Thermosetting composition, method for producing thermosetting sheet, thermally conductive sheet, heat-dissipating layered product, heat-dissipating circuit board, and power semiconductor device

Abstract

The present invention relates to a thermosetting composition that contains an inorganic filler and a thermosetting compound. The present invention provides a thermosetting composition, as a thermosetting composition having excellent heat resistance such that when a cured product of the thermosetting composition is joined to a substrate under high temperature conditions of 150ºC or higher, such as in a reflow process or sinter bonding, cracks do not appear in the cured product and the join does not separate. The thermosetting composition contains an inorganic filler and a thermosetting compound and is characterized in that the fracture energy value, which is obtained by subjecting a cured product formed by curing the thermosetting composition to 3-point bending measurements at 190ºC, is 55 kPa or more and the fracture energy value obtained through 3-point bending measurements at 150ºC is 80 kPa or more.

Description

Thermosetting composition, method for producing thermosetting sheet, thermally conductive sheet, heat dissipation laminate, heat dissipation circuit board, and power semiconductor device

[0001] The present invention relates to a thermosetting composition having thermosetting properties, for example, a thermosetting composition whose cured product can be suitably used as a heat sink for a power semiconductor device, a method for producing a thermosetting sheet using the thermosetting composition, a thermally conductive sheet using the thermosetting composition, and a heat-dissipating laminate, a heat-dissipating circuit board, and a power semiconductor device each using the thermally conductive sheet.

[0002] Among devices using semiconductors, devices that control or convert power from a power supply or the like are called "power semiconductor devices." Power semiconductor devices generally have a configuration in which power semiconductors that convert or control power and electronic components are mounted on a substrate that functions as a heat sink. In recent years, power semiconductor devices used in various fields such as railways, automobiles, industry, and general home appliances are transitioning from conventional Si power semiconductors to power semiconductors using SiC, AlN, GaN, etc. in order to achieve further miniaturization, cost reduction, and efficiency improvement.

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

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

[0005] Ceramic substrates with high thermal conductivity, such as alumina substrates and aluminum nitride substrates, have traditionally been used as materials that can provide both thermal conductivity and insulation. However, ceramic substrates have issues such as being easily cracked by impact, and being difficult to make thin and compact.

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

[0007] Attempts have been made to use hexagonal boron nitride as a filler in heat-dissipating resin sheets. Hexagonal boron nitride is generally a thin plate-like 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-like boron nitride is incorporated into a heat-dissipating resin 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] Boron nitride agglomerated particles are an example of a material that increases the thermal conductivity of a sheet in the thickness direction. It is widely known that the use of boron nitride agglomerated particles can improve the thermal conductivity of a sheet in the thickness direction. In particular, the present applicant has previously developed boron nitride agglomerated particles with a house-of-cards structure (see, for example, Patent Document 2). Furthermore, the present applicant has developed boron nitride agglomerated particles with a house-of-cards structure that have a relatively large average particle size and are less likely to collapse even when pressure is applied (see, for example, Patent Document 3).

[0009] These boron nitride agglomerated particles ensure a heat conduction path due to their card-house structure, and when incorporated into a heat-dissipating resin sheet, excellent thermal conductivity in the thickness direction of the sheet is achieved. Furthermore, the boron nitride agglomerated particles are agglomerated without the use of a separate binder. Therefore, even when external force is applied during sheeting, the card-house structure does not easily collapse, maintaining the heat conduction path, allowing heat to be dissipated in the thickness direction of the sheet, thereby achieving excellent thermal conductivity (see, for example, Patent Documents 4 and 5). Another known molding method for increasing the thermal conductivity in the thickness direction of a sheet is to increase thermal conductivity by bringing the boron nitride agglomerated particles into surface contact with each other within the sheet (see, for example, Patent Document 6).

[0010] The present applicant has proposed a resin composition containing an inorganic filler and a thermosetting compound, wherein the inorganic filler accounts for 50% by volume or more of the solid content of the resin composition, the inorganic filler accounts for 82% by volume or more of a boron nitride filler (A) among the inorganic fillers, the boron nitride filler includes an aggregated filler, the thermosetting compound contains an epoxy resin having a mass average molecular weight of 5,000 or more, the epoxy equivalent (WPE) of the resin component in the resin composition is 100≦WPE≦300, and the storage modulus E' of a cured product of the resin composition is 1≧(E' at 270°C) / (E' at 30°C)≧0.2 (Patent Document 7).

[0011] The present applicant has also proposed a thermosetting resin composition containing a thermosetting compound, an inorganic filler, and a polymer having a mass average molecular weight of 10,000 or more, wherein the inorganic filler contains boron nitride agglomerated particles, and the thermosetting compound contains an epoxy compound and a benzoxazine compound, as well as a thermally conductive sheet formed from the thermosetting resin composition (Patent Document 8).

[0012] Japanese Patent Publication No. 2013-089670 Japanese Patent Publication No. 2015-006985 Japanese Patent Publication No. 2016-135730 International Publication No. 2015 / 119198 Japanese Patent Publication No. 2017-036415 International Publication No. 2019 / 189746 International Publication No. 2022 / 210686 International Publication No. 2023 / 182470

[0013] One of the processes for assembling power semiconductor devices is the solder reflow process. In the solder reflow process, components are rapidly heated to melt the solder and join the metal components together. When exposed to high temperatures during this reflow process, internal stress is applied due to the expansion of the components and moisture, which can deteriorate the components used in the power semiconductor device. For example, the insulating performance of the cured product can decrease, resulting in a decrease in the reliability of the power semiconductor device. Therefore, a cured product of a thermosetting composition containing an inorganic filler and a thermosetting compound is required to have sufficient insulating performance even after reflow.

[0014] In recent years, the development of next-generation power semiconductor devices has led to increased demand for more reliable packaging technologies, including improved electrical transmission efficiency and continuous bonding stability under high-temperature and external force conditions. Silver-based sinter bonding has therefore attracted attention. For example, when a semiconductor chip equipped with a thermally conductive sheet is bonded to a support substrate by sinter bonding, the semiconductor chip is first placed at the intended chip bonding location on the support substrate via a sinter bonding material under predetermined temperature and load conditions. Subsequently, a heat treatment is performed under high-temperature and high-pressure conditions between the support substrate and the semiconductor chip to volatilize the solvent in the sinter bonding material and promote sintering between the sinterable particles. This forms a sintered layer between the support substrate and the semiconductor chip, electrically connecting and mechanically bonding the semiconductor chip to the support substrate.

[0015] It has been found that when a cured product of a thermosetting composition containing an inorganic filler and a thermosetting compound is bonded to a substrate under high temperature conditions, such as by sinter bonding, an external force is applied in addition to internal stress at high temperature, which can cause cracks to develop in the cured product or separation of the bond.

[0016] Therefore, an object of the present invention is to provide a thermosetting composition containing an inorganic filler and a thermosetting compound, in which the cured product obtained by curing the thermosetting composition (also referred to as the "cured product of the thermosetting composition") not only has sufficient insulating performance after a reflow process, but also has excellent high-temperature resistance such that when the cured product is bonded to a substrate under conditions in which an external force is applied at high temperatures, such as sinter bonding, the cured product does not crack or the bond does not peel off, as well as a method for producing a thermosetting sheet using the thermosetting composition, a thermally conductive sheet made of a sheet-like cured product of the thermosetting composition, and a heat-dissipating laminate, a heat-dissipating circuit board, and a power semiconductor device each including the thermally conductive sheet.

[0017] In order to solve the above problems, the present invention proposes a thermosetting composition, a thermally conductive sheet, a heat dissipating laminate, a heat dissipating circuit board, a power semiconductor device, and a method for producing a thermosetting sheet, each of which has the following aspects.

[0018] [1] A first aspect of the present invention is a thermosetting composition containing an inorganic filler and a thermosetting compound, characterized in that a cured product of the thermosetting composition (also referred to as a "cured product of the thermosetting composition") has a breaking energy of 55 kPa or more as measured by three-point bending at 190°C and a breaking energy of 80 kPa or more as measured by three-point bending at 150°C.

[0019] [2] A second aspect of the present invention is a thermosetting composition containing an inorganic filler and a thermosetting compound, wherein the breaking energy of a cured product (also referred to as a "cured product of the thermosetting composition") obtained by curing the thermosetting composition, as determined by three-point bending measurement at 190°C, is x, and the breaking energy of a cured product (also referred to as a "cured product of the thermosetting composition") is y, the value of x / y being 0.7 to 1.15, and the value of x being 55 kPa or greater. It is also contemplated that the second aspect of the present invention may be the first aspect described above but also the second aspect.

[0020] [3] A third aspect of the present invention is the thermosetting composition according to the first or second aspect, characterized in that a cured product of the thermosetting composition has a Young's modulus of 5.5 GPa or more as measured by three-point bending at 190°C. [4] A fourth aspect of the present invention is the thermosetting composition according to any one of the first to third aspects, characterized in that a sheet-shaped cured product obtained by curing the thermosetting composition (also referred to as a "sheet-shaped cured product of the thermosetting composition") has a thermal conductivity of 14 W / m K or more in the thickness direction at 25°C. [5] A fifth aspect of the present invention is the thermosetting composition according to any one of the first to fourth aspects, characterized in that a sheet-shaped cured product of the thermosetting composition has a breakdown voltage of 6.5 kV or more when the thickness of the sheet-shaped cured product of the thermosetting composition is 150 μm. [6] A sixth aspect of the present invention is the thermosetting composition according to any one of the first to fifth aspects, characterized in that the volume resistivity (1000 V, 200°C) of the sheet-shaped cured product of the thermosetting composition is 3.0E+10 Ωcm or higher. [7] A seventh aspect of the present invention is the thermosetting composition according to any one of the first to sixth aspects, characterized in that the moisture absorption rate of the sheet-shaped cured product of the thermosetting composition is 0.7% by mass or higher and 1.2% by mass or lower. [8] An eighth aspect of the present invention is the thermosetting composition according to any one of the first to seventh aspects, characterized in that the storage modulus at 200°C of the sheet-shaped cured product of the thermosetting composition is 6.0 GPa or higher and 100 GPa or lower. [9] A ninth aspect of the present invention is the thermosetting composition according to any one of the first to eighth aspects, characterized in that the glass transition temperature (Tg) of the sheet-shaped cured product of the thermosetting composition is 170°C or higher.

[0021]

[10] A tenth aspect of the present invention is a thermosetting composition according to any one of the first to ninth aspects, which includes an epoxy compound and at least one of a phenolic resin, a benzoxazine compound, a polyarylate, a cyanate, and a maleimide.

[11] A eleventh aspect of the present invention is a thermosetting composition according to any one of the first to tenth aspects, which includes an epoxy compound and a phenolic resin.

[12] A twelfth aspect of the present invention is a thermosetting composition according to any one of the first to eleventh aspects, which includes a multifunctional epoxy compound having three or more epoxy groups in one molecule and a mass average molecular weight (Mw) of less than 5,000.

[13] A thirteenth aspect of the present invention is a thermosetting composition according to any one of the first to twelfth aspects, which includes a high molecular weight epoxy compound having a mass average molecular weight (Mw) of 5,000 or more.

[0022]

[14] A fourteenth aspect of the present invention is the thermosetting composition of any one of the first to thirteenth aspects, further comprising a polymer having a mass average molecular weight (Mw) of 5,000 or more in an amount of 5% by mass or more and less than 30% by mass, based on 100% by mass of the solid content excluding the inorganic filler.

[15] A fifteenth aspect of the present invention is the thermosetting composition of any one of the first to thirteenth aspects, further comprising a polymer having a mass average molecular weight (Mw) of 5,000 or more in an amount of 5% by mass or more and less than 23% by mass, based on 100% by mass of the solid content excluding the inorganic filler.

[0023]

[16] A sixteenth aspect of the present invention is the thermosetting composition according to any one of the first to fifteenth aspects, which contains an epoxy compound, and the epoxy equivalent (WPE) of the solid content of the thermosetting composition excluding the inorganic filler from the solid content of the thermosetting composition is 200 g / equivalent or more and less than 250 g / equivalent.

[17] A seventeenth aspect of the present invention is the thermosetting composition according to any one of the first to sixteenth aspects, which contains boron nitride agglomerated particles as the inorganic filler.

[18] An eighteenth aspect of the present invention is the thermosetting composition according to any one of the first to seventeenth aspects, which contains the inorganic filler in a proportion of 30 mass% or more and less than 90 mass% based on 100 mass% of the solid content of the total composition.

[0024]

[19] A nineteenth aspect of the present invention is a thermally conductive sheet comprising a sheet-shaped cured product of the thermosetting composition of any one of the first to eighteenth aspects.

[20] A twentieth aspect of the present invention is a heat dissipation laminate comprising the thermally conductive sheet of the nineteenth aspect.

[21] A twenty-first aspect of the present invention is a heat dissipation circuit board comprising the thermally conductive sheet of the nineteenth aspect.

[22] A twenty-second aspect of the present invention is a power semiconductor device comprising the thermally conductive sheet of the nineteenth aspect.

[0025]

[23] A 23rd aspect of the present invention is a method for producing a thermosetting sheet, comprising forming a thermosetting composition according to any one of the first to eighteenth aspects into a sheet and subjecting the sheet to low-temperature aging at an ambient temperature of 0°C or lower.

[0026] The thermosetting composition proposed by the present invention not only exhibits sufficient insulating properties after the reflow process, but also prevents cracking and peeling of the cured product when the cured product is bonded to a substrate under conditions of high temperatures of 150°C or higher and additional external force, such as sinter bonding. Because of its excellent high-temperature resistance, the cured product of the thermosetting composition proposed by the present invention can be suitably applied to various processes at high temperatures of 150°C or higher. For example, even when bonded to a substrate by sinter bonding, it can ensure excellent electrical conductivity and continuous bonding stability. Therefore, a thermally conductive sheet suitable for use in heat dissipation laminates, heat dissipation circuit boards, power semiconductor devices, etc. can be provided.

[0027] FIG. 1 is a conceptual diagram of a particle cross section according to an example of a boron nitride agglomerated particle having a house-of-card structure.

[0028] An example of an embodiment of the present invention will be described in detail below. However, the present invention is not limited to the following embodiment, and various modifications can be made within the scope of the present invention.

[0029] <<Composition of the Present Invention>> A composition according to an embodiment of the present invention (also referred to as "composition of the present invention") is a thermosetting composition containing a thermosetting compound and an inorganic filler.

[0030] In the present invention, the term "thermosetting composition" refers to a composition containing a compound or resin that can be cured by heat. That is, the term "thermosetting composition" refers to any composition that has the ability to be cured by heat and still has room to be cured. The term "thermosetting composition" may be a composition that has already been cured (also referred to as "pre-cured") and still has room to be cured, or a composition that has not yet been cured (also referred to as "uncured"). Furthermore, in the present invention, the term "resin" encompasses organic compounds, monomers, oligomers, and polymers, regardless of molecular weight. The composition of the present invention may be in the form of a powder, a slurry, a liquid, a solid, or a molded product such as a sheet. Therefore, for example, the composition of the present invention also encompasses a slurry thermosetting composition to be subjected to the coating process described below, a sheet that has been subjected to the coating process, and a sheet that has been subjected to coating and drying processes.

[0031] The thermosetting composition of the present invention, i.e., a cured product obtained by curing the composition of the present invention (also referred to as the "cured product of the thermosetting composition"), is also referred to as the "cured product," and a sheet-like cured product obtained by curing the sheet-like composition of the present invention (also referred to as the "sheet-like cured product of the thermosetting composition") is also referred to as the "cured product of the present sheet." Thus, the composition of the present invention can be made into the cured product of the present by heating. Furthermore, the composition of the present invention can be molded into a sheet to form a sheet-like thermosetting composition (also referred to as the "thermosetting sheet"), and the thermosetting sheet can be cured to form a sheet with thermal conductivity (also referred to as the "thermoconductive sheet"). In other words, the thermally conductive sheet is the cured product of the present sheet and also a cured product of the present thermosetting sheet.

[0032] (First Aspect) In the first aspect of the composition of the present invention, when the composition of the present invention is cured, i.e., when the composition is formed into a fully cured product, the breaking energy of the fully cured product measured by three-point bending at 190°C is preferably 55 kPa or more, and the breaking energy of the fully cured product measured by three-point bending at 150°C is preferably 80 kPa or more.

[0033] Three-point bending measurements involve bending a measurement sample at three positions, one from the center and two from below. Because this is a stress-inducing test, it is believed to correlate with resistance when bonding under conditions of high temperature, internal stress, or external force, such as in a reflow process or sintering. That is, thermosetting compositions tend to accumulate strain during curing, and stress due to strain tends to accumulate at temperatures around the curing temperature. For example, in the case of a thermosetting composition containing an epoxy compound, stress due to strain tends to accumulate at temperatures between 120 and 200°C. Therefore, by measuring the breaking strength at 150°C and 190°C in a three-point bending test and keeping these strengths within a predetermined range, resistance to, for example, reflow conditions, which impose internal stress at 200°C or higher, and sintering conditions, which impose external force, can be obtained. This is believed to not only improve insulation resistance, but also reduce cracking of the sheet and peeling at the interface with the substrate.

[0034] If the breaking energy of the cured product obtained by three-point bending measurement at 190°C is 55 kPa or more and the breaking energy of the cured product obtained by three-point bending measurement at 150°C is 80 kPa or more, not only will the sheet-like cured product be less likely to crack when stressed by warping, distortion, etc., but the cured product will also be less likely to deteriorate and be able to maintain its dielectric strength even after being exposed to conditions of internal stress at high temperatures, such as in a reflow process, and will be able to prevent cracking and peeling when bonded to a substrate by sinter bonding under conditions of additional external force at high temperatures. From these perspectives, the composition of the present invention is preferably one that gives a breaking energy of 55 kPa or more, preferably 60 kPa or more, more preferably 70 kPa or more, and even more preferably 80 kPa or more, of these, when bonded to a substrate by sinter bonding under conditions of additional external force at high temperatures. The upper limit is not particularly limited, but is estimated to be around 500 kPa, and may be 300 kPa or less, or 150 kPa or less. Furthermore, the composition of the present invention is preferably one in which the breaking energy value obtained by three-point bending measurement of the cured product at 150°C is 80 kPa or more, more preferably 85 kPa or more, even more preferably 90 kPa or more, and even more preferably 100 kPa or more. The upper limit is not particularly limited, but is estimated to be around 500 kPa, and may be 300 kPa or less, or 200 kPa or less.

[0035] (Second Aspect) In a second aspect of the composition of the present invention, when the composition of the present invention is cured, i.e., when a cured product is formed, the value of x / y is preferably 0.7 to 1.15, and the value of x is 55 kPa or greater, where x is the breaking energy of the cured product measured by three-point bending at 190°C and y is the breaking energy of the cured product measured by three-point bending at 150°C. If the ratio (x / y) of the breaking energy x of the cured product measured by three-point bending at 190°C to the breaking energy y of the cured product measured by three-point bending at 150°C is 0.7 or greater and the value of x is 55 kPa or greater, bending stress can be maintained even in a high temperature range of 150°C or greater. Therefore, even after exposure to conditions in which internal stress is applied at high temperatures, such as in a reflow process, the cured product is less likely to deteriorate and can maintain its dielectric strength. Furthermore, when the cured product is bonded to a substrate by sinter bonding under conditions in which external force is applied at high temperatures, cracks can be prevented from occurring in the cured product and the bond can be prevented from peeling off. On the other hand, if the ratio (x / y) is 1.15 or less, the breaking energy is similar at 150°C and 190°C, resulting in less deterioration when the heating cycle is repeated. In this case, the difference in breaking strength between 150°C and 190°C is reduced, and the ratio (x / y) approaches 1. This reduces the difference in breaking strength between 150°C and 190°C, and the stress is dispersed even when internal stress or external force is applied under conditions of 200°C or higher, or when the temperature is subsequently lowered. This is thought to improve insulation resistance in reflow tests and sinter resistance tests, as well as to prevent cracks from occurring in the sheet and peeling at the interface with the substrate. From this perspective, the composition of the present invention preferably has a ratio (x / y) of the breaking energy x obtained by three-point bending measurement at 190°C to the breaking energy y obtained by three-point bending measurement at 150°C of the cured product, of 0.7 or more, more preferably 0.72 or more, even more preferably 0.74 or more, and even more preferably 0.76 or more. On the other hand, it is preferably 1.15 or less, more preferably 1.1 or less, even more preferably 1.05 or less, and even more preferably 1.03 or less.Furthermore, the composition of the present invention is preferably one in which the breaking energy x of the cured product, as measured by three-point bending at 190° C., is 55 kPa or more, more preferably 60 kPa or more, even more preferably 70 kPa or more, and even more preferably 80 kPa or more. The upper limit is not particularly limited, but is likely to be around 500 kPa, and may be 300 kPa or less, or may be 150 kPa or less.

[0036] To prepare the composition of the present invention so that the breaking energy value of the cured product obtained by three-point bending measurement at 190°C, the breaking energy value obtained by three-point bending measurement at 150°C, or the ratio (x / y) of the breaking energy x obtained by three-point bending measurement at 190°C to the breaking energy y obtained by three-point bending measurement at 150°C falls within the above-mentioned ranges, it is preferable to prepare the composition of the present invention so that the bending stress can be maintained even at temperatures above the glass transition temperature (Tg) of the cured product, for example, by adjusting the type and content of the thermosetting compound or curing agent to increase the crosslink density of the cured product, and by adjusting the polymer concentration or the low-temperature aging conditions. One preferred example is to prepare the composition of the present invention by increasing the content of a polyfunctional epoxy compound as a thermosetting compound and reducing the content of a polymer, such as an epoxy polymer, to increase the number of crosslinking points, and further using a phenolic resin-based curing agent as a curing agent to promote crosslinking, thereby increasing the crosslink density of the cured product, and by performing low-temperature aging. Increasing the crosslink density of the present cured product increases the force that maintains contact between inorganic fillers, resulting in an increase in the breaking energy at high temperatures. Furthermore, increasing the force that maintains contact between inorganic fillers reduces the thermal resistance between the inorganic fillers, thereby increasing, for example, the thermal conductivity. However, the method is not limited to the above. For the methods for measuring the breaking energy obtained by three-point bending measurement of the present cured product at 190°C and the breaking energy obtained by three-point bending measurement at 150°C, please refer to the methods in the Examples described below.

[0037] It is more preferred that the composition of the present invention, when cured, i.e., when formed into a fully cured product, has a breaking energy value at 190°C within the above-mentioned range, a breaking energy value at 150°C within the above-mentioned range, and a ratio (x / y) of the breaking energy x at 190°C to the breaking energy y at 150°C within the above-mentioned range.

[0038] (Three-point bending measurement at 190°C: Young's modulus) It is preferable that when the composition of the present invention is cured, i.e., when the composition is formed into a cured product, the Young's modulus of the cured product obtained by three-point bending measurement at 190°C is 5.5 GPa or more. If the cured product has a Young's modulus of 5.5 GPa or more obtained by three-point bending measurement at 190°C, not only is the sheet-shaped cured product less likely to crack when stress due to warping or distortion is applied, but the cured product also exhibits little deterioration and can maintain its dielectric strength even after being exposed to conditions in which internal stress is applied at high temperatures, such as in a reflow process, and is also able to prevent cracking and peeling when bonded to a substrate by sinter bonding under conditions in which an external force is applied at high temperatures of 150°C or more. From this viewpoint, the composition of the present invention is preferably one in which the Young's modulus of the cured product, as determined by three-point bending measurement at 190° C., is 5.5 GPa or more, more preferably 5.6 GPa or more, even more preferably 5.7 GPa or more, even more preferably 5.8 GPa or more, even more preferably 5.9 GPa or more, and even more preferably 6.0 GPa or more. The upper limit is not particularly limited, but is presumed to be around 100 GPa, and may be 50 GPa or less, or even 10 GPa or less.

[0039] (Three-point bending measurement at 150°C: Young's modulus) It is preferable that when the composition of the present invention is cured, i.e., when the composition is formed into a cured product, the Young's modulus of the cured product obtained by three-point bending measurement at 150°C is 5.5 GPa or more. If the cured product has a Young's modulus of 5.5 GPa or more obtained by three-point bending measurement at 150°C, not only is the sheet-shaped cured product less likely to crack when stress due to warping or distortion is applied, but the cured product also exhibits little deterioration and can maintain its dielectric strength even after being exposed to conditions in which internal stress is applied at high temperatures, such as in a reflow process, and is also able to prevent cracking and peeling when bonded to a substrate by sinter bonding under conditions in which an external force is applied at high temperatures of 150°C or more. From this perspective, the composition of the present invention is preferably one in which the Young's modulus of the cured product, as determined by three-point bending measurement at 150° C., is 5.5 GPa or more, more preferably 5.8 GPa or more, even more preferably 6.0 GPa or more, and even more preferably 6.3 GPa or more. The upper limit is not particularly limited, but is presumed to be around 100 GPa, and may be 50 GPa or less, or even 10 GPa or less.

[0040] To prepare the composition of the present invention so that the Young's modulus values ​​of the cured product obtained by three-point bending measurement at 190°C and 150°C fall within the above-mentioned ranges, it is preferable to adjust the type and content of the thermosetting compound or curing agent to increase the crosslink density of the cured product, and to adjust the polymer concentration or low-temperature aging conditions, thereby preparing the composition of the present invention so that the cured product can maintain its bending stress at temperatures above the glass transition temperature (Tg). One preferred example is to increase the content of a polyfunctional epoxy compound as a thermosetting compound and reduce the content of a polymer, such as an epoxy polymer, to increase the number of crosslinking points, and further use a phenolic resin-based curing agent as a curing agent to promote crosslinking, thereby increasing the crosslink density of the cured product, and then perform low-temperature aging. Increasing the crosslink density of the cured product can increase the Young's modulus at high temperatures. However, the present invention is not limited to the above method. For the method of measuring the Young's modulus of the cured product by three-point bending at 150°C and 190°C, see the method described in the Examples below.

[0041] (Thermal Conductivity) When the composition of the present invention is formed into a sheet and cured, i.e., when the composition is formed into a sheet-like cured product, the cured product preferably has a thermal conductivity in the thickness direction at 25°C of 14 W / m K or more. If the cured product has a thermal conductivity in the thickness direction at 25°C of 14 W / m K or more, it can be suitably used in power semiconductor devices that operate power semiconductors at high temperatures. From this perspective, the composition of the present invention preferably has a thermal conductivity in the thickness direction at 25°C of 14 W / m K or more, more preferably 15 W / m K or more, and even more preferably 17 W / m K or more.

[0042] To prepare the composition of the present invention so that the thermal conductivity of the sheet-like cured product falls within the above range, for example, the type of thermosetting compound, the type and content of the inorganic filler, the conditions in the low-temperature aging step, the conditions in the pressurizing step, the conditions in the curing step, etc. may be adjusted. However, the present invention is not limited to these methods. For the method of measuring the thermal conductivity of the sheet-like cured product in the thickness direction, please refer to the method in the Examples described below.

[0043] (Breakdown voltage (BDV)) When the composition of the present invention is formed into a sheet and cured, i.e., when the composition is formed into the present sheet cured product, the breakdown voltage of the present sheet cured product is preferably 6.5 kV or more when the thickness of the present sheet cured product is 150 μm. If the breakdown voltage of the present sheet cured product is 6.5 kV or more, it can also be suitably used in power semiconductor devices that operate power semiconductors at high voltages. From this perspective, the composition of the present invention is preferably one that gives a breakdown voltage of the present sheet cured product of 6.5 kV or more, and even more preferably one that gives a breakdown voltage of 7 kV or more, of which 7.5 kV or more, of which 8 kV or more, and of which 9 kV or more.

[0044] To prepare the composition of the present invention so that the breakdown voltage of the sheet-like cured product falls within the above range, for example, the type of thermosetting compound, the type and content of the inorganic filler, the conditions in the low-temperature aging step, the conditions in the pressure step, the conditions in the curing step, etc. may be adjusted. However, the present invention is not limited to these methods. For the method of measuring the breakdown voltage of the sheet-like cured product, please refer to the method in the Examples described below.

[0045] (Volume Resistivity) When the composition of the present invention is formed into a sheet and cured, i.e., when the composition of the present invention is formed into a sheet-like cured product, the volume resistivity (1000 V, 200°C) of the sheet-like cured product is preferably 3.0E+10 Ωcm or more. If the volume resistivity of the sheet-like cured product is 3.0E+10 Ωcm or more, this is preferable because it is good from the viewpoint of electrical insulation. From this viewpoint, the composition of the present invention is preferably such that the volume resistivity of the sheet-like cured product is 3.0E+10 Ωcm or more, more preferably 3.1E+10 Ωcm or more, and even more preferably 3.2E+10 Ωcm or more.

[0046] To prepare the composition of the present invention so that the volume resistivity of the sheet-like cured product falls within the above-mentioned range, for example, methods can be used such that the type and content of the thermosetting compound or curing agent is adjusted to increase the crosslink density of the cured product, and the polymer concentration is adjusted to allow the cured product to maintain electrical insulation even at temperatures above the glass transition temperature (Tg). A preferred example is to increase the content of a polyfunctional epoxy compound as a thermosetting compound, reduce the content of a polymer, such as an epoxy polymer, to increase the number of crosslinking points, and further use a phenolic resin-based curing agent as a curing agent to promote crosslinking, thereby increasing the crosslink density of the cured product, and then perform low-temperature aging to prepare the composition of the present invention. However, the present invention is not limited to these methods. For the method for measuring the volume resistivity (1000 V, 200°C) of the sheet-like cured product, see the method in the Examples described below.

[0047] (Moisture Absorption Rate) When the composition of the present invention is formed into a sheet and cured, i.e., when the composition is formed into a sheet-like cured product, the moisture absorption rate of the sheet-like cured product is preferably 0.7% by mass or more and 1.2% by mass or less. A moisture absorption rate of 0.7% by mass or more of the sheet-like cured product is preferable because the absorbed moisture and the hydroxyl groups in the sheet-like cured product form hydrogen bonds to toughen the sheet-like cured product and improve its bending resistance. On the other hand, a moisture absorption rate of 1.2% by mass or less is preferable because it is good in terms of moisture absorption reflow resistance. From this perspective, the composition of the present invention is preferable such that the moisture absorption rate of the sheet-like cured product is 0.7% by mass or more, preferably 0.72% by mass or more, and even more preferably 0.75% by mass or more. On the other hand, a moisture absorption rate of 1.2% by mass or less is preferable, and even more preferably 1.1% by mass or less, and even more preferably 1.0% by mass or less.

[0048] To prepare the composition of the present invention so that the moisture absorption rate of the sheet-like cured product falls within the above range, methods such as adjusting the amount of epoxy monomer (i.e., epoxy compound other than epoxy polymer) and the amount of curing agent to strengthen crosslinking or adjust the hydroxyl group concentration in the resin component, or adjusting low-temperature aging conditions, are possible. A preferred example is to increase the content of a polyfunctional epoxy compound as a thermosetting compound and reduce the content of a polymer, such as an epoxy polymer, to increase the number of crosslinking points. Furthermore, a phenolic resin-based curing agent is used as a curing agent to promote crosslinking, thereby increasing the crosslink density of the cured product, and then aging the composition at low temperature. However, the present invention is not limited to these methods. For a method for measuring the moisture absorption rate of the sheet-like cured product, see the method in the Examples described below.

[0049] (Storage Modulus (E')) When the composition of the present invention is formed into a sheet and cured, i.e., when the composition of the present invention is formed into a sheet-like cured product, the storage modulus of the sheet-like cured product at 200°C is preferably 6.0 GPa or more and 100 GPa or less. When the storage modulus of the sheet-like cured product at 200°C is within the above range, the effect of making the sheet-like cured product less susceptible to cracking at high temperatures can be obtained. From this perspective, the storage modulus of the composition of the present invention is preferably 6.0 GPa or more, more preferably 7.0 GPa or more, even more preferably 7.5 GPa or more, and even more preferably 7.7 GPa or more. On the other hand, it is preferably 100 GPa or less, even more preferably 90 GPa or less, even more preferably 80 GPa or less, and may be 50 GPa or less, 20 GPa or less, or 15 GPa or less.

[0050] To prepare the composition of the present invention so that the storage modulus of the sheet-like cured product at 200°C falls within the above range, for example, adjustment of the epoxy equivalent weight of the resin component, adjustment of the amount of polyfunctional epoxy, adjustment of the ratio of epoxy polymer to epoxy compound other than epoxy polymer, or adjustment of low-temperature aging conditions may be performed. In one preferred example, the composition of the present invention is prepared by increasing the content of polyfunctional epoxy compound as a thermosetting compound and decreasing the content of polymer, e.g., epoxy polymer, to increase the number of crosslinking points, and further using a phenolic resin-based curing agent as a curing agent to promote crosslinking, thereby increasing the crosslink density of the cured product, and then performing low-temperature aging. However, the present invention is not limited to these methods. The storage modulus of the sheet-like cured product at 200°C can be measured by laminating a sheet-like thermosetting composition, adjusting the sample thickness to 0.1 to 1.0 mm, heat-curing the sheet-like cured product, and then cutting the sheet-like cured product into 4 mm-wide strips, followed by dynamic viscoelasticity testing in a tensile mode. For more details, see the method in the Examples below for measuring the storage modulus of the sheet-like cured product at 200°C.

[0051] (Glass Transition Temperature (Tg)) When the composition of the present invention is formed into a sheet and cured, i.e., when the composition is formed into the present sheet-like cured product, the glass transition temperature (Tg) of the present sheet-like cured product is preferably 170°C or higher. If the glass transition temperature (Tg) of the present sheet-like cured product is 170°C or higher, the present sheet-like cured product is strong even at high temperatures of 175°C or higher, which is preferable. With regard to the upper limit, from the viewpoint of the cracking tendency of the present sheet-like cured product, it is preferably 300°C or lower. From this viewpoint, the composition of the present invention is preferably one that gives a sheet-like cured product with a glass transition temperature (Tg) of 170°C or higher, more preferably 175°C or higher, and even more preferably 180°C or higher. On the other hand, it is preferably one that gives a glass transition temperature (Tg) of 300°C or lower, more preferably 275°C or lower, and even more preferably 250°C or lower.

[0052] To prepare the composition of the present invention so that the glass transition temperature (Tg) of the sheet-like cured product falls within the above range, for example, methods such as adjusting the type and content of the thermosetting compound or curing agent to increase the crosslink density of the cured product and adjusting the polymer concentration can be mentioned. A preferred example is to increase the content of a polyfunctional epoxy compound as a thermosetting compound and reduce the content of a polymer, such as an epoxy polymer, to increase the number of crosslinking points, and further use a phenolic resin-based curing agent as a curing agent to promote crosslinking, thereby increasing the crosslink density of the cured product, and then aging the composition at a low temperature. However, the present invention is not limited to these methods. For a method for measuring the glass transition temperature (Tg) of the sheet-like cured product, see the method in the Examples described below.

[0053] (WPE of Resin Component) When the composition of the present invention contains an epoxy compound, the epoxy equivalent (WPE) of the component excluding the solvent and inorganic filler from the composition of the present invention (also referred to as the "resin component"), in other words, the solid content of the composition of the present invention excluding the inorganic filler, is preferably WPE < 250 g / equivalent. The solid content of the composition of the present invention means the component excluding the solvent from the composition of the present invention. Here, the epoxy equivalent (WPE) is the mass (g / equivalent) of the resin component per equivalent of epoxy group.

[0054] By adjusting the epoxy equivalent (WPE) of the resin component of the composition of the present invention within the above range, it is possible to adjust the flexibility of the composition of the present invention and to adjust the crosslink density of the cured product, thereby increasing the bending resistance. Furthermore, it is possible to adjust the retention force of the inorganic filler and improve the thermal conductivity of the cured sheet. From this perspective, the epoxy equivalent (WPE) of the resin component of the composition of the present invention is preferably less than 250 g / eq, more preferably 245 g / eq or less, even more preferably 240 g / eq or less, even more preferably 235 g / eq or less, and even more preferably 230 g / eq or less. On the other hand, from the viewpoint of ensuring the film-forming properties of the present thermosetting sheet in an uncured state and the toughness of the present sheet-like cured product, the epoxy equivalent (WPE) of the resin component of the composition of the present invention is preferably 100 g / eq or more, more preferably 110 g / eq or more, even more preferably 120 g / eq or more, even more preferably 150 g / eq or more, even more preferably 170 g / eq or more, even more preferably 200 g / eq or more, and even more preferably 210 g / eq or more.

[0055] In order to adjust the epoxy equivalent (WPE) of the resin component of the composition of the present invention within the above range, methods such as adjusting the content ratio of an epoxy compound having a predetermined epoxy equivalent, such as an epoxy polymer and a polyfunctional epoxy compound, or adjusting the type and content of a curing agent can be mentioned. A preferred example is to increase the content ratio of a polyfunctional epoxy compound as a thermosetting compound, while reducing the content ratio of a polymer, such as an epoxy polymer, and further use a phenolic resin-based curing agent as a curing agent and adjust its content to adjust the epoxy equivalent (WPE) of the resin component of the composition of the present invention within the above range. However, the present invention is not limited to these methods.

[0056] <Thermosetting Compound> Examples of the thermosetting compound contained in the composition of the present invention include epoxy compounds, phenolic resins, unsaturated polyester resins, melamine resins, urea resins, benzoxazine compounds, cyanates, and maleimides.

[0057] The content of the thermosetting compound is preferably 10% by mass or more and 70% by mass or less, based on 100% by mass of the components in the composition of the present invention excluding volatile components, such as solvents (also referred to as the "solid content"). A content of the thermosetting compound of 10% by mass or more is preferred because it improves moldability, while a content of 70% by mass or less allows the content of other components to be ensured, and is therefore preferred because it can improve thermal conductivity. From this perspective, the content of the thermosetting compound is preferably 10% by mass or more and 70% by mass or less, based on 100% by mass of the solid content in the composition of the present invention, with 15% by mass or more, 20% by mass or more, and 25% by mass or more being more preferred, while a content of 60% by mass or less being even more preferred. When an epoxy compound is used as the thermosetting compound, it is preferable to use a curing agent or a thermosetting catalyst, as described below, in combination. In this case, the curing agent or the thermosetting catalyst corresponds to the thermosetting compound, and are therefore included in the thermosetting compound in the above-mentioned "content of the thermosetting compound."

[0058] (Epoxy Compound) The composition of the present invention preferably contains an epoxy compound as the thermosetting compound.

[0059] Of the thermosetting compounds contained in the composition of the present invention, epoxy compounds preferably account for 30 to 100 mass %, more preferably 40 mass % or more, even more preferably 50 mass % or more, even more preferably 60 mass % or more, and even more preferably 70 mass % or more. In this case, epoxy compounds also include epoxy polymers, which will be described later.

[0060] The epoxy compound as the thermosetting compound contained in the composition of the present invention may be any compound having one or more oxirane rings, i.e., epoxy groups, in one molecule.

[0061] The epoxy group contained in the epoxy compound may be either an alicyclic epoxy group or a glycidyl group, but from the viewpoint of reaction rate or heat resistance, a glycidyl group is more preferable.

[0062] Examples of the epoxy compound include an epoxy group-containing silicon compound, an aliphatic epoxy compound, a bisphenol A or F type epoxy compound, a novolac type epoxy compound, an aromatic epoxy compound, an alicyclic epoxy compound, a glycidyl ester type epoxy compound, a polyfunctional epoxy compound, and a polymeric epoxy compound.

[0063] The epoxy compound may be an aromatic epoxy group-containing compound. Specific examples thereof include bisphenol-type epoxy compounds 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 compounds, epoxy compounds obtained by glycidylating dihydric phenols such as dihydroxynaphthalene and 9,9-bis(4-hydroxyphenyl)fluorene, epoxy compounds obtained by glycidylating trisphenols such as 1,1,1-tris(4-hydroxyphenyl)methane, epoxy compounds obtained by glycidylating tetrakisphenols such as 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane, novolac-type epoxy compounds obtained by glycidylating novolacs such as phenol novolac, cresol novolac, bisphenol A novolac, and brominated bisphenol A novolac, epoxy compounds having a dicyclopentadiene skeleton, and epoxy compounds having a naphthalene skeleton. Among these, it is preferable to use an epoxy compound having at least one skeleton selected from the group consisting of an epoxy compound having a biphenyl skeleton, an epoxy compound having a dicyclopentadiene skeleton, and an epoxy compound having a naphthalene skeleton.

[0064] (Polyfunctional Epoxy Compound) The composition of the present invention preferably contains a polyfunctional epoxy compound described below.

[0065] A multifunctional epoxy compound refers to an epoxy compound having two or more epoxy groups per molecule and a mass-average molecular weight (Mw) of less than 5,000. The composition of the present invention preferably contains a multifunctional epoxy compound having three or more epoxy groups per molecule and a mass-average molecular weight (Mw) of less than 5,000. A compound having four or more epoxy groups per molecule is more preferred. The inclusion of such a multifunctional epoxy compound allows for the introduction of highly polar epoxy groups at a high density, thereby enhancing the effects of physical interactions such as van der Waals forces and hydrogen bonding, thereby improving the adhesion between the thermally conductive sheet formed from the composition of the present invention and conductors such as metal plates and circuit boards. Furthermore, the inclusion of a multifunctional epoxy compound increases the storage modulus of the thermally conductive sheet, thereby providing a strong anchoring effect after the cured product penetrates into the irregularities on the surface of the conductor to be adhered, thereby improving the adhesion between the thermally conductive sheet and conductors such as metal plates and circuit boards. Furthermore, by including a polyfunctional epoxy compound in the composition of the present invention, particularly a polyfunctional epoxy compound having three or more epoxy groups in one molecule, the crosslink density of the cured product can be further increased, and the breaking energy of the cured product obtained by three-point bending measurement at 150°C and 190°C can be increased. Meanwhile, although the inclusion of a polyfunctional epoxy compound tends to increase the hygroscopicity of the composition of the present invention, improving the reactivity of the epoxy groups reduces the amount of hydroxyl groups during the reaction, thereby suppressing the increase in hygroscopicity. Furthermore, by preparing the composition of the present invention by combining the epoxy polymer described below with a polyfunctional epoxy compound, it becomes possible to achieve both high elasticity and low hygroscopicity in the thermally conductive sheet.

[0066] The polyfunctional epoxy compound may be an epoxy compound having two or more epoxy groups per molecule, from the viewpoint of increasing the storage modulus of the cured product, particularly at high temperatures, which is important in devices such as power semiconductor devices that generate a large amount of heat. Among these, epoxy compounds having three or more epoxy groups per molecule are preferred, and epoxy compounds having four or more epoxy groups per molecule are even more preferred. Having multiple epoxy groups, particularly glycidyl groups, per molecule improves the crosslink density of the cured product, resulting in a higher strength of the cured product, the thermally conductive sheet. This prevents the thermally conductive sheet from deforming or breaking when internal stress is generated in the thermally conductive sheet at high temperatures, such as during a reflow process or sintering, thereby preventing the formation of voids or other voids within the thermally conductive sheet.

[0067] Furthermore, from the viewpoint of adjusting the crosslinkability of the present thermal conductive sheet, the molecular weight of the polyfunctional epoxy compound, particularly a polyfunctional epoxy compound having three or more epoxy groups in one molecule, is preferably 800 or less, more preferably 700 or less, even more preferably 650 or less, particularly preferably 100 or more or 630 or less, even more preferably 200 or more or 600 or less. Furthermore, to improve the handleability of the composition of the present invention and the present thermosetting sheet, it is preferable that the polyfunctional epoxy compound contains a compound that is liquid at 25°C. Furthermore, from the viewpoint of achieving lower moisture absorption and higher crosslinking, it is preferable that the polyfunctional epoxy compound does not contain an amine-based or amide-based structure containing a nitrogen atom.

[0068] The epoxy equivalent of the polyfunctional epoxy compound, particularly a polyfunctional epoxy compound having three or more epoxy groups in one molecule, is preferably 75 g / equivalent or more, more preferably 80 g / equivalent or more, from the viewpoint of improving the heat resistance of the thermally conductive sheet, while from the viewpoint of improving the solubility in solvents, it is preferably 200 g / equivalent or less, more preferably 180 g / equivalent or less, more preferably 160 g / equivalent or less, and even more preferably 150 g / equivalent or less.

[0069] The polyfunctional epoxy compound may be any compound having two or more epoxy groups in one molecule, and is preferably a polyfunctional epoxy compound having three or more epoxy groups in one molecule and a molecular weight of 800 or less, and more preferably 650 or less. For example, EX321L, DLC301, DLC402, etc., manufactured by Nagase ChemteX Corporation can be used. These polyfunctional epoxy compounds may be used alone or in combination of two or more.

[0070] (Epoxy Polymer) From the viewpoint of ensuring film-forming properties, the composition of the present invention preferably contains a high-molecular-weight epoxy compound (also referred to as "epoxy polymer") having a mass-average molecular weight (Mw) of 5,000 or more.

[0071] Examples of the epoxy polymer include phenoxy resins having at least one skeleton selected from the group consisting of a bisphenol A type skeleton, a bisphenol F type skeleton, a bisphenol A / F mixed type skeleton, a naphthalene skeleton, a fluorene skeleton, a biphenyl skeleton, an anthracene skeleton, a pyrene skeleton, a xanthene skeleton, an adamantane skeleton, and a dicyclopentadiene skeleton.

[0072] Among these, the epoxy polymer is preferably an epoxy polymer having at least one structure selected from the structure represented by the following formula (1) (also referred to as "structure (1)") and the structure represented by the following formula (2) (also referred to as "structure (2)"):

[0073]

[0074] In formula (1), R １ and R ２ each represents an organic group, at least one of which is an organic group having a molecular weight of 16 or more, and in formula (2), R ３ represents a divalent cyclic organic group. The "organic group" may be any group containing carbon atoms. Specific examples include alkyl groups, alkenyl groups, and aryl groups, which may be substituted with halogen atoms, groups containing heteroatoms, or other hydrocarbon groups. The same applies hereinafter.

[0075] In the above formula (1), R １and R ２ At least one of R represents an organic group having a molecular weight of 16 or more, preferably a molecular weight of 16 to 1,000, and examples thereof include alkyl groups such as ethyl, propyl, butyl, pentyl, hexyl, and heptyl groups, and aryl groups such as phenyl, tolyl, xylyl, naphthyl, and fluorenyl groups. １ and R ２ may both be organic groups with a molecular weight of 16 or more, or one may be an organic group with a molecular weight of 16 or more and the other may be an organic group with a molecular weight of 15 or less or a hydrogen atom. Preferably, one is an organic group with a molecular weight of 16 or more and the other is an organic group with a molecular weight of 15 or less, and in particular, one of them is a methyl group and the other is a phenyl group, which is preferred from the viewpoints of facilitating control of handleability such as resin viscosity and of the strength of the cured product.

[0076] In the above formula (2), R ３ is a divalent cyclic organic group, and may be an aromatic ring structure such as a benzene ring structure, a naphthalene ring structure, or a fluorene ring structure, or an aliphatic ring structure such as cyclobutane, cyclopentane, or cyclohexane. These may also independently have a substituent such as a hydrocarbon group or a halogen atom. The divalent bond may be a divalent group on a single carbon atom, or may be a divalent group on different carbon atoms. Preferred examples include divalent aromatic groups having 6 to 100 carbon atoms, and groups derived from cycloalkanes having 2 to 100 carbon atoms, such as cyclopropane and cyclohexane. In particular, a 3,3,5-trimethyl-1,1-cyclohexylene group (also referred to as "structure (4)") represented by the following formula (4) is preferred from the viewpoints of controlling handleability such as resin viscosity and the strength of the cured product.

[0077]

[0078] The epoxy polymer preferably has a fluorene skeleton represented by the following formula (5): The rigidity of the fluorene skeleton represented by the following formula (5) results in excellent heat resistance and low linear expansion, and the molecular weight per unit is larger than that of ordinary epoxy compounds, so that the proportion of secondary hydroxyl groups, which cause hygroscopicity, in the entire molecular structure is relatively low, thereby enabling the epoxy polymer to exhibit low hygroscopicity.

[0079]

[0080] Further, the epoxy polymer may include an epoxy polymer having a structure represented by the following formula (3) (also referred to as "structure (3)").

[0081]

[0082] In the above formula (3), R ４ , R ５ , R ６ , R ７ are each an organic group having a molecular weight of 15 or more. Preferably, they are alkyl groups having a molecular weight of 15 to 1,000, and particularly preferably R ４ , R ５ , R ６ , R ７ It is preferable that all of the groups be methyl groups from the viewpoint of controlling the resin viscosity and other handling properties and the strength of the cured product.

[0083] From the viewpoint of achieving both reduced moisture absorption and strength retention of the present cured product and the present thermal conductive sheet, it is particularly preferable for the epoxy polymer to be an epoxy polymer containing either one of Structure (1) or Structure (2) and Structure (3). Compared with general epoxy polymers having a bisphenol A or bisphenol F skeleton, such epoxy polymers contain a large amount of hydrophobic hydrocarbon and aromatic structures, and therefore, by blending such epoxy polymers, it is possible to reduce the moisture absorption amount of the present cured product, that is, the present thermal conductive sheet.

[0084] In addition, from the viewpoint of reducing the amount of moisture absorption, it is preferable that the epoxy polymer contains a large amount of the hydrophobic structures (1), (2) and (3).

[0085] The weight average molecular weight (Mw) of the epoxy polymer is preferably 5,000 or more, more preferably 10,000 or more, even more preferably 15,000 or more, even more preferably 20,000 or more, even more preferably 25,000 or more, and even more preferably 30,000 or more. The upper limit can be 100,000 or less. By keeping the Mw in this range, the film-forming properties of the composition of the present invention are improved, and the handleability of the present thermosetting sheet in an uncured state tends to be improved. Furthermore, the improved film-forming properties have the effect of connecting fillers together in the present thermosetting sheet in an uncured state, making voids less likely to occur.

[0086] The epoxy equivalent of the epoxy polymer is preferably 5,000 g / equivalent or more, more preferably 7,000 g / equivalent or more, and even more preferably 8,000 g / equivalent or more, from the viewpoint of ensuring the film-forming ability and flexibility of the composition of the present invention, while from the viewpoint of solubility in solvents, it is preferably 25,000 g / equivalent or less, and even more preferably 20,000 g / equivalent or less.

[0087] The mass average molecular weight (Mw) of the epoxy polymer is a value calculated as polystyrene as determined by gel permeation chromatography. The epoxy equivalent is defined as the mass of the epoxy polymer containing one equivalent of epoxy groups and can be measured in accordance with JIS K7236.

[0088] The above epoxy polymers may be used alone or in combination of two or more.

[0089] (Epoxy Compound Content) The content of the epoxy polymer is preferably 5% by mass or more and less than 30% by mass based on the component (resin component) excluding the solvent and inorganic filler from the composition of the present invention, in other words, 100% by mass of the solid content of the composition of the present invention excluding the inorganic filler. By incorporating an epoxy polymer in an amount of 5% by mass or more based on 100% by mass of the solid content of the composition of the present invention excluding the inorganic filler, film-forming properties can be maintained, which is preferred. On the other hand, by incorporating an epoxy polymer in an amount of less than 30% by mass, flexibility of the thermosetting sheet in an uncured state can be maintained, which is preferred. From this perspective, the content of the epoxy polymer is preferably 5% by mass or more based on 100% by mass of the solid content of the composition of the present invention excluding the inorganic filler, more preferably 7.5% by mass or more, and even more preferably 10% by mass or more. On the other hand, from the viewpoint of increasing the crosslink density of the present cured product, it is preferably less than 30% by mass, and even more preferably 27.5% by mass or less, even more preferably 25% by mass or less, even more preferably 24% by mass or less, even more preferably 23% by mass or less, and even more preferably 22% by mass or less.

[0090] The content of the polyfunctional epoxy compound is preferably 5% by mass or more and 95% by mass or less based on 100% by mass of the components (resin components) excluding the solvent and inorganic filler from the composition of the present invention, in other words, 100% by mass of the solid content excluding the inorganic filler from the composition of the present invention. A content of the polyfunctional epoxy compound of 5% by mass or more can increase the crosslink density of the cured product, and can improve resistance to conditions such as high temperature internal stress, such as reflow resistance and sintering resistance. On the other hand, a content of 95% by mass or less can ensure the amount of other components necessary to maintain the film-forming properties of the composition of the present invention. From this perspective, the content of the polyfunctional epoxy compound is preferably 5% by mass or more based on 100% by mass of the solid content excluding the inorganic filler from the composition of the present invention, more preferably 10% by mass or more, and even more preferably 15% by mass or more. On the other hand, a content of 95% by mass or less is preferred, and even more preferably 90% by mass or less.

[0091] In particular, the content of the polyfunctional epoxy compound having three or more epoxy groups per molecule is preferably 5% by mass or more and 50% by mass or less, based on 100% by mass of the solid content of the composition of the present invention excluding the inorganic filler. A content of 5% by mass or more of the polyfunctional epoxy compound having three or more epoxy groups per molecule can increase the crosslink density of the cured product and maintain the storage modulus of the cured product, thereby improving resistance, for example, to conditions of exposure to internal stress or external force at high temperatures, such as reflow resistance and sintering resistance. From this perspective, the content of the polyfunctional epoxy compound having three or more epoxy groups per molecule is preferably 5% by mass or more, based on 100% by mass of the solid content of the composition of the present invention excluding the inorganic filler, more preferably 7.5% by mass or more, and even more preferably 10% by mass or more. On the other hand, a content of 50% by mass or less of the polyfunctional epoxy compound having three or more epoxy groups per molecule can maintain the toughness of the thermosetting sheet in an uncured state and reduce the moisture absorption rate of the sheet-like cured product, which is preferred. From this viewpoint, the content of the polyfunctional epoxy compound having three or more epoxy groups in one molecule is preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less, based on 100% by mass of the solid content of the composition of the present invention excluding the inorganic filler.

[0092] In particular, the content of the polyfunctional epoxy compound having three or more epoxy groups in one molecule and an epoxy equivalent of 25 to 200 g / equivalent is preferably 5% by mass or more and 50% by mass or less, more preferably 7.5% by mass or more or 45% by mass or less, and even more preferably 10% by mass or more or 40% by mass or less, relative to 100% by mass of the solids content excluding the inorganic filler, from the viewpoint of adjusting the epoxy equivalent (WPE) of the resin component of the composition of the present invention within a suitable range.

[0093] When an epoxy polymer and a polyfunctional epoxy compound are used in combination, from the viewpoint of improving both the film-forming ability of the composition of the present invention and the elastic modulus of the cured sheet, the content of the polyfunctional epoxy compound having three or more epoxy groups in one molecule is preferably 20 parts by mass or more and 500 parts by mass or less per 100 parts by mass of the epoxy polymer. In particular, if the content of the polyfunctional epoxy compound having three or more epoxy groups in one molecule is 20 parts by mass or more per 100 parts by mass of the epoxy polymer, this is preferred because it can increase the crosslink density of the cured product and improve resistance, for example, when exposed to conditions where internal stress or external force is applied at high temperatures, such as reflow resistance and sintering resistance. From this viewpoint, the content of the polyfunctional epoxy compound having three or more epoxy groups in one molecule is preferably 20 parts by mass or more and 500 parts by mass or less, more preferably 30 parts by mass or more or 400 parts by mass or less, even more preferably 40 parts by mass or more or 350 parts by mass or less, even more preferably 60 parts by mass or more or 300 parts by mass or less, and even more preferably 90 parts by mass or more or 200 parts by mass or less, relative to 100 parts by mass of the epoxy polymer.

[0094] The content ratio of the inorganic filler to the epoxy polymer (epoxy polymer / inorganic filler) is preferably 0.01 or more, more preferably 0.02 or more, and even more preferably 0.03 or more, from the viewpoint of maintaining the film-forming properties of the thermosetting sheet. On the other hand, from the viewpoint of improving the bending resistance of the uncured thermosetting sheet, it is preferably less than 0.2, more preferably 0.15 or less, and even more preferably 0.14 or less.

[0095] The mass ratio of the inorganic filler to the polyfunctional epoxy compound having three or more epoxy groups in one molecule (polyfunctional epoxy compound having three or more epoxy groups in one molecule / inorganic filler) is preferably 0.02 or more, more preferably 0.03 or more, and even more preferably 0.04 or more, from the viewpoint of improving the retention of the inorganic filler. On the other hand, from the viewpoint of improving the thermal conductivity of the thermally conductive sheet, it is preferably 0.2 or less, more preferably 0.18 or less, and even more preferably 0.16 or less.

[0096] The mass ratio of the inorganic filler to the epoxy compound (epoxy compound / inorganic filler) is preferably 0.2 or more, more preferably 0.22 or more, and even more preferably 0.25 or more, from the viewpoint of improving the sheet handling properties of the thermosetting sheet, and is preferably 0.6 or less, more preferably 0.57 or less, and even more preferably 0.55 or less, from the viewpoint of improving the thermal conductivity of the thermally conductive sheet.

[0097] (Other polymers with molecular weights of 5,000 or more) The composition of the present invention can contain, instead of or together with the epoxy polymer, a polymer other than the epoxy polymer (also referred to as "other polymers") having a mass average molecular weight (Mw) of 5,000 or more. In the present invention, the term "polymer" encompasses both epoxy polymers and other polymers. When the composition of the present invention contains such polymers, it is possible to improve film formability even when the content of agglomerated boron nitride particles is increased.

[0098] The other polymers may be either thermoplastic resins or thermosetting resins. Examples of the thermoplastic resins and thermosetting resins include thermoplastic resins such as polyphenylene ether, polyphenylene sulfide, polyarylate, polysulfone, polyether sulfone, polyether ether ketone, and polyether ketone. Furthermore, as the thermoplastic resins and thermosetting resins, heat-resistant resins known as super engineering plastics, such as thermoplastic polyimide, thermosetting polyimide, benzoxazine, and reaction products of polybenzoxazole and benzoxazine, can also be used. Furthermore, styrene-based polymers such as styrene and alkylstyrene, (meth)acrylic polymers such as alkyl (meth)acrylate and glycidyl (meth)acrylate, styrene-based-(meth)acrylic copolymers such as styrene-glycidyl methacrylate, polyvinyl alcohol derivatives such as polyvinyl butyral, polyvinyl benzal, and polyvinyl acetal, norbornene-based polymers containing norbornene compounds, and phenoxy resins can also be used. Among these, phenoxy resin is preferred in terms of heat resistance and compatibility with thermosetting resins. The thermoplastic resin and the thermosetting resin may each be used alone or in combination of two or more. Either the thermoplastic resin or the thermosetting resin may be used alone, or a thermoplastic resin and a thermosetting resin may be used in combination.

[0099] The content of polymers having a mass average molecular weight (Mw) of 5,000 or more (total content of epoxy polymers and other polymers) is preferably 5% by mass or more and less than 30% by mass, based on 100% by mass of the solid content excluding the inorganic filler from the composition of the present invention. By including 5% by mass or more of polymers having a mass average molecular weight (Mw) of 5,000 or more, the inorganic filler retention and film-forming ability are maintained, while by including them at a content of less than 30% by mass, the strength upon curing can be maintained, which is preferable. From this viewpoint, the content of polymers having a mass average molecular weight (Mw) of 5,000 or more is preferably 5% by mass or more, more preferably 7.5% by mass or more, and even more preferably 10% by mass or more, based on 100% by mass of the solid content excluding the inorganic filler from the composition of the present invention. On the other hand, it is preferably less than 30% by mass, and even more preferably 27.5% by mass or less, even more preferably 25% by mass or less, even more preferably 24% by mass or less, even more preferably 23% by mass or less, and even more preferably 20% by mass or less. Among these, from the viewpoint of maintaining the flexibility of the sheet-shaped thermosetting composition in an uncured state and improving the handleability, the content is more preferably 18% by mass or less.

[0100] Among the above, the other polymer is preferably one having a functional group reactive with the epoxy compound. Here, examples of the functional group reactive with the epoxy compound include a phenolic hydroxyl group, an epoxy group, a carboxylic acid group, a carboxylic anhydride group, and an active ester.

[0101] <Curing Agent> The composition of the present invention preferably contains a curing agent as needed. Examples of curing agents include phenolic resins, compounds having a heterocyclic structure containing a nitrogen atom (also referred to as "nitrogen-containing heterocyclic compounds"), acid anhydrides having an aromatic skeleton or an alicyclic skeleton, water additives of such acid anhydrides, or modified products of such acid anhydrides. Only one type of curing agent may be used, or two or more types may be used in combination. The use of these preferred curing agents makes it possible to obtain a cured product having an excellent balance of heat resistance, moisture resistance, and electrical properties.

[0102] In particular, when the composition of the present invention contains the above-mentioned epoxy compound as a thermosetting compound, it is preferable to use in combination with a curing agent having an active group capable of reacting with an epoxy group. For example, it is preferable to use in combination with an epoxy compound at least one of a phenolic resin, a benzoxazine compound, a polyarylate, a cyanate, and a maleimide. That is, it is preferable that the composition of the present invention contains an epoxy compound and at least one of a phenolic resin, a benzoxazine compound, a polyarylate, a cyanate, and a maleimide. In particular, from the viewpoint of increasing the crosslinking density, adjusting the crosslinking rate, and maintaining heat resistance, it is preferable to contain an epoxy compound and a phenolic resin. Furthermore, from the viewpoint of suppressing a decrease in thermal conductivity at high temperatures, it is preferable to contain an epoxy compound and a benzoxazine compound together with a phenolic resin.

[0103] (Phenol Resin) Examples of the phenol 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 with rigid main chain skeletons and phenolic resins with triazine skeletons are preferred for further improving the flexibility of the composition of the present invention, the cured product, and the thermally conductive sheet, and for improving the mechanical properties and heat resistance of the cured product. Furthermore, phenolic resins with allyl groups are preferred for improving the flexibility of the uncured thermosetting sheet and the toughness of the cured product. The inclusion of a phenolic resin increases the curing rate of the epoxy compound and reduces residual groups, thereby effectively improving heat resistance.

[0104] (Benzoxazine Compound) The benzoxazine compound is a compound that crosslinks and hardens when heated, and also functions as a curing agent for an epoxy compound. Therefore, by using an epoxy compound and a benzoxazine compound in combination, a hydroxyl group generated when the benzoxazine compound crosslinks reacts with an epoxy group of the epoxy compound to bond, and the crosslinked structure of the epoxy compound and the crosslinked structure of the benzoxazine compound are combined to form a stronger crosslinked structure, which can increase the glass transition temperature (Tg) of the cured product and further improve heat resistance.

[0105] The benzoxazine compound preferably has a structure represented by the following formula (I) or (II).

[0106]

[0107]

[0108] In formula (I), a represents an integer of 0 to 3, preferably 0 or 1, and more preferably 0. １ and R ２ R each independently represents a hydrogen atom or a monovalent organic group. １ Specific examples of R include a hydrogen atom, an alkyl group, an alkenyl group, a cycloalkyl group, an aryl group, an aralkyl group, and an alkynyl group. １ may be substituted with any substituent. ２ Specific examples of include aliphatic hydrocarbon groups, aromatic hydrocarbon groups, etc. * indicates a bond to another chemical structure.

[0109] In formula (II), b represents an integer of 0 to 4, preferably 0 or 1, and more preferably 0. ３ represents a hydrogen atom or a monovalent organic group. When b is 2 or more, a plurality of R ３ may be the same or different. ３ Specific examples of include aliphatic hydrocarbon groups, aromatic hydrocarbon groups, etc. * indicates a bond to another chemical structure.

[0110] The benzoxazine compound preferably has a plurality of structures represented by formula (I) and / or formula (II) in one molecule. More specifically, the benzoxazine compound preferably has 2 to 4, and more preferably 2, structures represented by formula (I) and / or formula (II) in one molecule. It is believed that the use of such a benzoxazine compound can further enhance curing performance and also improve heat resistance.

[0111] The benzoxazine compound preferably includes a benzoxazine compound represented by formula (III). The benzoxazine compound represented by formula (III) is often also called Pd-type benzoxazine.

[0112]

[0113] In formula (III), X ２ is a single bond or a divalent linking group. ２ represents a single bond, a linear or branched alkylene group having 1 to 10 carbon atoms, —O—, —SO ２ -, -CO-, or a structure in which two or more of these are linked together.

[0114] The benzoxazine compound may include a benzoxazine compound represented by the following formula (IV). Incidentally, the benzoxazine compound represented by the following formula (IV) is often also called Fa-type benzoxazine. In formula (IV), X ２ The definition and specific examples of X in the above formula (III) are as follows: ２ is the same as:

[0115]

[0116] Benzoxazine compounds include those that are solid at 25°C and those that are liquid at 25°C. From the viewpoint of increasing the glass transition temperature (Tg) of the composition of the present invention and the cured product thereof and thereby improving the heat resistance, those that are solid at 25°C are more preferred.

[0117] The content of the benzoxazine compound is preferably 3% by mass or more and 50% by mass or less, more preferably 5% by mass or more or 30% by mass or less, and even more preferably 7% by mass or more or 25% by mass or less, relative to 100% by mass of the solid content of the composition of the present invention excluding the inorganic filler.

[0118] If the proportion of the benzoxazine compound is high, the film may become brittle when formed, possibly resulting in a decrease in film formability, and therefore the content of the benzoxazine compound in the composition of the present invention is preferably lower than the content of the epoxy compound, and in particular, the mass ratio of the content of the benzoxazine compound to the content of the epoxy compound in the solid content excluding the inorganic filler from the composition of the present invention (benzoxazine compound / epoxy compound) is preferably less than 0.8, and more preferably 0.7 or less, more preferably 0.6 or less, and even more preferably 0.5 or less. On the other hand, from the viewpoint of improving heat resistance, the mass ratio is preferably 0.05 or more, more preferably 0.07 or more, and even more preferably 0.08 or more.

[0119] (Polyarylate) By containing an epoxy compound and a polyarylate, the ester group in the main chain skeleton of the polyarylate or the terminal hydroxyl group reacts with the epoxy group of the epoxy compound to bond, so that the crosslinked structure of the epoxy compound and the crosslinked structure formed by the reaction of the epoxy compound and the polyarylate are combined to form a stronger crosslinked structure.Therefore, the glass transition temperature (Tg) of the composition of the present invention can be increased, the heat resistance can be improved, and for example, the change in elastic modulus of the cured product at high temperatures can be suppressed.

[0120] The polyarylate may, for example, be a compound represented by the following formula (A).

[0121]

[0122] In the formula (A), each X may independently represent a hydrogen atom, an aliphatic group, or an aromatic group. Specific examples include a hydrogen atom, a substituted or unsubstituted alkyl group, and an aryl group. Each Y independently represents a single bond, -CR １ R ２-, O, CO or S. １ , R ２ each independently represents a hydrogen atom, a methyl group, or an ethyl group, or R １ and R ２ and represents a cyclohexylidene group formed by bonding. Examples include linear, branched, or cyclic alkylene groups having 1 to 12 carbon atoms. Each Z may independently be a hydrogen atom, a hydroxy group, or an alkoxy group. n is the number of repeating units, and may be an integer of 1 or more, for example, an integer of 1 to 100 is preferred, and an integer of 1 or more or 90 or less, and even more preferred is an integer of 2 or more or 80 or less.

[0123] From the viewpoint of improving heat resistance, the molecular weight of the polyarylate is preferably 500 or more, more preferably 700 or more, and even more preferably 1,000 or more. On the other hand, from the viewpoint of resin fluidity, it is preferably 10,000 or less, more preferably 8,000 or less, and even more preferably 5,000 or less. From the viewpoint of dimensional stability at high temperatures, the glass transition temperature of the polyarylate is preferably 80°C or more, more preferably 100°C or more, and even more preferably 120°C or more. On the other hand, from the viewpoint of improving toughness, it is preferably 300°C or less, more preferably 270°C or less, and even more preferably 250°C or less. From the viewpoint of reducing moisture absorption, the functional group equivalent weight (amount of hydroxyl groups and ester groups) of the polyarylate is preferably 100 g / equivalent or more, more preferably 120 g / equivalent or more, and even more preferably 140 g / equivalent or more. On the other hand, from the viewpoint of improving heat resistance, it is preferably 1000 g / equivalent or less, more preferably 800 g / equivalent or less, and even more preferably 600 g / equivalent or less.

[0124] (Cyanate) The cyanate may be, for example, a compound having an -OCN group in the molecule, which reacts with the -OCN group upon heating. Specific examples include 1,3-dicyanatobenzene, 1,4-dicyanatobenzene, 1,3,5-tricyanatobenzene, 1,3-dicyanatonaphthalene, 1,4-dicyanatonaphthalene, 1,6-dicyanatonaphthalene, 1,8-dicyanatonaphthalene, 2,6-dicyanatonaphthalene, 2,7-dicyanatonaphthalene, 1,3,6-tricyanatonaphthalene, 4,4'-dicyanatobiphenyl, bis(4-cyanatophenyl)methane, bis(3,5-dimethyl-4-cyanatophenyl)methane, and 2,2-bis(4-cyanatophenyl)propane. Examples of suitable cyanates include bis(4-cyanatophenyl)propane, 2,2-bis(3,5-dibromo-4-cyanatophenyl)propane, bis(4-cyanatophenyl)ether, bis(4-cyanatophenyl)thioether, bis(4-cyanatophenyl)sulfone, tris(4-cyanatophenyl)phosphite, tris(4-cyanatophenyl)phosphate, and cyanates obtained by reacting a novolak resin with a cyanogen halide. Prepolymers having a triazine ring formed by trimerizing the cyanate groups of these polyfunctional cyanates can also be used.

[0125] (Maleimide) The maleimide may be a compound having one or more, preferably two or more, maleimide groups (2,5-dihydro-2,5-dioxo-1H-pyrrol-1-yl groups) per molecule. Maleimides can react with epoxy compounds in the presence of an appropriate catalyst to form bonds, and can also bond with other maleimides because radical polymerization can occur due to the ethylenic carbon-carbon unsaturated bond contained in the maleimide group. The maleimide may be, for example, an aliphatic maleimide containing an aliphatic amine skeleton, or an aromatic maleimide containing an aromatic amine skeleton.

[0126] (Content of Curing Agent) The curing agent is preferably contained in a proportion of 1% by mass or more and 50% by mass or less, more preferably 3% by mass or more or 40% by mass or less, more preferably 5% by mass or more or 30% by mass or less, and even more preferably 10% by mass or more or 25% by mass or less, based on 100% by mass of the solid content of the composition of the present invention excluding the inorganic filler. When the content of the curing agent is equal to or more than the lower limit, the reaction proceeds effectively and sufficient curing performance can be obtained, while when the content is equal to or less than the upper limit, the crosslinking density can be increased, which is preferable, and therefore strength can be increased.

[0127] <Curing Accelerator> The composition of the present invention may contain a thermosetting catalyst as a curing accelerator, if necessary, in order to adjust the curing rate and the physical properties of the cured product.

[0128] The thermosetting catalyst is preferably selected appropriately depending on the type of thermosetting compound and curing agent. Specific examples of the thermosetting catalyst include chain or cyclic tertiary amines, organophosphorus compounds, diazabicycloalkenes such as quaternary phosphonium salts or organic acid salts, and imidazoles. 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. Furthermore, the nitrogen-containing heterocyclic compounds described above as curing agents also function as thermosetting catalysts, and may therefore be incorporated as thermosetting catalysts.

[0129] Among these, from the viewpoints of storage stability, heat resistance, and curing speed, the thermosetting catalyst is preferably a compound having an imidazole (also referred to as an "imidazole-based compound"). Preferred imidazole-based compounds include, for example, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 2-phenyl-4-methylimidazole, 1-cyanoethyl-2-phenylimidazolium trimellitate, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine, 2, Examples of suitable compounds include 4-diamino-6-[2'-undecylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-ethyl-4'methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanuric acid adduct, 2-phenylimidazole isocyanuric acid adduct, 2-phenyl-4,5-dihydroxymethylimidazole, and 2-phenyl-4-methyl-5-hydroxymethylimidazole. By using an imidazole compound with a melting point of 100°C or higher, and more preferably 200°C or higher, a cured product with excellent storage stability and adhesion can be obtained. Furthermore, compounds containing a nitrogen-containing heterocyclic compound other than the aforementioned imidazole ring are more preferred from the standpoint of adhesion.

[0130] The thermosetting catalyst may be used alone or in combination of two or more. By using two or more imidazole compounds having a melting point of 100°C or higher, the composition of the present invention can be obtained with excellent storage stability, and the cured product can be obtained with excellent heat resistance. In particular, it is more preferable that at least one of the two or more imidazole compounds has a melting point of 200°C or higher, and even more preferable that two or more of the imidazole compounds have a melting point of 200°C or higher.

[0131] The thermosetting catalyst is preferably contained in an amount of 0.1% by mass or more and 10% by mass or less, and more preferably 0.1% by mass or more and 5% by mass or less, based on 100% by mass of the solids content of the composition of the present invention excluding the inorganic filler. When the content of the thermosetting catalyst is equal to or more than the lower limit, the progress of the curing reaction can be sufficiently promoted to achieve good curing, while when it is equal to or less than the upper limit, the curing rate is not too fast, and therefore the storage stability of the composition of the present invention can be improved.

[0132] <Inorganic Filler> The inorganic filler contained in the composition of the present invention preferably has a thermal conductivity of 2.0 W / m·K or more, more preferably 3.0 W / m·K or more, particularly preferably 5.0 W / m·K or more, and even more preferably 10.0 W / m·K or more.

[0133] Examples of inorganic fillers include electrically insulating fillers made only of carbon, fillers made of metal carbides or semi-metal carbides, metal oxides or semi-metal oxides, and metal nitrides or semi-metal nitrides.

[0134] An example of the electrically insulating filler made only of carbon is diamond (thermal conductivity: approximately 2000 W / m·K). Examples of the metal carbide or semi-metal carbide include silicon carbide (thermal conductivity: approximately 60 to 270 W / m·K), titanium carbide (thermal conductivity: approximately 21 W / m·K), and tungsten carbide (thermal conductivity: approximately 120 W / m·K).

[0135] Examples of the metal oxide or semi-metal oxide 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 semi-metal 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), and silicon nitride (thermal conductivity: about 30 to 80 W / m·K).

[0136] These inorganic fillers may be used alone or in combination of two or more.

[0137] From the viewpoint of electrical insulation, the volume resistivity of the inorganic filler at 20°C is 10 １３ It is preferable that the resistivity is Ω·cm or more, and particularly 10 １４ It is more preferable that the electrical resistance is Ω·cm or more. Among them, metal oxides, semi-metal oxides, metal nitrides, or semi-metal nitrides are preferable because they can easily provide sufficient electrical insulation for the thermally conductive sheet. Specific examples of such inorganic 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: >10 １４Among these, aluminum oxide, aluminum nitride, and boron nitride are preferred, with aluminum oxide and boron nitride being particularly preferred since they can impart high insulating properties to the thermally conductive sheet.

[0138] The shape of the inorganic filler may be irregular particles, spheres, whiskers, fibers, plates, or an aggregate or mixture thereof.

[0139] In the present invention, "spherical" generally means that the aspect ratio (ratio of major axis to minor axis) is from 1 to 2, preferably from 1 to 1.75, more preferably from 1 to 1.5, and even more preferably from 1 to 1.4. The aspect ratio can be determined by randomly selecting 10 or more particles from an image of a cross section of the composition of the present invention or the thermally conductive 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.

[0140] (Boron nitride agglomerated particles) The inorganic filler contained in the composition of the present invention preferably contains "boron nitride agglomerated particles" formed by agglomeration of primary particles of boron nitride, because these have fewer problems with moisture absorption when the composition of the present invention is formed into a sheet and cured, i.e., when the sheet-shaped cured product is obtained, and are low in toxicity, can efficiently increase thermal conductivity, and can impart high insulating properties to the thermally conductive sheet. That is, the composition of the present invention preferably contains boron nitride agglomerated particles as the inorganic filler.

[0141] The boron nitride agglomerated particles may also be used in combination with other inorganic fillers. However, as described below, the heat transfer behavior in the present thermally conductive sheet does not depend solely on the thermal conductivity within the inorganic filler. Therefore, even if diamond particles or the like, which have extremely high thermal conductivity but are also extremely expensive, are used among the inorganic fillers exemplified above, the thermal conductivity of the present thermally conductive sheet in the thickness direction does not increase significantly. Therefore, when using boron nitride agglomerated particles in combination with other inorganic fillers, the main focus is on reducing the cost of the composition of the present invention. Therefore, because of their relatively low cost and relatively high thermal conductivity, the inorganic filler used in combination with the boron nitride agglomerated particles is preferably selected from magnesium oxide, aluminum oxide, tungsten carbide, silicon carbide, aluminum nitride, etc., with aluminum oxide being more preferred.

[0142] In particular, from the viewpoint of high thermal conductivity, it is preferred that the boron nitride agglomerated particles account for 75 mass % or more of the inorganic filler contained in the composition of the present invention, more preferably 80 mass % or more, and even more preferably 85 mass % or more (including 100 mass %) of the inorganic filler contained in the composition of the present invention.

[0143] The shape of the agglomerated particles of boron nitride is preferably spherical.

[0144] The agglomerated structure of the boron nitride agglomerated particles is preferably a house-of-card structure from the viewpoint of improving thermal conductivity. The agglomerated structure of the boron nitride agglomerated particles can be confirmed by a scanning electron microscope (SEM).

[0145] The house-of-card structure, in which plate-shaped particles are stacked in a complex manner without orientation, 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 flat surfaces of primary particles forming an agglomerate particle are in contact with the end faces of other primary particles present within the agglomerate particle. A schematic diagram of the house-of-card structure is shown in Figure 1. Due to their structural strength, the agglomerate particles of this house-of-card structure have extremely high fracture strength and do not collapse even during the pressurization process performed during sheet formation of this thermally conductive sheet. Therefore, primary particles that are normally oriented in the longitudinal direction of this thermally conductive sheet can be made to exist in a random direction. Therefore, the use of agglomerate particles with a house-of-card structure can further increase the proportion of primary particles with ab planes oriented in the thickness direction of this thermally conductive sheet, thereby enabling effective heat conduction in the thickness direction of the sheet and further increasing the thermal conductivity in the thickness direction.

[0146] The boron nitride agglomerated particles having a house-of-card structure can be produced, for example, by the method described in WO 2015 / 119198.

[0147] When using boron nitride agglomerated particles having a house-of-card structure, the particles may be surface-treated with a surface treatment agent. Examples of such surface treatment agents include known surface treatment agents such as silane coupling treatment. It is believed that increasing the adhesion at the interface between the inorganic filler and the thermosetting compound, i.e., the matrix resin, through chemical treatment can further reduce thermal conductivity attenuation at the interface. In the composition of the present invention, the thermosetting compound is also referred to as the "matrix resin" because it encapsulates the inorganic filler and plays a role in maintaining the overall shape of the composition of the present invention.

[0148] By using aggregated particles formed by aggregation of primary particles as the inorganic filler used in the composition of the present invention, it is possible to increase the particle size compared to inorganic fillers that use only primary particles. By increasing the particle size of the inorganic filler, it is possible to reduce the number of heat transfer paths between inorganic fillers via a thermosetting compound with low thermal conductivity, and therefore to reduce the increase in thermal resistance in the heat transfer paths in the thickness direction.

[0149] From the above viewpoints, the lower limit of the maximum particle size of the boron nitride agglomerated particles is preferably 20 μm or more, more preferably 30 μm or more, and even more preferably 40 μm or more, while the upper limit of the maximum particle size is preferably 300 μm or less, more preferably 200 μm or less, even more preferably 100 μm or less, and still more preferably 90 μm or less.

[0150] The average particle size of the boron nitride agglomerated particles is not particularly limited. It is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 15 μm or more. It is preferably 100 μm or less, more preferably 90 μm or less. When the average particle size of the boron nitride agglomerated particles is 5 μm or more, the number of particles in the composition of the present invention and the present cured product is relatively small, and the number of interparticle interfaces is reduced, resulting in low thermal resistance and possibly high thermal conductivity of the present thermal conductive sheet. When the average particle size is equal to or less than the upper limit, the present cured product tends to have good surface smoothness.

[0151] When the average particle size or maximum particle size of the boron nitride agglomerated particles is equal to or less than the above upper limit, when the boron nitride agglomerated particles are contained in a thermosetting compound, i.e., a matrix resin, a high-quality film without surface roughness can be formed. When the average particle size or maximum particle size is equal to or greater than the above lower limit, the interface between the matrix resin and the boron nitride agglomerated particles is reduced, resulting in lower thermal resistance and achieving high thermal conductivity, while also providing a sufficient thermal conductivity-improving effect as an inorganic filler required for thermally conductive sheets for power semiconductor devices.

[0152] Furthermore, it is believed that the effect of thermal resistance at the interface between the matrix resin and the boron nitride agglomerated particles becomes significant when the size of the boron nitride agglomerated particles is 1 / 10 or less of the thickness of the thermal conductive sheet. In particular, for power semiconductor devices, the thermal conductive sheet is often applied with a thickness of 100 μm to 300 μm, so from the viewpoint of thermal conductivity, it is preferable that the maximum particle size of the boron nitride agglomerated particles be greater than the above-mentioned lower limit. Furthermore, by having the maximum particle size of the boron nitride agglomerated particles be greater than the above-mentioned lower limit, not only is the increase in thermal resistance caused by the interface between the boron nitride agglomerated particles and the matrix resin suppressed, but the number of required thermal conduction paths between particles is reduced, thereby increasing the probability of thermally conductive connection from one side to the other in the thickness direction of the thermal conductive sheet. On the other hand, by ensuring that the maximum particle size of the boron nitride agglomerated particles is equal to or less than the above upper limit, the boron nitride agglomerated particles are prevented from protruding onto the surface of the thermal conductive sheet, resulting in a good surface shape without surface roughness.As a result, for example, when producing a sheet bonded to a copper substrate, sufficient adhesion can be achieved and excellent voltage resistance characteristics can be obtained.

[0153] The ratio of the size (maximum particle diameter) of the boron nitride agglomerated particles to the thickness of the thermally conductive sheet (maximum particle diameter / thickness) is preferably 0.3 or more and 1.0 or less, more preferably 0.35 or more or 0.95 or less, and even more preferably 0.4 or more or 0.9 or less.

[0154] The maximum particle size and average particle size of the boron nitride agglomerated particles can be measured, for example, by the following method. The maximum particle size and average particle size of the boron nitride agglomerated particles used as a raw material can be determined by measuring the particle size distribution of a sample prepared by dispersing boron nitride agglomerated particles in a solvent, specifically, a sample prepared by dispersing boron nitride agglomerated particles in a pure water medium containing a dispersion stabilizer, using a laser diffraction / scattering particle size analyzer, and determining the maximum particle size Dmax and average particle size D50 of the boron nitride agglomerated particles from the obtained particle size distribution. Here, Dmax and D50 are the maximum particle size and the particle size at 50% cumulative volume in the volume-based particle size distribution obtained by measurement using a laser diffraction / scattering particle size distribution analyzer. Alternatively, the maximum particle size and average particle size can also be determined using a dry particle size analyzer such as a Morphologi G3 (manufactured by Malvern Instruments).

[0155] On the other hand, the maximum particle size Dmax and average particle size D50 of the boron nitride agglomerated particles in the composition of the present invention or the present thermally conductive sheet can also be measured in the same manner as above by dissolving and removing organic components such as thermosetting compounds in a solvent (including a heated solvent), or by swelling the organic components to reduce the adhesive strength to the boron nitride agglomerated particles and then physically removing them, and then heating and ashing the organic components in air to remove them. Furthermore, the maximum particle size of the boron nitride agglomerated particles in the composition of the present invention or the present thermally conductive sheet can also be determined by directly observing a cross section of the composition of the present invention or the present thermally conductive sheet with a scanning electron microscope, a transmission electron microscope, a micro-Raman spectrometer, an atomic force microscope, or the like, and determining the maximum particle size among them. The average particle size of the boron nitride agglomerated particles in the composition of the present invention or the thermally conductive sheet can also be determined by directly observing a cross section of the composition of the present invention or the thermally conductive sheet with a scanning electron microscope, a transmission electron microscope, a micro-Raman spectrometer, an atomic force microscope, etc., and calculating the arithmetic mean value of the particle diameters. When the particles are non-spherical, the longest and shortest diameters are measured, and the mean value is used as the particle size of the particles.

[0156] (Inorganic Filler Content) The inorganic filler content is preferably 30% by mass or more and less than 90% by mass relative to 100% by mass of the solid content in the composition of the present invention, i.e., 100% by mass of the solid content of the entire composition. If the inorganic filler content is 30% by mass or more relative to 100% by mass of the solid content in the composition of the present invention, the insulating properties and thermal conductivity can be improved. From this perspective, the inorganic filler content is preferably 30% by mass or more relative to 100% by mass of the solid content in the composition of the present invention, more preferably 40% by mass or more, even more preferably 50% by mass or more, and even more preferably 60% by mass or more. Of these, from the perspective of further increasing thermal conductivity, 65% by mass or more is even more preferable. On the other hand, if the content is less than 90% by mass, handleability and film-forming properties can be maintained. From this perspective, the inorganic filler content is preferably less than 90% by mass, even more preferably 85% by mass or less, even more preferably 80% by mass or less, and even more preferably 75% by mass or less.

[0157] The content of the boron nitride agglomerated particles is preferably 50% by mass or more relative to 100% by mass of the total inorganic filler. If the content of the boron nitride particles is 50% by mass or more relative to 100% by mass of the total inorganic filler, insulation and thermal conductivity can be improved. From this viewpoint, the content of the boron nitride agglomerated particles is preferably 50% by mass or more relative to 100% by mass of the total inorganic filler, more preferably 60% by mass or more, and even more preferably 70% by mass or more.

[0158] <Solvent> The composition of the present invention may contain an organic solvent as needed, for example, to improve the coatability when forming a sheet-shaped cured product through a coating process. Examples of organic solvents that may be contained in the composition of the present invention include methyl ethyl ketone, cyclohexanone, propylene glycol monomethyl ether acetate, butyl acetate, isobutyl acetate, and propylene glycol monomethyl ether. These organic solvents may be used alone or in combination of two or more.

[0159] When the composition of the present invention contains an organic solvent, its content is appropriately determined depending on the handleability during production of the thermally conductive sheet. Usually, the organic solvent is preferably used so that the solid content (total of components other than the solvent) of the composition of the present invention is 10% by mass or more and 90% by mass or less, and particularly preferably 40% by mass or more or 80% by mass or less. Furthermore, when the composition of the present invention is formed into a sheet, the organic solvent is preferably used so that the solid content (total of components other than the solvent) of the composition of the present invention is 95% by mass or more, more preferably 97% by mass or more, even more preferably 98% by mass or more, and even more preferably 99% by mass or more.

[0160] <Other Components> The composition of the present invention may contain other components in addition to the above components. Examples of such other components include additives such as dispersants, thermoplastic resins, organic fillers, and silane coupling agents that improve the interfacial adhesion strength between inorganic fillers and resin components, additives that are expected to increase the adhesion strength between the thermally conductive sheet and conductors such as metal plates and circuit boards, insulating carbon components such as reducing agents, viscosity modifiers, thixotropic agents, flame retardants, colorants, various antioxidants such as phosphorus-based and phenol-based, phenol acrylate-based and other process stabilizers, heat stabilizers, hindered amine radical scavengers (HAAS), impact modifiers, processing aids, metal deactivators, copper inhibitors, antistatic agents, and extenders. When these additives are used, the amount added may be within the range typically used for the purpose.

[0161] (Silane Coupling Agent) The composition of the present invention preferably contains a silane coupling agent as needed. By incorporating a silane coupling agent, the interfacial adhesive strength between the inorganic filler and the thermosetting compound can be increased, and when the composition of the present invention is cured, voids and the like can be suppressed, thereby maintaining insulation resistance and insulation stability.

[0162] Examples of silane coupling agents include N-phenyl-γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, p-styryltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, etc. One of these agents may be used alone, or two or more may be used in combination.

[0163] The content of the silane coupling agent is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, even more preferably 0.15 parts by mass or more, even more preferably 0.18 parts by mass or more, relative to 100 parts by mass of the total inorganic filler, from the viewpoint of improving the adhesion at the interface between the inorganic filler and the thermosetting compound. On the other hand, from the viewpoint of maintaining heat resistance, the content is preferably 5 parts by mass or less, even more preferably 3 parts by mass or less, even more preferably 1 part by mass or less, relative to 100 parts by mass of the total inorganic filler.

[0164] <<Uses of the Composition of the Present Invention>> The composition of the present invention can be turned into a cured product by heating. Furthermore, the composition of the present invention can be formed into a sheet to form a thermosetting sheet, and the thermosetting sheet can be cured to form a sheet-like cured product, which can be used as a thermally conductive sheet. The cured product and the thermally conductive sheet can be used in a variety of applications. For example, they can be used as components of composite molded products, heat-dissipating laminates, heat-dissipating circuit boards, and power semiconductor devices, as described below. However, the applications are not limited to these.

[0165] <Method for producing the present thermosetting sheet> Next, an example of a method for producing the present thermosetting sheet will be described.

[0166] The thermosetting sheet can be obtained by forming the composition of the present invention into a sheet (this step is also referred to as the "film-forming step"), optionally drying the film (this step is also referred to as the "drying step"), optionally performing low-temperature aging by placing the film in an environment at a temperature of 0°C or below (this step is also referred to as the "low-temperature aging step"), and optionally applying pressure (this step is also referred to as the "pressuring step"). One example of a method for producing the thermosetting sheet is a production method characterized by forming the composition of the present invention into a sheet and then performing low-temperature aging by placing the film in an environment at a temperature of 0°C or below. However, the order of the steps can be reversed as appropriate. For example, the low-temperature aging step may be performed after the pressurizing step.

[0167] (Film-forming step) For example, a thermosetting compound, an inorganic filler, and optionally other components (raw materials) are mixed, and the solvent is added to the mixture, if necessary, and kneaded to prepare a slurry of the composition of the present invention. This slurry of the composition of the present invention can be formed into a sheet by a coating method such as a blade method, a solvent casting method, or an extrusion film-forming method.

[0168] When forming a sheet-shaped film by the above coating method, a coating film is first formed by coating the surface of a substrate with the slurry composition of the present invention. That is, a coating film is formed on the substrate using the slurry composition of the present invention by a dip method, a spin coating method, a spray coating method, a blade coating 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 composition of the present invention. Such a coating device can uniformly form a coating film of a predetermined thickness on the substrate. Note that, as the substrate, a copper plate or copper foil or a PET film, as described below, is generally used, but is not limited thereto.

[0169] (Drying Process) The composition of the present invention formed into a sheet as described above is dried at a temperature (heated atmosphere temperature) of typically 10 to 150°C, preferably 25°C or higher or 120°C or lower, more preferably 30°C or higher or 110°C or lower, and most preferably 100°C or lower, to remove the solvent and low-molecular-weight components. By keeping the drying temperature below the upper limit, curing of the resin in the composition of the present invention is suppressed, and the resin in the sheet-shaped composition of the present invention tends to flow in the subsequent pressurization step, making it easier to remove voids. By keeping the drying temperature above the lower limit, the solvent can be effectively removed, and productivity tends to be improved. The drying time is not particularly limited and can be adjusted appropriately depending on the state of the composition of the present invention, the drying environment, etc. The drying time is preferably 1 minute or longer, more preferably 2 minutes or longer, and even more preferably 5 minutes or longer. The drying time is preferably 24 hours or shorter, more preferably 10 hours or shorter, even more preferably 4 hours or shorter, and particularly preferably 2 hours or shorter. A drying time of at least the lower limit tends to sufficiently remove the solvent and inhibit the residual solvent from forming voids in the sheet-like cured product, whereas a drying time of not more than the upper limit tends to improve productivity and reduce production costs.

[0170] (Low-temperature aging step) Next, it is preferable to carry out low-temperature aging, in which the sheet-shaped composition of the present invention thus formed is placed in a temperature environment of 0° C. or lower. By subjecting the sheet-shaped composition of the present invention to such low-temperature aging, the moisture inside the sheet can be frozen and dispersed as fine ice, and small chambers of moisture are created that are confined in fine spaces even after the temperature is returned to room temperature, preventing the formation of large voids and preventing deterioration of insulating properties, while suppressing the occurrence of cracks when the sheet is bent.

[0171] The temperature (environmental temperature) during low-temperature aging is preferably lower because a faster cooling rate results in finer ice. From this perspective, a temperature of 0°C or lower is preferred, with -5°C or lower being particularly preferred, -10°C or lower being particularly preferred, and -15°C or lower being even more preferred. On the other hand, if the temperature is too low, the uncured thermosetting sheet will fall below its glass transition temperature (Tg) and become prone to cracking, so a temperature of -50°C or higher is preferred, and when an epoxy compound is included, a temperature of -30°C or higher is particularly preferred, with -25°C or higher being even more preferred.

[0172] The time for low-temperature aging is not particularly limited as long as the composition of the present invention is frozen. It is sufficient to rapidly freeze and hold the composition for 10 minutes or more, preferably 30 minutes or more, more preferably 1 hour or more, more preferably 2 hours or more, more preferably 4 hours or more, more preferably 8 hours or more, more preferably 16 hours or more, and more preferably 24 hours or more. On the other hand, since the reaction of epoxy compounds proceeds gradually even at low temperatures, from the viewpoint of avoiding long-term storage, the time for low-temperature aging is preferably 365 days or less, more preferably 180 days or less, more preferably 90 days or less, more preferably 30 days or less, and even more preferably 7 days or less.

[0173] It is not necessary to apply pressure during low-temperature aging, but a minute pressure of 0.1 kPa or less may be applied.

[0174] (Pressure application step) Next, it is desirable to apply pressure to the resulting sheet-like composition of the present invention for the purposes of bonding inorganic fillers together to form heat conduction paths, eliminating voids and gaps within the cured product of the thermosetting sheet, i.e., the thermally conductive sheet, and improving adhesion between the cured product of the thermosetting sheet, i.e., the thermally conductive sheet, and the substrate. However, depending on the purpose, pressure may not be applied. For example, when there is a large amount of solvent or a large amount of inorganic filler, many holes may remain due to the escape of the solvent. In such cases, it is preferable to perform the pressure application step. By performing the pressure application step, it is possible to reduce or make smaller the gaps (voids), particularly the interconnected holes, within the cured product of the thermosetting sheet, i.e., the thermally conductive sheet.

[0175] In the pressurizing step, it is desirable to apply a load of 2 MPa or more to the sheet-like composition of the present invention on the substrate. Examples of pressurizing methods include platen presses, isostatic presses, vacuum presses, calendar presses, belt presses, and servo presses. However, the present invention is not limited to these methods. The load is preferably 5 MPa or more, more preferably 7 MPa or more, and even more preferably 9 MPa or more. The load is preferably 1500 MPa or less, more preferably 1000 MPa or less, and even more preferably 800 MPa or less. By applying a load at or below the upper limit, voids in the sheet-like composition of the present invention can be eliminated without destroying the secondary particles of the inorganic filler, such as boron nitride agglomerated particles, and the thermal conductivity of the cured product of the thermosetting sheet, i.e., the thermal conductive sheet, can be increased. By applying a load at or above the lower limit, contact between the inorganic fillers is improved, facilitating the formation of thermal conductive paths, thereby increasing the thermal conductivity of the cured product of the thermosetting sheet, i.e., the thermal conductive sheet.

[0176] The heating temperature of the sheet-like composition of the present invention on the substrate during the pressurizing step is not particularly limited. The heating temperature (product temperature) is preferably 0°C or higher, more preferably 5°C or higher, and even more preferably 10°C or higher. The heating temperature is preferably 300°C or lower, more preferably 250°C or lower, even more preferably 200°C or lower, even more preferably 100°C or lower, and particularly preferably 90°C or lower. By performing the pressurizing step within this temperature range, the melt viscosity of the resin in the sheet-like composition of the present invention can be reduced, and voids and gaps in the cured product of the thermosetting sheet, i.e., the thermally conductive sheet, can be further reduced. Furthermore, heating at or below the above upper limit tends to suppress decomposition of organic components in the thermosetting sheet and its cured product, i.e., the thermally conductive sheet, and voids caused by residual solvent.

[0177] The time for the pressure step is not particularly limited. The time for the pressure step is preferably 30 seconds or more, more preferably 1 minute or more, even more preferably 3 minutes or more, and particularly preferably 5 minutes or more. The time for the pressure step is preferably 1 hour or less, more preferably 30 minutes or less, and even more preferably 20 minutes or less. When the pressure step time is equal to or less than the above upper limit, the production time of the thermosetting sheet can be reduced, and production costs tend to be reduced. When the pressure step time is equal to or greater than the above lower limit, voids and gaps in the cured product of the thermosetting sheet, i.e., the thermal conductive sheet, can be sufficiently removed, and heat transfer performance and voltage resistance characteristics tend to be improved.

[0178] <Present Cured Product and Present Sheet-Like Cured Product> The present cured product and the present sheet-like cured product can have the above-mentioned physical properties, i.e., the breaking energy obtained by three-point bending measurement at 190°C, the breaking energy obtained by three-point bending measurement at 150°C, the ratio (x / y) of the breaking energy x obtained by three-point bending measurement at 190°C to the breaking energy y obtained by three-point bending measurement at 150°C, the Young's modulus obtained by three-point bending measurement at 190°C, the Young's modulus obtained by three-point bending measurement at 150°C, the thermal conductivity in the thickness direction at 25°C, the breakdown voltage at a thickness of 150 μm, the volume resistivity (1000 V, 200°C), the moisture absorption rate, the storage modulus at 200°C, and the glass transition temperature (Tg), within the above-mentioned ranges.

[0179] <Thermal Conductive Sheet> The thermal conductive sheet according to one embodiment of the present invention may be a thermal conductive sheet formed from the cured product. In other words, it may be a thermal conductive sheet made of the sheet-like cured product. The thermal conductive sheet may also have the above-described physical properties, i.e., the breaking energy obtained by three-point bending measurement at 190°C, the breaking energy obtained by three-point bending measurement at 150°C, the ratio (x / y) of the breaking energy x obtained by three-point bending measurement at 190°C to the breaking energy y obtained by three-point bending measurement at 150°C, the Young's modulus obtained by three-point bending measurement at 190°C, the Young's modulus obtained by three-point bending measurement at 150°C, the thermal conductivity in the thickness direction at 25°C, the breakdown voltage, the volume resistivity (1000V, 200°C), the moisture absorption rate, the storage modulus at 200°C, and the glass transition temperature (Tg), all within the above-described ranges.

[0180] (Thickness) The lower limit of the thickness of the thermally conductive sheet is preferably 50 μm or more, more preferably 60 μm or more, and even more preferably 70 μm or more. 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 making the thickness of the thermally conductive sheet 50 μm or more, sufficient voltage resistance characteristics can be ensured. On the other hand, by making the thickness 400 μm or less, particularly when using the thermally conductive sheet in a power semiconductor device, etc., miniaturization and thinning can be achieved, and the effect of reducing thermal resistance in the thickness direction due to the thin film can be obtained compared to insulating thermally conductive layers made of ceramic materials.

[0181] <Method for Manufacturing the Present Thermally Conductive Sheet> Next, an example of a method for manufacturing the present thermally conductive sheet will be described.

[0182] The present thermally conductive sheet can be produced as a sheet-like cured product by curing the present thermosetting sheet produced as described above (this step is also referred to as the "curing step").

[0183] (Curing step) The thermosetting sheet prepared as described above can be cured by heating. In this case, the heating temperature (product temperature) is preferably 30 to 400°C, and more preferably 50°C or higher, more preferably 90°C or higher, more preferably 120°C or higher, more preferably 150°C or higher, and even more preferably 175°C or higher. On the other hand, it is preferably 300°C or lower, and even more preferably 250°C or lower.

[0184] The curing step for completely curing the thermosetting sheet may be carried out under pressure or without pressure. The pressurizing step and the curing step may be carried out simultaneously. In particular, in the sheet forming step that involves the pressurizing step and the curing step, it is preferable to apply a load within the above range to carry out the pressurizing and curing.

[0185] The load when pressurizing and curing are performed simultaneously is not particularly limited. In this case, for example, it is preferable to apply a load of 5 MPa or more to the thermosetting sheet on the substrate, and the load at that time is more preferably 7 MPa or more, and even more preferably 9 MPa or more. The load is preferably 2000 MPa or less, more preferably 1500 MPa or less, more preferably 1000 MPa or less, even more preferably 500 MPa or less, and even more preferably 100 MPa or less. By setting the load when pressurizing and curing are performed simultaneously to the above upper limit value or less, the secondary particles of the inorganic filler, such as boron nitride agglomerated particles, are not destroyed, and voids and the like can be eliminated in the thermosetting sheet, thereby improving the thermal conductivity of the thermal conductive sheet. Furthermore, by setting the load to the above lower limit value or more, contact between the inorganic fillers is improved, making it easier to form a thermal conduction path, thereby improving the thermal conductivity of the thermal conductive sheet.

[0186] The pressurizing time when pressing and curing are performed simultaneously is not particularly limited. The pressurizing time is preferably 30 seconds or more, more preferably 1 minute or more, even more preferably 3 minutes or more, and particularly preferably 5 minutes or more. The pressurizing time is preferably 4 hours or less, more preferably 3 hours or less, and even more preferably 2 hours or less. When the pressurizing time is equal to or less than the upper limit, the manufacturing time of the thermally conductive sheet can be shortened, and production costs tend to be reduced. When the pressurizing time is equal to or more than the lower limit, voids and gaps in the thermally conductive sheet can be sufficiently removed, and heat transfer performance and voltage resistance tend to be improved.

[0187] <Present Composite Molded Product> A composite molded product (also referred to as "present composite molded product") as an example of an embodiment of the present invention has a sheet-like cured product of the composition of the present invention, i.e., a cured product portion made of the present thermally conductive sheet and a metal portion, with the cured product portion and the metal portion being laminated together. In this case, the metal portion may be provided on only one side of the cured product portion made of the present thermally conductive sheet, or on two or more sides. For example, the present thermally conductive sheet may have a metal portion on only one side, or may have a metal portion on both sides. Furthermore, the metal portion may be patterned.

[0188] Such a composite molded product can be produced by using a metal part as the substrate and forming the thermally conductive sheet on this substrate according to the method described above. Alternatively, the thermally conductive sheet can be formed on a substrate other than the metal part, peeled from the substrate, and then heat-pressed onto a metal member that will become the metal part. In this case, the thermally conductive sheet 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 from the substrate. The thermally conductive sheet is then placed on another metal plate or sandwiched between two metal plates and pressed together.

[0189] 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 thermally conductive sheet and conductors such as metal plates and circuit boards, it is more preferable that the surface of the metal plate be subjected to such treatment.

[0190] Specific examples of the present composite molded article include a heat dissipating laminate, a heat dissipating circuit board, and a power semiconductor device, which will be described below in order, although the present invention is not limited to these.

[0191] <Present Heat-Dissipating Laminate> A heat-dissipating laminate according to one embodiment of the present invention (also referred to as "the present heat-dissipating laminate") may be a laminate including the present thermally conductive sheet.

[0192] An example of the present heat dissipation laminate is one in which a heat dissipation metal layer containing a heat dissipation material is laminated on one surface of the present heat conductive sheet.

[0193] The heat dissipating material is not particularly limited as long as it is made of a material with good thermal conductivity. In particular, it is preferable to use a heat dissipating metal material in order to increase the thermal conductivity in the laminated structure, and it is more preferable to use a flat metal material. The material of the metal material is not particularly limited. In particular, copper plate, aluminum plate, aluminum alloy plate, etc. are preferred because they have good thermal conductivity and are relatively inexpensive.

[0194] The thermally conductive sheet and the heat-dissipating metal layer can be laminated and integrated by press molding, which is a batch process. In this case, the press equipment and press conditions may be the same as the press molding conditions for obtaining the thermally conductive sheet described above. However, they do not necessarily have to be the same.

[0195] <Heat Dissipating Circuit Board> A heat dissipating circuit board according to an embodiment of the present invention (also referred to as the "heat dissipating circuit board") may include the heat conductive sheet. An example of the heat dissipating circuit board is one having a configuration in which the heat dissipating metal layer is laminated on one surface of the heat conductive sheet, and a conductive circuit, such as a circuit board, is formed on the surface of the heat conductive sheet opposite the heat dissipating metal layer, for example, by etching. Specifically, the heat dissipating circuit board may be an integrated structure of "heat dissipating metal layer / heat conductive sheet / conductive circuit." The state before circuit etching may be, for example, an integrated structure of "heat dissipating metal layer / heat conductive sheet / conductive circuit-forming metal layer," in which the conductive circuit-forming metal layer is flat and formed on the entire surface of one side of the heat conductive sheet, or formed on a partial area.

[0196] The material of the conductive circuit-forming metal layer is not particularly limited. In particular, it is generally preferable to form the conductive circuit-forming metal layer from a copper thin plate having a thickness of 0.05 mm to 1.2 mm in terms of electrical conductivity, etching properties, cost, and the like.

[0197] <Present Power Semiconductor Device> A power semiconductor device according to an embodiment of the present invention (also referred to as "present power semiconductor device") is a product in which a circuit combining multiple power semiconductors is integrated into a single package module, and may include the present thermally conductive sheet. An example of the present power semiconductor device is one in which power semiconductors are mounted using the present thermally conductive sheet as a heat dissipation circuit board. In the present power semiconductor device, conventionally known materials can be used as appropriate for components other than the present thermally conductive sheet or the present heat dissipation laminate, such as aluminum wiring, sealing material, packaging material, heat sink, thermal paste, and solder.

[0198] <<Explanation of Terms>> In the present invention, when it is stated that "α to β" (α and β are any numbers), it means "α or more and β or less" unless otherwise specified, and also includes the meaning of "preferably greater than α" or "preferably smaller than β". Furthermore, when it is stated that "α or more" or "α≦" (α is any number), it also includes the meaning of "preferably greater than α" unless otherwise specified, and when it is stated that "β or less" or "≦β" (β is any number), it also includes the meaning of "preferably smaller than β" unless otherwise specified. In the present invention, the term "sheet" conceptually includes a sheet, a film, and a tape. Furthermore, in this specification, the expression "to" means "and / or".

[0199] An example of an embodiment of the present invention will be described below, but the present invention is not limited to the embodiment described below.

[0200] <Raw Materials> The raw materials used in the examples and comparative examples are as follows.

[0201] (Inorganic Filler) Inorganic Filler 1: Spherical boron nitride agglomerated particles having a house-of-card structure, produced in accordance with the method for producing boron nitride agglomerated particles disclosed in the examples of WO 2015 / 561028. Maximum particle size (Dmax): 90 μm Average particle size (D50): 45 μm

[0202] Inorganic filler 2: Spherical alumina particles manufactured by Admatechs Co., Ltd. Average particle size (D50): 7 to 13 μm

[0203] The maximum particle size (Dmax) and average particle size (D50) of the inorganic filler are determined by dispersing the inorganic filler in a pure water medium containing sodium hexametaphosphate as a dispersion stabilizer, measuring the volumetric particle size distribution using a laser diffraction / scattering particle size distribution analyzer LA-300 (manufactured by Horiba, Ltd.), and determining the maximum particle size (Dmax) and the particle size at 50% cumulative volume (average particle size (D50)) from the obtained particle size distribution.

[0204] (Epoxy Compounds) Epoxy compound 1: manufactured by Mitsubishi Chemical Corporation, biphenyl-type solid epoxy compound having two glycidyl groups per molecule. Mass average molecular weight (Mw): approximately 400. Epoxy equivalent (WPE): 200 g / equivalent.

[0205] Epoxy compound 2: manufactured by Nagase ChemteX Corporation, a multifunctional epoxy compound containing a structure having four or more glycidyl groups in one molecule, but not containing an amine or amide structure containing a nitrogen atom. Mass average molecular weight (Mw): approximately 400. Epoxy equivalent (WPE): 100 g / equivalent.

[0206] Epoxy compound 3: alkyl diglycidyl ether manufactured by Mitsubishi Chemical Corporation, a multifunctional epoxy compound having two glycidyl groups in one molecule; mass average molecular weight (Mw): approximately 240; epoxy equivalent (WPE): 120 g / equivalent.

[0207] Epoxy compound 4: bisphenol A novolac solid epoxy compound manufactured by Mitsubishi Chemical Corporation, a multifunctional epoxy compound containing a structure having four or more glycidyl groups in one molecule, not containing an amine or amide structure containing a nitrogen atom, Mass average molecular weight (Mw): 1,000 or more but less than 5,000, Epoxy equivalent (WPE): 210 g / equivalent

[0208] Epoxy compound 5: manufactured by Mitsubishi Chemical Corporation, bisphenol A diglycidyl ether, a multifunctional epoxy compound having two glycidyl groups in one molecule. Mass average molecular weight (Mw): approximately 400. Epoxy equivalent (WPE): 200 g / equivalent.

[0209] (Curing Agents) Curing agent 1: "H-4", a phenolic resin-based curing agent (phenol novolac), manufactured by UBE Corporation Curing agent 2: Pd-type benzoxazine, solid (25°C), in formula (III), manufactured by Shikoku Kasei Corporation ２ is CH ２ Curing agent 3: "MEH-8000H" manufactured by Meiwa Kasei Co., Ltd., a phenolic resin curing agent (allylphenol novolac)

[0210] (Polymer) Epoxy polymer 1: a bifunctional epoxy polymer manufactured by Mitsubishi Chemical Corporation and disclosed as resin component 1 in JP-A-2020-63438, having the above structures (2) and (3), and R in formula (2) ３ is structure (4), R in formula (3) ４ , R ５ , R ６ , R ７ All of the groups were methyl groups. Polystyrene-equivalent weight average molecular weight (Mw): 30,000 Epoxy equivalent (WPE): 9,000 g / equivalent

[0211] (Thermosetting catalyst) Thermosetting catalyst 1: 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-s-triazine, which has both an imidazole-derived structure and a triazine-derived structure in one molecule (manufactured by Shikoku Chemical Industries, Ltd., "Curesol 2E4MZ-A"); melting point: 215-225°C Thermosetting catalyst 2: 2-phenyl-4,5-dihydroxymethylimidazole (manufactured by Shikoku Chemical Industries, Ltd., "Curesol 2PHZ-PW"); melting point: dec. 230, so the melting point is 230°C or higher

[0212] (Silane Coupling Agent) Silane Coupling Agent 1: Glycidyloxypropyltrimethoxysilane (KBM-403, manufactured by Shin-Etsu Chemical Co., Ltd.)

[0213] Examples 1 to 4, Comparative Examples 1 to 5 Raw materials were weighed and mixed using a planetary centrifugal stirrer to obtain mixtures having the compositions (parts by mass) shown in Table 1. When preparing these mixtures, 20% by mass each of methyl ethyl ketone and cyclohexanone was used to prepare a slurry-like thermosetting composition so that the mixture accounted for 60% by mass (solid content concentration) of the coating slurry.

[0214] The resulting slurry-like thermosetting composition was applied to a PET substrate using a doctor blade method and dried by heating at 60°C (heated ambient temperature) for 120 minutes to obtain a sheet-like thermosetting composition. The total content of methyl ethyl ketone and cyclohexanone in the sheet-like thermosetting composition was 1% by mass or less. Next, for Examples 1 to 4 and Comparative Examples 1 to 4, the sheet-like thermosetting composition was placed in a vacuum-packed bag, the air was removed from the bag, and the opening of the bag was heat-sealed to seal it. The bag was then stored in a freezer at -20°C for 72 hours to undergo low-temperature aging. For Comparative Example 5, the low-temperature aging was not performed, and the sealed vacuum-packed bag containing the sheet-like thermosetting composition was aged for 72 hours in a 60°C environment. Next, the sheet-shaped thermosetting compositions obtained in Examples 1 to 4 and Comparative Examples 1 to 5 were set in a pressure press and pressed at 40°C under a load of 150 MPa for 10 minutes to prepare sheet-shaped thermosetting compositions (samples).

[0215] <Measurements and Evaluations> The raw materials used in each of the Examples and Comparative Examples were subjected to WPE measurement as follows. In addition, the cured products (sheet-shaped cured products) of the sheet-shaped thermosetting compositions (samples) were subjected to three-point bending measurement, and measurements of thermal conductivity, breakdown voltage, volume resistivity, moisture absorption rate, storage modulus, and glass transition temperature (Tg) were also performed as follows. Furthermore, a reflow resistance evaluation test and a sinter resistance evaluation test were also performed. The results of each of the Examples and Comparative Examples are shown in Table 1.

[0216] In Table 1, for the cured product (sheet-shaped cured product) of the sheet-shaped thermosetting composition (sample), the numerical values ​​indicating the amount of each component in the thermosetting composition indicate the mass proportion (parts by mass) of each component, and "WPE" is the epoxy equivalent (g / equivalent) of the resin component excluding the solvent and inorganic filler from the thermosetting composition.

[0217] (Measurement of Epoxy Equivalent (WPE) of Resin Component) The resin components (components of the thermosetting composition excluding the solvent and inorganic filler) used in each of the Examples and Comparative Examples, i.e., the thermosetting compositions obtained by mixing the epoxy compounds 1, 2, 3, 4, and 5, the curing agents 1, 2, and 3, the epoxy polymer 1, the thermosetting catalysts 1 and 2, and the silane coupling agent 1 in the mass ratios shown in Table 1 below, were measured for potential by potentiometric titration in accordance with JIS K7236, and the epoxy equivalent (g / equivalent) was calculated by converting the potential into a value for the entire resin component.

[0218] (Three-point bending measurement of cured thermosetting composition) Four sheets of the thermosetting composition (sample) prepared in each Example and Comparative Example were stacked and heated under a load of 10 MPa at 120°C (product temperature) for 30 minutes, 175°C (product temperature) for 30 minutes, and then 200°C (product temperature) for 30 minutes to cure the composition, yielding a sheet-like cured product with a thickness of 0.6 mm, which was then cut into a 50 mm x 8 mm test piece.

[0219] The obtained test specimen was measured using an Autograph AG-20kNXplus (manufactured by Shimadzu Corporation) under the following conditions: Test specimen shape: approximately 50 mm x 8 mm x 0.6 mm Test temperature: 150°C, 190°C Number of tests: n = 2 Distance between supports: 40 mm Support table radius: 2 mm Indenter radius: 3.2 mm Test speed: 0.01 mm / sec

[0220] A load was applied from the top of the test piece to the center between the supports, and the load was terminated at the point where the test piece broke (break point). Here, strain ε was calculated using the following formula: ε = (6 × ω × h) / (L × L), where ω is the displacement at the break point (mm), h is the thickness of the test piece before the load was applied (mm), and L is the distance between the supports (mm). The breaking bending stress σ (kPa) was calculated using the following formula: σ = (3 × P × L) / (2 × b × h × h) × 1000, where P is the load at the break point (N), b is the width (mm) of the measurement sample before the load was applied, h is the thickness (mm) of the test piece before the load was applied, and L is the distance (mm) between the supports. The bending breaking energy (kPa) per unit volume was calculated by calculating the area under the stress-strain curve up to the break point, with the vertical axis representing stress and the horizontal axis representing strain.

[0221] In the above stress-strain curve, the slope from 0.01% to 0.1% strain was taken as Young's modulus, which was calculated using the following formula: Young's modulus (GPa) = {σ(ε; 0.1) - σ(ε; 0.01)} / (0.1-0.01) / 1000000 where σ(ε; 0.1) is the stress when the strain is 0.1, and σ(ε; 0.01) is the stress when the strain is 0.01.

[0222] (Measurement of thermal conductivity in the thickness direction of sheet-like cured thermosetting composition) The sheet-like thermosetting composition (sample) prepared in each Example and Comparative Example was heated and cured at 175°C (product temperature) for 30 minutes, and then at 200°C (product temperature) for 30 minutes while applying pressure under a load of 10 MPa, thereby obtaining a sheet-like cured product (sample) with a thickness of 150 μm. Furthermore, four types of sheet-like cured products (samples) with different thicknesses were obtained by stacking two, three, or four sheets of the sheet-like thermosetting composition (sample) prepared in each Example and Comparative Example and applying pressure and heating in the same manner as above.

[0223] The following measurements were carried out on these four types of sheet-shaped cured products (samples) with different thicknesses, and the thermal conductivity at 25°C in the sheet thickness direction was measured by a steady-state method from the slope represented by the thermal resistance value versus sheet thickness (in accordance with ASTM D5470). (1) Thickness: Thickness (μm) when pressed at a pressure of 3400 kPa using a T3Ster-DynTIM manufactured by Mentor Graphics. (2) Measurement area: Area (cm) of the heat-transmitting portion when measured using a T3Ster-DynTIM manufactured by Mentor Graphics. ２ ) (3) Thermal resistance value: Thermal resistance value (K / W) when pressed at a pressure of 3,400 kPa using a T3Star-DynTIM manufactured by Mentor Graphics. (4) Thermal conductivity: Thermal resistance values ​​of four types of sheet-shaped cured products (samples) with different thicknesses were measured, and the thermal conductivity (W / m·K) was calculated using the following formula. Formula: Thermal conductivity (W / m·K) = 1 / ((slope (thermal resistance value / thickness): K / (W·μm)) × (area: cm ２ )) x 10 －２

[0224] (Measurement of BDV (breakdown voltage) of sheet-like cured thermosetting composition) The sheet-like thermosetting composition (sample) prepared in each Example and Comparative Example was placed on a 2 mm thick copper plate, and heated under pressure at 175 ° C (product temperature) for 30 minutes, then at 200 ° C (product temperature) for 30 minutes while applying a load of 10 MPa to bond the composition by heat and pressure curing. A 150 μm thick sheet-like cured product was laminated on the copper plate to prepare a composite molded body (evaluation sample). The composite molded body (evaluation sample) was immersed in insulating oil (3M "Fluorinert FC-40"), and an ultra-high voltage withstand voltage tester 7470 (manufactured by Keisoku Gijutsu Kenkyusho) was used. An electrode was placed on a patterned φ25 mm copper plate, and a voltage of 0.5 kV was applied, increasing the voltage by 500 V every minute. The voltage (BDV: breakdown voltage) until the sheet-like cured product was destroyed was measured.

[0225] (Measurement of volume resistivity of sheet-shaped cured product of thermosetting composition) The sheet-shaped thermosetting composition (sample) prepared in each Example and Comparative Example was cut into a test piece of 8.5 cm × 8.5 cm, and while applying pressure from above and below with a load of 10 MPa, the sheet-shaped cured product was obtained by heating and curing at 120 ° C (product temperature) for 30 minutes, 175 ° C (product temperature) for 30 minutes, and then at 200 ° C (product temperature) for 30 minutes, and was used as an evaluation sample with a thickness of 150 μm. For this evaluation sample, the volume resistivity was measured under the following conditions using a measuring device: Digital Superresistance / Microcurrent Meter 5451 (manufactured by ACDMT), Resistivity Chamber 12708 (manufactured by Espec Corporation).

[0226] Main electrode outer diameter: 50 mm Guard electrode inner diameter: 70 mm Measurement temperature conditions: 200°C Measurement voltage: 1000 V Power supply frequency: 50 Hz Current limiter: 10 mA Discharge time: 10 seconds Charge time: 1 minute Measurement interval: 2 seconds Number of measurements: 90 seconds

[0227] (Measurement of moisture absorption rate of sheet-like cured thermosetting composition) The sheet-like thermosetting composition (sample) prepared in each Example and Comparative Example was cut into 6 cm x 7 cm pieces, and while applying a load of 10 MPa from above and below, it was heated and cured at 120 ° C (product temperature) for 30 minutes, 175 ° C (product temperature) for 30 minutes, and then at 200 ° C (product temperature) for 30 minutes to obtain a sheet-like cured product having a thickness of 150 μm, which was used as an evaluation sample. This evaluation sample was dried at 150 ° C (product temperature) for 1 hour, and the mass a was measured. Furthermore, these sheet-like resin cured products were stored for a certain period of time in an environment of 85 ° C and 85% RH using a thermo-hygrostat SH-221 (manufactured by Espec Corporation), and the mass was measured over time and stored until a constant mass (constant weight) b was reached. The mass increase rate was calculated using the following formula, and this mass increase rate was taken as the moisture absorption rate. Moisture absorption rate (mass%) = mass increase rate (%) = ((b-a) / a) x 100

[0228] (Measurement of storage modulus (E') of sheet-like cured thermosetting composition) Three sheets of the sheet-like thermosetting composition (sample) prepared in each Example and Comparative Example were stacked, and while applying a load of 10 MPa from above and below, they were heated and cured at 120 ° C (product temperature) for 30 minutes, 175 ° C (product temperature) for 30 minutes, and then at 200 ° C (product temperature) for 30 minutes to obtain a sheet-like cured product having a thickness of 450 μm. This cured product was cut into a test piece of 4 mm width × 50 to 60 mm length to obtain an evaluation sample. For this evaluation sample, the storage modulus (E') was measured under the following conditions using a measuring device: Hitachi High-Tech Science Corporation "DMS6100", and the storage modulus (E') at 200 ° C is shown in the table. Measurement temperature conditions: -110 to 270°C, heating rate 10°C / min, measurement mode: tension mode, measurement frequency: 1Hz, chuck distance: 35mm, strain amplitude (μm): 5μm, force amplitude initial value (mN): 50mN

[0229] (Measurement of Glass Transition Temperature (Tg) of Sheet-Shaped Cured Product of Thermosetting Composition) Evaluation samples were prepared in the same manner as in the storage modulus measurement described above, and the storage modulus and loss modulus were measured using a Hitachi High-Tech Science DMS6100 under the same conditions as in the storage modulus measurement described above, and Tg (°C) was calculated from the peak value of Tan δ.

[0230] (Reflow Resistance Evaluation) Copper plates with thicknesses of 500 μm and 2,000 μm were prepared, the surfaces of which were roughened 100 times with a #120 file. Each of these copper plates was sandwiched between two copper plates, and the sheet-like thermosetting composition (sample) obtained in each Example and Comparative Example was sandwiched between two copper plates. A pressure of 10 MPa was applied, and the composition was cured by heating and pressurizing at 120 ° C (product temperature) for 30 minutes, then at 175 ° C (product temperature) for 30 minutes, and then at 200 ° C (product temperature) for 30 minutes to obtain a composite molded body for reflow testing. The layer thickness of the sheet-like cured product of the composite molded body was 150 μm. The composite molded body obtained above was etched to pattern a 500 μm copper plate. The pattern was designed so that two φ25 mm circular patterns remained. The composite molded body for the reflow test prepared as described above was stored for 3 days in an environment of 85°C and 85% RH using a thermo-hygrostat SH-221 (manufactured by Espec Corporation), and then heated from room temperature to 290°C (product temperature) in 12 minutes within 30 minutes in a nitrogen atmosphere, held at 290°C (product temperature) for 10 minutes, and then cooled to room temperature (moisture absorption reflow test). If the BDV (dielectric breakdown voltage) after the reflow test was less than 5 kV, the reflow resistance was evaluated as "×: Fail", and if it was 5 kV or higher, it was evaluated as "◯: Pass".

[0231] (Sinter resistance evaluation) Chemically roughened copper plates with thicknesses of 500 μm and 1,000 μm were prepared. Each of these copper plates was sandwiched between the sheet-shaped thermosetting compositions (samples) obtained in each Example and Comparative Example, and pressed at 120 ° C (product temperature) for 30 minutes at a pressure of 10 MPa, then at 175 ° C (product temperature) for 30 minutes at a pressure of 10 MPa, and then at 200 ° C (product temperature) for 30 minutes at a pressure of 10 MPa to heat and pressurize the cured sheet to produce a laminate having metal parts (copper plates) on the top and bottom of the cured sheet, and a 500 μm thick copper plate was etched to pattern it, thereby obtaining a composite molded product having a circuit pattern on the upper surface. At this time, the layer thickness of the cured sheet was 150 μm.

[0232] Next, an evaluation sample was prepared by simulating the silver sintering process. ２A copper plate of 0.2mm thick x 5mm x 4mm that resembles a chip is placed on the circuit pattern, and a 0.1mm thick Teflon sheet is placed on top of it as a cushioning material. ＴＭ Then, the composite molding, copper plate and Teflon ＴＭ This laminate was sandwiched between SUS plates and heated and pressurized at 250°C (product temperature) for 10 minutes while adjusting the pressure applied to the 0.2 mmt copper plate to 19 MPa to prepare an evaluation sample.

[0233] The evaluation sample obtained by the process simulating the silver sintering process as described above was subjected to heating and pressing, and the interface between the 500 μm thick copper plate and the sheet-like cured product was observed using an ultrasonic imaging device FinSAT (FS300III) (manufactured by Hitachi Power Solutions). The observation using the ultrasonic imaging device was performed using a probe with a frequency of 50 MHz, with a gain of 30 dB and a pitch of 0.1 mm, and the evaluation sample was placed in water. When peeling occurred at the interface between the copper plate and the sheet-like cured product, the sintering resistance was evaluated as "×: Fail", and when no peeling occurred, it was evaluated as "◯: Pass".

[0234] (Laser flash thermal conductivity) Three sheets of the sheet-like thermosetting composition (sample) prepared in Examples 1 and 2 were stacked, and while applying a load of 10 MPa from above and below, they were heated and cured at 120°C (product temperature) for 30 minutes, 175°C (product temperature) for 30 minutes, and then at 200°C (product temperature) for 30 minutes, to obtain a sheet-like cured product with a thickness of approximately 450 μm. This cured product was cut to a predetermined size to obtain a test piece, which was used as an evaluation sample. Thermal diffusivity, density, and specific heat were measured as described below, and thermal conductivity was calculated using these values.

[0235] =Measurement of thermal diffusivity= Diffusivity (m ２ / sec) was measured. Measuring device: Xe flash analyzer LFA447 Measuring temperature: 25°C to 175°C temperature rise measurement (results at 150°C and 175°C) Evaluation sample: sheet 1cm x 1cm, thickness approximately 400 to 500µm

[0236] =Measurement of specific heat= Specific heat (J / KgK) was measured under the following conditions. Analysis method: Differential scanning calorimetry. Apparatus: Differential Scanning Calorimetry (DSC) Hitachi High-Tech Science Corporation DSC600 (electric cooler). Sample amount: Approximately 10 mg. Temperature program: Hold at 0°C (5 minutes) - Hold at 50°C (5 minutes) - Hold at 150°C (5 minutes) - Hold at 200°C (5 minutes). Heating rate: 10°C / min. Atmosphere: N ２ 30 ml / min Sample container: Aluminum sample container Measurement set: Empty container, standard sample + container, sample + container Standard sample: Synthetic sapphire (9.925 mg) [0.775 J / g*°C (25°C)] Measurement: The specific heat of the cured product was measured at 150°C and 175°C.

[0237] =Measurement of Linear Expansion Coefficient= The linear expansion coefficient was measured by thermomechanical analysis (TMA) under the following conditions: Measurement device: Thermomechanical analyzer TMA7100 (manufactured by Hitachi High-Tech Science Corporation) Measurement mode: Tensile mode Sample: Sheet-like 30 mm x 3 mm x 400 to 500 μm Chuck gap: 20 mm Atmosphere: 200 mL / min nitrogen flow, Heating rate: 5°C / min Measurement temperature: 1st step: -50 to 230°C, 2nd step: 230 to -50°C, 3rd step: -50 to 230°C The linear expansion coefficient was measured at 21°C to 150°C and 21°C to 175°C in the 3rd step.

[0238] = Measurement of Density = The density was measured under the following conditions: Device name: Archimedes densitometer manufactured by METTLER TOLEDO Water temperature: 21°C The volume expansion coefficient was set to three times the linear expansion coefficient measured by TMA, and the densities at 150°C and 175°C were determined.

[0239] = Calculation and Evaluation of Thermal Conductivity = Using the thermal diffusivity, density, and specific heat measured as described above, the thermal conductivity at 150°C and 175°C was calculated according to the following formula: Thermal conductivity (W / mK) = Thermal diffusivity (m ２ / sec) x density (kg / m ３ ) x specific heat (J / kgK)

[0240] The ratio of the thermal conductivity λ(175°C) at 175°C to the thermal conductivity λ(150°C) at 150°C: λ(175°C) / λ(150°C) was evaluated as "× (very unsatisfactory)" when it was less than 0.92, "△ (unsatisfactory)" when it was 0.92 or more and less than 0.95, "◯ (satisfactory)" when it was 0.85 or more and less than 0.97, and "◎ (very satisfied)" when it was 0.97 or more.

[0241] (Bending Resistance of Sheet-Shaped Thermosetting Composition (Mandrel Test)) For Examples 1 to 4, each raw material was weighed to obtain the composition (parts by mass) shown in Table 1, and mixed using a planetary centrifugal stirrer to prepare a mixture. When preparing this mixture, a slurry thermosetting composition was prepared using 20% ​​by mass each of methyl ethyl ketone and cyclohexanone so that the mixture accounted for 60% by mass (solids concentration) of the coating slurry. The obtained slurry thermosetting composition was applied to a PET substrate by a doctor blade method and heated and dried at 60°C (heated atmosphere temperature) for 120 minutes to obtain a sheet-shaped thermosetting composition. The total content of methyl ethyl ketone and cyclohexanone in the sheet-shaped thermosetting composition was 1% by mass or less.

[0242] The sheet-like thermosetting composition was then placed in a vacuum packing bag, the air inside the bag was removed, and the opening of the bag was heat-sealed. The bag was then stored in a freezer at −20° C. for 72 hours to perform low-temperature aging, thereby obtaining a sheet-like thermosetting composition (sample).

[0243] The prepared sheet-like thermosetting composition (sample) was cut into a piece 2 cm wide and 15 cm or longer, and bending resistance was evaluated according to the test method of JIS K5600-5-1. ◯ (Pass): The diameter of the jig where the sheet broke was less than 10 mm. × (Fail): The diameter of the jig where the sheet broke was 10 mm or greater. When this sheet-like thermosetting composition was placed in a pressure press and pressed at 40°C under a load of 150 MPa for 10 minutes, the film thickness was 140 to 160 μm.

[0244]

[0245] From the above examples and the results of tests conducted by the inventors up to now, it has been found that if the breaking energy value obtained by three-point bending measurement at 190°C of a cured product of a thermosetting composition containing an inorganic filler and a thermosetting compound is 55 kPa or more, as obtained by three-point bending measurement at 150°C, and the breaking energy value obtained by three-point bending measurement is 80 kPa or more, the dielectric strength voltage can be maintained even after the reflow process, and further, even when bonded to a substrate under conditions in which an external force is applied at high temperatures, such as sinter bonding, the cured product will have such high temperature resistance that cracks will not occur in the cured product or the bond will not peel off. Furthermore, it was found that, for a cured product of a thermosetting composition containing an inorganic filler and a thermosetting compound, if the ratio (x / y) of the breaking energy x at 190°C to the breaking energy y at 150°C obtained by three-point bending measurement is 0.7 or more and 1.15 or less, and the value of x is 55 kPa or more, the dielectric strength voltage can be maintained even after being exposed to a state in which internal stress is applied at high temperatures, such as in a reflow process, and further, high temperature resistance can be obtained such that the cured product does not crack or the bond does not peel off even when bonded to a substrate under conditions in which external force is applied at high temperatures, such as in sinter bonding.

[0246] Thermosetting compositions tend to accumulate strain during curing, and stress due to strain tends to accumulate at temperatures around the curing temperature. For example, in the case of a thermosetting composition containing an epoxy compound, stress due to strain tends to accumulate at 120 to 200°C. Therefore, by measuring the fracture energy at 150°C and 190°C in a three-point bending test and ensuring that these values ​​are consistent, it is believed that resistance to reflow, which applies internal stress at temperatures above 200°C, and sintering conditions, which also apply external forces, can be obtained, thereby improving insulation resistance and preventing cracks from occurring in the sheet and peeling at the interface with the substrate. Furthermore, by maintaining a fracture energy at 190°C above a certain value and a small difference in fracture energy between 150°C and 190°C, stress is dispersed even when internal stress or external force is applied under conditions above 200°C, or when the temperature is subsequently lowered. This is believed to improve insulation resistance and prevent cracks from occurring in the sheet and peeling at the interface with the substrate during the reflow process and sintering.

[0247] In contrast, in the comparative examples, Comparative Example 1 and Comparative Example 2, the amount of polymer with a mass average molecular weight (Mw) of 5,000 or more per 100% by mass of solid content excluding inorganic filler was large, resulting in small breaking energy at 190°C and a small value of x / y. Comparative Example 3, the amount of polymer with a mass average molecular weight (Mw) of 5,000 or more per 100% by mass of solid content excluding inorganic filler was large, and the compound did not contain a polyfunctional epoxy compound having three or more epoxy groups in one molecule, resulting in small breaking energy at 150°C and a small value of x / y. Comparative Example 4 contains a polyfunctional epoxy compound having three or more epoxy groups in one molecule but does not contain a polymer with a mass average molecular weight (Mw) of 5,000 or more, and therefore has a high storage modulus at 200°C but insufficient toughness, resulting in a small breaking energy at 150°C and a large value of x / y. Comparative Example 5 does not undergo low-temperature aging, which prevents freezing and dispersion of water, resulting in the formation of voids, which are thought to be the reasons for the small breaking energy and x / y values ​​at 150°C and 190°C. As a result, it is thought that the value of the breaking energy obtained by three-point bending measurement at 190°C and / or the value of the breaking energy obtained by three-point bending measurement at 150°C no longer satisfied the specified range, or the ratio (x / y) of the breaking energy x obtained by three-point bending measurement at 190°C to the breaking energy y obtained by three-point bending measurement at 150°C and / or the value of x no longer satisfied the specified range, and the dielectric strength voltage could not be maintained when exposed to a state in which internal stress is applied at high temperatures, such as in a reflow process, or that when bonded to a substrate under conditions in which further external force is applied at high temperatures, such as in sinter bonding, cracks may occur in the cured product or the bond may peel off.

[0248] On the other hand, the factors that enable the effects of the Examples to be obtained include blending a curing agent that acts on the epoxy compound, and further adjusting the blending amount of polymer, for example, epoxy polymer, to adjust the WPE of the resin component within a predetermined range, adjusting the blending amount of polyfunctional epoxy compound to adjust the number of functional groups and molecular weight of the resin component, selecting a skeletal structure, adjusting low-temperature aging conditions, etc., which can be considered to increase the crosslink density and cohesive strength when cured, increase elasticity and fracture energy at high temperatures, and provide insulation resistance when exposed to high temperatures and sinter resistance under high-temperature conditions.

[0249] In view of the above, in order to obtain the thermosetting composition of the present invention, it is considered even more preferable to prepare the composition of the present invention by increasing the content of the polyfunctional epoxy compound as the thermosetting compound, reducing the content of the polymer, for example, the epoxy polymer, and further using a phenolic resin-based curing agent as the curing agent to increase the crosslink density of the cured product, and by performing low-temperature aging.

[0250] Among the Examples satisfying the high-temperature resistance as described above, the evaluation results of the mandrel test showed that the handleability of the sheet-shaped thermosetting composition of Example 1 was even more favorable, while the evaluation results of the laser flash thermal conductivity showed that the decrease in thermal conductivity at high temperatures was even less in Example 2. This is presumably because Example 1 contains a smaller amount of epoxy polymer than Example 2, allowing the flexibility of the sheet-shaped thermosetting composition in an uncured state to be maintained, while Example 2 contains a benzoxazine compound in addition to the phenolic resin, thereby suppressing the decrease in thermal conductivity at high temperatures compared to Example 1, resulting in less change in physical properties at high temperatures.

Claims

1. A thermosetting composition containing an inorganic filler and a thermosetting compound, characterized in that the cured product of the thermosetting composition (also referred to as the "cured product of the thermosetting composition") has a breaking energy of 55 kPa or more when measured by three-point bending at 190°C, and a breaking energy of 80 kPa or more when measured by three-point bending at 150°C.

2. A thermosetting composition containing an inorganic filler and a thermosetting compound, wherein the breaking energy of a cured product (also referred to as "cured product of the thermosetting composition") obtained by curing the thermosetting composition, as determined by a three-point bending test at 190°C, is x, and the breaking energy of a cured product (also referred to as "cured product of the thermosetting composition") obtained by a three-point bending test at 150°C is y, the value of x / y is 0.7 or more and 1.15 or less, and the value of x is 55 kPa or more.

3. The thermosetting composition according to claim 1 or 2, wherein the Young's modulus of the cured product of the thermosetting composition obtained by three-point bending measurement at 190°C is 5.5 GPa or more.

4. The thermosetting composition according to claim 1 or 2, wherein the thermal conductivity in the thickness direction at 25°C of a sheet-like cured product obtained by curing the thermosetting composition (also referred to as a "sheet-like cured product of the thermosetting composition") is 14 W / m·K or more.

5. The thermosetting composition according to claim 1 or 2, wherein the breakdown voltage of the sheet-shaped cured product of the thermosetting composition is 6.5 kV or more when the thickness of the sheet-shaped cured product is 150 μm.

6. The thermosetting composition according to claim 1 or 2, wherein the volume resistivity (1000 V, 200°C) of the sheet-shaped cured product of the thermosetting composition is 3.0E+10 Ωcm or more.

7. The thermosetting composition according to claim 1 or 2, wherein the moisture absorption rate of the sheet-shaped cured product of the thermosetting composition is 0.7% by mass or more and 1.2% by mass or less.

8. The thermosetting composition according to claim 1 or 2, wherein the storage modulus of the sheet-shaped cured product of the thermosetting composition at 200°C is 6.0 GPa or more and 100 GPa or less.

9. The thermosetting composition according to claim 1 or 2, wherein the sheet-shaped cured product of the thermosetting composition has a glass transition temperature (Tg) of 170°C or higher.

10. The thermosetting composition according to claim 1 or 2, which contains an epoxy compound and at least one of a phenolic resin, a benzoxazine compound, a polyarylate, a cyanate, and a maleimide.

11. The thermosetting composition according to claim 1 or 2, which contains an epoxy compound and a phenolic resin.

12. The thermosetting composition according to claim 1 or 2, which contains a polyfunctional epoxy compound having three or more epoxy groups in one molecule and a mass average molecular weight (Mw) of less than 5,000.

13. The thermosetting composition according to claim 1 or 2, which contains a high molecular weight epoxy compound having a mass average molecular weight (Mw) of 5,000 or more.

14. A thermosetting composition according to claim 1 or 2, containing a polymer having a mass average molecular weight (Mw) of 5,000 or more in a proportion of 5% by mass or more but less than 30% by mass, based on 100% by mass of solids excluding the inorganic filler.

15. A thermosetting composition according to claim 1 or 2, containing a polymer having a mass average molecular weight (Mw) of 5,000 or more in a proportion of 5% by mass to 23% by mass, based on 100% by mass of solids excluding the inorganic filler.

16. The thermosetting composition according to claim 1 or 2, which contains an epoxy compound and has a weight per epoxy equivalent (WPE) of the solid content of the thermosetting composition excluding the inorganic filler, of 200 g / equivalent or more and less than 250 g / equivalent.

17. The thermosetting composition according to claim 1 or 2, containing agglomerated particles of boron nitride as the inorganic filler.

18. A thermosetting composition according to claim 1 or 2, containing the inorganic filler in an amount of 30% by mass or more but less than 90% by mass relative to 100% by mass of the solid content of the total composition.

19. A thermally conductive sheet comprising a sheet-like cured product of the thermosetting composition according to claim 1 or 2.

20. A heat dissipation laminate comprising the thermally conductive sheet according to claim 19.

21. A heat dissipating circuit board comprising the thermally conductive sheet according to claim 19.

22. A power semiconductor device equipped with the thermally conductive sheet according to claim 19.

23. A method for producing a thermosetting sheet, comprising forming the thermosetting composition according to claim 1 or 2 into a sheet and subjecting it to low-temperature aging in an ambient temperature of 0°C or below.

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