JP2012211259A - Heat conductive sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat conductive sheet having a desired thickness obtained, high heat conductivity in the thickness direction, and excellent mechanical strength.SOLUTION: The heat conductive sheet 11 is formed to be sheet-like by mixing graphite pieces 13 and a resin 12, wherein the graphite pieces 13 contain a plurality of first graphite pieces 13a made by cutting a pyrolytic graphite sheet into elongate pieces, at least the plurality of first graphite pieces 13a connect an upper face and a lower face of the heat conductive sheet 11, thus, heat conductivity in the thickness direction can be improved.

Description

  The present invention relates to a heat conductive sheet capable of smoothly transferring generated heat in a thickness direction while filling a relatively large gap of about 0.5 mm to 20 mm.

  In recent years, the operating speed of electronic devices has been remarkably improved, and accordingly, heat generation from electronic components such as semiconductor elements has increased. On the other hand, in order to stably operate the electronic apparatus, heat is diffused or dissipated using a heat conductive sheet such as a graphite sheet for these heating elements. However, the graphite sheet is generally as thin as about 0.05 mm, and it has been difficult to function sufficiently when there is a relatively large gap between the heating element and the heat sink.

  As shown in FIG. 3, the graphite sheet has a scale-like crystal structure that spreads in a plane, has a large thermal conductivity in the plane direction (a-b axis direction in which carbon 6-membered rings are connected), The thermal conductivity in the c-axis direction, which is the vertical direction, is relatively small. Therefore, as shown in FIG. 2, a plurality of graphite sheets 1 are bonded and cut to improve heat conduction in the thickness direction.

  As prior art document information related to the invention of this application, for example, Patent Document 1 is known.

JP 2006-303240 A

  However, although a conventional heat conductive sheet having a high thermal conductivity in the thickness direction can be obtained, pressurization may be required when attaching heat-generating components and heat-dissipating components such as a heat sink and a heat spreader. In this case, when a thin sheet is bonded and cut perpendicularly to the bonding surface, the pressing force also acts in the direction in which the bonding surface falls. As a result, it may peel off between the bonding surface and the graphite sheet. Moreover, since the process of cutting after laminating increases, it has become a factor of cost increase. Further, in the above heat conductive sheet, heat is hardly conducted only in one direction where the graphite sheet is facing, so that the thermal conductivity in the surface direction is inferior.

  An object of the present invention is to solve such problems, and to provide a heat conductive sheet that can obtain a desired thickness, has high thermal conductivity in the thickness direction and in the surface direction, and is excellent in mechanical strength. .

  In order to achieve the above object, the present invention is a heat conductive sheet formed by mixing a graphite piece and a resin into a sheet shape, and the graphite piece is formed by cutting a pyrolytic graphite sheet into a plurality of pieces. A first graphite piece is included, and at least the plurality of first graphite pieces connect the upper surface and the lower surface of the heat conductive sheet.

  By doing in this way, since the upper surface and lower surface of the heat conductive sheet are connected in the ab axis direction of the graphite piece excellent in heat conductivity, the heat conductive sheet excellent in heat conductivity also in the thickness direction. Can be obtained.

  As described above, according to the present invention, it is possible to obtain a heat conductive sheet having a desired thickness, a high thermal conductivity in the thickness direction and in the surface direction, and excellent mechanical strength.

Sectional drawing of the heat conductive sheet in one embodiment of this invention A perspective view of a conventional heat conductive sheet Diagram showing the general graphite crystal structure

(Embodiment 1)
Hereinafter, the heat conductive sheet in one embodiment of the present invention is explained, referring to drawings.

  FIG. 1 is a cross-sectional view of a heat conductive sheet 11 according to an embodiment of the present invention. The heat conductive sheet 11 is composed of a resin 12 made of acrylic and a graphite piece 13. An acrylic resin is used for the resin 12, and the thickness of the heat conductive sheet 11 is about 1 mm. The graphite piece 13 includes a first graphite piece 13a obtained by cutting a flexible pyrolytic graphite sheet into a width of about 0.1 mm and a length of about 5 mm, and a second graphite piece 13b pulverized to a size of about 0.01 mm. And consists of a mixture.

  By comprising in this way, the 1st graphite piece 13a can be intertwined, the upper surface and lower surface of the heat conductive sheet 11 can be connected with many 1st graphite pieces 13a, and the heat conductive sheet 11 can be connected. The thermal conductivity in the thickness direction can be increased. Further, since the second graphite piece 13b enters between the entangled first graphite pieces 13a, the thermal conductivity can be further improved.

  Further, since the first graphite pieces 13a are intertwined with each other, they are very strong against external force.

  Next, the manufacturing method of the heat conductive sheet in one embodiment of this invention is demonstrated.

  First, a polyimide film having a flexibility of about 25 μm in thickness is obtained by heat treating the polyimide film and then tanning. This is cut into a width of about 0.1 mm and a length of about 5 mm using a cutter or a shredder to obtain a first graphite piece 13a. At this time, the thickness of the first graphite piece 13a may be reduced. The length in the longitudinal direction does not need to be constant, and may be varied as long as it can be easily formed into a sheet later. Therefore, the pyrolytic graphite sheet for making the first graphite piece 13a does not have to be a large sheet, and may be a peripheral edge material or a waste material after being extracted with a mold. By doing in this way, a lower-cost heat conductive sheet can be obtained.

  Next, a part of the first graphite piece 13a, or a piece thereof, or the waste material after the pyrolytic graphite sheet is extracted with a die is further finely cut, or pulverized using a jet mill. A second graphite piece 13b of about 0.01 mm is obtained. The second graphite piece 13b may not be made from a pyrolytic graphite sheet, and may be made by pulverizing natural graphite or the like, for example.

  Next, the first graphite piece 13a and the second graphite piece 13b are mixed at approximately the same weight in a resin solvent in which acrylic polymer (12%), butyl acetate (48%), and ethyl acetate (40%) are mixed in a weight ratio. The heat conductive sheet 11 having a thickness of about 1 mm is obtained by mixing the obtained materials, forming into a sheet by extrusion, and removing the solvent. In addition, when it is desired to obtain a thicker sheet, a desired thickness may be obtained by bonding a plurality of sheets formed as described above.

  By doing so, the first graphite pieces 13a are entangled with each other, so that the longitudinal direction of the first graphite pieces 13a is directed not only in the surface direction but also in the thickness direction, and the length in the longitudinal direction is increased. By making it sufficiently long with respect to the thickness of the conductive sheet 11, a large number of first graphite pieces 13 a can be connected to the upper surface and the lower surface of the heat conductive sheet 11. Since the longitudinal direction of the first graphite piece 13a is the surface direction of the pyrolytic graphite sheet, it is excellent in heat conduction, and the obtained heat conduction sheet 11 is thermally conductive both in the thickness direction and in the surface direction. It will be excellent. Furthermore, since the first graphite pieces 13a are intertwined with each other, the mechanical strength of the heat conductive sheet 11 is also very strong.

  As described above, in order to obtain the effect of the present invention, it is important to intertwine the graphite pieces, and for that purpose, the shape to be cut is important. If the pyrolytic graphite sheet is cut into a rectangular shape and the ratio of the long side direction to the short side direction is changed, it becomes very easy to get entangled when it becomes 4 times or more, so it should be 4 times or more. Is desirable. If this ratio is large, there is no problem in characteristics, but if it is too large, sheet molding becomes difficult, and the upper limit is determined by moldability.

  Furthermore, in order to connect the upper surface and the lower surface of the heat conductive sheet 11 with the first graphite piece 13, the length of the long side of the first graphite piece 13 a is at least three times the thickness of the heat conductive sheet 11. It is desirable to make it. By doing in this way, many 1st graphite pieces 13a can be made into the state which has connected the upper surface and lower surface of the heat conductive sheet 11, and can improve the heat conductivity of the thickness direction.

  The weight ratio of the first graphite piece 13a in the graphite piece 13 is preferably at least 10% or more, more preferably 40 to 60%.

  The weight ratio between the resin 12 and the graphite piece 13 is preferably 10 to 97%, more preferably 30 to 45%, of the resin content in the heat conductive sheet 11.

  In addition, it is desirable to use a clay-like resin that is slightly sticky after being cured, for example, an acrylic ester copolymer, and the hardness of the heat conductive sheet is 40 with an Asker C-type hardness meter. In the following, it is desirable to make it 20 or less. By doing in this way, adhesiveness with a heat generating body can be improved, and effective thermal conductivity can be improved more by reducing a thermal resistance.

  The heat conductive sheet of the present invention has a desired thickness, has a high thermal conductivity in the thickness direction, and has excellent mechanical strength, and is industrially useful.

11 Thermal Conductive Sheet 12 Resin 13 Graphite Piece 13a First Graphite Piece 13b Second Graphite Piece

Claims (4)

A heat conductive sheet formed by mixing a graphite piece and a resin into a sheet shape, wherein the graphite piece includes a plurality of first graphite pieces formed by cutting a pyrolytic graphite sheet into an elongated shape. Each said 1st graphite piece has connected the upper surface and lower surface of the said heat conductive sheet, The heat conductive sheet characterized by the above-mentioned. 2. The heat conductive sheet according to claim 1, wherein the first graphite piece has a length on a long side of four or more times a length on a short side. 2. The heat conductive sheet according to claim 1, wherein a length of a long side of the first graphite piece is not less than three times a thickness of the heat conductive sheet. The heat conductive sheet according to claim 1, wherein the graphite piece includes a second graphite piece that is smaller than a length of a short side of the first graphite piece.

Images