Resin composition, cured sheet, composite molded body, and semiconductor device

Abstract

The present invention provides: a resin composition which has high thermal conductivity, high insulation properties and high heat resistance, while forming a sheet that has excellent handling properties; a cured product sheet; a composite molded body; and a semiconductor device. The present invention uses a resin composition which contains an inorganic filler and a thermosetting resin, wherein: the inorganic filler content in the solid content of the resin composition is 50% by volume or more; the inorganic filler contains 82% by volume or more of a boron nitride filler (A); the boron nitride filler contains filler aggregates; the thermosetting resin contains an epoxy resin that has a mass average molecular weight of 5,000 or more; the epoxy equivalent weight (WPE) of the resin component in the resin composition satisfies 100 ≤ WPE ≤ 300; and the storage elastic modulus E' of a cured product of the resin composition satisfies 1 ≥ (E' at 270°C) / (E' at 30°C) ≥ 0.2.

Description

[Technical Field]

[0001] The present invention relates to a resin composition, and the resin composition and a cured product using the resin composition can be suitably used as a heat dissipation sheet for a power semiconductor device, for example. This application claims priority based on Japanese Patent Application No. 2021-55114, filed on March 29, 2021, the contents of which are incorporated herein by reference. [Background technology]

[0002] In recent years, power semiconductor devices used in various fields such as railways, automobiles, and general home appliances are shifting from conventional Si power semiconductors to power semiconductors using SiC, AlN, GaN, etc. in order to become smaller, lower cost, and more efficient. Power semiconductor devices are generally used as a power semiconductor module in which a plurality of semiconductor devices are arranged on a common heat sink and packaged.

[0003] Various challenges have been identified for the practical application of such power semiconductor devices, one of which is the problem of dissipating heat generated by the devices. This problem generally affects the reliability of power semiconductor devices, which are capable of high output and high density when operated at high temperatures. There are concerns that the heat generated by device switching will reduce reliability.

[0004] In recent years, particularly in the electrical and electronics fields, heat generation due to the increasing density of integrated circuits and higher voltages due to higher output have become major problems, and how to dissipate heat and maintain high insulation properties have become urgent issues.

[0005] One method to solve this problem is to use highly thermally conductive ceramic substrates such as alumina substrates and aluminum nitride substrates as heat dissipation substrates on which power semiconductor devices are mounted. However, ceramic substrates have drawbacks such as being easily cracked by impact and being difficult to make thin and compact.

[0006] To solve the problems with ceramic substrates described above, much research has been conducted on heat-dissipating sheets with good thermal conductivity and excellent insulation. In particular, attempts have been made to obtain heat-dissipating resin sheets that satisfy high levels of thermal conductivity and insulation by mixing fillers into resins. Various oxides and nitrides are used as fillers in such heat-dissipating resin sheets, and much research has been conducted on these fillers (e.g., Patent Document 1).

[0007] Attempts have been made to use hexagonal boron nitride as a filler in heat-dissipating sheets. Hexagonal boron nitride is generally a thin plate-shaped crystal, and while the thermal conductivity in the planar direction of the thin plate is high, the thermal conductivity in the thickness direction of the thin plate is low. Furthermore, when thin plate-shaped boron nitride is incorporated into a heat-dissipating sheet, it is oriented parallel to the sheet surface when formed into a sheet, so the thermal conductivity in the thickness direction of the sheet is never good.

[0008] Agglomerated boron nitride fillers are one example of a material that increases the thermal conductivity of a sheet in the thickness direction. It is widely known that the use of agglomerated boron nitride fillers can improve the thermal conductivity of a sheet in the thickness direction. In particular, the present inventors have previously developed a house-of-cards structured agglomerated boron nitride filler (see, for example, Patent Document 2). Furthermore, they have developed a house-of-cards structured agglomerated boron nitride filler that has a relatively large average particle size and is less likely to collapse even when pressure is applied (see, for example, Patent Document 3). These agglomerated boron nitride fillers ensure a thermal conduction path through their house-of-cards structure, and their inclusion in a heat-dissipating sheet improves the thermal conductivity of the sheet in the thickness direction. Furthermore, agglomerated boron nitride fillers are composed of agglomerated boron nitride particles without the use of a separate binder. Therefore, even when external force is applied during sheeting, the house-of-cards structure does not easily collapse, maintaining the thermal conduction path and enabling heat dissipation in the thickness direction of the sheet, thereby achieving excellent thermal conductivity (see, for example, Patent Documents 4 and 5). Furthermore, as a molding method for increasing the thermal conductivity in the thickness direction of a sheet, a method is known in which the agglomerated boron nitride fillers in the sheet are brought into surface contact with each other to increase the thermal conductivity (see, for example, Patent Document 6). [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-089670 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-006985 [Patent Document 3] Japanese Patent Application Laid-Open No. 2016-135730 [Patent Document 4] International Publication No. 2015 / 119198 [Patent Document 5] Japanese Patent Application Laid-Open No. 2017-036415 [Patent Document 6] International Publication No. 2019 / 189746 Summary of the Invention [Problem to be solved by the invention]

[0010] However, the present inventors have found that with the compositions disclosed in Patent Documents 2 to 6, increasing the filler content to increase thermal conductivity can result in the problem of reduced insulating properties due to remaining voids in the sheet. Furthermore, the present inventors have also found that the composition disclosed in Patent Document 1 does not achieve both heat resistance and easy handling of the sheet before curing. An object of the present invention is to provide a resin composition, a cured sheet, a composite molded product, and a semiconductor device that have high thermal conductivity and high insulating properties, preferably high heat resistance and excellent sheet handling properties. [Means for solving the problem]

[0011] As a result of extensive investigations into solving the above problems, the present inventors have found that the above problems can be solved by using a resin composition containing a specific filler and resin. The present invention was achieved based on these findings and is summarized as follows.

[0012] [1] A resin composition containing an inorganic filler and a thermosetting resin, The content of the inorganic filler in the solid content of the resin composition is 50% by volume or more, and the content of the boron nitride filler (A) in the inorganic filler is 82% by volume or more, the boron nitride filler comprises an agglomerated filler; the thermosetting resin contains an epoxy resin having a mass average molecular weight of 5000 or more, The epoxy equivalent (WPE) of the resin component in the resin composition is 100≦WPE≦300, A resin composition having a storage modulus E' of a cured product of the resin composition, wherein 1≧(E' at 270°C) / (E' at 30°C)≧0.2. [2] The resin composition according to [1], wherein the modulus of rigidity G' of the cured product of the resin component satisfies 1≧(G' at 200°C) / (G' at 30°C)>0.1. [3] The storage modulus E' of the cured product of the resin composition is 1 × 10 at 30 ° C. 8 The resin composition according to [1] or [2], wherein the temperature is 100°C or higher. [4] The inorganic filler contains an inorganic filler (B) other than the boron nitride filler (A), the inorganic filler (B) contains spherical particles having an average particle size of 0.1 μm or more and 1 μm or less, The resin composition according to any one of [1] to [3], wherein the inorganic filler contains spherical particles having an average particle size of 0.1 μm or more and 1 μm or less at a content of 2.4% by volume or less. [5] The resin composition according to any one of [1] to [4], wherein the thermosetting resin comprises an epoxy resin having a mass average molecular weight of 10,000 or more and an epoxy resin having a mass average molecular weight of 600 or less. [6] The resin composition according to [5], wherein the epoxy resin having a mass average molecular weight of 600 or less contains three or more epoxy groups in one molecule. [7] The resin composition according to any one of [1] to [6], wherein the inorganic filler (B) is a metal oxide and / or a non-metal oxide. [8] A sheet cured product obtained by using the resin composition according to any one of [1] to [7]. [9] A composite molded article having a cured part made of the sheet cured product according to [8] and a metal part.

[10] A semiconductor device comprising the composite molded body according to [9]. [Effects of the Invention]

[0013] The resin composition containing the specific filler and resin of the present invention can provide a cured sheet, a composite molded product, and a semiconductor device that combine high thermal conductivity, high insulation, and high heat resistance while maintaining the handleability of the uncured sheet. DETAILED DESCRIPTION OF THE INVENTION

[0014] The following describes in detail the embodiments of the present invention, but the present invention is not limited to the following embodiments and can be practiced in various modified forms within the scope of the gist thereof.

[0015] [Resin composition] The resin composition of the present invention contains an inorganic filler and a thermosetting resin, and refers to a composition in a state before curing in a molding and pressurizing step, etc. Examples include a slurry-like resin composition to be subjected to a coating step described below, a sheet that has been subjected to a coating step, a sheet that has been subjected to a step of coating and drying, etc.

[0016] The reasons why the resin composition of the present invention exhibits the above-mentioned effects include the following. 1) For high thermal conductivity, by containing 50% by volume or more of inorganic filler and including 82% by volume or more of boron nitride filler (A) among the inorganic fillers, it is possible to ensure sufficient thermal conduction paths in the sheet thickness direction after the sheet is cured, and it is possible to increase the thermal conductivity. 2) For high insulation, by setting the WPE of the resin component to 100≦WPE≦300, it is possible to reduce voids in the cured sheet by improving resin fluidity and improve the dielectric strength voltage by increasing crosslink density. Therefore, it is possible to improve the insulation of the cured sheet made using the resin composition. In particular, when the proportion of boron nitride filler, which is an agglomerated filler, is high, voids are likely to occur, so it is effective to set the WPE of the resin component within the above range. Furthermore, when the sheet is depressurized after being pressurized, so-called springback, in which voids reappear, may occur. It is believed that by setting the WPE of the resin component within this range, springback can be suppressed by improving crosslink density. 3) In terms of high heat resistance, by controlling the change in the storage modulus E' of the cured resin composition within a specific range, it is possible to suppress deformation of the cured sheet at high temperatures and increase the mechanical strength of the cured product, thereby improving heat resistance. 4) Regarding the handleability of the sheet, by including a resin with a molecular weight of 5000 or more, the film-forming properties of the sheet before curing are improved, and the handleability of the uncured sheet can be improved.

[0017] The ratio of the storage modulus E' at 270°C and 30°C of the cured resin composition of the present invention ((E' at 270°C) / (E' at 30°C)) is 1 ≧ (E' at 270°C) / (E' at 30°C) ≧ 0.20. Preferably, it is 0.99 ≧ (E' at 270°C) / (E' at 30°C), more preferably 0.95 ≧ (E' at 270°C) / (E' at 30°C). Also, it is preferably (E' at 270°C) / (E' at 30°C) ≧ 0.22, more preferably (E' at 270°C) / (E' at 30°C) ≧ 0.25, and even more preferably (E' at 270°C) / (E' at 30°C) ≧ 0.28. When the ratio is within these ranges, it tends to be possible to maintain the interfacial adhesive strength by maintaining the elastic modulus at high temperatures and to suppress cracking by reducing thermal stress. The cured resin composition is prepared by laminating sheets of the resin composition of the present invention, adjusting the sample thickness to 0.1 to 1.0 mm, and then heating and curing the laminate. During the heating process, the resin composition is cured until the exothermic peak obtained when the temperature is increased from 40°C to 250°C at a rate of 10°C / min using a differential scanning calorimeter (DSC) is 10 J / g or less. In addition, E' at 30°C and 270°C was measured by laminating sheets of the resin composition, adjusting the sample thickness to 0.1 to 1.0 mm, and heat-curing the resulting cured product, which was then cut into strips 4 mm wide and subjected to a dynamic viscoelasticity test in a tensile mode.

[0018] There are no particular limitations on the method for adjusting the ratio of the storage modulus E' at 270°C and 30°C of the cured product of the resin composition to fall within the above range. Examples include improving the crosslink density by reducing the WPE of the resin component, increasing the glass transition temperature (Tg) (hereinafter, glass transition temperature may be referred to as Tg) by incorporating a resin with a high Tg, and increasing the amount of filler incorporated.

[0019] There are no particular limitations as long as the ratio of the storage modulus E' at 270°C and 30°C of the cured product of the resin composition is within the above range. The storage modulus E' at 30°C is 1 x 10 8 Pa or more, and 5 × 10 8 Pa or more is more preferable, and 1×10 9 It is more preferable that the viscosity is 1×10 Pa or more. 12 Pa or less, and 11 It is more preferable that the viscosity is not more than 100 Pa. When the viscosity is in this range, the effect of increasing the mechanical strength of the cured product at room temperature tends to be obtained. The storage modulus E at 270°C is 2 x 10 7 Pa or more, and 5 × 10 7 Pa or more is more preferable, and 1×10 8 It is more preferable that the viscosity is 1×10 Pa or more. 11 Pa or less, and 10It is more preferable that the modulus of elasticity is not more than 1 Pa. By keeping the modulus of elasticity in this range, it is possible to maintain the interfacial adhesive strength by maintaining the modulus of elasticity at high temperatures and to suppress cracking by reducing thermal stress.

[0020] <Thermosetting resin> The thermosetting resin of the present invention contains an epoxy resin having a mass average molecular weight of at least 5000. As long as the resin having a mass average molecular weight of at least 5000 contains an epoxy resin, it may contain a thermosetting resin other than an epoxy resin or an epoxy resin having a different molecular weight. The thermosetting resin contained in the resin composition of the present invention is not particularly limited as long as it can be cured in the presence of a curing agent or a thermosetting catalyst to give a cured product. Specific examples of thermosetting resins include epoxy resins, phenolic resins, polycarbonate resins, unsaturated polyester resins, urethane resins, melamine resins, and urea resins. Among these, epoxy resins are preferred from the viewpoints of viscosity, heat resistance, moisture absorption, and ease of handling. Examples of epoxy resins include epoxy group-containing silicon compounds, aliphatic epoxy resins, bisphenol A or F epoxy resins, novolac epoxy resins, biphenyl epoxy resins, alicyclic epoxy resins, glycidyl ester epoxy resins, multifunctional epoxy resins, and polymeric epoxy resins.

[0021] (epoxy resin) Epoxy resin is a general term for compounds that have one or more oxirane rings (epoxy groups) in the molecule. The oxirane rings (epoxy groups) contained in epoxy resins may be either alicyclic epoxy groups or glycidyl groups, but from the viewpoints of reaction rate and heat resistance, glycidyl groups are more preferable.

[0022] The epoxy resin used in the present invention contains an epoxy resin having a mass average molecular weight of 5,000 or more. The mass average molecular weight of the epoxy resin is preferably 10,000 or more, more preferably 20,000 or more, and even more preferably 30,000 or more. The upper limit is 100,000 or less. By keeping the mass average molecular weight within these ranges, the film-forming properties of the resin composition and the handling properties of the uncured sheet tend to be improved. Furthermore, the improved film properties have the effect of binding fillers together at the uncured sheet stage, making voids less likely to occur. The mass average molecular weight of the epoxy resin of the present invention is a value calculated as polystyrene equivalent measured by gel permeation chromatography. The epoxy equivalent is defined as "the mass of an epoxy resin containing one equivalent of epoxy groups" and can be measured in accordance with JIS K7236.

[0023] Furthermore, the thermosetting resin of the present invention preferably contains an epoxy resin having a molecular weight of 600 or less. It is more preferably 550 or less, and even more preferably 500 or less. The lower limit is not particularly limited, but is preferably 100 or more. By containing an epoxy resin within these ranges, voids tend to be reduced due to improved resin fluidity.

[0024] The epoxy equivalent (WPE) of the resin component of the resin composition of the present invention is 100≦WPE≦300. When the resin composition of the present invention contains an inorganic filler and a solvent, the resin component referred to here is the component excluding the solvent. The lower limit of the epoxy equivalent (WPE) is preferably 110 or more, more preferably 120 or more. The upper limit of the epoxy equivalent (WPE) is preferably 290 or less, more preferably 270 or less. By keeping the WPE within these ranges, the effects of suppressing deformation of the cured product at high temperatures due to improved crosslink density and improving the mechanical strength of the cured product tend to be obtained. The method for measuring the epoxy equivalent of the resin component is not particularly limited, but it can be measured by potentiometric titration or the like.

[0025] The epoxy resin used in the present invention may be an aromatic oxirane ring (epoxy group)-containing compound. Specific examples thereof include bisphenol-type epoxy resins obtained by glycidylating bisphenols such as bisphenol A, bisphenol F, bisphenol AD, bisphenol S, tetramethylbisphenol A, tetramethylbisphenol F, tetramethylbisphenol AD, tetramethylbisphenol S, and tetrafluorobisphenol A; biphenyl-type epoxy resins; epoxy resins obtained by glycidylating dihydric phenols such as dihydroxynaphthalene and 9,9-bis(4-hydroxyphenyl)fluorene; epoxy resins obtained by glycidylating trisphenols such as 1,1,1-tris(4-hydroxyphenyl)methane; epoxy resins obtained by glycidylating tetrakisphenols such as 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane; and novolac-type epoxy resins obtained by glycidylating novolacs such as phenol novolac, cresol novolac, bisphenol A novolac, and brominated bisphenol A novolac.

[0026] The epoxy resin contained in the resin composition of the present invention is not particularly limited, but is preferably one or more selected from the group consisting of various bisphenol-type epoxy resins obtained by glycidylating bisphenols, such as bisphenol A-type epoxy resins and bisphenol F-type epoxy resins; various biphenyl-type epoxy resins obtained by glycidylating biphenyls; epoxy resins obtained by glycidylating aromatic compounds having two hydroxyl groups, such as dihydroxynaphthalene and 9,9-bis(4-hydroxyphenyl)fluorene; epoxy resins obtained by glycidylating trisphenols, such as 1,1,1-tris(4-hydroxyphenyl)methane; and epoxy resins obtained by glycidylating tetrakisphenols, such as 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane. Novolac-type epoxy resins obtained by glycidylating novolacs, such as phenol novolac, cresol novolac, bisphenol A novolac, and brominated bisphenol A novolac; and silicone-containing epoxy resins. In particular, as the epoxy resin having a mass average molecular weight of 5000 or more, a bisphenol type epoxy resin or a biphenyl type epoxy resin is preferred because the heat resistance and adhesiveness of the sheet tend to be improved. Furthermore, the epoxy resin having a mass average molecular weight of 600 or less is preferably a multifunctional epoxy resin containing three or more epoxy groups (oxirane rings) per molecule. Examples of such epoxy resins include EX321L, DLC301, and DLC402 manufactured by Nagase ChemteX Corporation, and BATG and PETG manufactured by Showa Denko K.K. The use of these resins tends to improve the elastic modulus of the cured product by increasing the crosslink density, and to reduce voids in the cured sheet by improving the resin fluidity.

[0027] (Content) When a solvent is contained, the thermosetting resin is preferably contained in an amount of 5 to 50% by volume, and particularly 10 to 40% by volume, based on 100% by volume of the resin composition (solid content) of the present invention excluding the solvent. When the content of the thermosetting resin component is equal to or greater than the lower limit, moldability is improved, and when it is equal to or less than the upper limit, the content of other components can be secured, resulting in improved thermal conductivity.

[0028] Furthermore, in the resin composition of the present invention, when an inorganic filler and a thermosetting catalyst described later are contained, the main component excluding the thermosetting catalyst is preferably an epoxy resin. Here, the main component refers to the component that is present in the largest amount. The proportion of epoxy resin in 100% by mass of the thermosetting resin contained in the resin composition of the present invention is not particularly limited, but is preferably 20% by mass or more, and more preferably 30% by mass or more. The upper limit may be 100% by mass, and all of the resin may be epoxy resin. Having the proportion of epoxy resin within the above range tends to improve the mechanical strength of the cured sheet and exhibit good adhesion to metal substrates.

[0029] Furthermore, among the epoxy resins contained in the thermosetting resin of the present invention, the epoxy resin having a mass average molecular weight of 5000 or more preferably comprises 5% by mass or more, more preferably 10% by mass or more. The epoxy resin preferably comprises 29% by mass or less, more preferably 27% by mass or less. These ranges tend to improve the film-forming properties of the resin composition and the handling properties of the uncured sheet. The epoxy resin contained in the thermosetting resin of the present invention preferably contains 30% by mass or more, more preferably 40% by mass or more, of epoxy resins having a mass average molecular weight of 600 or less. The content is also preferably 90% by mass or less, more preferably 80% by mass or less. These ranges tend to improve the crosslink density, thereby improving the elastic modulus of the cured sheet material, and to reduce voids in the cured sheet material, due to improved resin flowability.

[0030] The ratio of the modulus of rigidity G' at temperatures of 200°C and 30°C of the cured product of the resin component of the present invention is preferably 1 ≧ (G' at 200°C) / (G' at 30°C) > 0.1. More preferably, it is 0.9 ≧ (G' at 200°C) / (G' at 30°C), and even more preferably, it is 0.8 ≧ (G' at 200°C) / (G' at 30°C). The lower limit is more preferably (G' at 200°C) / (G' at 30°C) ≧ 0.2, and even more preferably (G' at 200°C) / (G' at 30°C) ≧ 0.25. By satisfying these ranges, it is possible to improve the interfacial adhesive strength of the filler at high temperatures by suppressing resin softening, and to improve the interfacial adhesive strength with the metal adherend by improving the mechanical strength of the cured product. The cured product of the resin component is the same as the cured product described above in E'. In addition, G' at 30°C and 200°C was measured by heating and curing a sheet molded product of a resin composition that did not contain inorganic filler using a rheometer under conditions of a strain of 0.3%, a frequency of 1 Hz, and a gap of 0.5 mm.

[0031] There are no particular limitations on the method for setting the ratio of the modulus of rigidity G' of the cured product of the resin composition at temperatures of 200°C and 30°C within the above range, but examples include improving the crosslink density by reducing the WPE of the resin component, and improving the crosslink density by adjusting the amount of curing agent to an appropriate amount.

[0032] <Inorganic filler> The resin composition of the present invention contains an inorganic filler in an amount of 50% by volume or more based on 100% by volume of the resin composition (solid content) of the present invention excluding the solvent if a solvent is contained, and contains 82% by volume or more of a boron nitride filler (A) based on 100% by volume of the inorganic filler. When a solvent is contained, the proportion of the inorganic filler in 100% by volume of the resin composition of the present invention excluding the solvent is preferably 51% by volume or more, more preferably 53% by volume or more, and the upper limit is preferably 90% by volume or less, more preferably 85% by volume or less. The proportion of the boron nitride filler (A) in 100% by volume of the inorganic filler is preferably 83% by volume or more, more preferably 85% by volume or more. There is no particular upper limit, and the boron nitride filler (A) may be 100% by volume. By ensuring that the inorganic filler content is within the above range, it is possible to ensure a heat conduction path between the inorganic fillers, thereby achieving high thermal conductivity.

[0033] Examples of inorganic fillers other than the boron nitride filler (A) include fillers composed of particles of at least one type selected from the group consisting of metal carbides, metal oxides, and metal nitrides. Examples of metal carbides include synthetic magnesite. Examples of metal oxides include aluminum oxide (alumina), magnesium oxide, aluminum oxide, silicon oxide, calcium oxide, zinc oxide, yttrium oxide, zirconium oxide, cerium oxide, ytterbium oxide, and sialon (ceramics composed of silicon, aluminum, oxygen, and nitrogen). Examples of metal nitrides include aluminum nitride and silicon nitride. The shape of the inorganic filler is not limited, and may be particulate, spherical, whisker-like, fibrous, plate-like, or an aggregate thereof, and inorganic fillers of the above types and shapes may be used in combination.

[0034] Among the above, it is preferable to contain a large amount of agglomerated inorganic filler in order to improve the thermal conductivity of the cured sheet of the present invention and control the linear expansion coefficient. By containing agglomerated inorganic filler, the agglomerated inorganic fillers come into contact with each other during the molding and pressurizing process and deform, and the surface contact forms more heat conduction paths, tending to result in high thermal conductivity. The agglomerated morphology of the agglomerated inorganic filler can be confirmed using a scanning electron microscope (SEM).

[0035] (Agglomerated inorganic filler) As the agglomerated inorganic filler, an electrically insulating filler can be used, and examples thereof include the above-mentioned filler composed of at least one type of particles selected from the group consisting of metal carbides, metal oxides, and metal nitrides. For power semiconductor applications, insulation is required, so the aggregated inorganic filler has a volume resistivity of 1×10 13 Ω·cm or more, especially 1×10 14 It is preferable that the filler is an inorganic compound having excellent insulating properties of Ω·cm or more. Among them, oxides and nitrides are preferable because the sheet cured product has sufficient electrical insulating properties. More specifically, alumina (Al2O3, volume resistivity 1×10 14 Ω·cm), aluminum nitride (AlN, volume resistivity 1×10 14 Ω·cm), boron nitride (BN, volume resistivity 1×10 14 Ω·cm), silicon nitride (Si3N4, volume resistivity 1×10 14 Ω·cm), silica (SiO2, volume resistivity 1×10 14 Among them, alumina, aluminum nitride, boron nitride, and silica are preferred, and alumina and boron nitride are particularly preferred.

[0036] The aggregated inorganic filler may be surface-treated with a surface treatment agent, and known surface treatment agents can be used.

[0037] These aggregated inorganic fillers may be used alone or in any combination and ratio of two or more. In particular, in the present invention, there are no particular limitations on the method or degree of aggregation of the aggregated inorganic filler.

[0038] (Boron nitride agglomerated particles) In the present invention, the boron nitride filler (A) contains agglomerated particles. Boron nitride has high thermal conductivity but is scaly, and while it conducts heat in the planar direction, it has high thermal resistance in the direction perpendicular to the planar direction. For ease of handling, it is preferable to use agglomerated particles in which the scales are gathered and agglomerated into a spherical shape. When the boron nitride agglomerated particles are stacked like cabbage, it is preferable to align them in the planar direction, with the radial direction of the agglomerated particles being the direction of good thermal conductivity. On the other hand, it is preferable that the boron nitride agglomerated particles have a house-of-cards structure. The "house-of-cards structure" is described, for example, in Ceramics 43 No. 2 (published by the Ceramic Society of Japan, 2008), and is a structure in which plate-shaped particles are stacked in a complex manner without being oriented. More specifically, boron nitride agglomerated particles having a house-of-card structure are aggregates of boron nitride primary particles, in which the flat surfaces and end surfaces of the primary particles come into contact with each other to form, for example, a T-shaped aggregate. As the boron nitride agglomerated particles used in the present invention, boron nitride agglomerated particles having the above-mentioned house-of-card structure are particularly preferred, and by using boron nitride agglomerated particles having a house-of-card structure, thermal conductivity can be further increased.

[0039] The new Mohs hardness of the boron nitride agglomerated particles is not particularly limited, but is preferably 5 or less, and although there is no particular lower limit, it is, for example, 1 or more. When the new Mohs hardness is 5 or less, the particles dispersed in the resin composition tend to come into surface contact with each other, forming heat conduction paths between the particles and tending to improve the thermal conductivity of the cured sheet. The volume average particle size of the boron nitride agglomerated particles is not particularly limited, but is preferably 10 μm or more, more preferably 15 μm or more. Also, it is preferably 100 μm or less, more preferably 90 μm or less. A volume average particle size of 10 μm or more results in a relatively large number of particles in the resin composition and in a cured product using the resin composition, which increases the number of interparticle interfaces, resulting in increased thermal resistance and possibly low thermal conductivity of the composite molded product. Furthermore, a volume average particle size of not more than the upper limit mentioned above tends to provide surface smoothness in a cured product using the resin composition.

[0040] Here, the volume-average particle size of boron nitride agglomerated particles refers to the particle size at which the cumulative volume reaches 50% when a cumulative curve is drawn, with the volume of the powder used for measurement being 100%. Measurement methods include wet measurement, in which a sample prepared by dispersing agglomerated particles in a pure water medium containing sodium hexametaphosphate as a dispersion stabilizer is measured using a laser diffraction / scattering particle size analyzer, and dry measurement, in which measurement is performed using a Malvern "Morphologi" analyzer. The same applies to the spherical filler described below. In the present invention, the "volume average particle size" may also be simply referred to as the "average particle size."

[0041] <Content of boron nitride agglomerated inorganic filler> The content of the boron nitride agglomerated inorganic filler in the inorganic filler of the present invention is preferably 30% by mass or more, more preferably 40% by mass or more, and particularly preferably 50% by mass or more, based on 100% by mass of the inorganic filler. The upper limit is not particularly limited and may be 100% by mass. When the content of the boron nitride agglomerated inorganic filler is equal to or greater than the above lower limit, the effect of improving thermal conductivity and the effect of controlling the linear expansion coefficient due to the inclusion of the boron nitride agglomerated inorganic filler tend to be sufficiently obtained.

[0042] The resin composition of the present invention may contain an inorganic filler (B) other than the boron nitride filler (A). Examples of the inorganic filler (B) include fillers composed of at least one type of particles selected from the group consisting of metal carbides, metal oxides, non-metal oxides, and metal nitrides. Among these, the inorganic filler (B) is preferably a metal oxide and / or a non-metal oxide. An example of a metal carbide is synthetic magnesite. Examples of metal oxides include aluminum oxide (alumina), magnesium oxide, aluminum oxide, silicon oxide, calcium oxide, zinc oxide, yttrium oxide, zirconium oxide, cerium oxide, ytterbium oxide, and sialon (ceramics composed of silicon, aluminum, oxygen, and nitrogen). An example of a non-metal oxide is silicon dioxide. An example of a metal nitride is aluminum nitride. Furthermore, there are no limitations on the shape of the inorganic filler (B), and it may be in the form of particles, spheres, whiskers, fibers, plates, or aggregates thereof, and inorganic fillers of the above types and shapes may be used in combination.

[0043] When the boron nitride filler (A) and the inorganic filler (B) are used in combination, the ratio of the inorganic filler contained in the resin composition is not particularly limited, but in order to improve the filler filling rate and thereby increase thermal conductivity, the volume ratio is preferably 99.5:0.5 to 10:90, and more preferably 97:3 to 15:85.

[0044] The inorganic filler (B) may contain spherical particles (hereinafter sometimes referred to as inorganic filler (B1)) containing particles with an average particle size in the range of 0.1 μm or more and 1 μm or less. Furthermore, the content of particles having an average particle size in the range of 0.1 μm to 1 μm contained in inorganic filler (B1) in inorganic filler (B) is preferably 2.4 vol% or less, more preferably 2.3 vol% or less, and even more preferably 2.0 vol% or less, based on 100 vol% of the inorganic filler contained in the resin composition of the present invention. There is no particular lower limit, and it may be 0 vol%. By having the content of spherical particles having an average particle size in the range of 0.1 μm to 1 μm in the above range, there is a tendency to obtain the effects of reducing voids and improving heat dissipation by improving filler fluidity. In the present invention, the average particle size is an average particle size determined from the volume-average particle size distribution measurement results measured using a laser diffraction particle size distribution measurement device.

[0045] Here, "spherical" means anything that is generally recognized as spherical; for example, an average circularity of 0.4 or more may be considered spherical, or an average circularity of 0.6 or more may be considered spherical. Usually, the upper limit of the average circularity is 1. The circularity can be measured by image processing the projected image, and can be measured, for example, with an FPIA series from Sysmex Corporation.

[0046] The resin composition of the present invention may contain an organic filler in addition to the inorganic filler. The organic filler may be either a thermoplastic resin filler or a thermosetting resin filler. Specific examples include acrylic resin particles, epoxy resin particles, nylon resin particles, polyester resin particles, polystyrene resin particles, and silicone resin particles. Only one type of organic filler may be used, or two or more types may be used in combination.

[0047] The upper limit of the average particle size of the organic filler is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 30 μm or less. By keeping the particle size below these upper limits, it is possible to produce heat dissipation and insulation sheets of various thicknesses without risking a decrease in thermal conductivity. The average particle size of the organic filler is also an average particle size determined from the results of volume-averaged particle size distribution measurement using a laser diffraction particle size distribution analyzer.

[0048] (Other ingredients) The resin composition of the present invention is not particularly limited as long as it contains the inorganic filler and thermosetting resin as described above, and may contain other components within a range that does not impair the effects of the present invention. Examples of other components include a thermosetting catalyst, a curing agent, a solvent, a surface treatment agent such as a silane coupling agent that improves the interfacial adhesive strength between the inorganic filler and the resin composition, which is optionally used when producing a sheet cured product using the resin composition, an insulating carbon component such as a reducing agent, a viscosity modifier, a dispersant, a thixotropy-imparting agent, a flame retardant, a colorant, an organic solvent, and a thermoplastic resin.

[0049] (Thermosetting catalyst) The resin composition of the present invention may contain a thermosetting catalyst. The thermosetting catalyst is not particularly limited, and known thermosetting catalysts can be used as appropriate. The thermosetting catalyst contained in the resin composition of the present invention may be one type or multiple types.

[0050] Examples of thermosetting catalysts include compounds having a structure derived from imidazole, dicyandiamide, linear or cyclic tertiary amines, organophosphorus compounds, quaternary phosphonium salts, diazabicycloalkenes such as organic acid salts, etc. Organometallic compounds, quaternary ammonium salts, metal halides, etc. can also be used. Examples of the organometallic compounds include zinc octoate, tin octoate, and aluminum acetylacetone complexes. Among these, compounds having a structure derived from imidazole and / or dicyandiamide are preferred from the viewpoint of heat resistance and adhesiveness. The proportion of the compound having a structure derived from imidazole and dicyandiamide in the thermosetting catalyst is not particularly limited, but is preferably 30% by mass or more, and more preferably 50% by mass or more. When a compound having a structure derived from imidazole and dicyandiamide are used in combination, the ratio between them is not particularly limited.

[0051] Examples of compounds having a structure derived from imidazole and dicyandiamide include 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(17')]-ethyl-s-triazine, 2-phenyl-4,5-dihydroxymethylimidazole, 2-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, and 1-cyanoethyl-2-phenylimidazoline. 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 isocyanuric acid adduct, 2-phenylimidazole isocyanuric acid adduct, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, and dicyandiamide.

[0052] The content of the thermosetting catalyst in the resin composition is preferably 5% by mass or less, more preferably 4% by mass or less, based on the thermosetting resin. Although there is no particular lower limit, the content is preferably 0.1% by mass or more, more preferably 0.5% by mass or more. By ensuring that the content of the thermosetting catalyst is within the above range, it is possible to expect improved heat resistance of the cured product and improved shelf life due to a slower reaction rate of the thermosetting resin during storage.

[0053] The average particle size of the thermosetting catalyst is not particularly limited, but the average particle size of at least one thermosetting catalyst is preferably 15 μm or less, more preferably 10 μm or less. It is also preferably 1 nm or more, more preferably 10 nm or more, and even more preferably 100 nm or more. Having an average particle size equal to or less than the upper limit above tends to improve the solubility of the thermosetting catalyst in the resin component, thereby improving the reaction rate. It also tends to increase the elastic modulus of the cured sheet and the glass transition temperature. It also tends to improve the dispersibility of the thermosetting catalyst and improve storage stability. On the other hand, having an average particle size equal to or greater than the lower limit above tends to suppress secondary aggregation of the thermosetting catalyst itself, improve the dispersibility of the thermosetting catalyst, and improve the storage stability of the resin composition. It also tends to improve the handleability during production of the resin composition. The average particle size of the plurality of thermosetting catalysts is not particularly limited, but may be within the above range.

[0054] (hardening agent) The thermosetting resin of the present invention may contain a curing agent. The curing agent is not particularly limited, but preferred examples include phenolic resins, acid anhydrides having an aromatic or alicyclic skeleton, or hydrides of the acid anhydrides or modified products of the acid anhydrides. The use of these preferred curing agents tends to produce a cured sheet having an excellent balance of heat resistance, moisture resistance, and electrical properties. Only one curing agent may be used, or two or more may be used in combination.

[0055] The phenolic resin used as the curing agent is not particularly limited. Specific examples of the phenolic resin include phenol novolac, o-cresol novolac, p-cresol novolac, t-butylphenol novolac, dicyclopentadiene cresol, polyparavinylphenol, bisphenol A novolac, xylylene-modified novolac, decalin-modified novolac, poly(di-o-hydroxyphenyl)methane, poly(di-m-hydroxyphenyl)methane, and poly(di-p-hydroxyphenyl)methane. Among these, novolac-type phenolic resins having a rigid main chain skeleton and phenolic resins having a triazine skeleton are preferred for further improving the flexibility and flame retardancy of the resin composition and the mechanical properties and heat resistance of the cured sheet.Furthermore, phenolic resins having an allyl group are preferred for improving the flexibility of the resin composition and the toughness of the cured sheet.

[0056] Commercially available phenolic resins include MEH-8005, MEH-8000H, and NEH-8015 (all manufactured by Meiwa Kasei Co., Ltd.), YLH903 (manufactured by Mitsubishi Chemical Corporation), LA-7052, LA-7054, LA-7751, LA-1356, and LA-3018-50P (all manufactured by Dainippon Ink Co., Ltd.), and PSM6200, PS6313, and PS6492 (manufactured by Gun-ei Chemical Industry Co., Ltd.).

[0057] The acid anhydride having an aromatic skeleton, the water additive of the acid anhydride, or the modified product of the acid anhydride used as the curing agent is not particularly limited. Specific examples include SMA Resin EF30 and SMA Resin EF60 (both manufactured by Sartomer Japan), ODPA-M and PEPA (both manufactured by Manac), Ricadit MTA-10, Ricadit TMTA, Ricadit TMEG-200, Ricadit TMEG-500, Ricadit TMEG-S, Ricadit TH, Ricadit MH-700, Ricadit MT-500, Ricadit DSDA, and Ricadit TDA-100 (all manufactured by New Japan Chemical Co., Ltd.), EPICLON B4400, and EPICLON B570 (all manufactured by Dainippon Ink and Chemicals Co., Ltd.).

[0058] The acid anhydride having an alicyclic skeleton, the hydration product of the acid anhydride, or the modified product of the acid anhydride is preferably an acid anhydride having a polyalicyclic skeleton, the hydration product of the acid anhydride, or the modified product of the acid anhydride, or an acid anhydride having an alicyclic skeleton obtained by an addition reaction of a terpene compound with maleic anhydride, the hydration product of the acid anhydride, or the modified product of the acid anhydride.Specific examples include Ricadit HNA and Ricadit HNA-100 (both manufactured by New Japan Chemical Co., Ltd.), and Epicure YH306 and Epicure YH309 (both manufactured by Mitsubishi Chemical Corporation).

[0059] The curing agent is preferably contained in an amount of 0 to 70% by mass, particularly 0 to 55% by mass, more preferably 0 to 40% by mass, even more preferably 0 to 30% by mass, and even more preferably 1 to 20% by mass, based on 100% by mass of the resin component of the present invention. When the content of the curing agent is equal to or greater than the lower limit, sufficient curing performance can be obtained, and when it is equal to or less than the upper limit, the reaction proceeds effectively, improving crosslink density, increasing strength, and further improving film formability.

[0060] Furthermore, when the thermosetting resin is an epoxy resin, the content of reactive groups in the curing agent is not limited, but may be 0 equivalents, preferably 0.05 equivalents or more, more preferably 0.1 equivalents or more, even more preferably 0.15 equivalents or more, and particularly preferably 0.2 equivalents or more, relative to the amount of epoxy groups in the thermosetting resin. Also, the content of reactive groups in the curing agent is preferably 2 equivalents or less, more preferably 0.9 equivalents or less, even more preferably 0.6 equivalents or less, and particularly preferably 0.4 equivalents or less, relative to the amount of epoxy groups in the thermosetting resin. When the content of reactive groups in the curing agent relative to the amount of epoxy groups in the thermosetting resin is equal to or greater than the lower limit, the curing rate is prevented from decreasing, epoxy groups are less likely to remain, and the strength of the cured sheet and the moisture absorption are likely to be improved. On the other hand, when the content is equal to or less than the upper limit, the elastic modulus of the cured sheet tends to be high.

[0061] (solvent) The resin composition according to the present invention may contain an organic solvent, for example, to improve the coatability when the resin composition is subjected to a coating step to form a sheet cured product. Examples of organic solvents that may be contained in the resin composition according to the present invention include methyl ethyl ketone, cyclohexanone, propylene glycol monomethyl ether acetate, butyl acetate, isobutyl acetate, propylene glycol monomethyl ether, etc. These organic solvents may be used alone or in combination of two or more.

[0062] When the resin composition according to the present invention contains an organic solvent, the content thereof is appropriately determined depending on the handleability of the resin composition when preparing a sheet cured product, the shape before curing, drying conditions, etc. When the resin composition according to the present invention is in the form of a slurry to be subjected to the coating step described below, the organic solvent is preferably used so that the solids concentration (total of components other than the solvent) in the resin composition according to the present invention or in the resin composition according to the present invention after adding the inorganic filler described below is 10 to 90 mass %, particularly 40 to 80 mass %. Furthermore, when the resin composition of the present invention is in the form of a sheet that has been subjected to processes such as coating and drying, it is more preferable to use an organic solvent so that the solid content (total of components other than the solvent) concentration in the resin composition of the present invention or in the resin composition of the present invention after the addition of an inorganic filler described below is 95 mass % or more, particularly 98 mass % or more.

[0063] (Method of producing resin composition) The resin composition of the present invention can be obtained by uniformly mixing the inorganic filler, the thermosetting resin, and other components added as needed by stirring or kneading. For mixing, a general kneading device such as a mixer, a kneader, or a single-screw or twin-screw kneader can be used, and heating may be performed during mixing as needed. The order of mixing the various components may also be arbitrary as long as there are no particular problems, such as the occurrence of reactions or precipitates. For example, a method may be used in which a thermosetting resin component is mixed and dissolved in an organic solvent (e.g., methyl ethyl ketone) to prepare a resin liquid, and a sufficiently mixed inorganic filler and other components are added to the obtained resin liquid and mixed, and then an organic solvent is further added to adjust the viscosity and mixed, and then additives such as a curing agent, a curing accelerator, or a dispersant are further added and mixed.

[0064] (Production of cured sheet) The method for producing the resin composition of the present invention and the cured sheet of the present invention will be described below with reference to examples.

[0065] The sheet cured product can be produced by a commonly used method, for example, by preparing the resin composition of the present invention, molding the resin composition into a sheet, laminating the sheets to an appropriate thickness, and curing the laminate.

[0066] The resin composition can be obtained by uniformly mixing the inorganic filler, the thermosetting resin, and other components that are added as needed by stirring or kneading. For mixing, a general kneading device such as a mixer, a kneader, or a single-screw or twin-screw kneader can be used, and heating may be performed during mixing, if necessary.

[0067] The order of mixing the various components can also be arbitrary as long as there are no particular problems, such as the occurrence of reactions or precipitates. For example, a method can be used in which a thermosetting resin component is mixed and dissolved in an organic solvent (e.g., methyl ethyl ketone) to prepare a resin liquid, and then a thoroughly mixed inorganic filler and other components are added to the obtained resin liquid and mixed, and then an organic solvent is further added to adjust the viscosity and mixed, and then additives such as a curing agent, a thermosetting catalyst, or a dispersant are further added and mixed.

[0068] The prepared resin composition can be formed into a sheet and cured by a commonly used method. The resin composition in a slurry state can be formed into a sheet by a doctor blade method, a solvent casting method, an extrusion film forming method or the like. The solvent in the resin composition can be removed by a known heating method such as using a hot plate, a hot air oven, an IR heating oven, a vacuum dryer, or a high-frequency heater.

[0069] An example of a method for producing a sheet cured product using this slurry resin composition will be described below.

[0070] <Coating process> First, a slurry resin composition is applied to the surface of a substrate to form a coating film (a sheet-like resin composition). That is, a coating film is formed on a substrate using a slurry resin composition by a dip 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, or a blade coater can be used to apply the slurry resin composition, and this makes it possible to form a coating film of a predetermined thickness uniformly on the substrate. The substrate is generally a copper foil or a PET film, as described below, but is not limited thereto.

[0071] <Drying process> The coating film formed by applying the slurry resin composition is typically dried at a temperature of 10 to 150°C, preferably 25 to 120°C, and more preferably 30 to 110°C to remove the solvent and low-molecular-weight components. By keeping the drying temperature at or below the upper limit, the curing of the thermosetting resin in the slurry resin composition is suppressed, and the resin in the sheet-shaped resin composition tends to flow in the subsequent pressing step, making it easier to remove voids. Furthermore, by keeping the drying temperature at or above the lower limit, the solvent can be effectively removed, tending to improve productivity.

[0072] The drying time is not particularly limited and can be adjusted appropriately depending on the state of the slurry resin composition, the drying environment, etc. It is preferably 1 minute or more, more preferably 2 minutes or more, even more preferably 5 minutes or more, still more preferably 10 minutes or more, particularly preferably 20 minutes or more, and most preferably 30 minutes or more. On the other hand, it is preferably 4 hours or less, more preferably 3 hours or less, and even more preferably 2 hours or less. When the drying time is equal to or longer than the lower limit, the solvent can be sufficiently removed, and the residual solvent tends to be prevented from forming voids in the cured sheet. When the drying time is equal to or shorter than the upper limit, productivity tends to be improved, and production costs tend to be reduced.

[0073] <Pressure process> After the drying step, it is desirable to subject the resulting sheet-shaped resin composition to a pressurizing step for purposes such as bonding inorganic fillers together to form heat paths, eliminating voids and gaps within the sheet, and improving adhesion to the substrate. The pressurizing step is desirably carried out by applying a load of 2 MPa or more to the sheet-shaped resin composition on the substrate. The load is preferably 5 MPa or more, more preferably 10 MPa or more. The load is also preferably 2000 MPa or less, more preferably 1800 MPa or less. By setting the load during pressing to the above upper limit or less, the secondary particles of the inorganic filler are not destroyed, and a sheet having high thermal conductivity and no voids in the cured sheet can be obtained. Furthermore, by setting the load to the above lower limit or more, good contact between the inorganic fillers is achieved, making it easier to form thermal conduction paths, and a cured sheet having high thermal conductivity can be obtained.

[0074] In the pressurizing step, the heating temperature of the sheet-shaped resin composition on the substrate is not particularly limited. It is preferably 10°C or higher, more preferably 20°C or higher, and even more preferably 30°C or higher. It is also preferably 300°C or lower, more preferably 280°C or lower, even more preferably 250°C or lower, even more preferably 100°C or lower, and particularly preferably 90°C or lower. By performing the pressurizing step within this temperature range, the melt viscosity of the resin in the coating film can be reduced, and voids and gaps in the cured sheet can be eliminated. Furthermore, heating at or below the upper limit mentioned above tends to suppress decomposition of organic components in the sheet-shaped resin composition and the cured sheet, and voids caused by residual solvent.

[0075] The time for the pressurization step is not particularly limited. It is preferably 30 seconds or more, more preferably 1 minute or more, even more preferably 3 minutes or more, and particularly preferably 5 minutes or more. It is also preferably 1 hour or less, more preferably 30 minutes or less, and even more preferably 20 minutes or less. By keeping the pressing time at or below the upper limit, the production time for the cured sheet can be reduced, which tends to reduce production costs, while by keeping the pressing time at or above the lower limit, voids and gaps in the cured sheet can be sufficiently removed, which tends to improve heat transfer performance and voltage resistance.

[0076] <Curing process> The curing step for completely curing the resin composition of the present invention may be carried out under pressure or without pressure. Alternatively, the pressurizing step and the curing step may be carried out simultaneously. The load to be applied when the pressurizing step and curing step are performed simultaneously is not particularly limited. It is preferable to apply a load of 3 MPa or more to the sheet-shaped resin composition on the substrate, more preferably 5 MPa or more. It is also preferably 2000 MPa or less, more preferably 1800 MPa or less. By applying a load below the upper limit, the secondary particles of the inorganic filler are not destroyed, and a sheet having high thermal conductivity without voids in the cured sheet can be obtained. Furthermore, by applying a load above the lower limit, contact between the inorganic fillers is improved, making it easier to form thermal conduction paths, thereby obtaining a cured sheet having high thermal conductivity.

[0077] When the pressing step and the curing step are carried out simultaneously, the pressing time is not particularly limited. It is preferably 30 seconds or more, more preferably 1 minute or more, even more preferably 3 minutes or more, and particularly preferably 5 minutes or more. It is also preferably 8 hours or less, more preferably 6 hours or less, and even more preferably 4 hours or less. By keeping the pressing time at or below the upper limit, the production time of the sheet-shaped cured product can be reduced, and production costs tend to be reduced. On the other hand, by keeping the pressing time at or above the lower limit, voids and gaps in the cured product can be sufficiently removed, and heat transfer performance and voltage resistance tend to be improved.

[0078] When the pressing step and curing step are performed simultaneously, the heating temperature of the sheet-shaped resin composition on the substrate is not particularly limited. It is preferably 10°C or higher, more preferably 20°C or higher, and even more preferably 30°C or higher. It is also preferably 300°C or lower, more preferably 250°C or lower, even more preferably 200°C or lower, even more preferably 100°C or lower, and particularly preferably 90°C or lower. By using this temperature range, the melt viscosity of the resin in the coating film can be reduced, and voids and gaps in the cured sheet can be eliminated. Furthermore, heating at or below the upper limit mentioned above tends to suppress decomposition of organic components in the sheet-shaped resin composition and the cured sheet, and voids caused by residual solvent.

[0079] When only the curing step is performed, the heating temperature of the sheet-shaped resin composition on the substrate is not particularly limited. It is preferably 10°C or higher, more preferably 50°C or higher, and even more preferably 100°C or higher. It is also preferably 500°C or lower, more preferably 400°C or lower, even more preferably 250°C or lower, even more preferably 180°C or lower, and particularly preferably 175°C or lower. By setting the temperature within this range, the curing reaction of the resin can be effectively promoted. Furthermore, by setting the temperature below the upper limit, thermal degradation of the resin can be prevented. Furthermore, by setting the temperature above the lower limit, the curing reaction of the resin can be more effectively promoted.

[0080] The thickness of the cured sheet thus formed is not particularly limited, but is preferably 50 μm or more, more preferably 80 μm or more, and even more preferably 100 μm or more. It is also preferably 400 μm or less, more preferably 300 μm or less. Having a thickness of the cured sheet at or above the lower limit tends to provide sufficient voltage resistance and improve breakdown voltage. Having a thickness below the upper limit tends to enable devices to be made smaller and thinner, and the thermal resistance of the resulting cured sheet (heat dissipation sheet) tends to be reduced.

[0081] [Composite molded body] The composite molded product of the present invention is formed by laminating a cured product part made of the cured sheet of the present invention and a metal part together. The metal part may be provided on only one surface of the cured product part made of the cured sheet of the present invention, or on two or more surfaces. For example, the cured sheet may have a metal part on only one surface or on both surfaces. The metal part may also be patterned.

[0082] Such a composite molded product of the present invention can be produced by using a metal part as the substrate and forming the sheet cured product of the present invention on this substrate according to the method described above. Alternatively, it can also be produced by peeling a sheet-like resin composition or sheet cured product formed on a substrate other than the metal part from the substrate, and then heat-pressing the sheet onto a metal member that will become the metal part.

[0083] In this case, the sheet-shaped resin composition or sheet cured product of the present invention is formed in the same manner as described above, except that it is applied to a substrate such as PET which may be treated with a release agent, and then peeled off from the substrate. The sheet-shaped resin composition or sheet cured product is placed on another metal plate or sandwiched between two metal plates and pressed to be integrated.

[0084] In this case, the metal plate may be a metal plate having a thickness of about 10 μm to 10 cm and made of copper, aluminum, nickel-plated metal, etc. The surface of the metal plate may be physically roughened or chemically treated with a surface treatment agent, etc. From the viewpoint of adhesion between the resin composition and the metal plate, it is more preferable that the surface of the metal plate is subjected to such treatment.

[0085] [Semiconductor Devices] The composite molded article of the present invention can be used as a semiconductor device, and is particularly useful in power semiconductor devices that can be operated at high temperatures to achieve high output and high density.

[0086] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention. Note that the various conditions and values ​​of evaluation results in the following examples indicate preferred ranges of the present invention, just as preferred ranges in the embodiments of the present invention, and the preferred ranges of the present invention can be determined by taking into consideration the preferred ranges in the above-mentioned embodiments and the values ​​in the following examples or the ranges indicated by a combination of values ​​between the examples.

[0087] [raw materials] The raw materials used in the examples and comparative examples are as follows.

[0088] <Epoxy resin> Resin component 1: a bifunctional epoxy resin disclosed as resin component 1 in JP 2020-63438 A Polystyrene equivalent weight average molecular weight: 30,000 Epoxy equivalent: 9,000g / equivalent Resin component 2: Biphenyl-type solid epoxy resin manufactured by Mitsubishi Chemical Corporation Molecular weight: approx. 400 Epoxy equivalent: 200g / equivalent Resin component 3: Showa Denko multifunctional epoxy resin containing a structure having four or more glycidyl groups per molecule Molecular weight: approx. 400 Epoxy equivalent: 100g / equivalent Resin component 4: Nagase ChemteX Corporation, multifunctional epoxy resin containing a structure having four or more glycidyl groups per molecule Molecular weight: approx. 400 Epoxy equivalent: 100g / equivalent Resin component 5: BisA type liquid epoxy resin manufactured by Mitsubishi Chemical Corporation Molecular weight: approx. 370 Epoxy equivalent: 190g / equivalent

[0089] <Inorganic filler> Inorganic filler A: agglomerated boron nitride particles having a house-of-cards structure, produced in accordance with the method for producing agglomerated boron nitride particles disclosed in the examples of WO 2015 / 561028. Average particle size: 45μm Inorganic filler B1-1: Spherical alumina particles manufactured by Admatechs Co., Ltd. Average particle size: 7 μm (peak particle size: 15 μm, 0.6 μm) Content of spherical particles between 0.1 and 1 μm: 13.5% Inorganic filler B1-2: Spherical alumina particles manufactured by Admatechs Co., Ltd. Average particle size: 9 μm (peak particle size: 12 μm, 0.3 μm) Content of spherical particles between 0.1 and 1 μm: 19.3% Inorganic filler B1-3: Spherical alumina particles manufactured by Admatechs Co., Ltd. Average particle size: 0.2μm Content of spherical particles between 0.1 and 1 μm: 82.3%

[0090] <Curing agent> Hardener 1: Meiwa Kasei "MEH-8000H" Phenolic resin curing agent

[0091] <Thermosetting catalyst> Thermosetting catalyst 1: 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-s-triazine. This catalyst contains both an imidazole-derived structure and a triazine-derived structure in a single molecule ("Curezol 2E4MZ-A" manufactured by Shikoku Chemical Industries, Ltd.). Heat curing catalyst 2: 2-phenyl-4,5-dihydroxymethylimidazole (Shikoku Chemicals Corporation, "Curezol 2PHZ-PW")

[0092] [Sample preparation, measurement, and evaluation] The methods for producing the molded bodies, the measurement conditions, and the evaluation methods in the examples and comparative examples are as follows.

[0093] Example 1 Using a planetary stirring device, resin component 1, resin component 2, resin component 3, curing agent 1, thermosetting catalyst 1, thermosetting catalyst 2, and inorganic filler A were mixed to obtain a mixture in the mass ratio shown in Example 1 of Table 1 below. When preparing this mixture, a slurry-like resin composition was prepared using 18.6 mass% each of methyl ethyl ketone and cyclohexanone so that the mixture accounted for 62.8 mass% (solids concentration) of the coating slurry.

[0094] The resulting slurry-like resin composition was applied to a PET substrate by a doctor blade method, and then heated and dried at 60°C for 120 minutes, followed by pressing to obtain a sheet-like resin composition having a thickness of 150µm. The total content of methyl ethyl ketone and cyclohexanone in the sheet-like resin composition was 1% by mass or less.

[0095] [Measurement method] <Measurement of epoxy equivalent (WPE) of resin component> The resin components described in each Example and Comparative Example were adjusted to the mass ratios shown in Tables 1 and 2 below, and the epoxy equivalent was determined by potentiometric titration and converted into the value for the entire resin components. 100≦WPE≦300 was marked as ◯, and others were marked as ×.

[0096] <Measurement of G' of cured resin component> The resin components described in each Example and Comparative Example were adjusted to the mass ratios shown in Tables 1 and 2 below and applied to a PET film. After heating and drying, the uncured resin components were heat-cured using an Anton Paar rheometer "MCR302" and the storage modulus (G') at 200°C was measured. Aluminum parallel plates were used for the measurements, and the measurement conditions were a strain of 0.3%, a frequency of 1 Hz, and a gap of 0.5 mm. The temperature profile during heat curing was as follows: starting from 25°C, the temperature was increased at 14°C per minute to 120°C, and after reaching 120°C, it was held for 30 minutes; then the temperature was increased at 7°C per minute to 175°C, and after reaching 175°C, it was held for 30 minutes; then the temperature was increased again at 7°C per minute to 200°C, and after reaching 200°C, it was held for 10 minutes. G' measured after holding at 200°C for 10 minutes was used for evaluation.

[0097] <Evaluation of sheet handling (cut test)> As in each of the Examples and Comparative Examples, a resin composition was prepared using a planetary stirring device, and the resin composition was heated, dried, and pressure-molded to obtain a sheet, which was then cut with scissors to evaluate the handling properties. 〇: No chips or cracks are found on the cut surface ×: Chipping and cracking occur on the cut cross section

[0098] <Measurement of E' of cured resin composition> As in each example and comparative example, a resin composition was prepared using a planetary stirring device, heated and dried, and pressure-molded to obtain three sheets, which were then stacked together and heat-cured to obtain a cured resin composition. Evaluation was carried out on test pieces approximately 4 mm wide and 50-60 mm long. The measurement was carried out using a Hitachi High-Tech Science DMS6100 measuring device under the following conditions. Measurement temperature conditions: -110~270℃ Measurement mode: Tensile mode Measurement frequency: 1Hz Chuck distance: 35mm Distortion amplitude (μm): 5μm Initial force amplitude (mN): 50 mN Furthermore, when E' at 270°C and 30°C satisfied the following, it was marked as ◯, and when it did not, it was marked as ×. 1 ≥ (E' at 270°C) / (E' at 30°C) ≥ 0.2

[0099] <Measurement of thermal conductivity in the thickness direction of the resin composition layer> Using a thermal resistance measuring device (Mentor Graphics Corporation, product name "T3ster"), the thermal resistance values ​​of cured resin compositions of different thicknesses prepared under the same composition and conditions were measured, and the thermal conductivity λ (W / m K) was calculated from the slope of the graph plotting the thermal resistance value against the thickness.

[0100] <Measurement of BDV (breakdown voltage) of cured resin composition> The resin composition was bonded to a 2 mm thick copper plate by heat and pressure curing to form a cured resin composition on the copper plate, and evaluation was performed on the cured resin composition. In insulating oil, the voltage was increased by 500 V every minute to determine the voltage at which the cured resin composition broke down.

[0101] <Examples 2 to 3, Comparative Examples 1 to 5> Resin components were prepared and sheet-shaped resin compositions were obtained in the same manner as in Example 1, except that the components were used to obtain the compositions shown in Tables 1 and 2. WPE measurement, G' measurement of the cured resin components, evaluation of the sheet's handleability, E' measurement of the cured resin composition, thermal conductivity measurement, and BDV measurement were performed. The results of each example and comparative example are shown in Tables 1 and 2.

[0102] The results of the examples show that the resin composition of the present invention, which contains a specific filler and resin, can produce a cured sheet that combines high thermal conductivity, high insulation, and high heat resistance while maintaining the handleability of the uncured sheet.

[0103] A comparison of Examples 1 to 3 with Comparative Examples 1 and 2 reveals that a high proportion of boron nitride agglomerated filler results in high thermal conductivity. A comparison of Example 1 with Comparative Example 3 reveals that, even when the proportion of boron nitride agglomerated filler is high, insulating properties are improved by ensuring that the WPE of the resin component is within a specified range. It is believed that the WPE within a specified range improves resin fluidity, reduces voids in the cured sheet, and improves crosslink density. A comparison of Example 1 with Comparative Examples 3 and 4 reveals that, even when the proportion of boron nitride agglomerated filler is the same, filler springback is suppressed and thermal conductivity is improved by ensuring that the range of 1 ≥ (E' at 270°C) / (E' at 30°C) ≥ 0.2 is met. A comparison of Example 1 with Comparative Example 5 reveals that the inclusion of an epoxy resin with a mass-average molecular weight of 5,000 or more improves the sheet's handleability.

[0104] [Table 1]

[0105] [Table 2]

[0106] However, "*" in Table 2 indicates that the sheet (cured product of the resin composition) was too brittle during the thermal conductivity measurement, and a sample for performance evaluation could not be prepared.

Claims

1. A resin composition containing an inorganic filler and a thermosetting resin, The content of the inorganic filler in the solid content of the resin composition is 50% by volume or more, and the content of the boron nitride filler (A) in the inorganic filler is 82% by volume or more, the boron nitride filler comprises an agglomerated filler; the thermosetting resin contains an epoxy resin having a mass average molecular weight of 5,000 or more, the epoxy resin contained in the thermosetting resin contains 29% by mass or less of an epoxy resin having a mass average molecular weight of 5,000 or more; the thermosetting resin contains an epoxy resin having a mass average molecular weight of 600 or less, the epoxy resin having a mass average molecular weight of 600 or less contains three or more epoxy groups in one molecule, The epoxy equivalent (WPE) of the resin component in the resin composition is 100≦WPE≦300, A resin composition having a storage modulus E' of a cured product of the resin composition, where E' is 1≧(E' at 270°C) / (E' at 30°C)≧0.

2.

2. 2. The resin composition according to claim 1, wherein the modulus of rigidity G' of a cured product of the resin component satisfies 1≧(G' at 200° C.) / (G' at 30° C.)>0.

1.

3. The storage modulus E' of the cured product of the resin composition is 1 x 10 at 30°C. ８ The resin composition according to claim 1 or 2, wherein the viscosity is 100 Pa or more.

4. The inorganic filler contains an inorganic filler (B) other than the boron nitride filler (A), the inorganic filler (B) contains spherical particles having an average particle size of 0.1 μm or more and 1 μm or less, 4. The resin composition according to claim 1, wherein the inorganic filler contains spherical particles having an average particle size of 0.1 μm or more and 1 μm or less in an amount of 2.4% by volume or less.

5. The resin composition according to any one of claims 1 to 4, wherein the thermosetting resin contains an epoxy resin having a mass average molecular weight of 10,000 or more.

6. The resin composition according to any one of claims 1 to 5, wherein the inorganic filler (B) is a metal oxide and / or a non-metal oxide.

7. A sheet cured product using the resin composition according to any one of claims 1 to 6.

8. A composite molded article having a cured part made of the sheet cured product according to claim 7 and a metal part.

9. A semiconductor device comprising the composite compact of claim 8.

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