The present invention relates to a heat-conductive sheet that has high thermal conductivity in a surface direction and a large amount of heat transport, and a method of manufacturing the heat-conductive sheet.
In recent years, an operating speed of various electronic devices has been significantly improved, and increases an amount of heat generated from electronic components, such as semiconductor devices, accordingly. In order to operate electronic devices stably, a heat-conductive sheet, such as a graphite sheet, is used in these heat generating electronic components to diffuse and dissipate the heat. However, if graphite powders are partially desorbed from a graphite sheet, the graphite sheet may cause a short circuit due to conductivity of the graphite sheet. For this reason, to seal a graphite sheet, insulating sheets are bonded to both main surfaces of the graphite sheet, and the insulating sheets are bonded to each other outside an outer circumferential edge of the graphite sheet.
As an amount of heat generated from a heating element increases, a heat-conductive sheet is required to have a large amount of heat transport, in addition to a high thermal conductivity in a surface direction.
A conventional heat-conductive sheet similar to the above-mentioned heat-conductive sheet is disclosed in PTL 1.
PTL 1: Japanese Patent Laid-Open Publication No. 2005-210035
A heat-conductive sheet includes a laminated sheet and first and insulating sheets bonded to first and second main surfaces of the laminated sheet. The laminated sheet includes graphite sheets and one or more adhesive layers disposed alternately on the graphite sheets to bonds the graphite sheets to each other. The first insulating sheet is bonded to the second insulating sheet outside an outer circumferential edge of the laminated sheet to seal the laminated sheet between the first and second insulating sheets. The laminated sheet includes an outer circumferential portion connected to the outer circumferential edge and an inner portion apart from the outer circumferential edge. The outer circumferential portion of the laminated sheet has a thickness smaller than a thickness of the inner portion.
The heat-conductive sheet has high reliability of sealing the insulating sheet.
Graphite sheet 11 is made of a pyrolytic graphite sheet with a thickness of about 10 μm. The heat conductivity of graphite sheet 11 in a surface direction is about 1950 W/m° K. Adhesive layer 12 is made of styrene butadiene rubber, has a thickness of about 3 μm, and can be bonded by heat pressing. Graphite sheets 11 are bonded with adhesive layers 12 to constitute laminated sheet 13. Insulating sheets 14 and 15 are films made of polyethylene terephthalate and have thicknesses of about 10 μm. Acrylic pressure sensitive adhesives are disposed on surfaces of insulating sheets 14 and 15 facing laminated sheet 13. Laminated sheet 13 is bonded to insulating sheets 14 and 15 with the adhesives while insulating sheet 14 is bonded to insulating sheet 15 with the adhesives to seal laminated sheet 13 between insulating sheets 14 and 15.
Adhesive layer 12 is disposed in an area inside apart from an outer circumferential edge of graphite sheet 11 by about 1 mm. Thus, an outer circumferential portion of laminated sheet 13 including the outer circumferential edge of the laminated sheet 13 is thinner than an inner portion of laminated sheet 13 by only the thickness of adhesive layer 12. Herein, the inner portion of laminated sheet 13 is apart from the outer circumferential edge of laminated sheet 13 and located inside the outer circumferential portion of laminated sheet 13. When laminated sheet 13 is placed between insulating sheets 14 and 15 to seal laminated sheet 13, the outer circumferential portion of the laminated sheet 13 has a thickness thinner than that of the inner portion located inside the outer circumferential portion. Thus, insulating sheet 14 and insulating sheet 15 are easily in contact with each other outside the outer circumferential edge of the laminated sheet 13, thereby improving reliability of sealing.
According to the embodiment, the adhesives are formed on only surfaces of insulating sheets 14 and sheet 15 facing laminated sheet 13, but either or both of insulating sheets 14 and 15 may be made of a double-sided adhesive tape. This configuration allows heat-conductive sheet 1000 to be easily bonded to, e.g. a heating element or a housing.
In heat-conductive sheet 1000, laminated sheet 13 includes plural graphite sheets 11 and one or more adhesive layers 12 which are arranged alternately on graphite sheets 11 and bond graphite sheets 11. Laminated sheet 13 has main surface 13a, main surface 13b opposite to main surface 13a, and outer circumferential edge 13c which are connected to main surfaces 13a and 13b and which surrounds main surfaces 13a and 13b. Insulating sheet 14 is bonded to main surface 13a of laminated sheet 13. Insulating sheet 15 is bonded to main surface 13b of laminated sheet 13. Laminated sheet 13 is sealed with insulating sheets 14 and 15 bonded to each other outside outer circumferential edge 13c of laminated sheet 13. Laminated sheet 13 has outer circumferential portion 13d that is connected to outer circumferential edge 13c, and inner portion 13e that is apart from outer circumferential edge 13c. Outer circumferential portion 13d of laminated sheet 13 has a thickness smaller than that of inner portion 13e. In laminated sheet 13, inner portion 13e is located inside outer circumferential portion 13d.
Outer circumferential edge 13c of laminated sheet 13 entirely surrounds main surfaces 13a and 13b.
Graphite sheet 11 has main surface 111a, main surface 111b opposite to main surface 111a, and outer circumferential edge 111c which that is connected to main surfaces 111a and 111b and which entirely surrounds main surfaces 111a and 111b. One or more adhesive layers 12 may be apart from outer circumferential edge 111c of graphite sheet 11. One outermost graphite sheet out of graphite sheets 11 stacked in laminating direction 1000a has main surface 111a constituting main surface 13a of laminated sheet 13 while the other outermost graphite sheet out of graphite sheets 11 has main surface 111b constituting main surface 13b of laminated sheet 13. Main surface 111b of one graphite sheet 11 is bonded to main surface 111a of graphite sheet 11 with adhesive layer 12.
A method of manufacturing heat-conductive sheet 1000 in accordance with the embodiment will be described with reference to drawings.
First, as shown in
Next, as shown in
Next, laminated sheet 113 including graphite sheets 11a and 11b stacked on one another is heat-pressed with an iron that is heated at about 150° C., thereby bonding graphite sheet 11a and graphite sheet 11b in areas 16. A graphite sheet has excellent thermal conductivity in surface directions 1000b and 1000c perpendicular to laminating direction 1000a, i.e., parallel to main surfaces 13a and 13b (main surfaces of graphite sheets 11a and 11b) of laminated sheet 13. This configuration allows heat to transmit uniformly, so that graphite sheets 11a and 11b can be bonded uniformly.
Next, as shown in
Next, laminated sheet 13 is stacked on insulating sheet 14. Then, insulating sheet 15 is stacked on laminated sheet 13 so as to sandwich laminated sheet 13 with insulating sheet 14. Subsequently, the stacked sheets are pressed with a roller to bond insulating sheet 14, laminated sheet 13, and insulating sheet 15, thereby providing laminated sheet 213. In laminated sheet 213, laminated sheet 13 is positioned in area 17. Laminated sheet 213 is punched with a metallic mold in area 18 which expands outward from laminated sheet 13 (area 17) by about 1 mm, thereby providing heat-conductive sheet 1000 shown in
In heat-conductive sheet 1000 according to the embodiments shown in
As mentioned above, heat-conductive sheet 1000 can be manufactured by the following method. One or more adhesive layers 12 are formed in one or more areas 16 of one or more graphite sheets 11a. Graphite sheet 11b is placed on one or more graphite sheets 11a in laminating direction 1000a with one or more adhesive layers 12 stacked on one or more graphite sheets 11a alternately. One or more graphite sheets 11a and graphite sheet 11b are bonded with one or more adhesive layers 12. One or more graphite sheets 11a and graphite sheet 11b are to allow laminated sheet 13 to have area 17. Insulating sheet 14 is placed on insulating sheet 15 while laminated sheet 13 is disposed between insulating sheets 14 and 15. Then, insulating sheet 14 is bonded to insulating sheet 15 in area 18, so that insulating sheets 14 and 15 are directly bonded in area 18, thereby providing heat-conductive sheet 1000. Viewing in laminating direction 1000a, one or more areas 16 are located inside area 17. Viewing in laminating direction 1000a, area 17 is located inside area 18.
One or more graphite sheets 11a and graphite sheet 11b may be bonded by heat pressing.
Areas 16 may be apart from outer circumferential edge 11c surrounding graphite sheet 11a.
One or more graphite sheets 11a and graphite sheet 11b may be punched in area 17 to obtain laminated sheet 13.
A heat-conductive sheet according to the present invention has high thermal conductivity in a surface direction and a large amount of heat transport, and is useful for heat dissipation of heating components.
Number | Date | Country | Kind |
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2014-079121 | Apr 2014 | JP | national |
Filing Document | Filing Date | Country | Kind |
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PCT/JP2015/001503 | 3/18/2015 | WO | 00 |