Heat-conductive sheet and electronic device

Abstract

This heat-conductive sheet comprises a thermosetting resin and boron nitride particles, wherein: the boron nitride particles have, in a particle size distribution profile, a first peak that has a first local maximum point in a particle diameter range from 5 μm (inclusive) to 30 μm (exclusive) and a second peak that has a second local maximum point in a particle diameter range from 30 μm (inclusive) to 150 μm (inclusive); the frequency of the first peak at the first local maximum point is 4.0%-20.0% inclusive; and the frequency of the second peak at the second local maximum point is 4.5%-20.0% inclusive.

Description

Thermal Conductive Sheet and Electronic Device

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

[0002] Insulating materials constituting electric and electronic devices etc. are required to have thermal conductivity. As technologies related to insulating materials having thermal conductivity, for example, the technologies described in Patent Documents 1 to 3 can be cited.

[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 also 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 rate 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 rate 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 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. In the particle size distribution based on the number of the boron nitride particles, the particle size D1 when the frequency is maximum is in the range of 60 μm to 90 μm. The value obtained by dividing the number of boron nitride particles A having a particle size in the range of 2 μm to 60 μm among the boron nitride particles by the number of boron nitride particles B having a particle size in the range of 90 μm to 150 μm among the boron nitride particles is 2.5 to 5.0. A heat dissipation sheet is described.

[0006] Japanese Patent Publication No. 2011-090868, International Publication No. 2021 / 059647, International Publication No. 2021 / 059648

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

[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 having a specific particle size distribution profile, can improve the balance between thermal conductivity and insulation performance, thus completing 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 comprising a thermosetting resin and boron nitride particles, wherein the boron nitride particles have, in the particle size distribution profile according to (Method 1) below, a first peak having a first maximum point in the range of particle diameters of 5 μm or more and less than 30 μm, and a second peak having a second maximum point in the range of particle diameters of 30 μm or more and 150 μm or less, the frequency of the first peak at the first maximum point being 4.0% or more and 20.0% or less, and the frequency of the second peak at the second maximum point being 4.5% or more and 20.0% or less. (Method 1) The particle size distribution of the boron nitride particles is measured under the following conditions by a laser diffraction / scattering measurement method using a laser diffraction / scattering particle size distribution analyzer. A semi-logarithmic graph is created with frequency (%) on the vertical axis and particle size (μm) on the horizontal axis, where the horizontal axis is logarithmic. The point with the highest frequency in the particle size range of 5 μm or more and less than 30 μm is defined as the first maximum point, and the point with the highest frequency in the particle size range of 30 μm or more and 150 μm or less is defined as the second maximum point. Dispersion solvent: pure water Sample: dispersed in pure water. Ultrasound built into the device for 30 seconds (irradiation intensity 5). Refractive index: boron nitride 1.74 Particle size standard: volume measurement Number of particle size points: 93 points from 0.011 μm to 3000 μm (equally spaced logarithmically) [2] The thermal conductive sheet described in [1] above, wherein the full width at half maximum ΔA of the first peak measured by (Method 2) is 5.0 μm or more and 20.0 μm or less. (Method 2) In the first peak measured by (Method 1), two points with a frequency of half the frequency (%) at the first maximum point are designated as A in descending order of particle size. １ and A ２ A １ The particle size value and A ２ The difference between the particle size value and the value in is defined as the half-width ΔA (μm). [3] The thermal conductive sheet according to [1] or [2] above, wherein the half-width ΔB of the second peak according to the following (Method 3) is 30.0 μm or more and 200.0 μm or less. (Method 3) In the second peak measured in (Method 1), two points with a frequency of half the frequency (%) of the second maximum point are listed in order of decreasing particle size as B １ and B ２ Let's assume that. B １ The particle size value and B ２The difference from the particle size value in [ ] is defined as the half-width ΔB (μm). [4] The heat-conductive sheet according to any one of [1] to [3] above, wherein the boron nitride particles have a minimum point in the range of a particle size of 10 μm or more and 100 μm or less in the particle size distribution profile by the following (Method 4). (Method 4) Measure the particle size distribution of the boron nitride particles under the following conditions by the laser diffraction / scattering type particle size distribution measurement method using a laser diffraction / scattering type particle size distribution measuring device. Create a semi-logarithmic graph with the frequency (%) on the vertical axis and the particle size (μm) on the horizontal axis, where the horizontal axis is logarithmic, and the point with the smallest frequency at a particle size of 10 μm or more and 100 μm or less is defined as the minimum point. Dispersion solvent: pure water Sample: Dispersed in pure water. 30 seconds with built-in ultrasonic waves in the device (irradiation intensity 5). Refractive index: 1.74 for boron nitride Particle size standard: volume measurement Particle size points: 93 points (equally spaced logarithmically) from 0.011 μm to 3000 μm [5] The heat-conductive sheet according to [4] above, wherein the difference between the frequency at the first maximum point and the frequency at the minimum point is 2.0% or more and 10.0% or less. [6] The heat-conductive sheet according to any one of [1] to [5] above, wherein the particle size distribution profile by the (Method 1) consists of only the two of the first peak and the second peak. [7] The heat-conductive sheet according to any one of [1] to [6] above, wherein in the particle size distribution profile by the (Method 1), the integrated value of the frequency in the range of a particle size of 0 μm or more and 3 μm or less is 1% or less. [8] The heat-conductive sheet according to any one of [1] to [7] above, wherein in the particle size distribution profile by the (Method 1), the integrated value of the frequency in the range of a particle size of 300 μm or more and 1000 μm or less is 1% or less. [9] The particle size D of 10% of the integrated value of the volume-based particle size distribution of the boron nitride particles by the laser diffraction / scattering type measurement method １０ is 0.1 μm or more and 50.0 μm or less, and the heat-conductive sheet according to any one of [1] to [8] above.

[10] The particle size D of 50% of the integrated value of the volume-based particle size distribution of the boron nitride particles by the laser diffraction / scattering type measurement method ５０ is 1.0 μm or more and 100.0 μm or less, and the heat-conductive sheet according to any one of [1] to [9] above.

[11] The particle size D of 90% of the integrated value of the volume-based particle size distribution of the boron nitride particles by the laser diffraction / scattering type measurement method ９０A thermal conductive sheet according to any one of [1] to

[10] above, wherein the particle size is 10.0 μm or more and 200.0 μm or less.

[12] A thermal conductive sheet according to any one of [1] to

[11] 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.

[13] A thermal conductive sheet according to any one of [1] to

[12] 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.

[14] A thermal conductive sheet according to any one of [1] to

[13] above, further comprising a curing agent.

[15] A thermal conductive sheet according to

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

[16] The thermal conductive sheet according to

[14] or

[15] 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.

[17] The thermal conductive sheet according to any one of [1] to

[16] above, wherein the thermal conductivity according to the following (Method 5) is 17.5 W / (m·K) or more and 30.0 W / (m·K) or less. (Method 5) The thermal conductive sheet is heated at a constant rate from 25°C to 180°C over 30 minutes while applying 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 out from the obtained sheet cured product. The thermal conductivity of the obtained test specimens 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

[18] A thermally conductive sheet according to any of [1] to

[17] above, wherein the glass transition temperature according to the following (Method 6) is 100°C or more and 300°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 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 measured using a dynamic viscoelasticity analyzer under the conditions of a heating rate of 5°C / min and a frequency of 1 Hz.

[19] Storage modulus E' at 25°C according to the following (Method 7) ２５ A thermally conductive sheet according to any of [1] to

[18] above, wherein the pressure is 1 GPa or more and 50 GPa 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 8 mm, and a length of 50 mm is cut out from the obtained sheet cured product. The storage modulus E' at 25°C is then measured on the obtained test piece using a dynamic viscoelasticity analyzer under the conditions of tensile mode and a frequency of 1 Hz. ２５ Measure the following:

[20] Storage modulus E' at 175°C according to Method 8 below. １７５ A thermally conductive sheet according to any of [1] to

[19] above, wherein the pressure is 1 GPa or more and 30 GPa 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 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 out from the obtained sheet cured product. 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

[21] The mean coefficient of linear expansion α at 50 to 100°C according to the method (Method 9) below. １A thermally conductive sheet according to any one of [1] to

[20] above, wherein the coefficient of thermal expansion α is 1 ppm / °C or more and 100 ppm / °C or less. (Method 9) The thermally conductive sheet is heated at a constant rate from 25°C to 180°C over 30 minutes while applying 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 under the conditions of a measurement temperature range of 0°C to 330°C and a heating rate of 5°C / min, and the average linear expansion coefficient α at 50 to 100°C is determined. １ Measure (ppm / °C).

[22] The average coefficient of linear expansion α at 270-290°C according to the method (Method 10) below. ２ A thermally conductive sheet according to any one of [1] to

[21] above, wherein the coefficient of thermal expansion α is 20 ppm / °C or more and 150 ppm / °C or less. (Method 10) The thermally conductive sheet is heated at a constant rate from 25°C to 180°C over 30 minutes while applying 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, and the average linear expansion coefficient α at 270 to 290°C is determined under the conditions of a measurement temperature range of 0°C to 330°C and a heating rate of 5°C / min. ２ (ppm / °C) is measured.

[23] The volume resistivity at 25°C according to the following (Method 11) is 1.0 × 10 １４ Ω・m or more 1.0×10 １５ A thermally conductive sheet according to any of [1] to

[22] above, having a resistivity of Ω·m or less. (Method 11) The thermally conductive sheet is heated at a constant rate from 25°C to 180°C over 30 minutes while applying 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 sheet is then measured in accordance with JIS C 2139:2008.

[24] An electronic device comprising a cured thermally conductive sheet according to any of [1] to

[23] above.

[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.

[0012] Embodiments of the present invention will be described below. In this specification, numerical ranges indicated using "~" represent ranges that include the numerical values ​​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 thermal conductive sheet of this embodiment is a thermal conductive sheet comprising a thermosetting resin and boron nitride particles, wherein the boron nitride particles have, in the particle size distribution profile according to the following (Method 1), a first peak having a first maximum point in the range of particle diameters of 5 μm or more and less than 30 μm, and a second peak having a second maximum point in the range of particle diameters of 30 μm or more and 150 μm or less, the frequency of the first peak at the first maximum point being 4.0% or more and 20.0% or less, and the frequency of the second peak at the second maximum point being 4.5% or more and 20.0% 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: A semi-logarithmic graph is created with frequency (%) on the vertical axis and particle size (μm) on the horizontal axis, with the horizontal axis being logarithmic. The point with the highest frequency in the particle size range of 5 μm to less than 30 μm is defined as the first maximum point, and the point with the highest frequency in the particle size range of 30 μm to 150 μm is defined as the second maximum point. Dispersion solvent: pure water. Sample: dispersed in pure water. Ultrasound treatment using the instrument's built-in device for 30 seconds (irradiation intensity 5). Refractive index: 1.74 for boron nitride. Particle size reference: volume measurement. Number of particle size points: 93 points from 0.011 μm to 3000 μm (equally spaced logarithmically).

[0015] If the particle size distribution of boron nitride particles is unimodal, it is thought that fluidity and moldability will improve, resulting in good dielectric breakdown voltage. On the other hand, if the particle size distribution of boron nitride particles is bimodal with two or more peaks, it is thought that the contactability of coarse particles in the boron nitride particles will improve, and fine particles will fill the gaps between the coarse particles, efficiently forming heat conduction paths, thus resulting in good thermal conductivity. In the thermal conductive sheet of this embodiment, the balance between dielectric breakdown voltage and thermal conductivity can be improved by controlling the particle size distribution of boron nitride particles in the thermal conductive sheet and designing the particle size distribution profile so that it has a first peak with a first maximum point in the particle diameter range of 5 μm to less than 30 μm, and a second peak with a second maximum point in the particle diameter range of 30 μm to 150 μm, each at a specific frequency.

[0016] In this embodiment, the boron nitride particles can be obtained by classifying commercially available boron nitride particles (hereinafter also referred to as "original powder") using an airflow classification method, and then blending the classified boron nitride powder having a specific particle size distribution in an appropriate proportion to achieve the above-mentioned particle size distribution profile. Although the mechanism is not entirely clear, 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 by the airflow, thus enabling accurate classification of boron nitride particles. Furthermore, since the particle size distribution of the accurately classified boron nitride powder becomes sharper, it becomes easier to achieve the intended particle size distribution by mixing the classified boron nitride powders together. As a result, the present invention can achieve the above-mentioned particle size distribution profile.

[0017] From the viewpoint of further improving the balance between thermal conductivity and insulating properties, the first peak has its first maximum point in the particle diameter range of 5 μm or more and less than 30 μm, preferably in the particle diameter range of 6 μm or more and less than 25 μm, more preferably in the particle diameter range of 7 μm or more and less than 20 μm, even more preferably in the particle diameter range of 8 μm or more and less than 18 μm, even more preferably in the particle diameter range of 9 μm or more and less than 16 μm, and even more preferably in the particle diameter range of 10 μm or more and less than 15 μm.

[0018] From the viewpoint of further improving the balance between thermal conductivity and insulating properties, the second peak has a second maximum point in the particle diameter range of 30 μm to 150 μm, preferably in the particle diameter range of 35 μm to 140 μm, more preferably in the particle diameter range of 40 μm to 130 μm, and even more preferably in the particle diameter range of 45 μm to 120 μm.

[0019] The frequency at the first maximum point of the first peak is 4.0% to 20.0%, preferably 4.5% to 15.0%, and more preferably 5.0% to 10.0%, from the viewpoint of further improving the balance between thermal conductivity and insulating properties.

[0020] The frequency at the second maximum point of the second peak is 4.5% to 20.0%, preferably 4.7% to 18.0%, and more preferably 5.0% to 15.0%, from the viewpoint of further improving the balance between thermal conductivity and insulating properties.

[0021] The following describes each component used in the thermally conductive sheet of this embodiment.

[0022] [Thermosetting Resin] The thermally conductive sheet of this embodiment includes a thermosetting resin. From the viewpoint of further improving the balance of thermal conductivity and insulating properties, the thermosetting resin preferably includes 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 includes one or more selected from the group consisting of epoxy resin, cyanate ester resin, bismaleimide resin, and phenoxy resin.

[0023] 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 to 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] From the viewpoint of further improving the balance of 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 reaction of a polyfunctional epoxy resin and polyfunctional phenols (phenoxy resin in the broad sense) are also included as phenoxy resins.

[0028] Examples of phenoxy resins include bisphenol-type phenoxy resins, naphthalene-type phenoxy resins, anthracene-type phenoxy resins, biphenyl-type phenoxy resins, biphenyl ester-type phenoxy resins, and phenylbenzoate-type phenoxy resins. Among these, from the viewpoint of further improving the balance of thermal conductivity and insulating properties, 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, for example, to the phenoxy resin described in Japanese Patent Application Publication No. 2021-098836.

[0029] From the viewpoint of further improving the balance between 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.

[0030] [Boron Nitride Particles] The thermal conductive sheet of this embodiment contains boron nitride particles. In the boron nitride particles used in the thermal conductive sheet of this embodiment, commercially available boron nitride particles (hereinafter also referred to as raw powder) are classified by an airflow classification method, and the above-mentioned particle size distribution profile can be achieved by blending the classified particles having a specific particle size distribution in an appropriate proportion. From the viewpoint of further improving the balance between thermal conductivity and insulating properties, the boron nitride particles of this embodiment preferably include flaky boron nitride particles.

[0031] In this embodiment, the full width at half maximum ΔA of the first peak obtained by the following (Method 2) of the boron nitride particles is preferably 5.0 μm to 20.0 μm, more preferably 6.0 μm to 19.0 μm, even more preferably 7.0 μm to 18.0 μm, even more preferably 8.0 μm to 17.0 μm, even more preferably 9.0 μm to 16.0 μm, and even more preferably 9.5 μm to 15.0 μm.

[0032] (Method 2) In the first peak measured in (Method 1), two points with a frequency equal to half the frequency (%) of the first maximum point are selected and listed in descending order of particle size as A. １ and A ２ A １ The particle size value and A ２ The difference between the particle size value and the value at half maximum is defined as the half-width ΔA (μm).

[0033] The boron nitride particles of this embodiment are obtained by classifying the raw powder using an airflow classification method and then mixing it with the classified boron nitride powder. Since the classified boron nitride powder obtained by the airflow classification method has little dispersion in particle size, it is expected that the half-width ΔA, which indicates the degree of dispersion in particle size, will be within a specific numerical range in the boron nitride particles of this embodiment obtained by mixing these powders.

[0034] In this embodiment, the half-width ΔB of the second peak of the boron nitride particles according to the following (Method 3) is preferably 30.0 μm to 200.0 μm, more preferably 35.0 μm to 175.0 μm, even more preferably 40.0 μm to 150.0 μm, even more preferably 45.0 μm to 125.0 μm, and even more preferably 50.0 μm to 100.0 μm, from the viewpoint of further improving the balance of thermal conductivity and insulating properties.

[0035] (Method 3) In the second peak measured in (Method 1), two points with a frequency equal to half the frequency (%) of the second maximum point are selected in descending order of particle size, and are designated as B １ and B ２ Let's assume that. B １ The particle size value and B ２ The difference between the particle size value and the value at half maximum is defined as the half-width ΔB (μm).

[0036] The boron nitride particles of this embodiment are obtained by classifying the raw powder using an airflow classification method and then mixing it with the classified boron nitride powder. Since the classified boron nitride powder obtained by the airflow classification method has little dispersion in particle size, it is expected that the half-width ΔB, which indicates the degree of dispersion in particle size, will be within a specific numerical range in the boron nitride particles of this embodiment obtained by mixing these powders.

[0037] From the viewpoint of further improving the balance between thermal conductivity and insulating properties, the boron nitride particles of this embodiment preferably have a minimum particle in the particle size distribution profile according to the following (Method 4), more preferably in the particle size range of 10 μm to 100 μm, more preferably in the particle size range of 15 μm to 75 μm, even more preferably in the particle size range of 20 μm to 50 μm, and even more preferably in the particle size range of 25 μm to 35 μm.

[0038] (Method 4) The particle size distribution of the boron nitride particles is measured using a laser diffraction / scattering particle size distribution analyzer under the following conditions: A semi-logarithmic graph is created with frequency (%) on the vertical axis and particle size (μm) on the horizontal axis, with the horizontal axis being logarithmic. The point where the frequency is lowest for particle sizes between 10 μm and 100 μm is defined as the minimum point. Dispersion solvent: pure water. Sample: dispersed in pure water. Ultrasound treatment using the instrument's built-in device for 30 seconds (irradiation intensity 5). Refractive index: 1.74 for boron nitride. Particle size reference: volume measurement. Number of particle size points: 93 points from 0.011 μm to 3000 μm (equally spaced logarithmically).

[0039] The boron nitride particles of this embodiment are obtained by classifying the raw powder using an airflow classification method, and then mixing the classified boron nitride powder. Since the classified boron nitride powder obtained by the airflow classification method has little dispersion in particle size, it is thought that a minimum point can be observed between the first and second peaks in the boron nitride particles of this embodiment obtained by mixing these particles.

[0040] From the viewpoint of further improving the balance between thermal conductivity and insulating properties, the frequency of boron nitride particles at the minimum points in this embodiment is preferably 0.5% to 10.0%, more preferably 0.6% to 9.0%, even more preferably 0.7% to 8.0%, even more preferably 0.8% to 7.0%, even more preferably 0.9% to 6.0%, even more preferably 1.0% to 5.0%, even more preferably 1.1% to 4.0%, and even more preferably 1.2% to 3.0%.

[0041] In this embodiment, the difference between the frequency of boron nitride particles at the first maximum point and the frequency at the minimum point is preferably 2.0% to 10.0%, more preferably 2.5% to 8.0%, even more preferably 3.0% to 7.5%, even more preferably 3.5% to 7.0%, even more preferably 3.5% to 6.5%, and even more preferably 4.0% to 6.0%, from the viewpoint of further improving the balance of thermal conductivity and insulating properties.

[0042] The particle size distribution profile of the boron nitride particles of this embodiment obtained by (Method 1) preferably consists of only two peaks, a first peak and a second peak, from the viewpoint of further improving the balance of thermal conductivity and insulating properties. Such boron nitride particles are obtained by mixing two to four types, more preferably two to three types, of classified boron nitride powders with different particle sizes, which have been classified by the airflow classification method. In the case of a mixture of three types of classified boron nitride powders with different particle sizes, the particle size D of two of the three boron nitride powders is calculated as 50% of the cumulative volume-based particle size distribution measured by laser diffraction scattering. ５０ By setting the difference between these two peaks to 1 μm or more and 10 μm or less, the particle size distribution profile of boron nitride particles obtained by (Method 1) can be made to consist of only two peaks: a first peak and a second peak.

[0043] In the particle size distribution profile of the boron nitride particles according to (Method 1) of this embodiment, the cumulative value of the frequency of particles with a diameter in the range of 0 μm to 3 μm is preferably 1% or less, more preferably 0.5% or less, and even more preferably 0.1% or less, from the viewpoint of further improving the balance of thermal conductivity and insulating properties. Such boron nitride particles are obtained by classifying the raw powder by an airflow classification method and then mixing the classified boron nitride powder.

[0044] In the particle size distribution profile of the boron nitride particles according to (Method 1) of this embodiment, the cumulative value of the frequency of particles with a diameter in the range of 300 μm to 1000 μm is preferably 1% or less, more preferably 0.5% or less, and even more preferably 0.1% or less, from the viewpoint of further improving the balance of thermal conductivity and insulating properties. Such boron nitride particles are obtained by classifying the raw powder by an airflow classification method and then mixing the classified boron nitride powder.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] [Curing Agent] The thermal 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 dicyamine diamides; acid anhydride-based curing agents such as alicyclic acid anhydrides and aromatic acid anhydrides; phenol 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 phenol resin-based curing agents and imidazole-based curing agents from the viewpoint of further improving the balance between thermal conductivity and insulating properties.

[0050] Examples of phenolic resin curing agents include novolac-type phenolic resin curing agents such as phenol novolac resins, cresol novolac resins, trisphenolmethane-type novolac resins, naphthol novolac resins, and aminotriazine novolac resins; modified phenolic resin curing agents such as terpene-modified phenolic resins and dicyclopentadiene-modified phenolic resins; aralkyl-type phenolic resin curing agents such as phenol aralkyl resins having a phenylene skeleton and / or biphenylene skeleton, and naphthol aralkyl resins 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 preferably include allylphenol resin curing agents from the viewpoint of further improving the balance of thermal conductivity and insulating properties.

[0051] From the viewpoint of further improving the balance between thermal conductivity and insulating properties, the imidazole-based curing agent preferably comprises 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.

[0052] 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.

[0053] [Other Components] 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.

[0054] 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.

[0055] [Physical Properties of Thermally Conductive Sheets] The thermal conductivity of the thermally conductive sheet of this embodiment, according to the following (Method 5), 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.

[0056] (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 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 ]

[0057] The glass transition temperature of the thermally conductive sheet of this embodiment, according to the following method (Method 6), 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.

[0058] (Method 6) The thermally conductive sheet is heated at a constant rate from 25°C to 180°C over 30 minutes while applying 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.

[0059] The storage modulus E' of the thermally conductive sheet of this embodiment at 25°C, as determined by the following method (Method 7). ２５Preferably, the pressure 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.

[0060] (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 8 mm, and a length of 50 mm is cut from the obtained sheet cured product. The storage modulus E' at 25°C is then measured on the obtained test piece using a dynamic viscoelasticity analyzer under the conditions of tensile mode and a frequency of 1 Hz. ２５ Measure.

[0061] The storage modulus E' of the thermally conductive sheet of this embodiment at 175°C, determined by the following method (8). １７５ Preferably, the pressure 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.

[0062] (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 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 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.

[0063] 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.

[0064] The average linear expansion coefficient α of the thermal conductive sheet of this embodiment at 50 to 100°C, as determined by the following method (Method 9). １Preferably, the concentration is 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.

[0065] (Method 9) 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 under the conditions of a measurement temperature range of 0°C to 330°C and a heating rate of 5°C / min, and the average linear expansion coefficient α between 50°C and 100°C is determined. １ Measure the concentration (ppm / °C).

[0066] The average linear expansion coefficient α of the thermal conductive sheet of this embodiment at 270 to 290°C according to the following (Method 10) ２ Preferably, the concentration is 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.

[0067] (Method 10) 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).

[0068] 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.

[0069] The volume resistivity of the thermal conductive sheet of this embodiment at 25°C according to the following method (Method 11) 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 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 １４ Ω・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.

[0070] (Method 11) The thermal 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 measured in accordance with JIS C 2139:2008.

[0071] The thermal conductive sheet of this embodiment is preferably in the B-stage state. The thermal conductive sheet of this embodiment can be obtained, for example, by dissolving a resin composition containing the above-mentioned thermosetting resin, boron nitride particles, curing agent, and other components in a solvent, applying a 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 thermal conductive sheet is preferably 10% by mass or less relative to the entire thermal 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.

[0072] 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 100 parts by mass.

[0073] 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 thermal 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.

[0074] <Electronic Device> The electronic device of this embodiment preferably includes a cured product of the thermal conductive sheet of this embodiment. Since the thermal conductive sheet of this embodiment has an improved balance of thermal conductivity and insulating properties, it can be used in various applications where heat dissipation and insulating properties are required, and can be used in electronic devices such as semiconductor devices.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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 the power module, other electronic components besides power semiconductor elements may be mounted on the thermally conductive sheet. Power semiconductor elements include, for example, SiC, GaN, Ga ２ O ３ These are either made of a wide bandgap material such as diamond, and are designed for use with high voltage and high current, so they generate more heat than ordinary silicon chips (semiconductor devices) and operate in even higher temperature environments. Power semiconductor devices are required to be used for long periods of time in high-temperature operating 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.

[0083] Although embodiments of the present invention have been described above, these are merely examples, and various other configurations can 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.

[0084] The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto.

[0085] <Examples and Comparative Examples> [Preparation of Thermally Conductive Sheets] The thermally conductive sheets of each example and comparative example were obtained by the following method. First, according to the formulation shown in Table 2, each component except boron nitride particles was added to methyl ethyl ketone and 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, the 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) thermally conductive sheet.

[0086] [Raw Material Components] Details of each component in Table 2 are as follows. The content of each component shown in Table 2 is the content (parts by mass) when the total content of thermosetting resin and curing agent is set to 100 parts by mass.

[0087] (Boron nitride particles) Boron nitride particles (also referred to as raw powder, manufactured by JFE Mineral Co., Ltd., product name: HP-40, D １０ : 9.5 μm, D ５０ : 22.6 μm, D ９０ The coarsest powder (D) is classified by airflow classification (85.3 μm). １０ : 36.6 μm, D ５０ : 57.9 μm, D ９０ :92.0μm), coarse powder (D １０ : 10.2 μm, D ５０ : 20.5 μm, D ９０ :36.7μm), fine powder (D １０ : 7.4 μm, D ５０ : 11.8 μm, D ９０ : 18.5 μm) and finest powder (D １０ : 5.0 μm, D ５０ : 7.5 μm, D ９０ Boron nitride powders with a size of 11.2 μm were 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.

[0088] (Particle Size Distribution Profile) The particle size distribution profiles were measured for the obtained boron nitride particles 1 to 6. The particle size distribution of boron nitride particles 1 to 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). A semi-logarithmic graph was created with frequency (%) on the vertical axis and particle size (μm) on the horizontal axis, with the horizontal axis being logarithmic. The point with the highest frequency in the range of particle size between 5 μm and 30 μm was defined as the first maximum point, the point with the highest frequency in the range of particle size between 30 μm and 150 μm was defined as the second maximum point, and the point with the lowest frequency in the range of particle size between 10 μm and 100 μm was defined as the minimum point. The particle size (μm) and frequency (%) at the first maximum point, second maximum point, and minimum point were measured. The results are shown in Table 1. Dispersion solvent: pure water. Sample: dispersed in pure water. The device uses built-in ultrasound for 30 seconds (irradiation intensity 5). Refractive index: Boron nitride 1.74. Particle size standard: Volume measurement. Number of particle size points: 93 points from 0.011 μm to 3000 μm (equally spaced logarithmically).

[0089] Furthermore, in the first peak, two points with half the frequency (%) of the first maximum point are listed in descending order of particle size as A. １ and A ２ A １ The particle size value and A ２ The difference between the particle size value at point A and point B was calculated as the half-width ΔA (μm). Similarly, at the second peak, two points with half the frequency (%) of the second maximum point were selected in descending order of particle size, B. １ and B ２ B １ The particle size value and B ２ The difference between the particle size value and the actual value was calculated as the half-width ΔB (μm). The results are shown in Table 1.

[0090] Furthermore, from the obtained particle size distribution of boron nitride particles 1 to 6, the difference between the frequency at the first maximum point and the frequency at the minimum point of boron nitride particles 1 to 6, the cumulative value of the frequency in the particle size range of 0 μm to 3 μm, the cumulative value of the frequency in the particle size range of 300 μm to 1000 μm, and the particle size D of 10% of the cumulative value of the volume-based particle size distribution measured by laser diffraction scattering method are obtained. 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 cumulative value of the volume-based particle size distribution measured by laser diffraction scattering method. ９０ The data was read. The results are shown in Table 1.

[0091] Boron nitride particles 1 and 2 used the original powder or the coarsest powder after classification, so only the second peak was observed, and neither the first peak nor the minimum point could be identified. On the other hand, boron nitride particles 3 to 6 were composed of two or more types of classified boron nitride powder with different particle sizes, so they consisted only of the first and second peaks, and the presence of a minimum point could be confirmed.

[0092]

[0093] (Thermosetting resins) ・Thermosetting resin 1: Novolac-type cyanate ester resin (manufactured by Arcsarda, product name: PT-30) ・Thermosetting resin 2: Naphthalene-type epoxy resin (manufactured by DIC, product name: EPICLON® HP-4032D) ・Thermosetting resin 3: Tetramethylbiphenyl-type epoxy resin (manufactured by Mitsubishi Chemical Corporation, product name: YX-4000) ・Thermosetting resin 4: Tetrafunctional naphthalene-type epoxy resin (with mesogenic structure, manufactured by DIC, product name: HP-4710) ・Thermosetting resin 5: Dicyclopentadiene-type epoxy resin (manufactured by DIC, product name: EPICLON® HP-7200) ・Thermosetting resin 6: Biphenyl ester-type phenoxy resin manufactured according to manufacturing example 1 below

[0094] (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.

[0095] • 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)

[0096]

[0097] (Phenol compounds) ・Phenol compound a: Ester group-containing bisphenol represented by the following chemical formula (difunctional phenol compound, with mesogenic structure, manufactured by Ueno Pharmaceutical Co., Ltd., HQPOB)

[0098]

[0099] The obtained 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).

[0100]

[0101] (Hardening agent) ・Hardening agent 1: Allylphenol resin-based hardening agent (manufactured by Ube Industries, product name: MEH-8000H)

[0102] [Evaluation] The thermal conductivity sheets of each example and comparative example obtained were evaluated as follows. The results are shown in Table 2.

[0103] (Density and Thermal Conductivity) For each example and comparative example, the obtained thermal 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 sheet cured product. From the obtained sheet cured product, 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 ]

[0104] (Glass transition temperature) For each of the obtained heat conductive sheets of the examples and comparative examples, while applying a pressure of 10 MPa, the temperature was raised at a constant rate from 25°C to 180°C over 30 minutes, and then heated at 180°C for 60 minutes to obtain a sheet cured product. From the obtained sheet cured product, a test piece having a thickness of 0.3 mm, a width of 8 mm, and a length of 50 mm was cut out. Then, for the obtained test piece, using a dynamic viscoelasticity measuring instrument (manufactured by Seiko Instruments Inc., product name: DMS6100), the glass transition temperature was measured under the conditions of a temperature increase rate of 5°C / min and a frequency of 1 Hz.

[0105] (Storage elastic modulus) For each of the obtained heat conductive sheets of the examples and comparative examples, while applying a pressure of 10 MPa, the temperature was raised at a constant rate from 25°C to 180°C over 30 minutes, and then heated at 180°C for 60 minutes to obtain a sheet cured product. From the obtained sheet cured product, a test piece having a thickness of 0.3 mm, a width of 8 mm, and a length of 50 mm was cut out. Then, for the obtained test piece, using a dynamic viscoelasticity measuring instrument, the storage elastic modulus E' at 25°C ２５ and the storage elastic modulus E' at 175°C １７５ were measured.

[0106] (Coefficient of linear expansion) For each of the obtained heat conductive sheets of the examples and comparative examples, while applying a pressure of 10 MPa, the temperature was raised at a constant rate from 25°C to 180°C over 30 minutes, and then heated at 180°C for 60 minutes to obtain a sheet cured product. From the obtained sheet cured product, a test piece having a thickness of 0.3 mm, a width of 4 mm, and a length of 50 mm was cut out. For the test piece, using a thermomechanical analyzer (manufactured by Seiko Instruments Inc., product name: TMA / SS6100), under the conditions of a measurement temperature range of 0°C to 330°C and a temperature increase rate of 5°C / min, the average coefficient of linear expansion α １ (ppm / °C) at 50 to 100°C and the average coefficient of linear expansion α ２ (ppm / °C) at 270 to 290°C were measured.

[0107] (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 was then measured for the obtained cured sheets in accordance with JIS C 2139:2008.

[0108] (Dielectric Strength) The dielectric strength of the thermal conductive sheets of each obtained example and comparative example was measured using an dielectric strength tester "TOS5101" (manufactured by Kikusui Electronics Co., Ltd.). Specifically, the thermal conductive sheets of each obtained example and comparative example 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 strength, 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 60 kV / mm B: Dielectric strength exceeds 40 kV / mm but is 60 kV / mm or less C: Dielectric strength is 40 kV / mm or less

[0109]

[0110] The thermal conductive sheets described in each example, which contain a thermosetting resin and boron nitride particles, and in which the boron nitride particles have a specific particle size distribution profile, showed an improved balance of thermal conductivity and insulation performance compared to the thermal conductive sheets described in each comparative example, in which the boron nitride particles do not have a specific particle size distribution profile.

[0111] This application claims priority based on Japanese Patent Application No. 2024-170287, filed on 30 September 2024, and Japanese Patent Application No. 2025-082511, 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, wherein the boron nitride particles have, in the particle size distribution profile according to (Method 1) below, a first peak having a first maximum point in the range of particle diameters of 5 μm or more and less than 30 μm, and a second peak having a second maximum point in the range of particle diameters of 30 μm or more and 150 μm or less, the frequency of the first peak at the first maximum point being 4.0% or more and 20.0% or less, and the frequency of the second peak at the second maximum point being 4.5% or more and 20.0% or less. (Method 1) The particle size distribution of the boron nitride particles is measured under the following conditions by a laser diffraction / scattering measurement method using a laser diffraction / scattering particle size distribution analyzer. A semi-logarithmic graph is created with frequency (%) on the vertical axis and particle size (μm) on the horizontal axis, where the horizontal axis is logarithmic. The point with the highest frequency in the particle size range of 5 μm to less than 30 μm is defined as the first maximum, and the point with the highest frequency in the particle size range of 30 μm to 150 μm is defined as the second maximum. Dispersion solvent: Pure water. Sample: Disperse in pure water. Use the device's built-in ultrasound for 30 seconds (irradiation intensity 5). Refractive index: Boron nitride 1.74 Particle size standard: Volume measurement Number of particle size points: 93 points from 0.011 μm to 3000 μm (equally spaced logarithmically) 2. The thermally conductive sheet according to claim 1, wherein the full width at half maximum ΔA of the first peak by the method described below (Method 2) is 5.0 μm or more and 20.0 μm or less. (Method 2) In the first peak measured in (Method 1), two points with a frequency equal to half the frequency (%) of the first maximum point are selected and listed in descending order of particle size as A. １ and A ２ A １ The particle size value and A ２ The difference between the particle size value and the value at half maximum is defined as the half-width ΔA (μm).

3. The thermally conductive sheet according to claim 1 or 2, wherein the full width at half maximum ΔB of the second peak according to the method (3) below is 30.0 μm or more and 200.0 μm or less. (Method 3) In the second peak measured in (Method 1), two points with a frequency equal to half the frequency (%) of the second maximum point are selected in descending order of particle size, and are designated as B １ and B ２ Let's assume that. B １ The particle size value and B ２ The difference between the particle size value and the value at half maximum is defined as the half-width ΔB (μm).

4. The thermally conductive sheet according to claim 1 or 2, wherein the boron nitride particles have a minimum in the particle size distribution profile according to the following (Method 4), with particle diameters ranging from 10 μm to 100 μm. (Method 4) The particle size distribution of the boron nitride particles is measured under the following conditions by a laser diffraction / scattering measurement method using a laser diffraction / scattering particle size distribution analyzer. A semi-logarithmic graph is created with frequency (%) on the vertical axis and particle diameter (μm) on the horizontal axis, with the horizontal axis being logarithmic, and the point with the smallest frequency in the particle diameter range of 10 μm to 100 μm is defined as the minimum. Dispersion solvent: Pure water. Sample: Disperse in pure water. Use the device's built-in ultrasound for 30 seconds (irradiation intensity 5). Refractive index: Boron nitride 1.74 Particle size standard: Volume measurement Number of particle size points: 93 points from 0.011 μm to 3000 μm (equally spaced logarithmically) 5. The thermally conductive sheet according to claim 4, wherein the difference between the frequency at the first maximum point and the frequency at the minimum point is 2.0% or more and 10.0% or less.

6. The thermal conductive sheet according to claim 1 or 2, wherein the particle size distribution profile obtained by the above (Method 1) consists of only two peaks: the first peak and the second peak.

7. The thermal conductive sheet according to claim 1 or 2, wherein in the particle size distribution profile according to method 1, the cumulative value of the frequency of particles with a diameter in the range of 0 μm to 3 μm is 1% or less.

8. The thermal conductive sheet according to claim 1 or 2, wherein, in the particle size distribution profile according to method 1, the cumulative value of the frequency of particles with a diameter in the range of 300 μm to 1000 μm is 1% or less.

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

10. The particle size D of the boron nitride particles, which 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.

11. The particle size D of the boron nitride particles, which is the 90% cumulative 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.

12. The thermal conductive sheet according to claim 1 or 2, 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.

13. 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.

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

15. The thermal conductive sheet according to claim 14, wherein the curing agent comprises one or more selected from the group consisting of phenolic resin curing agents and imidazole curing agents.

16. The thermal conductive sheet according to claim 14, 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.

17. The thermally conductive sheet according to claim 1 or 2, wherein the thermal conductivity obtained by the following method (Method 5) is 17.5 W / (m·K) or more and 30.0 W / (m·K) 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 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 ] 18. The thermally conductive sheet according to claim 1 or 2, wherein the glass transition temperature according to the following method (method 6) is 100°C or more and 300°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 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.

19. Storage modulus E' at 25°C according to the following method (Method 7) 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 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 8 mm, and a length of 50 mm is cut from the obtained sheet cured product. The storage modulus E' at 25°C is then measured on the obtained test piece using a dynamic viscoelasticity analyzer under the conditions of tensile mode and a frequency of 1 Hz. ２５ Measure.

20. Storage modulus E' at 175°C according to the following method (Method 8) 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 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 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 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.

21. The average coefficient of linear expansion α at 50-100°C, as determined by the method described below (Method 9). １ A thermally conductive sheet according to claim 1 or 2, wherein the coefficient of thermal expansion α is 1 ppm / °C or more and 100 ppm / °C or less. (Method 9) The thermally conductive sheet is heated at a constant rate from 25°C to 180°C over 30 minutes while applying 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, and the average linear expansion coefficient α at 50 to 100°C is determined under the conditions of a measurement temperature range of 0°C to 330°C and a heating rate of 5°C / min. １ Measure the concentration (ppm / °C).

22. The mean coefficient of linear expansion α at 270-290°C according to the method described below (Method 10). ２ A thermally conductive sheet according to claim 1 or 2, wherein the coefficient of thermal expansion α is 20 ppm / °C or more and 150 ppm / °C or less. (Method 10) The thermally conductive sheet is heated at a constant rate from 25°C to 180°C over 30 minutes while applying 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, and the average coefficient of linear expansion α at 270 to 290°C is determined 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).

23. The volume resistivity at 25°C determined by the following method (Method 11) 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 resistivity is Ω·m or less. (Method 11) The thermally conductive sheet is heated at a constant rate from 25°C to 180°C over 30 minutes while applying 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 sheet is then measured in accordance with JIS C 2139:2008.

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

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