Thermally conductive sheets and electronic devices

Abstract

A thermally conductive sheet comprising a thermosetting resin and boron nitride particles, wherein the slope of region A of the particle size frequency cumulative histogram of the boron nitride particles is 0 or more and 1.45 or less.

Description

Technical Field

[0001] The present invention relates to a thermally conductive sheet and an electronic device.

Background Art

[0002] Thermal conductivity is required for insulating materials that make up electrical and electronic devices, etc. Examples of technologies related to insulating materials having thermal conductivity include the technologies described in Patent Documents 1 to 3.

[0003] Patent Document 1 has an object of providing a method for manufacturing an insulating sheet and a substrate that have excellent thermal conductivity and excellent insulation reliability. The resin composition has an epoxy resin, a curing agent, and an inorganic filler. Either one or both of the epoxy resin and the curing agent contain a naphthalene structure. The inorganic filler contains hexagonal boron nitride. The inorganic filler is 70 to 85% by volume of the entire resin composition. An insulating sheet formed by shaping the resin composition into a sheet is described.

[0004] Patent Document 2 has an object of providing a heat dissipation sheet having excellent thermal conductivity and insulation properties. It contains a resin binder and boron nitride particles. Among the boron nitride particles, the content of boron nitride particles having a particle size of 1 μm to 10 μm is 40% to 60% with respect to the total number of the boron nitride particles. Among the boron nitride particles, the content of boron nitride particles having a particle size of 20 μm to 70 μm and an aspect ratio of 1.3 or more is 20% to 30% with respect to the total number of the boron nitride particles. A heat dissipation sheet is described.

[0005] Patent Document 3 describes a heat dissipation sheet that has excellent thermal conductivity and insulating properties, comprising a resin binder and boron nitride particles, wherein the particle size distribution based on the number of boron nitride particles has a maximum particle size D1 in the range of 60 μm to 90 μm, and the value obtained by dividing the number of boron nitride particles A, which have a particle size in the range of 2 μm to 60 μm, by the number of boron nitride particles B, which have a particle size in the range of 90 μm to 150 μm, is 2.5 to 5.0. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2011-090868 [Patent Document 2] International Publication No. 2021 / 059647 [Patent Document 3] International Publication No. 2021 / 059648 [Overview of the project] [Problems that the invention aims to solve]

[0007] This invention provides a thermally conductive sheet and an electronic device with improved balance between thermal conductivity and insulating properties. [Means for solving the problem]

[0008] The inventors diligently conducted research to achieve the above objectives. As a result, they discovered that a thermally conductive sheet containing a thermosetting resin and boron nitride particles, and that the boron nitride particles have a specific region in the particle size frequency cumulative histogram, thereby improving the balance between thermal conductivity and insulating properties, and thus completed the present invention.

[0009] According to the present invention, the following thermally conductive sheet and electronic device are provided.

[0010] [1] A thermally conductive sheet containing a thermosetting resin and boron nitride particles, The thermally conductive sheet, wherein the slope of region A of the particle size frequency cumulative histogram of the boron nitride particles by the following (Method 1) is 0 or more and 1.45 or less. (Method 1) Using a laser diffraction / scattering type particle size distribution measuring device, measure the particle size distribution of the boron nitride particles under the following conditions by laser diffraction scattering measurement method. Let the particle size at the point with the highest frequency in the range where the particle size is 5.0 μm or more and less than 30.0 μm be d min , and let the particle size at the point with the lowest frequency in the range where the particle size is 10.0 μm or more and 100.0 μm or less be d max . Then, create a particle size frequency cumulative histogram with the cumulative frequency (%) on the vertical axis and the particle size (μm) on the horizontal axis (logarithmic horizontal axis), and calculate the slope of region A by the following formula (1). [(Cumulative frequency at d max ) - (Cumulative frequency at d min )] / (d max - d min ) ··· Formula (1) Conditions: Dispersion solvent: pure water Sample: Disperse in pure water. Use built-in ultrasonic wave in the device for 30 seconds (irradiation intensity 5). Refractive index: 1.74 for boron nitride Particle size standard: volume Number of measured particle sizes: 93 points (logarithmically equally spaced) from 0.011 μm to 3000 μm [2] The thermally conductive sheet according to [1] above, wherein d min is 7.0 μm or more and less than 20.0 μm. [3] The thermally conductive sheet according to [1] or [2] above, wherein d max is 15.0 μm or more and 50.0 μm or less. [4] The thermally conductive sheet according to any one of [1] to [3] above, wherein the difference between d max and d min is 5.0 μm or more and 40.0 μm or less. [5] The particle size D of the above boron nitride particles, which is the 10% integrated value of the volume-based particle size distribution measured by laser diffraction scattering. 10 A thermally conductive sheet as described in any of the above [1] to [4], wherein the thickness is between 0.1 μm and 50.0 μm. [6] The particle size D of the above boron nitride particles, which is the 50% integrated value of the volume-based particle size distribution measured by laser diffraction scattering. 50 A thermally conductive sheet as described in any of the above [1] to [5], wherein the thickness is between 1.0 μm and 100.0 μm. [7] The particle size D of the above boron nitride particles, which is the 90% integrated value of the volume-based particle size distribution measured by laser diffraction scattering. 90 However, a thermally conductive sheet as described in any of the above [1] to [6], having a thickness of 10.0 μm or more and 200.0 μm or less. [8] A thermally conductive sheet according to any of [1] to [7] above, wherein the content of the boron nitride particles is 100 parts by mass or more and 1000 parts by mass or less, when the content of the thermosetting resin is 100 parts by mass. [9] The thermally conductive sheet according to any one of [1] to [8] above, wherein the thermosetting resin comprises one or more selected from the group consisting of epoxy resin, cyanate ester resin, bismaleimide resin, and phenoxy resin.

[10] A thermally conductive sheet according to any of the above [1] to [9], further comprising a curing agent.

[11] The thermal conductive sheet according to

[10] above, wherein the curing agent comprises one or more selected from the group consisting of phenolic resin curing agents and imidazole curing agents.

[12] The thermal conductive sheet according to

[10] or

[11] above, wherein the content of the curing agent is 0.1 parts by mass or more and 5.0 parts by mass or less, when the content of the thermosetting resin is 100 parts by mass.

[13] A thermally conductive sheet as described in any of the above [1] to

[12] , wherein the thermal conductivity according to the method (2) below is 17.5 W / (m·K) or more and 30.0 W / (m·K) or less. (Method 2) The aforementioned thermally conductive sheet is heated at a constant rate from 25°C to 180°C over 30 minutes while applying a pressure of 10 MPa, and then heated at 180°C for 60 minutes to obtain a sheet-cured material. From the obtained sheet-cured material, a test piece with a thickness of 0.3 mm, a width of 10 mm, and a length of 10 mm is cut out. The thermal conductivity of the obtained test piece is then calculated using the following formula based on the thermal diffusivity (α) measured by the xenon flash method (half-time method) at 25°C, the specific heat (Cp) measured by the DSC method, and the density (ρ) measured in accordance with JIS K 6911:2006. Thermal conductivity [W / (m·K)]=α[mm 2 / s] × Cp[J / (kg·K)] × ρ[g / cm 3 ]

[14] A thermally conductive sheet as described in any of [1] to

[13] above, wherein the glass transition temperature according to the method (3) below is 100°C or more and 300°C or less. (Method 3) The aforementioned thermally conductive sheet is heated at a constant rate from 25°C to 180°C over 30 minutes while applying a pressure of 10 MPa, and then heated at 180°C for 60 minutes to obtain a sheet-cured material. A test piece with a thickness of 0.3 mm, a width of 8 mm, and a length of 50 mm is cut from the obtained sheet-cured material. The glass transition temperature of the obtained test piece is then measured using a dynamic viscoelasticity analyzer under the conditions of a heating rate of 5°C / min and a frequency of 1 Hz.

[15] Storage modulus E' at 25°C as described below (Method 4) 25 A thermally conductive sheet as described in any of the above [1] to

[14] , wherein the thermal conductivity is 1 GPa or more and 50 GPa or less. (Method 4) The aforementioned thermally conductive sheet is heated at a constant rate from 25°C to 180°C over 30 minutes while applying a pressure of 10 MPa, and then heated at 180°C for 60 minutes to obtain a hardened sheet. A test specimen with a thickness of 0.3 mm, a width of 8 mm, and a length of 50 mm is cut from the obtained hardened sheet. The storage modulus E' at 25°C is then measured on the obtained test specimen using a dynamic viscoelasticity analyzer under tensile mode and a frequency of 1 Hz. 25 Measure.

[16] Storage modulus E' at 175°C according to the method (Method 5) below. 175 A thermally conductive sheet as described in any of the above [1] to

[15] , wherein the thermal conductivity is 1 GPa or more and 30 GPa or less. (Method 5) The aforementioned thermally conductive sheet is heated at a constant rate from 25°C to 180°C over 30 minutes while applying a pressure of 10 MPa, and then heated at 180°C for 60 minutes to obtain a sheet-cured material. A test specimen with a thickness of 0.3 mm, a width of 8 mm, and a length of 50 mm is cut from the obtained sheet-cured material. The storage modulus E' of the obtained test specimen is then measured at 175°C using a dynamic viscoelasticity analyzer under tensile mode and a frequency of 10 Hz. 175 Measure.

[17] A thermally conductive sheet as described in any of [1] to

[16] above, wherein the average linear expansion coefficient α1 at 50 to 100°C, as determined by the method described below (Method 6), is 1 ppm / °C or more and 100 ppm / °C or less. (Method 6) The aforementioned thermally conductive sheet is heated at a constant rate from 25°C to 180°C over 30 minutes while being pressurized at 10 MPa, and then heated at 180°C for 60 minutes to obtain a hardened sheet. A test piece with a thickness of 0.3 mm, a width of 4 mm, and a length of 50 mm is cut from the obtained hardened sheet. The average linear expansion coefficient α1 (ppm / °C) of the obtained test piece is then measured using a thermomechanical analyzer under the conditions of a measurement temperature range of 0°C to 330°C and a heating rate of 5°C / min, at temperatures between 50°C and 100°C.

[18] A thermally conductive sheet as described in any of [1] to

[17] above, wherein the average coefficient of linear expansion α2 at 270 to 290°C, as determined by the method described below (Method 7), is 20 ppm / °C or more and 150 ppm / °C or less. (Method 7) The aforementioned thermally conductive sheet is heated at a constant rate from 25°C to 180°C over 30 minutes while being pressurized at 10 MPa, and then heated at 180°C for 60 minutes to obtain a sheet-cured material. A test piece with a thickness of 0.3 mm, a width of 4 mm, and a length of 50 mm is cut from the obtained sheet-cured material. The average linear expansion coefficient α2 (ppm / °C) of the obtained test piece is then measured using a thermomechanical analyzer under the conditions of a measurement temperature range of 0°C to 330°C and a heating rate of 5°C / min, at temperatures between 270°C and 290°C.

[19] The volume resistivity at 25°C, as determined below (Method 8), is 1.0 × 10⁻⁶. 14 Ω m or more 1.0×10 15 A thermally conductive sheet as described in any of the above [1] to

[18] , having a conductivity of Ω·m or less. (Method 8) The aforementioned thermally conductive sheet is heated at a constant rate from 25°C to 180°C over 30 minutes while applying a pressure of 10 MPa, and then heated at 180°C for 60 minutes to obtain a cured sheet. The volume resistivity (Ω·m) of the obtained cured sheet at 25°C is then measured in accordance with JIS C 2139:2008.

[20] An electronic device comprising a cured product of a thermally conductive sheet as described in any of the above [1] to

[19] . [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a thermally conductive sheet and an electronic device with an improved balance of thermal conductivity and insulating properties. [Modes for carrying out the invention]

[0012] Embodiments of the present invention will be described below. In this specification, numerical ranges indicated using "~" represent a range that includes the numbers before and after "~" as the minimum and maximum values, respectively. In numerical ranges described stepwise in this specification, the upper or lower limit of a numerical range in one step can be arbitrarily combined with the upper or lower limit of a numerical range in another step. In numerical ranges described in this specification, the upper or lower limit of that numerical range may be replaced with the values ​​shown in the examples. "A or B" means that either A or B is included, or both are included. Unless otherwise specified, the materials exemplified in this specification can be used individually or in combination of two or more. In this specification, the content of each component in a composition means the total amount of multiple substances present in the composition if there are multiple substances corresponding to each component in the composition, unless otherwise specified.

[0013] <Thermal conductive sheet> The thermally conductive sheet of this embodiment is a thermally conductive sheet comprising a thermosetting resin and boron nitride particles, wherein the slope of region A of the particle size frequency cumulative histogram of the boron nitride particles, calculated according to the following (Method 1), is 0 or greater and 1.45 or less.

[0014] (Method 1) The particle size distribution of the boron nitride particles is measured using a laser diffraction / scattering particle size distribution analyzer under the following conditions: The particle size at the point with the highest frequency in the range of particle size between 5.0 μm and less than 30.0 μm is defined as d min The particle size at the point with the lowest frequency in the range of 10.0 μm to 100.0 μm is d max Then, a particle size frequency cumulative histogram is created with the cumulative frequency (%) on the vertical axis and particle size (μm) on the horizontal axis, with the horizontal axis being logarithmic, and the slope of region A is calculated using the following equation (1). [(d max (Cumulative frequency in)-(d min (Cumulative frequency in) / (d max -d min )...Equation (1) conditions: Dispersion solvent: pure water Sample: Dispersed in pure water. Examined for 30 seconds using the device's built-in ultrasound (irradiation intensity 5). Refractive index: Boron nitride 1.74 Particle size standard: volume Number of measurement points for particle size: 93 points (equally spaced logarithmically) ranging from 0.011 μm to 3000 μm.

[0015] The thermally conductive sheet of this embodiment can improve the balance between thermal conductivity and insulating properties. While the reason for this effect is not entirely clear, the following reasons can be inferred, for example. First, the presence of a region A in the particle size frequency cumulative histogram of boron nitride particles with a low slope, i.e., a slope of 0 to 1.45, suggests that it contains both finer and coarser boron nitride particles, and that the amount of boron nitride particles with intermediate particle sizes is small. Furthermore, if boron nitride particles have such a particle size frequency cumulative histogram, the packing state of the boron nitride particles is more optimized, and as a result, the balance between the thermal conductivity and insulating properties of the resulting thermal conductive sheet is expected to improve.

[0016] The boron nitride particles of this embodiment can have a specific region in the particle size frequency cumulative histogram described above by classifying commercially available boron nitride particles (hereinafter also referred to as raw powder) by an airflow classification method and blending the classified boron nitride powder having a specific particle size distribution in an appropriate proportion. Although the exact mechanism is unclear, it is thought that the airflow classification method allows for the classification of boron nitride particles, which have aggregated into secondary particles, into coarse powder with larger particle sizes and fine powder with smaller particle sizes using airflow, thus enabling accurate classification of boron nitride particles. Furthermore, the particle size distribution of the accurately classified boron nitride powder becomes sharper, making it easier to achieve the desired particle size distribution by mixing the classified boron nitride powders. As a result, it is thought that the boron nitride particles contained in the thermal conductive sheet of this embodiment will have a region with a specific slope in the particle size frequency cumulative histogram.

[0017] The slope of region A is preferably 1.40 or less, more preferably 1.35 or less, and even more preferably 1.30 or less, from the viewpoint of further improving the balance between thermal conductivity and insulating properties. The lower limit of the slope of region A is not particularly limited, but may be 0.10 or more, 0.30 or more, 0.50 or more, 0.70 or more, or 0.80 or more. Furthermore, the slope of region A is preferably 0.10 to 1.40, more preferably 0.30 to 1.35, even more preferably 0.50 to 1.30, even more preferably 0.70 to 1.30, and even more preferably 0.80 to 1.30, from the viewpoint of further improving the balance of thermal conductivity and insulating properties.

[0018] The following describes each component used in the thermally conductive sheet of this embodiment.

[0019] [Thermosetting resin] The thermally conductive sheet of this embodiment contains a thermosetting resin. From the viewpoint of further improving the balance of thermal conductivity and insulating properties, the thermosetting resin preferably comprises one or more selected from the group consisting of epoxy resin, cyanate ester resin, polyimide resin, benzoxazine resin, unsaturated polyester resin, phenolic resin, melamine resin, silicone resin, bismaleimide resin, (meth)acrylic resin, and phenoxy resin, and more preferably comprises one or more selected from the group consisting of epoxy resin, cyanate ester resin, bismaleimide resin, and phenoxy resin.

[0020] Examples of epoxy resins include bisphenol type epoxy resins such as bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol E type epoxy resin, bisphenol S type epoxy resin, bisphenol M type epoxy resin (4,4'-(1,3-phenylenediisopridiene)bisphenol type epoxy resin), bisphenol P type epoxy resin (4,4'-(1,4-phenylenediisopridiene)bisphenol type epoxy resin), and bisphenol Z type epoxy resin (4,4'-cyclohexydiene bisphenol type epoxy resin); phenol novolac type epoxy resin, cresol novolac type epoxy resin, trisphenol group methane type novolac type epoxy resin, tetraphenol group ethane type novolac type epoxy resin, and condensed ring aromatic carbonized water. Examples include novolac epoxy resins such as novolac epoxy resins having an elementary structure; biphenyl epoxy resins such as tetramethylbiphenyl epoxy resins; arylalkylene epoxy resins such as xylylene epoxy resins and biphenylaralkyl epoxy resins; naphthalene epoxy resins such as naphthylene ether epoxy resins, naphthol epoxy resins, naphthalenediol epoxy resins, bifunctional or tetrafunctional epoxy naphthalene resins, binaphthyl epoxy resins, and naphthalenearalkyl epoxy resins; anthracene epoxy resins; phenoxy epoxy resins; dicyclopentadiene epoxy resins; norbornene epoxy resins; adamantane epoxy resins; fluorene epoxy resins; and epoxy resins having a phenylbenzoate structure.

[0021] Among these, the epoxy resin preferably comprises one or more selected from the group consisting of bisphenol-type epoxy resin, novolac-type epoxy resin, biphenyl-type epoxy resin, arylalkylene-type epoxy resin, naphthalene-type epoxy resin, anthracene-type epoxy resin, and dicyclopentadiene-type epoxy resin, from the viewpoint of further improving the balance of thermal conductivity and insulating properties. More preferably, it comprises one or more selected from the group consisting of bisphenol-type epoxy resin, biphenyl-type epoxy resin, naphthalene-type epoxy resin, and dicyclopentadiene-type epoxy resin.

[0022] Examples of cyanate ester resins include bisphenol A dicyanate, polyphenol cyanate (oligo(3-methylene-1,5-phenylene cyanate), 4,4'-methylenebis(2,6-dimethylphenyl cyanate), 4,4'-ethylidene diphenyl dicyanate, hexafluorobisphenol A dicyanate, 2,2-bis(4-cyanate)phenylpropane, 1,1-bis(4-cyanatephenylmethane), bis(4-cyanate-3,5-dimethylphenyl)methane, 1,3-bis(4-cyanatephenyl-1-(methylethylidene))benzene, bis( Examples include difunctional cyanate ester resins such as 4-cyanatephenyl)thioether and bis(4-cyanatephenyl)ether; polyfunctional cyanate ester resins derived from novolac-type cyanate ester resins such as phenol novolac and cresol novolac, and phenol resins containing dicyclopentadiene structures; and prepolymers in which a portion of the above-exemplified cyanate ester resins has been triazinated. Among these, the cyanate ester resin preferably includes a novolac-type cyanate ester resin from the viewpoint of further improving the balance between thermal conductivity and insulating properties.

[0023] The bismaleimide resin is not particularly limited as long as it is a resin having maleimide groups at both ends of the molecular chain, but examples include N,N'-(4,4'-diphenylmethane)bismaleimide, bis(3-ethyl-5-methyl-4-maleimidophenyl)methane, 2,2-bis[4-(4-maleimidophenoxy)phenyl]propane, m-phenylenebismaleimide, p-phenylenebismaleimide, 4-methyl-1,3-phenylenebismaleimide, N,N'-ethylenedimaleimide, and N,N'-hexamethylenedimaleimide.

[0024] From the viewpoint of further improving the balance between thermal conductivity and insulating properties, the thermosetting resin preferably includes a resin having a mesogenic structure. The resin having a mesogenic structure preferably includes a phenoxy resin. In other words, the thermosetting resin preferably includes a phenoxy resin having a mesogenic structure. Here, "phenoxy resin" in the narrow sense refers to a polyhydroxy polyether synthesized from bisphenols and epichlorohydrin, but in this specification, polymers obtained by polyaddition reactions of polyfunctional epoxy resins and polyfunctional phenols (phenoxy resins in the broad sense) are also included as phenoxy resins.

[0025] Examples of phenoxy resins include bisphenol-type phenoxy resins, naphthalene-type phenoxy resins, anthracene-type phenoxy resins, biphenyl-type phenoxy resins, phenylbenzoate-type phenoxy resins, and biphenyl ester-type phenoxy resins. Among these, from the viewpoint of further improving the balance between thermal conductivity and insulation performance, the phenoxy resin preferably includes biphenyl-type phenoxy resins, phenylbenzoate-type phenoxy resins, or biphenyl ester-type phenoxy resins. Here, biphenyl ester type phenoxy resin refers to, for example, the phenoxy resin described in Japanese Patent Publication No. 2021-098836.

[0026] From the viewpoint of further improving the balance of thermal conductivity and insulating properties, the content of thermosetting resin in the thermal conductive sheet of this embodiment is preferably 5% to 45% by mass, more preferably 10% to 40% by mass, even more preferably 15% to 35% by mass, and even more preferably 20% to 30% by mass, when the total solid content of the thermal conductive sheet is considered to be 100% by mass.

[0027] [Boron nitride particles] The thermally conductive sheet of this embodiment contains boron nitride particles. In the boron nitride particles used in the thermal conductive sheet of this embodiment, the above-mentioned particle size distribution profile can be achieved by classifying commercially available boron nitride particles (hereinafter also referred to as raw powder) by airflow classification and blending the classified particles having a specific particle size distribution in an appropriate proportion. The boron nitride particles of this embodiment preferably include flaky boron nitride particles, from the viewpoint of further improving the balance between thermal conductivity and insulating properties.

[0028] The above d min From the viewpoint of further improving the balance between thermal conductivity and insulating properties, the particle size is preferably 6.0 μm or more and less than 25.0 μm, more preferably 7.0 μm or more and less than 20.0 μm, even more preferably 8.0 μm or more and less than 18.0 μm, even more preferably 9.0 μm or more and less than 16.0 μm, and even more preferably 9.5 μm or more and less than 15.0 μm.

[0029] The above d min The cumulative frequency in this case is preferably 10% to 40%, more preferably 13% to 38%, even more preferably 16% to 36%, even more preferably 19% to 34%, even more preferably 22% to 33%, and even more preferably 25% to 32%, from the viewpoint of further improving the balance of thermal conductivity and insulating properties.

[0030] The above d maxFrom the viewpoint of further improving the balance between thermal conductivity and insulating properties, the particle size is preferably 15.0 μm to 75.0 μm, more preferably 15.0 μm to 60.0 μm, even more preferably 15.0 μm to 50.0 μm, even more preferably 18.0 μm to 50.0 μm, even more preferably 20.0 μm to 50.0 μm, even more preferably 25.0 μm to 40.0 μm, and even more preferably 25.0 μm to 35.0 μm.

[0031] The above d max The cumulative frequency in this case is preferably 30% to 70%, more preferably 32% to 67%, even more preferably 34% to 64%, even more preferably 36% to 61%, even more preferably 38% to 58%, and even more preferably 40% to 55%, from the viewpoint of further improving the balance of thermal conductivity and insulating performance.

[0032] The boron nitride particles of this embodiment are such that the balance between thermal conductivity and insulating properties can be further improved, as described above d max and the above d min The difference between the two is preferably 5.0 μm to 40.0 μm, more preferably 8.0 μm to 35.0 μm, even more preferably 10.0 μm to 30.0 μm, even more preferably 12.0 μm to 25.0 μm, and even more preferably 13.0 μm to 23.0 μm. Such boron nitride particles are obtained by classifying the raw powder using an air-flow classification method, and then mixing it with the classified boron nitride powder.

[0033] The particle size D of the boron nitride particles in this embodiment is the 10% integrated value of the volume-based particle size distribution measured by laser diffraction scattering. 10From the viewpoint of further improving the balance between thermal conductivity and insulating properties, the thickness is preferably 0.1 μm to 50.0 μm, more preferably 0.5 μm to 45.0 μm, even more preferably 1.0 μm to 40.0 μm, even more preferably 2.0 μm to 35.0 μm, even more preferably 3.0 μm to 30.0 μm, even more preferably 4.0 μm to 25.0 μm, even more preferably 5.0 μm to 20.0 μm, and even more preferably 6.0 μm to 10.0 μm.

[0034] The particle size D of the boron nitride particles in this embodiment is the 50% integrated value of the volume-based particle size distribution measured by laser diffraction scattering. 50 From the viewpoint of further improving the balance between thermal conductivity and insulating properties, the particle size is preferably 1.0 μm to 100.0 μm, more preferably 5.0 μm to 95.0 μm, even more preferably 10.0 μm to 90.0 μm, even more preferably 15.0 μm to 85.0 μm, and even more preferably 20.0 μm to 80.0 μm.

[0035] The particle size D of the boron nitride particles in this embodiment is the 90% integrated value of the volume-based particle size distribution measured by laser diffraction scattering. 90 From the viewpoint of further improving the balance between thermal conductivity and insulating properties, the thickness is preferably 10.0 μm to 200.0 μm, more preferably 20.0 μm to 190.0 μm, even more preferably 30.0 μm to 180.0 μm, even more preferably 40.0 μm to 170.0 μm, even more preferably 50.0 μm to 160.0 μm, even more preferably 60.0 μm to 155.0 μm, even more preferably 70.0 μm to 145.0 μm, even more preferably 75.0 μm to 140.0 μm, even more preferably 80.0 μm to 135.0 μm, and even more preferably 86.5 μm to 130.0 μm.

[0036] From the viewpoint of further improving the balance of thermal conductivity and insulating properties, the content of boron nitride particles in the thermally conductive sheet of this embodiment is preferably 100 parts by mass or more and 1000 parts by mass or less, more preferably 150 parts by mass or more and 800 parts by mass or less, even more preferably 200 parts by mass or more and 600 parts by mass or less, even more preferably 250 parts by mass or more and 500 parts by mass or less, and even more preferably 300 parts by mass or more and 400 parts by mass or less, when the content of the thermosetting resin is 100 parts by mass.

[0037] [Hardening agent] The thermally conductive sheet of this embodiment preferably includes a curing agent, from the viewpoint of further improving the balance between thermal conductivity and insulating properties. Examples of curing agents include amine-based curing agents such as aliphatic polyamines, aromatic polyamines, aromatic diamines, and disiamindiamides; acid anhydride-based curing agents such as alicyclic acid anhydrides and aromatic acid anhydrides; phenolic resin-based curing agents; and imidazole-based curing agents. Among these, the curing agent preferably includes one or more selected from the group consisting of phenolic resin-based curing agents and imidazole-based curing agents, from the viewpoint of further improving the balance of thermal conductivity and insulating properties.

[0038] Examples of phenolic resin curing agents include novolac-type phenolic resin curing agents such as phenol novolac resin, cresol novolac resin, trisphenolmethane-type novolac resin, naphthol novolac resin, and aminotriazine novolac resin; modified phenolic resin curing agents such as terpene-modified phenolic resin and dicyclopentadiene-modified phenolic resin; aralkyl-type phenolic resin curing agents such as phenol aralkyl resin having a phenylene skeleton and / or biphenylene skeleton, and naphthol aralkyl resin having a phenylene skeleton and / or biphenylene skeleton; bisphenol compound curing agents such as bisphenol A and bisphenol F; resol-type phenolic resin curing agents; and allylphenol resin curing agents. Among these, phenolic resin curing agents are preferably allylphenolic resin curing agents, from the viewpoint of further improving the balance between thermal conductivity and insulating properties.

[0039] From the viewpoint of further improving the balance of thermal conductivity and insulating properties, the imidazole-based curing agent preferably contains one or more selected from the group consisting of 2-methylimidazole, 2-phenyl-4-methylimidazole, 2-ethyl-4-methylimidazole, 2,4-diethylimidazole, 2-phenyl-4-methyl-5-hydroxyimidazole, and 2-phenyl-4,5-dihydroxymethylimidazole.

[0040] From the viewpoint of further improving the balance of thermal conductivity and insulating properties, the curing agent content in the thermal conductive sheet of this embodiment is preferably 0.1 parts by mass or more and 5.0 parts by mass or less, more preferably 0.3 parts by mass or more and 4.5 parts by mass or less, even more preferably 0.5 parts by mass or more and 4.0 parts by mass or less, even more preferably 0.7 parts by mass or more and 3.5 parts by mass or less, and even more preferably 1.0 part by mass or more and 3.0 parts by mass or less, when the thermosetting resin content is 100 parts by mass.

[0041] [Other ingredients] The thermally conductive sheet of this embodiment may contain other components besides the thermosetting resin, boron nitride particles, and curing agent of this embodiment. Examples of other components include solvents, fillers, coupling agents, antioxidants, leveling agents, antifoaming agents, and dispersants. Examples of fillers include silica, alumina, aluminum nitride, and silicon carbide. Examples of coupling agents include epoxysilane coupling agents, cationic silane coupling agents, aminosilane coupling agents, titanate-based coupling agents, and silicone oil-type coupling agents.

[0042] The content of other components in the thermal conductive sheet of this embodiment is not particularly limited as long as it achieves the effects of this embodiment, but when the content of the thermosetting resin is 100 parts by mass, for example, it may be 0.01 parts by mass or more and 50 parts by mass or less.

[0043] [Physical properties of thermally conductive sheets] The thermal conductivity of the thermally conductive sheet of this embodiment, according to the following method (Method 2), is preferably 17.5 W / (m·K) or more and 30.0 W / (m·K) or less, more preferably 18.0 W / (m·K) or more and 28.0 W / (m·K) or less, even more preferably 18.5 W / (m·K) or more and 25.0 W / (m·K) or less, and even more preferably 19.0 W / (m·K) or more and 23.0 W / (m·K) or less.

[0044] (Method 2) The aforementioned thermally conductive sheet is heated at a constant rate from 25°C to 180°C over 30 minutes while applying a pressure of 10 MPa, and then heated at 180°C for 60 minutes to obtain a sheet-cured product. A test piece with a thickness of 0.3 mm, a width of 10 mm, and a length of 10 mm is cut from the obtained sheet-cured product. The thermal conductivity of the obtained test piece is then calculated using the following formula based on the thermal diffusivity (α) measured by the xenon flash method (half-time method) at 25°C, the specific heat (Cp) measured by the DSC method, and the density (ρ) measured in accordance with JIS K 6911:2006. Thermal conductivity [W / (m·K)]=α[mm 2 / s] × Cp[J / (kg·K)] × ρ[g / cm 3 ]

[0045] The glass transition temperature of the thermally conductive sheet of this embodiment, according to the following method (3), is preferably 100°C to 300°C, more preferably 120°C to 280°C, even more preferably 140°C to 260°C, even more preferably 160°C to 240°C, and even more preferably 180°C to 220°C.

[0046] (Method 3) The aforementioned thermally conductive sheet is heated at a constant rate from 25°C to 180°C over 30 minutes while applying a pressure of 10 MPa, and then heated at 180°C for 60 minutes to obtain a sheet-cured material. A test piece with a thickness of 0.3 mm, a width of 8 mm, and a length of 50 mm is cut from the obtained sheet-cured material. The glass transition temperature of the obtained test piece is then measured using a dynamic viscoelasticity analyzer under the conditions of a heating rate of 5°C / min and a frequency of 1 Hz.

[0047] The storage modulus E' of the thermally conductive sheet of this embodiment at 25°C, determined by the following method (Method 4). 25 Preferably, the glucose level is 1 GPa or more and 50 GPa or less, more preferably 3 GPa or more and 45 GPa or less, even more preferably 5 GPa or more and 40 GPa or less, even more preferably 8 GPa or more and 35 GPa or less, even more preferably 10 GPa or more and 30 GPa or less, and even more preferably 15 GPa or more and 25 GPa or less.

[0048] (Method 4) The aforementioned thermally conductive sheet is heated at a constant rate from 25°C to 180°C over 30 minutes while applying a pressure of 10 MPa, and then heated at 180°C for 60 minutes to obtain a hardened sheet. A test specimen with a thickness of 0.3 mm, a width of 8 mm, and a length of 50 mm is cut from the obtained hardened sheet. The storage modulus E' at 25°C is then measured on the obtained test specimen using a dynamic viscoelasticity analyzer under tensile mode and a frequency of 1 Hz. 25 Measure.

[0049] The storage modulus E' of the thermally conductive sheet of this embodiment at 175°C, determined by the following method (Method 5). 175 Preferably, the pulse rate is 1 GPa or more and 30 GPa or less, more preferably 3 GPa or more and 25 GPa or less, even more preferably 5 GPa or more and 20 GPa or less, and even more preferably 8 GPa or more and 15 GPa or less.

[0050] (Method 5) The aforementioned thermally conductive sheet is heated at a constant rate from 25°C to 180°C over 30 minutes while applying a pressure of 10 MPa, and then heated at 180°C for 60 minutes to obtain a sheet-cured material. A test specimen with a thickness of 0.3 mm, a width of 8 mm, and a length of 50 mm is cut from the obtained sheet-cured material. The storage modulus E' of the obtained test specimen is then measured at 175°C using a dynamic viscoelasticity analyzer under tensile mode and a frequency of 10 Hz. 175 Measure.

[0051] In measuring the physical properties of the thermally conductive sheet in this embodiment, a dynamic viscoelasticity measuring instrument such as the Hitachi High-Technologies Corporation model number DMA-6100 can be used.

[0052] The average linear expansion coefficient α1 of the thermally conductive sheet of this embodiment at 50 to 100°C, as determined by the following method (Method 6), is preferably 1 ppm / °C or more and 100 ppm / °C or less, more preferably 3 ppm / °C or more and 75 ppm / °C or less, even more preferably 5 ppm / °C or more and 50 ppm / °C or less, even more preferably 8 ppm / °C or more and 25 ppm / °C or less, and even more preferably 10 ppm / °C or more and 20 ppm / °C or less.

[0053] (Method 6) The aforementioned thermally conductive sheet is heated at a constant rate from 25°C to 180°C over 30 minutes while being pressurized at 10 MPa, and then heated at 180°C for 60 minutes to obtain a hardened sheet. A test piece with a thickness of 0.3 mm, a width of 4 mm, and a length of 50 mm is cut from the obtained hardened sheet. The average linear expansion coefficient α1 (ppm / °C) of the obtained test piece is then measured using a thermomechanical analyzer under the conditions of a measurement temperature range of 0°C to 330°C and a heating rate of 5°C / min, at temperatures between 50°C and 100°C.

[0054] The average linear expansion coefficient α2 of the thermally conductive sheet of this embodiment at 270-290°C, as determined by the following method (Method 7), is preferably 20 ppm / °C or more and 150 ppm / °C or less, more preferably 25 ppm / °C or more and 125 ppm / °C or less, even more preferably 30 ppm / °C or more and 100 ppm / °C or less, even more preferably 35 ppm / °C or more and 80 ppm / °C or less, and even more preferably 40 ppm / °C or more and 60 ppm / °C or less.

[0055] (Method 7) The aforementioned thermally conductive sheet is heated at a constant rate from 25°C to 180°C over 30 minutes while being pressurized at 10 MPa, and then heated at 180°C for 60 minutes to obtain a sheet-cured material. A test piece with a thickness of 0.3 mm, a width of 4 mm, and a length of 50 mm is cut from the obtained sheet-cured material. The average linear expansion coefficient α2 (ppm / °C) of the obtained test piece is then measured using a thermomechanical analyzer under the conditions of a measurement temperature range of 0°C to 330°C and a heating rate of 5°C / min, at temperatures between 270°C and 290°C.

[0056] In measuring the physical properties of the thermally conductive sheet in this embodiment, thermomechanical analyzers such as Seiko Instruments Corporation's TMA / SS6000, TMA / SS6100, or Hitachi High-Tech Science Corporation's TMA7100 can be used.

[0057] The volume resistivity of the thermally conductive sheet of this embodiment at 25°C, as determined by the following method (8), is preferably 1.0 × 10⁻⁶. 14 Ω m or more 1.0×10 15 Ω·m or less, more preferably 1.5 × 10 14 Ω m or more 9.5×10 14 Ω·m or less, more preferably 2.0 × 10⁻⁶ 14 Ω m or more 9.0×10 14 Ω·m or less, more preferably 2.5 × 10 14 Ω m or more 8.5×10 14 Ω·m or less, more preferably 3.0 × 10 14 Ω m or more 8.0×10 14 Ω·m or less, more preferably 3.5 × 10 14Ω m or more 7.5×10 14 Ω·m or less, more preferably 4.0 × 10 14 Ω m or more 7.0×10 14 It is less than or equal to Ω·m.

[0058] (Method 8) The aforementioned thermally conductive sheet is heated at a constant rate from 25°C to 180°C over 30 minutes while applying a pressure of 10 MPa, and then heated at 180°C for 60 minutes to obtain a cured sheet. The volume resistivity (Ω·m) of the obtained cured sheet at 25°C is then measured in accordance with JIS C 2139:2008.

[0059] The thermally conductive sheet in this embodiment is preferably in the B-stage state. The thermally conductive sheet of this embodiment can be obtained, for example, by dissolving a varnish-like resin composition containing the above-mentioned thermosetting resin, boron nitride particles, curing agent, and other components in a solvent, applying the resulting varnish-like resin composition to a substrate to obtain a coating film, and then performing a solvent removal treatment on the coating film. The solvent content in the thermally conductive sheet is preferably 10% by mass or less relative to the entire thermally conductive sheet. For example, the solvent removal treatment can be performed under conditions of 80°C to 200°C and 1 minute to 30 minutes.

[0060] Examples of solvents include methyl ethyl ketone, methyl isobutyl ketone, propylene glycol monomethyl ether, and cyclohexanone. The solvent content in the varnish-like resin composition is, for example, 40 parts by mass or more and 85 parts by mass or less, when the total content of boron nitride particles and thermosetting resin in the varnish-like resin composition is taken as 100 parts by mass.

[0061] The planar shape of the thermal conductive sheet in this embodiment is not particularly limited and can be appropriately selected according to the shape of the heat sink or heat generating element, but it can be rectangular, for example. The thickness of the thermally conductive sheet in this embodiment is, for example, 50 μm to 500 μm, from the viewpoint of further improving the balance of mechanical strength, heat resistance, insulation, and heat dissipation.

[0062] <Electronic equipment> The electronic device of this embodiment preferably includes a cured product of the thermally conductive sheet of this embodiment. The thermally conductive sheet of this embodiment has an improved balance of thermal conductivity and insulating properties, and can therefore be used in various applications requiring heat dissipation and insulation, such as in electronic devices like semiconductor devices.

[0063] The electronic device of this embodiment preferably comprises, in this order, a metal substrate, an insulating layer containing a cured product of the thermally conductive sheet of this embodiment, a metal layer, and an electronic component.

[0064] The thickness of the insulating layer is preferably 10 μm to 400 μm, more preferably 30 μm to 350 μm, even more preferably 50 μm to 300 μm, and even more preferably 100 μm to 250 μm, from the viewpoint of improving mechanical strength, heat resistance, and insulating properties, as well as improving heat dissipation in the electronic device of this embodiment.

[0065] The metal layer is a layer provided on the insulating layer and used for circuit processing. Examples of metals that make up the metal layer include copper, copper alloys, aluminum, aluminum alloys, nickel, iron, and tin.

[0066] The thickness of the metal layer is preferably 0.01 mm to 10.0 mm, more preferably 0.025 mm to 5.0 mm, even more preferably 0.05 mm to 3.0 mm, even more preferably 0.10 mm to 2.5 mm, and even more preferably 0.25 mm to 2.0 mm, from the viewpoint of reducing heat generation in the circuit pattern even in applications requiring high current, as well as improving circuit processability and making the entire substrate thinner.

[0067] The metal layer may be processed with a circuit pattern by etching or other methods. Alternatively, a solder resist layer may be formed between the metal layer and the electronic component, and connection electrodes may be exposed so that the electronic component can be mounted by exposure and development.

[0068] The metal substrate serves to dissipate the heat accumulated in the electronic device of this embodiment. The metal substrate is not particularly limited as long as it is a heat-dissipating metal substrate.

[0069] The thickness of the metal substrate is preferably 0.01 mm to 20.0 mm, more preferably 0.1 mm to 15.0 mm, even more preferably 0.5 mm to 7.5 mm, and even more preferably 1.0 mm to 5.0 mm, from the viewpoint of improving processability in processes such as external shaping and cutting, making the entire substrate thinner, and improving heat dissipation.

[0070] As electronic components, for example, power semiconductor elements can be used. This makes it possible to make the electronic device of this embodiment a power module. In a power module, other electronic components besides power semiconductor elements may be mounted on the thermally conductive sheet. Power semiconductor devices, such as those using wide-bandgap materials like SiC, GaN, Ga2O3, or diamond, are designed for use with high voltage and high current. As a result, they generate more heat than ordinary silicon chips (semiconductor devices) and operate in even higher temperature environments. Power semiconductor devices are required to operate for extended periods in high-temperature environments, such as 200°C or 250°C or higher. Examples of power semiconductor devices include rectifier diodes, power transistors, power MOSFETs, insulated-gate bipolar transistors (IGBTs), thyristors, gate-turn-off thyristors (GTOs), and triacs.

[0071] The embodiments of the present invention have been described above, but these are merely examples, and various other configurations can also be adopted. Furthermore, the present invention is not limited to the embodiments described above, and any modifications, improvements, etc., that can achieve the objectives of the present invention are included in the present invention. [Examples]

[0072] The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto.

[0073] <Examples, Comparative Examples> [Preparation of thermally conductive sheets] The thermally conductive sheets for each example and each comparative example were obtained by the following method. First, according to the formulation shown in Table 2, each component except for the boron nitride particles was added to methyl ethyl ketone, and the mixture was stirred to obtain a solution of the thermosetting resin composition. Next, according to the formulation shown in Table 2, boron nitride particles were added to the solution of the thermosetting resin composition and stirred and mixed using a stirring blade to obtain a varnish-like thermosetting resin composition in which the boron nitride particles were uniformly dispersed. Next, a varnish-like thermosetting resin composition was applied onto a PET film, and the PET film and the applied thermosetting resin composition were heat-treated at 115°C for 12 minutes to produce a B-stage (semi-cured) thermal conductive sheet.

[0074] [Raw material ingredients] The details of each component in Table 2 are as follows. Furthermore, the content of each component shown in Table 2 represents the content (parts by mass) when the total content of thermosetting resin and curing agent is set to 100 parts by mass.

[0075] (Boron nitride particles) Boron nitride particles (also known as raw powder, manufactured by JFE Mineral Co., Ltd., product name: HP-40, D 10 :9.5μm, D 50 :22.6μm, D 90 The coarsest powder (D) is classified by the airflow classification method (85.3 μm). 10 :36.6μm, D 50 : 57.9 μm, D 90 :92.0μm), coarse powder (D10 :10.2μm, D 50 :20.5μm, D 90 :36.7μm), fine powder (D 10 : 7.4 μm, D 50 :11.8μm, D 90 :18.5μm) and finest powder (D 10 : 5.0 μm, D 50 : 7.5 μm, D 90 Each boron nitride powder (11.2 μm) was obtained. The obtained coarseest, coarse, fine, and finest boron nitride powders were mixed in the proportions (mass%) shown in Table 1 to obtain boron nitride particles 1 to 6.

[0076] (Particle size frequency cumulative histogram) A particle size frequency cumulative histogram was created for the obtained boron nitride particles 1-6. The particle size distribution of boron nitride particles 1-6 obtained under the following conditions was measured using the laser diffraction / scattering method with a laser diffraction / scattering particle size distribution analyzer (manufactured by Horiba, Ltd., product name: LA-950 series). The particle size at the point with the highest frequency in the range of particle size between 5.0 μm and less than 30.0 μm was defined as d min The particle size at the point with the lowest frequency in the range of 10.0 μm to 100.0 μm is d max Subsequently, a particle size frequency cumulative histogram was created with the cumulative frequency (%) on the vertical axis and particle size (μm) on the horizontal axis, with the horizontal axis being logarithmic. The slope of region A was then calculated using the following equation (1). The results are shown in Table 1. Furthermore, since boron nitride particles 2 are not a mixture of boron nitride particles with finer particle sizes and boron nitride particles with coarser particle sizes, region A does not exist, d min d max d max Cumulative frequency in d min Because it was not possible to measure the cumulative frequency in and calculate the slope of region A, these values ​​are indicated with "-" in Table 1. (d max (Cumulative frequency in)-(d min (Cumulative frequency in) / (d max -d min )...Equation (1) conditions: Dispersion solvent: pure water Sample: Dispersed in pure water. Examined for 30 seconds using the device's built-in ultrasound (irradiation intensity 5). Refractive index: Boron nitride 1.74 Particle size standard: volume Number of measurement points for particle size: 93 points (equally spaced logarithmically) ranging from 0.011 μm to 3000 μm.

[0077] Furthermore, based on the particle size distribution of the obtained boron nitride particles 1-6, the particle size D of 10% of the cumulative value of the volume-based particle size distribution measured by laser diffraction scattering was determined. 10 , particle size D of 50% of the integrated value of the volume-based particle size distribution measured by laser diffraction scattering method 50 and the particle size D of 90% of the integrated volume-based particle size distribution measured by laser diffraction scattering. 90 The data was read. The results are shown in Table 1.

[0078] [Table 1]

[0079] (thermosetting resin) • Thermosetting resin 1: Novolac-type cyanate ester resin (manufactured by Arcsarda, product name: PT-30S) • Thermosetting resin 2: Naphthalene-type epoxy resin (manufactured by DIC Corporation, product name: EPICLON® HP-4032D) • Thermosetting resin 3: Tetramethylbiphenyl epoxy resin (manufactured by Mitsubishi Chemical Corporation, product name: YX-4000) • Thermosetting resin 4:4-functional naphthalene-type epoxy resin (with mesogenic structure, manufactured by DIC Corporation, product name: HP-4710) • Thermosetting resin 5: Dicyclopentadiene type epoxy resin (manufactured by DIC Corporation, product name: EPICLON® HP-7200) • Thermosetting resin 6: Biphenyl ester type phenoxy resin produced by the following manufacturing example 1

[0080] (Manufacturing Example 1) 59 parts by mass of epoxy compound a represented by the following chemical formula, 35 parts by mass of phenol compound a represented by the following chemical formula, 0.05 parts by mass of triphenylphosphine (TPP), and 6 parts by mass of solvent (cyclohexanone) were added to a reactor and melted and mixed at 100°C to 110°C for 1 hour. The mixture was then heated to 150°C, and the reaction was carried out under reduced pressure at this temperature while removing the solvent. The reaction was stopped after confirming that the desired molecular weight was reached by GPC, and a biphenyl ester type phenoxy resin represented by the following chemical formula was obtained. The weight-average molecular weight Mw of the biphenyl ester type phenoxy resin, in terms of polystyrene, was 12089.

[0081] • Epoxy compound a: Tetramethylbiphenyl type epoxy resin represented by the following chemical formula (bifunctional epoxy compound, with mesogenic structure, manufactured by Mitsubishi Chemical Corporation, YX4000)

[0082] [ka]

[0083] (Phenol compounds) • Phenol compound a: Ester group-containing bisphenol (difunctional phenol compound, with mesogenic structure, manufactured by Ueno Pharmaceutical Co., Ltd., HQPOB) represented by the following chemical formula)

[0084] [ka]

[0085] The resulting biphenyl ester-type phenoxy resin is represented by the following chemical formula (the average value of the number of repeating units n in the chemical formula is 15).

[0086] [ka]

[0087] (Hardening agent) • Hardener 1: Allylphenol resin-based hardener (manufactured by Ube Industries, product name: MEH-8000H)

[0088] [evaluation] The thermal conductivity sheets obtained for each example and comparative example were evaluated as follows. The results are shown in Table 2.

[0089] (Density and thermal conductivity) For each example and comparative example obtained, the thermally conductive sheets were heated at a constant rate from 25°C to 180°C over 30 minutes while applying a pressure of 10 MPa, and then heated at 180°C for 60 minutes to obtain a cured sheet. From the obtained cured sheet, test pieces with a thickness of 0.3 mm, a width of 10 mm, and a length of 10 mm were cut out. The thermal conductivity of the obtained test pieces was then calculated using the following formula based on the thermal diffusivity (α) measured by the xenon flash method (half-time method) at 25°C, the specific heat (Cp) measured by the DSC method, and the density (ρ) measured in accordance with JIS K 6911:2006. Thermal conductivity [W / (m·K)]=α[mm 2 / s] × Cp[J / (kg·K)] × ρ[g / cm 3 ]

[0090] (Glass transition temperature) For each example and comparative example, the thermally conductive sheets were heated at a constant rate from 25°C to 180°C over 30 minutes while applying a pressure of 10 MPa, and then heated at 180°C for 60 minutes to obtain a cured sheet. From the obtained cured sheet, test pieces with a thickness of 0.3 mm, a width of 8 mm, and a length of 50 mm were cut out. The glass transition temperature of the obtained test pieces was then measured using a dynamic viscoelasticity analyzer (Seiko Instruments, product name: DMS6100) under conditions of a heating rate of 5°C / min and a frequency of 1 Hz.

[0091] (Storage modulus) For each example and comparative example, the thermally conductive sheets were heated at a constant rate from 25°C to 180°C over 30 minutes while applying a pressure of 10 MPa, and then heated at 180°C for 60 minutes to obtain a cured sheet. From the obtained cured sheet, test pieces with a thickness of 0.3 mm, a width of 8 mm, and a length of 50 mm were cut out. The storage modulus E' at 25°C was then measured on the obtained test pieces using a dynamic viscoelasticity analyzer under tensile mode and a frequency of 1 Hz. 25 and the storage modulus E' at 175°C 175 We measured it.

[0092] (Coefficient of linear expansion) For each example and comparative example, the thermally conductive sheets were heated at a constant rate from 25°C to 180°C over 30 minutes while applying a pressure of 10 MPa, and then heated at 180°C for 60 minutes to obtain a cured sheet. From the obtained cured sheet, test pieces with a thickness of 0.3 mm, a width of 4 mm, and a length of 50 mm were cut out. Using a thermomechanical analyzer (Seiko Instruments, product name: TMA / SS6100), the average linear expansion coefficient α1 (ppm / °C) at 50-100°C and the average linear expansion coefficient α2 (ppm / °C) at 270-290°C were measured for the above test pieces under the conditions of a measurement temperature range of 0°C to 330°C and a heating rate of 5°C / min.

[0093] (Volume resistivity) For each example and comparative example, the thermally conductive sheets were heated at a constant rate from 25°C to 180°C over 30 minutes while applying a pressure of 10 MPa, and then heated at 180°C for 60 minutes to obtain a cured sheet. The volume resistivity (Ω·m) at 25°C of the obtained cured sheets was then measured in accordance with JIS C 2139:2008.

[0094] (Dielectric strength) The dielectric strength of the thermal conductive sheets of each obtained example and comparative example was tested using the dielectric strength tester "TOS5101" (manufactured by Kikusui Electronics Co., Ltd.). Specifically, for each example and comparative example, the thermally conductive sheets were heated at a constant rate from 25°C to 180°C over 30 minutes while applying a pressure of 10 MPa, and then heated at 180°C for 60 minutes to obtain a cured sheet. A test piece with an outer diameter of 50 mmΦ was cut from the obtained cured sheet. Next, the test piece was placed in an oil bath containing silicone oil (compliant with JIS C 2320 insulating oil) and sandwiched between electrodes, and lead wires were connected to the electrodes. Then, the voltage was increased at a rate of 0.5 kV / sec and the dielectric breakdown voltage was measured. The dielectric withstand voltage, which is the value obtained by dividing the dielectric breakdown voltage by the thickness of the test piece, was evaluated according to the following criteria. A: Dielectric strength exceeds 60kV / mm B: Dielectric strength exceeding 40kV / mm and 60kV / mm or less C: Dielectric strength is 40kV / mm or less

[0095] [Table 2]

[0096] The thermal conductive sheets described in each embodiment, which contain a thermosetting resin and boron nitride particles and in which the boron nitride particles have a specific slope region A, showed an improved balance of thermal conductivity and insulating properties compared to the thermal conductive sheets described in each comparative example, in which the boron nitride particles do not have a specific slope region A.

[0097] This application claims priority based on Japanese Patent Application No. 2024-170310, filed on 30 September 2024, and Japanese Patent Application No. 2025-082529, filed on 16 May 2025, and incorporates all of their disclosures herein.

Claims

1. A thermally conductive sheet comprising a thermosetting resin and boron nitride particles, The slope of region A of the particle size frequency cumulative histogram of the boron nitride particles, calculated by the following method (Method 1), is 0 or greater and 1.45 or less. A thermally conductive sheet in which the content of the boron nitride particles is 150 parts by mass or more and 800 parts by mass or less, when the content of the thermosetting resin is 100 parts by mass. (Method 1) The particle size distribution of the boron nitride particles is measured using a laser diffraction / scattering particle size distribution analyzer under the following conditions: The particle size at the point with the highest frequency in the range of 5.0 μm to less than 30.0 μm is defined as d. ｍｉｎ The particle size at the point with the lowest frequency in the range of 10.0 μm to 100.0 μm is d. ｍａｘ Then, a particle size frequency cumulative histogram is created with the cumulative frequency (%) on the vertical axis and particle size (μm) on the horizontal axis, with the horizontal axis being logarithmic, and the slope of region A is calculated using the following equation (1). [(d ｍａｘ (Cumulative frequency in) - (d ｍｉｎ (Cumulative frequency in) / (d ｍａｘ -d ｍｉｎ )...Formula (1) conditions: Dispersion solvent: pure water Sample: Dispersed in pure water. Amplified for 30 seconds using the device's built-in ultrasound (irradiation intensity 5). Refractive index: Boron nitride 1.74 Particle size standard: volume Number of measurement points for particle size: 93 points ranging from 0.011 μm to 3000 μm (equally spaced logarithmically)

2. The aforementioned d ｍｉｎ The thermally conductive sheet according to claim 1, wherein the thickness is 7.0 μm or more and less than 20.0 μm.

3. The aforementioned d ｍａｘ The thermally conductive sheet according to claim 1 or 2, wherein the thickness is 15.0 μm or more and 50.0 μm or less.

4. the aforementioned d ｍａｘ and the aforementioned d ｍｉｎ The heat-conductive sheet according to claim 1 or 2, wherein the difference between them is 5.0 μm or more and 40.0 μm or less.

5. The particle size D of the boron nitride particles is the 10% integrated value of the volume-based particle size distribution measured by laser diffraction scattering. １０ The thermally conductive sheet according to claim 1 or 2, wherein the thickness is 0.1 μm or more and 50.0 μm or less.

6. The particle size D of the boron nitride particles is 50% of the integrated volume-based particle size distribution measured by laser diffraction scattering. ５０ The thermally conductive sheet according to claim 1 or 2, wherein the thickness is 1.0 μm or more and 100.0 μm or less.

7. The particle size D of the boron nitride particles is the 90% integrated value of the volume-based particle size distribution measured by laser diffraction scattering. ９０ The thermally conductive sheet according to claim 1 or 2, wherein the thickness is 10.0 μm or more and 200.0 μm or less.

8. The thermally conductive sheet according to claim 1 or 2, wherein the thermosetting resin comprises one or more selected from the group consisting of epoxy resin, cyanate ester resin, bismaleimide resin, and phenoxy resin.

9. The thermally conductive sheet according to claim 1 or 2, further comprising a curing agent.

10. The thermal conductive sheet according to claim 9, wherein the curing agent comprises one or more selected from the group consisting of phenolic resin curing agents and imidazole curing agents.

11. The thermal conductive sheet according to claim 9, wherein the content of the curing agent is 0.1 parts by mass or more and 5.0 parts by mass or less, when the content of the thermosetting resin is 100 parts by mass.

12. A thermally conductive sheet according to claim 1 or 2, wherein the thermal conductivity by the method described below (Method 2) is 17.5 W / (m·K) or more and 30.0 W / (m·K) or less. (Method 2) The thermally conductive sheet is heated at a constant rate from 25°C to 180°C over 30 minutes while applying a pressure of 10 MPa, and then heated at 180°C for 60 minutes to obtain a hardened sheet. A test piece with a thickness of 0.3 mm, a width of 10 mm, and a length of 10 mm is cut from the obtained hardened sheet. The thermal conductivity of the obtained test piece is then calculated using the following formula based on the thermal diffusivity (α) measured by the xenon flash method (half-time method) at 25°C, the specific heat (Cp) measured by the DSC method, and the density (ρ) measured in accordance with JIS K 6911:2006. Thermal conductivity [W / (m·K)] = α[mm] ２ / s] × Cp [J / (kg・K)] × ρ [g / cm ３ ]

13. A thermally conductive sheet according to claim 1 or 2, wherein the glass transition temperature by the following method (3) is 100°C or more and 300°C or less. (Method 3) The thermally conductive sheet is heated at a constant rate from 25°C to 180°C over 30 minutes while applying a pressure of 10 MPa, and then heated at 180°C for 60 minutes to obtain a sheet-cured product. A test piece with a thickness of 0.3 mm, a width of 8 mm, and a length of 50 mm is cut from the obtained sheet-cured product. The glass transition temperature of the obtained test piece is then measured using a dynamic viscoelasticity analyzer under the conditions of a heating rate of 5°C / min and a frequency of 1 Hz.

14. Storage modulus E' at 25°C according to the method (Method 4) described below. ２５ A thermally conductive sheet according to claim 1 or 2, wherein the thermal conductivity is 1 GPa or more and 50 GPa or less. (Method 4) The thermally conductive sheet is heated at a constant rate from 25°C to 180°C over 30 minutes while applying a pressure of 10 MPa, and then heated at 180°C for 60 minutes to obtain a sheet-cured material. A test piece with a thickness of 0.3 mm, a width of 8 mm, and a length of 50 mm is cut from the obtained sheet-cured material. The storage modulus E' at 25°C is then measured on the obtained test piece using a dynamic viscoelasticity analyzer under tensile mode and a frequency of 1 Hz. ２５ Measure.

15. Storage modulus E' at 175°C according to the method (Method 5) described below. １７５ A thermally conductive sheet according to claim 1 or 2, wherein the thermal conductivity is 1 GPa or more and 30 GPa or less. (Method 5) The thermally conductive sheet is heated at a constant rate from 25°C to 180°C over 30 minutes while applying a pressure of 10 MPa, and then heated at 180°C for 60 minutes to obtain a sheet-cured material. A test piece with a thickness of 0.3 mm, a width of 8 mm, and a length of 50 mm is cut from the obtained sheet-cured material. The storage modulus E' of the obtained test piece is then measured at 175°C using a dynamic viscoelasticity analyzer under the conditions of tensile mode and a frequency of 10 Hz. １７５ Measure.

16. The mean coefficient of linear expansion α at 50-100°C according to the method (Method 6) below. １ The thermally conductive sheet according to claim 1 or 2, wherein the concentration is 1 ppm / °C or more and 100 ppm / °C or less. (Method 6) The thermally conductive sheet is heated at a constant rate from 25°C to 180°C over 30 minutes while applying a pressure of 10 MPa, and then heated at 180°C for 60 minutes to obtain a sheet-cured product. A test piece with a thickness of 0.3 mm, a width of 4 mm, and a length of 50 mm is cut from the obtained sheet-cured product. The obtained test piece is then analyzed using a thermomechanical analyzer under the conditions of a measurement temperature range of 0°C to 330°C and a heating rate of 5°C / min to determine the average linear expansion coefficient α between 50°C and 100°C. １ Measure the concentration (ppm / °C).

17. The mean linear expansion coefficient α at 270-290°C according to the method described below (Method 7) ２ The thermally conductive sheet according to claim 1 or 2, wherein the concentration is 20 ppm / °C or more and 150 ppm / °C or less. (Method 7) The thermally conductive sheet is heated at a constant rate from 25°C to 180°C over 30 minutes while applying a pressure of 10 MPa, and then heated at 180°C for 60 minutes to obtain a sheet-cured product. A test piece with a thickness of 0.3 mm, a width of 4 mm, and a length of 50 mm is cut from the obtained sheet-cured product. The obtained test piece is then subjected to a thermomechanical analyzer to determine the average linear expansion coefficient α at 270 to 290°C under the conditions of a measurement temperature range of 0°C to 330°C and a heating rate of 5°C / min. ２ Measure the concentration (ppm / °C).

18. The volume resistivity at 25°C determined by the following method (Method 8) is 1.0 × 10⁻⁶. １４ Ω・m or more 1.0×10 １５ A thermally conductive sheet according to claim 1 or 2, wherein the thermal conductivity is Ω·m or less. (Method 8) The thermally conductive sheet is heated at a constant rate from 25°C to 180°C over 30 minutes while applying a pressure of 10 MPa, and then heated at 180°C for 60 minutes to obtain a cured sheet. The volume resistivity (Ω·m) of the obtained cured sheet at 25°C is then measured in accordance with JIS C 2139:2008.

19. An electronic device comprising a cured product of a thermally conductive sheet according to claim 1 or 2.

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