Liquid thermally conductive material, combination of members for manufacturing thermally conductive sheet, thermally conductive sheet, heat dissipation device, and method for producing thermally conductive sheet

Abstract

A liquid thermally conductive material that has a thermal conductivity of 5 W / (m•K) or more and that is for forming a liquid layer by being applied on at least a part of a thermally conductive layer containing thermally conductive particles.

Description

Liquid thermally conductive material, combination of components for producing thermally conductive sheet, thermally conductive sheet, heat dissipation device, and method for producing thermally conductive sheet

[0001] The present disclosure relates to a liquid thermally conductive material, a combination of members for producing a thermally conductive sheet, a thermally conductive sheet, a heat dissipation device, and a method for producing 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] The object of the present disclosure is to provide a liquid thermal conductive material that can reduce thermal resistance when applied to a thermal conductive layer such as a thermal conductive sheet, a combination of components for producing a thermal conductive sheet that includes the above-mentioned liquid thermal conductive material or a liquid thermal conductive material containing a metal component and that can produce a thermal conductive sheet with low thermal resistance, as well as a thermal conductive sheet with low thermal resistance, a heat dissipation device that includes the same, and a method for producing a thermal conductive sheet that can produce a thermal conductive sheet with low thermal resistance.

[0009] Specific means for solving the above problems include the following aspects. <1> A liquid thermally conductive material having a thermal conductivity of 5 W / (m·K) or more, for forming a liquid layer by applying it to at least a part of a thermally conductive layer containing thermally conductive particles. <2> The liquid thermally conductive material according to <1>, comprising a thermally conductive filler and a resin component. <3> The liquid thermally conductive material according to <2>, wherein the particle size of the thermally conductive filler is 0.1 μm to 50 μm. <4> The liquid thermally conductive material according to <2> or <3>, wherein the resin component contains a thermosetting resin component. <5> The liquid thermally conductive material according to any one of <1> to <4>, having a viscosity at 25°C of 4000 Pa·s or less. <6> A combination of a member for producing a thermally conductive sheet, comprising the liquid thermally conductive material according to any one of <1> to <5> and a thermally conductive material containing thermally conductive particles. <7> A combination of members for producing a thermal conduction sheet, comprising a liquid thermal conduction material containing a metal component and a thermal conduction material containing thermally conductive particles. <8> The combination of members for producing a thermal conduction sheet according to <7>, in which the melting point of the metal component is 50°C or lower. <9> A thermal conduction sheet comprising: a thermal conduction layer containing a thermal conduction material containing thermally conductive particles; and a liquid layer located on at least a part of a main surface of the thermal conduction layer, the liquid layer containing a first liquid thermal conduction material which is the liquid thermal conduction material according to any one of <1> to <5>, or a second liquid thermal conduction material which is a liquid thermal conduction material containing a metal component. <10> The thermal conduction sheet according to <9>, in which the thermally conductive particles include at least one type of graphite particles (A) selected from the group consisting of scaly particles, ellipsoidal particles, and rod-shaped particles, and in which 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 of the thermal conduction layer. <11> The thermally conductive sheet according to <9> or <10>, wherein the liquid layer has a maximum thickness of 0.5 μm to 20 μm. <12> The thermally conductive sheet according to any one of <9> to <11>, wherein the liquid layer contains the first liquid thermally conductive material and is curable by heating.<13> A heat dissipation device comprising: a heat generating element, a heat dissipation element, and the thermally conductive sheet according to any one of <9> to <11>, which is disposed between the heat generating element and the heat dissipation element, wherein the liquid 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 element and the main surface that faces the heat dissipation element. <14> A heat dissipation device comprising: a heat generating element, a heat dissipation element, and a thermally conductive sheet disposed between the heat generating element and the heat dissipation element, and which comprises an adhesive layer formed by curing the liquid layer of the thermally conductive sheet according to <12>, 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 element and the main surface that faces the heat dissipation element. <15> A method for manufacturing a thermally conductive sheet according to any one of <9> to <12>, comprising the steps of: preparing a composition containing the thermally conductive particles; forming the thermally conductive layer using the composition; and forming a liquid layer on at least a portion of a main surface of the thermally conductive layer. <16> A method for manufacturing a thermally conductive sheet according to <10>, comprising the steps of: preparing a composition containing the graphite particles (A); forming the composition into a sheet to obtain a sheet; producing a laminate of the sheets; slicing side end surfaces of the laminate; and forming a liquid layer on at least a portion of a main surface of the sliced ​​sheet, which corresponds to the thermally conductive layer.

[0010] According to the present disclosure, it is possible to provide a liquid thermally conductive material that can reduce thermal resistance when applied to a thermally conductive layer such as a thermally conductive sheet, a combination of components for producing a thermally conductive sheet that includes the above-mentioned liquid thermally conductive material or a liquid thermally conductive material containing a metal component and that can produce a thermally conductive sheet with low thermal resistance, as well as a thermally conductive sheet with low thermal resistance, a heat dissipation device including the same, and a method for producing a thermally conductive sheet that can produce a thermally conductive sheet with low thermal resistance.

[0011] 1 is a schematic diagram of a thermal conductive sheet according to one embodiment of the present invention; 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; 3 is a diagram showing the state of the interface by image analysis in Examples 1 to 4 and Comparative Examples 1 and 2.

[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] [Liquid Thermal Conduction Material] The liquid thermal conduction material of the present disclosure has a thermal conductivity of 5 W / (m·K) or more and is a material that forms a liquid layer by being applied to at least a portion of a thermally conductive layer containing thermally conductive particles. In the present disclosure, the liquid thermal conduction material refers to a thermally conductive material that is liquid at at least a portion of a temperature between 0°C and 50°C. In the present disclosure, the thermal conductivity can be measured by the xenon flash (Xe-flash) method.

[0014] Resistance due to gaps arising from contact between a thermally conductive sheet and an adherend, such as a heat-generating body or a heat-dissipating body, is difficult to reduce by varying the configuration of the thermally conductive particles contained in the thermally conductive sheet or the composition of the thermally conductive sheet. The liquid thermally conductive material of the present disclosure is a material for forming a thermally conductive sheet or the like having a liquid layer by being applied to at least a portion of a thermally conductive layer containing thermally conductive particles. When the thermally conductive layer having the liquid layer formed thereon is thermocompressed to an adherend, such as a heat-generating body or a heat-dissipating body, the liquid layer flows between the thermally conductive layer and the adherend. This allows gaps between the thermally conductive sheet and the adherend (e.g., gaps resulting from the unevenness of the thermally conductive sheet) to be filled with the flowing liquid layer, thereby allowing the thermally conductive sheet and the adherend to be closely attached via the liquid layer. As a result, contact thermal resistance is significantly reduced. Furthermore, since the thermal conductivity of the liquid thermal conductive material is 5 W / (m·K) or more, the decrease in thermal conductivity of the thermal conductive sheet due to the liquid layer being placed on the thermal conductive layer is suppressed, and the increase in thermal resistance of the thermal conductive sheet is suppressed.

[0015] 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 liquid thermally conductive material of the present disclosure, the thermally conductive sheet can be closely attached to an adherend having an uneven surface via a liquid 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 liquid layer, thereby significantly reducing contact thermal resistance.

[0016] The liquid thermally conductive material of the present disclosure preferably contains a thermally conductive filler and a resin component. The resin component may contain a component that is liquid at 25°C.

[0017] Examples of the thermally conductive filler include metal-containing particles and non-metallic particles that have excellent thermal conductivity. 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.

[0018] The thermally conductive filler may be at least one type of particle selected from silver, aluminum oxide, aluminum hydroxide, magnesium oxide, beryllium oxide, boron nitride, aluminum nitride, silicon nitride, silicon carbide, silicon dioxide, aluminum fluoride, calcium fluoride, zinc oxide, diamond, gallium, indium, and tin. The thermally conductive filler contained in the liquid thermally conductive material may be one type alone or a combination of two or more types. The liquid thermally conductive material of the present disclosure may or may not contain low-melting-point metal particles having a melting point of 200°C or less.

[0019] 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.

[0020] 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.

[0021] The resin component may be a non-curable resin component, or may be a curable resin component such as a thermosetting or photocurable resin component. From the viewpoint of adhesion to an adherend upon curing, thermal conductivity, etc., the resin component preferably contains a thermosetting resin component. The resin component may contain one type of resin component, or may contain two or more types of resin components.

[0022] The non-curable resin component is preferably a non-curable resin component that is liquid at 25° C., and more preferably a liquid silicone compound, a liquid (meth)acrylic compound, a liquid polyester compound, etc. The thermosetting resin component is preferably a thermosetting resin component that is liquid at 25° C., and more preferably a liquid epoxy compound, a curable liquid silicone compound, a curable liquid (meth)acrylic compound, etc.

[0023] From the viewpoint of the balance between thermal conductivity and adhesion, the content of the thermally conductive filler contained in the liquid thermally conductive material is preferably 70% by mass to 98% by mass, more preferably 75% by mass to 95% by mass, and even more preferably 80% by mass to 93% by mass, relative to the total amount of the liquid thermally conductive material.

[0024] From the viewpoint of the balance between thermal conductivity and adhesion, the content of the resin component contained in the liquid thermal conductive material is preferably 2% by mass to 30% by mass, more preferably 5% by mass to 25% by mass, and even more preferably 7% by mass to 20% by mass, relative to the total amount of the liquid thermal conductive material.

[0025] The total content of the thermally conductive filler and resin component contained in the liquid thermally conductive material may be 80% by mass to 100% by mass, or 90% by mass to 100% by mass, based on the total amount of the liquid thermally conductive material.

[0026] The liquid thermally conductive material may or may not contain components other than the thermally conductive filler and the resin component.

[0027] The liquid thermally conductive material of the present disclosure preferably has a viscosity at 25°C of 4000 Pa·s or less, and may be 0.001 Pa·s to 3000 Pa·s, or may be 10 Pa·s to 2000 Pa·s. When the viscosity at 25°C is 4000 Pa·s or less, the liquid layer tends to flow easily between the thermally conductive layer and the adherend, and the gap between the thermally conductive sheet and the adherend tends to be easily filled with the liquid layer. The viscosity at 25°C is 5.0 s or less using a rheometer at 25°C. －１Specifically, the "viscosity" is measured as shear viscosity at a temperature of 25°C using a rotational shear viscometer equipped with a cone plate (diameter 40 mm, cone angle 0°).

[0028] [Combination 1 of members for producing a thermally conductive sheet] Combination 1 of members for producing a thermally conductive sheet of the present disclosure comprises the liquid thermally conductive material of the present disclosure and a thermally conductive material containing thermally conductive particles. The thermally conductive material is a material for forming the thermally conductive layer of the thermally conductive sheet. A thermally conductive sheet can be obtained by applying the liquid thermally conductive material to at least a portion of the thermally conductive layer made of the thermally conductive material to form a liquid layer. The thermally conductive material preferably contains thermally conductive particles and is solid at 25°C.

[0029] The thermally conductive material includes thermally conductive particles. The thermally conductive particles are preferably at least one type of particles selected from graphite, carbon, silver, 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. From the viewpoint of thermal conductivity when formed into a thermally conductive layer, the thermally conductive particles are preferably graphite particles, carbon particles, and boron nitride particles, and more preferably graphite particles.

[0030] The thermally conductive particles are preferably at least one selected from the group consisting of scaly particles, ellipsoidal particles, and rod-shaped particles, and more preferably at least one type of graphite particle selected from the group consisting of scaly particles, ellipsoidal particles, and rod-shaped particles (hereinafter also referred to as "graphite particles (A)"). When the thermally conductive particles are scaly particles, the plane direction is preferably oriented in the thickness direction of the thermally conductive material, when the thermally conductive particles are ellipsoidal particles, the major axis direction is preferably oriented in the thickness direction of the thermally conductive material, and when the thermally conductive particles are rod-shaped particles, the major axis direction is preferably oriented in the thickness direction of the thermally conductive material.

[0031] A preferred embodiment in which the thermally conductive particles are graphite particles (A) will be described below.

[0032] The graphite particles (A) are preferably oriented in the thickness direction 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. Furthermore, the graphite particles (A) are more preferably 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. The six-membered ring plane is a plane on which a six-membered ring is formed in a hexagonal crystal system, and refers to the (0001) crystal plane.

[0033] 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 material.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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

[0041] 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 conductive material in the case of rod-shaped particles" means that the angle (hereinafter also referred to as "orientation angle") between 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 and the surface (main surface) of the thermal conductive material is 60° or more. The orientation angle is preferably 80° or more, more preferably 85° or more, and even more preferably 88° or more.

[0042] The orientation angle is an average value obtained by observing a cross section of the thermal conductive material with a SEM (scanning electron microscope) and measuring the angle (orientation angle) formed by 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 with the surface (main surface) of the thermal conductive material for 50 random graphite particles (A).

[0043] The particle size of the graphite particles (A) is not particularly limited. The average particle size of the graphite particles (A), as the mass average particle size, is preferably at least half the average thickness of the thermal conductive material 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 thermal conductive material, an efficient heat conduction path is formed in the thermal conductive material, 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 thermal conductive material, protrusion of the graphite particles (A) from the surface of the thermal conductive material is suppressed, and the surface adhesion of the thermal conductive material tends to be excellent.

[0044] The method for producing a thermally conductive material 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").

[0045] When using the above-mentioned laminated slicing method, the particle diameter of the graphite particles (A) used as the raw material is preferably at least half the average thickness of the thermal conductive material 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 thermal conductive material is, for example, because even if the thermal conductive material contains graphite particles (A) with a particle diameter exceeding the average thickness of the thermal conductive material, the thermal conductive material 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 thermal conductive material. Furthermore, when the graphite particles (A) are sliced ​​together in this way, a large number of graphite particles (A) are produced that penetrate the thermal conductive material in the thickness direction, forming an extremely efficient thermal conduction path and tending to further improve thermal conductivity.

[0046] 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 thermally conductive material 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 thermally conductive material, 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 thermally conductive material, 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.

[0047] 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.

[0048] The thermally conductive material 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.

[0049] From the viewpoint of the balance between thermal conductivity and adhesion, the content of graphite particles (A) in the thermal conductive material 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 thermal conductive material 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.

[0050] 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.

[0051] 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.

[0052] <Component (B) that is liquid at 25°C> The thermal conductive material 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. The viscosity of a component that is liquid at 25°C is 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 rotational shear viscometer equipped with a cone plate (diameter 40 mm, cone angle 0°).

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] As polybutene, for example, NOF Corporation's "NOF Polybutene ＴＭExamples 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.

[0058] 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 (E) described below, the cohesive strength and fluidity upon heating tend to be further enhanced.

[0059] In order to further improve adhesive strength, adhesion, sheet strength, hydrolysis resistance, etc., the content of liquid component (B) in the thermal conductive material 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 liquid component (B) is 10% by volume or more, adhesive strength and adhesion tend to be further improved. When the content of liquid component (B) is 55% by volume or less, decreases in sheet strength and thermal conductivity tend to be more effectively suppressed.

[0060] <Acrylate Ester-Based Polymer (C)> The thermally conductive material may contain an acrylate ester-based polymer (C). The acrylate ester-based polymer (C) is thought to mainly function, for example, as both a tackifier and an elasticity imparting agent that restores the thickness to accommodate warpage.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] The acrylate polymer (C) may be present throughout the thermal conductive material by internal addition, or may be localized on the surface by coating or impregnating the surface. Coating or impregnation on one side is particularly preferred in that strong tackiness can be imparted to only one side, resulting in a sheet with good handleability.

[0065] 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.

[0066] <Hot-melt agent (D)> The thermally conductive material may contain a hot-melt agent (D). The hot-melt agent (D) has the effect of improving the strength of the thermally conductive material and improving the fluidity when heated.

[0067] 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.

[0068] 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 material.

[0069] 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.

[0070] 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).

[0071] The content of the hot melt agent (D) in the thermal conductive material 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.

[0072] <Antioxidant (E)> The thermal conductive material may contain an antioxidant (F) 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 under which it is used, and phenol-based antioxidants are more preferred. The antioxidant (E) may be used alone or in combination of two or more types.

[0073] Commercially available phenolic antioxidants include, for example, Adekastab AO-50, Adekastab AO-60, and Adekastab AO-80 manufactured by ADEKA Corporation.

[0074] The content of the antioxidant (E) in the thermal conductive material 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 thermal conductive material tends to be suppressed.

[0075] <Other Components> The thermally conductive material 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 material 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 viewpoints of excellent safety and improved adhesion due to the plasticizing effect.

[0076] 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.

[0077] 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.

[0078] The content of the flame retardant in the thermal conductive material 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 preventing deterioration of thermal resistance due to the flame retardant components seeping out onto the surface of the thermal conductive layer.

[0079] [Combination 2 of members for producing a thermally conductive sheet] Combination 2 of members for producing a thermally conductive sheet of the present disclosure comprises a liquid thermally conductive material containing a metal component and a thermally conductive material containing thermally conductive particles. A thermally conductive sheet can be obtained by applying the liquid thermally conductive material containing a metal component to at least a portion of a thermally conductive layer composed of the thermally conductive material to form a liquid layer. The preferred form of the thermally conductive material in combination 2 of members for producing a thermally conductive sheet of the present disclosure is the same as the preferred form of the thermally conductive material in combination 1 of members for producing a thermally conductive sheet of the present disclosure described above.

[0080] The combination 2 of members for producing a thermally conductive sheet of the present disclosure is a material for forming a thermally conductive sheet having a liquid layer by applying a liquid thermally conductive material containing a metal component to at least a portion of a thermally conductive layer composed of a thermally conductive material. When the thermally conductive layer having the liquid layer formed thereon is thermocompressed to an adherend such as a heat generating element or a heat dissipating element, the liquid layer flows between the thermally conductive layer and the adherend. This allows the fluidized liquid layer to fill the gap between the thermally conductive sheet and the adherend, thereby allowing the thermally conductive sheet and the adherend to be closely attached via the liquid layer. As a result, contact thermal resistance is significantly reduced. Furthermore, the inclusion of a metal component in the liquid layer gives the liquid layer excellent thermal conductivity, thereby suppressing an increase in the thermal resistance of the thermally conductive sheet.

[0081] (Metal component-containing liquid thermal conductive material) A metal component-containing liquid thermal conductive material refers to a thermally conductive material containing a metal component that is liquid at at least a part of the temperature range of 0° C. to 50° C. The thermal conductivity of the metal component-containing liquid thermal conductive material is preferably 5 W / (m·K) or more, more preferably 10 W / (m·K) or more, and even more preferably 30 W / (m·K) or more.

[0082] The liquid thermally conductive material containing a metal component may be a material consisting of a liquid metal component, or may be a material consisting of a liquid metal component and other components. The content of the metal component in the liquid thermally conductive material may be 50% by mass to 100% by mass, 70% by mass to 100% by mass, or 90% by mass to 100% by mass, based on the total amount of the liquid thermally conductive material.

[0083] The melting point of the metal component is preferably 50°C or lower, more preferably 45°C or lower, and even more preferably 0°C to 40°C.

[0084] Examples of the metal component include gallium, indium, tin, etc. Among these, a metal component containing gallium is preferred.

[0085] [Thermal Conduction Sheet] The thermal conduction sheet of the present disclosure comprises a thermal conduction layer containing a thermally conductive material including thermally conductive particles, and a liquid layer located on at least a portion of a main surface of the thermal conduction layer and containing a first liquid thermal conduction material which is the liquid thermal conduction material of the present disclosure, or a second liquid thermal conduction material which is a liquid thermal conduction material containing a metal component. The preferred form of the first liquid thermal conduction material is the same as the preferred form of the liquid thermal conduction material described above. The preferred form of the second liquid thermal conduction material is the same as the liquid thermal conduction material containing a metal component in the combination 2 of components for preparing a thermal conduction sheet described above.

[0086] The thermally conductive sheet of the present disclosure may have unevenness on the surface that comes into contact with the adherend. In this case, the majority of the thermal resistance is due to resistance (contact thermal resistance) caused by gaps that arise when the thermally conductive sheet contacts an adherend, such as a heat-generating body or a heat-dissipating body. In the thermally conductive sheet of the present disclosure, a liquid layer containing a first liquid thermally conductive material or a second liquid thermally conductive material is disposed on at least a portion of the main surface of the thermally conductive layer. This causes the liquid layer to flow due to heat, pressure, etc., when the thermally conductive sheet is thermocompressed to an adherend, such as a heat-generating body or a heat-dissipating body. The fluidity of the liquid layer fills gaps that arise when the thermally conductive sheet is thermocompressed to an adherend (e.g., gaps caused by the unevenness of the thermally conductive sheet). This reduces the gaps between the thermally conductive sheet and the adherend, allowing the thermally conductive sheet and the adherend to be closely attached, thereby significantly reducing contact thermal resistance.

[0087] 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 a liquid 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 liquid layer, thereby significantly reducing contact thermal resistance.

[0088] 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 measuring the thickness at three random locations by observing the cross section of the object to be measured using an electron microscope, and the arithmetic average value of the measured values.

[0089] In the thermally conductive sheet of the present disclosure, the liquid layer may be located on at least a portion of the main surface of the thermally conductive layer, and the liquid 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 an adherend such as a heating element or a heat sink).

[0090] The thermally conductive layer may have a liquid layer positioned on one main surface or two main surfaces.

[0091] The maximum thickness of the liquid layer is preferably 0.5 μm to 50 μm, more preferably 0.5 μm to 30 μm, and even more preferably 0.5 μm to 20 μm. A maximum liquid layer thickness of 0.5 μm or more tends to further reduce the gap between the adherend and the thermally conductive sheet, thereby further reducing the contact thermal resistance. A maximum liquid layer thickness of 50 μm or less tends to improve the thermal conductivity of the thermally conductive sheet and inhibit leakage of the liquid layer to the outside when the adherend and the thermally conductive sheet are brought into contact. The maximum thickness of the thermally conductive layer and the maximum thickness of the liquid layer may be measured by observing the cross section of the measurement object 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 including the liquid layer may be measured, and the maximum thickness of the liquid layer may be measured by subtracting the maximum thickness of the thermally conductive layer from the maximum thickness of the thermally conductive sheet. When a liquid layer is formed on two main surfaces of the thermally conductive layer, the maximum thickness of the liquid layer means the maximum value of the total thickness of the liquid layer formed on the two main surfaces.

[0092] When the liquid layer contains the first liquid thermal conductive material, the liquid layer may be curable or may be curable by heating. When the liquid layer is curable by heating, for example, the first liquid thermal conductive material preferably contains the above-mentioned thermosetting resin component that is liquid at 25°C.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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 1 shown in FIG. 1 includes a thermally conductive layer 11 and liquid layers 12 and 13. The liquid layer 12 is located on one main surface of the thermally conductive layer 11, and the liquid layer 13 is located on the other main surface of the thermally conductive layer 11. As shown in FIG. 1 , the two main surfaces of the thermally conductive sheet 1 may be provided with the liquid layers 12 and 13 to reduce unevenness. By providing the liquid layers 12 and 13 on the main surfaces of the thermally conductive layer 11, the unevenness of the thermally conductive layer 11 can be filled with the liquid layers 12 and 13. When the thermally conductive sheet 1 is brought into contact with an adherend, the unevenness of the surface of the adherend can also be filled with the liquid layers 12 and 13.

[0097] [Method for manufacturing thermally conductive sheet] The method for manufacturing 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-mentioned configuration. The method for manufacturing the thermally conductive sheet includes a step of preparing a composition containing the thermally conductive particles (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 a liquid layer on at least a portion of the main surface of the thermally conductive layer (also referred to as a "liquid layer formation step").

[0098] In the preparation step, a composition containing thermally conductive particles and any other components is prepared. The method for blending the components may be any method that can uniformly mix the components, and is not particularly limited.

[0099] <Forming Step> In the forming step, the thermally conductive layer is formed using a composition containing thermally conductive particles and any other components. For example, the thermally conductive layer may be formed by molding the composition into a sheet.

[0100] The liquid layer forming step may be performed by any method that can form a liquid layer on at least a portion of the main surface of the thermally conductive layer, and is not particularly limited. For example, the first liquid thermally conductive material or the second liquid thermally conductive material may be applied to at least a portion of the main surface of the thermally conductive layer.

[0101] In the method for producing a thermally conductive sheet, from the viewpoint of high thermal conductivity of the thermally conductive sheet, it is preferable to produce a thermally conductive sheet in which the thermally conductive particles are the above-mentioned graphite particles (A). Examples of the method for producing a thermally conductive sheet containing graphite particles (A) include the following method.

[0102] In one embodiment, the method for producing a thermally conductive sheet includes the steps of preparing a composition containing graphite particles (A) and any other components (the aforementioned preparation step), forming the composition into a sheet (part of the aforementioned formation step, also referred to as the "sheet preparation step"), producing a laminate of the sheets (part of the aforementioned formation step, also referred to as the "laminate preparation step"), slicing the side end surfaces of the laminate (part of the aforementioned formation step, also referred to as the "slicing step"), and forming a liquid layer on at least a portion of the main surface of the sliced ​​sheet (corresponding to the thermally conductive layer) (the aforementioned liquid layer formation step). The method for producing a thermally conductive sheet may further include the step of laminating a protective film on the thermally conductive sheet after the liquid layer formation step (also referred to as the "lamination step").

[0103] 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.

[0104] <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.

[0105] <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.

[0106] <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.

[0107] <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.

[0108] <Liquid Layer Forming Step> The liquid layer forming step may be performed by any method as long as it can form a liquid layer on at least a portion of the main surface of the sliced ​​sheet (corresponding to the thermally conductive layer) obtained by slicing. For example, the first liquid thermally conductive material or the second liquid thermally conductive material may be applied to at least a portion of the main surface of the thermally conductive layer.

[0109] <Laminating Step> The laminating step may be performed by any method as long as it can attach the thermally conductive sheet obtained in the liquid layer forming step to the protective film, and is not particularly limited.

[0110] [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 liquid 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 liquid 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 liquid 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.

[0111] 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.

[0112] 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. A liquid layer is 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. 1, the liquid layer 13 is located on the main surface of the thermally conductive sheet 1 facing the semiconductor chip 2, and the liquid layer 12 is located on the main surface of the thermally conductive sheet 1 facing the heat spreader 3. Furthermore, the liquid layer 13 may be in contact with the semiconductor chip 2, and the liquid layer 12 may be in contact with the heat spreader 3.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] 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.

[0119] 1 is used, when the thermally conductive sheet 1 is placed between a heat generating element and a heat dissipating element and then heated and pressurized, the liquid layers 12 and 13 located on the main surfaces of the thermally conductive sheet 1 flow. The liquid layers fill any gaps that occur when the thermally conductive sheet 1 is heated and pressed to bond the heat generating element and the heat dissipating element together. This reduces the gaps between the thermally conductive sheet and the adherend.

[0120] For example, if the first liquid thermally conductive material contains a thermosetting resin component, and the liquid layer is curable by heating, the thermosetting resin component will harden when the liquid layer flows by thermocompression bonding to fill the gap between the thermally conductive sheet and the adherend, thereby allowing the thermally conductive sheet and the adherend to be closely attached via the adhesive layer formed by the hardened liquid layer.

[0121] 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.

[0122] Fixing may be performed using a jig such as a clip, a screw, or a spring, and it is preferable to further fix it using a commonly used means such as an adhesive in order to maintain adhesion.

[0123] 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 20.0%, and more preferably 0% to 15.0%. 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 thermocompression bonded 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 liquid thermally conductive material is located and the main surface side of the thermally conductive layer where the liquid thermally conductive material is not located.

[0124] 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)

[0125] The numerical range of the porosity of the interface can be adjusted by adjusting, for example, the viscosity of the liquid thermal conductive material at 25°C, the amount of liquid thermal conductive material applied to the thermal conductive layer, the compressibility of the thermal conductive sheet, etc.

[0126] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0127] [Examples 1 to 4] 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 compositions.

[0128] <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")

[0129] (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. The thickness of the thermally conductive layer used in each example and each comparative example was approximately the same.

[0130] (Preparation of Thermally Conductive Sheets) Liquid thermally conductive materials having the compositions shown below were prepared. The prepared liquid thermally conductive material was applied to one or two main surfaces of the thermally conductive layer obtained as described above, and the liquid component was uniformly spread using a special spatula to obtain a thermally conductive sheet having a liquid layer formed on one or two main surfaces of the thermally conductive layer. <Composition of Liquid Thermally Conductive Materials> First liquid thermally conductive material (liquid material 1 in the table): AS-05A from Artic Silver, Inc. (containing a liquid ester compound and silver particles, filler content of 86% by mass, viscosity at 25°C of 145 Pa·s, thermal conductivity of 9 W / (m·K)) Second liquid thermally conductive material (liquid material 2 in the table): AS-05A from JunPus International Co., Ltd. JP-DX1 from Thermal Grizzly (containing a liquid silicone compound and nanodiamonds, a filler content of 92% by mass, a viscosity of 3,000 Pa·s at 25°C, and a thermal conductivity of 16 W / (m·K)) Third liquid thermal conductive material (liquid material 3 in the table): Conductonaut from Thermal Grizzly (a metal containing tin, gallium, and indium, a viscosity of 0.0021 Pa·s at 25°C, and a thermal conductivity of 73 W / (m·K))

[0131] (Comparative Examples 1 and 2) A thermally conductive layer was produced by kneading, laminating, pressing, and slicing the materials shown in Table 1 to obtain the mixing ratio (volume %) shown in Table 1 in the same manner as in Examples 1 to 4. In Comparative Example 1, a liquid layer was not formed and the thermally conductive layer was used as the thermally conductive sheet. In Comparative Example 2, a thermally conductive sheet with a liquid layer was obtained in the same manner as in each Example, except that a grease with a thermal conductivity of less than 5 W / (m·K) shown below was used. Liquid material (Liquid material 4 in the table): G-747 from Shin-Etsu Chemical Co., Ltd. (containing a liquid silicone compound and zinc oxide, a filler content of 84% by mass, a viscosity of 50 Pa·s at 25°C, and a thermal conductivity of 0.9 W / (m·K))

[0132]

[0133] The thermal conductive sheets of Examples 1 to 4 and Comparative Examples 1 and 2 were evaluated by the following methods. The results are shown in Table 2 and FIG.

[0134] (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 was prepared under the following conditions: a temperature of 150°C, a pressure of 0.14 MPa for 3 minutes, and then cooled sufficiently 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) 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 Examples 1 and 2 λ: thermal conductivity (W / m·K)

[0135] (Evaluation of Interfacial Porosity) In the three-layer structure sample prepared by the method described in (Measurement of Thermal Resistance), the interfacial porosity was evaluated as follows. Using an ultrasound imaging diagnostic device (Insight-300, Insight Corporation), the state of adhesion at the interface was observed under the conditions of reflection, 35 MHz, a gain level of 10 dB, and a contrast threshold of 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 (the area of ​​the measurement region; in Figure 3, an image of Φ14 mm is shown) was calculated, and the interfacial porosity (%) was determined based on the following formula. Note that the porosity was not measured for Example 3. Interfacial porosity (%) = 100 x (area of ​​gas region / area of ​​measurement region)

[0136] (Thickness Evaluation) Compression was performed under the same conditions for the thermally conductive sheets of Examples 1 to 4 and Comparative Example 1. Next, the maximum thickness of the thermally conductive sheet after compression ("Thickness after compression" in Table 2) was measured using a micrometer. The maximum thickness of the liquid layer was determined by subtracting the maximum thickness of the thermally conductive sheet with a liquid layer from the maximum thickness of the thermally conductive sheet without a liquid layer.

[0137]

[0138] It was confirmed that Examples 1 to 4, which used a liquid material with a thermal conductivity of 5 W / (m·K) or more, were able to reduce thermal resistance more than Comparative Example 1, which did not use a liquid material, and Comparative Example 2, which used a liquid material with a thermal conductivity of less than 5 W / (m·K).

[0139] The disclosure of PCT / JP2022 / 028528 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. A liquid thermally conductive material having a thermal conductivity of 5 W / (m·K) or more, for forming a liquid layer by applying the liquid layer to at least a portion of a thermally conductive layer containing thermally conductive particles.

2. 2. The liquid thermally conductive material according to claim 1, comprising a thermally conductive filler and a resin component.

3. 3. The liquid thermal conductive material according to claim 2, wherein the particle size of the thermally conductive filler is 0.1 μm to 50 μm.

4. 4. The liquid thermally conductive material according to claim 2, wherein the resin component includes a thermosetting resin component.

5. The liquid thermal conductive material according to any one of claims 1 to 3, having a viscosity of 4000 Pa·s or less at 25°C.

6. A combination of a heat conductive sheet-making member comprising the liquid heat conductive material according to any one of claims 1 to 3 and a heat conductive material containing heat conductive particles.

7. A combination of a liquid thermally conductive material containing a metal component and a thermally conductive material containing thermally conductive particles.

8. The combination of members for use in producing a thermal conductive sheet according to claim 7 , wherein the melting point of the metal component is 50° C. or lower.

9. a thermally conductive layer including a thermally conductive material including thermally conductive particles; A liquid layer including a first liquid thermal conductive material, which is the liquid thermal conductive material according to any one of claims 1 to 3, or a second liquid thermal conductive material, which is a liquid thermal conductive material containing a metal component, located on at least a part of a main surface of the thermal conductive layer; A thermal conductive sheet comprising:

10. The thermally conductive particles include at least one type of graphite particles (A) selected from the group consisting of scaly particles, ellipsoidal particles, and rod-shaped particles, The thermal conductive sheet according to claim 9, wherein in the thermal conductive layer, the planar 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-shaped particles are oriented in the thickness direction.

11. The thermal conductive sheet according to claim 9, wherein the maximum thickness of the liquid layer is 0.5 μm to 20 μm.

12. The thermally conductive sheet according to claim 9 , wherein the liquid layer includes the first liquid thermally conductive material, and the liquid layer is curable by heating.

13. A heat generating element, a heat sink, and the thermally conductive sheet according to claim 9 disposed between the heat generating element and the heat sink, A heat dissipation device, wherein the liquid 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 body and the main surface facing the heat dissipating body.

14. a heat conducting sheet disposed between the heat conducting sheet and the heat dissipating sheet, the heat conducting sheet comprising an adhesive layer formed by curing the liquid layer in the heat conducting sheet according to claim 12; 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, the main surface facing the heat generating body and the main surface facing the heat dissipating body.

15. A method for producing the thermal conductive sheet according to claim 9, comprising the steps of: A method for manufacturing a thermally conductive sheet, comprising the steps of: preparing a composition containing the thermally conductive particles; forming the thermally conductive layer using the composition; and forming a liquid layer on at least a portion of a main surface of the thermally conductive layer.

16. A method for producing the thermal conductive sheet according to claim 10, comprising the steps of: preparing a composition containing the graphite particles (A); forming the composition into a sheet to obtain a sheet; preparing a laminate of the sheets; Slicing the side end surface of the laminate; and forming a liquid layer on at least a portion of a main surface of the sliced ​​sheet, which corresponds to the thermally conductive layer, obtained by slicing.