Cured product of a thermosetting composition, thermally conductive sheet, heat dissipation laminate, heat dissipation circuit board, power semiconductor device, and method for manufacturing a cured product of a thermosetting composition.

Abstract

The present invention provides a cured product of a thermosetting composition containing an inorganic filler and a thermosetting compound, which exhibits excellent high-temperature resistance, specifically, even after a reflow process, does not undergo interfacial delamination between the cured product and the metal, preventing the bonding from breaking or cracking in the cured product, and furthermore, can exhibit sufficient insulating performance. [Solution] A cured product of a thermosetting composition containing an inorganic filler and a thermosetting compound, wherein the inorganic filler contains boron nitride aggregate particles and the thermosetting compound contains an epoxy compound, and when the components contained in the cured product are separated into three components, a hard component, a middle component, and a soft component, based on the relaxation curve of the transverse magnetization of 1H obtained using pulsed NMR, the ratio (M(170°C) / M(30°C)) of the content of the middle component in the total content of the three components (hard component, middle component, and soft component) at 170°C to the content of the middle component in the total content of the three components (hard component, middle component, and soft component) at 30°C (M(30°C):(middle component / total of three components)×100) is 2.5 or more and 7.5 or less.

Description

[Technical Field]

[0001] The present invention relates to a cured product of a thermosetting composition, such as a heat sink for a power semiconductor device, and a method for producing the same, a thermally conductive sheet using the cured product, and a heat dissipation laminate, a heat dissipation circuit board, and a power semiconductor device using the thermally conductive sheet. [Background technology]

[0002] Among semiconductor-based devices, those that control or convert power, such as power supplies, are called "power semiconductor devices." Power semiconductor devices typically consist of power semiconductors that perform power conversion and control, along with electronic components, mounted on a substrate that functions as a heat sink. In recent years, power semiconductor devices used in various fields such as railways, automobiles, industrial applications, and general consumer electronics are shifting from conventional Si power semiconductors to power semiconductors using SiC, AlN, GaN, etc., in order to achieve further miniaturization, cost reduction, and increased efficiency.

[0003] While various challenges have been pointed out regarding the practical application of such power semiconductor devices, one of them is the problem of heat generation from the devices. Although high power output and density can be achieved by operating power semiconductor devices at high temperatures, there are concerns that the heat generated due to device switching and other processes will reduce the reliability of the power semiconductor devices.

[0004] In recent years, heat generation associated with the increasing density of integrated circuits has become a major problem in the electrical and electronic fields, making heat dissipation an urgent issue. For example, when ensuring the stable operation of power semiconductors used in the control of central processing units in personal computers and motors in electric vehicles, heat dissipation components such as heat sinks and heat sink fins are indispensable. Therefore, there is a need for components that can achieve both thermal conductivity and insulation when joining components such as circuits containing power semiconductors to heat dissipation components such as heat sinks.

[0005] Conventionally, highly thermally conductive ceramic substrates such as alumina substrates and aluminum nitride substrates have been used as materials that can achieve both thermal conductivity and insulation. However, ceramic substrates have had drawbacks, such as being prone to cracking under impact and being difficult to thin and miniaturize.

[0006] To address the challenges of ceramic substrates as described above, much research has been conducted on heat dissipation sheets that possess both good thermal conductivity and excellent insulating properties. In particular, attempts have been made to obtain heat dissipation resin sheets that satisfy high levels of both thermal conductivity and insulating properties by mixing fillers into the resin. Various oxides and nitrides have been used as fillers in such heat dissipation resin sheets, and much research has been conducted on them (see, for example, Patent Document 1).

[0007] Attempts have been made to use hexagonal boron nitride as a filler in heat-dissipating resin sheets. Hexagonal boron nitride generally exists as thin plate-like crystals, and while its thermal conductivity is high in the planar direction, its thermal conductivity is low in the thickness direction. Furthermore, when plate-like boron nitride is incorporated into a heat-dissipating resin sheet, it orients parallel to the sheet surface during sheet formation, resulting in poor thermal conductivity in the thickness direction of the sheet.

[0008] Boron nitride aggregates are cited as a material that increases the thermal conductivity in the thickness direction of a sheet. It is widely known that the use of boron nitride aggregates can improve the thermal conductivity in the thickness direction of a sheet. In particular, the present applicant has previously developed boron nitride aggregates with a cardhouse structure (see, for example, Patent Document 2). Furthermore, the applicant has developed boron nitride aggregated particles with a relatively large average particle size and a cardhouse structure that does not easily collapse even when pressure is applied (see, for example, Patent Document 3).

[0009] Since these boron nitride aggregated particles ensure a heat conduction path due to the card house structure, when incorporated into a heat-dissipating resin sheet, the sheet will have excellent heat conductivity in the thickness direction. Also, the boron nitride aggregated particles are formed by aggregation of boron nitride particles without using a separate binder. Therefore, even when an external force is applied during sheet formation, the card house structure does not easily collapse and maintains the heat conduction path, enabling heat dissipation in the thickness direction of the sheet and achieving excellent heat conductivity (see, for example, Patent Documents 4 and 5). Also, as a molding method for increasing the heat conductivity in the thickness direction of the sheet, a method of increasing the thermal conductivity by bringing the boron nitride aggregated particles in the sheet into surface contact with each other is known (see, for example, Patent Document 6).

[0010] The applicant of the present application has proposed a resin composition containing an inorganic filler and a thermosetting resin, wherein the inorganic filler content is 50% by volume or more of the solid content of the resin composition, and among the inorganic fillers, the boron nitride filler (A) is 82% by volume or more. The boron nitride filler contains aggregated fillers, the thermosetting resin contains an epoxy resin having a mass average molecular weight of 5000 or more, the epoxy equivalent (WPE) of the resin component in the resin composition is 100 ≤ WPE ≤ 300, and the storage elastic modulus E' of the cured product of the resin composition is 1 ≥ (E' at 270°C) / (E' at 30°C) ≥ 0.2 (Patent Document 7).

[0011] The applicant of the present application has also proposed a thermosetting resin composition containing a thermosetting resin, an inorganic filler, and a polymer having a mass average molecular weight of 10,000 or more, characterized in that the inorganic filler includes boron nitride aggregated particles and the thermosetting resin includes an epoxy compound and a benzoxazine compound, and a heat-conductive sheet formed from the thermosetting resin composition (Patent Document 8).

Prior Art Documents

Patent Documents

[0012]

Patent Document 1

[0013] One of the steps of assembling a power semiconductor device is the solder reflow process. In the solder reflow process, the members are rapidly heated to melt the solder and join the metal members together. In this reflow process, the members used in the power semiconductor device deteriorate. For example, problems have been that the reliability of the power semiconductor device decreases due to interface peeling between the cured product and the metal, resulting in peeling of the joint, cracking in the cured product, or a decrease in the insulation performance of the cured product. Therefore, it is required that the cured product of a thermosetting composition containing an inorganic filler and a thermosetting compound has excellent high-temperature resistance. Specifically, even after the reflow process, there is no interface peeling between the cured product and the metal, resulting in peeling of the joint, or cracking in the cured product, and furthermore, it has sufficient insulation performance.

[0014] Therefore, the object of the present invention is to provide a cured product of a thermosetting composition containing an inorganic filler and a thermosetting compound, which has excellent high-temperature resistance, specifically, even after a reflow process, does not undergo interfacial delamination between the cured product and the metal, preventing the bonding from peeling off or cracking in the cured product, and furthermore, can exhibit sufficient insulating performance, as well as a heat-conductive sheet made of the cured product, a heat-dissipating laminate equipped with the heat-conductive sheet, a heat-dissipating circuit board, and a power semiconductor device. [Means for solving the problem]

[0015] To solve the above problems, the present invention proposes a cured product of a thermosetting composition, a method for producing the same, a thermally conductive sheet, a heat dissipation laminate, a heat dissipation circuit board, and a power semiconductor device in the following embodiments.

[0016] [1] A first aspect of the present invention is a cured product of a thermosetting composition containing an inorganic filler and a thermosetting compound, wherein the inorganic filler contains boron nitride aggregate particles and the thermosetting compound contains an epoxy compound, and when the components contained in the cured product are separated into three components, a hard component, a middle component, and a soft component, based on the relaxation curve of the transverse magnetization of 1H obtained using pulsed NMR, the ratio (M(170°C) / M(30°C)) of the content of the middle component in the total content of the three components (hard component, middle component, and soft component) at 170°C to the content of the middle component in the total content of the three components (hard component, middle component, and soft component) at 30°C (M(30°C):(middle component / total of three components)×100) is 2.5 or more and 7.5 or less.

[0017] [2] A second aspect of the present invention is a cured product of a thermosetting composition in which, in the first aspect, the ratio of the content of the soft component in the total content of the three components (hard component / middle component / total of three components) at 170°C (S(170°C):(soft component / total of three components)×100) to the content of the soft component in the total content of the three components (hard component / middle component / total of three components) at 30°C (S(30°C):(soft component / total of three components)×100) is 1.38 or less (S(170°C) / S(30°C)).

[0018] [3] A third aspect of the present invention is a cured product of a thermosetting composition, in which, in the first or second aspect, the ratio (H(170°C) / H(30°C)) of the ratio of the hard component in the total content of the hard component, middle component and soft component at 170°C (H(170°C):(hard component / total of 3 components)×100) to the ratio of the hard component in the total content of the hard component, middle component and soft component at 30°C (H(30°C):(hard component / total of 3 components)×100) is 0.3 or more and 1.0 or less.

[0019] [4] A fourth aspect of the present invention is a cured product of a thermosetting composition in which, in any one of the first to third aspects, the content ratio of the hard component in the total content of the three components (H(30°C):(hard component / total of three components)×100) at 30°C is 90.0% or less. [5] A fifth aspect of the present invention is a cured product of a thermosetting composition in any one of the first to fourth aspects, wherein the content ratio of the soft component in the total content of the three components (S(30°C):(soft component / total of three components)×100) at 30°C is 2.4% or more and 10.0% or less. [6] A sixth aspect of the present invention is a cured product of a thermosetting composition, in any one of the first to fifth aspects, wherein the content ratio of the hard component in the total content of the three components (H(170°C): (hard component / total of three components) × 100) at 170°C is 30% or more and 70% or less, and the content ratio of the middle component in the total content of the three components (hard component, middle component, and soft component) at 170°C (M(170°C): (middle component / total of three components) × 100) is 30% or more and 70% or less.

[0020] [7] A seventh aspect of the present invention is a cured product of a thermosetting composition, wherein, in any one of the first to sixth aspects, the epoxy equivalent (WPE) of the solid content of the thermosetting composition excluding the inorganic filler is 120 g / equivalent or more and 400 g / equivalent or less. [8] An eighth aspect of the present invention is a cured product of a thermosetting composition, in any one of the first to seventh aspects, wherein the thermosetting composition comprises a polyfunctional epoxy compound having three or more epoxy groups in one molecule and a mass-average molecular weight (Mw) of less than 5,000, and a high molecular weight epoxy compound having a mass-average molecular weight (Mw) of 5,000 or more.

[0021] [9] The ninth aspect of the present invention is a cured product of a thermosetting composition, in any one of the first to eight embodiments, wherein the thermosetting composition further comprises at least one of a phenol resin, a benzoxazine compound, a polyarylate, a cyanate, and a maleimide.

[10] A tenth aspect of the present invention is a cured product of a thermosetting composition, wherein the thermosetting composition further comprises a benzoxazine compound, in any one of the first to eight embodiments described above.

[0022]

[11] An eleventh aspect of the present invention is a cured product of a thermosetting composition, wherein, in any one of the first to ten aspects, the boron nitride aggregated particles include those having a cardhouse structure.

[0023]

[12] A twelfth aspect of the present invention is a thermally conductive sheet made of a cured product of any one of the first to eleven aspects of the present invention.

[13] A thirteenth aspect of the present invention is a heat dissipation laminate comprising the thermally conductive sheet of the twelfth aspect.

[14] A fourteenth aspect of the present invention is a heat-dissipating circuit board equipped with the thermally conductive sheet of the twelfth aspect.

[15] A fifteenth aspect of the present invention is a power semiconductor device comprising the thermally conductive sheet of the twelfth aspect.

[0024]

[16] The sixteenth aspect of the present invention is a method for producing a cured product of a thermosetting composition according to any one of the first to eleven aspects, characterized in that a thermosetting composition containing an inorganic filler and a thermosetting compound is subjected to low-temperature aging in a temperature environment of 0°C or lower, pressurized, and cured. [Effects of the Invention]

[0025] The cured product of the thermosetting composition proposed in this invention exhibits excellent high-temperature resistance. Specifically, even after the reflow process, the interfacial delamination between the cured product and the metal does not occur, preventing the bond from breaking or cracking in the cured product. Furthermore, it can exhibit sufficient insulating performance. The cured product of the thermosetting composition proposed in this invention exhibits excellent high-temperature resistance. Therefore, even when bonded to a substrate by a reflow process, for example, it can ensure excellent electrical conductivity and continuous bonding stability. Thus, it is possible to provide a thermally conductive sheet that can be suitably used in heat dissipation laminates, heat dissipation circuit boards, and power semiconductor devices. [Modes for carrying out the invention]

[0026] An example of an embodiment of the present invention will be described in detail below. However, the present invention is not limited to the following embodiment and can be implemented in various ways within the scope of its gist.

[0027] <<Cured product of the present invention>> A cured product of a thermosetting composition according to an example of an embodiment of the present invention (referred to as "the cured product of the present invention") is a cured product of a thermosetting composition containing an inorganic filler and a thermosetting compound (referred to as "the composition of the present invention").

[0028] In the present invention, "thermosetting composition" means a composition containing a compound or resin that has the property of hardening with heat. That is, it is sufficient if it is a composition that has curability that leaves room for further hardening with heat, and it may be a composition that has already hardened to a state where there is room for further hardening (referred to as "partially hardened") or a composition that has not yet hardened at all (referred to as "unhardened"). In this invention, "resin" includes compounds, monomers, oligomers, and polymers, regardless of their molecular weight. Furthermore, a sheet-like cured product of the present invention, in other words, a sheet-like cured product obtained by curing the composition of the present invention, is referred to as the "sheet-like cured product of the present invention."

[0029] The composition of the present invention may be in the form of a powder, slurry, liquid, solid, or molded article formed into a sheet. Therefore, the composition of the present invention includes, for example, a slurry-like thermosetting composition used in the coating process described later, a sheet that has undergone the coating process, and a sheet that has undergone coating and drying processes.

[0030] The composition of the present invention can be cured by heating to produce a cured product of the present invention. Furthermore, by molding the composition of the present invention into a sheet, a sheet-like thermosetting composition (also referred to as the "thermosetting sheet of the present invention") can be obtained, and by curing the thermosetting sheet of the present invention, a sheet with thermal conductivity (also referred to as the "thermoconductive sheet of the present invention") can be obtained. In other words, the thermal conductive sheet of the present invention is both a cured sheet-like product of the present invention and a cured product of the thermosetting sheet of the present invention.

[0031] <Pulsed NMR Measurement> The cured product of the present invention can be characterized as follows using the results of pulsed NMR measurements.

[0032] (Method for separating the three components) Based on the relaxation curve of the transverse magnetization of 1H obtained using pulsed NMR, the components contained in the cured product of the present invention can be separated into three components: a hard component, a middle component, and a soft component. Component separation from the relaxation curve can be performed using the analysis software provided with the instrument; for example, it can be separated into three components using TD-NMRA. In the cured product of the present invention, the hard component can be considered to be the crystalline region and the region near the crosslinking point, including the crosslinking point. The middle component can be considered to be the molecular chain portion near the hard component that exists between the crosslinking points. The soft component can be considered to be the terminal molecular chains and the molecular chain portion where the distance between crosslinking points is long and loose. A higher number of crosslinking points increases the hard component. As the temperature rises, the molecular chains become more mobile, so it can be thought that the molecular chains of the hard component are incorporated into the middle component, increasing the proportion of the middle component.

[0033] (Middle component content ratio by temperature) When the components contained in the cured product of the present invention are separated into three components, a hard component, a middle component, and a soft component, based on the relaxation curve of the transverse magnetization of 1H obtained using pulsed NMR, It is preferable that the ratio of the middle component content in the total content of the three components (hard, middle, and soft) at 170°C (M(170°C):(middle component / total of three components)×100) to the ratio of the middle component content in the total content of the three components (hard, middle, and soft) at 30°C (M(30°C):(middle component / total of three components)×100), i.e., the temperature ratio of the middle component content (M(170°C) / M(30°C)), is between 2.5 and 7.5.

[0034] It was found that the cured product of the present invention exhibits better high-temperature resistance when the temperature ratio of the middle component content (M(170℃) / M(30℃)) is between 2.5 and 7.5. As the temperature rises, molecular chains become more mobile, so it can be thought that the molecular chains of the hard components are incorporated into the middle components, increasing the proportion of the middle components. More specifically, when the temperature ratio of the middle component content (M(170°C) / M(30°C)) is 7.5 or less, the variation in molecular weight between crosslinking points is reduced, and the crosslinking density is uniform. As a result, even when exposed to high temperatures, cracks will not form or the bonds will not delaminate, and the decrease in insulating properties will be suppressed. On the other hand, when the temperature ratio of the middle component content (M(170°C) / M(30°C)) is 2.5 or more, it is presumed that the stress is relieved in response to expansion at high temperatures, making it less likely for cracks to form or the bonds to delaminate. Because cracks and delamination are less likely to occur when exposed to high temperatures, the decrease in insulating properties will also be suppressed.

[0035] From this viewpoint, the cured product of the present invention preferably has a middle component content temperature ratio (M(170℃) / M(30℃)) of 2.5 or higher, more preferably 2.7 or higher, more preferably 2.8 or higher, and more preferably 3.0 or higher. On the other hand, it is preferably 7.5 or lower, more preferably 7.0 or lower, and more preferably 6.5 or lower.

[0036] To adjust the temperature ratio of the middle component content (M(170°C) / M(30°C)) of the cured product of the present invention to the above range, it is preferable to select the composition and adjust the composition ratio of, for example, a polyfunctional epoxy compound, a polymer having functional groups that contribute to the curing reaction, particularly a high molecular weight epoxy compound, and a curing agent, as well as to select the amount of thermosetting catalyst, curing conditions, and aging conditions. However, the present invention is not limited to such methods.

[0037] (Soft component content ratio by temperature) In the cured product of the present invention, when the temperature ratio of the middle component content (M(170°C) / M(30°C)) is within the above range, it is preferable that the ratio of the soft component content in the total content of the three components (hard component / middle component / total of three components) at 170°C (S(170°C):(soft component / total of three components)×100) to the soft component content in the total content of the three components (hard component / middle component / total of three components) at 30°C (S(30°C):(soft component / total of three components)×100), i.e., the temperature ratio of the soft component content (S(170°C) / S(30°C)) is 1.38 or less.

[0038] The cured product of the present invention is preferable if the temperature ratio of the soft component content (S(170℃) / S(30℃)) is 1.38 or less, because this suppresses the increased molecular motion at high temperatures, thereby further suppressing cracking and delamination of the joints. From this viewpoint, the cured product of the present invention is preferably such that the temperature ratio of the soft component content (S(170℃) / S(30℃)) is 1.38 or less, and more preferably such that it is 1.35 or less, 1.20 or less, 1.0 or less, and 0.9 or less. On the other hand, from the viewpoint of heat resistance, it is preferable that the temperature ratio of the soft component content (S(170℃) / S(30℃)) of the cured product of the present invention is 0 or greater.

[0039] To adjust the temperature ratio of the soft component content of the cured product of the present invention (S(170°C) / S(30°C)) to the above range, it is preferable to select the composition and adjust the composition ratio of, for example, a polyfunctional epoxy compound, a polymer having functional groups that contribute to the curing reaction, particularly a high molecular weight epoxy compound, and a curing agent, as well as to select the amount of thermosetting catalyst, curing conditions, and aging conditions. However, the method is not limited to this.

[0040] (Temperature ratio of hard component content) In the cured product of the present invention, when the temperature ratio of the middle component content (M(170°C) / M(30°C)) is within the above range, it is even more preferable that the ratio of the hard component content in the total content of the three components (hard component / total of three components) at 170°C (H(170°C):(hard component / total of three components)×100) to the hard component content in the total content of the three components (hard component / total of three components) at 30°C (H(30°C):(hard component / total of three components)×100), i.e., the temperature ratio of the hard component content (H(170°C) / H(30°C)) is 0.3 or more and 1.0 or less.

[0041] The cured product of the present invention is preferable if the temperature ratio of the hard component content (H(170℃) / H(30℃)) is 0.3 or higher, because this reduces the change in the crosslinking state at high temperatures and suppresses expansion and distortion. From this viewpoint, the temperature ratio of the hard component content (H(170℃) / H(30℃)) is preferably 0.3 or higher, more preferably 0.35 or higher, more preferably 0.4 or higher, and more preferably 0.5 or higher. On the other hand, if the temperature ratio of the hard component content (H(170°C) / H(30°C)) is 1.0 or less, stress is relieved against expansion at high temperatures, which is preferable. From this viewpoint, the temperature ratio of the hard component content (H(170°C) / H(30°C)) is preferably 1.0 or less, more preferably 0.9 or less, and even more preferably 0.8 or less.

[0042] In a particularly preferred form of the cured product of the present invention, if the temperature ratio of the middle component content (M(170°C) / M(30°C)) is 2.5 or more and 7.5 or less, and the temperature ratio of the hard component content (H(170°C) / H(30°C)) is 0.5 or more and 1.0 or less, the crosslinking density is sufficiently high and uniform, and even when external stress is applied at high temperatures, the stress is dispersed, preventing cracks from forming in the cured product or delamination from occurring at the interface and causing the bond to break. Therefore, it can be suitably applied to various processing in the high-temperature range of 150°C to 300°C, and for example, even when bonded to a substrate by sinter bonding, excellent electrical conductivity and continuous bonding stability can be ensured.

[0043] To adjust the temperature ratio of the hard component content of the cured product of the present invention (H(170°C) / H(30°C)) to the above range, it is preferable to select the composition and adjust the composition ratio of, for example, a polyfunctional epoxy compound, a polymer having functional groups that contribute to the curing reaction, particularly a high molecular weight epoxy compound, and a curing agent, as well as to select the amount of thermosetting catalyst, curing conditions, and aging conditions. However, the present invention is not limited to such methods.

[0044] (Percentage of hard, medium, and soft components at 30°C) In the cured product of the present invention, it is preferable that the content ratio of the hard component in the total content of the three components (hard component, middle component, and soft component) at 30°C (H(30°C):(hard component / total of 3 components)×100) is 90.0% or less. From the viewpoint of stress relaxation, it is preferable that the content of the hard component (H(30℃)) is 90.0% or less. From this viewpoint, it is preferable that the content of the hard component (H(30℃)) is 90.0% or less. On the other hand, it is preferable that the content of the hard component (H(30℃)) is 50.0% or more, and more preferably 60.0% or more, 70.0% or more, and 80.0% or more.

[0045] In the cured product of the present invention, it is preferable that the content ratio of the middle component in the total content of the three components (hard component, middle component, and soft component) at 30°C (M(30°C):(Middle component / total of 3 components)×100) is 5.0% or more and 30.0% or less. A content of the middle component (M(30°C)) of 5.0% or more is preferable from the viewpoint of stress relaxation. From this viewpoint, a content of the middle component (M(30°C)) of 5.0% or more is preferable, more preferably 5.5% or more, and more preferably 6.0% or more. On the other hand, a content of 30.0% or less is preferable because deformation is suppressed. From this viewpoint, a content of the middle component (M(30°C)) of 30.0% or less is preferable, and more preferably 25.0% or less.

[0046] In the cured product of the present invention, the content ratio of the soft component in the total content of the three components (hard component, middle component, and soft component) at 30°C (S(30°C):(soft component / total of 3 components)×100) is preferably 2.4% or more and 10.0% or less. A content of the soft component (S(30°C)) of 2.4% or more is preferable from the viewpoint of stress relaxation. From this viewpoint, a content of the soft component (S(30°C)) of 2.4% or more is preferable, more preferably 2.6% or more, and more preferably 2.8% or more. On the other hand, a content of 10.0% or less is preferable because it does not lower the elastic modulus and improves reliability. From this viewpoint, a content of the soft component (S(30°C)) of 10.0% or less is preferable, more preferably 8.0% or less, and more preferably 7.0% or less.

[0047] In the cured product of the present invention, to adjust the content ratio of the hard component (H(30°C)), the middle component (M(30°C)), and the soft component (S(30°C)) in the total content of the three components (hard component, middle component, and soft component) at 30°C to the above range, it is preferable to select the composition and adjust the composition ratio of, for example, a polyfunctional epoxy compound, a polymer having functional groups that contribute to the curing reaction, particularly a high molecular weight epoxy compound, and a curing agent, as well as to select the amount of thermosetting catalyst, curing conditions, and aging conditions. However, the present invention is not limited to such methods.

[0048] (Percentage of hard, medium, and soft components at 170°C) Preferably, the cured product of the present invention has a hard component content ratio (H(170°C): (hard component / total of 3 components) × 100) of 30% to 70% of the total content of the three components (hard component, middle component, and soft component) at 170°C, and a middle component content ratio (M(170°C): (middle component / total of 3 components) × 100) of 30% to 70% of the total content of the three components (hard component, middle component, and soft component) at 170°C.

[0049] A higher number of crosslinking points increases the amount of hard components. The proportion of hard components at high temperatures can be considered to reflect the amount of crosslinking points remaining at high temperatures. If the content of the hard component (H(170°C)) is 30% or more, the cross-linked state at high temperatures is maintained to the required extent, and expansion and strain are suppressed, which is preferable. From this viewpoint, it is preferable that the content of the hard component (H(170°C)) is 30% or more. On the other hand, if it is 70% or less, it is preferable from the viewpoint of stress relaxation. From this viewpoint, it is preferable that the content of the hard component (H(170°C)) is 70% or less, more preferably 68% or less, and even more preferably 65% ​​or less.

[0050] Furthermore, a content ratio of the middle component (M(170°C)) of 30% or more is preferable from the viewpoint of stress relaxation. From this viewpoint, a content ratio of the middle component (M(170°C)) of 30% or more is preferable, and more preferably 31% or more, of which 35% or more, and more preferably 40% or more. On the other hand, a content ratio of 70% or less is preferable because deformation can be further suppressed. From this viewpoint, a content ratio of the middle component (M(170°C)) of 65% or less is preferable, and more preferably 60% or less, and more preferably 50% or less.

[0051] In the cured product of the present invention, it is preferable that the content ratio of the soft component in the total content of the three components (hard component, middle component, and soft component) at 170°C (S(170°C):(soft component / total of 3 components)×100) is 0.0% or more and 15.0% or less. A content of the soft component (S(170℃)) of 15.0% or less is preferable because it can suppress the increased molecular motion at high temperatures, further reducing the likelihood of cracking or delamination of the joints. From this viewpoint, the content of the soft component (S(170℃)) is preferably 15.0% or less, and more preferably 10.0% or less. On the other hand, the lower limit is 0.0% or more. That is, the content of the soft component (S(170℃)) is 0.0% or more.

[0052] In the cured product of the present invention, to adjust the content ratio of the hard component (H(170°C)), the middle component (M(170°C)), and the soft component (S(170°C)) in the total content of the three components (hard component, middle component, and soft component) at 170°C to the above range, it is preferable to select the composition and adjust the composition ratio of, for example, a polyfunctional epoxy compound, a polymer having functional groups that contribute to the curing reaction, particularly a high molecular weight epoxy compound, and a curing agent, as well as to select the amount of thermosetting catalyst, curing conditions, and aging conditions. However, the present invention is not limited to such methods.

[0053] <WPE resin component> Preferably, the epoxy equivalent (WPE) of the solid content of the composition of the present invention, excluding the inorganic filler, or in other words, the component of the composition of the present invention excluding the solvent and inorganic filler (referred to as the "resin component"), is 120 g / equivalent or more and 400 g / equivalent or less. The solid content of the composition of the present invention refers to the components of the composition of the present invention excluding the solvent. Here, epoxy equivalent (WPE) refers to the mass of the resin component per equivalent of epoxy groups (g / equivalent).

[0054] By adjusting the proportions of high molecular weight epoxy compounds, polyfunctional epoxy compounds, and other components, the epoxy equivalent (WPE) of the resin component of the composition of the present invention can be adjusted to the above range. As a result, even when exposed to high temperatures, the strength is maintained while allowing for appropriate stress relaxation, preventing cracking and delamination of the joints. Furthermore, the holding power of the inorganic filler can be adjusted, improving the thermal conductivity of the sheet-like cured product of the present invention. From this viewpoint, the epoxy equivalent (WPE) of the resin component of the composition of the present invention is preferably 400 g / equivalent or less, more preferably 350 g / equivalent or less, more preferably 300 g / equivalent or less, and more preferably 250 g / equivalent or less. On the other hand, from the viewpoint of ensuring the film-forming properties of the thermosetting sheet of the present invention in its uncured state and the toughness of the sheet-like cured product of the present invention, the epoxy equivalent (WPE) of the resin component of the composition of the present invention is preferably 120 g / equivalent or more, more preferably 150 g / equivalent or more, and more preferably 200 g / equivalent or more.

[0055] To adjust the epoxy equivalent (WPE) of the resin component of the present invention's composition to the above range, methods include adjusting the content ratio of epoxy compounds having a predetermined epoxy equivalent (WPE), such as high molecular weight epoxy compounds and polyfunctional epoxy compounds, or adjusting the type and content of the curing agent. However, the invention is not limited to these methods.

[0056] <Physical properties of the cured product of the present invention> The cured product of the present invention may have the following physical properties.

[0057] (Thermal conductivity) The sheet-like cured product of the present invention, i.e., the sheet-like cured product of the present invention, preferably has a thermal conductivity in the thickness direction at 25°C of 10 W / m·K or more. If the thermal conductivity in the thickness direction of the sheet-like cured material of the present invention is 10 W / m·K or higher at 25°C, it can be suitably used in power semiconductor devices and the like that which operate power semiconductors at high temperatures. From this viewpoint, it is preferable that the sheet-like cured product of the present invention has a thermal conductivity in the thickness direction at 25°C of 10 W / m·K or more, and more preferably 12 W / m·K or more, more preferably 14 W / m·K or more, and more preferably 15 W / m·K or more.

[0058] To prepare the composition of the present invention so that the thermal conductivity of the sheet-like cured product of the present invention falls within the above range, for example, the type of thermosetting compound, the type and content of the inorganic filler, the method and conditions of mixing the thermosetting compound and the inorganic filler can be adjusted. However, the method is not limited to these. For the method of measuring the thermal conductivity in the thickness direction of the sheet-like cured material of the present invention, please refer to the method described in the examples below.

[0059] (Dielectric Breakdown Voltage (BDV)) Preferably, the sheet-like cured product of the present invention, i.e., the sheet-like cured product of the present invention, has a dielectric breakdown voltage of 4.5kV or more when its thickness is 150μm. If the dielectric breakdown voltage of the sheet-like cured material of the present invention is 4.5kV or higher, it can be suitably used in power semiconductor devices and the like that operate power semiconductors at high voltages. From this viewpoint, it is preferable that the sheet-like cured product of the present invention has a dielectric breakdown voltage of 4.5kV or more when its thickness is 150μm, and more preferably 5kV or more, 6kV or more, 7kV or more, 8kV or more, and 9kV or more.

[0060] To prepare the composition of the present invention so that the dielectric breakdown voltage of the sheet-like cured product of the present invention falls within the above range, for example, the type of thermosetting compound, the type and content of the inorganic filler, the mixing method and conditions of the thermosetting compound and the inorganic filler, the aging conditions, etc., can be adjusted. However, the method is not limited to these. For the method of measuring the dielectric breakdown voltage of the sheet-like cured material of the present invention, please refer to the method described in the examples below.

[0061] <Thermosetting compounds> Examples of thermosetting compounds contained in the composition of the present invention include epoxy compounds, phenolic resins, unsaturated polyester resins, melamine resins, urea resins, benzoxazine compounds, cyanates, and maleimides.

[0062] The thermosetting compound content is preferably 10% by mass or more and 70% by mass or less, based on 100% by mass of the volatile components, i.e., the components excluding the solvent (referred to as "solid content") in the composition of the present invention. A content of 10% by mass or more of the thermosetting compound is preferable because it results in good moldability, while a content of 70% by mass or less is preferable because it allows for the content of other components to be maintained and improves thermal conductivity. From this viewpoint, the content of the thermosetting compound is preferably 10% by mass or more and 70% by mass or less based on 100% by mass of the solid content in the composition of the present invention, more preferably 15% by mass or more, more preferably 20% by mass or more, and more preferably 25% by mass or more, while it is even more preferably contained in a proportion of 70% by mass or less. Furthermore, when using epoxy compounds as thermosetting compounds, it is preferable to use curing agents and thermosetting catalysts as described later. In this case, the curing agents and thermosetting catalysts are equivalent to thermosetting compounds and are therefore included in the thermosetting compounds in the "Content of Thermosetting Compounds" section above.

[0063] (Epoxy compound) The composition of the present invention preferably contains an epoxy compound as the thermosetting compound.

[0064] In the composition of the present invention, it is preferable that epoxy compounds account for 30 to 100% by mass of the thermosetting compounds, and more preferably that epoxy compounds account for 40% by mass or more, of which 50% by mass or more, of which 60% by mass or more, and of which 70% by mass or more. Furthermore, the epoxy compounds used in this context also include high-molecular-weight epoxy compounds, which will be discussed later.

[0065] The epoxy compound used as the thermosetting compound in the composition of the present invention may be any compound having one or more oxirane rings, i.e., epoxy groups, in one molecule.

[0066] The epoxy group contained in the epoxy compound can be either an alicyclic epoxy group or a glycidyl group. From the viewpoint of reaction rate or heat resistance, a glycidyl group is more preferable.

[0067] Examples of epoxy compounds include epoxy group-containing silicon compounds, aliphatic epoxy compounds, bisphenol A or F type epoxy compounds, novolac type epoxy compounds, aromatic epoxy compounds, alicyclic epoxy compounds, glycidyl ester type epoxy compounds, polyfunctional epoxy compounds, and high molecular weight epoxy compounds.

[0068] The epoxy compound may also be an aromatic epoxy group-containing compound. Specific examples include bisphenol-type epoxy compounds obtained by glycidly fermenting bisphenols such as bisphenol A, bisphenol F, bisphenol AD, bisphenol S, tetramethylbisphenol A, tetramethylbisphenol F, tetramethylbisphenol AD, tetramethylbisphenol S, and tetrafluorobisphenol A; biphenyl-type epoxy compounds; epoxy compounds obtained by glycidly fermenting divalent phenols such as dihydroxynaphthalene and 9,9-bis(4-hydroxyphenyl)fluorene; epoxy compounds obtained by glycidly fermenting trisphenols such as 1,1,1-tris(4-hydroxyphenyl)methane; epoxy compounds obtained by glycidly fermenting tetrakisphenols such as 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane; novolac-type epoxy compounds obtained by glycidly fermenting novolacs such as phenol novolac, cresol novolac, bisphenol A novolac, and brominated bisphenol A novolac; epoxy compounds having a dicyclopentadiene skeleton; and epoxy compounds having a naphthalene skeleton. In particular, it is preferable to include an epoxy compound having at least one structure selected from epoxy compounds having a biphenyl skeleton, epoxy compounds having a dicyclopentadiene skeleton, and epoxy compounds having a naphthalene skeleton. Among these, it is preferable to include an epoxy compound having a biphenyl skeleton.

[0069] (Polyfunctional epoxy compounds and high molecular weight epoxy compounds) The composition of the present invention preferably comprises a polyfunctional epoxy compound having three or more epoxy groups in one molecule and a mass-average molecular weight (Mw) of less than 5,000, and a high molecular weight epoxy compound having a mass-average molecular weight (Mw) of 5,000 or more.

[0070] (Polyfunctional epoxy compound) The aforementioned polyfunctional epoxy compound refers to an epoxy compound having three or more epoxy groups in one molecule and having a mass-average molecular weight (Mw) of less than 5,000. By incorporating such a polyfunctional epoxy compound, the degree of crosslinking can be further increased, thereby improving the adhesion between the thermal conductive sheet formed from the composition of the present invention and conductors such as metal plates and circuit boards. Furthermore, by including a polyfunctional epoxy compound, the storage modulus of the thermal conductive sheet of the present invention can be increased, thereby allowing the cured product of the present invention to penetrate into the irregularities on the surface of the conductor to which it is adhered, and exhibiting a strong anchoring effect, thereby improving the adhesion between the thermal conductive sheet of the present invention and conductors such as metal plates and circuit boards. On the other hand, the inclusion of polyfunctional epoxy compounds tends to increase the hygroscopicity of the composition of the present invention. However, by improving the reactivity of the epoxy groups, the amount of hydroxyl groups during the reaction can be reduced, thereby suppressing the increase in hygroscopicity. Furthermore, by preparing the composition of the present invention by combining the high molecular weight epoxy compound and the polyfunctional epoxy compound described later, it becomes possible to achieve both high elasticity and low moisture absorption in the thermal conductive sheet of the present invention.

[0071] As the polyfunctional epoxy compound, any epoxy compound having three or more epoxy groups in one molecule is acceptable, from the viewpoint of increasing the storage modulus of the cured product of the present invention, particularly the storage modulus at high temperatures which is important when generating a large amount of heat, such as in power semiconductor devices. Among these, epoxy compounds having four or more epoxy groups in one molecule are preferred. Having multiple epoxy groups, especially glycidyl groups, in one molecule improves the crosslinking density of the cured product of the present invention, resulting in higher strength for the thermal conductive sheet of the present invention, which is the cured product of the present invention. As a result, when internal stress occurs in the thermal conductive sheet of the present invention during a reflow test, the thermal conductive sheet of the present invention maintains its shape without deforming or breaking, thereby suppressing the generation of voids or other air pockets within the thermal conductive sheet of the present invention.

[0072] Furthermore, from the viewpoint of adjusting the crosslinkability of the thermally conductive sheet of the present invention, the molecular weight of the polyfunctional epoxy compound is preferably 800 or less, more preferably 700 or less, more preferably 650 or less, particularly preferably 100 or more or 630 or less, and more preferably 200 or more or 600 or less. Furthermore, in order to improve the handling properties of the composition and thermosetting sheet of the present invention, it is preferable that the polyfunctional epoxy compound includes one that is liquid at 25°C. Furthermore, from the viewpoint of achieving lower moisture absorption and higher crosslinking, it is preferable that the polyfunctional epoxy compound does not contain amine-based or amide-based structures that contain nitrogen atoms.

[0073] The epoxy equivalent (WPE) of the polyfunctional epoxy compound is preferably 75 g / equivalent or more from the viewpoint of the heat resistance of the heat-conductive sheet of the present invention. On the other hand, from the viewpoint of solubility in solvents, it is preferably 200 g / equivalent or less, more preferably 180 g / equivalent or less, more preferably 160 g / equivalent or less, and more preferably 150 g / equivalent or less.

[0074] As polyfunctional epoxy compounds, for example, EX321L, DLC301, DLC402, etc., manufactured by Nagase ChemteX Corporation can be used. These polyfunctional epoxy compounds may be used individually or in combination of two or more.

[0075] (High molecular weight epoxy compounds) High molecular weight epoxy compounds are epoxy compounds with a mass-average molecular weight (Mw) of 5,000 or more (also referred to as "epoxy polymers"). From the viewpoint of ensuring film-forming properties, the composition of the present invention preferably contains a high molecular weight epoxy compound (epoxy polymer). High molecular weight epoxy compounds enhance film-forming properties and, by having epoxy groups, also contribute to the curing reaction, thereby improving the durability and toughness of the cured product of the present invention.

[0076] Examples of epoxy polymers include phenoxy resins having at least one skeleton selected from the group consisting of a bisphenol A type skeleton, a bisphenol F type skeleton, a bisphenol A / F mixed type skeleton, a naphthalene skeleton, a fluorene skeleton, a biphenyl skeleton, anthracene skeleton, a pyrene skeleton, a xanthene skeleton, an adamantane skeleton, and a dicyclopentadiene skeleton.

[0077] In particular, the epoxy polymer is preferably one having at least one structure selected from, for example, the structure represented by the following formula (1) (referred to as "structure (1)") and the structure represented by the following formula (2) (referred to as "structure (2)").

[0078] TIFF2026106092000001.tif74167

[0079] In formula (1), R 1 and R 2 Each represents an organic group, and at least one of them is an organic group with a molecular weight of 16 or more, in formula (2), R 3 The symbol represents a divalent cyclic organic group. Furthermore, the term "organic group" includes any group containing a carbon atom, specifically, alkyl groups, alkenyl groups, aryl groups, etc., and these may be substituted with halogen atoms, heteroatoms, or other hydrocarbon groups. The same applies below.

[0080] In the above equation (1), R 1 and R 2 At least one of these represents an organic group with a molecular weight of 16 or more, preferably 16 to 1000, and examples include alkyl groups such as ethyl, propyl, butyl, pentyl, hexyl, and heptyl groups, and aryl groups such as phenyl, tolyl, xylyl, naphthyl, and fluorenyl groups. 1 and R 2 Both may be organic groups with a molecular weight of 16 or more, or one may be an organic group with a molecular weight of 16 or more and the other may be an organic group or hydrogen atom with a molecular weight of 15 or less. Preferably, one is an organic group with a molecular weight of 16 or more and the other is an organic group with a molecular weight of 15 or less, and in particular, it is preferable that one is a methyl group and the other is a phenyl group, as this facilitates control of handling properties such as resin viscosity and is preferable from the viewpoint of the strength of the cured product of the present invention.

[0081] In equation (2) above, R 3is a divalent cyclic organic group, which may be an aromatic ring structure such as a benzene ring structure, a naphthalene ring structure, or a fluorene ring structure, or an aliphatic ring structure such as cyclobutane, cyclopentane, or cyclohexane. Further, they may independently have a substituent such as a hydrocarbon group or a halogen atom. The divalent bonding portion may be a divalent group on a single carbon atom or a divalent group on different carbon atoms. Preferably, a divalent aromatic group having 6 to 100 carbon atoms and a group derived from a cycloalkane having 2 to 100 carbon atoms such as cyclopropane or cyclohexane can be mentioned. In particular, a 3,3,5-trimethyl-1,1-cyclohexylene group (referred to as "structure (4)") represented by the following formula (4) is preferable from the viewpoints of controlling handleability such as resin viscosity and the strength of the cured product of the present invention.

[0082] TIFF2026106092000002.tif55167

[0083] Due to the rigidity of the fluorene skeleton represented by the following formula (5), excellent heat resistance and low linear expansion are exhibited. Also, since the molecular weight per unit unit is larger than that of ordinary epoxy compounds, the proportion of secondary hydroxyl groups that cause hygroscopicity in the entire molecular structure is relatively low, and low hygroscopicity is exhibited. From this viewpoint, it is preferable that the epoxy polymer has a fluorene skeleton represented by the following formula (5).

[0084] TIFF2026106092000003.tif61167

[0085] Examples of the epoxy polymer include an epoxy polymer having a structure represented by the following formula (3) (referred to as "structure (3)").

[0086] TIFF2026106092000004.tif50167

[0087] In the above formula (3), R 4 、R 5 、R 6 、R 7Each of these is an organic group with a molecular weight of 15 or more. Preferably, it is an alkyl group with a molecular weight of 15 to 1000, and especially R 4 , R 5 , R 6 , R 7 It is preferable that all of them are methyl groups from the viewpoint of controlling handling properties such as resin viscosity and the strength of the cured product of the present invention.

[0088] In particular, it is preferable that the epoxy polymer is an epoxy polymer containing either structure (1) or structure (2) and structure (3) from the viewpoint of achieving both reduced hygroscopicity and strength retention of the cured product and the thermally conductive sheet of the present invention. Such epoxy polymers contain more hydrophobic hydrocarbons and aromatic structures compared to typical epoxy polymers having bisphenol A and bisphenol F skeletons. By incorporating these epoxy polymers, the moisture absorption of the resulting cured product, the thermally conductive sheet of the present invention, can be reduced.

[0089] Furthermore, from the viewpoint of reducing moisture absorption, epoxy polymers that contain a large amount of hydrophobic structures (1), (2), and (3) are preferred.

[0090] The mass-average molecular weight (Mw) of the epoxy polymer is preferably 5,000 or more, more preferably 10,000 or more, more preferably 15,000 or more, more preferably 20,000 or more, more preferably 25,000 or more, and more preferably 30,000 or more. The upper limit is 100,000 or less. Within this range, the film-forming properties of the composition of the present invention are improved, and the handling properties of the thermosetting sheet of the present invention in its uncured state tend to improve. Furthermore, because the film-forming properties are improved, the fillers are bound together at the stage of the thermosetting sheet of the present invention in its uncured state, making it less likely for voids to occur.

[0091] The epoxy equivalent weight (WPE) of the epoxy polymer is preferably 5,000 g / equivalent or more, more preferably 7,000 g / equivalent or more, and more preferably 8,000 g / equivalent or more, from the viewpoint of ensuring the film-forming properties of the composition of the present invention and imparting flexibility to the composition of the present invention. On the other hand, from the viewpoint of solubility in solvents, it is preferably 25,000 g / equivalent or less, and more preferably 20,000 g / equivalent or less.

[0092] Note that the mass-average molecular weight (Mw) of epoxy polymers is a polystyrene-equivalent value measured by gel permeation chromatography. Furthermore, epoxy equivalent (WPE) is defined as "the mass of an epoxy polymer containing one equivalent of epoxy groups" and can be measured in accordance with JIS K7236.

[0093] The epoxy polymers described above may be used individually or in combination of two or more.

[0094] (Epoxy compound content) The content of the polyfunctional epoxy compound is preferably 5% by mass or more and 50% by mass or less based on the solid content of the composition of the present invention excluding the solvent and inorganic filler (resin component), or in other words, based on 100% by mass of the solid content of the composition of the present invention excluding the inorganic filler. It is preferable to include a polyfunctional epoxy compound in the composition of the present invention at a concentration of 5% by mass or more, based on 100% by mass of the solid content excluding inorganic fillers, because this helps maintain the storage modulus of the cured product of the present invention. On the other hand, it is preferable to include it at a concentration of 50% by mass or less, because this helps maintain the toughness of the thermosetting sheet of the present invention in its uncured state and suppress the moisture absorption rate of the sheet-like cured product of the present invention, thereby maintaining its insulating performance. From this viewpoint, the content of the polyfunctional epoxy compound is preferably 5% by mass or more, more preferably 7.5% by mass or more, and more preferably 10% by mass or more, based on 100% by mass of the solid content of the composition of the present invention excluding the inorganic filler. On the other hand, it is preferably 50% by mass or less, more preferably 45% by mass or less, and more preferably 40% by mass or less.

[0095] Preferably, the epoxy polymer content is 5% by mass or more and less than 30% by mass relative to 100% by mass of the solid content (resin component) of the composition of the present invention excluding the solvent and inorganic filler. It is preferable to include epoxy polymer in the composition of the present invention at a concentration of 5% by mass or more, relative to 100% by mass of solid content excluding inorganic fillers, because this maintains film-forming properties. On the other hand, it is preferable to include it at a concentration of less than 30% by mass, because this maintains the flexibility of the thermosetting sheet of the present invention in its uncured state. From this viewpoint, the epoxy polymer content is preferably 5% by mass or more, more preferably 7.5% by mass or more, and more preferably 10% by mass or more, based on 100% by mass of the solid content of the composition of the present invention excluding inorganic fillers. On the other hand, it is preferably less than 30% by mass, more preferably 27.5% by mass or less, more preferably 25% by mass or less, and more preferably 24% by mass or less.

[0096] When a polyfunctional epoxy compound and an epoxy polymer are used in combination, from the viewpoint of the film-forming properties of the composition of the present invention and the elastic modulus of the sheet-like cured product of the present invention, it is preferable that the content of the polyfunctional epoxy compound is 20 parts by mass or more and 500 parts by mass or less per 100 parts by mass of epoxy polymer, and more preferably 30 parts by mass or more or 400 parts by mass or less, of which 40 parts by mass or more or 350 parts by mass or less, of which 60 parts by mass or more or 300 parts by mass or less, and of which 90 parts by mass or more or 200 parts by mass or less.

[0097] The content ratio of inorganic filler to polyfunctional epoxy compound (polyfunctional epoxy compound / inorganic filler) is preferably 0.02 or higher, more preferably 0.03 or higher, and more preferably 0.04 or higher, from the viewpoint of improving the retention capacity of the inorganic filler. On the other hand, from the viewpoint of improving the thermal conductivity of the thermal conductive sheet of the present invention, it is preferably 0.2 or lower, more preferably 0.18 or lower, and more preferably 0.16 or lower.

[0098] The ratio of inorganic filler to epoxy polymer (epoxy polymer / inorganic filler) is preferably 0.01 or higher, more preferably 0.02 or higher, and more preferably 0.03 or higher, from the viewpoint of maintaining the film-forming properties of the thermosetting sheet of the present invention. On the other hand, from the viewpoint of improving the bending resistance (handling properties) of the thermosetting sheet of the present invention in its uncured state and suppressing the decrease in dielectric strength due to defects such as cracks and fissures in the uncured state, it is preferably less than 0.2, more preferably 0.18 or lower, and more preferably 0.17 or lower.

[0099] The ratio of inorganic filler to epoxy compound (epoxy compound / inorganic filler) is preferably 0.2 or higher, more preferably 0.22 or higher, and more preferably 0.25 or higher, from the viewpoint of improving the handling properties of the thermosetting sheet of the present invention in its uncured state. On the other hand, from the viewpoint of improving the thermal conductivity of the thermally conductive sheet of the present invention, it is preferably 0.6 or lower, more preferably 0.57 or lower, and more preferably 0.55 or lower.

[0100] <Other polymers with a molecular weight of 5,000 or more> The composition of the present invention may contain, in place of or together with the above epoxy polymer, a polymer other than the above epoxy polymer with a mass-average molecular weight (Mw) of 5,000 or more (also referred to as "other polymers"). In this invention, epoxy polymers and other polymers are collectively referred to as "polymers." By including the polymer in the composition of the present invention, the film-forming properties can be improved even if the content ratio of boron nitride aggregated particles is increased.

[0101] The aforementioned other polymers may be any of the following: thermoplastic resins, thermosetting resins, etc. Examples of thermoplastic resins and thermosetting resins include polyphenylene ether, polyphenylene sulfide, polyarylate, polysulfone, polyethersulfone, polyetheretherketone, or polyetherketone. Furthermore, as the thermoplastic resin and thermosetting resin, a group of heat-resistant resins known as super engineering plastics, such as thermoplastic polyimide, thermosetting polyimide, benzoxazine, and reaction products of polybenzoxazole and benzoxazine, can also be used. Additionally, styrene-based polymers such as styrene and alkylstyrene, (meth)acrylic polymers such as alkyl (meth)acrylate and glycidyl (meth)acrylate, styrene-(meth)acrylic copolymers such as styrene-glycidyl methacrylate, polyvinyl alcohol derivatives such as polyvinyl butyral, polyvinyl benzal, and polyvinyl acetal, norbornene-based polymers containing norbornene compounds, and phenoxy resins can also be used. Among these, phenoxy resins are preferred in terms of heat resistance and compatibility with thermosetting resins. The thermoplastic resin and the thermosetting resin may each be used individually, or two or more may be used in combination. Either the thermoplastic resin or the thermosetting resin may be used, or the thermoplastic resin and the thermosetting resin may be used in combination.

[0102] Among the above, the other polymers are preferably those that have functional groups that contribute to the curing reaction, such as functional groups that react with epoxy compounds. Examples of functional groups that react with the epoxy compound include phenolic hydroxyl groups, epoxy groups, carboxylic acid groups, carboxylic anhydride groups, and activated esters.

[0103] The content of polymers with a mass-average molecular weight (Mw) of 5,000 or more (total content of epoxy polymers and other polymers) is preferably 5% by mass or more and less than 30% by mass, based on 100% by mass of the solid content of the composition of the present invention excluding inorganic fillers. It is preferable to include 5% by mass or more of a polymer with a mass-average molecular weight (Mw) of 5,000 or more, as this maintains the retention capacity and film-forming properties of the inorganic filler, while including it at a ratio of less than 30% by mass maintains the strength during curing. From this viewpoint, the content of polymers with a mass-average molecular weight (Mw) of 5,000 or more is preferably 5% by mass or more, more preferably 7.5% by mass or more, and more preferably 10% by mass or more, based on 100% by mass of the solid content of the composition of the present invention excluding inorganic fillers. On the other hand, it is preferably less than 30% by mass, more preferably 27.5% by mass or less, more preferably 25% by mass or less, more preferably 24% by mass or less, and more preferably 20% by mass or less.

[0104] <Hardening agent> The composition of the present invention preferably contains a curing agent, if necessary. Examples of curing agents include phenolic resins, compounds having a heterocyclic structure containing nitrogen atoms (referred to as "nitrogen-containing heterocyclic compounds"), acid anhydrides having an aromatic or alicyclic skeleton, aqueous additives of said acid anhydrides, or modified products of said acid anhydrides. The hardening agent may be used alone or in combination of two or more types. By using these preferred curing agents, a cured product of the present invention can be obtained that exhibits an excellent balance of heat resistance, moisture resistance, and electrical properties.

[0105] In particular, when the composition of the present invention contains the epoxy compound, it is preferable to use a curing agent having an active group that can react with epoxy groups. For example, it is preferable to use at least one of phenol resin, benzoxazine compound, polyarylate, cyanate, and maleimide in combination with the epoxy compound. That is, it is preferable that the composition of the present invention contains an epoxy compound and further contains at least one of phenol resin, benzoxazine compound, polyarylate, cyanate, and maleimide. Of these, it is preferable that the composition of the present invention contains an epoxy compound and further contains a phenol resin or a benzoxazine compound, and it is even more preferable that it contains an epoxy compound and further contains a benzoxazine compound. Furthermore, when it contains an epoxy compound and a benzoxazine compound, it is preferable to further include a phenol resin because it improves the balance between curing speed and crosslinking density. By including compounds with different crosslinking properties in addition to epoxy compounds, the density and uniformity of the crosslinking distribution in the cured product can be maintained more effectively. This not only ensures sufficient insulation performance after the reflow process, but also prevents cracking or delamination of the cured product when external stress is applied at high temperatures, such as when bonding to a substrate under high-temperature conditions of 150°C to 300°C, as in sinter bonding.

[0106] (Phenolic resin) Examples of the phenolic resins include phenol novolac, o-cresol novolac, p-cresol novolac, t-butylphenol novolac, dicyclopentadiene cresol, poly-p-vinylphenol, bisphenol A type novolac, xylylene-modified novolac, decalin-modified novolac, poly(di-o-hydroxyphenyl)methane, poly(di-m-hydroxyphenyl)methane, or poly(di-p-hydroxyphenyl)methane. In particular, novolac-type phenolic resins having a rigid main chain skeleton or phenolic resins having a triazine skeleton are preferred in order to further improve the flexibility of the composition, cured product, and thermally conductive sheet of the present invention, and to improve the mechanical properties and heat resistance of the cured product. Furthermore, phenolic resins having allyl groups are preferred in order to improve the flexibility of the uncured thermosetting sheet of the present invention and the toughness of the cured product.

[0107] (Benzoxazine compound) The aforementioned benzoxazine compound is a compound that crosslinks and hardens when heated, and also functions as a curing agent for epoxy compounds. Therefore, by using the epoxy compound and the benzoxazine compound in combination, the hydroxyl groups generated when the benzoxazine compound is crosslinked react with and bond with the epoxy groups of the epoxy compound. As a result, the crosslinked structure of the epoxy compound and the crosslinked structure of the benzoxazine compound are combined to form a stronger crosslinked structure, which can increase the glass transition temperature (Tg) of the cured product of the present invention and provide excellent heat resistance.

[0108] The benzoxazine compound is preferably one having a structure represented by the following formula (I) or formula (II).

[0109] TIFF2026106092000005.tif62167

[0110] TIFF2026106092000006.tif50167

[0111] In formula (I), a represents an integer between 0 and 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 hydrogen atoms, alkyl groups, alkenyl groups, cycloalkyl groups, aryl groups, aralkyl groups, and alkynyl groups. R1 may also be substituted with any substituent. Specific examples of R2 include aliphatic hydrocarbon groups and aromatic hydrocarbon groups. * indicates a bond with another chemical structure.

[0112] In formula (II), b represents an integer between 0 and 4, preferably 0 or 1, and more preferably 0. R3 represents a hydrogen atom or a monovalent organic group. If b is 2 or more, multiple R3s may be the same or different. Specific examples of R3 include aliphatic hydrocarbon groups and aromatic hydrocarbon groups. * indicates a bond with another chemical structure.

[0113] The benzoxazine compound preferably has multiple 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 using such a benzoxazine compound can further enhance curing performance and improve heat resistance.

[0114] 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.

[0115] TIFF2026106092000007.tif51167

[0116] In formula (III), X 2 It is a single bond or a divalent linking group. More specifically, X 2 These can be single bonds, linear or branched alkylene groups with 1 to 10 carbon atoms, -O-, -SO2-, -CO-, or structures in which two or more of these are linked together.

[0117] The benzoxazine compound may include the benzoxazine compound represented by the following formula (IV). Incidentally, the benzoxazine compound represented by the following formula (IV) is often also called Fa-type benzoxazine. In equation (IV), X 2 The definition and specific examples are given by X in equation (III) above. 2 It is similar to that.

[0118] TIFF2026106092000008.tif68167

[0119] Benzooxazine compounds include those that are solid at 25°C and those that are liquid. However, from the viewpoint of increasing the glass transition temperature (Tg) of the composition and its cured product of the present invention and thereby improving heat resistance, those that are solid at 25°C are more preferable.

[0120] The content of the benzoxazine compound is preferably 3% by mass or more and 50% by mass or less based on 100% by mass of the solid content of the composition of the present invention excluding inorganic fillers, and more preferably 5% by mass or more or 30% by mass or less, and more preferably 7% by mass or more or 25% by mass or less.

[0121] If the proportion of benzoxazine compounds increases, the resulting film may become brittle and its film-forming properties may decrease. Therefore, it is preferable that the content of benzoxazine compounds in the composition of the present invention be less than the content of epoxy compounds. In particular, the mass ratio of the content of benzoxazine compounds to the content of epoxy compounds in the solid content of the composition of the present invention, excluding inorganic fillers (benzoxazine compound / epoxy compound), is preferably less than 0.8, 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, it is preferable that the mass ratio is 0.05 or more, more preferably 0.07 or more, and even more preferably 0.08 or more.

[0122] (Polyarylate) By including both an epoxy compound and a polyarylate, the ester groups or terminal hydroxyl groups in the main chain skeleton of the polyarylate react with and bond to the epoxy groups of the epoxy compound. As a result, the crosslinked structure formed by the reaction of the epoxy compound and the crosslinked structure formed by the reaction of the epoxy compound and the polyarylate become combined to form a stronger crosslinked structure. Therefore, the glass transition temperature (Tg) of the composition of the present invention can be increased, resulting in excellent heat resistance, and for example, the change in the elastic modulus of the cured product of the present invention at high temperatures can be suppressed.

[0123] Examples of the polyarylate include compounds represented by the following formula (A).

[0124] TIFF2026106092000009.tif49167

[0125] In formula (A) above, X can be independently a hydrogen atom group, an aliphatic group, or an aromatic group. Specifically, examples include a hydrogen atom, a substituted or unsubstituted alkyl group, an aryl group, and so on. Each Y bond is independent, consisting of a single bond and a -CR bond. 1 R 2 -, O, CO, or S is acceptable. Note that the above R 1 , R 2Each independently represents a hydrogen atom, a methyl group, or an ethyl group, or R 1 and R 2 This refers to a cyclohexylidene group formed by the bonding of two atoms. Examples include linear, branched, or cyclic alkylene groups having 1 to 12 carbon atoms. Z can be any of the following, independently: a hydrogen atom, a hydroxyl group, or an alkoxy group. n is the number of repetitions, and can be any integer greater than or equal to 1. For example, it is preferably an integer between 1 and 100, and more preferably an integer between 1 and 90, and even more preferably an integer between 2 and 80.

[0126] The molecular weight of the polyarylate is preferably 500 or more from the viewpoint of improving heat resistance, more preferably 700 or more, and more preferably 1,000 or more. On the other hand, from the viewpoint of resin fluidity, it is preferably 10,000 or less, more preferably 8,000 or less, and more preferably 5,000 or less. The glass transition temperature of the polyarylate is preferably 80°C or higher from the viewpoint of dimensional stability at high temperatures, more preferably 100°C or higher, and more preferably 120°C or higher. On the other hand, from the viewpoint of improving toughness, it is preferably 300°C or lower, more preferably 270°C or lower, and more preferably 250°C or lower. The functional group equivalents (amount of hydroxyl groups and ester groups) of the polyarylate are preferably 100 g / equivalent or more, more preferably 120 g / equivalent or more, and more preferably 140 g / equivalent or more, from the viewpoint of reducing hygroscopicity. On the other hand, from the viewpoint of improving heat resistance, they are preferably 1000 g / equivalent or less, more preferably 800 g / equivalent or less, and more preferably 600 g / equivalent or less.

[0127] (Cyanate) The aforementioned cyanate can be, for example, a compound having an -OCN group in its molecule, in which the -OCN group reacts upon heating. Specifically, this includes 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)propyl Examples include pan, 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 the reaction of novolac resin with cyanide halides. Prepolymers having a triazine ring formed by trimerizing the cyanate group of these polyfunctional cyanates can also be used.

[0128] (Maleimide) The maleimide mentioned above may be any compound having one or more, preferably two or more, maleimide groups (2,5-dihydro-2,5-dioxo-1H-pyrrole-1-yl groups) in one molecule. Maleimide can react with epoxy compounds to form bonds in the presence of a suitable catalyst, and can also bond with other maleimides due to radical polymerization caused by the ethylenically active carbon-carbon unsaturated bonds 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.

[0129] (Hardening agent content) The curing agent is preferably contained in the components (resin components) of the composition of the present invention excluding the solvent and inorganic filler, or in other words, in a proportion of 1% to 50% by mass relative to 100% by mass of the solid content of the composition of the present invention excluding the inorganic filler, and more preferably in a proportion of 3% to 40% by mass, more preferably 5% to 30% by mass, and more preferably 10% to 25% by mass. If the curing agent content is above the lower limit, sufficient curing performance can be obtained. If it is below the upper limit, the reaction proceeds effectively, improving crosslinking density, increasing strength, and further improving film-forming properties.

[0130] <Curing accelerator> The composition of the present invention may, if necessary, contain a thermosetting catalyst as a curing accelerator to adjust the curing speed, the physical properties of the cured product, and other factors.

[0131] The thermosetting catalyst should preferably be selected appropriately depending on the type of thermosetting compound and curing agent. Specific examples of thermosetting catalysts include diazabicycloalkenes such as linear or cyclic tertiary amines, organophosphorus compounds, quaternary phosphonium salts, or organic acid salts, and imidazoles. Organometallic compounds, quaternary ammonium salts, or metal halides can also be used. Examples of the above organometallic compounds include zinc octoate, tin octoate, or aluminum acetylacetone complexes. Furthermore, the nitrogen-containing heterocyclic compounds described above as curing agents also act as thermosetting catalysts, and may therefore be incorporated as thermosetting catalysts.

[0132] Among these, compounds containing imidazole (referred to as "imidazole compounds") are particularly preferred from the viewpoint of storage stability, heat resistance, and curing speed. Preferred imidazole compounds include, for example, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 2-phenyl-4-methylimidazole, 1-cyanoethyl-2-phenylimidazolium trimellitate, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine, 2, Examples include 4-diamino-6-[2'-undecylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-ethyl-4'methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanurate adduct, 2-phenylimidazole isocyanurate adduct, 2-phenyl-4,5-dihydroxymethylimidazole, and 2-phenyl-4-methyl-5-hydroxymethylimidazole. In particular, by using an imidazole compound with a melting point of 100°C or higher, and more preferably 200°C or higher, a cured product of the present invention with excellent storage stability and adhesion can be obtained. Furthermore, compounds containing nitrogen-containing heterocyclic compounds other than the aforementioned imidazole ring are more preferable from the viewpoint of adhesion.

[0133] Furthermore, the thermosetting catalyst may be used alone or in a mixture of two or more types. By using two or more imidazole compounds with a melting point of 100°C or higher, the composition of the present invention with excellent storage stability can be obtained, and a cured product of the present invention with excellent heat resistance can be obtained. In particular, it is more preferable that at least one of the two or more imidazole compounds has a melting point of 200°C or higher, and even more preferable that two or more have a melting point of 200°C or higher.

[0134] (Content of hardening accelerator) The curing accelerator is preferably included in the components (resin components) of the composition of the present invention excluding the solvent and inorganic filler, or in other words, in a proportion of 0.1% to 10% by mass per 100% by mass of the solid content of the composition of the present invention excluding the inorganic filler, and more preferably in a proportion of 0.1% to 5% by mass. If the content of the curing accelerator is above the lower limit, the curing reaction can be sufficiently accelerated to achieve good curing, and if it is below the upper limit, the curing speed will not be too fast, and therefore the storage stability of the composition of the present invention can be improved.

[0135] <Inorganic filler> The inorganic filler contained in the composition of the present invention preferably has a thermal conductivity of 2.0 W / m·K or higher, more preferably 3.0 W / m·K or higher, more preferably 5.0 W / m·K or higher, and more preferably 10.0 W / m·K or higher.

[0136] Examples of inorganic fillers include electrically insulating fillers consisting solely of carbon, metal carbides or metalloid carbides, metal oxides or metalloid oxides, and metal nitrides or metalloid nitrides.

[0137] Examples of electrically insulating fillers consisting solely of carbon include diamond (thermal conductivity: approximately 2000 W / m·K). Examples of the aforementioned metal carbides or metalloid carbides include silicon carbide (thermal conductivity: approximately 60-270 W / m·K), titanium carbide (thermal conductivity: approximately 21 W / m·K), and tungsten carbide (thermal conductivity: approximately 120 W / m·K).

[0138] Examples of the aforementioned metal oxides or metalloids include magnesium oxide (thermal conductivity: approximately 40 W / m·K), aluminum oxide (thermal conductivity: approximately 20-35 W / m·K), zinc oxide (thermal conductivity: approximately 54 W / m·K), yttrium oxide (thermal conductivity: approximately 27 W / m·K), zirconium oxide (thermal conductivity: approximately 3 W / m·K), ytterbium oxide (thermal conductivity: approximately 38.5 W / m·K), beryllium oxide (thermal conductivity: approximately 250 W / m·K), and SiAlON (ceramics composed of silicon, aluminum, oxygen, and nitrogen, thermal conductivity: approximately 21 W / m·K). Examples of the aforementioned metal nitrides or metalloid nitrides include boron nitride (thermal conductivity in the plane direction of plate-like hexagonal boron nitride (h-BN) particles: approximately 200-500 W / m·K), aluminum nitride (thermal conductivity: approximately 160-285 W / m·K), silicon nitride (thermal conductivity: approximately 30-80 W / m·K), and the like.

[0139] These inorganic fillers may be used individually or in combination of two or more types.

[0140] From the standpoint of electrical insulation, the volume resistivity of inorganic fillers at 20°C is 10 13 It is preferable that it is Ω·cm or greater, and especially 10 14 It is more preferable that the resistivity is Ω·cm or greater. Among these, metal oxides, metalloid oxides, metal nitrides, or metalloid nitrides are preferred because they make it easier to ensure sufficient electrical insulation of the thermal conductive sheet of the present invention. Specifically, such inorganic fillers include aluminum oxide (Al2O3, volume resistivity: >10) 14 Ω·cm), aluminum nitride (AlN, volume resistivity: >10 14 Ω·cm), Boron nitride (BN, volume resistivity: >10 14 Ω·cm), silicon nitride (Si3N4, volume resistivity: >10 14 Ω·cm), silica (SiO2, volume resistivity: >10 14 Examples include Ω·cm. Among these, aluminum oxide, aluminum nitride, and boron nitride are preferred, and aluminum oxide and boron nitride are particularly preferred because they can impart high insulation properties to the thermally conductive sheet of the present invention.

[0141] The inorganic filler may be in the form of amorphous parts, spheres, whiskers, fibers, plates, or aggregates or mixtures thereof.

[0142] In this invention, "spherical" usually refers to a shape whose aspect ratio (ratio of major axis to minor axis) is 1 or more and 2 or less, preferably 1 or more and 1.75 or less, more preferably 1 or more and 1.5 or less, and even more preferably 1 or more and 1.4 or less. The aspect ratio can be determined by arbitrarily selecting 10 or more particles from an image of a cross-section of the composition or thermally conductive sheet of the present invention taken with a scanning electron microscope (SEM), determining the ratio of the major axis to the minor axis of each particle, and calculating the average value.

[0143] (Boron nitride aggregated particles) The inorganic filler contained in the composition of the present invention preferably contains "boron nitride aggregated particles" formed by the aggregation of primary boron nitride particles, because it has fewer problems with moisture absorption during heat molding, low toxicity, can efficiently increase thermal conductivity, and can impart high insulation properties to the thermally conductive sheet of the present invention.

[0144] Furthermore, boron nitride aggregate particles may be used in combination with other inorganic fillers. However, as described later, the heat transfer behavior in the thermally conductive sheet of the present invention does not depend solely on the thermal conductivity within the inorganic filler. Therefore, even when using diamond particles or the like, which have extremely high thermal conductivity but are also extremely expensive, among the inorganic fillers exemplified above, the thermal conductivity in the thickness direction of the thermally conductive sheet of the present invention will not increase drastically. Accordingly, when boron nitride aggregate particles are used in combination with other inorganic fillers, the main focus is on reducing the cost of the composition of the present invention. For this reason, since it is relatively inexpensive and has relatively high thermal conductivity, it is preferable to appropriately select from magnesium oxide, aluminum oxide, tungsten carbide, silicon carbide, aluminum nitride, etc., as the inorganic filler to be used in combination with boron nitride aggregate particles, with aluminum oxide being more preferable.

[0145] The shape of the boron nitride aggregate particles is preferably spherical.

[0146] From the viewpoint of improving thermal conductivity, the aggregate structure of the boron nitride aggregate particles is preferably a card-house structure. That is, it is preferable that the boron nitride aggregate particles include those having a card-house structure. Furthermore, the aggregation structure of boron nitride aggregated particles can be confirmed using a scanning electron microscope (SEM).

[0147] A cardhouse structure is a complex layering of plate-like particles that are not oriented, and is described in "Ceramics 43 No. 2" (published by the Ceramic Society of Japan in 2008). More specifically, it refers to a structure in which the planar portion of a primary particle forming an aggregated particle is in contact with the end face portion of other primary particles present within the aggregated particle. The aggregated particles in the cardhouse structure have extremely high fracture strength due to their structure and do not collapse even during the pressurization process performed when forming the thermal conductive sheet of the present invention. Therefore, primary particles, which normally orient in the longitudinal direction of the thermal conductive sheet of the present invention, can be arranged in random directions. Consequently, by using aggregated particles with a cardhouse structure, the proportion of primary particles with ab-planes oriented in the thickness direction of the thermal conductive sheet of the present invention can be increased, thereby enabling effective heat conduction in the thickness direction of the sheet and further increasing the thermal conductivity in the thickness direction.

[0148] Boron nitride aggregate particles having a cardhouse structure can be manufactured, for example, by the method described in International Publication No. 2015 / 119198.

[0149] When using boron nitride aggregated particles having a cardhouse structure, these particles may be surface-treated with a surface treatment agent. As the surface treatment agent, for example, known surface treatment agents such as silane coupling treatment can be used. It is believed that the adhesion at the interface between the inorganic filler and the thermosetting compound can be improved by chemical treatment, thereby further reducing the attenuation of thermal conductivity at the interface.

[0150] By using aggregated particles, which are formed by the aggregation of primary particles, as the inorganic filler used in the composition of the present invention, the particle size can be increased compared to inorganic fillers that use primary particles as they are. By increasing the particle size of the inorganic filler, the heat transfer paths between inorganic fillers via thermosetting compounds with low thermal conductivity can be reduced, and therefore, the increase in thermal resistance in the heat transfer paths in the thickness direction can be reduced.

[0151] From the above viewpoint, the lower limit of the maximum particle diameter of the boron nitride aggregate particles is preferably 20 μm or more, more preferably 30 μm or more, and even more preferably 40 μm or more. On the other hand, the upper limit of the maximum particle diameter is preferably 300 μm or less, more preferably 200 μm or less, even more preferably 100 μm or less, and even more preferably 90 μm or less.

[0152] Furthermore, the average particle size of the boron nitride aggregate particles is not particularly limited. Among these, 5 μm or more is preferred, 10 μm or more is more preferred, and 15 μm or more is even more preferred. Also, 100 μm or less is preferred, and 90 μm or less is even more preferred. When the average particle size of the boron nitride aggregate particles is 5 μm or more, the relative number of particles in the composition and cured product of the present invention is reduced, resulting in fewer interparticle interfaces and thus lower thermal resistance, which may lead to a high thermal conductivity in this thermally conductive sheet. Additionally, when the average particle size is below the above upper limit, the surface smoothness of the cured product of the present invention tends to be obtained.

[0153] If the average or maximum particle diameter of the boron nitride aggregate particles is below the above upper limit, a high-quality film without surface roughness can be formed when boron nitride aggregate particles are included in a thermosetting compound. If the average or maximum particle diameter is above the above lower limit, the interface between the thermosetting compound and the boron nitride aggregate particles is reduced, resulting in lower thermal resistance and achieving high thermal conductivity, as well as obtaining sufficient thermal conductivity improvement as an inorganic filler required for thermal conductive sheets for power semiconductor devices.

[0154] Furthermore, the influence of the thermal resistance at the interface between the thermosetting compound and the boron nitride aggregate particles on the thickness of the thermal conductive sheet of the present invention becomes significant when the size of the boron nitride aggregate particles is 1 / 10 or less of the thickness of the thermal conductive sheet of the present invention. In particular, for power semiconductor devices, the thermal conductive sheet of the present invention with a thickness of 100 μm to 300 μm is often applied, so from the viewpoint of thermal conductivity, it is preferable that the maximum particle diameter of the boron nitride aggregate particles is greater than the lower limit mentioned above. Furthermore, by ensuring that the maximum particle diameter of the boron nitride aggregate particles is above the lower limit mentioned above, not only is the increase in thermal resistance caused by the interface between the boron nitride aggregate particles and the thermosetting compound suppressed, but the number of required heat conduction paths between particles is reduced, increasing the probability that connections occur from one surface to the other in the thickness direction of the heat-conductive sheet of the present invention. On the other hand, because the maximum particle size of the boron nitride aggregate particles is below the above upper limit, the protrusion of boron nitride aggregate particles onto the surface of the thermally conductive sheet of the present invention is suppressed, and a good surface shape without surface roughness is obtained. As a result, when manufacturing a sheet bonded to a copper substrate, sufficient adhesion is achieved and excellent dielectric strength characteristics can be obtained.

[0155] The ratio of the size (maximum particle diameter) of boron nitride aggregated particles to the thickness of the thermally conductive sheet of the present invention (maximum particle diameter / sheet thickness) is preferably 0.3 or more and 1.0 or less, more preferably 0.35 or more or 0.95 or less, and more preferably 0.4 or more or 0.9 or less.

[0156] The maximum and average particle diameters of boron nitride aggregates can be measured, for example, by the following method. The maximum particle size and average particle size of boron nitride aggregates used as raw materials can be determined by measuring the particle size distribution of a sample in which boron nitride aggregates are dispersed in a solvent, specifically in a pure water medium containing a dispersion stabilizer, using a laser diffraction / scattering particle size distribution analyzer. The maximum particle size Dmax and average particle size D50 of the boron nitride aggregates can then be determined from the obtained particle size distribution. Here, Dmax and D50 are the maximum particle diameter and the 50% cumulative volume particle diameter in the volume-based particle size distribution obtained by the laser diffraction scattering particle size distribution method. Additionally, the maximum and average particle size can be determined using dry particle size distribution analyzers such as the Morfologi G3 (manufactured by Malvern).

[0157] On the other hand, the maximum particle diameter Dmax and average particle diameter D50 of boron nitride aggregated particles in the composition or thermally conductive sheet of the present invention can also be measured in the same manner as described above by dissolving and removing organic components such as thermosetting compounds in a solvent (including a heating solvent), or by physically removing them after reducing their adhesion strength to the boron nitride aggregated particles by swelling them, and further by removing the organic components by heating and ashing them in the atmosphere. Furthermore, to determine the maximum particle size of boron nitride aggregates in the composition or thermally conductive sheet of the present invention, it is also possible to directly observe 10 or more arbitrary boron nitride aggregates in the cross-section of the composition or thermally conductive sheet of the present invention using a scanning electron microscope, transmission electron microscope, micro-Raman spectrometer, atomic force microscope, etc., and determine the maximum particle size among them. Furthermore, the average particle diameter of boron nitride aggregates in the composition or thermally conductive sheet of the present invention can also be determined by directly observing 10 or more arbitrary boron nitride aggregates in the cross-section of the composition or thermally conductive sheet of the present invention using a scanning electron microscope, transmission electron microscope, micro-Raman spectrometer, atomic force microscope, etc., and calculating the arithmetic mean of the particle diameters. If the particle is non-spherical, the longest and shortest diameters are measured, and the average value of these two values ​​is taken as the particle diameter.

[0158] (Content of inorganic fillers) The inorganic filler content is preferably 30% by mass or more and less than 90% by mass, based on 100% by mass of the solid content in the composition of the present invention, i.e., 100% by mass of the solid content of the entire composition. If the inorganic filler content is 30% by mass or more relative to 100% by mass of the solid content in the composition of the present invention, the insulating properties and thermal conductivity can be enhanced. From this viewpoint, the inorganic filler content is preferably 30% by mass or more relative to 100% by mass of the solid content in the composition of the present invention, more preferably 40% by mass or more, more preferably 50% by mass or more, and more preferably 60% by mass or more. On the other hand, if the content is less than 90% by mass, handling properties and film-forming properties can be maintained. From this viewpoint, the content of the inorganic filler is preferably less than 90% by mass, and more preferably 85% by mass or less, more preferably 80% by mass or less, and more preferably 75% by mass or less.

[0159] The content of the boron nitride aggregated particles is preferably 50% by mass or more, relative to 100% by mass of the total inorganic filler. If the content of the boron nitride particles is 50% by mass or more relative to 100% by mass of the total inorganic filler, the insulating properties and thermal conductivity can be improved. From this viewpoint, the content of the boron nitride aggregated particles is preferably 50% by mass or more, with respect to 100% by mass of the total inorganic filler, and more preferably 60% by mass or more, of which 70% by mass or more, of which 80% by mass or more, and of which 90% by mass or more (including 100% by mass).

[0160] <Solvent> The composition of the present invention may optionally contain an organic solvent as a solvent, for example, to improve the applicability when forming a sheet-like cured product through a coating process. Examples of organic solvents that may be contained in the composition of the present invention include methyl ethyl ketone, cyclohexanone, propylene glycol monomethyl ether acetate, butyl acetate, isobutyl acetate, and propylene glycol monomethyl ether. These organic solvents may be used individually or in combination of two or more.

[0161] If the composition of the present invention contains an organic solvent, its content is appropriately determined according to the handling requirements during the production of the thermally conductive sheet of the present invention. Generally, the organic solvent is used such that the solid content (total of components other than the solvent) concentration in the composition of the present invention is 10% by mass or more and 90% by mass or less, and is particularly preferably 40% by mass or more or 80% by mass or less. Furthermore, when forming the composition of the present invention into a sheet, it is preferable to use the organic solvent such that the concentration of solids (total of components other than the solvent) in the composition of the present invention is 95% by mass or more, more preferably 97% by mass or more, even more preferably 98% by mass or more, and even more preferably 99% by mass or more.

[0162] <Other ingredients> The composition of the present invention may contain other components in addition to the components described above. Other components include, for example, additives such as dispersants, thermoplastic resins, organic fillers, silane coupling agents that improve the interfacial adhesion strength between inorganic fillers and resin components, additives that can be expected to enhance the adhesion strength between the thermal conductive sheet of the present invention and conductors such as metal plates and circuit boards, insulating carbon components such as reducing agents, viscosity modifiers, thixotropic agents, flame retardants, colorants, phosphorus-based, phenol-based and other various antioxidants, phenol acrylate-based and other process stabilizers, heat stabilizers, hindered amine-based radical scavengers (HAAS), impact modifiers, processing aids, metal deactivators, copper damage inhibitors, antistatic agents, bulking agents, and the like. When using these additives, the amount added should generally be within the range used for their intended purpose.

[0163] <<Uses of the present invention composition>> The composition of the present invention can be cured by heating to produce a cured product of the present invention. Furthermore, the composition of the present invention can be formed into a sheet to create the thermosetting sheet of the present invention, and by curing the thermosetting sheet of the present invention, a sheet-like cured product of the present invention can be formed and used as the thermally conductive sheet of the present invention. Furthermore, the cured product and the thermally conductive sheet of the present invention can be used in a variety of applications. For example, they can be used as components of composite molded bodies, heat-dissipating laminates, heat-dissipating circuit boards, and power semiconductor devices, as described later. However, their applications are not limited to these.

[0164] <Thermal conductive sheet of the present invention> An example of an embodiment of the present invention is a thermally conductive sheet formed from the cured product of the present invention. In other words, it is a thermally conductive sheet made from the sheet-like cured product of the present invention.

[0165] (Thickness) The lower limit of the thickness of the thermally conductive sheet of the present invention is preferably 50 μm or more, more preferably 60 μm or more, and even more preferably 70 μm or more. On the other hand, the upper limit of the thickness is preferably 400 μm or less, more preferably 300 μm or less, and even more preferably 250 μm or less. By making the thickness of the thermal conductive sheet of the present invention 50 μm or more, sufficient dielectric strength can be ensured. On the other hand, by making the thickness 400 μm or less, miniaturization and thinning can be achieved, especially when the thermal conductive sheet of the present invention is used in power semiconductor devices, and the effect of reducing thermal resistance in the thickness direction due to thinning can be obtained compared to insulating thermal conductive layers made of ceramic materials.

[0166] <Method for producing the cured product of the present invention> Next, an example of a sheet-like cured product of the present invention, that is, an example of a method for manufacturing the thermally conductive sheet of the present invention, will be described.

[0167] The thermal conductive sheet of the present invention is produced by forming a film of the composition of the present invention containing an inorganic filler and a thermosetting compound in a sheet form (this step is referred to as the "film forming step"), drying it as necessary (this step is referred to as the "drying step"), performing low-temperature aging in an environment with a temperature of 0°C or lower as necessary (this step is referred to as the "low-temperature aging step"), and further pressurizing it as necessary (this step is referred to as the "pressurizing step"). Then, the sheet-like thermosetting composition obtained in this way (the thermosetting sheet of the present invention), that is, the sheet-like composition of the present invention, can be cured to produce the thermal conductive sheet of the present invention as a sheet-like cured product (this step is referred to as the "curing step"). However, the order of each step can be changed as appropriate. For example, the low-temperature aging step may be performed after the pressurization step. Furthermore, if the cured product of the present invention is not in the form of a sheet, the steps of forming the composition of the present invention into a sheet (film-forming step) and drying it (drying step) can be omitted. As an example of a preferred method for producing the cured product of the present invention, a method can be described in which a composition of the present invention containing an inorganic filler and a thermosetting compound is subjected to low-temperature aging in a temperature environment of 0°C or lower, pressurized, and cured to obtain the cured product of the present invention.

[0168] (Film forming process) For example, the slurry-like composition of the present invention is formed into a sheet using a coating method such as the blade method, a solvent casting method, or an extrusion film formation method.

[0169] When forming a film in sheet form using the above coating method, first, the slurry-like composition of the present invention is applied to the surface of the substrate to form a coating film. That is, a coating film is formed on the substrate using the slurry-like composition of the present invention by the dip method, spin coating method, spray coating method, blade method, or any other method. For applying the slurry-like composition of the present invention, coating devices such as spin coaters, slit coaters, die coaters, and blade coaters can be used. Such coating devices make it possible to uniformly form a coating film of a predetermined thickness on a substrate. While copper plates or copper foils, PET films, and paper are commonly used as base materials, they are not limited to these. Furthermore, the PET film may be treated with a release agent.

[0170] (drying process) As described above, the composition of the present invention, which has been formed into a sheet-like film, is dried at a temperature of typically 10 to 150°C, preferably 25 to 120°C, and more preferably 30 to 110°C (heating atmosphere temperature) in order to remove solvents and low molecular weight components. When the drying temperature is below the upper limit, the hardening of the resin in the composition of the present invention is suppressed, and the resin in the sheet-like composition of the present invention tends to flow during the subsequent pressurizing process, making it easier to remove voids. When the drying temperature is above the lower limit, the solvent can be effectively removed, which tends to improve productivity. The drying time is not particularly limited and can be adjusted as appropriate depending on the state of the composition of the present invention, the drying environment, etc. The drying time is preferably 1 minute or more, more preferably 2 minutes or more, and even more preferably 5 minutes or more. The drying time is preferably 24 hours or less, more preferably 10 hours or less, even more preferably 4 hours or less, and particularly preferably 2 hours or less. When the drying time is above the lower limit, the solvent can be sufficiently removed, and the formation of voids in the sheet-like cured product of the present invention by residual solvent tends to be suppressed. When the drying time is below the upper limit, productivity tends to be improved and manufacturing costs tend to be reduced.

[0171] (Low-temperature aging process) Next, it is preferable to perform low-temperature aging by placing the sheet-like composition of the present invention thus formed in a temperature environment of 0°C or lower. By performing such low-temperature aging on the sheet-like composition of the present invention, moisture inside the sheet can be frozen and dispersed as tiny ice crystals. Even after returning to room temperature, these crystals create small chambers of trapped moisture, preventing the formation of large voids and thus preventing deterioration of insulation properties. Furthermore, the high degree of dispersion of these tiny voids within the sheet increases the fluidity of the resin components when pressurized, facilitating the rearrangement of inorganic fillers, such as boron nitride aggregate particles. This increases contact between inorganic fillers, improving thermal conductivity. In addition, the stress-relaxing effect makes the thermally conductive sheet of the present invention less prone to cracking and deformation.

[0172] In low-temperature aging, the ambient temperature is preferably lower because a faster cooling rate results in the formation of minute ice crystals. From this viewpoint, it is preferable that the temperature be 0°C or lower, more preferably -5°C or lower, more preferably -10°C or lower, and more preferably -15°C or lower. On the other hand, if the temperature is too low, it will fall below the glass transition temperature (Tg) of the uncured thermosetting sheet of the present invention, making it prone to cracking. Therefore, it is preferable that the temperature be -50°C or higher, and if an epoxy compound is included, more preferably -30°C or higher, and more preferably -25°C or higher.

[0173] The duration of the low-temperature aging is not particularly limited, as long as the composition of the present invention is frozen. Rapid freezing and holding for 10 minutes or more is sufficient, more preferably 30 minutes or more, more preferably 1 hour or more, more preferably 2 hours or more, more preferably 4 hours or more, more preferably 8 hours or more, more preferably 16 hours or more, and more preferably 24 hours or more. On the other hand, since epoxy compounds react gradually even at low temperatures, from the viewpoint of avoiding prolonged storage, it is preferable that the aging period be 365 days or less, more preferably 180 days or less, more preferably 90 days or less, more preferably 30 days or less, and more preferably 7 days or less.

[0174] While it is not necessary to apply pressure during low-temperature aging, applying a small pressure of 0.1 kPa or less is acceptable. Furthermore, the timing of the low-temperature aging process can be anytime after the solvent has dried, for example, after the pressurization process described later.

[0175] (Pressurization process) Next, it is desirable to apply pressure to the resulting sheet-like composition of the present invention for purposes such as bonding the inorganic fillers together to form heat conduction paths, eliminating voids and air gaps within the heat-conductive sheet of the present invention, and improving the adhesion between the heat-conductive sheet of the present invention and the substrate. However, depending on the purpose, pressurization may not be necessary. For example, when there is a large amount of solvent or inorganic filler, many pores may remain after the solvent has evaporated, so it is preferable to perform a pressurization process in such cases. By performing a pressurization process, it is possible to reduce or shrink the voids, especially the connecting pores, inside the thermal conductive sheet of the present invention.

[0176] In the pressurization process, it is desirable to apply a load of 2 MPa or more to the sheet-like composition of the present invention on the substrate. Examples of pressurization methods include flat plate presses, hydrostatic presses, vacuum presses, calender presses, belt presses, and servo presses. However, the method is not limited to these. The load is preferably 5 MPa or more, more preferably 7 MPa or more, and even more preferably 9 MPa or more. Furthermore, the load is preferably 1500 MPa or less, more preferably 1000 MPa or less, and even more preferably 800 MPa or less. By keeping the load during pressurization below the above upper limit, the voids in the sheet-like composition of the present invention can be eliminated without damaging the secondary particles of the inorganic filler, such as boron nitride aggregate particles, thereby obtaining the thermally conductive sheet of the present invention with high thermal conductivity. By keeping the load above the above lower limit, contact between the inorganic fillers is improved, making it easier to form heat conduction paths, thus obtaining the thermally conductive sheet of the present invention with high thermal conductivity.

[0177] The heating temperature of the sheet-like composition of the present invention on the substrate during the pressurization process is not particularly limited. The heating temperature (product temperature) is preferably 0°C or higher, more preferably 5°C or higher, and even more preferably 10°C or higher. The heating temperature is preferably 140°C or lower, more preferably 120°C or lower, even more preferably 110°C or lower, even more preferably 100°C or lower, and particularly preferably 90°C or lower. By performing the pressurization process within this temperature range, the melt viscosity of the resin in the sheet-like composition of the present invention can be reduced, thereby further reducing voids and air pockets in the cured product of the present invention. Furthermore, heating at or below the above upper limit tends to suppress the decomposition of organic components in the sheet-like composition of the present invention and the cured product of the present invention, as well as the generation of voids due to residual solvents.

[0178] The duration of the pressurization process is not particularly limited. Preferably, the pressurization process duration is 30 seconds or more, more preferably 1 minute or more, even more preferably 3 minutes or more, and especially preferably 5 minutes or more. Preferably, the pressurization process duration is 1 hour or less, more preferably 30 minutes or less, and even more preferably 20 minutes or less. By keeping the pressurization time below the upper limit, the manufacturing time of this thermal conductive sheet can be reduced, and production costs tend to decrease. By keeping the pressurization time above the lower limit, voids and air pockets within the cured product of this invention can be sufficiently removed, and the heat transfer performance and dielectric strength tend to improve.

[0179] (hardening process) The composition of the present invention can be cured by heating. In this case, the heating temperature (product temperature) is preferably 30 to 400°C, more preferably 50°C or higher, and more preferably 90°C or higher. On the other hand, it is preferably 300°C or lower, and more preferably 250°C or lower.

[0180] The curing step for completely curing the composition of the present invention may be carried out under pressure or without pressure. If pressure is applied, it is desirable to carry it out under the same conditions as the pressure step described above for the same reasons as above. The pressure step and the curing step may be carried out simultaneously. In particular, in the sheet formation process which involves a pressurizing process and a curing process, it is preferable to apply a load within the above range when performing the pressurizing and curing.

[0181] The load applied when the pressurizing and curing processes are performed simultaneously is not particularly limited. In this case, it is preferable to apply a load of 5 MPa or more to the sheet-like composition of the present invention on the substrate, more preferably 7 MPa or more, and even more preferably 9 MPa or more. Furthermore, the load is preferably 2000 MPa or less, more preferably 1500 MPa or less, more preferably 1000 MPa or less, even more preferably 500 MPa or less, and even more preferably 100 MPa or less. By setting the load below the upper limit when the pressurizing and curing processes are performed simultaneously, the secondary particles of the inorganic filler, such as boron nitride aggregate particles, are not destroyed, and a highly thermally conductive sheet of the present invention, free from voids, can be obtained. Furthermore, by setting the load above the lower limit, good contact between the inorganic fillers is achieved, making it easier to form heat conduction paths, thus enabling the production of a highly thermally conductive sheet of the present invention.

[0182] The pressurizing time when the pressurizing and curing processes are performed simultaneously is not particularly limited. The pressurizing time is preferably 30 seconds or more, more preferably 1 minute or more, even more preferably 3 minutes or more, and especially preferably 5 minutes or more. Furthermore, the pressurizing time is preferably 4 hours or less, more preferably 3 hours or less, and even more preferably 2 hours or less. If the pressurization time is below the above upper limit, the manufacturing time of the thermal conductive sheet of the present invention can be shortened, and production costs tend to be reduced. If the pressurization time is above the above lower limit, air gaps and voids within the thermal conductive sheet of the present invention can be sufficiently removed, and the heat transfer performance and dielectric strength characteristics tend to be improved.

[0183] <This composite molded product> A composite molded article (referred to as "this composite molded article") as an example of an embodiment of the present invention has a sheet-like cured material of the composition of the present invention, that is, a cured material portion made of the thermally conductive sheet of the present invention, and a metal portion, wherein the cured material portion and the metal portion are laminated and integrated. In this case, the metal portion may be provided on only one surface of the cured product made of the thermal conductive sheet of the present invention, or it may be provided on two or more surfaces. For example, the thermal conductive sheet of the present invention may have the metal portion on only one surface, or it may have the metal portion on both surfaces. Furthermore, the metal portion may be patterned.

[0184] Such a composite molded body can be manufactured by using the metal part as the base material and forming the thermal conductive sheet of the present invention on this base material according to the method described above. Alternatively, it can also be manufactured by peeling off the thermal conductive sheet of the present invention, which has been formed on a base material separate from the metal part, from the base material, and then heat-pressing it onto a metal member that will become the metal part. In this case, the thermal conductive sheet of the present invention can be peeled off the base material, placed on another metal plate, or sandwiched between two metal plates, and then integrated by applying pressure.

[0185] As the aforementioned metal plate, a metal plate with a thickness of approximately 10 μm to 10 cm made of copper, aluminum, nickel-plated metal, etc., can be used. Furthermore, the surface of the metal plate may be physically roughened or chemically treated with a surface treatment agent, and these treatments are more preferable from the viewpoint of adhesion between the thermal conductive sheet of the present invention and conductors such as metal plates and circuit boards.

[0186] Specific examples of this composite molded body include heat dissipation laminates, heat dissipation circuit boards, and power semiconductor devices. These will be explained in turn below. However, the invention is not limited to these examples.

[0187] <This heat dissipation laminate> An example of an embodiment of the present invention (referred to as "this heat dissipation laminate") may be any laminate comprising the thermal conductive sheet of the present invention.

[0188] As an example of this heat dissipation laminate, one can refer to a case in which a heat dissipation metal layer containing a heat dissipation material is laminated on one surface of the heat conductive sheet of the present invention.

[0189] The heat-dissipating material is not particularly limited as long as it is made of a material with good thermal conductivity. In particular, it is preferable to use a heat-dissipating metal material in order to increase the thermal conductivity in a laminated structure, and it is even more preferable to use a flat metal material. The material of the metal is not particularly limited. Among them, copper plates, aluminum plates, and aluminum alloy plates are preferred because they have good thermal conductivity and are relatively inexpensive.

[0190] For the lamination and integration of the heat-conductive sheet of the present invention and the heat-dissipating metal layer, a batch process such as press molding can be preferably used. In this case, the press equipment and press conditions are the same as those used in the curing process for obtaining the heat-conductive sheet of the present invention described above.

[0191] <This heat dissipating circuit board> A heat-dissipating circuit board according to one embodiment of the present invention (referred to as "this heat-dissipating circuit board") may be any board that includes the thermally conductive sheet of the present invention. As an example of a heat-dissipating circuit board, one can be cited which has a configuration in which the heat-dissipating metal layer is laminated on one surface of the heat-conductive sheet of the present invention, and a conductive circuit is formed on the surface of the heat-conductive sheet of the present invention that is not separated from the heat-dissipating metal layer, for example, by etching. Specifically, a configuration in which the "heat-dissipating metal layer / heat-conductive sheet of the present invention / conductive circuit" is integrated is more preferable. As for the state before circuit etching, for example, an integrated configuration of "heat-dissipating metal layer / heat-conductive sheet of the present invention / metal layer for forming a conductive circuit" can be cited in which the metal layer for forming a conductive circuit is in the shape of a flat plate and is formed on the entire surface of one side of the heat-conductive sheet of the present invention, or it can be formed on a part of the area.

[0192] The material for the metal layer used to form the conductive circuit is not particularly limited. In particular, from the viewpoint of good electrical conductivity, etching properties, and cost, it is generally preferable to form it from a thin copper sheet with a thickness of 0.05 mm to 1.2 mm. More preferably, it is 0.1 mm or more or 1.0 mm or less, and even more preferably 0.3 mm or more or 0.8 mm or less.

[0193] <This power semiconductor device> An example of an embodiment of the present invention (referred to as "this power semiconductor device") is a product that integrates a circuit combining multiple power semiconductors into a single package module, and is equipped with the thermal conductive sheet of the present invention. As an example of this power semiconductor device, one can cite a device in which a power semiconductor is mounted on a heat-dissipating circuit board using the heat-conductive sheet of the present invention. In this power semiconductor device, components other than the thermal conductive sheet or heat dissipation laminate of the present invention, such as aluminum wiring, sealing materials, packaging materials, heat sinks, thermal paste, and solder, can be replaced with conventionally known components as appropriate.

[0194] <<Explanation of terms>> In this invention, when "α~β" (where α and β are arbitrary numbers) is written, unless otherwise specified, it means "α or greater and β or less," and also includes the meaning of "preferably greater than α" or "preferably less than β." Furthermore, when written as "α or greater" or "α ≤" (where α is any number), unless otherwise specified, it includes the meaning of "preferably greater than α," and when written as "β or less" or "≤β" (where β is any number), unless otherwise specified, it also includes the meaning of "preferably less than β." In this invention, "sheet" conceptually encompasses sheets, films, and tapes. Furthermore, in this specification, the expression "and / or" means "and / or". [Examples]

[0195] The following describes an example of an embodiment of the present invention. However, the present invention is not limited to the embodiment described below.

[0196] <Ingredients> The raw materials used in the examples and comparative examples are as follows:

[0197] (Inorganic filler) • Inorganic filler 1: Spherical boron nitride aggregates having a cardhouse structure, manufactured in accordance with the method for producing boron nitride aggregates disclosed in the examples of International Publication No. 2015 / 561028. Maximum particle diameter (Dmax): 90μm Average particle diameter (D50): 45μm

[0198] • Inorganic filler 2: Spherical alumina particles manufactured by Admatex. Average particle diameter (D50): 7~13μm

[0199] The maximum particle size (Dmax) and average particle size (D50) of the inorganic filler were determined by dispersing the inorganic filler in a pure water medium containing sodium hexametaphosphate as a dispersion stabilizer, measuring the volume-based particle size distribution using a laser diffraction / scattering particle size distribution analyzer LA-300 (manufactured by Horiba, Ltd.), and then obtaining the maximum particle size (Dmax) and cumulative volume 50% particle size (average particle size (D50)) from the resulting particle size distribution.

[0200] (Epoxy compound) • Epoxy compound 1: Manufactured by Mitsubishi Chemical Corporation, a biphenyl-type solid epoxy compound containing two glycidyl groups in one molecule. Mass average molecular weight (Mw): Approx. 400 Epoxy equivalent (WPE): 200g / equivalent

[0201] • Epoxy compound 2: A polyfunctional epoxy compound manufactured by Nagase ChemteX Corporation, containing a structure with four or more glycidyl groups in one molecule. It does not contain amine or amide structures that contain nitrogen atoms. Mass average molecular weight (Mw): Approx. 400 Epoxy equivalent (WPE): 100g / equivalent

[0202] (Hardening agent) • Hardener 1: Manufactured by UBE Corporation, "H-4", phenolic resin-based hardener (phenol novolac) • Hardener 2: Manufactured by Shikoku Chemicals Co., Ltd., Pd-type benzoxazine, solid (25°C), in formula (III) X2 Those in which it is CH2 · Hardener 3: Manufactured by Meiwafosis Co., Ltd., "MEH-8000H", a phenolic resin-based hardener (allylphenol novolak)

[0203] (Polymer) · Epoxy polymer 1: Manufactured by Mitsubishi Chemical Corporation, a bifunctional epoxy polymer disclosed as resin component 1 in Japanese Patent Application Laid-Open No. 2020-63438, having the above structures (2) and (3), and R in formula (2) 3 is structure (4), and R in formula (3) 4 , R 5 , R 6 , R 7 were all methyl groups. Mass average molecular weight (Mw) in terms of polystyrene: 30,000 Epoxy equivalent (WPE): 9,000 g / equivalent

[0204] (Thermosetting catalyst) · Thermosetting catalyst 1: Manufactured by Shikoku Chemicals Corporation, "Curezol 2E4MZ-A", 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-s-triazine, having both a structure derived from imidazole and a structure derived from triazine in one molecule · Thermosetting catalyst 2: Manufactured by Shikoku Chemicals Corporation, "Curezol 2PHZ-PW", 2-phenyl-4,5-dihydroxymethylimidazole

[0205] <Examples 1 to 3, Comparative Example 1> Weighed each raw material so as to obtain the composition (parts by mass) shown in Table 1, and mixed them using a planetary mixer to obtain a mixture. When preparing this mixture, a slurry-like thermosetting composition was prepared using 20% by mass each of methyl ethyl ketone and cyclohexanone so that the above mixture would be 60% by mass (solid content concentration) in the coating slurry.

[0206] The obtained slurry-like thermosetting composition was applied to a PET substrate using the doctor blade method, and heated and dried at 60°C (heating atmosphere temperature) for 120 minutes to obtain a sheet-like thermosetting composition. The total content of methyl ethyl ketone and cyclohexanone in the sheet-like thermosetting composition was 1% by mass or less. Next, the sheet-like thermosetting composition was placed in a pressure press and heated and pressurized at 41.5°C under a load of 150 MPa for 10 minutes. Next, for Examples 1 to 3, the sheet-like thermosetting composition was cut to a size of 200 mm x 200 mm, placed in a vacuum-sealed bag, the air inside the bag was removed, and the opening of the bag was heat-sealed. Then, the bag was stored in a freezer at -20°C for 72 hours to perform low-temperature aging. In Comparative Example 1, the low-temperature aging described above was omitted, and a sheet-like thermosetting composition was placed inside a sealed vacuum-packed bag and aged at 60°C for 72 hours.

[0207] The thermosetting compositions obtained in the examples and comparative examples were subjected to epoxy equivalent (WPE) measurements as follows. The sheet-like cured products of the thermosetting compositions were subjected to pulsed NMR, thermal conductivity, and dielectric breakdown voltage (BDV) measurements as follows. Furthermore, reflow resistance evaluation tests I, II, and sinter resistance evaluation tests were conducted, and the results are shown in Table 1.

[0208] In Table 1, the numerical values ​​indicating the amount of each component in the thermosetting composition represent the mass percentage (parts by mass) of each component, and "WPE" is the epoxy equivalent (g / equivalent) of the resin component excluding the solvent and inorganic filler from the thermosetting composition.

[0209] <Measurement and Evaluation> The raw materials used in each example and comparative example, and the thermosetting compositions and cured sheets of the thermosetting compositions (cured sheets) prepared in each example and comparative example, were measured and evaluated as follows.

[0210] (Measurement of epoxy equivalent (WPE) of resin components) For each example and comparative example, the resin components (components obtained by excluding the solvent and inorganic filler from the thermosetting composition), i.e., epoxy compounds 1 and 2, curing agents 1, 2 and 3, epoxy polymer 1, and thermosetting catalysts 1 and 2, were mixed in the mass ratios shown in Table 1 below to obtain thermosetting compositions. The potential was measured by potentiometric titration in accordance with JIS K7236, and the epoxy equivalent (g / equivalent) was determined by converting it to the value of the entire resin component.

[0211] (Pulsed NMR measurement) Four sheets of the thermosetting composition prepared in each example and comparative example were stacked and heated under a load of 10 MPa at 120°C (product temperature) for 30 minutes, 175°C (product temperature) for 30 minutes, and then at 200°C (product temperature) for 30 minutes to cure, obtaining a sheet-like cured material with a thickness of 0.6 mm. This was then cut into 50 mm x 8 mm pieces to prepare test specimens.

[0212] The obtained test specimens were crushed and packed into a 10mm diameter glass sample tube (BRUKER, part number 1824511, 180mm length, flat bottom) to a depth of approximately 15mm from the bottom. The sample tube was placed in a pulsed NMR spectrometer (BRUKER "the minispec mq20") and the temperature was gradually increased to 30°C (held for 10 minutes), 70°C (held for 10 minutes), 100°C (held for 10 minutes), 150°C (held for 10 minutes), and 170°C (held for 10 minutes). The heating rate was 4°C / min.

[0213] At 30°C and 170°C, measurements were performed using the Solid Echo method under the following conditions to obtain the relaxation curve for the transverse magnetization of 1H. Using BRUKER's TD-NMRA analysis software, we performed analysis of three components according to the product manual. The first component was fitted using a Gaussian type fitting, while the second and third components were fitted using an exponential type fitting. Furthermore, the analysis involved fitting the relaxation curve using points up to 0.6 msec to determine the amount of each component and the relaxation time.

[0214] [Solid Echo method] Scans: 128 times Recycle Delay: 1 sec Acquisition scale: 1.0 ms

[0215] The relaxation curve of the obtained transverse magnetization of 1H was separated into three components and fitted to obtain the ratio of each component and the spin-spin relaxation time.

[0216] Note that the following formula (X1) is used for fitting using TD-NMRA. When analyzing by separating into three components, the maximum number of i is 3.

[0217] A(t) = ΣA(i) × exp(-1 / wi × (t / T2(i))^wi) ··· Formula (X1) i = 1, 2, 3

[0218] In the above formula (X1), i is the Weibull coefficient, w1 is 2, w2 and w3 are 1. When wi is 1, the term of formula (X1) becomes exponential type, and when wi is 2, it becomes Gaussian type. In TD-NMRA, A(i) and T2(i) can be obtained by defining the number of terms and the Weibull coefficient of each term. In this analysis, the number of terms was set to 3. (i = 3) When this measurement was carried out, T2(1) < T2(2) < T2(3). T2 relatively represents the molecular mobility, and the smaller the value, the lower the mobility. Therefore, i = 1 was defined as the hard component (H), i = 2 as the middle component (M), and i = 3 as the soft component (S). Then, using A(1), A(2), and A(3) obtained by measuring at K°C, the content ratio of the hard component at K°C (H(K°C)), the content ratio of the middle component at K°C (M(K°C)), and the content ratio of the soft component at K°C (S(K°C)) are defined by the following formulas, respectively.

[0219] H(K°C) = 100 × A(1) / (A(1) + A(2) + A(3)) ·· Formula (X2) M(K℃)=100×A(2) / (A(1)+A(2)+A(3)) Formula (X3) S(K℃)=100×A(3) / (A(1)+A(2)+A(3)) Formula (X4) In the above equations (X2) to (X4), A(1), A(2), and A(3) are quantities proportional to the number of hydrogen atoms in the molecule.

[0220] By performing the pulsed NMR measurements and analyses described above using the obtained test specimens, the following was determined. • The percentage of each component in the total 100% of the combined content of hard components, medium components, and soft components at 30°C, i.e., the percentage of hard components (H(30°C)), the percentage of medium components (M(30°C)), and the percentage of soft components at 30°C (S(30°C)). • The percentage of each component in the total 100% of the combined content of hard components, medium components, and soft components at 170°C, i.e., the percentage of hard components (H(170°C)), the percentage of medium components (M(170°C)), and the percentage of soft components at 170°C (S(170°C)).

[0221] (Measurement of thermal conductivity in the thickness direction of a sheet-like cured thermosetting composition) The sheet-like thermosetting compositions prepared in each example and comparative example were cured by heating them at 140°C (product temperature) for 40 minutes while applying pressure of 10 MPa, thereby obtaining a sheet-like cured product (sample) with a thickness of 150 μm. Furthermore, by stacking two, three, or four sheets of the thermosetting composition prepared in each example and comparative example, and applying pressure and heating in the same manner as described above, four types of sheet-like cured materials (samples) with different thicknesses were obtained.

[0222] For these four types of sheet-like cured materials (samples) with different thicknesses, the following measurements were performed, and the thermal conductivity at 25°C in the sheet thickness direction was determined by the steady-state method from the slope represented by the thermal resistance value with respect to the sheet thickness (according to ASTM D5470). (1) Thickness: Thickness (μm) when pressed at a press pressure of 3400 kPa using Mentor Graphics' T3Ster-DynTIM. (2) Measurement area: The area of ​​the heat-transferring part (cm²) when measuring using Mentor Graphics T3Ster-DynTIM. 2 ) (3) Thermal resistance value: Thermal resistance value (K / W) when pressed at a press pressure of 3400 kPa using Mentor Graphics T3Ster-DynTIM. (4) Thermal conductivity: The thermal resistance values ​​of four types of sheet-like cured materials (samples) with different thicknesses are measured, and the thermal conductivity (W / m·K) is calculated from the following formula. Formula: Thermal conductivity (W / m·K) = 1 / ((Slope (Difference in thermal resistance value / Thickness): K / (W·μm)) × (Area: cm) 2 )) × 10 -2

[0223] (Measurement of BDV (Dielectric Breakdown Voltage) of sheet-like cured thermosetting compositions) Copper plates with thicknesses of 500 μm and 2,000 μm were prepared by roughening the surface 100 times each with #120 grit sandpaper. One of each copper plate was used to sandwich the sheet-like thermosetting composition obtained in each example and comparative example. The plates were then pressurized at 120°C (product temperature) and 10 MPa for 30 minutes, followed by raising the temperature to 175°C (product temperature) and 10 MPa for 30 minutes, and then at 200°C (product temperature) and 10 MPa for 30 minutes to obtain a composite molded body for reflow testing. The sheet-like cured layer of the composite molded body was 150 μm thick. A 500 μm copper plate was patterned by etching the composite molded body obtained above. The pattern was designed so that two circular patterns with a diameter of φ25 mm remained. The composite molded body (evaluation sample) prepared as described above was immersed in insulating oil (3M's "Fluorinert FC-40"). Using a 7470 ultra-high voltage withstand voltage tester (manufactured by Keisoku Gijutsu Kenkyusho), electrodes were placed on one of the patterned φ25mm copper plates, a voltage of 0.5kV was applied, and the voltage was increased by 500V every minute until the sheet-like hardened material broke down (BDV: dielectric breakdown voltage).

[0224] (Reflow resistance evaluation I: Insulation evaluation) The composite molded body for reflow testing, prepared as described above, was stored for 3 days in an 85°C, 85%RH environment using an ESPEC constant temperature and humidity chamber SH-221. Within 30 minutes, it was heated from room temperature to 290°C (product temperature) in 12 minutes under a nitrogen atmosphere, held at 290°C (product temperature) for 10 minutes, and then cooled to room temperature (moisture-absorbing reflow test). After the reflow test described above, the BDV (dielectric breakdown voltage) was measured using the method described above. If the value was less than 5kV, the reflow tolerance evaluation I was evaluated as "×: Fail," and if it was 5kV or higher, it was evaluated as "〇: Pass."

[0225] (Reflow Resistance Evaluation II: Crack and Peeling Evaluation) The composite molded body for reflow testing, prepared as described above, was subjected to a moisture-absorbing reflow test in the same manner as in the reflow resistance evaluation I described above. The interface between the copper plate and the sheet-like hardened material was then observed using an ultrasonic imaging device, FinSAT (FS300III) (manufactured by Hitachi Power Solutions). A 50 MHz probe was used for the measurement, with a gain of 30 dB and a pitch of 0.2 mm, and the sample was placed in water. If the sheet-like cured material had cracks or delamination occurred at the interface between the copper plate and the sheet-like cured material, the reflow resistance evaluation II was rated as "×: Fail". If the sheet-like cured material had no cracks and no delamination occurred at the interface between the copper plate and the sheet-like cured material, it was rated as "〇: Pass".

[0226] (Sinter tolerance evaluation) For Examples 1-3, which passed the reflow resistance evaluations I and II, composite molded bodies for sinter resistance testing were prepared in the same manner as the composite molded bodies for reflow testing described above. A copper plate was soldered to a portion of the Φ25 mm pattern of the composite molded body, and Teflon was placed on top as a cushioning material. The body was then sandwiched between SUS plates and heated and pressurized at 250°C (product temperature) and 15 MPa for 5 minutes to perform an evaluation that simulated the silver sintering process. The interface between the copper plate and the sheet-like hardened material was observed in the composite molded body after heating and pressurizing using an ultrasonic imaging device FinSAT (FS300III) (manufactured by Hitachi Power Solutions). For the measurement, a 50 MHz probe was used with a gain of 30 dB and a pitch of 0.2 mm, and the sample was placed in water. If the sheet-like cured material had cracks or if delamination occurred at the interface between the copper plate and the sheet-like cured material, the sinter resistance evaluation was rated as "×: Fail". If the sheet-like cured material had no cracks and no delamination occurred at the interface between the copper plate and the sheet-like cured material, it was rated as "〇: Pass".

[0227] [Table 1]

[0228] (Consideration) In the above formulas (X2) to (X4), H (K°C), i.e., the hard component content at K°C, represents the percentage (%) of the molecular chain portion with the lowest molecular mobility among the components of the cured product of this thermosetting composition excluding inorganic fillers at K°C; S (K°C), i.e., the soft component content at K°C, represents the percentage (%) of the molecular chain portion with the highest molecular mobility; and M (K°C), i.e., the middle component content at K°C, represents the percentage (%) of the molecular chain portion in between. The hard components are thought to correspond to molecular chain regions near crosslinking points and entanglement regions, the soft components to free molecular chains such as terminals, and the middle components to correspond to the intermediate regions, i.e., molecular chains between crosslinking points.

[0229] At low temperatures (e.g., 30°C), the molecular chains between crosslinking points are thought to be classified as hard components near the crosslinking points, and as they move away from the crosslinking points, the molecular chains become middle and soft components. When the crosslinking density is high, it is thought that almost all of the molecular chains between crosslinking points are classified as hard components. When the crosslinking density is low, they are classified as hard components and medium components, and when it is even lower, they are thought to be classified as hard components, medium components, and soft components. When comparing a sample with the same degree of crosslinking but with non-uniform crosslinking and a sample with uniform crosslinking, the following can be considered. When crosslinking is uneven, areas with high crosslink density are created. These areas with high crosslink density are classified as hard components at low temperatures, resulting in a decrease in middle components. Therefore, at low temperatures, M(K°C), i.e., the proportion of middle components at K°C, is estimated to be smaller than in uniform samples. On the other hand, as the temperature increases (for example, to 170°C), the molecular chains between crosslinking points become more mobile, so the value of M(K°C) increases. Two samples with similar degrees of crosslinking are thought to have nearly the same middle component content at high temperatures. Therefore, M(170℃) / M(30℃) is considered to be an indicator that includes the degree of crosslinking and uniformity.

[0230] Regions with high crosslink density are thought to become hard components at low temperatures. When there are samples with uniform and non-uniform crosslink density, the non-uniform sample will have regions with high crosslink density, and these regions will become hard components. Therefore, at low temperatures (e.g., 30°C), the H(K°C) of the non-uniform crosslink density sample is estimated to be higher than that of the uniform sample. Furthermore, as the temperature increases (for example, to 170°C), the molecular chain portions of the hard component that are far from the crosslinking points become the middle component. Therefore, it is estimated that if the degree of crosslinking is the same, H(K°C) will approach the same value as the temperature increases. Therefore, H(170℃) / H(30℃) serves as an indicator that includes the degree of crosslinking and uniformity.

[0231] From the above examples and comparative examples, as well as the test results conducted by the inventors to date, it has been found that when the ratio of the content of the middle component at 170°C (M(170°C)) to the content of the middle component at 30°C (M(30°C)) (M(170°C) / M(30°C)) is between 2.5 and 7.5, the cured product of a thermosetting composition containing an inorganic filler and a thermosetting compound exhibits better high-temperature resistance. Even after the flow process, delamination at the interface between the cured product and the metal does not occur, preventing the joint from peeling off or cracking in the cured product. Furthermore, it exhibits sufficient insulating performance. This can be attributed to the fact that as the temperature increases, molecular chains become more mobile, allowing the molecular chains of the hard component to be incorporated into the middle component, thereby increasing the proportion of the middle component. It is presumed that when the ratio (M(170℃) / M(30℃)) is 7.5 or less, the variation in molecular weight between crosslinking points is reduced, and the crosslinking density is uniform, so even when exposed to high temperatures, cracks will not form in the cured product, and interfacial delamination will not occur, preventing the bonds from separating. On the other hand, it is presumed that when the ratio (M(170℃) / M(30℃)) is 2.5 or more, the stress is relieved in response to expansion at high temperatures, making it less likely for cracks to form in the cured product, or for interfacial delamination to occur, preventing the bonds from separating.

[0232] Furthermore, in the case of Example 1, it was found that not only was the insulation performance after the reflow process sufficient, but it was also possible to prevent cracks from forming in the cured material or delamination of the bond when external stress was applied at high temperatures, such as when bonding to a substrate under high-temperature conditions of 150°C to 300°C, as in sinter bonding. Therefore, if the ratio (M(170℃) / M(30℃)) is between 2.5 and 7.5, and (H(170℃) / H(30℃)) is between 0.5 and 1.0, the crosslinking density is sufficiently high and uniform, and even when external stress is applied at high temperatures, the stress is distributed, preventing cracks in the cured product or delamination at the interface that causes the bond to break. For example, it can be suitably applied to various processing in the high-temperature range of 150℃ to 300℃, and it is estimated that even when bonded to a substrate by sinter bonding, excellent electrical conductivity and continuous bonding stability can be ensured.

Claims

1. A cured product of a thermosetting composition containing an inorganic filler and a thermosetting compound, The inorganic filler contains boron nitride aggregated particles, The aforementioned thermosetting compound contains an epoxy compound, When the components contained in the cured product are separated into three components—a hard component, a middle component, and a soft component—based on the relaxation curve of the transverse magnetization of 1H obtained using pulsed NMR, A cured product of a thermosetting composition in which the ratio (M(170°C) / M(30°C)) of the proportion of the middle component in the total content of the three components (hard component, middle component, and soft component) at 170°C (M(170°C): (middle component / total of three components) × 100) to the proportion of the middle component in the total content of the three components (hard component, middle component, and soft component) at 30°C (M(30°C): (middle component / total of three components) × 100) is 2.5 or more and 7.5 or less.

2. A cured product of a thermosetting composition according to claim 1, wherein the ratio of the content of the soft component in the total content of the three components (hard component / soft component / total of three components) at 170°C (S(170°C):(soft component / total of three components) × 100) to the content of the soft component in the total content of the three components (hard component / medium component / soft component) at 30°C (S(30°C):(soft component / total of three components) × 100) is 1.38 or less (S(170°C) / S(30°C)).

3. A cured product of a thermosetting composition according to claim 1, wherein the ratio of the content of the hard component in the total content of the three components (hard component / total of three components) at 170°C (H(170°C):(hard component / total of three components)×100) to the content of the hard component in the total content of the three components (hard component / total of three components) at 30°C (H(30°C):(hard component / total of three components)×100) is 0.3 or more and 1.0 or less.

4. A cured product of a thermosetting composition according to claim 1, wherein the proportion of the hard component in the total content of the three components (H(30°C): (hard component / total of three components) × 100) at 30°C is 90.0% or less.

5. A cured product of a thermosetting composition according to claim 1, wherein the content ratio of the soft component in the total content of the three components (hard component, middle component, and soft component) at 30°C (S(30°C): (soft component / total of three components) × 100) is 2.4% or more and 10.0% or less.

6. A cured product of a thermosetting composition according to claim 1, wherein the content ratio of the hard component in the total content of the three components (hard component, middle component, and soft component) at 170°C (H(170°C): (hard component / total of three components) × 100) is 30% or more and 70% or less, and the content ratio of the middle component in the total content of the three components (hard component, middle component, and soft component) at 170°C (M(170°C): (middle component / total of three components) × 100) is 30% or more and 70% or less.

7. The cured product of the thermosetting composition according to claim 1, wherein the epoxy equivalent (WPE) of the solid content of the thermosetting composition, excluding the inorganic filler, is 120 g / equivalent or more and 400 g / equivalent or less.

8. The thermosetting composition is a cured product of the thermosetting composition according to claim 1, comprising a polyfunctional epoxy compound having three or more epoxy groups in one molecule and a mass-average molecular weight (Mw) of less than 5,000, and a high molecular weight epoxy compound with a mass-average molecular weight (Mw) of 5,000 or more.

9. The thermosetting composition further comprises at least one of a phenol resin, a benzoxazine compound, a polyarylate, a cyanate, and a maleimide, wherein the cured product of the thermosetting composition is as described in claim 1.

10. The cured product of the thermosetting composition according to claim 1, wherein the thermosetting composition further comprises a benzoxazine compound.

11. The cured product of the thermosetting composition according to claim 1, wherein the boron nitride aggregated particles include those having a cardhouse structure.

12. A thermally conductive sheet comprising a cured product of a thermosetting composition according to any one of claims 1 to 11.

13. A heat dissipation laminate comprising the thermally conductive sheet described in claim 12.

14. A heat-dissipating circuit board comprising the thermally conductive sheet described in claim 12.

15. A power semiconductor device comprising the thermally conductive sheet described in claim 12.

16. A method for producing a cured product of a thermosetting composition according to any one of claims 1 to 11, A method for producing a cured product of a thermosetting composition, characterized by performing low-temperature aging by placing the thermosetting composition containing an inorganic filler and a thermosetting compound in a temperature environment of 0°C or lower, and then curing it under pressure.

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