Heat conductive sheet and device provided with the same

Abstract

The invention relates to a thermally conductive sheet and a device provided with the thermally conductive sheet. One embodiment of the present invention relates to a thermally conductive sheet containing graphite particles (A) containing at least one type selected from scale-like particles, ellipsoid-like particles, and rod-like particles, the graphite particles (A) being oriented in the thickness direction and having a thickness compression ratio of 24% or more at a temperature of 150 DEG C and a compressive stress of 0.14 MPa.

Description

[0001] This application is a divisional application of Chinese application number 202080102591.7, filed on August 7, 2020, entitled "Heat-conducting sheet and apparatus having a heat-conducting sheet". Technical Field

[0002] This disclosure relates to a heat-conducting sheet, an apparatus having a heat-conducting sheet, and a method for manufacturing an apparatus having a heat-conducting sheet. Background Technology

[0003] With the increasing density and thinning of electronic devices, electronic components such as semiconductor elements and devices require good heat dissipation, that is, the ability to efficiently dissipate the generated heat. For example, semiconductor devices have a structure that transfers heat from the heat-generating element to the heat-dissipating element by sandwiching a heat-conducting sheet between the heat-generating element (such as a semiconductor element) and a heat-dissipating element (such as an aluminum or copper heat sink).

[0004] Patent document 1 describes a heat-conducting sheet containing graphite particles, with an elastic modulus of less than 1.4 MPa when the compressive stress is 0.1 MPa at 150°C, and an adhesion of more than 5.0 N•mm at 25°C.

[0005] Existing technical documents Patent documents Patent Document 1: International Publication No. 2019 / 159340 Summary of the Invention

[0006] The technical problem that the invention aims to solve In recent years, due to the increasing density and thinning of electronic devices, there has been a trend towards thinner heating elements and heat sinks. For heat-conducting sheets used to bond heating elements and heat sinks, it is desirable to achieve good thermal conductivity even when bonding them under low pressure.

[0007] Therefore, this disclosure provides a heat-conducting sheet with improved thermal conductivity. Furthermore, this disclosure provides an apparatus incorporating the heat-conducting sheet with improved thermal conductivity. Moreover, this disclosure provides a method for manufacturing an apparatus incorporating the heat-conducting sheet with improved thermal conductivity.

[0008] Means for solving technical problems This invention includes various embodiments. Examples of embodiments are listed below. This invention is not limited to the following embodiments.

[0009] One embodiment relates to a heat-conducting sheet containing graphite particles (A) selected from at least one of flake-shaped particles, ellipsoidal particles, and rod-shaped particles, wherein the graphite particles (A) are oriented in the thickness direction and the thickness compressibility is 24% or more at a temperature of 150°C and a compressive stress of 0.14 MPa.

[0010] Another embodiment relates to a heat-conducting sheet containing graphite particles (A) selected from at least one of flake-shaped particles, ellipsoidal particles, and rod-shaped particles, wherein the graphite particles (A) are oriented in the thickness direction and the average particle size of the graphite particles (A) is 50 to 75% of the thickness.

[0011] Another embodiment relates to an apparatus comprising a heating element, a heat sink, and a heat-conducting sheet in contact with the heating element and the heat sink, as described in any of the above embodiments.

[0012] Another embodiment relates to a method of manufacturing an apparatus, comprising the steps of: disposing a heat-conducting sheet of any of the above embodiments between a heating element and a heat sink, to obtain a composite comprising the heating element, the heat sink, and the heat-conducting sheet in contact with the heating element and the heat sink; and applying pressure in the thickness direction of the heat-conducting sheet to the composite, thereby bonding the heating element and the heat sink together through the heat-conducting sheet.

[0013] Invention Effects According to this disclosure, a heat-conducting sheet with improved thermal conductivity can be provided. Furthermore, according to this disclosure, an apparatus incorporating the heat-conducting sheet with improved thermal conductivity can be provided. Moreover, according to this disclosure, a method for manufacturing an apparatus incorporating the heat-conducting sheet with improved thermal conductivity can be provided. Detailed Implementation

[0014] Embodiments of the present invention will be described below. The present invention is not limited to the following embodiments. The following embodiments may be implemented individually or in combination.

[0015] <Heat-conducting sheet> The heat-conducting sheet contains graphite particles (A) selected from at least one type of flake-shaped particles, ellipsoidal particles, and rod-shaped particles. In the heat-conducting sheet, the graphite particles (A) are oriented in the thickness direction of the heat-conducting sheet.

[0016] In some embodiments, the heat-conducting sheet has a compression ratio of 24% or more at a temperature of 150°C and a compressive stress of 0.14 MPa. Alternatively, in some embodiments, the heat-conducting sheet used to bond the heat-generating element and the heat-dissipating element has a compression ratio of 24% or more at the temperature and compressive stress during the bonding of the heat-generating element and the heat-dissipating element.

[0017] In some embodiments, the ratio of the average particle size of graphite particles (A) in the heat-conducting sheet to the thickness of the heat-conducting sheet is 50 to 75%.

[0018] [Element] The heat-conducting sheet contains at least graphite particles (A). The heat-conducting sheet may further contain any components such as resin.

[0019] (Graphite particles (A)) The graphite particles (A) comprise at least one type selected from flake-shaped particles, ellipsoidal particles, and rod-shaped particles. From the viewpoint of improving thermal conductivity, the graphite particles (A) preferably comprise flake-shaped particles. Flake-shaped particles tend to be easily oriented in the desired direction in a thermally conductive sheet. From the viewpoint of high crystallinity, the graphite particles (A) preferably comprise flake-shaped expanded graphite particles obtained by pulverizing expanded graphite formed into a sheet shape.

[0020] In the heat-conducting sheet, graphite particles (A) are oriented in the thickness direction of the heat-conducting sheet. "Graphite particles (A) are oriented in the thickness direction of the heat-conducting sheet" preferably refers to a state where the angle between the graphite particles (A) and the surface (main surface) of the heat-conducting sheet is 60° or more. In this disclosure, this angle is sometimes referred to as the "orientation angle." The orientation angle can also be 80° or more, 85° or more, or 88° or more. The orientation angle can be measured, for example, by the following methods.

[0021] The heat-conducting sheet is cut to obtain a cross-section. The heat-conducting sheet is cut in a manner that allows for the determination of orientation angles. For example, when the heat-conducting sheet contains flake-like particles, it is cut such that the cross-section of the heat-conducting sheet contains a section perpendicular (or substantially perpendicular) to the direction of the flake-like particles. Next, the cross-section of the heat-conducting sheet is observed using a SEM (scanning electron microscope), and the orientation angles of any 50 graphite particles (A) are determined. A total of 50 graphite particles (A) can be selected from one cross-section of the heat-conducting sheet, or a total of 50 graphite particles (A) can be selected from two or more cross-sections of the heat-conducting sheet. For flake-shaped particles, the angle between the thickness direction of the heat-conducting sheet (i.e., the length direction of the cross-section of the flake-shaped particle) and the surface of the heat-conducting sheet is measured; for ellipsoidal particles, the angle between the major axis of the ellipsoidal particle and the surface of the heat-conducting sheet is measured; for rod-shaped particles, the angle between the major axis of the rod-shaped particle and the surface of the heat-conducting sheet is measured. The arithmetic mean of the obtained measurements (50 particles) is taken as the orientation angle of the graphite particle (A).

[0022] The average particle size of graphite particles (A) is, for example, 50 μm or more, 60 μm or more, 70 μm or more, or 80 μm or more. The average particle size of graphite particles (A) is, for example, 300 μm or less, 200 μm or less, or 180 μm or less. The average particle size of graphite particles can be determined, for example, by the following methods.

[0023] The graphite particles (A) were recovered by dissolving them in an organic solvent to remove all components except graphite particles (A) from the thermally conductive sheet. The recovered graphite particles (A) were washed with the organic solvent and then thoroughly dried. Using a scanning electron microscope (SEM), 200 random particles from the graphite particles (A) were selected, and the particle size of each particle was measured. For flake-shaped particles, the major axis was measured; for ellipsoidal particles, the major axis was measured; and for rod-shaped particles, the major axis was measured. The arithmetic mean of the 200 measurements was taken as the average particle size of the graphite particles (A).

[0024] The preferred orientations of the six-membered rings in the crystallization of graphite particles (A) are as follows: when the graphite particles (A) are flake-shaped, the orientation is such that the plane orientation of the six-membered ring is the same as the plane orientation of the flake-shaped particles; when the graphite particles (A) are ellipsoidal particles, the orientation is such that the plane orientation of the six-membered ring is the same as the long axis orientation of the ellipsoidal particles; or when the graphite particles (A) are rod-shaped particles, the orientation is such that the plane orientation of the six-membered ring is the same as the long axis orientation of the rod-shaped particles. The plane of the six-membered ring refers to the plane containing the six-membered ring in the hexagonal crystal system, specifically the (0001) crystal plane.

[0025] Whether the six-membered rings in the crystallization of graphite particles (A) are oriented as described above can be confirmed by X-ray diffraction. Specifically, the following method can be used for confirmation. The following explanation uses the case where graphite particles (A) are flake-like particles as an example.

[0026] First, a sample sheet for testing is prepared, which contains scaly particles oriented such that their surface direction is the same as the surface direction of the sheet. Examples of methods for preparing the sample sheet for testing include the following.

[0027] A mixture of resin and flake-like particles (graphite particles (A)) in an amount of 10% by volume or more relative to the resin is prepared, and a sheet is made using the mixture. Here, the term "resin" is not particularly limited to any material that does not produce peaks that would hinder X-ray diffraction measurements and is capable of forming a sheet. Specifically, amorphous resins with cohesive properties, such as acrylic rubber, NBR (acrylonitrile butadiene rubber), and SIBS (styrene-isobutylene-styrene copolymer), can be used.

[0028] The mixture of sheets is pressed to a thickness of less than 1 / 10 of its original thickness. Multiple pressed sheets are then stacked to form a laminate. The laminate is further compressed to less than 1 / 10 of its original thickness. This process is repeated three or more times to obtain a sample sheet for testing. In the resulting sample sheet for testing, the plane orientation of the so-called flaky particles is aligned with the plane orientation of the sample sheet for testing.

[0029] Subsequently, X-ray diffraction measurements were performed on the surface of the sample sheet. The heights H1 of the peak corresponding to the graphite (110) plane appearing near 2θ = 77° and H2 of the peak corresponding to the graphite (002) plane appearing near 2θ = 27° were measured. When the value (H1 / H2) obtained by dividing H1 by H2 was 0~0.02, it was determined that the plane orientation of the six-membered ring was in the same direction as the plane orientation of the flake particles. A CuKα X-ray source could be used.

[0030] Regarding the six-membered ring of ellipsoidal particles and the six-membered ring of rod-shaped particles, the same explanation applies, except that "the direction of the surface of the scale-like particles" is changed to "the direction of the major axis of the ellipsoidal particles" or "the direction of the major axis of the rod-shaped particles".

[0031] From the above, "the six-membered ring in the crystal of graphite particles (A) is oriented in such a way that the plane direction of the six-membered ring is the same as the plane direction of the scale particles when the graphite particles (A) are flake-shaped particles; in such a way that the plane direction of the six-membered ring is the same as the plane direction of the ellipsoidal particles when the graphite particles (A) are ellipsoidal particles; or in such a way that the plane direction of the six-membered ring is the same as the plane direction of the ellipsoidal particles when the graphite particles (A) are rod-shaped particles" preferably refers to the state where the peak height corresponding to the (110) plane of graphite particles (A) appearing near 2θ=77° is divided by the peak height corresponding to the (002) plane of graphite particles (A) appearing near 2θ=27°, which is 0~0.02.

[0032] In this disclosure, X-ray diffraction measurements can be performed, for example, under the following conditions.

[0033] Device: "D8DISCOVER" manufactured by Bruker AXS Co., Ltd. X-ray source: CuKα with a wavelength of 1.5406 nm, 40 kV, 40 mA Step size (measured step length): 0.01° Step time: 720 sec From the viewpoint of balancing thermal conductivity and adhesion, the content of graphite particles (A) in the thermally conductive sheet is preferably 15 to 50% by volume, more preferably 20 to 45% by volume, and even more preferably 25 to 40% by volume. When the content of graphite particles (A) is 15% by volume or more, there is a tendency to improve thermal conductivity. In addition, when the content of graphite particles (A) is 50% by volume or less, there is a tendency to suppress the decrease in adhesion and adhesion.

[0034] The content (volume %) of graphite particles (A) can be calculated, for example, using the following formula. The same method can be used to calculate the content (volume %) of components other than graphite particles (A) contained in thermally conductive sheets.

[0035] The content (volume %) of graphite particles (A) = [(Aw / Ad) / {(Aw / Ad)+(Bw / Bd)+(Cw / Cd)+(Dw / Dd)+(Ew / Ed)+(Xw / Xd)}]×100 Aw: Mass composition (mass%) of graphite particles (A) Bw: Mass composition (mass%) of polymer (B) that is liquid at 25°C Cw: Mass composition (mass%) of polymers (C) with a glass transition temperature below 20°C. Dw: Mass composition (mass%) of hot melt flux (D) Ew: Mass composition of antioxidant (E) (mass %) Xw: Mass composition (mass%) of any other component Ad: Density of graphite particles (A) (g / cm³) 3 (In this disclosure, Ad is 2.1 g / cm³) 3 ) Bd: Density (g / cm³) of polymer (B) that is liquid at 25°C. 3 ) Cd: Density (g / cm³) of polymers (C) with a glass transition temperature below 20°C. 3 ) Dd: Density of hot melt flux (D) (g / cm³) 3 ) Ed: Density of antioxidant (E) (g / cm³) 3 ) Xd: Density of any other component (g / cm³) 3 ) Furthermore, the mass composition is a mass percentage (mass %) based on the total mass of all components contained in the heat-conducting sheet. In addition, when the heat-conducting sheet contains two or more "other arbitrary components", "Xw / Xd" is calculated for each component and all of them are added to the denominator.

[0036] Graphite particles (A) may also include graphite particles other than flake-shaped particles, ellipsoidal particles, and rod-shaped particles. Examples of graphite particles other than flake-shaped particles, ellipsoidal particles, and rod-shaped particles include spherical graphite particles, artificial graphite particles, flake graphite particles, acid-treated graphite particles, expanded graphite particles, and carbon fiber flakes.

[0037] (Any component such as resin) The heat-conducting sheet may also contain any component such as resin. The heat-conducting sheet may contain one or more resins. The resin may include, for example, at least one selected from thermosetting resins and thermoplastic resins. Specifically, the resin may include at least one selected from acrylic resins, epoxy resins, acrylonitrile resins, bismaleimide resins, benzocyclobutene resins, phenolic resins, diallyl phthalate resins, terpene resins, petroleum resins, polyolefins, conjugated diene polymers, silicones, polyesters, polyurethanes, polyimides, polyphenylene ethers, and polysulfides. The petroleum resin may include, for example, at least one selected from aromatic petroleum resins and hydrogenated aromatic petroleum resins. The resin contains at least a binder resin, and graphite particles (A) may be dispersed in the binder resin.

[0038] The heat-conducting sheet preferably contains a polyolefin. The polyolefin can function as an adhesive resin. For example, the polyolefin includes at least one selected from polyethylene, polypropylene, polybutene, and ethylene / α-olefin copolymers. For example, the heat-conducting sheet contains polybutene.

[0039] The heat-conducting sheet preferably contains an acrylic resin. The acrylic resin functions as an adhesive resin. For example, the heat-conducting sheet contains a (meth)acrylic acid polymer. In this disclosure, "(meth)acrylic acid" is a collective term for "acrylic acid" and "methacrylic acid," and "(meth)acrylate" is a collective term for "acrylate" and "methacrylate."

[0040] The adhesive resin used in thermally conductive sheets may also contain polyolefins and acrylic resins, and may also contain polybutene and (meth)acrylic acid polymers. When the adhesive resin contains polyolefins, the content of polybutene, from the viewpoint of obtaining good thermal conductivity, is, for example, 80% by mass or more, 85% by mass or more, 90% by mass or more, 95% by mass or more, or 100% by mass, based on the mass of the polyolefin. When the adhesive resin contains polybutene and (meth)acrylic acid polymers, the total content of polybutene and (meth)acrylic acid polymers in the adhesive resin, from the viewpoint of obtaining good thermal conductivity, is, for example, 80% by mass or more, 85% by mass or more, 90% by mass or more, 95% by mass or more, or 100% by mass, based on the mass of the adhesive resin.

[0041] The heat-conducting sheet may further contain any components other than resin. The heat-conducting sheet may contain one or more of these components. Examples of such components include hot melt agents, antioxidants, flame retardants, toughness modifiers, hygroscopic agents, coupling agents, surfactants, and ion traps.

[0042] The adhesive resin may include, for example, a polymer (B) that is liquid at 25°C and / or a polymer (C) with a glass transition temperature below 20°C.

[0043] In some embodiments, the heat-conducting sheet contains graphite particles (A), a polymer that is liquid at 25°C (B), and a polymer with a glass transition temperature below 20°C (C). In other embodiments, the heat-conducting sheet contains graphite particles (A), a polymer that is liquid at 25°C (B), a polymer with a glass transition temperature below 20°C (C), and a hot melt agent (D) and / or an antioxidant (E). The heat-conducting sheet may further contain a flame retardant.

[0044] (Polymer (B) is liquid at 25°C) Heat-conducting sheets may also contain polymer (B) which is liquid at 25°C (hereinafter sometimes simply referred to as "polymer (B)"). When heat-conducting sheets contain polymer (B), they tend to have increased flexibility and reduced contact thermal resistance. When heat-conducting sheets contain both polymer (B) and hot melt flux (D), they tend to have further improved cohesion and flowability upon heating.

[0045] In this disclosure, "polymer that is liquid at 25°C" refers to a polymer that is fluid at 25°C. "Polymer that is liquid at 25°C" can also be a polymer that is viscous at 25°C, for example, with a viscosity of 0.0001~10,000 Pa•s as a measure of viscosity. In this disclosure, viscosity can be measured at 25°C using a rheometer at 5.0 s⁻¹. -1 The shear rate is measured. Viscosity, for example, can be taken as shear viscosity and measured at 25°C using a rotary shear viscometer equipped with a cone plate (40 mm in diameter and 0° cone angle). The viscosity of polymer (B) at 25°C is, for example, 0.0001 Pa•s or more, 0.001 Pa•s or more, or 0.01 Pa•s or more. The viscosity of polymer (B) at 25°C is, for example, 10,000 Pa•s or less, 1,000 Pa•s or less, or 100 Pa•s or less.

[0046] As polymer (B), a resin that is liquid at 25°C can be selected from the examples of the resins described above. Polymer (B) may include, for example, at least one selected from polybutene, polyisoprene, polysulfides, silicone, (meth)acrylonitrile polymers, (meth)acrylic acid polymers, terpene resins, and petroleum resins. When used in a thermally conductive sheet in a semiconductor device, polymer (B) preferably includes at least one selected from polybutene and polyisoprene. Particularly from the viewpoint of suppressing the contact thermal resistance of the thermally conductive sheet, polymer (B) preferably includes polybutene. When the thermally conductive sheet contains polybutene, which is liquid at 25°C, there is a tendency to improve the adhesion and stress relief of the thermally conductive sheet. Polymer (B) may include one or more polymers.

[0047] Polybutene is a polymer obtained by polymerizing monomers containing isobutylene and / or n-butene. Polybutene can also be a homopolymer obtained by polymerizing isobutylene or n-butene; a copolymer obtained by copolymerizing isobutylene and n-butene; or a copolymer obtained by polymerizing monomers containing isobutylene and / or n-butene with other monomers. Examples of other monomers include α-olefins such as ethylene, propylene, and styrene. The copolymer can be any of a random copolymer, block copolymer, or graft copolymer.

[0048] Polybutene is a polymer containing at least one structural unit selected from the structural units shown in -[CH2-C(CH3)2]- and -[CH2-CH(CH2CH3)]-. Polybutene may further contain any arbitrary structural units. Polybutene is sometimes also called polybutylene.

[0049] Examples of polybutene include "Nichiyu Polybutene" from Nichiyu Corporation, "Nichishi Polybutene" from JXTG Energy Corporation, "Tetrax" from JXTG Energy Corporation, "HI-MOL" from JXTG Energy Corporation, and "Polyisobutylene" from Bakogyo Co., Ltd.

[0050] The content of polymer (B) in the heat-conducting sheet is, for example, 10% by volume or more, 15% by volume or more, or 20% by volume or more, based on the volume of the heat-conducting sheet. When the content of polymer (B) is 10% by volume or more, there is a tendency to further improve the flexibility, adhesion, and sealing properties of the heat-conducting sheet. The content of polymer (B) in the heat-conducting sheet is, for example, 55% by volume or less, 50% by volume or less, or 45% by volume or less, based on the volume of the heat-conducting sheet. When the content of polymer (B) is 55% by volume or less, there is a tendency for the heat-conducting sheet to have sufficient strength and thermal conductivity. From the viewpoint of improving adhesion, sealing properties, sheet strength, hydrolysis resistance, etc., the content of polymer (B) is also preferably within the above range.

[0051] (Polymers with a glass transition temperature below 20°C (C)) Heat-conducting sheets may also contain polymers (C) with a glass transition temperature below 20°C (hereinafter sometimes simply referred to as "polymer (C)"). When heat-conducting sheets contain polymers (C), they tend to have increased flexibility and reduced contact thermal resistance. Polymer (C) is a polymer that is not liquid at 25°C (polymer (B)). That is, polymer (C) is a polymer with a glass transition temperature below 20°C and is not liquid at 25°C.

[0052] The glass transition temperature (Tg) of polymer (C) is, for example, below 20°C, below 0°C, or below -20°C. When the glass transition temperature is below 20°C, there is a tendency for improved flexibility and adhesion in the thermally conductive sheet. The glass transition temperature (Tg) of polymer (C) is, for example, above -70°C, above -50°C, or above -30°C. In this disclosure, the glass transition temperature (Tg) can be calculated from tanδ measured using dynamic viscoelasticity determination (tensile). The peak temperature of tanδ can be used as the glass transition temperature (Tg).

[0053] The weight-average molecular weight of polymer (C) is, for example, 100,000 or more, 250,000 or more, or 400,000 or more. When the weight-average molecular weight is 100,000 or more, there is a tendency for increased film strength in the thermally conductive sheet. The weight-average molecular weight of polymer (C) is, for example, 1,000,000 or less, 700,000 or less, or 600,000 or less. When the weight-average molecular weight is 1,000,000 or less, there is a tendency for increased flexibility in the thermally conductive sheet. The weight-average molecular weight can be determined using gel permeation chromatography and a standard curve of standard polystyrene.

[0054] As polymer (C), a resin with a glass transition temperature of 20°C or lower can be selected from the examples of the resins described above. Polymer (C) may, for example, contain at least one selected from (meth)acrylic acid polymers, silicones, and conjugated diene polymers, preferably containing (meth)acrylic acid polymers. Examples of conjugated diene polymers include polybutadiene and polyisoprene. The (meth)acrylic acid polymer is a polymer obtained by polymerizing a monomer containing a (meth)acrylic acid monomer. The (meth)acrylic acid monomer has at least one (meth)acryloyl group within its molecule. Preferably, the (meth)acrylic acid monomer contains at least a monomer having a (meth)acryloyloxy group. In this disclosure, "(meth)acrylic acid monomer" refers to the collective term for acrylic acid monomers and methacrylic acid monomers, and "(meth)acryloyl group" is the collective term for acryloyl groups and methacryloyl groups. When the heat-conducting sheet contains a (meth)acrylic acid polymer with a glass transition temperature of 20°C or lower, it exhibits improved adhesion and a tendency to increase the elasticity of thickness recovery to accommodate warpage. Polymer (C) may contain one or more polymers.

[0055] Examples of monomers for (meth)acrylic acid include alkyl methacrylates such as butyl methacrylate, ethyl methacrylate, methyl methacrylate, and 2-ethylhexyl methacrylate; (meth)acrylic acid; hydroxyl-containing (meth)acrylates such as 2-hydroxy(meth)acrylate; glycidyl methacrylate and other (meth)acrylates containing glycidyl groups; (meth)acrylic acid; and (meth)acrylamide. The (meth)acrylic acid polymer can be a homopolymer or a copolymer. The (meth)acrylic acid polymer is preferably a copolymer, but it can also be a copolymer of alkyl methacrylates with (meth)acrylic acid and (meth)acrylonitrile. For example, (meth)acrylic acid polymers known as acrylic rubbers can be used as (meth)acrylic acid polymers.

[0056] The polymer (C) content in the heat-conducting sheet is, for example, 5% by volume or more, 8% by volume or more, or 10% by volume or more, based on the volume of the heat-conducting sheet. When the polymer (C) content is 5% by volume or more, there is a tendency for the flexibility, adhesion, and sealing properties of the heat-conducting sheet to be further improved. The polymer (C) content in the heat-conducting sheet is, for example, 55% by volume or less, 50% by volume or less, 45% by volume or less, 30% by volume or less, or 20% by volume, based on the volume of the heat-conducting sheet. When the polymer (C) content is 55% by volume or less, there is a tendency for the heat-conducting sheet to have sufficient strength and thermal conductivity. From the viewpoint of improving adhesion, sealing properties, sheet strength, hydrolysis resistance, etc., the polymer (C) content is also preferably within the above range.

[0057] (Hot melt (D)) Thermal conductive sheets may also contain a hot melt agent (D). When thermal conductive sheets contain a hot melt agent (D), there is a tendency for the strength of the thermal conductive sheets and their fluidity during heating to increase.

[0058] The hot melt agent (D) may contain at least one selected from aromatic petroleum resins, hydrogenated aromatic petroleum resins, terpene phenolic resins, hydrogenated terpene phenolic resins, and cyclopentadiene petroleum resins. The heat-conducting sheet may contain one or more hot melt agents (D). In particular, when the heat-conducting sheet contains a polybutene-containing polymer (B) and a hot melt agent (D), the hot melt agent (D) preferably contains at least one selected from hydrogenated aromatic petroleum resins and hydrogenated terpene phenolic resins. Hydrogenated aromatic petroleum resins and hydrogenated terpene phenolic resins, due to their high stability and excellent compatibility with polybutene, tend to achieve superior thermal conductivity, flexibility, and processability.

[0059] Examples of hydrogenated aromatic petroleum resins include "ARKON" from Arakawa Chemical Industry Co., Ltd., and "I-MARV" from Idemitsu Kosan Co., Ltd. Examples of hydrogenated terpene phenolic resins include "CLEARON" from Yschem Co., Ltd. Examples of cyclopentadiene petroleum resins include "Quintone" from Zeon Co., Ltd., and "Marukarez" from Maruzen Petrochemical Co., Ltd.

[0060] The hot melt flux (D) can be solid at 25°C and have a softening temperature of 40°C to 150°C. When the hot melt flux (D) contains a thermoplastic resin, its fluidity during hot pressing is improved, resulting in a tendency for improved adhesion. When the softening temperature is above 40°C, sufficient sheet strength is easily obtained because cohesion near room temperature can be ensured, and it tends to have excellent processability. When the softening temperature is below 150°C, the improved fluidity during hot pressing also tends to improve adhesion. A softening temperature of 60°C to 120°C is more preferred. The softening temperature can be determined according to the ring and ball method (JIS K 2207:1996).

[0061] From the perspective of improving adhesion, bonding, and sheet strength, the content of hot melt flux (D) in thermally conductive sheets is typically 3-25% by volume, 5-20% by volume, or 5-15% by volume, based on the volume of the thermally conductive sheet. When the content of hot melt flux (D) is 3% by volume or more, adhesion, flowability during heating, and sheet strength tend to be sufficiently improved. When the content of hot melt flux (D) is 25% by volume or less, flexibility is sufficiently improved, thus exhibiting excellent processability and resistance to heat cycling.

[0062] (Antioxidant (E)) Heat-conducting sheets may also contain antioxidants (E). When heat-conducting sheets contain antioxidants (E), they tend to have improved thermal stability at high temperatures.

[0063] The antioxidant (E) may include, for example, at least one selected from phenolic antioxidants, phosphorus antioxidants, amine antioxidants, sulfur antioxidants, hydrazine antioxidants, and amide antioxidants. The heat-conducting sheet may contain one or more antioxidants (E). The antioxidant (E) may be appropriately selected according to the temperature conditions used, etc. The antioxidant (E) may include, for example, phenolic antioxidants. As an example, hindered phenolic antioxidants may be included among phenolic antioxidants.

[0064] Examples of phenolic antioxidants include "ADK STAB AO-50", "ADK STABAO-60", and "ADK STAB AO-80" from ADEKA Corporation.

[0065] The content of antioxidant (E) in the heat-conducting sheet is, for example, 0.1 to 5 vol%, 0.2 to 3 vol%, or 0.3 to 1 vol%, based on the volume of the heat-conducting sheet. When the content of antioxidant (E) is 0.1 vol% or more, there is a tendency to obtain sufficient antioxidant effect. When the content of antioxidant (E) is 5 vol% or less, there is a tendency to obtain sufficient strength of the heat-conducting sheet.

[0066] (Flame retardant) For example, from a flame-retardant perspective, heat-conducting sheets may also contain flame retardants. There are no particular limitations on the flame retardant; it can be appropriately selected from commonly used flame retardants. Examples of flame retardants include red phosphorus-based flame retardants and phosphate ester-based flame retardants. From the viewpoint of excellent safety and improved adhesion due to plasticizing effect, phosphate ester-based flame retardants are preferred.

[0067] Examples of phosphate ester-based flame retardants include aliphatic phosphates such as trimethyl phosphate, triethyl phosphate, and tributyl phosphate; aromatic phosphates such as triphenyl phosphate, tricresyl phosphate, and toluene diphenyl phosphate; and aromatic condensed phosphates such as resorcinol bis(diphenyl phosphate), bisphenol A bis(diphenyl phosphate), and resorcinol bis(dimethyl phosphate).

[0068] The content of flame retardant in the heat-conducting sheet is, for example, less than 30% by volume based on the volume of the heat-conducting sheet. From the viewpoint of preventing flame retardant components from seeping to the surface of the heat-conducting sheet, it can be less than 20% by volume.

[0069] [thickness] The thickness of the heat-conducting sheet can be selected according to the application. For example, the thickness of the heat-conducting sheet can be 500 μm or less, 400 μm or less, 320 μm or less, 300 μm or less, 280 μm or less, 250 μm or less, 230 μm or less, 200 μm or less, 180 μm or less, 150 μm or less, or 130 μm or less. A smaller thickness tends to suppress bulk thermal resistance and easily improve thermal conductivity. From a processability perspective, the thickness of the heat-conducting sheet can be, for example, 50 μm or more, 80 μm or more, 100 μm or more, 110 μm or more, or 120 μm or more. A thickness of 280 μm or less tends to result in a particularly high improvement in thermal conductivity. The thickness of the heat-conducting sheet can be calculated by measuring the thickness of the heat-conducting sheet at any three points using a micrometer at room temperature (25°C) and taking the arithmetic mean of the measured values.

[0070] Compression ratio The compression ratio of the heat-conducting sheet thickness is, for example, 24% or more. In some embodiments, the compression ratio of the heat-conducting sheet is measured at a temperature of 150°C and a compressive stress of 0.14 MPa. Alternatively, in some embodiments, the compression ratio of the heat-conducting sheet is measured at the temperature and compressive stress at which the heat-generating element and the heat-dissipating element are bonded together by the heat-conducting sheet. The temperature and compressive stress at which the heat-generating element and the heat-dissipating element are bonded together by the heat-conducting sheet will be described later. In this disclosure, "compression ratio" refers to the ratio (percentage (%)) of the compression amount (μm) to the thickness (μm) of the heat-conducting sheet before pressure is applied (compression ratio (%) = compression amount (μm) / thickness (μm) of the heat-conducting sheet before pressure is applied × 100). The thickness of the heat-conducting sheet before pressure is the thickness at room temperature (25°C) calculated using the method described above with a micrometer.

[0071] The compression ratio of the heat-conducting sheet is, for example, 24% or more, 25% or more, 28% or more, 30% or more, 35% or more, 40% or more, 43% or more, or 44% or more. A high compression ratio of the heat-conducting sheet tends to suppress contact thermal resistance and easily achieve improved thermal conductivity. This effect is more significant when the thickness of the heat-conducting sheet is smaller and / or when the bonding pressure is lower. From a processability point of view, the compression ratio of the heat-conducting sheet is, for example, 60% or less, 55% or less, or 50% or less. When the compression ratio of the heat-conducting sheet is 24% or more, it particularly tends to achieve a high improvement in thermal conductivity.

[0072] In this disclosure, "compression amount" refers to the amount of compression of the heat-conducting sheet obtained by applying pressure in the thickness direction of the sheet. The compression amount can be determined using the following method: The heat-conducting sheet is heated to 150°C, and a load is applied in the thickness direction at a displacement rate of 0.1 mm / min. The displacement (mm) and load (N) are measured. The displacement (mm) at a stress of 0.14 MPa is taken as the compression amount (μm).

[0073] The compression amount of the heat-conducting sheet is, for example, 30 μm or more, 40 μm or more, 45 μm or more, or 50 μm or more. A higher compression amount tends to easily improve thermal conductivity. From the viewpoints of processability and improved thermal conductivity, the compression amount of the heat-conducting sheet is, for example, 100 μm or less, 90 μm or less, 80 μm or less, 70 μm or less, 60 μm or less, or 55 μm or less. For example, when the thickness of the heat-conducting sheet is 280 μm or less, a compression amount of 45 μm or more is preferred.

[0074] The compressibility can be adjusted by changing the ratio of the average particle size of the graphite particles (A) described later, the composition of the thermally conductive sheet, etc. For example, when the ratio of the average particle size is 75% or less, there is a tendency to obtain a large compressibility. For example, when the thermally conductive sheet contains polymers (B) and (C) as an adhesive, there is a tendency to obtain a large compressibility.

[0075] [Ratio of average particle size to thickness of graphite particles (A)] In the heat-conducting sheet, the average particle size of the graphite particles (A) is, for example, 50 to 75% of the thickness of the heat-conducting sheet. In this disclosure, the ratio (percentage (%)) of the average particle size (A) of the graphite particles (A) to the thickness (μm) of the heat-conducting sheet is sometimes simply stated as "ratio of average particle size" (ratio of average particle size (%) = average particle size (A) of the graphite particles (A) / thickness (μm) of the heat-conducting sheet × 100).

[0076] The average particle size ratio is, for example, 50% or more, 55% or more, 60% or more, 65% or more, or 68% or more. When the average particle size ratio is 50% or more, it tends to suppress bulk thermal resistance and easily achieve an improvement in thermal conductivity. The average particle size ratio is, for example, 75% or less, 73% or less, or 70% or less. When the average particle size ratio is 75% or less, it tends to suppress contact thermal resistance and easily achieve an improvement in thermal conductivity. This effect is more significant when the thickness of the thermally conductive sheet is smaller and / or when the bonding pressure is smaller.

[0077] Surface roughness (Ra) The arithmetic mean roughness (Ra) of the surface of the heat-conducting sheet is, for example, 8.0 μm or less. In this disclosure, the arithmetic mean roughness (Ra) of the surface can be determined using the following method. First, five arbitrary locations are selected on the surface of the heat-conducting sheet. At each location, the surface is analyzed along the two diagonals of a 40 mm × 30 mm rectangle, and the arithmetic mean roughness (Ra) is measured. The arithmetic mean of the ten measurements (five locations × two diagonals) is taken as the arithmetic mean roughness (Ra) of the surface of the heat-conducting sheet. The arithmetic mean roughness (Ra) of each diagonal can be measured using a 3D shape measuring machine (e.g., with a magnification of 12x).

[0078] The arithmetic mean roughness (Ra) is, for example, 8.0 μm or less, 7.5 μm or less, 7.0 μm or less, or 6.5 μm or less. When the arithmetic mean roughness (Ra) is 8.0 μm or less, the contact thermal resistance can be suppressed, and there is a tendency to easily obtain an improvement in thermal conductivity. There is no particular limitation on the lower limit of the arithmetic mean roughness (Ra). The arithmetic mean roughness (Ra) is, for example, 1.0 μm or more, 2.0 μm or more, or 3.0 μm or more.

[0079] The arithmetic mean roughness (Ra) can be adjusted by changing the average particle size of graphite particles (A) and the ratio of the average particle size of graphite particles (A). For example, the smaller the average particle size, the smaller the arithmetic mean roughness (Ra) tends to be. For example, when the ratio of the average particle size is below 75%, a small arithmetic mean roughness (Ra) tends to be obtained.

[0080] [Elastic Modulus] The elastic modulus (compressive modulus) of the thickness of the heat-conducting sheet is, for example, 0.60 MPa or less at a temperature of 150°C and a compressive stress of 0.03 MPa. In this disclosure, the elastic modulus can be determined using the following method: The heat-conducting sheet is heated to 150°C, and a load is applied in the thickness direction at a displacement rate of 0.1 mm / min. The displacement (mm) and load (N) are measured. The deformation (dimensionless) obtained from displacement (mm) / thickness (mm) is plotted on the horizontal axis, and the deformation obtained from load (N) / area (mm²) is plotted on the horizontal axis. 2 The obtained stress (MPa) is plotted on the vertical axis, and the slope at a stress of 0.03 MPa is taken as the elastic modulus (MPa). The determination can be performed using a compression testing apparatus.

[0081] The elastic modulus is, for example, 0.60 MPa or less, 0.55 MPa or less, 0.50 MPa or less, 0.40 MPa or less, or 0.35 MPa or less. When the elastic modulus is 0.60 MPa or less, contact thermal resistance can be suppressed, and there is a tendency to easily obtain an improvement in thermal conductivity. There is no particular limitation on the lower limit of the elastic modulus. From a processability point of view, the elastic modulus is, for example, 0.10 MPa or more, 0.20 MPa or more, or 0.25 MPa or more.

[0082] The elastic modulus can be adjusted by changing the thickness of the thermally conductive sheet and the ratio of the average particle size of the graphite particles (A). For example, the thinner the thermally conductive sheet, the smaller the elastic modulus tends to be. For example, when the thickness of the thermally conductive sheet is the same, the smaller the ratio of the average particle size of the graphite particles (A), the smaller the elastic modulus tends to be.

[0083] [Protective film] Heat-conducting sheets can be protected with a protective film on at least one or both sides. Examples of protective films include resin films made of polyethylene, polyester, polypropylene, polyethylene terephthalate, polyimide, polyetherimide, polyether naphthalate, and methylpentene; metal foils such as aluminum; coated paper; and coated cloth. The protective film can be a single layer or a multilayer film. The protective film can be surface-treated with release agents such as silicone-based or silica-based agents.

[0084] [Manufacturing Method] There are no particular limitations on the manufacturing method of the thermally conductive sheet. For example, the manufacturing method includes the following steps: preparing a composition containing graphite particles (A) and any other component; using the composition to make a sheet; stacking multiple sheets to form a laminate; and slicing the side faces of the laminate to obtain the thermally conductive sheet. The manufacturing method may further include the step of attaching a protective film to the sliced ​​thermally conductive sheet. According to this manufacturing method, a thermally conductive sheet in which graphite particles (A) are oriented in the thickness direction can be easily manufactured.

[0085] The step of preparing the composition can be a step of mixing graphite particles (A) and any component such as resin to obtain the composition. The average particle size of the graphite particles (A) before mixing is, from the viewpoint of obtaining good thermal conductivity, for example, 100 μm or more, 150 μm or more, or 200 μm or more. The average particle size of the graphite particles (A) before mixing is 500 μm or less, 400 μm or less, or 300 μm or less. Preferably, the particle size of the graphite particles (A) is less than 1,000 μm, that is, the graphite particles (A) do not contain particles with a particle size of 1,000 μm or more.

[0086] The average particle size of the graphite particles (A) before mixing can be determined by sieving. Sieving was performed using sieves with nominal mesh sizes of 1,000 μm, 850 μm, 710 μm, 600 μm, 500 μm, 425 μm, 300 μm, 212 μm, and 106 μm. First, all graphite particles (A) were passed through a sieve with a nominal mesh size of 1,000 μm to confirm that the fraction obtained from the 1,000 μm sieve was 0 g. Then, sieves with nominal mesh sizes from 850 μm to 106 μm were used for sieving. The average particle size of the graphite particles (A) before mixing was calculated from the mass percentage (%) of each fraction relative to the total fraction and the particle size of each fraction. For example, the particle size of the fraction remaining on a sieve with a nominal mesh size of 850 μm is 925 μm ((1,000 + 850) / 2). The particle size of the fraction remaining on a sieve with a nominal mesh size of 710–212 μm is also obtained using the same method. The particle size of the fraction passing through a sieve with a nominal mesh size of 106 μm is 53 μm ((106 + 0) / 2). The average particle size of the graphite particles (A) before mixing can be obtained by calculating the particle size (μm) of each fraction × the mass percentage (%) of that fraction, and then summing the results.

[0087] The average particle size of the graphite particles (A) before mixing is, for example, less than 2.5 times, less than 2.3 times, or less than 2.1 times the thickness of the thermally conductive sheet. The average particle size of the graphite particles (A) is, for example, more than 0.6 times, more than 0.7 times, or more than 0.8 times the thickness of the thermally conductive sheet.

[0088] Sheet fabrication can be carried out using at least one forming method selected from rolling, pressing, extrusion, and coating. Laminated bodies can be fabricated by sequentially overlapping multiple independent sheets, by folding a single sheet, or by rolling a single sheet.

[0089] Slicing can be done using a slicer, knife, or other cutting tools. Preferably, the side end face of the laminate is sliced ​​at an angle of 0° to 30° relative to the normal extending from the main surface of the laminate, in a manner that yields a heat-conducting sheet of the desired thickness.

[0090] The aforementioned heat-conducting sheet can be used in devices comprising a heating element and a heat sink. For example, the device includes a heating element, a heat sink, and a heat-conducting sheet in contact with both the heating element and the heat sink. The device can be a laminate comprising a heating element, a heat-conducting sheet, and a heat sink. The heat-conducting sheet efficiently transfers heat from the heating element to the heat sink. Efficient heat conduction improves the device's lifespan, allowing it to function stably even during long-term use. A temperature range of -10 to 150°C is particularly preferred for using the heat-conducting sheet.

[0091] Examples of heat-generating elements include semiconductor chips, semiconductor devices, displays, LEDs, LED devices, light bulbs, semiconductor modules, automotive power modules, and industrial power modules. The heat-generating element may include at least one selected from semiconductor chips and semiconductor devices.

[0092] Examples of heat sinks include aluminum or copper heat sinks; heat sinks that utilize aluminum or copper sheets or plates; aluminum or copper blocks connected to heat pipes; aluminum or copper blocks that have cooling liquid circulated internally by a pump; Peltier elements and aluminum or copper blocks incorporating such elements.

[0093] The manufacturing method of the device is not particularly limited. For example, the manufacturing method includes the following steps: placing the heat-conducting sheet between a heating element and a heat sink to obtain a composite comprising the heating element, the heat sink, and the heat-conducting sheet in contact with the heating element and the heat sink; and applying pressure along the thickness direction of the heat-conducting sheet to the composite, thereby bonding the heating element and the heat sink together using the heat-conducting sheet. The pressure applied to the composite is, for example, 0.05 MPa or more, 0.10 MPa or more, or 0.12 MPa or more. The pressure applied to the composite is, for example, 0.30 MPa or less, 0.20 MPa or less, or 0.15 MPa or less. Pressure can be applied using a fixing tool, a pressing machine, or the like. The heat-conducting sheet exhibits good thermal conductivity even when bonded under low pressure.

[0094] When pressurizing, it is preferable to heat the composite. Heating can be achieved by heating a heating element or by using an oven, press, etc. The heating temperature is, for example, above 80°C, above 100°C, or above 120°C. The heating temperature is, for example, below 180°C, below 170°C, or below 160°C.

[0095] Examples of conditions for bonding include a pressure of 0.05 to 0.30 MPa and a temperature of 80 to 160°C; a pressure of 0.10 to 0.20 MPa and a temperature of 100 to 170°C; or a pressure of 0.12 to 0.15 MPa and a temperature of 120 to 160°C.

[0096] Devices that have both a heat source and a heat sink include, for example, semiconductor devices, displays, LED devices, lamps, semiconductor modules, automotive power modules, and industrial power modules.

[0097] <Examples of Implementation> The following are preferred examples of embodiments of the present invention. However, the embodiments of the present invention are not limited to these examples.

[0098] (1) A heat-conducting sheet containing graphite particles (A) selected from at least one of flake-shaped particles, ellipsoidal particles, and rod-shaped particles, wherein the graphite particles (A) are oriented in the thickness direction and the thickness compressibility is 24% or more at a temperature of 150°C and a compressive stress of 0.14 MPa.

[0099] (2) A heat-conducting sheet containing graphite particles (A) selected from at least one of flake-shaped particles, ellipsoidal particles, and rod-shaped particles, wherein the graphite particles (A) are oriented in the thickness direction and the average particle size of the graphite particles (A) is 50 to 75% of the thickness.

[0100] (3) The heat-conducting sheet according to (1) above, wherein the average particle size of the graphite particles (A) is 50 to 75% of the thickness of the heat-conducting sheet.

[0101] (4) The heat-conducting sheet according to any one of (1) to (3) above has an arithmetic mean surface roughness of 8.0 μm or less.

[0102] (5) The heat-conducting sheet according to any one of (1) to (4) above has a thickness of 320 μm or less.

[0103] (6) The heat-conducting sheet according to any one of (1) to (5) above further contains a polymer (B) that is liquid at 25°C.

[0104] (7) The heat-conducting sheet according to (6) above, wherein the polymer (B) comprises polybutene.

[0105] (8) The heat-conducting sheet according to any one of (1) to (7) above further contains a polymer (C) with a glass transition temperature of 20°C or less.

[0106] (9) The heat-conducting sheet according to (8) above, wherein the polymer (C) comprises a (meth)acrylic acid polymer.

[0107] (10) The heat-conducting sheet according to any one of (1) to (9) above, wherein the graphite particles (A) comprise flake-like particles.

[0108] (11) An apparatus comprising a heating element, a heat sink, and a heat-conducting sheet in contact with the heating element and the heat sink as described in any one of (1) to (10) above.

[0109] (12) The apparatus according to (11) above, wherein the heating element comprises at least one selected from semiconductor chips and semiconductor devices.

[0110] (13) A method for manufacturing an apparatus, comprising the following steps: The step of placing the heat-conducting sheet as described in any one of (1) to (10) above between the heating element and the heat sink, and obtaining a composite comprising the heating element, the heat sink, and the heat-conducting sheet in contact with the heating element and the heat sink; and The step of applying pressure in the thickness direction of the heat-conducting sheet to the composite and bonding the heat-generating element and the heat-dissipating element together through the heat-conducting sheet.

[0111] (14) The manufacturing method according to (13) above, wherein the heating element comprises at least one selected from semiconductor chips and semiconductor devices.

[0112] [Example] The embodiments of the present invention are illustrated in detail below. However, the embodiments of the present invention are not limited to the following examples.

[0113] <Fabrication of Heat-Conducting Sheets> [Example 1] The following components—graphite particles (A)-1, polymers (B)-1, (B)-2, polymer (C), hot melt agent (D), and antioxidant (E)—were added to a kneading mixer (Moriyama Corporation's "DS3-SGHM-E type pressure double-arm kneading machine") at volume fractions of 32.3%, 29.0%, 13.4%, 10.2%, 14.6%, and 0.5% respectively relative to their total amount. The mixture was kneaded at 150°C to obtain the composition. The volume fraction was calculated using the specific gravity (density) method described above, based on the calculation method for the content (volume%).

[0114] Graphite particles (A)-1: Expanded graphite particles in the form of flakes (manufactured by Hitachi Chemical Co., Ltd., specific gravity 2.1, average particle size 241 μm) Polymer (B)-1: Isobutylene-n-butene copolymer (manufactured by Nippon Oil Corporation, "Nippon Oil Polybutene, Grade 30N", specific gravity 0.90, liquid at 25°C) Polymer (B)-2: Homopolymer of isobutylene (Tetrax 6T manufactured by Nippon Oil Co., Ltd., specific gravity 0.92, liquid at 25°C) Polymer (C): Acrylic copolymer resin (manufactured by Nagase Chemtex Co., Ltd., butyl acrylate / ethyl acrylate / acrylonitrile / acrylic acid copolymer, weight average molecular weight: 530,000, Tg=-39℃, specific gravity 1.06) Hot melt flux (D): Hydrogenated petroleum resin (ARKON P90 manufactured by Arakawa Chemical Industry Co., Ltd., specific gravity 0.99) Antioxidant (E): Hindered phenolic antioxidant (ADK STAB AO-60 manufactured by ADEKA Co., Ltd., specific gravity 1.15) For graphite particles (A)-1, the orientation of the six-membered toroidal planes in the crystallization of expanded graphite particles in the plane direction of the flake particles was confirmed using the X-ray diffraction method described above.

[0115] The average particle size of graphite particles (A)-1 was determined according to the method described above. Specifically, 1.7 g of graphite particles (A)-1 was fractionated using sieves with nominal mesh sizes of 1,000 μm, 850 μm, 710 μm, 600 μm, 500 μm, 425 μm, 300 μm, 212 μm, and 106 μm. The mass of fractions remaining on each sieve was measured. No fractions were obtained on the 1,000 μm sieve (0% by mass). The particle sizes of the fractions remaining on each sieve were 925 μm, 780 μm, 655 μm, 550 μm, 462 μm, 362 μm, 256 μm, 159 μm, and 53 μm, respectively, and the average particle size of graphite particles (A)-1 was calculated.

[0116] Next, the compound obtained through mixing is placed into an extrusion molding machine (HKS40-15 type extruder manufactured by Parker Co., Ltd.) and extruded into a flat sheet shape with a width of 20 cm and a thickness of 1.5~1.6 mm to obtain a sheet. The obtained sheet is pressed and punched using a 40 mm × 150 mm die cutter. 61 punched sheets are stacked, and a spacer with a height of 80 mm is sandwiched between them. Pressure is applied in the stacking direction at 90°C for 30 minutes to obtain a 40 mm × 150 mm × 80 mm laminate. The average particle size of the graphite particles (A) contained in the laminate is 177 μm. Then, the 80 mm × 150 mm side end face of the laminate is sliced ​​using a woodworking slicer to obtain a heat-conducting sheet.

[0117] The thickness of the heat-conducting sheet is 122 μm. The thickness was calculated by taking the arithmetic mean of the thickness measured at any three points using a micrometer (Mitutoyo Corporation "406-250-30").

[0118] Graphite particles (A)-1 are oriented in the thickness direction of the thermally conductive sheet at an orientation angle of 82°. The orientation direction and the orientation angle were confirmed and measured using the SEM (SU5000, manufactured by Hitachi High-Tech Co., Ltd.) method described above.

[0119] The average particle size of the graphite particles (A)-1 contained in the heat-conducting sheet is 84 μm, and the average particle size ratio is 69%. The average particle size of the graphite particles (A)-1 was determined according to the method described above. Specifically, the heat-conducting sheet was repeatedly dissolved and washed using acetone and butyl acetate to remove all components except graphite particles (A)-1 from the heat-conducting sheet, thus obtaining graphite particles (A)-1. Next, the graphite particles (A)-1 were thoroughly dried in an oven at 150°C. Using a scanning electron microscope (Hitachi High-Tech Co., Ltd. "SU5000"), 200 particles were randomly selected from the obtained graphite particles (A)-1, and the surface of each particle was observed, and the major diameter was measured. The arithmetic mean of the major diameters of the obtained 200 particles was taken as the average particle size of the graphite particles (A)-1. In addition, the median diameter (D50) based on the number of particles was calculated from the major diameters of the obtained 200 particles. Furthermore, the average particle size of the graphite particles (A)-1 contained in the aforementioned laminate was also determined using the same method. The ratio (%) of the average particle size was calculated from the thickness (μm) of the thermally conductive sheet before compression and the average particle size (μm) of the graphite particles (A)-1.

[0120] The thermally conductive sheet has a compression ratio of 44% and an elastic modulus of 0.32. The elastic modulus was determined using a compression testing apparatus with a thermostatic bath (INSTRON 5948 Micro Tester). The thermally conductive sheet was cut into circles with a diameter of 14 mm for testing. The sheet was sandwiched between 0.1 mm thick paper (release paper), and a load was applied along the thickness direction of the sheet at a displacement rate of 0.1 mm / min at a thermostatic bath temperature of 150°C. The displacement (mm) and load (N) were measured. The deformation (dimensionless) calculated from displacement (mm) / thickness (mm) is plotted on the horizontal axis, and the deformation is plotted from load (N) / area (mm²)... 2 The calculated stress (MPa) is plotted on the vertical axis, and the slope at a stress of 0.03 MPa is taken as the compressive modulus (MPa). The displacement at a stress of 0.14 MPa is taken as the compression amount (μm). The compression ratio (%) is calculated from the thickness (μm) of the heat-conducting sheet before compression and the compression amount (μm).

[0121] The arithmetic mean roughness (Ra) of the surface of the heat-conducting sheet is 5.0 μm. The arithmetic mean roughness (Ra) is calculated by measuring Ra at any 5 locations using a 3D shape measuring machine (Keyence Co., Ltd. "VR-3200") according to the method described above, and then arithmetically averaging the 10 measured values.

[0122] [Example 2 and Example 3] Except for changing the thickness of the heat-conducting sheet, the heat-conducting sheet was manufactured in the same manner as in Example 1. In Example 2, the thickness was 204 μm, and in Example 3, the thickness was 303 μm. The thickness, orientation angle, etc., of the resulting heat-conducting sheets were measured using the same method as in Example 1. The measurement results are shown in Table 1.

[0123] [Comparative Examples 1 to 3] Except for using graphite particles (A)-2 (flaky expanded graphite particles (manufactured by Hitachi Chemical Co., Ltd., specific gravity: 2.1, average particle size: 568 μm, mass of fractionated material remaining on a sieve with a particle size of 1,000 μm: 0% by mass)) instead of graphite particles (A)-1, thermally conductive sheets were prepared using the same method as in Examples 1 to 3. The thickness, orientation angle, etc., of the resulting thermally conductive sheets were measured using the same method as in Example 1. The measurement results are shown in Table 1.

[0124] <Evaluation of Heat-Conducting Sheets> [Measurement of Resistance Temperature Detector] A heat-conducting sheet was cut into 10mm squares and sandwiched between a transistor (2SC2233) serving as the heat source and a copper block serving as the heat sink. While pressing the transistor at 80°C with a pressure of 0.14MPa, the temperatures of the transistor (T1°C) and the copper block (T2°C) were measured when current flowed. Based on the measured values ​​and the applied power (W1W), the temperature per unit area (cm²) was calculated using the following formula. 2 The thermal resistance value X (K•cm) 2 / W). The results are shown in Table 1.

[0125] X = (T1 - T2) × 1 / W1 As shown in Table 1, the thermal conductive sheets of Examples 1-3 exhibited lower thermal resistance and better thermal conductivity compared to the thermal conductive sheets of Comparative Examples 1-3. In the thermal conductive sheets of Examples 1-3, it was considered that by having a compression ratio of 24% or higher, an average particle size ratio (average particle size of graphite particles (A) in the thermal conductive sheet / thickness of the thermal conductive sheet × 100) of 50-75%, or an arithmetic mean surface roughness (Ra) of 8.0 μm or less, even when bonded under a low pressure of 0.14 MPa, the contact thermal resistance was reduced. Furthermore, the thermal conductive sheet of Example 1 exhibited particularly excellent thermal conductivity. It was believed that the thermal conductive sheet of Example 1 also showed reduced bulk thermal resistance due to its smaller thickness.

Claims

1. A heat-conducting sheet comprising graphite particles (A) selected from at least one of flake-shaped particles, ellipsoidal particles, and rod-shaped particles. The graphite particles (A) are oriented in the thickness direction. The compressibility of the thickness is above 24% at a temperature of 150℃ and a compressive stress of 0.14MPa. The six-membered rings in the crystallization of the graphite particles (A) are oriented as follows: When the graphite particles (A) are flake-shaped particles, they are oriented in such a way that the orientation of the six-membered ring is the same as the orientation of the flake-shaped particles. When the graphite particle (A) is an ellipsoidal particle, it is oriented so that the face of the six-membered ring is aligned with the major axis of the ellipsoidal particle; or When the graphite particles (A) are rod-shaped, they are oriented so that the plane of the six-membered ring is aligned with the long axis of the rod-shaped particles.

2. The heat-conducting sheet according to claim 1, wherein the arithmetic mean roughness of its surface is below 8.0 μm.

3. A heat-conducting sheet containing graphite particles (A) selected from at least one of flake-shaped particles, ellipsoidal particles, and rod-shaped particles. The graphite particles (A) are oriented in the thickness direction. The average particle size of the graphite particles (A) is 50-75% of the thickness. The six-membered rings in the crystallization of the graphite particles (A) are oriented as follows: When the graphite particles (A) are flake-shaped particles, they are oriented in such a way that the orientation of the six-membered ring is the same as the orientation of the flake-shaped particles. When the graphite particle (A) is an ellipsoidal particle, it is oriented so that the face of the six-membered ring is aligned with the major axis of the ellipsoidal particle; or When the graphite particles (A) are rod-shaped, they are oriented so that the plane of the six-membered ring is aligned with the long axis of the rod-shaped particles.

4. The heat-conducting sheet according to any one of claims 1 to 3, wherein the thickness is 320 μm or less.

5. The heat-conducting sheet according to any one of claims 1 to 3, further comprising a polymer (B) that is liquid at 25°C.

6. The heat-conducting sheet according to claim 5, wherein, The polymer (B) comprises polybutene.

7. The heat-conducting sheet according to any one of claims 1 to 3, further comprising a polymer (C) having a glass transition temperature of 20°C or less.

8. The heat-conducting sheet according to claim 7, wherein, The polymer (C) comprises a (meth)acrylic acid polymer.

9. The heat-conducting sheet according to any one of claims 1 to 3, wherein, The graphite particles (A) comprise flake-like particles.

10. An apparatus comprising a heating element, a heat sink, and a heat-conducting sheet in contact with the heating element and the heat sink according to any one of claims 1 to 9.

11. The apparatus according to claim 10, wherein, The heating element comprises at least one selected from semiconductor chips and semiconductor devices.

12. A method for manufacturing an apparatus, comprising the following steps: The step of distributing a heat-conducting sheet according to any one of claims 1 to 9 between a heating element and a heat sink, thereby obtaining a composite comprising the heating element, the heat sink, and the heat-conducting sheet in contact with the heating element and the heat sink; and The step of applying pressure in the thickness direction of the heat-conducting sheet to the composite, and bonding the heat-generating element and the heat-dissipating element through the heat-conducting sheet.

13. The manufacturing method according to claim 12, wherein, The heating element comprises at least one selected from semiconductor chips and semiconductor devices.

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