Thermal conductive sheets, devices with thermal conductive sheets

Abstract

The present invention addresses the problem of providing a heat conductive sheet and a device equipped with a heat conductive sheet, which demonstrate excellent adherence to an adherend when attached to the adherend with a low pressure and demonstrate excellent heat conductivity after bonding. This heat conductive sheet comprises a first heat conductive layer having two main surfaces and a second heat conductive layer disposed only on one of the two main surfaces of the first heat conductive layer. The average film thickness of the first heat conductive layer is greater than the average film thickness of the second heat conductive layer. The first heat conductive layer includes first heat conductive inorganic particles, and the second heat conductive layer includes second heat conductive inorganic particles and a curable compound. The content of the first heat conductive inorganic particles relative to the entire volume of the first heat conductive layer is greater than the content of the second heat conductive inorganic particles relative to the entire volume of the second heat conductive layer. The second heat conductive inorganic particles in the second heat conductive layer include aggregated boron nitride and heat conductive inorganic particles X that are different from the aggregated boron nitride and have an average aspect ratio of 1.0-1.6. The content of the second heat conductive inorganic particles relative to the entire volume of the second heat conductive layer is 40.0-60.0 vol%.

Description

[Technical Field]

[0001] The present invention relates to a thermal conductive sheet and a device equipped with a thermal conductive sheet. [Background technology]

[0002] Power semiconductor devices used in electrical equipment such as personal computers, general home appliances, and automobiles have been rapidly miniaturized in recent years. Controlling the heat generated by these increasingly dense power semiconductor devices is becoming a problem. To address the above problem, thermal conductive materials are used to promote heat dissipation from power semiconductor devices. For example, Patent Document 1 discloses a thermal conductive sheet having multiple layers. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2011-040565 [Overview of the project] [Problems that the invention aims to solve]

[0004] The present inventors investigated thermal conductive sheets as described in Patent Document 1, etc., and found that there is room for improvement in the adhesion of the thermal conductive sheet to the substrate when the thermal conductive sheet is bonded to the substrate at a low pressure (for example, 5 MPa or less). Furthermore, the thermal conductive sheet is required to exhibit excellent thermal conductivity after the bonding process described above.

[0005] Therefore, the object of the present invention is to provide a thermal conductive sheet that exhibits excellent adhesion to a substrate when bonded to a substrate at low pressure, and that shows excellent thermal conductivity after bonding. Furthermore, the present invention also aims to provide a device with a thermal conductive sheet. [Means for solving the problem]

[0006] As a result of intensive studies to solve the above problems, the inventors of the present invention have found that the above problems can be solved by the following configuration.

[0007] 〔1〕A first heat conduction layer having two main surfaces, and a second heat conduction layer disposed only on one of the two main surfaces of the first heat conduction layer, where the average film thickness of the first heat conduction layer is larger than the average film thickness of the second heat conduction layer, the first heat conduction layer contains first heat conductive inorganic particles, the second heat conduction layer contains second heat conductive inorganic particles and a curable compound, the content of the first heat conductive inorganic particles with respect to the total volume of the first heat conduction layer is larger than the content of the second heat conductive inorganic particles with respect to the total volume of the second heat conduction layer, the second heat conductive inorganic particles in the second heat conduction layer contain aggregated boron nitride and heat conductive inorganic particles X having an average aspect ratio of 1.0 to 1.6 and different from the aggregated boron nitride, a heat conduction sheet in which the content of the second heat conductive inorganic particles is 40.0 to 60.0% by volume with respect to the total volume of the second heat conduction layer. 〔2〕The heat conduction sheet according to 〔1〕, wherein the volume ratio of the aggregated boron nitride to the heat conductive inorganic particles X in the second heat conduction layer is 2.5 to 10.5. 〔3〕The heat conduction sheet according to 〔1〕 or 〔2〕, wherein the heat conductive inorganic particles X are aluminum oxide. 〔4〕The heat conduction sheet according to any one of 〔1〕 to 〔3〕, wherein the average particle diameter of the heat conductive inorganic particles X is 2.0 to 10.0 μm. 〔5〕The heat conduction sheet according to any one of 〔1〕 to 〔4〕, wherein the curable compound contains one or more selected from the group consisting of an epoxy compound and a maleimide compound. 〔6〕The heat conduction sheet according to any one of 〔1〕 to 〔5〕, wherein the curable compound contains a phenol compound. [7] A thermal conductive sheet according to any one of [1] to [6], wherein the average thickness of the second thermal conductive layer is 10 to 70 μm. [8] A thermal conductive sheet according to any one of [1] to [7], wherein the average thickness of the first thermal conductive layer is 100 to 150 μm. [9] A thermal conductive sheet according to any one of [1] to [8], wherein the average particle size of the aggregated boron nitride is 10.0 to 80.0 μm.

[10] At least one of the first thermal conductive layer and the second thermal conductive layer further comprises a surface modifier. A thermal conductive sheet according to any one of [1] to [9], wherein the aggregated boron nitride, together with the surface modifier adsorbed on the surface of the aggregated boron nitride, constitutes surface-modified aggregated boron nitride.

[11] A device with a thermal conductive sheet, comprising a device and a thermal conductive sheet described in any one of [1] to

[10] placed on the device. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a thermal conductive sheet that exhibits excellent adhesion to a substrate when bonded to the substrate at low pressure, and shows excellent thermal conductivity after bonding. Furthermore, according to the present invention, a device with a thermal conductive sheet can be provided. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram showing an example of a thermal conductive sheet. [Figure 2] This is a schematic diagram showing an example of a semiconductor module. [Figure 3] This is a schematic diagram showing an example of a semiconductor module. [Figure 4] This is a schematic diagram showing an example of a semiconductor module. [Figure 5] This is a schematic diagram showing an example of a semiconductor module. [Figure 6] This is a schematic diagram showing an example of a semiconductor module. [Modes for carrying out the invention]

[0010] The following description of the constituent elements may be based on a typical embodiment of the present invention, but the present invention is not limited to such embodiments. In this specification, a numerical range represented by "~" means a range that includes the numbers written before and after "~" as the lower and upper limits, respectively.

[0011] Furthermore, in this specification, the term "(meth)acryloyl group" means "either or both of an acryloyl group and a methacryloyl group."

[0012] In this specification, the acid anhydride group may be either a monovalent or a divalent group. When the acid anhydride group represents a monovalent group, examples include substituents obtained by removing any hydrogen atom from acid anhydrides such as maleic anhydride, phthalic anhydride, pyromellitic anhydride, and trimellitic anhydride. When the acid anhydride group represents a divalent group, it means a group represented by *-CO-O-CO-*, where * represents the bond position. In this specification, the bonding direction of the divalent group (e.g., -COO-) is not particularly limited unless otherwise specified. For example, if Y in a compound represented by the formula "XYZ" is -COO-, the compound may be either "XO-CO-Z" or "X-CO-OZ".

[0013] In this specification, substituents that are not explicitly stated as substituted or unsubstituted may have further substituents on their base, to the extent that they do not impair the desired effect. For example, the term "alkyl group" means a substituted or unsubstituted alkyl group (an alkyl group that may have substituents) to the extent that it does not impair the desired effect. In this specification, the type, position, and number of substituents when "may have substituents" are used are not particularly limited. Examples of substituents include one and two or more. The type of substituent is not particularly limited and examples include halogen atoms and alkyl groups. In this specification, examples of halogen atoms include chlorine atoms, fluorine atoms, bromine atoms, and iodine atoms.

[0014] [Thermal conductive sheet] The heat conductive sheet of the present invention A first thermal conductive layer having two main surfaces, The first thermal conductive layer has a second thermal conductive layer which is disposed on only one of the two main surfaces of the first thermal conductive layer. The average thickness of the first thermal conductive layer is greater than the average thickness of the second thermal conductive layer. The first thermal conductive layer contains first thermally conductive inorganic particles, The second thermal conductive layer contains second thermally conductive inorganic particles and a curable compound. The content of the first thermally conductive inorganic particles relative to the total volume of the first thermally conductive layer is greater than the content of the second thermally conductive inorganic particles relative to the total volume of the second thermally conductive layer. The second thermal conductive inorganic particles in the second thermal conductive layer include aggregated boron nitride and thermal conductive inorganic particles X having an average aspect ratio of 1.0 to 1.6 and being different from aggregated boron nitride. The content of the second thermally conductive inorganic particles is 40.0 to 60.0 volume percent relative to the total volume of the second thermally conductive layer.

[0015] The mechanism by which the above configuration solves the problems of the present invention is not clear, but the inventors speculate as follows. A key feature of the heat-conducting sheet of the present invention is that it has a first heat-conducting layer and a second heat-conducting layer. When a thermal conductive sheet is bonded to a substrate at low pressure, the second thermal conductive layer that comes into contact with the substrate contains not only aggregated boron nitride, which exhibits high thermal conductivity, but also thermally conductive inorganic particles X, thus providing excellent adhesion to the substrate. The first thermal conductive layer contains the first thermally conductive inorganic particles and therefore exhibits high thermal conductivity. It is presumed that having these two layers results in excellent thermal conductivity and excellent adhesion. Hereinafter, if at least one of the effects of thermal conductivity and adhesion is superior, this is also referred to as the effect of the present invention being superior.

[0016] An example of an embodiment of a thermal conductive sheet will be described. The thermal conductive sheet 10 shown in Figure 1 has a first thermal conductive layer 12 having two main surfaces, and a second thermal conductive layer 14 disposed on one of the main surfaces of the first thermal conductive layer 12. The second thermal conductive layer is disposed on only one of the two main surfaces of the first thermal conductive layer. In other words, the second thermal conductive layer is not disposed on the other main surface of the first thermal conductive layer 12. The first thermal conductive layer 12 contains first thermal conductive inorganic particles 16, and the second thermal conductive layer 14 contains second thermal conductive inorganic particles 18, which include aggregated boron nitride 20 and thermal conductive inorganic particles X22. Furthermore, the thermal conductive sheet may have other components besides the first thermal conductive layer 12 and the second thermal conductive layer 14. Examples of other components include the base material, which will be described later. In a thermal conductive sheet, at least one of the first thermal conductive layer and the second thermal conductive layer further contains a surface modifier. It is preferable that the aggregated boron nitride, together with a surface modifier adsorbed on the surface of the aggregated boron nitride, constitutes surface-modified aggregated boron nitride. Further details will be described later.

[0017] The following details the components included in the thermal conductive sheet.

[0018] [First thermal conductive layer] The thermal conductive sheet has a first thermal conductive layer having two main surfaces. The first thermal conductive layer is not particularly limited, as long as it includes first thermally conductive inorganic particles. Preferably, the first thermal conductive layer includes first thermally conductive inorganic particles and a curable compound.

[0019] <First thermally conductive inorganic particles> The first thermal conductive layer contains first thermally conductive inorganic particles.

[0020] Examples of the shapes of the first thermally conductive inorganic particles include rice grain-like, spherical, cubic, spindle-shaped, flaky, aggregated, and irregular shapes.

[0021] Examples of the first thermally conductive inorganic particles include inorganic nitrides and inorganic oxides. Examples of inorganic nitrides include boron nitride (BN), carbon nitride (C3N4), silicon nitride (Si3N4), gallium nitride (GaN), indium nitride (InN), aluminum nitride (AlN), chromium nitride (Cr2N), copper nitride (Cu3N), iron nitride (Fe4N), iron nitride (Fe3N), lanthanum nitride (LaN), lithium nitride (Li3N), magnesium nitride (Mg3N2), molybdenum nitride (Mo2N), niobium nitride (NbN), tantalum nitride (TaN), titanium nitride (TiN), tungsten nitride (W2N), tungsten nitride (WN2), yttrium nitride (YN), and zirconium nitride (ZrN). The inorganic nitride preferably contains aluminum atoms, boron atoms, or silicon atoms, more preferably aluminum nitride, boron nitride, or silicon nitride, even more preferably aluminum nitride or boron nitride, and particularly preferably boron nitride.

[0022] Examples of boron nitride include cubic boron nitride and hexagonal boron nitride. The shape of boron nitride may be spherical, plate-like, flaky, or aggregated, with aggregated boron nitride being preferred. Aggregated boron nitride refers to secondary aggregated particles formed by agglomerating primary particles of boron nitride (e.g., flaky boron nitride).

[0023] Examples of inorganic oxides include zirconium oxide (ZrO2), titanium oxide (TiO2), silicon oxide (SiO2), aluminum oxide (Al2O3), iron oxide (e.g., Fe2O3, FeO, and Fe3O4), copper oxide (e.g., CuO and Cu2O), zinc oxide (ZnO), yttrium oxide (Y2O3), niobium oxide (Nb2O5), molybdenum oxide (MoO3), indium oxide (In2O3, In2O), and tin oxide. Examples include (SnO2), tantalum oxide (Ta2O5), tungsten oxide (e.g., WO3 and W2O5), lead oxide (e.g., PbO and PbO2), bismuth oxide (Bi2O3), cerium oxide (e.g., CeO2 and Ce2O3), antimony oxide (e.g., Sb2O3 and Sb2O5), germanium oxide (e.g., GeO2 and GeO), lanthanum oxide (La2O3), and ruthenium oxide (RuO2). Inorganic oxides may also be inorganic oxides that are produced when inorganic non-oxides undergo oxidation over time or other processes. As inorganic oxides, titanium oxide, aluminum oxide, or zinc oxide are preferred, with aluminum oxide being more preferred.

[0024] The first thermally conductive inorganic particles may be surface-treated. The above surface treatment is a different process from surface modification using a surface modifier, which will be described later. It is presumed that surface treatment introduces functional groups to the surface of the first thermally conductive inorganic particles, making them more likely to interact with curable compounds, etc., thereby further improving the thermal conductivity and peel strength of the thermal conductive sheet. Examples of surface treatments include plasma treatment (e.g., vacuum plasma treatment, atmospheric pressure plasma treatment, and aqua plasma treatment), ultraviolet irradiation, corona treatment, electron beam irradiation, ozone treatment, firing, flame treatment, and oxidizing agent treatment. Oxidizing agent treatment may be carried out under either acidic conditions (e.g., pH 6 or lower) or basic conditions (e.g., pH 12 or higher).

[0025] <Surface modifier, surface-modified first-order thermally conductive inorganic particles> Preferably, the first thermal conductive layer contains a surface modifier, and the first thermal conductive inorganic particles, together with the surface modifier adsorbed on the surface of the first thermal conductive inorganic particles, constitute surface-modified first thermal conductive inorganic particles. In this specification, surface modification using a surface treatment agent means a state in which the surface treatment agent is adsorbed on at least a portion of the surface of the first thermally conductive inorganic particles. The form of adsorption is not particularly limited, and any bonded state is acceptable. That is, surface modification also includes a state in which organic groups obtained by the detachment of a portion of the surface treatment agent are bonded to the surface of the first thermally conductive inorganic particles. The bond may be any of the following: covalent bond, coordination bond, ionic bond, hydrogen bond, van der Waals bond, or metallic bond. Surface modification may be carried out in such a way as to form a monolayer on at least a portion of the surface. The monolayer is a single layer film formed by the chemical adsorption of the surface treatment agent and is known as a Self-Assembled MonoLayer (SAM). In this specification, surface modification using a surface treatment agent may be applied to only a portion of the surface of the first thermally conductive inorganic particles or to the entire surface.

[0026] In this specification, "surface-modified first thermally conductive inorganic particles" refers to first thermally conductive inorganic particles whose surface has been modified with a surface modifier. That is, surface-modified first thermally conductive inorganic particles are a material comprising first thermally conductive inorganic particles and a surface modifier adsorbed on the surface of the first thermally conductive inorganic particles. In other words, in the first thermal conductive layer, it is preferable that the first thermal conductive inorganic particles, together with a surface modifier adsorbed on the surface of the first thermal conductive inorganic particles, constitute surface-modified first thermal conductive inorganic particles. Furthermore, the first thermal conductive layer may contain surface-modified first thermal conductive inorganic particles and a surface modifier. Some or all of the first thermally conductive inorganic particles in the first thermally conductive layer may constitute surface-modified first thermally conductive inorganic particles together with a surface modifier. For example, in the first thermally conductive layer, some of the first thermally conductive inorganic particles may constitute surface-modified first thermally conductive inorganic particles, while at the same time, there may be first thermally conductive inorganic particles that do not participate in the formation of surface-modified first thermally conductive inorganic particles. The surface modifier in the first thermal conductive layer may, in part or in whole, constitute surface-modified first thermal conductive inorganic particles together with the first thermal conductive inorganic particles. For example, in the first thermal conductive layer, some of the surface modifier may constitute surface-modified first thermal conductive inorganic particles, while at the same time, there may be surface modifiers that do not participate in the formation of the surface-modified first thermal conductive inorganic particles. In particular, the first thermal conductive layer preferably contains a surface-modified inorganic nitride (preferably surface-modified boron nitride), wherein the first thermal conductive inorganic particles constituting the surface-modified first thermal conductive inorganic particles are inorganic nitrides (preferably boron nitride or aggregated boron nitride). Some or all of the inorganic nitrides (preferably boron nitride) in the first thermal conductive layer may constitute a surface-modified inorganic nitride (preferably surface-modified boron nitride) together with the surface modifier. Furthermore, the first thermal conductive layer may also contain a surface-modified inorganic oxide (preferably surface-modified aluminum) in which the first thermal conductive inorganic particles constituting the surface-modified first thermal conductive inorganic particles are inorganic oxides (preferably aluminum oxide). Some or all of the inorganic oxides (preferably aluminum oxide) in the first thermal conductive layer may constitute a surface-modified inorganic oxide (preferably surface-modified aluminum oxide) together with the surface modifier.

[0027] Surface-modified first thermally conductive inorganic particles can be formed, for example, by contacting first thermally conductive inorganic particles with a surface modifier. For example, in the process of forming the first thermally conductive layer described later, surface-modified first thermally conductive inorganic particles may be formed in the process of manufacturing the first thermally conductive layer by mixing the first thermally conductive inorganic particles, a surface modifier, and other components constituting the composition. Alternatively, for example, a mixture containing surface-modified first thermal conductive inorganic particles may be prepared by mixing the first thermal conductive inorganic particles and a surface modifier in a solvent beforehand. The surface-modified first thermal conductive inorganic particles may then be separated from the mixture by means of filtration or other means to obtain the separated surface-modified first thermal conductive inorganic particles. A composition for forming the first thermal conductive layer, as described later, may be prepared using the separated surface-modified first thermal conductive inorganic particles, and the first thermal conductive layer may then be formed using the composition.

[0028] As surface modifiers, conventionally known surface modifiers such as carboxylic acids such as long-chain alkyl fatty acids, organic phosphonic acids, organic phosphate esters, and organic silane molecules (e.g., silane coupling agents) can be used. Furthermore, surface modifiers described in, for example, Japanese Patent Publication No. 2009-502529, Japanese Patent Publication No. 2001-192500, and Japanese Patent No. 4694929 may also be used.

[0029] The silane coupling agent described above is, for example, a compound having a hydrolyzable group directly bonded to a Si atom. Examples of the hydrolyzable groups mentioned above include alkoxy groups (preferably having 1 to 10 carbon atoms) and halogen atoms such as chlorine atoms. The number of hydrolyzable groups directly bonded to Si atoms in the silane coupling agent is preferably 1 or more, more preferably 2 or more, and even more preferably 3 or more. There is no upper limit to the above number; for example, it may be 10,000 or less. It is also preferable that the silane coupling agent has a reactive group. Specific examples of the above-mentioned reactive groups include epoxy groups, oxetanyl groups, vinyl groups, (meth)acrylic groups, styryl groups, amino groups, isocyanate groups, mercapto groups, and acid anhydride groups. The number of reactive groups in the silane coupling agent is preferably 1 or more, more preferably 2 or more, and even more preferably 3 or more. There is no upper limit to the above number; for example, it may be 10,000 or less. Examples of silane coupling agents include 3-aminopropyltriethoxysilane, 3-(2-aminoethyl)aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-(2-aminoethyl)aminopropyltrimethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, 3-mercaptotriethoxysilane, and 3-ureidopropyltriethoxysilane. Furthermore, the silane coupling agent may be a polyfunctional silane coupling agent. Examples include the silane coupling agent X-12 series (e.g., X-12-1048, X-12-1050, X-12-981S, and X-12-984S, manufactured by Shin-Etsu Chemical Co., Ltd.).

[0030] Surface modifiers may be used individually or in combination of two or more types. If the first thermal conductive layer contains a surface modifier, the content of the surface modifier is preferably 0.005 to 5% by mass, and more preferably 0.05 to 3% by mass, relative to the total mass of the first thermal conductive layer. If the first thermal conductive layer contains a surface modifier, the content of the surface modifier is preferably 0.01 to 10% by mass, and more preferably 0.10 to 5% by mass, relative to the total first thermal conductive inorganic particles. In surface-modified first thermally conductive inorganic particles, the mass ratio of the surface modifier to the first thermally conductive inorganic particles (mass of surface modifier adsorbed on the surface of the first thermally conductive inorganic particles / mass of the first thermally conductive inorganic particles) is preferably 0.00001 to 0.5, and more preferably 0.0001 to 0.1. When the first thermal conductive layer contains surface-modified first thermal conductive inorganic particles, the content of the surface-modified first thermal conductive inorganic particles is preferably 50.0 to 80.0 volume%, more preferably 55.0 to 75.0 volume%, and even more preferably 60.0 to 70.0 volume%, relative to the total volume of the first thermal conductive layer. When the first thermal conductive layer contains a surface-modified nitride (preferably surface-modified boron nitride), the content of the surface-modified nitride (preferably surface-modified boron nitride) is preferably 10 to 100% by mass, more preferably 40 to 100% by mass, and even more preferably 60 to 100% by mass, relative to the total surface-modified first thermal conductive inorganic particles.

[0031] When the first thermally conductive inorganic particles are inorganic nitrides (for example, when the first thermally conductive inorganic particles are aggregated boron nitride), the average particle size of the first thermally conductive inorganic particles is preferably 1.0 to 300.0 μm, more preferably 5.0 to 100.0 μm, and even more preferably 10.0 to 80.0 μm. When the first thermally conductive inorganic particles are inorganic oxides, the average particle size of the first thermally conductive inorganic particles is preferably 0.1 to 30.0 μm, more preferably 1.0 to 15.0 μm, even more preferably 2.0 to 10.0 μm, and particularly preferably 2.0 to 7.0 μm. When the first thermally conductive inorganic particles include both inorganic nitrides and inorganic oxides, it is preferable that each of them is in the above-described preferred embodiment. The average particle size of the first thermally conductive inorganic particles can be measured, for example, using a scanning electron microscope (SEM) or a laser diffraction particle size distribution analyzer. For example, a transmission microscope HT7700 (manufactured by Hitachi High-Technologies Corporation) can be used as a scanning electron microscope. The maximum length (Dmax: the maximum length at two points on the contour of the particle image) and the perpendicular length (DV-max: the shortest perpendicular length between two lines when the image is enclosed by two lines parallel to the maximum length) of the particle image obtained using a scanning electron microscope were measured, and their geometric mean value (Dmax × DV-max) was calculated. 1 / 2 This value was used as the particle size. The particle sizes of 100 particles were measured using this method, and the arithmetic mean was taken as the average particle size of the particles.

[0032] The first thermally conductive inorganic particles preferably contain an inorganic nitride, more preferably contain boron nitride, even more preferably contain boron nitride and not contain aluminum oxide (corresponding to thermally conductive inorganic particles X) having an average aspect ratio of 1.0 to 1.6, and particularly preferably consist only of boron nitride.

[0033] The first thermally conductive inorganic particles may be used individually or in combination of two or more types. The content of the first thermally conductive inorganic particles is preferably 50.0 to 80.0 volume%, more preferably 55.0 to 75.0 volume%, and even more preferably 60.0 to 70.0 volume%, relative to the total volume of the first thermally conductive layer.

[0034] <Curable compound> The first thermal conductive layer may contain a curable compound. A curable compound is a compound that has a crosslinking group. Examples of crosslinkable groups include groups having ethylenically unsaturated bonds such as vinyl groups, (meth)allyl groups, and (meth)acryloyl groups; cyclic ether groups such as epoxy groups and oxetane groups; hydroxyl groups such as phenolic hydroxyl groups and methylol groups; and carboxylic acid anhydrides.

[0035] Examples of curable compounds include known compounds that can be crosslinked by radicals, acids, bases and / or heat, specifically epoxy compounds, maleimide compounds, phenolic compounds and acid anhydrides. The curable compound preferably contains one or more selected from the group consisting of epoxy compounds, maleimide compounds, phenolic compounds, and acid anhydrides, more preferably contains one or more selected from the group consisting of epoxy compounds, maleimide compounds, and phenolic compounds, and even more preferably contains one or more selected from the group consisting of epoxy compounds and maleimide compounds.

[0036] (Epoxy compound) Epoxy compounds are compounds that have one or more epoxy groups in a single molecule. The epoxy group is a group obtained by removing one or more hydrogen atoms (preferably one hydrogen atom) from an oxirane ring. The epoxy group may, if possible, have further substituents (for example, linear or branched alkyl groups having 1 to 5 carbon atoms).

[0037] The number of epoxy groups in an epoxy compound is preferably 2 or more per molecule, more preferably 2 to 1000, and even more preferably 2 to 40.

[0038] The molecular weight of the epoxy compound is preferably 150 or more, and more preferably 300 or more. The upper limit is preferably 100,000 or less, and more preferably 10,000 or less. If the above molecular weight has a molecular weight distribution, then the above molecular weight is the weight-average molecular weight. The weight-average molecular weight is the weight-average molecular weight calculated on a polystyrene basis using gel permeation chromatography (GPC).

[0039] The epoxy group content of the epoxy compound is preferably 2.0 to 20.0 mmol / g, and more preferably 5.0 to 15.0 mmol / g. The epoxy group content mentioned above refers to the number of epoxy groups present in 1 gram of the epoxy compound. The epoxy compound may also preferably have an aromatic ring group (preferably an aromatic hydrocarbon ring group).

[0040] The epoxy compound may or may not exhibit liquid crystalline properties. In other words, the epoxy compound may be a liquid crystal compound. To put it another way, it may be a liquid crystal compound having an epoxy group.

[0041] Examples of epoxy compounds include bisphenol A-type epoxy compounds, bisphenol F-type epoxy compounds, bisphenol S-type epoxy compounds, and bisphenol AD-type epoxy compounds, which are glycidyl ethers of bisphenol A, F, S, and AD; hydrogenated bisphenol A-type epoxy compounds and hydrogenated bisphenol AD-type epoxy compounds; phenol novolac-type glycidyl ethers (phenol novolac-type epoxy compounds), cresol novolac-type glycidyl ethers (cresol novolac-type epoxy compounds), and bisphenol A novolac-type glycidyl ethers; dicyclopentadiene-type glycidyl ethers (dicyclopentadiene-type epoxy compounds); dihydroxypentadiene-type glycidyl ethers (dihydroxypentadiene-type epoxy compounds); polyhydroxybenzene-type glycidyl ethers (polyhydroxybenzene-type epoxy compounds), such as glycidyl ethers of dihydroxybenzene like resorcinol; benzene polycarboxylic acid-type glycidyl esters (benzene polycarboxylic acid-type epoxy compounds); trisphenolmethane-type epoxy compounds; phenoxy resins; and acrylic resins having epoxy groups in their side chains. Compounds in which one or more glycidyl ether groups and / or glycidyl ester groups in each of the above-mentioned compounds are replaced with diglycidylamino groups or diglycidylaminoalkylene groups (such as diglycidylaminomethylene groups) may be used as epoxy compounds. Each of the above-mentioned compounds may have substituents. For example, the aromatic ring group, cycloalkane ring group and / or alkylene group contained in each of the above-mentioned compounds may have substituents other than glycidyl ether group, glycidyl ester group, diglycidylamino group and / or diglycidylaminoalkylene group.

[0042] The epoxy compound may be used individually or in combination of two or more types. The epoxy compound content is preferably 1.0 to 90.0% by mass, more preferably 2.0 to 50.0% by mass, and even more preferably 4.0 to 20.0% by mass, relative to the total mass of the first thermal conductive layer.

[0043] (Maleimide compounds) The first thermal conductive layer may contain a maleimide compound. It is believed that the first thermal conductive layer improves the density of the polymer structure of the first thermal conductive layer by forming an interpenetrating network structure between the maleimide compound and the phenol compound in an addition reaction, and / or between the polymer structure formed by the above addition reaction and the polymer structure formed by other components in the composition, thereby further improving the thermal conductivity and heat resistance (Tg) of the thermal conductive sheet. Furthermore, because a denser polymer structure is formed in the first thermal conductive layer, water is less likely to penetrate the thermal conductive sheet, and hygroscopicity is suppressed. In addition, when the thermal conductive sheet is exposed to high temperatures, the thermal decomposition of its components and the generation of volatile low-molecular-weight substances within the thermal conductive sheet are suppressed. As a result, even when the thermal conductive sheet is placed under high temperatures, the vaporization of volatile components from the thermal conductive sheet and the resulting decrease in adhesion are suppressed, and the solder heat resistance of the thermal conductive seed is thought to be further improved.

[0044] A maleimide compound is a compound that has one or more maleimide groups. Among these, maleimide compounds having one or two maleimide groups are preferred, and compounds having two maleimide groups (bismaleimide compounds) are more preferred.

[0045] The number of maleimide groups in the maleimide compound is 1 or more, preferably 1 to 100, more preferably 2 to 10, and even more preferably 2. The maleimide compound may be either a high-molecular-weight compound or a low-molecular-weight compound. The molecular weight of the maleimide compound is preferably 100 to 3000, more preferably 200 to 2000, and even more preferably 300 to 1000.

[0046] The maleimide group in the maleimide compound is preferably the group represented by formula (M).

[0047] [ka]

[0048] In formula (M), * represents a bonding position. X and Y each independently represent a hydrogen atom or a substituent.

[0049] X and Y each independently represent a hydrogen atom or a substituent. Examples of the above-mentioned substituent include known substituents (such as an alkyl group, etc.). As X and Y, a hydrogen atom is preferable.

[0050] The maleimide compound is also preferably a compound having one or more (preferably 1 to 10) aromatic ring groups (such as a benzene ring group, etc.). The maleimide compound is preferably a compound represented by formula (1).

[0051]

Chemical formula

[0052] In formula (1), m represents 0 or 1. As m, 1 is preferable. n represents 0 or 1. As n, 1 is preferable.

[0053] In formula (1), R 1 and R 2 each independently represent a hydrogen atom or a substituent. As the above-mentioned substituent, an alkyl group is preferable. The alkyl group may be linear or branched, and the number of carbon atoms of the alkyl group is preferably 1 to 10. R 1 and / or R 2 When representing a substituent, R 1 and / or R 2 is also preferably present at a position adjacent to the maleimide group on the benzene ring. R 1 and R 2 When both represent substituents, R 1 and R 2Preferably, each of the substituents is different, R 1 R represents a methyl group, 2 It is more preferable that represents an ethyl group.

[0054] In formula (1), L 1 This represents a divalent linking group. Examples of the above-mentioned divalent linking groups include ether groups (-O-), carbonyl groups (-CO-), ester groups (-COO-), thioether groups (-S-), -SO2-, -NR- (where R is a hydrogen atom or an alkyl group), divalent aliphatic hydrocarbon groups (e.g., alkylene groups, cycloalkylene groups, alkenylene groups (-CH=CH- etc.), alkylylene groups (-C≡C- etc.)), and divalent aromatic ring groups (arylene groups and heteroarylene groups), as well as groups formed by combining these. In formula (1), L 1 The number of carbon atoms in the divalent linking group represented by is preferably 1 or more, more preferably 1 to 100, and even more preferably 3 to 15.

[0055] Among them, L 1 teeth,"* p -(L 2 -Ar) k -* q A base represented by " is preferred. * q * represents the bond position on the side that directly bonds with the maleimide group. p This indicates the opposite bonding position. k represents an integer greater than or equal to 1, preferably an integer between 1 and 10, and more preferably 1. L 2 This is a single bond, -C(R 3 )(R 4 )-, -O- or -CO- represents -C(R 3 )(R 4 )- is preferable. R 3 and R 4 Each of these independently represents a hydrogen atom or a substituent, and alkyl groups (which may be linear or branched, with 1 to 10 carbon atoms) are preferred. Ar represents an arylene group. The number of ring member atoms of the arylene group is preferably 6 to 15, more preferably 6. If the arylene group has substituents, the number of substituents is preferably 1 to 4, more preferably 1 to 2. Preferred substituents that the arylene group may have are alkyl groups (which may be linear or branched, and have 1 to 10 carbon atoms). Possible structures of Ar include, for example, R as explicitly shown in formula (1). 1 and R 2 Another possible structure is one in which a benzene ring group can bond with it. L 2 And if there are multiple Ars, then there are multiple Ls. 2 Each Ar element, and each other, may be identical or different.

[0056] If n is 1, R 1 and R 2 On the benzene ring group bonded to the maleimide group, "-(L 1 ) m The two groups represented by the "-maleimide group" may be positioned in the ortho, meta, or para positions relative to each other. In particular, it is preferable that the two groups are positioned in the meta or para positions.

[0057] In particular, the compound represented by formula (1) is one in which m represents 1, n represents 1, and L 1 The number of carbon atoms in the divalent linking group represented by is preferably 3 to 15.

[0058] Maleimide compounds may be used individually or in combination of two or more. The maleimide compound content is preferably 0.1 to 40.0% by mass, more preferably 1.0 to 15.0% by mass, and even more preferably 5.0 to 20.0% by mass, relative to the total mass of the first thermal conductive layer.

[0059] (Phenol compounds) A phenolic compound is a compound having one or more phenolic hydroxyl groups. The number of phenolic hydroxyl groups in the phenol compound is preferably two or more, and more preferably 2 to 10. The phenol compound preferably has a triazine skeleton. Having a triazine skeleton means that the phenol compound has one or more (preferably 1 to 5) triazine ring groups in its molecule.

[0060] - Compound represented by formula (Z1) - The phenol compound is also preferably a compound represented by formula (Z1). The phenol compound preferably contains the compound represented by formula (Z1), and the phenol compound may be the compound represented by formula (Z1) itself. The content of the compound represented by formula (Z1) is preferably 10 to 100% by mass, more preferably 25 to 100% by mass, and even more preferably 50 to 100% by mass, relative to the total mass of the phenol compound.

[0061] [ka]

[0062] In equation (Z1), r represents a non-negative integer. For r, an integer between 0 and 20 is preferred, and an integer between 0 and 10 is more preferred. L represents a divalent organic group. Examples of the above divalent organic groups include a substituted divalent aromatic ring group, a substituted divalent aliphatic hydrocarbon group, a substituted divalent aliphatic ring group, -O-, -S-, -N(R N Examples include groups with - or -CO-, and combinations thereof. R N R represents a hydrogen atom or substituent. N Examples of substituents represented by include linear alkyl groups having 1 to 5 carbon atoms and branched alkyl groups. Furthermore, examples of substituents that L may have include the aromatic ring group, the aliphatic hydrocarbon group, and linear alkyl groups having 1 to 5 carbon atoms, and branched alkyl groups. R Z represents a hydrogen atom or substituent. R Z The substituents represented are preferably substituents having 1 to 6 carbon atoms, more preferably hydrocarbon groups having 1 to 6 carbon atoms, and even more preferably linear or branched alkyl groups having 1 to 6 carbon atoms. In equation (Z1), there are (3+r) R Z Among them, R represents a substituent. Z The proportion of (R representing substituents) Z The number of R elements is divided by (3+r). Z The ratio of (number of items) × 100 is preferably 30% or more, more preferably 50% or more, and even more preferably 65% ​​or more. The upper limit is preferably 90% or less, and more preferably 80% or less. There are (3+r) R in equation (Z1). Z At least one of them (for example, 1 or 2) may represent a hydrogen atom. R in equation (Z1) z (preferably R is a substituent) z ) and in a benzene ring group to which OH is bonded, the above R z (preferably R is a substituent) z It is also preferable that the above-mentioned benzene ring group is located at the para position relative to the NH to which it is attached.

[0063] In addition to the above, other phenolic compounds may also be included. Other phenolic compounds include, for example, benzene polyols such as bisphenol A, F, S, AD, benzenediol, and benzenetriol, biphenyl aralkyl type phenolic resins, phenol novolac resins, cresol novolac resins, aromatic hydrocarbon formaldehyde resin-modified phenolic resins, dicyclopentadienephenol addition type resins, phenol aralkyl resins, polyvalent phenol novolac resins synthesized from polyvalent hydroxy compounds and formaldehyde, naphthol aralkyl resins, trimethylol methane resins, tetraphenyloleethane resins, naphthol novolac resins, naphthol phenol co-condensed novolac resins, naphthol cresol co-condensed novolac resins, biphenyl-modified phenolic resins, biphenyl-modified naphthol resins, aminotriazine-modified phenolic resins, and alkoxy group-containing aromatic ring-modified novolac resins.

[0064] The molecular weight of the phenol compound is preferably 225 to 2000, and more preferably 225 to 1000. If the above molecular weight has a molecular weight distribution, then the above molecular weight is the weight-average molecular weight.

[0065] The hydroxyl group content of the phenol compound is preferably 2.0 mmol / g or more, and more preferably 4.0 mmol / g or more. The upper limit is preferably 25.0 mmol / g or less, and more preferably 10.0 mmol / g or less. The hydroxyl group content mentioned above refers to the number of hydroxyl groups (preferably phenolic hydroxyl groups) present in 1 g of the phenol compound. Furthermore, the phenol compound may or may not have active hydrogen-containing groups (e.g., carboxyl groups) that can polymerize with epoxy compounds, in addition to hydroxyl groups. The active hydrogen content of the phenol compound (total hydrogen atom content in hydroxyl groups and carboxyl groups, etc.) is preferably 2.0 mmol / g or more, and more preferably 4.0 mmol / g or more. The upper limit is preferably 25.0 mmol / g or less, and more preferably 10.0 mmol / g or less.

[0066] The composition of the present invention may also contain, in addition to the phenol compound described above, a compound having a group that can react with an epoxy compound (hereinafter also referred to as "other active hydrogen-containing compound"). The mass ratio of the content of other active hydrogen-containing compounds to the content of phenol compounds (content of other active hydrogen-containing compounds / content of phenol compounds) is preferably 0 to 1, more preferably 0 to 0.1, and even more preferably 0 to 0.05.

[0067] The phenolic compounds may be used individually or in combination of two or more. The phenol compound content is preferably 1.0 to 90.0% by mass, more preferably 1.0 to 50.0% by mass, even more preferably 2.0 to 30.0% by mass, and particularly preferably 3.0 to 10.0% by mass, relative to the total mass of the first thermal conductive layer.

[0068] The maleimide compound content is preferably 1 to 200% by mass, more preferably 5 to 100% by mass, more preferably 10 to 80% by mass, and even more preferably 20 to 80% by mass, relative to the total content of the epoxy compound and the phenol compound. The maleimide compound content is preferably 1 to 500% by mass, more preferably 20 to 300% by mass, even more preferably 50 to 200% by mass, and particularly preferably 70 to 180% by mass, relative to the phenol compound content.

[0069] The total content of epoxy compounds and phenolic compounds is preferably 3 to 90% by mass, more preferably 5 to 50% by mass, and even more preferably 7 to 40% by mass, relative to the total mass of the first thermal conductive layer.

[0070] The ratio of the total number of epoxy groups in the epoxy compound to the number of hydroxyl groups (preferably phenolic hydroxyl groups) in the phenol compound (number of epoxy groups / number of hydroxyl groups) is preferably 3 / 97 to 97 / 3, more preferably 30 / 70 to 70 / 30, even more preferably 40 / 60 to 60 / 40, and particularly preferably 45 / 55 to 55 / 45. In other words, the ratio of the phenol compound to the epoxy compound is preferably such that the ratio of "number of epoxy groups / number of phenolic hydroxyl groups" falls within the above range.

[0071] The equivalent ratio (number of epoxy groups / number of active hydrogens) of epoxy groups in an epoxy compound to active hydrogen (which may be active hydrogen derived from phenolic hydroxyl groups, or active hydrogen from other active hydrogen-containing compounds) is preferably 3 / 97 to 97 / 3, more preferably 30 / 70 to 70 / 30, even more preferably 40 / 60 to 60 / 40, and particularly preferably 45 / 55 to 55 / 45.

[0072] (acid anhydride) The first heat-conducting layer may contain an acid anhydride. Acid anhydrides are compounds that have one or more acid anhydride groups (groups represented by -CO-O-CO-).

[0073] The number of acid anhydride groups in an acid anhydride is 1 or more, preferably 2 or more, and more preferably 3 or more. The upper limit of the above number is, for example, 1000 or less. The molecular weight of the acid anhydride (or weight-average molecular weight if there is a molecular weight distribution) is preferably 100 or more, more preferably 2000 or more, and even more preferably 6000 or more. The upper limit of the above molecular weight is preferably 100000 or less, more preferably 30000 or less, and even more preferably 17000 or less. The acid anhydride may be a low-molecular-weight compound or a high-molecular-weight compound. Examples of low molecular weight acid anhydrides include maleic anhydride, phthalic anhydride, pyromellitic anhydride, and trimellitic anhydride. In a polymer compound, such as an acid anhydride, the acid anhydride group may be incorporated into the main chain or present in the side chain. For example, if the polymer compound has repeating units based on maleic acid, the acid anhydride group included in the repeating units shall be considered incorporated into the main chain.

[0074] Commercially available acid anhydrides may be used. Examples of commercially available acid anhydrides include the SMA series from Tomoe Engineering Co., Ltd. (XIRAN series from Polyscope Polymers BV), the OREVAC T series from Arkema, and the Alastor series from Arakawa Chemical Industries, Ltd.

[0075] Acid anhydrides may be used individually or in combination of two or more types. The acid anhydride content is preferably 0.01 to 40.0% by mass, more preferably 0.1 to 10.0% by mass, and even more preferably 0.6 to 5.0% by mass, relative to the total mass of the first thermal conductive layer.

[0076] <Curing accelerator> The first heat conduction layer preferably contains a curing accelerator. Examples of curing accelerators include onium salt-based curing accelerators such as tris-orthotolylphosphine, triphenylphosphine, boron trifluoride amine complex, the compound described in paragraph

[0052] of Japanese Patent Application Publication No. 2012-067225, tetraphenylphosphonium tetraphenylborate (TPP-K), tetraphenylphosphonium tetra-p-tolylborate (TPP-MK), tetra-n-butylphosphonium laurate (TBP-LA), bis(tetra-n-butylphosphonium) pyromelitate, and quaternary phosphonium compounds (phosphonium salts) such as bis(naphthalene-2,3-dioxy)phenylsilicate adducts of tetraphenylphosphonium.

[0077] The curing accelerator preferably contains a compound having a phosphorus atom or a phosphonium salt, and more preferably contains a compound having a phosphorus atom. The curing accelerator may be a compound containing a phosphorus atom or the phosphonium salt itself. When the curing accelerator contains a phosphonium salt, the storage stability of the first thermal conductive layer is excellent.

[0078] The curing accelerator may be used individually or in combination of two or more types. The content of the curing accelerator is preferably 0.002% by mass or more, more preferably 0.02% by mass or more, and even more preferably 0.07% by mass or more, relative to the total mass of the first thermal conductive layer. The upper limit is preferably 5.0% by mass or less, more preferably 2.0% by mass or less, and even more preferably 1.0% by mass or less, relative to the total mass of the first thermal conductive layer.

[0079] The first thermal conductive layer may contain a resin. Examples of resins include cured products of the curable compounds mentioned above. Specifically, examples include cured products of one or more compounds selected from the group consisting of epoxy compounds and maleimide compounds and phenolic compounds. Preferably, this cured product has one or more compounds selected from the group consisting of epoxy groups and maleimide groups, and a phenolic hydroxyl group.

[0080] The total content of the curable compound and its cured product is preferably 20 to 50% by volume, more preferably 25 to 45% by volume, and even more preferably 30 to 40% by volume, relative to the total volume of the first thermal conductive layer.

[0081] As will be described later, the first thermal conductive layer may be a layer that has been subjected to pressure treatment. By applying pressure treatment, voids and the like in the first thermal conductive layer are removed, and as a result, the thermal conductivity of the thermal conductive sheet after lamination is improved.

[0082] [Second thermal conductive layer] The thermal conductive sheet has a second thermal conductive layer, which is disposed on only one of the two main surfaces of the first thermal conductive layer. The second thermal conductive layer contains second thermal conductive inorganic particles and a curable compound. Preferably, the second thermal conductive layer contains a surface modifier, and the second thermal conductive inorganic particles, together with the surface modifier adsorbed on the surface of the second thermal conductive inorganic particles, constitute surface-modified second thermal conductive inorganic particles. Aggregated boron nitride is preferred as the second thermal conductive inorganic particles constituting the surface-modified second thermal conductive inorganic particles. The aggregated boron nitride, the surface modifier, and the surface-modified second thermally conductive inorganic particles are synonymous with surface-modified inorganic particles composed of the second thermally conductive inorganic particles among the aggregated boron nitride, surface modifier, and surface-modified first thermally conductive inorganic particles, which can each be included in the first thermally conductive inorganic particles, and the preferred embodiments are also the same.

[0083] The second thermally conductive inorganic particle comprises aggregated boron nitride and thermally conductive inorganic particle X. The thermally conductive inorganic particles X have an average aspect ratio of 1.0 to 1.6 and are different from the aggregated boron nitride described above. Examples of thermally conductive inorganic particles that can constitute thermally conductive inorganic particles X include the inorganic particles exemplified in the first thermally conductive inorganic particles described above (specifically, inorganic nitrides and inorganic oxides, etc.). Examples of thermally conductive inorganic particles X include first thermally conductive inorganic particles other than aggregated boron nitride, which are inorganic nitrides and inorganic oxides, and which have an average aspect ratio of 1.0 to 1.6. As the thermally conductive inorganic particles X, inorganic oxides with an average aspect ratio of 1.0 to 1.6 are preferred, and aluminum oxide with an average aspect ratio of 1.0 to 1.6 is more preferred.

[0084] The second thermally conductive inorganic particle may contain other thermally conductive inorganic particles in addition to aggregated boron nitride and thermally conductive inorganic particle X. The above-mentioned other thermally conductive inorganic particles are not particularly limited as long as they are not aggregated boron nitride and thermally conductive inorganic particles X.

[0085] The average particle size of the thermally conductive inorganic particles X is often 0.1 to 300.0 μm, preferably 1.0 to 100.0 μm, more preferably 1.0 to 15.0 μm, even more preferably 2.0 to 10.0 μm, and particularly preferably 2.0 to 7.0 μm. The average aspect ratio of the thermally conductive inorganic particles X is 1.0 to 1.6, preferably 1.0 to 1.55, and more preferably 1.0 to 1.50. In this specification, the average aspect ratio is determined by measuring the major axis and minor axis of any 100 inorganic particles observed using a TEM (transmission electron microscope) or SEM (scanning electron microscope), calculating the aspect ratio (major axis / minor axis) for each inorganic particle, and then taking the arithmetic mean of the 100 aspect ratios. The major axis of a particle refers to the length along its major axis, and the minor axis refers to the length of the particle perpendicular to its major axis.

[0086] The content of the second thermally conductive inorganic particles is 40.0 to 60.0 volume%, preferably 45.0 to 55.0 volume%, and more preferably 50.0 to 55.0 volume%, relative to the total volume of the second thermally conductive layer. The content of the second thermally conductive inorganic particles refers to, for example, the total content of aggregated boron nitride and thermally conductive inorganic particles X when the second thermally conductive inorganic particles consist of aggregated boron nitride and thermally conductive inorganic particles X. The content of aggregated boron nitride is preferably 25.0 to 55.0 volume%, more preferably 30.0 to 55.0 volume%, and even more preferably 35.0 to 50.0 volume%, relative to the total volume of the second thermal conductive layer. The content of thermally conductive inorganic particles X is preferably 5.0 to 30.0 volume%, more preferably 7.5 to 27.5 volume%, and even more preferably 10.0 to 25.0 volume%, relative to the total volume of the second thermal conductive layer. In the second heat-conducting layer, the volume ratio of aggregated boron nitride to heat-conducting inorganic particles X (volume of aggregated boron nitride / volume of heat-conducting inorganic particles X) is preferably 2.5 to 10.5, and more preferably 2.8 to 5.0.

[0087] The term "curable compound" is synonymous with the term "curable compound that can be contained in the first thermal conductive layer," and the preferred embodiments are also the same.

[0088] The second thermal conductive layer may contain a cured product of a curable compound. Specifically, this includes a cured product of one or more compounds selected from the group consisting of epoxy compounds and maleimide compounds and a phenolic compound. Preferably, this cured product has one or more compounds selected from the group consisting of epoxy groups and maleimide groups, and a phenolic hydroxyl group. The second thermal conductive layer may also contain components that the first thermal conductive layer may contain (for example, a curing accelerator).

[0089] [Relationship between the first and second thermal conductive layers] The first and second thermal conductive layers satisfy requirements A and B.

[0090] Requirement A: The average thickness of the first thermal conductive layer is greater than the average thickness of the second thermal conductive layer. The average thickness of the first thermal conductive layer is not particularly limited, as long as it is greater than the average thickness of the second thermal conductive layer. In particular, the value obtained by subtracting the average thickness of the second thermal conductive layer from the average thickness of the first thermal conductive layer is preferably 55 to 190 μm, more preferably 65 to 170 μm, and even more preferably 75 to 150 μm. The average thickness of the first thermal conductive layer is preferably 70 to 250 μm, more preferably 85 to 225 μm, even more preferably 100 to 200 μm, and particularly preferably 100 to 150 μm. The average thickness of the second thermal conductive layer is preferably 5 to 100 μm, more preferably 10 to 80 μm, and even more preferably 10 to 70 μm. One method for measuring the average thickness of the first and second thermal conductive layers is to cut a cross-section of the thermal conductive sheet and observe the cross-section using a scanning electron microscope (SEM). Methods for adjusting the average thickness of the first and second thermal conductive layers include, for example, adjusting the amount of each layer-forming composition used and applying pressure at an arbitrary pressure after each layer has been formed.

[0091] Requirement B: The content of the first thermally conductive inorganic particles relative to the total volume of the first thermally conductive layer is greater than the content of the second thermally conductive inorganic particles relative to the total volume of the second thermally conductive layer. The content of the first thermally conductive inorganic particles relative to the total volume of the first thermally conductive layer is not particularly limited, as long as it is greater than the content of the second thermally conductive inorganic particles relative to the total volume of the second thermally conductive layer. In particular, the value obtained by subtracting the content of the second thermally conductive inorganic particles relative to the total volume of the second thermally conductive layer from the content of the first thermally conductive inorganic particles relative to the total volume of the first thermally conductive layer is preferably 5.0 to 65.0 volume%, more preferably 8.0 to 45.0 volume%, and even more preferably 10.0 to 25.0 volume%. The content of each thermally conductive inorganic particle in each thermal conductive layer is as described above.

[0092] [Base material] The thermal conductive sheet may have a base material. The base material is a component that supports the thermal conductive sheet and may ultimately be peeled off. The base material may have either a single-layer structure or a multi-layer structure. The base material is preferably in the form of a sheet. Examples of substrates include plastic materials, metal materials, and glass. Examples of plastic materials include polyester such as polyethylene terephthalate (PET), polycarbonate, acrylic resin, epoxy resin, polyurethane, polyamide, polyolefin, cellulose derivatives, and silicone. Examples of metal materials include copper and aluminum. The substrate is preferably surface-treated. Examples of surface treatments include mold release treatment and roughening treatment. The film thickness of the substrate is preferably 50 to 300 μm, and more preferably 75 to 250 μm.

[0093] The thermal conductive sheet is preferably insulating (electrically insulating). The volume resistivity of the thermal conductive sheet at 23°C and 65% relative humidity is 10 10 Preferably Ω·cm or more, 10 12 Ω·cm or more is more preferable, 10 14 A value of Ω·cm or higher is even more preferable. The upper limit is 10 18 A value of Ω·cm or less is preferable. The thermal conductivity of the thermal conductive sheet is preferably isotropic.

[0094] [Method for manufacturing a heat conductive sheet] Examples of methods for manufacturing a thermal conductive sheet include known methods. Specifically, the method for manufacturing a thermal conductive sheet includes a first thermal conductive layer formation step of applying a first thermal conductive layer forming composition onto a first substrate to form a first thermal conductive layer, A second heat conduction layer formation step, in which a composition for forming a second heat conduction layer is applied to a second substrate to form a second heat conduction layer, A manufacturing method is preferred that includes a bonding step of bonding the surface of the first thermal conductive layer opposite to the first substrate and the surface of the second thermal conductive layer opposite to the second substrate.

[0095] The method for manufacturing a thermal conductive sheet preferably further includes a step of modifying the surface of first thermal conductive inorganic particles or second thermal conductive inorganic particles using a surface modifier (surface modification step). Furthermore, the method for manufacturing a thermal conductive sheet may also preferably further include a step of surface treating the first thermal conductive inorganic particles or second thermal conductive inorganic particles to obtain modified inorganic particles (modification step). If the above modification step is included, it is preferable to perform the modification step before the surface modification step. In other words, it is preferable to perform the surface modification step on the surface of the modified inorganic particles. The following details each step.

[0096] <Modification process> The modification process involves surface-treating either first thermally conductive inorganic particles or second thermally conductive inorganic particles to obtain modified inorganic particles. The modification step described above preferably involves contacting first thermally conductive inorganic particles or second thermally conductive inorganic particles with an oxidizing agent in an aqueous solution to obtain modified inorganic particles. The first thermally conductive inorganic particles or the second thermally conductive inorganic particles subjected to the above modification process are as described above.

[0097] The above aqueous solution is preferably an alkaline aqueous solution. The pH of the above alkaline aqueous solution is often 8 or higher, preferably 12 or higher, more preferably greater than 12, even more preferably 13 or higher, and particularly preferably greater than 13. The upper limit is preferably 14 or lower. The pH of the above aqueous solution refers to the pH of the aqueous solution in a state in which the first thermally conductive inorganic particles or the second thermally conductive inorganic particles and the above oxidizing agent are included. In other words, the above aqueous solution optionally contains an alkaline compound, water, the first thermally conductive inorganic particles or the second thermally conductive inorganic particles, and an oxidizing agent.

[0098] In the above aqueous solution, the contact time between the first thermally conductive inorganic particles or the second thermally conductive inorganic particles and the oxidizing agent is preferably 0.1 to 24 hours, more preferably 0.5 to 10 hours, and even more preferably 1.5 to 6 hours. Furthermore, the temperature of the aqueous solution when the first thermally conductive inorganic particles or the second thermally conductive inorganic particles are brought into contact with the oxidizing agent is preferably 1 to 95°C, more preferably 25 to 80°C, and even more preferably 45 to 65°C.

[0099] One method for bringing the first thermally conductive inorganic particles or the second thermally conductive inorganic particles into contact with the oxidizing agent in the above aqueous solution is, for example, contact in a mixed solution.

[0100] Examples of organic solvents include methanol, ethanol, 2-propanol, acetonitrile, cyclopentanone, cyclohexanone, ethyl acetate, methyl ethyl ketone, dichloromethane, and tetrahydrofuran. Organic solvents may be used individually or in combination of two or more.

[0101] Methods for bringing the first thermally conductive inorganic particles or the second thermally conductive inorganic particles into contact with an oxidizing agent include, for example, a method of contacting them while stirring using a mechanical stirrer such as a three-one motor or a magnetic stirrer, and a method of bringing the first thermally conductive inorganic particles or the second thermally conductive inorganic particles into contact with a cartridge filled with them while circulating a solution containing the oxidizing agent using a pump or the like.

[0102] In the above aqueous solution, it is preferable to bring the first thermally conductive inorganic particles or the second thermally conductive inorganic particles into contact with an oxidizing agent, and then remove the resulting modified inorganic particles from the aqueous solution. One method for extracting modified inorganic particles from the above aqueous solution is to filter the aqueous solution and separate the modified inorganic particles as a filter. It is also preferable to wash the extracted modified inorganic particles with water and / or an organic solvent. After washing, it is also preferable to dry the inorganic particles in an oven or the like.

[0103] In the above aqueous solution, the water content is preferably 20 to 99% by mass, more preferably 50 to 95% by mass, and even more preferably 65 to 90% by mass, based on the total mass of the aqueous solution.

[0104] (Oxidizing agent) Examples of oxidizing agents used in the modification process include persulfates such as sodium persulfate, potassium persulfate, and ammonium persulfate; nitrates such as cerium ammonium nitrate, sodium nitrate, and ammonium nitrate; peroxides such as hydrogen peroxide and tert-butyl hydroperoxide; transition metal compounds such as divalent copper compounds and manganese compounds; hypervalent iodine compounds such as potassium periodate and sodium periodate; quinone compounds such as benzoquinone, naphthoquinone, anthraquinone, and chloranil; and salts of halogen oxoacids such as sodium hypochlorite and sodium chlorite. The oxidizing agent preferably contains a persulfate, and more preferably is a persulfate. Furthermore, a catalyst may be used separately from the oxidizing agent to assist its action. Examples of such catalysts include divalent iron compounds (e.g., FeSO4) and trivalent iron compounds. The oxidizing agent and / or catalyst may also be in hydrate form.

[0105] The standard oxidation-reduction potential of the oxidizing agent is preferably 0.30V or higher, more preferably 1.50V or higher, and even more preferably 1.70V or higher. The upper limit is preferably 4.00V or lower, and more preferably 2.50V or lower. The above standard oxidation-reduction potential is a value based on a standard hydrogen electrode.

[0106] The oxidizing agent may be used alone or in combination of two or more types. In the above aqueous solution, the content of the oxidizing agent is preferably 0.05 to 20 parts by mass, more preferably 0.1 to 20 parts by mass, and even more preferably 1 to 20 parts by mass, per 100 parts by mass of water in the aqueous solution.

[0107] The catalyst may be used individually or in combination of two or more types. If the aqueous solution contains a catalyst, the amount of catalyst is preferably 0.005 to 2 parts by mass, more preferably 0.01 to 2 parts by mass, and even more preferably 0.1 to 2 parts by mass, per 100 parts by mass of water in the aqueous solution.

[0108] (Alkaline compounds) The above aqueous solution may also preferably contain an alkaline compound in addition to the above-mentioned components in order to adjust the pH of the aqueous solution. Examples of the alkali compounds mentioned above include inorganic bases such as alkali metal hydroxides (e.g., sodium hydroxide) and alkaline earth metal hydroxides, as well as organic bases. The amount of the alkaline compound in the aqueous solution may be such that it is used to appropriately adjust the pH of the aqueous solution to a desired value. For example, the amount may be 0.1 to 10 parts by mass per 100 parts by mass of water in the aqueous solution.

[0109] <Surface modification process> The surface modification step is a step of modifying the surface of the first thermally conductive inorganic particles or the second thermally conductive inorganic particles using a surface modifier. The surface modification step preferably involves bringing first thermally conductive inorganic particles or second thermally conductive inorganic particles into contact with a surface modifier. Methods for bringing the first thermally conductive inorganic particles or second thermally conductive inorganic particles into contact with the surface modifier include those similar to those used in the modification step described above. The surface modifier to be brought into contact with the first or second thermally conductive inorganic particles is preferably a hydrolyzed product or hydrolyzed condensate of the surface modifier. In other words, it is preferable to subject the surface modifier to hydrolysis treatment before bringing it into contact with the first or second thermally conductive inorganic particles.

[0110] (Hydrolysis treatment) Hydrolysis is a process that hydrolyzes surface modifiers. When the surface modifier is a silane coupling agent, hydrolysis treatment can hydrolyze the alkoxysilyl group of the silane coupling agent to generate a silanol group, which can then form a bond with the surface of the first or second thermally conductive inorganic particle.

[0111] The method of hydrolysis is not particularly limited, as long as the conditions are such that the surface modifier is hydrolyzed. Specifically, it is preferable to carry out the procedure using an acidic solution (for example, hydrochloric acid and aqueous acetic acid solutions). The above acidic solution may contain an organic solvent.

[0112] The first substrate and the second substrate are synonymous with the above-mentioned substrates, and the preferred embodiments are also the same. The first and second substrates may be the same or different. The first thermal conductive layer forming composition and the second thermal conductive layer forming composition will be described in detail later.

[0113] Examples of methods for applying the first thermal conductive layer forming composition or the second thermal conductive layer forming composition (hereinafter also simply referred to as "composition") include known methods. Specifically, these include printing, spraying, roll coating, bar coating, curtain coating, spin coating, and die coating (slit coating).

[0114] After applying the composition, the resulting coating may be dried if necessary. Heat treatment is preferred as the drying treatment. The heat treatment temperature is preferably one at which the curing reaction of the curable compound does not proceed easily, and is more preferably between 50 and 130°C.

[0115] Furthermore, the obtained coating film may be subjected to a semi-curing treatment to a semi-cured state. In other words, the first and second thermal conductive layers may be semi-cured films. In particular, the first thermal conductive layer is preferably a semi-cured layer because it provides excellent thermal conductivity to the thermal conductive sheet after bonding. Examples of semi-curing treatments include heat treatment, and the heating conditions are preferably above the temperature at which the curing of the curable compound progresses. Furthermore, the first thermal conductive layer is preferably a layer that has been subjected to pressure treatment (for example, press working). By applying pressure treatment, voids in the first thermal conductive layer are reduced, resulting in superior thermal conductivity of the thermal conductive sheet after bonding. The semi-curing treatment and the pressurizing treatment may be performed separately or simultaneously. For example, after applying the composition to a substrate to form a coating film, the coating film on the substrate may be heated without pressure to create a semi-cured product, or it may be heated while press processing is used to create a semi-cured product. When press working is performed, the press working may be carried out before or after the semi-hardening treatment described above, or it may be carried out during the heating process described above. Performing press working during the semi-curing process can sometimes facilitate adjustment of the film thickness of the resulting semi-cured material and / or reduction of the amount of voids in the semi-cured material.

[0116] Furthermore, the pressurizing process (pressing process) may be carried out under either normal pressure or reduced pressure. For press work, for example, a flat plate press or a roll press may be used. When using a roll press, for example, it is preferable to clamp a coated substrate, obtained by forming a coating film on a substrate, between a pair of opposing rolls, and apply pressure in the film thickness direction of the coated substrate while rotating the pair of rolls to pass the coated substrate through it. The coated substrate may have the substrate on only one side of the coating film, or it may have the substrate on both sides of the coating film. The coated substrate may pass through the roll press only once or multiple times. During the curing process in the semi-curing treatment and / or the full curing treatment, either the flat plate press treatment or the roll press treatment may be performed alone or both.

[0117] One example of a bonding process is to bring the surface of the first thermal conductive layer opposite to the first substrate into contact with the surface of the second thermal conductive layer opposite to the second substrate and press them together. As for the bonding method, for example, a method of applying pressure and heating using lamination and rolls is preferred. Specifically, this refers to the press working used in the above-mentioned hardening treatment.

[0118] The method for manufacturing a thermal conductive sheet may further include a first thermal conductive layer formation step, a second thermal conductive layer formation step, and / or a bonding step. In other words, the thermal conductive sheet may have one or more first thermal conductive layers and one or more second thermal conductive layers.

[0119] Another method for manufacturing a heat conductive sheet is to apply a composition for forming a first heat conductive layer onto a first substrate to form a first heat conductive layer, A manufacturing method is also preferable that includes the step of further applying a composition for forming a second heat conduction layer onto the first heat conduction layer to form a second heat conduction layer. Alternatively, the manufacturing method may involve simultaneously applying a first thermal conductive layer-forming composition and a second thermal conductive layer-forming composition onto a substrate in a superimposed layer to form the first thermal conductive layer and the second thermal conductive layer.

[0120] [Composition for forming the first thermal conductive layer and composition for forming the second thermal conductive layer] The compositions (the first thermal conductive layer forming composition and the second thermal conductive layer forming composition) include the components contained in each thermal conductive layer and a solvent. The composition for forming the first thermal conductive layer is a composition for forming the first thermal conductive layer and contains at least the first thermal conductive inorganic particles described above. The composition for forming the first thermal conductive layer may contain other components (e.g., curable compounds) in addition to the first thermal conductive inorganic particles. The composition for forming the second thermal conductive layer is a composition for forming the second thermal conductive layer and contains at least the second thermal conductive inorganic particles and curable compound described above. The composition for forming the second thermal conductive layer may contain other components besides the second thermal conductive inorganic particles and the curable compound.

[0121] <Solvent> The composition preferably contains a solvent. Organic solvents are preferred as solvents. Examples of organic solvents include cyclopentanone, cyclohexanone, ethyl acetate, methyl ethyl ketone, dichloromethane, and tetrahydrofuran. If the composition contains a solvent, the amount of solvent is preferably such that the solid content concentration of the composition is 20 to 90% by mass, more preferably 30 to 85% by mass, and even more preferably 50 to 80% by mass. The "solid content" of the composition refers to the components that form each heat conduction layer formed using the composition, and if the composition contains a solvent, it refers to all components excluding the solvent. Furthermore, liquid components that form each heat conduction layer are also considered solid content. The solvent content is preferably 10 to 80% by mass, more preferably 15 to 70% by mass, and even more preferably 20 to 50% by mass, based on the total mass of the composition.

[0122] Examples of methods for producing the composition include known methods. One method for manufacturing the composition is to mix the components contained in each thermal conductive layer with a solvent. When mixing, the components may be mixed all at once or sequentially. For mixing the components, known methods can be used, for example. The mixing apparatus used is preferably a liquid-based disperser, such as a stirrer (e.g., a rotary-orbit mixer, high-speed rotary shear type stirrer), a colloidal mill, a roll mill, a high-pressure jet disperser, an ultrasonic disperser, a bead mill, and a homogenizer. The mixing apparatus may be used individually or in combination of two or more. Degassing treatment may be performed before, after, and / or simultaneously with the mixing.

[0123] [Applications of thermal conductive materials] The thermal conductive sheet of the present invention can be used, for example, as a heat dissipation material and can be used for heat dissipation applications in various devices. Specifically, by placing the thermal conductive sheet on a device to create a device with a thermal conductive sheet, heat generated from the device can be efficiently dissipated by the thermal conductive layer of the thermal conductive sheet. In particular, the thermal conductive sheet of the present invention exhibits excellent adhesion to devices even when bonded at low pressure, allowing the thermal conductive sheet to be placed on the device at low pressure, thereby reducing the risk of device damage. The above-mentioned thermal conductive layer may be a thermal conductive layer including a thermally conductive multilayer sheet, as described later. The thermal conductive sheet of the present invention is suitable for heat dissipation applications of power semiconductor devices used in electrical equipment such as personal computers, general home appliances, and automobiles.

[0124] One preferred application for the thermal conductive sheet of the present invention is a semiconductor module. One preferred embodiment of the semiconductor module including the thermal conductive sheet of the present invention is the embodiment shown in Figure 2. The semiconductor module 100A is a so-called case-type semiconductor module and includes a heat sink 30, a metal layer 32, the thermal conductive sheet 10 of the present invention, two devices 34, a case frame 36 provided to surround the area on which the devices 34 are mounted, and a sealing material 38 disposed within the case frame 36. A conductive paste layer may be placed between the heat sink 30 and the metal layer 32. The second thermal conductive layer 14 in the thermal conductive sheet 10 is positioned on the device 34 side. Furthermore, while the configuration of the device 34 is not particularly limited, it is preferable that it includes a semiconductor chip, and more preferably that the circuit portion, the conductive paste layer, and the semiconductor chip are stacked from the thermal conductive sheet 10 side. In semiconductor module 100A, two devices 34 are shown, but the number is not particularly limited, and the optimal number can be selected according to the various applications. Furthermore, electrical connections to device 34 may be made using metal electrodes or wire bonds (not shown). Examples of sealing materials 38 include silicone gel. In the semiconductor module 100A, the heat generated by the device 34 is transferred to the heat sink 30 via the thermal conductive sheet 10 and dissipated outside the semiconductor module 100A system.

[0125] Another preferred embodiment of the semiconductor module including the thermal conductive sheet of the present invention is the embodiment shown in Figure 3. The semiconductor module 100B is a so-called molded semiconductor module and includes a heat sink 30, a metal layer 32, the thermal conductive sheet 10 of the present invention, two devices 34, and a sealing resin 40 that seals the devices 34. The molded semiconductor module 100B can more securely fix and seal the device 34 than the cased semiconductor module 100A. The method for manufacturing the semiconductor module 100B is not particularly limited. Examples include a method of manufacturing a semiconductor module by placing resin pellets on a laminate device having components other than the encapsulating material 40 of the semiconductor module 100B, and then subjecting the resin pellets to a heat and pressure treatment to form the encapsulating resin 40, and a method of manufacturing a semiconductor module by performing a transfer molding process in which a laminate having components other than the encapsulating material 40 of the semiconductor module 100B is placed in a mold, mold resin is poured into it, and then heat is applied to cure it. A conductive paste layer may be placed between the heat sink 30 and the metal layer 32. In semiconductor module 100B, two devices 34 are described, but the number is not particularly limited, and the optimal number can be selected according to the various applications. Furthermore, electrical connections to the devices 34 may be made using metal electrodes or wire bonds (not shown). As for the encapsulating resin 40, examples include resins obtained by thermosetting epoxy resin. In the semiconductor module 100B, the heat generated by the device 34 is transferred to the heat sink 30 via the thermal conductive sheet 10 and dissipated outside the semiconductor module 100B system.

[0126] In semiconductor module 100B, a metal layer 32 was placed between the heat sink 30 and the thermal conductive sheet 10, but as shown in semiconductor module 100C in Figure 4, the metal layer 32 does not necessarily have to be placed. In addition, in the semiconductor module 100C, a conductive paste layer may be placed between the heat sink 30 and the thermal conductive sheet 10.

[0127] Another preferred embodiment of the semiconductor module is one in which two semiconductor modules are arranged facing each other, as shown in Figure 5. In the semiconductor module 100D, a laminate containing a heat sink 30, a metal layer 32, the thermal conductive sheet 10 of the present invention, and a device 34 is arranged facing each other, and a sealing resin 40 is placed between the two laminates to seal the device 34 in the two laminates. In this embodiment, heat is dissipated from both sides of the semiconductor module 100D.

[0128] Another preferred embodiment of the semiconductor module is one in which thermal conductive sheets 10 are arranged on both sides of a single device 34, as shown in Figure 6. The semiconductor module 100E includes a device 34, a thermal conductive sheet 10, a metal layer 32, and a heat sink 30 disposed on one side of the device 34, a thermal conductive sheet 10, a metal layer 32, and a heat sink 30 disposed on the other side of the device 34, and a sealing resin 40 that seals the device 34. In the semiconductor module 100E, the heat generated by the device 34 is transferred to the two heat sinks 30 via the thermal conductive sheets 10 placed on both sides of the device 34, and then dissipated outside the semiconductor module 100E system. [Examples]

[0129] The present invention will be described in more detail below based on the following examples. The materials, amounts used, proportions, processing content, and processing procedures shown in the following examples can be modified as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the following examples.

[0130] [Preparation and evaluation of compositions] [Various ingredients] The various components used in the examples and comparative examples are shown below.

[0131] <Thermally conductive inorganic particles> • HP40MF100: Aggregated boron nitride (average particle size: 40 μm, manufactured by Mizushima Iron Alloy Co., Ltd.) • Surface-modified BN: Surface-modified aggregated boron nitride produced by manufacturing method A described later. • AA-5: Aluminum oxide (average particle size: 5.0 μm, average aspect ratio: 1.1, manufactured by Sumitomo Chemical Co., Ltd.) • AA-7: Aluminum oxide (average particle size: 0.7 μm, average aspect ratio: 1.05, manufactured by Sumitomo Chemical Co., Ltd.) • AA-2: Aluminum oxide (average particle size: 2.0 μm, average aspect ratio: 1.1, manufactured by Sumitomo Chemical Co., Ltd.) • AA-10: Aluminum oxide (average particle size: 10.0 μm, average aspect ratio: 1.4, manufactured by Sumitomo Chemical Co., Ltd.) • AA-18: Aluminum oxide (average particle size: 18.0 μm, average aspect ratio: 1.6, manufactured by Sumitomo Chemical Co., Ltd.)

[0132] (Manufacturing method A) Agglomerated boron nitride (HP40MF100) (50g) was added to sodium persulfate solution (NaOH: 40g / water: 400mL) and stirred. Sodium persulfate solution (sodium persulfate: 9.6g / water: 100mL) was then added to the above sodium persulfate solution, and the above sodium persulfate solution was heated to 50°C and stirred for a further 3 hours (modification step). Stirring was performed using a Three One Motor (manufactured by Shinto Kagaku Co., Ltd.) at 150 rpm. After cooling the above NaOH solution to room temperature, the aggregated boron nitride in the NaOH solution was filtered off, and the filtered aggregated boron nitride was washed with water (500 mL) and acetonitrile (250 mL) to obtain modified aggregated boron nitride 1. The obtained modified aggregated boron nitride 1 was stirred in acetonitrile (100 mL), and then 1.25 g of a hydrolysis-adjusted solution of a silane coupling agent (Shin-Etsu Chemical Co., Ltd.: X12-984S) was added to the acetonitrile. The acetonitrile was stirred at room temperature for 3 hours to perform the adsorption treatment (adsorption step). After filtering out the modified aggregated boron nitride 1 from the acetonitrile, the filtered modified aggregated boron nitride 1 was washed with acetonitrile (100 mL) and dried in an oven at 40°C to obtain surface-modified aggregated boron nitride. The hydrolysis preparation solution for the silane coupling agent was prepared by mixing silane coupling agent (1 g), ethanol (500 μL), 2-propanol (500 μL), water (720 μL), and acetic acid (100 μL), and stirring for 1 hour. Furthermore, "X12-984S" is a polymer-type silane coupling agent having epoxy groups and ethoxysilyl groups. In addition, in manufacturing method 1, the pH of the solution (aqueous solution) obtained by mixing NaOH water (NaOH: 40g / water: 400ml), aggregated boron nitride (HP40MF100, 50g), and sodium persulfate water (sodium persulfate: 9.6g / water: 100ml) was 14. The content of the surface modifier in the surface-modified BN was greater than 0% by mass and less than 1% by mass relative to the total mass of the surface-modified BN.

[0133] <Epoxy compounds> • EXA-830LVP (manufactured by DIC Corporation)

[0134] <Maleimide compounds> • BMI-70: Bismaleimide resin (manufactured by K.I. Chemicals Co., Ltd.)

[0135] <Phenol compounds>

[0136] [ka]

[0137] <Acid anhydride> • SMA EF-40: Styrene maleic anhydride copolymer (manufactured by Tomoe Industrial Co., Ltd.)

[0138] <Curing accelerator> TPP-MK: Tetraphenylphosphonium tetra-p-tolylborate (manufactured by Hokko Chemical Industry Co., Ltd.)

[0139] <Solvent> • Cyclopentanone (manufactured by Zeon Corporation)

[0140] [Preparation of the composition] The first thermal conductive layer forming composition and the second thermal conductive layer forming composition were prepared according to the following procedure, as shown in Tables 1 and 2 below. Specifically, a mixture was first prepared by combining an epoxy compound and a phenol compound in equivalent amounts (the amount in which the number of epoxy groups in the epoxy compound and the number of hydroxyl groups in the phenol compound are equal). After mixing the above mixture and solvent, an acid anhydride, a curing accelerator, and a maleimide compound were added. Then, each thermally conductive inorganic particle was added. The resulting mixture was treated for 5 minutes in a rotary-orbit mixer (Awatori Rentaro ARE-310, manufactured by THINKY Inc.) to obtain the compositions (curable compositions) for each example and comparative example. In Tables 1 and 2, the content (mass%) of each component relative to the total mass of the first or second heat-conducting layer forming composition is shown. "Remainder" means that the amount of solvent was adjusted so that the total amount of the other components combined equals 100% by mass.

[0141] [Table 1]

[0142] [Table 2]

[0143] [evaluation] [Fabrication of thermal conductive sheets] Using a micrometer-equipped applicator, each first thermal conductive layer-forming composition was uniformly applied to the release surface of a release-treated PET film (PET756501, manufactured by Lintec Corporation, film thickness 75 μm) with a clearance of 450 μm. The film was dried at 50°C for 4 minutes to obtain a first laminate having a first thermal conductive layer with a film thickness of 220 μm. The obtained first laminate was further dried at 120°C for 5 minutes and then cut into 5 cm × 5 cm pieces. The resulting cut pieces were subjected to vacuum pressurization at a temperature of 188°C and a pressure of 20 MPa. Furthermore, using a micrometer-equipped applicator, each second thermal conductive layer-forming composition was uniformly applied to the release surface of a release-treated PET film (PET756501, manufactured by Lintec Corporation, film thickness 75 μm) with a clearance of 60 μm, and dried at 50°C for 2 minutes to obtain a second laminate having a second thermal conductive layer with a film thickness of 53 μm. The obtained second laminate was further dried at 120°C for 2 minutes and then cut into 5 cm × 5 cm pieces.

[0144] The surface of the second thermal conductive layer on the side opposite to the PET film of the second laminate having the second thermal conductive layer described above was attached to the surface of the first thermal conductive layer on the side opposite to the PET of the first laminate having the first thermal conductive layer described above, and a resin sheet was obtained by vacuum pressurizing at a temperature of 188°C and a pressure of 5 MPa. The PET films on both sides of the obtained resin sheet were peeled off to obtain thermal conductive sheets for each example and each comparative example. In all thermal conductive sheets, the thickness of the first thermal conductive layer of the obtained thermal conductive sheet was 120 μm, and the thickness of the second thermal conductive layer of the obtained thermal conductive sheet was 36 μm.

[0145] [Evaluation of thermal conductivity] The resin sheet obtained above (a laminate having PET film / first thermal conductive layer / second thermal conductive layer / PET film in this order) was subjected to hot pressing under air (hot plate temperature 180°C, pressure 5MPa for 5 minutes), and then further treated under atmospheric pressure at 180°C for 90 minutes. The PET films on both sides of the resulting laminate were peeled off to obtain samples for thermal conductivity measurement. Using the resin sheets obtained from each composition, samples for thermal conductivity measurement were prepared in the same manner as described above, and thermal conductivity evaluation was performed. Thermal conductivity was measured using the method described below, and thermal conductivity was evaluated according to the criteria described below.

[0146] <Measurement of thermal conductivity (W / mk) in the film thickness direction> (1) The thermal diffusivity in the thickness direction of the sample for thermal conductivity measurement was measured using the laser flash method with the "LFA467" manufactured by NETZSCH. (2) The specific gravity of the sample for thermal conductivity measurement was measured using the Archimedes method (using the "Solid Specific Gravity Measurement Kit") with a Mettler-Toledo balance "XS204". (3) Using the "DSC320 / 6200" manufactured by Seiko Instruments, the specific heat of the samples for thermal conductivity measurement was determined at 25°C and 175°C under a heating condition of 10°C / min. (4) The thermal conductivity in the film thickness direction of the sample for thermal conductivity measurement was calculated by multiplying the obtained thermal diffusivity by the specific gravity and specific heat. The thermal conductivity of the samples used for thermal conductivity measurement was evaluated by classifying them according to the following criteria. A:15W / mK or more B: 10W / mK or higher, less than 15W / mK C: Less than 10W / mK

[0147] [Evaluation of adhesion (copper peel strength)] Using a micrometer-equipped applicator, each first thermal conductive layer-forming composition was uniformly applied to the release surface of a release-treated PET film (PET756501, manufactured by Lintec Corporation, film thickness 75 μm) with a clearance of 450 μm. The film was dried at 50°C for 4 minutes to obtain a laminate having a first thermal conductive layer with a film thickness of 220 μm. The obtained laminate was further dried at 120°C for 5 minutes and then cut into 5 cm × 5 cm pieces. The surface of the first thermal conductive layer was placed on top of an aluminum plate with a thickness of 1 mm and a size of 5 cm × 5 cm, and vacuum pressurized at a temperature of 188°C and a pressure of 20 MPa to obtain a first laminate having the release-treated PET film (first layer) / first thermal conductive layer (second layer) / aluminum plate (third layer) in this order. Furthermore, instead of using a release-treated PET film, a surface-treated copper foil (product name: surface-treated electrolytic copper foil CF-T8G-UN-35, manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd., film thickness 35 μm) was used. Each second thermal conductive layer-forming composition was uniformly applied with a clearance of 48 μm, and dried at 50°C for 3 minutes to obtain a second laminate having a second thermal conductive layer with a film thickness of 37 μm. The release PET film of the first laminate was peeled off, and the exposed first thermal conductive layer of the second laminate was directly joined with the exposed second thermal conductive layer of the second laminate and vacuum-pressurized at a temperature of 188°C and a pressure of 5 MPa to obtain a laminate 3 having copper foil (first layer) / second thermal conductive layer (second layer) / first thermal conductive layer (third layer) / aluminum plate (fourth layer) in this order. The thickness of the first thermal conductive layer of the obtained laminate 3 was 120 μm, and the thickness of the second thermal conductive layer of the obtained thermal conductive sheet for adhesion evaluation was 36 μm. Furthermore, the laminate 3 was cut into sizes of 2.0 cm wide × 5.0 cm long and 0.5 cm wide × 5.0 cm long. The copper foil peel strength of each laminate 3 obtained above was measured using a digital force gauge (ZTS-200N, manufactured by IMADA Corporation) and a 90-degree peel test fixture (P90-200N-BB, manufactured by IMADA Corporation) in accordance with the method for measuring peel strength under the conditions described in JIS C 6481. In the peel strength test, the copper foil was peeled at a 90° angle to the laminate 3 at a peeling speed of 50 mm / min. A: 5.0N / cm or more B: 2.5 N / cm or more, less than 5.0 N / cm C: Less than 2.5 N / cm

[0148] [Evaluation of insulating properties] To evaluate the insulating properties, insulation reliability measurements were performed under high temperature and high humidity conditions.

[0149] <Insulation reliability measurement under high temperature and high humidity conditions> Samples for insulation reliability measurement were prepared using the same procedure as for "thermal conductivity measurement samples". Using the "ETAC Insulation Reliability Measurement System SIR13" manufactured by Kusumoto Kasei Co., Ltd., a voltage of 1kV was applied to an insulation reliability measurement sample in an environment of 85°C and 85%RH, and the time until the insulation reliability measurement sample underwent dielectric breakdown was measured. The time until dielectric breakdown occurred in the insulation reliability measurement samples was classified according to the following criteria, and the insulation reliability under high temperature and high humidity conditions was evaluated. A: Over 500 hours B: 100 hours or more but less than 500 hours C: 50 hours or more but less than 100 hours D: Less than 50 hours

[0150] <Measurement of dielectric breakdown voltage> Samples for dielectric breakdown voltage measurement were prepared using the same procedure as for samples for insulation reliability measurement. Using the "YST-243-100RHO" manufactured by Yamayo Testing Instrument Co., Ltd., in oil at 25°C and 175°C, if 1 kV was applied to the sample for measuring dielectric breakdown voltage and it did not break down within 20 seconds, the applied voltage was increased by 0.5 V each time and the measurement was repeated for 20 seconds for evaluation. The maximum voltage at which breakdown did not occur was taken as the dielectric breakdown voltage, and it was classified according to the following criteria to evaluate the dielectric breakdown voltage property. A: 5 kV or more B: 2 kV or more and less than 5 kV C: Less than 2 kV

[0151] [Evaluation of void generation suppression property] Using the thermal conductive sheet obtained in the above [Production of thermal conductive sheet (semi-cured film)], the specific gravity of the thermal conductive sheet was measured by the Archimedes method (using the "Solid Specific Gravity Measurement Kit") using the balance "XS204" manufactured by Mettler Toledo, and V was calculated by the following formula using the measured specific gravity g / cc and the theoretical specific gravity (a value obtained from the volume fraction of resin component 1.2 g / cc, alumina 3.90 g / cc, and boron nitride 2.27 g / cc). T V = (theoretical specific gravity - measured specific gravity) / theoretical specific gravity × 100 A: V is less than 1.0% B: V is 1.0% or more and less than 2.0% C: V is 2.0% or more

[0152] [Results] The evaluation results are shown in Table 3 below. In the table, the column "Agglomerated boron nitride / aluminum oxide" shows the volume ratio of agglomerated boron nitride to aluminum oxide (thermal conductive inorganic particle X).

[0153] [Table 3]

[0154] From the results shown in Table 3, it was confirmed that the thermal conductive sheet of the present invention is excellent in thermal conductivity and also excellent in adhesion. When the content of the second thermal conductive inorganic particle is 45.0 to 55.0 volume% with respect to the total volume of the second thermal conductive layer, it was confirmed that the effect of the present invention is more excellent (comparison with Examples 1 to 5, etc.). In the second heat conduction layer, when the volume ratio of aggregated boron nitride to the thermally conductive inorganic particles X is 2.8 to 5.0, it was confirmed that the effects of the present invention are more excellent (comparisons such as Examples 1, 6 to 10, etc.). When the average particle diameter of the thermally conductive inorganic particles X is 2.0 to 10.0 μm, it was confirmed that the effects of the present invention are more excellent (comparisons such as Examples 1, 11 to 14, etc.). When at least one of the first heat conduction layer and the second heat conduction layer further contains a surface modifier, and the aggregated boron nitride constitutes surface-modified aggregated boron nitride together with the surface modifier adsorbed on the surface of the aggregated boron nitride (using surface-modified first thermally conductive inorganic particles and / or surface-modified first thermally conductive inorganic particles), it was confirmed that the thermal conductivity, adhesion, insulation, and suppression of void generation are more excellent (comparisons such as Examples 3, 11, 15, and 16, etc.).

Explanation of Signs

[0155] 10 Heat conduction sheet 12 First heat conduction layer 14 Second heat conduction layer 16 First thermally conductive inorganic particles 18 Second thermally conductive inorganic particles 20 Aggregated boron nitride 22 Thermally conductive inorganic particles X 30 Heat sink 32 Metal layer 34 Device 36 Case frame 38 Sealing material 40 Sealing resin [[ID=3']] 100A, 100B, 100C, 100D, 100E Semiconductor module

Claims

1. A first thermal conductive layer having two main surfaces, The first thermal conductive layer comprises a second thermal conductive layer disposed on only one of the two main surfaces of the first thermal conductive layer, The average thickness of the first thermal conductive layer is greater than the average thickness of the second thermal conductive layer. The first thermal conductive layer contains first thermally conductive inorganic particles, The second thermal conductive layer comprises second thermal conductive inorganic particles and a curable compound, The content of the first thermally conductive inorganic particles relative to the total volume of the first thermally conductive layer is greater than the content of the second thermally conductive inorganic particles relative to the total volume of the second thermally conductive layer. The second thermally conductive inorganic particles in the second thermally conductive layer include aggregated boron nitride and thermally conductive inorganic particles X having an average aspect ratio of 1.0 to 1.6 and different from the aggregated boron nitride. The content of the second thermally conductive inorganic particles is 40.0 to 60.0 volume percent relative to the total volume of the second thermally conductive layer. The content of the first thermally conductive inorganic particles is 55.0% by volume or more relative to the total volume of the first thermally conductive layer. A thermal conductive sheet wherein the curable compound comprises one or more selected from the group consisting of epoxy compounds and maleimide compounds.

2. The thermal conductive sheet according to claim 1, wherein the volume ratio of aggregated boron nitride to the thermally conductive inorganic particles X in the second thermal conductive layer is 2.5 to 10.

5.

3. The thermal conductive sheet according to claim 1 or 2, wherein the thermally conductive inorganic particles X are aluminum oxide.

4. The thermal conductive sheet according to claim 1 or 2, wherein the average particle size of the thermally conductive inorganic particles X is 2.0 to 10.0 μm.

5. The thermal conductive sheet according to claim 1 or 2, wherein the curable compound comprises a phenol compound.

6. The thermal conductive sheet according to claim 1 or 2, wherein the average thickness of the second thermal conductive layer is 10 to 70 μm.

7. The thermal conductive sheet according to claim 1 or 2, wherein the average thickness of the first thermal conductive layer is 100 to 150 μm.

8. The thermal conductive sheet according to claim 1 or 2, wherein the average particle size of the aggregated boron nitride is 10.0 to 80.0 μm.

9. At least one of the first thermal conductive layer and the second thermal conductive layer further comprises a surface modifier, The thermal conductive sheet according to claim 1 or 2, wherein the aggregated boron nitride, together with the surface modifier adsorbed on the surface of the aggregated boron nitride, constitutes surface-modified aggregated boron nitride.

10. A device with a thermal conductive sheet, comprising a device and a thermal conductive sheet according to claim 1 or 2 disposed on the device.

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