Cured product, composite molded article, semiconductor device, and method for producing composite molded article

Abstract

To provide a cured product of a curable composition containing an inorganic filler and a curable resin, the cured product having good solder reflow resistance while maintaining thermal conductivity and insulation properties.SOLUTION: The cured product has a free volume (V200) of 0. 165nm3 or less as measured by a positron annihilation method at 200 °C, or has a ratio (V25 / V200) of a free volume (V200) as measured by a positron annihilation method at 25 °C to a free volume (V25) as measured by a positron annihilation method at 200 °C of 1.80 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a cured product of a curable composition containing an inorganic filler and a curable resin, which can be suitably used as a heat dissipation member, an insulating member, etc., a composite molded body and a semiconductor device using the same, and a method for producing the composite molded body. [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, and how to dissipate heat has become an urgent issue. For example, to ensure stable operation of semiconductor devices used to control central processing units in personal computers and motors in electric vehicles, heat sinks, heat dissipation fins, etc. are essential for heat dissipation, and materials that can combine thermal conductivity and insulation are required to connect semiconductor devices to heat sinks, etc.

[0003] Ceramic substrates with high thermal conductivity, such as alumina substrates and aluminum nitride substrates, have traditionally been used as materials that can provide both thermal conductivity and insulation. However, ceramic substrates have issues such as being easily cracked by impact, and being difficult to make thin and compact. Therefore, a heat dissipation sheet using a curable resin such as an epoxy resin and an inorganic filler has been proposed.

[0004] Regarding heat dissipation sheets using a curable resin and an inorganic filler, various resin sheets containing boron nitride as the inorganic filler have been proposed (see Patent Documents 1 to 8). Boron nitride is an insulating ceramic that has attracted particular attention in recent years in the field of electrical and electronic materials due to its excellent thermal conductivity, solid lubricity, chemical stability, and heat resistance. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2015-6980 A [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-189823 [Patent Document 3] Japanese Patent Application Laid-Open No. 2015-195287 [Patent Document 4] Japanese Patent Application Laid-Open No. 2016-011358 [Patent Document 5] Japanese Patent Application Laid-Open No. 2016-135731 [Patent Document 6] Japanese Patent Application Publication No. 2019-119883 [Patent Document 7] Patent Publication No. 2021-6507 [Patent Document 8] Patent Publication No. 2021-38140 Summary of the Invention [Problem to be solved by the invention]

[0006] When a heat dissipation sheet made of a cured product of a curable composition containing a curable resin and an inorganic filler is used as a component of a power semiconductor module, it is common to mount other components on a laminate formed by bonding a metal plate or the like to a circuit board via the heat dissipation sheet through a reflow process. In this case, repeated temperature changes during the reflow process cause thermal expansion and contraction, and the difference in the thermal expansion coefficients of the resin and the metal plate can cause interfacial peeling between the heat dissipation sheet and the metal plate or the circuit board, resulting in a decrease in the performance of the power semiconductor module.

[0007] Therefore, an object of the present invention is to provide a cured product of a curable composition containing an inorganic filler and a curable resin, which can be used as a heat dissipation sheet or the like, which maintains thermal conductivity and insulation properties and does not peel even when thermal expansion and contraction occur due to repeated temperature changes in a reflow process, as well as a composite molded product and semiconductor device using the same, and a method for producing a composite molded product using the cured product. [Means for solving the problem]

[0008] The cured product proposed by the present invention, a composite molded product and a semiconductor device using the same, and a method for producing a composite molded product using the cured product have the following features in order to solve the above-mentioned problems.

[0009] [1] A first aspect of the present invention is a cured product of a curable composition containing an inorganic filler and a curable resin, which has a free volume (V200) of 0.165 nm at 200°C as determined by positron annihilation method. 3 The cured product is characterized by the following:

[0010] [2] A second aspect of the present invention is a cured product of a curable composition containing an inorganic filler and a curable resin, characterized in that the ratio (V200 / V25) of the free volume (V25) measured by positron annihilation method at 25°C to the free volume (V200) measured by positron annihilation method at 200°C is 1.80 or less.

[0011] [3] A third aspect of the present invention is the cured product of the first or second aspect, wherein the content of the inorganic filler is 50% by mass or more relative to 100% by mass of the total solid content of the curable composition.

[0012] [4] A fourth aspect of the present invention is the cured product of any one of the first to third aspects, wherein the inorganic filler comprises agglomerated particles of boron nitride. [5] A fifth aspect of the present invention is the cured product of any one of the first to fourth aspects, wherein the curable resin is an epoxy resin. [6] A sixth aspect of the present invention is the cured product of any one of the first to fifth aspects, wherein the curable resin is an epoxy resin having three or more oxirane rings (epoxy groups) in one molecule and having a mass average molecular weight of less than 5,000. [7] A seventh aspect of the present invention is the cured product of the sixth aspect, wherein the epoxy resin having three or more oxirane rings (epoxy groups) in one molecule and having a mass average molecular weight of less than 5,000 is an epoxy resin having four or more oxirane rings (epoxy groups) in one molecule.

[0013] [8] An eighth aspect of the present invention is the cured product of any one of the first to seventh aspects, wherein the curable resin is a high molecular weight epoxy resin having a mass average molecular weight of 5,000 or more. [9] A ninth aspect of the present invention is the cured product of any one of the first to eighth aspects, wherein the curable resins include an epoxy resin having three or more oxirane rings (epoxy groups) in one molecule and a mass-average molecular weight of less than 5,000, and a high-molecular-weight epoxy resin having a mass-average molecular weight of 5,000 or more, and the content of the epoxy resin having three or more oxirane rings (epoxy groups) in one molecule and a mass-average molecular weight of less than 5,000 in the curable composition is 40 parts by mass or more and 400 parts by mass or less per 100 parts by mass of the high-molecular-weight epoxy resin having a mass-average molecular weight of 5,000 or more in the curable composition.

[10] A tenth aspect of the present invention is the cured product of any one of the first to ninth aspects, wherein the curable composition further comprises a curing agent, and the curing agent comprises a phenolic resin.

[0014]

[11] An eleventh aspect of the present invention is a composite molded article having a cured product part made of the cured product of any one of the first to tenth aspects and a metal part.

[12] A twelfth aspect of the present invention is a semiconductor device having the composite compact of the eleventh aspect.

[0015]

[13] A thirteenth aspect of the present invention is a method for producing a composite molded product, which comprises laminating a metal plate and a circuit board via the cured product of any one of the first to tenth aspects to produce a laminate, and then bonding another member to the laminate by a reflow process. [Effects of the Invention]

[0016] The cured product proposed by the present invention maintains its thermal conductivity and electrical insulation properties, and does not peel even when thermal expansion and contraction occur due to repeated temperature changes during the reflow process. In other words, it has excellent solder reflow resistance. Therefore, the cured product proposed by the present invention can be suitably mounted on a circuit board or the like by the reflow process. For example, a composite molded product can be suitably produced by laminating a metal plate and a circuit board via a heat dissipation sheet made of the cured product proposed by the present invention to form a laminate, and then joining other components to the laminate by the reflow process. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a diagram showing a procedure for measuring free volume by positron annihilation method, which was carried out in an example of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] An example of an embodiment of the present invention will be described below, but the present invention is not limited to the embodiment described below.

[0019] <Cured product of the present invention> A cured product according to one embodiment of the present invention (also referred to as the "cured product of the present invention") is a cured product of a curable composition containing a curable resin and an inorganic filler (also referred to as the "curable composition of the present invention").

[0020] Here, the "curable composition" means a composition containing a compound or resin that has the property of being cured by heat, light, etc. That is, it is sufficient as long as the composition has the property of being cured by heat, light, etc., and may be one that has already been cured to a state where there is still room for curing (also referred to as "pre-cured"), or one that has not yet been cured at all (referred to as "uncured"). The curable composition may be in any form, such as powder, slurry, liquid, or solid, or may be in the form of a molded product such as a sheet. Therefore, the present curable composition also includes, for example, a slurry curable composition to be subjected to the coating step described below, a sheet that has been subjected to the coating step, a sheet that has been subjected to steps such as coating and drying, and the like. The term "cured product" refers to a product obtained by curing a curable composition and containing a crosslinked structure.

[0021] For example, the present curable composition formed into a sheet can be cured to form a sheet-like cured product, i.e., the sheet-like cured product of the present invention. In this case, the curing increases the thermal conductivity and the insulating properties, so the sheet-like cured product of the present invention can be used as, for example, a heat dissipation sheet (thermally conductive sheet) or an insulating sheet.

[0022] (free volume) The cured product of the present invention has a free volume (V200) of 0.165 nm at 200°C as measured by positron annihilation. 3 Preferably, it is: The present inventors have found that there is a correlation between the free volume of a cured product of a curable composition containing a curable resin and an inorganic filler, measured at 200°C by positron annihilation method, and the solder reflow resistance of the cured product. Specifically, the free volume (V200) of the cured product measured at 200°C by positron annihilation method is 0.165 nm 3 We have successfully discovered that if the temperature is below this range, peeling will not occur even if thermal expansion and contraction occur due to repeated temperature changes during the reflow process. From this perspective, the free volume (V200) of the cured product of the present invention measured by positron annihilation at 200°C is 0.165 nm 3 Preferably, it is 0.160 nm or less, and more preferably, it is 0.160 nm or less. 3 More preferably, it is 0.155 nm or less. 3 Below, among them, 0.150 nm 3 It is particularly preferred that: The lower limit of the free volume (V200) of the cured product of the present invention as determined by positron annihilation at 200°C is not particularly limited, but from the viewpoint of toughness, it is probably 0.10 nm 3 The above is preferable.

[0023] From the same viewpoint as above, it is preferable that the ratio (V200 / V25) of the free volume (V25) measured by positron annihilation method at 25°C to the free volume (V200) measured by positron annihilation method at 200°C of the cured product of the present invention is 1.80 or less. We have successfully discovered that if the ratio (V200 / V25) of the free volume at 25°C (V25) to the free volume at 200°C (V200) is 1.80 or less, peeling will not occur even if thermal expansion and contraction occur due to repeated temperature changes during the reflow process. From this viewpoint, it is more preferable that the ratio (V200 / V25) of the free volume at 25°C (V25) to the free volume at 200°C (V200) in the cured product of the present invention is 1.75 or less, and even more preferably 1.70 or less, even more preferably 1.68 or less, and even more preferably 1.65 or less. In the cured product of the present invention, the lower limit of the ratio (V200 / V25) of the free volume at 25°C (V25) to the free volume at 200°C (V200) is not particularly limited, but is likely to be 1.0 or more from the viewpoint of expansion of the free volume due to thermal vibration.

[0024] On the other hand, in the cured product of the present invention, the free volume measured at 25°C by positron annihilation method shows no correlation with the solder reflow resistance. Therefore, in the cured product of the present invention, the free volume (V25) measured by the positron annihilation method at 25°C is not particularly limited, but from the viewpoint of hygroscopicity, it is preferably 0.10 nm 3 Preferably, it is 0.095 nm or less. 3 More preferably, it is 0.09 nm or less. 3 Below, among them, 0.085 nm 3 On the other hand, from the viewpoint of ease of handling, it is particularly preferable that the thickness is 0.05 nm or less. 3 It is preferable that the thickness is equal to or greater than 0.06 nm. 3 More preferably, it is 0.07 nm or more. 3 Above all, 0.08 nm 3 More preferably, the above is the case.

[0025] With regard to the cured product of the present invention, the free volume of the cured product measured at 200°C by positron annihilation method reflects the influence of crosslink density, and therefore can be adjusted by, for example, the composition, such as the molecular weight and structure of the curable resin contained in the curable composition, the amount of crosslinking groups in the curable composition, and the type and content of the curing agent, as well as production conditions, such as aging and curing conditions. On the other hand, the free volume of the cured product measured at 25°C by positron annihilation method can be adjusted by the composition, such as the molecular weight and structure of the curable resin contained in the curable composition, the amount of crosslinking groups in the curable composition, and the type and content of the curing agent, as well as by production conditions, such as aging and curing conditions. It should be noted that the factors of variation in the free volume of the cured product measured by positron annihilation method at either 25°C or 200°C are not limited to the above conditions.

[0026] <Composition of the cured product of the present invention> The cured product of the present invention is a cured product of the present curable composition containing an inorganic filler and a curable resin.

[0027] (inorganic filler) In the cured product of the present invention, the free volume measured by positron annihilation method is hardly affected by the type and content of the inorganic filler. Therefore, from the viewpoint of the effect on the free volume of the cured product of the present invention, the type and content of the inorganic filler (also referred to as the "present inorganic filler") in the cured product of the present invention and the present curable composition are not particularly limited.

[0028] From the viewpoint of thermal conductivity, the inorganic filler is preferably inorganic particles having a thermal conductivity of 10 W / m·K or more. Examples of such inorganic fillers include electrically insulating inorganic fillers made only of carbon, and inorganic fillers made of metal carbides or semi-metal carbides, metal oxides or semi-metal oxides, metal nitrides or semi-metal nitrides, etc. These inorganic fillers may be used alone or in combination of two or more.

[0029] An example of the electrically insulating inorganic filler made only of carbon is diamond (thermal conductivity: approximately 2000 W / m·K). Examples of the metal carbide or semi-metal carbide include silicon carbide (thermal conductivity: approximately 60 to 270 W / m·K), titanium carbide (thermal conductivity: approximately 21 W / m·K), and tungsten carbide (thermal conductivity: approximately 120 W / m·K). Examples of the metal oxide or semi-metal oxide include aluminum oxide (thermal conductivity: 29 W / m·K), magnesium oxide (thermal conductivity: approximately 40 W / m·K), zinc oxide (thermal conductivity: approximately 54 W / m·K), yttrium oxide (thermal conductivity: approximately 27 W / m·K), ytterbium oxide (thermal conductivity: approximately 38.5 W / m·K), beryllium oxide (thermal conductivity: approximately 250 W / m·K), and "sialon" (ceramics composed of silicon, aluminum, oxygen, and nitrogen, thermal conductivity: approximately 21 W / m·K). Examples of the metal nitride or semi-metal nitride include boron nitride (thermal conductivity in the plane direction of plate-like particles of hexagonal boron nitride (h-BN): approximately 200 to 500 W / m·K), aluminum nitride (thermal conductivity: approximately 160 to 285 W / m·K), and silicon nitride (thermal conductivity: approximately 30 to 80 W / m·K).

[0030] Increasing the content of the inorganic filler of the present invention can improve the insulating properties and thermal conductivity, so the content of the inorganic filler of the present invention is preferably 50% by mass or more, more preferably 55% by mass or more, and even more preferably 60% by mass or more, relative to 100% by mass of the cured product of the present invention. On the other hand, from the viewpoint of maintaining good handleability (brittleness), it is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less.

[0031] (Boron nitride agglomerated particles) Among the inorganic fillers described above, it is particularly preferable to use boron nitride agglomerated particles (also referred to as "BN") formed by agglomeration of primary particles of boron nitride, because they have excellent insulating properties, thermal conductivity, solid lubricity, chemical stability, and heat resistance.

[0032] The boron nitride agglomerated particles include those formed by agglomerating plate-like, scale-like or needle-like primary particles into a spherical shape. Here, "spherical" means that the aspect ratio (ratio of major axis to minor axis) is from 1 to 2, and preferably from 1 to 1.5. The aspect ratio of the boron nitride agglomerated particles is determined by randomly selecting 200 or more particles from an image taken with an SEM, determining the ratio of the major axis to the minor axis of each particle, and calculating the average value.

[0033] Examples of boron nitride agglomerated particles include those having a conventionally known form in which crystals of scale-like or needle-like primary particles grow radially from the center to the surface of the agglomerated particle, a spherical form in which plate-like primary particles are sintered and agglomerated, and a form having a house-of-card structure made of plate-like primary particles. Here, the "house of card structure" refers to a structure in which plate-like particles are layered in a complex manner without being oriented, as described in, for example, Ceramics 43 No. 2 (published by the Ceramic Society of Japan in 2008). More specifically, boron nitride agglomerated particles having a house of card structure are aggregates of boron nitride primary particles, and have a structure in which the flat surfaces and edge surfaces of the primary particles are in contact with each other.

[0034] The average particle size (D50) of the boron nitride agglomerated particles is not particularly limited, but is preferably 20 μm or more, more preferably 25 μm or more, even more preferably 30 μm or more, and most preferably 40 μm or more. On the other hand, the D50 of the boron nitride agglomerated particles is preferably 150 μm or less, more preferably 130 μm or less, even more preferably 100 μm or less, and particularly preferably 95 μm or less. When the D50 of the boron nitride agglomerated particles is at least the above lower limit, the thermal conductivity of the boron nitride agglomerated particles themselves is high. On the other hand, when the D50 is at most the above upper limit, the surface smoothness of the cured product of the present invention when made into a sheet-like cured product is improved, and contact between the sheet-like cured product and a substrate is improved, thereby improving thermal conductivity.

[0035] The maximum particle size of the boron nitride agglomerated particles is preferably 20 μm or more, more preferably 30 μm or more, and even more preferably 40 μm or more, while the upper limit of the maximum particle size is preferably 300 μm or less, more preferably 200 μm or less, even more preferably 100 μm or less, and even more preferably 90 μm or less. With regard to the particle size of the boron nitride agglomerated particles, by increasing the particle size, it is possible to reduce the number of heat transfer paths between the inorganic filler particles via the curable resin having low thermal conductivity, and therefore to reduce the increase in thermal resistance in the heat transfer paths in the thickness direction. From this viewpoint, it is preferable that the maximum particle size of the boron nitride agglomerated particles be in the above-mentioned range.

[0036] Here, the average particle size (D50) of the boron nitride agglomerated particles means the particle size at which the cumulative volume is 50% when a cumulative curve is drawn with the volume of the boron nitride agglomerated particles used for measurement set to 100%, and the maximum particle size means the maximum particle size when a cumulative curve is drawn in this manner. Wet measurement methods include a method in which a sample of boron nitride agglomerated particles dispersed in a pure water medium containing naphthalene sulfonate-formalin condensate as a dispersion stabilizer is measured using a laser diffraction / scattering particle size distribution analyzer, etc. Dry measurement methods include a method using the "MORPHOLOGI" manufactured by MALVERN. In order to measure the D50 or maximum particle size of the boron nitride agglomerated particles, the cured product is washed with an organic solvent or baked to remove the resin component and separate the filler, i.e., the cured product is subjected to a washing treatment or an ashing treatment, and the D50 or maximum particle size of the filler contained in the resulting residue can be measured by laser diffraction or morphologization, or the D50 or maximum particle size can be calculated by cross-sectional SEM observation of the cured product.

[0037] The boron nitride agglomerated particles may be combined with other inorganic fillers. In this case, the "other inorganic filler" preferably has a thermal conductivity of 10 W / m K or more, and examples thereof include particles of flaky boron nitride, aluminum oxide (alumina), aluminum nitride, silica, magnesium oxide, etc. Among these, from the viewpoints of packing ability, water resistance, and thermal conductivity, it is preferable to contain alumina particles, especially spherical alumina particles, together with the boron nitride agglomerated particles.

[0038] When the "other inorganic filler" is contained, the mass proportion of the boron nitride agglomerated particles in the cured product of the present invention, relative to the total inorganic filler content (100 mass%) in the cured product of the present invention (the present inorganic filler and other inorganic fillers), is preferably 50 mass% or more, more preferably 55 mass% or more, even more preferably 60 mass% or more, even more preferably 65 mass% or more, and even more preferably 70 mass% or more, from the viewpoint of increasing thermal conductivity. On the other hand, the upper limit may be 99 mass% or less, and is preferably 98 mass% or less, from the viewpoint of increasing thermal conductivity.

[0039] (curable resin) The curable resin in the cured product of the present invention (also referred to as the "curable resin") is a matrix resin, that is, a component that forms the continuous phase (matrix) of the cured product of the present invention. In the present invention, the term "resin" includes compounds, monomers, oligomers, and polymers regardless of molecular weight.

[0040] Regarding the cured product of the curable composition containing the curable resin and the inorganic filler, regardless of the type of curable resin, if the free volume (V200) measured by the positron annihilation method at 200°C is small, it is considered to have high heat resistance and to be difficult to move even at high temperatures. Therefore, regardless of the type of curable resin, 3 If the temperature is below this level, it can be assumed that peeling will not occur even if thermal expansion and contraction occur due to repeated temperature changes during the reflow process. On the other hand, the free volume (V200) of the cured product of the present invention can be adjusted by the type and amount of the curable resin, such as the number of functional groups in the curable resin and the amount of polymer. However, the free volume (V200) of the cured product of the present invention is affected not only by the composition but also by manufacturing conditions such as aging.

[0041] The curable resin may be any compound (including polymers) that has the property of being cured by heat, such as epoxy resin, cyanate resin, benzoxazine resin, unsaturated polyester resin, phenol resin, melamine resin, silicone resin, maleimide resin, acrylic resin, and methacrylic resin, and may be any one of these, or may contain two or more of these. However, among these, it is preferable to include an epoxy resin from the viewpoints of viscosity, heat resistance, moisture absorption, and ease of handling.

[0042] [Epoxy resin] The cured product of the present invention preferably contains an epoxy resin as the curable resin.

[0043] Of the curable resins contained in the cured product of the present invention, the epoxy resin preferably accounts for 30 to 100 mass%, more preferably 40 mass% or more, even more preferably 50 mass% or more, even more preferably 60 mass% or more, and even more preferably 70 mass% or more. The epoxy resin in this case also includes the epoxy polymer described below.

[0044] The epoxy resin as the present curable resin may be any compound having one or more oxirane rings (epoxy groups) in one molecule.

[0045] The oxirane ring (epoxy group) contained in the epoxy resin may be either an alicyclic epoxy group or a glycidyl group, but from the viewpoint of reaction rate or heat resistance, a glycidyl group is more preferable.

[0046] Examples of epoxy resins include epoxy group-containing silicon compounds, aliphatic epoxy resins, bisphenol A or F epoxy resins, novolac epoxy resins, aromatic epoxy resins, alicyclic epoxy resins, glycidyl ester epoxy resins, polyfunctional epoxy resins, and polymeric epoxy resins.

[0047] The epoxy resin may be an aromatic oxirane ring (epoxy group)-containing compound. Specific examples thereof include bisphenol-type epoxy resins obtained by glycidylating bisphenols such as bisphenol A, bisphenol F, bisphenol AD, bisphenol S, tetramethylbisphenol A, tetramethylbisphenol F, tetramethylbisphenol AD, tetramethylbisphenol S, and tetrafluorobisphenol A; biphenyl-type epoxy resins; epoxy resins obtained by glycidylating dihydric phenols such as dihydroxynaphthalene and 9,9-bis(4-hydroxyphenyl)fluorene; epoxy resins obtained by glycidylating trisphenols such as 1,1,1-tris(4-hydroxyphenyl)methane; epoxy resins obtained by glycidylating tetrakisphenols such as 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane; novolac-type epoxy resins obtained by glycidylating 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. Among these, it is preferable to use an epoxy resin having at least one structure selected from the group consisting of an epoxy resin having a biphenyl skeleton, an epoxy resin having a dicyclopentadiene skeleton, and an epoxy resin having a naphthalene skeleton.

[0048] [Multifunctional epoxy resin] The cured product of the present invention preferably contains, as the present curable resin, a polyfunctional epoxy resin as described below.

[0049] A multifunctional epoxy resin is an epoxy resin that has three or more oxirane rings (epoxy groups) in one molecule and has a mass average molecular weight of less than 5,000. The inclusion of such a polyfunctional epoxy resin makes it possible to introduce highly polar oxirane rings (epoxy groups) at a high density, thereby enhancing the effects of physical interactions such as van der Waals forces and hydrogen bonds, and improving the adhesion between the cured product of the present invention and a conductor, for example. Furthermore, the inclusion of a polyfunctional epoxy resin makes it possible to increase the storage modulus of the cured product of the present invention, thereby exerting a strong anchoring effect after the cured product of the present invention penetrates into the irregularities on the surface of the conductor as an adherend, thereby improving the adhesion between the cured product of the present invention and the conductor. Furthermore, by preparing the present curable composition by combining an epoxy polymer and a polyfunctional epoxy resin, which will be described later, it is possible to improve the handleability of the cured product of the present invention while also increasing its elasticity.

[0050] The multifunctional epoxy resin may be an epoxy resin having three or more oxirane rings (epoxy groups) per molecule to increase the storage modulus of the cured product of the present invention, particularly at high temperatures, which is important for applications such as power semiconductors that generate a large amount of heat. Among these, an epoxy resin having four or more oxirane rings (epoxy groups) per molecule is preferred to reduce the free volume of the cured product of the present invention. Having multiple oxirane rings (epoxy groups), particularly glycidyl groups, per molecule improves the crosslink density of the cured product of the present invention, reduces the free volume of the cured product of the present invention, and increases its strength. This prevents the cured product of the present invention from deforming or breaking when internal stress is generated in the cured product during the reflow process, thereby maintaining its shape and preventing the formation of voids or other voids within the cured product of the present invention.

[0051] Furthermore, from the viewpoint of adjusting the flexibility of the cured product of the present invention, the molecular weight of the polyfunctional epoxy resin, particularly a polyfunctional epoxy resin having three or more epoxy groups in one molecule, is preferably 800 or less, more preferably 700 or less, even more preferably 650 or less, particularly preferably 100 or more or 630 or less, even more preferably 200 or more or 600 or less. Furthermore, to improve the handleability of the cured product of the present invention, it is preferable to include one that is liquid at 25°C. Furthermore, from the viewpoint of achieving higher crosslinking, it is preferable that the resin does not contain an amine-based or amide-based structure containing a nitrogen atom.

[0052] The epoxy equivalent of a polyfunctional epoxy resin, particularly one having three or more epoxy groups in one molecule, is preferably 50 g / equivalent or more, more preferably 75 g / equivalent or more, while from the viewpoint of further reducing the free volume of the cured product of the present invention, it is preferably 200 g / equivalent or less, more preferably 180 g / equivalent or less, more preferably 160 g / equivalent or less, and even more preferably 150 g / equivalent or less.

[0053] Examples of polyfunctional epoxy resins that can be used include EX321L, DLC301, and DLC402 manufactured by Nagase ChemteX Corporation. The polyfunctional epoxy resin may be used alone or in combination of two or more kinds.

[0054] [Epoxy polymer] From the viewpoint of ensuring film-forming properties, the cured product of the present invention preferably contains, as the curable resin, a high molecular weight epoxy resin (also referred to as "epoxy polymer") having a mass average molecular weight of 5,000 or more.

[0055] 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, an anthracene skeleton, a pyrene skeleton, a xanthene skeleton, an adamantane skeleton, and a dicyclopentadiene skeleton.

[0056] The weight average molecular weight of the epoxy polymer is preferably 5,000 or more, more preferably 10,000 or more, even more preferably 15,000 or more, even more preferably 20,000 or more, even more preferably 25,000 or more, and even more preferably 30,000 or more. The upper limit can be 100,000 or less. By keeping the weight average molecular weight within these ranges, the film-forming properties and handling properties of the curable composition tend to be improved. Furthermore, the improved film-forming properties of the curable composition have the effect of binding fillers together in the uncured stage, making it more difficult for voids to form in the cured product of the present invention.

[0057] The epoxy equivalent of the epoxy polymer is preferably 5,000 g / equivalent or more, more preferably 7,000 g / equivalent or more, and even more preferably 8,000 g / equivalent or more, from the viewpoints of ensuring film-forming ability and imparting flexibility, while it is preferably 25,000 g / equivalent or less, and even more preferably 20,000 g / equivalent or less, from the viewpoints of improving the solubility of the curable composition in solvents and reducing the free volume of the cured product of the present invention.

[0058] The mass average molecular weight is a value calculated as polystyrene measured by gel permeation chromatography. The epoxy equivalent is defined as "the mass of an epoxy resin containing one equivalent of epoxy groups" and can be measured in accordance with JIS K7236.

[0059] <Thickness> When the cured product of the present invention is in the form of a sheet, its thickness is preferably 80 μm or more, more preferably 100 μm or more, even more preferably 110 μm or more, and still more preferably 120 μm or more, while the upper limit of the thickness is preferably 300 μm or less, more preferably 250 μm or less, even more preferably 220 μm or less, even more preferably 200 μm or less, and still more preferably 180 μm or less. By making the thickness of the cured product of the present invention 80 μm or more, not only can high heat dissipation properties be ensured but also sufficient voltage resistance characteristics can be ensured, while by making the thickness 300 μm or less, it is possible to achieve a reduction in size or thickness of the composite molded body using the cured product of the present invention, and furthermore, compared to an insulating thermally conductive layer made of a ceramic material, it is possible to obtain the effect of reducing thermal resistance in the thickness direction due to the thinner film.

[0060] <Physical Properties of the Cured Product of the Present Invention> The cured product of the present invention may have the following physical properties.

[0061] (glass transition temperature (Tg)) From the viewpoint of stability in the operating temperature range of semiconductors, the glass transition temperature (Tg) of the cured product of the present invention is preferably 150° C. or higher, more preferably 160° C. or higher, and even more preferably 175° C. or higher. On the other hand, from the viewpoint of imparting flexibility to the film quality when an inorganic filler is incorporated, the glass transition temperature (Tg) is preferably 300° C. or lower, more preferably 280° C. or lower, even more preferably 260° C. or lower, even more preferably 250° C. or lower, and even more preferably 230° C. or lower.

[0062] The glass transition temperature (Tg) of the cured product of the present invention can be adjusted to fall within the above range by, for example, adjusting the type of curable resin, the type and content of inorganic filler, the method of mixing the curable resin and inorganic filler, and the conditions in the heat-kneading step described below, but is not limited to these methods.

[0063] (Storage modulus E' at 200°C) The storage modulus E' of the cured product of the present invention at 200°C is preferably 1 GPa or more and 100 GPa or less. When the storage modulus E' of the cured product at 200°C is within this range, the effect of improving durability can be obtained even in reliability tests. From this viewpoint, the storage modulus E' at 200°C of the cured product of the present invention is preferably 1 GPa or more, more preferably 2 GPa or more, even more preferably 3 GPa or more, even more preferably 4 GPa or more, even more preferably 5 GPa or more, even more preferably 6 GPa or more, while it is preferably 100 GPa or less, even more preferably 80 GPa or less, even more preferably 60 GPa or less, even more preferably 40 GPa or less, even more preferably 30 GPa or less.

[0064] The storage modulus E' at 200°C of the cured product of the present invention can be adjusted to fall within the above range by adjusting, for example, the type of curable resin, the type and content of the inorganic filler, the method of mixing the curable resin and the inorganic filler, the conditions in the heat-kneading step described below, etc. However, the method is not limited to these.

[0065] (Young's modulus measured by three-point bending at 190°C) The cured product of the present invention preferably has a Young's modulus of 5.5 GPa or more as determined by three-point bending measurement at 190°C. If the Young's modulus of the cured product of the present invention obtained by three-point bending measurement at 190°C is 5.5 GPa or more, not only will the cured product of the present invention be less likely to crack when bent, but it will also be possible to prevent cracks from occurring in the cured product of the present invention and separation of the bond even when the cured product is bonded to a substrate, for example, by sinter bonding, under high-temperature conditions of 150°C or more. From this perspective, the cured product of the present invention preferably has a Young's modulus of 5.5 GPa or more as measured by three-point bending at 190°C, and more preferably 5.6 GPa or more, more preferably 5.7 GPa or more, even more preferably 5.8 GPa or more, even more preferably 5.9 GPa or more, and even more preferably 6.0 GPa or more. The upper limit is not particularly limited, but is estimated to be around 100 GPa.

[0066] The Young's modulus of the cured product of the present invention measured by three-point bending at 90°C can be adjusted to fall within the above range by adjusting, for example, the type of curable resin, the type and content of the inorganic filler, the method of mixing the curable resin and the inorganic filler, the conditions in the heat-kneading step described below, etc. However, the method is not limited to these.

[0067] (thermal conductivity) The cured product of the present invention preferably has a thermal conductivity in the thickness direction at 25°C of 14 W / m·K or more. If the thermal conductivity of the cured product of the present invention in the thickness direction at 25°C is 14 W / m·K or more, it can also be suitably used in power semiconductor devices that operate at high temperatures. From this perspective, the cured product of the present invention preferably has a thermal conductivity in the thickness direction at 25°C of 14 W / m·K or more, and more preferably 15 W / m·K or more.

[0068] The thermal conductivity of the cured product of the present invention can be adjusted to fall within the above range by adjusting, for example, the type of curable resin, the type and content of the inorganic filler, the method of mixing the curable resin and the inorganic filler, the conditions in the heat-kneading step described below, etc. However, the method is not limited to these. For the thermal conductivity in the thickness direction of the cured product of the present invention, please refer to the method in the examples described below.

[0069] (Breakdown voltage (BDV)) The cured product of the present invention preferably has a breakdown voltage of 6.5 kV or more when the thickness is 150 μm. If the dielectric breakdown voltage of the cured product of the present invention is 6.5 kV or more, it can be suitably used in power semiconductor devices that operate at high voltages. From this viewpoint, the cured product of the present invention preferably has a breakdown voltage of 6.5 kV or more, more preferably 7 kV or more, even more preferably 7.5 kV or more, and even more preferably 8 kV or more.

[0070] The dielectric breakdown voltage of the cured product of the present invention can be adjusted to fall within the above range by adjusting, for example, the type of curable resin, the type and content of the inorganic filler, the method of mixing the curable resin and the inorganic filler, the conditions in the heat-kneading step described below, etc. However, the method is not limited to these. For the method of measuring the dielectric breakdown voltage of the cured product of the present invention, please refer to the method in the Examples described below.

[0071] <Method of producing the cured product of the present invention> As an example of the method for producing the cured product of the present invention, a method for producing a sheet-shaped cured product (also referred to as a "sheet-shaped cured product") will be described. However, the cured product of the present invention is not limited to a sheet shape.

[0072] First, a curable composition containing the curable resin and the inorganic filler is prepared ("curable composition preparation step"). The prepared curable composition is then formed into a coating or sheet ("sheet forming step") and heated to remove the solvent ("solvent removal step"). Next, after low-temperature aging in a temperature environment of 0°C or below ("low-temperature aging step"), pressure is applied at a predetermined temperature as needed ("heat and pressure step"), and the resulting sheet-like curable composition is cured to produce a sheet-like cured product of the present invention ("curing step"). However, the method for producing the cured product of the present invention is not limited to this production method.

[0073] (This curable composition) The present curable composition may further contain other resin components as needed, in addition to the present curable resin and the present inorganic filler described above. The "other resin components" may be compositions containing polymers, curing agents, curing accelerators, organic solvents, dispersants, surfactants, and other components, and these may be conventionally known compositions. For example, compositions described in WO 2021 / 085593 and WO 2023 / 189030 can be mentioned.

[0074] [Hardening agent] The present curable composition preferably contains a curing agent as needed. Examples of the curing agent include phenolic resins, compounds having a heterocyclic structure containing a nitrogen atom (referred to as "nitrogen-containing heterocyclic compounds"), acid anhydrides having an aromatic skeleton or an alicyclic skeleton, water additives of such acid anhydrides, and modified products of such acid anhydrides. The curing agent may be used alone or in combination of two or more kinds. By using these preferred curing agents, it is possible to obtain the cured product of the present invention that has an excellent balance of heat resistance, moisture resistance, and electrical properties.

[0075] In particular, when the curable composition uses the above-mentioned epoxy resin as the curable resin, it is preferable to use a curing agent having an active group capable of reacting with an epoxy group in combination with the epoxy resin. For example, it is preferable to use at least one of a phenolic resin, a benzoxazine compound, a cyanate, and a maleimide in combination with the epoxy resin. Of these, it is particularly preferable to use a phenolic resin.

[0076] Furthermore, from the viewpoint of decreasing the free volume (V200) of the cured product of the present invention, in other words, from the viewpoint of increasing the crosslink density, a curing agent having a structure that does not have a branched portion hanging from the molecular chain is preferred. More specifically, a curing agent having a structure that does not have a branched portion hanging from the molecular chain means, for example, a curing agent having no allyl groups, and among these, a curing agent having a structure that does not have a saturated or unsaturated aliphatic group having 3 or more carbon atoms is preferred, and a curing agent having a structure that does not have a saturated or unsaturated aliphatic group having 2 or more carbon atoms is more preferred.

[0077] Examples of the phenolic resin include phenol novolac, o-cresol novolac, p-cresol novolac, t-butylphenol novolac, dicyclopentadiene cresol, polyparavinylphenol, bisphenol A novolac, xylylene-modified novolac, decalin-modified novolac, poly(di-o-hydroxyphenyl)methane, poly(di-m-hydroxyphenyl)methane, poly(di-p-hydroxyphenyl)methane, etc. Among these, novolac-type phenolic resins having a rigid main chain skeleton and phenolic resins having a triazine skeleton are preferred in order to further improve the flexibility of the curable composition and the cured product of the present invention and to improve the mechanical properties and heat resistance of the cured product of the present invention.

[0078] The benzoxazine compound is a compound that crosslinks and hardens when heated, and also functions as a curing agent for epoxy resins. Therefore, by using an epoxy resin and a benzoxazine compound in combination, hydroxyl groups generated when the benzoxazine compound crosslinks react with and bond to epoxy groups of the epoxy resin, so that the crosslinked structure of the epoxy resin and the crosslinked structure of the benzoxazine compound are combined to form a stronger crosslinked structure, thereby increasing the glass transition temperature (Tg) of the cured product of the present invention and improving heat resistance.

[0079] The benzoxazine compound preferably has a structure represented by the following formula (I) or (II).

[0080] TIFF2026021971000001.tif56149

[0081] TIFF2026021971000002.tif60149

[0082] In formula (I), a represents an integer of 0 to 3, preferably 0 or 1, and more preferably 0. R1 and R2 each independently represent a hydrogen atom or a monovalent organic group. Specific examples of R1 include a hydrogen atom, an alkyl group, an alkenyl group, a cycloalkyl group, an aryl group, an aralkyl group, an alkynyl group, etc. R1 may be substituted with any substituent. Specific examples of R2 include an aliphatic hydrocarbon group and an aromatic hydrocarbon group. * indicates a bond to another chemical structure.

[0083] In formula (II), b represents an integer of 0 to 4, preferably 0 or 1, and more preferably 0. R3 represents a hydrogen atom or a monovalent organic group, and when b is 2 or greater, multiple R3s may be the same or different. Specific examples of R3 include an aliphatic hydrocarbon group and an aromatic hydrocarbon group. * indicates a bond to another chemical structure.

[0084] The benzoxazine compound preferably has a plurality of structures represented by formula (I) and / or formula (II) in one molecule. More specifically, the benzoxazine compound preferably has 2 to 4, more preferably 2, structures represented by formula (I) and / or formula (II) in one molecule. It is believed that the use of such a compound can further enhance curing performance and also improve heat resistance.

[0085] The benzoxazine compound preferably includes a benzoxazine compound represented by formula (III): The benzoxazine compound represented by formula (III) is often also called a Pd-type benzoxazine.

[0086] TIFF2026021971000003.tif60149

[0087] In formula (III), X 2 is a single bond or a divalent linking group. More specifically, X 2can be a single bond, a linear or branched alkylene group having 1 to 10 carbon atoms, -O-, -SO2-, -CO-, or a structure in which two or more of these are linked together.

[0088] The benzoxazine compound may include a benzoxazine compound represented by formula (IV): Incidentally, the benzoxazine compound represented by formula (IV) is often also called Fa-type benzoxazine. In formula (IV), X 2 The definition and specific examples of X in formula (III) 2 is the same as:

[0089] TIFF2026021971000004.tif64149

[0090] Among benzoxazine compounds, there are those that are solid and those that are liquid at 25°C. From the viewpoint of increasing the glass transition temperature (Tg) of the present curable composition and the cured product thereof and thereby improving the heat resistance, those that are solid at 25°C are more preferred.

[0091] The content of the benzoxazine compound in the present curable composition is preferably 3% by mass or more and 50% by mass or less, more preferably 5% by mass or more or 30% by mass or less, and even more preferably 7% by mass or more or 25% by mass or less, relative to 100% by mass of the solid content of the present curable composition excluding the inorganic filler.

[0092] If the proportion of the benzoxazine compound is high, the film may become brittle when formed, possibly resulting in reduced film-forming properties, and therefore the content of the benzoxazine compound in the curable composition is preferably lower than the content of the epoxy resin. In particular, the mass ratio of the content of the benzoxazine compound in the curable composition to the content of the epoxy resin in the solid content excluding the inorganic filler from the curable composition (benzoxazine compound / epoxy resin) is preferably less than 0.8, and more preferably 0.7 or less, even more preferably 0.6 or less, and even more preferably 0.5 or less. On the other hand, from the viewpoint of improving heat resistance, the mass ratio is preferably 0.05 or more, even more preferably 0.07 or more, and even more preferably 0.08 or more.

[0093] The cyanate may be, for example, a compound having an -OCN group in the molecule, which reacts with the -OCN group upon heating. Specific examples include 1,3-dicyanatobenzene, 1,4-dicyanatobenzene, 1,3,5-tricyanatobenzene, 1,3-dicyanatonaphthalene, 1,4-dicyanatonaphthalene, 1,6-dicyanatonaphthalene, 1,8-dicyanatonaphthalene, 2,6-dicyanatonaphthalene, 2,7-dicyanatonaphthalene, 1,3,6-tricyanatonaphthalene, 4,4'-dicyanatobiphenyl, bis(4-cyanatophenyl)methane, bis(3,5-dimethyl-4-cyanatophenyl)methane, and 2,2-bis(4-cyanatophenyl)propane. Examples of suitable cyanates include bis(4-cyanatophenyl)propane, 2,2-bis(3,5-dibromo-4-cyanatophenyl)propane, bis(4-cyanatophenyl)ether, bis(4-cyanatophenyl)thioether, bis(4-cyanatophenyl)sulfone, tris(4-cyanatophenyl)phosphite, tris(4-cyanatophenyl)phosphate, and cyanates obtained by reacting novolak resin with cyanogen halide. Prepolymers having a triazine ring formed by trimerizing the cyanate groups of these polyfunctional cyanates can also be used.

[0094] The maleimide may be a compound having one or more, preferably two or more, maleimide groups (2,5-dihydro-2,5-dioxo-1H-pyrrol-1-yl groups) in one molecule. Maleimides can react with epoxy resins in the presence of an appropriate catalyst to form bonds, and can also bond with other maleimides because radical polymerization can occur due to the ethylenic carbon-carbon unsaturated bond contained in the maleimide group. The maleimide may be, for example, an aliphatic maleimide containing an aliphatic amine skeleton, or an aromatic maleimide containing an aromatic amine skeleton.

[0095] The content of the curing agent in the present curable composition is preferably 1% by mass or more and 50% by mass or less, more preferably 3% by mass or more or 40% by mass or less, even more preferably 5% by mass or more or 30% by mass or less, and even more preferably 10% by mass or more or 25% by mass or less, based on 100% by mass of the solid content of the present curable composition excluding the inorganic filler. When the content of the curing agent is equal to or greater than the lower limit, sufficient curing performance can be obtained, and when the content is equal to or less than the upper limit, the reaction proceeds effectively, improving the crosslink density, increasing the strength, and further improving the film-forming properties.

[0096] [Curing accelerator] The present curable composition may contain a thermosetting catalyst as a curing accelerator, if necessary, in order to adjust the curing rate and the physical properties of the cured product.

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

[0098] Among these, compounds containing imidazole (referred to as "imidazole-based compounds") are preferred, particularly from the viewpoints of storage stability, heat resistance, and curing speed. Preferred imidazole compounds include, for example, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 2-phenyl-4-methylimidazole, 1-cyanoethyl-2-phenylimidazolium trimellitate, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine, 2, Examples include 4-diamino-6-[2'-undecylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-ethyl-4'methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanuric acid adduct, 2-phenylimidazole isocyanuric acid adduct, 2-phenyl-4,5-dihydroxymethylimidazole, and 2-phenyl-4-methyl-5-hydroxymethylimidazole. In particular, by using an imidazole compound having a melting point of 100° C. or higher, more preferably 200° C. or higher, a cured product of the present invention having excellent storage stability and adhesion can be obtained. Furthermore, from the viewpoint of adhesion, those containing a nitrogen-containing heterocyclic compound other than the above-mentioned imidazole ring are more preferred. The thermosetting catalyst may be used alone or in combination of two or more.

[0099] The content of the thermosetting catalyst in the curable composition is preferably 0.1% by mass or more and 10% by mass or less, and particularly preferably 0.1% by mass or more and 5% by mass or less, based on 100% by mass of the solid content of the curable composition excluding the inorganic filler. When the content of the thermosetting catalyst is equal to or greater than the lower limit, the progress of the curing reaction can be sufficiently promoted to achieve good curing, whereas when the content is equal to or less than the upper limit, the curing rate is not too fast, and therefore the storage stability of the curable composition can be improved.

[0100] [Other ingredients] The present curable composition may contain other components in addition to the above components. Examples of such other components include additives such as thermoplastic resins, organic fillers, inorganic fillers, and silane coupling agents that improve the interfacial adhesion strength between the inorganic filler and the resin component, additives that are expected to have the effect of increasing the adhesion strength between the cured product of the present invention and a metal plate, insulating carbon components such as reducing agents, viscosity modifiers, thixotropic agents, flame retardants, colorants, various antioxidants such as phosphorus-based and phenol-based, phenol acrylate-based and other process stabilizers, heat stabilizers, hindered amine radical scavengers (HAAS), impact modifiers, processing aids, metal deactivators, copper inhibitors, antistatic agents, extenders, etc. When these additives are used, the amount added may generally be within the range used for the purpose.

[0101] [WPE resin component] From the viewpoints of adjusting the free volume (V200) at 200°C of the present curable composition within a preferred range and adjusting the flexibility of the present curable composition to increase bending resistance, when adjusting the composition of the present curable composition, it is preferable that the epoxy equivalent (WPE) of the components remaining after excluding the solvent and inorganic filler from the present curable composition (referred to as the "resin component"), in other words, the solid content remaining after excluding the inorganic filler from the solid content of the present curable composition, is WPE ≦ 300 g / equivalent. From this viewpoint, the epoxy equivalent weight (WPE) of the resin component of the present curable composition is preferably 300 g / equivalent or less, more preferably 270 g / equivalent or less, of which 250 g / equivalent or less, of which 240 g / equivalent or less, of which 235 g / equivalent or less, and of which 230 g / equivalent or less is even more preferable. On the other hand, from the viewpoint of ensuring the toughness of the present curable composition, the epoxy equivalent (WPE) of the resin component of the present curable composition is preferably 100 g / equivalent or more, more preferably 110 g / equivalent or more, even more preferably 120 g / equivalent or more, even more preferably 150 g / equivalent or more, and even more preferably 180 g / equivalent or more. Furthermore, by adjusting the epoxy equivalent (WPE) of the resin component of the curable composition within the above range, the retention force of the inorganic filler can be adjusted, and the thermal conductivity of the cured product of the present invention can be improved.

[0102] To adjust the epoxy equivalent weight (WPE) of the resin component of the curable composition to fall within the above range, methods such as adjusting the content ratio of an epoxy resin having a predetermined epoxy equivalent weight, such as an epoxy polymer and a polyfunctional epoxy resin, can be used, but the method is not limited to these.

[0103] [Content ratio] The content of the present curable resin in the present curable composition is preferably 5% by mass or more and 100% by mass or less, relative to 100% by mass of the total solid content of the present curable composition excluding all inorganic fillers (the present inorganic filler and other inorganic fillers). If the content of the present curable resin in the present curable composition is 5% by mass or more, good moldability is achieved, which is preferable. On the other hand, if the content is 99% by mass or less, the contents of other components can be ensured, and thermal conductivity can be increased, which is preferable. From this viewpoint, the content of the curable resin in the curable composition is preferably 5% by mass or more, more preferably 10% by mass or more, more preferably 20% by mass or more, more preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more, relative to 100% by mass of the total solid content of the curable composition excluding all inorganic fillers, while the content is preferably 99% by mass or less, and even more preferably 98% by mass or less.

[0104] The "total solid content" in the present curable composition refers to all components excluding the solvent, that is, all inorganic fillers (the present inorganic filler and other inorganic fillers) and resin components. In this case, the "resin component" refers to the present curable resin and other organic components, and the "other organic components" include a curing agent, a curing accelerator, a dispersant, a viscosity modifier, and the like.

[0105] The content of the inorganic filler in the present curable composition is preferably 50% by mass or more relative to 100% by mass of the total solid content of the present curable composition. When the total content of the inorganic filler in the curable composition is 50% by mass or more, the thermal conductivity can be increased. On the other hand, although there is no upper limit, when the content is 95% by mass or less, the adhesion and insulating properties can be increased. From this viewpoint, the total content of the inorganic filler in the curable composition is preferably 50% by mass or more, more preferably 55% by mass or more, and even more preferably 60% by mass or more, relative to 100% by mass of the total solid content of the curable composition, and is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less.

[0106] When the present curable composition contains an epoxy resin as the present curable resin and boron nitride agglomerated particles as the present inorganic filler, the content of the boron nitride agglomerated particles in the present curable composition is preferably 50% by mass or more and 95% by mass or less, more preferably 55% by mass or more or 90% by mass or less, and even more preferably 60% by mass or more or 85% by mass or less, relative to 100% by mass of the total solid content of the present curable composition. Furthermore, the content of the epoxy resin in the present curable composition is preferably 30% by mass or more and 100% by mass or less, and more preferably 40% by mass or more, more preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, relative to 100% by mass of the total amount of the present curable resins in the present curable composition. The term "epoxy resin" as used herein includes epoxy resins, polyfunctional epoxy resins, and epoxy polymers.

[0107] When the present curable resin contains a polyfunctional epoxy resin having three or more oxirane rings (epoxy groups) in one molecule and a mass average molecular weight of less than 5,000, the content of the polyfunctional epoxy resin in the present curable composition is preferably 5% by mass or more and 80% by mass or less, relative to 100% by mass of the solid content in the present curable composition excluding the inorganic filler. When the content of the polyfunctional epoxy resin in the curable composition is 5% by mass or more, the curable composition can maintain its curability. On the other hand, when the content is 80% by mass or less, the curable composition can contain other components that maintain the film-forming properties of the curable composition and can suppress performance degradation due to moisture absorption. From this viewpoint, the content of the polyfunctional epoxy resin in the curable composition is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, relative to 100% by mass of the solid content of the curable composition excluding the inorganic filler, and is preferably 80% by mass or less, more preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less.

[0108] When the present curable resin contains an epoxy polymer having a mass average molecular weight of 5,000 or more, the content of the epoxy polymer in the present curable composition is preferably 5% by mass or more and 30% by mass or less, relative to 100% by mass of the solid content in the present curable composition excluding the inorganic filler. When the content of the epoxy polymer in the curable composition is 5% by mass or more, the film-forming properties of the curable composition can be maintained, while when the content is 30% by mass or less, the curability of the curable composition can be maintained. From this viewpoint, the content of the epoxy polymer in the curable composition is preferably 5% by mass or more, more preferably 6% by mass or more, and even more preferably 8% by mass or more, relative to 100% by mass of the solid content of the curable composition excluding the inorganic filler, and is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 21% by mass or less.

[0109] When the curable resin contains a polyfunctional epoxy resin having three or more oxirane rings (epoxy groups) in one molecule and a mass-average molecular weight of less than 5,000, and an epoxy polymer having a mass-average molecular weight of 5,000 or more, from the viewpoint of the balance between the curability, film-forming ability, and water absorption of the curable composition, the content of the polyfunctional epoxy resin in the curable composition is preferably 40 parts by mass or more and 400 parts by mass or less, more preferably 50 parts by mass or more or 300 parts by mass or less, more preferably 70 parts by mass or more or 250 parts by mass or less, more preferably 80 parts by mass or more or 280 parts by mass or less, and even more preferably 85 parts by mass or more or 260 parts by mass or less, per 100 parts by mass of the epoxy polymer in the curable composition.

[0110] (Main curable composition preparation process) The present curable composition is preferably prepared into a coating liquid by further adding an organic solvent.

[0111] Regarding the method for preparing the present curable composition, it is preferable to mix the raw materials uniformly by stirring or kneading. For this mixing, a general kneading device such as a mixer, kneader, three-roll mill, single-screw or twin-screw kneader, or planetary-rotating mixer can be used. During mixing, heating may be performed as necessary, and if heat is generated by stirring or kneading, cooling may be performed.

[0112] When an organic solvent is added to the present curable composition to prepare a fluid slurry-like coating liquid, it is preferable to mix and stir the coating liquid using a general kneading device such as a paint shaker, a bead mill, a planetary mixer, an agitation disperser, a planetary stirring mixer, a rotary homogenizer, a three-roll mill, a kneader, or a single-screw or twin-screw kneader, for the purpose of improving the uniformity of the coating liquid, degassing, etc. As the organic solvent, any known solvent capable of dissolving a resin can be used as appropriate. Examples include methyl ethyl ketone, acetone, cyclohexanone, toluene, xylene, monochlorobenzene, dichlorobenzene, trichlorobenzene, phenol, and hexafluoroisopropanol. These may be used alone or in combination of two or more. The organic solvent is usually used in an amount of 0 to 10,000 parts by mass relative to 100 parts by mass of the total solid content.

[0113] (Sheet forming process) The present curable composition prepared as described above may be applied to the surface of a substrate to form a sheet-like coating film, for example. In this case, the coating method may be a dipping method, a spin coating method, a spray coating method, a blade method, or any other method. The present curable composition can be applied using a coating device such as a spin coater, a slit coater, a die coater, a blade coater, a comma coater, screen printing, a doctor blade, an applicator, or a spray coater, which makes it possible to form a coating film of a predetermined thickness uniformly on a substrate, and a blade coater capable of adjusting the gap is preferred.

[0114] The present curable composition can be formed into a film on a known substrate such as a metal foil or plate (copper, aluminum, silver, gold), a resin film such as polyethylene terephthalate or polyethylene naphthalate, glass, etc. Depending on the form of use, these substrates can be peeled off before use, or may have a laminated structure such as substrate / present curable composition / substrate. The substrate is generally made of copper foil having a thickness as described below, but is not limited to a copper substrate. The substrate surface may be uneven or may have been subjected to a surface treatment. However, the present curable composition or the present cured product can also be prepared as a self-supporting film.

[0115] (Solvent removal process) Next, the present curable composition formed into a coating film or sheet is heated to 40° C. or higher and 140° C. or lower to remove the solvent. From the viewpoint of drying speed, the temperature at this time is preferably 40° C. or higher, more preferably 60° C. or higher, and even more preferably 80° C. or higher. On the other hand, from the viewpoint of suppressing the reaction of the curable resin, the temperature is preferably 140° C. or lower, more preferably 130° C. or lower, even more preferably 120° C. or lower, and even more preferably 100° C. or lower.

[0116] (Low temperature aging process) Next, the sheet-shaped curable composition thus formed is subjected to low-temperature aging by placing it in a temperature environment of 0°C or lower. By subjecting the sheet-shaped curable composition to such low-temperature aging, the free volume (V200) of the cured product of the present invention can be adjusted and stabilized within a desired range. Furthermore, low-temperature aging can freeze and disperse the moisture inside the sheet as tiny ice particles, creating small spaces of moisture that remain trapped in tiny spaces even after the temperature is returned to room temperature. This prevents the formation of large voids, preventing deterioration of insulation properties, and suppressing cracking when the sheet is bent.

[0117] The temperature in low-temperature aging is preferably lower because a faster cooling rate results in finer ice. From this perspective, a temperature of 0°C or lower is preferred, with -5°C or lower being particularly preferred, -10°C or lower being particularly preferred, and -15°C or lower being even more preferred. On the other hand, if the temperature is too low, the temperature will be below the glass transition temperature (Tg) of the uncured curable resin, making it prone to cracking, so a temperature of -50°C or higher is preferred, and when an epoxy resin is contained, a temperature of -30°C or higher is particularly preferred, with -25°C or higher being even more preferred.

[0118] The time for low-temperature aging is not particularly limited as long as the curable composition is frozen. It is sufficient to rapidly freeze and hold the composition for 10 minutes or more, preferably 30 minutes or more, and more preferably 1 hour or more, more preferably 2 hours or more, more preferably 4 hours or more, more preferably 8 hours or more, more preferably 16 hours or more, and more preferably 24 hours or more. On the other hand, since the reaction of epoxy resins proceeds gradually even at low temperatures, in order to avoid leaving the composition for a long period of time, the time for low-temperature aging is preferably 365 days or less, more preferably 180 days or less, more preferably 90 days or less, more preferably 30 days or less, and even more preferably 7 days or less.

[0119] It is not necessary to apply pressure during low-temperature aging, but a minute pressure of 0.1 kPa or less than atmospheric pressure may be applied.

[0120] (heating and pressurizing process) Next, a heating and pressurizing step is carried out as necessary. However, the heating and pressurizing step is not an essential step. For example, when there is a large amount of solvent or a large amount of inorganic filler, many holes may remain where the solvent has escaped, so in such cases it is preferable to carry out the heating and pressurizing step. By carrying out the heating and pressurizing step, voids (particularly interconnected pores) inside the sheet can be reduced or made smaller. Examples of pressurizing methods include flat press, hydrostatic press, vacuum press, calendar press, belt press, and servo press. However, the pressurizing method is not limited to these methods.

[0121] The heating temperature in the heating and pressurizing step is preferably a temperature at which the curable resin does not cure. For example, when an epoxy resin is used as the curable resin, the heating temperature is preferably less than 140°C, and from the viewpoint of suppressing the reaction of the epoxy resin, it is more preferably 100°C or less, and even more preferably 80°C or less. On the other hand, from the viewpoint of the elastic modulus of the curable composition, it is more preferably 0°C or more, and 20°C or more, and of these, it is even more preferably 40°C or more. For example, when the heating and pressurizing step is carried out using a platen press, the temperature of the platen used for pressing may be adjusted to fall within the above temperature range.

[0122] In the heating and pressing step, for example, in the case of flat pressing, the pressure applied to the sheet (also referred to as "hot press load") is preferably 1 MPa or more and 200 MPa or less, more preferably 5 MPa or more or 100 MPa or less, and even more preferably 7.5 MPa or more or 50 MPa or less. In this case, the pressing time (also referred to as "hot press pressing time") is preferably 1 second to 60 minutes, more preferably 10 seconds to 45 minutes, and even more preferably 30 seconds to 30 minutes.

[0123] In the case of the calendar press method, the linear pressure applied to the sheet is preferably 20 kgf / cm or more and 200 kgf / cm or less, more preferably 25 kgf / cm or more and 150 kgf / cm or less, and even more preferably 30 kgf / cm or more and 125 kgf / cm or less. A normal calendar roll machine with one (2) or more pairs of rollers through which the sheet passes can be used. Note that one (2) means one pair and two rollers. The pressing time is 10 seconds or less due to the characteristics of the calendar press method.

[0124] (hardening process) The sheet-shaped curable composition of the present invention obtained as described above can be cured by heating to form a sheet-shaped cured product of the present invention. In this case, the heating temperature is preferably 30 to 400° C., more preferably 50° C. or higher, and even more preferably 90° C. or higher. On the other hand, it is preferably 300° C. or lower, and even more preferably 250° C. or lower.

[0125] In particular, in the sheet forming process which involves a pressing step and a curing step, it is preferable to apply a load to carry out the pressing and curing.

[0126] The load to be applied when the pressing step and the curing step are performed simultaneously is not particularly limited. In this case, the sheet-shaped curable composition is preferably subjected to a load of 0.1 MPa or more, more preferably 1.0 MPa or more, even more preferably 5.0 MPa or more, and particularly preferably 10 MPa or more. The load is preferably 1000 MPa or less, more preferably 200 MPa or less. By setting the load when the pressurizing step and the curing step are carried out simultaneously to the above upper limit or less, the secondary particles of the boron nitride agglomerated particles are not destroyed, and a sheet-like cured product of the present invention having high thermal conductivity and no voids in the sheet can be obtained. Furthermore, by setting the load to the above lower limit or more, good contact between the inorganic fillers is achieved, making it easier to form thermal conduction paths, and a cured product of the present invention having high thermal conductivity can be obtained.

[0127] When the pressing step and the curing step are carried out simultaneously, the pressing time is not particularly limited. The pressing time is preferably 30 seconds or more, more preferably 1 minute or more, even more preferably 3 minutes or more, and particularly preferably 5 minutes or more. The pressing time is preferably 1 hour or less, more preferably 30 minutes or less, and even more preferably 20 minutes or less. By keeping the pressing time at or below the upper limit, the production time for the sheet-shaped cured product of the present invention can be reduced, which tends to reduce production costs.By keeping the pressing time at or above the lower limit, voids and gaps in the sheet-shaped cured product of the present invention can be sufficiently removed, which tends to improve heat transfer performance and voltage resistance characteristics.

[0128] <Use of the cured product of the present invention> One example of a form of use of the cured product of the present invention is a composite molded article having a cured product part made of the cured product of the present invention and a metal part. In particular, the cured product of the present invention can maintain thermal conductivity while preventing peeling from circuit boards and the like during the reflow process, and therefore can be suitably used for applications such as heat dissipating insulation materials used to insulate semiconductor circuit boards, heat dissipating insulation materials for attaching heat generating elements to heat sinks, and heat dissipating insulation materials used for heat dissipation in computers in data centers and the like. For example, a composite molded article can be produced by laminating a metal plate and a circuit board via the cured product of the present invention to form a laminate, and then bonding other members to the laminate by a reflow process.

[0129] More specifically, the cured product of the present invention can be used as a constituent material for, for example, a heat dissipation laminate (referred to as "the present heat dissipation laminate"), a heat dissipation circuit board (referred to as "the present heat dissipation circuit board"), a semiconductor device (referred to as "the present semiconductor device"), a power module (referred to as "the present power module"), etc. These are described below.

[0130] (The present heat dissipation laminate) An example of the present heat-dissipating laminate is one in which a heat-dissipating metal layer containing a heat-dissipating material is laminated on one surface of the cured product 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, in order to increase the thermal conductivity of the laminated structure, it is preferable to use a heat dissipating metal material, and it is more preferable to use a flat metal material. Alternatively, the cooler may be a flat metal with rod-shaped or plate-shaped fins attached to the bottom. The metal material is not particularly limited, but among them, copper plate, aluminum plate, aluminum alloy plate, etc. are preferred because they have good thermal conductivity and are relatively inexpensive. The cured product of the present invention can be laminated and integrated with a heat-dissipating metal layer by press molding, which is a batch process. In this case, the press equipment and press conditions are the same as those for obtaining the sheet-like curable composition of the present invention.

[0131] (This heat dissipating circuit board) An example of the heat-dissipating circuit board is one having a configuration in which the heat-dissipating metal layer is laminated on one surface of the cured product of the present invention, and a circuit board is formed on the surface opposite the heat-dissipating metal layer of the cured product of the present invention, for example, by etching. Specifically, an integrated structure of "heat-dissipating metal layer / cured product of the present invention / conductive circuit" is more preferable. The state before circuit etching can be, for example, an integrated structure of "heat-dissipating metal layer / cured product of the present invention / conductive circuit-forming metal layer," in which the conductive circuit-forming metal layer is flat and formed over the entire surface of one side of the cured product of the present invention, or formed over a partial area. The material of the conductive circuit-forming metal layer is not particularly limited, but in general, it is preferable to use a copper plate having a thickness of 0.05 mm to 5 mm from the viewpoints of good electrical conductivity, etching properties, cost, etc.

[0132] (This semiconductor device) An example of the present semiconductor device is one having a configuration in which a silicon wafer or a rewiring layer on which pre-diced semiconductor chips are mounted is formed on the present heat dissipation circuit substrate.

[0133] (This power module) An example of the power module is one in which the cured product of the present invention is mounted on a power semiconductor device as a heat dissipating circuit board. In this power semiconductor device, conventionally known materials can be used as appropriate for the components other than the cured product of the present invention, such as aluminum wiring, sealing material, packaging material, heat sink, thermal paste, solder, etc.

[0134] <Explanation of terms, etc.> In the present invention, the term "film" includes the term "sheet", and the term "sheet" includes the term "film".

[0135] In the present invention, when it is written "α to β" (α and β are arbitrary numbers), unless otherwise specified, it means "not less than α and not more than β", and also means "preferably greater than α" or "preferably smaller than β". Furthermore, when it is stated that "α or more" or "α≦" (α is any number), it also means "preferably greater than α" unless otherwise specified, and when it is stated that "β or less" or "≦β" (β is any number), it also means "preferably smaller than β" unless otherwise specified. [Example]

[0136] An example of an embodiment of the present invention will be described below, but the present invention is not limited to the embodiment described below.

[0137] <Ingredients> The raw materials used in the examples and comparative examples are as follows.

[0138] (inorganic filler) Inorganic filler 1: Spherical agglomerated boron nitride particles having a house-of-cards structure formed by agglomeration of plate-like primary particles, produced in accordance with the method for producing agglomerated boron nitride particles disclosed in the examples of WO 2015 / 561028. Maximum particle size: 90μm Average particle size (D50): 45μm

[0139] The maximum particle size and average particle size (D50) of the inorganic filler are determined by dispersing the inorganic filler in a pure water medium containing sodium hexametaphosphate as a dispersion stabilizer, measuring the volumetric particle size distribution using a laser diffraction / scattering particle size distribution analyzer LA-300 (manufactured by Horiba, Ltd.), and calculating the maximum particle size and the particle size at 50% of the cumulative volume (average particle size D50) from the obtained particle size distribution.

[0140] (epoxy resin) Epoxy resin 1: Biphenyl-type solid epoxy resin manufactured by Mitsubishi Chemical Corporation, with two glycidyl groups per molecule Molecular weight: approx. 400 Epoxy equivalent: 200g / equivalent Epoxy resin 2: Multifunctional epoxy resin containing a structure with four or more glycidyl groups per molecule, not containing amine or amide structures containing nitrogen atoms Molecular weight: approx. 400 Epoxy equivalent: 100g / equivalent Epoxy resin 3: Mitsubishi Chemical Corporation's liquid epoxy resin with a bisphenol A skeleton, containing two glycidyl groups per molecule Molecular weight: 372 Epoxy equivalent: 186g / equivalent Epoxy resin 4: A liquid epoxy resin with an aliphatic backbone manufactured by Mitsubishi Chemical Corporation, containing two glycidyl groups per molecule. Molecular weight: 310 Epoxy equivalent: 155g / equivalent

[0141] (hardening agent) Hardener 1: UBE H-4 phenolic resin hardener (phenol novolac resin) Hardener 2: Meiwa Kasei's "MEH-8000H", a phenolic resin hardener (allylphenol novolac resin)

[0142] (polymer) Epoxy polymer 1: a bifunctional epoxy polymer manufactured by Mitsubishi Chemical Corporation and disclosed as resin component 1 in JP 2020-63438 A Polystyrene equivalent weight average molecular weight: 30,000 Epoxy equivalent: 9,000g / equivalent

[0143] (Thermosetting catalyst) Thermosetting catalyst 1: 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-s-triazine, which contains both an imidazole-derived structure and a triazine-derived structure in a single molecule ("Curezol 2E4MZ-A" manufactured by Shikoku Chemical Industries, Ltd.) Heat curing catalyst 2: 2-phenyl-4,5-dihydroxymethylimidazole (Shikoku Chemical Industry Co., Ltd. "Curezol 2PHZ-PW")

[0144] <Example 1, Comparative Example 1> Each raw material was weighed out to obtain the composition (parts by mass) shown in Table 1, and mixed using a planetary centrifugal stirrer to obtain a mixture. When preparing this mixture, a slurry-like curable composition was prepared using 20% ​​by mass each of methyl ethyl ketone and cyclohexanone so that the mixture would constitute 60% by mass (solid content concentration) of the coating slurry.

[0145] The obtained curable composition in a slurry form was applied to a PET substrate by a doctor blade method, and then dried by heating at 60° C. for 120 minutes to obtain a sheet-like curable composition. The total content of methyl ethyl ketone and cyclohexanone in the sheet-like curable composition was 1% by mass or less, and the thickness of this sheet after pressing was 150 μm. Next, the sheet-shaped curable composition was placed in a vacuum pack bag, the air inside the bag was expelled, and the opening of the bag was heat-sealed to seal it.The bag was then stored in a freezer at −20° C. for 48 hours to perform low-temperature aging. Next, the mixture was pressed at 145 MPa at 40° C. for 15 minutes to obtain a sheet-like curable composition (sample).

[0146] <Measurement and evaluation> The curable compositions (samples) obtained in the examples and comparative examples were subjected to WPE measurement as follows. Furthermore, the cured products obtained by curing the curable compositions obtained in the Examples and Comparative Examples were measured for free volume, thermal conductivity, and breakdown voltage (BDV), and further subjected to a solder reflow resistance evaluation test, as described below. The results for each Example and Comparative Example are shown in Table 1. In Table 1, the numerical values ​​indicating the amount of each component in the composition indicate the mass proportion (parts by mass) of each component, and "WPE" is the epoxy equivalent (g / equivalent) of the resin component excluding the solvent and inorganic filler from the curable composition.

[0147] (Measurement of epoxy equivalent (WPE) of resin component) The resin components (components excluding solvent and inorganic filler) used in each of the Examples and Comparative Examples, i.e., epoxy resins 1, 2, 3, and 4, curing agents 1 and 2, epoxy polymer 1, and thermosetting catalysts 1 and 2, were mixed in the mass ratios shown in Table 1 below to obtain curable compositions. The epoxy equivalent weight (g / equivalent) was calculated by potentiometric titration and converted into the value of the entire resin components.

[0148] (Free volume measurement by positron annihilation lifetime spectroscopy) Multiple sheets of the sheet-like curable composition (sample) prepared in each Example and Comparative Example were stacked, and then heated and cured at 120°C for 40 minutes (product temperature) while applying a load of 10 MPa from above and below, to obtain a sheet-like cured product with a thickness of 1 mm to 1.5 mm. This cured product was then cut into a size of 2 cm x 2 cm to obtain a test piece. With the two test pieces prepared in this way, 22 The Na radiation source was sandwiched and wrapped in aluminum foil to prepare an evaluation sample. This evaluation sample was placed in the measurement device as shown in Figure 1. At this time, the detector was placed at a right angle, and the evaluation sample was placed facing in a direction at an angle of 45° to it.

[0149] The positron annihilation lifetime measurement was performed under the following conditions. Measuring device: DPALMS-LH (manufactured by Techno AP) Positron source: 22 Na source, thin film positron source (manufactured by Japan Radioisotope Association, a public interest incorporated association) Detector: BaF2 detector XBF251820 and XBF251810 Integration time: Gross count is 2 million or more Temperature control means: Nagase Techno Engineering Cryostat PS-HT-200 Vacuum system: Pfeiffer Vacuum HiCube 80 Eco Measurement atmosphere: vacuum Measurement temperature: 25℃, 200℃

[0150] After setting the temperature, measurements of the positron lifetime were started more than one hour after the temperature was reached. Measurements were made at 25°C and then at 200°C.

[0151] Data analysis was performed using PALSfit3. The decay curves of the positron annihilation lifetimes were analyzed using a three-component nonlinear least-squares method to determine the lifetimes and relative intensities of each component. A single Gaussian function was used as the resolution function. The number of lifetime components was set to three, and the lifetimes were designated τ1, τ2, and τ3 in ascending order of their values, and their relative intensities were designated I1, I2, and I3 in ascending order of their lifetime values. The relationship between the radius (R, nm) and the orthopositron lifetime (τ3, ns) is τ3=0.5[1-(R / R+ΔR)+(1 / (2π))sin(2πR / R+ΔR)]-1 Using this formula, R was calculated from the lifespan. ΔR is empirically determined, ΔR = 0.166 nm It was decided. (Nakanishi et al., Journal of Polymer Science, Part B: Polymer Physics, Vol. 27, p. 1419, John Wiley & Sons, Inc. (1989)) The free volume was assumed to be spherical, and the volume was calculated using V=(4πR^3) / 3.

[0152] (Measurement of thermal conductivity in the thickness direction of the cured product) The sheet-shaped curable compositions (samples) prepared in each of the Examples and Comparative Examples were heated and cured at 120°C (product temperature) for 40 minutes while being pressed under a load of 10 MPa, thereby obtaining sheet-shaped cured products (samples) with a thickness of 150 μm. Furthermore, four types of sheet-shaped curable compositions (samples) with different thicknesses were obtained by stacking two, three, or four sheets of each of the sheet-shaped curable compositions (samples) prepared in each of the Examples and Comparative Examples and applying pressure and heat in the same manner as above. The following measurements were carried out on these four types of sheet-shaped cured products (samples) with different thicknesses, and the thermal conductivity at 25°C in the sheet thickness direction using the steady-state method was measured from the slope represented by the thermal resistance value versus sheet thickness (in accordance with ASTM D5470). (1) Thickness: Thickness (μm) when pressed at a pressure of 3400 kPa using a Mentor Graphics T3Ster-DynTIM. (2) Measurement area: The area (cm) of the heat transfer part when measuring using a Mentor Graphics T3Ster-DynTIM. 2 ) (3) Thermal resistance: Thermal resistance (K / W) when pressed at a pressure of 3400 kPa using a Mentor Graphics T3Ster-DynTIM. (4) Thermal conductivity: The thermal resistance of four types of sheets with different thicknesses was measured, and the thermal conductivity (W / m·K) was calculated using the following formula. Formula: Thermal conductivity (W / m K) = 1 / ((Slope (thermal resistance value / thickness): K / (W μm)) × (area: cm 2 )) x 10 -2

[0153] (Measurement of BDV (breakdown voltage) of cured sheet material) The sheet-like curable composition (sample) prepared in each Example and Comparative Example was placed on a 2 mm thick copper plate, and heated at 175°C (product temperature) for 30 minutes while applying a load of 10 MPa to bond the composition by heat-pressure curing. A 150 μm thick sheet-like cured product was laminated on the copper plate to prepare a composite molded body (evaluation sample). The composite molding (evaluation sample) was immersed in insulating oil (Fluorinert FC-40 manufactured by 3M), and using an ultra-high voltage withstand voltage tester 7470 (manufactured by Keisoku Gijutsu Kenkyusho), electrodes were placed on the patterned copper with a diameter of 25 mm, and a voltage of 0.5 kV was applied. The voltage was increased by 500 V every minute, and the voltage until the sheet-like cured product was destroyed (BDV: dielectric breakdown voltage) was measured. Furthermore, the sheet-shaped curable composition after the bending resistance test was adhered to a copper plate by heat and pressure curing in the same manner as above, and the BDV of the composite molded product (BDV after bending test) was measured.

[0154] (Solder reflow resistance evaluation test) The sheet-like curable composition (sample) obtained in each of the Examples and Comparative Examples was sandwiched between two copper plates, each 500 μm thick and 2,000 μm thick, whose surfaces had been roughened in advance with a #120 file 100 times each. The plates were then pressurized at 120°C and 10 MPa for 30 minutes, then heated to 175°C and 10 MPa for 30 minutes, and then pressurized at 200°C and 10 MPa for 30 minutes to obtain a composite molded product for use in a solder reflow resistance evaluation test (reflow test). The composite molded body obtained above was etched by a predetermined method to pattern a copper plate with a thickness of 500 μm, so that two circular patterns with a diameter of 25 mm remained.

[0155] The composite molded body for the reflow test prepared as described above was stored in an SH-221 thermo-hygrostat (manufactured by Espec Corp.) at 85°C and 85% RH for three days. Within 30 minutes, the temperature was raised from room temperature to 290°C in 12 minutes under a nitrogen atmosphere, held at 290°C for 10 minutes, and then cooled to room temperature. The interface between the copper plate and the cured sheet was then observed using a FineSAT (FS300III) ultrasonic imaging system (manufactured by Hitachi Power Solutions). Measurements were performed using a 50 MHz probe with a gain of 30 dB and a pitch of 0.2 mm, with the sample placed in water. Evaluation was based on the following criteria.

[0156] =Criteria for Judgment= ◯ (pass): No interfacial peeling observed. × (fail): Peeling was observed at the interface.

[0157] [Table 1]

[0158] Even when the composition was changed, no difference was observed in the value of free volume (V25) measured by positron annihilation at 25°C, but a significant difference was observed in the value of free volume (V200) measured by positron annihilation at 200°C.

[0159] In Example 1, the free volume (V200) measured by positron annihilation at 200°C was sufficiently low, and no peeling was observed in the reflow test. In Example 1, a tetrafunctional epoxy resin was used as the multifunctional epoxy resin, a phenolic resin was used as the curing agent, and low-temperature aging was performed, which is presumably why the crosslink density increased, the free volume (V200) was sufficiently low, and the solder reflow resistance was good. In Comparative Example 1, the free volume (V200) measured by positron annihilation at 200°C was relatively large, and peeling was observed in the reflow test. In Comparative Example 1, since only a bifunctional epoxy resin was used as the multifunctional epoxy resin, the crosslink density was not increased, and the free volume (V200) became relatively large, which is presumably why the solder reflow resistance was poor.

[0160] From the above examples and the test results that the present inventors have conducted, it has been found that the free volume (V200) of the cured product of the curable composition containing the curable resin and the inorganic filler is 0.165 nm 3 It has been found that if the thickness is less than this, peeling does not occur during the reflow process. Similarly, it was found that peeling does not occur during the reflow process even when the ratio (V200 / V25) of the free volume (V25) measured by positron annihilation at 25°C to the free volume (V200) measured by positron annihilation at 200°C is 1.80 or less. It is presumed that if the free volume (V200) measured by positron annihilation at 200°C is small, the molecular chains will be less likely to move even at high temperatures, and even if thermal expansion and contraction occurs due to repeated temperature changes in the reflow process, peeling will not occur at the interface between the substrate and the cured product. Based on this mechanism, it can be assumed that the same effect can be obtained regardless of the type of curable resin or the type of inorganic filler.

Claims

1. A cured product of a curable composition containing an inorganic filler and a curable resin, having a free volume (V200) of 0.165 nm at 200°C as determined by positron annihilation method. ３ A cured product characterized by the following:

2. A cured product of a curable composition containing an inorganic filler and a curable resin, characterized in that the ratio (V200 / V25) of the free volume (V25) measured by a positron annihilation method at 25°C to the free volume (V200) measured by a positron annihilation method at 200°C is 1.80 or less.

3. The cured product according to claim 1 or 2, wherein the content of the inorganic filler is 50% by mass or more relative to 100% by mass of the total solid content of the curable composition.

4. The cured product according to claim 1 or 2, wherein the inorganic filler comprises agglomerated particles of boron nitride.

5. The cured product according to claim 1 or 2, wherein the curable resin is an epoxy resin.

6. 3. The cured product according to claim 1, wherein the curable resin comprises an epoxy resin having three or more oxirane rings (epoxy groups) in one molecule and a mass average molecular weight of less than 5,000.

7. 7. The cured product according to claim 6, wherein the epoxy resin having three or more oxirane rings (epoxy groups) in one molecule and a mass average molecular weight of less than 5,000 comprises an epoxy resin having four or more oxirane rings (epoxy groups) in one molecule.

8. The cured product according to claim 1 or 2, wherein the curable resin comprises a high-molecular-weight epoxy resin having a mass-average molecular weight of 5,000 or more.

9. The curable resin includes an epoxy resin having three or more oxirane rings (epoxy groups) in one molecule and a mass average molecular weight of less than 5,000, and a high molecular weight epoxy resin having a mass average molecular weight of 5,000 or more, 3. The cured product according to claim 1 or 2, wherein the content of the epoxy resin having three or more oxirane rings (epoxy groups) in one molecule and having a mass average molecular weight of less than 5,000 in the curable composition is 40 parts by mass or more and 400 parts by mass or less, relative to 100 parts by mass of the high molecular weight epoxy resin having a mass average molecular weight of 5,000 or more in the curable composition.

10. The cured product according to claim 1 or 2, wherein the curable composition further comprises a curing agent, and the curing agent comprises a phenolic resin.

11. A composite molded article having a cured product part made of the cured product according to claim 1 or 2 and a metal part.

12. A semiconductor device comprising the composite compact of claim 11.

13. A method for producing a composite molded product, comprising laminating a metal plate and a circuit board via the cured product according to claim 1 or 2 to produce a laminate, and then bonding another member to the laminate by a reflow process.

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