JP2021128953A - Thermal conductive sheet, electronic device, and manufacturing method of electronic device - Google Patents

Abstract

To realize a heat conductive sheet and an electronic device having excellent heat dissipation by using a graphite sheet.SOLUTION: A heat conductive sheet according to an embodiment of the present invention has a first surface and a second surface facing the first surface, includes at least two graphite sheets, and the thermal conductivity in the thickness direction of the first graphite sheet located closest to the first surface is higher than the thermal conductivity in the thickness direction of the second graphite sheet located closer to the second surface.SELECTED DRAWING: Figure 1

Description

The present invention relates to a heat conductive sheet, an electronic device, and a method for manufacturing the electronic device.

The graphite sheet has excellent heat dissipation characteristics, and has been conventionally used as a heat dissipation material for cooling a heating element (for example, a semiconductor element mounted on an electronic device or an electric device).

For example, Patent Documents 1 and 2 disclose heat-dissipating parts and heat-conducting sheets using graphite sheets.

Japanese Unexamined Patent Publication No. 2008-60527 International release 2015/155940

However, the above-mentioned conventional technique does not have sufficient heat dissipation performance, and there is room for improvement.

One aspect of the present invention is to realize a heat conductive sheet and an electronic device having excellent heat dissipation by using a graphite sheet.

As a result of diligent studies to solve the above problems, the present inventors have made a heat conductive sheet using a graphite sheet in the thickness direction on the first surface (the surface not in contact with the heating element) side of the heat conductive sheet. Excellent heat dissipation by arranging a graphite sheet with high thermal conductivity and arranging a graphite sheet with lower thermal conductivity in the thickness direction than the graphite sheet on the second surface (the surface in contact with the heating element). The present invention was completed by finding that That is, the present invention includes the following aspects.

<1> The heat conductive sheet according to one aspect of the present invention is a heat conductive sheet having a first surface and a second surface facing the first surface, and includes at least two graphite sheets. Among the graphite sheets, the thermal conductivity in the thickness direction of the first graphite sheet located closest to the first surface is the thermal conductivity in the thickness direction of the second graphite sheet located closest to the second surface. Higher than.

<2> The heat conductive sheet according to one aspect of the present invention has a thermal conductivity of the first graphite sheet at 25 ° C. in the thickness direction of 10 W / m · K or more and 30 W / m · K or less.

<3> The heat conductive sheet according to one aspect of the present invention has a thermal conductivity of 1 W / m · K or more and less than 10 W / m · K in the thickness direction of the second graphite sheet at 25 ° C.

<4> In the heat conductive sheet according to one aspect of the present invention, the thickness of the first graphite sheet is 50 to 100 μm.

<5> In the heat conductive sheet according to one aspect of the present invention, the thickness of the second graphite sheet is 10 to 40 μm.

<6> The heat conductive sheet according to one aspect of the present invention includes a first heat conductive layer that covers the surface of the first graphite sheet on the first surface side, and the second surface side of the second graphite sheet. A second heat conductive layer, which covers the surface of the surface, is further provided.

<7> The electronic device according to one aspect of the present invention includes the heat conductive sheet according to one aspect of the present invention and a heating element arranged on the second surface, and includes the heat conductive sheet and the heat generation. The body is in contact or adhered.

<8> The method for manufacturing an electronic device according to one aspect of the present invention includes a step of arranging a heating element on the second surface of the heat conductive sheet according to one aspect of the present invention.

According to one aspect of the present invention, it is possible to provide a heat conductive sheet and an electronic device having excellent heat dissipation using a graphite sheet.

It is sectional drawing which shows typically an example of the electronic device which concerns on one aspect of this invention. It is sectional drawing which shows typically another example of the electronic device which concerns on one aspect of this invention. It is sectional drawing which shows typically another example of the electronic device which concerns on one aspect of this invention. It is sectional drawing which shows typically an example of the heat conduction sheet which concerns on one aspect of this invention. It is sectional drawing explaining the installation place of the thermocouple used in the evaluation of an Example. It is a top view explaining the installation place of the thermocouple used in the evaluation of an Example. It is sectional drawing which shows typically the electronic device which includes the conventional heat conduction sheet and a heating element.

Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to this, and various modifications can be made within the scope described, and the present invention also relates to an embodiment obtained by appropriately combining the technical means disclosed in each of the different embodiments. Included in the technical scope of. Unless otherwise specified in the present specification, "A to B" representing a numerical range means "A or more and B or less".

In the process of developing a heat conductive sheet using a graphite sheet, the present inventors use the heat derived from the heating element not only for a part of the heat conductive sheet in contact with the heating element, but for the entire heat conductive sheet. We considered using it to dissipate heat efficiently.

Generally, the graphite sheet has excellent thermal conductivity in the plane direction, but is inferior in thermal conductivity in the thickness direction. In particular, a heat conductive sheet composed of a laminated graphite sheet in which a plurality of graphite sheets are laminated via an adhesive layer may have further inferior heat conductivity in the thickness direction.

More specifically, FIG. 7 shows an electronic device 101 including a conventional general heat conductive sheet 5 and a heating element 6. In this configuration, heat is transferred from the contact portion between the heating element 6 and the heat conductive sheet 5 to the heat conductive sheet 5 (white arrow 101 in FIG. 7). At this time, the heat conductivity in the surface direction of the heat conductive sheet 5 is excellent, but the heat conductivity in the thickness direction of the heat conductive sheet 5 is inferior. Therefore, the temperature unevenness occurs inside the heat conductive sheet 5, and the high temperature region 10 and the low temperature region 11 having a lower temperature than the high temperature region 10 exist inside the heat conductive sheet 5. In this case, there is a problem that the heat of the heating element 6 cannot be efficiently dissipated by utilizing the entire heat conductive sheet 5.

On the other hand, the present inventor has attempted to solve the above problems by using a graphite sheet having improved thermal conductivity in the thickness direction. However, as shown in Comparative Example 2 described later, the above problem could not be solved. This is because the heat of the heating element 6 is sufficiently transferred to the back surface side before it is sufficiently spread in the surface direction. It is considered that this is because

Therefore, in the heat conductive sheet using the graphite sheet, the present inventors heat heat on the first surface (the surface not in contact with the heating element) and the second surface (the surface in contact with the heating element) of the heat conductive sheet. It was examined to form a gradient of conductivity.

Then, by arranging a graphite sheet having a high thermal conductivity in the thickness direction on the first surface side and arranging a graphite sheet having a lower thermal conductivity in the thickness direction than the graphite sheet on the second surface side. , We found a new finding that heat can be efficiently transferred from the front side that is in contact with the heating element to the back side that is not in direct contact with the heating element by utilizing the entire heat conductive sheet, and the heat dissipation is improved. rice field.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[1. Heat conduction sheet]
(Structure of heat conductive sheet 50)
FIG. 1 is a cross-sectional view schematically showing an electronic device 102 including a heat conductive sheet 50 and a heating element 6 according to an embodiment of the present invention. As shown in FIG. 1, the heat conductive sheet 50 has a first surface (a surface not in contact with the heating element 6) 1 and a second surface (a surface in contact with the heating element 6) 2 on the first surface 1 side. It includes a first graphite sheet 51 located, a second graphite sheet 52 located on the second surface 2 side, and an adhesive layer 53 arranged between them as needed.

A heating element 6 is provided on the second surface 2 side of the heat conductive sheet 50 via an adhesive material. The heat conductive sheet 50 and the heating element 6 are collectively referred to as an electronic device 102.

In the heat conductive sheet 50 having the above layer structure, the heat conductivity of the first graphite sheet 51 in the thickness direction is higher than the heat conductivity of the second graphite sheet 52 in the thickness direction, so that the heat of the heating element 6 is increased. Can be efficiently transmitted in the surface direction and the thickness direction by utilizing the entire heat conductive sheet. As a result, the heat dissipation of the entire heat conductive sheet 50 can be improved.

This is not limited to a specific theory, but a graphite sheet having a high thermal conductivity in the thickness direction (first graphite sheet 51) has a low thermal conductivity in the thickness direction (second graphite sheet). It is considered that this is due to the higher specific heat and higher heat capacity than the sheet 52). The first graphite sheet 51 can hold a large amount of heat inside as a heat receiver of the heating element 6, and quickly dissipates heat from the first surface 1 side at a substantially constant and stable speed.

The heat of the heating element 6 is first spread mainly in the plane direction by the second graphite sheet 52. Next, the heat spread in the surface direction of the second graphite sheet 52 is transferred to the first surface 1 side by the first graphite sheet 51 via the adhesive layer 53 and is dissipated. Therefore, the temperature becomes substantially uniform inside the heat conductive sheet 50, and the entire heat conductive sheet 50 can be utilized to improve heat dissipation.

If necessary, the heat conductive sheet 50 may include an adhesive layer (not shown) for adhering the heating element 6 on the second surface 2. Further, as shown in FIG. 4, the heat conductive sheet 50 has a protective layer 57 as an outermost layer forming the first surface 1 and a protective layer 58 as the outermost layer forming the second surface 2, if necessary. , At least one of may be included.

Each configuration will be described below.

(First Graphite Sheet 51)
As the first graphite sheet 51 constituting the heat conductive sheet 50, a graphite sheet whose thermal conductivity in the thickness direction is higher than the thermal conductivity in the thickness direction of the second graphite sheet 52 can be used.

The thermal conductivity of the first graphite sheet 51 in the thickness direction at 25 ° C. is preferably 10 W / m · K or more, preferably 13 W / m · K or more, in order to enhance the heat dissipation of the heat conductive sheet 50. Is more preferable.

The upper limit of the thermal conductivity of the first graphite sheet 51 in the thickness direction at 25 ° C. is not particularly limited, but can be, for example, 25 W / m · K or less. As the thermal conductivity in the thickness direction increases, the thermal conductivity in the surface direction tends to decrease. Therefore, it may be appropriately adjusted according to the balance of the thermal conductivity in both directions.

In the specification of the present application, the thermal conductivity λ ₁ (W / m · K) in the thickness direction at 25 ° C. is the thermal diffusivity α ₁ (m ² / s) at 25 ° C. and the density ρ (kg / m ^3). ) And the specific heat Cp (J / kg · K), it is a value obtained by the following formula (1).
λ ₁ = α ₁ × ρ × Cp (1)
The thermal diffusivity α _{1 at} 25 ° C. is a value measured in the thickness direction of the sheet by a laser spot periodic heating radiation temperature measurement method using a Thermowave Analyzer TA33 (manufactured by Bethel Co., Ltd.). The density ρ is a value measured by the gravimetric method. The specific heat Cp is a value measured using a DSC (differential scanning calorimetry meter, manufactured by Hitachi High-Technologies Corporation, trade name DSC7020).

The thermal conductivity of the first graphite sheet 51 in the plane direction at 25 ° C. is not particularly limited, but is 800 W / m · K or more from the viewpoint of realizing a heat conductive sheet having higher heat dissipation. It is preferably 900 W / m · K or more, and more preferably 900 W / m · K or more.

Further, the upper limit of the thermal conductivity of the first graphite sheet 51 in the plane direction at 25 ° C. is not particularly limited. As the thermal conductivity in the plane direction increases, the thermal conductivity in the thickness direction tends to decrease. Therefore, it may be appropriately adjusted according to the balance of the thermal conductivity in both directions.

In the specification of the present application, the thermal conductivity λ ₂ (W / m · K) in the plane direction at 25 ° C. is the thermal diffusivity α ₂ (m ² / s) and the density ρ (kg / m ³ ) at 25 ° C. , And the specific heat Cp (J / kg · K), which is a value obtained by the following formula (2).
λ ₂ = α ₂ × ρ × Cp (2)
The thermal diffusivity α _{2 at} 25 ° C. is a value measured in the surface direction of the sheet by a laser spot periodic heating radiation temperature measurement method using a Thermowave Analyzer TA33 (manufactured by Bethel Co., Ltd.). The density ρ is a value measured by the gravimetric method. The specific heat Cp is a value measured using a DSC (differential scanning calorimetry meter, manufactured by Hitachi High-Technologies, trade name DSC7020).

From the viewpoint of heat transport capacity, the thickness of the first graphite sheet 51 is preferably 50 μm or more, and more preferably 80 μm or more. From the viewpoint of productivity, the thickness of the first graphite sheet 51 is preferably 200 μm or less, and more preferably 100 μm or less.

Examples of the method for producing the first graphite sheet 51 preferably used in the present invention include (i) a method of heat-treating a polymer film to foam it, and (ii) a method of cutting a graphite block into a sheet.

Examples of the method (i) include the method for producing a polymer graphite film described in JP-A-2009-190962.

More specifically, the polymer film as a raw material is carbonized by heat treatment at about 1000 ° C. in a vacuum or in an inert gas such as argon gas or nitrogen gas to obtain a carbonized film ( Carbonization process).

Next, the obtained carbonized film is graphitized by further heat treatment in vacuum or in an inert gas such as argon gas or nitrogen gas to obtain a foamed graphite sheet (graphization step). The heat treatment temperature in the graphitization step is preferably 2400 ° C. or higher, more preferably 2700 ° C. or higher.

The foamed graphite sheet is a graphite sheet in a foamed state having a thickness of 100% or more with respect to the thickness of the polymer film as a raw material. By pressurizing the foamed graphite sheet by compression or rolling (pressurization step), a first graphite sheet 51 having particularly improved thermal conductivity in the thickness direction can be obtained. By controlling the conditions of the carbonization step, the graphitization step, and the pressurization step, it is possible to obtain the first graphite sheet 51 having the above-mentioned preferable range of thermal conductivity (thickness direction / plane direction) and thickness. can.

Examples of the polymer film as a raw material include a polyimide film using an acid dianhydride component and a diamine component as raw materials.

Examples of the acid dianhydride component include pyromellitic acid dianhydride, 2,3,6,7, -naphthalenetetracarboxylic hydride, 3,3', 4,4'-biphenyltetracarboxylic dianhydride. Anhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 2,2', 3,3'-biphenyltetracarboxylic hydride, 3,3', 4,4'-benzophenone tetracarboxylic Acid dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride, 3,4,9,10-perylenetetracarboxylic acid dianhydride, 1,1- (3,4-di) Carboxyphenyl) ethane dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride, 1,1-bis (3,4-dicarboxyphenyl) ethane dianhydride, bis (2, 3-Dicarboxyphenyl) methane dianhydride, bis (3,4-dicarboxyphenyl) methane dianhydride, oxydiphthalic acid dianhydride, bis (3,4-dicarboxyphenyl) sulfonate dianhydride, p-phenylene Examples thereof include bis (trimellitic acid monoesteric anhydride), ethylene bis (trimellitic acid monoesteric anhydride), bisphenol A bis (trimellitic acid monoesteric anhydride), and their analogs. ..

Examples of the diamine component include 4,4'-diaminodiphenyl ether, p-phenylenediamine, 4,4'-diaminodiphenylmethane, benzidine, 3,3'-dichlorobenzidine, 4,4'-diaminodiphenyl sulfide, and 3,3'. −Diaminodiphenylsulfone, 4,4′-diaminodiphenylsulfone, 3,3′-diaminodiphenylether, 3,4′-diaminodiphenylether, 1,5-diaminonaphthalene, 4,4′-diaminodiphenyldiethylsilane, 4,4 ′ -Diaminodiphenylsilane, 4,4′-diaminodiphenylethylphosphine oxide, 4,4′-diaminodiphenylN-methylamine, 4,4′-diaminodiphenylN-phenylamine, 1,3-diaminobenzene, 1, 2-Diaminobenzene and its analogs can be mentioned.

The method (ii) described above is a method of cutting a graphite block having a graphene structure into a sheet shape. The graphene structure is a structure in which six-membered rings of carbon atoms are connected by a covalent bond, and has high thermal conductivity in the plane direction.

As a first method for producing a graphite block having a graphene structure, a method of introducing a carbonaceous gas such as methane into a furnace and heating it to about 2000 ° C. with a heater to form fine carbon nuclei can be mentioned. Be done. The formed carbon nuclei are deposited in layers on the substrate, whereby a pyrolytic graphite block can be obtained. Further, the orientation can be improved by heat-treating the obtained pyrolytic graphite block to 2800 ° C. or higher.

As a second method for producing a graphite block having a graphene structure, there is a method in which polymer films are laminated in multiple layers and then heat-treated while pressurizing. Specifically, first, a laminate in which a polymer film as a starting material is laminated in multiple layers is preheated to a temperature of about 1000 ° C. under reduced pressure or in an inert gas to be carbonized to form a carbonized block. do. Then, the carbonized block is graphitized by heat-treating to a temperature of 2800 ° C. or higher while pressing and pressing in an inert gas atmosphere. As a result, a good graphite crystal structure can be formed, so that a graphite block having excellent thermal conductivity in the plane direction can be obtained.

Further, a carbonized film is produced by firing the polymer films one by one, and the obtained carbonized films are laminated in multiple layers and then heat-treated to a temperature of 2800 ° C. or higher to conduct heat conduction in the plane direction. A graphite block having excellent properties can be obtained.

When laminating the polymer films in multiple layers, the polymer films may be laminated so that all the crystal orientation planes are aligned, or several polymer films having different 90 ° orientations may be laminated.

As a method for cutting the graphite block, a known technique such as a diamond cutter, a wire saw, or machining can be appropriately selected. Above all, it is preferable to use a wire saw as the cutting method from the viewpoint that it can be easily processed into a substantially rectangular parallelepiped shape.

Further, the surface of the cut graphite block may be polished or roughened, and known techniques such as sanding, buffing, and blasting may be appropriately used as the method.

By cutting the graphite block obtained by the above method into a sheet in the direction perpendicular to the crystal orientation plane of the graphite layer, a first graphite sheet 51 having particularly improved thermal conductivity in the thickness direction can be obtained. ..

Examples of the polymer film used for producing the graphite block include a polyimide film similar to that used in the method (i) described above.

(2nd graphite sheet 52)
The second graphite sheet 52 constituting the heat conductive sheet 50 is not particularly limited as long as it is a graphite sheet whose surface direction thermal conductivity is higher than that of the first graphite sheet 51 in the surface direction. You can use the one normally used in.

In order to stably transfer the heat of the heating element 6 arranged on the second surface to the first graphite sheet 51, the thermal conductivity of the second graphite sheet 52 in the thickness direction at 25 ° C. is 3 W / m · K. It is preferably 4 W / m · K or more, and more preferably 4 W / m · K or more.

Further, in order to spread the heat of the heating element 6 mainly in the plane direction and utilize the entire heat conductive sheet 50, the thermal conductivity of the second graphite sheet 52 in the thickness direction at 25 ° C. is 8 W / m. It is preferably K or less, and more preferably 7 W / m · K or less.

The thermal conductivity of the second graphite sheet 52 in the plane direction at 25 ° C. is preferably 1200 W / m · K or more, preferably 1400 W / m · K or more, in order to enhance the heat dissipation of the heat conductive sheet 50. Is more preferable.

Further, the upper limit of the thermal conductivity of the second graphite sheet 52 in the plane direction at 25 ° C. is not particularly limited. As the thermal conductivity in the plane direction increases, the thermal conductivity in the thickness direction tends to decrease, so that it can be appropriately adjusted according to the balance of the thermal conductivity in both directions.

From the viewpoint of productivity, the thickness of the second graphite sheet 52 is preferably 10 μm or more, and more preferably 25 μm or more. Further, from the viewpoint of thermal conductivity, the thickness of the second graphite sheet 52 is preferably 40 μm or less, and more preferably 32 μm or less.

The second graphite sheet 52 can be produced according to a known method. Examples of such a method include (i) a method of forming a graphite powder such as natural graphite and artificial graphite into a sheet, and (ii) a method of heat-treating a polymer film.

According to the method of heat-treating a polymer film, for example, a polyimide film or a carbonized film obtained by carbonizing a polyimide film at a high temperature (for example, 800 ° C. or higher) is heat-treated at a high temperature (for example, 2400 ° C. or higher). Thereby, the second graphite sheet 52 having the above-mentioned preferable range of thermal conductivity (thickness direction / plane direction) and thickness can be obtained. As the polyimide film, the same polyimide film as that used for producing the above-mentioned graphite block can be used.

(Adhesive layer 53)
The adhesive layer 53 located between the first graphite sheet 51 and the second graphite sheet 52 and adhering them is made of a known adhesive or adhesive (for example, Pressure Sensitive Adhesive (PSA)). It may be a layer.

More specifically, the adhesives or adhesives constituting the adhesive layer 53 include polyester-based adhesives, polyimide-based adhesives, epoxy-based adhesives, acrylic-based adhesives, polyurethane-based adhesives, silicone-based adhesives, and Examples include rubber-based adhesives. These may be used alone or as a mixture.

Further, as the adhesive layer 53, a film-shaped optical adhesive sheet can also be used. A polyester-based adhesive or an acrylic-based adhesive is preferable, and a polyester-based adhesive is particularly preferable, as the adhesive material constituting the adhesive layer 53 because of its excellent heat dissipation.

When the adhesive layer 53 is provided, its thickness is preferably 1 μm or more, preferably 50 μm or less, more preferably 20 μm or less, and further preferably 10 μm or less. According to the above configuration, a heat conductive sheet having high heat dissipation performance can be realized.

(Manufacturing method of heat conductive sheet 50)
The method for producing a heat conductive sheet according to an embodiment of the present invention can be produced by laminating a first graphite sheet 51 and a second graphite sheet 52. The first graphite sheet 51 and the second graphite sheet 52 can be laminated via the above-mentioned adhesive layer 53 or by directly joining the two.

The first graphite sheet 51 and the second graphite sheet 52 may be bonded or bonded to the entire surface of the sheet, or may be partially bonded or bonded.

When the graphite sheets are partially bonded or joined to each other, the graphite sheets are not firmly fixed to each other, so that a heat conductive sheet whose shape can be easily changed can be realized.

(Adhesive layer)
The adhesive layer is a layer provided on the second surface 2 as needed to join the heating element 6 and the heat conductive sheet 50.

Examples of the material constituting the pressure-sensitive adhesive layer include an acrylic pressure-sensitive adhesive, a silicone-based pressure-sensitive adhesive, and a rubber-based pressure-sensitive adhesive. These may be used alone or as a mixture. Further, as the adhesive layer, an adhesive sheet such as double-sided tape can also be used.

The thickness of the adhesive layer is not particularly limited, but is preferably 1 μm or more, more preferably 2 μm or more, and preferably 20 μm or less, more preferably 10 μm or less. When the thickness of the adhesive layer is within the above range, a good connection between the heating element 6 and the heat conductive sheet 50 can be obtained, and the heat dissipation of the heat conductive sheet 50 is not impaired.

The adhesive surface of the adhesive layer may be covered by the separator until the time when the heat conductive sheet 50 is used. As the separator, a conventional sheet in which a release layer is laminated on a base film can be used.

(Protective layers 57, 58)
The protective layers 57 and 58 are laminated for the purpose of protecting the heat conductive sheet 50, imparting electrical insulation, suppressing the generation of graphite powder, reinforcing the heat conductive sheet 50, and the like.

The thickness of the protective layers 57 and 58 is not particularly limited, but is preferably 2 μm or more, more preferably 6 μm or more, and preferably 200 μm or less, more preferably 100 μm or less. When the thicknesses of the protective layers 57 and 58 are 200 μm or less, the heat dissipation characteristics of the heat conductive sheet are not impaired. On the other hand, if the thickness is 2 μm or more, the function can be fully exhibited.

The material of the protective layers 57 and 58 is not particularly limited, and for example, a polymer film such as a polyethylene terephthalate (PET) film, a polypropylene film, a polyethylene film, a polystyrene film, or a polyimide film can be used.

The protective layers 57 and 58 can be laminated on the surface of each graphite sheet via the adhesive layers 53c and 53d. The adhesive constituting the adhesive layers 53c and 53d is not particularly limited, and a known adhesive or an adhesive similar to that used for the adhesive layer 53 can be used.

The thickness of the adhesive layers 53c and 53d is preferably 1 μm or more, more preferably 5 μm or more, preferably 50 μm or less, more preferably 20 μm or less, and further preferably 10 μm or less. According to the above configuration, a heat conductive sheet having high heat dissipation performance can be realized.

Alternatively, as the material of the protective layers 57 and 58, a tape in which the adhesive layer is preliminarily laminated on the polymer film, for example, PET tape or the like can be used.

(Structure of heat conductive sheet 60)
FIG. 2 is a cross-sectional view schematically showing an electronic device 103 including a heat conductive sheet 60 and a heating element 6 according to an embodiment of the present invention. As shown in FIG. 2, the heat conductive sheet 60 covers the surface of the first graphite sheet 51 on the first surface side and the surface of the second graphite sheet 52 on the second surface side of the first heat conductive layer 54. It differs from the above-mentioned heat conductive sheet 50 in that the second heat conductive layer 55 is further included. Each other configuration is the same as the configuration described for the heat conductive sheet 50. By further including the first heat conductive layer 54 and the second heat conductive layer 55 in the heat conductive sheet 60, the heat dissipation property can be further improved.

In FIG. 2, the heat conductive sheet 60 includes both the first heat conductive layer 54 and the second heat conductive layer 55, but the present invention is not limited to this embodiment. For example, even when either the first heat conductive layer 54 or the second heat conductive layer 55 is included, the heat dissipation can be improved.

(First heat conductive layer 54, second heat conductive layer 55)
Each of the first heat conductive layer 54 and the second heat conductive layer 55 is a layer made of metal. Examples of the metal include gold, silver, copper, aluminum, stainless steel, brass, and iron.

Among these materials, copper is preferable from the viewpoint of exerting an advantageous effect of increasing heat transferability in the thickness direction. Further, from the viewpoint of realizing the heat conductive sheet 60 having high heat dissipation at low cost, copper and brass are preferable among these materials. The first heat conductive layer 54 and the second heat conductive layer 55 may be made of the same material or may be made of different materials.

The lower limit of the thermal conductivity of the first heat conductive layer 54 and the second heat conductive layer 55 at 25 ° C. is independently, preferably 100 W / m · K or more, more preferably 200 W / m · K or more. It is more preferably 400 W / m · K or more, and most preferably 1000 W / m · K or more.

On the other hand, the upper limit of the thermal conductivity of the first heat conductive layer 54 and the second heat conductive layer 55 at 25 ° C. is not particularly limited. According to the above configuration, a heat conductive sheet having high heat dissipation performance can be realized.

The thicknesses of the first heat conductive layer 54 and the second heat conductive layer 55 are not particularly limited, but are preferably 5 μm or more, more preferably 5 μm or more, respectively, in order to obtain the effect of improving heat dissipation. It is 10 μm or more, more preferably 20 μm or more. The thickness is preferably 200 μm or less, more preferably 100 μm or less, and more preferably 50 μm or less.

The method of coating the surface of the graphite sheet with the first heat conductive layer 54 or the second heat conductive layer 55 is not particularly limited, and for example, a metal foil made of a metal constituting each heat conductive layer is attached to an adhesive layer (FIG. A method of laminating on the surface of a graphite sheet via (not shown) can be mentioned.

The adhesive constituting the adhesive layer is not particularly limited, and a known adhesive or an adhesive similar to that used for the adhesive layer 53 can be used. The thickness of the adhesive layer may be such that each of the first heat conductive layer 54 and the second heat conductive layer 55 and the graphite sheet can transfer heat from one to the other. It is preferably 10 μm or more, and more preferably 25 μm or more. The upper limit of the thickness of the adhesive layer is not particularly limited and can be set as appropriate.

(Structure of heat conductive sheet 70)
FIG. 3 is a cross-sectional view schematically showing an electronic device 104 including a heat conductive sheet 70 and a heating element 6 according to an embodiment of the present invention. As shown in FIG. 3, the heat conductive sheet 70 is described above in that the third graphite sheet 56 is further included between the first graphite sheet 51 and the second graphite sheet 52 via the adhesive layers 53a and 53b. It is different from the heat conductive sheet 50 of. Each other configuration is the same as the configuration described for the heat conductive sheet 50.

Similar to the mechanism described for the heat conductive sheet 50, the temperature becomes substantially uniform inside the heat conductive sheet 70, and the entire heat conductive sheet 70 can be utilized to improve heat dissipation.

(Third Graphite Sheet 56)
The third graphite sheet 56 may be a single-layer graphite sheet composed of one layer of graphite sheet, or may be a laminated graphite sheet in which a plurality of single-layer graphite sheets are laminated.

The single-layer graphite sheet constituting the third graphite sheet 56 is not particularly limited, and a graphite sheet similar to that used for the first graphite sheet 51 or the second graphite sheet 52 may be used. can.

The laminated graphite sheet may include an adhesive layer and / or other configurations other than the single-layer graphite sheet and the adhesive layer in addition to the single-layer graphite sheet. In such a laminated graphite sheet, (i) the single-layer graphite sheets are at least partially bonded to each other via an adhesive layer, and (ii) a laminate of the single-layer graphite sheet and the adhesive layer is at least partially bonded to each other. It can be made by crimping, (iii) at least partially crimping a laminate of a single-layer graphite sheet with an adhesive layer and other configurations.

When the single-layer graphite sheets are partially bonded to each other via the adhesive layer, when the laminate of the single-layer graphite sheet and the adhesive layer is partially crimped, and when the single-layer graphite sheet, the adhesive layer and other configurations are formed. When the laminate with and is partially crimped, the shapes are easily changed because the configurations are not firmly fixed to each other.

As the material of the adhesive layer constituting the laminated graphite sheet, a known adhesive or an adhesive similar to that used for the adhesive layer 53 can be used. The thickness of the adhesive layer is preferably 1 μm or more, more preferably 5 μm or more, preferably 50 μm or less, more preferably 20 μm or less, still more preferably 10 μm or less. According to the above configuration, a heat conductive sheet having high heat dissipation performance can be realized.

The thickness of the single-layer graphite sheet constituting the third graphite sheet 56 is not particularly limited, and is preferably 10 μm to 100 μm, more preferably 20 μm to 80 μm, and further preferably 30 μm to 50 μm. ..

When the third graphite sheet 56 is a laminated graphite sheet, the lower limit of the number of single-layer graphite sheets constituting the laminated graphite sheet is not particularly limited, and for example, one layer or more is preferable, and two or more layers are more preferable. Three or more layers are more preferable, and five or more layers are particularly preferable.

The upper limit of the number of single-layer graphite sheets constituting the laminated graphite sheet is not particularly limited, and for example, 100 layers or less is preferable, 60 layers or less is more preferable, 30 layers or less is further preferable, and 20 layers or less is particularly preferable. preferable.

The upper limit of the thickness of the third graphite sheet 56 is 2500 μm or less, preferably 2000 μm or less, more preferably 1500 μm or less, still more preferably 1000 μm or less, and particularly preferably 700 μm or less.

The thermal conductivity of the third graphite sheet 56 in the plane direction is not particularly limited. From the viewpoint of realizing a heat conductive sheet having higher heat dissipation performance, the thermal conductivity of the third graphite sheet 56 in the plane direction at 25 ° C. is preferably 1000 W / m · K or more, more preferably 1300 W / m · K or more. , More preferably 1500 W / m · K or more, and most preferably 1700 W / m · K or more.

The thermal conductivity of the third graphite sheet 56 in the thickness direction is not particularly limited. The thermal conductivity of the single-layer graphite sheet in the thickness direction at 25 ° C. is generally about 5 W / m · K, and the thermal conductivity of the laminated graphite sheet in the thickness direction at 25 ° C. is generally about 5 W / m · K. It is approximately 1 W / m · K.

[2. Electronic device]
An electronic device according to an embodiment of the present invention includes a heat conductive sheet according to an embodiment of the present invention and a heating element arranged on a second surface of the heat conductive sheet, and includes the heat conductive sheet and heat generation. The body is in contact or adhered.

The heating element is not particularly limited, and examples thereof include a CPU, a GPU, an amplifier, a camera, a module, and a battery.

According to the configuration in which the heat conductive sheet and the heating element are in contact with each other or adhered to each other, heat can be efficiently transferred from the heating element to the heat conductive sheet, and the heat can be efficiently dissipated by the heat conductive sheet. ..

The heat conductive sheet and the heating element may be adhered to each other via an adhesive material. The adhesive material is not limited, and examples thereof include polyester-based adhesives, acrylic-based adhesives, polyurethane-based adhesives, epoxy-based adhesives, and silicone-based adhesives. The adhesive material may be a film-shaped optical adhesive sheet. The thickness of the adhesive material is not limited, and is preferably, for example, 1 μm to 15 μm, more preferably 2 μm to 10 μm, and even more preferably 3 μm to 7 μm.

Compared with the case where the heating element is arranged on the first surface of the heat conductive sheet, when the heating element is arranged on the second surface, the heat dissipation property is remarkably improved.

The heating element may be arranged on the second surface of the heat conductive sheet, and its position is not particularly limited. For example, the heating element may be arranged near the center of the second surface or near the end of the second surface. In the electronic device according to the embodiment of the present invention, the heat conductive sheet and the heating element are in contact with or adhered to each other at the end of the heat conductive sheet. From the viewpoint of efficiently dissipating heat by the heat conductive sheet, the heating element is preferably arranged in the vicinity of the end portion of the second surface.

Specifically, the electronic device according to the embodiment of the present invention may be a smartphone, a tablet, a laptop computer, an AI speaker, a smart glass, a battery module, or a radio base station.

Examples of the present invention will be described below, but the present invention is not limited to these examples.

[Manufacturing Example 1]
A polyimide film (manufactured by Kaneka, trade name 95 NPI, thickness 95 μm) is heated from room temperature (25 ° C.) to 1000 ° C. at a rate of 3 ° C./min under an argon gas atmosphere, and then 1.2 ° C./min. The temperature was raised to 2900 ° C. at the same rate as above, and the temperature was maintained at 2900 ° C. for 10 minutes. Then, the temperature was lowered at a rate of 5 ° C./min, and after the temperature reached 1000 ° C., the heater was turned off and the rest was naturally cooled. The obtained foamed graphite sheet was rolled at a pressure of 1 MPa to prepare a graphite sheet (X).

The graphite sheet (X) has a thickness of 80 μm, a density of 1.5 g / cm ³ , a specific heat of 850 J / kg · K, and a thermal conductivity in the thickness direction (z direction) at 25 ° C.: 13 W / m · K, The thermal conductivity in the plane direction (xy direction) at 25 ° C. was 900 W / m · K.

[Example 1]
As the first graphite sheet, the graphite sheet (X) obtained in Production Example 1 was prepared.

As the second graphite sheet, a graphite sheet (Y) (manufactured by Kaneka Corporation, XGX-032R-RL-P) was prepared. The graphite sheet (Y) has a thickness of 32 μm, a density of 2.0 g / cm ³ , a specific heat of 798 J / kg · K, and a thermal conductivity in the thickness direction (z direction) at 25 ° C.: 5-6 W / m ·. The thermal conductivity in the plane direction (xy direction) at K and 25 ° C. was 1400 W / m · K.

The graphite sheet (X) and the graphite sheet (Y) were bonded together as an adhesive layer via a pressure-sensitive adhesive (PSA) (DIC acrylic pressure-sensitive adhesive, thickness 5 μm). Next, a black PET tape (manufactured by Niei Kako, trade name GL-10B, thickness 10 μm) was attached to the surface on the first graphite sheet side as a protective layer. Further, a double-sided tape (manufactured by Niei Kako, trade name NeoFix10, thickness 10 μm) was attached as an adhesive layer to the surface on the second graphite sheet side to manufacture a heat conductive sheet.

The obtained heat conductive sheet has the following layer structure: (first surface) protective layer / graphite sheet (X) / adhesive layer / graphite sheet (Y) / adhesive layer (second surface).

[Comparative Example 1]
Three graphite sheets (Y) are bonded together as an adhesive layer via a pressure-sensitive adhesive (PSA) (DIC acrylic pressure-sensitive adhesive, thickness 5 μm), and black as a protective layer on one surface. PET tape (manufactured by Niei Kako, trade name GL-10B, thickness 10 μm) was adhered. Further, a double-sided tape (manufactured by Niei Kako, trade name NeoFix10, thickness 10 μm) was attached to the other surface as an adhesive layer to manufacture a heat conductive sheet.

The obtained heat conductive sheet has the following layer structure: (first surface) protective layer / graphite sheet (Y) / adhesive layer / graphite sheet (Y) / adhesive layer / graphite sheet (Y) / adhesive layer ( Second side).

[Comparative Example 2]
A black PET tape (manufactured by Niei Kako, trade name GL-10B, thickness 10 μm) was attached to one surface of one graphite sheet (X) as a protective layer. Further, a double-sided tape (manufactured by Niei Kako, trade name NeoFix10, thickness 10 μm) was attached to the other surface as an adhesive layer to manufacture a heat conductive sheet.

The obtained heat conductive sheet has the following layer structure: (first surface) protective layer / graphite sheet (X) / adhesive layer (second surface).

〔evaluation〕
The heat conductive sheets obtained in Examples and Comparative Examples were cut into a size of 60 mm in width × 100 mm in length to prepare a sample 100.

For each sample 100, a heating element 6 (ceramic heater) and four thermocouples 3a, 3b, 3c, 3d were installed as shown in FIGS. 5 and 6.

Specifically, for each sample 100, a ceramic heater (manufactured by Sakaguchi Heat Transfer Co., Ltd., trade name: Micro Ceramic Heater MS) is placed on the upper end of the second surface (the surface on the adhesive layer side) (distance from the upper end of the sample is 15 mm). -3, size 10 mm x 10 mm) was pasted.

Further, a thermocouple 3a is installed on the ceramic heater, a thermocouple 3b is installed at the upper end of the first surface (distance from the upper end of the sample 15 mm), and the thermocouple 3b is installed at the center of the first surface (distance 50 mm from the upper end of the sample). The thermocouple 3c was installed, and the thermocouple 3d was installed at the lower end of the first surface (distance 85 mm from the upper end of the sample).

An electric power of 3.5 W was applied to the ceramic heater to raise the temperature of the ceramic heater. The temperature at each thermocouple installation location was measured for 30 minutes after the start of application, and the temperature in the steady state after temperature stabilization was determined.

The test results are shown in Table 1.

The heat conductive sheet of Example 1 showed a lower temperature than the heat conductive sheet of Comparative Example 1 at all the installation locations of the thermocouples 3a to 3d. This indicates that the heat conductive sheet of Example 1 is less likely to cause temperature unevenness inside the heat conductive sheet, and efficiently dissipates heat by utilizing the entire heat conductive sheet, so that high heat dissipation is obtained. ..

On the other hand, the heat conductive sheet of Comparative Example 1 had a higher temperature than the heat conductive sheet of Example 1 at all the installation locations of the thermocouples 3a to 3d, and was inferior in heat dissipation. Further, the heat conductive sheet of Comparative Example 2 had a higher temperature than the heat conductive sheet of Example 1 at the installation location of the thermocouples 3a and 3b. This indicates that the entire heat conductive sheet could not be utilized due to the large temperature unevenness inside the heat conductive sheet of Comparative Example 2, and sufficient heat dissipation could not be obtained.

The present invention can be suitably used as a heat radiating component. More specifically, the present invention can be suitably used as a heat radiating component of an electronic device (for example, a smartphone, a tablet, a notebook computer, an AI speaker, a smart glass, a battery module, or a radio base station).

1 1st surface 2 2nd surface 3a, 3b, 3c, 3d Thermocouple 5, 50, 60, 70 Heat conductive sheet 6 Heating element 10 High temperature region 11 Low temperature region 51 First graphite sheet 52 Second graphite sheet 53, 53a, 53b, 53c, 53d Adhesive layer 54 First thermoelectric layer 55 Second thermoelectric layer 56 Third graphite sheet 57, 58 Protective layer 100 Sample 101, 102, 103, 104 Electronic device

Claims (8)

A heat conductive sheet having a first surface and a second surface facing back from the first surface.
Contains at least two graphite sheets,
Among the graphite sheets, the thermal conductivity in the thickness direction of the first graphite sheet located closest to the first surface is the thermal conductivity in the thickness direction of the second graphite sheet located closest to the second surface. Higher than, heat conductive sheet. The heat conductive sheet according to claim 1, wherein the first graphite sheet has a thermal conductivity in the thickness direction at 25 ° C. of 10 to 25 W / m · K. The heat conductive sheet according to claim 1 or 2, wherein the second graphite sheet has a thermal conductivity in the thickness direction at 25 ° C. of 5 to 8 W / m · K. The heat conductive sheet according to any one of claims 1 to 3, wherein the thickness of the first graphite sheet is 50 to 100 μm. The heat conductive sheet according to any one of claims 1 to 4, wherein the thickness of the second graphite sheet is 10 to 40 μm. Either the first heat conductive layer that covers the surface of the first graphite sheet on the first surface side or the second heat conductive layer that covers the surface of the second graphite sheet on the second surface side. The heat conductive sheet according to any one of claims 1 to 5, further comprising both. The heat conductive sheet according to any one of claims 1 to 6,
It is provided with a heating element arranged on the second surface.
An electronic device in which the heat conductive sheet and the heating element are in contact with or adhered to each other. A method for manufacturing an electronic device, which comprises a step of arranging a heating element on the second surface of the heat conductive sheet according to any one of claims 1 to 6.

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