Thermal conductive sheet and method for manufacturing a thermal conductive sheet

Abstract

To provide a heat-conductive sheet that has excellent adhesion to a heating element and can suppress excessive bleeding of a binder resin.SOLUTION: A heat-conductive sheet 1 is made of a cured product of a composition containing a binder resin 2, an anisotropic heat-conductive filler 3, and a heat-conductive filler 4 other than the anisotropic heat-conductive filler 3, and satisfies the following conditions 1 and 2. [Condition 1]: The tack force of the heat-conductive sheet 1 is 80 gf or more. [Condition 2]: The heat conductive sheet 1 having a size of 25 mm×25 mm and a thickness of 1 mm is compressed by 40%, and the amount of bleeding of the binder resin 2 after standing at 125°C for 48 hours is 0.20 g or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This technology relates to a heat conductive sheet and a method for manufacturing a heat conductive sheet. [Background technology]

[0002] As electronic devices become more high-performance, semiconductor elements are becoming more densely packed and easier to mount. Consequently, it is becoming increasingly important to dissipate the heat generated by the electronic components that make up these devices more efficiently. For example, in semiconductor devices, electronic components are attached to heat sinks such as cooling fans and heat sinks via thermal conductive sheets to efficiently dissipate heat. Thermal conductive sheets widely used are those made of silicone resin containing (dispersed) fillers such as inorganic fillers (see, for example, Patent Documents 1 and 2).

[0003] Heat dissipation materials such as thermal conductive sheets require further improvements in thermal conductivity. For example, increasing the packing density of inorganic fillers incorporated into the matrix, such as binder resin, is being considered to improve the thermal conductivity of thermal conductive sheets. However, increasing the packing density of inorganic fillers may impair the flexibility of the thermal conductive sheet or cause the inorganic fillers to fall off. Therefore, there are limits to how much the packing density of inorganic fillers can be increased in thermal conductive sheets.

[0004] Examples of inorganic fillers include alumina, aluminum nitride, and aluminum hydroxide. Furthermore, to achieve high thermal conductivity, flaky particles such as boron nitride and graphite, or carbon fibers may be filled into the matrix. This is due to the anisotropy of the thermal conductivity of these particles. For example, carbon fibers are known to have a thermal conductivity of approximately 600-1200 W / m·K in the fiber direction. Boron nitride, a flaky particle, is known to have a thermal conductivity of approximately 110 W / m·K in the plane direction and approximately 2 W / m·K in the direction perpendicular to the plane direction. Thus, carbon fibers and flaky particles are known to exhibit anisotropy in their thermal conductivity. By aligning the fiber direction of carbon fibers or the plane direction of flaky particles with the thickness direction of the thermal conductive sheet, which is the direction of heat transfer—that is, by orienting the carbon fibers or flaky particles in the thickness direction of the thermal conductive sheet—the thermal conductivity of the thermal conductive sheet can be dramatically improved.

[0005] Incidentally, in electronic devices using thermal conductive sheets, it is necessary to prevent the bleeding (residue) of the binder resin (e.g., silicone resin) constituting the thermal conductive sheet from scattering or adhering to electrical contacts, from the perspective of the aesthetics of the surrounding electronic components and other components using the thermal conductive sheet, and from its impact on conductivity to electrical contacts. Furthermore, the bleeding of the binder resin in the thermal conductive sheet is caused, for example, by an imbalance in the blending ratio of addition-reaction type silicone resin. Since the bleeding of the binder resin also affects the tackiness of the thermal conductive sheet, it also affects the quality of the adhesion (temporary fixation) of the thermal conductive sheet to the adherend (heat-generating element). In the technologies described in Patent Documents 1 and 2, it was difficult to provide a thermal conductive sheet that had excellent adhesion to the heat-generating element and could suppress excessive bleeding of the binder resin. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2012-201106 [Patent Document 2] International Publication No. 2019 / 026745 [Overview of the project] [Problems that the invention aims to solve]

[0007] This technology was proposed in light of the conventional situation described above, and provides a thermal conductive sheet that has excellent adhesion to the heating element and can suppress excessive bleeding of the binder resin. [Means for solving the problem]

[0008] The thermal conductive sheet relating to this technology consists of a cured product of a composition containing a binder resin, an anisotropic thermal conductive filler, and other thermal conductive fillers other than the anisotropic thermal conductive filler, and satisfies the following conditions 1 and 2. [Condition 1]: The tack force of the thermal conductive sheet is 80 gf or more. [Condition 2]: A 1mm thick thermal conductive sheet measuring 25mm x 25mm is compressed by 40%, and after standing at 125°C for 48 hours, the amount of binder resin bleed is 0.20g or less.

[0009] The method for manufacturing a thermal conductive sheet according to this technology comprises: Step A, preparing a thermal conductive composition containing a binder resin, an anisotropic thermal conductive filler, and a thermal conductive filler other than the anisotropic thermal conductive filler; Step B, extruding and curing the thermal conductive composition to obtain a columnar cured product; and Step C, cutting the columnar cured product to a predetermined thickness in a direction substantially perpendicular to the length direction of the column to obtain a thermal conductive sheet, wherein the thermal conductive sheet satisfies the following conditions 1 and 2. [Condition 1]: The tack force of the thermal conductive sheet is 80 gf or more. [Condition 2]: A 1mm thick thermal conductive sheet measuring 25mm x 25mm is compressed by 40%, and after standing at 125°C for 48 hours, the amount of binder resin bleed is 0.20g or less. [Effects of the Invention]

[0010] This technology provides a thermal conductive sheet that offers excellent adhesion to the heating element and can suppress excessive bleeding of the binder resin.

Brief Description of the Drawings

[0011] [Figure 1] FIG. 1 is a cross-sectional view showing an example of a heat conduction sheet. [Figure 2] FIG. 2 is a perspective view schematically showing an example of an anisotropic thermal conductive filler, namely, flaky boron nitride having a hexagonal crystal shape. [Figure 3] FIG. 3 is a cross-sectional view showing an example of a semiconductor device to which a heat conduction sheet is applied. [Figure 4] FIG. 4(A) is a cross-sectional view showing a state where a heat conduction sheet is sandwiched by a compression jig, and FIG. 4(B) is a plan view showing a state where the heat conduction sheet is placed on a lower jig. [Figure 5] FIG. 5(A) is a plan view showing a state where a heat conduction sheet is sandwiched by a compression jig, and FIG. 5(B) is a side view showing a state where the heat conduction sheet is sandwiched by a compression jig. [Figure 6] FIG. 6 is a diagram for explaining a method of evaluating whether a heat conduction sheet slips off when placed on an aluminum plate and shifted by 90°.

Embodiments for Carrying Out the Invention

[0012] In this specification, the average particle diameter (D50) of an anisotropic thermal conductive filler and other thermal conductive fillers refers to the particle diameter when the cumulative curve of the particle diameter values is obtained from the small particle diameter side of the particle diameter distribution of the anisotropic thermal conductive filler or other thermal conductive fillers with the entire particle diameter distribution being 100%, and the cumulative value becomes 50%. Note that the particle size distribution (particle diameter distribution) in this specification is obtained based on a volume basis. Examples of the method for measuring the particle size distribution include, for example, a method using a laser diffraction type particle size distribution measuring machine.

[0013] <Heat Conduction Sheet> Figure 1 is a cross-sectional view showing an example of a thermal conductive sheet 1 related to this technology. The thermal conductive sheet 1 is made of a cured product of a composition containing a binder resin 2, an anisotropic thermal conductive filler 3, and other thermal conductive fillers 4 other than the anisotropic thermal conductive filler 3. In the thermal conductive sheet 1, the anisotropic thermal conductive filler 3 and the other thermal conductive fillers 4 are dispersed in the binder resin 2, and the anisotropic thermal conductive filler 3 is oriented in the thickness direction B of the thermal conductive sheet 1.

[0014] Here, the orientation of the anisotropic thermal conductive filler 3 in the thickness direction B of the thermal conductive sheet 1 means, for example, that of all the anisotropic thermal conductive filler 3 in the thermal conductive sheet 1, the proportion of anisotropic thermal conductive filler 3 whose long axis is oriented in the thickness direction B of the thermal conductive sheet 1 is 50% or more, may be 55% or more, may be 60% or more, may be 65% or more, may be 70% or more, may be 80% or more, may be 90% or more, may be 95% or more, or may be 99% or more.

[0015] Anisotropic thermal conductive filler 3 is a thermal conductive filler that has anisotropy in shape. An example of anisotropic thermal conductive filler 3 is a thermal conductive filler having a long axis, a short axis, and a thickness (for example, a flake-shaped thermal conductive filler). A flake-shaped thermal conductive filler is a thermal conductive filler having a long axis, a short axis, and a thickness, having a high aspect ratio (long axis / thickness), and having isotropic thermal conductivity in the plane direction including the long axis. The short axis of the flake-shaped thermal conductive filler is the direction that intersects the plane including the long axis of the flake-shaped thermal conductive filler, passing through the midpoint of the long axis of the flake-shaped thermal conductive filler, and refers to the length of the shortest part of the flake-shaped thermal conductive filler. The thickness of the flake-shaped thermal conductive filler is the average value obtained by measuring the thickness of the plane including the long axis of the flake-shaped thermal conductive filler at 10 points. The aspect ratio of the anisotropic thermal conductive filler 3 is not particularly limited and can be appropriately selected depending on the purpose. For example, the aspect ratio of the anisotropic thermal conductive filler 3 can be in the range of 10 to 100, or it may be in the range of 20 to 50, or it may be in the range of 15 to 40. The long axis, short axis, and thickness of the anisotropic thermal conductive filler 3 can be measured, for example, by a microscope, scanning electron microscope (SEM), particle size analyzer, etc.

[0016] Other thermally conductive fillers 4 are thermally conductive fillers other than the anisotropic thermally conductive filler 3, that is, thermally conductive fillers that do not have anisotropy in shape.

[0017] The thermal conductive sheet 1 satisfies the following conditions 1 and 2. [Condition 1]: The tack force of thermal conductive sheet 1 is 80 gf or more. [Condition 2]: A thermal conductive sheet 1 measuring 25 mm x 25 mm and 1 mm thick is compressed by 40%, and after standing at 125°C for 48 hours, the amount of bleed of the binder resin 2 is 0.20 g or less.

[0018] Regarding condition 1, the tack force of the thermal conductive sheet 1 is 80 gf or more, may be 85 gf or more, may be 88 gf or more, may be 92 gf or more, or may be in the range of 80 to 92 gf, from the viewpoint of the adhesion of the thermal conductive sheet 1 to the heat-generating element that is adhered to. The method for measuring the tack force of the thermal conductive sheet 1 is the same as the method in the embodiment described later.

[0019] Regarding condition 2, considering the circumstances (environment) in which the thermal conductive sheet 1 is used, the amount of bleed of the binder resin 2 after standing for 48 hours at 125°C in a 40% compressed state is 0.20 g or less, but may be 0.19 g or less, 0.18 g or less, 0.17 g or less, or 0.15 g or less. Furthermore, from the viewpoint of satisfying condition 1, it is preferable that the amount of bleed of the binder resin 2 after standing for 48 hours at 125°C in a 40% compressed state is greater than or equal to a predetermined amount, but may be 0.15 g or more, in the range of 0.15 to 0.20 g, or in the range of 0.15 to 0.19 g. The method for measuring the amount of bleed of the binder resin 2 in the thermal conductive sheet 1 is the same as the method in the examples described later. For example, a thermal conductive sheet 1 measuring 25mm x 25mm and 1mm thick is compressed by 40%, and after being left standing at 125°C for 48 hours, the amount of bleed of the binder resin 2 is measured.

[0020] Thus, since the thermal conductive sheet 1 satisfies conditions 1 and 2 described above, it exhibits excellent adhesion to the heat-generating element and can suppress excessive bleeding of the binder resin 2. Furthermore, from the viewpoint of achieving high thermal conductivity, it is preferable that the thermal conductive sheet 1 also satisfies the following condition 3 in addition to conditions 1 and 2 described above. [Condition 3]: The bulk thermal conductivity of thermal conductive sheet 1 is 9.5 W / m·K or higher.

[0021] Regarding condition 3, the bulk thermal conductivity of the thermal conductive sheet 1 is preferably 9.5 W / m·K or higher, but may also be 9.9 W / m·K or higher, 10.5 W / m·K or higher, 10.6 W / m·K or higher, 11.3 W / m·K or higher, 11.4 W / m·K or higher, 12.3 W / m·K or higher, 13.1 W / m·K or higher, may be in the range of 9.5 to 13.1 W / m·K, or may be in the range of 9.9 to 13.1 W / m·K. The bulk thermal conductivity of the thermal conductive sheet 1 can be measured by the method described in the examples below.

[0022] The thermal conductive sheet 1 may have an effective thermal conductivity in the thickness direction B of 7.5 W / m·K or higher, 8.0 W / m·K or higher, 8.3 W / m·K or higher, 8.5 W / m·K or higher, 9.1 W / m·K or higher, 9.2 W / m·K or higher, 9.3 W / m·K or higher, 10.5 W / m·K or higher, 11.1 W / m·K or higher, or in the range of 7.5 to 9.2 W / m·K, or in the range of 7.5 to 11.1 W / m·K. The effective thermal conductivity of the thermal conductive sheet 1 can be measured by the method described in the examples below.

[0023] The thickness of the thermal conductive sheet 1 is not particularly limited and can be appropriately selected depending on the purpose. For example, the thickness of the thermal conductive sheet can be 0.05 mm or more, or 0.1 mm or more. The upper limit of the thickness of the thermal conductive sheet can be 5 mm or less, 4 mm or less, or 3 mm or less. From the viewpoint of handling the thermal conductive sheet 1, it is preferable that the thickness of the thermal conductive sheet 1 be between 0.1 and 4 mm. The thickness of the thermal conductive sheet 1 can be determined, for example, by measuring the thickness B of the thermal conductive sheet 1 at any five locations and taking the arithmetic mean.

[0024] The heat conduction sheet 1 preferably has a change rate of the thermal resistance value measured at a compression rate of 10% after standing at 150°C for 1000 hours with respect to the thermal resistance value measured at a compression rate of 10% immediately after production within 10%, and may be 8.7% or less, may be 8.6% or less, may be 8.2% or less, may be 8.1% or less, may be 8.0% or less, may be 7.8% or less, may be 7.7% or less, may be 7.6% or less, may be 7.4% or less, may be 7.1% or less, may be 6.7% or less, or may be in the range of 6.7 to 10%, may be in the range of 6.7 to 8.7%, or may be in the range of 6.7 to 8.2%. Being within this range results in a tendency for less fluctuation in the thermal resistance value even when used for a long time. The change rate of the thermal resistance value of the heat conduction sheet 1 can be measured by the method described in the examples below.

[0025] The heat conduction sheet 1 has a thermal resistance value measured at a compression rate of 10% immediately after production, for example, 2 of 1.27 °C·cm 2 / W or less, may be 1.19 °C·cm 2 / W or less, may be 1.16 °C·cm 2 / W or less, may be 1.05 °C·cm 2 / W or less, may be 0.92 °C·cm 2 / W or less, may be 0.88 °C·cm 2 / W or less, or may be in the range of 0.88 to 1.27 °C·cm 2 / W.

[0026] The heat conduction sheet 1 has a thermal resistance value measured at a compression rate of 10% after standing at 150°C for 1000 hours, for example, 2 of 1.36 °C·cm 2 / W or less, may be 1.27 °C·cm 2 / W or less, may be 1.25 °C·cm 2 / W or less, may be 1.14 °C·cm 2 / W or less, may be 1.13 °C·cm 2It may be less than or equal to / W, and 1.00℃·cm 2 It may be less than / W, and 0.95℃·cm 2 It may be less than / W, and 0.95~1.36℃·cm 2 The range / W is also acceptable.

[0027] In terms of flexibility, thermal conductive sheet 1 withstands a load of 3 kgf / cm after being left standing at 150°C for 1000 hours. 2 The compressibility measured is preferably 20% or more, but may also be 21% or more, 22% or more, 23% or more, 25% or more, 26% or more, 28% or more, or in the range of 20-28% or 21-28%. In this way, the thermal conductive sheet 1 can maintain good flexibility even after being left standing at 150°C for 1000 hours. Load of thermal conductive sheet 1: 3 kgf / cm 2 The compression ratio can be measured by the method described in the examples below.

[0028] The heat conductive sheet 1 preferably has a hardness in the Shore type OO immediately after manufacturing (initial Shore hardness) of 20 to 90, but may also be in the range of 40 to 70 or 55 to 60. Furthermore, the heat conductive sheet 1 preferably has a hardness in the Shore type OO after standing at 150°C for 1000 hours, but may also be in the range of 40 to 95, or 65 to 90. Having a hardness in this range allows the heat conductive sheet 1 to conform better to the adherend, and the adherend and heat conductive sheet to make surface contact, thereby enabling more effective heat conduction. The hardness of the heat conductive sheet 1 can be measured by the method described in the examples below.

[0029] The thermal conductive sheet 1 preferably has a high dielectric breakdown voltage. When the thickness is 1 mm, the dielectric breakdown voltage may be 7.0 kV or higher, 7.5 kV or higher, 8.1 kV or higher, 8.4 kV or higher, 8.5 kV or higher, 8.6 kV or higher, 8.7 kV or higher, 9.0 kV or higher, or in the range of 8.1 to 9.0 kV. The dielectric breakdown voltage of the thermal conductive sheet 1 can be measured by the method of the embodiment described later.

[0030] The following describes specific examples of the components of the thermal conductive sheet 1.

[0031] <Binder resin> The binder resin 2 is used to hold the anisotropic thermally conductive filler 3 and other thermally conductive fillers 4 within the thermal conductive sheet 1. The binder resin 2 is selected according to the mechanical strength, heat resistance, electrical properties, and other characteristics required of the thermal conductive sheet 1. The binder resin 2 can be selected from thermoplastic resins, thermoplastic elastomers, and thermosetting resins.

[0032] Examples of thermoplastic resins include polyethylene, polypropylene, ethylene-α-olefin copolymers such as ethylene-propylene copolymer, polymethylpentene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyvinyl alcohol, polyvinyl acetal, polyvinylidene fluoride, and fluorine-based polymers such as polytetrafluoroethylene, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polystyrene, polyacrylonitrile, styrene-acrylonitrile copolymer, acrylonitrile-butadiene-styrene copolymer (ABS) resin, polyphenylene-ether copolymer (PPE) resin, modified PPE resin, aliphatic polyamides, aromatic polyamides, polyimides, polyamide-imides, polymethacrylic acid esters such as polymethacrylic acid and polymethyl methacrylate, polyacrylic acids, polycarbonate, polyphenylene sulfide, polysulfone, polyethersulfone, polyethernitrile, polyetherketone, polyketone, liquid crystal polymer, silicone resin, and ionomer.

[0033] Examples of thermoplastic elastomers include styrene-butadiene block copolymers or their hydrogenated derivatives, styrene-isoprene block copolymers or their hydrogenated derivatives, styrene-based thermoplastic elastomers, olefin-based thermoplastic elastomers, vinyl chloride-based thermoplastic elastomers, polyester-based thermoplastic elastomers, polyurethane-based thermoplastic elastomers, and polyamide-based thermoplastic elastomers.

[0034] Examples of thermosetting resins include crosslinked rubber, epoxy resin, phenolic resin, polyimide resin, unsaturated polyester resin, and diallyl phthalate resin. Specific examples of crosslinked rubber include natural rubber, acrylic rubber, butadiene rubber, isoprene rubber, styrene-butadiene copolymer rubber, nitrile rubber, hydrogenated nitrile rubber, chloroprene rubber, ethylene-propylene copolymer rubber, chlorinated polyethylene rubber, chlorosulfonated polyethylene rubber, butyl rubber, halogenated butyl rubber, fluororubber, urethane rubber, and silicone rubber.

[0035] As the binder resin 2, for example, a silicone resin is preferred from the viewpoint of adhesion between the heating surface of a heating element (e.g., an electronic component) and the heat sink surface. As the silicone resin, for example, a two-component addition reaction type silicone resin can be used, which consists of a main component containing a curing catalyst and a curing agent having hydrosilyl groups (Si-H groups), with alkenyl groups (polyorganosiloxane) as the main component. As the silicone having alkenyl groups, a polyorganosiloxane having at least two alkenyl groups in one molecule can be used. As an example, a polyorganosiloxane having vinyl groups can be used. The curing catalyst is a catalyst for promoting the addition reaction between the alkenyl groups in the silicone having alkenyl groups and the hydrosilyl groups in the curing agent having hydrosilyl groups. As the curing catalyst, well-known catalysts used in hydrosilylation reactions can be used, for example, platinum group curing catalysts, such as elemental platinum group metals such as platinum, rhodium, and palladium, or platinum chloride can be used. As a curing agent having a hydrosilyl group, for example, a polyorganosiloxane having a hydrosilyl group (an organohydrogenpolysiloxane having at least two hydrogen atoms directly bonded to a silicon atom in one molecule) can be used.

[0036] In particular, from the viewpoint of ensuring that the heat conductive sheet 1 has excellent adhesion to the heating element and that excessive bleeding of the binder resin 2 is suppressed, it is preferable to use an addition-reaction type silicone resin in which the binder resin 2 consists of a polyorganosiloxane having an alkenyl group in one molecule and an organohydrogenpolysiloxane having a hydrogen atom directly bonded to a silicon atom in one molecule, wherein the blending ratio of the polyorganosiloxane to the organohydrogenpolysiloxane satisfies the following formula 1. Equation 1: Number of moles of hydrogen atoms directly bonded to silicon atoms / Number of moles of alkenyl groups = 0.40 or more and 0.60 or less

[0037] In Equation 1, the number of moles of hydrogen atoms directly bonded to silicon atoms refers to the number of moles of hydrogen atoms directly bonded to silicon atoms in an organohydrogenpolysiloxane having hydrogen atoms directly bonded to silicon atoms. Also, in Equation 1, the number of moles of alkenyl groups refers to the number of moles of alkenyl groups in a polyorganosiloxane having alkenyl groups. When the molar ratio of binder resin 2 represented by Equation 1 (hereinafter also referred to as the "Si-H / alkenyl group ratio") is 0.40 or higher, the amount of bleeding of binder resin 2 tends to be suppressed, and the thermal conductive sheet 1 is more likely to satisfy the above-mentioned condition 2. Furthermore, when the molar ratio of binder resin 2 represented by Equation 1 is 0.60 or lower, the tack strength of the thermal conductive sheet 1 tends to improve, and the above-mentioned condition 1 is more likely to be satisfied. The molar ratio of binder resin 2 represented by Equation 1 may be in the range of 0.45 to 0.58.

[0038] Polyorganosiloxanes containing alkenyl groups have a kinematic viscosity of 10 to 100,000 mmHg at 23°C. 2 The range may be within / s, and 500 to 50,000 mm. 2 The range may be in the range of / s. Polyorganosiloxanes having alkenyl groups have a kinematic viscosity of 10 mm at 23°C. 2 When the kinematic viscosity is 100,000 mmHg or higher, the resulting composition tends to have better storage stability. Furthermore, polyorganosiloxanes having alkenyl groups have a kinematic viscosity of 100,000 mmHg at 23°C. 2 When the viscosity is less than / s, the resulting composition tends to have higher spreadability. Note that the kinematic viscosity of the polyorganosiloxane having an alkenyl group refers to the value measured using an Ostwald viscometer. The polyorganosiloxane having an alkenyl group may be used alone, or two or more types with different viscosities (kinematic viscosity) may be used in combination.

[0039] The content of the binder resin 2 in the thermal conductive sheet 1 is not particularly limited and can be appropriately selected depending on the purpose. For example, the content of the binder resin 2 in the thermal conductive sheet 1 can be 30 volume% or more, may be 32 volume% or more, may be 34 volume% or more, or may be 36 volume% or more. Furthermore, the upper limit of the content of the binder resin 2 in the thermal conductive sheet 1 can be 60 volume% or less, may be 50 volume% or less, may be 40 volume% or less, may be 38 volume% or less, or may be 37 volume% or less. In particular, from the viewpoint of satisfying the above-mentioned conditions 1 and 2, the content of the binder resin 2 in the thermal conductive sheet 1 can be in the range of 30 to 38 volume%, or may be in the range of 32 to 36 volume%. The binder resin 2 may be used alone, or two or more types may be used in combination.

[0040] In particular, the content of the addition-reaction type silicone resin in the thermal conductive sheet 1, which has a molar ratio of 0.40 or more and 0.60 or less represented by formula 1, is preferably 80% by volume or more, may be 90% by volume or more, may be 95% by volume or more, may be 99% by volume or more, or may be substantially 100%.

[0041] <Anisotropic thermally conductive filler> The material of the anisotropic thermal conductive filler 3 is not particularly limited, and examples include boron nitride (BN), mica, alumina, aluminum nitride, silicon carbide, silica, zinc oxide, molybdenum disulfide, etc., with boron nitride being preferred from the viewpoint of thermal conductivity. The anisotropic thermal conductive filler 3 may be used alone or in combination of two or more types.

[0042] Figure 2 is a schematic perspective view showing a flaky boron nitride 3A with a hexagonal crystal structure, which is an example of an anisotropic thermal conductive filler 3. In Figure 2, a represents the long axis of the flaky boron nitride 3A, b represents the thickness of the flaky boron nitride 3A, and c represents the short axis of the flaky boron nitride 3A. From the viewpoint of thermal conductivity, it is preferable to use flaky boron nitride 3A with a hexagonal crystal structure as the anisotropic thermal conductive filler 3, as shown in Figure 2. In this technology, by using a flaky thermal conductive filler (e.g., flaky boron nitride 3A), which is less expensive than a spherical thermal conductive filler (e.g., spherical boron nitride), a thermal conductive sheet 1 that achieves both low cost and excellent thermal properties (high thermal conductivity) can be obtained.

[0043] The average particle size of the anisotropic thermal conductive filler 3 can be appropriately selected depending on the purpose. From the viewpoint of improving the thermal conductivity of the thermal conductive sheet 1, the average particle size of the anisotropic thermal conductive filler 3 in the thermal conductive sheet 1 is 15 μm or more, may be 20 μm or more, may be 25 μm or more, may be 30 μm or more, may be 35 μm or more, or may be 40 μm or more. Furthermore, from the viewpoint of improving the thermal conductivity of the thermal conductive sheet 1, the average particle size of the anisotropic thermal conductive filler 3 in the thermal conductive sheet 1 may be in the range of 30 to 60 μm, may be in the range of 30 to 50 μm, may be in the range of 35 to 55 μm, or may be in the range of 35 to 45 μm.

[0044] The content of anisotropic thermal conductive filler 3 in the thermal conductive sheet 1 can be appropriately selected depending on the purpose. From the viewpoint of condition 2 described above, the content of anisotropic thermal conductive filler 3 in the thermal conductive sheet 1 is preferably more than 20 volume%, may be 21 volume% or more, may be 23 volume% or more, may be 25 volume% or more, or may be 26 volume% or more. Furthermore, from the viewpoint of condition 1 described above, the content of anisotropic thermal conductive filler 3 in the thermal conductive sheet 1 is preferably less than 30 volume%, may be 28 volume% or less, or may be 27 volume% or less. Furthermore, the content of anisotropic thermal conductive filler 3 in the thermal conductive sheet 1 may be in the range of 23 to 27 volume%, may be in the range of 23 to 25 volume%, or may be in the range of 25 to 27 volume%.

[0045] <Other thermally conductive fillers> Other thermally conductive fillers 4 include spherical, powdered, and granular thermally conductive fillers. From the viewpoint of the thermal conductivity of the thermal conductive sheet 1, the material of the other thermally conductive fillers 4 is preferably a ceramic filler, for example. Specific examples include aluminum oxide (alumina, sapphire), aluminum nitride, aluminum hydroxide, zinc oxide, boron nitride, zirconia, and silicon carbide. The other thermally conductive fillers 4 may be used alone or in combination of two or more types (two or more thermally conductive fillers with different average particle sizes).

[0046] In particular, the other thermally conductive filler 4 is preferably one or more of alumina, aluminum nitride, zinc oxide, and aluminum hydroxide, taking into consideration the thermal conductivity of the thermally conductive sheet 1 and the specific gravity of the thermally conductive sheet 1, and may be aluminum nitride and alumina used in combination, or aluminum nitride, alumina, and zinc oxide used in combination.

[0047] The average particle size of aluminum nitride can be less than 30 μm from the viewpoint of the specific gravity of the thermal conductive sheet 1, and may be 0.1 to 10 μm, 0.5 to 5 μm, 1 to 3 μm, or 1 to 2 μm. The average particle size of alumina can be 0.1 to 10 μm from the viewpoint of the specific gravity of the thermal conductive sheet 1, and may be 0.1 to 8 μm, 0.1 to 7 μm, or 0.1 to 3 μm. The average particle size of zinc oxide can be, for example, 0.01 to 5 μm from the viewpoint of the specific gravity of the thermal conductive sheet 1, and may be 0.03 to 3 μm, or 0.05 to 2 μm.

[0048] The content of other thermally conductive fillers 4 in the thermal conductive sheet 1 can be appropriately selected depending on the purpose. The content of other thermally conductive fillers 4 in the thermal conductive sheet 1 may be 10 volume% or more, 15 volume% or more, 20 volume% or more, 25 volume% or more, 30 volume% or more, or 35 volume% or more. Furthermore, the upper limit of the content of other thermally conductive fillers 4 in the thermal conductive sheet 1 may be 50 volume% or less, 45 volume% or less, or 40 volume% or less. Furthermore, the content of other thermally conductive fillers 4 in the thermal conductive sheet 1 may be in the range of 30 to 50 volume% or in the range of 35 to 45 volume%.

[0049] When using other thermally conductive fillers 4, for example, aluminum nitride particles, alumina particles, and zinc oxide particles in combination, it is preferable that the content of aluminum nitride particles in the thermally conductive sheet 1 be 10 to 25 volume% (particularly 17 to 23 volume%), the content of alumina particles be 10 to 25 volume% (particularly 17 to 23 volume%), and the content of zinc oxide particles be 0.1 to 5 volume% (particularly 0.5 to 3 volume%).

[0050] In the thermal conductive sheet 1, the total content of anisotropic thermal conductive filler 3 and other thermal conductive fillers 4 is preferably greater than 61 volume%, may be 64 volume% or more, or 66 volume% or more, from the viewpoint of satisfying conditions 1 and 2 described above. Furthermore, in the thermal conductive sheet 1, the total content of anisotropic thermal conductive filler 3 and other thermal conductive fillers 4 is preferably 68 volume% or less, may be 67 volume% or less, may be 66 volume% or less, or may be 65 volume% or less, from the viewpoint of satisfying conditions 1 and 2 described above. In the viewpoint of the thermal conductive sheet 1 satisfying conditions 1 and 2 described above, the total content of anisotropic thermal conductive filler 3 and other thermal conductive fillers 4 in the thermal conductive sheet 1 can be in the range of 64 to 68 volume%, or may be in the range of 64 to 66 volume%.

[0051] The thermal conductive sheet 1 may further contain other components besides those described above, to the extent that it does not impair the effects of this technology. Examples of other components include coupling agents, dispersants, curing accelerators, retarders, tackifiers, plasticizers, flame retardants, antioxidants, stabilizers, colorants, and solvents. For example, the thermal conductive sheet 1 may use anisotropic thermal conductive filler 3 and / or other thermal conductive fillers 4 treated with a coupling agent, in order to further improve the dispersibility of the anisotropic thermal conductive filler 3 and other thermal conductive fillers 4.

[0052] <Method for manufacturing a thermal conductive sheet> The method for manufacturing the thermal conductive sheet 1 comprises the following steps A, B, and C.

[0053] <Process A> In step A, a thermally conductive composition containing the binder resin 2, the anisotropic thermally conductive filler 3, and the other thermally conductive filler 4 is prepared by dispersing the anisotropic thermally conductive filler 3 and the other thermally conductive filler 4 in the binder resin 2. The thermally conductive composition can be prepared by uniformly mixing the binder resin 2, the anisotropic thermally conductive filler 3, the other thermally conductive filler 4, and, if necessary, the other components mentioned above, using known methods.

[0054] <Process B> In step B, the thermally conductive composition prepared in step A is extruded and then cured to obtain a columnar cured product (molded block). The extrusion method is not particularly limited and can be appropriately selected from various known extrusion methods depending on the viscosity of the thermally conductive composition and the properties required of the thermally conductive sheet 1. In the extrusion method, when the thermally conductive composition is extruded from the die, the binder resin 2 in the thermally conductive composition flows, and the anisotropic thermally conductive filler 3 is oriented along the direction of this flow.

[0055] The size and shape of the columnar hardened material obtained in step B can be determined according to the required size of the heat conductive sheet 1. For example, a rectangular prism with a cross-section of 0.5 to 15 cm in length and 0.5 to 15 cm in width can be used. The length of the rectangular prism can be determined as needed.

[0056] <Process C> In step C, the columnar hardened material obtained in step B is cut to a predetermined thickness along the length of the column to obtain a thermal conductive sheet 1. The surface (cut surface) of the thermal conductive sheet 1 obtained in step C exposes the anisotropic thermal conductive filler 3. There are no particular restrictions on the cutting method, and it can be appropriately selected from known slicing devices depending on the size and mechanical strength of the columnar hardened material. As for the cutting direction of the columnar hardened material, if the molding method is extrusion molding, the anisotropic thermal conductive filler 3 may be oriented in the extrusion direction, so it is preferable to cut at 60 to 120 degrees, more preferably at 70 to 100 degrees, and even more preferably at 90 degrees (approximately perpendicular) with respect to the extrusion direction. There are no particular restrictions on the cutting direction of the columnar hardened material other than those mentioned above, and it can be appropriately selected depending on the intended use of the thermal conductive sheet 1.

[0057] Thus, in the method for manufacturing a thermal conductive sheet having steps A, B, and C, a thermal conductive sheet 1 that satisfies the above-described conditions 1 and 2 can be obtained.

[0058] The method for manufacturing the thermal conductive sheet 1 is not limited to the example described above, and may further include, for example, a step D of pressing the cut surface after step C. By further including the pressing step D, the surface of the thermal conductive sheet 1 obtained in step C can be made smoother, and the adhesion to other members can be further improved. As for the pressing method, a pair of pressing devices consisting of a flat plate and a press head with a flat surface can be used. Alternatively, pressing may be done with pinch rolls. The pressure during pressing can be, for example, 0.1 to 100 MPa. In order to further enhance the effect of pressing and shorten the pressing time, it is preferable to perform the pressing at or above the glass transition temperature (Tg) of the binder resin 2. For example, the pressing temperature can be 0 to 180°C, and may be within the temperature range of room temperature (e.g., 25°C) to 100°C, or 30 to 100°C.

[0059] <Electronic equipment> The thermal conductive sheet 1 can be used, for example, to be placed between a heat-generating element and a heat-sinking element to create an electronic device (thermal device) in which heat generated by the heat-generating element is dissipated to the heat-sinking element. The electronic device has at least a heat-generating element, a heat-sinking element and the thermal conductive sheet 1, and may further have other components as needed. In this way, the electronic device to which the thermal conductive sheet 1 is applied has the thermal conductive sheet 1 sandwiched between the heat-generating element and the heat-sinking element, so that high thermal conductivity is achieved by the thermal conductive sheet 1, the adhesion of the thermal conductive sheet 1 to the heat-generating element is excellent, and excessive bleeding of the binder resin 2 from the thermal conductive sheet 1 can be suppressed.

[0060] The heat-generating elements are not particularly limited and include, for example, integrated circuit elements such as CPUs, GPUs (Graphics Processing Units), DRAMs (Dynamic Random Access Memory), and flash memory, as well as electronic components that generate heat in electrical circuits, such as transistors and resistors. Heat-generating elements also include components that receive optical signals, such as optical transceivers in communication equipment.

[0061] The heat sink is not particularly limited and can be any heat sink or heat spreader used in combination with integrated circuit elements, transistors, optical transceiver housings, etc. Examples of materials for heat sinks and heat spreaders include copper and aluminum. In addition to heat spreaders and heat sinks, any heat sink that conducts heat generated from a heat source and dissipates it to the outside can be used as a heat sink, such as a heat sink, cooler, die pad, printed circuit board, cooling fan, Peltier element, heat pipe, vapor chamber, metal cover, housing, etc. A heat pipe is, for example, a hollow structure that is cylindrical, substantially cylindrical, or flattened cylindrical.

[0062] Figure 3 is a cross-sectional view showing an example of a semiconductor device to which a thermal conductive sheet is applied. For example, as shown in Figure 3, the thermal conductive sheet 1 is mounted on a semiconductor device 50 built into various electronic devices and sandwiched between a heat-generating element and a heat-sinking element. The semiconductor device 50 shown in Figure 3 comprises an electronic component 51, a heat spreader 52, and a thermal conductive sheet 1, with the thermal conductive sheet 1 sandwiched between the heat spreader 52 and the electronic component 51. By being sandwiched between the heat spreader 52 and the heat sink 53, the thermal conductive sheet 1, together with the heat spreader 52, constitutes a heat dissipation member that dissipates heat from the electronic component 51. The mounting location of the thermal conductive sheet 1 is not limited to between the heat spreader 52 and the electronic component 51, or between the heat spreader 52 and the heat sink 53, but can be appropriately selected according to the configuration of the electronic device or semiconductor device. The heat spreader 52 is formed, for example, in the shape of a rectangular plate and has a main surface 52a facing the electronic component 51 and side walls 52b erected along the outer circumference of the main surface 52a. The heat spreader 52 has a thermal conductive sheet 1 provided on the main surface 52a surrounded by the side walls 52b, and a heat sink 53 is provided on the other surface 52c opposite to the main surface 52a via the thermal conductive sheet 1.

[0063] The embodiments of the heat conductive sheet and the method for manufacturing the heat conductive sheet related to this technology have been described above, but various configurations other than those described above can also be adopted. Examples of embodiments are listed below. (Note 1) A thermal conductive sheet comprising a cured product of a composition containing a binder resin, an anisotropic thermal conductive filler, and other thermal conductive fillers other than the anisotropic thermal conductive filler, and satisfying the following conditions 1 and 2. [Condition 1]: The tack force of the thermal conductive sheet is 80 gf or more. [Condition 2]: The amount of bleed of the binder resin after standing for 48 hours at 125°C in a 25mm x 25mm, 1mm thick thermal conductive sheet compressed by 40% is 0.20g or less. (Note 2) The above binder resin is an addition-reaction type silicone resin. The above addition-reaction type silicone resin consists of a polyorganosiloxane having an alkenyl group in one molecule and an organohydrogenpolysiloxane having a hydrogen atom directly bonded to a silicon atom in one molecule. A thermal conductive sheet as described in Appendix 1, wherein the mixing ratio of the above polyorganosiloxane and the above organohydrogenpolysiloxane satisfies the following formula 1. Equation 1: Number of moles of hydrogen atoms directly bonded to silicon atoms / Number of moles of alkenyl groups = 0.40 or more and 0.60 or less (Note 3) A thermal conductive sheet as described in Appendix 1 or 2, wherein the binder resin content is 30% by volume or more and 38% by volume or less. (Note 4) A thermal conductive sheet as described in any of the appendices 1 to 3, wherein the content of the above-mentioned anisotropic thermal conductive filler is 22% by volume or more and 29% by volume or less. (Note 5) The above anisotropic thermally conductive filler is boron nitride. A thermal conductive sheet as described in any of the appendices 1 to 4, wherein the above-mentioned other thermal conductive filler is one or more of alumina, aluminum nitride, zinc oxide, and aluminum hydroxide, including at least alumina. (Note 6) The above anisotropic thermal conductive filler is flaky boron nitride. A thermal conductive sheet according to any of the appendices 1 to 5, wherein the above-mentioned flaky boron nitride is oriented in the thickness direction of the thermal conductive sheet. (Note 7) A thermal conductive sheet described in any of the appendices 1 to 6, which also satisfies condition 3 below. [Condition 3]: The bulk thermal conductivity of the thermal conductive sheet is 9.5 W / m·K or higher. (Note 8) A thermal conductive sheet as described in any of the appendices 1 to 7, wherein the rate of change of the thermal resistance value measured at a compression ratio of 10% after standing at 150°C for 1000 hours is within 10% compared to the thermal resistance value measured at a compression ratio of 10% immediately after manufacturing. (Note 9) After standing for 1000 hours at 150°C, a load of 3 kgf / cm was applied. 2 A thermal conductive sheet as described in any of the appendices 1 to 8, having a compressibility of 20% or more as measured by [method / method]. (Note 10) Step A involves preparing a thermally conductive composition containing a binder resin, an anisotropic thermally conductive filler, and a thermally conductive filler other than the anisotropic thermally conductive filler. Step B involves extruding the above-mentioned thermally conductive composition and then curing it to obtain a columnar cured product. The process includes step C, which involves cutting the above-mentioned columnar hardened material to a predetermined thickness in a direction substantially perpendicular to the length of the column to obtain a heat conductive sheet. A method for manufacturing a heat conductive sheet, wherein the heat conductive sheet satisfies the following conditions 1 and 2. [Condition 1]: The tack force of the above thermal conductive sheet is 80 gf or more. [Condition 2]: The above thermal conductive sheet, measuring 25 mm x 25 mm and 1 mm thick, is compressed by 40%, and after standing at 125°C for 48 hours, the amount of bleed of the binder resin is 0.20 g or less. (Note 11) The above binder resin is an addition-reaction type silicone resin. The above addition-reaction type silicone resin consists of a polyorganosiloxane having an alkenyl group in one molecule and an organohydrogenpolysiloxane having a hydrogen atom directly bonded to a silicon atom in one molecule. A method for producing a thermal conductive sheet as described in Appendix 10, wherein the blending ratio of the above polyorganosiloxane and the above organohydrogenpolysiloxane satisfies the following formula 1. Equation 1: Number of moles of hydrogen atoms directly bonded to silicon atoms / Number of moles of alkenyl groups = 0.40 or more and 0.60 or less (Note 12) A method for manufacturing a thermal conductive sheet as described in Appendix 10 or 11, further satisfying the following condition 3. [Condition 3]: The bulk thermal conductivity of the above thermal conductive sheet is 9.5 W / m·K or higher. (Note 13) Heating element and Heat sink and, An electronic device comprising a heat-generating element and a heat-conducting sheet described in any of the appendices 1 to 9, sandwiched between the heating element and the heat sink. [Examples]

[0064] The following describes some embodiments of this technology. However, this technology is not limited to these embodiments.

[0065] <Example 1> A thermally conductive composition was prepared by uniformly mixing 32 volume% of a silicone resin with a Si-H / alkenyl group ratio of 0.45 represented by Formula 1 above, 27 volume% of flaky boron nitride (D50 of 40 μm, aspect ratio of 20-50) with a hexagonal crystal structure, 20 volume% of aluminum nitride (D50 of 1.2 μm), 20 volume% of spherical alumina particles (D50 of 2 μm), and 1 volume% of zinc oxide particles (D50 of 0.1 μm). This thermally conductive composition was poured into a mold with a rectangular internal space (opening: 50 mm x 50 mm) by extrusion molding and heated in a 60°C oven for 4 hours to form a columnar cured product (molded block). A release polyethylene terephthalate film was attached to the inner surface of the mold so that the release treatment surface was facing inward. By slicing the resulting columnar hardened material into 1 mm thick sheets using a slicer in a direction approximately perpendicular to the length of the column, a thermally conductive sheet was obtained in which flaky boron nitride was oriented in the thickness direction of the sheet.

[0066] <Example 2> In Example 2, a thermal conductive composition was prepared by uniformly mixing 32 volume% of a silicone resin having a Si-H / alkenyl group ratio of 0.58 represented by Formula 1 described above, 27 volume% of flaky boron nitride (D50 of 40 μm, aspect ratio of 20-50) with a hexagonal crystal shape, 20 volume% of aluminum nitride (D50 of 1.2 μm), 20 volume% of spherical alumina particles (D50 of 2 μm), and 1 volume% of zinc oxide particles (D50 of 0.1 μm), except that a thermal conductive composition was prepared by uniformly mixing these components.

[0067] <Example 3> In Example 3, a thermal conductive composition was prepared by uniformly mixing 34 volume% of a silicone resin having a Si-H / alkenyl group ratio of 0.45 represented by Formula 1, 25 volume% of flaky boron nitride (D50 of 40 μm, aspect ratio of 15-40) with a hexagonal crystal structure, 20 volume% of aluminum nitride (D50 of 1.2 μm), 20 volume% of spherical alumina particles (D50 of 2 μm), and 1 volume% of zinc oxide particles (D50 of 0.1 μm), except that a thermal conductive composition was prepared by uniformly mixing these components.

[0068] <Example 4> In Example 4, a thermal conductive composition was prepared by uniformly mixing 36 volume% of a silicone resin having a Si-H / alkenyl group ratio of 0.45 represented by Formula 1, 23 volume% of flaky boron nitride (D50 of 40 μm, aspect ratio of 15-40) with a hexagonal crystal shape, 20 volume% of aluminum nitride (D50 of 1.2 μm), 20 volume% of spherical alumina particles (D50 of 2 μm), and 1 volume% of zinc oxide particles (D50 of 0.1 μm), except that a thermal conductive composition was prepared by uniformly mixing these components.

[0069] <Example 5> In Example 5, a thermal conductive sheet was obtained in the same manner as in Example 1, except that a thermal conductive composition was prepared using hexagonal flaky boron nitride (D50 of 50 μm, aspect ratio of 25-60) instead of hexagonal flaky boron nitride (D50 of 40 μm, aspect ratio of 20-50).

[0070] <Example 6> In Example 6, a thermal conductive sheet was obtained in the same manner as in Example 2, except that a thermal conductive composition was prepared using hexagonal flaky boron nitride (D50 of 50 μm, aspect ratio of 25-60) instead of hexagonal flaky boron nitride (D50 of 40 μm, aspect ratio of 20-50).

[0071] <Example 7> In Example 7, a thermal conductive sheet was obtained in the same manner as in Example 3, except that a thermal conductive composition was prepared using hexagonal flaky boron nitride (D50 of 50 μm, aspect ratio of 20-50) instead of hexagonal flaky boron nitride (D50 of 40 μm, aspect ratio of 15-40).

[0072] <Example 8> In Example 8, a thermal conductive sheet was obtained in the same manner as in Example 4, except that a thermal conductive composition was prepared using hexagonal flaky boron nitride (D50 of 50 μm, aspect ratio of 20-50) instead of hexagonal flaky boron nitride (D50 of 40 μm, aspect ratio of 15-40).

[0073] <Example 9> In Example 9, a thermal conductive composition was prepared by uniformly mixing 33 volume% of a silicone resin having a Si-H / alkenyl group ratio of 0.45 represented by Formula 1, 27 volume% of flaky boron nitride (D50 of 40 μm, aspect ratio of 15-40) with a hexagonal crystal structure, 20 volume% of aluminum nitride (D50 of 1.2 μm), and 20 volume% of spherical alumina particles (D50 of 2 μm), except that a thermal conductive composition was prepared by the same method as in Example 1.

[0074] <Example 10> In Example 10, a thermal conductive sheet was obtained in the same manner as in Example 1, except that a thermal conductive composition was prepared by uniformly mixing 33 volume% of a silicone resin having a Si-H / alkenyl group ratio of 0.45 represented by Formula 1, 27 volume% of flaky boron nitride (D50 of 40 μm, aspect ratio of 15-40) with a hexagonal crystal structure, 30 volume% of aluminum nitride (D50 of 1.2 μm), and 10 volume% of spherical alumina particles (D50 of 2 μm).

[0075] <Comparative Example 1> In Comparative Example 1, a thermal conductive composition was prepared by uniformly mixing 32 volume% of a silicone resin having a Si-H / alkenyl group ratio of 0.33 represented by Formula 1 described above, 27 volume% of flaky boron nitride (D50 of 40 μm, aspect ratio of 10-30) with a hexagonal crystal shape, 20 volume% of aluminum nitride (D50 of 1.2 μm), 20 volume% of spherical alumina particles (D50 of 2 μm), and 1 volume% of zinc oxide particles (D50 of 0.1 μm), except that a thermal conductive composition was prepared by uniformly mixing these components.

[0076] <Comparative Example 2> In Comparative Example 2, a thermal conductive sheet was obtained in the same manner as in Example 1, except that a thermal conductive composition was prepared by uniformly mixing 32 volume% of a silicone resin having a Si-H / alkenyl group ratio of 0.84 represented by Formula 1 described above, 27 volume% of flaky boron nitride (D50 of 40 μm, aspect ratio of 10-30) with a hexagonal crystal shape, 20 volume% of aluminum nitride (D50 of 1.2 μm), 20 volume% of spherical alumina particles (D50 of 2 μm), and 1 volume% of zinc oxide particles (D50 of 0.1 μm).

[0077] <Comparative Example 3> In Comparative Example 3, a thermal conductive sheet was obtained in the same manner as in Example 1, except that a thermal conductive composition was prepared by uniformly mixing 29 volume% of a silicone resin having a Si-H / alkenyl group ratio of 0.45 represented by Formula 1 described above, 30 volume% of flaky boron nitride (D50 of 40 μm, aspect ratio of 10-30) with a hexagonal crystal shape, 20 volume% of aluminum nitride (D50 of 1.2 μm), 20 volume% of spherical alumina particles (D50 of 2 μm), and 1 volume% of zinc oxide particles (D50 of 0.1 μm).

[0078] <Comparative Example 4> In Comparative Example 4, a thermal conductive sheet was obtained in the same manner as in Example 1, except that a thermal conductive composition was prepared by uniformly mixing 39 volume% of a silicone resin having a Si-H / alkenyl group ratio of 0.45 represented by Formula 1 described above, 20 volume% of flaky boron nitride (D50 of 40 μm, aspect ratio of 10-30) with a hexagonal crystal shape, 20 volume% of aluminum nitride (D50 of 1.2 μm), 20 volume% of spherical alumina particles (D50 of 2 μm), and 1 volume% of zinc oxide particles (D50 of 0.1 μm).

[0079] <Comparative Example 5> In Comparative Example 5, a thermal conductive composition was prepared by uniformly mixing 39 volume% of a silicone resin having a Si-H / alkenyl group ratio of 0.45 represented by Formula 1, 20 volume% of flaky boron nitride (D50 of 40 μm, aspect ratio of 10-30) with a hexagonal crystal structure, 10 volume% of aluminum nitride (D50 of 1.2 μm), 30 volume% of spherical alumina particles (D50 of 2 μm), and 1 volume% of zinc oxide particles (D50 of 0.1 μm), except that a thermal conductive composition was prepared by uniformly mixing these components.

[0080] <Comparative Example 6> In Comparative Example 6, a thermal conductive sheet was obtained in the same manner as in Example 1, except that a thermal conductive composition was prepared by uniformly mixing 39 volume% of a silicone resin having a Si-H / alkenyl group ratio of 0.45 represented by Formula 1 described above, 20 volume% of flaky boron nitride (D50 of 40 μm, aspect ratio of 10-30) with a hexagonal crystal shape, 30 volume% of aluminum nitride (D50 of 1.2 μm), 10 volume% of spherical alumina particles (D50 of 2 μm), and 1 volume% of zinc oxide particles (D50 of 0.1 μm).

[0081] <Comparative Example 7> In Comparative Example 7, a thermal conductive sheet was obtained in the same manner as in Comparative Example 1, except that a thermal conductive composition was prepared using hexagonal flaky boron nitride (D50 of 50 μm, aspect ratio of 15-40) instead of hexagonal flaky boron nitride (D50 of 40 μm, aspect ratio of 10-30).

[0082] <Comparative Example 8> In Comparative Example 8, a thermal conductive sheet was obtained in the same manner as in Comparative Example 2, except that a thermal conductive composition was prepared using hexagonal flaky boron nitride (D50 of 50 μm, aspect ratio of 15-40) instead of hexagonal flaky boron nitride (D50 of 40 μm, aspect ratio of 10-30).

[0083] <Comparative Example 9> In Comparative Example 9, a thermal conductive sheet was obtained in the same manner as in Comparative Example 3, except that a thermal conductive composition was prepared using hexagonal flaky boron nitride (D50 of 50 μm, aspect ratio of 15-40) instead of hexagonal flaky boron nitride (D50 of 40 μm, aspect ratio of 10-30).

[0084] <Comparative Example 10> In Comparative Example 10, a thermal conductive sheet was obtained in the same manner as in Comparative Example 4, except that a thermal conductive composition was prepared using hexagonal flaky boron nitride (D50 of 50 μm, aspect ratio of 15-40) instead of hexagonal flaky boron nitride (D50 of 40 μm, aspect ratio of 10-30).

[0085] <Comparative Example 11> In Comparative Example 11, a thermal conductive sheet was obtained in the same manner as in Comparative Example 5, except that a thermal conductive composition was prepared using hexagonal flaky boron nitride (D50 of 50 μm, aspect ratio of 15-40) instead of hexagonal flaky boron nitride (D50 of 40 μm, aspect ratio of 10-30).

[0086] <Comparative Example 12> In Comparative Example 12, a thermal conductive sheet was obtained in the same manner as in Comparative Example 6, except that a thermal conductive composition was prepared using hexagonal flaky boron nitride (D50 of 50 μm, aspect ratio of 15-40) instead of hexagonal flaky boron nitride (D50 of 40 μm, aspect ratio of 10-30).

[0087] <Oil bleed amount> Figure 4(A) is a cross-sectional view showing the heat conductive sheet 1 sandwiched between compression jigs (upper jig 61 and lower jig 62), and Figure 4(B) is a plan view showing the heat conductive sheet 1 placed on the lower jig 62. Figure 5(A) is a plan view showing the heat conductive sheet 1 sandwiched between compression jigs (upper jig 61 and lower jig 62), and Figure 5(B) is a side view showing the heat conductive sheet 1 sandwiched between compression jigs (upper jig 61 and lower jig 62).

[0088] For each example and comparative example, a heat conductive sheet 10 was prepared by processing the heat conductive sheet obtained in each example and comparative example to a size of 25 mm x 25 mm, and a mesh 60 (product name: PET mesh sheet, product number: TN180, manufactured by Sanplatec Co., Ltd.) was prepared by processing it to a size of 40 mm x 75 mm, and the weight of each was measured. The weight (g) of the heat conductive sheet 10 (25 mm x 25 mm x 1 mm thick) prepared in each example and comparative example is shown in Tables 1 and 2. An upper jig 61 and a lower jig 62 were prepared, and three sheets of filter paper 63 (model number: qualitative filter paper NO. 101, diameter 90 mm) were stacked and placed on the lower jig 62. Two sheets of mesh 60 were placed on top of the filter paper 63, and the heat conductive sheet 10 and spacer 64 were placed on top of the mesh 60. The distance between the heat conductive sheet 10 and spacer 64 was approximately 1 cm, as shown in Figure 4(B). Two sheets of mesh 65 were placed on top of the heat conductive sheet 10 and spacer 64. Three sheets of filter paper 66 were placed on top of the mesh 65. The upper jig 61 was placed on top of the filter paper 66, and the four nuts 67 on the upper jig 61 were tightened evenly until the heat conductive sheet 10 was compressed by 40%. The heat conductive sheet 10, sandwiched between the upper jig 61 and the lower jig 62 and compressed by 40%, was placed in an oven heated to 125°C. The heat conductive sheet 10 sandwiched between the upper jig 61 and the lower jig 62 was removed from the oven 48 hours later and left at room temperature to cool. The four nuts 67 on the upper jig 61 were removed, and the heat conductive sheet 10 and mesh 60, 65 (a total of four sheets) were weighed as a single unit. From the measured weight, the amount of silicone resin (binder resin) bleed (g) in the heat conductive sheet 10 was determined. The results are shown in Tables 1 and 2.

[0089] <Bulk thermal conductivity> The bulk thermal conductivity was determined by measuring the thermal resistance of each thermal conductive sheet according to the ASTM-D5470 method. The horizontal axis represents the thickness of the thermal conductive sheet at the time of measurement (mm), and the vertical axis represents the thermal resistance of the thermal conductive sheet (°C·cm). 2 The thermal conductivity (W / m·K) was plotted, and the bulk thermal conductivity of the thermal conductive sheet was calculated from the slope of the plot. The thermal resistance of the thermal conductive sheet was measured for each example and comparative example, using three types of thermal conductive sheets with the same composition but different thicknesses. The results are shown in Tables 1 and 2.

[0090] <Effective thermal conductivity> The effective thermal conductivity (W / m·K) of a thermal conductive sheet was determined using a thermal resistance measuring device compliant with ASTM-D5470, with a thickness of 1 mm and a thermal conductive sheet measured at 0.3 to 3 kgf / cm². 2 The values ​​were measured under load, and the value with the highest thermal conductivity was selected. The results are shown in Tables 1 and 2.

[0091] <Tackiness> The obtained thermal conductive sheet was sandwiched between two peeled PET films and pressed at 0.5 MPa for 30 seconds. After that, the PET film was peeled off the thermal conductive sheet, and the thermal conductive sheet was again sandwiched between two more peeled PET films and left for 7 days. After 7 days, immediately after peeling the peeled PET film off the thermal conductive sheet (within 3 minutes), a tack tester (Malcolm) was used to measure the tack force (gf) on the surface of the thermal conductive sheet when a 5.1 mm diameter probe was pressed into the thermal conductive sheet at a speed of 2 mm / second to a depth of 50 μm and then pulled out at a speed of 10 mm / second. The results are shown in Tables 1 and 2.

[0092] <Fixing to aluminum plate> Figure 6 illustrates a method for evaluating whether a thermal conductive sheet slides off an aluminum plate when it is placed on the aluminum plate and rotated by 90°. As shown in Figure 6(A), a thermal conductive sheet 20 was placed on a horizontally positioned aluminum plate 70. Then, as shown in Figure 6(B), the aluminum plate 70 was tilted by 90° while holding the thermal conductive sheet 20, and it was evaluated whether the thermal conductive sheet 20 slides off. The results are shown in Tables 1 and 2. In Tables 1 and 2, ○ indicates that the thermal conductive sheet 20 did not slide off (OK). Also, × indicates that the thermal conductive sheet 20 slid off (NG).

[0093] <Changes in thermal resistance> Thermal resistance value of thermal conductive sheet (°C·cm) 2The change in (W) was determined as follows. First, the thermal resistance value (initial thermal resistance value at 10% compression: first thermal resistance value) was measured when the thermal conductive sheet was compressed by 10% relative to its initial thickness immediately after manufacturing. After leaving this thermal conductive sheet at 150°C for 1000 hours, the thermal resistance value (thermal resistance value after 150°C × 1000H at 10% compression: second thermal resistance value) was measured when it was compressed by 10% relative to the thickness after 1000 hours at 150°C. From these first and second thermal resistance values, the percentage change (%) of the thermal resistance value at 10% compression before and after leaving the thermal conductive sheet at 150°C for 1000 hours was determined. The results are shown in Tables 1 and 2.

[0094] <Load 3kgf / cm 2 Compression ratio > The resulting heat-conducting sheet was left standing at 150°C for 1000 hours, and then subjected to a load of 3 kgf / cm². 2 The compressibility (%) of the thermal conductive sheet when a certain temperature was applied was measured. The results are shown in Tables 1 and 2.

[0095] <Changes in Shore hardness> The hardness of the thermal conductive sheet in Shore type OO was measured using a measurement method compliant with ASTM-D2240. Specifically, the Shore hardness (initial Shore hardness) of 10 thermal conductive sheets with a thickness of 1 mm immediately after manufacturing, and the Shore hardness of 10 thermal conductive sheets with a thickness of 1 mm that had been left to stand at 150°C for 1000 hours, were measured. The Shore hardness of the thermal conductive sheet was calculated as the average of the measurement results from 10 points in total (5 points on each side). The results are shown in Tables 1 and 2.

[0096] <Dielectric Breakdown Voltage> The dielectric breakdown voltage of the thermal conductive sheet was measured using an ultra-high voltage withstand voltage tester (7473, manufactured by Keisoku Gijutsu Kenkyusho) under the conditions of a thermal conductive sheet thickness of 1 mm, a voltage boosting rate of 0.05 kV / sec, and room temperature. The dielectric breakdown voltage (kV) was defined as the voltage at which dielectric breakdown occurred. The results are shown in Tables 1 and 2.

[0097] [Table 1]

[0098] [Table 2]

[0099] The thermal conductive sheets obtained in Examples 1 to 10 consisted of cured products of a composition containing a binder resin, an anisotropic thermal conductive filler, and another thermal conductive filler, satisfying conditions 1 and 2 described above, and were found to have excellent adhesion to the heating element and to be able to suppress excessive bleeding of the binder resin. Furthermore, the thermal conductive sheets obtained in Examples 1 to 10 satisfied condition 3 described above and were found to have good thermal conductivity.

[0100] The thermal conductive sheets obtained in Examples 1-10 showed that the change in thermal resistance value measured at a compression ratio of 10% after standing at 150°C for 1000 hours was within 10% of the change in thermal resistance value measured at a compression ratio of 10% immediately after manufacturing. Furthermore, the thermal conductive sheets obtained in Examples 1-10 were subjected to a load of 3 kgf / cm after standing at 150°C for 1000 hours. 2 The measured compression ratio was found to be 20% or higher.

[0101] The thermal conductive sheets obtained in Comparative Examples 1, 4-7, and 10-12 did not satisfy condition 2 described above, and it was found that they could not suppress excessive bleeding of the binder resin.

[0102] The thermal conductive sheets obtained in Comparative Examples 2, 3, 8, and 9 did not satisfy condition 1 described above, and it was found that they did not have good fixation properties to the aluminum plate.

[0103] It was found that the thermal conductive sheets obtained in Comparative Examples 3, 9-12 did not show a change of less than 10% in their thermal resistance value, measured at a compression ratio of 10% after standing at 150°C for 1000 hours, compared to the thermal resistance value measured at a compression ratio of 10% immediately after manufacturing. Furthermore, the thermal conductive sheets obtained in Comparative Examples 2, 3, 8, and 9 were subjected to a load of 3 kgf / cm after standing at 150°C for 1000 hours. 2 The measured compression ratio was found to be less than 20%. [Explanation of symbols]

[0104] 1 Thermal conductive sheet, 1A Surface, 2 Binder resin, 3 Anisotropic thermal conductive filler, 4 Other thermal conductive filler, 10 Thermal conductive sheet, 20 Thermal conductive sheet, 51 Electronic component, 52 Heat spreader, 53 Heat sink, 52a Main surface, 52b Side wall, 60 Mesh, 61 Upper jig, 62 Lower jig, 63 Filter paper, 64 Spacer, 65 Mesh, 66 Filter paper, 67 Nut, 70 Aluminum plate

Claims

1. A thermal conductive sheet comprising a cured product of a composition containing a binder resin, an anisotropic thermal conductive filler, and other thermal conductive fillers other than the anisotropic thermal conductive filler, and satisfying the following conditions 1 and 2. [Condition 1]: The tack force of the thermal conductive sheet is 80 gf or more. [Condition 2]: The amount of bleed of the binder resin after standing for 48 hours at 125°C in a 25 mm x 25 mm, 1 mm thick thermal conductive sheet compressed by 40% is 0.20 g or less.

2. The above binder resin is an addition-reaction type silicone resin. The above addition-reaction type silicone resin consists of a polyorganosiloxane having an alkenyl group in one molecule and an organohydrogenpolysiloxane having a hydrogen atom directly bonded to a silicon atom in one molecule. The thermal conductive sheet according to claim 1, wherein the blending ratio of the above polyorganosiloxane and the above organohydrogenpolysiloxane satisfies the following formula 1. Equation 1: Number of moles of hydrogen atoms directly bonded to silicon atoms / Number of moles of alkenyl groups = 0.40 or more and 0.60 or less

3. The thermal conductive sheet according to claim 1 or 2, wherein the content of the binder resin is 30% by volume or more and 38% by volume or less.

4. The thermal conductive sheet according to claim 1 or 2, wherein the content of the above-mentioned anisotropic thermal conductive filler is 22% by volume or more and 29% by volume or less.

5. The above anisotropic thermal conductive filler is boron nitride. The thermal conductive sheet according to claim 1 or 2, wherein the above-mentioned other thermal conductive filler is one or more of alumina, aluminum nitride, zinc oxide, and aluminum hydroxide, including at least alumina.

6. The above anisotropic thermal conductive filler is flaky boron nitride. The thermal conductive sheet according to claim 1 or 2, wherein the above-mentioned flaky boron nitride is oriented in the thickness direction of the thermal conductive sheet.

7. The thermal conductive sheet according to claim 1 or 2, further satisfying the following condition 3. [Condition 3]: The bulk thermal conductivity of the thermal conductive sheet is 9.5 W / m·K or higher.

8. The thermal conductive sheet according to claim 1 or 2, wherein the rate of change of the thermal resistance value measured at a compression ratio of 10% after standing at 150°C for 1000 hours is within 10% compared to the thermal resistance value measured at a compression ratio of 10% immediately after manufacture.

9. After standing for 1000 hours at 150°C, a load of 3 kgf / cm was applied. ２ The thermal conductive sheet according to claim 1 or 2, wherein the compressibility measured is 20% or more.

10. Step A involves preparing a thermally conductive composition containing a binder resin, an anisotropic thermally conductive filler, and a thermally conductive filler other than the anisotropic thermally conductive filler. Step B involves extruding the above-mentioned thermally conductive composition and then curing it to obtain a columnar cured product. The process includes step C, which involves cutting the above-mentioned columnar hardened material to a predetermined thickness in a direction substantially perpendicular to the length of the column to obtain a heat conductive sheet. A method for manufacturing a heat conductive sheet, wherein the heat conductive sheet satisfies the following conditions 1 and 2. [Condition 1]: The tack force of the above thermal conductive sheet is 80 gf or more. [Condition 2]: The above thermal conductive sheet, measuring 25 mm x 25 mm and 1 mm thick, is compressed by 40%, and after standing at 125°C for 48 hours, the amount of bleed of the binder resin is 0.20 g or less.

11. The above binder resin is an addition-reaction type silicone resin. The above addition-reaction type silicone resin consists of a polyorganosiloxane having an alkenyl group in one molecule and an organohydrogenpolysiloxane having a hydrogen atom directly bonded to a silicon atom in one molecule. A method for producing a thermal conductive sheet according to claim 10, wherein the blending ratio of the polyorganosiloxane and the organohydrogenpolysiloxane satisfies the following formula 1. Equation 1: Number of moles of hydrogen atoms directly bonded to silicon atoms / Number of moles of alkenyl groups = 0.40 or more and 0.60 or less

12. A method for manufacturing a heat conductive sheet according to claim 10 or 11, further satisfying the following condition 3. [Condition 3]: The bulk thermal conductivity of the above-mentioned thermal conductive sheet is 9.5 W / m·K or higher.

13. Heating element and Heat sink and, An electronic device comprising a heat-conducting sheet according to claim 1 or 2, sandwiched between a heat-generating element and a heat-sinking element.

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