Resin sheet and method for manufacturing same

Abstract

Provided is a resin sheet containing a filler formed by aggregation of primary particles that have a plate shape, a scale shape, or a needle shape, the resin sheet making it possible to enhance thermal conductivity.　This resin sheet is characterized in that: the ratio (Pi / Po) of the peak area intensity ratio Pi ((002) / (100)) of a (002) plane and a (100) plane of the filler in the resin sheet, said peak area intensity ratio Pi ((002) / (100)) being obtained by measuring the resin sheet using in-plane X-ray diffraction, to the peak area intensity ratio Po ((002) / (100)) of the (002) plane and the (100) plane of the filler in the resin sheet, said peak area intensity ratio Po ((002) / (100)) being obtained by measuring the resin sheet using concentrated X-ray diffraction, is 0.13-0.41; or the peak area intensity ratio Pi ((002) / (100)) is 1.5-10.0, and the peak area intensity ratio Po ((002) / (100)) is 9.0-13.0.

Description

Resin sheet and method for manufacturing the same

[0001] The present invention relates to a resin sheet containing a filler that can be suitably used as, for example, a heat dissipation member for a power semiconductor device, and a method for producing the same.

[0002] Among devices using semiconductors, devices that control or convert power from a power supply or the like are called "power semiconductor devices." Power semiconductor devices generally have a configuration in which power semiconductors that convert or control power and electronic components are mounted on a substrate that functions as a heat sink. In recent years, power semiconductor devices used in various fields such as railways, automobiles, industry, and general home appliances are transitioning from conventional Si power semiconductors to power semiconductors using SiC, AlN, GaN, etc. in order to achieve further miniaturization, cost reduction, and efficiency improvement.

[0003] Various issues have been raised in the practical application of such power semiconductor devices, one of which is the issue of heat generation from the devices. While power semiconductor devices can achieve high output and high density by operating at high temperatures, there are concerns that heat generated by device switching and other operations will reduce the reliability of the power semiconductor devices.

[0004] Furthermore, in recent years, heat generation due to the increasing density of integrated circuits has become a major problem in the electrical and electronic fields, and how to dissipate heat has become an urgent issue. For example, to ensure stable operation of semiconductor devices used to control central processing units of personal computers, motors of electric vehicles, etc., heat sinks, heat dissipation fins, etc. are essential for heat dissipation, and there is a demand for materials that can combine thermal conductivity and insulation properties as materials for joining components such as circuits containing semiconductors to heat dissipation components such as heat sinks.

[0005] Ceramic substrates with high thermal conductivity, such as alumina substrates and aluminum nitride substrates, have traditionally been used as components that offer both thermal conductivity and electrical insulation. However, ceramic substrates have issues such as being easily cracked by impact and being difficult to make thin and compact. To address this issue, heat dissipation sheets using thermosetting resins, such as epoxy resins, and fillers have been proposed.

[0006] Regarding heat dissipation sheets using thermosetting resins and fillers, various resin sheets containing boron nitride as a filler have been proposed (see Patent Documents 1 to 8). Boron nitride is an insulating ceramic that has attracted particular attention in recent years in the field of electrical and electronic materials due to its excellent thermal conductivity, solid lubricity, chemical stability, and heat resistance.

[0007] JP 2015-6980 A JP 2015-189823 A JP 2015-195287 A JP 2016-011358 A JP 2016-135731 A JP 2019-119883 A JP 2021-6507 A

[0008] Regarding resin sheets containing fillers, when the filler is a plate-like, scale-like, or needle-like primary particle, such as boron nitride particles, the filler has anisotropic thermal conductivity, which tends to increase thermal conductivity in the sheet surface direction while decreasing thermal conductivity in the sheet thickness direction. Even when isotropically aggregated particles are used to avoid this, anisotropy occurs during sheet production, making it difficult to increase thermal conductivity in the sheet thickness direction. Therefore, the object of the present invention is to provide a resin sheet containing a filler formed by aggregation of plate-like, scale-like, or needle-like primary particles, which can increase thermal conductivity, and a method for producing the same.

[0009] In order to solve the above problems, the resin sheet and the method for producing the same proposed by the present invention have the following configuration.

[0010] [1] A first aspect of the present invention is a resin sheet containing a filler formed by an aggregation of plate-like, scale-like, or needle-like primary particles, characterized in that the ratio (Pi / Po) of the peak area intensity ratio Pi((002) / (100)) of the (002) plane to the (100) plane of the filler in the resin sheet, obtained by measuring the resin sheet using in-plane X-ray diffraction, to the peak area intensity ratio Po((002) / (100)) of the (002) plane to the (100) plane of the filler in the resin sheet, obtained by measuring the resin sheet using an X-ray diffraction method with a focusing method, is 0.13 or more and 0.41 or less.

[0011] [2] A second aspect of the present invention is a resin sheet containing a filler formed by an aggregation of plate-like, scale-like, or needle-like primary particles, characterized in that the resin sheet is measured by in-plane X-ray diffraction, and the peak area intensity ratio Pi((002) / (100)) of the (002) plane to the (100) plane of the filler in the resin sheet is 1.5 or more and 10.0 or less, and the resin sheet is measured by X-ray diffraction using a focusing method, and the peak area intensity ratio Po((002) / (100)) of the (002) plane to the (100) plane of the filler in the resin sheet is 9.0 or more and 13.0 or less.

[0012] [3] A third aspect of the present invention is the resin sheet of the first aspect, wherein the peak area intensity ratio Pi((002) / (100)) is 1.5 or more and 10.0 or less. [4] A fourth aspect of the present invention is the resin sheet of the first or third aspect, wherein the peak area intensity ratio Po((002) / (100)) is 9.0 or more and 13.0 or less.

[0013] [5] A fifth aspect of the present invention is a resin sheet according to any one of the first to fourth aspects, which is a cured product of a thermosetting resin composition containing the filler and a thermosetting resin. [6] A sixth aspect of the present invention is a resin sheet according to the fifth aspect, wherein the thermosetting resin contains an epoxy resin. [7] A seventh aspect of the present invention is a resin sheet according to any one of the first to sixth aspects, wherein the filler has a thermal conductivity of 10 W / m·k or more. [8] An eighth aspect of the present invention is a resin sheet according to any one of the first to seventh aspects, wherein the filler contains boron nitride agglomerated particles. [9] A ninth aspect of the present invention is a resin sheet according to the eighth aspect, wherein the boron nitride agglomerated particles have a house-of-cards structure.

[0014]

[10] A tenth aspect of the present invention is the resin sheet according to any one of the first to ninth aspects, wherein the thermal conductivity in the sheet thickness direction at 25° C. is 10 W / m·K or more.

[11] An eleventh aspect of the present invention is the resin sheet according to any one of the first to tenth aspects, wherein the resin sheet is used as a heat dissipation member for a power semiconductor device.

[0015]

[12] A twelfth aspect of the present invention is a method for producing a resin sheet according to any one of the first to eleventh aspects, characterized in that a thermosetting resin composition containing the filler and the thermosetting resin is formed into a coating or sheet, pressurized, and thermally cured.

[0016]

[13] A thirteenth aspect of the present invention is the method for producing a resin sheet according to the twelfth aspect, wherein the pressing is performed by calendar pressing under conditions of a linear pressure on the sheet of 20 to 200 kgf / cm and a roller temperature of 0 to 50°C, or a pressure on the sheet of 10 to 2000 kgf / cm ２

[14] A fourteenth aspect of the present invention is a method for producing a resin sheet according to the twelfth or thirteenth aspect, characterized in that the heat curing is performed by heating to 80 to 300°C and applying a pressure of 50 to 2000 kgf / cm. ２

[15] A fifteenth aspect of the present invention is the method for producing a resin sheet according to any one of the twelfth to fourteenth aspects, characterized in that low-temperature aging is performed by placing the thermosetting resin composition in an environment at a temperature of 0°C or lower.

[16] A sixteenth aspect of the present invention is the method for producing a resin sheet according to the fifteenth aspect, characterized in that the low-temperature aging is performed after the thermosetting resin composition is formed into a coating or sheet shape and before pressing.

[0017] The resin sheet proposed by the present invention is a resin sheet in which the orientation direction of the filler is controlled throughout the entire sheet, particularly near the surface of the sheet, and which can have excellent thermal conductivity, particularly thermal conductivity in the thickness direction of the sheet.

[0018] 1 is an X-ray diffraction profile diagram (XRD profile) obtained by measuring the resin sheet (sample) obtained in Example 1 by in-plane X-ray diffraction. FIG. 2 is a schematic diagram illustrating the in-plane X-ray diffraction method.

[0019] An example of an embodiment of the present invention will be described below, but the present invention is not limited to the embodiment described below.

[0020] <Resin Sheet of the Present Invention> A resin sheet according to an embodiment of the present invention (also referred to as "resin sheet of the present invention") is a resin sheet containing a filler (also referred to as "the present filler") formed by an aggregation of plate-like, scale-like, or needle-like primary particles. An example of the resin sheet of the present invention can be one made from a cured product of a thermosetting resin composition (also referred to as "the present thermosetting resin composition") containing the present filler and a thermosetting resin. A more specific example can be a sheet-like cured product obtained by thermally curing a sheet-like product obtained by pressing a thermosetting resin composition containing the present filler and a thermosetting resin into a sheet.

[0021] In the present invention, the term "resin sheet" refers to a sheet in which the component forming the continuous phase (matrix) of the sheet is a synthetic resin, and the "synthetic resin" includes thermoplastic resins, thermosetting resins, and their cured products, regardless of molecular weight. In the present invention, the term "resin" includes compounds, monomers, oligomers, and polymers, regardless of molecular weight. In the present invention, the term "sheet surface direction" refers to the direction parallel to the sheet surface, and is also referred to as the "transverse direction." On the other hand, the term "sheet thickness direction" refers to the film thickness direction of the sheet, and is also referred to as the "longitudinal direction."

[0022] <Present Filler> The present filler is a particle or aggregate thereof made of an organic or inorganic substance, which is formed by the aggregation of plate-like, scale-like, or needle-like primary particles. Preferably, it is a particle (inorganic particle) made of an inorganic substance, which is formed by the aggregation of plate-like, scale-like, or needle-like primary particles. The primary particles of the present filler exhibit anisotropy in thermal conductivity and tend to be oriented in a specific direction in the resin sheet of the present invention. Therefore, the orientation of the present filler in the resin sheet of the present invention significantly affects the thermal conductivity of the resin sheet of the present invention. Normally, during sheet production, the primary particles of the filler tend to be oriented in the sheet surface direction, which tends to reduce thermal conductivity in the sheet thickness direction. However, since the present filler is an agglomerated particle, the primary particles within the particle are more likely to be isotropically oriented than non-agglomerated particles, which can be said to make it easier to increase the thermal conductivity in the sheet thickness direction.

[0023] The filler preferably has a thermal conductivity of 10 W / m K or higher. Examples of such fillers include electrically insulating fillers made only of carbon, and fillers made of metal carbides or semi-metal carbides, metal oxides or semi-metal oxides, and metal nitrides or semi-metal nitrides. These fillers may be used alone or in combination of two or more.

[0024] Examples of electrically insulating fillers consisting solely of carbon include diamond (thermal conductivity: approximately 2000 W / m·K). Examples of metal carbides or semi-metal carbides include silicon carbide (thermal conductivity: approximately 60 to 270 W / m·K), titanium carbide (thermal conductivity: approximately 21 W / m·K), and tungsten carbide (thermal conductivity: approximately 120 W / m·K). Examples of metal oxides or semi-metal oxides include magnesium oxide (thermal conductivity: approximately 40 W / m·K), zinc oxide (thermal conductivity: approximately 54 W / m·K), yttrium oxide (thermal conductivity: approximately 27 W / m·K), ytterbium oxide (thermal conductivity: approximately 38.5 W / m·K), beryllium oxide (thermal conductivity: approximately 250 W / m·K), and sialon (ceramics consisting of silicon, aluminum, oxygen, and nitrogen, thermal conductivity: approximately 21 W / m·K). Examples of the metal nitride or semi-metal nitride include boron nitride (thermal conductivity in the sheet surface direction of plate-like particles of hexagonal boron nitride (h-BN): about 200 to 500 W / m·K), aluminum nitride (thermal conductivity: about 160 to 285 W / m·K), and silicon nitride (thermal conductivity: about 30 to 80 W / m·K).

[0025] The maximum particle size of the filler is preferably 20 μm or more, more preferably 30 μm or more, and even more preferably 40 μm or more, from the viewpoint that the number of particles in the resin sheet of the present invention is relatively small, and the interparticle interfaces are reduced, thereby reducing thermal resistance and increasing thermal conductivity. On the other hand, from the viewpoint of obtaining surface smoothness of the resin sheet of the present invention, it is preferably 300 μm or less, more preferably 200 μm or less, and even more preferably 100 μm or less. The average particle size of the filler is preferably 5 μm or more, more preferably 10 μm or more, more preferably 15 μm or more, more preferably 20 μm or more, more preferably 25 μm or more, and even more preferably 30 μm or more, from the viewpoint that the number of particles in the resin sheet of the present invention is relatively small, and the interparticle interfaces are reduced, thereby reducing contact thermal resistance and increasing thermal conductivity. On the other hand, from the viewpoint of obtaining surface smoothness of the resin sheet of the present invention, it is preferably 150 μm or less, more preferably 120 μm or less, and even more preferably 90 μm or less.

[0026] The maximum particle size and average particle size of the filler can be measured, for example, by the following method. A sample of the filler dispersed in a solvent, specifically, a sample of the filler dispersed in a pure water medium containing a dispersion stabilizer, is subjected to volumetric particle size distribution measurement using a laser diffraction / scattering particle size distribution analyzer, and the maximum particle size Dmax and average particle size D50 of the filler can be determined from the obtained particle size distribution. Here, Dmax and D50 are the maximum particle size and the particle size at 50% cumulative volume in the volumetric particle size distribution obtained by measurement using a laser diffraction / scattering particle size distribution measurement method. The maximum particle size and average particle size can also be determined using a dry particle size distribution analyzer such as a Morphologi G3 (manufactured by Malvern Instruments). When the filler is an inorganic particle, the resin sheet (cured product) of the present invention is baked to remove the resin component and separate the filler. For example, the organic components of the resin sheet (cured product) of the present invention may be heated in the atmosphere to be ashed and removed, and the Dmax and D50 of the filler contained in the resulting ashed residue may be measured by laser diffraction or Morphologi. Alternatively, the cross section of the resin sheet (cured product) of the present invention may be directly observed with a scanning electron microscope, a transmission electron microscope, a micro-Raman spectrometer, an atomic force microscope, or the like to determine the maximum particle size among the ten or more particles of the filler, or the average particle size may be determined by directly observing ten or more particles of the filler and arithmetically averaging the diameter. In this case, if the particles of the filler are non-spherical, the longest and shortest diameters are measured, and the average value is used as the particle size of the particles.

[0027] The elastic modulus of the filler is preferably 48 MPa or more, more preferably 50 MPa or more, and even more preferably 55 MPa or more, from the viewpoint of preventing the filler from undergoing plastic deformation in the direction of the pressing pressure and collapsing the aggregated structure. On the other hand, from the viewpoint of easily obtaining sufficient deformation, the elastic modulus is preferably 1000 MPa or less, more preferably 500 MPa or less, and even more preferably 100 MPa or less.

[0028] The crushing strength of the filler is preferably 4 MPa or more, more preferably 5 MPa or more, and is preferably 20 MPa or less, more preferably 15 MPa or less, and even more preferably 10 MPa or less. By keeping the crushing strength within this range, it is possible to prevent the primary particles of the filler from becoming excessively oriented in the sheet thickness direction after pressurization, and the primary particles of the filler are present in an appropriate amount so that they can be in surface contact with each other, in other words, the filler is oriented in the sheet surface direction, which makes it easier to form heat conduction paths and improves thermal conductivity.

[0029] When the filler is present in the resin sheet of the present invention, the elastic modulus and crushing strength of the filler can be measured after baking the resin of the resin sheet of the present invention and removing the filler so as not to deteriorate the filler. The measurement method is as described in the Examples.

[0030] From the viewpoint of improving the insulating property and the thermal conductivity, the content of the filler is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more, relative to 100% by mass of the resin sheet of the present invention. On the other hand, from the viewpoint of maintaining good handling properties (brittleness), the content is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less.

[0031] (Boron nitride agglomerated particles) Among the above-mentioned fillers, boron nitride agglomerated particles formed by agglomeration of plate-like, scale-like, or needle-like boron nitride primary particles are particularly preferred because they have excellent electrical insulation, thermal conductivity, solid lubricity, chemical stability, and heat resistance.

[0032] Examples of boron nitride agglomerated particles include those formed by spherical aggregation of plate-like, scale-like, or needle-like primary particles. Here, "spherical" refers to an aspect ratio (ratio of major axis to minor axis) of 1 or more and 2 or less, preferably 1 or more and 1.5 or less. The aspect ratio of the boron nitride agglomerated particles is determined by randomly selecting 200 or more particles from an image taken with a scanning electron microscope, determining the ratio of the major axis to the minor axis of each, and calculating the average value.

[0033] Examples of boron nitride agglomerated particles include those having a conventionally known form in which scale-like or needle-like primary particles grow radially from the center to the surface of the agglomerated particles, those having a spherical form in which plate-like primary particles are sintered and agglomerated, and those having a house-of-card structure composed of plate-like primary particles. Among these, from the viewpoint of improving thermal conductivity, it is preferable for the boron nitride agglomerated particles to have a house-of-card structure. Here, the "house-of-card structure" refers to a structure in which plate-like particles are stacked in a complex manner without being oriented, as described, for example, in Ceramics 43 No. 2 (published by the Ceramic Society of Japan in 2008). More specifically, boron nitride agglomerated particles having a house-of-card structure are boron nitride agglomerated particles that are an aggregate of boron nitride primary particles and have a structure in which the flat surfaces and end surfaces of the primary particles are in contact with each other.

[0034] <Other Fillers> The resin sheet of the present invention may contain "other fillers" other than the present filler, i.e., a filler formed by agglomeration of plate-, scaly, or needle-shaped primary particles. The "other fillers" preferably have a thermal conductivity of 10 W / m·K or higher, and examples thereof include agglomerated particles and non-agglomerated particles formed by agglomeration of primary particles formed by agglomeration of shapes other than plate-, scaly, or needle-shaped primary particles, such as boron nitride, aluminum oxide (alumina), aluminum nitride, silica, and magnesium oxide. When the "other fillers" are contained, it is preferable to use alumina particles, particularly spherical alumina particles, as the "other fillers" from the viewpoints of packing ability, water resistance, and thermal conductivity.

[0035] From the viewpoint of reducing the contact thermal resistance between fillers, the average particle size of the other fillers is preferably 0.5 μm or more, more preferably 1 μm or more, and even more preferably 3 μm or more. On the other hand, from the viewpoint of optimizing the filling rate, it is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 20 μm or less. The average particle size of the other fillers can be measured by the same method as that used for measuring the average particle size of the filler.

[0036] When the "other filler" is contained, the content of all fillers (this filler and other fillers) is preferably 40% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more, relative to 100% by mass of the resin sheet of the present invention, from the viewpoint of increasing thermal conductivity. On the other hand, from the viewpoint of preventing a decrease in withstand voltage due to a decrease in the resin amount and from the viewpoint of the handleability of the resin sheet of the present invention, it is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less.

[0037] When the "other filler" is contained, the mass proportion of the present filler in 100 mass% of all fillers (the present filler and other fillers) is preferably 50 mass% or more, more preferably 55 mass% or more, even more preferably 60 mass% or more, even more preferably 65 mass% or more, and even more preferably 70 mass% or more, from the viewpoint of increasing thermal conductivity. On the other hand, there is no particular upper limit, but it may be, for example, 99 mass% or less, or even 98 mass% or less. It is not necessary to contain other fillers other than the present filler, but by containing other fillers, the fillers may be packed more densely, in which case the amount of resin with higher thermal resistance can be reduced and thermal conductivity can be increased.

[0038] <Resin> The resin in the resin sheet of the present invention is a matrix resin, i.e., a component that forms the continuous phase (matrix) of the resin sheet of the present invention. A thermoplastic resin and / or a thermosetting resin is preferred, and a thermosetting resin is particularly preferred from the viewpoints of heat durability, adhesion to metals, and handleability.

[0039] Examples of the thermoplastic resin for the resin sheet of the present invention include polyolefin resin, polyester resin, polycarbonate resin, polystyrene resin, polyvinyl alcohol resin, acrylic resin, polyurethane resin, polyphenylene ether resin, polysulfone resin, polyphenylsulfone resin, polyethersulfone resin, polyetherimide resin, polyamide resin, polyetherketone resin, polytetrafluoroethylene resin, tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin, tetrafluoroethylene-hexafluoropropylene copolymer resin, and the like.

[0040] The thermosetting resin of the resin sheet of the present invention may be any compound (including polymers) that has the property of being cured by heat. Examples include epoxy resins, phenolic resins, polycarbonate resins, unsaturated polyester resins, urethane resins, melamine resins, urea resins, maleimide resins, cyanate resins, benzoxazine, and (meth)acrylic resins. Among these, epoxy resins are preferred from the viewpoints of viscosity, heat resistance, moisture absorption, and ease of handling.

[0041] (Epoxy Resin) The epoxy resin may be any compound having one or more oxirane rings, i.e., epoxy groups, in the molecule. The epoxy group contained in the epoxy resin may be either an alicyclic epoxy group or a glycidyl group. From the viewpoint of reaction rate or heat resistance, a glycidyl group is more preferable.

[0042] Examples of epoxy resins include epoxy group-containing silicon resins, aliphatic epoxy resins, bisphenol A or F epoxy resins, novolac epoxy resins, alicyclic epoxy resins, glycidyl ester epoxy resins, polyfunctional epoxy resins, polymeric epoxy resins, etc. The epoxy resin may be an aromatic epoxy group-containing resin. Specific examples thereof include bisphenol-type epoxy resins obtained by glycidylating bisphenols such as bisphenol A, bisphenol F, bisphenol AD, bisphenol S, tetramethylbisphenol A, tetramethylbisphenol F, tetramethylbisphenol AD, tetramethylbisphenol S, and tetrafluorobisphenol A; biphenyl-type epoxy resins; epoxy resins obtained by glycidylating dihydric phenols such as dihydroxynaphthalene and 9,9-bis(4-hydroxyphenyl)fluorene; epoxy resins obtained by glycidylating trisphenols such as 1,1,1-tris(4-hydroxyphenyl)methane; epoxy resins obtained by glycidylating tetrakisphenols such as 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane; and novolac-type epoxy resins obtained by glycidylating novolacs such as phenol novolac, cresol novolac, bisphenol A novolac, and brominated bisphenol A novolac.

[0043] Among epoxy resins, polyfunctional epoxy resins are particularly preferred. The polyfunctional epoxy resins may be epoxy resins having three or more epoxy groups in one molecule, and more preferably epoxy resins having four or more epoxy groups in one molecule.

[0044] The molecular weight of the polyfunctional epoxy resin is preferably 600 or less, particularly 100 or more or 590 or less, and even more preferably 200 or more or 580 or less. Furthermore, from the viewpoint of achieving lower moisture absorption and higher crosslinking, it is preferable that the polyfunctional epoxy resin does not contain an amine-based or amide-based structure containing a nitrogen atom. From the viewpoint of maintaining the heat resistance of the resin sheet of the present invention, the epoxy equivalent of the polyfunctional epoxy resin is more preferably 75 g / equivalent or more. On the other hand, from the viewpoint of solubility in solvents, it is preferably 200 g / equivalent or less, more preferably 180 g / equivalent or less, even more preferably 160 g / equivalent or less, and even more preferably 150 g / equivalent or less.

[0045] It is also preferable that the thermosetting resin composition contains a high-molecular-weight epoxy compound (also referred to as an "epoxy polymer") having a mass-average molecular weight of more than 5,000. By containing an epoxy polymer, the thermosetting resin composition can form a stronger crosslinked structure. On the other hand, the curing reaction rate of the thermosetting resin composition can be slowed, improving stability, for example, shelf life. Furthermore, even if the content of the filler, for example, agglomerated boron nitride particles, is increased, good handleability (brittleness) can be maintained.

[0046] Examples of the epoxy polymer include phenoxy resins having at least one skeleton selected from the group consisting of a bisphenol A skeleton, a bisphenol F skeleton, a bisphenol A / F mixed skeleton, a naphthalene skeleton, a fluorene skeleton, a biphenyl skeleton, an anthracene skeleton, a pyrene skeleton, a xanthene skeleton, an adamantane skeleton, and a dicyclopentadiene skeleton.

[0047] The weight average molecular weight (Mw) of the epoxy polymer is preferably greater than 5,000, more preferably 10,000 or greater, even more preferably 15,000 or greater, even more preferably 20,000 or greater, and even more preferably 25,000 or greater. The upper limit can be 100,000 or less. These ranges tend to improve the handleability of the resin sheet of the present invention. Furthermore, the improved film-forming properties of the thermosetting resin composition effectively bind the fillers together, making voids less likely to occur. From the viewpoint of ensuring the flexibility of the thermosetting resin composition, the epoxy equivalent of the epoxy polymer is preferably 5,000 g / equivalent or greater, more preferably 7,000 g / equivalent or greater, even more preferably 8,000 g / equivalent or greater. On the other hand, from the viewpoint of solubility in solvents, it is preferably 25,000 g / equivalent or less, even more preferably 20,000 g / equivalent or less. The mass average molecular weight is a value calculated as polystyrene as measured by gel permeation chromatography. The epoxy equivalent is defined as the mass of an epoxy resin containing one equivalent of epoxy groups, and can be measured in accordance with JIS K7236.

[0048] <Orientation of the Filler in the Resin Sheet of the Present Invention> Conventionally, with regard to heat dissipation sheets made of resin sheets containing fillers, the peak area intensity ratio obtained by X-ray diffraction measurement using a focusing method (hereinafter also referred to as the "focusing method") has been said to be correlated with the thermal conductivity of the resin sheet. However, it has been confirmed that even when the Po value (described below) obtained by the focusing method is the same, there are differences in thermal conductivity, and it has been found that the correlation between filler orientation and thermal conductivity cannot be fully explained by the peak area intensity ratio measured by the focusing method alone. The present inventors have discovered that the thermal conductivity of a resin sheet can be increased by combining and specifying the peak area intensity ratio obtained by measurement using the focusing method and the peak area intensity ratio obtained by measurement using an in-plane X-ray diffraction method (hereinafter also referred to as the "in-plane method"). Based on this knowledge, the present invention was conceived. That is, as mentioned above, the concentration method can measure the orientation of the filler throughout the entire sheet, whereas the in-plane method can measure the orientation of the filler near the surface of the sheet. Therefore, by combining and defining the results of both of these measurements, it was found that it was possible to correlate the filler orientation determined by the X-ray diffraction measurement results with the thermal conductivity of the resin sheet, thereby increasing the thermal conductivity of the resin sheet.

[0049] [Ratio (Pi / Po)] In the resin sheet of the present invention, the resin sheet is measured by the in-plane method. The ratio (Pi / Po) of the peak area intensity ratio Pi((002) / (100)) of the (002) plane to the (100) plane of the filler in the resin sheet, Po((002) / (100)), is 0.13 or more and 0.41 or less, from the viewpoint of increasing thermal conductivity.

[0050] As described above, the peak area intensity ratio Pi((002) / (100)) of the filler in the resin sheet obtained by measurement using the in-plane method is an index indicating the orientation of the filler near the surface of the sheet, particularly the degree of orientation of the filler in the thickness direction of the sheet. On the other hand, the peak area intensity ratio Po((002) / (100)) of the filler in the resin sheet obtained by measurement using the focusing method is an index indicating the orientation of the filler in the entire sheet, particularly the degree of orientation of the filler in the lateral direction of the sheet, i.e., the sheet surface direction. These ratios (Pi / Po) are considered to indicate the tendency of the orientation state near the surface of the sheet in the orientation state of the filler in the entire sheet, particularly the degree of orientation of the filler in the thickness direction of the sheet. Therefore, when the ratio (Pi / Po) is 0.13 or more and 0.41 or less, the ratio (Pi / Po) is relatively high, and therefore, when viewed from the entire sheet, the primary particles of the filler are more oriented in the sheet thickness direction, especially near the surface, which facilitates heat diffusion near the heat source and facilitates the formation of a heat conduction path from the surface to the inside of the film thickness, thereby improving the thermal conductivity of the entire resin sheet. Furthermore, since the ratio (Pi / Po) is not too high, contact between the heat dissipation surface and the filler and / or contact between the filler particles is not point contact, and contact thermal resistance is not high. From this perspective, the ratio (Pi / Po) is preferably 0.13 or more, more preferably 0.15 or more, even more preferably 0.18 or more, even more preferably 0.20 or more, and even more preferably 0.22 or more. On the other hand, the upper limit of the ratio (Pi / Po) is preferably 0.41 or less, and more preferably 0.40 or less.

[0051] In the present invention, the "orientation of the filler" refers to the orientation of the primary particles when the filler is an aggregate of primary particles.

[0052] Examples of conditions that can adjust the ratio (Pi / Po) include adjusting the pressing conditions (pressure, temperature, time, number of presses), adjusting the type and content of each component in the resin sheet of the present invention, adjusting the type and content of the filler, and adjusting the aging conditions of the resin sheet of the present invention. However, these are not limited to these. Currently, it is considered preferable to mold the thermosetting resin composition containing the filler and the thermosetting resin into a coating or sheet, perform low-temperature aging, and then apply pressure while taking into consideration the pressing conditions so that the pressing temperature, pressing pressure, and pressing time are not too high, and then perform thermal curing while further applying pressure, thereby adjusting the ratio (Pi / Po) to within the above range. Pressing may be performed several times to adjust the ratio (Pi / Po) to within the above range. However, the present invention is not limited to this method.

[0053] [Pi((002) / (100)) and Po((002) / (100))] Furthermore, the resin sheet of the present invention preferably has a peak area intensity ratio Pi((002) / (100)) of the (002) plane to the (100) plane of the filler in the resin sheet, obtained by measuring the resin sheet by an in-plane method, of 1.5 or more and 10.0 or less, and a peak area intensity ratio Po((002) / (100)) of the (002) plane to the (100) plane of the filler in the resin sheet, obtained by measuring the resin sheet by a focusing method, of 9.0 or more and 13.0 or less. In this way, by specifying the numerical ranges for both the peak area intensity ratio Pi ((002) / (100)) obtained by measurement using the in-plane method and the peak area intensity ratio Po ((002) / (100)) obtained by measurement using the focusing method, it is possible to identify the tendency of the orientation state near the sheet surface in the orientation state of the filler of the present invention throughout the sheet, particularly the degree of orientation of the filler of the present invention in the sheet thickness direction, and the thermal conductivity of the resin sheet of the present invention can be increased.

[0054] [Pi((002) / (100))] The peak area intensity ratio Pi((002) / (100)) of the filler in the resin sheet, obtained by measurement using the in-plane method, is an index showing the orientation of the filler near the sheet surface (at a depth of about 1 to 50 μm from the surface), particularly the degree of orientation of the filler in the sheet thickness direction. Therefore, if the peak area intensity ratio Pi((002) / (100)) is 1.5 or more, this indicates that the primary particles of the filler near the sheet surface are oriented in the sheet thickness direction to a relatively high degree, and is therefore preferable. On the other hand, if the peak area intensity ratio Pi((002) / (100)) is 10.0 or less, excessive orientation of the primary particles of the filler in the sheet thickness direction can be prevented, and the primary particles lie horizontally to such an extent that they can be in surface contact with each other. In other words, the presence of a moderate amount of the filler oriented in the sheet surface direction facilitates the formation of heat conduction paths and improves thermal conductivity, which is preferable. From this viewpoint, the peak area intensity ratio Pi((002) / (100)) is preferably 1.5 or more, more preferably 1.7 or more, more preferably 2.0 or more, even more preferably 2.5 or more, and even more preferably 3.0 or more. On the other hand, the peak area intensity ratio Pi((002) / (100)) is preferably 10.0 or less, more preferably 8.0 or less, even more preferably 7.0 or less, and even more preferably 6.0 or less.

[0055] [Po((002) / (100))] On the other hand, if the peak area intensity ratio Po((002) / (100)) of the filler in the resin sheet, measured by the focusing method, is 9.0 or higher, this indicates that the primary particles of the filler are oriented in the sheet plane direction to a relatively high extent throughout the sheet. This prevents excessive orientation of the primary particles of the filler in the thickness direction, and the primary particles lie horizontally to the extent that they can be in surface contact with each other. In other words, the presence of a moderate amount of the filler oriented in the sheet plane direction facilitates the formation of heat conduction paths and improves thermal conductivity, which is preferable. On the other hand, if the peak area intensity ratio Po((002) / (100)) is 13 or less, the primary particles of the filler are not oriented in the sheet plane direction to an excessive extent throughout the sheet, and the primary particles of the filler are oriented appropriately in the sheet thickness direction, which improves thermal conductivity, which is preferable. From this viewpoint, the peak area intensity ratio Po((002) / (100)) is preferably 9.0 or more, more preferably 9.5 or more, even more preferably 10.0 or more, and even more preferably 10.5 or more. On the other hand, the peak area intensity ratio Po((002) / (100)) is preferably 13.0 or less, even more preferably 12.8 or less, even more preferably 12.6 or less, and even more preferably 12.4 or less.

[0056] Conditions that can bring the peak area intensity ratios Pi and Po into the above range include, for example, adjusting the pressing conditions (pressure, temperature, time, number of presses), adjusting the type and content of each component in the resin sheet of the present invention, adjusting the type and content of the filler, and adjusting the aging conditions of the resin sheet of the present invention. However, these are not limited to these. Currently, a preferred method is to mold the thermosetting resin composition containing the filler and the thermosetting resin into a coating or sheet, perform low-temperature aging, and then apply pressure while taking into consideration the pressing conditions so that the pressing temperature, pressure, and pressing time are not too high, and then perform thermal curing while further applying pressure, thereby adjusting the ratio (Pi / Po) into the above range. Pressing may be performed several times to adjust the ratio (Pi / Po) into the above range. However, the present invention is not limited to this method.

[0057] [Ratio (Pi / Po) and Pi((002) / (100))] It is more preferable that the resin sheet of the present invention has the ratio (Pi / Po) within the above range and the peak area intensity ratio Pi((002) / (100)) within the above range. As described above, the peak area intensity ratio Pi((002) / (100)) is an index showing the degree of orientation in the sheet thickness direction of the primary particles of the filler in the vicinity of the sheet surface, and the ratio (Pi / Po) is an index showing the degree of orientation in the sheet thickness direction of the primary particles of the filler in the vicinity of the sheet surface, including the filler in the entire sheet. Therefore, when the resin sheet of the present invention has both the ratio (Pi / Po) and the peak area intensity ratio Pi((002) / (100)) within the above ranges, the primary particles of the filler near the surface of the sheet and the primary particles of the filler throughout the thickness of the sheet are appropriately oriented in the sheet thickness direction, which further increases the thermal conductivity of the resin sheet of the present invention, which is even more preferable.

[0058] [Ratio (Pi / Po) and Po((002) / (100))] Furthermore, it is more preferable that the resin sheet of the present invention has the ratio (Pi / Po) within the above range and the peak area intensity ratio Po((002) / (100)) within the above range. As mentioned above, if the peak area intensity ratio Po((002) / (100)) is 9.0 or more, particularly 9.5 or more, this indicates that the degree to which the primary particles of the filler are oriented in the sheet surface direction throughout the sheet is relatively high, which can prevent excessive orientation of the primary particles of the filler in the thickness direction. The primary particles are preferably horizontally aligned to such an extent that the fillers can be in surface contact with each other, in other words, the filler is oriented in the sheet surface direction, which makes it easier to form heat conduction paths and improves thermal conductivity, which is preferable. On the other hand, if the peak area intensity ratio Po ((002) / (100)) is 13.0 or less, particularly 12.8 or less, the degree to which the primary particles of the filler are oriented in the sheet surface direction throughout the sheet is not too high, so the primary particles of the filler are moderately oriented in the sheet thickness direction, improving the thermal conductivity, which is preferable. Therefore, if the resin sheet of the present invention has both the ratio (Pi / Po) and the peak area intensity ratio Po ((002) / (100)) within the above ranges, the thermal conductivity of the resin sheet of the present invention can be improved more than when the ratio (Pi / Po) is within the above range.

[0059] [Ratios (Pi / Po), Pi((002) / (100)) and Po((002) / (100))] Furthermore, from the viewpoint of further increasing the thermal conductivity of the resin sheet of the present invention, it is more preferable that the ratio (Pi / Po) is within the above range, the peak area intensity ratio Pi((002) / (100)) is within the above range, and the peak area intensity ratio Po((002) / (100)) is within the above range.

[0060] <Thickness> The thickness of the resin sheet of the present invention is not particularly limited. When the resin sheet of the present invention is used, for example, in power semiconductor devices, industrial equipment, automotive equipment, power generation energy, etc., the thickness of the resin sheet of the present invention is preferably 80 μm or more, more preferably 100 μm or more, even more preferably 110 μm or more, and even more preferably 120 μm or more. On the other hand, the upper limit of the thickness is preferably 300 μm or less, more preferably 250 μm or less, even more preferably 220 μm or less, even more preferably 200 μm or less, and even more preferably 180 μm or less. By making the thickness of the resin sheet of the present invention 80 μm or more, not only can high heat dissipation properties be ensured, but also sufficient voltage resistance characteristics can be ensured. On the other hand, by making the thickness 300 μm or less, it is possible to achieve miniaturization or thinning of power semiconductor devices using the resin sheet of the present invention, and furthermore, compared to insulating thermally conductive layers made of ceramic materials, the effect of reducing thermal resistance in the sheet thickness direction due to the thin film can be obtained.

[0061] <Physical Properties of Resin Sheet of the Present Invention> The resin sheet of the present invention can have the following physical properties.

[0062] (Thermal Conductivity) The thermal conductivity of the resin sheet of the present invention in the thickness direction at 25° C. is preferably 10 W / m K or more, more preferably 13 W / m K or more, and particularly preferably 16 W / m K or more. When the thermal conductivity of the resin sheet of the present invention in the thickness direction is equal to or greater than the above-mentioned lower limit, it can be suitably used in power semiconductor devices that operate at high temperatures.

[0063] The thermal conductivity in the thickness direction of the resin sheet of the present invention can be measured by the following method. For example, the thermal conductivity can be determined from the slope of a graph obtained by plotting thermal resistance values ​​against thickness using a thermal resistance measuring device.

[0064] <Method for producing resin sheet of the present invention> The resin sheet of the present invention can be produced, for example, by forming the present thermosetting resin composition containing the present filler and the thermosetting resin into a coating film or sheet, and then preferably performing low-temperature aging, pressurizing, and thermal curing.

[0065] (Thermosetting Resin Composition) The thermosetting resin composition preferably contains the filler and the thermosetting resin, and further contains an organic solvent to form a coating liquid. Here, the term "thermosetting resin composition" refers to a composition containing a resin that has the property of being cured by heat. In other words, the thermosetting resin composition may be a composition that has curability that leaves room for curing by heat, and may be one that has already been cured (also referred to as "temporarily cured") to a state where there is still room for curing, or one that has not yet been cured (referred to as "uncured").

[0066] In particular, the present thermosetting resin composition preferably contains an epoxy resin as the thermosetting resin, and the present filler preferably contains agglomerated particles of boron nitride from the viewpoints of water resistance and low dielectric constant.

[0067] The present thermosetting resin composition may be a composition containing, in addition to the thermosetting resin and filler (the present filler and other fillers), other polymers, curing agents, curing catalysts, organic solvents, and other components as necessary. These may be conventionally known compositions, such as those described in WO 2021 / 085593 and WO 2023 / 189030.

[0068] In the present thermosetting resin composition, the content of the thermosetting resin is preferably 5% by mass or more and 99% by mass or less, based on 100% by mass of the total solid content of the present thermosetting resin composition excluding all fillers (the present filler and other fillers). A thermosetting resin content of 5% by mass or more is preferred because it improves moldability, while a content of 99% by mass or less allows the content of other components to be ensured and improves thermal conductivity. From this perspective, the content of the thermosetting resin is preferably 5% by mass or more, based on 100% by mass of the total solid content of the present thermosetting resin composition excluding all fillers, with 10% by mass or more being more preferred, 10% by mass or more being more preferred, 20% by mass or more being more preferred, 30% by mass or more being more preferred, 40% by mass or more being more preferred, and 50% by mass or more being more preferred. A content of 99% by mass or less is preferred, with a content of 98% by mass or less being more preferred.

[0069] The "total solids" in the present thermosetting resin composition refers to all components excluding the solvent, i.e., all fillers (the present filler and other fillers) and resin components. In this case, the "resin components" refer to the thermosetting resin and other organic components, and the "other organic components" include the curing agent, curing catalyst, dispersant, viscosity modifier, etc.

[0070] In the present thermosetting resin composition, the total filler content (the present filler and other fillers) is preferably 40% by mass or more and 95% by mass or less, relative to 100% by mass of the total solids content of the present thermosetting resin composition. If the total filler content is 40% by mass or more, thermal conductivity can be improved, while if it is 95% by mass or less, adhesion and insulation properties can be improved. From this perspective, the total filler content is preferably 40% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more, relative to 100% by mass of the total solids content of the present thermosetting resin composition. On the other hand, it is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less.

[0071] When the thermosetting resin composition contains an epoxy resin as the thermosetting resin and boron nitride agglomerated particles as the filler, the content of the boron nitride agglomerated particles is preferably 40% by mass or more and 95% by mass or less, more preferably 45% by mass or more or 90% by mass or less, and even more preferably 50% by mass or more or 85% by mass or less, based on 100% by mass of the total solids content of the thermosetting resin composition. The content of the epoxy resin is preferably 20% by mass or more and 100% by mass or less, more preferably 40% by mass or more or 95% by mass or less, and even more preferably 50% by mass or more or 90% by mass or less, based on 100% by mass of the total amount of the "resin components." The term "epoxy resin" as used herein encompasses epoxy compounds, polyfunctional epoxy resins, and epoxy polymers.

[0072] (Mixing) In preparing the present thermosetting resin composition, it is preferable to mix uniformly by stirring or kneading to form a slurry. For the mixing, a general kneading device such as a mixer, a kneader, a single-screw or twin-screw kneader, etc. can be used. During mixing, heating may be performed as necessary, and if heat is generated by stirring or kneading, cooling may be performed.

[0073] When an organic solvent is added to the thermosetting resin composition to prepare a fluid slurry, it is preferable to mix and stir the mixture using a common kneading device such as a paint shaker, bead mill, planetary mixer, agitator disperser, planetary mixer, rotary and revolutionary mixer, rotary homogenizer, triple roll mill, kneader, or single- or twin-screw kneader, for the purpose of improving the uniformity of the coating liquid and degassing. As the organic solvent, any known solvent capable of dissolving resins can be used appropriately. Examples include methyl ethyl ketone, acetone, cyclohexanone, toluene, xylene, monochlorobenzene, dichlorobenzene, trichlorobenzene, phenol, and hexafluoroisopropanol. These solvents may be used alone or in combination of two or more. The organic solvent is typically used in an amount of 0 to 10,000 parts by mass per 100 parts by mass of the total solids content.

[0074] (Formation in the form of a sheet or coating film) The present thermosetting resin composition prepared in a slurry form is, for example, applied to the surface of a substrate to form a sheet-like coating film. In this case, any coating method, such as dipping, spin coating, spray coating, or blade coating, can be used. The present thermosetting resin composition can be applied using a coating device such as a spin coater, slit coater, die coater, blade coater, comma coater, screen printing, doctor blade, applicator, or spray coating, to form a uniform coating film of a predetermined thickness on the substrate. Of these, a blade coater with an adjustable gap is preferred.

[0075] The resin sheet of the present invention can be used as a free-standing film, or can be formed on a known substrate such as a metal foil or plate (copper, aluminum, silver, gold), a resin film such as polyethylene terephthalate or polyethylene naphthalate, or glass. Depending on the form of use, the resin sheet of the present invention can be peeled off from these substrates and used, or it can be formed into a laminate structure such as substrate / resin sheet of the present invention / substrate. In this case, copper foil having the thickness described below is generally used as the substrate, but it is not limited to a copper substrate. In addition, the surface of the substrate may have irregularities or may be surface-treated.

[0076] (Low-Temperature Aging) The thermosetting resin composition is preferably subjected to low-temperature aging in an environment at a temperature of 0°C or below. For example, the sheet-shaped thermosetting resin composition formed as described above is preferably subjected to low-temperature aging in an environment at a temperature of 0°C or below. By subjecting the sheet-shaped thermosetting resin composition to such low-temperature aging, the moisture inside the sheet can be frozen and dispersed as fine ice. This creates small chambers of moisture trapped in fine spaces even after the temperature is returned to room temperature, preventing the formation of large voids and preventing deterioration of insulation properties while suppressing the occurrence of cracks when the sheet is bent due to moisture retention. Furthermore, the high dispersion of fine voids within the sheet increases the fluidity of the resin components when pressurized, facilitating rearrangement of the filler, e.g., agglomerated particles of boron nitride. This increases contact between the fillers, thereby increasing thermal conductivity. In addition, the stress relaxation effect makes the resin sheet of the present invention less susceptible to cracking and deformation. The low-temperature aging can be performed at any timing. However, from the viewpoint of the effect of rearranging and orienting the filler, it is preferable to perform the low-temperature aging after molding the present thermosetting resin composition into a coating film or a sheet and before applying pressure.

[0077] The temperature (environmental temperature) during low-temperature aging is preferably lower because a faster cooling rate results in finer ice. From this perspective, the environmental temperature is preferably 0°C or lower, more preferably -5°C or lower, even more preferably -10°C or lower, and even more preferably -15°C or lower. On the other hand, if the temperature is too low, the temperature will be below the glass transition temperature (Tg) of the uncured thermosetting resin and will be prone to cracking, so a temperature of -50°C or higher is preferred, and when an epoxy resin is included, a temperature of -30°C or higher is preferred, even more preferably -25°C or higher.

[0078] The time for low-temperature aging is not particularly limited as long as the thermosetting resin composition is frozen. It is sufficient to rapidly freeze and hold the composition for 10 minutes or more, preferably 30 minutes or more, and more preferably 1 hour or more, more preferably 2 hours or more, more preferably 4 hours or more, more preferably 8 hours or more, more preferably 16 hours or more, and more preferably 24 hours or more. On the other hand, since the reaction of epoxy resins proceeds gradually even at low temperatures, in order to avoid leaving the composition for a long period of time, the time for low-temperature aging is preferably 365 days or less, more preferably 180 days or less, more preferably 90 days or less, more preferably 30 days or less, and most preferably 7 days or less.

[0079] It is not necessary to apply pressure during low-temperature aging, but a minute pressure of 0.1 kPa or less may be applied. The low-temperature aging may also be performed after the next pressurization.

[0080] (Pressing) Next, after drying as necessary, it is preferable to pressurize the mixture in a temperature range where the epoxy resin does not harden. Examples of the pressing method include calendar pressing, plate pressing, compression molding, and isostatic pressing. However, the method is not limited to these methods.

[0081] The pressure application is preferably performed by calender pressing under conditions of, for example, a linear pressure of 20 to 200 kgf / cm on the sheet and a roller temperature of 0 to 50°C. Specifically, the linear pressure on the sheet in the calender press is preferably 20 to 200 kgf / cm, more preferably 25 kgf / cm or more or 150 kgf / cm or less, and even more preferably 30 kgf / cm or more or 125 kgf / cm or less. The roller temperature is preferably 0 to 50°C, more preferably 5°C or more or 45°C or less, and even more preferably 10°C or more or 40°C or less. The roller temperature can be considered to be the same as the product temperature of the thermosetting resin composition. A conventional calendering machine with one or more pairs of rollers through which the sheet passes can be used. "One or two" refers to one pair and two rollers. The pressure application time is 10 seconds or less due to the characteristics of the calendering press.

[0082] The pressure applied to the sheet is, for example, 10 to 2000 kgf / cm ２ It is preferable to perform plate pressing under the conditions of a metal plate temperature of 0 to 100°C and a pressing time of 1 to 1500 seconds. Specifically, in the case of plate pressing, the pressure on the sheet (also referred to as "press load") is 10 to 2000 kgf / cm. ２ is preferable, and 50 kgf / cm ２ or more than 1000 kgf / cm ２ Below, among them, 75 kgf / cm ２ or more or 500 kgf / cm ２ The temperature of the metal plate (also referred to as "pressing temperature") is preferably 0 to 100°C, more preferably 5°C or higher or 80°C or lower, and even more preferably 15°C or higher or 50°C or lower. The temperature of the metal plate can be considered to be the same temperature as the product temperature of the thermosetting resin composition. The pressing time (also referred to as "pressing time") is preferably 1 to 1500 seconds, more preferably 2 seconds or higher or 1000 seconds or lower, and even more preferably 3 seconds or higher or 500 seconds or lower.

[0083] (Curing) After the pressing, the sheet can be cured (thermosetting) by heating while applying pressure as needed (this pressing is also called "curing press"). The thermosetting can be performed, for example, by heating to 80 to 300°C and applying a pressure of 50 to 2000 kgf / cm. ２ It is preferable to apply pressure for 0.5 to 240 minutes at a pressure of 1000 kgf / cm. Specifically, the upper and lower top plates of the pressure press are preheated, and the press is then set in the pressure press, whereby pressure and heating can be performed simultaneously. In this case, the heating temperature of the top plates is preferably 80 to 300°C, more preferably 100°C or higher, and even more preferably 120°C or higher. On the other hand, it is preferably 280°C or lower, more preferably 250°C or lower, and even more preferably 220°C or lower. The heating time is preferably 0.5 to 240 minutes, more preferably 1 minute or more or 180 minutes or less, more preferably 5 minutes or more or 120 minutes or less, and even more preferably 10 minutes or more or 60 minutes or less. The pressure during curing is 50 to 2000 kgf / cm. ２ is preferable, and 60 kgf / cm ２ or more or 1500 kgf / cm ２ Below, among them, 70 kgf / cm ２ or more than 1000 kgf / cm ２ Below, among them, 80 kgf / cm ２ or more or 500 kgf / cm ２ Below, among them, 90 kgf / cm ２ or more than 200 kgf / cm ２ More preferably, it is:

[0084] <Use of Resin Sheet of the Present Invention> The resin sheet of the present invention can be used, for example, as a constituent material of a heat dissipation laminate (referred to as the "heat dissipation laminate"), a heat dissipation circuit board (referred to as the "heat dissipation circuit board"), a semiconductor device (referred to as the "semiconductor device"), a power semiconductor device (referred to as the "power semiconductor device"), etc. That is, the resin sheet of the present invention is preferably used as a heat dissipation member for a power semiconductor device. Of course, the uses are not limited to these.

[0085] (Heat-Dissipating Laminate) An example of the heat-dissipating laminate is one in which a heat-dissipating metal layer containing a heat-dissipating material is laminated on one surface of the resin sheet of the present invention. The heat-dissipating material is not particularly limited as long as it is made of a material with good thermal conductivity. In particular, to increase the thermal conductivity of the laminated structure, it is preferable to use a heat-dissipating metal material, and it is more preferable to use a flat metal material. It may also be a cooler with rod-shaped or plate-shaped fins attached to the bottom of a flat metal plate. The material of the metal material is not particularly limited. Among them, copper plate, aluminum plate, aluminum alloy plate, etc. are preferred because of their good thermal conductivity and relatively low cost. Press molding, a batch process, can be preferably used to laminate and integrate the resin sheet of the present invention and the heat-dissipating metal layer. In this case, the press equipment and press conditions are the same as the press molding conditions for obtaining the resin sheet of the present invention described above.

[0086] (Heat-Dissipating Circuit Board) An example of the heat-dissipating circuit board is one having a configuration in which the heat-dissipating metal layer is laminated on one surface of the resin sheet of the present invention, and a circuit board is formed on the other surface of the resin sheet of the present invention, for example, by etching. Specifically, a circuit board in which "heat-dissipating metal layer / resin sheet of the present invention / conductive circuit" is integrated is more preferable. Examples of the state before circuit etching include an integrated configuration of "heat-dissipating metal layer / resin sheet of the present invention / metal layer for forming a conductive circuit," in which the metal layer for forming a conductive circuit is flat and formed on the entire surface of one side of the resin sheet of the present invention, or on only a portion of the surface of one side of the resin sheet of the present invention. The material for the metal layer for forming a conductive circuit is not particularly limited. In particular, it is generally preferable to use a thin copper sheet having a thickness of 0.05 mm to 1.2 mm, from the viewpoints of electrical conductivity, etchability, cost, etc.

[0087] (Semiconductor Device) An example of the present semiconductor device is one having a configuration in which a silicon wafer or a rewiring layer on which pre-diced semiconductor chips are mounted is formed on the present heat dissipation circuit substrate.

[0088] (Power Semiconductor Device) The power semiconductor device is a product in which a circuit combining multiple power semiconductors is integrated into a single package module, and may include the resin sheet of the present invention. An example of the power semiconductor device is one in which a power semiconductor is mounted on the heat dissipation circuit board of the present invention. In the power semiconductor device, components other than the resin sheet of the present invention, such as aluminum wiring, sealing material, packaging material, heat sink, thermal paste, solder, etc., may be any conventionally known components.

[0089] <Explanation of Terms, etc.> In the present invention, when the term "film" is used, it includes "sheet," and when the term "sheet" is used, it includes "film." In the present invention, when it is written "α to β" (α and β are any numbers), it means "α or more and β or less," unless otherwise specified, and it also means "preferably greater than α" or "preferably smaller than β." Furthermore, when it is written "α or more" or "α≦" (α is any number), it means "preferably greater than α" unless otherwise specified, and when it is written "β or less" or "≦β" (β is any number), it also means "preferably smaller than β" unless otherwise specified.

[0090] An example of an embodiment of the present invention will be described below, but the present invention is not limited to the embodiment described below.

[0091] <Raw materials> Epoxy resin 1: High molecular weight epoxy resin (mass average molecular weight in polystyrene equivalent: 30,000, epoxy equivalent: 9,000 g / equivalent, density: approximately 1.2 g / cm ３ ) Epoxy resin 2: A multifunctional epoxy resin containing a structure having four or more glycidyl groups in one molecule (molecular weight: 500 or less, density: approximately 1.2 g / cm ３ ) Epoxy resin 3: Biphenyl type solid epoxy resin (molecular weight: about 400, density: about 1.2 g / cm ３ )

[0092] Boron nitride agglomerated particles: spherical boron nitride agglomerated particles formed by agglomeration of plate-like primary particles, having a house-of-card structure (average particle size (D50): 45 μm, maximum particle size (Dmax): 90 μm, elastic modulus: 65 MPa, crushing strength: 6 MPa)

[0093] The maximum particle size (Dmax) and average particle size (D50) of the boron nitride agglomerated particles are determined by dispersing the boron nitride agglomerated particles in a pure water medium containing a naphthalenesulfonate-formalin condensate as a dispersion stabilizer, measuring the volumetric particle size distribution using a laser diffraction / scattering particle size distribution analyzer LA-300 (manufactured by Horiba, Ltd.), and then determining the maximum particle size Dmax and the particle size at 50% of the cumulative volume (average particle size D50) from the obtained particle size distribution.

[0094] The elastic modulus and crushing strength of the boron nitride agglomerated particles were measured by the following method. The crushing strength of the boron nitride agglomerated particles was measured using a micro-compression tester (manufactured by Shimadzu Corporation, product name "MCT-510"). A very small amount of sample was scattered on a pressure plate installed at the bottom of the micro-compression tester, and a compression test was performed on each particle. The crushing strength was calculated using the following formula from the breaking test force at which the particle broke and the particle diameter of the particle. Measurement was performed on five particles, and the average value was taken as the crushing strength of the boron nitride agglomerated particles. Cs=2.48P / πd ２ 　 In the above formula, "Cs" is the crushing strength (MPa), "P" is the breaking test force (N), and "d" is the particle diameter (mm). Normally, the crushing strength is calculated using the test force at the breaking point, but when the breaking point is unclear (for example, the sample deforms but does not break suddenly), the test force when a 10% deformation is applied is used as the reference strength, and this is used for comparison as the 10% strength. The 10% strength was calculated using the following formula: Cx = 2.48P / πd ２ 　 In the above formula, "Cx" is the 10% strength (MPa), "P" is the test force (N) at 10% displacement of the particle diameter, and "d" is the particle diameter (mm).

[0095] The elastic modulus of the boron nitride agglomerated particles was calculated from the test force at the time of fracture and the compressive displacement at that time using the same apparatus used to measure the crushing strength, according to the following formula: E=3×(1−ν ２ )×P / 4×(d / 2) １／２ ×Y ３／２ 　 In the above formula, "E" is the elastic modulus (MPa), "ν" is the Poisson's ratio, "P" is the breaking test force (N), "d" is the particle diameter (mm), and "Y" is the compression displacement (mm). The Poisson's ratio was assumed to be constant (0.13).

[0096] Aluminum oxide particles: spherical alumina (average particle size (D50): 8.8 μm, thermal conductivity: 20 to 30 W / m·k) The average particle size (D50) of the aluminum oxide particles is the particle size at 50% cumulative volume (average particle size D50) calculated from the particle size distribution obtained by dispersing aluminum oxide particles in a pure water medium containing naphthalenesulfonate-formalin condensate as a dispersion stabilizer, measuring the volumetric particle size distribution using a batch-type laser diffraction / scattering particle size distribution analyzer LA-300 (manufactured by HORIBA, Ltd.).

[0097] Curing agent: Phenolic resin curing agent Curing catalyst 1: 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(17')]-ethyl-s-triazine (molecular weight: 247, properties: solid, melting point: 215-225°C) Curing catalyst 2: 2-phenyl-4,5-dihydroxymethylimidazole (molecular weight: 204, properties: solid, melting point: dec. 230, so the melting point is 230°C or higher)

[0098] <Preparation of Thermosetting Resin Composition> A slurry-like thermosetting resin composition was prepared by mixing 6 parts by mass of epoxy resin 1, 6 parts by mass of epoxy resin 2, 11 parts by mass of epoxy resin 3, 53 parts by mass of boron nitride agglomerated particles, 20 parts by mass of aluminum oxide particles, 3.5 parts by mass of a curing agent, 0.25 parts by mass of curing catalyst 1, and 0.25 parts by mass of curing catalyst 2, to which methyl ethyl ketone and cyclohexanone were added so as to give a solids concentration of 74% by mass using a planetary centrifugal stirrer.

[0099] Example 1 The slurry-like thermosetting resin composition prepared as described above was applied to a polyethylene terephthalate (PET) film using an applicator with a gap of 400 μm. The film was then dried on a hot plate at 60°C for 60 minutes, followed by vacuum drying at 60°C (heating environment temperature) for 60 minutes to produce a sheet with a thickness of 240 μm. The resulting sheet was then subjected to low-temperature aging for 72 hours in a freezer at -20°C without applying any particular load. A PET film having a release agent applied to one side thereof was then overlaid on the sheet so that the coated surface was in contact with the resin, to produce a laminated sheet consisting of a PET film / thermosetting resin composition / PET film. This was then passed through a pair of metal rolls at 25°C and subjected to a calender press in which a linear pressure (calender pressure) of 50 kgf / cm was applied once, followed by calender press at 120°C (product temperature) and 100 kgf / cm. ２ The resin was cured by pressing under a load of 1000 kJ for 40 minutes to obtain a resin sheet (sample) having a thickness of 150 μm.

[0100] Furthermore, two, three, four, or five of the resin sheets (samples) calendered as described above were stacked and cured under the same conditions as above to obtain four types of resin sheets (samples) with different thicknesses. Thus, together with the resin sheet (sample) consisting of one sheet, five types of cured samples with thicknesses ranging from one sheet to five sheets were obtained.

[0101] Example 2 Resin sheets (samples) were obtained in the same manner as in Example 1, except that the calender pressure was changed from 50 kgf / cm to 100 kgf / cm in Example 1. Furthermore, as in Example 1, five types of cured samples having thicknesses ranging from one sheet to five sheets were obtained.

[0102] Comparative Example 1 The slurry-like thermosetting resin composition prepared as described above was applied to a polyethylene terephthalate (PET) film using an applicator with a gap of 400 μm, and dried on a hot plate at 60°C for 60 minutes. This was followed by vacuum drying at 60°C (heating environment temperature) for 60 minutes to produce a sheet with a thickness of 240 μm. The resulting sheet was subjected to low-temperature aging for 72 hours in a freezer at -20°C without applying any particular weight. A PET film with a release agent applied to one side was then placed on top of this sheet, with the coated surface in contact with the sheet, to produce a laminate sheet consisting of PET film / thermosetting resin composition / PET film. This was then placed in a pressure press and subjected to a pressure of 1500 kgf / cm at 41.5°C (press temperature). ２ After pressing the sheet under a pressure of 100 kgf / cm at 120°C (product temperature) for 15 minutes (press time), ２ The resin was cured by pressing under a load of 1000 kJ for 40 minutes to obtain a resin sheet (sample) having a thickness of 150 μm.

[0103] Furthermore, two, three, four, or five of the resin sheets (samples) that had been plate-pressed as described above were stacked and cured under the same conditions as above to obtain four types of resin sheets (samples) with different thicknesses. Thus, together with the resin sheet (sample) consisting of a single sheet, five types of cured samples with thicknesses ranging from one sheet to five sheets were obtained.

[0104] Example 3 In Comparative Example 1, the pressing temperature was changed from 41.5°C to 25°C, and the pressing load was 1500 kgf / cm ２ at 100 kgf / cm ２ A resin sheet (sample) was obtained in the same manner as in Comparative Example 1, except that the pressing time was changed from 15 minutes to 5 seconds. Also, as in Comparative Example 1, five types of cured samples having thicknesses ranging from one sheet to five sheets were obtained.

[0105] Example 4 In Comparative Example 1, the press load was 1500 kgf / cm ２ at 100 kgf / cm ２A resin sheet (sample) was obtained in the same manner as in Comparative Example 1. Furthermore, as in Comparative Example 1, five types of cured samples having thicknesses ranging from one sheet to five sheets were obtained.

[0106] Comparative Example 2 The slurry-like thermosetting resin composition prepared as described above was applied to a polyethylene terephthalate (PET) film using an applicator with a gap of 400 μm, and dried on a hot plate at 60°C for 60 minutes. This was followed by vacuum drying at 60°C (heating environment temperature) for 60 minutes to produce a sheet with a thickness of 240 μm. The resulting sheet was subjected to low-temperature aging for 72 hours in a freezer at -20°C without applying any particular weight. A PET film with a release agent applied to one side was then placed on top of this sheet, with the coated surface in contact with the sheet, to produce a laminated sheet consisting of PET film / thermosetting resin composition / PET film. This was then subjected to a pressure press at 170°C (product temperature) and 70 kgf / cm ２ The resin was cured by pressing under a load of 1.000 for 180 minutes to obtain a resin sheet (sample) having a thickness of 150 μm.

[0107] Furthermore, two, three, four, or five of the resin sheets (samples) that had been subjected to low-temperature aging as described above were stacked and cured under the same conditions as above to obtain four types of resin sheets (samples) with different thicknesses. Thus, together with the resin sheet (sample) consisting of one sheet, five types of cured samples with thicknesses ranging from one sheet to five sheets were obtained.

[0108] Comparative Example 3 A resin sheet (sample) was obtained in the same manner as in Example 4, except that the low-temperature aging in Example 4 was not performed and aging was performed at 60°C for 72 hours using a fan oven. Furthermore, as in Comparative Example 1, five types of cured samples having thicknesses ranging from one sheet to five sheets were obtained.

[0109] <X-ray diffraction (XRD)> For the resin sheets (samples) obtained in the examples and comparative examples, X-ray diffraction measurement was performed using the in-plane method as well as the focusing method. The in-plane X-ray diffraction method is also simply referred to as the "in-plane method", and the focusing X-ray diffraction method is also simply referred to as the "focusing method". In both the focusing method and the in-plane method, a 2 cm x 2 cm x 150 μm sample was placed at the sample position of each diffraction device with the surface perpendicular to the sheet thickness direction facing up.

[0110] The X-ray diffraction measurement by the focusing method was carried out using "X'Pert Pro MPD (product name)" manufactured by PANalytical under the following conditions.

[0111] ・Optical system: Concentration method ・Radiation source: Sealed-type X-ray tube (CuKα) ・Incidence slit: Soller slit (0.04 rad) ・Divergence slit (Variable slit) ・Receiving slit: Ni-Filter Soller slit (0.04 rad) ・Goniometer radius: 243 mm ・X-ray output: 40 kV 30 mA ・Scan axis: θ / 2θ ・Scan range (2θ): 10° to 70° ・Measurement mode: Continuous scanning ・Read width: 0.016° ・Measurement time: 29.8 sec ・Automatic variable slit: 10 mm (irradiation width) ・Horizontal divergence mask: 10 mm (irradiation width)

[0112] The in-plane X-ray diffraction measurement was carried out using a "SmartLab (product name)" manufactured by RIGAKU Corporation under the following conditions.

[0113] Optical system: Parallel beam method; Radiation source: Rotating anode X-ray tube (CuKα); Incident slit: Soller slit in-plane PSC 0.5°; Incident slit: 0.100 mm; Length limiting slit: 10 mm; Receiving slit: Receiving optical unit: PSA open; Soller slit in-plane PSA 0.5°; Receiving slit 2: 20 mm; X-ray output: 45 kV, 200 mA; Scan axis: 2θχ / Φ (°); Incident angle (ω): 0.2°; Measurement mode: Step scan; Scan range (2θχ): 10° to 70°; Operation step: 0.096°; Scan speed: 2.0° / min; Goniometer radius: 300 mm

[0114] In the XRD profiles obtained by each measurement method, the area (I ００２ and I １００ ) were determined, and the peak area intensity ratio Po((002) / (100)) and the peak area intensity ratio Pi((002) / (100)) were calculated. In this case, in both the focusing method and the in-plane method XRD profiles, the diffraction peak of the (002) plane of the boron nitride agglomerated particles was the maximum peak at 25.0°<scan axis<28.0°, and the diffraction peak of the (100) plane was the maximum peak at 40.5°<scan axis<42.5°. The scanning axis for the focusing method was 2θ, and the scanning axis for the in-plane method was 2θχ. Profile fitting was performed using the XRD analysis software Jade. For each profile, the background was defined by a cubic spline curve, and peak fitting was performed using a Pearson VII function or a pseudo-Voigt function. Peak fitting was performed using the least squares method in the range of 25.0° < 2θ (2θχ) < 28.0° for the diffraction peak of the (002) plane and in the range of 40.5° < 2θ (2θχ) < 42.5° for the diffraction peak of the (100) plane.

[0115] <Measurement of thermal conductivity (λ)> Measurements were carried out under the conditions (1) to (4) below for five types of cured samples of different thicknesses produced in the Examples and Comparative Examples. The thermal conductivity at 25°C in the sheet thickness direction using a steady-state method was measured from the slope represented by the thermal resistance value versus sheet thickness (in accordance with ASTM D5470). The probe size during measurement was φ12.8 mm, the fixing pressure was 3400 kPa, and the measurement time was 300 seconds. Shin-Etsu Chemical Co., Ltd.'s "OIL COMPOUND (product name: G-747)" was used to improve adhesion between the cured sample and the probe.

[0116] (1) Thickness: Thickness (μm) when pressed at a pressure of 3400 kPa using a "T3Ster-DynTIM" manufactured by Mentor Graphics. (2) Measurement area: Area (cm) of the heat-transferring portion when measuring using a "T3Ster-DynTIM" manufactured by Mentor Graphics. ２ (3) Thermal resistance value: Thermal resistance value (K / W) when pressed at a pressure of 3,400 kPa using a "T3Star-DynTIM" manufactured by Mentor Graphics. (4) Thermal conductivity: Thermal resistance values ​​of five types of cured samples with different thicknesses were measured, and the thermal conductivity (W / m·K) was calculated using the following formula. Formula: Thermal conductivity (W / m·K) = 1 / ((slope (thermal resistance value / thickness): K / (W·μm)) × (area: cm ２ )) x 10 －２

[0117]

[0118] (Discussion) All of Examples 1 to 4 exhibited high thermal conductivity, with the ratio (Pi / Po) being in the range of 0.13 to 0.41. It was also found that Pi ((002) / (100)) was 1.5 to 10.0, and Po ((002) / (100)) was 9.0 to 13.0. In contrast, Comparative Example 1 had lower Pi ((002) / (100)) and ratio (Pi / Po), and lower thermal conductivity than Examples 1 to 4. This is thought to be because the pressure applied in the flat press in Comparative Example 1 was too high, causing the primary particles of the filler, particularly those near the surface of the resin sheet, to be oriented in the sheet plane direction, resulting in lower thermal conductivity. It was also found that Comparative Example 2 had lower Po ((002) / (100)), a higher ratio (Pi / Po), and lower thermal conductivity than Examples 1 to 4. This is thought to be because in Comparative Example 2, the resin sheet was cured and pressed directly without either calender pressing or plate pressing, so the primary particles of the filler were excessively oriented in the sheet thickness direction both on the surface and inside of the resin sheet, preventing contact between the fillers and resulting in low thermal conductivity. It was found that Comparative Example 3 had a lower Po ((002) / (100)), a higher ratio (Pi / Po), and a lower thermal conductivity than Examples 1 to 4. This is thought to be because in Comparative Example 3, low-temperature aging was not performed, making it difficult for the fillers to rearrange, and the primary particles of the filler were excessively oriented in the sheet thickness direction both on the surface and inside of the resin sheet, preventing contact between the fillers and resulting in low thermal conductivity.

[0119] From the above examples and comparative examples, as well as the test results conducted by the inventors so far, it has been found that the peak area intensity ratio Pi ((002) / (100)) of the (002) plane and the (100) plane of the filler in the resin sheet, obtained by measuring the resin sheet using an in-plane X-ray diffraction method, is 1.5 or more and 10.0 or less, and the peak area intensity ratio Po ((002) / (100)) of the (002) plane and the (100) plane of the filler in the resin sheet, obtained by measuring the resin sheet using an X-ray diffraction method using a focusing method, is 9.0 or more and 13.0 or less. It has been found that the thermal conductivity can be increased. This can be considered to be due to the following mechanism of action.

[0120] The peak area intensity ratio Pi((002) / (100)) of the filler in the resin sheet obtained by measurement using the in-plane method is considered to be an index indicating the orientation of the filler near the surface of the sheet, particularly the degree of orientation of the filler in the thickness direction of the sheet. On the other hand, the peak area intensity ratio Po((002) / (100)) of the filler in the resin sheet obtained by measurement using the focusing method is considered to be an index indicating the orientation of the filler throughout the sheet, particularly the degree of orientation of the filler in the lateral direction of the sheet, i.e., the sheet surface direction. If the primary particles of the filler near the surface of the sheet are oriented in the lateral direction, i.e., the sheet surface direction, a structure equivalent to a heat resistance film is formed in the portion in contact with the heating unit, and the contact thermal resistance becomes significantly high, resulting in a significant decrease in the thermal conductivity of the entire sheet. On the other hand, if the primary particles of the filler are oriented in the sheet thickness direction near the sheet surface, the thermal conductivity near the sheet surface increases and the contact thermal resistance decreases, which increases the thermal conductivity of the portion in contact with the heating unit, and as a result, it can be considered that the thermal conductivity of the entire sheet also increases significantly. Furthermore, when looking at the entire sheet, if the primary particles of the filler are appropriately oriented in the sheet surface direction and the primary particles are horizontally aligned to the extent that surface contact between fillers is possible, in other words, if there is an appropriate amount of filler oriented in the sheet surface direction, it can be considered that heat conduction paths are easily formed and the thermal conductivity is improved. However, it should be noted that if the primary particles of the filler are too oriented in the sheet thickness direction, either on the surface or inside of the resin sheet, contact between fillers in the sheet thickness direction is not ensured, and the thermal conductivity will actually decrease.

[0121] Considering these points, if the peak area intensity ratio Pi((002) / (100)) obtained by measurement using the in-plane method is 1.5 or more and 10.0 or less, it is a relatively high value but not too high, and it can be considered that this indicates that the primary particles of the filler on the sheet surface are oriented in the sheet thickness direction, but not excessively oriented. On the other hand, if the peak area intensity ratio Po((002) / (100)) obtained by measurement using the focusing method is 9.0 or more and 13.0 or less, it is a relatively high value but not too high, and it indicates that the primary particles of the filler are oriented in the sheet thickness direction throughout the sheet, but not excessively oriented, and it can be considered that the thermal conductivity is high.

[0122] Furthermore, from the above examples and comparative examples, as well as the results of tests conducted by the inventors, it has been found that the thermal conductivity can be increased if the ratio (Pi / Po) of the peak area intensity ratio Pi ((002) / (100)) obtained by measuring a resin sheet using the in-plane method to the peak area intensity ratio Po ((002) / (100)) obtained by measuring using the focusing method is 0.13 or more and 0.41 or less. This can be attributed to the following mechanism of action.

[0123] The ratio (Pi / Po) is considered to indicate the tendency of the orientation state of the filler near the surface of the sheet in the orientation state of the filler throughout the sheet, particularly the degree of orientation of the filler in the sheet thickness direction, and so if the ratio (Pi / Po) is within the above range, since the ratio (Pi / Po) is a relatively high value, when viewed from the entire sheet, the primary particles of the filler are more oriented in the sheet thickness direction, particularly near the surface, making it easier for heat to diffuse near the heat source and further facilitating the formation of a heat conduction path from the surface to the inside of the film thickness, thereby improving the thermal conductivity of the entire resin sheet. Furthermore, since the ratio (Pi / Po) is not too high, it can be considered that the contact between the heat dissipation surface and the filler and / or the contact between the fillers does not become point contact, and therefore the contact thermal resistance does not increase.

[0124] In the above examples and comparative examples, boron nitride agglomerated particles are used as the filler, and calender press or flat plate press is used as the pressing method. However, considering the mechanism by which the thermal conductivity of the sheet increases as described above, it is believed that a filler whose primary particles have anisotropy with respect to thermal conductivity, i.e., a filler formed by agglomeration of plate-like, scale-like, or needle-like primary particles, can achieve the same effect as boron nitride agglomerated particles. Furthermore, if the primary particles of the filler are oriented as described above in the sheet, it is believed that the thermal conductivity can be increased regardless of the manufacturing method, such as calender press or flat plate press. It has been confirmed by cross-sectional SEM that the boron nitride agglomerated particles that have aggregated to form spherical shapes remain spherically aggregated even within the resin sheet.

Claims

1. A resin sheet containing a filler formed by an aggregation of plate-like, scale-like or needle-like primary particles, characterized in that the ratio (Pi / Po) of the peak area intensity ratio Po((002) / (100)) of the (002) plane to the (100) plane of the filler in the resin sheet, obtained by measuring the resin sheet using an X-ray diffraction method with a focusing method, to the peak area intensity ratio Pi((002) / (100)) of the (002) plane to the (100) plane of the filler in the resin sheet, obtained by measuring the resin sheet using an in-plane X-ray diffraction method, is 0.13 or more and 0.41 or less.

2. A resin sheet containing a filler formed by agglomeration of plate-, scale- or needle-like primary particles, characterized in that the resin sheet is measured by an in-plane X-ray diffraction method, resulting in a peak area intensity ratio Pi((002) / (100)) of the (002) plane to the (100) plane of the filler in the resin sheet being 1.5 or more and 10.0 or less, and the resin sheet is measured by an X-ray diffraction method using a focusing method, resulting in a peak area intensity ratio Po((002) / (100)) of the (002) plane to the (100) plane of the filler in the resin sheet being 9.0 or more and 13.0 or less.

3. The resin sheet according to claim 1, wherein the peak area intensity ratio Pi((002) / (100)) is 1.5 or more and 10.0 or less.

4. The resin sheet according to claim 1, wherein the peak area intensity ratio Po((002) / (100)) is 9.0 or more and 13.0 or less.

5. The resin sheet according to claim 1 or 2, which is a cured product of a thermosetting resin composition containing the filler and a thermosetting resin.

6. The resin sheet according to claim 5, wherein said thermosetting resin comprises an epoxy resin.

7. The resin sheet according to claim 1 or 2, wherein the filler has a thermal conductivity of 10 W / m·k or more.

8. The resin sheet according to claim 1 or 2, wherein the filler comprises agglomerated particles of boron nitride.

9. The resin sheet according to claim 8, wherein the boron nitride agglomerated particles have a house of cards structure.

10. The resin sheet according to claim 1 or 2, having a thermal conductivity at 25° C. in the thickness direction of the sheet of 10 W / m·K or more.

11. The resin sheet according to claim 1 or 2, which is used as a heat dissipation member for a power semiconductor device.

12. A method for producing a resin sheet according to claim 1 or 2, characterized in that a thermosetting resin composition containing the filler and the thermosetting resin is formed into a coating or sheet, pressurized, and thermally cured.

13. The pressing is carried out by calendar pressing under conditions of a linear pressure of 20 to 200 kgf / cm on the sheet and a roller temperature of 0 to 50°C, or by applying a pressure of 10 to 2000 kgf / cm on the sheet. ２ The method for producing a resin sheet according to claim 12, characterized in that the plate pressing is performed under conditions of a metal plate temperature of 0 to 100° C. and a pressing time of 1 to 1500 seconds.

14. The heat curing is performed by heating to 80 to 300°C and applying a pressure of 50 to 2000 kgf / cm ２ The method for producing a resin sheet according to claim 12, wherein the pressure is applied for 0.5 to 240 minutes.

15. The method for producing a resin sheet according to claim 12, further comprising the step of subjecting the thermosetting resin composition to low-temperature aging in an environment having a temperature of 0° C. or lower.

16. The method for producing a resin sheet according to claim 15, wherein the low-temperature aging is carried out after the thermosetting resin composition is formed into a coating film or sheet and before it is pressed.

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