Thermosetting composition, thermosetting sheet, thermally conductive sheet, composite molding, heat dissipating laminate, heat dissipating circuit board, semiconductor device and power module

Abstract

To provide a novel thermosetting composition containing inorganic fillers and thermosetting resins, which improves the brittleness of the thermosetting composition in its uncured state, suppresses chipping or cracking upon cutting, and yet inhibits a decrease in thermal conductivity.SOLUTION: There is provided a thermosetting composition containing inorganic fillers and thermosetting resins. The inorganic fillers contain two or more types, and the content of one type of inorganic filler (referred to as "first inorganic filler") is 60 mass% or more and 85 mass% or less of the solid content in the thermosetting composition and another type of inorganic filler (referred to as "second inorganic filler") is alumina particles with a primary particle size of 1 nm or more and less than 100 nm, and its content is 0.01 mass% or more and 10 mass% or less of the solid content in the thermosetting composition.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a thermosetting composition that exhibits thermal conductivity after curing, a thermosetting sheet, a thermally conductive sheet made from a cured product of the thermosetting sheet, a composite molded product comprising the thermosetting sheet or the thermally conductive sheet, and a heat-dissipating laminate, a heat-dissipating circuit board, a semiconductor device, and a power module that comprise the thermally conductive sheet. [Background technology]

[0002] In recent years, power semiconductor devices used in various fields such as railways, automobiles, industry, and general home appliances are being replaced by power semiconductors that use SiC, AlN, GaN, etc. in order to achieve further miniaturization, cost reduction, and efficiency improvement. Power semiconductor devices are generally used as a power semiconductor module in which a plurality of semiconductor devices are arranged on a common heat sink and packaged.

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

[0004] Furthermore, in recent years, heat generation due to the increasing density of integrated circuits has become a major problem in the electrical and electronic fields, and how to dissipate heat has become an urgent issue in these fields as well. For example, to ensure stable operation of semiconductor devices used to control the central processing unit of a personal computer or the motor of an electric vehicle, heat sinks, heat dissipation fins, etc. are essential for heat dissipation, and there is a demand for materials that can combine thermal conductivity and insulation to connect semiconductor devices and heat sinks, etc.

[0005] Ceramic substrates with high thermal conductivity, such as alumina substrates and aluminum nitride substrates, have traditionally been used as materials that can provide both thermal conductivity and insulation. However, ceramic substrates have issues such as being easily cracked by impact, and being difficult to make thin and compact. Therefore, a thermally conductive sheet (also called a "heat dissipation sheet") using a thermosetting resin such as an epoxy resin and an inorganic filler has been proposed.

[0006] Regarding thermally conductive sheets using a thermosetting resin and an inorganic filler, for example, Patent Document 1 proposes a heat-dissipating resin sheet containing an epoxy resin with a Tg of 60°C or less and boron nitride, in which the boron nitride content is 30% by volume or more and 60% by volume or less.

[0007] Boron nitride (hereinafter referred to as "BN") is an insulating ceramic that has attracted particular attention in recent years in the field of electrical and electronic materials due to its excellent thermal conductivity, solid lubricity, chemical stability, and heat resistance.

[0008] Patent Document 2 discloses a resin composition for a thermally conductive sheet, which contains a thermosetting resin and secondary sintered particles of boron nitride, and is characterized in that nanoparticles of an amphoteric oxide are blended into the resin composition so that the pH of the water extracted from the thermally conductive sheet after 72 hours in a pressure cooker test at 121°C is 6.5 or more and 8.5 or less.

[0009] Patent Document 3 discloses a thermosetting composition with excellent storage stability that can be used to stably produce semiconductor devices with excellent reliability, the thermosetting composition containing an epoxy resin, a thermally conductive filler, and silica nanoparticles having an average particle size D50 of 1 to 100 nm as measured by a dynamic light scattering method, in which the content of the silica nanoparticles is 0.3 to 2.5 mass% relative to 100 mass% of the total solid content of the thermosetting composition, and the thermally conductive filler contains secondary agglomerated particles composed of primary particles of scaly boron nitride.

[0010] Patent Document 4 discloses a thermosetting composition that can suppress unevenness on the coating surface, i.e., the surface of a resin sheet, even if the content of agglomerated particles of boron nitride is increased to a certain extent in order to further enhance thermal conductivity. The thermosetting composition contains a thermosetting resin, a thermally conductive filler, and silica nanoparticles, wherein the average particle size of the silica nanoparticles is 1 nm or more and 100 nm or less, the content of the silica nanoparticles is more than 2.5 mass% and 10 mass% or less, relative to 100 mass% of the total solid content of the thermosetting composition, the thermally conductive filler comprises agglomerated particles of boron nitride, the average particle size of the agglomerated particles is 5 μm or more and 100 μm or less, and the content of the thermally conductive filler is 60 mass% or more and 85 mass% or less, relative to 100 mass% of the total solid content of the thermosetting composition. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-036415 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-224676 [Patent Document 3] Japanese Patent Application Publication No. 2017-025186 [Patent Document 4] Japanese Patent Publication No. 2023-102284 Summary of the Invention [Problem to be solved by the invention]

[0012] When producing a thermally conductive sheet from a thermosetting composition containing an inorganic filler and a thermosetting resin, a typical procedure is to form a sheet-like molded body by forming a thermosetting composition containing a solvent into a film, evaporate the solvent, and then cut the sheet-like molded body to the required size using a cutting machine or the like, and then heat-cure the sheet. In order to improve the thermal conductivity of a thermally conductive sheet, it is necessary to include as much inorganic filler as possible. However, if the inorganic filler content is too high, the thermosetting composition in its uncured state becomes brittle, which can lead to problems such as chipping or cracking when the sheet-shaped molded product is cut with a cutting machine. Furthermore, if a thermosetting resin that is liquid at room temperature is added to reduce voids between the inorganic filler particles, the resin that connects the filler particles becomes brittle, weakening the ability to hold the filler particles in the sheet, which tends to exacerbate the problem.

[0013] The object of the present invention is to provide a novel thermosetting composition that contains an inorganic filler and a thermosetting resin, which improves the brittleness of the thermosetting composition in an uncured state, and which can prevent chipping or cracking even when a sheet-shaped molded product before curing is cut, while still preventing a decrease in thermal conductivity; and to provide a thermosetting sheet, a thermally conductive sheet, a composite molded product, a heat-dissipating laminate, a heat-dissipating circuit board, a semiconductor device, and a power module that use the thermosetting composition. [Means for solving the problem]

[0014] The thermosetting composition, thermosetting sheet, thermally conductive sheet, composite molded body, heat dissipating laminate, heat dissipating circuit board, semiconductor device, and power module proposed by the present invention have the following configurations in order to solve the above-mentioned problems.

[0015] [1] A first aspect of the present invention is a thermosetting composition containing an inorganic filler and a thermosetting resin, The thermosetting composition contains two or more types of inorganic fillers, and the content of one type of inorganic filler (referred to as the "first inorganic filler") is 60% by mass or more and 85% by mass or less of the solid content in the thermosetting composition, and the content of another type of inorganic filler (referred to as the "second inorganic filler") is alumina particles having a primary particle diameter of 1 nm or more and less than 100 nm, and is 0.01% by mass or more and 10% by mass or less of the solid content in the thermosetting composition.

[0016] [2] A second aspect of the present invention is the first aspect, wherein the second inorganic filler has a BET specific surface area of ​​20 m 2 / g or more 500m 2 / g or less. [3] A third aspect of the present invention is the thermosetting composition of the first or second aspect, wherein the content of the second inorganic filler is 0.1% by mass or more and 5% by mass or less of the solid content in the thermosetting composition.

[0017] [4] A fourth aspect of the present invention is the thermosetting composition according to any one of the first to third aspects, wherein the first inorganic filler is agglomerated particles of boron nitride. [5] A fifth aspect of the present invention is the thermosetting composition according to any one of the first to fourth aspects, wherein the first inorganic filler has an average particle size of 10 μm or more and 100 μm or less.

[0018] [6] A sixth aspect of the present invention is the thermosetting composition of any one of the first to fifth aspects, wherein the ratio of the BET specific surface area of ​​the second inorganic filler to the BET specific surface area of ​​the first inorganic filler is 6 or more and 150 or less. [7] A seventh aspect of the present invention is the thermosetting composition of any one of the first to sixth aspects, wherein the ratio of the primary particle diameter of the second inorganic filler to the primary particle major diameter of the first inorganic filler is 0.001 or more and 0.01 or less. [8] An eighth aspect of the present invention is the thermosetting composition of any one of the first to seventh aspects, wherein the ratio of the primary particle size of the second inorganic filler to the average particle size of the first inorganic filler is 0.0001 or more and 0.001 or less.

[0019] [9] A ninth aspect of the present invention is the thermosetting composition according to any one of the first to eighth aspects, wherein the thermosetting resin is an epoxy resin that is liquid at 25°C.

[10] A tenth aspect of the present invention is the thermosetting composition of the ninth aspect, wherein the content of the liquid epoxy resin is 8% by mass or more and 60% by mass or less of the resin components excluding the inorganic filler from the solid content of the thermosetting composition.

[0020]

[11] An eleventh aspect of the present invention is a thermosetting composition according to any one of the first to tenth aspects, wherein the thermosetting resin is a multifunctional epoxy resin having three or more epoxy groups per molecule and a molecular weight of 800 or less.

[12] A twelfth aspect of the present invention is the thermosetting composition according to the eleventh aspect, wherein the polyfunctional epoxy resin has four or more glycidyl groups per molecule.

[0021]

[13] A thirteenth aspect of the present invention is a thermosetting composition according to the ninth or tenth aspect, wherein the liquid epoxy resin is a multifunctional epoxy resin having three or more epoxy groups per molecule and a molecular weight of 800 or less.

[14] A fourteenth aspect of the present invention is the thermosetting composition according to the thirteenth aspect, wherein the polyfunctional epoxy resin has four or more glycidyl groups per molecule.

[0022]

[15] A fifteenth aspect of the present invention is a thermosetting composition according to any one of the first to fourteenth aspects, wherein the thermosetting resin is a polymer compound having a molecular weight of 10,000 or more.

[0023]

[16] A sixteenth aspect of the present invention is a thermosetting sheet made of the thermosetting composition of any one of the first to fifteenth aspects.

[17] The seventeenth aspect of the present invention is a thermally conductive sheet comprising a cured product of the thermosetting sheet of the sixteenth aspect.

[18] The eighteenth aspect of the present invention is a composite molded product having the thermosetting sheet of the sixteenth aspect and a metal part.

[19] A nineteenth aspect of the present invention is a composite molded product having the thermally conductive sheet of the seventeenth aspect and a metal part.

[20] A twentieth aspect of the present invention is a heat dissipation laminate, a heat dissipation circuit board, a semiconductor device, or a power module, which includes the thermally conductive sheet of the seventeenth aspect. [Effects of the Invention]

[0024] The thermosetting composition proposed by the present invention is a thermosetting composition containing two or more types of inorganic fillers and a thermosetting resin, and one of the inorganic fillers contains a predetermined amount of alumina particles having a primary particle diameter of 1 nm or more and less than 100 nm.This makes it possible to improve the brittleness of the thermosetting composition before curing, even if the content of the inorganic filler is relatively high, and to prevent chipping or cracking when the sheet-shaped molded product before curing is cut, while still suppressing a decrease in thermal conductivity. Furthermore, even when a thermosetting resin that is liquid at room temperature is added to reduce voids between inorganic fillers, the brittleness of the thermosetting composition before curing can be improved, and even when the sheet-like molded product before curing is cut, chipping or cracking can be suppressed, while still improving thermal conductivity. DETAILED DESCRIPTION OF THE INVENTION

[0025] An example of an embodiment of the present invention will be described in detail below. However, the present invention is not limited to the following embodiment, and various modifications can be made within the scope of the present invention.

[0026] <<Thermosetting composition of the present invention>> A thermosetting composition according to one embodiment of the present invention (referred to as the "thermosetting composition of the present invention") is a thermosetting composition containing two or more types of inorganic fillers and a thermosetting resin, in which one of the two or more types of inorganic fillers is alumina particles having a primary particle diameter of 1 nm or more and less than 100 nm (also referred to as "nano alumina particles"), and optionally further containing other inorganic fillers, other polymers, curing agents, curing accelerators, organic solvents, and other components.

[0027] In the present invention, the term "thermosetting composition" means a composition that has the property of being cured by heat, and is sufficient as long as it has the curability to be cured by heat. The composition may be one that has already been cured to a state where there is still room for curing (also referred to as "pre-cured"), or one that has not yet been cured at all (referred to as "uncured"). The thermosetting composition of the present invention may be in any form such as powder, slurry, liquid, solid, or a molded product such as a sheet.

[0028] In the present invention, the term "resin" refers to an organic compound excluding solvents, and includes organic compounds ranging from low molecular weight compounds to high molecular weight polymers. Therefore, for example, "thermosetting resin" can be read as "thermosetting compound," and "epoxy resin" can be read as "epoxy compound."

[0029] <First inorganic filler> One of the two or more inorganic fillers contained in the thermosetting composition of the present invention (referred to as the "first inorganic filler") is preferably a particle having a thermal conductivity of 2.0 W / m·K or more, more preferably 3.0 W / m·K or more, particularly 5.0 W / m·K or more, and even more preferably 10.0 W / m·K or more.

[0030] (Average particle size) The average particle size of the first inorganic filler is preferably 10 μm or more and 100 μm or less. When the average particle size of the first inorganic filler is 10 μm or more, the number of particles of the first inorganic filler in the thermosetting composition of the present invention is relatively small, and the number of interparticle interfaces is reduced, thereby reducing the thermal resistance and increasing the thermal conductivity of the cured product of the thermosetting composition of the present invention. On the other hand, if the average particle size is 100 μm or less, this leads to reduced unevenness on the sheet surface and reduced voids between the fillers, and is therefore preferable. From this viewpoint, the average particle size of the first inorganic filler is preferably 10 μm or more, more preferably 15 μm or more, and particularly preferably 20 μm or more, and is preferably 100 μm or less, more preferably 90 μm or less.

[0031] The average particle size of the first inorganic filler can be measured, for example, by the following method. The average particle diameter of the first inorganic filler used as a raw material can be determined as the average particle diameter D50 of the first inorganic filler from the particle size distribution obtained by measuring the particle size distribution of a sample in which the first inorganic filler is dispersed in a solvent, specifically, a sample in which the first inorganic filler is dispersed in a pure water medium containing a dispersion stabilizer, using a laser diffraction / scattering particle size distribution analyzer. Here, D50 is the particle size at 50% cumulative volume in the volume-based particle size distribution obtained by measurement using a laser diffraction / scattering particle size distribution measurement method. Alternatively, the average particle size can be determined using a dry particle size distribution measuring device such as Morphologi G3 (manufactured by Malvern Instruments).

[0032] On the other hand, the average particle diameter D50 of the first inorganic filler in the thermosetting composition of the present invention or its cured product can also be measured in the same manner as above by heating the resin component in air, ashing it, and removing it. The average particle diameter of the first inorganic filler in the thermosetting composition of the present invention or a cured product thereof can also be determined by directly observing a cross section of the thermosetting composition of the present invention or a cured product thereof using a scanning electron microscope, a transmission electron microscope, a Raman microscope, an atomic force microscope, etc., and calculating the arithmetic mean value of the particle diameters of 10 or more arbitrary first inorganic fillers. When the particles are non-spherical, the longest and shortest diameters are measured, and the average value is used as the particle diameter of the particles.

[0033] (primary particle major axis) The primary particle length of the first inorganic filler is preferably 0.5 μm or more and 20 μm or less. When the primary particle major axis of the first inorganic filler is 0.5 μm or more, the voids in the aggregates become an appropriate size, which is preferable because it facilitates compounding with the second inorganic filler. On the other hand, when the primary particle major axis is 20 μm or less, the voids do not become too large, which is preferable. From this viewpoint, the primary particle length of the first inorganic filler is preferably 0.5 μm or more, more preferably 1 μm or more, and particularly preferably 1.5 μm or more, and is preferably 20 μm or less, more preferably 10 μm or less, and even more preferably 8 μm or less.

[0034] The major axis of the primary particles of the first inorganic filler can be measured, for example, by the following method. The particles are photographed at 5,000x magnification using a scanning electron microscope (SEM), and the long diameters of 50 or more primary particles that make up the agglomerated particles are measured and averaged to determine the long diameter of the primary particles that make up the agglomerated particles. The term "major diameter of primary particles" refers to the diameter of the longest part when the primary particles are non-spherical or irregular in shape.

[0035] (specific surface area) The BET specific surface area of ​​the first inorganic filler is 1m 2 / g or more 15m 2 / g or less is preferable. The BET specific surface area of ​​the first inorganic filler is 1m 2 / g or more is preferable because it increases the contact area with the second filler. 2 / g or less is preferable from the viewpoint of reducing voids in the filler. From this viewpoint, the BET specific surface area of ​​the first inorganic filler is 1 m 2 / g or more, and 1.5m 2 / g or more, among which 2m 2 / g or more, among which 3m 2 / g or more is more preferable. 2 / g or less, and particularly 12m 2 / g or less, and among them, 10m 2 / g or less, among which 8m 2 It is more preferable that the molecular weight is not more than 1 / g.

[0036] The BET specific surface area of ​​the first inorganic filler can be measured, for example, by the BET single-point method (adsorption gas: nitrogen).

[0037] (material) Examples of the first inorganic filler include electrically insulating fillers made only of carbon, fillers made of metal carbides or semi-metal carbides, metal oxides or semi-metal oxides, and metal nitrides or semi-metal nitrides. Among these, it is preferable to contain "boron nitride agglomerated particles (also referred to as "BN agglomerated particles") formed by agglomeration of primary particles of boron nitride, because they have little problem with moisture absorption during heat molding, are low in toxicity, can efficiently increase thermal conductivity, and can impart high insulating properties to a cured product of the thermosetting composition of the present invention.

[0038] [Boron nitride agglomerated particles] The shape of the agglomerated particles of boron nitride is preferably spherical.

[0039] The agglomerated structure of the boron nitride agglomerated particles is preferably a house-of-card structure from the viewpoint of improving thermal conductivity. The agglomerated structure of the boron nitride agglomerated particles can be confirmed by a scanning electron microscope (SEM).

[0040] The house-of-card structure is a complex stack of plate-like particles that are not oriented, as described in "Ceramics 43 No. 2" (published by the Ceramic Society of Japan in 2008). More specifically, it refers to a structure in which the flat surfaces of the primary particles that form an agglomerate are in contact with the edge surfaces of other primary particles present within the agglomerate. The house-of-card structured agglomerated particles have extremely high fracture strength due to their structure, and do not collapse even during the pressurizing process performed when forming the thermosetting composition of the present invention into a sheet. Therefore, primary particles that are normally oriented in the longitudinal direction of the sheet can be made to exist in a random direction. Therefore, the use of house-of-card structured agglomerated particles can further increase the proportion of primary particles with their ab planes oriented in the thickness direction of the sheet, thereby enabling effective heat conduction in the thickness direction of the sheet and further increasing the thermal conductivity in the thickness direction. The boron nitride agglomerated particles having a house-of-card structure can be produced, for example, by the method described in WO 2015 / 119198.

[0041] By using agglomerated particles of boron nitride as the first inorganic filler used in the thermosetting composition of the present invention, the particle size can be made larger than that of a first inorganic filler that uses primary particles as they are. By increasing the particle size of the first inorganic filler, the number of heat transfer paths between the first inorganic fillers via the resin with low thermal conductivity can be reduced, and therefore the increase in thermal resistance in the heat transfer paths in the thickness direction can be reduced.

[0042] The agglomerated particles of boron nitride may be surface-treated with a surface treatment agent. As the surface treatment agent, for example, a known surface treatment agent such as a silane coupling treatment agent can be used. It is believed that by increasing the adhesion at the interface between the first inorganic filler and the matrix resin such as a thermosetting resin by chemical treatment, it is possible to further reduce the attenuation of thermal conductivity at the interface.

[0043] (Content) The content of the first inorganic filler is preferably 60% by mass or more and 85% by mass or less relative to 100% by mass of the total solid content of the thermosetting composition of the present invention. If the content of the first inorganic filler is 60% by mass or more, high thermal conductivity can be obtained, and if it is 85% by mass or less, the brittleness of the thermosetting composition of the present invention can be improved by containing nanoalumina particles. From this viewpoint, the content of the first inorganic filler is preferably 60% by mass or more, more preferably 62% by mass or more, and even more preferably 65% ​​by mass or more, relative to 100% by mass of the total solid content of the thermosetting composition of the present invention, and is preferably 85% by mass or less, more preferably 83% by mass or less, and even more preferably 81% by mass or less.

[0044] <Second inorganic filler> The thermosetting composition of the present invention contains alumina particles (also referred to as "nanoalumina particles") having a primary particle diameter of 1 nm or more and less than 100 nm as one inorganic filler (referred to as "second inorganic filler") among the two or more inorganic fillers.

[0045] When the thermosetting composition of the present invention contains a predetermined amount of nano-alumina particles, the nano-alumina particles penetrate into the aggregated particles of the first inorganic filler and between the first inorganic filler particles. This allows the nano-alumina particles to adsorb to the surface of the first inorganic filler without interrupting the thermal conduction paths between the first inorganic filler particles, thereby increasing affinity with the surrounding resin and retaining the first inorganic filler within the sheet. This improves the brittleness of the thermosetting composition of the present invention in its pre-cured state, even when the content of the first inorganic filler is increased. For example, chipping or cracking when cut can be suppressed, and a decrease in thermal conductivity can be suppressed. Furthermore, even when a thermosetting resin that is liquid at room temperature is included, the brittleness of the thermosetting composition of the present invention in its pre-cured state can be improved. For example, chipping or cracking can be suppressed when cut, and a decrease in thermal conductivity can be suppressed. These effects are characteristic of nano-alumina particles compared to titanium oxide particles and silica particles.

[0046] (particle shape) The primary particle shape of the second inorganic filler, i.e., nano-alumina particles, may be crushed, flake-like, columnar, angular (tetrahedral, hexahedral, etc.), spherical, or other shapes, but is preferably spherical. The primary particles may form aggregates.

[0047] (primary particle size) The second inorganic filler, ie, the nano-alumina particles, preferably have an average particle size of the primary particles (referred to as "primary particle size") of 1 nm or more and less than 100 nm. If the primary particle diameter of the nano alumina particles is 1 nm or more, it is preferable because it suppresses particle aggregation and makes them easier to disperse in the resin, and if it is less than 100 nm, it can efficiently adhere to the surface of the thermally conductive particles with a small amount added, improving the brittleness of the thermosetting composition of the present invention, and is also preferable because even if it enters between the first inorganic fillers, it does not interfere with the thermal conduction paths formed between the first inorganic fillers. From this viewpoint, the primary particle diameter of the nano alumina particles is preferably 1 nm or more, more preferably 5 nm or more, even more preferably 8 nm or more, even more preferably 10 nm or more, and is preferably less than 100 nm, even more preferably 80 nm or less, even more preferably 70 nm or less, even more preferably 60 nm or less.

[0048] The primary particle diameter of the second inorganic filler, i.e., nano-alumina particles, can be measured, for example, by a transmission electron microscope. Specifically, the particle diameter of each particle is the equivalent circle diameter calculated for each particle from a transmission electron microscope photograph, and the average particle diameter of at least 200 particles can be taken as the average particle diameter of the nanoparticles.

[0049] (BET specific surface area) The BET specific surface area of ​​the second inorganic filler, i.e., nano-alumina particles, is 20m 2 / g or more 500m 2 / g or less is preferable. The BET specific surface area of ​​nano alumina particles is 20m 2 If the content is 500 m / g or more, it is preferable because even a small amount of addition can efficiently adhere to the surface of the thermally conductive particles, thereby improving the brittleness of the thermosetting composition of the present invention. 2 / g or less is preferable because aggregation is suppressed and dispersion in the resin is facilitated. From this perspective, the BET specific surface area of ​​nano-alumina particles is 20m 2 / g or more is preferable, and 30m2 / g or more, among which 40m 2 / g or more, among which 50m 2 / g or more is more preferable. 2 / g or less, and above all, 400m 2 / g or less, among which 350m 2 / g or less, and 300m 2 It is more preferable that the molecular weight is not more than 1 / g.

[0050] The BET specific surface area of ​​the second inorganic filler, that is, the nano-alumina particles, can be measured by the BET one-point method (adsorption gas: nitrogen).

[0051] (Second inorganic filler / First inorganic filler) The ratio of the BET specific surface area of ​​the second inorganic filler to the BET specific surface area of ​​the first inorganic filler is preferably 6 or more and 150 or less. If the ratio of the BET specific surface area of ​​the second inorganic filler to the BET specific surface area of ​​the first inorganic filler is 6 or more, the second inorganic filler is easily adsorbed to the surface of the first inorganic filler, which is preferable. On the other hand, if the ratio is 150 or less, the affinity with the resin can be efficiently increased when the second inorganic filler is adsorbed to the surface of the first inorganic filler, which is preferable. From this viewpoint, the ratio of the BET specific surface area of ​​the second inorganic filler to the BET specific surface area of ​​the first inorganic filler is preferably 6 or more, more preferably 8 or more, even more preferably 10 or more, and even more preferably 15 or more. On the other hand, it is preferably 150 or less, even more preferably 120 or less, even more preferably 100 or less, and even more preferably 80 or less.

[0052] Furthermore, the surface area of ​​the second inorganic filler relative to the surface area of ​​the first inorganic filler, ie, the surface area ratio, is preferably 0.06 to 2.0. If the surface area ratio is 0.06 or more, the second inorganic filler can be adsorbed to the surface of the first inorganic filler, thereby achieving a more effective effect. On the other hand, if the surface area ratio is 2.0 or less, it is possible to prevent an excessive amount of the second inorganic filler from increasing the viscosity of the resin and impairing its flowability. From this viewpoint, the surface area ratio of the second filler to the first filler is preferably 0.06 or more, more preferably 0.07 or more, more preferably 0.08 or more, and even more preferably 0.09 or more. Also, it is preferably 2.0 or less, more preferably 1.5 or less, and even more preferably 1.0 or less. The surface area ratio is calculated as follows: Surface area ratio=(BET specific surface area of ​​second inorganic filler×mass ratio) / (BET specific surface area of ​​first inorganic filler×mass ratio)

[0053] The ratio of the primary particle diameter of the second inorganic filler to the primary particle major diameter of the first inorganic filler is preferably 0.001 or more and 0.01 or less. If the ratio of the primary particle diameter of the second inorganic filler to the major axis of the primary particle of the first inorganic filler is 0.01 or less, the second inorganic filler will penetrate between the aggregates of the first inorganic filler, which is preferable. On the other hand, if the ratio is 0.001 or more, the second inorganic filler will not penetrate deep into the first filler when it penetrates between the aggregates of the first inorganic filler, which is preferable because it will increase the affinity with the surface resin. From this viewpoint, the ratio of the primary particle diameter of the second inorganic filler to the primary particle major diameter of the first inorganic filler is preferably 0.001 or more, more preferably 0.0015 or more, even more preferably 0.002 or more, even more preferably 0.003 or more, and is preferably 0.01 or less, even more preferably 0.009 or less, even more preferably 0.0085 or less, even more preferably 0.008 or less.

[0054] The ratio of the primary particle size of the second inorganic filler to the average particle size of the first inorganic filler is preferably 0.0001 or more and 0.001 or less. A ratio of the primary particle size of the second inorganic filler to the average particle size of the first inorganic filler of 0.0001 or more is preferable because it suppresses aggregation of the second inorganic filler and facilitates dispersion on the surface of the first inorganic filler. On the other hand, a ratio of 0.001 or less is preferable because even a small amount of the second inorganic filler can efficiently adhere to the surface of the thermally conductive particles, improving the brittleness of the thermosetting composition of the present invention and not interfering with the thermal conduction paths formed between the first inorganic fillers even when the second inorganic filler is present between the first inorganic fillers. From this viewpoint, the ratio of the primary particle size of the second inorganic filler to the average particle size of the first inorganic filler is preferably 0.0001 or more, more preferably 0.00012 or more, even more preferably 0.00015 or more, even more preferably 0.00018 or more, and is preferably 0.001 or less, even more preferably 0.0009 or less, even more preferably 0.0008 or less, even more preferably 0.0007 or less.

[0055] [Nano alumina particles] The nano-alumina particles may be either hollow particles or solid particles.

[0056] The nano-alumina particles may further be surface-treated with an organometallic compound. When nano-alumina particles are surface-treated with an organometallic compound, the surface is made hydrophobic, which can further increase the fluidity, and even a small amount can improve the low-profile of the thermosetting composition of the present invention.In addition, compared to nano-alumina particles that are not surface-treated, it can prevent the viscosity of the slurry prepared for coating from increasing too much, which can deteriorate the coatability. Examples of such organometallic compounds include organosilicon compounds, organotitanium compounds, organozirconium compounds, organoaluminum compounds, etc. Among these, organosilicon compounds are preferred. Examples of the organosilicon compound include silicone oils such as dimethylpolysiloxane, dimethylpolysiloxane having a reactive group at the end, and methylhydrogenpolysiloxane; organosilanes such as methyldimethoxysilane and diphenyldimethoxysilane; silazanes such as hexamethyldisilazane; silane coupling agents such as 3-methacryloyloxypropyltrimethoxysilane, 3-acryloyloxypropyltrimethoxysilane, vinyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, and γ-aminopropyltriethoxysilane; and phenyl group-containing silane coupling agents. In particular, from the viewpoint of ease of imparting hydrophobicity, methylhydrogenpolysiloxane, methyltrimethoxysilane, dimethyldimethoxysilane, trimethylmethoxysilane, hexamethyldisilazane, dimethylpolysiloxane having a reactive group at the terminal, and phenyl group-containing silane coupling agents are preferred, methylhydrogenpolysiloxane, dimethyldimethoxysilane, trimethylmethoxysilane, and phenyl group-containing silane coupling agents are more preferred, and dimethyldimethoxysilane, trimethylmethoxysilane, and phenyl group-containing silane coupling agents are even more preferred.

[0057] (Content) The content of the second inorganic filler, ie, nano-alumina particles, is preferably 0.01% by mass or more and 10% by mass or less relative to 100% by mass of the total solid content of the thermosetting composition of the present invention. When the content of nano-alumina particles is 0.01% by mass or more, the brittleness of the thermosetting composition of the present invention can be improved even if the content of the first inorganic filler (boron nitride agglomerated particles) is increased to a certain extent to further increase the thermal conductivity, specifically, even if the content of the first inorganic filler (boron nitride agglomerated particles) is set to 60% by mass or more as described above. On the other hand, when the content of nano-alumina particles is 10% by mass or less, the fluidity of the resin is not reduced, which is preferable. From this viewpoint, the content of the second inorganic filler, i.e., nano-alumina particles, is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.2% by mass or more, relative to 100% by mass of the total solid content of the thermosetting composition of the present invention, and is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 4% by mass or less.

[0058] The content of the second inorganic filler, ie, the nanoalumina particles, is preferably 0.02 parts by mass or more and 18 parts by mass or less relative to 100 parts by mass of the content of the first inorganic filler. When the content of the nano-alumina particles is 0.02 parts by mass or more, the brittleness of the thermosetting composition of the present invention can be improved even if the content of the first inorganic filler (boron nitride agglomerated particles) is increased to a certain extent to further increase the thermal conductivity, specifically, even if the content of the first inorganic filler (boron nitride agglomerated particles) is set to 60 mass% or more as described above. On the other hand, when the content of the nano-alumina particles is 18 parts by mass or less, the fluidity of the resin is not reduced, which is preferable. From this viewpoint, the content of the second inorganic filler, i.e., nano-alumina particles, is preferably 0.02 parts by mass or more, more preferably 0.2 parts by mass or more, even more preferably 0.3 parts by mass or more, even more preferably 0.4 parts by mass or more, relative to 100 parts by mass of the first inorganic filler, and is preferably 18 parts by mass or less, even more preferably 10 parts by mass or less, even more preferably 8 parts by mass or less.

[0059] <Other inorganic fillers> The thermosetting composition of the present invention may contain inorganic fillers other than the first inorganic filler and the second inorganic filler (also referred to as "other inorganic fillers"). As the other inorganic filler, particles having a thermal conductivity of 2.0 W / m·K or more are preferred, particularly 3.0 W / m·K or more, particularly 5.0 W / m·K or more, and particularly 10.0 W / m·K or more are even more preferred.

[0060] Other inorganic fillers include, for example, electrically insulating fillers made only of carbon, fillers made of metal carbides or semi-metal carbides, metal oxides or semi-metal oxides, and metal nitrides or semi-metal nitrides.

[0061] An example of the electrically insulating filler made only of carbon is diamond (thermal conductivity: approximately 2000 W / m·K). Examples of the metal carbide or semi-metal carbide include silicon carbide (thermal conductivity: approximately 60 to 270 W / m·K), titanium carbide (thermal conductivity: approximately 21 W / m·K), and tungsten carbide (thermal conductivity: approximately 120 W / m·K).

[0062] Examples of the metal oxide or semi-metal oxide include magnesium oxide (thermal conductivity: approximately 40 W / m·K), aluminum oxide (thermal conductivity: approximately 20 to 35 W / m·K), zinc oxide (thermal conductivity: approximately 54 W / m·K), yttrium oxide (thermal conductivity: approximately 27 W / m·K), zirconium oxide (thermal conductivity: approximately 3 W / m·K), ytterbium oxide (thermal conductivity: approximately 38.5 W / m·K), beryllium oxide (thermal conductivity: approximately 250 W / m·K), and "sialon" (ceramics composed of silicon, aluminum, oxygen, and nitrogen, thermal conductivity: approximately 21 W / m·K). Examples of the metal nitride or semi-metal nitride include boron nitride (thermal conductivity in the plane direction of plate-like particles of hexagonal boron nitride (h-BN): approximately 200 to 500 W / m·K), aluminum nitride (thermal conductivity: approximately 160 to 285 W / m·K), and silicon nitride (thermal conductivity: approximately 30 to 80 W / m·K).

[0063] From the viewpoint of electrical insulation, the volume resistivity of other inorganic fillers at 20°C is 10 13 It is preferable that the resistivity is Ω·cm or more, and particularly 10 14 It is more preferable that the resistivity is Ω·cm or more. Among these, metal oxides, semi-metal oxides, metal nitrides, and semi-metal nitrides are preferred because they can easily provide sufficient electrical insulation to the cured product of the thermosetting composition of the present invention. Specific examples of other inorganic fillers include aluminum oxide (Al2O3, volume resistivity: >10 14 Ω·cm), aluminum nitride (AlN, volume resistivity: >10 14 Ω·cm), boron nitride (BN, volume resistivity: >10 14 Ω·cm), silicon nitride (Si3N4, volume resistivity:>10 14 Ω·cm), silica (SiO2, volume resistivity: >10 14 Ω·cm). Among these, aluminum oxide, aluminum nitride, and boron nitride are preferred, with aluminum oxide and boron nitride being particularly preferred since they can impart high insulating properties to the cured product of the thermosetting composition of the present invention.

[0064] The shape of the other inorganic fillers may be irregular particles, spheres, whiskers, fibers, plates, or aggregates or mixtures thereof, among which spherical alumina particles are preferred.

[0065] In the present invention, "spherical" generally means that the aspect ratio (ratio of major axis to minor axis) is 1 or more and 2 or less, preferably 1 or more and 1.75 or less, more preferably 1 or more and 1.5 or less, and even more preferably 1 or more and 1.4 or less. The aspect ratio can be determined by randomly selecting 10 or more particles from an image of the cross section of the thermosetting composition or its cured product taken with a scanning electron microscope (SEM), determining the ratio of the major axis to the minor axis of each particle, and calculating the average value.

[0066] The other inorganic fillers may be used alone or in combination of two or more.

[0067] (Average particle size) The average particle size (D50) of the other inorganic filler is not particularly limited. In particular, it is preferably 5 μm or more, more preferably 10 μm or more, and particularly preferably 15 μm or more. It is also preferably 100 μm or less, more preferably 90 μm or less. When the average particle size (D50) of the other inorganic filler is 5 μm or more, the number of particles in the thermosetting composition of the present invention and its cured product is relatively small, and the number of interparticle interfaces is reduced, which may result in lower thermal resistance and higher thermal conductivity of the cured product of the thermosetting composition of the present invention. Furthermore, when the average particle size is equal to or less than the upper limit, the surface smoothness of the cured product of the thermosetting composition of the present invention tends to be higher. The average particle size (D50) of the other inorganic fillers can be determined in the same manner as the average particle size (D50) of the first inorganic filler.

[0068] (Content of first inorganic filler when other inorganic fillers are contained) When the boron nitride agglomerated particles as the first inorganic filler are used in combination with other inorganic fillers, the main focus is on reducing the cost of the composition, and therefore, it is preferable to appropriately select the other inorganic filler to be used in combination with the boron nitride agglomerated particles from magnesium oxide, aluminum oxide, tungsten carbide, silicon carbide, aluminum nitride, etc., because they are relatively inexpensive and have relatively high thermal conductivity. In particular, from the viewpoint of high thermal conductivity, it is preferable that the boron nitride agglomerated particles account for 75 mass% or more of the total content (100 mass%) of all two or more types of inorganic fillers, and even more preferably 80 mass% or more, and even more preferably 85 mass% or more (including 100 mass%) of that.

[0069] <Thermosetting resin> The thermosetting resin contained in the thermosetting composition of the present invention may be any resin that is cured by heat. Examples include epoxy resins, phenolic resins, polycarbonate resins, unsaturated polyester resins, urethane resins, melamine resins, and urea resins. Among these, epoxy resins are preferred from the viewpoints of viscosity, heat resistance, moisture absorption, and ease of handling.

[0070] The content of the thermosetting resin is preferably 5% by mass or more and 99% by mass or less relative to 100% by mass of the resin component obtained by excluding the inorganic filler from the solid content of the thermosetting composition of the present invention. A thermosetting resin content of 5% by mass or more is preferable because it provides good moldability, while a content of 99% by mass or less is preferable because it ensures the content of other components and increases thermal conductivity. From this viewpoint, the content of the thermosetting resin is preferably 5% by mass or more and 99% by mass or less, more preferably 10% by mass or more, more preferably 20% by mass or more, more preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more, relative to 100% by mass of the resin component obtained by excluding the inorganic filler from the solid content of the thermosetting composition of the present invention, and more preferably 98% by mass or less.

[0071] (epoxy resin) As mentioned above, epoxy resins are particularly preferred as the thermosetting resin contained in the thermosetting composition of the present invention. Epoxy resin is a general term for compounds having one or more oxirane rings (epoxy groups) in the molecule. The oxirane rings (epoxy groups) contained in epoxy resins may be either alicyclic epoxy groups or glycidyl groups. From the viewpoint of reaction speed or heat resistance, glycidyl groups are more preferable.

[0072] Examples of epoxy resins include epoxy group-containing silicon compounds, aliphatic epoxy resins, bisphenol A or F epoxy resins, novolac epoxy resins, alicyclic epoxy resins, glycidyl ester epoxy resins, polyfunctional epoxy resins, and polymeric epoxy resins.

[0073] The epoxy resin may be an aromatic oxirane ring (epoxy group)-containing compound. Specific examples thereof include bisphenol-type epoxy resins obtained by glycidylating bisphenols such as bisphenol A, bisphenol F, bisphenol AD, bisphenol S, tetramethylbisphenol A, tetramethylbisphenol F, tetramethylbisphenol AD, tetramethylbisphenol S, and tetrafluorobisphenol A; biphenyl-type epoxy resins; epoxy resins obtained by glycidylating dihydric phenols such as dihydroxynaphthalene and 9,9-bis(4-hydroxyphenyl)fluorene; epoxy resins obtained by glycidylating trisphenols such as 1,1,1-tris(4-hydroxyphenyl)methane; epoxy resins obtained by glycidylating tetrakisphenols such as 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane; and novolac-type epoxy resins obtained by glycidylating novolacs such as phenol novolac, cresol novolac, bisphenol A novolac, and brominated bisphenol A novolac.

[0074] In particular, the thermosetting composition of the present invention preferably contains either one or both of the "liquid epoxy resin" and the "high molecular weight epoxy resin" described below. Examples of epoxy resins other than the liquid epoxy resin and high molecular weight epoxy resin contained in the thermosetting composition of the present invention include, but are not limited to, various bisphenol-type epoxy resins obtained by glycidylating bisphenols, such as bisphenol A-type epoxy resins and bisphenol F-type epoxy resins; various biphenyl-type epoxy resins obtained by glycidylating biphenyls; epoxy resins obtained by glycidylating aromatic compounds having two hydroxyl groups, such as dihydroxynaphthalene and 9,9-bis(4-hydroxyphenyl)fluorene; epoxy resins obtained by glycidylating trisphenols, such as 1,1,1-tris(4-hydroxyphenyl)methane; epoxy resins obtained by glycidylating tetrakisphenols, such as 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane; novolac-type epoxy resins obtained by glycidylating novolacs, such as phenol novolac, cresol novolac, bisphenol A novolac, and brominated bisphenol A novolac; and silicone-containing epoxy resins, either alone or in combination.

[0075] (liquid epoxy resin) The thermosetting composition of the present invention preferably contains, as the thermosetting resin, an epoxy resin that is liquid at 25° C. (also referred to as a “liquid epoxy resin”). By including a liquid epoxy resin in the thermosetting composition of the present invention, the liquid epoxy resin can penetrate between the first inorganic fillers and eliminate the voids between the first inorganic fillers, thereby further improving the insulating properties of the thermosetting composition of the present invention.

[0076] The content of the liquid epoxy resin is preferably 5% by mass or more and 80% by mass or less relative to 100% by mass of the resin component obtained by excluding the inorganic filler from the solid content of the thermosetting composition of the present invention. A liquid epoxy resin content of 5% by mass or more is preferable because it can reduce voids in the thermosetting composition, and a liquid epoxy resin content of 80% by mass or less is preferable because it can prevent the resin composition before curing from becoming too brittle and collapsing when a large amount of filler is added. From this viewpoint, the content of the liquid epoxy resin is preferably 5% by mass or more, more preferably 8% by mass or more, and even more preferably 10% by mass or more, relative to 100% by mass of the resin component (solid content of the thermosetting composition of the present invention excluding the inorganic filler), while being preferably 80% by mass or less, more preferably 70% by mass or less, even more preferably 60% by mass or less, and even more preferably 50% by mass or less.

[0077] It is preferable to use a polyfunctional epoxy resin as the liquid epoxy resin. A polyfunctional epoxy resin is an epoxy resin that has two or more oxirane rings (epoxy groups) in the molecule. The addition of such a polyfunctional epoxy resin makes it possible to introduce highly polar oxirane rings (epoxy groups) at a high density, thereby enhancing the effects of physical interactions such as van der Waals forces and hydrogen bonds, and improving the adhesion between, for example, a cured product of the thermosetting composition of the present invention and a conductor. Furthermore, the addition of a polyfunctional epoxy resin increases the crosslink density, thereby increasing the storage modulus of the cured product of the thermosetting composition of the present invention. This allows the cured product of the thermosetting composition of the present invention to penetrate into the irregularities on the surface of the conductor (the adherend), thereby exerting a strong anchoring effect and improving the adhesion between the cured product of the thermosetting composition of the present invention and a conductor. On the other hand, the introduction of a polyfunctional epoxy resin tends to increase the hygroscopicity of the thermosetting composition of the present invention, but by improving the reactivity of the oxirane ring (epoxy group), the amount of hydroxyl groups during the reaction can be reduced, thereby suppressing the increase in hygroscopicity. Furthermore, by producing the thermosetting composition of the present invention by combining the above-mentioned high molecular weight epoxy resin and polyfunctional epoxy resin, it is possible to achieve both high elasticity and low hygroscopicity in the cured product of the thermosetting composition of the present invention.

[0078] The multifunctional epoxy resin is preferably an epoxy resin having two or more oxirane rings (epoxy groups) in the molecule, from the viewpoint of increasing the storage modulus of the cured product of the thermosetting composition of the present invention, particularly the storage modulus at high temperatures, which is important in applications such as power semiconductors that generate a large amount of heat. Of these, epoxy resins having three or more oxirane rings (epoxy groups) in the molecule are more preferred, and epoxy resins having four or more glycidyl groups in the molecule are even more preferred. Having multiple oxirane rings (epoxy groups), particularly glycidyl groups, in the molecule improves the crosslink density of the cured product of the thermosetting composition of the present invention, resulting in a higher strength of the resulting cured product. This prevents the cured product from deforming or breaking when internal stress is generated in the cured product during a moisture absorption reflow test, thereby preventing the formation of voids or other voids in the cured product.

[0079] Furthermore, from the viewpoint of increasing the storage modulus of the cured product of the thermosetting composition of the present invention, in order to increase the crosslink density, the molecular weight of the polyfunctional epoxy resin is preferably 800 or less, particularly 100 or more or 700 or less, more preferably 200 or more or 650 or less, even more preferably 200 or more or 600 or less, and even more preferably 200 or more or 550 or less. Furthermore, since an amine-based or amide-based structure is hydrophilic, the presence of such a structure tends to increase water absorption, and therefore, from the viewpoint of achieving lower moisture absorption and higher crosslinking, the polyfunctional epoxy resin is preferably a polyfunctional epoxy resin that does not contain an amine-based or amide-based structure.

[0080] The epoxy equivalent of the liquid polyfunctional epoxy resin is preferably 70 g / equivalent or more, more preferably 80 g / equivalent or more, and even more preferably 90 g / equivalent or more, from the viewpoint of suppressing the moisture absorption of the sheet, while from the viewpoint of maintaining the elastic modulus after curing, it is preferably 600 g / equivalent or less, more preferably 50 g / equivalent or less, even more preferably 400 g / equivalent or less, even more preferably 300 g / equivalent or less, and even more preferably 200 g / equivalent or less. The epoxy equivalent is defined as "the mass of an epoxy resin containing one equivalent of epoxy groups" and can be measured in accordance with JIS K7236.

[0081] Specific examples of the liquid epoxy resin include polyfunctional epoxy resins having three or more epoxy groups per molecule and a molecular weight of 800 or less, and particularly epoxy resins having four or more glycidyl groups per molecule. Examples of suitable polyfunctional epoxy resins include EX321L, DLC301, and DLC402 manufactured by Nagase ChemteX Corporation. These polyfunctional epoxy resins may be used alone or in combination of two or more.

[0082] When a high molecular weight epoxy resin and a polyfunctional epoxy resin are used in combination, from the viewpoint of improving the film-forming properties of the sheet and the elastic modulus of the cured product, the content of the polyfunctional epoxy resin is preferably 20 parts by mass or more and 300 parts by mass or less, more preferably 30 parts by mass or more and 250 parts by mass or less, and even more preferably 40 parts by mass or more and 200 parts by mass or less, per 100 parts by mass of the high molecular weight epoxy resin.

[0083] (High molecular weight epoxy resin) The thermosetting composition of the present invention preferably contains a polymer, that is, a polymer, having a mass average molecular weight of 10,000 or more, and a preferred example of such a polymer is a high molecular weight epoxy resin. Examples of the high molecular weight epoxy resin include phenoxy resins having at least one skeleton selected from the group consisting of a bisphenol A skeleton, a bisphenol F skeleton, a bisphenol A / F mixed skeleton, a naphthalene skeleton, a fluorene skeleton, a biphenyl skeleton, an anthracene skeleton, a pyrene skeleton, a xanthene skeleton, an adamantane skeleton, and a dicyclopentadiene skeleton.

[0084] Examples of the high molecular weight epoxy resin include epoxy resins having at least one structure selected from the structure represented by the following formula (1) (hereinafter, sometimes referred to as "structure (1)") and the structure represented by the following formula (2) (hereinafter, sometimes referred to as "structure (2)").

[0085] TIFF2025130241000001.tif71170

[0086] In formula (1), R 1 and R 2 each represents an organic group, at least one of which is an organic group having a molecular weight of 16 or more, and in formula (2), R 3 represents a divalent cyclic organic group.

[0087] The term "organic group" includes any group containing carbon atoms, and specific examples thereof include alkyl groups, alkenyl groups, and aryl groups, which may be substituted with halogen atoms, groups containing heteroatoms, or other hydrocarbon groups. The same applies hereinafter.

[0088] Furthermore, examples of high molecular weight epoxy resins include epoxy resins having a structure represented by the following formula (3) (hereinafter, sometimes referred to as "structure (3)").

[0089] TIFF2025130241000002.tif45170

[0090] In formula (3), R 4 , R 5 , R 6 , R 7represents an organic group with a molecular weight of 15 or more.

[0091] In the above formula (1), R 1 and R 2 At least one of R represents an organic group having a molecular weight of 16 or more, preferably a molecular weight of 16 to 1000, and examples thereof include alkyl groups such as ethyl, propyl, butyl, pentyl, hexyl, and heptyl groups, and aryl groups such as phenyl, tolyl, xylyl, naphthyl, and fluorenyl groups. 1 and R 2 may both be organic groups with a molecular weight of 16 or more, or one may be an organic group with a molecular weight of 16 or more and the other an organic group with a molecular weight of 15 or less or a hydrogen atom. Preferably, one is an organic group with a molecular weight of 16 or more and the other an organic group with a molecular weight of 15 or less, and in particular, one of them is a methyl group and the other a phenyl group, which is preferred from the viewpoints of facilitating control of handleability such as resin viscosity and of the strength of the cured product.

[0092] In the above formula (2), R 3 is a divalent cyclic organic group, and may be an aromatic ring structure such as a benzene ring structure, a naphthalene ring structure, or a fluorene ring structure, or an aliphatic ring structure such as cyclobutane, cyclopentane, or cyclohexane. These may each independently have a substituent such as a hydrocarbon group or a halogen atom. The divalent bond may be a divalent group on a single carbon atom or on different carbon atoms. Preferred examples include divalent aromatic groups having 6 to 100 carbon atoms and groups derived from cycloalkanes having 2 to 100 carbon atoms, such as cyclopropane and cyclohexane. In particular, a 3,3,5-trimethyl-1,1-cyclohexylene group represented by the following formula (4) (hereinafter sometimes referred to as "structure (4)") is preferred from the viewpoints of controlling handleability such as resin viscosity and strength of the cured product.

[0093] TIFF2025130241000003.tif44170

[0094] In the above formula (3), R 4 , R5 , R 6 , R 7 are each an organic group having a molecular weight of 15 or more. Preferably, they are alkyl groups having a molecular weight of 15 to 1000, and particularly preferably, R 4 , R 5 , R 6 , R 7 It is preferable that all of the groups be methyl groups from the viewpoint of controlling the handling properties such as the viscosity of the resin and the strength of the cured product.

[0095] The high molecular weight epoxy resin is preferably an epoxy resin containing either one of Structure (1) or Structure (2) and Structure (3), from the viewpoint of achieving both reduced moisture absorption and strength retention in the resulting cured heat dissipation sheet.

[0096] Compared to typical epoxy resins with bisphenol A or bisphenol F skeletons, these high molecular weight epoxy resins contain more hydrophobic hydrocarbon and aromatic structures, so by incorporating a high molecular weight epoxy resin, the moisture absorption of the resulting cured heat dissipation sheet can be reduced. Furthermore, from the viewpoint of reducing moisture absorption, it is preferable that the high molecular weight epoxy resin contains a large amount of structures (1), (2), and (3), which are hydrophobic structures. Specifically, it is preferable that the high molecular weight epoxy resin has a mass average molecular weight of 10,000 or more, more preferably an epoxy resin having a mass average molecular weight of 20,000 or more, and even more preferably an epoxy resin having a mass average molecular weight of 30,000 or more, for example, 30,000 to 40,000.

[0097] Furthermore, it is preferable that the high molecular weight epoxy resin is more hydrophobic, and from this viewpoint, the epoxy equivalent of the epoxy component is preferably large, specifically, 5,000 g / equivalent or more is preferable, 7,000 g / equivalent or more is more preferable, for example, 8,000 g / equivalent or more and 15,000 g / equivalent or less is more preferable.

[0098] The mass average molecular weight of the epoxy resin is a value calculated as polystyrene measured by gel permeation chromatography. The epoxy equivalent is defined as "the mass of an epoxy resin containing one equivalent of epoxy groups" and can be measured in accordance with JIS K7236.

[0099] Such high molecular weight epoxy resins may be used alone or in combination of two or more.

[0100] The content of the high molecular weight epoxy resin is preferably 10% by mass or more and less than 30% by mass relative to 100% by mass of the resin component obtained by excluding the inorganic filler from the solid content of the thermosetting composition of the present invention. A content of high molecular weight epoxy resin of 10% by mass or more is preferred because it maintains the inorganic filler retention and film-forming properties, and a content of less than 30% by mass is preferred because it maintains the strength when cured. From this viewpoint, the content of the high molecular weight epoxy resin is preferably 10% by mass or more and less than 30% by mass, more preferably 13% by mass or more or 29% by mass or less, and even more preferably 15% by mass or more or 28% by mass or less, relative to 100% by mass of the resin component (solid content of the thermosetting composition of the present invention excluding the inorganic filler).

[0101] <Polymer> The thermosetting composition of the present invention may contain, as necessary, another polymer having a mass average molecular weight of 10,000 or more in place of or together with the high molecular weight epoxy resin. Such polymers can serve as a resin matrix component or a binder resin component in the thermosetting composition of the present invention.

[0102] The polymer may be either a thermoplastic resin or a thermosetting resin. Examples of the thermoplastic resins and thermosetting resins include thermoplastic resins such as polyphenylene ether, polyphenylene sulfide, polyarylate, polysulfone, polyether sulfone, polyether ether ketone, and polyether ketone. Furthermore, the thermoplastic resins and thermosetting resins may also include heat-resistant resins known as super engineering plastics, such as thermoplastic polyimide, thermosetting polyimide, benzoxazine, and reaction products of polybenzoxazole and benzoxazine. Other examples include styrene-based polymers such as styrene and alkylstyrene, (meth)acrylic polymers such as alkyl (meth)acrylate and glycidyl (meth)acrylate, styrene-based-(meth)acrylic copolymers such as styrene-glycidyl methacrylate, polyvinyl alcohol derivatives such as polyvinyl butyral, polyvinyl benzal, and polyvinyl acetal, norbornene-based polymers containing norbornene compounds, and phenoxy resins. Among these, phenoxy resins are preferred in terms of heat resistance and compatibility with thermosetting resins. The thermoplastic resin and the thermosetting resin may each be used alone or in combination of two or more thereof. Either a thermoplastic resin or a thermosetting resin may be used alone, or a thermoplastic resin and a thermosetting resin may be used in combination.

[0103] The content of the polymer having a mass average molecular weight of 10,000 or more (when used in combination with a high molecular weight epoxy resin, this also includes the high molecular weight epoxy resin) is preferably 10 mass % or more and less than 30 mass % relative to 100 mass % of the resin component calculated by excluding the inorganic filler from the solid content of the thermosetting composition of the present invention. By including the polymer in an amount of 10% by mass or more, the retention of the inorganic filler and film-forming properties are maintained, and by including the polymer in an amount of less than 30% by mass, the strength upon curing can be maintained, which is preferable. From this viewpoint, the content of the polymer is preferably 10% by mass or more, more preferably 13% by mass or more, and even more preferably 15% by mass or more, relative to 100% by mass of the resin component (solid content of the thermosetting composition of the present invention excluding the inorganic filler), and is preferably less than 30% by mass, and even more preferably less than 29% by mass.

[0104] <Curing agent> The thermosetting composition of the present invention may contain a curing agent, if necessary. Examples of the curing agent include phenolic resins, compounds having a heterocyclic structure containing a nitrogen atom (hereinafter sometimes referred to as "nitrogen-containing heterocyclic compounds"), acid anhydrides having an aromatic skeleton or an alicyclic skeleton, hydrides of the acid anhydrides, or modified products of the acid anhydrides. Only one type of curing agent may be used, or two or more types may be used in combination. By using these preferred curing agents, it is possible to obtain a cured resin product that has an excellent balance of heat resistance, moisture resistance, and electrical properties.

[0105] Examples of the phenolic resin include phenol novolac, o-cresol novolac, p-cresol novolac, t-butylphenol novolac, dicyclopentadiene cresol, polyparavinylphenol, bisphenol A novolac, xylylene-modified novolac, decalin-modified novolac, poly(di-o-hydroxyphenyl)methane, poly(di-m-hydroxyphenyl)methane, poly(di-p-hydroxyphenyl)methane, etc. Among these, novolac-type phenolic resins having a rigid main chain skeleton and phenolic resins having a triazine skeleton are preferred in order to further improve the flexibility and flame retardancy of the thermosetting composition and to improve the mechanical properties and heat resistance of the cured resin. Furthermore, in order to improve the flexibility of the uncured thermosetting composition and the toughness of the cured resin, a phenolic resin having an allyl group is preferred.

[0106] Examples of the heterocyclic structure of the nitrogen-containing heterocyclic compound include structures derived from imidazole, triazine, triazole, pyrimidine, pyrazine, pyridine, and azole. From the viewpoint of improving the insulating properties and adhesion to metals of the thermosetting composition, imidazole-based compounds and triazine-based compounds are preferred. Preferable imidazole compounds and triazine compounds include, for example, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 2-phenyl-4-methylimidazole, 1-cyanoethyl-2-phenylimidazolium trimellitate, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-undecylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-ethyl 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanuric acid adduct, 2-phenylimidazole isocyanuric acid adduct, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2,4-diamino-6-vinyl-s-triazine, 2,4-diamino-6-vinyl-s-triazine isocyanuric acid adduct, 2,4-diamino-6-methacryloyloxyethyl-s-triazine, 2,4-diamino-6-methacryloyloxyethyl-s-triazine isocyanuric acid adduct, and the like can be mentioned.

[0107] Among these, those having a structure derived from imidazole or triazine are particularly preferred, since their high resin compatibility and high reaction activation temperature allow for easy adjustment of the curing rate and post-curing physical properties, thereby improving the storage stability of the thermosetting composition of the present invention and further improving the adhesive strength after heat molding. As the heterocyclic structure of the nitrogen-containing heterocyclic compound, a structure derived from 1,3,5-triazine is particularly preferred. Furthermore, the compound may have a plurality of these exemplified structural moieties.

[0108] Depending on the structure, the nitrogen-containing heterocyclic compound may contain a curing catalyst, which will be described later. Therefore, the thermosetting composition of the present invention may contain a nitrogen-containing heterocyclic compound as a curing catalyst. The nitrogen-containing heterocyclic compound may be used alone or in combination of two or more kinds, and may have multiple heterocyclic structures simultaneously in one molecule. The molecular weight of the nitrogen-containing heterocyclic compound is preferably 1,000 or less, and more preferably 500 or less.

[0109] The acid anhydride having an aromatic skeleton, the hydrate of the acid anhydride, or the modified product of the acid anhydride is not particularly limited.

[0110] The acid anhydride having an alicyclic skeleton, a hydrate of the acid anhydride, or a modified product of the acid anhydride is preferably an acid anhydride having a polyalicyclic skeleton, a hydrate of the acid anhydride, or a modified product of the acid anhydride, or an acid anhydride having an alicyclic skeleton obtained by an addition reaction of a terpene compound with maleic anhydride, a hydrate of the acid anhydride, or a modified product of the acid anhydride.

[0111] The curing agent is preferably contained in a proportion of 0 to 70% by mass, particularly 0 to 55% by mass, based on 100% by mass of the thermosetting composition of the present invention excluding the solvent and inorganic filler. When the content of the curing agent is equal to or greater than the lower limit, sufficient curing performance can be obtained, while when the content is equal to or less than the upper limit, the reaction proceeds effectively, improving crosslink density, increasing strength, and further improving film formability.

[0112] <Curing accelerator> The thermosetting composition of the present invention may contain a curing catalyst as a curing accelerator, if necessary, in order to adjust the curing rate and the physical properties of the cured product.

[0113] It is preferable to select the curing catalyst appropriately depending on the type of thermosetting resin component and curing agent. Specific examples of the curing catalyst include linear or cyclic tertiary amines, organophosphorus compounds, diazabicycloalkenes such as quaternary phosphonium salts or organic acid salts, and imidazoles. Also usable are organometallic compounds, quaternary ammonium salts, and metal halides. Examples of the organometallic compounds include zinc octoate, tin octoate, and aluminum acetylacetone complexes. These may be used alone or in combination of two or more.

[0114] Among these, imidazoles are preferred, particularly from the viewpoints of storage stability, heat resistance, and curing speed. Preferred imidazole compounds include, for example, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 2-phenyl-4-methylimidazole, 1-cyanoethyl-2-phenylimidazolium trimellitate, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine, 2, Examples include 4-diamino-6-[2'-undecylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-ethyl-4'methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanuric acid adduct, 2-phenylimidazole isocyanuric acid adduct, 2-phenyl-4,5-dihydroxymethylimidazole, and 2-phenyl-4-methyl-5-hydroxymethylimidazole. In particular, by using an imidazole compound having a melting point of 100° C. or higher, more preferably 200° C. or higher, a cured product with excellent storage stability and adhesion can be obtained. Furthermore, from the viewpoint of adhesion, those containing a nitrogen-containing heterocyclic compound other than the above-mentioned imidazole ring are more preferred.

[0115] The curing catalyst is preferably contained in a proportion of 0.1 to 10% by mass, particularly 0.1 to 5% by mass, based on 100% by mass of the thermosetting composition of the present invention excluding the solvent and inorganic filler. When the content of the curing catalyst is equal to or greater than the lower limit, the progress of the curing reaction can be sufficiently promoted to achieve good curing, while when the content is equal to or less than the upper limit, the curing rate is not too fast, and therefore the storage stability of the thermosetting composition of the present invention can be improved.

[0116] <Organic solvents> The thermosetting composition of the present invention may contain an organic solvent, if necessary, for example, to improve the coating properties when the composition is subjected to a coating step to form a sheet-like cured product. Examples of organic solvents that may be contained in the thermosetting composition of the present invention include, but are not limited to, methyl ethyl ketone, cyclohexanone, propylene glycol monomethyl ether acetate, butyl acetate, isobutyl acetate, and propylene glycol monomethyl ether. These organic solvents may be used alone or in combination of two or more.

[0117] When the thermosetting composition of the present invention contains an organic solvent, the content thereof is appropriately determined depending on the handleability during sheet production, etc. Usually, the organic solvent is preferably used so that the solids concentration (total of components other than the solvent) in the thermosetting composition of the present invention is 10% by mass or more and 90% by mass or less, particularly 40% by mass or more or 80% by mass or less. When the thermosetting composition is formed into a sheet, the organic solvent is preferably used so that the solid content (total of components other than the solvent) in the thermosetting composition of the present invention is 95% by mass or more, more preferably 97% by mass or more, even more preferably 98% by mass or more, and even more preferably 99% by mass or more.

[0118] <Other ingredients> The thermosetting composition of the present invention may contain other components in addition to the above components. Examples of such other components include, but are not limited to, dispersants, additives such as silane coupling agents that improve the interfacial adhesion strength between thermoplastic resins, organic fillers, and inorganic fillers and resin components, additives that are expected to increase the adhesion strength between the cured product of the thermosetting composition of the present invention and a metal plate, insulating carbon components such as reducing agents, viscosity modifiers, thixotropic agents, flame retardants, colorants, various antioxidants such as phosphorus-based and phenol-based, phenol acrylate-based and other process stabilizers, heat stabilizers, hindered amine radical scavengers (HAAS), impact modifiers, processing aids, metal deactivators, copper inhibitors, antistatic agents, and extenders. When these additives are used, the amount added may be within the range of the amount normally used for the purpose.

[0119] <Physical Properties of the Thermosetting Composition of the Present Invention> The thermosetting composition of the present invention, when formed into a sheet and cured, can have a thermal conductivity in the thickness direction of 14 W / m K or more, preferably 15 W / m K or more, and more preferably 16 W / m K or more.

[0120] <<Uses of the thermosetting composition of the present invention>> The thermosetting composition of the present invention can be used in a variety of applications where thermal conductivity is required.

[0121] <Thermosetting sheets and thermally conductive sheets> A thermally conductive sheet according to one embodiment of the present invention (referred to as "the present thermally conductive sheet") may be a sheet that is a cured product of a thermosetting sheet (referred to as "the present thermosetting sheet") formed from the thermosetting composition of the present invention.

[0122] The thermosetting sheet of the present invention is a sheet that has the property of being cured by heat, and may be a sheet that has the property of being cured by heat while still having room to be cured, and may be a sheet that has already been cured to a state where there is still room to be cured (also referred to as "pre-cured"), or may be a sheet that has not yet been cured at all (referred to as "uncured"). Thus, the thermosetting sheet may be a sheet formed from the thermosetting composition of the present invention, or may be a sheet made from a cured product that has been cured so that there is still room to be cured.

[0123] The thermal conductivity of the thermally conductive sheet in the thickness direction at 25°C is preferably 14 W / m·K or more, more preferably 15 W / m·K or more, and even more preferably 17 W / m·K or more. When the thermal conductivity of the thermal conductive sheet in the thickness direction is equal to or greater than the above lower limit, the sheet can be suitably used in power semiconductor devices that operate at high temperatures. The thermal conductivity can be adjusted by the type of thermosetting resin and its physical properties such as melt viscosity, the type and content of the first inorganic filler, the method of mixing the thermosetting resin and the first inorganic filler, and the conditions in the heating and kneading process described below.

[0124] The thermal conductivity of the thermally conductive sheet in the thickness direction can be measured by the following method. For example, a thermal resistance measuring device (manufactured by Mentor Graphics Corporation, product name "T3ster") can be used to measure the thermal resistance of sheets of different thicknesses made under the same composition and conditions, and the thermal conductivity can be calculated from the slope of the graph plotting the thermal resistance against the thickness.

[0125] The lower limit of the thickness of the thermally conductive sheet is preferably 50 μm or more, more preferably 60 μm or more, and even more preferably 70 μm or more, while the upper limit is preferably 400 μm or less, more preferably 300 μm or less, and even more preferably 250 μm or less. By making the thickness of this thermally conductive sheet 50 μm or more, sufficient voltage resistance characteristics can be ensured. On the other hand, by making the thickness 400 μm or less, it is possible to achieve miniaturization and thinning, especially when using this thermally conductive sheet in power semiconductor devices, and it is also possible to obtain the effect of reducing thermal resistance in the thickness direction by making the thickness thinner compared to insulating thermally conductive layers made of ceramic materials.

[0126] <Method for manufacturing thermally conductive sheets> An example of a method for producing the thermally conductive sheet will now be described.

[0127] The present thermally conductive sheet can be produced by forming the thermosetting composition of the present invention into a sheet to produce the present thermosetting sheet (this process is referred to as the "film-forming process"), drying it as needed (this process is referred to as the "drying process"), cutting the present thermosetting sheet to a predetermined size as needed (this process is referred to as the "cutting process"), and further applying pressure as needed (this process is referred to as the "pressuring process"), and then curing the present thermosetting sheet (this process is referred to as the "curing process").

[0128] (Film forming process) For example, the thermosetting composition of the present invention in a slurry state can be formed into a sheet by a coating method such as a blade method, a solvent casting method, or an extrusion film forming method, to form the present thermosetting sheet.

[0129] When forming a sheet-like film by the above coating method, a coating film is formed by first coating the surface of a substrate with the thermosetting composition of the present invention in a slurry form, i.e., by dipping, spin coating, spray coating, blade coating, or any other method using the thermosetting composition of the present invention in a slurry form on the substrate. The thermosetting composition of the present invention in a slurry form can be applied using a coating device such as a spin coater, a slit coater, a die coater, a blade coater, etc. Such a coating device makes it possible to form a coating film of a predetermined thickness uniformly on a substrate. As the substrate, a copper plate or copper foil or a PET film, as described below, is generally used, but there is no limitation thereto. However, the film formation method is not limited to the above.

[0130] (drying process) The thermosetting composition of the present invention formed into a sheet as described above, i.e., the present thermosetting sheet, is dried at a temperature generally in the range of 10°C to 150°C, preferably in the range of 25°C to 120°C, and more preferably in the range of 30°C to 110°C, in order to remove the solvent and low-molecular-weight components. When the drying temperature is equal to or lower than the upper limit, curing of the resin in the thermosetting composition of the present invention is suppressed, and the resin in the sheet-shaped resin composition tends to flow in the subsequent pressurizing step, making it easier to remove voids.When the drying temperature is equal to or higher than the lower limit, the solvent can be effectively removed, and productivity tends to improve. The drying time is not particularly limited, and is preferably adjusted appropriately depending on the state of the thermosetting composition of the present invention, the drying environment, etc. The drying time is preferably 1 minute or more, more preferably 2 minutes or more, and even more preferably 5 minutes or more. The drying time is preferably 24 hours or less, more preferably 10 hours or less, even more preferably 4 hours or less, and particularly preferably 2 hours or less. When the drying time is equal to or greater than the lower limit, the solvent can be sufficiently removed, and the residual solvent tends to be prevented from forming voids in the cured resin. When the drying time is equal to or less than the upper limit, productivity tends to be improved, and production costs tend to be reduced.

[0131] (Cutting process) If necessary, the thermosetting sheet may be rolled up, unwound, and cut to a predetermined size using a cutter or the like.

[0132] (Pressure process) After the drying step, it is desirable to apply pressure to the obtained sheet-like thermosetting composition of the present invention, i.e., the present thermosetting sheet, for the purposes of bonding the first inorganic fillers together to form heat conduction paths, eliminating voids and gaps in the sheet, improving adhesion to the substrate, etc. However, depending on the purpose, pressure may not be applied.

[0133] In the pressing step, it is desirable to apply a load of 2 MPa or more to the thermosetting sheet on the substrate. The load is preferably 5 MPa or more, more preferably 7 MPa or more, and even more preferably 9 MPa or more. The load is preferably 1500 MPa or less, more preferably 1000 MPa or less, and even more preferably 800 MPa or less. By setting the load during pressing to the above upper limit or less, the first inorganic filler will not be destroyed, and the thermosetting sheet can be obtained with high thermal conductivity and no voids, etc. By setting the load to the above lower limit or more, good contact between the first inorganic filler particles is achieved, making it easier to form thermal conduction paths, and a cured resin product with high thermal conductivity can be obtained.

[0134] The heating temperature of the thermosetting sheet on the substrate in the pressing step is not particularly limited. The heating temperature is preferably 10°C or higher, more preferably 20°C or higher, and even more preferably 30°C or higher. The heating temperature is preferably 300°C or lower, more preferably 250°C or lower, even more preferably 200°C or lower, even more preferably 100°C or lower, and particularly preferably 90°C or lower. By carrying out the pressure step within this temperature range, the melt viscosity of the resin in the thermosetting sheet can be reduced, further reducing voids and gaps in the cured resin. Furthermore, heating at or below the upper limit of the above range tends to suppress decomposition of organic components in the thermosetting sheet and its cured product, as well as voids caused by residual solvent.

[0135] The time for the pressurizing step is not particularly limited. The time for the pressurizing step is preferably 30 seconds or more, more preferably 1 minute or more, even more preferably 3 minutes or more, and particularly preferably 5 minutes or more. The time for the pressurizing step is preferably 1 hour or less, more preferably 30 minutes or less, and even more preferably 20 minutes or less. By keeping the pressurizing time at or below the upper limit, the production time for the cured resin can be reduced, which tends to reduce production costs.By keeping the pressurizing time at or above the lower limit, voids and gaps in the cured resin can be sufficiently removed, which tends to improve heat transfer performance and voltage resistance characteristics.

[0136] (hardening process) The thermosetting sheet is then heated to cure. In this case, the heating temperature is preferably 30° C. or higher and 400° C. or lower, more preferably 50° C. or higher, and even more preferably 90° C. or higher. On the other hand, it is preferably 300° C. or lower, and even more preferably 250° C. or lower.

[0137] The curing step for completely curing the thermosetting sheet may be carried out under pressure or without pressure. When pressure is applied, it is desirable to carry out the step under the same conditions as the pressure application step for the same reasons as above. The pressure application step and the curing step may be carried out simultaneously. In particular, in the sheet forming process which involves a pressing step and a curing step, it is preferable to apply a load within the above range to carry out pressing and curing.

[0138] The load applied when the pressing step and the curing step are performed simultaneously is not particularly limited. In this case, the thermosetting sheet is preferably subjected to a load of 5 MPa or more, more preferably 7 Pa or more, even more preferably 9 MPa or more, and particularly preferably 20 MPa or more. The load is preferably 2000 MPa or less, more preferably 1500 MPa or less. By setting the load when the pressing step and curing step are performed simultaneously to the above upper limit or less, the first inorganic filler will not be destroyed, and a sheet-like cured product having high thermal conductivity and no voids in the thermosetting sheet can be obtained. Furthermore, by setting the load to the above lower limit or more, good contact between the first inorganic filler particles is achieved, making it easier to form thermal conduction paths, and a cured resin product having high thermal conductivity can be obtained.

[0139] When the pressing step and the curing step are carried out simultaneously, the pressing time is not particularly limited. The pressing time is preferably 30 seconds or more, more preferably 1 minute or more, even more preferably 3 minutes or more, and particularly preferably 5 minutes or more. On the other hand, the pressing time is preferably 1 hour or less, more preferably 30 minutes or less, and even more preferably 20 minutes or less. By keeping the pressing time at or below the upper limit, the time required to produce a sheet-shaped cured resin product can be reduced, which tends to reduce production costs.By keeping the pressing time at or above the lower limit, voids and gaps in the sheet-shaped cured resin product can be sufficiently removed, which tends to improve heat transfer performance and voltage resistance characteristics.

[0140] <<Composite molded body>> A composite molded article according to one embodiment of the present invention (referred to as "the present composite molded article") is a composite molded article having the present thermosetting sheet or thermally conductive sheet and a metal part. Next, as examples of the present composite molded article, a heat dissipating laminate, a heat dissipating circuit board, and a semiconductor device will be described, although the present composite molded article is not limited to these.

[0141] <<Heat dissipation laminate>> A heat dissipation laminate according to one embodiment of the present invention (referred to as "the present heat dissipation laminate") may be a laminate including a cured product of the thermosetting composition of the present invention, for example, the present thermally conductive sheet.

[0142] An example of the present heat dissipation laminate is one in which a heat dissipation metal layer containing a heat dissipation material is laminated on one surface of the present heat conductive sheet.

[0143] The heat dissipating material is not particularly limited as long as it is made of a material with good thermal conductivity. In particular, in order to increase the thermal conductivity in the laminated structure, it is preferable to use a heat dissipating metal material, and it is more preferable to use a flat metal material. The metal material is not particularly limited, but among them, copper plate, aluminum plate, aluminum alloy plate, etc. are preferred because they have good thermal conductivity and are relatively inexpensive.

[0144] The thermally conductive sheet and the heat-dissipating metal layer can be laminated and integrated by press molding, which is a batch process. In this case, the press equipment and press conditions are the same as those for obtaining the thermally conductive sheet.

[0145] <<Heat dissipation circuit board>> A heat dissipating circuit board according to one embodiment of the present invention (referred to as "the present heat dissipating circuit board") may be any circuit board provided with a cured product of the thermosetting composition of the present invention, such as the present thermally conductive sheet. An example of the present heat dissipating circuit board is one having a configuration in which the above-mentioned heat dissipating metal layer is laminated on one surface of the present heat conductive sheet, and a circuit board is formed on the surface of the heat conductive sheet opposite the heat dissipating metal layer, for example, by etching or the like. Specifically, an integrated structure of "heat dissipation metal layer / thermal conductive sheet / conductive circuit" is more preferable. The state before the circuit etching is, for example, an integrated structure of "heat dissipation metal layer / thermal conductive sheet / conductive circuit forming metal layer", in which the conductive circuit forming metal layer is flat and formed on the entire surface of one side of the thermal conductive sheet, or on a partial area.

[0146] The material of the conductive circuit-forming metal layer is not particularly limited, but it is generally preferable to form it from a copper thin plate having a thickness of 0.05 mm to 1.2 mm in terms of electrical conductivity, etching properties, cost, etc.

[0147] <<Semiconductor Devices>> A semiconductor device according to an example of an embodiment of the present invention (hereinafter referred to as "the present semiconductor device") may be any device that includes the present heat dissipation circuit board. An example of the present semiconductor device is one having a configuration in which a silicon wafer or a rewiring layer on which pre-diced semiconductor chips are mounted is formed on the present heat dissipation circuit substrate.

[0148] <<Power module>> A power module according to one embodiment of the present invention (referred to as "the present power module") may be any module provided with a cured product of the thermosetting composition of the present invention, such as the present thermally conductive sheet. An example of the power module of the present invention is one in which the thermally conductive sheet is mounted on a power semiconductor device as a heat dissipating circuit board. In this power semiconductor device, conventionally known materials can be appropriately used for the aluminum wiring, sealing material, packaging material, heat sink, thermal paste, solder, and other materials other than the thermally conductive sheet.

[0149] <<Explanation of terms>> In the present invention, when the expression "X to Y" (X and Y are any numbers) is used, unless otherwise specified, it means "X or more and Y or less," as well as "preferably larger than X" or "preferably smaller than Y." Furthermore, when it is expressed as "X or more" (X is any number) or "Y or less" (Y is any number), it also includes the intention that "it is preferable that it is greater than X" or "it is preferable that it is less than Y." In the present invention, the term "sheet" conceptually encompasses sheets, films, and tapes. [Example]

[0150] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to the following examples as long as the gist of the present invention is not exceeded.

[0151] <Materials used> The materials used in the examples and comparative examples are as follows.

[0152] (thermosetting resin) High molecular weight epoxy resin A: a bifunctional epoxy polymer disclosed in JP-A-6497292, having the structures of the above formulas (1), (2), and (3). Polystyrene-equivalent weight average molecular weight: 40,000, epoxy equivalent: 11,000 g / equivalent Aromatic epoxy resin B: Mitsubishi Chemical Corporation, biphenyl-type epoxy compound. Does not contain amine or amide structures. Epoxy equivalent: 200 g / equivalent, molecular weight approximately 400, solid at 25°C. Liquid Epoxy Resin C: Nagase Chemtec Corporation, a multifunctional epoxy resin containing four or more glycidyl groups per molecule. It does not contain amine or amide structures containing nitrogen atoms. Molecular weight: approximately 400, epoxy equivalent: 100 g / equivalent, liquid at 25°C.

[0153] (inorganic filler) First inorganic filler D: spherical boron nitride agglomerates having a house-of-cards structure manufactured in accordance with International Publication No. 2015 / 119198 (average particle diameter (D50) 45 μm, primary particle length 2.4 μm, BET specific surface area 4.5 μm) 2 / g Nano alumina particles E: Primary particle diameter 13 nm, primary particle shape is spherical, BET specific surface area 100 m 2 / g, compacted bulk density 50g / L, no surface treatment.

[0154] (Other ingredients) Hardener F: Phenolic resin hardener "MEH-8000H" (manufactured by Meiwa Kasei Co., Ltd.) Curing accelerator G: 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-17')]-ethyl-s-triazine ("2E4MZ-A", manufactured by Shikoku Chemicals Corporation, a compound having a triazine ring as a heterocyclic structure containing a nitrogen atom. Molecular weight: 247), melting point: 215-225°C Curing accelerator H: 2-phenyl-4,5-dihydroxymethylimidazole (Shikoku Chemicals Corporation "2PHZ-PW"), melting point: 230°C or higher (decomposes at 230°C) Organic solvent: Mixture of methyl ethyl ketone and cyclohexanone

[0155] The average particle diameter (D50) of the particles of the first inorganic filler D is the cumulative volume 50% particle diameter (average particle diameter D50) calculated from the particle size distribution obtained by dispersing the first inorganic filler in a pure water medium containing sodium hexametaphosphate as a dispersion stabilizer, measuring the volume-based particle size distribution using a laser diffraction / scattering particle size distribution analyzer LA-300 (manufactured by Horiba, Ltd.). The primary particle length of the first inorganic filler D is a value determined by SEM. The BET specific surface area of ​​the first inorganic filler D is a value determined by the BET single-point method (adsorption gas: nitrogen). The primary particle diameter of the nano alumina particles E is a value determined using a transmission electron microscope. The BET specific surface area of ​​the nano alumina particles E is a value determined by the BET one-point method (adsorption gas: nitrogen).

[0156] <Examples 1 to 4, Comparative Examples 1 and 2> Using a planetary stirring device, high molecular weight epoxy resin A, aromatic epoxy resin B, multifunctional epoxy resin C, first inorganic filler D, nanoalumina particles E, curing agent F, curing accelerator G, and curing accelerator H were added to and mixed with an organic solvent consisting of methyl ethyl ketone and cyclohexanone in the mass ratios shown in Table 1 to prepare a resin composition as a coating slurry. At this time, methyl ethyl ketone and cyclohexanone were used so that the solids concentration would be 65 mass%. The obtained coating slurry (slurry for sheet) was applied to a PET substrate by the doctor blade method, and then dried by heating at 60° C. for 120 minutes to obtain a sheet-like molded product (sample) having a thickness of 150 μm.

[0157] <Evaluation> The sheet-like molded articles obtained in the above Examples and Comparative Examples were evaluated as follows.

[0158] (Evaluation of brittleness of sheet-shaped molded body (before hardening)) The sheet-like molded articles (before curing) obtained in the above Examples and Comparative Examples were cut with scissors, and the cut cross sections were observed to evaluate brittleness according to the following criteria. × (fail): Cracks were observed in three or more places on the cross section. △ (pass): One or two cracks were observed on the cross section. ◯ (pass): No cracks were observed on the cross section.

[0159] (Thermal conductivity (λ) of the sheet-shaped molded body (after curing) in the thickness direction) The sheet-like molded bodies (samples) produced in the examples and comparative examples were heated and cured under pressure at 175° C. for 30 minutes to obtain cured sheet-like molded bodies (samples) having a thickness of 150 μm. In addition to one sheet of this cured sheet-like molded product (sample), four types of sheets with different thicknesses were prepared by stacking two to four of these cured sheet-like molded products (samples). Measurements were carried out under the following conditions (1) to (4), and the thermal conductivity at 25°C in the sheet thickness direction was measured using a steady-state method from the slope represented by the thermal resistance value relative to the sheet thickness (in accordance with ASTM D5470). The probe size during measurement was φ12.8 mm, the fixing pressure was 3400 kPa, and the measurement time was 300 seconds. To improve the adhesion between the sample and the probe, Shin-Etsu Chemical Co., Ltd.'s "OIL COMPOUND (product name: G-747)" was used.

[0160] (1) Thickness: Thickness (μm) when pressed at a pressure of 3400 kPa using a Mentor Graphics T3Ster-DynTIM. (2) Measurement area: The area (cm) of the heat transfer part when measuring using a Mentor Graphics T3Ster-DynTIM. 2 ) (3) Thermal resistance: Thermal resistance (K / W) when pressed at a pressure of 3400 kPa using a Mentor Graphics T3Ster-DynTIM. (4) Thermal conductivity: The thermal resistance of four sheets with different thicknesses was measured, and the thermal conductivity (W / m·K) was calculated using the following formula. Formula: Thermal conductivity (W / m K) = 1 / ((Slope (thermal resistance value / thickness): K / (W μm)) × (area: cm 2 ))×10 -2

[0161] [Table 1]

[0162] From the above examples and the results of tests conducted by the inventors up to now, it has been found that by adding a predetermined amount of alumina particles having a primary particle diameter of 1 nm or more and less than 100 nm to a thermosetting composition containing an inorganic filler and a thermosetting resin, even if the content of the inorganic filler is relatively high, the brittleness in the state before curing can be improved, chipping or cracking can be suppressed when cut, and a decrease in thermal conductivity can be suppressed. Furthermore, it was found that even when the material contains a thermosetting resin that is liquid at room temperature, it is possible to improve the brittleness of the material before it hardens, prevent chipping or cracking when cut, and still prevent a decrease in thermal conductivity.

Claims

1. A thermosetting composition containing an inorganic filler and a thermosetting resin, a thermosetting composition comprising two or more types of inorganic fillers, wherein the content of one type of inorganic filler (referred to as a "first inorganic filler") is 60% by mass or more and 85% by mass or less of the solid content of the thermosetting composition, and another type of inorganic filler (referred to as a "second inorganic filler") is alumina particles having a primary particle diameter of 1 nm or more and less than 100 nm, and the content of the second inorganic filler is 0.01% by mass or more and 10% by mass or less of the solid content of the thermosetting composition.

2. The BET specific surface area of ​​the second inorganic filler is 20 m ２ / g or more 500m ２ The thermosetting composition of claim 1 , wherein the viscosity is 1 / g or less.

3. The thermosetting composition according to claim 1 , wherein the content of the second inorganic filler is 0.1% by mass or more and 5% by mass or less of the solid content in the thermosetting composition.

4. The thermosetting composition of claim 1 , wherein the first inorganic filler is agglomerated boron nitride particles.

5. The thermosetting composition according to claim 1 , wherein the first inorganic filler has an average particle size of 10 μm or more and 100 μm or less.

6. The thermosetting composition according to claim 1 , wherein a ratio of a BET specific surface area of ​​the second inorganic filler to a BET specific surface area of ​​the first inorganic filler is 6 or more and 150 or less.

7. The thermosetting composition according to claim 1 , wherein a ratio of a primary particle diameter of the second inorganic filler to a primary particle major diameter of the first inorganic filler is 0.001 or more and 0.01 or less.

8. The thermosetting composition according to claim 1 , wherein a ratio of a primary particle size of the second inorganic filler to an average particle size of the first inorganic filler is 0.0001 or more and 0.001 or less.

9. The thermosetting composition according to claim 1 , wherein the thermosetting resin comprises an epoxy resin that is liquid at 25° C.

10. 10. The thermosetting composition according to claim 9, wherein the content of the liquid epoxy resin is 8% by mass or more and 60% by mass or less of the resin component obtained by excluding the inorganic filler from the solid content of the thermosetting composition.

11. The thermosetting composition according to claim 1 , wherein the thermosetting resin comprises a multifunctional epoxy resin having three or more epoxy groups per molecule and a molecular weight of 800 or less.

12. 12. The thermosetting composition of claim 11, wherein the multifunctional epoxy resin has four or more glycidyl groups per molecule.

13. The thermosetting composition according to claim 9 , wherein the liquid epoxy resin comprises a multifunctional epoxy resin having three or more epoxy groups per molecule and a molecular weight of 800 or less.

14. 14. The thermosetting composition of claim 13, wherein the multifunctional epoxy resin has four or more glycidyl groups per molecule.

15. The thermosetting composition according to claim 1 , wherein the thermosetting resin comprises a polymer compound having a molecular weight of 10,000 or more.

16. A thermosetting sheet comprising the thermosetting composition according to any one of claims 1 to 15.

17. A thermally conductive sheet comprising a cured product of the thermosetting sheet according to claim 16.

18. A composite molded article comprising the thermosetting sheet according to claim 16 and a metal part.

19. A composite molded product comprising the thermally conductive sheet according to claim 17 and a metal part.

20. A heat dissipation laminate, a heat dissipation circuit board, a semiconductor device, or a power module, comprising the thermally conductive sheet according to claim 17.

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