Sheet-like cured products, composite molded articles, and power semiconductor devices

Abstract

The present invention relates to a sheet-like cured product of a thermosetting composition containing a thermally conductive inorganic filler and a thermosetting resin, which can prevent the sheet from becoming prone to dielectric breakdown or delamination from metal even after being subjected to high-temperature environments during the reflow process, and further provides a sheet-like cured product that is reliable enough to withstand use in high-temperature and high-humidity environments. [Solution] A sheet-like cured product of a thermosetting composition containing a thermally conductive inorganic filler and a thermosetting resin, wherein the corona discharge initiation voltage is 0.78kV or higher.

Description

[Technical Field]

[0001] The present invention relates to a sheet-like cured product obtained by curing a thermosetting composition, which can be suitably used as a heat dissipation insulating sheet in, for example, a power semiconductor device, a composite molded body using the sheet-like cured product, and a power semiconductor device. [Background technology]

[0002] In recent years, heat generation due to the increasing density of integrated circuits has become a major problem in the electrical and electronic fields, making heat dissipation an urgent issue. For example, when power semiconductors used in the control of central processing units in personal computers and motors in electric vehicles are used for stable operation, heat dissipation components such as heat sinks and heat sink fins are indispensable for heat dissipation. Therefore, there is a need for components that possess both thermal conductivity and insulation properties to join components such as circuits containing power semiconductors to heat dissipation components such as heat sinks.

[0003] Conventionally, highly thermally conductive ceramic substrates such as alumina substrates and aluminum nitride substrates have been used as materials that combine thermal conductivity and insulation properties. However, ceramic substrates have had drawbacks, such as being easily broken by impact, and being difficult to thin and miniaturize. Therefore, a heat-dissipating insulating sheet using a thermosetting resin such as epoxy resin and a thermally conductive inorganic filler has been proposed.

[0004] Regarding heat-dissipating insulating sheets using thermosetting resins and thermally conductive inorganic fillers, various resin sheets containing boron nitride as the thermally conductive inorganic filler have been proposed (see Patent Documents 1-6). Boron nitride is an insulating ceramic that possesses excellent thermal conductivity, solid lubricity, chemical stability, and heat resistance, and has therefore attracted particular attention in the field of electrical and electronic materials in recent years. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2015-6980 [Patent Document 2] Japanese Patent Publication No. 2015-189823 [Patent Document 3] Japanese Patent Publication No. 2015-195287 [Patent Document 4] Japanese Patent Publication No. 2016-011358 [Patent Document 5] Japanese Patent Publication No. 2016-135731 [Patent Document 6] Japanese Patent Publication No. 2019-119883 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] When using a heat-dissipating insulating sheet, which is made of a sheet-like cured thermosetting composition containing a thermosetting resin and a thermally conductive inorganic filler, as a component of a power semiconductor device, it is common practice to mount other components to a laminate formed by bonding a metal plate and a circuit board via the heat-dissipating insulating sheet using a reflow process. In this reflow process, the solder is melted by raising the temperature of the components, and the metal components are joined together. In this reflow process, the components used in the power semiconductor device may deteriorate, or the heat-dissipating insulating sheet may become prone to dielectric breakdown due to the difference in thermal expansion coefficients between the heat-dissipating insulating sheet and the metal, or the heat-dissipating insulating sheet may easily delaminate from the metal plate or circuit board. Furthermore, automotive power semiconductor devices and similar equipment require durability in high-temperature and high-humidity environments.

[0007] Therefore, the object of the present invention is to provide a sheet-like cured product of a thermosetting composition containing a thermally conductive inorganic filler and a thermosetting resin that can be used as a heat dissipation insulating sheet, which can prevent dielectric breakdown and delamination from metal even after going through the high-temperature environment of the reflow process, and which has the reliability to withstand use in high-temperature and high-humidity environments, as well as to provide a composite molded body and a power semiconductor device using the same.

Means for Solving the Problems

[0008] In order to solve the above problems, the present invention proposes a sheet-like cured product, a composite molded body, and a power semiconductor device according to the following aspects.

[0009] [1] The first aspect of the present invention is a sheet-like cured product of a thermosetting composition containing a thermally conductive inorganic filler and a thermosetting resin, which is a sheet-like cured product having a corona discharge initiation voltage measured by the following measurement test of 0.78 kV or more. Measurement Test: Adjust the thickness of the measurement sample to 140 to 160 μm, apply a voltage using a corona discharge tester tuned at a test frequency of 40 kHz, measure the applied voltage at a corona discharge occurrence rate of 5%, and regard this voltage as the corona discharge initiation voltage.

[0010] [2] The second aspect of the present invention is, in the first aspect, a sheet-like cured product in which 5% by mass or more of the thermosetting resin is occupied by an epoxy resin. [3] The third aspect of the present invention is, in the first or second aspect, a sheet-like cured product containing a polyfunctional epoxy resin having 3 or more epoxy groups in one molecule and a mass average molecular weight (Mw) of less than 5,000 as the thermosetting resin. [4] The fourth aspect of the present invention is, in the third aspect, a sheet-like cured product in which the polyfunctional epoxy resin has 4 or more epoxy groups in one molecule. [5] The fifth aspect of the present invention is, in any one of the first to fourth aspects, a sheet-like cured product containing a high molecular weight epoxy resin having a mass average molecular weight (Mw) of 5,000 or more as the thermosetting resin.

[0011] [6] The sixth aspect of the present invention is, in any one of the first to fifth aspects, a sheet-like cured product in which the thermosetting composition contains a phenolic resin as a curing agent. [7] A seventh aspect of the present invention is a sheet-like cured product in which, in any one of the first to sixth aspects, the thermosetting resin includes an epoxy resin, and the epoxy equivalent (WPE) of the solid content of the thermosetting composition, excluding the inorganic filler containing the thermally conductive inorganic filler, is 220 g / equivalent or more and 270 g / equivalent or less. [8] An eighth aspect of the present invention is a sheet-like cured product in any one of the first to seventh aspects, wherein the content of the thermally conductive inorganic filler is 60% by mass or more and 85% by mass or less based on 100% by mass of solids in the thermosetting composition. [9] The ninth aspect of the present invention is a sheet-like cured product in any one of the first to eighth aspects, wherein the thermosetting composition contains a silane coupling agent.

[0012]

[10] A tenth aspect of the present invention is a sheet-like cured product in which, in any one of the first to ninth aspects, the thermally conductive inorganic filler comprises one or more of the following: magnesium oxide, aluminum oxide, zinc oxide, yttrium oxide, zirconium oxide, ytterbium oxide, beryllium oxide, boron nitride, aluminum nitride, and silicon nitride.

[11] An eleventh aspect of the present invention is a sheet-like cured product in any one of the first to tenth aspects, wherein the thermally conductive inorganic filler contains boron nitride aggregate particles.

[12] A twelfth aspect of the present invention is a sheet-like cured product in which, in the eleventh aspect, the boron nitride aggregated particles have a cardhouse structure.

[0013]

[13] The thirteenth aspect of the present invention is a sheet-like cured product used as a heat-dissipating insulating sheet for power semiconductor devices in any one of the first to twelfth aspects.

[14] A fourteenth aspect of the present invention is a composite molded body having a cured portion made of a sheet-like cured material according to any one of the first to twelfth aspects, and a metal portion.

[15] A fifteenth aspect of the present invention is a power semiconductor device comprising a sheet-like cured material according to any one of the first to twelfth aspects. [Effects of the Invention]

[0014] The sheet-like cured material proposed in this invention can be made resistant to dielectric breakdown and delamination from metal even after passing through the high-temperature environment of the reflow process, by adjusting the corona discharge initiation voltage to 0.78kV or higher. Furthermore, it can be made reliable enough to withstand use in high-temperature and high-humidity environments. [Brief explanation of the drawing]

[0015] [Figure 1] This is a schematic diagram of the corona discharge tester used in the example. [Modes for carrying out the invention]

[0016] 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 can be implemented in various ways within the scope of its gist.

[0017] <<The sheet-like cured product of the present invention>> A sheet-like cured product according to one embodiment of the present invention (referred to as "the sheet-like cured product of the present invention") is a sheet-like cured product of a thermosetting composition (referred to as "the thermosetting composition") containing a thermally conductive inorganic filler and a thermosetting resin.

[0018] In the present invention, "thermosetting composition" means a composition containing a resin that has the property of hardening with heat. That is, it is sufficient to have a composition that has the property of hardening with heat, and it may be a composition that has already hardened to a state where there is still room for hardening (also called "partially hardened"), or it may be a composition that has not yet hardened at all (also called "unhardened"). The sheet-like cured product of the present invention can be obtained by forming this thermosetting composition into a sheet and heating it. Furthermore, this thermosetting composition may be in the form of a powder, slurry, liquid, solid, or molded article such as a sheet. Furthermore, in this invention, "resin" includes compounds, monomers, oligomers, and polymers, regardless of their molecular weight.

[0019] (Corona discharge initiation voltage) The sheet-like cured material of the present invention preferably has a corona discharge initiation voltage of 0.78kV or higher, as measured by the following measurement test. By adjusting the composition of this thermosetting composition and the manufacturing method of the sheet-like cured product of the present invention so that the corona discharge initiation voltage of the sheet-like cured product of the present invention is 0.78kV or higher, it is possible to develop a sheet-like cured product of the present invention that not only exhibits heat resistance in reflow tests but also has a long lifespan in reliability tests, i.e., THB tests. The corona discharge initiation voltage is governed by defects and local dielectric constant distributions within the sheet-like cured material. Since these defects and local dielectric constant distributions cannot be observed through macroscopic analysis, we believe that measuring the corona discharge initiation voltage allows for highly sensitive detection. Here, the aforementioned defects include surface irregularities of the sheet, localized dielectric constant distribution, voids, unevenness of the thermally conductive inorganic filler due to damage to the thermally conductive inorganic filler during sheet molding, unreacted functional groups within the molecules of the thermosetting composition, and unevenness of the crosslinking points of the thermosetting composition. In particular, the unevenness of the unreacted functional groups within the molecules of the thermosetting composition and the unevenness of the crosslinking points are influenced by the composition of the thermosetting composition, the aging conditions and curing conditions when manufacturing the sheet-like cured product of the present invention. The composition is particularly influenced by the ratio of epoxy polymer to polyfunctional epoxy resin, the type and content of curing agent, the type and content of thermosetting catalyst, and additives, as described later. Furthermore, macroscopic analyses include the elastic modulus, volume resistivity, glass transition temperature (Tg), and bulk dielectric constant of the sheet-like cured material of the present invention.

[0020] The inventors have found that if the corona discharge initiation voltage is 0.78kV or higher, it is possible to prevent dielectric breakdown and delamination from the metal even after going through the high-temperature environment of the reflow process. Furthermore, as shown in the THB test results described later, they have also found that it is possible to obtain reliability that can withstand use in high-temperature and high-humidity environments. From this viewpoint, the corona discharge initiation voltage of the sheet-like cured product of the present invention is preferably 0.78kV or higher, more preferably 0.80kV or higher, more preferably 0.82kV or higher, and more preferably 0.83kV or higher. The upper limit is not particularly limited, but may be 2.0kV or lower, 1.5kV or lower, or 1.2kV or lower.

[0021] The above method for measuring the corona discharge initiation voltage involves adjusting the thickness of the measurement sample to 140-160 μm, applying a voltage using a corona discharge tester tuned to a test frequency of 40 kHz, measuring the applied voltage when the corona discharge occurrence rate is 5%, and obtaining this voltage as the corona discharge initiation voltage. In this case, "adjust the thickness of the measurement sample to 140-160 μm" means that if the thickness of the measurement sample is not 140-160 μm, adjust it to 140-160 μm.

[0022] In order to adjust the corona discharge initiation voltage of the sheet-like cured product of the present invention to the above range, it is preferable to adjust the composition of the thermosetting composition and then manufacture it by a method including low-temperature aging. However, the invention is not limited to this method.

[0023] <This thermosetting composition> This thermosetting composition contains a thermally conductive inorganic filler and a thermosetting resin, and optionally includes a curing agent, a curing accelerator, a silane coupling agent, an organic solvent, and other components.

[0024] <Thermosetting resin> Examples of thermosetting resins included in this thermosetting composition include epoxy resins, phenolic resins, polycarbonate resins, unsaturated polyester resins, urethane resins, melamine resins, urea resins, and benzoxazine compounds. One of these may be used alone, or two or more may be used in combination.

[0025] The thermosetting resin content is preferably 5% by mass or more and 40% by mass or less, based on 100% by mass of the components in the thermosetting composition excluding volatile components, i.e., solvents (referred to as "solid content"). A thermosetting resin content of 5% by mass or more is preferable because it results in good moldability, while a content of 40% by mass or less is preferable because it allows for the content of other components to be maintained and improves thermal conductivity. From this viewpoint, the content of the thermosetting resin is preferably 5% by mass or more, more preferably 10% by mass or more, more preferably 20% by mass or more, and more preferably 25% by mass or more, with the content being 40% by mass or less, which is even more preferable.

[0026] (Epoxy resin) This thermosetting composition preferably contains an epoxy resin as the thermosetting resin.

[0027] Preferably, epoxy resin accounts for 50% or more by mass of the thermosetting resin contained in this thermosetting composition, and more preferably, epoxy resin accounts for 60% or more by mass, of which 70% or more by mass, of which 80% or more by mass, and of which 90% or more by mass. Furthermore, the epoxy resin used in this context also includes epoxy polymers and polyfunctional epoxy resins, which will be discussed later.

[0028] The epoxy resin used as the thermosetting resin in this thermosetting composition may be any compound having one or more oxirane rings, i.e., epoxy groups, in one molecule.

[0029] The epoxy groups contained in the epoxy resin can be either alicyclic epoxy groups or glycidyl groups. From the viewpoint of reaction rate or heat resistance, glycidyl groups are more preferable.

[0030] Examples of epoxy resins include epoxy group-containing silicon compounds, aliphatic epoxy resins, bisphenol A or F type epoxy resins, novolac type epoxy resins, aromatic epoxy resins, alicyclic epoxy resins, glycidyl ester type epoxy resins, polyfunctional epoxy resins, and polymer epoxy resins.

[0031] The epoxy resin may be an aromatic epoxy group-containing compound. Specific examples include bisphenol-type epoxy resins obtained by glycidly modifying bisphenols such as bisphenol A, bisphenol F, bisphenol AD, bisphenol S, tetramethylbisphenol A, tetramethylbisphenol F, tetramethylbisphenol AD, tetramethylbisphenol S, and tetrafluorobisphenol A; biphenyl-type epoxy resins; epoxy resins obtained by glycidly modifying divalent phenols such as dihydroxynaphthalene and 9,9-bis(4-hydroxyphenyl)fluorene; epoxy resins obtained by glycidly modifying trisphenols such as 1,1,1-tris(4-hydroxyphenyl)methane; epoxy resins obtained by glycidly modifying tetrakisphenols such as 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane; novolac-type epoxy resins obtained by glycidly modifying novolacs such as phenol novolac, cresol novolac, bisphenol A novolac, and brominated bisphenol A novolac; epoxy resins having a dicyclopentadiene skeleton; and epoxy resins having a naphthalene skeleton. In particular, it is preferable to include an epoxy resin having at least one structure selected from epoxy resins having a biphenyl skeleton, epoxy resins having a dicyclopentadiene skeleton, and epoxy resins having a naphthalene skeleton.

[0032] (Epoxy polymer) From the viewpoint of ensuring the film-forming properties of the sheet, this thermosetting composition preferably contains a high molecular weight epoxy resin (referred to as "epoxy polymer") with a mass-average molecular weight (Mw) of 5,000 or more.

[0033] Examples of epoxy polymers 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, anthracene skeleton, a pyrene skeleton, a xanthene skeleton, an adamantane skeleton, and a dicyclopentadiene skeleton.

[0034] In particular, the epoxy polymer is preferably one having at least one structure selected from, for example, 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)").

[0035] TIFF2026061821000001.tif69170

[0036] In formula (1), R 1 and R 2 Each represents an organic group, and at least one of them is an organic group with a molecular weight of 16 or more, in formula (2), R 3 The symbol represents a divalent cyclic organic group. Furthermore, the term "organic group" includes any group containing a carbon atom, specifically, alkyl groups, alkenyl groups, aryl groups, etc., and these may be substituted with halogen atoms, heteroatoms, or other hydrocarbon groups. The same applies below.

[0037] In the above equation (1), R 1 and R 2At least one of these represents an organic group with a molecular weight of 16 or more, preferably 16 to 1000, and examples 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 Both may be organic groups with a molecular weight of 16 or more, or one may be an organic group with a molecular weight of 16 or more and the other may be an organic group or hydrogen atom with a molecular weight of 15 or less. 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, it is preferable that one is a methyl group and the other is a phenyl group, as this facilitates control of handling properties such as resin viscosity and is preferable from the viewpoint of the strength of the sheet-like cured product of the present invention.

[0038] In equation (2) above, R 3 The group 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. Furthermore, these may independently have substituents such as hydrocarbon groups or halogen atoms. The divalent bond may be a divalent group located on a single carbon atom or on different carbon atoms. Preferably, 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, the 3,3,5-trimethyl-1,1-cyclohexylene group represented by the following formula (4) (also referred to as "structure (4)") is preferred from the viewpoint of controlling handling properties such as resin viscosity and the strength of the sheet-like cured product of the present invention.

[0039] TIFF2026061821000002.tif44170

[0040] In addition, due to the rigidity of the fluorene skeleton represented by the following formula (5), excellent heat resistance and low linear expansion are exhibited. Also, since the molecular weight per unit unit is larger than that of ordinary epoxy resins, the proportion of secondary hydroxyl groups, which cause hygroscopicity, in the entire molecular structure is relatively low, and low hygroscopicity is exhibited. From this viewpoint, it is preferable that the epoxy polymer has a fluorene skeleton represented by the following formula (5).

[0041] TIFF2026061821000003.tif56151

[0042] Moreover, examples of the epoxy polymer include an epoxy polymer having a structure represented by the following formula (3) (also referred to as "structure (3)").

[0043] TIFF2026061821000004.tif40170

[0044] In the above formula (3), R 4 , R 5 , R 6 , R 7 are each organic groups having a molecular weight of 15 or more. Preferably, they are alkyl groups having a molecular weight of 15 to 1000. In particular, it is preferable that all of R 4 , R 5 , R 6 , R 7 are methyl groups from the viewpoints of controlling handling properties such as resin viscosity and the strength of the sheet-like cured product of the present invention.

[0045] The epoxy polymer is preferably an epoxy polymer containing either one of structure (1) and structure (2) and structure (3) from the viewpoint of achieving both reduction in hygroscopicity and retention of strength of the sheet-like cured product of the present invention. Such an epoxy polymer contains a large amount of hydrophobic hydrocarbon and aromatic structures as compared with epoxy polymers having a general bisphenol A or bisphenol F skeleton. Therefore, by blending the epoxy polymer, the amount of moisture absorption of the sheet-like cured product of the present invention can be reduced.

[0046] Furthermore, from the viewpoint of reducing moisture absorption, epoxy polymers that contain a large amount of hydrophobic structures (1), (2), and (3) are preferred.

[0047] The mass-average molecular weight (Mw) of the epoxy polymer is preferably 5,000 or more, more preferably 10,000 or more, more preferably 15,000 or more, more preferably 20,000 or more, more preferably 25,000 or more, and more preferably 30,000 or more. The upper limit is 100,000 or less. Within this range, the film-forming properties and handling properties of the thermosetting composition tend to improve. Furthermore, the improved film-forming properties have the effect of binding the fillers together before the thermosetting composition is cured, thus reducing the likelihood of void formation.

[0048] Furthermore, the epoxy equivalent of the epoxy polymer is preferably 5,000 g / equivalent or more, more preferably 7,000 g / equivalent or more, and more preferably 8,000 g / equivalent or more, from the viewpoint of ensuring film-forming properties of the sheet and imparting flexibility. On the other hand, from the viewpoint of solubility in solvents, it is preferably 25,000 g / equivalent or less, and more preferably 20,000 g / equivalent or less.

[0049] Note that the mass-average molecular weight (Mw) of epoxy polymers is a polystyrene-equivalent value measured by gel permeation chromatography. Furthermore, epoxy equivalent is defined as "the mass of an epoxy polymer containing one equivalent of epoxy groups" and can be measured in accordance with JIS K7236.

[0050] The epoxy polymers described above may be used individually or in combination of two or more.

[0051] (Polyfunctional epoxy resin) This thermosetting composition preferably contains the following polyfunctional epoxy resin.

[0052] A polyfunctional epoxy resin is an epoxy resin that has three or more epoxy groups in one molecule and has a mass-average molecular weight (Mw) of less than 5,000. By including such a polyfunctional epoxy resin, it is possible to introduce highly polar epoxy groups at high density, thereby increasing the effects of physical interactions such as van der Waals forces and hydrogen bonding, and improving the adhesion between the sheet-like cured product of the present invention and conductors such as metal plates and circuit boards. Furthermore, by including the polyfunctional epoxy resin, the storage modulus of the sheet-like cured product of the present invention can be increased, thereby allowing the thermosetting composition to penetrate into the irregularities on the surface of the conductive adherend and exhibit a strong anchoring effect, thereby improving the adhesion between the sheet-like cured product of the present invention and conductors such as metal plates and circuit boards. On the other hand, the inclusion of polyfunctional epoxy resin tends to increase the hygroscopicity of this thermosetting composition. However, by improving the reactivity of the epoxy groups, the amount of hydroxyl groups during the reaction can be reduced, thereby suppressing the increase in hygroscopicity. Furthermore, by combining the aforementioned epoxy polymer and polyfunctional epoxy resin to produce this thermosetting composition, it becomes possible to achieve both high elasticity and low moisture absorption in the sheet-like cured product of the present invention.

[0053] As the polyfunctional epoxy resin, any epoxy resin having three or more epoxy groups in one molecule is acceptable, from the viewpoint of increasing the storage modulus of the sheet-like cured product of the present invention, particularly the storage modulus at high temperatures which is important when generating a large amount of heat, such as in power semiconductor devices. In particular, it is even more preferable to include an epoxy resin having four or more epoxy groups in one molecule. Having multiple epoxy groups, especially glycidyl groups, in one molecule improves the crosslinking density of the sheet-like cured product of the present invention, resulting in a higher strength. As a result, when internal stress occurs in the sheet-like cured product of the present invention during a reflow test, the sheet-like cured product of the present invention maintains its shape without deforming or breaking, thereby suppressing the generation of voids and other air pockets within the sheet-like cured product of the present invention, and making it less susceptible to corona discharge.

[0054] Furthermore, from the viewpoint of adjusting the flexibility of the sheet, the mass-average molecular weight (Mw) of the polyfunctional epoxy resin, particularly the polyfunctional epoxy resin having three or more epoxy groups in one molecule, is preferably 800 or less, more preferably 700 or less, more preferably 650 or less, more preferably 100 or more or 630 or less, and more preferably 200 or more or 600 or less. Furthermore, to improve the handling properties of the sheet, it is preferable to include a substance that is liquid at 25°C. Furthermore, from the viewpoint of achieving lower moisture absorption and higher crosslinking, it is preferable that the structure does not contain amine-based or amide-based structures that include nitrogen atoms.

[0055] The epoxy equivalent of a polyfunctional epoxy resin having three or more epoxy groups in one molecule is preferably 25 g / equivalent or more, more preferably 50 g / equivalent or more, and more preferably 75 g / equivalent or more, from the viewpoint of heat resistance of the sheet. On the other hand, from the viewpoint of 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 more preferably 150 g / equivalent or less.

[0056] Specific examples of polyfunctional epoxy resins having three or more epoxy groups in one molecule include, for example, polyfunctional epoxy resins having three or more epoxy groups in one molecule and a mass-average molecular weight (Mw) of 800 or less, with a preference for 650 or less. For example, EX321L, DLC301, DLC402, etc., manufactured by Nagase ChemteX, can be used. These polyfunctional epoxy resins may be used individually or in combination of two or more.

[0057] (Content) The epoxy polymer content is preferably 5% by mass or more and 19% by mass or less relative to 100% by mass of the solid content of the thermosetting composition excluding the solvent and the inorganic filler containing the thermally conductive inorganic filler (resin component), or in other words, the solid content of the thermosetting composition excluding the inorganic filler containing the thermally conductive inorganic filler. A epoxy polymer content of 5% by mass or more is preferable because it allows the sheet to maintain its film-forming properties. On the other hand, a epoxy polymer content of 19% by mass or less is preferable because it allows the thermosetting composition to maintain its flexibility. From this viewpoint, the epoxy polymer content is preferably 5% by mass or more, more preferably 6% by mass or more, more preferably 7% by mass or more, more preferably 8% by mass or more, and more preferably 10% by mass or more, based on 100% by mass of the solid content of the thermosetting composition excluding the inorganic filler containing the thermally conductive inorganic filler. On the other hand, it is preferably 19% by mass or less, more preferably 18.5% by mass or less, and more preferably 18% by mass or less.

[0058] The content of polyfunctional epoxy resin, that is, polyfunctional epoxy resin having three or more epoxy groups in one molecule, is preferably 5% by mass or more and 50% by mass or less, based on 100% by mass of the solid content in the thermosetting composition, excluding inorganic fillers including thermally conductive inorganic fillers. A content of polyfunctional epoxy resin having three or more epoxy groups in one molecule is preferred if it is 5% by mass or more, as this allows the elastic modulus of the sheet-like cured product of the present invention to be maintained. From this viewpoint, the content of polyfunctional epoxy resin having three or more epoxy groups in one molecule is preferably 5% by mass or more, and more preferably 6% by mass or more, and more preferably 7% by mass or more, based on 100% by mass of solids in the thermosetting composition, excluding inorganic fillers including thermally conductive inorganic fillers. On the other hand, if the content of polyfunctional epoxy resin having three or more epoxy groups in one molecule is 50% by mass or less, it is preferable because it can maintain the toughness of the thermosetting composition and suppress the water absorption rate of the sheet-like cured product of the present invention. From this viewpoint, the content of polyfunctional epoxy resin having three or more epoxy groups in one molecule is preferably 50% by mass or less, with respect to 100% by mass of the solid content in the thermosetting composition excluding inorganic fillers including thermally conductive inorganic fillers, and more preferably 45% by mass or less, and even more preferably 40% by mass or less. In particular, the content of polyfunctional epoxy resin having three or more epoxy groups in one molecule and having an epoxy equivalent of 50 to 200 g / equivalent is preferably 5% to 50% by mass, based on 100% by mass of the solid content in the thermosetting composition excluding inorganic fillers including thermally conductive inorganic fillers, from the viewpoint of adjusting the epoxy equivalent (WPE) of the resin component of the thermosetting composition to a suitable range. More preferably, it is 6% to 45% by mass, and even more preferably 7% to 40% by mass.

[0059] As described later, when epoxy polymers and polyfunctional epoxy resins are used in combination, from the viewpoint of film-forming properties of the sheet and the elastic modulus of the sheet-like cured product of the present invention, it is preferable that the content of polyfunctional epoxy resins having three or more epoxy groups in one molecule is 20 parts by mass or more and 500 parts by mass or less per 100 parts by mass of epoxy polymer, and more preferably 30 parts by mass or more or 400 parts by mass or less, and more preferably 40 parts by mass or more or 350 parts by mass or less.

[0060] The mass ratio of thermally conductive inorganic filler to epoxy resin (epoxy resin / thermally conductive inorganic filler) is preferably 0.20 or higher, more preferably 0.22 or higher, and more preferably 0.25 or higher, from the viewpoint of improving sheet handling properties. On the other hand, from the viewpoint of improving the thermal conductivity of the sheet-like cured product of the present invention, it is preferably 0.53 or lower, more preferably 0.52 or lower, and more preferably 0.51 or lower.

[0061] <Thermally conductive inorganic filler> The thermally conductive inorganic filler contained in this thermosetting composition is preferably one with a thermal conductivity of 2.0 W / m·K or higher, more preferably one with a thermal conductivity of 3.0 W / m·K or higher, more preferably one with a thermal conductivity of 5.0 W / m·K or higher, and more preferably one with a thermal conductivity of 10.0 W / m·K or higher.

[0062] Examples of thermally conductive inorganic fillers include electrically insulating fillers consisting solely of carbon, metal carbides or metalloid carbides, metal oxides or metalloid oxides, and metal nitrides or metalloid nitrides.

[0063] Examples of electrically insulating fillers consisting solely of carbon include diamond (thermal conductivity: approximately 2000 W / m·K). Examples of the aforementioned metal carbides or metalloid carbides include silicon carbide (thermal conductivity: approximately 60-270 W / m·K), titanium carbide (thermal conductivity: approximately 21 W / m·K), and tungsten carbide (thermal conductivity: approximately 120 W / m·K).

[0064] Examples of the aforementioned metal oxides or metalloids include magnesium oxide (thermal conductivity: approximately 40 W / m·K), aluminum oxide (thermal conductivity: approximately 20-35 W / m·K), zinc oxide (thermal conductivity: approximately 54 W / m·K), yttrium oxide (thermal conductivity: approximately 27 W / m·K), zirconium oxide (thermal conductivity: approximately 3 W / m·K), ytterbium oxide (thermal conductivity: approximately 38.5 W / m·K), beryllium oxide (thermal conductivity: approximately 250 W / m·K), and SiAlON (ceramics composed of silicon, aluminum, oxygen, and nitrogen, thermal conductivity: approximately 21 W / m·K).

[0065] Examples of the aforementioned metal nitrides or metalloid nitrides include boron nitride (thermal conductivity in the plane direction of plate-like hexagonal boron nitride (h-BN) particles: approximately 200-500 W / m·K), aluminum nitride (thermal conductivity: approximately 160-285 W / m·K), silicon nitride (thermal conductivity: approximately 30-80 W / m·K), and the like.

[0066] These thermally conductive inorganic fillers may be used individually or in combination of two or more types.

[0067] From the standpoint of electrical insulation, the volume resistivity of thermally conductive inorganic filler at 20°C is 10 13 It is preferable that it is Ω·cm or greater, and especially 10 14A value of Ω·cm or greater is more preferable. In particular, metal oxides, metalloid oxides, metal nitrides, or metalloid nitrides are preferred because they easily provide sufficient electrical insulation for the sheet-like cured product of the present invention. Specifically, aluminum oxide (Al2O3, volume resistivity: >10) is used as such a thermally conductive inorganic filler. 14 Ω·cm), aluminum nitride (AlN, volume resistivity: >10 14 Ω·cm), Boron nitride (BN, volume resistivity: >10 14 Ω·cm), silicon nitride (Si3N4, volume resistivity: >10 14 Ω·cm), silica (SiO2, volume resistivity: >10 14 Examples include Ω·cm. Among these, aluminum oxide, aluminum nitride, and boron nitride are preferred, and aluminum oxide and boron nitride are particularly preferred because they can impart high insulation properties to the sheet-like cured product of the present invention.

[0068] The shape of the thermally conductive inorganic filler may be amorphous particulate, spherical, whisker-like, fibrous, plate-like, or aggregates or mixtures thereof. Among these, a spherical shape is preferred.

[0069] In this invention, "spherical" usually refers to a shape whose aspect ratio (ratio of major axis to minor axis) is 1 or more and 2 or less, preferably 1 or more and 1.75 or less, more preferably 1 or more and 1.5 or less, and even more preferably 1 or more and 1.4 or less. The aspect ratio can be determined by arbitrarily selecting 10 or more particles from an image of the cross-section of the thermosetting composition or the sheet-like cured product of the present invention, taken with a scanning electron microscope (SEM), and calculating the average value of the ratio of the major axis to the minor axis of each particle.

[0070] (Boron nitride aggregated particles) The thermally conductive inorganic filler contained in this thermosetting composition preferably contains "boron nitride aggregated particles" formed by the aggregation of primary boron nitride particles, because it has fewer problems with moisture absorption during heat molding, low toxicity, can efficiently increase thermal conductivity, and can impart high insulation properties to the sheet-like cured product of the present invention.

[0071] Furthermore, boron nitride aggregate particles may be used in combination with other thermally conductive inorganic fillers. However, as described later, the heat transfer behavior in the sheet-like cured product of the present invention does not depend solely on the thermal conductivity within the thermally conductive inorganic filler. Therefore, even when using diamond particles or the like, which have extremely high thermal conductivity but are also extremely expensive, among the thermally conductive inorganic fillers exemplified above, the thermal conductivity in the thickness direction of the sheet-like cured product of the present invention will not increase drastically. Accordingly, when boron nitride aggregate particles are used in combination with other thermally conductive inorganic fillers, the main focus is on reducing the cost of this thermosetting composition. For this reason, it is preferable to appropriately select from magnesium oxide, aluminum oxide, tungsten carbide, silicon carbide, aluminum nitride, etc., as the other thermally conductive inorganic filler to be used in combination with boron nitride, given that it is relatively inexpensive and has relatively high thermal conductivity, with aluminum oxide being more preferable among them.

[0072] In particular, from the viewpoint of high thermal conductivity, it is preferable that boron nitride aggregated particles account for 75% or more by mass of the thermally conductive inorganic filler, and more preferably 80% or more by mass, and of that, 85% or more by mass (including 100% by mass) by boron nitride aggregated particles.

[0073] The shape of the boron nitride aggregate particles is preferably spherical.

[0074] From the viewpoint of improving thermal conductivity, the aggregated structure of boron nitride aggregated particles is preferably a cardhouse structure. Furthermore, the aggregation structure of boron nitride aggregated particles can be confirmed using a scanning electron microscope (SEM).

[0075] A cardhouse structure is a complex layering of plate-like particles that are not oriented, and is described in "Ceramics 43 No. 2" (published by the Ceramic Society of Japan in 2008). More specifically, this refers to a structure in which the planar portion of a primary particle forming an aggregated particle is in contact with the end face portion of other primary particles present within the aggregated particle. Due to its structure, the aggregated particles of this cardhouse structure have very high fracture strength and do not collapse even during the pressurization process performed when forming the sheet-like cured material of the present invention. Therefore, primary particles that would normally be oriented in the longitudinal direction of the sheet-like cured material can be arranged in random directions. Consequently, by using aggregated particles with a cardhouse structure, the proportion of primary particles whose ab-planes are oriented in the thickness direction of the sheet-like cured material of the present invention can be increased, thereby enabling effective heat conduction in the thickness direction of the sheet-like cured material of the present invention and further increasing the thermal conductivity in the thickness direction.

[0076] Boron nitride aggregate particles having a cardhouse structure can be manufactured, for example, by the method described in International Publication No. 2015 / 119198.

[0077] When using boron nitride aggregate particles having a cardhouse structure, these boron nitride aggregate particles may be surface-treated with a surface treatment agent. As the surface treatment agent, for example, known surface treatment agents such as silane coupling treatment can be used. It is believed that the adhesion at the interface between the thermally conductive inorganic filler and the thermosetting resin can be improved by chemical treatment, thereby further reducing the attenuation of thermal conductivity at the interface.

[0078] By using aggregated particles, which are formed by the aggregation of primary particles, as the thermally conductive inorganic filler used in the sheet-like cured product of the present invention, the particle size can be increased compared to thermally conductive inorganic fillers that use primary particles as they are. By increasing the particle size of the thermally conductive inorganic filler, the heat transfer paths between the thermally conductive inorganic fillers via the thermosetting resin with low thermal conductivity can be reduced, and therefore, the increase in thermal resistance in the heat transfer path in the thickness direction can be reduced.

[0079] From the above viewpoint, the lower limit of the maximum particle diameter of the boron nitride aggregate particles is preferably 20 μm or more, more preferably 30 μm or more, and even more preferably 40 μm or more. On the other hand, the upper limit of the maximum particle diameter is preferably 300 μm or less, more preferably 200 μm or less, even more preferably 100 μm or less, and even more preferably 90 μm or less.

[0080] Furthermore, the average particle size of the boron nitride aggregate particles is not particularly limited. Among these, 5 μm or more is preferred, 10 μm or more is more preferred, and 15 μm or more is even more preferred. Also, 100 μm or less is preferred, and 90 μm or less is even more preferred. When the average particle size of the boron nitride aggregate particles is 5 μm or more, the relative number of particles in the sheet-like cured product of the present invention is reduced, resulting in fewer interparticle interfaces, which in turn reduces thermal resistance and can increase the thermal conductivity of the sheet-like cured product of the present invention. Additionally, when the average particle size is below the above upper limit, surface smoothness tends to be obtained in the sheet-like cured product of the present invention.

[0081] If the average or maximum particle diameter of the boron nitride aggregate particles is below the above upper limit, a high-quality film without surface roughness can be formed when boron nitride aggregate particles are included in a thermosetting resin. If the average or maximum particle diameter is above the above lower limit, the interface between the thermosetting resin and the boron nitride aggregate particles is reduced, resulting in lower thermal resistance and achieving high thermal conductivity. At the same time, a sufficient improvement in thermal conductivity as a thermally conductive inorganic filler required for heat dissipation insulating sheets for power semiconductor devices can be obtained.

[0082] Furthermore, the influence of thermal resistance at the interface between the thermosetting resin and the boron nitride aggregate particles in the sheet-like cured product of the present invention becomes significant when the size of the boron nitride aggregate particles is 1 / 10 or less of the thickness of the sheet-like cured product of the present invention. In particular, in the case of power semiconductor devices, the sheet-like cured product of the present invention with a thickness of 100 to 300 μm is often applied, so from the viewpoint of thermal conductivity, it is preferable that the maximum particle diameter of the boron nitride aggregate particles is greater than the lower limit mentioned above. Furthermore, by ensuring that the maximum particle diameter of the boron nitride aggregate particles is greater than or equal to the lower limit mentioned above, not only is the increase in thermal resistance caused by the interface between the boron nitride aggregate particles and the thermosetting resin suppressed, but the number of required heat conduction paths between particles is reduced, increasing the probability that the sheet-like cured material of the present invention will connect from one surface to the other in the thickness direction. On the other hand, because the maximum particle size of the boron nitride aggregate particles is below the above upper limit, the protrusion of boron nitride aggregate particles onto the surface of the sheet-like cured material of the present invention is suppressed, and a good surface shape without surface roughness is obtained. Therefore, when manufacturing a sheet bonded to a copper substrate, sufficient adhesion is achieved and excellent dielectric strength characteristics can be obtained.

[0083] From the same viewpoint as described above, the ratio of the size (maximum particle diameter) of boron nitride aggregated particles to the thickness of the sheet-like cured product of the present invention (maximum particle diameter / thickness of the sheet-like cured product of the present invention) is preferably 0.3 or more and 1.0 or less, more preferably 0.35 or more or 0.95 or less, and more preferably 0.4 or more or 0.9 or less.

[0084] The maximum and average particle diameters of boron nitride aggregates can be measured, for example, by the following method. The maximum particle size and average particle size of boron nitride aggregates used as raw materials can be determined by measuring the particle size distribution of a sample in which boron nitride aggregates are dispersed in a solvent, specifically in a sample in which boron nitride aggregates are dispersed in a pure water medium containing a dispersion stabilizer, using a laser diffraction / scattering particle size distribution analyzer. The maximum particle size Dmax and average particle size D50 of the boron nitride aggregates can then be determined from the obtained particle size distribution. Here, the maximum particle diameter Dmax and the average particle diameter D50 are the maximum particle diameter and the 50% cumulative volume particle diameter in the volume-based particle size distribution obtained by the laser diffraction scattering particle size distribution method. Additionally, the maximum and average particle size can be determined using dry particle size distribution analyzers such as the Morfologi G3 (manufactured by Malvern).

[0085] On the other hand, the maximum particle diameter Dmax and average particle diameter D50 of boron nitride aggregated particles in the sheet-like cured product of the present invention can be measured by the same method as described above, by dissolving and removing the resin component containing the thermosetting resin in a solvent (including a heating solvent), or by reducing the adhesion strength with the boron nitride aggregated particles by swelling and then physically removing it, and further by heating and ashing the resin component in the atmosphere to remove it. Furthermore, to determine the maximum particle size of boron nitride aggregates in the sheet-like cured product of the present invention, it is also possible to directly observe 10 or more arbitrary boron nitride aggregates in the cross-section of the sheet-like cured product of the present invention using a scanning electron microscope, transmission electron microscope, micro-Raman spectrometer, atomic force microscope, etc., and determine the maximum particle size among them. Furthermore, the average particle diameter of the boron nitride aggregate particles in the sheet-like cured product of the present invention can also be determined by directly observing 10 or more arbitrary boron nitride aggregate particles in the cross-section of the sheet-like cured product of the present invention using a scanning electron microscope, transmission electron microscope, micro-Raman spectrometer, atomic force microscope, etc., and calculating the arithmetic mean of the particle diameters. If the particles are non-spherical, the longest and shortest diameters are measured, and their average value is taken as the average particle diameter.

[0086] (Content) The content of the thermally conductive inorganic filler is preferably 60% by mass or more, based on 100% by mass of the solid content in the thermosetting composition. If the content of the thermally conductive inorganic filler is 60% by mass or more relative to 100% by mass of the solid content in the thermosetting composition, the insulating properties and thermal conductivity can be enhanced. From this viewpoint, the content of the thermally conductive inorganic filler is preferably 60% by mass or more relative to 100% by mass of the solid content in the thermosetting composition, more preferably 63% by mass or more, and more preferably 65% ​​by mass or more. On the other hand, if the content is 85% by mass or less, handling properties and film-forming properties can be maintained. From this viewpoint, the content of the thermally conductive inorganic filler is preferably 85% by mass or less, more preferably 83% by mass or less, and more preferably 81% by mass or less.

[0087] The content of the boron nitride aggregate particles is preferably 50% by mass or more relative to 100% by mass of the total thermally conductive inorganic filler. If the content of the boron nitride aggregate particles is 50% by mass or more relative to 100% by mass of the total thermally conductive inorganic filler, the insulating properties and thermal conductivity can be improved. From this viewpoint, the content of the boron nitride aggregate particles is preferably 50% by mass or more, more preferably 60% by mass or more, and more preferably 70% by mass or more, based on 100% by mass of the total thermally conductive inorganic filler.

[0088] <Hardening agent> This thermosetting composition preferably contains a curing agent, if necessary. Examples of curing agents include phenolic resins, compounds having a heterocyclic structure containing nitrogen atoms (referred to as "nitrogen-containing heterocyclic compounds"), acid anhydrides having an aromatic or alicyclic skeleton, aqueous additives of the acid anhydrides, or modified products of the acid anhydrides. Preferably, the curing agent contains a phenolic resin. The curing agent may be used alone or in combination of two or more types. By using these preferred curing agents, a sheet-like cured product of the present invention can be obtained that exhibits an excellent balance of heat resistance, moisture resistance, and electrical properties.

[0089] Examples of the phenolic resins include phenol novolac, o-cresol novolac, p-cresol novolac, t-butylphenol novolac, dicyclopentadiene cresol, poly-p-vinylphenol, bisphenol A type novolac, xylylene-modified novolac, decalin-modified novolac, poly(di-o-hydroxyphenyl)methane, poly(di-m-hydroxyphenyl)methane, or poly(di-p-hydroxyphenyl)methane. Among these, novolac-type phenolic resins having a rigid main chain skeleton or phenolic resins having a triazine skeleton are preferred for further improvement of the flexibility and flame retardancy of the sheet-like cured product of the present invention, as well as for improvement of mechanical properties and heat resistance. On the other hand, phenolic resins having allyl groups are preferred for improving the flexibility of the thermosetting composition and the toughness of the sheet-like cured product of the present invention.

[0090] Examples of heterocyclic structures of the nitrogen-containing heterocyclic compounds include structures derived from imidazole, triazine, triazole, pyrimidine, pyrazine, pyridine, and azole. From the viewpoint of improving the insulating properties and adhesion to conductive materials such as metal plates and circuit boards of the sheet-like cured product of the present invention, imidazole-based compounds and triazine-based compounds are preferred. Preferred imidazole and triazine compounds include, for example, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 2-phenyl-4-methylimidazole, 1-cyanoethyl-2-phenylimidazolium trimellitate, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-undecylimidazolyl-(1')]-ethyl-s-triazine, and 2,4-diamino-6-[2'-ethyl Examples include -4'methylimidazolyl-(1')-ethyl-s-triazine, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanurate adduct, 2-phenylimidazole isocyanurate adduct, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2,4-diamino-6-vinyl-s-triazine, 2,4-diamino-6-vinyl-s-triazine isocyanurate adduct, 2,4-diamino-6-methacryloyloxyethyl-s-triazine, and 2,4-diamino-6-methacryloyloxyethyl-s-triazine isocyanurate adduct.

[0091] Among these, those with high resin compatibility and a high reaction activation temperature allow for easy adjustment of the curing rate and post-curing physical properties, thereby improving the storage stability of the thermosetting composition and further enhancing the adhesive strength after heat molding. Therefore, those having a structure derived from imidazole and those having a structure derived from triazine are particularly preferred, and those having a structure derived from triazine are especially preferred. Among the heterocyclic structures of nitrogen-containing heterocyclic compounds, those derived from 1,3,5-triazine are particularly preferred. Furthermore, the compound may have multiple of these exemplified structural parts.

[0092] Furthermore, depending on the structure, nitrogen-containing heterocyclic compounds may contain thermosetting catalysts as described later; therefore, this thermosetting composition may contain nitrogen-containing heterocyclic compounds as thermosetting catalysts. Nitrogen-containing heterocyclic compounds may be used individually or in combination of two or more. Furthermore, a single molecule may simultaneously contain multiple heterocyclic structures. The molecular weight of the nitrogen-containing heterocyclic compound is preferably 1,000 or less, and more preferably 500 or less.

[0093] The acid anhydride having an aromatic skeleton, the aqueous additive of the acid anhydride, or the modified product of the acid anhydride are not particularly limited.

[0094] The acid anhydride having an alicyclic skeleton, the aqueous additive of the acid anhydride, or the modified product of the acid anhydride is preferably an acid anhydride having a polyalicyclic skeleton, the aqueous additive of the acid anhydride, or the modified product of the acid anhydride, or an acid anhydride having an alicyclic skeleton obtained by an addition reaction between a terpene compound and maleic anhydride, the aqueous additive of the acid anhydride, or the modified product of the acid anhydride.

[0095] If the thermosetting composition contains a curing agent, it is preferable that the curing agent is present in an amount of 1% to 70% by mass, particularly 2% to or 55% by mass, per 100% by mass of the solid content of the thermosetting composition, excluding the inorganic filler containing the thermally conductive inorganic filler. If the curing agent content is above the lower limit, sufficient curing performance can be obtained, and if it is below the upper limit, the reaction proceeds effectively, improving the crosslinking density, increasing strength, and further improving film-forming properties.

[0096] <Curing accelerator> This thermosetting composition may, if necessary, contain a thermosetting catalyst as a curing accelerator to adjust the curing rate and the physical properties of the sheet-like cured product of the present invention.

[0097] It is preferable to select the thermosetting catalyst appropriately depending on the type of thermosetting resin and curing agent. Specific examples of thermosetting catalysts include diazabicycloalkenes such as linear or cyclic tertiary amines, organophosphorus compounds, quaternary phosphonium salts, or organic acid salts, and imidazoles. Organometallic compounds, quaternary ammonium salts, or metal halides can also be used. Examples of the above-mentioned organometallic compounds include zinc octoate, tin octoate, or aluminum acetylacetone complexes. Furthermore, the nitrogen-containing heterocyclic compounds described above as curing agents also act as thermosetting catalysts, and may therefore be incorporated as thermosetting catalysts.

[0098] Among these, compounds containing imidazole (referred to as "imidazole compounds") are particularly preferred from the viewpoint of storage stability, heat resistance, and curing speed. Preferred imidazole compounds include, for example, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 2-phenyl-4-methylimidazole, 1-cyanoethyl-2-phenylimidazolium trimellitate, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine, 2, Examples include 4-diamino-6-[2'-undecylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-ethyl-4'methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanurate adduct, 2-phenylimidazole isocyanurate adduct, 2-phenyl-4,5-dihydroxymethylimidazole, and 2-phenyl-4-methyl-5-hydroxymethylimidazole. In particular, by using an imidazole compound with a melting point of 100°C or higher, and more preferably 200°C or higher, a sheet-like cured product of the present invention with excellent storage stability and adhesion can be obtained. Furthermore, compounds containing nitrogen-containing heterocyclic compounds other than the aforementioned imidazole ring are more preferable from the viewpoint of adhesion. Furthermore, the thermosetting catalyst may be used alone or in a mixture of two or more types. By using two or more imidazole compounds with a melting point of 100°C or higher as the thermosetting catalyst, it is possible to obtain the thermosetting composition with excellent storage stability and the sheet-like cured product of the present invention 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 have a melting point of 200°C or higher.

[0099] When the thermosetting composition contains a thermosetting catalyst, the thermosetting catalyst is preferably contained in a proportion of 0.1% to 10% by mass per 100% by mass of the solid content of the thermosetting composition, excluding the inorganic filler containing the thermally conductive inorganic filler, and more preferably in a proportion of 0.1% to 5% by mass. If the content of the thermosetting catalyst is above the lower limit, the curing reaction can be sufficiently promoted to achieve good curing, and if it is below the upper limit, the curing rate will not be too fast, and therefore the storage stability of this thermosetting composition can be improved.

[0100] <Silane coupling agent> This thermosetting composition preferably contains a silane coupling agent, if necessary. By incorporating a silane coupling agent, the adhesion at the interface between the thermally conductive inorganic filler and the thermosetting resin can be further enhanced, and the reliability for use in high-temperature and high-humidity environments can be further improved, as shown in the THB test (high-temperature and high-humidity bias test) described later.

[0101] Examples of silane coupling agents include N-phenylγ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, p-styryltrimethoxysilane, vinyltrimethoxysilane, and vinyltriethoxysilane. One of these can be used alone, or two or more can be used in combination. Furthermore, these silane coupling agents may be formulated after undergoing a hydrolysis reaction in advance.

[0102] From the viewpoint of improving adhesion at the interface between the thermally conductive inorganic filler and the thermosetting resin, 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, and more preferably 0.15 parts by mass or more, per 100 parts by mass of total thermally conductive inorganic filler. On the other hand, from the viewpoint of maintaining heat resistance, the content is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, and more preferably 1 part by mass or less, per 100 parts by mass of total thermally conductive inorganic filler.

[0103] <Organic solvents> This thermosetting composition may optionally contain an organic solvent as a solvent, for example, to improve the applicability when forming the sheet-like cured product of the present invention through a coating process. Examples of organic solvents that may be contained in this thermosetting composition 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 individually or in combination of two or more.

[0104] If the thermosetting composition contains an organic solvent, its content is appropriately determined according to the handling requirements when preparing the sheet-like cured product of the present invention from the thermosetting composition. Generally, the organic solvent is used such that the solid content (total of components other than the solvent) concentration in the thermosetting composition is 10% by mass or more and 90% by mass or less, and is particularly preferably 40% by mass or more or 80% by mass or less. Furthermore, when forming the thermosetting composition into a sheet, it is preferable to use the organic solvent such that the concentration of solids (total of components other than the solvent) in the thermosetting composition 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.

[0105] <Other ingredients> This thermosetting composition may contain other components in addition to the components listed above. Other components include, for example, dispersants, thermoplastic resins, organic fillers, additives that are expected to enhance the adhesion strength between the sheet-like cured product of the present invention and conductive materials such as metal plates and circuit boards, insulating carbon components such as reducing agents, viscosity modifiers, thixotropic agents, flame retardants, colorants, phosphorus-based, phenol-based and other antioxidants, phenol acrylate-based and other process stabilizers, heat stabilizers, hindered amine-based radical scavengers (HAAS), impact modifiers, processing aids, metal deactivators, copper damage inhibitors, antistatic agents, and bulking agents. When using these additives, the amount added should generally be within the range used for their respective purposes.

[0106] <Resin components> When the thermosetting composition contains an epoxy resin as the thermosetting resin, it is preferable that the epoxy equivalent (WPE) of the components obtained by excluding the solvent and the inorganic filler containing the thermally conductive inorganic filler from the thermosetting composition (referred to as the "resin component"), or in other words, the epoxy equivalent (WPE) of the solids obtained by excluding the inorganic filler containing the thermally conductive inorganic filler from the solids of the thermosetting composition, is 220 g / equivalent or more and 270 g / equivalent or less. That is, it is preferable that the epoxy equivalent (WPE) is 220 g / equivalent or more and 270 g / equivalent or less. The solid content of this thermosetting composition refers to the components remaining after removing the solvent. Note that epoxy equivalent (WPE) here refers to the mass of the resin component per equivalent of epoxy groups (g / equivalent). By adjusting the proportions of epoxy polymer, polyfunctional epoxy resin, and other epoxy resins, the epoxy equivalent (WPE) of the resin component of this thermosetting composition can be adjusted to the above range. As a result, the toughness of this thermosetting composition can be adjusted, and the resistance to corona discharge can be improved. Furthermore, the retention force of the thermally conductive inorganic filler can be adjusted, and the thermal conductivity of the sheet-like cured product of the present invention can be improved. From this viewpoint, the epoxy equivalent (WPE) of the resin component of this thermosetting composition is preferably 270 g / equivalent or less, more preferably 265 g / equivalent or less, more preferably 260 g / equivalent or less, more preferably 255 g / equivalent or less, and more preferably 250 g / equivalent or less. On the other hand, the epoxy equivalent (WPE) of the resin component of this thermosetting composition is preferably 220 g / equivalent or more, and more preferably 221 g / equivalent or more.

[0107] To adjust the epoxy equivalent (WPE) of the resin component of this thermosetting composition to the above range, one method is to adjust the content ratio of epoxy resins having a predetermined epoxy equivalent, such as epoxy polymers and polyfunctional epoxy resins. However, the method is not limited to these methods.

[0108] <Method for manufacturing the sheet-like cured product of the present invention> An example of a method for producing the sheet-like cured product of the present invention will be described. However, the method for producing the sheet-like cured product of the present invention is not limited to this method.

[0109] The thermosetting composition is prepared ("Preparation of Thermosetting Composition Step"), the prepared thermosetting composition is formed into a sheet ("Sheet Forming Step"), and the solvent is removed by heating ("Solvent Removal Step"). Next, the composition is subjected to low-temperature aging in a temperature environment of 0°C or lower ("Low-Temperature Aging Step"), and if necessary, pressurized at a predetermined temperature ("Pressurization Step") to cure the sheet-like thermosetting composition thus obtained, thereby producing the sheet-like cured product of the present invention ("Curing Step"). However, the order of each step can be appropriately changed. For example, the low-temperature aging step may be performed after the pressurization step.

[0110] (Main thermosetting composition preparation process) It is preferable to prepare this thermosetting composition as a coating solution by adding the aforementioned organic solvent.

[0111] Regarding the method for preparing this thermosetting composition, it is preferable to uniformly mix each raw material by stirring or kneading. For mixing, general kneading equipment such as mixers, kneaders, three-roll kneaders, single-screw or twin-screw kneaders, and rotary-orbit stirring mixers can be used. During mixing, heating may be applied as needed, and if heat is generated by stirring or kneading, cooling may be applied.

[0112] When adding an organic solvent to this thermosetting composition to prepare a fluid slurry-like coating solution, it is preferable to mix and stir the mixture using a general mixing device such as a paint shaker, bead mill, planetary mixer, agitated disperser, orbital agitator mixer, rotary homogenizer, three-roll mixer, kneader, single-screw or twin-screw kneader, etc., in order to improve the uniformity of the coating solution and remove foam. As the aforementioned organic solvent, any solvent that dissolves resins can be appropriately selected from known solvents. Examples include methyl ethyl ketone, acetone, cyclohexanone, toluene, xylene, monochlorobenzene, dichlorobenzene, trichlorobenzene, phenol, and hexafluoroisopropanol. These may be used individually or in combination of two or more.

[0113] (Sheet forming process) The thermosetting composition prepared as described above can, for example, be applied to the surface of a substrate to form a sheet-like coating. In this case, any coating method such as dip coating, spin coating, spray coating, blade coating, or other methods can be used. For coating this thermosetting composition, it is possible to uniformly form a coating film of a predetermined thickness on the substrate by using coating equipment such as a spin coater, slit coater, die coater, blade coater, comma coater, screen printing, doctor blade, applicator, or spray coating, and a blade coater with an adjustable gap is preferred.

[0114] This thermosetting composition can be formed on known substrates such as metal foils or plates (copper, aluminum, silver, gold), resin films such as polyethylene terephthalate or polyethylene naphthalate, and glass. Depending on the application, these substrates can be peeled off or used in a laminated structure such as substrate / thermosetting composition / substrate. While copper foil of the thickness described later is commonly used as the substrate, it is not limited to copper substrates. Furthermore, the surface of the substrate may have irregularities or be surface-treated. However, this thermosetting composition or the sheet-like cured product of the present invention can also be prepared as a self-supporting film.

[0115] (Solvent removal process) Next, the thermosetting composition, which has been formed into a sheet, is heated to a temperature between 40°C and 140°C to remove the solvent. The temperature at this time (heating atmosphere temperature) is preferably 40°C or higher from the viewpoint of drying rate, more preferably 60°C or higher, and more preferably 80°C or higher. On the other hand, from the viewpoint of suppressing the reaction of the thermosetting resin, it is preferably 140°C or lower, more preferably 130°C or lower, more preferably 120°C or lower, and more preferably 100°C or lower.

[0116] (Low-temperature aging process) Next, it is preferable to perform low-temperature aging by placing the sheet-like thermosetting composition thus formed in a temperature environment of 0°C or below. By performing such low-temperature aging on this sheet-like thermosetting composition, moisture inside the sheet can be frozen and dispersed as tiny ice crystals. Even after returning to room temperature, these trapped moisture chambers are created, preventing deterioration of insulation without generating large voids, and suppressing cracking when the sheet is bent. As a result, corona discharge becomes less likely, and the corona discharge initiation voltage can be increased.

[0117] In low-temperature aging, the ambient temperature is preferably lower because a faster cooling rate results in the formation of tiny ice crystals. From this viewpoint, the ambient temperature is preferably 0°C or lower, more preferably -5°C or lower, more preferably -10°C or lower, and more preferably -15°C or lower. On the other hand, if the temperature is too low, it will fall below the glass transition temperature (Tg) of the uncured thermosetting resin, making it prone to cracking. Therefore, it is preferable that the temperature be -50°C or higher, and if epoxy resin is included, more preferably -30°C or higher, and more preferably -25°C or higher.

[0118] The duration of the low-temperature aging is not particularly limited as long as the thermosetting composition is frozen. Rapid freezing and holding for 10 minutes or more is sufficient, 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 epoxy resins react gradually even at low temperatures, from the viewpoint of avoiding prolonged storage, it is preferable that the aging period be 365 days or less, more preferably 180 days or less, more preferably 90 days or less, more preferably 30 days or less, and more preferably 7 days or less.

[0119] While it is not necessary to apply pressure during low-temperature aging, applying a small pressure of 0.1 kPa or less is acceptable.

[0120] (Pressurization process) Next, a pressurization process is carried out as needed. However, the pressurization process is not mandatory. For example, if there is a large amount of solvent or a large amount of thermally conductive inorganic filler, many pores may remain after the solvent has evaporated, so it is preferable to carry out the pressurization process in such cases. By carrying out the pressurization process, it is possible to reduce or shrink the voids inside the sheet, especially the connecting pores.

[0121] Examples of pressurization methods include flat plate presses, hydrostatic presses, vacuum presses, calender presses, belt presses, and servo presses. However, the method is not limited to these. The heating temperature during the pressurization process should preferably be such that the thermosetting resin does not harden. For example, when epoxy resin is used as the thermosetting resin, the heating temperature (product temperature) should preferably be less than 140°C, more preferably 100°C or less, and even more preferably 80°C or less, from the viewpoint of suppressing the reaction of the epoxy resin. On the other hand, from the viewpoint of the elastic modulus of the thermosetting composition, it is more preferably 0°C or higher, more preferably 20°C or higher, and even more preferably 40°C or higher. For example, when performing a pressurizing process using a flat plate press, the temperature of the flat plate being pressed should be adjusted to the above temperature range.

[0122] In the pressurization process, for example in the case of a flat plate press, it is preferable to apply pressure to the sheet at 1 MPa or more and 200 MPa or less, and more preferably 5 MPa or more or 100 MPa or less, and more preferably 7.5 MPa or more or 50 MPa or less. In this case, the pressurization time is preferably 1 second or more and 60 minutes or less, more preferably 10 seconds or more or 45 minutes or less, and more preferably 30 seconds or more or 30 minutes or less.

[0123] (hardening process) The sheet-like thermosetting composition obtained as described above can be cured by heating to obtain the sheet-like cured product of the present invention. In this case, the heating temperature (product temperature) is preferably 30°C or higher and 400°C or lower, more preferably 50°C or higher, and more preferably 90°C or higher. On the other hand, it is preferably 300°C or lower, and more preferably 250°C or lower.

[0124] In particular, in the sheet formation process, which involves a pressurizing process and a curing process, it is preferable to apply a load while performing the pressurizing and curing.

[0125] The load applied when the pressurizing and curing processes are performed simultaneously is not particularly limited. In this case, it is preferable to apply a load of 0.1 MPa or more to the sheet-like thermosetting composition, more preferably 1.0 MPa or more, even more preferably 5.0 MPa or more, and particularly preferably 10 MPa or more. Furthermore, the load is preferably 1000 MPa or less, and more preferably 200 MPa or less. By setting the load below the upper limit when performing the pressurization and curing processes simultaneously, the secondary particles of the boron nitride aggregate particles are not destroyed, and a sheet-like cured product of the present invention with high thermal conductivity and no voids in the sheet can be obtained. Furthermore, by setting the load above the lower limit, contact between the thermally conductive inorganic fillers is improved, making it easier to form thermal conduction paths, and thus a sheet-like cured product of the present invention with high thermal conductivity can be obtained.

[0126] The pressurizing time when the pressurizing and curing processes 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 especially preferably 5 minutes or more. Alternatively, the pressurizing time is preferably 1 hour or less, more preferably 30 minutes or less, and even more preferably 20 minutes or less. When the pressurizing time is below the above upper limit, the manufacturing time of the sheet-like cured product of the present invention can be shortened, and production costs tend to be reduced. When the pressurizing time is above the above lower limit, voids and air pockets within the sheet-like cured product of the present invention can be sufficiently removed, and the heat transfer performance and dielectric strength characteristics tend to be improved.

[0127] <Thickness> The thickness of the sheet-like cured product of the present invention is preferably 50 μm or more, more preferably 60 μm or more, and even more preferably 70 μm or more. On the other hand, it is preferably 400 μm or less, more preferably 300 μm or less, and even more preferably 250 μm or less. By setting the thickness of the sheet-like cured material of the present invention to 50 μm or more, sufficient dielectric strength can be ensured. On the other hand, by setting the thickness to 400 μm or less, miniaturization and thinning can be achieved, especially when the sheet-like cured material of the present invention is used in power semiconductor devices, and the effect of reducing thermal resistance in the thickness direction due to thinning can be obtained compared to an insulating thermal conductive layer made of ceramic material.

[0128] <Physical properties of the sheet-like cured product of the present invention> The sheet-like cured material of the present invention can obtain the following physical properties.

[0129] (Thermal conductivity) The thermal conductivity in the thickness direction of the sheet-like cured material of the present invention at 25°C is preferably 15 W / m·K or higher, more preferably 15.5 W / m·K or higher, more preferably 16 W / m·K or higher, more preferably 16.5 W / m·K or higher, and more preferably 17 W / m·K or higher. Since the thermal conductivity in the thickness direction is above the above lower limit, it can be suitably used in power semiconductor devices and the like that operate at high temperatures. The sheet-like cured product of the present invention can be prepared so that its thermal conductivity falls within the above range by, for example, adjusting the type of thermosetting resin, the type and content of the thermally conductive inorganic filler, the method of mixing the thermosetting resin and the thermally conductive inorganic filler, and the conditions in the preparation process of the thermosetting composition described above. However, the method is not limited to these.

[0130] The thermal conductivity in the thickness direction of the sheet-like cured material of the present invention can be measured by the following method. For example, using a thermal resistance measuring device (manufactured by Mentor Graphics Co., Ltd., product name "T3ster"), the thermal conductivity can be determined from the slope of a graph plotting the thermal resistance value against the thickness. For more specific details, please refer to the method described in the examples below.

[0131] <Applications of the sheet-like cured material of the present invention> The sheet-like cured material of the present invention is preferably used as a heat-dissipating insulating sheet for power semiconductor devices. As an example of how the sheet-like cured material of the present invention can be used, a composite molded body having a cured material portion made of the sheet-like cured material of the present invention and a metal portion can be cited. In particular, the sheet-like cured material of the present invention can prevent dielectric breakdown and delamination from metals such as metal plates and circuit boards even after going through the high-temperature environment of the reflow process. Therefore, it can be suitably used in applications such as heat dissipation insulating material used for insulating circuit boards of power semiconductor devices, heat dissipation insulating material for attaching heat-generating elements to heat sinks, and heat dissipation insulating material used for heat dissipation of computers in data centers. For example, a composite molded body can be manufactured by laminating a metal plate and a circuit board via a sheet-like cured material of the present invention, and then joining other components to the laminate by a reflow process.

[0132] More specifically, the sheet-like cured material of the present invention can be used as a constituent material for, for example, a heat dissipation laminate (referred to as "this heat dissipation laminate"), a heat dissipation circuit board (referred to as "this heat dissipation circuit board"), and a power semiconductor device (referred to as "this power semiconductor device"). These will be described below.

[0133] (This heat dissipation laminate) As an example of this heat-dissipating laminate, one can refer to a case in which a heat-dissipating metal layer containing a heat-dissipating material is laminated on one surface of the sheet-like cured material of the present invention. 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 to increase the thermal conductivity in a laminated structure, and it is even more preferable to use a flat metal material. Alternatively, a cooler may be provided with rod-shaped or plate-shaped fins attached to the bottom of the flat metal plate. The material of the metal is not particularly limited. Among them, copper plates, aluminum plates, and aluminum alloy plates are preferred because they have good thermal conductivity and are relatively inexpensive. For the lamination and integration of the sheet-like cured material of the present invention with the heat-dissipating metal layer, a batch process such as press molding can be preferably used. In this case, the press equipment and press conditions are the same as the range of press molding conditions for obtaining the sheet-like thermosetting composition.

[0134] (This heat dissipating circuit board) As an example of a heat-dissipating circuit board, one can be cited which has a configuration in which the heat-dissipating metal layer is laminated on one surface of the sheet-like cured material of the present invention, and a circuit board is formed on the other surface from the heat-dissipating metal layer by, for example, etching. Specifically, a configuration in which the "heat-dissipating metal layer / sheet-like cured material of the present invention / circuit board" are integrated is more preferable. As for the state before circuit etching, for example, an integrated configuration of "heat-dissipating metal layer / sheet-like cured material of the present invention / metal layer for forming conductive circuits" can be cited, in which the metal layer for forming conductive circuits is in the shape of a flat plate and is formed on the entire surface of one side of the sheet-like cured material of the present invention, or on a partial area. The material for the metal layer used to form the conductive circuit is not particularly limited. In particular, a copper plate with a thickness of 0.05 mm to 5 mm is generally preferred from the viewpoint of good electrical conductivity, etching properties, and cost.

[0135] (This power semiconductor device) This power semiconductor device is a product that integrates a circuit combining multiple power semiconductors into a single package module, and is equipped with the sheet-like cured material of the present invention. As an example of this power semiconductor device, a power semiconductor can be mounted on a sheet-like cured material of the present invention as a heat-dissipating circuit board. In this power semiconductor device, components other than the sheet-like cured material of the present invention, such as aluminum wiring, sealing material, packaging material, heat sink, thermal paste, and solder, can be replaced with conventionally known components as appropriate.

[0136] <Explanation of terms and phrases> In this invention, the term "film" includes "sheets," and the term "sheet" includes "film."

[0137] In this invention, when "α~β" (where α and β are arbitrary numbers) is written, unless otherwise specified, it means "α or greater and β or less," and also includes the meaning of "preferably greater than α" or "preferably less than β." Furthermore, when written as "α or greater" or "α ≤" (where α is any number), unless otherwise specified, it includes the meaning of "preferably greater than α," and when written as "β or less" or "≤β" (where β is any number), unless otherwise specified, it also includes the meaning of "preferably less than β." [Examples]

[0138] The following describes an example of an embodiment of the present invention. However, the present invention is not limited to the embodiment described below.

[0139] <Ingredients> The raw materials used in the examples and comparative examples are as follows:

[0140] (Thermally conductive inorganic filler) • Thermally conductive inorganic filler 1: Spherical boron nitride aggregates having a cardhouse structure, manufactured in accordance with the method for manufacturing boron nitride aggregates disclosed in the examples of International Publication No. 2015 / 561028. Maximum particle diameter (Dmax): 90μm Average particle diameter (D50): 45μm

[0141] The maximum particle size (Dmax) and average particle size (D50) of the thermally conductive inorganic filler were determined by dispersing the thermally conductive inorganic filler in a pure water medium containing sodium hexametaphosphate as a dispersion stabilizer, measuring the volume-based particle size distribution using a laser diffraction / scattering particle size distribution analyzer LA-300 (manufactured by Horiba, Ltd.), and then obtaining the maximum particle size (Dmax) and cumulative volume 50% particle size (average particle size (D50)) from the resulting particle size distribution.

[0142] (Epoxy resin) • Epoxy resin 1: Manufactured by Mitsubishi Chemical Corporation, biphenyl-type solid epoxy resin, containing two glycidyl groups per molecule. Mass average molecular weight (Mw): Approx. 400 Epoxy equivalent (WPE): 200g / equivalent • Epoxy resin 2: A polyfunctional epoxy resin manufactured by Nagase ChemteX Corporation, containing a structure with four or more glycidyl groups in one molecule. It does not contain amine or amide structures that include a nitrogen atom. Mass average molecular weight (Mw): Approx. 400 Epoxy equivalent (WPE): 100g / equivalent • Epoxy resin 3: YED216D, manufactured by Mitsubishi Chemical Corporation, alkyl diglycidyl ether, having two glycidyl groups in one molecule. Mass average molecular weight (Mw): Approx. 240 Epoxy equivalent (WPE): 120g / equivalent • Epoxy resin 4: E828, manufactured by Mitsubishi Chemical Corporation, bisphenol A type epoxy resin, containing two glycidyl groups per molecule. Mass average molecular weight (Mw): Approx. 380 Epoxy equivalent (WPE): 190g / equivalent

[0143] (Hardening agent) • Hardener 1: "H-4" manufactured by UBE Corporation, phenolic resin-based hardener (phenol novolac) • Hardener 2: MEH-8000H manufactured by Meiwa Kasei Co., Ltd., phenolic resin-based hardener (allylphenol novolac)

[0144] (polymer) ·Epoxy polymer 1: A bifunctional epoxy polymer manufactured by Mitsubishi Chemical Corporation, disclosed as resin component 1 in Japanese Patent Publication No. 2020-63438, having the above structures (2) and (3), and R in formula (2) 3 R in structure (4) and equation (3) 4 , R 5 , R 6 , R 7 They were all methyl groups. Mass-average molecular weight (Mw) in polystyrene equivalent: 30,000 Epoxy equivalent (WPE): 9,000 g / equivalent

[0145] (Thermosetting catalyst) • Thermosetting catalyst 1: 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-s-triazine. It contains both structures derived from imidazole and structures derived from triazine in a single molecule (Shikoku Chemicals, Ltd. "Curesol 2E4MZ-A"). Melting point: 215-225℃ • Thermosetting catalyst 2: 2-phenyl-4,5-dihydroxymethylimidazole (Shikoku Chemicals Co., Ltd. "Curesol 2PHZ-PW"), melting point: dec. 230, therefore the melting point is 230°C or higher.

[0146] (Other ingredients) • Silane coupling agent: Shin-Etsu Chemical Co., Ltd. "KBM-403", 3-glycidoxypropyltrimethoxysilane • Reactive polyamide: "TPAE-826-4S" manufactured by T&K TOKA Corporation, polyamide elastomer • Urethane resin: Washin Paint Co., Ltd. Product name "No. 26001"

[0147] <Example 1> Each raw material was weighed to achieve the composition (parts by mass) shown in Table 1, and equal amounts of methyl ethyl ketone and cyclohexanone were added and mixed to prepare a slurry-like thermosetting composition. The slurry-like thermosetting composition obtained as described above was applied to a PET substrate using the doctor blade method and heated and dried at 60°C (heating atmosphere temperature) for 120 minutes. Next, the sheet-like curable composition was placed in a vacuum-sealed bag, the air inside the bag was removed, and the opening of the bag was heat-sealed. Then, this bag was stored in a -20°C freezer for 72 hours to perform low-temperature aging, and then pressurized at 40°C (product temperature) at 145 MPa for 10 minutes using a pressurizer to obtain a sheet-like thermosetting composition (sample). This sheet-like thermosetting composition (sample) was cured under various curing conditions described later to obtain a sheet-like cured product.

[0148] <Examples 2, 3 and Comparative Examples 2-5> Examples 2 and 3 and Comparative Examples 2 to 5 were prepared in the same manner as in Example 1, by weighing each raw material to obtain the composition (parts by mass) shown in Table 1, and then obtaining a sheet-like thermosetting composition (sample) and a sheet-like cured product.

[0149] <Comparative Example 1> In Example 1, instead of performing low-temperature aging of the sheet-like curable composition in a freezer at -20°C for 72 hours, a sheet-like thermosetting composition (sample) was prepared in the same manner as in Example 1, except that the sheet-like curable composition was placed in a sealed vacuum-packed bag and aged at 60°C for 72 hours. A sheet-like cured product was obtained.

[0150] <Measurement and Evaluation> The raw materials used in the examples and comparative examples, and the sheet-like thermosetting compositions (samples) prepared in the examples and comparative examples, were measured and evaluated as follows.

[0151] (Measurement of epoxy equivalent (WPE) of resin components) For each example and comparative example, the resin components used (components obtained by excluding the solvent and the inorganic filler containing the thermally conductive inorganic filler from the thermosetting composition), namely epoxy resin 1-4, curing agent 1-2, epoxy polymer 1, thermosetting catalyst 1-2, silane coupling agent, and reactive polyamide, were mixed in the mass ratios shown in Table 1 below to obtain a thermosetting composition. The potential was measured by potentiometric titration in accordance with JIS K7236, and the epoxy equivalent (g / equivalent) was determined by converting it to the value of the entire resin component.

[0152] (Corona discharge initiation voltage) The sheet-like thermosetting compositions (samples) obtained in the examples and comparative examples were cured by heating them under pressure of 10 MPa at 120°C (product temperature) for 30 minutes and then at 175°C (product temperature) for 30 minutes, thereby obtaining sheet-like cured materials (measurement samples) measuring 40 mm in length, 40 mm in width, and 140 μm to 160 μm in thickness.

[0153] The corona discharge initiation voltage was measured using the "XT-350 PB39b" corona discharge tester manufactured by Adfox Corporation. As shown in Figure 1, a sheet-like hardened material (measurement sample) was placed between the electrodes, a voltage was applied between the electrodes, and corona discharge was detected by measuring the feedback at a frequency different from the frequency of the applied voltage. Before measurement, the device was started and allowed to stand for at least 30 minutes to stabilize. Then, the sheet-like cured material (measurement sample) was placed between the electrodes as shown in Figure 1, and tuning was performed. The tuning procedure involved pressing the Manual switch, setting the test frequency to 40kHz, applying a voltage of 0.1kV, and adjusting the tuning dial to minimize the drive current. The target drive current was 0.1A or less. The test conditions were set by pressing the Prog / End button, and the program was designed to automatically stop when the corona discharge initiation voltage was reached.

[0154] (1) HV MAX, MIN: 3.00, 0.00 (2) Target HV: 2 (3) Flashover MAX: 255 (4) Corona MAX: 5 (5)Drive Current MAX,MIN:9.90,0.00 (6)Drive Voltage MAX, MIN:40.0V,0.00V (7) Wakeup Time MAX: 1.0 sec (8) Real Time MAX: 1.0 sec (9) HV Current MAX: 700mA (10) Ignore Voltage: 0kV

[0155] In this case, condition (4) means that the corona discharge rate is 5%, and this was defined as the corona discharge initiation voltage. This is because it is difficult to isolate the effects of external noise and other factors when the corona discharge rate is less than 5%. A corona discharge rate of 100% was defined as when a corona discharge occurs once for every half wavelength of the applied AC frequency. Before applying voltage, ensure the voltage adjustment dial is turned counterclockwise to its maximum extent. Then, press the start button and turn the voltage adjustment dial clockwise to apply a voltage of approximately 0.1 kV / second, continuing to apply voltage until it automatically stops at the corona discharge initiation voltage. In this case, if equipment such as a safety box is used where air tends to stagnate, there is a possibility that ionized gas due to corona discharge may accumulate. Since the presence of ionized gas molecules near the sheet-like hardened material (measurement sample) may affect corona discharge, when taking continuous measurements, an airflow was created and measurements were taken with an interval of at least one minute between them.

[0156] (Measurement of thermal conductivity in the thickness direction of a sheet-like cured material) The sheet-like thermosetting compositions (samples) prepared in each example and comparative example were heated at 120°C (product temperature) for 40 minutes under pressure of 10 MPa to cure them, by stacking them in single, double, triple, and quadruple layers. This resulted in obtaining four types of sheet-like cured materials (measurement samples) with different thicknesses: 40 mm (length) x 40 mm (width) x 150 μm to 600 μm (thickness).

[0157] For these four types of sheet-like cured materials (measurement samples) with different thicknesses, the following measurements were performed, and the thermal conductivity at 25°C in the sheet thickness direction was measured using the steady-state method from the slope represented by the thermal resistance value with respect to the sheet thickness (according to ASTM D5470). (1) Sheet thickness: Thickness (μm) when pressed at a press pressure of 3400 kPa using Mentor Graphics' T3Ster-DynTIM. (2) Measurement area: The area of ​​the heat-transmitting part (cm²) when measuring using Mentor Graphics' T3Ster-DynTIM. 2 ) (3) Thermal resistance value: Thermal resistance value (K / W) when pressed at a press pressure of 3400 kPa using Mentor Graphics T3Ster-DynTIM. (4) Thermal conductivity: The thermal resistance values ​​of four types of sheet-like cured materials (measurement samples) with different thicknesses are measured, and the thermal conductivity (W / m·K) is calculated from the following formula. Formula: Thermal conductivity (W / m·K) = 1 / ((Slope (thermal resistance value / thickness): K / (W·μm)) × (Area: cm) 2 )) × 10 -2

[0158] (Measurement of BDV (Dielectric Breakdown Voltage) of sheet-like cured material after reflow process) Copper plates with thicknesses of 500 μm and 2,000 μm were prepared by roughening the surface 100 times each with #120 grit sandpaper. One of each copper plate was used to sandwich a sheet-like thermosetting composition (sample) obtained in the examples and comparative examples. The plates were then pressurized at 120°C (product temperature) and 10 MPa for 30 minutes, followed by raising the temperature and pressurizing at 175°C (product temperature) and 10 MPa for 30 minutes to obtain a composite molded body for reflow testing. The sheet-like cured layer of the composite molded body was 140-160 μm thick. By etching the composite molded body obtained above, a 500 μm copper plate was patterned to obtain a composite molded body (evaluation sample). The pattern was a circular pattern with a diameter of φ25 mm.

[0159] The composite molded body (evaluation sample) was heated from room temperature to 290°C (product temperature) in 12 minutes under a nitrogen atmosphere, held at 290°C (product temperature) for 10 minutes, and then cooled to room temperature (reflow test). Subsequently, the composite molded body (evaluation sample) was immersed in insulating oil (3M's "Fluorinert FC-40"). Using a 7470 ultra-high voltage withstand voltage tester (manufactured by Keisoku Gijutsu Kenkyusho Co., Ltd.), electrodes were placed on a patterned φ25 mm copper plate, a voltage of 0.5 kV was applied, and the voltage was increased by 500 V every minute until the sheet-like hardened material broke down (BDV: dielectric breakdown voltage). The following criteria were used for evaluation. ○ (Passed): BDV was 5kV or higher. × (Fail): BDV was less than 5kV

[0160] (SAT of sheet-like cured material after reflow process) Copper plates with thicknesses of 500 μm and 2,000 μm were prepared by roughening the surface 100 times each with #120 grit sandpaper. One of each copper plate was used to sandwich a sheet-like thermosetting composition (sample) obtained in the examples and comparative examples. The plates were then pressurized at 120°C (product temperature) and 10 MPa for 30 minutes, followed by raising the temperature and pressurizing at 175°C (product temperature) and 10 MPa for 30 minutes to obtain a composite molded body for reflow testing. The sheet-like cured layer of the composite molded body was 140-160 μm thick. By etching the composite molded body obtained above, a 500 μm copper plate was patterned to obtain a composite molded body (evaluation sample). The pattern was a circular pattern with a diameter of φ25 mm.

[0161] The composite molded body (evaluation sample) was heated from room temperature to 290°C (product temperature) in 12 minutes under a nitrogen atmosphere, held at 290°C (product temperature) for 10 minutes, and then cooled to room temperature (reflow test). The interface between the copper plate and the resin curing material was observed using a FineSAT (FS300III) acoustic imaging system (manufactured by Hitachi Power Solutions). A 50 MHz probe was used for measurement, with a gain of 30 dB and a pitch of 0.2 mm, and the sample was placed in water. The following criteria were used for evaluation. ○ (Pass): No delamination was observed at the interface. × (Fail): Delamination was observed at the interface.

[0162] (THB test life) Copper plates with thicknesses of 500 μm and 2,000 μm were prepared by roughening the surface 100 times each with #120 grit sandpaper. One of each copper plate was used to sandwich the sheet-like thermosetting composition (sample) obtained in the example, and the plates were pressurized at 120°C (product temperature) and 10 MPa for 30 minutes. Subsequently, the temperature was increased, and the plates were pressurized at 175°C (product temperature) and 10 MPa for 30 minutes to obtain a composite molded body for THB testing. The sheet-like cured layer of the composite molded body was 140-160 μm thick. By etching the composite molded body obtained above, a 500 μm copper plate was patterned to obtain a composite molded body (evaluation sample). The pattern was a circular pattern with a diameter of φ25 mm.

[0163] Electrodes were soldered to a 25φ pattern and copper plate of a composite molded body (evaluation sample), placed in an environmental testing machine, and the side opposite the soldered electrode was connected to a DC voltage power supply. The environmental testing machine was set to 85°C and 85%RH, and the atmosphere inside the machine was kept constant by leaving it undisturbed for more than 4 hours. After that, a DC voltage was applied at a boosting rate of approximately 0.01kV / s until it reached DC1.36kV. After reaching DC1.36kV, the voltage was continued to be applied, and the time until dielectric breakdown of the sample (lifetime) was measured. The following criteria were used for evaluation. ◎ (Better): Time (lifespan) exceeds 1,000 hours ○ (Pass): The time (lifespan) was between 500 hours and 1,000 hours. × (Fail): The time (lifespan) was less than 500 hours.

[0164] [Table 1]

[0165] From the results of the examples and comparative examples, as well as the test results conducted by the inventors to date, it was found that for sheet-like cured thermosetting compositions containing a thermally conductive inorganic filler and a thermosetting resin, if the corona discharge initiation voltage is 0.78kV or higher when the sheet thickness is 150±10μm, the dielectric breakdown voltage (BDV) after the reflow process is 5kV or higher, thus preventing the material from easily breaking down dielectric strength. Furthermore, since no interfacial delamination was observed in the interface observation (SAT) after the reflow process, it was found that delamination from the metal can be prevented. In addition, as shown in the results of Examples 1 to 3 in the THB test (high temperature high humidity bias test), it was found that the material has durability even in high temperature and high humidity environments. Among these, Example 3, which contains a silane coupling agent, had a longer THB test life and was found to be the most durable compared to Examples 1 to 2.

Claims

1. A sheet-like cured product of a thermosetting composition containing a thermally conductive inorganic filler and a thermosetting resin, A sheet-like cured material having a corona discharge initiation voltage of 0.78 kV or higher, as measured by the following measurement test. Measurement test: The thickness of the measurement sample is adjusted to 140-160 μm, and a voltage is applied using a corona discharge tester tuned to a test frequency of 40 kHz. The applied voltage at which the corona discharge occurrence rate is 5% is measured, and this voltage is defined as the corona discharge initiation voltage.

2. The sheet-like cured product according to claim 1, wherein epoxy resin accounts for 50% or more by mass of the thermosetting resin.

3. The sheet-like cured product according to claim 1, wherein the thermosetting resin includes a polyfunctional epoxy resin having three or more epoxy groups in one molecule and a mass-average molecular weight (Mw) of less than 5,000.

4. The sheet-like cured product according to claim 3, wherein the polyfunctional epoxy resin has four or more epoxy groups in one molecule.

5. The sheet-like cured product according to claim 1, wherein the thermosetting resin includes a polymer epoxy resin with a mass-average molecular weight (Mw) of 5,000 or more.

6. The sheet-like cured product according to claim 1, wherein the thermosetting composition contains a phenolic resin as a curing agent.

7. The sheet-like cured product according to claim 1, wherein the thermosetting resin includes an epoxy resin, and the epoxy equivalent (WPE) of the solid content of the thermosetting composition, excluding the inorganic filler containing the thermally conductive inorganic filler, is 220 g / equivalent or more and 270 g / equivalent or less.

8. The sheet-like cured product according to claim 1, wherein the content of the thermally conductive inorganic filler is 60% by mass or more and 85% by mass or less based on 100% by mass of solid content in the thermosetting composition.

9. The sheet-like cured product according to claim 1, wherein the thermosetting composition comprises a silane coupling agent.

10. The sheet-like cured product according to claim 1, wherein the thermally conductive inorganic filler comprises one or more of the following: magnesium oxide, aluminum oxide, zinc oxide, yttrium oxide, zirconium oxide, ytterbium oxide, beryllium oxide, boron nitride, aluminum nitride, and silicon nitride.

11. The sheet-like cured product according to claim 1, wherein the thermally conductive inorganic filler contains boron nitride aggregated particles.

12. The sheet-like cured product according to claim 11, wherein the boron nitride aggregated particles have a cardhouse structure.

13. A sheet-like cured product according to any one of claims 1 to 12, for use as a heat-dissipating insulating sheet for power semiconductor devices.

14. A composite molded body having a cured portion made of a sheet-like cured material according to any one of claims 1 to 12, and a metal portion.

15. A power semiconductor device comprising a sheet-like cured material according to any one of claims 1 to 12.

Images