Heat transfer sheet, heat dissipation device, and method for producing heat transfer sheet

Abstract

The present invention provides a heat transfer sheet which comprises a heat transfer layer that contains at least one kind of graphite particles (A) selected from the group consisting of scale-like particles, ellipsoidal particles and rod-like particles, wherein the surface direction in the case of the scale-like particles, the major axis direction in the case of the ellipsoidal particles, and the major axis direction in the case of the rod-like particles, are oriented in the thickness direction. This heat transfer sheet contains a metal component that has a melting point of 200°C or less.

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 thermally conductive fillers are also known as thermally conductive sheets. Various resin sheets filled with thermally conductive fillers and having excellent thermal conductivity have been proposed, including those in which highly thermally conductive inorganic particles are selected as the thermally conductive filler and the inorganic particles are oriented perpendicular to the sheet surface. For example, a thermally conductive sheet in which the thermally conductive filler (boron nitride) is oriented in a direction approximately 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 the present disclosure is to provide a thermally conductive sheet with 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 with 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 the thermally conductive sheet contains a metal component having a melting point of 200°C or lower. <2> The thermally conductive sheet according to <1>, wherein the metal component is in particulate form. <3> The thermally conductive sheet according to <1> or <2>, wherein the metal component is located on at least a portion of a main surface of the thermally conductive layer. <4> The thermally conductive sheet according to any one of <1> to <3>, wherein the melting point of the metal component is 60°C or higher. <5> The thermally conductive sheet according to any one of <1> to <4>, wherein the metal component includes at least one element selected from the group consisting of tin, bismuth, indium, zinc, lead, gallium, cadmium, thallium, and antimony. <6> The thermally conductive sheet according to any one of <1> to <5>, wherein the mass ratio of the graphite particles (A) to the carbon fibers in the thermally conductive layer is 100:0 to 100:30. <7> 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 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, and wherein, when the thermally conductive sheet is pressure-bonded between a heating element and a heat dissipating element, the porosity calculated as the ratio of the area of ​​a gas region to the area of ​​a measurement region is 0% to 8% at at least one of the interface between the heating element and the thermally conductive sheet and the interface between the heat dissipating element and the thermally conductive sheet. <8> 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 <6>, which is disposed between the heat generating element and the heat dissipation element; wherein the thermally conductive layer has a metal region containing the metal component located on at least a part 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.<9> A heat dissipation device comprising a heat generating element, a heat radiator, and the thermally conductive sheet according to any one of <1> to <7> disposed between the heat generating element and the heat radiator, wherein at least one of the interface between the heat generating element and the thermally conductive sheet and the interface between the heat radiator and the thermally conductive sheet has a porosity of 0% to 8%, calculated as a ratio of the area of ​​a gas region to the area of ​​a measurement region. <10> A method for producing the thermally conductive sheet according to any one of <1> to <6>, comprising the steps of: preparing a composition containing the graphite particles (A); and producing a thermally conductive sheet containing the metal component using the composition. <11> A method for producing a thermally conductive sheet according to <10>, wherein the step of producing the thermally conductive sheet comprises the steps of forming the thermally conductive layer and attaching the metal component to at least a portion of the surface of the thermally conductive layer. <12> A method for producing a thermally conductive sheet according to <10> or <11>, wherein the composition prepared in the step of preparing the composition contains the graphite particles and the metal component.

[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, in which a particulate low-melting-point metal component is located on the main surface of a thermally conductive layer. FIG. 2 is a schematic diagram of a thermally conductive sheet according to one embodiment of the present invention, in which a particulate low-melting-point metal component is located inside a thermally conductive layer. FIG. 3 is a schematic diagram of a thermally conductive sheet according to one embodiment of the present invention, in which a metal region containing a low-melting-point metal component is located on the main surface of a thermally conductive layer. FIG. 4 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. 5 is a diagram showing the interface state determined by image analysis in Examples 1 to 4 and Comparative Example 1.

[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) (also simply referred to as "graphite particles (A)") selected from the group consisting of scaly particles, ellipsoidal particles, and rod-shaped particles, in which 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 the thermal conduction sheet contains a metal component having a melting point of 200°C or lower (also referred to as a "low-melting-point metal component").

[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 the inclusion of a low-melting-point metal component in a thermally conductive sheet results in lower thermal resistance. The reason for this is speculated as follows. However, the present disclosure is not limited to the following 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 heating element or a heat sink, that contacts the thermally conductive sheet (also referred to as "contact thermal resistance"). In the thermally conductive sheet of the present disclosure, a low-melting-point metal component with a relatively low melting point is used, and the low-melting-point metal component is melted by heat when the thermally conductive sheet is heated and pressed to an adherend, such as a heating element or a heat sink. Furthermore, pressure application makes it easier for the molten low-melting-point metal component to localize at the interface between the thermally conductive sheet and the adherend, allowing the thermally conductive sheet and the adherend to be closely attached via the molten low-melting-point metal component. In this case, gaps that occur when the thermal conductive sheet and the adherend are heated and pressed together (for example, gaps resulting from the unevenness of the thermal conductive sheet) are filled with molten low-melting point metal components, 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 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 a low-melting-point metal component melted by heating. 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 melted low-melting-point metal component, significantly reducing contact thermal resistance.

[0017] The thermal conductive sheet of the present disclosure contains at least graphite particles (A) and a low-melting-point metal component, and may contain other components described below within the scope of the present disclosure. Materials used in the thermal conductive sheet of the present disclosure will be described below.

[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 fibers, 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] The content of spherical graphite particles, artificial graphite particles, acid-treated graphite particles, or carbon fibers in the thermally conductive layer may each independently be 0% by volume to 10% by volume, 0% by volume to 5% by volume, or 0% by volume to 1% by volume. The mass ratio of graphite particles (A) to carbon fibers in the thermally conductive layer, graphite particles (A):carbon fibers, may be 100:0 to 100:30, 100:0 to 100:20, or 100:0 to 100:10. Carbon fibers are generally hard, so having a smaller amount of carbon fibers than graphite particles (A) ensures the flexibility of the thermally conductive sheet and tends to suppress an increase in contact thermal resistance.

[0038] <Metal Component> The thermally conductive sheet of the present disclosure contains a metal component having a melting point of 200° C. or lower (low-melting-point metal component).

[0039] In the thermally conductive sheet of the present disclosure, the low-melting-point metal component may be in particulate form. In this case, the thermally conductive sheet of the present disclosure may be a member before being thermocompression-bonded to an adherend such as a heating element or a heat dissipating element. In the thermally conductive sheet that has been thermocompression-bonded to an adherend such as a heating element or a heat dissipating element, the particulate low-melting-point metal component has been in a molten state, so the low-melting-point metal component does not need to be in particulate form.

[0040] When the low-melting point metal component is in the form of particles, the particle size of the low-melting point metal component is not particularly limited, and may be 0.5 μm to 60 μm, 1 μm to 30 μm, or 5 μm to 15 μm.

[0041] The particle size (D50) of the low-melting-point metal component 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.

[0042] In the thermally conductive sheet of the present disclosure, the location of the low-melting-point metal component is not particularly limited, and may be, for example, located on the surface of the thermally conductive layer or may be contained within the thermally conductive layer. In the thermally conductive sheet of the present disclosure, it is preferable that the low-melting-point metal component is located on at least a portion of the main surface of the thermally conductive layer, from the viewpoint that gaps that occur when the thermally conductive sheet and the adherend are thermocompression-bonded can be suitably filled with the molten low-melting-point metal component, thereby suitably reducing contact thermal resistance.

[0043] When a low-melting point metal component is located on at least a portion of the main surface of the thermal conduction layer, the low-melting point metal component may be disposed on the entire main surface, or on a portion of the main surface (for example, the portion that comes into contact with an adherend such as a heating element or a heat sink).

[0044] When a low-melting point metal component is located on at least a portion of the main surface of the thermal conduction layer, the low-melting point metal component may be arranged on one main surface, or the low-melting point metal component may be arranged on two main surfaces.

[0045] The melting point of the low-melting-point metal component is not particularly limited as long as it is 200°C or less, and is preferably 60°C or higher from the viewpoint of suppressing melting of the low-melting-point metal component when the thermal conductive sheet is used for heat dissipation purposes. From the viewpoint of more suitably reducing contact thermal resistance, it is preferably 80°C to 180°C, and more preferably 80°C to 160°C.

[0046] The composition of the low-melting-point metal component is not limited as long as it contains a metal element. Metal elements also include non-metal elements that can exhibit properties similar to those of metal elements. The low-melting-point metal component preferably contains at least one element selected from the group consisting of tin, bismuth, indium, zinc, lead, gallium, cadmium, thallium, and antimony.

[0047] The low-melting point metal component is preferably a low-melting point solder having a melting point of 200° C. or less, and more preferably a low-melting point lead-free solder having a melting point of 200° C. or less. Specific examples of low-melting point solder include Sn—Bi solder, Sn—In solder, Bi—In solder, Sn—Zn solder, Bi—Sn—In solder, and Sn—Zn—Bi solder.

[0048] From the viewpoint of the balance between thermal conductivity and adhesion, the content of the low-melting-point metal component contained in the thermal conductive sheet is preferably 0.1 to 20% by volume, more preferably 0.5 to 15% by volume, and even more preferably 1 to 10% by volume, of the total amount of the thermal conductive sheet. In the present disclosure, the content of the low-melting-point metal component contained in the thermal conductive sheet refers to the total content of the low-melting-point metal component disposed on the surface of the thermal conductive layer and the low-melting-point metal component contained inside the thermal conductive layer.

[0049] <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°).

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] <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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] <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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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).

[0068] 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.

[0069] <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.

[0070] Commercially available phenolic antioxidants include, for example, Adekastab AO-50, Adekastab AO-60, and Adekastab AO-80 manufactured by ADEKA Corporation.

[0071] 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.

[0072] <Other Components> The thermally conductive layer included in the thermally conductive sheet may contain other components in addition to the graphite particles (A), low-melting-point metal component, liquid component (B), acrylic ester-based polymer (C), hot-melt agent (D), and 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] The average thickness of the thermally conductive sheet is not particularly limited and can be selected appropriately depending on the purpose. The thickness of the thermally conductive sheet 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 sheet may be 50 μm to 3000 μm, and from the viewpoint of thermal conductivity and adhesion, it is preferably 100 μm to 500 μm, and more preferably 100 μm to 300 μm. The average thickness of the thermally conductive sheet is obtained by measuring the thickness at three random locations using a micrometer and calculating the arithmetic mean value.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] Embodiments of the thermally conductive sheet will be described with reference to FIGS. 1 to 3. The thermally conductive sheet of the present disclosure is not limited to the following embodiments. In the thermally conductive sheet 1A shown in FIG. 1, a particulate low-melting-point metal component 12A is located on one main surface of the thermally conductive layer 11, and a particulate low-melting-point metal component 12C is located on the other main surface of the thermally conductive layer 11. In the thermally conductive sheet 1B shown in FIG. 2, a particulate low-melting-point metal component 12B is contained within the thermally conductive layer 11. In the thermally conductive sheet 1 shown in FIG. 3, a metal region 13A containing a low-melting-point metal component is located on one main surface of the thermally conductive layer 11, and a metal region 13C containing a particulate low-melting-point metal component is located on the other main surface of the thermally conductive layer 11.

[0081] (Modified Example of Thermal Conduction Sheet) A modified example of 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, 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 when the thermal conduction sheet is pressure-bonded between a heating element and a heat dissipation element, the porosity calculated as the ratio of the area of ​​the gas region to the area of ​​the measurement region is 0% to 8% at at least one of the interface between the heating element and the thermal conduction sheet and the interface between the heat dissipation element and the thermal conduction sheet.

[0082] When the thermally conductive sheet is pressure-bonded between a heat generating element and a heat dissipating element, for example, when the heat dissipating device described below is formed, the void ratio is 0% to 8%. As a result, gaps that occur when the thermally conductive sheet and the heat generating element or heat dissipating element are heat-bonded together by heat compression (for example, gaps due to the unevenness of the thermally conductive sheet and gaps due to the unevenness of the heat generating element or heat dissipating element) are filled with the molten low-melting-point metal component, significantly reducing the contact thermal resistance.

[0083] From the viewpoint of further reducing the contact thermal resistance, the porosity is preferably 0% to 6%, and more preferably 0% to 4%. 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 proportion of the area of ​​the unadhered gas region is calculated, and the porosity of the interface can be determined based on the following formula: Porosity of the interface (%) = 100 x (area of ​​the gas region / area of ​​the measurement region)

[0084] The thermal conductive sheet according to the present disclosure may be combined with the thermal conductive sheet according to the present disclosure and its preferred embodiments as described above. For example, the thermal conductive sheet according to the present disclosure may further include a metal component having a melting point of 200° C. or less.

[0085] [Method for producing thermally conductive sheet] The method for producing the thermally conductive sheet is not particularly limited as long as it is a method that can produce a thermally conductive sheet having the above-described configuration. Examples of the method for producing the thermally conductive sheet include the following methods.

[0086] In one embodiment, the method for producing a thermally conductive sheet includes a step of preparing a composition containing graphite particles (A) and any other components (also referred to as a "preparation step"), and a step of producing a thermally conductive sheet containing a low-melting-point metal component using the composition (also referred to as a "production step").

[0087] The method for incorporating a low-melting point metal component into the thermal conductive sheet is not particularly limited, and examples thereof include Method 1, in which the low-melting point metal component is mixed with graphite particles (A) or the like when preparing the composition, and Method 2, in which the low-melting point metal component is attached to at least a portion of the surface of the thermal conductive layer after the thermal conductive layer is formed.

[0088] In Method 1, for example, the composition prepared in the preparing step may contain graphite particles (A), a low-melting-point metal component, and any other components. The composition may be prepared by mixing the graphite particles (A), the low-melting-point metal component, and any other components. In Method 1, the step of producing the thermally conductive sheet may include a step of forming the thermally conductive layer (also referred to as a "forming step").

[0089] As a method 2, for example, the process of producing a thermally conductive sheet may include a process of forming the thermally conductive layer (also referred to as a "forming process") and a process of adhering a low-melting-point metal component to at least a portion of the surface of the thermally conductive layer (also referred to as an "adhering process").

[0090] The forming step in Method 1 and Method 2 preferably includes a step of forming the composition prepared in the preparation step into a sheet to obtain a sheet (also referred to as a "sheet preparation step"), a step of preparing a laminate of the sheets (also referred to as a "laminate preparation step"), and a step of slicing the side end surfaces of the laminate (also referred to as a "slicing step").

[0091] In Method 1, a thermally conductive sheet containing a low-melting-point metal component is obtained through the above-mentioned slicing step. If necessary, after obtaining the thermally conductive sheet containing a low-melting-point metal component, the low-melting-point metal component may be attached to at least a portion of the surface of the thermally conductive layer (i.e., Method 1 and Method 2 may be used in combination).

[0092] In Method 2, it is preferable to carry out a step of adhering a low-melting-point metal component to at least a portion of the surface of the thermally conductive layer obtained in the slicing step (also referred to as an "adhering step"). By going through the adhering step, a thermally conductive sheet containing a low-melting-point metal component can be produced.

[0093] The method for manufacturing a thermally conductive sheet may further include a step of laminating the sliced ​​sheet obtained in the slicing step (or, if an adhesion step is included, a thermally conductive sheet containing a low-melting point metal component) by attaching it to a protective film (also referred to as a "lamination step").

[0094] 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.

[0095] <Preparation Step> In the preparation step, a composition containing graphite particles (A) and any other components (for example, a low-melting point metal component, 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.

[0096] <Sheet Preparation Step> The sheet preparation step may be carried out 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 carried out 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.

[0097] <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.

[0098] <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 thermally 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.

[0099] The adhesion step may be performed by any method as long as it can adhere the low-melting-point metal component to at least a portion of the surface of the thermally conductive layer obtained in the slicing step. For example, metal particles having a melting point of 200° C. or less may be sprinkled on at least a portion of the surface of the thermally conductive layer, or the low-melting-point metal component may be adhered by a method such as coating, vapor deposition, or sputtering.

[0100] <Laminating step> The laminating step may be any method as long as it can attach the sliced ​​sheet obtained in the slicing step (or the thermally conductive sheet containing a low-melting point metal component, if an adhesion step is included) to the protective film, and is not particularly limited.

[0101] [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 a metal region containing a low-melting-point metal component 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 metal region 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 metal region is located on a region of the main surface located on the heat generating element side facing the heat generating element and a region of the main surface located on the heat dissipation element side facing the heat dissipation element.

[0102] The metal region containing the low-melting-point metal component may be layered or may be scattered on the main surface of the thermally conductive sheet. The metal region may be located on at least a portion of the main surface of the thermally conductive sheet, and may also be contained within the thermally conductive sheet.

[0103] 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.

[0104] From the viewpoint of reducing contact thermal resistance and thermal conductivity, the maximum thickness of the metal region may be 3 μm to 20 μm or 5 μm to 15 μm on one side. A maximum thickness of 20 μm or less tends to suppress an increase in bulk thermal resistance, which corresponds to the thermal conductivity of the metal itself. A maximum thickness of 3 μm or more tends to sufficiently fill gaps that occur when the thermally conductive sheet and the adherend are thermocompressed together, and tends to more suitably reduce contact thermal resistance. The maximum thickness of the thermally conductive layer and the maximum thickness of the metal region may be measured by observing the cross section of the object to be measured using an electron microscope. Alternatively, the maximum thickness of the thermally conductive layer may be measured using a micrometer, or the maximum thickness of the thermally conductive layer and the maximum thickness of the thermally conductive sheet having the metal region may be measured, and the maximum thickness of the metal region may be measured by subtracting the maximum thickness of the thermally conductive layer from the maximum thickness of the thermally conductive sheet.

[0105] An example of a heat dissipation device will be described in more detail below with reference to FIG. 4 . 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 (heat sink). 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, the semiconductor chip 2, and the 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. Metal regions containing a low-melting point metal component are located on the main surface of the thermal conductive sheet 1 facing the semiconductor chip 2 and on the main surface of the thermal conductive sheet 1 facing the heat spreader 3. For example, as in the thermal conductive sheet 1 shown in Figure 3, metal regions 13A and 13C may be located on the main surface of the thermal conductive sheet 1 facing the semiconductor chip 2 and on the main surface of the thermal conductive sheet 1 facing the heat spreader 3, respectively. Furthermore, the metal region 13A may be in contact with the heat spreader 3, and the metal region 13C may be in contact with the semiconductor chip 2.

[0106] 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.

[0107] The temperature range in which the thermally conductive sheet can be particularly suitably used may be, for example, −40° 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.

[0108] 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.

[0109] 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.

[0110] For example, a thermally conductive sheet is placed between the heating element and the heat sink, fixed with a jig capable of applying a pressure of approximately 0.05 MPa to 1 MPa, and the heating element is then heated in this state, or heated to approximately 80°C to 200°C (e.g., a temperature above the melting point of the low-melting-point metal component) 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 thermally conductive sheet can prevent it from becoming thin or causing excessive distortion or residual stress in surrounding components.

[0111] 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 thermally conductive sheet described above. For example, the thermally conductive sheets shown in Figures 1 to 3 may be placed between the heat generating element and the heat dissipating element.

[0112] When the thermally conductive sheet 1A shown in Figure 1 is used, by applying heat and pressure to the thermally conductive sheet 1A placed between the heat generating element and the heat dissipating element, the low-melting-point metal components 12A and 12C located on the main surfaces of the thermally conductive sheet 1A melt. The gaps that occur when the thermally conductive sheet 1A is heated and pressed to the heat generating element and the heat dissipating element are filled with the molten low-melting-point metal components (corresponding to the metal regions). This reduces the gaps between the thermally conductive sheet and the heat generating element or the heat dissipating element, significantly reducing the contact thermal resistance.

[0113] When the thermally conductive sheet 1B shown in Figure 2 is used, by applying heat and pressure to the thermally conductive sheet 1B placed between the heat generating element and the heat dissipating element, the low-melting-point metal component 12B contained within the thermally conductive sheet 1B melts and easily seeps out onto the surface of the thermally conductive sheet 1B. This causes the gaps that occur when the thermally conductive sheet 1B is heated and pressed to the heat generating element and the heat dissipating element to be filled with the melted low-melting-point metal component (corresponding to the metal region). This reduces the gap between the thermally conductive sheet and the heat generating element or heat dissipating element, significantly reducing the contact thermal resistance.

[0114] As described above, by manufacturing a heat dissipation device using the thermally conductive sheets 1A and 1B shown in Figures 1 and 2, the particulate low-melting-point metal component melts in the gap between the thermally conductive sheet and the heat generating element or heat dissipation element. As a result, the gap is filled with a metal region derived from the low-melting-point metal component, significantly reducing the contact thermal resistance. When a heat dissipation device is manufactured using the thermally conductive sheets 1A and 1B shown in Figures 1 and 2, the thermally conductive sheet included in the heat dissipation device has metal regions derived from the low-melting-point metal component on two main surfaces of the thermally conductive layer, as shown in Figure 3, and the metal regions located on the two main surfaces are in surface contact with the heat generating element and the heat dissipation element, respectively.

[0115] 3 is used, the metal regions 13A and 13C melt when the thermally conductive sheet 1 is placed between the heat generating element and the heat dissipating element and then heated and pressurized. The gaps that occur when the thermally conductive sheet 1 is heated and pressed to the heat generating element and the heat dissipating element are filled with the melted metal regions 13A and 13C. This reduces the gaps between the thermally conductive sheet and the heat generating element or the heat dissipating element, significantly reducing the contact thermal resistance.

[0116] 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.

[0117] 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.

[0118] (Modified example of heat dissipation device) A modified example of the heat dissipation device of the present disclosure comprises a heating element, a heat dissipation element, and a thermally conductive sheet according to the modified example described above that is placed between the heating element and the heat dissipation element, and at least one of the interface between the heating element and the thermally conductive sheet and the interface between the heat dissipation element and the thermally conductive sheet, the void ratio calculated as the ratio of the area of ​​the gas region to the area of ​​the measurement region is 0% to 8%.

[0119] In a heat dissipation device in which the heat conduction sheet is disposed between a heat generating element and a heat dissipation element, the void ratio is 0% to 8%. As a result, gaps that occur when the heat conduction sheet and the heat generating element or heat dissipation element are thermocompressed together (for example, gaps resulting from the unevenness of the heat conduction sheet and gaps resulting from the unevenness of the heat generating element or heat dissipation element) are filled with the molten low-melting-point metal component, significantly reducing contact thermal resistance.

[0120] The heat dissipation device according to the present disclosure may be appropriately combined with the heat dissipation device according to the present disclosure and its preferred embodiments described above. For example, in the heat dissipation device according to the present disclosure, the heat conduction layer may have a metal region containing a low-melting-point metal component 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.

[0121] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0122] [Examples 1 and 2] The following materials were charged into a kneader mixer (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 compositions.

[0123] <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")

[0124] (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.

[0125] (Preparation of thermally conductive sheet) Solder particles (component Sn-Bi (tin-bismuth alloy), Tin bismuth alloy powder (manufactured by 5N Plus Inc.) MCP137 (melting point 137°C), average particle size: 10 μm) were sprinkled on the two main surfaces of the thermally conductive layer obtained as described above. This resulted in a thermally conductive sheet with solder particles attached to the two main surfaces of the thermally conductive layer. The maximum thickness of the area of ​​the solder particles attached to the thermally conductive sheet is shown in Table 1.

[0126] [Examples 3 and 4] Instead of the process of dusting solder particles on the two main surfaces of the thermally conductive layer in Examples 1 and 2, solder particles (component Sn-Bi (tin-bismuth alloy), melting point 137°C) were added to the composition during the kneading process for producing the thermally conductive layer, and the composition was prepared to have the mixing ratio (volume %) shown in Table 1. The thermally conductive layers were produced by kneading, laminating, pressing, and slicing in the same manner as in Examples 1 and 2. In Examples 3 and 4, the thermally conductive layer containing solder particles was used as the thermally conductive sheet.

[0127] [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 to 4. In Comparative Example 1, the thermally conductive layer was used as a thermally conductive sheet without using solder particles.

[0128]

[0129] The thermal conductive sheets of Examples 1 to 4 and Comparative Example 1 were evaluated by the following methods. The results are shown in Table 2 and FIG.

[0130] (Measurement of thermal resistance) The thermal resistance was measured using a tabletop xenon flash analyzer (LFA 467 Hyper Flash). The thermally conductive sheets of Examples 1 to 4 or Comparative Example 1, punched to a diameter of 14 mm, were sandwiched between 1 mm copper plates to prepare samples with a three-layer structure. The sample preparation conditions were a temperature of 150°C, pressure of 120 psi for 3 minutes, and then sufficient cooling at 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-layer structure, and the thermal conductivity λ was calculated from the obtained thermal conductivity λ and the 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)

[0131] (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 Co., Ltd.), 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 in the black area and 84 to 255 in the white area), and the proportion of the area of ​​the unadhered gas region out of the Φ11 mm 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)

[0132] (Thickness Evaluation) Using a micrometer, the maximum thickness of the thermally conductive sheet before compression ("Thickness before compression" in Table 2), the maximum thickness of the metal region before compression ("Thickness of the metal region before compression" in Table 2), and the maximum thickness of the thermally conductive sheet after compression ("Thickness after compression" in Table 2) were measured. Regarding the maximum thickness of the metal region before compression, the maximum thickness of the thermally conductive layer before compression and the maximum thickness of the thermally conductive sheet before compression were each determined, and the maximum thickness of the metal region was determined by subtracting the maximum thickness of the thermally conductive layer before compression from the maximum thickness of the thermally conductive sheet before compression.

[0133]

[0134] As shown in Examples 1 to 4 and Comparative Example 1, it was possible to reduce the thermal resistance of the thermally conductive sheet by using a low-melting-point metal component. Furthermore, it was possible to reduce the thermal resistance of the thermally conductive sheet by reducing the porosity at the interface.

[0135] The disclosure of PCT / JP2022 / 028527 is incorporated herein by reference in its entirety. All publications, patent applications, and technical standards mentioned herein are incorporated herein by reference to the same extent as if each individual publication, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. The thermal conductive layer includes at least one type of graphite particles (A) selected from the group consisting of scaly particles, ellipsoidal particles, and rod-shaped particles, and 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, A thermally conductive sheet comprising a metal component having a melting point of 200°C or lower.

2. The thermal conductive sheet according to claim 1 , wherein the metal component is in particulate form.

3. The thermally conductive sheet according to claim 1 , wherein the metal component is located on at least a portion of a main surface of the thermally conductive layer.

4. 3. The thermal conductive sheet according to claim 1, wherein the melting point of the metal component is 60° C. or higher.

5. 3. The thermal conductive sheet according to claim 1, wherein the metal component comprises at least one element selected from the group consisting of tin, bismuth, indium, zinc, lead, gallium, cadmium, thallium, and antimony.

6. The heat conductive sheet according to claim 1 or 2, wherein the mass ratio of the graphite particles (A) to the carbon fibers in the heat conductive layer, that is, graphite particles (A):carbon fibers, is 100:0 to 100:

30.

7. a heat conductive sheet including a heat 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, 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 being oriented in a thickness direction, A thermally conductive sheet in which, when the thermally conductive sheet is pressed between a heating element and a heat dissipating element, at least one of the interfaces between the heating element and the thermally conductive sheet and the interface between the heat dissipating element and the thermally conductive sheet, the void ratio calculated as the ratio of the area of ​​the gas region to the area of ​​the measurement region is 0% to 8%.

8. A heat generating element, a heat sink, and the thermally conductive sheet according to claim 1 or 2, which is disposed between the heat generating element and the heat sink, a metal region containing the metal component is located on at least a portion 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.

9. A heat generating element, a heat sink, and the thermally conductive sheet according to claim 1 or 2, which is disposed between the heat generating element and the heat sink, 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 is 0% to 8% 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.

10. A method for producing the thermal conductive sheet according to claim 1 or 2, comprising the steps of: A method for producing a thermal conductive sheet, comprising: preparing a composition containing the graphite particles (A); and producing a thermal conductive sheet containing the metal component using the composition.

11. The method for producing a thermally conductive sheet according to claim 10 , wherein the step of producing the thermally conductive sheet comprises the steps of: forming the thermally conductive layer; and adhering the metal component to at least a portion of a surface of the thermally conductive layer.

12. The method for producing a thermal conductive sheet according to claim 10 , wherein the composition prepared in the step of preparing the composition contains the graphite particles and the metal component.