

  Moreover, the graphite sheet produced from a polymer film has very high flexibility and flexibility. This is because graphite as a raw material is produced from a single polymer film, and is due to graphite arranged without gaps in the plane direction. On the other hand, a product obtained by rolling normal natural graphite has poor flexibility and flexibility, and is easily damaged when actually bent. HOPG, glassy carbon and the like have a very high hardness but tend to have poor flexibility and flexibility.

<Carbonization / graphitization>
Next, a method for carbonization / graphitization of a polymer film represented by polyimide will be described. In the present invention, the starting polymer film is preheated in an inert gas to perform carbonization. As the inert gas, nitrogen, argon or a mixed gas of argon and nitrogen is preferably used. Preheating is usually performed at about 1000 ° C. Usually, a polyimide film thermally decomposes around 500 to 600 ° C. and carbonizes around 1000 ° C. In the pretreatment stage, it is effective to apply a pressure in the plane direction that does not cause the film to break so that the orientation of the starting polymer film is not lost.

  The film carbonized by the above method is set in a high temperature furnace and graphitized. The carbonized film is preferably set between a CIP material and a glassy carbon substrate. Graphitization is usually carried out at a high temperature of 2600 ° C. or higher or 2800 ° C. or higher. In order to produce such a high temperature, a current is usually passed directly to the graphite heater, and heating is carried out by utilizing the Joule heat. Graphitization is performed in an inert gas. Argon is most suitable as the inert gas, and a small amount of helium may be added to argon. The higher the treatment temperature, the higher the quality graphite can be converted. By pyrolysis and carbonization, the area shrinks by about 10 to 40% from the original polyimide film, and in the process of graphitization, on the contrary, it is often expanded by about 10%. Due to such shrinkage and expansion, internal stress is generated in the graphite sheet, and distortion is generated in the graphite sheet. Such strain and internal stress are alleviated by treating at 3000 ° C. or higher, the graphite layers are regularly arranged, and the thermal conductivity is further increased. In order to obtain the graphite of the present invention, it is insufficient at 2600 ° C., the treatment temperature is preferably 2800 ° C. or more, more preferably 3000 ° C. or more, more preferably 3100 ° C. or more, and more preferably 3200 ° C. or more. Is most preferred. Of course, this treatment temperature may be the maximum treatment temperature in the graphitization process, and the obtained graphite sheet may be reheated in the form of annealing. The upper limit of the heat treatment temperature is, for example, 3700 ° C. or lower, preferably 3600 ° C. or lower, more preferably 3500 ° C. or lower. The holding time at the treatment temperature is, for example, 20 minutes or longer, preferably 30 minutes or longer, and may be 1 hour or longer. The upper limit of the holding time is not particularly limited, but it may be usually 5 hours or less, particularly 3 hours or less. In the case of graphitizing by heat treatment at a temperature of 3000 ° C. or higher, the atmosphere in the high temperature furnace is preferably pressurized by the inert gas. When the heat treatment temperature is high, sublimation of carbon starts from the sheet surface, and deterioration phenomena such as holes on the graphite sheet surface, expansion of cracks and thinning occur, but such deterioration phenomenon can be prevented by applying pressure, and excellent graphite A sheet can be obtained. The atmospheric pressure (gauge pressure) of the high-temperature furnace with the inert gas is, for example, 0.10 MPa or more, preferably 0.12 MPa or more, and more preferably 0.14 MPa or more. The upper limit of the atmospheric pressure is not particularly limited, but may be, for example, about 2 MPa or less, particularly about 1.8 MPa or less.

<Characteristics of high thermal conductivity graphite sheet>
The high thermal conductivity graphite sheet of the present invention having a thermal conductivity of 1800 W / mK or more or 1960 W / mK or more has a thickness of 9.6 μm or less and more than 0.5 μm or 0.5 μm or more. In order to obtain a sheet, the thickness of the raw material polymer film is preferably in the range of 25 μm to 1 μm. This is because the thickness of the finally obtained graphite sheet is generally about 60 to 30% of the thickness when the starting polymer film is 1 μm or more, and often about 50 to 20% when the thickness is 1 μm or less. Yes. Therefore, in order to finally obtain a graphite sheet having a thickness of 9.6 μm or less and 0.5 μm or more of the present invention, the thickness of the starting polymer film is preferably in the range of 30 μm or less and 1 μm or more.

  In order to obtain a graphite sheet having a thermal conductivity of 1300 W / mK or more, 1350 W / mK or more, 50 μm or less, 9.6 μm or more, or 20 μm or more, the starting polymer film has a thickness of 125 μm or less, It is preferably in the range of 40 μm or more, and the length direction is preferably reduced to about 100 to 70%.

  The high thermal conductivity graphite sheet having a thermal conductivity of 1800 W / mK or more or 1960 W / mK or more of the present invention is 9.6 μm or less and 0.5 μm or more from the viewpoint that the thinner the sheet, the better the thermal conductivity. This is considered as follows. That is, in the graphite sheet production by the polymer firing method, it is considered that the graphitization reaction forms a graphite structure in the outermost surface layer of the polymer carbonized sheet and the graphite structure grows toward the inside of the film. When the film thickness of the graphite sheet is increased, the graphite structure inside the carbonized sheet is disturbed during graphitization, and cavities and defects are easily formed. On the contrary, if the sheet becomes thinner, graphitization proceeds to the inside with the graphite layer structure on the surface of the sheet being in order, and as a result, it is easy to form a graphite structure in the entire sheet. Since the graphite layer structure is in place as described above, it is considered that the graphite sheet exhibits high thermal conductivity. The range of the thickness of the graphite sheet of the present invention is 9.6 μm or less and 0.5 μm or more, preferably 7.5 μm or less and 1 μm or more, more preferably 2 μm or more and 5 μm or less. When the thickness of the graphite sheet is larger than 9.6 μm, the graphite structure inside the carbonized sheet is disturbed during graphitization, and cavities and defects are easily formed, and a film having a thermal conductivity of 1800 W / m or more or 1950 W / mK or more is produced. Is difficult. Also, if it is less than 0.5 μm, it is not preferable because it has high thermal conductivity and flexibility but lacks physical strength and may be damaged during polishing.

  In another aspect, the high thermal conductivity graphite sheet having a thermal conductivity of 1300 W / mK or more or 1350 W / mK or more is preferably 9.6 μm or more and 50 μm or less, more preferably 40 μm or less, and further preferably 30 μm or less. If the thickness of the graphite sheet is larger than 50 μm, the graphite structure inside the carbonized sheet is disturbed during graphitization, and cavities and defects are easily formed.

<Density>
The density of the graphite sheet according to the present invention is preferably 1.8 g / cm ³ or more. In general, a highly heat conductive graphite sheet has a very dense structure with no defects or cavities in the sheet. If defects or cavities enter the graphite sheet, the density tends to decrease and the thermal conductivity tends to decrease. Accordingly, the density of the graphite sheet is preferably 1.80 g / cm ³ or more, more preferably 2.0 g / cm ³ or more, and most preferably 2.1 g / cm ³ or more. The upper limit of the density is, for example, 2.26 g / cm ³ or less, and may be 2.20 g / cm ³ or less.

  In order to increase flexibility, the graphite sheet may be roll-pressed. During carbonization or graphitization, foaming may occur partially depending on the type of polyimide film and additives. This foaming may partially lower the flexibility and thermal conductivity. By crushing the foaming of the film to make the laminated state dense, the thermal conductivity and flexibility are improved. This rolling does not lower the thermal conductivity.

  The graphite sheet of the present invention has a thermal conductivity in the ab plane direction at a temperature of 25 ° C. of 1800 W / mK or more or 1950 W / mK or more when the thickness is 9.6 μm or less and 0.5 μm or more. The rate is preferably 1960 W / mK or more, more preferably 2000 W / mK or more, further preferably 2050 W / mK or more, particularly preferably 2080 W / mK or more, and most preferably 2100 W / mK or more. is there. Further, the thermal conductivity may be, for example, 2400 W / mK or less, or 2300 W / mK or less.

  These flexible electronic devices are also used in wearable devices such as eyeglass-type devices, clothing-mounted devices, and sensors that are attached directly to the skin, and are emitted from devices (communication coils, batteries, sensors, CPUs, wiring, etc.). It is preferable that the substrate has a high thermal conductivity from the viewpoint that the higher the thermal conductivity is, the more the heat generated can be mitigated because there is a risk of burns due to heat.

  When these flexible electronic devices are worn for a long time, the uncomfortable feeling caused by heat between the devices and the body also becomes a problem. For this reason, the board | substrate used for a flexible electronic device is so preferable that heat dissipation is high, It is preferable that it is 1800 W / mK or more, More preferably, it is 1850 W / mK or more, More preferably, it is 1900 W / mK or more, More preferably, it is 1960 W / mK or more, even more preferably 2000 W / mK or more, even more preferably 2050 W / mK or more, particularly preferably 2080 W / mK or more, and most preferably 2100 W / mK or more. Further, the thermal conductivity may be, for example, 2400 W / mK or less, or 2300 W / mK or less.

  When the thickness of the graphite sheet of the present invention is 9.6 μm or more and 50 μm or less, the thermal conductivity in the ab plane direction at a temperature of 25 ° C. is preferably 1300 W / mK or more, or 1350 W / mK or more, more preferably 1400 W / m mK or more, more preferably 1500 W / mK or more. In this case, since the amount of heat transfer increases even when the film thickness is increased, the generated heat can be sufficiently diffused.

<Polishing method>
The present invention also includes a method for producing a high thermal conductive heat dissipation substrate, which includes a step of polishing a graphite sheet.
Although not particularly limited, examples of the method for polishing the obtained graphite sheet include blast polishing, belt polishing, lapping polishing, buff polishing, shot polishing, electrolytic polishing, ion milling, and focused ion beam (FIB). Polishing of the graphite sheet having a film thickness of 50 μm to 5 μm is preferably buffing or lapping. In particular, it is possible to suppress scratches on the surface of the graphite sheet by polishing with a buff or the like. As the abrasive used at this time, any of alumina, diamond (diamond slurry), colloidal silica, cerium oxide, or a combination thereof may be used.

  These abrasives may be surface-treated in order to improve dispersibility and the like. Diamond may be single crystal or polycrystalline. For this polishing, a polishing apparatus may be used. In that case, after polishing the graphite sheet to a graphite block or the like, the polishing can be performed to perform good polishing. Affixing to the block may be performed at room temperature or high temperature, and is preferably performed at high temperature from the viewpoint of removal again.

  Affixing temperature is 10 degreeC or more and 200 degrees C or less, for example, Preferably it is 30 degreeC or more and 150 degrees C or less. The material used for pasting may be a fixing wax such as a hot melt adhesive, and more specifically, an adfix adhesive, a sky wax adhesive, a shift wax adhesive, an alcohol wax. It is possible to use a base adhesive, an aqua wax adhesive, a natural resin, or the like.

When the graphite sheet is peeled from the block after polishing, it may be heated again.
The wax adhering to the graphite sheet is preferably washed with a solvent, warm water or the like. Examples of the solvent include alcohol solvents such as water, methanol, ethanol, isopropyl alcohol, ethylene glycol, diethylene glycol, triethylene glycol, and propylene glycol, ester solvents such as methyl acetate, ethyl acetate, and butyl acetate, acetone, methyl ethyl ketone, methyl Examples thereof include ketone solvents such as isobutyl ketone and hydrocarbon solvents such as benzene, toluene and xylene. Among them, the solvent is preferably water or an acetone-based solvent, and more preferably water or acetone. The solvent may be used alone or in combination of two or more.

  For polishing a graphite sheet of 5 μm or less, buffing, ion milling, FIB or the like is preferable, and ion milling is particularly preferable. This ion milling method is a method of polishing the graphite surface by causing argon ions to collide with the substrate, and is particularly suitable for thin graphite because it can be polished without damaging the sample. In addition to this, the above polishing methods may be combined.

  The particle size of the abrasive is, for example, from 0.01 μm to 100 μm, preferably from 0.02 μm to 50 μm, more preferably from 0.05 μm to 30 μm. In the polishing of the present invention, an abrasive having one type of particle size may be used, or two or more types of abrasives having different particle sizes may be combined and used simultaneously or separately. Among these, it is preferable to use abrasives having different particle diameters separately in preliminary processing, precision workability, ultra-precision processing, etc., to reduce the particle diameter used in the subsequent process, and to polish the graphite sheet.

  The particle size may be, for example, a particle size (d50) having a cumulative height of 50%, and can be measured by a known light transmission sedimentation method or sedimentation test method.

  The abrasive may have a hardness value represented by, for example, Mohs hardness, and preferably has a Mohs hardness of 5 or more, more preferably a Mohs hardness of 5.5 or more, and even more preferably 6.0 or more. Has Mohs hardness. Diamond has a Mohs hardness of 10.

  The abrasive may be used either dry or wet, and the solvent used in the wet process may be water, alcohol such as ethanol, methanol, or the like.

  The material to which the abrasive is applied is not particularly limited, but may be urethane, cloth or the like.

  The polishing member coated with the abrasive may be rotated at 1 to 1000 rpm with respect to the target graphite sheet, preferably 5 to 500 rpm, more preferably 10 to 300 rpm.

The abrasive member coated with the abrasive may be pressed against the target graphite sheet with a load of 0.01 to 1500 gf / cm ² , preferably 0.1 to 1000 gf / cm ² , more preferably 1 to 700 gf / cm ² . Press with cm ² .

<Arithmetic (average) surface roughness (Ra) measurement>
The arithmetic average surface roughness of the graphite sheet is 2.0 μm or less or 1.5 μm or less, preferably 1.0 μm or less, more preferably 0.8 μm or less, and still more preferably 0.5 μm or less. The arithmetic surface roughness of the graphite sheet is, for example, more than 200 nm, preferably 300 nm or more, more preferably 400 nm or more.
For use as a substrate, it is preferably as flat as possible. Further, when an insulating film is formed on a graphite sheet, further planarization is possible, and Ra of the insulating film is preferably 0.1 μm or less, more preferably 0.05 μm or less, and most preferably 0.02 μm or less. When there is flatness like the present graphite sheet, it is possible to easily obtain higher flatness by making an insulating film and to make the insulating film as thin as possible. The higher the flatness is, the more preferable it is because the generated heat can be efficiently transported. The arithmetic surface roughness in this case may be 0.001 μm or more or 0.002 μm or more, for example.
The arithmetic surface roughness can be measured using, for example, a 3D shape measurement microscope (manufactured by Keyence, VK9500).
In the high thermal conductivity heat dissipation board of the present invention, the value of Ra correlates with the value of thermal conductivity. For example, when the Ra value is low, the thermal conductivity value tends to be high.

<Insulating film>
The high thermal conductivity heat dissipation board of the present invention may include the graphite sheet and an insulating layer having a predetermined thickness.
The thickness of the insulating layer is preferably more than 1 μm and not more than 100 μm, more preferably not less than 2 μm and not more than 80 μm, still more preferably not less than 3 μm and not more than 70 μm.
The insulating film is preferably a polymer film because of its high flexibility. Polyurethane resin, polyester resin, polyvinyl chloride resin, polyacrylonitrile resin, polyvinyl toluene resin, melamine resin, silicone resin, epoxy resin, polystyrene resin, polyethylene Resin, polymethyl methacrylate resin, polycarbonate resin, polyimide resin, polyamide resin, polyethylene terephthalate resin, polyethylene naphthalate resin, fluorine resin, cycloolefin polymer resin, polyvinylphenol resin, polyvinyl alcohol resin, polyparaxylylene resin, polyhydroxy One or two or more materials selected from the group consisting of methyl styrene resin, polyvinyl acetate resin, polyvinyl styrene resin, polyvinyl denfluoride resin A combination is preferred.

  The method for producing the insulating film is not particularly limited, but lamination, vapor deposition, pressure press, heat pressure press, etc. may be used, and the above polymer or curing precursor is solubilized in a solvent, etc. The coater method, blade coater method, rod coater method, knife coater method, squeeze coater method, reverse roll coater method, transfer roll coater method, gravure coater method, kiss coater method, cast coater method, spray coater method, slit orifice coater method, You may apply | coat to the surface using various coating methods, such as a calender coater method and a dipping method.

  As the insulating layer, an insulating inorganic compound is also preferable, and the insulating inorganic compound includes aluminum nitride, aluminum oxide, aluminum nitride oxide, magnesium oxide, crystalline silica, aluminum hydroxide, boron nitride, silicon nitride, silicon carbide, or oxide. A beryllium single layer or a stacked layer may be used. Particularly preferred are aluminum oxide, boron nitride, crystalline silica and the like.

  The insulating film formation method is not particularly limited, and examples thereof include physical vapor deposition and chemical vapor deposition (chemical vapor deposition) or a combination thereof. Examples of the physical vapor deposition method include a vapor deposition method (resistance heating method, electron beam vapor deposition, molecular beam epitaxy), an ion plating method, a sputtering method, and the like. On the other hand, chemical vapor deposition (Chemical Vapor Deposition) supplies a raw material gas containing the desired thin film components onto a substrate and deposits the film by chemical reaction on the substrate surface or in the gas phase. It is a method to do. For the purpose of activating the chemical reaction, there are methods for generating plasma and the like, and known CVD methods such as thermal CVD method, catalytic chemical vapor deposition method, photo CVD method, plasma CVD method, atmospheric pressure plasma CVD method, etc. Although not particularly limited, the above method can be preferably used from the viewpoint of the film forming speed and the processing area.

<Flexibility>
Higher bendability is preferable, and it is desirable that graphite is not damaged or peeled off even in a bend test using a mandrel test rod having a diameter of 10 mm. Further, it is more preferable to have more flexibility, and the diameter of the mandrel test rod used in the flexibility test is more preferably 8 mm, and most preferably 6 mm. The higher the bendability, the more it can be used in a place where it bends, such as clothes or skin, and the device is less likely to be damaged when it is folded or rolled and stored in a bag or the like.

  Examples will be shown below to describe the embodiments of the present invention in more detail. Of course, the present invention is not limited to these examples, and it goes without saying that various aspects are possible in detail.

(Thickness measurement)
The thicknesses of the polymer sheet and the graphite sheet, which are raw materials, have an error of plus or minus about 5 to 10%, and the average thickness of 10 points of the obtained sheet was taken as the thickness of the sample.

(SEM surface measurement)
The graphite sheet was affixed to the measurement stage with a conductive double-sided tape. This sample was set in a SEM (scanning electron microscope (SU8000) manufactured by Hitachi High-Technology Service Co., Ltd.), the inclination of the sample stage was 15 degrees, the surface of the graphite sheet was observed at an acceleration voltage of 5 to 20 kV and a magnification of 1000 times. .

(Surface roughness measurement)
An ultra-deep color 3D shape measurement microscope (manufactured by Keyence, VK9500) was used. The arithmetic surface roughness Ra was calculated based on the standard of JIS B0601-1994 by analyzing the measurement data using the analysis software attached to the microscope.

<Density>
The density of the produced graphite sheet was determined by measuring the volume of the graphite sheet with a helium gas displacement type densitometer [AccuPyc II 1340 Shimadzu Corp.], measuring the mass separately, and density (g / cm ³ ) = mass (g ) / Volume (cm ³ ). In this method, it was impossible to measure the density of the graphite sheet having a thickness of 200 nm or less because the error was too large. Therefore, when calculating the thermal conductivity from the thermal diffusivity of the graphite sheet having a thickness of 200 nm or less, the calculation was performed assuming that the density is 2.1.

<Thermal conductivity>
The thermal diffusivity of the graphite sheet was measured at 25 ° C. under vacuum (about 10 ⁻² Pa) at a frequency of 10 Hz using a thermal diffusivity measurement device (ULVAC Riko Co., Ltd. “LaserPit” device) by a periodic heating method. And measured. In this method, a thermocouple is attached to a point separated from the laser heating point by a certain distance, and the temperature change is measured. Here, the thermal conductivity (W / mK) was calculated by multiplying the thermal diffusivity (m ² / s), the density (kg / m ³ ), and the specific heat (798 kJ / (kg · K)). However, this apparatus was able to measure the thermal diffusivity when the thickness of the graphite sheet was 1 μm or more. However, when the thickness of the graphite sheet is 1 μm or less, the measurement error becomes so large that accurate measurement is impossible.

  Therefore, as a second measurement method, measurement was performed using a periodic heating radiation temperature measurement method (BETHEL Thermo Analyzer TA3). This is a device that performs periodic heating with a laser and performs temperature measurement with a radiation thermometer. Since it is completely non-contact with the graphite sheet at the time of measurement, it is possible to measure even a sample with a graphite sheet thickness of 1 μm or less. . In order to confirm the reliability of the measured values of both apparatuses, some samples were measured with both apparatuses, and it was confirmed that the numerical values coincided.

  In the BETHEL apparatus, the frequency of periodic heating can be changed in a range up to 800 Hz. That is, this apparatus is characterized in that the measurement of the temperature that is normally performed by a thermocouple is performed by a radiation thermometer, and the measurement frequency can be varied. In principle, a constant thermal diffusivity should be measured even if the frequency is changed. Therefore, in the measurement using this apparatus, the frequency was changed and the measurement was performed. When a sample having a thickness of 1 μm or less was measured, the measurement value was often varied in the measurement at 10 Hz or 20 Hz, but the measurement value was almost constant in the measurement from 70 Hz to 800 Hz. Therefore, the thermal diffusivity was determined using a numerical value (a value at 70 to 800 Hz) showing a constant value regardless of the frequency.

<Flexibility test>
The produced high thermal conductivity substrate was cut into a rectangle of 100 mm × 50 mm, and then set on a testing machine on which a mandrel test rod having a diameter of 10 mm was set and bent. It was decided to visually confirm and judge that the sample after bending had no crack or graphite peeling and had the same appearance as before bending. In Tables 1 to 3, ◯ means that the sample after bending does not have cracks or graphite peeling, and shows the same appearance as before bending. X means that the sample after bending is cracked or peeled off graphite and does not show the same appearance as before bending.

  Hereinafter, the present invention will be described more specifically with reference to examples.

(Production Example 1)
A curing agent composed of 20 g of acetic anhydride and 10 g of isoquinoline was mixed with 100 g of an 18 wt% DMF solution prepared by synthesizing pyromellitic anhydride and 4,4′-diaminodiphenyl ether in a molar ratio of 1/1 and stirred. After defoaming by centrifugation, it was cast on aluminum foil. 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, 300 ° C., 400 ° C., and 500 ° C. for 30 seconds, and then the aluminum foil was removed to prepare a polyimide film (polymer sample A). Similarly to sample A, pyromellitic anhydride and p-phenylenediamine were used as raw materials, polyimide film (polymer sample B), 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride and p. A polyimide film (polymer sample C) was prepared using phenylenediamine as a raw material. Regarding the thickness of the polyimide film, several types of films with different thicknesses in the range of 100 μm to 1 μm were prepared by adjusting the casting speed and the like.

(Production Example 2)
14 types of polyimide films (polymer sample A), (polymer sample B), and (polymer sample C) having a thickness in the range of 100 μm to 1 μm produced in Production Example 1 were placed in nitrogen gas using an electric furnace. The temperature was raised to 1000 ° C. at a rate of 10 ° C./min, and pretreated by keeping at 1000 ° C. for 1 hour. Next, the obtained carbonized sheet was set inside a cylindrical graphite heater and heated to a processing temperature (maximum temperature) of 3000 ° C. at a temperature rising rate of 20 ° C./min. This temperature was maintained for 30 minutes (treatment time), and then the temperature was lowered at a rate of 40 ° C./min to produce a graphite sheet having a thickness of 0.52 μm to 50 μm. The treatment was performed under a pressure of 0.15 MPa in an argon atmosphere.

(Examples 1 to 11)
Surface polishing of the graphite sheet having a thickness of 0.52 μm to 9.0 μm produced in Production Example 2 was performed. After heating the surface-polished graphite block at 120 ° C, a fixing wax is applied to the surface of the graphite block, and the graphite sheet is attached using a Teflon (registered trademark) roller so that air does not enter, and is cooled and fixed at room temperature. did. Thereafter, a diamond slurry (particle size 3 to 0.1 μm) as a polishing agent was applied to the buff, and the particle size was gradually fined and polished (buff polishing). After polishing, the graphite sheet was again heated at 120 ° C. to remove it from the block. The residue of the wax adhering to the surface was washed twice with toluene for 20 minutes, and then dried by replacing the solvent with acetone and water. Table 1 shows values of thickness (μm), density (g / cm ³ ), thermal conductivity (W / mK), and arithmetic surface roughness Ra (μm) of the obtained graphite sheet. In any of the films with the thicknesses shown in this table, Ra was 1.5 μm or less, and it was found that excellent flatness and thermal conductivity of 1800 W / mK or more or 1950 W / mK or more were exhibited. Furthermore, no major damage was observed in the graphite sheet in the bending test.

(Examples 12 to 14)
Polishing was carried out in the same manner as in Example 1 except that the graphite sheets with thicknesses of 30, 30, and 50 μm prepared in Production Example 2 were used. Table 2 shows values of thickness (μm), density (g / cm ³ ), thermal conductivity (W / mK), and arithmetic surface roughness Ra (μm) of the obtained graphite sheet. In the films having the thicknesses shown in this table, Ra was 2.0 μm or less in any sample, and it was found that excellent flatness and thermal conductivity of 1300 W / mK or more or 1350 W / mK or more were exhibited. Furthermore, no major damage was observed in the graphite sheet in the bending test.

  In addition, the SEM photograph before buffing the graphite sheet produced in Example 13 and after buffing is shown in FIG. As a result, the arithmetic surface roughness before buffing showed Ra 7.3 μm (FIG. 1A), whereas the arithmetic surface roughness after buffing showed Ra 1.8 μm (FIG. 1). (B)) When manufacturing a device by patterning, vapor deposition, or the like, it is possible to adjust the width setting and positioning of the electrode with high accuracy.

(Comparative Examples 1-5)
Instead of the graphite sheet, commercially available natural graphite sheet (Toyo Tanso, PF-UHP, thickness 200 μm), glassy carbon (Tokai Carbon, thickness 1000 μm), CIP molded graphite (Nippon Nippon Techno Carbon, IGS-603, Thickness 1000 μm), HOPG (manufactured by MiNTQ, PYROID-HT, thickness 1000 μm), graphite sheet (prepared in the same manner as in Production Examples 1 and 2 using a polymer sample A polyimide film having a thickness of 96 μm and a thickness of 200 μm) The same procedure as in Example 1 was performed except that. Natural graphite sheet, glassy carbon, CIP molded graphite, HOPG, thickness (μm), density (g / cm ³ ), thermal conductivity (W / mK), arithmetic surface roughness Ra (μm) of the obtained graphite sheet The measurement results and the results of the flexibility test are shown in Table 3. From this result, a graphite sheet having thermal conductivity, flatness, and flexibility could not be produced.

  The high thermal conductive heat dissipation board of the present invention can be preferably used not only for flexible electronics devices but also for conventional electronics devices, stretchable electronics with stretchability, wireless charging devices, flexible batteries, heat dissipation boards for power semiconductors, and the like. Further, the high thermal conductive heat dissipation substrate can be used not only for a conventional inorganic semiconductor device but also for an organic LED, an organic thin film transistor, an organic thin film solar cell, an organic memory and the like using an organic semiconductor.

Claims (15)

  The thickness of the graphite sheet is 9.6 μm or less, 0.5 μm or more, the arithmetic surface roughness of the graphite sheet is 1.5 μm or less, and the thermal conductivity in the plane direction of the graphite sheet is 1800 W / mK or more. High heat conductive heat dissipation board.   The graphite sheet has a thickness of 9.6 μm or more and 50 μm or less, the arithmetic surface roughness of the graphite sheet is 2.0 μm or less, and the thermal conductivity in the surface direction of the graphite sheet is 1300 W / mK or more. High heat conductive heat dissipation board.   The highly heat-conductive heat dissipation substrate according to claim 1 or 2, wherein the graphite sheet does not break even in a bending test using a mandrel having a diameter of 10 mm. The graphite sheet density is 1.8 g / cm ³ or more, high thermal conductivity heat dissipation substrate according to any one of claims 1 to 3, characterized in that 2.26 g / cm ³ or less.   5. The high thermal conductive heat dissipation substrate according to claim 1, comprising the graphite sheet and an insulating layer having a thickness of more than 1 μm and not more than 100 μm.   The high thermal conductive heat dissipation substrate according to claim 5, wherein the insulating layer is a polymer film or an insulating inorganic compound.   The polymer film is made of polystyrene resin, polyethylene resin, polyimide resin, polymethyl methacrylate resin, polycarbonate resin, silicone resin, epoxy resin, polyamide resin, polyethylene terephthalate resin, polyethylene naphthalate resin, fluorine resin, cycloolefin polymer resin. It consists of any one, The high heat conductive heat dissipation board | substrate of Claim 6.   The insulating inorganic compound is composed of a single layer or a stack of aluminum nitride, aluminum oxide, aluminum nitride oxide, magnesium oxide, crystalline silica, aluminum hydroxide, boron nitride, silicon nitride, silicon carbide, or beryllium oxide. The high thermal conductivity heat dissipation board according to claim 6.   The method for producing a highly heat-conductive heat dissipation substrate according to claim 1, comprising a step of polishing a graphite sheet.   The method for polishing a graphite sheet is selected from the group consisting of blast polishing, belt polishing, lapping polishing, buff polishing, shot polishing, electrolytic polishing, ion milling, and focused ion beam (FIB). Item 10. A method for producing a high thermal conductivity heat dissipation board according to Item 9.   The method for manufacturing a high thermal conductive heat dissipation substrate according to claim 10, wherein the method for polishing the graphite sheet is lapping or buffing.   It polishes using 1 or more types of abrasives selected from the group which consists of an alumina, a diamond slurry, colloidal silica, and a cerium oxide, The high heat conductivity of any one of Claims 9-11 characterized by the above-mentioned. Manufacturing method for conductive heat dissipation substrate.   The method for producing a highly heat-conductive heat dissipation substrate according to any one of claims 9 to 12, wherein when the polishing apparatus is used, the graphite sheet is attached to a graphite block and then polished. .   The high thermal conductivity heat dissipation substrate according to any one of claims 9 to 13, wherein the graphite sheet having a film thickness of 5 µm or less is subjected to buffing, ion milling, or focused ion beam (FIB). Method.   The method for manufacturing a high thermal conductive heat dissipation substrate according to claim 14, wherein ion milling is performed.