JP2023102284A - Heat-conductive resin composition, heat-conductive resin sheet, heat dissipation laminate, heat dissipation circuit board, semiconductor device, and power module - Google Patents

Abstract

To provide a heat-conductive resin composition which can suppress unevenness of a coating surface, that is, a resin sheet surface, even when a content of boron nitride aggregated particles is increased to a certain degree in order to further improve heat conductivity.SOLUTION: Provided is a heat-conductive resin composition comprising a heat-curable resin, heat-conductive filler, and silica nanoparticles, wherein an average particle diameter of the silica nanoparticles in 1 nm to 100 nm, a content of the silica nanoparticles is more than 2.5 mass% and equal to or less than 10 mass% relative to 100 mass% of a total solid content of the heat-conductive resin composition, the heat-conductive filler includes boron nitride aggregated particles, an average particle diameter of the aggregated particles is 5 μm to 100 μm, and a content of the heat-conductive filler is 60 mass% to 85 mass% relative to 100 mass% of the total solid content of the heat-conductive resin composition.SELECTED DRAWING: None

Description

The present invention relates to a thermally conductive resin composition having thermal conductivity, a thermally conductive resin sheet formed from the composition, a heat-dissipating laminate, a heat-dissipating circuit board, a semiconductor device, and a power module comprising the thermally-conductive resin sheet.

In recent years, power semiconductor devices used in various fields such as railways, automobiles, industry, and general home appliances are shifting from conventional Si power semiconductors to power semiconductors using SiC, AlN, GaN, etc. for further miniaturization, cost reduction, efficiency improvement, etc.
A power semiconductor device is generally used as a power semiconductor module in which a plurality of semiconductor devices are arranged on a common heat sink and packaged.

Various problems have been pointed out for the practical use of such power semiconductor devices, one of which is the problem of heat generation from the devices. Power semiconductor devices can be operated at high temperatures to achieve high output and high density. On the other hand, there is concern that heat generated due to device switching, etc., will reduce the reliability of power semiconductor devices.

In addition, in recent years, in the electrical and electronic fields, heat generation accompanying high density of integrated circuits has become a serious problem, and how to dissipate heat has become an urgent issue in these fields as well. For example, when a semiconductor device used to control the central processing unit of a personal computer, a motor of an electric vehicle, etc., is operated stably, a heat sink, heat radiation fin, etc. are indispensable for heat dissipation, and a member that can combine thermal conductivity and insulation is required as a member that connects the semiconductor device and the heat sink.

Ceramic substrates with high thermal conductivity, such as alumina substrates and aluminum nitride substrates, have conventionally been used as members capable of achieving both thermal conductivity and insulation. However, ceramic substrates had problems such as being susceptible to cracking due to impact, and being difficult to make thinner and more compact.
Therefore, a heat dissipation sheet using a thermosetting resin such as an epoxy resin and an inorganic filler has been proposed.

Regarding a heat-dissipating sheet using a thermosetting resin and an inorganic filler, for example, Patent Document 1 proposes a heat-dissipating resin sheet containing an epoxy resin having a Tg of 60° C. or less and boron nitride, wherein the boron nitride content is 30% by volume or more and 60% by volume or less.

Boron nitride (hereinafter also referred to as “BN”) is an insulating ceramic, and has the characteristics of excellent thermal conductivity, solid lubricity, chemical stability, and heat resistance.

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

Patent Document 3 describes a thermally conductive resin composition that can stably produce a semiconductor device with excellent reliability and has excellent storage stability, as a thermally conductive resin composition that includes an epoxy resin, a thermally conductive filler, and silica nanoparticles having an average particle diameter D50 of 1 to 100 nm according to a dynamic light scattering method. A thermally conductive resin composition containing secondary aggregated particles is disclosed.

JP 2017-036415 A JP 2012-224676 A JP 2017-025186 A

As described above, aggregated particles of boron nitride are excellent in insulating properties and thermal conductivity, and therefore are extremely useful materials for forming resin sheets that require thermal conductivity and insulating properties.
However, if the content of the boron nitride agglomerated particles is increased to some extent in order to further increase the thermal conductivity, when the resin sheet is formed, the surface of the sheet becomes uneven, and the resin sheet becomes easy to create gaps when joined to the conductor. Therefore, it tends to be a factor such as a decrease in thermal conductivity and a decrease in insulation.

Therefore, the present invention aims to provide a thermally conductive resin composition and a thermally conductive resin sheet that can suppress the unevenness of the coated surface, that is, the surface when the resin sheet is formed, even if the content of the boron nitride aggregated particles is increased to a certain extent in order to further increase the thermal conductivity.

In order to solve the above-described problems, the present invention preferably has the first to fifteenth aspects described below.
[1] A first aspect of the present invention is a thermally conductive resin composition comprising a thermosetting resin, and a thermally conductive filler and silica nanoparticles as inorganic fillers,
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% by mass and 10% by mass or less with respect to 100% by mass of the total solid content of the thermally conductive resin composition,
The thermally conductive filler contains aggregated particles of boron nitride, and the average particle diameter of the aggregated particles is 5 μm or more and 100 μm or less,
Content of the said thermally conductive filler is a thermally conductive resin composition which is 60 mass % or more and 85 mass % or less with respect to 100 mass % of total solid content of the said thermally conductive resin composition.
[2] A second aspect of the present invention is the thermally conductive resin composition according to the first aspect, wherein the aggregated particles of boron nitride account for 75% by mass or more of the thermally conductive filler.
[3] A third aspect of the present invention is the thermally conductive resin composition according to the first or second aspect, wherein the elastic modulus of the aggregated particles of boron nitride is 48 MPa or more.
[4] A fourth aspect of the present invention is the thermally conductive resin composition according to any one of the first to third aspects, wherein the breaking strength of the aggregated particles of boron nitride is 20 MPa or less.
[5] A fifth aspect of the present invention is a thermally conductive resin composition according to any one of the first to fourth aspects, wherein the particle size ratio of the average particle size of the aggregated particles of boron nitride to the average particle size of the silica nanoparticles (BN/silica) is 100 to 50,000.
[6] A sixth aspect of the present invention is the thermally conductive resin composition according to any one of the first to fifth aspects, wherein the silica nanoparticles are surface-treated with an organometallic compound.
[7] A seventh aspect of the present invention is a thermally conductive resin composition according to any one of the first to sixth aspects, wherein the thermosetting resin comprises a polyfunctional epoxy resin having three or more epoxy groups per molecule and a molecular weight of 650 or less.
[8] An eighth aspect of the present invention is the thermally conductive resin composition according to the seventh aspect, wherein the polyfunctional epoxy resin is an epoxy resin having 4 or more glycidyl groups in the molecule.
[9] A ninth aspect of the present invention is a thermally conductive resin composition according to any one of the first to eighth aspects, comprising a polymer having a mass average molecular weight of 10,000 or more in an amount of 10% by mass or more and less than 30% by mass, based on 100% by mass of the resin component excluding inorganic particles from the solid content of the thermally conductive resin composition.

[10] A tenth aspect of the present invention is a thermally conductive resin sheet formed from the thermally conductive resin composition according to any one of the first to ninth aspects.
[11] An eleventh aspect of the present invention is the thermally conductive resin sheet according to the tenth aspect, which has a thermal conductivity of 10 W/mK or more in the thickness direction after curing.
[12] A twelfth aspect of the present invention is a heat dissipation laminate comprising the thermally conductive resin sheet according to the tenth or eleventh aspect.
[13] A thirteenth aspect of the present invention is a heat dissipating circuit board comprising the thermally conductive resin sheet according to the tenth or eleventh aspect.
[14] A fourteenth aspect of the present invention is a semiconductor device comprising the heat-dissipating circuit board according to the thirteenth aspect.
[15] A fifteenth aspect of the present invention is a power module comprising the thermally conductive resin sheet according to the tenth or eleventh aspect.

In the thermally conductive resin composition proposed by the present invention, even if the content of the aggregated particles of boron nitride is increased to some extent in order to further increase the thermal conductivity, specifically, the total solid content of the thermally conductive resin composition is 100%. Therefore, when the resin sheet is bonded to a conductor to form a laminate, it is possible to suppress the formation of a gap at the bonding interface between the resin sheet and the conductor, and it is possible to prevent deterioration in the thermal conductivity and insulation of the laminate.
It is not clear why the unevenness of the sheet surface can be suppressed when the thermally conductive resin composition proposed by the present invention is used to produce the sheet surface, but it is presumed that the inclusion of a predetermined amount or more of silica nanoparticles reduces the friction between the aggregated particles of boron nitride and increases the fluidity of the thermally conductive resin composition.

FIG. 2 is a conceptual diagram of a cross-sectional view of particles according to an example of aggregated boron nitride particles having a card house structure.

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 embodiments, and various modifications can be made within the scope of the gist of the present invention.

<<This Thermally Conductive Resin Composition>>
A thermally conductive resin composition according to an example of the embodiment of the present invention (referred to as "the present thermally conductive resin composition") contains a thermosetting resin, and a thermally conductive filler and silica nanoparticles as inorganic fillers, and if necessary, further contains other polymers, curing agents, curing accelerators, organic solvents, and other components.

The thermally conductive resin composition may be in the form of powder, slurry, liquid, solid, or a sheet-like molded body.

<Thermosetting resin>
The thermosetting resin contained in the present thermally conductive resin composition may be any resin that is cured by heat. Examples thereof include epoxy resins, phenol resins, polycarbonate resins, unsaturated polyester resins, urethane resins, melamine resins, and urea resins. Among these, epoxy resins are preferred from the viewpoint of viscosity, heat resistance, hygroscopicity, and handleability.

The content of the thermosetting resin is preferably 5 to 99% by mass with respect to 100% by mass of the resin component excluding the inorganic filler from the solid content of the present thermally conductive resin composition.
If the content of the thermosetting resin is 5% by mass or more, it is preferable because the moldability is improved.
From this point of view, the content of the thermosetting resin is preferably 5 to 99% by mass with respect to 100% by mass of the resin component excluding the inorganic filler from the solid content of the present thermally conductive resin composition, 10% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, and more preferably 50% by mass or more.

(Epoxy resin)
Epoxy resin is particularly preferable as the thermosetting resin contained in the present thermally conductive resin composition.
Epoxy resin is a general term for compounds having one or more oxirane rings (epoxy groups) in the molecule. The oxirane ring (epoxy group) contained in the epoxy resin may be either an alicyclic epoxy group or a glycidyl group. A glycidyl group is more preferable from the viewpoint of reaction rate or heat resistance.

Examples of epoxy resins include epoxy group-containing silicon compounds, aliphatic type epoxy resins, bisphenol A or F type epoxy resins, novolac type epoxy resins, alicyclic epoxy resins, glycidyl ester type epoxy resins, polyfunctional epoxy resins, polymer type epoxy resins, and the like.

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; dihydroxynaphthalene; Examples include epoxy resins obtained by glycidylating trisphenols such as hydroxyphenyl)methane; epoxy resins obtained by glycidylating tetrakisphenols such as 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane;

Above all, the epoxy resin contained in the present thermally conductive resin composition preferably contains either one of "high molecular weight epoxy resin" and "polyfunctional epoxy resin" or both of them.

Epoxy resins other than the high molecular weight epoxy resin and the polyfunctional epoxy resin contained in the present thermally conductive resin composition include, for example, various bisphenol-type epoxy resins obtained by glycidylating bisphenols such as bisphenol A-type epoxy resin and bisphenol F-type epoxy resin, various biphenyl-type epoxy resins obtained by glycidylating biphenyls, and epoxy resins obtained by glycidylating aromatic compounds having two hydroxyl groups such as dihydroxynaphthalene and 9,9-bis(4-hydroxyphenyl)fluorene. , 1,1,1-tris(4-hydroxyphenyl)methane or the like, 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 novolak, cresol novolak, bisphenol A novolak, brominated bisphenol A novolak, and silicone-containing epoxy resins. I can. However, it is not limited to these.

(high molecular weight epoxy resin)
The thermally conductive resin composition preferably contains a polymer having a mass average molecular weight of 10,000 or more, and a preferred example of the 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 vocative, anthracene skeleton, a pyrene skeleton, a xanthene skeleton, an adamantane skeleton, and a dicyclopentadiene skeleton.

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

In formula (1), R ¹ and R ² each represent 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.

The term "organic group" includes any group as long as it contains a carbon atom, and specific examples thereof include alkyl groups, alkenyl groups, aryl groups, etc., which may be substituted with a halogen atom, a heteroatom-containing group, or another hydrocarbon group. The same applies to the following.

Further, as the high-molecular-weight epoxy resin, an epoxy resin having a structure represented by the following formula (3) (hereinafter sometimes referred to as "structure (3)") can be mentioned.

In formula (3), R ⁴ , R ⁵ , R ⁶ and R ⁷ each represent an organic group having a molecular weight of 15 or more.

In the above formula (1), at least one of R ¹ and R ² represents an organic group having a molecular weight of 16 or more, preferably 16 to 1000, and examples thereof include alkyl groups such as ethyl group, propyl group, butyl group, pentyl group, hexyl group and heptyl group, and aryl groups such as phenyl group, tolyl group, xylyl group, naphthyl group and fluorenyl group. Both R ¹ and R ² may 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 may be an organic group with a molecular weight of 15 or less or a hydrogen atom. Preferably, one is an organic group having a molecular weight of 16 or more and the other is an organic group having a molecular weight of 15 or less, and in particular, one of them is a methyl group and the other is a phenyl group.

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. Moreover, they may independently have a substituent such as a hydrocarbon group or a halogen atom. A divalent bond can be a divalent group on a single carbon atom or a divalent group on different carbon atoms. Preferred are 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 preferable from the viewpoint of control of handleability such as resin viscosity and strength of the cured product.

In formula (3) above, R ⁴ , R ⁵ , R ⁶ and R ⁷ each represent an organic group having a molecular weight of 15 or more. An alkyl group having a molecular weight of 15 to 1000 is preferable, and it is particularly preferable that all of R ⁴ , R ⁵ , R ⁶ and R ⁷ are methyl groups from the viewpoint of control of handleability such as resin viscosity and strength of the cured product.

The high-molecular-weight epoxy resin is preferably an epoxy resin containing either one of the structure (1) and the structure (2) and the structure (3), from the viewpoint of both reducing the hygroscopicity of the resulting cured heat-dissipating sheet and maintaining its strength.

Such high-molecular-weight epoxy resins contain more hydrophobic hydrocarbons and aromatic structures than general epoxy resins having a bisphenol A or bisphenol-F skeleton. Therefore, by blending high-molecular-weight epoxy resins, it is possible to reduce the amount of moisture absorbed by the resulting heat-dissipating sheet, which is a cured product.
From the viewpoint of reducing moisture absorption, the high-molecular-weight epoxy resin preferably contains a large amount of structures (1), (2), and (3) which are hydrophobic structures. Specifically, it is preferably an epoxy resin having a weight average molecular weight of 10,000 or more, more preferably an epoxy resin having a weight average molecular weight of 20,000 or more, and even more preferably an epoxy resin having a weight average molecular weight of 30,000 or more, for example, 30,000 to 40,000. .

Further, the high-molecular-weight epoxy resin is preferably more hydrophobic, and from this point of view, the epoxy equivalent of the epoxy component is preferably large, specifically preferably 5,000 g/equivalent or more, more preferably 7,000 g/equivalent or more, for example, 8,000 to 15,000 g/equivalent.

In addition, the mass average molecular weight of the epoxy resin is a polystyrene-equivalent value measured by gel permeation chromatography.
The epoxy equivalent is defined as "the mass of an epoxy resin containing one equivalent of an epoxy group" and can be measured according to JIS K7236.

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

The content of the high molecular weight epoxy resin is preferably 10% by mass or more and less than 30% by mass with respect to 100% by mass of the resin component excluding the inorganic filler from the solid content of the present thermally conductive resin composition.
When the content of the high-molecular-weight epoxy resin is 10% by mass or more, the holding power and film-forming properties of the inorganic filler are maintained, and when the content is less than 30% by mass, the strength during curing can be maintained.
From this point of view, 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 more preferably 15% by mass or more or 28% by mass or less, based on 100% by mass of the resin component excluding the inorganic filler from the solid content of the present thermally conductive resin composition.

(Polyfunctional epoxy resin)
A polyfunctional epoxy resin refers to an epoxy resin having two or more oxirane rings (epoxy groups) in the molecule.
By adding such a polyfunctional epoxy resin, it is possible to introduce highly polar oxirane rings (epoxy groups) at a high density, thereby increasing the effects of physical interactions such as van der Waals forces and hydrogen bonding, and for example, the adhesion between the present thermally conductive resin sheet formed from the present thermally conductive resin composition and the conductor can be improved. In addition, by adding a polyfunctional epoxy resin, the storage elastic modulus of the present thermally conductive resin sheet can be increased, and as a result, after the cured product of the present thermally conductive resin composition enters the unevenness of the surface of the conductor, which is the adherend, a strong anchoring effect can be exhibited, and the adhesion between the present thermally conductive resin sheet and the conductor can be improved.
On the other hand, the introduction of a polyfunctional epoxy resin tends to increase the hygroscopicity of the present thermally conductive resin composition, but by improving the reactivity of the oxirane ring (epoxy group), it is possible to reduce the amount of hydroxyl groups during the reaction and suppress the increase in hygroscopicity. In addition, by producing the present thermally conductive resin composition by combining the above-described high molecular weight epoxy resin and polyfunctional epoxy resin, it is possible to achieve both high elasticity and low moisture absorption of the present thermally conductive resin sheet.

The polyfunctional epoxy resin may be an epoxy resin having two or more oxirane rings (epoxy groups) in the molecule, preferably an epoxy resin having three or more oxirane rings (epoxy groups) in the molecule, and more preferably an epoxy resin having four or more glycidyl groups in the molecule, from the viewpoint of increasing the storage elastic modulus of the cured product after thermosetting, and in particular, increasing the storage elastic modulus at high temperatures, which is important in the case of a power semiconductor or the like that generates a large amount of heat. By having a plurality of oxirane rings (epoxy groups), particularly glycidyl groups, in the molecule, the crosslink density of the cured product is improved, and the resulting cured product, that is, the heat-dissipating sheet, has higher strength. As a result, when internal stress is generated in the heat-dissipating sheet in the moisture absorption reflow test, the heat-dissipating sheet does not deform or break, and by maintaining its shape, it is possible to suppress the formation of voids or other voids in the heat-dissipating sheet.

In addition, from the viewpoint of increasing the storage elastic modulus of the thermally cured heat-dissipating sheet, the molecular weight of the polyfunctional epoxy resin is preferably 650 or less, particularly 100 or more or 630 or less, more preferably 200 or more or 600 or less, and further preferably 200 or more or 550 or less.
In addition, since an amine-based or amide-based structure is hydrophilic, having such a structure tends to increase water absorption. Therefore, from the viewpoint of achieving lower moisture absorption and higher cross-linking, the polyfunctional epoxy resin is more preferably a polyfunctional epoxy resin that does not contain an amine or amide structure.

A specific example of the polyfunctional epoxy resin is preferably a polyfunctional epoxy resin having 3 or more epoxy groups per molecule and a molecular weight of 650 or less. For example, EX321L, DLC301, DLC402, etc. manufactured by Nagase ChemteX Corporation can be used.
These polyfunctional epoxy resins may be used alone or in combination of two or more.

The content of the polyfunctional epoxy resin is preferably 5% by mass or more and 80% by mass or less with respect to 100% by mass of the resin component excluding the inorganic filler from the solid content of the present thermally conductive resin composition.
If the content of the polyfunctional epoxy resin is 5% by mass or more, the elastic modulus of the cured product of the thermally conductive resin composition can be maintained, and if it is 80% by mass or less, the water absorption rate does not become too high.
From this point of view, the content of the polyfunctional epoxy resin is preferably 5% by mass or more and 80% by mass or less, more preferably 10% by mass or more or 70% by mass or less, and more preferably 15% by mass or more or 50% by mass or less, based on 100% by mass of the resin component excluding the inorganic filler from the solid content of the present thermally conductive resin composition.

When a high molecular weight epoxy resin and a polyfunctional epoxy resin are used together, 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 more preferably 40 parts by mass or more and 200 parts by mass or less, with respect to 100 parts by mass of the high molecular weight epoxy resin, from the viewpoint of the film-forming properties of the sheet and the elastic modulus of the cured sheet.

<Thermal conductive filler>
The thermally conductive filler contained in the present thermally conductive resin composition preferably has a thermal conductivity of 2.0 W/m K or higher, particularly 3.0 W/m K or higher, particularly 5.0 W/m K or higher, and more preferably 10.0 W/m K or higher.

Examples of thermally conductive fillers include electrically insulating fillers composed only of carbon, fillers composed of metal carbides, metalloid carbides, metal oxides, metalloid oxides, metal nitrides, metalloid nitrides, and the like.

Examples of the electrically insulating filler composed of only carbon include diamond (thermal conductivity: about 2000 W/m·K).
Examples of the metal carbide or metalloid carbide include silicon carbide (thermal conductivity: about 60 to 270 W/m K), titanium carbide (thermal conductivity: about 21 W/m K), and tungsten carbide (thermal conductivity: about 120 W/m K).

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

These thermally conductive fillers may be used alone or in combination of two or more.

From the viewpoint of electrical insulation, the volume resistivity of the thermally conductive filler at 20° C. is preferably 10 ¹³ Ω·cm or more, more preferably 10 ¹⁴ Ω·cm or more.
Among them, metal oxides, semi-metal oxides, metal nitrides, and semi-metal nitrides are preferable because they can easily provide sufficient electrical insulation of the present thermally conductive resin sheet. Specific examples of such thermally conductive fillers include aluminum oxide (Al ₂ O ₃ , 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 (Si ₃ N ₄ , volume resistivity: >10 ¹⁴ Ω·cm), silica (SiO ₂ , volume resistivity ratio: >10 ¹⁴ Ω·cm).
Among them, aluminum oxide, aluminum nitride, and boron nitride are preferable, and aluminum oxide and boron nitride are particularly preferable because they can impart high insulating properties to the present thermally conductive resin sheet.

The shape of the conductive filler may be amorphous particles, spheres, whiskers, fibers, plates, or aggregates or mixtures thereof.
However, the shape of the thermally conductive filler of the present invention is preferably spherical.

In the present invention, the term "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 still more preferably 1 or more and 1.4 or less.
The aspect ratio can be determined by arbitrarily selecting 10 or more particles from an image of the cross section of the present thermally conductive resin composition or the present thermally conductive resin sheet 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.

[Boron Nitride Agglomerated Particles]
The thermally conductive filler contained in the thermally conductive resin composition has little problem of moisture absorption during heat molding, has low toxicity, can efficiently increase thermal conductivity, and can impart high insulation to the present thermally conductive resin sheet.

In addition, aggregated boron nitride particles may be used in combination with other thermally conductive fillers. However, the heat transfer behavior in this thermally conductive resin sheet does not simply depend on the thermal conductivity inside the thermally conductive filler, as will be described later. Therefore, among the particles exemplified above, even when diamond particles, etc., which have extremely high thermal conductivity but are extremely expensive, are used, the thermal conductivity in the thickness direction of the present thermally conductive resin sheet does not increase extremely. Therefore, when aggregated boron nitride particles and other thermally conductive fillers are used in combination, the main point is to reduce the cost of the composition. Therefore, since it is relatively inexpensive and has relatively high thermal conductivity, the thermally conductive filler used in combination with boron nitride is appropriately selected from magnesium oxide, aluminum oxide, tungsten carbide, silicon carbide, aluminum nitride, etc. It is preferable.

Among them, from the viewpoint of high thermal conductivity, the boron nitride aggregated particles preferably account for 75% by mass or more of the thermally conductive filler, among which 80% by mass or more, and among them 85% by mass or more (including 100% by mass). It is preferable that the boron nitride aggregated particles occupy.

The shape of the aggregated boron nitride particles is preferably spherical.

The aggregated structure of the boron nitride aggregated particles is preferably a card house structure from the viewpoint of improving thermal conductivity.
The aggregate structure of the aggregated boron nitride particles can be confirmed with a scanning electron microscope (SEM).

The card house structure is a structure in which tabular particles are not oriented and are intricately laminated, and is described in "Ceramics 43 No. 2" (published by the Ceramic Society of Japan, 2008).
More specifically, it refers to a structure in which the plane portion of a primary particle forming an aggregated particle and the end face portion of another primary particle present in the aggregated particle are in contact with each other. A schematic diagram of the card house structure is shown in FIG.
The agglomerated particles having a card house structure have a very high breaking strength due to their structure, and are not crushed even in the pressurizing process performed during sheet molding of the present thermally conductive resin sheet. Therefore, the primary particles, which are normally oriented in the longitudinal direction of the present thermally conductive resin sheet, can be present in random directions. Therefore, the use of agglomerated particles with a card house structure can further increase the ratio of the ab planes of the primary particles oriented in the thickness direction of the present thermally conductive resin sheet, so that heat can be effectively conducted in the thickness direction of the sheet, and the thermal conductivity in the thickness direction can be further increased.

The aggregated boron nitride particles having a card house structure can be produced, for example, by the method described in International Publication No. 2015/119198.

When using aggregated boron nitride particles having a card house structure, the particles may be surface-treated with a surface-treating agent.
As the surface treatment agent, for example, a known surface treatment agent such as silane coupling treatment can be used. In general, there is often no direct affinity or adhesion between the thermally conductive filler and the thermoplastic resin, and this is also the case when aggregated boron nitride particles having a card house structure are used as the thermally conductive filler. It is considered that the thermal conductivity attenuation at the interface can be further reduced by increasing the adhesion at the interface between the thermally conductive filler and the matrix resin by chemical treatment.

By using aggregated boron nitride particles as the thermally conductive filler used in the present thermally conductive resin sheet, the particle size can be increased compared to the thermally conductive filler using the primary particles as they are.
By increasing the particle size of the thermally conductive filler, it is possible to reduce the number of heat transfer paths between the thermally conductive fillers via the thermoplastic resin with low thermal conductivity, thus reducing the increase in thermal resistance in the heat transfer path in the thickness direction.

From the above viewpoint, the lower limit of the maximum particle size of the aggregated boron nitride particles is preferably 20 µm or more, more preferably 30 µm or more, and still more preferably 40 µm or more. On the other hand, the upper limit of the maximum particle size is preferably 300 µm or less, more preferably 200 µm or less, still more preferably 100 µm or less, and even more preferably 90 µm or less.

Moreover, the average particle size of the aggregated boron nitride particles is not particularly limited. Among them, 5 μm or more is preferable, 10 μm or more is more preferable, and 15 μm or more is particularly preferable. Moreover, 100 micrometers or less are preferable and 90 micrometers or less are more preferable. When the average particle size of the aggregated boron nitride particles is 5 μm or more, the number of particles in the resin composition and the cured product using the resin composition is relatively reduced, so the interface between particles is reduced, resulting in a decrease in thermal resistance, and the composite resin sheet may have a high thermal conductivity. Moreover, it exists in the tendency for the surface smoothness of the hardened|cured material using a resin composition to be obtained because the said average particle diameter is below the said upper limit.

By setting the average particle size or the maximum particle size of the aggregated boron nitride particles to be equal to or less than the above upper limit, when the aggregated boron nitride particles are contained in the matrix resin, it is possible to form a high-quality film free from surface roughening. When the average particle size or the maximum particle size is at least the above lower limit, the interface between the matrix resin and the boron nitride aggregated particles is reduced, resulting in a decrease in thermal resistance, achieving high thermal conductivity, and a sufficient effect of improving thermal conductivity as a thermally conductive filler required for power semiconductor devices.

In addition, the effect of the thermal resistance at the interface between the matrix resin and the aggregated boron nitride particles on the thickness of the present thermally conductive resin sheet becomes significant when the size of the aggregated boron nitride particles is 1/10 or less with respect to the thickness of the present thermally conductive resin sheet. In particular, in the case of power semiconductor devices, the present thermally conductive resin sheet having a thickness of 100 μm to 300 μm is often applied, so from the viewpoint of thermal conductivity, the maximum particle size of the aggregated boron nitride particles is preferably larger than the above lower limit.
In addition, when the maximum particle size of the boron nitride aggregated particles is equal to or greater than the above lower limit, not only is the increase in thermal resistance caused by the interface between the boron nitride aggregated particles and the matrix resin suppressed, but the number of required heat conduction paths between the particles is reduced, and the probability of connecting from one surface to the other surface in the thickness direction of the present thermally conductive resin sheet is increased.
On the other hand, when the maximum particle size of the aggregated boron nitride particles is equal to or less than the above upper limit, protrusion of the aggregated boron nitride particles to the surface of the present thermally conductive resin sheet is suppressed, and a good surface shape without surface roughness is obtained. Therefore, when producing a sheet bonded to a copper substrate, it has sufficient adhesion and excellent withstand voltage characteristics can be obtained.

The ratio (maximum particle diameter/thickness) of the size (maximum particle diameter) of the aggregated boron nitride particles to the thickness of the present thermally conductive resin sheet is preferably 0.3 or more and 1.0 or less, more preferably 0.35 or more or 0.95 or less, and more preferably 0.4 or more or 0.9 or less.

The maximum particle size and average particle size of the aggregated boron nitride particles can be measured, for example, by the following methods.
The maximum particle size and average particle size of the aggregated boron nitride particles used as a raw material can be obtained as the maximum particle size Dmax and the average particle size D50 of the aggregated boron nitride particles by measuring the particle size distribution of a sample obtained by dispersing the aggregated boron nitride particles in a solvent, specifically, by measuring the particle size distribution of a sample obtained by dispersing the aggregated boron nitride particles in a pure water medium containing a dispersion stabilizer with a laser diffraction/scattering particle size distribution analyzer, and obtaining the resulting particle size distribution.
Here, Dmax and D50 are the maximum particle diameter and the cumulative volume 50% particle diameter in the volume-based particle size distribution obtained by measuring the particle size distribution using laser diffraction scattering.
The maximum particle size and average particle size can also be obtained with a dry particle size distribution analyzer such as Morphologi G3 (manufactured by Malvern).

On the other hand, the maximum particle size Dmax and the average particle size D50 of the aggregated boron nitride particles in the present thermally conductive resin composition or the present thermally conductive resin sheet can also be measured in the same manner as described above by removing the thermoplastic resin by dissolving or swelling the thermoplastic resin in a solvent (including a heating solvent) to reduce the adhesive strength with the boron nitride aggregated particles, then physically removing the particles, and then removing the resin components by heating and incinerating them in the atmosphere. is.
As for the maximum particle size of the aggregated boron nitride particles in the present thermally conductive resin composition or the present thermally conductive resin sheet, the cross section of the present thermally conductive resin composition or the present thermally conductive resin sheet can be directly observed with a scanning electron microscope, a transmission electron microscope, a microscopic Raman spectrometer, an atomic force microscope, or the like to directly observe 10 or more arbitrary boron nitride aggregated particles, and the maximum particle size of them can be determined.
Further, the average particle size of the boron nitride aggregated particles in the present thermally conductive resin composition or the present thermally conductive resin sheet can be obtained by directly observing 10 or more arbitrary boron nitride aggregated particles in the cross section of the present thermally conductive resin composition or the present thermally conductive resin sheet with a scanning electron microscope, a transmission electron microscope, a microscopic Raman spectroscope, an atomic force microscope, etc., and calculating the arithmetic mean value of the particle diameter.
When the particles are non-spherical, the longest diameter and the shortest diameter are measured, and the average value is taken as the particle diameter of the particles.

(destruction strength)
The breaking strength of the aggregated boron nitride particles is preferably 20 MPa or less, more preferably 15 MPa or less, and more preferably 10 MPa or less.
When the boron nitride aggregated particles have a breaking strength of 20 MPa or less, the portions where the boron nitride aggregated particles are in contact with each other are deformed and can come into surface contact. Therefore, while maintaining high thermal conductivity inside the boron nitride aggregated particles, the contact thermal resistance at the interface between the boron nitride aggregated particles and the interface between the metal substrate and the heat dissipation sheet, which will be described later, can be reduced, and the overall thermal conductivity can be improved.
However, if the breaking strength of the aggregated boron nitride particles is too small, the particles are likely to be broken by the pressure during the production of the compact, and the thermal conductivity tends not to improve.

The breaking strength can be calculated by the following formula after subjecting one particle to a compression test according to JIS R 1639-5. Particles are usually measured at 5 or more points, and the average value is adopted.
Formula: Cs = 2.48P/(πd ² )
Cs: breaking strength (MPa)
P: breaking test force (N)
d: particle diameter (mm)

(elastic modulus)
The elastic modulus of the aggregated boron nitride particles is preferably 48 MPa or higher, more preferably 50 MPa or higher, and more preferably 55 MPa or higher.
If the elastic modulus of the aggregated boron nitride particles is within the above range, it is possible to prevent the aggregated boron nitride particles from being plastically deformed in the direction of the pressing pressure and collapsing the aggregated structure. On the other hand, the upper limit of the elastic modulus is not particularly limited. However, the elastic modulus of the aggregated boron nitride particles is preferably 2,000 MPa or less, more preferably 1,500 MPa or less, and still more preferably 1,000 MPa or less, from the viewpoint of easily obtaining sufficient deformation.

The modulus of elasticity of the aggregated boron nitride particles can be calculated from the following formula from the test force at the time when the fracture occurred and the compression displacement at that time using the device used for measuring the fracture strength.
E=3×(1−ν ² )×P/4×(d/2) ^1/2 ×Y ^3/2
(“E” is the elastic modulus (MPa), “ν” is the Poisson’s ratio, “P” is the breaking test force (N), “d” is the particle diameter (mm), and “Y” is the compression displacement (mm). Note that the Poisson's ratio can be assumed to be constant (0.13).)

(Content of thermally conductive filler)
The content of the thermally conductive filler is preferably 60% by mass or more and 85% by mass or less with respect to 100% by mass of the total solid content of the present thermally conductive resin composition.
If the content of the thermally conductive filler is 60% by mass or more, high thermal conductivity can be obtained. On the other hand, if the content is 85% by mass or less, the inclusion of silica nanoparticles can reduce the unevenness of the surface.
From this point of view, the content of the thermally conductive filler is preferably 60% by mass or more, more preferably 62% by mass or more, and more preferably 65% by mass or more, based on 100% by mass of the total solid content of the present thermally conductive resin composition. On the other hand, it is preferably 85% by mass or less, more preferably 83% by mass or less, more preferably 81% by mass or less.

<Silica nanoparticles>
Silica nanoparticles are insulators and have excellent electrical properties due to their low dielectric constant. In addition, by including a predetermined amount or more of silica nanoparticles, unevenness of the sheet surface can be suppressed even if the content of aggregated particles of boron nitride is increased. From this point of view, silica nanoparticles are particularly suitable as the inorganic filler for the use of the present invention, compared to titanium oxide particles and alumina particles.

The average particle size of the silica nanoparticles is preferably 1 nm or more and 100 nm or less.
If the average particle size of the silica nanoparticles is 1 nm or more, aggregation of the particles is suppressed, and fluidity is maintained.
From this point of view, the average particle size of the silica nanoparticles is preferably 1 nm or more and 100 nm or less, more preferably 2 nm or more or 80 nm or less, more preferably 3 nm or more or 70 nm or less, and more preferably 5 nm or more or 60 nm or less.

The particle size ratio (BN/silica) of the average particle size of the aggregated particles of boron nitride to the average particle size of the silica nanoparticles is preferably 100 to 50,000.
If the particle size ratio (BN/silica) is 100 or more, aggregation is suppressed, which is preferable. On the other hand, if it is 50,000 or less, it is preferable because it efficiently adheres to the surface of the aggregated particles of boron nitride and imparts fluidity.
From this point of view, the particle size ratio (BN/silica) is preferably 100 or more, more preferably 500 or more, and more preferably 1,000 or more. On the other hand, it is preferably 50,000 or less, more preferably 30,000 or less, more preferably 10,000 or less.

The average particle size of the silica nanoparticles used as a raw material can be determined as the average particle size D50 of the silica nanoparticles from the particle size distribution obtained by measuring the particle size distribution of a sample obtained by dispersing the silica nanoparticles in a solvent, specifically, a sample obtained by dispersing the silica nanoparticles in a pure water medium containing a dispersion stabilizer, using a laser diffraction/scattering particle size distribution analyzer.
On the other hand, the average particle size of the silica nanoparticles in the present thermally conductive resin composition or the present thermally conductive resin sheet can be determined by, for example, directly observing 10 or more arbitrary silica nanoparticles in the cross section of the present thermally conductive resin composition or the present thermally conductive resin sheet with a scanning electron microscope, a transmission electron microscope, a microscopic Raman spectrometer, an atomic force microscope, etc., and calculating the arithmetic average value of the particle diameters.
When the particles are non-spherical, the longest diameter and the shortest diameter are measured, and the average value is taken as the particle diameter of the particles.

Silica nanoparticles may be either hollow particles or solid particles.

Silica nanoparticles may also be surface-treated with an organometallic compound.
When the silica nanoparticles are surface-treated with an organometallic compound, the surface is hydrophobized, fluidity can be further enhanced, and even a small amount has the effect of suppressing unevenness on the surface. In addition, it is possible to prevent deterioration of coating properties due to an excessive increase in the viscosity of the slurry prepared for coating, as compared with silica nanoparticles that have not been surface-treated.
Examples of such organometallic compounds include organosilicon compounds, organotitanium compounds, organozirconium compounds, and organoaluminum compounds. Among them, organosilicon compounds are preferred.
Examples of the organosilicon compound include dimethylpolysiloxane, dimethylpolysiloxane having a terminal reactive group, silicone oils such as methylhydrogenpolysiloxane, organosilanes such as methyldimethoxysilane and diphenyldidimethoxysilane, silazanes such as hexamethyldisilazane, silane coupling agents such as 3-methacryloyloxypropyltrimethoxysilane, 3-acryloyloxypropyltrimethoxysilane, vinyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane and γ-aminopropyltriethoxysilane, and phenyl group-containing silane cups. A ring agent and the like can be mentioned.
In particular, from the viewpoint of easily imparting hydrophobicity, methylhydrogenpolysiloxane, methyltrimethoxysilane, dimethyldimethoxysilane, trimethylmethoxysilane, hexamethyldisilazane, dimethylpolysiloxane having a reactive group at the terminal, and a phenyl group-containing silane coupling agent are preferable, methylhydrogenpolysiloxane, dimethyldimethoxysilane, trimethylmethoxysilane, and a phenyl group-containing silane coupling agent are more preferable, and dimethyldimethoxysilane, trimethylmethoxysilane, and a phenyl group-containing silane coupling agent are more preferable.

(Content)
The content of silica nanoparticles is preferably more than 2.5% by mass and not more than 10% by mass with respect to 100% by mass of the total solid content of the thermally conductive resin composition.
If the content of the silica nanoparticles is more than 2.5% by mass, even if the content of the aggregated particles of boron nitride is increased to some extent in order to further increase the thermal conductivity, specifically, even if the content of the aggregated particles of boron nitride is 60% by mass or more, unevenness on the surface of the resin sheet formed from the present thermally conductive resin composition can be suppressed. On the other hand, if it is 10% by mass or less, it is preferable from the viewpoint of sheet handling.
From this point of view, the content of silica nanoparticles is preferably more than 2.5% by mass, more preferably 2.6% by mass or more, and more preferably 2.7% by mass or more, based on 100% by mass of the total solid content of the thermally conductive resin composition. On the other hand, it is preferably 10% by mass or less, more preferably 9% by mass or less, more preferably 8% by mass or less.

Further, the content ratio (silica/BN) of the content of the silica nanoparticles to the content of the aggregated particles of boron nitride is preferably 0.01 to 0.2.
If the content ratio (silica/BN) is 0.01 or more, it is preferable because the fluidity of BN can be improved. On the other hand, if it is 0.2 or less, it is preferable because it does not lower the thermal conductivity.
From this point of view, the content ratio (silica/BN) is preferably 0.01 or more, more preferably 0.02 or more, and more preferably 0.025 or more. On the other hand, it is preferably 0.2 or less, more preferably 0.15 or less, more preferably 0.1 or less.

<Polymer>
The present thermally conductive resin composition may optionally contain other polymers having a mass average molecular weight of 10,000 or more instead of the high molecular weight epoxy resin or together with the high molecular weight epoxy resin.
Such a high-molecular-weight polymer can serve as a resin matrix component or a binder resin component in the present thermally conductive resin composition.

The polymer may be either a thermoplastic resin, a thermosetting resin, or the like.
Examples of the thermoplastic resin and thermosetting resin include thermoplastic resins such as polyphenylene ether, polyphenylene sulfide, polyarylate, polysulfone, polyethersulfone, polyetheretherketone, and polyetherketone. As the thermoplastic resin and thermosetting resin, a group of heat-resistant resins called super engineering plastics such as thermoplastic polyimide, thermosetting polyimide, benzoxazine, and a reaction product of polybenzoxazole and benzoxazine can also be used. In addition, styrene-based polymers such as styrene and alkylstyrene, (meth)acrylic polymers such as alkyl (meth)acrylate and glycidyl (meth)acrylate, styrene-(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, phenoxy resins, and the like can also be used. Of these, phenoxy resins are preferred in terms of heat resistance and compatibility with thermosetting resins.
Each of the thermoplastic resin and the thermosetting resin may be used alone or in combination of two or more. Either one of a thermoplastic resin and a thermosetting resin may be used, or a combination of the thermoplastic resin and the thermosetting resin may be used.

The content of the polymer having a mass average molecular weight of 10,000 or more (including the high molecular weight epoxy resin when used in combination with the high molecular weight epoxy resin) is preferably 10% by mass or more and less than 30% by mass with respect to 100% by mass of the resin component excluding the inorganic filler from the solid content of the present thermally conductive resin composition.
By containing the polymer in an amount of 10% by mass or more, the holding power and film-forming property of the inorganic filler can be maintained.
From this point of view, the content of the polymer is preferably 10% by mass or more, more preferably 13% by mass or more, more preferably 15% by mass or more, based on 100% by mass of the resin component excluding the inorganic filler from the solid content of the present thermally conductive resin composition. On the other hand, it is preferably less than 30% by mass, more preferably less than 29% by mass.

<Curing agent>
This thermally conductive resin composition can contain a curing agent, if necessary.
Examples of the curing agent include phenol 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, hydrogenated products of the acid anhydrides, or modified products of the acid anhydrides. Only one curing agent may be used, or two or more curing agents may be used in combination.
By using these preferable curing agents, it is possible to obtain cured resin products having an excellent balance of heat resistance, moisture resistance and electrical properties.

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

Examples of the heterocyclic structure possessed by 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 of the thermosetting resin composition and the adhesion to metals, imidazole-based compounds and triazine-based compounds are preferred.
Preferred 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 tri Melitate, 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-4′-methylimidazolyl-(1′)]-ethyl-s-triazine, 2,4-diamino-6-[2′-methyl imidazolyl-(1′)]-ethyl-s-triazine isocyanurate, 2-phenylimidazole isocyanurate, 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 isocyanurate, 2,4-diamino-6-meth Acryloyloxyethyl-s-triazine, 2,4-diamino-6-methacryloyloxyethyl-s-triazine isocyanuric acid adduct and the like can be mentioned.

Among these, the high resin compatibility and the high reaction activation temperature make it possible to easily adjust the curing speed and the physical properties after curing, thereby improving the storage stability of the present thermally conductive resin composition and further improving the adhesive strength after heat molding. As the heterocyclic structure possessed by the nitrogen-containing heterocyclic compound, a structure derived from 1,3,5-triazine is particularly preferred. Moreover, it is also possible to have a plurality of these illustrated structural portions.

The nitrogen-containing heterocyclic compound may contain a curing catalyst, which will be described later, depending on the structure. Therefore, the present thermally conductive resin composition can contain the nitrogen-containing heterocyclic compound as a curing catalyst.
Only one type of nitrogen-containing heterocyclic compound may be used, or two or more types may be used in combination. Also, one molecule may have a plurality of heterocyclic structures at the same time.
The molecular weight of the nitrogen-containing heterocyclic compound is preferably 1,000 or less, more preferably 500 or less.

The acid anhydride having an aromatic skeleton, the hydrogenated acid anhydride, or the modified acid anhydride is not particularly limited.

The acid anhydride having an alicyclic skeleton, the hydrogenated acid anhydride or the modified acid anhydride is preferably an acid anhydride having a polyalicyclic skeleton, a hydrogenated acid anhydride or a modified acid anhydride, an acid anhydride having an alicyclic skeleton obtained by an addition reaction of a terpene compound and maleic anhydride, a hydrogenated acid anhydride or a modified acid anhydride.

The curing agent is preferably contained in an amount of 0 to 70% by mass, particularly 0 to 55% by mass, based on 100% by mass of the present thermally conductive resin composition excluding the solvent and inorganic filler. When the content of the curing agent is at least the above lower limit, sufficient curing performance can be obtained, and when it is at most the above upper limit, the reaction proceeds effectively, the crosslink density can be improved, the strength can be increased, and the film formability is improved.

<Curing accelerator>
The present thermally conductive resin composition can contain a curing catalyst as a curing accelerator, if necessary, in order to adjust the curing speed, the physical properties of the cured product, and the like.

It is preferable to appropriately select the curing catalyst according to the type of the thermosetting resin component and the curing agent.
Specific examples of curing catalysts include linear or cyclic tertiary amines, organophosphorus compounds, diazabicycloalkenes such as quaternary phosphonium salts or organic acid salts, and imidazoles. Organic metal compounds, quaternary ammonium salts, metal halides, and the like can also be used. Examples of the organometallic compounds include zinc octylate, tin octylate, and aluminum acetylacetone complexes.
These may be used singly or in combination of two or more.

Among them, imidazoles are particularly preferred from the viewpoint 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, 2,4-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 isocyanurate, 2-phenylimidazole isocyanurate, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole and the like.
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 having excellent storage stability and adhesion can be obtained. Furthermore, from the viewpoint of adhesiveness, those containing a nitrogen-containing heterocyclic compound other than the aforementioned imidazole ring are more preferable.

The curing catalyst is preferably contained in an amount of 0.1 to 10% by mass, particularly 0.1 to 5% by mass in 100% by mass of the thermally conductive resin composition excluding the solvent and the inorganic filler. When the content of the curing catalyst is at least the above lower limit, the progress of the curing reaction can be sufficiently accelerated and the composition can be cured satisfactorily.

<Organic solvent>
The present thermally conductive resin composition may contain an organic solvent, if necessary, for example, to improve coatability when forming a sheet-like cured product through a coating step.
Examples of organic solvents that may be contained in the present thermally conductive resin composition include methyl ethyl ketone, cyclohexanone, propylene glycol monomethyl ether acetate, butyl acetate, isobutyl acetate, propylene glycol monomethyl ether, and the like.
These organic solvents may be used alone or in combination of two or more.

When the present thermally conductive resin composition contains an organic solvent, the content thereof is appropriately determined according to the handleability and the like when producing the heat-dissipating sheet. Usually, the organic solvent is preferably used so that the solid content (total of components other than the solvent) concentration in the present thermally conductive resin composition is 10 to 90% by mass, particularly 40% by mass or more or 80% by mass or less.
In the case of forming a sheet, the organic solvent is preferably used so that the solid content (total of components other than the solvent) concentration in the present thermally conductive resin composition is 95% by mass or more, more preferably 97% by mass or more, more preferably 98% by mass or more, and still more preferably 99% by mass or more.

<Other ingredients>
The present thermally conductive resin composition may contain other components in addition to the above components.
Examples of other components include dispersants, thermoplastic resins, organic fillers, inorganic fillers, additives such as silane coupling agents that improve the interfacial adhesive strength between the inorganic filler and the resin component, additives that can be expected to increase the adhesive strength between the resin sheet and the metal plate, insulating carbon components such as reducing agents, viscosity modifiers, thixotropic agents, flame retardants, colorants, various antioxidants such as phosphorus and phenol, phenol acrylate and other process stabilizers, heat stabilizers, and hindered amine radical scavengers. agents (HAAS), impact modifiers, processing aids, metal deactivators, copper damage inhibitors, antistatic agents, extenders and the like. When these additives are used, the amount to be added may be within the range of amounts normally used for these purposes.

<Physical properties of the present thermally conductive resin composition>
When the thermally conductive resin composition is molded into a sheet and cured, the thermal conductivity in the thickness direction can be 10 W/mK or more, especially 13 W/mK or more, especially 15 W/mK or more.

<<Uses of this thermally conductive resin composition>>
The thermally conductive resin composition can be used for various applications that require thermal conductivity.

<Thermal conductive resin sheet>
A thermally conductive resin sheet (referred to as "the present thermally conductive resin sheet") according to an example of the embodiment of the present invention may be a thermally conductive resin sheet formed from the present thermally conductive resin composition.
Since the present thermally conductive resin sheet can suppress irregularities on the surface of the sheet, it has the characteristic that gaps are less likely to occur when laminated with a conductor such as a metal plate.

The thermal conductivity in the thickness direction at 25° C. when the thermally conductive resin sheet is cured is preferably 10 W/m K or more, particularly preferably 15 W/m K or more, and more preferably 17 W/m K or more. Since the thermal conductivity in the thickness direction is equal to or higher than the above lower limit, it can be suitably used for power semiconductor devices and the like that operate at high temperatures.
The thermal conductivity can be adjusted by the type of thermoplastic resin and physical properties such as melt viscosity, the structure, oil absorption and content of the aggregated boron nitride particles, the method of mixing the thermoplastic resin and the aggregated boron nitride particles, and the conditions in the heating and kneading step described later.

The thermal conductivity in the thickness direction when the present thermally conductive resin sheet is cured, or the thermal conductivity in the thickness direction when the present thermally conductive resin composition is molded into a sheet and cured can be measured by the following method.
For example, using a thermal resistance measuring device (manufactured by Mentor Graphics Co., Ltd., product name “T3ster”), the thermal resistance value of a cured product of a resin composition having the same composition and different thicknesses prepared under the same conditions is measured, and the thermal conductivity can be obtained from the slope of the graph plotting the thermal resistance value against the thickness.

The lower limit of the thickness of the present thermally conductive resin sheet is preferably 50 µm or more, more preferably 60 µm or more, and even more preferably 70 µm or more. On the other hand, the upper limit of the thickness is preferably 400 µm or less, more preferably 300 µm or less, and even more preferably 250 µm or less.
By setting the thickness of the present thermally conductive resin sheet to 50 μm or more, sufficient withstand voltage characteristics can be ensured. On the other hand, by setting the thickness to 400 μm or less, it is possible to achieve miniaturization and thinning, especially when the thermally conductive resin sheet is used for a power semiconductor device, etc., and compared to an insulating thermally conductive layer made of a ceramic material, it is possible to obtain the effect of reducing thermal resistance in the thickness direction by thinning.

<Method for producing thermally conductive resin sheet and sheet-like cured product>
An example of a method for producing the present thermally conductive resin sheet and a sheet-like cured product as a cured product of the sheet will be described below.

The present thermally conductive resin sheet can be produced by forming the present thermally conductive resin composition into a sheet (this process is referred to as a "film forming process"), drying it as necessary (this process is referred to as a "drying process"), and further applying pressure as necessary (this process is referred to as a "pressurizing process"). Then, the thermally conductive resin sheet obtained in this way can be cured to produce a sheet-like cured product (this process is referred to as a "curing process").

(Film forming process)
For example, the present thermally conductive resin composition in a slurry state can be formed into a sheet by a coating method such as a blade method, a solvent casting method, an extrusion film forming method, or the like.

When forming a sheet-like film by the coating method, first, the surface of a base material is coated with the present thermally conductive resin composition in slurry form to form a coating film. That is, using the present thermally conductive resin composition in slurry form, a coating film is formed on a substrate by a dipping method, a spin coating method, a spray coating method, a blade method, or any other method.
A coating device such as a spin coater, a slit coater, a die coater, a blade coater, or the like can be used to apply the present thermally conductive resin composition in slurry form. With such a coating device, it is possible to uniformly form a coating film having a predetermined thickness on a substrate.
As the substrate, a copper plate or copper foil or a PET film, which will be described later, is generally used, but the substrate is not limited at all.

(Drying process)
The thermally conductive resin composition formed into a sheet as described above is usually dried at a temperature of 10 to 150° C., preferably 25 to 120° C., more preferably 30 to 110° C. in order to remove solvents and low-molecular-weight components.
When the drying temperature is equal to or lower than the above upper limit, curing of the resin in the present thermally conductive resin composition is suppressed, and the resin in the sheet-shaped resin composition flows in the subsequent pressurization step, making it easier to remove voids. When the drying temperature is equal to or higher than the above lower limit, the solvent can be effectively removed, and productivity tends to improve.
The drying time is not particularly limited, and can be appropriately adjusted depending on the state of the present thermally conductive resin composition, the drying environment, and the like. The drying time is preferably 1 minute or longer, more preferably 2 minutes or longer, and still more preferably 5 minutes or longer. The drying time is preferably 24 hours or less, more preferably 10 hours or less, still more preferably 4 hours or less, and particularly preferably 2 hours or less.
When the drying time is at least the above lower limit, the solvent can be sufficiently removed, and there is a tendency that the residual solvent can be prevented from forming voids in the cured resin. When the drying time is equal to or less than the above upper limit, productivity tends to improve and production costs can be suppressed.

(pressurization process)
After the drying step, it is desirable to pressurize the obtained sheet-like present thermally conductive resin composition for the purpose of bonding the aggregated inorganic fillers together to form a heat conduction path, the purpose of eliminating voids and gaps in the sheet, the purpose of improving the adhesion to the base material, and the like. However, depending on the purpose, it is not necessary to pressurize.

In the pressing step, it is desirable to apply a load of 2 MPa or more to the present thermally conductive resin composition in sheet form on the substrate.
The load is preferably 5 MPa or more, more preferably 7 MPa or more, still more preferably 9 MPa or more. Also, the load is preferably 1500 MPa or less, more preferably 1000 MPa or less, and still more preferably 800 MPa or less.
By setting the load during pressurization to the above upper limit or less, the secondary particles of the aggregated inorganic filler are not destroyed, and a sheet having high thermal conductivity without voids in the present thermally conductive resin composition in sheet form can be obtained. When the weight is equal to or higher than the above lower limit, the contact between the aggregated inorganic fillers is improved and heat conduction paths are easily formed, so that a cured resin product having high heat conductivity can be obtained.

The heating temperature of the sheet-like present thermally conductive resin composition 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 still more preferably 30° C. or higher. The heating temperature is preferably 300° C. or lower, more preferably 250° C. or lower, still more preferably 200° C. or lower, even more preferably 100° C. or lower, particularly preferably 90° C. or lower.
By performing the pressurization step in this temperature range, the melt viscosity of the resin in the present thermally conductive resin composition in sheet form can be reduced, and voids and spaces in the cured resin can be further reduced. Further, by heating at a temperature not higher than the above upper limit, decomposition of organic components in the sheet-like resin composition and cured resin and voids generated by residual solvent tend to be suppressed.

The time for the pressurization step is not particularly limited. The time for the pressurizing step is preferably 30 seconds or longer, more preferably 1 minute or longer, still more preferably 3 minutes or longer, and particularly preferably 5 minutes or longer. The time for the pressurization step is preferably 1 hour or less, more preferably 30 minutes or less, still more preferably 20 minutes or less.
When the pressurization time is equal to or less than the above upper limit, the production time of the cured resin can be suppressed, and the production cost tends to be reduced. When the pressurization time is at least the above lower limit, voids and voids in the cured resin can be sufficiently removed, and heat transfer performance and withstand voltage characteristics tend to be improved.

(Curing process)
The thermally conductive resin composition can be cured by heating.
At this time, the heating temperature is preferably 30 to 400° C., more preferably 50° C. or higher, and more preferably 90° C. or higher. On the other hand, the temperature is preferably 300° C. or lower, and more preferably 250° C. or lower.

The curing step in which the thermally conductive resin composition is completely cured may be performed under pressure or without pressure. When pressurizing, it is desirable to carry out under the same conditions as the above pressurizing step for the same reason as above. Note that the pressurizing step and the curing step may be performed at the same time.
In particular, in the sheeting process that includes the pressurizing process and the curing process, it is preferable to pressurize and cure by applying a load within the above range.

There is no particular limitation on the load when the pressing step and the curing step are performed simultaneously. In this case, it is preferable to apply a load of 5 MPa or more to the sheet-like present thermally conductive resin composition on the substrate, and the load is more preferably 7 Pa or more, still more preferably 9 MPa or more, and particularly preferably 20 MPa or more. Also, the load is preferably 2000 MPa or less, more preferably 1500 MPa or less.
By setting the load when the pressurizing step and the curing step are performed simultaneously to the above upper limit or less, the secondary particles of the aggregated inorganic filler do not break, and a sheet-like cured product having high thermal conductivity without voids in the sheet-like present thermally conductive resin composition can be obtained. In addition, by setting the weight to the above lower limit or more, the contact between the aggregated inorganic fillers becomes good, making it easier to form a thermal conduction path, so that a cured resin product having high thermal conductivity can be obtained.

The pressurization time is not particularly limited when the pressurization step and the curing step are performed simultaneously. The pressurization time is preferably 30 seconds or longer, more preferably 1 minute or longer, still more preferably 3 minutes or longer, and particularly preferably 5 minutes or longer. Also, the pressurization time is preferably 1 hour or less, more preferably 30 minutes or less, and still more preferably 20 minutes or less.
When the pressurization time is equal to or less than the above upper limit, the production time of the sheet-shaped resin cured product can be suppressed, and the production cost tends to be reduced. When the pressurization time is at least the above lower limit, gaps and voids in the cured resin sheet can be sufficiently removed, and heat transfer performance and withstand voltage characteristics tend to be improved.

<<Heat dissipation laminate>>
A heat-dissipating laminate (referred to as "the present heat-dissipating laminate") according to an example of an embodiment of the present invention may be a laminate including the present thermally conductive resin sheet.

As an example of the heat-dissipating laminate, a heat-dissipating metal layer containing a heat-dissipating material is laminated on one surface of the heat-conducting resin sheet.

The heat dissipating material is not particularly limited as long as it is made of a material having good thermal conductivity. Among them, in order to increase the thermal conductivity in the laminated structure, it is preferable to use a metal material for heat radiation, and among them, it is more preferable to use a flat metal material.
The material of the metal material is not particularly limited. Among them, a copper plate, an aluminum plate, an aluminum alloy plate, and the like are preferable because they have good thermal conductivity and are relatively inexpensive.

Press molding, which is a batch process, can be preferably used for the lamination and integration of the present thermally conductive resin sheet and the metal layer for heat dissipation. The press equipment, press conditions, etc. in this case are the same as the range of the press molding conditions for obtaining the above-mentioned thermally conductive resin sheet.

<<Heat dissipation circuit board>>
A heat-dissipating circuit board (referred to as "the present heat-dissipating circuit board") according to an example of an embodiment of the present invention may be provided with the present thermally conductive resin sheet.
As an example of the present heat-dissipating circuit board, one having a configuration in which the heat-dissipating metal layer is laminated on one surface of the present heat-conducting resin sheet, and a circuit board is formed on the other surface of the heat-dissipating metal layer of the heat-conducting resin sheet by, for example, etching. Specifically, it is more preferable to integrate "metal layer for heat radiation/thermal conductive resin sheet/conductive circuit". The state before circuit etching includes, for example, an integrated structure of "heat-dissipating metal layer/thermally conductive resin 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 thermally conductive resin sheet, or formed on a partial area.

The material of the conductive circuit forming metal layer is not particularly limited. Above all, it is generally preferable to use a copper thin plate having a thickness of 0.05 mm or more and 1.2 mm or less from the viewpoint of good electrical conductivity, etching properties, and cost.

<<Semiconductor Device>>
A semiconductor device (referred to as "the present semiconductor device") according to an example of the embodiment of the present invention may be provided with the present heat dissipation circuit board.
As an example of the present semiconductor device, there can be mentioned a device having a configuration in which a silicon wafer or a rewiring layer is formed on which semiconductor chips that have been singulated in advance are mounted on the present heat dissipating circuit board.

<<Power Module>>
A power module (referred to as "the present power module") according to an example of an embodiment of the present invention may be provided with the present thermally conductive resin sheet.
An example of the power module is a power semiconductor device in which the thermally conductive resin sheet is used as a heat dissipating circuit board.
In this power semiconductor device, conventionally known members such as aluminum wiring, sealing material, packaging material, heat sink, thermal paste, and solder other than the thermally conductive resin sheet or the laminated heat dissipation sheet can be appropriately employed.

<<explanation of words>>
In the present invention, the expression "X to Y" (X and Y are arbitrary numbers) includes the meaning of "X or more and Y or less" and "preferably larger than X" or "preferably smaller than Y" unless otherwise specified.
In addition, when expressing "X or more" (X is an arbitrary number) or "Y or less" (Y is an arbitrary number), it also includes the meaning of "preferably larger than X" or "preferably less than Y".
In the present invention, the term "sheet" conceptually includes sheets, films and tapes.

EXAMPLES The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples as long as the gist thereof is not exceeded.

<Materials used>
Materials used in Examples and Comparative Examples are as follows.

(Thermosetting resin)
High-molecular-weight epoxy resin A: A high-molecular-weight epoxy resin (mass average molecular weight in terms of polystyrene: 30,000, epoxy equivalent: 9,000 g/equivalent) having the structure (2) (R ³ = structure (4)) and structure (3) (R ⁴ , R ⁵ , R ⁶ , R ⁷ = methyl group) and containing no amine-based or amide-based structure
• Aromatic epoxy resin B: A bifunctional epoxy resin that does not contain an amine or amide structure. molecular weight about 400
- Polyfunctional epoxy resin C: a polyfunctional epoxy resin (molecular weight of 500 or less) containing 4 or more glycidyl groups per molecule and not containing an amine or amide structure

(Inorganic filler)
・ Thermally conductive filler D: Spherical boron nitride aggregate particles having a card house structure manufactured based on International Publication No. 2015/119198 (average particle size (D50) 45 μm, maximum particle size (Dmax) 90 μm), breaking strength 6 MPa, elastic modulus 65 MPa
・ Silica nanoparticles E: Admanano YA010C-SP3 manufactured by Admatechs
Average particle size 10 nm, with surface phenyl group treatment
Specific surface area 296 m ² /g

(other ingredients)
・ Curing agent F: Phenolic resin curing agent “MEH-8000H” (manufactured by Meiwa Kasei Co., Ltd.)
Curing catalyst G: 2,4-diamino-6-[2′-ethyl-4′-methylimidazolyl-17′)]-ethyl-s-triazine (“2E4MZ-A”, manufactured by Shikoku Kasei Co., Ltd., a compound having a triazine ring as a nitrogen atom-containing heterocyclic structure. Molecular weight: 247)
Melting point: 215-225°C
・Organic solvent: mixed solvent of methyl ethyl ketone and cyclohexanone

The average particle diameter (D50) and the maximum particle diameter (Dmax) of the particles of the thermally conductive filler D are the maximum particle diameter Dmax and the cumulative volume 50% particle diameter (average particle diameter D50) obtained by dispersing the thermally conductive filler in a pure water medium containing sodium hexametaphosphate as a dispersion stabilizer, measuring the volume-based particle size distribution with a laser diffraction/scattering particle size distribution analyzer LA-300 (manufactured by Horiba, Ltd.), and obtaining the obtained particle size distribution. .
The average particle diameter and specific surface area of the silica nanoparticles E are catalog values manufactured by Admatechs.

(Measurement of breaking strength and elastic modulus of aggregated inorganic filler)
The breaking strength and elastic modulus of the aggregated inorganic filler were measured by the following methods.

The breaking strength of the aggregated inorganic filler was measured using a microcompression tester (manufactured by Shimadzu Corporation, product name "MCT-510").
A very small amount of the sample was sprinkled on the pressure plate installed at the bottom of the microcompression tester, and the compression test was performed one by one, and the breaking strength was obtained using the following formula from the breaking test force when the particles broke and the particle diameter of the particles. Five particles were measured, and the average value was taken as the breaking strength of the aggregated inorganic filler.
Cs = 2.48P/( ^πd2 )
(“Cs” is breaking strength (MPa), “P” is breaking test force (N), and “d” is particle diameter (mm).)

Normally, the breaking strength is calculated using the test force at the breaking point, but if the breaking point is not clear (for example, the sample deforms but does not suddenly break), 10% deformation is used as a reference strength. The 10% strength was calculated from the following formula.
Cx=2.48P/( ^πd2 )
(“Cx” is the 10% strength (MPa), “P” is the test force (N) at 10% displacement of the particle diameter, and “d” is the particle diameter (mm).)

The elastic modulus of the aggregated inorganic filler was calculated from the following formula from the test force at the time when the fracture occurred and the compression displacement at that time, using the device used for measuring the fracture strength.
E=3×(1−ν ² )×P/4×(d/2) ^1/2 ×Y ^3/2
(“E” is the elastic modulus (MPa), “ν” is the Poisson’s ratio, “P” is the breaking test force (N), “d” is the particle diameter (mm), and “Y” is the compression displacement (mm), where the Poisson's ratio was assumed to be constant (0.13).)

<Examples 1 and 2, Comparative Examples 1 to 3>
Using a rotation-revolution stirring device, high-molecular-weight epoxy resin A, aromatic epoxy resin B, polyfunctional epoxy resin C, thermally conductive filler D, silica nanoparticles E, curing agent F, and curing catalyst G were added to an organic solvent composed of methyl ethyl ketone and cyclohexanone at the mass ratio shown in the table, and mixed to prepare a resin composition as a coating slurry. At this time, methyl ethyl ketone and cyclohexanone were used so that the solid content concentration was 65% by mass.

The resulting coating slurry (slurry for sheet) was applied to a PET base material by a doctor blade method and dried by heating at 60° C. for 120 minutes to obtain a sheet-like compact with a thickness of 150 μm.

<Evaluation of sheet-shaped compact>
The sheet-shaped moldings obtained in the above examples and comparative examples were evaluated as follows.

(Thermal conductivity in the thickness direction of the sheet-shaped compact)
The sheet-like molding was heated and cured at 175° C. for 30 minutes while being pressurized.
The thermal resistance values of four sheets with different thicknesses were measured using the following apparatus and conditions, and the thermal conductivity in the sheet thickness direction was measured by a steady method from the slope represented by the thermal resistance value with respect to the thickness of the sheet (conforms to ASTM D5470).
(1) Thickness: Thickness (μm) when pressed at a press pressure of 3400 kPa using Mentor Graphics T3Ster-DynTIM
(2) Measurement area: area (cm ² ) of the portion that transfers heat when measured using Mentor Graphics T3Ster-DynTIM
(3) Thermal resistance value: Thermal resistance value (K/W) when pressed at a press pressure of 3400 kPa using Mentor Graphics T3Ster-DynTIM
(4) Thermal conductivity: The thermal resistance values of four sheets with different thicknesses are measured, and the thermal conductivity (W/m·K) is calculated from the following formula.
Formula: Thermal conductivity (W/m·K) = 1/((slope (thermal resistance/thickness): K/(W·μm)) × (area: cm ² )) × 10 ^-2

(Surface smoothness of sheet-like molding)
For the surfaces of the sheet-shaped moldings (before curing) obtained in the above examples and comparative examples, the arithmetic mean height Ra was measured using a surfcom, and those with an Ra of 6.3 or more were evaluated as "x" (failed), and those with an Ra of less than 6.3 were evaluated as "o" (accepted) and shown in Table 1.
The measurement conditions are as follows Measurement speed: 0.3 mm/s
Λc: 0.8mm
Calculation standard: JIS2001/2013
Cutoff type: Gaussian Evaluation length: 25.00 mm
Shape Removal: Straight Line

From the above examples and the results of tests conducted by the present inventors so far, in order to further increase the thermal conductivity, the aggregate particles of boron nitride as a thermally conductive filler are contained in an amount of 60% by mass or more with respect to 100% by mass of the total solid content of the thermally conductive resin composition. It was found that unevenness on the surface of the formed resin sheet can be suppressed.
As for the reason for this, it can be presumed that by including a predetermined amount or more of silica nanoparticles, the friction between the aggregated particles of boron nitride is reduced and the fluidity of the thermally conductive resin composition is increased, so that when the thermally conductive resin composition is applied and dried, rearrangement of the coated surface easily occurs, and unevenness of the sheet surface can be suppressed.
Considering such a mechanism of action, it can be considered that similar effects can be obtained even when other thermosetting resins are used in place of the epoxy resin in the above examples.

Claims (15)

A thermally conductive resin composition comprising a thermosetting resin, and a thermally conductive filler and silica nanoparticles as inorganic fillers,
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% by mass and 10% by mass or less with respect to 100% by mass of the total solid content of the thermally conductive resin composition,
The thermally conductive filler contains aggregated particles of boron nitride, and the average particle diameter of the aggregated particles is 5 μm or more and 100 μm or less,
The thermally conductive resin composition, wherein the content of the thermally conductive filler is 60% by mass or more and 85% by mass or less with respect to 100% by mass of the total solid content of the thermally conductive resin composition. The thermally conductive resin composition according to claim 1, wherein the aggregated particles of boron nitride account for 75% by mass or more of the thermally conductive filler. 2. The thermally conductive resin composition according to claim 1, wherein the aggregated particles of boron nitride have an elastic modulus of 48 MPa or more. 2. The thermally conductive resin composition according to claim 1, wherein the aggregated particles of boron nitride have a breaking strength of 20 MPa or less. 2. The thermally conductive resin composition according to claim 1, wherein the particle size ratio (BN/silica) of the average particle size of the aggregated particles of boron nitride to the average particle size of the silica nanoparticles is 100 to 50,000. 2. The thermally conductive resin composition according to claim 1, wherein said silica nanoparticles are surface-treated with an organometallic compound. 2. The thermally conductive resin composition according to claim 1, wherein the thermosetting resin comprises a polyfunctional epoxy resin having three or more epoxy groups per molecule and a molecular weight of 650 or less. 8. The thermally conductive resin composition according to claim 7, wherein the polyfunctional epoxy resin is an epoxy resin having 4 or more glycidyl groups in the molecule. The thermally conductive resin composition according to claim 1, comprising 10% by mass or more and less than 30% by mass of a polymer having a mass average molecular weight of 10,000 or more with respect to 100% by mass of the resin component excluding inorganic particles from the solid content of the thermally conductive resin composition. A thermally conductive resin sheet formed from the thermally conductive resin composition according to any one of claims 1 to 9. 11. The thermally conductive resin sheet according to claim 10, wherein the thermal conductivity in the thickness direction after curing is 10 W/mK or more. A heat dissipation laminate comprising the thermally conductive resin sheet according to claim 10 . A heat dissipating circuit board comprising the heat conductive resin sheet according to claim 10. A semiconductor device comprising the heat dissipation circuit board according to claim 13 . A power module comprising the thermally conductive resin sheet according to claim 10.