Thermally conductive sheet, heat dissipation device, and method for producing thermally conductive sheet

Abstract

A thermally conductive sheet comprising: a thermally conductive layer containing at least one kind of graphite particles (A) selected from the group consisting of scale-like particles, ellipsoidal particles, and rod-like particles, the face direction in the case of the scale-like particles, the major axis direction in the case of the ellipsoidal particles, and the longitudinal axis direction in the case of the rod-like particles being oriented in the thickness direction of said thermally conductive layer; and an adhesive layer containing a resin component and a thermally conductive filler, wherein said adhesive layer is disposed on at least a portion of the main face of the thermally conductive layer.

Description

Thermally conductive sheet, heat dissipation device, and method for manufacturing the thermally conductive sheet

[0001] The present disclosure relates to a thermally conductive sheet, a heat dissipation device, and a method for manufacturing a thermally conductive sheet.

[0002] In recent years, the amount of heat generated has increased due to the mounting density of wiring and electronic components in semiconductor packages using multilayer wiring boards, and the amount of heat generated per unit area has increased due to the high integration of semiconductor elements, so there is a demand for improving the heat dissipation from semiconductor packages.

[0003] Heat dissipation devices are commonly used simply by sandwiching thermally conductive grease or a thermally conductive sheet between a heat-generating body such as a semiconductor package and a heat sink such as aluminum or copper, thereby dissipating heat. Thermally conductive sheets are usually easier to assemble than thermally conductive grease.

[0004] In recent years, there has been a trend toward larger CPU (Central Processing Unit) chips due to the adoption of multiple cores and multiple chips. There is also a trend toward lowering the pressure required to press the CPU, which is a heat-generating element, against the heat sink. Therefore, thermally conductive sheets are required to be flexible during compression. Furthermore, thermally conductive sheets are required to have excellent thermal conductivity so that they maintain low thermal resistance even when the thickness of the thermally conductive sheet increases due to chip step differences.

[0005] Resin sheets filled with a thermally conductive filler are also known as thermally conductive sheets. Various resin sheets have been proposed as thermally conductive resin sheets filled with a thermally conductive filler to achieve excellent thermal conductivity. These resin sheets use highly thermally conductive inorganic particles as the thermally conductive filler, and the inorganic particles are oriented perpendicular to the sheet surface. For example, a thermally conductive sheet in which a thermally conductive filler (boron nitride) is oriented in a direction substantially perpendicular to the sheet surface (see, for example, Patent Document 1) and a thermally conductive sheet in which carbon fibers dispersed in a gel-like substance are oriented perpendicular to the sheet surface (see, for example, Patent Document 2) have been proposed.

[0006] JP 2002-26202 A JP 2001-250894 A

[0007] In Patent Documents 1 and 2, a method of suppressing thermal resistance by orienting thermally conductive fillers, carbon fibers, etc. in a direction perpendicular to the sheet surface is studied. To cope with the increase in heat generation due to the higher performance and larger size of semiconductors, it is desirable to further reduce the thermal resistance of thermally conductive sheets. Therefore, it is preferable to attempt to reduce thermal resistance by taking into account methods other than the orientation of thermally conductive fillers, carbon fibers, etc. contained in thermally conductive sheets.

[0008] An object of one aspect of the present invention is to provide a thermally conductive sheet having low thermal resistance, a heat dissipation device including the same, and a method for manufacturing a thermally conductive sheet that can produce a thermally conductive sheet having low thermal resistance.

[0009] Specific means for solving the above problems include the following aspects. <1> A thermally conductive sheet comprising: a thermally conductive layer containing at least one type of graphite particles (A) selected from the group consisting of scaly particles, ellipsoidal particles, and rod-shaped particles, wherein the planar direction in the case of the scaly particles, the major axis direction in the case of the ellipsoidal particles, and the major axis direction in the case of the rod-shaped particles are oriented in the thickness direction; and an adhesive layer containing a resin component and a thermally conductive filler and positioned on at least a part of a main surface of the thermally conductive layer. <2> The thermally conductive sheet according to <1>, wherein the resin component includes at least one selected from the group consisting of a curable resin component, an adhesive resin component, and a thermoplastic resin component. <3> The thermally conductive sheet according to <2>, wherein the resin component is a curable resin component and the adhesive layer is in a semi-cured state. <4> The thermally conductive sheet according to any one of <1> to <3>, wherein the resin component includes a thermoplastic resin component. <5> The thermally conductive sheet according to any one of <1> to <4>, wherein the thermoplastic resin component includes a thermoplastic epoxy resin. <6> The thermally conductive sheet according to any one of <1> to <5>, wherein the thermally conductive filler is at least one particle selected from silver, copper, aluminum, aluminum oxide, aluminum hydroxide, magnesium oxide, beryllium oxide, boron nitride, aluminum nitride, silicon nitride, silicon carbide, silicon dioxide, aluminum fluoride, calcium fluoride, and zinc oxide. <7> The thermally conductive sheet according to <6>, wherein the thermally conductive filler is silver particles. <8> The thermally conductive sheet according to any one of <1> to <7>, wherein the content of the thermally conductive filler is 70% by mass to 99% by mass with respect to the total amount of the adhesive layer. <9> The thermally conductive sheet according to any one of <1> to <8>, wherein the average thickness of the adhesive layer is 2 μm to 50 μm. <10> A heat dissipation device comprising: a heat generating element; a heat dissipation element; and the thermally conductive sheet according to any one of <1> to <9>, which is disposed between the heat generating element and the heat dissipation element; wherein the adhesive layer is located on at least a part of at least one of the main surfaces of the thermally conductive layer, the main surface facing the heat generating element and the main surface facing the heat dissipation element.<11> A heat dissipation device comprising: a heat generating element; a heat radiating element; and the thermally conductive sheet according to any one of <1> to <9>, which is disposed between the heat generating element and the heat radiating element, wherein at least one of the interface between the heat generating element and the thermally conductive sheet and the interface between the heat radiating element and the thermally conductive sheet has a porosity of 0% to 25%, calculated as a ratio of the area of ​​a gas region to the area of ​​a measurement region. <11> A method for producing the thermally conductive sheet according to any one of <1> to <9>, comprising the steps of: preparing a composition containing the graphite particles (A); forming the thermally conductive layer using the composition; and forming an adhesive layer on at least a part of a main surface of the thermally conductive layer.

[0010] According to the present disclosure, it is possible to provide a thermally conductive sheet having low thermal resistance, a heat dissipation device including the same, and a method for manufacturing a thermally conductive sheet capable of manufacturing a thermally conductive sheet having low thermal resistance.

[0011] FIG. 1 is a schematic diagram of a thermally conductive sheet according to one embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of a heat dissipation device according to one embodiment of the present invention, in which a heat generating element is a semiconductor chip and a heat dissipation element is a heat spreader. FIG. 3 is a schematic diagram of a thermally conductive sheet incorporated in a heat dissipation device according to one embodiment of the present invention. FIG. 4 is a diagram showing the interface state determined by image analysis in Examples 1 and 2 and Comparative Example 1. FIG. 5 is a diagram showing the interface state determined by image analysis in Examples 3 to 7 and Comparative Examples 2 to 4.

[0012] Modes for carrying out the present invention are described in detail below. However, the present invention is not limited to the following embodiments. In the following embodiments, components (including elementary steps, etc.) are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges, and do not limit the present invention. In this disclosure, the term "process" includes not only processes that are independent of other processes, but also processes that cannot be clearly distinguished from other processes as long as the purpose of the process is achieved. In this disclosure, numerical ranges indicated using "to" include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In numerical ranges described in stages in this disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in numerical ranges described in this disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples. In this disclosure, each component may contain multiple corresponding substances. When a composition contains multiple substances corresponding to each component, the content or amount of each component refers to the total content or amount of the multiple substances present in the composition, unless otherwise specified. In the present disclosure, multiple types of particles corresponding to each component may be included. When a composition contains multiple types of particles corresponding to each component, the particle size of each component refers to the value for a mixture of the multiple types of particles present in the composition, unless otherwise specified. In the present disclosure, the terms "layer" and "film" include cases where the layer or film is formed over the entire area when the area where the layer or film is present is observed, as well as cases where the layer or film is formed only over a portion of the area. In the present disclosure, the term "laminated" refers to stacking layers, and two or more layers may be bonded or detachable.

[0013] [Thermal Conduction Sheet] The thermal conduction sheet of the present disclosure comprises a thermal conduction layer containing at least one type of graphite particles (A) selected from the group consisting of scaly particles, ellipsoidal particles, and rod-shaped particles, with the planar direction in the case of the scaly particles, the major axis direction in the case of the ellipsoidal particles, and the major axis direction in the case of the rod-shaped particles being oriented in the thickness direction; and an adhesive layer containing a resin component and a thermally conductive filler, and located on at least a part of a main surface of the thermal conduction layer.

[0014] It is believed that the thermally conductive sheet of the present disclosure has excellent thermal conductivity in the thickness direction and exhibits low thermal resistance, since it has a thermally conductive layer in which the graphite particles (A) are oriented in the thickness direction.

[0015] Furthermore, it is believed that a thermally conductive sheet exhibits lower thermal resistance by including the aforementioned adhesive layer in addition to a thermally conductive layer containing graphite particles (A). The reason for this is speculated as follows. Note that the present disclosure is not limited to the speculation. In a thermally conductive sheet in which graphite particles (A) are oriented in the thickness direction, unevenness exists on the surface that contacts the adherend, and most of the thermal resistance is derived from resistance due to gaps that arise due to contact between the thermally conductive sheet and an adherend, such as a heat-generating body or a heat-dissipating body, that contacts the thermally conductive sheet (also referred to as "contact thermal resistance"). In the thermally conductive sheet of the present disclosure, an adhesive layer containing a resin component and a thermally conductive filler is disposed on at least a portion of the main surface of the thermally conductive layer. This allows the adhesive layer to soften, deform, etc. due to heat, pressure, etc., when the thermally conductive sheet is thermocompression-bonded to an adherend, such as a heat-generating body or a heat-dissipating body. The softening, deformation, etc. of the adhesive layer allows gaps that arise when the thermally conductive sheet and the adherend are thermocompression-bonded (for example, gaps due to the unevenness of the thermally conductive sheet) to be filled by the adhesive layer. This allows the thermally conductive sheet and the adherend to be closely attached via the adhesive layer while reducing the gap between them, thereby significantly reducing contact thermal resistance.

[0016] Contact thermal resistance is also likely to occur when the surface of an adherend, such as a heat-generating body or a heat-dissipating body, is uneven. In this case, it is difficult to reduce the thermal resistance by adjusting the orientation of thermally conductive fillers contained in the thermally conductive sheet. On the other hand, by using the thermally conductive sheet of the present disclosure, the thermally conductive sheet can be closely attached to an adherend having an uneven surface via an adhesive layer. In this case, gaps that occur when the thermally conductive sheet and the adherend are thermocompression-bonded (for example, gaps resulting from the unevenness of the adherend) are filled with the adhesive layer, thereby significantly reducing contact thermal resistance.

[0017] The thermally conductive layer included in the thermally conductive sheet of the present disclosure contains at least graphite particles (A) and may contain the components described below within the range in which the effects of the present disclosure are exhibited. Hereinafter, materials used in the thermally conductive layer of the present disclosure will be described.

[0018] <Graphite Particles (A)> The thermally conductive layer included in the thermally conductive sheet contains graphite particles (A). The graphite particles (A) are believed to function primarily as a highly thermally conductive filler. The graphite particles (A) are at least one type selected from the group consisting of scaly particles, ellipsoidal particles, and rod-shaped particles. The graphite particles (A) are oriented in the thickness direction in the planar direction in the case of scaly particles, the long axis direction in the case of ellipsoidal particles, and the long axis direction in the case of rod-shaped particles. Preferably, the six-membered ring planes in the crystal of the graphite particles (A) are oriented in the planar direction in the case of scaly particles, the long axis direction in the case of ellipsoidal particles, and the long axis direction in the case of rod-shaped particles. The six-membered ring plane is the plane on which a six-membered ring is formed in a hexagonal crystal system, and refers to the (0001) crystal plane.

[0019] The shape of the graphite particles (A) is more preferably flaky. By selecting flaky graphite particles, thermal conductivity tends to be further improved. This is thought to be because, for example, flaky graphite particles are more easily oriented in a predetermined direction in the thermally conductive layer.

[0020] Whether the six-membered ring planes in the crystals of graphite particles (A) are oriented in the plane direction of scale-like particles, the long axis direction of ellipsoidal particles, or the long axis direction of rod-shaped particles can be confirmed by X-ray diffraction measurement. Specifically, the orientation direction of the six-membered ring planes in the crystals of graphite particles (A) is confirmed by the following method.

[0021] First, a measurement sample sheet is prepared in which the planar direction of the scaly particles, the major axis direction of the ellipsoidal particles, or the major axis direction of the rod-shaped particles of the graphite particles (A) is oriented along the planar direction of the sheet. Specific methods for preparing the measurement sample sheet include, for example, the following methods.

[0022] A mixture of resin and graphite particles (A) in an amount of 10% by volume or more relative to the resin is formed into a sheet. The "resin" used here is not particularly limited as long as it is a material that does not exhibit peaks that interfere with X-ray diffraction and can be formed into a sheet. Specifically, amorphous resins that have cohesive strength as a binder, such as acrylic rubber, NBR (acrylonitrile butadiene rubber), and SIBS (styrene-isobutylene-styrene copolymer), can be used.

[0023] A sheet of this mixture is pressed to a thickness of 1 / 10 or less of its original thickness, and several pressed sheets are stacked to form a laminate. This laminate is further crushed to 1 / 10 or less, and this operation is repeated three or more times to obtain a measurement sample sheet. This operation causes the graphite particles (A) in the measurement sample sheet to be oriented in the plane direction if they are scaly particles, in the major axis direction if they are ellipsoidal particles, and in the major axis direction if they are rod-shaped particles, along the plane direction of the measurement sample sheet.

[0024] X-ray diffraction measurement is performed on the surface of the measurement sample sheet prepared as described above. The height H of the peak corresponding to the (110) plane of graphite, which appears around 2θ=77°, is １ and the height H of the peak corresponding to the (002) plane of graphite that appears around 2θ = 27°. ２ In the measurement sample sheet prepared in this way, H １ H ２ The value divided by this is between 0 and 0.02.

[0025] From this, the phrase "the six-membered ring planes in the crystals of the graphite particles (A) are oriented in the plane direction in the case of scaly particles, in the long axis direction in the case of ellipsoidal particles, and in the long axis direction in the case of rod-shaped particles" means that, when X-ray diffraction measurement is performed on the surface of a sheet containing the graphite particles (A), the value obtained by dividing the height of the peak which appears around 2θ = 77° and corresponds to the (110) plane of the graphite particles (A) by the height of the peak which appears around 2θ = 27° and corresponds to the (002) plane of the graphite particles (A) is 0 to 0.02.

[0026] In the present disclosure, X-ray diffraction measurements are performed under the following conditions: Apparatus: for example, Bruker AXS "D8DISCOVER" X-ray source: CuKα with a wavelength of 1.5406 nm, 40 kV, 40 mA Step (measurement step width): 0.01° Step time: 720 sec

[0027] Here, "the graphite particles are oriented in the planar direction in the case of scaly particles, in the major axis direction in the case of ellipsoidal particles, and in the thickness direction of the thermal conduction layer in the case of rod-shaped particles" means that the angle (hereinafter also referred to as "orientation angle") formed by the planar direction in the case of scaly particles, the major axis direction in the case of ellipsoidal particles, and the major axis direction in the case of rod-shaped particles with the surface (main surface) of the thermal conduction layer is 60° or more. The orientation angle is preferably 80° or more, more preferably 85° or more, and even more preferably 88° or more.

[0028] The orientation angle is the average value of the angles (orientation angles) formed by the surface (main surface) of the thermal conduction layer in the case of scaly particles, the direction of the long axis in the case of ellipsoidal particles, and the direction of the long axis in the case of rod-shaped particles, measured for 50 random graphite particles (A) by observing the cross section of the thermal conduction layer with a SEM (scanning electron microscope).

[0029] The particle size of the graphite particles (A) is not particularly limited. The average particle size of the graphite particles (A), as a mass average particle size, is preferably at least half the average thickness of the thermally conductive layer but not more than the average thickness. When the mass average particle size of the graphite particles (A) is at least half the average thickness of the thermally conductive layer, an efficient heat conduction path is formed in the thermally conductive layer, and the thermal conductivity tends to be improved. When the mass average particle size of the graphite particles (A) is not more than the average thickness of the thermally conductive layer, protrusion of the graphite particles (A) from the surface of the thermally conductive layer is suppressed, and the surface adhesion of the thermally conductive layer tends to be excellent.

[0030] The method for producing a thermally conductive layer so that the planar direction in the case of scale-like particles, the major axis in the case of ellipsoidal particles, and the major axis in the case of rod-shaped particles are oriented in the thickness direction is not particularly limited, and for example, the method described in JP 2008-280496 A can be used. Specifically, a method can be used in which sheets are produced using a composition, the sheets are stacked to produce a laminate, and the side end faces of the laminate are sliced ​​(for example, at an angle of 0° to 30° with respect to the normal to the main surface of the laminate) (hereinafter also referred to as the "stacking slicing method").

[0031] When the laminated slicing method is used, the particle diameter of the graphite particles (A) used as the raw material is preferably at least half the average thickness of the thermally conductive layer as a mass average particle diameter, and may exceed the average thickness. The reason why the particle diameter of the graphite particles (A) used as the raw material may exceed the average thickness of the thermally conductive layer is, for example, because even if the thermally conductive layer contains graphite particles (A) with a particle diameter exceeding the average thickness of the thermally conductive layer, the thermally conductive layer is formed by slicing the graphite particles (A) together, and as a result, the graphite particles (A) do not protrude from the surface of the thermally conductive layer. Furthermore, when the graphite particles (A) are sliced ​​together in this way, a large number of graphite particles (A) are generated that penetrate the thermally conductive layer in the thickness direction, forming an extremely efficient thermal conduction path and tending to further improve thermal conductivity.

[0032] When the laminate slicing method is used, the particle diameter of the graphite particles (A) used as the raw material is preferably 1 to 5 times, and even more preferably 2 to 4 times, the average thickness of the heat conduction layer, as a mass average particle diameter. When the mass average particle diameter of the graphite particles (A) is 1 time or more the average thickness of the heat conduction layer, a more efficient heat conduction path is formed, and thermal conductivity is further improved. When the mass average particle diameter is 5 times or less the average thickness of the heat conduction layer, the area occupied by the surface of the graphite particles (A) is prevented from becoming too large, and a decrease in adhesion can be suppressed.

[0033] The mass average particle diameter (D50) of the graphite particles (A) is measured using a laser diffraction particle size distribution device (e.g., "Microtrac Series MT3300" manufactured by Nikkiso Co., Ltd.) that applies a laser diffraction / scattering method, and corresponds to the particle diameter at which the cumulative mass becomes 50% when a cumulative mass particle size distribution curve is plotted from the small particle size side.

[0034] The thermally conductive layer may contain graphite particles other than scaly particles, ellipsoidal particles, and rod-shaped particles, and may contain spherical graphite particles, artificial graphite particles, exfoliated graphite particles, acid-treated graphite particles, expanded graphite particles, carbon fiber flakes, etc. As the graphite particles (A), scaly particles are preferred, and from the viewpoint of high crystallinity and ease of obtaining large-diameter flakes, scaly expanded graphite particles obtained by pulverizing sheet-formed expanded graphite are preferred.

[0035] From the viewpoint of the balance between thermal conductivity and adhesion, the content of graphite particles (A) in the thermally conductive layer is preferably 15% by volume to 50% by volume, more preferably 20% by volume to 45% by volume, and even more preferably 25% by volume to 40% by volume. When the content of graphite particles (A) is 15% by volume or more, thermal conductivity tends to improve. Furthermore, when the content of graphite particles (A) is 50% by volume or less, deterioration in adhesiveness and adhesion tends to be suppressed. Note that when the thermally conductive layer contains graphite particles other than scaly particles, ellipsoidal particles, and rod-shaped particles, the total content of graphite particles is preferably within the above range.

[0036] The content (volume %) of graphite particles (A) is a value calculated by the following formula: Content (volume %) of graphite particles (A) = [(Aw / Ad) / {(Aw / Ad) + (Xw / Xd)}] × 100, where Aw: mass composition (mass %) of graphite particles (A), Xw: mass composition (mass %) of other optional components, Ad: density of graphite particles (A) (in the present disclosure, Ad is calculated using 2.1), and Xd: density of other optional components.

[0037] <Component (B) that is liquid at 25°C> The thermally conductive layer included in the thermally conductive sheet of the present disclosure may contain a component that is liquid at 25°C (hereinafter also referred to as "liquid component (B)"). In the present disclosure, "liquid at 25°C" means a substance that exhibits fluidity and viscosity at 25°C and has a viscosity, which is a measure of viscosity, of 0.0001 Pa·s to 1000 Pa·s at 25°C. In the present disclosure, "viscosity" refers to a viscosity of 5.0 s or less using a rheometer at 25°C. －１ Specifically, the "viscosity" is measured as shear viscosity at a temperature of 25°C using a rotary shear viscometer equipped with a cone plate (diameter 40 mm, cone angle 0°).

[0038] The viscosity of the liquid component (B) at 25°C is preferably 0.001 Pa·s to 100 Pa·s, and more preferably 0.01 Pa·s to 10 Pa·s.

[0039] The liquid component (B) is not particularly limited as long as it is liquid at 25°C, and is preferably a polymer. Examples of the liquid component (B) include polybutene, polyisoprene, polysulfide, acrylonitrile rubber, silicone rubber, hydrocarbon resin, terpene resin, and acrylic resin. Among these, from the viewpoint of heat resistance, it is preferable that the liquid component (B) contains polybutene. The liquid component (B) may be used alone or in combination of two or more types.

[0040] Here, polybutene refers to a polymer obtained by polymerizing isobutene or normal butene. It also includes a polymer obtained by copolymerizing isobutene and normal butene. The structure includes "-CH ２ -C(CH ３ ) ２-" or "-CH ２ -CH(CH ２ CH ３ It is also called polyisobutylene. Polybutene is not limited as long as it contains the above structure, and there are no other restrictions on the structure.

[0041] Polybutene includes homopolymers of butene and copolymers of butene with other monomer components. Examples of copolymers with other monomer components include copolymers of isobutene and styrene or copolymers of isobutene and ethylene. The copolymers may be random copolymers, block copolymers, or graft copolymers.

[0042] As polybutene, for example, NOF Corporation's "NOF Polybutene ＴＭ Examples of such polyisobutylene include "Emawet (registered trademark)" from JXTG Nippon Oil & Energy Corporation, "Nippon Oil Polybutene" from JXTG Nippon Oil & Energy Corporation, "Tetrax" from JXTG Nippon Oil & Energy Corporation, "Himol" from JXTG Nippon Oil & Energy Corporation, and "Polyisobutylene" from Tomoe Engineering Co., Ltd.

[0043] The liquid component (B) is thought to function primarily as a stress relaxant and a tackifier, for example, having excellent heat resistance and humidity resistance. Furthermore, when used in combination with the hot-melt agent (D), which will be described later, the cohesive strength and fluidity upon heating tend to be further enhanced.

[0044] In order to further improve adhesive strength, adhesion, sheet strength, hydrolysis resistance, etc., the content of the liquid component (B) in the thermally conductive layer is preferably 10% by volume to 55% by volume, more preferably 15% by volume to 50% by volume, and even more preferably 20% by volume to 50% by volume. When the content of the liquid component (B) is 10% by volume or more, adhesive strength and adhesion tend to be further improved. When the content of the liquid component (B) is 55% by volume or less, deterioration in sheet strength and thermal conductivity tends to be more effectively suppressed.

[0045] <Acrylate ester-based polymer (C)> The thermally conductive layer included in the thermally conductive sheet may contain an acrylate ester-based polymer (C). The acrylate ester-based polymer (C) is thought to function primarily as, for example, a tackifier and an elasticity imparting agent that restores the thickness to accommodate warpage.

[0046] The acrylic acid ester polymer (C) is preferably an acrylic acid ester polymer (so-called acrylic rubber) obtained by copolymerizing, as a main raw material component, for example, butyl acrylate, ethyl acrylate, acrylonitrile, acrylic acid, glycidyl methacrylate, 2-ethylhexyl acrylate, etc., with methyl acrylate, etc., as necessary. The acrylic acid ester polymer (C) may be used alone or in combination of two or more.

[0047] The weight-average molecular weight of the acrylic acid ester polymer (C) is preferably 100,000 to 1,000,000, more preferably 250,000 to 700,000, and even more preferably 400,000 to 600,000. A weight-average molecular weight of 100,000 or more tends to provide excellent film strength, while a weight-average molecular weight of 1,000,000 or less tends to provide excellent flexibility. The weight-average molecular weight can be measured by gel permeation chromatography using a calibration curve of standard polystyrene.

[0048] The glass transition temperature (Tg) of the acrylic acid ester-based polymer (C) is preferably 20° C. or lower, more preferably −70° C. to 0° C., and even more preferably −50° C. to −20° C. If the glass transition temperature is 20° C. or lower, the flexibility and adhesiveness tend to be excellent. The glass transition temperature (Tg) can be calculated from tan δ derived by measuring dynamic viscoelasticity under tension.

[0049] The acrylic acid ester-based polymer (C) may be present throughout the thermally conductive layer by internal addition, or may be localized on the surface by coating or impregnating the surface. In particular, coating or impregnating one surface is preferred in that strong tackiness can be imparted to only one surface, resulting in a sheet with good handleability.

[0050] The content of the acrylic ester polymer (C) in the thermally conductive layer is preferably 3 to 25% by volume, more preferably 5 to 20% by volume, and even more preferably 7 to 15% by volume.

[0051] <Hot-melt agent (D)> The thermally conductive layer included in the thermally conductive sheet may contain a hot-melt agent (D). The hot-melt agent (D) has the effect of improving the strength of the thermally conductive layer and improving the fluidity when heated.

[0052] Examples of the hot-melt agent (D) include aromatic petroleum resins, terpene phenol resins, and cyclopentadiene petroleum resins. The hot-melt agent (D) may also be a hydrogenated aromatic petroleum resin or a hydrogenated terpene phenol resin. The hot-melt agent (D) may be used alone or in combination of two or more.

[0053] In particular, when polybutene is used as the liquid component (B), the hot-melt agent (D) preferably contains at least one selected from the group consisting of hydrogenated aromatic petroleum resins and hydrogenated terpene phenol resins. These hot-melt agents (D) are highly stable and have excellent compatibility with polybutene, and therefore tend to achieve better thermal conductivity, flexibility, and handleability when used to form a thermally conductive layer.

[0054] Commercially available hydrogenated aromatic petroleum resins include, for example, "Alcon" from Arakawa Chemical Industries, Ltd. and "Imarve" from Idemitsu Kosan Co., Ltd. Commercially available hydrogenated terpene phenol resins include, for example, "Clearon" from Yasuhara Chemical Co., Ltd. Commercially available cyclopentadiene petroleum resins include, for example, "Quinton" from Zeon Corporation and "Marukarets" from Maruzen Petrochemical Co., Ltd.

[0055] The hot melt agent (D) is preferably solid at 25°C and has a softening temperature of 40°C to 150°C. When a thermoplastic resin is used as the hot melt agent (D), the softening fluidity during thermocompression bonding is improved, which tends to improve adhesion. Furthermore, when the softening temperature is 40°C or higher, the cohesive force can be maintained at around room temperature, which tends to make it easier to obtain the required sheet strength and improve handleability. When the softening temperature is 150°C or lower, the softening fluidity during thermocompression bonding is increased, which tends to improve adhesion. The softening temperature is more preferably 60°C to 120°C. The softening temperature is measured by the ring and ball method (JIS K 2207:1996).

[0056] The content of the hot melt agent (D) in the thermally conductive layer is preferably 3 to 25% by volume, more preferably 5 to 20% by volume, and even more preferably 5 to 15% by volume, from the viewpoint of improving adhesive strength, adhesion, sheet strength, etc. When the content of the hot melt agent (D) is 3% by volume or more, adhesive strength, heat flowability, sheet strength, etc. tend to be sufficient, and when it is 25% by volume or less, flexibility tends to be sufficient, resulting in excellent handleability and thermal cycle resistance.

[0057] <Antioxidant (E)> The thermal conductive layer included in the thermal conductive sheet may contain an antioxidant (E) for the purpose of imparting thermal stability at high temperatures, for example. Examples of the antioxidant (E) include phenol-based antioxidants, phosphorus-based antioxidants, amine-based antioxidants, sulfur-based antioxidants, hydrazine-based antioxidants, and amide-based antioxidants. The antioxidant (E) may be appropriately selected depending on the temperature conditions used, and phenol-based antioxidants are more preferred. The antioxidant (E) may be used alone or in combination of two or more types.

[0058] Commercially available phenolic antioxidants include, for example, Adekastab AO-50, Adekastab AO-60, and Adekastab AO-80 manufactured by ADEKA Corporation.

[0059] The content of the antioxidant (E) in the thermally conductive layer is not particularly limited, but is preferably 0.1 vol% to 5 vol%, more preferably 0.2 vol% to 3 vol%, and even more preferably 0.3 vol% to 1 vol%. When the content of the antioxidant (E) is 0.1 vol% or more, a sufficient antioxidant effect tends to be obtained. When the content of the antioxidant (E) is 5 vol% or less, a decrease in the strength of the thermally conductive layer tends to be suppressed.

[0060] <Other Components> The thermally conductive layer included in the thermally conductive sheet may contain other components in addition to the graphite particles (A), the liquid component (B), the acrylic ester-based polymer (C), the hot-melt agent (D), and the antioxidant (E) depending on the purpose. For example, the thermally conductive layer may contain a flame retardant from the viewpoint of flame retardancy. The flame retardant is not particularly limited and can be appropriately selected from commonly used flame retardants. Examples include red phosphorus-based flame retardants and phosphate ester-based flame retardants. Among these, phosphate ester-based flame retardants are preferred from the viewpoint of excellent safety and improved adhesion due to the plasticizing effect.

[0061] As the red phosphorus-based flame retardant, in addition to pure red phosphorus particles, those coated with various coatings for the purpose of enhancing safety or stability, masterbatches, etc., may be used. Specific examples include NOVA RED, NOVA EXCEL, NOVA QUEL, and NOVA PELLET (all trade names) manufactured by RIN KAGAKU KOGYO CO., LTD.

[0062] Examples of phosphate ester-based flame retardants include aliphatic phosphate esters such as trimethyl phosphate, triethyl phosphate, and tributyl phosphate; aromatic phosphate esters such as triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, trixylenyl phosphate, cresyl di-2,6-xylenyl phosphate, tris(t-butylated phenyl)phosphate, tris(isopropylated phenyl)phosphate, and triarylisopropyl phosphate; and aromatic condensed phosphate esters such as resorcinol bisdiphenyl phosphate, bisphenol A bis(diphenyl phosphate), and resorcinol bisdixylenyl phosphate. Among these, bisphenol A bis(diphenyl phosphate) is preferred from the viewpoints of its excellent hydrolysis resistance and its excellent plasticizing effect, which improves adhesion.

[0063] The content of the flame retardant in the thermal conduction layer is not limited and can be used in an amount that exhibits flame retardancy, preferably about 30% by volume or less, and more preferably 20% by volume or less from the viewpoint of suppressing deterioration of thermal resistance due to the flame retardant components seeping out onto the surface of the thermal conduction layer.

[0064] The average thickness of the thermally conductive layer is not particularly limited and can be selected appropriately depending on the purpose. The thickness of the thermally conductive layer can be selected appropriately depending on the specifications of the semiconductor package to be used, etc. The smaller the thickness, the lower the thermal resistance tends to be, and the larger the thickness, the better the warpage compliance tends to be. The average thickness of the thermally conductive layer may be 20 μm to 3000 μm, and from the viewpoint of thermal conductivity and adhesion, it is preferably 30 μm to 500 μm, and more preferably 50 to 400 μm. The average thickness of the thermally conductive layer is obtained by observing the cross section of the object to be measured using an electron microscope or by measuring the thickness at three random locations using a micrometer, and then calculating the arithmetic average value.

[0065] <Adhesive Layer> The thermally conductive sheet of the present disclosure includes an adhesive layer that contains a resin component and a thermally conductive filler and is located on at least a portion of the main surface of the thermally conductive layer.

[0066] Examples of the resin component include a curable resin component, an adhesive resin component, a thermoplastic resin component, etc. Examples of the curable resin component include a thermosetting resin component, a photocurable resin component, etc. The resin component may contain one or more curable resin components, one or more adhesive resin components, or one or more thermoplastic resin components. The resin component may also be a mixture of two or more resin components.

[0067] Examples of the curable resin component include epoxy resins, phenolic resins, melamine resins, urea resins, unsaturated polyester resins, alkyd resins, urethane resins, polyimide resins such as bismaleimide resins, polyamide resins, polyamideimide resins, silicone resins, and thermosetting (meth)acrylic resins. Among these, epoxy resins are preferred from the viewpoint of adhesion.

[0068] Examples of adhesive resin components and thermoplastic resin components include polyethylene (PE), polypropylene (PP), polycarbonate (PC), polystyrene, polyvinyl chloride, vinyl polymers, polyesters, polyamides, acrylonitrile-butadiene-styrene copolymer resins (ABS resins), thermoplastic (meth)acrylic resins, acrylonitrile-ethylene-propylene-diene-styrene copolymer resins (AES resins), thermoplastic epoxy resins, phenoxy resins, and thermoplastic elastomers. The use of thermoplastic resin components facilitates the softening and melting of the adhesive layer by heating, resulting in excellent recyclability and repairability. Furthermore, thermally conductive sheets using thermoplastic resin components have superior storage stability compared to thermally conductive sheets using curable resin components (particularly thermosetting resin components), and can be stored at room temperature. Among these, thermoplastic resin components are preferred because they can be lowered in viscosity by heating, further reducing the gap between the adherend and the thermally conductive sheet.

[0069] The thermoplastic resin component may be an amorphous thermoplastic resin, and the amorphous thermoplastic resin may be, for example, at least one of a thermoplastic epoxy resin and a phenoxy resin. An amorphous thermoplastic resin is a resin that has a melting point (Tm), but in measurement using a differential scanning calorimeter (DSC), the endothermic peak associated with melting is not confirmed as a clear endothermic peak, or the endothermic peak is very small.

[0070] The heat of fusion of the amorphous thermoplastic resin is preferably 15 J / g or less, more preferably 11 J / g or less, even more preferably 7 J / g or less, particularly preferably 4 J / g or less, and most preferably the melting peak is below the detection limit.

[0071] The heat of fusion is calculated from the area of ​​the endothermic peak in a DSC (differential scanning calorimeter) and the mass of the thermoplastic resin component. The heat of fusion is calculated using the mass of the thermoplastic resin component excluding components contained in the adhesive layer, such as thermally conductive fillers. For example, the heat of fusion can be determined as follows. First, 2 mg to 10 mg of a sample is weighed out, placed in an aluminum pan, and heated to 200°C or higher at 10°C / min using a DSC (e.g., DSC8231 manufactured by Rigaku Corporation) to obtain a DSC curve. The heat of fusion is then calculated from the area of ​​the endothermic peak at the time of melting determined from the DSC curve and the weighed value.

[0072] The thermoplastic epoxy resin is preferably a polymer of (a) a bifunctional epoxy resin monomer or oligomer and (b) a bifunctional compound containing two identical or different functional groups selected from the group consisting of a phenolic hydroxyl group, a carboxyl group, a mercapto group, an isocyanate group, and a cyanate ester group. The polymer can be produced by heating components (a) and (b) in the presence of a catalyst such as an imidazole catalyst.

[0073] The (a) bifunctional epoxy resin monomer or oligomer refers to an epoxy resin monomer or oligomer having two epoxy groups in the molecule. Specific examples of the (a) include bisphenol A type epoxy resins, bisphenol F type epoxy resins, bifunctional phenol novolac type epoxy resins, bisphenol AD ​​type epoxy resins, biphenyl type epoxy resins, bifunctional naphthalene type epoxy resins, bifunctional alicyclic epoxy resins, bifunctional glycidyl ester type epoxy resins (e.g., diglycidyl phthalate, diglycidyl tetrahydrophthalate, and dimer acid diglycidyl ester), bifunctional glycidyl amine type epoxy resins (e.g., diglycidyl aniline and diglycidyl toluidine), bifunctional heterocyclic epoxy resins, bifunctional diarylsulfone type epoxy resins, and hydroquinone type epoxy resins (e.g., hydroquinone diglycidyl ether, 2,5-di-tert-butyl ... t-butylhydroquinone diglycidyl ether and resorcinol diglycidyl ether), bifunctional alkylene glycidyl ether compounds (e.g., butanediol diglycidyl ether, butenediol diglycidyl ether, and butynediol diglycidyl ether), bifunctional glycidyl group-containing hydantoin compounds (e.g., 1,3-diglycidyl-5,5-dialkylhydantoin and 1-glycidyl-3-(glycidoxyalkyl)-5,5-dialkylhydantoin), bifunctional glycidyl group-containing siloxanes (e.g., 1,3-bis(3-glycidoxypropyl)-1,1,3,3-tetramethyldisiloxane and α,β-bis(3-glycidoxypropyl)polydimethylsiloxane), and modified products thereof. Of these, bisphenol A type epoxy resins, bisphenol F type epoxy resins, and biphenyl type epoxy resins are preferred in terms of reactivity and workability.

[0074] Examples of the (b) bifunctional compound containing a phenolic hydroxyl group include mononuclear aromatic dihydroxy compounds having one benzene ring such as catechol, resorcinol, and hydroquinone; bisphenols such as bis(4-hydroxyphenyl)propane (bisphenol A), bis(4-hydroxyphenyl)methane (bisphenol F), bis(4-hydroxyphenyl)ethane (bisphenol AD), and bis(4-hydroxyphenyl)sulfone (bisphenol S); compounds having a condensed ring such as dihydroxynaphthalene; bifunctional phenol compounds into which an allyl group has been introduced such as diallylresorcinol, diallylbisphenol A, and triallyldihydroxybiphenyl; and dibutylbisphenol A.

[0075] Examples of the (b) bifunctional compound containing a carboxyl group include adipic acid, succinic acid, malonic acid, cyclohexanedicarboxylic acid, phthalic acid, isophthalic acid, and terephthalic acid.

[0076] Examples of the (b) bifunctional compound containing a mercapto group include ethylene glycol bisthioglycolate and ethylene glycol bisthiopropionate.

[0077] Examples of the (b) bifunctional compound containing an isocyanate group include diphenylmethane diisocyanate (MDI), isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HMDI), and tolylene diisocyanate (TDI).

[0078] Examples of the bifunctional compound containing a cyanate ester group (b) include 2,2-bis(4-cyanatophenyl)propane, 1,1-bis(4-cyanatophenyl)ethane, and bis(4-cyanatophenyl)methane.

[0079] Among the compounds (b), bifunctional compounds containing a phenolic hydroxyl group are preferred from the viewpoint of obtaining a thermoplastic polymer, bifunctional compounds containing two phenolic hydroxyl groups and a bisphenol structure or a biphenyl structure are preferred from the viewpoint of heat resistance and adhesiveness, and bisphenol A, bisphenol F, or bisphenol S are preferred from the viewpoint of heat resistance and cost.

[0080] When (a) is a bisphenol A epoxy resin, a bisphenol F epoxy resin, a bisphenol S epoxy resin, or a biphenyl epoxy resin, and (b) is bisphenol A, bisphenol F, or bisphenol S, the polymer obtained by polymerizing (a) and (b) preferably has a structure in which a paraphenylene structure and an ether bond are connected by an alkylene group to form a main chain, and hydroxyl groups generated by polyaddition are arranged in side chains. The linear structure consisting of the paraphenylene skeleton can increase the mechanical strength of the polymer after polymerization, and the hydroxyl groups arranged in the side chains can improve adhesion. As a result, high adhesive strength can be achieved while maintaining the workability of a thermosetting resin.

[0081] The epoxy equivalent (molecular weight / number of epoxy groups) of the thermoplastic epoxy resin may be 1600 g / eq or more, 2000 g / eq or more, 5000 g / eq or more, or 9000 g / eq or more. The epoxy equivalent of the epoxy resin is a value measured by a method in accordance with JIS K 7236:2009.

[0082] The adhesive layer may contain a phenoxy resin as a thermoplastic resin component. The phenoxy resin is, for example, a polyhydroxy polyether synthesized from bisphenols and epichlorohydrin, and has thermoplastic properties.

[0083] Known methods for producing phenoxy resins include a method involving a direct reaction between a dihydric phenol and epichlorohydrin and a method involving an addition polymerization reaction between a diglycidyl ether of a dihydric phenol and another dihydric phenol. In the case of the direct reaction between a dihydric phenol and epichlorohydrin, examples of the dihydric phenol include phenols such as bisphenol A, bisphenol F, bisphenol S, biphenol, biphenylenediol, and fluorenediphenyl; and aliphatic glycols such as ethylene glycol, propylene glycol, and diethylene glycol. Among these, bisphenol A, bisphenol F, and bisphenol S are preferred from the standpoints of cost, adhesiveness, viscosity, heat resistance, and the like. These may be used alone or in combination of two or more. The phenoxy resin preferably has a chemical structure similar to that of an epoxy resin, and includes a main chain formed by linking a paraphenylene structure and an ether bond to each other, and a structure in which hydroxyl groups are arranged in side chains.

[0084] For the thermoplastic epoxy resin and the phenoxy resin, the weight-average molecular weight, which is a value converted into polystyrene by GPC (gel permeation chromatography), is preferably 10,000 to 500,000, more preferably 18,000 to 300,000, and even more preferably 20,000 to 200,000. The weight-average molecular weight is calculated from the elution peak position detected by GPC, and each is a molecular weight value converted into standard polystyrene. A weight-average molecular weight within this range provides a good balance between thermoplasticity and heat resistance. A weight-average molecular weight of 10,000 or more provides excellent heat resistance, while a weight-average molecular weight of 500,000 or less provides low viscosity when melted and high adhesiveness.

[0085] Examples of the thermally conductive filler include metal-containing particles and non-metal particles having excellent thermal conductivity, such as metals, metal oxides, metal nitrides, metal hydroxides, metal carbides, metal fluorides, and carbon. The thermally conductive filler may be, for example, a filler having a thermal conductivity of 10 W / (m·K) or more. The thermally conductive filler may be insulating or conductive.

[0086] The thermally conductive filler may be at least one particle selected from silver, copper, aluminum, aluminum oxide, aluminum hydroxide, magnesium oxide, beryllium oxide, boron nitride, aluminum nitride, silicon nitride, silicon carbide, silicon dioxide, aluminum fluoride, calcium fluoride, and zinc oxide. Among these, silver particles are preferred from the viewpoint of thermal conductivity.

[0087] Boron nitride is an insulating particle and is therefore preferably used in applications requiring insulation. However, boron nitride has a scaly shape and anisotropic thermal conductivity, and tends to be oriented in the plane direction, resulting in a tendency for low thermal conductivity in the thickness direction. Therefore, when using boron nitride, from the viewpoint of thermal conductivity, it is necessary to form an adhesive layer so that the boron nitride is oriented in the thickness direction, which tends to make the adhesive layer formation process complicated.

[0088] On the other hand, metal particles such as silver, copper, and aluminum have higher thermal conductivity and smaller anisotropy of thermal conductivity than ceramic fillers such as boron nitride. Therefore, there is no need to orient the metal particles in the thickness direction when forming the adhesive layer, and an adhesive layer with excellent thermal conductivity can be easily formed, resulting in a favorable reduction in the thermal resistance of the thermal conductive sheet. Furthermore, by using silver particles as the metal particles, sintering of the particles proceeds at a relatively low temperature. Therefore, a network of silver particles is formed by sintering, which tends to result in a higher thermal conductivity than other thermally conductive fillers. Furthermore, sintered silver particles have excellent adhesion to adherends such as heating elements and heat sinks, which tends to further reduce thermal resistance.

[0089] The thermally conductive filler preferably contains silver particles. When the thermally conductive filler contains silver particles, the content of the silver particles may be 50% by mass to 100% by mass, 80% by mass to 100% by mass, or 90% by mass to 100% by mass, relative to 100% by mass of the thermally conductive filler.

[0090] The particle size of the thermally conductive filler may be 0.1 μm to 50 μm, 0.2 μm to 20 μm, or 0.5 μm to 10 μm, from the viewpoint of excellent thermal conductivity and further reducing the gap between the adherend and the thermally conductive sheet.

[0091] The particle size (D50) of the thermally conductive filler is measured using a laser diffraction particle size distribution device (for example, "Microtrac Series MT3300" manufactured by Nikkiso Co., Ltd.) that applies a laser diffraction / scattering method, and corresponds to the particle size at which the cumulative mass becomes 50% when the cumulative mass particle size distribution curve is plotted from the small particle size side.

[0092] In the thermally conductive sheet of the present disclosure, the adhesive layer may be located on at least a portion of the main surface of the thermally conductive layer, and the adhesive layer may be located on the entire main surface, or on a portion of the main surface (for example, the portion that comes into contact with the adherend, such as a heating element or a heat sink).

[0093] The adhesive layer may be located on one main surface or on two main surfaces.

[0094] The content of the resin component contained in the adhesive layer is preferably 1% by mass to 30% by mass, more preferably 3% by mass to 25% by mass, and even more preferably 5% by mass to 20% by mass, relative to the total amount of the adhesive layer, from the viewpoint of, for example, the balance between thermal conductivity and adhesion.

[0095] When the adhesive layer contains a thermoplastic resin component, the content of the thermoplastic resin component may be 50% by mass or more, 60% by mass or more, 80% by mass or more, or 90% by mass or more, based on the total amount of the resin components. The upper limit of the content of the thermoplastic resin component is not particularly limited, and may be 100% by mass or 95% by mass or less.

[0096] The content of the thermally conductive filler contained in the adhesive layer is preferably 70% by mass to 99% by mass, more preferably 75% by mass to 97% by mass, and even more preferably 80% by mass to 95% by mass, relative to the total amount of the adhesive layer, from the viewpoint of, for example, the balance between thermal conductivity and adhesion.

[0097] The total content of the resin component and the thermally conductive filler contained in the adhesive layer may be 80% by mass to 100% by mass, or 90% by mass to 100% by mass, based on the total amount of the adhesive layer.

[0098] The adhesive layer may or may not contain components other than the resin component and the thermally conductive filler, such as the hot melt agent (D), the antioxidant (E), and other components described above in the section on the thermally conductive layer.

[0099] When the adhesive layer contains a thermosetting resin component, the adhesive layer is preferably in a semi-cured state from the viewpoint of improving handleability. For example, a resin composition containing a thermosetting resin component and a thermally conductive filler can be subjected to treatment such as heating and drying to obtain an adhesive layer in a semi-cured state.

[0100] In the present disclosure, the semi-cured state refers to a state in which the viscosity of the adhesive layer is 10 at room temperature (25 to 30°C). ４ Pa·s~10 ６ The viscosity is measured by a dynamic mechanical analyzer (DMA; frequency 1 Hz, load 10 g, heating rate 20° C. / min).

[0101] The method for obtaining a semi-cured adhesive layer is not particularly limited. For example, a resin composition containing a thermosetting resin component, a thermally conductive filler, a solvent, etc. may be applied to the main surface of the thermally conductive layer, and the applied resin composition may be heated, dried, etc. Alternatively, a resin composition may be applied to a release film, which may then be heated, dried, etc., and the adhesive layer made of the heated, dried, etc. resin composition may be hot roll laminated onto the main surface of the thermally conductive layer. Examples of methods for heating, drying, etc. include hot vacuum pressing and hot roll lamination.

[0102] The average thickness of the adhesive layer is preferably 2 μm to 50 μm, more preferably 2 μm to 30 μm, and even more preferably 2 μm to 20 μm. An average adhesive layer thickness of 2 μm or more tends to further reduce the gap between the adherend and the thermally conductive sheet, thereby further reducing contact thermal resistance. An average adhesive layer thickness of 50 μm or less tends to improve the thermal conductivity of the thermally conductive sheet. The thickness may be measured at three random locations by observing the cross section of the thermally conductive layer to be measured using an electron microscope, and the arithmetic mean value may be used as the average thickness of the adhesive layer. Alternatively, the thickness of a thermally conductive layer not including an adhesive layer and a thermally conductive sheet including an adhesive layer may be measured at three random locations using a micrometer, and the arithmetic mean values ​​may be used as the average thickness of the thermally conductive layer and the average thickness of the thermally conductive sheet, respectively. The average thickness of the adhesive layer may then be calculated by subtracting the average thickness of the thermally conductive sheet from the average thickness of the thermally conductive layer. When adhesive layers are formed on the two main surfaces of the thermally conductive layer, the average thickness of the adhesive layers means the total thickness of the adhesive layers formed on the two main surfaces.

[0103] The surface roughness Ra of the thermally conductive sheet (before bonding to the adherend) may be 10 μm or less from the viewpoint of further reducing the gap between the adherend and the thermally conductive sheet when bonded to the adherend, and may be 2 μm to 20 μm from the viewpoint of productivity of the thermally conductive sheet. In the present disclosure, the surface roughness Ra refers to a value measured based on JIS B0601:2013.

[0104] In the thermally conductive sheet, the thermal conductivity of the thermally conductive layer in the thickness direction is preferably greater than the thermal conductivity of the adhesive layer in the thickness direction. For example, the ratio of the thermal conductivity of the thermally conductive layer in the thickness direction to the thermal conductivity of the adhesive layer in the thickness direction (thermal conductivity of the thermally conductive layer / thermal conductivity of the adhesive layer) may be greater than 1, for example, greater than 1 and less than 20, greater than 1 and less than 10, or even 2 to 8. The thermal conductivity of the thermally conductive layer in the thickness direction and the thermal conductivity of the adhesive layer can be measured by the xenon flash (Xe-flash) method. Note that when the resin component contains a curable resin component, the thermal conductivity of the adhesive layer refers to the thermal conductivity of the adhesive layer after curing.

[0105] The thermal conductivity of the adhesive layer may be 5.0 W / (m·K) or more, may be 5.0 W / (m·K) to 20 W / (m·K), or may be 7.0 W / (m·K) to 15 W / (m·K).

[0106] The thermally conductive sheet may have a protective film on at least one side, and preferably has protective films on both sides, which can protect the adhesive surface of the thermally conductive sheet.

[0107] Examples of the protective film that can be used include resin films such as polyethylene, polyester, polypropylene, polyethylene terephthalate, polyimide, polyetherimide, polyether naphthalate, and methylpentene, coated paper, coated cloth, and metal foil such as aluminum. These protective films may be used alone or in combination of two or more to form a multilayer film. The protective film is preferably surface-treated with a silicone-based, silica-based, or other mold release agent.

[0108] The use of the thermally conductive sheet is not particularly limited. The thermally conductive sheet of the present disclosure is particularly suitable as a thermally conductive sheet (TIM1; Thermal Interface Material 1) that interposes a semiconductor chip and a heat spreader when the semiconductor chip is a heat generating body and the heat spreader is a heat dissipating body, or as a film-like adhesive material for semiconductor chips such as a die bonding film. When the thermally conductive sheet is used as a die bonding film, it may be laminated with a dicing tape to form an integrated dicing and die bonding film.

[0109] An embodiment of a thermally conductive sheet will be described using FIG. 1 . The thermally conductive sheet of the present disclosure is not limited to the following embodiment. The thermally conductive sheet 1A shown in FIG. 3 includes a thermally conductive layer 11A and adhesive layers 12A and 13A, with the adhesive layer 12A located on one main surface of the thermally conductive layer 11A and the adhesive layer 13A located on the other main surface of the thermally conductive layer 11A. As shown in FIG. 1 , the thermally conductive layer 11A in the thermally conductive sheet 1A may have two uneven main surfaces that are not flat. Alternatively, the thermally conductive layer 11A in the thermally conductive sheet 1A may have two flat main surfaces (see, for example, FIG. 3 ).

[0110] [Method for manufacturing thermally conductive sheet] The method for manufacturing a thermally conductive sheet is not particularly limited as long as it is a method that can produce a thermally conductive sheet having the above-mentioned configuration. The method for manufacturing a thermally conductive sheet includes a step of preparing a composition containing the graphite particles (A) (also referred to as a "preparation step"), a step of forming the thermally conductive layer using the composition (also referred to as a "formation step"), and a step of forming an adhesive layer on at least a part of a main surface of the thermally conductive layer (also referred to as an "adhesive layer formation step").

[0111] <Preparation Step> In the preparation step, a composition containing graphite particles (A) and any other components (for example, a component (B) that is liquid at 25°C, an acrylic acid ester polymer (C), a hot-melt agent (D), an antioxidant (E), and other components) is prepared. Any method may be used to blend the components as long as it is possible to uniformly mix the components, and there are no particular limitations. The composition may also be prepared by obtaining a commercially available product. For details on the preparation of the composition, see paragraph

[0033] of JP 2008-280496 A.

[0112] <Forming Step> In the forming step, the thermally conductive layer is formed using a composition containing graphite particles (A) and any other components. For example, the thermally conductive layer may be formed by molding the composition into a sheet.

[0113] The forming step preferably includes a step of forming the composition into a sheet to obtain a sheet (also referred to as a "sheet producing step"), a step of producing a laminate of the sheets (also referred to as a "laminate producing step"), and a step of slicing the side end surfaces of the laminate (also referred to as a "slicing step").

[0114] <Sheet Preparation Step> The sheet preparation step may be performed by any method as long as it can form the composition obtained in the previous step into a sheet, and is not particularly limited. For example, it is preferably performed using at least one molding method selected from the group consisting of rolling, pressing, extrusion, and coating. For details of the sheet preparation step, see paragraph

[0034] of JP 2008-280496 A.

[0115] <<Laminate Preparation Step>> In the laminate preparation step, a laminate of the sheets obtained in the previous step is formed. The laminate may be prepared, for example, by stacking multiple independent sheets in order, by folding a single sheet, or by rolling up a single sheet. For details of the laminate preparation step, see paragraphs

[0035] to

[0037] of JP 2008-280496 A.

[0116] <<Slicing Step>> The slicing step may be performed by any method capable of slicing the side end surface of the laminate obtained in the previous step, and is not particularly limited. From the viewpoint of forming an extremely efficient heat conduction path by the graphite particles (A) penetrating the thermal conductive layer in the thickness direction and further improving thermal conductivity, it is preferable to slice the laminate to a thickness of not more than twice the mass average particle diameter of the graphite particles (A). For details of the slicing step, see paragraph

[0038] of JP 2008-280496 A.

[0117] <Adhesive Layer Forming Step> The adhesive layer forming step may be any method that can form an adhesive layer on at least a portion of the main surface of the thermally conductive layer (e.g., a sliced ​​sheet obtained by slicing), and is not particularly limited. For example, a resin composition containing a thermosetting resin component, a thermally conductive filler, a solvent, etc. may be applied to the main surface of the thermally conductive layer, and the applied resin composition may be heated, dried, etc. to volatilize the solvent. Alternatively, a resin composition may be applied to a release film, and then heated, dried, etc., and an adhesive layer made of the heated, dried, etc. resin composition may be hot roll laminated onto the main surface of the thermally conductive layer. Examples of heating, drying, etc. techniques include hot vacuum pressing and hot roll lamination. The adhesive layer formed on the main surface of the thermally conductive layer may be in a semi-cured state.

[0118] The method for producing a thermally conductive sheet may further include a step of laminating the thermally conductive sheet by attaching a protective film thereto (also referred to as a "laminating step") after the adhesive layer forming step.

[0119] <Laminating Step> The laminating step may be performed by any method as long as it can attach the thermally conductive sheet obtained in the adhesive layer forming step to the protective film, and is not particularly limited.

[0120] By producing a thermally conductive sheet using this method, efficient thermal conduction paths are easily formed, and therefore a thermally conductive sheet with high thermal conductivity and excellent adhesion tends to be obtained.

[0121] [Heat Dissipation Device] The heat dissipation device of the present disclosure includes a heat generating element, a heat dissipation element, and a thermally conductive sheet of the present disclosure disposed between the heat generating element and the heat dissipation element, wherein the thermally conductive layer has the adhesive layer located on at least a portion of at least one of the main surfaces located on the heat generating element side and the main surface located on the heat dissipation element side. Preferably, the adhesive layer is located on at least a portion of the main surface located on the heat generating element side and at least a portion of the main surface located on the heat dissipation element side, and more preferably, the adhesive layer is located on a region of the main surface located on the heat generating element side that faces the heat generating element and a region of the main surface located on the heat dissipation element side that faces the heat dissipation element.

[0122] Examples of heat generating elements include semiconductor chips, semiconductor packages, power modules, etc. Examples of heat dissipating elements include heat spreaders, heat sinks, water-cooled pipes, etc.

[0123] An example of a heat dissipation device will be described in more detail below with reference to FIG. 2 . A heat dissipation device using a semiconductor chip as a heat generating element and a heat spreader as a heat sink will be described. The semiconductor chip and heat spreader are examples of a heat generating element and a heat sink, respectively, and the present disclosure is not limited thereto. A thermally conductive sheet 1 is used by closely adhering one side to a semiconductor chip 2 and the other side to a heat spreader 3. The semiconductor chip 2 is fixed to a substrate 4 using an underfill material 5, and the heat spreader 3 is fixed to the substrate 4 with a sealing material 6. The adhesion between the thermally conductive sheet 1 and the semiconductor chip 2 and heat spreader 3 is improved by pressing them together. It should be noted that there does not need to be one heat generating element and one heat sink per thermally conductive sheet 1. For example, multiple semiconductor chips 2 may be provided per thermally conductive sheet 1, one semiconductor chip 2 may be provided per multiple thermally conductive sheets 1, or multiple semiconductor chips 2 may be provided per multiple thermally conductive sheets 1. Adhesive layers are located on the main surface of the thermally conductive sheet 1 facing the semiconductor chip 2 and on the main surface of the thermally conductive sheet 1 facing the heat spreader 3. For example, in the thermally conductive sheet 1 shown in Fig. 3, adhesive layer 13 is located on the main surface of the thermally conductive sheet 1 facing the semiconductor chip 2, and adhesive layer 12 is located on the main surface of the thermally conductive sheet 1 facing the heat spreader 3. Furthermore, adhesive layer 13 may be in contact with the semiconductor chip 2, and adhesive layer 12 may be in contact with the heat spreader 3.

[0124] The heat dissipation device is formed by disposing the thermally conductive sheet of the present disclosure between a heat generating element and a heat dissipation element. By stacking the heat generating element and the heat dissipation element with the thermally conductive sheet interposed therebetween, heat from the heat generating element can be efficiently conducted to the heat dissipation element. This efficient heat conduction improves the lifespan of the heat dissipation device during use, and a heat dissipation device that functions stably even during long-term use can be provided.

[0125] The temperature range in which the thermally conductive sheet can be particularly suitably used may be, for example, −10° C. to 150° C., −10° C. to 100° C., or −10° C. to 80° C. Therefore, suitable examples of the heat generating element include semiconductor packages, displays, LEDs, electric lights, automotive power modules, and industrial power modules.

[0126] Examples of heat sinks include aluminum or copper fins, plates, etc., aluminum or copper blocks connected to heat pipes, aluminum or copper blocks with cooling liquid circulated inside by a pump, and Peltier elements and aluminum or copper blocks equipped with them.

[0127] The heat dissipation device is constructed by contacting the heat generating element and the heat dissipation element with each side of a thermally conductive sheet. The method of contacting the heat generating element with one side of the thermally conductive sheet and the method of contacting the heat dissipation element with the other side of the thermally conductive sheet are not particularly limited as long as they can be fixed in a state of sufficient close contact.

[0128] For example, a thermally conductive sheet is placed between the heat generating element and the heat sink, fixed in place with a jig capable of applying a pressure of approximately 0.05 MPa to 1 MPa, and the heat generating element is then heated in this state, or heated to approximately 80°C to 200°C using an oven or the like. Another method is to use a press capable of applying heat and pressure at 80°C to 200°C and 0.05 MPa to 1 MPa. In this method, the preferred pressure range is 0.10 MPa to 1 MPa, and the preferred temperature range is 100°C to 180°C. A pressure of 0.10 MPa or higher or a heating temperature of 100°C or higher tends to provide excellent adhesion. Furthermore, a pressure of 1 MPa or lower or a heating temperature of 180°C or lower tends to further improve adhesion reliability. This is thought to be because excessive compression of the heat conducting sheet can prevent it from becoming thin or causing excessive distortion or residual stress in surrounding components.

[0129] The thermally conductive sheet to be placed between the heat generating element and the heat dissipating element is not particularly limited as long as it is the above-mentioned thermally conductive sheet. For example, the thermally conductive sheet shown in FIG. 1 may be placed between the heat generating element and the heat dissipating element.

[0130] When the thermal conductive sheet 1A shown in FIG. 1 is used, the adhesive layers 12A and 13A located on the main surfaces of the thermal conductive sheet 1A are softened or deformed by applying heat and pressure while the thermal conductive sheet 1A is positioned between the heat generating element and the heat dissipating element. The softened and deformed adhesive layers fill any gaps that arise when the thermal conductive sheet 1A is heated and pressed to the heat generating element and the heat dissipating element. This reduces the gap between the thermal conductive sheet and the adherend while allowing the thermal conductive sheet and the adherend to be closely attached via the adhesive layers. Even when the thermal conductive sheet 1A having an uneven surface as shown in FIG. 1 is used, the thermal conductive sheet 1A is heated and pressurized while being positioned between the heat generating element and the heat dissipating element. This flattens the uneven thermal conductive sheet 1A by pressure, resulting in a flat thermal conductive sheet 1 as shown in FIG. 3 when the heat dissipating device is manufactured, thereby suppressing the occurrence of gaps between the thermal conductive sheet and the adherend. For example, by applying an adhesive layer containing a thermosetting resin component, the adhesive layer deformed by thermocompression fills the gap between the thermally conductive sheet and the adherend, and the thermosetting resin component hardens by heating. This allows the thermally conductive sheet and the adherend to be tightly attached via the adhesive layer. For example, by applying an adhesive layer containing a thermoplastic resin component, the adhesive layer softened by thermocompression fills the gap between the thermally conductive sheet and the adherend. As a result, the gap between the thermally conductive sheet and the heat-generating or heat-dissipating body is reduced, significantly reducing the contact thermal resistance.

[0131] The thermally conductive sheet may have a reduced thickness (compression rate) of 1% to 35% after being placed between the heat generating element and the heat dissipating element and compressed relative to its initial thickness before being compressed.

[0132] Fixing may be performed using a jig such as a screw or a spring in addition to a clip, and it is preferable to further fix it using a commonly used means such as an adhesive in order to maintain adhesion.

[0133] At the interface between the heat generating element and the thermally conductive sheet and at the interface between the heat dissipating element and the thermally conductive sheet, the porosity calculated as the ratio of the area of ​​the gas region to the area of ​​the measurement region is preferably 0% to 25.0%, and more preferably 0% to 20.0%. This reduces gaps (e.g., gaps due to the unevenness of the thermally conductive sheet and gaps due to the unevenness of the heat generating element or the heat dissipating element) that occur when the thermally conductive sheet and the heat generating element or the heat dissipating element are thermocompressed together. As a result, it is presumed that the contact thermal resistance is significantly reduced. In the present disclosure, it is preferable that the porosity satisfy the aforementioned numerical range on both the main surface side of the thermally conductive layer where the adhesive layer is located and the main surface side of the thermally conductive layer where the adhesive layer is not located.

[0134] On the main surface side of the thermally conductive layer where the adhesive layer is located, the porosity is preferably 0% to 10.0%, more preferably 0% to 5.0%, and even more preferably 0% to 2.0%.

[0135] In the present disclosure, the porosity of the interface can be determined as follows. First, an ultrasound imaging diagnostic device (for example, Insight-300, Insight Corporation) is used to observe the adhesion state of the interface under the conditions of a reflection method and 35 MHz. The ratio of the area of ​​the unattached gas region is calculated, and the porosity of the interface can be determined based on the following formula: Interfacial porosity (%) = 100 × (area of ​​the gas region / area of ​​the measurement region)

[0136] The numerical range of the porosity of the interface can be adjusted by adjusting, for example, the thickness of the adhesive layer, the composition of the resin composition forming the adhesive layer, the compressibility of the heat conductive sheet, and the like.

[0137] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0138] (Examples 1 and 2) The following materials were charged into a kneader (Moriyama Corporation, DS3-SGHM-E type pressure double-arm kneader) so as to have the mixing ratio (volume %) shown in Table 1, and kneaded at a temperature of 150°C to obtain a composition.

[0139] <Graphite particles (A)> (A)-1: scaly expanded graphite particles ("HGF-L" from Showa Denko Materials Co., Ltd., mass average particle diameter: 270 μm, it was confirmed by the above-mentioned X-ray diffraction measurement method that the six-membered ring planes in the crystals were oriented in the plane direction of the scaly particles). <Liquid component (B)> (B)-1: isobutene-normal butene copolymer ("NOF Polybutene" from NOF Corporation). ＴＭ - Emawet (registered trademark), Grade 30N) (B)-2: isobutene homopolymer (Nippon Oil Corporation's "Tetrax 6T") <Acrylate ester polymer (C)> (C)-1: acrylate copolymer resin (butyl acrylate / ethyl acrylate / acrylonitrile / acrylic acid copolymer, weight average molecular weight: 530,000, Tg=-39°C) <Hot melt agent (D)> (D)-1: hydrogenated petroleum resin (Arakawa Chemical Industries, Ltd.'s "Arcon P90") <Antioxidant (E)> (E)-1: hindered phenol-based antioxidant (ADEKA Corporation's "ADEKA STAB AO-60")

[0140] (Preparation of Thermally Conductive Layer) The kneaded composition was placed in an extrusion molding machine (Parker Corporation, product name: HKS40-15 extruder) and extruded into a flat plate shape with a width of 20 cm and a thickness of 1.5 mm to 1.6 mm to obtain a primary sheet. The obtained primary sheet was press-punched using a 40 mm x 150 mm die blade, and 61 punched sheets were stacked. Pressure was applied in the stacking direction at 90 ° C for 30 minutes with an 80 mm high spacer sandwiched between them to obtain a height of 80 mm, obtaining a 40 mm x 150 mm x 80 mm laminate. Next, the 80 mm x 150 mm side end surface of this laminate was sliced ​​with a woodworking slicer to obtain a thermally conductive layer with a thickness of 0.11 mm.

[0141] (Preparation of Thermally Conductive Sheet) (Example 1) A resin composition containing 6 parts by mass of a thermosetting resin component (bisphenol F type epoxy resin), 4 parts by mass of a cresol novolac type epoxy resin, 8 parts by mass of a phenolic resin, 6 parts by mass of an acrylic ester resin, 76 parts by mass of a thermally conductive filler (silver particles, particle diameter 1.5 μm), and 39 parts by mass of a solvent (cyclohexanone) was prepared. The prepared resin composition was applied to a release film and dried in an oven at 130°C. One main surface of the thermally conductive layer obtained as described above was hot roll laminated at 70°C to obtain a thermally conductive sheet having an adhesive layer (adhesive layer 1 in Table 2) formed on one main surface. Example 2 A resin composition containing 4 parts by mass of a thermosetting resin component (bisphenol F epoxy resin), 3 parts by mass of a cresol novolac epoxy resin, 6 parts by mass of a phenolic resin, 5 parts by mass of an acrylic ester resin, 83 parts by mass of a thermally conductive filler (silver particles, particle diameter 1.5 μm), and 39 parts by mass of a solvent (cyclohexanone) was prepared. The prepared resin composition was applied to a release film and dried in an oven at 130°C. One main surface of the thermally conductive layer obtained as described above was hot roll laminated at 70°C to obtain a thermally conductive sheet having an adhesive layer (adhesive layer 2 in Table 2) formed on one main surface.

[0142] (Comparative Example 1) A thermally conductive layer was produced by kneading, laminating, pressing, and slicing each material shown in Table 1 to achieve the mixing ratio (volume %) shown in Table 1 in the same manner as in Examples 1 and 2. In each comparative example, the thermally conductive layer was used as a thermally conductive sheet without forming an adhesive layer.

[0143]

[0144] The thermal conductive sheets of Examples 1 and 2 and Comparative Example 1 were evaluated by the following methods. The results are shown in Table 2 and FIG.

[0145] (Measurement of Thermal Resistance) Thermal resistance was measured using a tabletop xenon flash analyzer (LFA 467 Hyper Flash). A 14 mm diameter thermal conductive sheet was sandwiched between 1 mm thick copper plates to prepare a three-layered sample. The sample preparation conditions were a temperature of 150°C and pressure of 0.14 MPa for 3 minutes. When a thermosetting resin was included, the sample was heated in an oven at 175°C for 1 hour to harden the resin, and then sufficiently cooled to room temperature. In addition, as a pretreatment for measurement, the copper surface was blackened with carbon spray, and then the measurement was performed. The thermal conductivity λ, excluding the influence of the copper plate, was obtained from the three-layered structure, and the thermal conductivity λ and thickness t were used to calculate the thermal conductivity per unit area (1 cm) using the following formula: ２ Thermal resistance value X (K cm ２ / W) was calculated as follows: X = (10 x t) / λ t: thickness (mm) of the thermally conductive sheet of Examples 1 to 4 or Comparative Example 1 λ: thermal conductivity (W / (m·K))

[0146] (Evaluation of Interfacial Porosity) In the three-layer structure sample prepared by the method described in (Measurement of Thermal Resistance), the evaluation of the interfacial porosity was evaluated as follows. Using an ultrasound imaging diagnostic device (Insight-300, Insight Corporation), the adhesion state of the interface was observed under the conditions of reflection method, 35 MHz, gain level 10 dB, and contrast threshold 30% to 70%. Furthermore, the image was binarized using image analysis software (ImageJ) (specifically, the histogram was converted to black and white, with 0 to 83 representing black and 84 to 255 representing white), and the proportion of the area of ​​the unadhered gas region out of the Φ11 mm area (area of ​​the measurement region; in Figure 4, an image of Φ14 mm is shown) was calculated, and the interfacial porosity (%) was calculated based on the following formula. Interfacial porosity (%) = 100 × (area of ​​the gas region / area of ​​the measurement region)

[0147] (Thickness Evaluation) In Examples 1 and 2, the thickness of the adhesive layer before heat roll lamination was measured using a micrometer. Next, the thermally conductive sheets of Examples 1 and 2 and Comparative Example 1 were compressed under the same conditions. Next, the maximum thickness of the thermally conductive sheet after compression ("Thickness after compression" in Table 2) was measured using a micrometer.

[0148]

[0149] In Examples 1 and 2, in which an adhesive layer was formed on the main surface of the thermally conductive layer using a resin composition containing a resin component and a thermally conductive filler, it was confirmed that the thermal resistance could be reduced more than in Comparative Example 1, in which the adhesive layer was not formed on the main surface of the thermally conductive layer.

[0150] (Preparation of Thermally Conductive Layer 1) The materials shown in Table 1 were kneaded, laminated, pressed, and sliced ​​in the same steps as in Examples 1 and 2 to obtain the mixing ratio (volume %) shown in Table 1, to prepare a thermally conductive layer 1.

[0151] (Preparation of Thermal Conduction Layer 2) A thermal conduction layer 2 was prepared in the same manner as the thermal conduction layer 1, except that the blending ratio of the graphite particles (A) was increased to 40.0 volume % with respect to the blending ratio in Table 1 and the blending ratios of the other components were changed as shown in Table 3.

[0152]

[0153] (Preparation of Thermally Conductive Sheet) (Example 3) A resin composition containing 16 parts by mass of the bisphenol A epoxy resin shown below, 1 part by mass of bisphenol S, 83 parts by mass of a thermally conductive filler (silver particles, particle diameter 1.5 μm), 0.1 parts by mass of triphenylphosphine, and 32 parts by mass of a solvent (methyl ethyl ketone) was prepared. The prepared resin composition was applied to a release film and heated at 70°C for 5 minutes, followed by heating at 160°C for 2 hours, thereby reacting the bisphenol A epoxy resin and bisphenol S to form a thermoplastic epoxy resin. One main surface of the thermally conductive layer 1 obtained as described above was hot-roll laminated at 140°C to obtain a thermally conductive sheet having an adhesive layer (adhesive layer 3 in Table 4) formed on one main surface. The thickness of the adhesive layer before hot-roll lamination was measured using a micrometer and was 10 μm. A pressure of 0.14 MPa was used to prepare a three-layer structure sample for thermal resistance measurement, as described below.

[0154] (Example 4) A thermally conductive sheet having an adhesive layer (adhesive layer 3 in Table 4) formed on one main surface was obtained in the same manner as in Example 3. The thermal resistance was measured in the same manner as in Example 3, except that the pressure condition when preparing a three-layer structure sample for thermal resistance measurement was changed to 0.28 MPa.

[0155] Example 5 A thermally conductive sheet having adhesive layers (adhesive layer 3 in Table 4) formed on two main surfaces was obtained in the same manner as in Example 3, except that the two main surfaces of the thermally conductive layer 1 obtained as described above were hot roll laminated. A pressure of 0.14 MPa was used to prepare a three-layer structure sample for measuring thermal resistance, which will be described later.

[0156] (Example 6) A thermally conductive sheet having adhesive layers (adhesive layer 3 in Table 4) formed on two main surfaces was obtained in the same manner as in Example 5. The thermal resistance was measured in the same manner as in Example 5, except that the pressure condition when preparing a three-layer structure sample for thermal resistance measurement was changed to 0.28 MPa.

[0157] Example 7 A thermally conductive sheet having adhesive layers (adhesive layer 3 in Table 4) formed on two main surfaces was obtained in the same manner as in Example 6, except that thermally conductive layer 1 was changed to thermally conductive layer 2. The pressure used to prepare a three-layer structure sample for measuring thermal resistance, which will be described later, was 0.28 MPa.

[0158] In Comparative Examples 2 and 3, the thermally conductive layer 1 was used as a thermally conductive sheet without forming an adhesive layer. The pressures applied when producing three-layer structure samples for thermal resistance measurement, which will be described later, were 0.14 MPa and 0.28 MPa, respectively.

[0159] Comparative Example 4 In Comparative Examples 2 and 3, no adhesive layer was formed and the thermally conductive layer 2 was used as a thermally conductive sheet. The pressure when producing a three-layer structure sample for measuring thermal resistance, which will be described later, was set to 0.28 MPa.

[0160] For the thermally conductive sheets of Examples 3 to 7 and Comparative Examples 2 to 4, the thickness of the thermally conductive sheet after compression was measured in the same manner as described above, and the thermal resistance of the thermally conductive sheet was measured as follows. The results are shown in Table 4.

[0161] (Measurement of Thermal Resistance) Thermal resistance was measured using a tabletop xenon flash analyzer (LFA 447 Hyper Flash). A 15 mm square thermally conductive sheet was sandwiched between 1 mm copper plates to prepare a three-layered sample. The sample preparation conditions were a temperature of 150°C and a pressure of 0.14 MPa or 0.28 MPa. To ensure sufficient adhesion of the resin to the copper plate, the sample was heated in an oven at 150°C for 30 minutes, then heated in an oven at 180°C for 1 hour, and then thoroughly cooled to room temperature. In addition, as a pretreatment for measurement, the copper surface was blackened with carbon spray, and then the measurement was performed. The thermal conductivity λ, excluding the influence of the copper plate, was obtained from the three-layered structure, and the thermal conductivity λ was calculated per unit area (1 cm) using the obtained thermal conductivity λ and thickness t using the following formula: ２ Thermal resistance value X (K cm ２ / W) was calculated as follows: X = (10 x t) / λ t: thickness (mm) of the thermally conductive sheet of Examples 1 to 4 or Comparative Example 1 λ: thermal conductivity (W / (m·K))

[0162]

[0163] The thermal conductivity of the thermally conductive layer / thermal conductivity of the adhesive layer was determined in Examples 3 to 7 in the same manner as in Examples 1 and 2. Furthermore, the porosity of the interface was determined as follows. The results are shown in Table 5 and FIG. 5. When adhesive layers were disposed on both sides of the thermally conductive layer, the porosity of the interface (the surface with the adhesive layer) was taken as the arithmetic mean value of the porosity of both surfaces. When adhesive layers were not disposed on both sides of the thermally conductive layer, the porosity of the interface (the surface without the adhesive layer) was taken as the arithmetic mean value of the porosity of both surfaces.

[0164] (Evaluation of Interfacial Porosity) In the three-layer structure sample prepared by the method described in (Measurement of Thermal Resistance), the evaluation of the interfacial porosity was evaluated as follows. Using an ultrasound imaging diagnostic device (Insight-350, Insight Co., Ltd.), the adhesion state of the interface was observed under the conditions of reflection method, 75 MHz, gain level 10 dB, and contrast threshold 30% to 70%. Furthermore, the image was binarized using image analysis software (ImageJ) (specifically, the histogram was converted to black and white, with 0 to 216 representing black and 217 to 255 representing white), and the proportion of the area of ​​the unattached gas region out of a 10.4 mm square area (area of ​​the measurement region) was calculated, and the interfacial porosity (%) was determined based on the following formula. Interfacial porosity (%) = 100 × (area of ​​the gas region / area of ​​the measurement region)

[0165]

[0166] As shown in Table 4, in Examples 3 to 7, in which an adhesive layer was formed on the main surface of the thermally conductive layer using a resin composition containing a thermoplastic resin component and a thermally conductive filler, it was confirmed that the thermal resistance could be reduced more than in Comparative Examples 2 to 4, in which the adhesive layer was not formed on the main surface of the thermally conductive layer. As shown in Table 5, in Examples 3 to 7, the interfacial porosity values ​​were lower than in Comparative Examples 2 to 4, and it is inferred that the thermal resistance can be reduced by reducing the interfacial porosity.

[0167] All publications, patent applications, and technical standards mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent application, or technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. a thermally conductive layer containing at least one type of graphite particles (A) selected from the group consisting of scaly particles, ellipsoidal particles, and rod-shaped particles, wherein the planar direction of the scaly particles, the major axis direction of the ellipsoidal particles, and the major axis direction of the rod-shaped particles are oriented in the thickness direction; an adhesive layer including a resin component and a thermally conductive filler and positioned on at least a portion of a main surface of the thermally conductive layer; A thermally conductive sheet comprising:

2. The thermal conductive sheet according to claim 1 , wherein the resin component comprises at least one selected from the group consisting of a curable resin component, an adhesive resin component, and a thermoplastic resin component.

3. The thermal conductive sheet according to claim 2 , wherein the resin component is a curable resin component, and the adhesive layer is in a semi-cured state.

4. The thermally conductive sheet according to claim 1 , wherein the resin component includes a thermoplastic resin component.

5. The thermally conductive sheet according to claim 1 , wherein the thermoplastic resin component includes a thermoplastic epoxy resin.

6. 2. The thermally conductive sheet according to claim 1, wherein the thermally conductive filler is at least one particle selected from silver, copper, aluminum, aluminum oxide, aluminum hydroxide, magnesium oxide, beryllium oxide, boron nitride, aluminum nitride, silicon nitride, silicon carbide, silicon dioxide, aluminum fluoride, calcium fluoride, and zinc oxide.

7. The thermally conductive sheet according to claim 6 , wherein the thermally conductive filler is silver particles.

8. 2. The thermal conductive sheet according to claim 1, wherein the content of the thermal conductive filler is 70% by mass to 99% by mass with respect to the total amount of the adhesive layer.

9. 2. The thermal conductive sheet according to claim 1, wherein the adhesive layer has an average thickness of 2 μm to 50 μm.

10. A heat generating element, a heat dissipating element, and the thermally conductive sheet according to any one of claims 1 to 9, which is disposed between the heat generating element and the heat dissipating element, a heat dissipation device, wherein the adhesive layer is located on at least a part of at least one of the main surfaces of the thermally conductive layer that faces the heat generating body and the main surface that faces the heat dissipating body;

11. A heat generating element, a heat dissipating element, and the thermally conductive sheet according to any one of claims 1 to 9, which is disposed between the heat generating element and the heat dissipating element, A heat dissipation device in which the void ratio calculated as the ratio of the area of ​​the gas region to the area of ​​the measurement region at at least one of the interface between the heat generating body and the thermally conductive sheet and the interface between the heat dissipating body and the thermally conductive sheet is 0% to 25%.

12. A method for producing a thermal conductive sheet according to any one of claims 1 to 9, comprising: A method for producing a thermal conductive sheet, comprising: a step of preparing a composition containing the graphite particles (A); a step of forming the thermal conductive layer using the composition; and a step of forming an adhesive layer on at least a part of a main surface of the thermal conductive layer.