Thermally conductive resin sheet, laminated heat dissipation sheet, heat dissipation circuit board and power semiconductor device

Abstract

To provide a thermally conductive resin sheet which has good withstand voltage performance and good thermal conductivity, while exhibiting excellent reflow resistance after moisture absorption.SOLUTION: A thermally conductive resin sheet according to one aspect of the present invention is formed from a resin composition, which contains a thermoplastic resin and boron nitride agglomerated particles. A pore size distribution curve is obtained by measurement by a mercury intrusion method of the boron nitride agglomerated particles contained in residual ash, which is obtained by heating the thermally conductive resin sheet at 700°C for five hours. The pore size distribution curve has at least one first peak caused by intraparticle pores and at least one second peak caused by interparticle pores, where the second peak top height is 1.0 mL / g or more and the second peak top diameter is 15 μm or more.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a thermally conductive resin sheet, a laminated heat dissipation sheet having a configuration in which a heat dissipation metal layer is laminated on the surface of the thermally conductive resin sheet, and a heat dissipation circuit board having a configuration in which a conductive circuit is further formed. [Background technology]

[0002] In recent years, power semiconductor devices used in various fields such as railways, automobiles, industry, and general home appliances are being replaced by power semiconductors that use SiC, AlN, GaN, etc. in order to achieve further miniaturization, cost reduction, and efficiency improvement. Power semiconductor devices are generally used as a power semiconductor module in which a plurality of semiconductor devices are arranged on a common heat sink and packaged.

[0003] Various issues have been raised in the practical application of such power semiconductor devices. One of these is the issue of heat generation from the devices. Power semiconductor devices can achieve high output and high density by operating at high temperatures. However, there are concerns that the heat generated by device switching may reduce the reliability of the power semiconductor devices.

[0004] In recent years, particularly in the electrical and electronics fields, heat generation due to the increasing density of integrated circuits has become a major problem, and how to dissipate heat has become an urgent issue. One method of solving this problem is to use highly thermally conductive ceramic substrates such as alumina substrates and aluminum nitride substrates as heat dissipation substrates on which power semiconductor devices are mounted. However, ceramic substrates have problems such as being easily cracked by impact, and being difficult to make thin and compact.

[0005] Therefore, thermally conductive resin sheets containing resin and inorganic filler are being considered as alternative products to the ceramic substrates. Among these, hexagonal boron nitride has attracted attention as an inorganic filler from the viewpoint of thermal conductivity and the like. However, because hexagonal boron nitride particles are plate-shaped, they have high thermal conductivity in the plane direction (ab-axis direction) but low thermal conductivity in the thickness direction (c-axis direction).When this hexagonal boron nitride is blended with resin and molded into a sheet, the hexagonal boron nitride tends to orient in the flow direction of the resin composition, i.e., the plane direction of the sheet, so the resulting thermally conductive resin sheet has high thermal conductivity in the plane direction but low thermal conductivity in the thickness direction.

[0006] In order to improve the anisotropy of the thermal conductivity of thermally conductive resin sheets, studies have been conducted to reduce particle orientation by using agglomerated boron nitride particles obtained by agglomerating boron nitride particles. For example, Patent Documents 1 and 2 propose spherical agglomerates obtained by binding boron nitride particles with a binder and then spray-drying them. Furthermore, Patent Document 3 proposes hexagonal boron nitride particles formed by primary particles of hexagonal boron nitride gathering together in a pinecone shape. Furthermore, Patent Document 4 proposes a granulated powder that contains spherical secondary particles formed by agglomerating scaly boron nitride, in which the density of the primary particles in the core portion of the secondary particles is lower than the density of the primary particles in the shell portion. Patent Document 5 proposes agglomerated particles of boron nitride in which primary particles of hexagonal boron nitride are aggregated, and the primary particles in the agglomerated particles have a house-of-cards structure. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-257392 [Patent Document 2] Special Publication No. 2008-510878 [Patent Document 3] Japanese Patent Application Publication No. 09-202663 [Patent Document 4] Japanese Patent Application Laid-Open No. 2016-044098 [Patent Document 5] Japanese Patent Application Laid-Open No. 2015-006985 Summary of the Invention [Problem to be solved by the invention]

[0008] Conventional thermally conductive resin sheets sometimes lack sufficient voltage resistance and thermal conductivity.

[0009] Furthermore, thermally conductive resin sheets for use in power semiconductor devices are required to be resistant to a reflow process. The reflow process is one of the processes used to assemble power semiconductor modules. In this process, the temperature of components is rapidly raised to melt the solder and join the metal components together. In recent years, as the operating temperatures of power semiconductor devices have increased with the increase in output and density, the solder used in the reflow process is also required to be heat resistant, and it has become common to use high-temperature solder that requires a reflow temperature of 290°C. Therefore, in the reflow process, the temperature is raised to around 290°C, at which point the high-temperature solder flows, and then the process of cooling is repeated. Furthermore, if the components absorb moisture before the reflow process is performed, deterioration of the components during the reflow process is greatly accelerated, which may result in a significant decrease in voltage resistance.

[0010] Therefore, an object of the present invention is to provide a thermally conductive resin sheet that has good voltage resistance and thermal conductivity, and is excellent in moisture absorption and reflow resistance. In this specification, "moisture absorption reflow resistance" means that even after a moisture absorption reflow test in which a thermally conductive resin sheet is laminated with a metal plate and stored under high temperature and high humidity conditions (for example, at 85°C and 85% RH for 3 days) and then subjected to a reflow test (for example, at 290°C), the thermally conductive resin sheet has high voltage resistance and does not undergo interfacial peeling with the metal plate or deformation due to foaming. [Means for solving the problem]

[0011] The gist of the present invention is as follows. [1] A thermally conductive resin sheet made of a resin composition containing a thermoplastic resin and agglomerated particles of boron nitride, In a pore size distribution curve obtained by measuring the residual ash content when the thermal conductive resin sheet is heated at 700°C for 5 hours by mercury intrusion porosimetry, a peak having a maximum value at a pore size of less than 5µm is defined as a first peak, and a peak having a maximum value at a pore size of 5µm or more is defined as a second peak, A thermally conductive resin sheet having a second peak top height of 1.0 mL / g or more and a second peak top diameter of 15 μm or more. [2] The thermally conductive resin sheet according to [1] above, wherein the main component of the thermoplastic resin is a crystalline thermoplastic resin having a melting point of 300°C or higher. [3] The thermally conductive resin sheet according to the above [2], wherein the crystalline thermoplastic resin having a melting point of 300°C or higher is a polyether ketone resin. [4] The thermally conductive resin sheet according to the above [3], wherein the polyether ketone-based resin is polyether ether ketone. [5] The thermally conductive resin sheet according to any one of the above [1] to [4], wherein the agglomerated boron nitride particles have a house-of-card structure. [6] The thermally conductive resin sheet according to any one of the above [1] to [5], wherein the volume-based average particle diameter D50 of the boron nitride agglomerated particles is 10 μm or more and 200 μm or less. [7] The thermally conductive resin sheet according to any one of [1] to [6] above, wherein the resin composition contains 15% by mass or more and 40% by mass or less of the thermoplastic resin and 60% by mass or more and 85% by mass or less of the boron nitride agglomerated particles, based on 100% by mass of the resin composition. [8] The thermally conductive resin sheet according to any one of the above [1] to [7], wherein the first peak top diameter is 0.4 μm or less. [9] The thermally conductive resin sheet according to any one of the above [1] to [8], wherein the first peak top height is 0.25 mL / g or more and 0.7 mL / g or less.

[10] The thermally conductive resin sheet according to any one of the above [1] to [9], wherein the circularity of boron nitride agglomerated particles contained in residual ash obtained by heating the thermally conductive resin sheet at 700°C for 5 hours exceeds 0.945.

[11] The thermally conductive resin sheet according to any one of the above [1] to

[10] , which has a thickness of 50 μm or more and 300 μm or less.

[12] The thermally conductive resin sheet according to any one of the above [1] to

[11] , which has a thermal conductivity in the thickness direction at 25°C of 18 W / m·K or more.

[13] A laminated heat-dissipating sheet having a configuration in which a heat-dissipating metal layer is laminated on one surface of the thermally conductive resin sheet according to any one of the above [1] to

[12] .

[14] A heat dissipation circuit board having the laminated heat dissipation sheet according to

[13] above.

[15] The heat dissipation circuit board according to the above

[14] , wherein a conductive circuit is formed on the other surface of the thermally conductive resin sheet.

[16] A power semiconductor device having the heat dissipation circuit board according to

[14] or

[15] above.

[17] A mixing step of obtaining a mixture of powder made of a thermoplastic resin and agglomerated particles of boron nitride; a press molding step of heating and pressurizing the mixture to form it into a sheet, In a pore size distribution curve obtained by measuring the residual ash content when the sheet is heated at 700°C for 5 hours by mercury intrusion porosimetry, a peak having a maximum value at a pore size of less than 5µm is defined as a first peak, and a peak having a maximum value at a pore size of 5µm or more is defined as a second peak. A method for producing a thermally conductive resin sheet, wherein the second peak top height is 1.0 mL / g or more and the second peak top diameter is 15 μm or more. [Effects of the Invention]

[0012] The thermally conductive resin sheet of the present invention has good voltage resistance and thermal conductivity, and is excellent in moisture absorption and reflow resistance. [Brief explanation of the drawings]

[0013] [Figure 1]FIG. 1 is a diagram showing the principle of measuring the intraparticle pore volume, interparticle space volume, peak top diameter, and peak top height of boron nitride agglomerated particles by mercury intrusion porosimetry. [Figure 2] FIG. 1 is a conceptual diagram of intra-particle pore volume. [Figure 3] FIG. 1 is a conceptual diagram of interparticle volume. [Figure 4] FIG. 1 is a conceptual diagram of a particle cross section according to an example of a boron nitride agglomerated particle having a small interparticle void volume. [Figure 5] 1 is an SEM photograph (a photograph substituted for a drawing) of the particle surface of an example of boron nitride agglomerated particles having a small interparticle void volume. [Figure 6] FIG. 1 is a conceptual diagram of a particle cross section according to an example of a boron nitride agglomerated particle having a large interparticle void volume. [Figure 7] 1 is an SEM photograph (a photograph substituted for a drawing) of the particle surface of an example of a boron nitride agglomerated particle having a large interparticle void volume. [Figure 8] FIG. 1 is a schematic diagram of a house of cards structure. [Figure 9] 1 shows an example of an SEM photograph of boron nitride agglomerated particles contained in residual ash when the thermally conductive resin sheet of Example 2 is heated at 700° C. for 5 hours. DETAILED DESCRIPTION OF THE INVENTION

[0014] An example of an embodiment of the present invention will be described in detail below. However, the present invention is not limited to the following embodiment, and various modifications can be made within the scope of the present invention.

[0015] 1.Resin composition The thermally conductive resin sheet of the present invention comprises a resin composition containing a thermoplastic resin and agglomerated particles of boron nitride. Each component will be described in detail below.

[0016] (1)Thermoplastic resin The thermoplastic resin used in the thermally conductive resin composition of the present invention is preferably resistant to resin flow, plastic deformation, and recovery of thermal recovery strain due to a decrease in elastic modulus even under reflow conditions for a heat dissipating circuit board, such as 290°C for 5 minutes. To satisfy these requirements, the thermoplastic resin preferably has a glass transition temperature (Tg) of 300°C or higher or a melting point (Tm) of 300°C or higher.

[0017] When the thermoplastic resin is a resin composition consisting of a combination of two or more thermoplastic resins that are mutually compatible, it is preferable that the glass transition temperature (Tg) of the resin composition is 300°C or higher, or the melting point (Tm) of the resin composition is 300°C or higher. On the other hand, when the thermoplastic resin is a resin composition consisting of a combination of two or more thermoplastic resins that are incompatible with each other, it is preferable that the glass transition temperature (Tg) of the thermoplastic resin that is the main component of the resin composition is 300°C or higher, or that the melting point (Tm) of the thermoplastic resin that is the main component of the resin composition is 300°C or higher. Here, "main component" means the resin that has the highest mass content in the resin composition, and refers to a resin that accounts for 50 mass% or more of the resin composition, particularly 60 mass% or more, particularly 70 mass% or more, particularly 80 mass% or more, particularly 90 mass% or more, particularly 95 mass% or more (including 100 mass%).

[0018] From the above viewpoint, the thermoplastic resin preferably contains a non-crystalline thermoplastic resin having a glass transition temperature (Tg) of 300°C or higher and / or a crystalline thermoplastic resin having a melting point (Tm) of 300°C or higher. In particular, it is preferable that the main component of the thermoplastic resin is a non-crystalline thermoplastic resin having a glass transition temperature (Tg) of 300°C or higher and / or a crystalline thermoplastic resin having a melting point (Tm) of 300°C or higher, i.e., that it accounts for 50% by mass or more of the total thermoplastic resin, more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more (including 100% by mass).

[0019] In the present invention, the term "amorphous thermoplastic resin" refers to a thermoplastic resin that does not have a melting point, while the term "crystalline thermoplastic resin" refers to a thermoplastic resin that has a melting point.

[0020] Examples of heat-resistant amorphous thermoplastic resins available as commercially available raw materials include polycarbonate resin (Tg: 152°C), modified polyphenylene ether resin (Tg: 211°C), polysulfone resin (Tg: 190°C), polyphenylsulfone resin (Tg: 220°C), polyethersulfone resin (Tg: 225°C), and polyetherimide resin (Tg: 217°C). However, none of these commercially available heat-resistant amorphous thermoplastic resins has a glass transition temperature of 300°C or higher. Thermoplastic polyimide resins with glass transition temperatures of 300°C or higher are commercially available. However, these thermoplastic polyimide resins have extremely high moldable temperatures and extremely high melt viscosities at these moldable temperatures, making it difficult to fill them with a large amount of agglomerated boron nitride particles. Furthermore, because the molecular structure contains imide groups, these resins are highly hygroscopic, making them unsuitable for use as the main component of the thermoplastic resin of the present invention.

[0021] For these reasons, the thermoplastic resin used in the thermally conductive resin composition of the present invention is preferably a resin primarily composed of a crystalline thermoplastic resin having a melting point of 300°C or higher. By using a crystalline thermoplastic resin having a melting point of 300°C or higher as the primary component, sufficient heat resistance and durability for use as a substrate for a power semiconductor device can be achieved. Furthermore, even when a large amount of boron nitride agglomerated particles is filled, the resin exhibits good moldability and is able to sufficiently reduce voids within the sheet caused by the shape or internal voids of the agglomerated particles, as well as voids within the sheet caused by moisture absorption by the resin components or agglomerated particles, resulting in good insulation. Furthermore, a crystalline thermoplastic resin having a melting point of 300°C or higher is less likely to flow, plastically deform, or recover from thermal recovery strain due to a decrease in elastic modulus under reflow conditions, resulting in good moisture absorption reflow resistance.

[0022] The melting point of a thermoplastic resin can be measured by the method specified in JIS K-7121 "Method for measuring transition temperature of plastics - Determination of melting temperature." Specifically, the thermoplastic resin composition is used as a test specimen using a differential scanning calorimeter (DSC: for example, "DSC-7" manufactured by PerkinElmer, etc.), and 10 mg of the sample is heated from -40°C to 380°C at a heating rate of 10°C / min, held at 380°C for 1 minute, cooled to -40°C at a cooling rate of 10°C / min, held at the same temperature for 1 minute, and then heated again at 10°C / min, and the temperature (Tpm) at the apex of the melting peak is read as the melting point (Tm). The crystalline thermoplastic resin used in the present invention is one in which at least endothermic peaks due to crystalline melting can be clearly confirmed and the temperature of the apex of the main peak among the peaks is 300°C or higher. When resin compositions containing boron nitride agglomerated particles are measured using a differential scanning calorimeter (DSC), there is no significant difference in melting point, except in cases where the addition of the boron nitride agglomerated particles accelerates deterioration of the matrix resin during heat molding.

[0023] From the viewpoint of moisture absorption reflow resistance at 290°C, the melting point of the crystalline thermoplastic resin is more preferably 310°C or higher, particularly 320°C or higher, and even more preferably 330°C or higher. On the other hand, the upper limit of the melting point is not particularly limited. From the viewpoint of moldability and productivity, it is more preferably 380°C or lower, particularly 370°C or lower, and even more preferably 360°C or lower.

[0024] When the melting point of the thermoplastic resin is 300° C. or higher, the elastic modulus of the resin raw material is unlikely to decrease even at the reflow condition of 290° C. Therefore, flow deformation of the resin can be suppressed even in the reflow process, and elastic strain of the resin layer is unlikely to be restored, so that deterioration of the surface appearance of the thermally conductive resin sheet and unevenness in the thickness of the thermally conductive resin sheet can be suppressed, and a thermally conductive resin sheet with sufficient strength can be obtained. Furthermore, because the elastic modulus of the resin raw material is unlikely to decrease at 290°C, even if the resin composition absorbs moisture in a humid and hot environment and moisture is present in the resin composition, the moisture in the resin composition is unlikely to expand during the reflow process or the process of mounting on a module, and foaming is unlikely to occur in the thermally conductive resin sheet, resulting in good voltage resistance performance and thermal conductivity.

[0025] It is believed that the foaming in the thermally conductive resin sheet during the reflow process, and the voltage resistance performance and thermal conductivity are related, for example, as follows. When moisture in the resin composition expands during the reflow process or the process of mounting on a module, foaming may occur inside the thermally conductive resin sheet, near the interface between the heat dissipation metal layer and the thermally conductive resin sheet, or near the interface between the conductive circuit pattern and the thermally conductive resin sheet. For example, if bubbles occur inside the thermally conductive resin sheet, the voltage resistance performance may be significantly reduced. When a heat-dissipating metal material is laminated on one surface of a thermally conductive resin sheet, if foaming occurs near the interface between the heat-dissipating metal material and the thermally conductive resin sheet, the heat-dissipating metal material may peel off, resulting in a significant decrease in thermal conductivity. Furthermore, if a conductive circuit pattern is formed on the other surface of the thermally conductive resin sheet, if foaming occurs near the interface between the conductive circuit pattern and the thermally conductive resin sheet, the conductive circuit pattern may peel off or fall off, causing abnormalities in the electrical circuit or a significant decrease in the thermal conductivity of the thermally conductive resin sheet.

[0026] Specific examples of heat-resistant crystalline thermoplastic resins include polybutylene terephthalate resin (PBT, melting point: 224°C), polyamide 6 (nylon 6, melting point: 225°C), polyamide 66 (nylon 66, melting point: 265°C), liquid crystal polymer (LCP, melting point: 320°C to 344°C), polyether ketone resin (melting point: 303°C to 400°C), polytetrafluoroethylene resin (PTFE, melting point: 327°C), tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin (PFA, melting point: 302°C to 310°C), and tetrafluoroethylene-hexafluoropropylene copolymer resin (FEP, melting point: 250°C to 290°C).

[0027] As the crystalline thermoplastic resin used in the present invention, liquid crystal polymers, polyether ketone resins, PTFE, and PFA are preferred because they have a melting point of 300° C. or higher. Among these crystalline thermoplastic resins having a melting point of 300° C. or higher, liquid crystal polymers and / or polyether ketone resins are particularly preferred from the viewpoint of moldability, etc. Furthermore, among these, polyether ketone resins are preferred from the viewpoint of adhesion to heat dissipation metal layers such as copper plates.

[0028] The polyether ketone resin that can be used in the present invention is a general term for thermoplastic resins having a repeating unit represented by the following formula (1) (wherein m and n are 1 or 2).

[0029] [ka]

[0030] Examples of polyetherketone resins include polyetherketone (PEK; m=1, n=1, melting point 373°C), polyetheretherketone (PEEK; m=2, n=1, melting point 343°C), polyetherketoneketone (PEKK; m=1, n=2, melting point 303°C to 400°C), polyetheretherketoneketone (PEEKK; m=2, n=2, melting point 358°C), and polyetherketoneetherketoneketone (PEKEKK; copolymer containing both m=1, n=1 structural units and m=1, n=2 structural units, melting point 387°C). All of these are commercially available raw materials.

[0031] Among polyether ketone resins, polyether ether ketone (PEEK) can be particularly preferably used, taking into consideration the following points: it has a sufficiently high melting point, and its molding processing temperature is relatively low, allowing for a shortened molding cycle; it has a continuous heat resistance temperature of 200°C or higher, demonstrating that it can be used in heat-resistant applications without any problems; various grades are available with respect to melt viscosity, which is related to molding processability; it is considered to have the most chemically stable structure among polyether ketone resins, and is also excellent in hot water resistance and chemical resistance; and its price has become reasonable due to its use in a wide range of applications.

[0032] When polyether ether ketone (PEEK) is used as the crystalline thermoplastic resin in the present invention, it may be blended with other thermoplastic resins. The type of other thermoplastic resin is not particularly limited, but among them, the other thermoplastic resin is preferably a compatible resin that has the effect of compensating for the performance that is insufficient when polyether ether ketone alone is used for the application of the present invention.

[0033] As the compatible resin, polyetherimide (PEI) is more preferable. Combining PEEK with PEI not only allows adjustment of the crystallinity (heat of crystalline fusion) of PEEK, but also adjusts the crystallization rate of PEEK, thereby increasing the glass transition temperature when the resin composition is in an amorphous state (Tg of PEEK is 143°C, while Tg of PEI is 217°C). Since PEI is an amorphous resin, the melting point of the resin itself does not change even when PEEK and PEI are combined. Additionally, in the present invention, by using PEI which has an imide group and is amorphous, it is possible to improve the adhesiveness to heat-dissipating metal materials such as copper plates.

[0034] The amount of PEI added is preferably 50% by mass or less, with the total amount of the resin composition being 100% by mass. By adding PEI in an amount of 50% by mass or less, heat resistance in a moisture absorption reflow test can be maintained by the crystallinity of PEEK, while good adhesion to heat-dissipating metal materials can be achieved.

[0035] Various commercially available PEEK products with various melt viscosities are available from various companies, such as "KetaSpire (registered trademark)" manufactured by Solvay, "Vestakeep (registered trademark)" manufactured by Daicel-Evonik, and "Victrex PEEK" manufactured by Victrex. These PEEK raw materials may be used in a single grade or in a blend of multiple grades with different melt viscosities and the like.

[0036] The melt viscosity of the crystalline thermoplastic resin in the present invention is not particularly limited. Since a relatively large amount of boron nitride agglomerated particles is blended, the melt viscosity of the crystalline thermoplastic resin is preferably 0.60 kPa·s or less, and more preferably 0.30 kPa·s or less, in order to facilitate heat molding. Having a melt viscosity within the above range eliminates the need to set the temperature of the molding machine excessively high, and deterioration of the raw materials can be suppressed. On the other hand, the lower limit of the melt viscosity is not particularly limited. A melt viscosity of 0.01 kPa·s or more is particularly preferred. The melt viscosity is measured in accordance with ASTM D3835 at a shear rate of 1000 s -1 The values ​​were measured at a temperature of 400°C.

[0037] From the viewpoint of long-term durability in a heated environment, the mass average molecular weight (Mw) of the crystalline thermoplastic resin is preferably 48,000 or more, more preferably 49,000 or more, and even more preferably 50,000 or more. On the other hand, from the viewpoint of moldability, it is preferably 120,000 or less, more preferably 110,000 or less, and even more preferably 100,000 or less.

[0038] The MFR of the crystalline thermoplastic resin is preferably 8 g / 10 min or more, more preferably 9 g / 10 min or more, and even more preferably 10 g / 10 min or more, from the viewpoints of moldability and preventing voids from forming between the resin and the added boron nitride agglomerated particles. On the other hand, from the viewpoint of long-term durability in a heated environment, the MFR is preferably 180 g / 10 min or less, more preferably 170 g / 10 min or less, and even more preferably 160 g / 10 min or less. The MFR is a value measured at 380°C and 5 kgf in accordance with JIS K7210:2014.

[0039] (2) Boron nitride agglomerated particles The shape of the agglomerated particles of boron nitride of the present invention is preferably spherical. In the present invention, the "circularity" measured using a particle image analyzer (Malvern Instruments, Morphologi G3S) is used as an index of the "sphericity" of boron nitride agglomerated particles. This measurement involves observing a projected planar image (two-dimensional image) of the particle, but the "sphericity" can be evaluated by increasing the number of measurements and averaging them. The circularity of the boron nitride agglomerated particles in the resin composition is preferably more than 0.945, with the upper limit being 1, more preferably 0.95 or more, and even more preferably 0.96 or more.

[0040] The agglomerated structure of the boron nitride agglomerated particles is preferably a card house structure from the viewpoint of improving thermal conductivity. The agglomerated structure of the boron nitride agglomerated particles can be confirmed by a scanning electron microscope (SEM).

[0041] The house-of-cards structure is a complex stack of plate-like particles that are not oriented, as described in "Ceramics 43 No. 2" (published by the Ceramic Society of Japan, 2008). More specifically, it is a structure in which the flat surfaces of the primary particles that form the agglomerate are firmly bonded or joined to the edge surfaces of the other primary particles present within the agglomerate, and each of the scale-like or flat primary particles is present within the agglomerate in a random orientation. A schematic diagram of the house-of-cards structure is shown in Figure 8. The house-of-card structure agglomerated particles have the above structure and a relatively high degree of sphericity for agglomerated particles, resulting in extremely high fracture strength and resistance to crushing even during the pressure application process performed during thermally conductive resin sheet molding. Therefore, primary particles, which are normally oriented in the longitudinal direction of a thermally conductive resin sheet, can be made to exist in a random direction. Therefore, the use of house-of-card structure agglomerated particles can further increase the proportion of primary particles with their ab planes oriented in the thickness direction of the thermally conductive resin sheet, thereby enabling effective thermal conduction in the thickness direction of the sheet and further increasing the thermal conductivity in the thickness direction.

[0042] The boron nitride agglomerated particles having a house-of-card structure can be produced, for example, by the method described in WO 2015 / 119198. The boron nitride agglomerated particles of the present invention are preferably not subjected to a treatment that applies force to the surface, such as a ball mill.

[0043] When using agglomerated boron nitride particles having a house-of-card structure, the particles may be surface-treated with a surface treatment agent. As the surface treatment agent, for example, a known surface treatment agent such as a silane coupling treatment can be used. Generally, direct affinity or adhesion between boron nitride agglomerated particles and thermoplastic resins is often not observed, and this is also the case when boron nitride agglomerated particles having a house-of-card structure are used. It is believed that by increasing the adhesion at the interface between the boron nitride agglomerated particles and the matrix resin by chemical treatment, it is possible to further reduce the attenuation of thermal conductivity at the interface.

[0044] The boron nitride agglomerated particles of the present invention can have a larger particle size than when primary particles are used as they are. By increasing the particle size of the boron nitride agglomerated particles, the heat transfer paths between the boron nitride agglomerated particles via the thermoplastic resin, which has 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.

[0045] From the above viewpoints, the lower limit of the volume-based maximum particle diameter Dmax (hereinafter also referred to as "maximum particle diameter") of the boron nitride agglomerated particles is preferably 20 μm or more, more preferably 30 μm or more, and even more preferably 50 μm or more. On the other hand, the upper limit of the maximum particle diameter Dmax is preferably 300 μm or less, more preferably 200 μm or less, even more preferably 100 μm or less, and still more preferably 90 μm or less.

[0046] The lower limit of the volume-based average particle diameter D50 of the boron nitride agglomerated particles is preferably 10 μm or more, more preferably 20 μm or more, and even more preferably 30 μm or more, while the upper limit of the average particle diameter D50 is preferably 200 μm or less, more preferably 100 μm or less, even more preferably 80 μm or less, and still more preferably 60 μm or less.

[0047] When the maximum particle size of the boron nitride agglomerated particles is equal to or less than the above upper limit, when the boron nitride agglomerated particles are contained in a matrix resin, the interface between the matrix resin and the boron nitride agglomerated particles is reduced, resulting in lower thermal resistance, achieving high thermal conductivity and forming a high-quality film without surface roughness, etc. When the maximum particle size is equal to or greater than the above lower limit, the boron nitride agglomerated particles can achieve a sufficient thermal conductivity improvement effect required for power semiconductor devices.

[0048] Furthermore, it is believed that the effect of the thermal resistance at the interface between the matrix resin and the boron nitride agglomerated particles on the thickness of the thermal conductive resin sheet becomes significant when the size of the boron nitride agglomerated particles relative to the thickness of the thermal conductive resin sheet is 1 / 10 or less. In particular, in the case of power semiconductor devices, thermal conductive resin sheets with thicknesses of 100 μm to 300 μm are often used, so from the viewpoint of thermal conductivity as well, it is preferable that the volume-based maximum particle size Dmax of the boron nitride agglomerated particles be larger than the above lower limit. Furthermore, by ensuring that the maximum particle diameter Dmax of the boron nitride agglomerated particles is equal to or greater than the above lower limit, not only is an increase in thermal resistance caused by the interface between the boron nitride agglomerated particles and the matrix resin suppressed, but the number of required heat conduction paths between particles is reduced, increasing the probability that paths will be connected from one surface to the other in the thickness direction of the thermal conductive resin sheet. Furthermore, when the maximum particle size Dmax of the boron nitride agglomerated particles is equal to or greater than the above lower limit, the interfacial area between the matrix resin and the boron nitride agglomerated particles is smaller than when the same mass of particles having a Dmax smaller than the above lower limit is used. This reduces the occurrence of voids that tend to occur at the interface between the matrix resin and the boron nitride agglomerated particles in the thermal conductive resin sheet, making it easier to obtain excellent voltage resistance characteristics. On the other hand, when the volume-based maximum particle diameter Dmax of the boron nitride agglomerated particles is equal to or less than the above upper limit, protrusion of the boron nitride agglomerated particles onto the surface of the thermal conductive resin sheet is suppressed, and a good surface shape without surface roughness is obtained. Therefore, when a sheet is produced by bonding the sheet to a copper substrate, sufficient adhesion can be obtained, and excellent voltage resistance characteristics can be obtained.

[0049] The ratio (Dmax / thickness) of the size (Dmax) of the boron nitride agglomerated particles to the thickness of the thermally conductive resin sheet is preferably 0.3 or more and 1.0 or less, more preferably 0.35 or more or 0.95 or less, and even more preferably 0.4 or more or 0.9 or less.

[0050] The maximum particle size Dmax and the average particle size D50 of the boron nitride agglomerated particles can be measured, for example, by the following method. A sample in which boron nitride agglomerated particles are dispersed in a solvent, specifically a sample in which boron nitride agglomerated particles are dispersed in a pure water medium containing sodium hexametaphosphate as a dispersion stabilizer, is subjected to particle size distribution measurement using a laser diffraction / scattering particle size distribution analyzer LA-920 (manufactured by Horiba, Ltd.), and the maximum particle diameter Dmax and average particle diameter D50 of the boron nitride agglomerated particles can be determined from the obtained particle size distribution. The maximum particle size and the average particle size can also be determined using a dry particle size distribution measuring device such as Morphologi G3S (manufactured by Malvern Instruments). The maximum particle size Dmax and average particle size D50 of the boron nitride agglomerated particles added to the thermoplastic resin can also be measured in the same manner as above by dissolving and removing the thermoplastic resin in a solvent (including a heated solvent), or by swelling the thermoplastic resin to reduce the adhesive strength to the boron nitride agglomerated particles and then physically removing it, and then heating the resin component in the atmosphere to incinerate it and remove it.

[0051] In the boron nitride agglomerated particles of the present invention, the intraparticle pore volume A1 measured by mercury intrusion porosimetry is preferably 0.30 mL / g or more, more preferably 0.35 mL / g or more, even more preferably 0.40 mL / g or more, and even more preferably 0.42 mL / g or more. The intraparticle pore volume A1 is preferably 0.80 mL / g or less, more preferably 0.70 mL / g or less, even more preferably 0.60 mL / g or less, even more preferably 0.55 mL / g or less, and particularly preferably 0.50 mL / g or less.

[0052] The intra-particle pore volume is the pores α present inside the agglomerated particles, excluding closed pores into which mercury has not been pressed in, as shown in Figure 2. This intra-particle pore volume is a value determined by the density, average aspect ratio, particle thickness, etc. of the boron nitride primary particles that make up the agglomerated particles, and is related to the mechanical properties of the boron nitride agglomerated particles and the thermal conductivity inside the agglomerated particles. When the intraparticle pore volume is appropriately reduced, there are not too many voids in the agglomerated particles, which increases the thermal resistance, and therefore the thermal conductivity inside the agglomerated particles tends to be efficiently increased. Furthermore, the strength of the agglomerated particles can be increased, and for example, even when a sheet is produced by press molding, the agglomerated particles themselves are not crushed or excessively deformed, and the isotropy of the agglomerated particles is maintained, so that the decrease in the thermal conductivity in the thickness direction of the thermal conductive resin sheet can be effectively suppressed. On the other hand, if the intra-particle pore volume is appropriately increased, the penetration of the resin into the internal pores of the agglomerated particles can be sufficiently ensured, and the generation of voids in the thermally conductive resin sheet can be suppressed, which tends to improve the voltage resistance performance.

[0053] In the boron nitride agglomerated particles of the present invention, the interparticle volume B1 measured by mercury intrusion porosimetry is preferably 0.50 mL / g or more, more preferably 0.55 mL / g or more, even more preferably 0.60 mL / g or more, and even more preferably 0.65 mL / g or more. It is further preferably 0.70 mL / g or more, more preferably 0.75 mL / g or more, even more preferably 0.80 mL / g or more, and even more preferably 0.85 mL / g or more. Furthermore, the interparticle volume B1 is preferably 1.0 mL / g or less, more preferably 0.95 mL / g or less, and even more preferably 0.90 mL / g or less.

[0054] In Figure 3, the interparticle volume is the pores β present between multiple agglomerated particles. Generally, this volume represents the degree of packing due to the shape, particle size, and particle distribution of the agglomerated particles. However, for boron nitride agglomerated particles, this value is a composite of the orientation of the primary particles on the agglomerated particle surface (e.g., whether the primary particle surfaces are oriented in the radial direction of the agglomerated particles or in the circumferential direction of the agglomerated particles), the density of the surface primary particles, the average aspect ratio, and particle thickness. Furthermore, it is also related to the density, average aspect ratio, and particle thickness of the primary particles that make up the entire agglomerated particle. This is because, when the primary particles are too large and not dense enough, the agglomerated particles themselves lack strength, resulting in particle fracture or shedding of surface primary particles during various operations prior to blending with the resin. These fractured particle fragments and isolated primary particles fill the gaps between the agglomerated particles during mercury intrusion porosimetry measurements.

[0055] Here, the interparticle volume will be explained in more detail with reference to FIGS. For example, when the thickness direction (c-axis direction) of the primary particles near the outermost surface of the agglomerated particles is aligned with the radial direction of the agglomerated particles, the interparticle volume tends to be small. Such agglomerated particles have the advantage of being easy to coat when a thermally conductive resin sheet is produced by a wet coating method, and it is easy to obtain a sheet with few residual voids. However, because the primary particles near the outermost surface lie flat so as to cover the agglomerated particles, the thermal resistance at the interface between the agglomerated particle surface and the resin or at the contact interface between multiple agglomerated particles may increase. Furthermore, when multiple agglomerated particles are packed so as to come into contact with each other within a thermally conductive resin sheet, thermal conduction occurs between the agglomerated particles shown in Figures 4 and 5 at the surface of each agglomerated particle via the thickness direction (c-axis direction) of the primary particles. Because the thermal conductivity of the primary particles is low in the thickness direction, there is a limit to the thermal conductivity of the thermally conductive resin sheet in the thickness direction. Furthermore, for example, when the primary particles constituting the agglomerated particles are excessively large and lack density, the interparticle volume becomes small. Because such agglomerated particles lack strength, there is a risk that the agglomerated particles will be destroyed or the surface primary particles will fall off when, for example, a sheet is produced by press molding. Because these isolated primary particles are plate-shaped or scale-shaped, the thickness direction (c-axis direction) of the particles may be oriented in the plane direction of the sheet, which may reduce the thermal conductivity of the thermal conductive resin sheet in the thickness direction.

[0056] On the other hand, for example, as shown in Figures 6 and 7, when the surface direction (ab-axis direction) of the primary particles near the outermost surface of the agglomerated particles is structured so that it coincides with the radial direction of the agglomerated particles, and these oriented surface primary particles are densely present, the interparticle volume tends to be large. When such agglomerated particles are packed so that multiple particles are in contact with each other within a thermally conductive resin sheet, the contact area between the particles is larger than when the primary particles near the outermost surface lie flat, covering the agglomerated particles. This reduces the thermal resistance between the particles, resulting in a higher thermal conductivity through the thickness of the thermally conductive resin sheet. Furthermore, if the interparticle void volume is large and the intraparticle pore volume, average particle size, and particle size distribution are the same, the contact surfaces of multiple agglomerated particles will deform during the pressurization process, such as sheet molding, as shown in Figure 9. This increases the contact area, creating a surface-like contact like state between polyhedra, further reducing the thermal resistance between the particles. Furthermore, for example, when the primary particles constituting the agglomerated particles are appropriately small and dense, the interparticle volume measured by the sheet ash content is large. Such agglomerated particles have good strength, which prevents the agglomerated particles from breaking during molding and the surface primary particles from falling off. Therefore, the isolation of the primary particles can be suppressed, thereby improving the thermal conductivity in the thickness direction of the thermal conductive resin sheet.

[0057] In the present invention, the intra-particle pore volume and inter-particle space volume of the boron nitride agglomerated particles are each determined by the method described in the Examples in accordance with JIS R1655:2003. Specifically, 200 mg of boron nitride agglomerated particles are first prepared, and a mercury intrusion / extrusion curve is measured by mercury intrusion porosimetry. Next, as illustrated in Figure 1, a pore size distribution curve is created, with pore size on the horizontal axis and logarithmic differential pore volume on the vertical axis. Peak a, which originates from intraparticle pores, is typically observed in the range of less than 5 μm, preferably between 0.1 μm and less than 5 μm, and peak b, which originates from interparticle gaps, is typically observed in the range of 5 μm or more, preferably between 5 μm and 100 μm. Between peaks a and b, the diameter at which the logarithmic differential pore volume takes a minimum value relative to the pore size (division diameter, X in Figure 1) is read. The integral of the mercury intrusion / extrusion curve in the region of the pore size larger than the division diameter (dashed arrow in Figure 1) is the interparticle gap volume. The integral value of the mercury intrusion-extrusion curve in the entire measurement region is the total pore volume, and the intra-particle pore volume is the value obtained by subtracting the inter-particle volume from the total pore volume.

[0058] (3) Content of each ingredient The lower limit of the thermoplastic resin content in 100% by mass of the resin composition of the present invention is preferably 15% by mass or more, more preferably 20% by mass or more, while the upper limit of the thermoplastic resin content is preferably 40% by mass or less, more preferably 35% by mass or less. The lower limit of the content of the boron nitride agglomerated particles in 100% by mass of the resin composition of the present invention is preferably 60% by mass or more, more preferably 65% ​​by mass or more, while the upper limit of the content of the boron nitride agglomerated particles is preferably 85% by mass or less, more preferably 80% by mass or less. When the content of the boron nitride agglomerated particles is equal to or greater than the above lower limit, the effects of the boron nitride agglomerated particles in improving thermal conductivity and controlling the linear expansion coefficient are satisfactorily exhibited, while when the content of the boron nitride agglomerated particles is equal to or less than the above upper limit, the moldability of the resin composition and the interfacial adhesion with different materials are improved.

[0059] Generally, the compounding ratio of a thermally conductive resin composition is often specified by the volume fraction of the matrix resin and the boron nitride agglomerated particles (hence, the area ratio in the cross section of the thermally conductive resin sheet). The thermal conductivity of the thermally conductive resin sheet in the thickness direction is not determined solely by the volume fraction, but is affected by various factors such as the aforementioned preferred particle size, particle orientation, and particle shape. Therefore, in the present invention, the mass fraction is used for the convenience of actual compounding. In particular, when using house-of-cards structured boron nitride agglomerated particles, the particles exhibit a house-of-cards internal structure, with numerous radially oriented, flat, plate-shaped boron nitride primary particles forming protrusions on the particle surface, often referred to as burrs or sugar candy. The protrusions of adjacent house-of-cards structured particles come into physical contact with each other, forming a heat transfer path with low thermal resistance in the thickness direction. Therefore, it may not be easy to determine the respective volume fractions of the matrix resin and the boron nitride agglomerated particles by observation with a conventional scanning electron microscope (SEM). Furthermore, as the amount of house-of-cards structured boron nitride agglomerated particles added increases, the pressure applied during hot press molding of the resin composition causes the particles to deform at the contact points, rather than contacting each other as spherical particles, resulting in linear, i.e., planar, contact. When this contact state is achieved, the addition of house-of-cards structured boron nitride enables the formation of an efficient heat transfer path. However, even in such cases, it is not easy to determine the volume fractions of the matrix resin and the boron nitride agglomerated particles by SEM observation.

[0060] The resin composition of the present invention may contain other components in addition to the thermoplastic resin and the boron nitride agglomerated particles, although from the viewpoint of increasing thermal conductivity, it is preferable that the resin composition does not contain other components. Other components include various phosphorus-based, phenol-based and other antioxidants, phenolic acrylate and other process stabilizers, heat stabilizers, hindered amine radical scavengers (HAAS), impact modifiers, processing aids, metal deactivators, copper inhibitors, antistatic agents, flame retardants, additives such as silane coupling agents that improve the affinity at the interface between the boron nitride agglomerated particles and thermoplastic resin, additives such as silane coupling agents that can be expected to increase the adhesive strength between the resin sheet and metal sheet material, extenders, etc. When these additives are used, the amount added may generally be within the range used for the purpose.

[0061] 2.Thermal conductive resin sheet The thermally conductive resin sheet of the present invention is made of the above-mentioned resin composition, and has the characteristics of having high thermal conductivity in the thickness direction, excellent moisture absorption reflow resistance, and being less likely to undergo interfacial peeling due to thermal expansion and thermal contraction when laminated with a metal plate.

[0062] A thermally conductive resin sheet made of a resin composition containing boron nitride agglomerated particles is heated at 700°C for 5 hours to remove the resin component, and a mercury intrusion-withdrawal curve of the ash is measured by mercury intrusion porosimetry. A pore size distribution curve is then plotted, with pore size on the horizontal axis and logarithmic differential pore volume on the vertical axis. Peaks are typically observed in the range of less than 5 μm, preferably 0.1 μm to less than 5 μm, and in the range of 5 μm or more, preferably 5 μm to 100 μm. In the present invention, the peak having a maximum value in the range of less than 5 μm, preferably 0.1 μm to less than 5 μm, is referred to as the first peak, and the peak having a maximum value in the range of 5 μm or more, preferably 5 μm to 100 μm, is referred to as the second peak. The range of less than 5 μm includes peak a, which is due to the intraparticle pores of the boron nitride agglomerated particles, and the range of 5 μm or more includes peak b, which is due to the interparticle gaps of the boron nitride agglomerated particles.

[0063] In the present invention, the maximum values ​​of the first peak and the second peak are referred to as the first peak top height and the second peak top height, respectively, and the pore diameters at which the first peak and the second peak show their respective maximum values ​​are referred to as the first peak top diameter and the second peak top diameter, respectively.

[0064] Incidentally, cases in which there are multiple peaks in the 5 μm or larger range are considered to be when a mixture of boron nitride agglomerated particles with two different particle size distributions is used in the residual ash, when a filler other than boron nitride is contained in addition to boron nitride agglomerated particles, or when peaks appear due to fragments generated when boron nitride agglomerated particles are disintegrated during the molding process or primary particles detached from the agglomerated particles. In these cases, the height of the second peak top is often smaller than in the present invention, and it is considered difficult to obtain high thermal conductivity.

[0065] To improve the thermal conductivity of a thermally conductive resin sheet, it is preferable to use agglomerated particles having a structure in which the primary particles near the outermost surface of the agglomerated particles are aligned with the radial direction of the agglomerated particles, and after forming the sheet, the agglomerated particles are deformed near the surface so that they are in surface contact with each other, and this deformation state is relatively uniform within the sheet, and further, there is little collapse of the agglomerated particles themselves and the resulting shedding of primary particles, and the contact area between the agglomerated particles is large. From this perspective, it is preferable that the distribution of the second peak is sharp (i.e., the second peak top height is large) and the second peak top diameter is large.

[0066] The second peak top height is preferably 1.0 mL / g or more, more preferably 1.2 mL / g or more, and even more preferably 1.5 mL / g or more. Although there are no particular limitations on the upper limit of the second peak top height, since the second peak top height of a boron nitride agglomerated particle raw material having a high circularity and a relatively narrow particle size distribution is about 3.5, the second peak top height is preferably 3.2 mL / g or less, more preferably 3.0 mL / g or less, even more preferably 2.7 mL / g or less, and even more preferably 2.5 mL / g or less. The height of the second peak top is an index showing the uniformity of the surface contact state between the aggregated particles in the sheet. As mentioned above, it is preferable that the aggregated particles in the sheet are in surface contact with each other due to deformation near their surfaces, but if the degree of deformation varies greatly among the aggregated particles and some of them are in near-point contact, the sheet as a whole will not achieve high thermal conductivity, and the height of the second peak top will be small. The second peak top height being equal to or greater than the lower limit indicates that the aggregated particles in the sheet are relatively uniformly deformed, are in a relatively uniform surface contact state, and the volume of interparticle space is relatively uniform.

[0067] The second peak top diameter is preferably 15 μm or more, more preferably 16 μm or more, and even more preferably 17 μm or more. On the other hand, from the viewpoint of bringing the aggregated particles into surface contact with each other, increasing the contact area, and reducing the thermal resistance between the aggregated particles, the second peak top diameter is preferably 30 μm or less, and more preferably 25 μm or less. If the second peak top diameter is large, there will be areas where only resin exists between multiple agglomerated particles, and therefore areas with high thermal resistance when viewed locally, with a relatively large volume, which is generally not desirable in terms of imparting high thermal conductivity to the heat dissipation sheet. However, when using boron nitride agglomerated particles as a thermally conductive filler, particularly in the case of house-of-card-shaped boron nitride agglomerated particles formed by strong bonding between primary particles constituting the agglomerated particles, it is important to maintain the strong bonding between the primary particles inside the agglomerated particles even after sheet formation. To maintain efficient heat transfer between the primary particles inside the agglomerated particles, it is preferable to prevent the agglomerated particles from being excessively deformed or crushed in the sheet. Agglomerated particles that have undergone excessive deformation or crushing may detach as a single primary particle or several bonded primary particles. When these particles are formed, the second peak top height or second peak top diameter tends to decrease, and the second peak tends to become broader.

[0068] In addition, the thermally conductive resin sheet of the present invention preferably has a small first peak top diameter, that is, small interparticle gaps and a dense aggregated particle structure. When the first peak top diameter is small, it is thought that the interparticle gaps of the raw material boron nitride agglomerated particles themselves are small, and as a result, the small interparticle gaps inherent in the raw material are maintained even after sheet formation. Boron nitride agglomerated particles with small interparticle gaps are thought to have a structure that makes it easy to obtain high thermal conductivity within the agglomerated particles, with the primary particles forming dense bonds. A small first peak top diameter reflects the fact that such agglomerated particles do not undergo excessive deformation, crushing, or primary particle shedding even after being subjected to pressure, etc. during sheet processing, and it is thought that a small first peak top diameter is likely to result in good thermal conductivity. It is possible that the aggregated particles are excessively deformed or disintegrated due to pressure or the like during sheet formation, resulting in a smaller first peak top diameter. In this case, the second peak top height and second peak top diameter described above will be outside the above ranges. From the above viewpoints, the first peak top diameter is preferably 0.4 μm or less, and more preferably 0.38 μm or less. On the other hand, from the viewpoints of ensuring sufficient penetration of the resin into the internal pores of the aggregated particles, suppressing the generation of voids in the thermal conductive resin sheet, and improving the withstand voltage performance, the first peak top diameter is preferably 0.1 μm or more, more preferably 0.15 μm or more, and even more preferably 0.2 μm or more.

[0069] The first peak top height is preferably 0.25 mL / g or more, more preferably 0.3 mL / g or more, and even more preferably 0.4 mL / g or more. The upper limit of the first peak top height is not particularly limited, but is preferably 0.7 mL / g or less, more preferably 0.65 mL / g or less, and even more preferably 0.6 mL / g or less. When the first peak top height is equal to or less than the upper limit, the pore volume inside the agglomerated particles does not become too large, and an appropriate amount of primary particles capable of efficient heat conduction is present inside the agglomerated particles. On the other hand, the first peak top height being equal to or greater than the above lower limit indicates that the agglomerated particles themselves used as raw materials have a moderate amount of internal voids, and it is believed that such agglomerated particles deform moderately near the surfaces of the agglomerated particles in the sheet, making them more likely to come into surface contact. Furthermore, when the first peak top height is below the lower limit, the first peak may be observed as a broad peak, which may be due to significant variations in the three-dimensional structure of the primary particles constituting the agglomerated particles used as raw material, or deformation or destruction of the agglomerated particles due to pressure or the like during sheet molding.

[0070] As described above, the first peak top height, the first peak top diameter, the second peak top height, and the second peak top diameter represent the strength of the aggregated particles, the orientation state of the primary particles after being formed into a sheet, and the like. The present inventors have found that, among these factors, the second peak top height and the second peak top diameter particularly affect the withstand voltage performance and thermal conductivity. The fact that the second peak top height and the second peak top diameter are within the above ranges indicates that agglomerated particles having sufficient strength are used, and in such a thermally conductive resin sheet, the agglomerated particles are less likely to collapse during molding, etc., and by using as a raw material house-of-card-type agglomerated boron nitride particles in which the primary particles on the surface of the agglomerated particles are radially oriented, sufficient heat conduction paths can be formed between the agglomerated particles.

[0071] Examples of boron nitride agglomerated particles having the second peak top height and second peak top diameter within the above ranges include agglomerated particles having a house-of-card structure. Alternatively, the boron nitride agglomerated particles may be obtained by a known method and then subjected to a physical or chemical surface roughening treatment to adjust the surface roughness. Generally, commercially available boron nitride agglomerated particles use boron nitride primary particles that are relatively highly crystallized during granulation. This results in the preferential stacking of stable primary particle planes (ab-planes), resulting in many a "cabbage structure" in which the thickness direction of the primary particles near the outermost surface of the agglomerated particles coincides with the radial direction of the agglomerated particles. Agglomerated particles with a "cabbage structure" tend to have primary particles near the outermost surface lying flat to cover the agglomerated particles, and the strength of the agglomerated particles themselves is often low, resulting in small second peak top heights and second peak top diameters in measurements of the heated ash content of the sheet. Therefore, when using agglomerated particles with a "cabbage structure," the surface roughening treatment described above may be performed to adjust the surface roughness.

[0072] The thermal conductivity of the thermally conductive resin sheet in the thickness direction at 25°C is preferably 18 W / m K or more, more preferably 19 W / m K or more, and even more preferably 20 W / m K or more. When the thermal conductivity in the thickness direction is equal to or greater than the above lower limit, the sheet can be suitably used in power semiconductor devices that operate at high temperatures. The thermal conductivity can be adjusted by the type of thermoplastic resin, physical properties such as melt viscosity, the values ​​of the first peak top height, first peak top diameter, second peak top height, and second peak top diameter in the thermal conductive resin sheet, the structure and content of the boron nitride agglomerated particles, the method of mixing the thermoplastic resin and the boron nitride agglomerated particles, the conditions in the heating and kneading step described below, and the like.

[0073] The thermal conductivity can be measured by the following method. First, the thermal diffusivity a (mm 2 Because there are no JIS standards for thermal diffusivity and thermal conductivity of resin-based materials, measurements are made in accordance with JIS R1611:2010 (Method for measuring thermal diffusivity, specific heat capacity, and thermal conductivity of fine ceramics using the flash method). Since JIS R1611:2010 stipulates that "the thickness of the sample must be 0.5 mm or more and 5 mm or less," measurements are made with the resin sheet adjusted to a thickness of 0.5 mm or more. If the resin sheet is less than 0.5 mm thick, multiple sheets may be stacked to adjust the total thickness to 0.5 mm or more for measurement. Next, the density ρ (g / m) of the resin sheet was measured using the Archimedes method in accordance with JIS K6268. 3 ) is found. Furthermore, the specific heat capacity c (J / (g·K)) at 25°C is measured using a DSC measuring device in accordance with JIS K7123. From these measured values, the thermal conductivity in the sheet thickness direction at 25°C can be calculated as "H = a x ρ x c".

[0074] The lower limit of the thickness of the thermally conductive resin sheet is preferably 50 μm or more, more preferably 60 μm or more, and even more preferably 70 μm or more, while the upper limit is preferably 300 μm or less, more preferably 200 μm or less, and even more preferably 160 μm or less. By making the thickness of the thermally conductive resin sheet 50 μm or more, sufficient voltage resistance characteristics can be ensured. On the other hand, by making the thickness 300 μm or less, it is possible to achieve miniaturization and thinning, especially when using the thermally conductive resin sheet in a power semiconductor device, and it is also possible to obtain the effect of reducing thermal resistance in the thickness direction by making the thickness thinner, compared to insulating thermally conductive layers made of ceramic materials.

[0075] In the thermally conductive resin sheet of the present invention, in order to reduce the anisotropy of thermal conductivity and increase the thermal conductivity in the thickness direction, it is preferable to reduce the orientation of the primary particles of the boron nitride agglomerated particles. The orientation of primary particles can be evaluated by measuring the thermally conductive resin sheet using X-ray diffraction, and calculating the ratio "I(002) / I(100)" where I(002) is the diffraction peak intensity of the (002) plane and I(100) is the diffraction peak intensity of the (100) plane. The ratio "I(002) / I(100)" is preferably 20 or less, more preferably 17 or less, and even more preferably 15 or less. If the ratio exceeds 20, the boron nitride agglomerated particles will have collapsed in the melt-kneading step or will have been excessively crushed in the pressing step, resulting in an increase in primary particles that are parallel to or form a small angle with the surface direction of the thermal conductive resin sheet. In this case, it will be difficult to increase the thermal conductivity in the thickness direction even if the content of boron nitride agglomerated particles is increased. The lower limit of the ratio "I(002) / I(100)" is not particularly limited. For example, when using boron nitride agglomerated particles that are highly isotropic and therefore have a house-of-card structure in which the boron nitride primary particles are hardly oriented in a specific direction, the ratio "I(002) / I(100)" of the particles alone is about 4.5 to 6.6, so 4.5 is considered to be the lower limit, unless intentional orientation is performed.

[0076] In the thermally conductive resin sheet of the present invention, when the boron nitride agglomerated particles contained in the residual ash are heated at 700°C for 5 hours, the intra-particle pore volume measured by mercury intrusion porosimetry is defined as A2, and the inter-particle void volume is defined as B2. Preferably, A2 / A1 is 0.70 or more, and B2 / B1 is 0.85 or less. An A2 / A1 ratio of 0.70 or greater indicates that the state of the primary particles within the agglomerates remains largely unchanged before and after sheet formation, thus indicating relatively high agglomerate strength. Therefore, an A2 / A1 ratio of 0.70 or greater indicates that the structure forming the thermal conductive paths within the original boron nitride agglomerates is adequately maintained after sheet formation. It also indicates that, despite deformation due to pressure during forming, the generation of isolated primary particles due to the crushing of agglomerates is minimal. This reduced generation of isolated primary particles reduces the thermal resistance through the thickness of the sheet. Isolated primary particles hinder efficient thermal conduction through the thickness because, due to their flat or scale-like shape, the thickness direction (c-axis direction) of the particles is oriented in the plane of the sheet in the formed sheet. On the other hand, a B2 / B1 ratio of 0.85 or less indicates that the surfaces of the agglomerated particles are significantly deformed before and after sheet formation. This deformation occurs because the contact area between the contact surfaces of multiple agglomerated particles increases, like polyhedrons coming into contact with each other, forming a surface-like contact state, as shown in Figure 9. Therefore, when agglomerated particles of boron nitride are present in the sheet with both A2 / A1 and B2 / B1 satisfying the above numerical ranges, high thermal conductivity can be obtained.

[0077] From the above viewpoints, A2 / A1 is preferably 0.70 or more, more preferably 0.72 or more, even more preferably 0.75 or more, and even more preferably 0.80 or more. Also, A2 / A1 is preferably 1.0 or less, more preferably 0.90 or less, and even more preferably 0.88 or less. On the other hand, B2 / B1 is preferably 0.85 or less, more preferably 0.80 or less, even more preferably 0.75 or less, and even more preferably 0.70 or less. Furthermore, B2 / B1 is preferably 0.65 or less, more preferably 0.60 or less, and even more preferably 0.50 or less. Furthermore, B2 / B1 is preferably 0.40 or more, and more preferably 0.45 or more.

[0078] The boron nitride agglomerated particles contained in the residual ash preferably have an intraparticle pore volume A2 of 0.20 mL / g or more, more preferably 0.25 mL / g or more, even more preferably 0.30 mL / g or more, even more preferably 0.32 mL / g or more, and particularly preferably 0.34 mL / g or more. The intraparticle pore volume A2 is preferably 0.60 mL / g or less, more preferably 0.50 mL / g or less, even more preferably 0.45 mL / g or less, and even more preferably 0.40 mL / g or less.

[0079] The interparticle volume B2 of the boron nitride agglomerated particles contained in the residual ash is preferably 0.35 mL / g or more, more preferably 0.40 mL / g or more, even more preferably 0.45 mL / g or more, and even more preferably 0.50 mL / g or more. The interparticle volume B2 is preferably 0.80 mL / g or less, more preferably 0.70 mL / g or less, and even more preferably 0.65 mL / g or less.

[0080] The circularity of the boron nitride agglomerated particles contained in the residual ash is preferably greater than 0.945, more preferably 0.95 or greater, from the viewpoint of suppressing excessive deformation of the agglomerated particles and improving the thermal conductivity of the sheet. Furthermore, since the thermal conductivity of the sheet improves when the agglomerated particles come into surface contact with each other, the circularity is preferably 0.99 or less, more preferably 0.98 or less, and even more preferably 0.97 or less.

[0081] 3. Manufacturing method of thermally conductive resin sheet An example of the method for producing the thermally conductive resin sheet of the present invention will be described below. An example of the method for producing the thermally conductive resin sheet of the present invention includes a mixing step and a press molding step.

[0082] A conventional manufacturing method for thermally conductive resin films is the wet coating method, in which a slurry containing a matrix resin and boron nitride agglomerated particles dispersed in a solvent is applied to a substrate. However, this method can result in reduced voltage resistance due to the inclusion of air bubbles during coating onto the substrate or the formation of bubbles due to residual solvent in the coating film if the solvent is not dried sufficiently. In particular, boron nitride agglomerated particles with a large second peak top diameter measured for the heated ash content of a sheet can be selected that have radially arranged primary particles on the agglomerated particle surface and a highly irregular agglomerated particle surface. While this method reduces the interfacial thermal resistance when agglomerated particles come into contact with each other due to pressure, such as during press molding of the sheet, it also tends to thicken the slurry and trap air bubbles during mixing with the resin or coating onto the substrate. This can lead to air bubbles remaining in the resin film, resulting in a reduction in voltage resistance. Furthermore, in the wet coating method, increasing the amount of boron nitride agglomerated particles added to improve thermal conductivity can result in the formation of streaks during coating, resulting in poor productivity. These streaks are particularly likely to occur when using boron nitride agglomerated particles that result in a large second peak top diameter measured for the heated ash content of the sheet.

[0083] In the manufacturing method of the present invention, the thermoplastic resin is pressed into the voids in the boron nitride agglomerated particles by forming the sheet at a temperature at which the thermoplastic resin exhibits fluidity, thereby preventing the inclusion of air bubbles in the sheet. Furthermore, since the sheet can be obtained without using a solvent, bubbles caused by residual solvent do not occur. Therefore, the manufacturing method of the present invention can improve the voltage resistance performance of the thermally conductive resin sheet. Furthermore, since the manufacturing method of the present invention does not involve a coating step, even if boron nitride agglomerated particles that have a large second peak top diameter measured for the heated ash content of the sheet are used as a raw material, problems associated with coating, such as the occurrence of streaks, do not occur, and productivity is good.

[0084] As described in the examples of Patent Documents 4 and 5, it has been common to use a thermosetting resin as a matrix resin, and therefore a wet coating method has been widely used as a method for producing a thermally conductive resin sheet. In this wet coating method, if the surface of the agglomerated particles is very uneven, the above-mentioned problems often occur, and therefore it is considered preferable to use agglomerated particles with as little surface unevenness as possible (i.e., agglomerated particles with a small second peak top diameter measured for the heated ash content of the sheet). On the other hand, from the viewpoint of thermal conductivity, it is preferable that the primary particles on the surface of the aggregated particles are radially arranged, and when a sheet is made from such particles, the second peak top diameter often becomes large. As described above, when the conventional manufacturing method is used, there is a trade-off between improvements in voltage resistance and productivity and improvements in thermal conductivity in terms of the second peak top diameter. According to the manufacturing method of the present invention, it is possible to use agglomerated particles that have a large second peak top diameter measured for the heated ash content of the sheet without having to consider the problems that occur in the wet coating method, and therefore it is possible to improve the voltage resistance performance and productivity while also increasing the thermal conductivity.

[0085] (1)Mixing process In the mixing step, the powder made of thermoplastic resin and the boron nitride agglomerated particles are stirred and mixed at room temperature. A conventional manufacturing method involves heating, melting, and kneading a matrix resin and agglomerated boron nitride particles. However, this melting and kneading can cause shear fracture of the agglomerated boron nitride particles. In particular, when using agglomerated boron nitride particles that have a large second peak top diameter measured for the heated ash content of the sheet, shear fracture is likely to occur due to the large surface irregularities. Therefore, in the present invention, instead of performing heat melt kneading, a powder made of a thermoplastic resin and boron nitride agglomerated particles that increase the second peak top height and second peak top diameter measured for the heated ash content of the sheet are stirred and mixed at room temperature, thereby making it difficult for the agglomerated particles to undergo shear fracture and increasing the thermal conductivity of the resulting sheet.

[0086] (2) Press molding process In the press molding step, the mixture obtained in the mixing step is heated and pressurized to be molded into a sheet.

[0087] As the press molding method, various known press machines for molding thermoplastic resins can be used. From the viewpoint of preventing deterioration of the resin during heat pressing, it is particularly preferable to use a vacuum press that can reduce the amount of oxygen inside the press during heating, or a press equipped with a nitrogen substitution device.

[0088] In the press molding step, it is preferable to set the applied pressure not only for the purpose of forming the molten kneaded material into a sheet body of uniform thickness, but also for the purposes of bonding the added boron nitride agglomerated particles together and further deforming the particle surfaces at the bonded portions to form heat paths, and to eliminate voids and air gaps within the sheet. From this viewpoint, the pressure in the press molding step, as the actual pressure applied to the sample, is usually 8 MPa or more, preferably 9 MPa or more, more preferably 10 MPa or more, and is preferably 50 MPa or less, more preferably 40 MPa or less, and even more preferably 30 MPa or less. By setting the pressure during pressing to be equal to or less than the above upper limit, it is possible to prevent the boron nitride agglomerated particles from being crushed, and a thermally conductive resin sheet with high thermal conductivity can be obtained. On the other hand, by setting the pressing pressure to be equal to or greater than the above lower limit, contact between the boron nitride agglomerated particles is improved, making it easier to form thermal conduction paths, and a sheet with high thermal conductivity can be obtained. In addition, since voids in the resin sheet can be reduced, a thermally conductive resin sheet with high breakdown voltage can be obtained even after a moisture absorption reflow test.

[0089] The temperature of the press machine in the press molding step is preferably set to a temperature at which the thermoplastic resin exhibits fluidity, for example, the melting point of the thermoplastic resin as the main component + 30° C. For example, when a polyether ketone resin is used as the main component, the temperature of the press machine is preferably set to 370° C. to 440° C., and more preferably 380° C. or higher or 420° C. or lower. Press molding within this temperature range can provide the resulting thermally conductive resin sheet with good thickness uniformity and high thermal conductivity due to good contact between the added boron nitride agglomerated particles. If the molding temperature is 370°C or higher, the resin viscosity is reduced to a level sufficient for shaping, allowing the molded thermally conductive resin sheet to have sufficient thickness uniformity. On the other hand, if the press temperature is set to 440°C or lower, deterioration of the resin itself and the deterioration of the physical properties of the molded thermally conductive resin sheet can be suppressed.

[0090] The pressurization time is usually 30 seconds or more, preferably 1 minute or more, more preferably 3 minutes or more, and even more preferably 5 minutes or more, and is preferably 1 hour or less, more preferably 30 minutes or less, and even more preferably 15 minutes or less. By keeping the thickness at or below the upper limit, the manufacturing process time for the thermally conductive resin sheet can be reduced, and the cycle time can be shortened compared to a thermally conductive resin sheet using a heat-resistant thermosetting resin, which tends to reduce production costs. Also, by keeping the thickness at or above the lower limit, the thermally conductive resin sheet can be sufficiently uniform, internal gaps and voids can be sufficiently removed, and unevenness in thermal conductivity performance and voltage resistance characteristics can be prevented.

[0091] 4.Laminated heat dissipation sheet The laminated heat-dissipating sheet of the present invention is obtained by laminating a heat-dissipating metal layer containing a heat-dissipating material on one surface of the above-mentioned thermally conductive resin sheet of the present invention. The heat dissipating material is not particularly limited as long as it is made of a material with good thermal conductivity. In particular, in order to increase the thermal conductivity in the laminated structure, it is preferable to use a heat dissipating metal material, and it is more preferable to use a flat metal material. The metal material is not particularly limited, but among them, copper plate, aluminum plate, aluminum alloy plate, etc. are preferred because they have good thermal conductivity and are relatively inexpensive.

[0092] When a flat metal material is used as the heat-dissipating metal material in a laminated heat-dissipating sheet, the thickness of the metal material is preferably 0.03 to 6 mm, and more preferably 0.1 mm or more or 5 mm or less, in order to ensure sufficient heat dissipation.

[0093] For adhesion to heat-dissipating metal materials, the surface of the metal material on the side that will be laminated with the thermally conductive resin sheet may be subjected to surface treatments such as roughening treatments such as soft etching, burnt plating, or oxidation-reduction treatment, plating treatments with various metals or metal alloys to ensure adhesion durability, organic surface treatments including silane coupling treatments such as amino-based and mercapto-based, and surface treatments with organic-inorganic composite materials. These surface treatments can further improve the initial adhesive strength, adhesive strength durability, and the effect of suppressing interfacial peeling after a moisture absorption reflow test.

[0094] On the other hand, the surface of the heat dissipating metal material opposite to the side laminated with the thermally conductive resin sheet does not have to be a simple flat plate, and may be processed to increase the surface area in order to ensure a contact area with the cooling medium, which may be gas or liquid. Examples of processing methods for increasing the surface area include roughening the surface by blasting or the like to increase the surface area; directly forming V-shaped or rectangular grooves or various shaped irregularities in the heat-dissipating metal material by cutting or pressing; joining another metal material that has been processed to increase the surface area to a heat-dissipating metal layer made of a flat metal material by casting, diffusion bonding, bolting, soldering, brazing, or the like, or embedding metal pins. It is also possible to directly press-laminated a thermally conductive resin sheet onto a heat-dissipating metal layer having a cavity for passing a cooling medium. However, because the pressing pressure between the thermally conductive resin sheet and the heat-dissipating metal plate is relatively high, in these cases, it is preferable to later integrate the laminated flat metal material and the thermally conductive resin sheet with a grooved metal plate or a metal layer having a cavity for passing a refrigerant by soldering, brazing, bolting, or the like.

[0095] The heat-dissipating metal material and the thermally conductive resin sheet can be laminated and integrated in the laminated heat-dissipating sheet by press molding, which is a batch process. In this case, the press equipment and press conditions are the same as those for obtaining the thermally conductive resin sheet described above.

[0096] 5. Heat dissipation circuit board The heat-dissipating circuit board of the present invention includes the above-mentioned laminated heat-dissipating sheet, i.e., has a configuration in which the above-mentioned heat-dissipating metal layer is laminated on one surface of the thermally conductive resin sheet of the present invention, and a circuit board is formed on the surface of the thermally conductive resin sheet opposite the heat-dissipating metal layer by, for example, etching or the like.

[0097] The heat dissipation circuit board is preferably configured as an integrated structure of "heat dissipation metal layer / thermally conductive resin sheet / conductive circuit." The state before circuit etching is, for example, an integrated structure of "heat dissipation metal layer / thermally conductive resin sheet / conductive circuit-forming metal layer," in which the conductive circuit-forming metal layer is flat and formed on the entire surface of one side of the thermally conductive resin sheet, or on a partial area.

[0098] The material of the conductive circuit-forming metal layer is not particularly limited, but it is generally preferable to form it from a copper thin plate having a thickness of 0.05 mm to 1.2 mm in terms of electrical conductivity, etching properties, cost, etc.

[0099] The breakdown voltage of the heat dissipating circuit board is preferably 40 kV / mm or more, more preferably 50 kV / mm or more, even more preferably 60 kV / mm or more, and even more preferably 80 kV / mm or more. With a breakdown voltage of 40 kV / mm or more, even a thermally conductive resin sheet with a thickness of, for example, 100 μm can achieve a breakdown voltage of 4 kV or more, and if the breakdown voltage is 80 kV / mm or more, even a thickness of 50 μm can achieve a breakdown voltage of 4 kV or more. Therefore, while using a thin thermally conductive resin layer that is advantageous in terms of thermal resistance, sufficient voltage resistance performance can be achieved and the occurrence of breakdown when a high voltage is applied can be suppressed.

[0100] 6. Power Semiconductor Devices The thermally conductive resin sheet of the present invention and the laminated heat dissipation sheet of the present invention can be suitably used as a heat dissipation sheet for a power semiconductor device, and can realize a highly reliable power semiconductor module. The power semiconductor device is a power semiconductor device that uses the above-mentioned thermally conductive resin sheet or the above-mentioned laminated heat dissipation sheet, and the above-mentioned thermally conductive resin sheet or the above-mentioned laminated heat dissipation sheet is mounted on a power semiconductor device apparatus as a heat dissipation circuit board. The power semiconductor device has a high thermal conductivity and a heat dissipation effect, which allows it to achieve high output and high density with high reliability. In the power semiconductor device, conventionally known materials can be appropriately used for the aluminum wiring, sealing material, packaging material, heat sink, thermal paste, solder, and the like, other than the thermally conductive resin sheet or laminated heat dissipation sheet.

[0101] <Explanation of terms> In the present invention, when the expression "X to Y" (X and Y are any numbers) is used, unless otherwise specified, it means "X or more and Y or less," as well as "preferably larger than X" or "preferably smaller than Y." Furthermore, when it is expressed as "X or more" (X is any number) or "Y or less" (Y is any number), it also includes the intention that "it is preferable that it is greater than X" or "it is preferable that it is less than Y." In the present invention, the term "sheet" conceptually encompasses sheets, films, and tapes. [Example]

[0102] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to the following examples as long as the gist of the invention is not exceeded.

[0103] <Examples 1 to 3 and Comparative Examples 1 to 4> The materials used, the manufacturing method, and the measurement conditions and evaluation methods for the thermally conductive resin sheets in Examples 1 to 3 and Comparative Examples 1 to 4 are as follows.

[0104] [Materials used] (thermoplastic resin) Thermoplastic resin 1: Polyether ether ketone "KetaSpire KT-880FP" (manufactured by Solvay, melting point: 343°C, melt viscosity: 0.15 kPa·s (400°C), average particle size (D50): 30.0 to 45.0 μm, MFR: 86 g / 10 min, mass average molecular weight (Mw): 58,000 was used.

[0105] (thermosetting resin) Thermosetting resin 1: Epoxy resin composition (8.74 parts by mass of bisphenol F epoxy resin (manufactured by Mitsubishi Chemical Corporation, mass average molecular weight in terms of polystyrene: 60,000), 10.93 parts by mass of hydrogenated bisphenol A liquid epoxy resin (manufactured by Mitsubishi Chemical Corporation), 2.62 parts by mass of p-aminophenol liquid epoxy resin (manufactured by Mitsubishi Chemical Corporation), 5.73 parts by mass of phenolic resin curing agent "MEH-8000H" (manufactured by Meiwa Chemical Industry Co., Ltd.), and 0.48 parts by mass of 1-cyanoethyl-2-undecylimidazole "C11Z-CN" (manufactured by Shikoku Chemical Industry Co., Ltd., molecular weight 275) as a curing catalyst) was used.

[0106] Boron nitride agglomerated particles (thermal conductive filler) The thermally conductive filler used as the boron nitride agglomerated particles is as follows: Thermally conductive filler 1: boron nitride agglomerated particles with a house-of-card structure (average particle size (D50): 35 μm, maximum particle size Dmax: 90 μm) Thermally conductive filler 2: boron nitride agglomerated particles with a house-of-card structure (average particle size (D50): 35 μm, maximum particle size Dmax: 90 μm) Thermally conductive filler 3: boron nitride agglomerated particles with a house-of-card structure (average particle size (D50): 35 μm, maximum particle size Dmax: 90 μm) Thermally conductive filler 4: boron nitride agglomerated particles with a house-of-card structure (average particle size (D50): 34 μm, maximum particle size Dmax: 90 μm) Thermally conductive filler 5: boron nitride agglomerated particles with a house-of-card structure (average particle size (D50): 40 μm, maximum particle size Dmax: 90 μm) Thermally conductive filler 6: Boron nitride agglomerated particles ("PTX25" manufactured by Momentive, average particle diameter (D50) 25 μm, specific surface area 7 m) with a cabbage structure (the thickness direction of the primary particles near the outermost surface of the agglomerated particles is the same as the radial direction of the agglomerated particles). 2 / g)

[0107] Thermally conductive fillers 1 and 2 were prepared by the following method. For thermally conductive fillers 1 and 2, the processes described below, including (raw materials), (slurry preparation), (granulation), and (thermal decomposition), were carried out as the same lot, except for the furnace treatment at 2000°C in the section (production of boron nitride agglomerated particles), which was carried out sequentially as separate batches.

[0108] (raw materials) The raw materials used were 10,000 g of hexagonal boron nitride (hereinafter referred to as "raw h-BN powder"), which had a (002) plane peak half-width of 2θ = 0.67° as determined by powder X-ray diffraction measurement (Cu-Kα) and an oxygen concentration of 6.0 mass%, 11,496 g of binder (Taki Chemical Industry Co., Ltd.'s "Taxeram M160L," solids concentration 21 mass%), and 250 g of surfactant (Kao Corporation's "ammonium lauryl sulfate," solids concentration 14 mass%).

[0109] (Preparation of Slurry) The raw material h-BN powder was weighed out in the above amount into a resin bottle, and then the binder was added in the above amount. Furthermore, the surfactant was added in the above amount, and then zirconia ceramic balls were added. The mixture was stirred on a pot mill rotating table for 1 hour to obtain a BN slurry. The viscosity of this slurry was 810 mPa·s.

[0110] (granulation) The BN slurry was spray-dried using a spray dryer (FOC-20 manufactured by Okawara Kakoki Co., Ltd.) at a disk rotation speed of 20,000 to 23,000 rpm and a drying temperature of 80° C. to obtain spherical BN granulated particles.

[0111] (pyrolysis) The BN granulated particles were heat treated in an air atmosphere at 700°C for 5 hours to obtain precursor particles.

[0112] (Preparation of boron nitride agglomerated particles) The precursor particles were packed into a circular graphite crucible with a lid in the shape of a disk, and the atmosphere in the furnace was replaced with a nitrogen gas flow at room temperature and atmospheric pressure. The temperature was increased to 2000°C at a rate of 83°C / hour while flowing nitrogen gas. After reaching 2000°C, the temperature was maintained for 5 hours while flowing nitrogen gas, and then cooled to room temperature. The fired product was removed from the crucible and the portion that had been in contact with the graphite was removed. The product was then crushed manually using a mortar and pestle, and then processed in a roll mill to obtain spherical agglomerated particles of boron nitride with a card house structure. The obtained agglomerated particles of boron nitride were sieved using a sieve with 90 μm openings, and only the particles that passed through the sieve were used as the thermally conductive filler. After the above-mentioned furnace treatment at 2000°C, thermally conductive fillers 1 and 2 were also manually crushed and roll milled separately. However, the fact that the treatments after the 2000°C furnace treatment were carried out sequentially as separate batches did not result in any difference in the measurement results of the mercury intrusion porosimetry.

[0113] Thermally conductive filler 3 was produced in the same manner as thermally conductive filler 1, except that 5,000 g each of hexagonal boron nitride with an oxygen concentration of 5 mass% and hexagonal boron nitride with an oxygen concentration of 7.5 mass% was mixed as raw materials. Thermally conductive filler 4 was made by dry-treating thermally conductive filler 2 for 30 minutes in a bead mill using 10 mm diameter nylon balls, resulting in spherical agglomerated particles with a structure in which the primary particles on the surface of the agglomerated particles were bent and folded over to cover the agglomerated particles. As shown in Figure 5, the SEM image of a single agglomerated particle indicates that the agglomerated particle itself is not disintegrated or damaged, and that the internal house-of-cards structure is also maintained. Thermally conductive filler 5 was produced in the same manner as thermally conductive filler 1, except that 10,000 g of hexagonal boron nitride with an oxygen concentration of 7.5% by mass was used as the raw material, and then dry-treated for 30 minutes in a bead mill using 10 mm diameter nylon balls to produce spherical agglomerated particles in which the primary particles on the surface of the agglomerated particles were bent and folded to cover the agglomerated particles. SEM images of these agglomerated particles alone showed that the agglomerated particles themselves were not disintegrated or damaged, and that the internal house-of-cards structure was also maintained.

[0114] [Preparation of Thermally Conductive Resin Sheets of Examples 1 to 3 and Comparative Examples 1 to 3] The matrix resin powder and the thermally conductive filler powder were mixed at room temperature, and the resulting powder mixture was pressed in a high-temperature vacuum press (Kitagawa Seiki Co., Ltd.) at a temperature of 395°C and a pressure of 10 MPa for 10 minutes to obtain a 15 cm square, 150 μm thick thermally conductive resin sheet and a 15 cm square, 500 μm thick thermally conductive resin sheet. The thickness of the sheet was adjusted by adjusting the amount of powder. However, only in Example 2, pressing was performed at a temperature of 395°C and a pressure of 20 MPa for 10 minutes. The 150 μm thick thermally conductive resin sheet was used as a specimen for a moisture absorption reflow test described later, and the 500 μm thick thermally conductive resin sheet was used as a specimen for measuring thermal conductivity described later.

[0115] Here, the 10 minutes mentioned above refers to the following: the inside of a vacuum press was preheated to 150°C, the powder mixture was charged therein as a press charge, and while operating the vacuum pump, a light pressure of several MPa was applied to the powder mixture. The temperature inside the press was set to 395°C, and after 40 minutes of temperature increase, the press surface pressure was set to 10 MPa for 10 minutes. After 10 minutes had elapsed, the temperature inside the press was again set to 150°C, and when the internal temperature approached 150°C, the vacuum was released and the thermally conductive resin sheet was removed.

[0116] The press-loaded structure described above is a structure necessary for one batch press, in which a frame-shaped spacer 6 mm thick, 20 cm long and wide on each side, and an internal opening measuring 15 cm x 15 cm are placed on the lower plated plate, the powdered mixture in the amount required to obtain a 150 μm-thick pressed sheet or a 500 μm-thick pressed sheet is scattered inside the spacer, and a drop lid measuring 14.6 cm x 14.6 cm long and wide, 5.85 mm thick (when collecting a 150 μm-thick sample) or 5.50 mm thick (when collecting a 500 μm-thick sample), is fitted into the 15 cm x 15 cm opening, or the upper plated plate is placed on top.

[0117] [Preparation of Thermally Conductive Resin Sheet of Comparative Example 4] The thermally conductive filler was added so that the total amount of the epoxy resin composition and the thermally conductive filler was 100% by mass, and then 37.2% by mass of a mixed solution of methyl ethyl ketone and cyclohexanone (mixing ratio (volume ratio) 1:1) was added and mixed so that the total solids concentration of the epoxy resin composition and the thermally conductive filler was 62.8% by mass, to obtain a coating slurry (coating liquid for sheets). When mixing these, after manual stirring, they were stirred for 2 minutes using a planetary mixer "Awatori Rentaro AR-250". The coating slurry obtained above was applied to a 38 μm-thick polyethylene terephthalate film (hereinafter also referred to as "PET film") by the doctor blade method, and after heat drying at 60°C for 120 minutes, it was pressed at a press temperature of 42°C and a press pressure of 15 MPa for 10 minutes to obtain an uncured epoxy resin sheet-shaped molded product. This epoxy resin sheet-shaped molded product was used as a specimen for the moisture absorption reflow test described below.

[0118] A 500-μm-thick thermally conductive resin sheet for use in measuring thermal conductivity (described later) was prepared by the following method. The uncured epoxy resin sheet was cut into a 10 cm × 10 cm piece, and four of these sheets were stacked together to form a press-prepared assembly. Using the same spacers and drop lids used to obtain 500-μm-thick sheets in Examples 1 to 3 and Comparative Examples 1 to 3, the press was performed at a temperature of 175°C and a pressure of 10 MPa for 1 hour to obtain a 500-μm-thick thermally conductive resin sheet. The excess thickness of the laminated uncured epoxy resin sheet was absorbed by the empty space between the 10 cm × 10 cm sheet and the 15 cm × 15 cm spacer.

[0119] <Measurement conditions and evaluation methods> The thermally conductive fillers 1 to 6 and the thermally conductive resin sheets of Examples 1 to 3 and Comparative Examples 1 to 4 were measured and evaluated by the following methods.

[0120] [Physical properties of agglomerated particles (raw powder)] (Dmax and D50) The maximum particle size Dmax and the average particle size D50 of the boron nitride agglomerated particles were measured by the following method. 20 mg of boron nitride agglomerated particles were dispersed ultrasonically in 10 mL of pure water containing sodium hexametaphosphate, and the particle size distribution of the sample was measured using a laser diffraction / scattering particle size distribution analyzer LA-920 (manufactured by Horiba, Ltd.). From the obtained particle size distribution, the maximum particle diameter Dmax and average particle diameter D50 of the boron nitride agglomerated particles were determined.

[0121] (Intra-particle pore volume A1 and inter-particle volume B1) The intraparticle pore volume A1 (mL / g) and interparticle volume B1 (mL / g) of the boron nitride agglomerated particles were measured according to JIS R1655:2003 "Test method for pore size distribution of fine ceramics compacts by mercury intrusion porosimetry." Specifically, a Micromeritics Autopore IV mercury porosimeter was used. 200 mg of sample was loaded into the measurement cell and subjected to a vacuum treatment (50 μmHg or less) for 10 minutes. The total pore volume was then determined, and a mercury intrusion / extrusion curve was also measured. A pore size distribution curve was plotted, with pore size on the horizontal axis and logarithmic differential pore volume on the vertical axis. Assuming the pores are cylindrical, the minimum value of the logarithmic differential pore volume relative to the pore size (the division diameter) was determined between peak a, representing intraparticle pores, and peak b, representing interparticle pores. The interparticle volume B1 (mL / g) was calculated from the integral of the mercury intrusion / extrusion curve in the region of the pore size larger than the division diameter. In addition, the inter-particle pore volume B1 was subtracted from the total pore volume to determine the intra-particle pore volume A1 (mL / g). When filling the cell of the mercury porosimeter with the sample, no special operations such as tapping are performed. However, since the measurement itself involves forcing mercury, which has a high specific gravity, the measurement results are independent of the initial filling condition of the sample and depend only on the properties of the boron nitride agglomerated particles. Although there may be agglomerated particles of boron nitride that are destroyed by the above-mentioned mercury intrusion, such particles do not satisfy the conditions of the present invention.

[0122] (Circularity) Thermally conductive fillers 2 to 5 were analyzed using a particle image analyzer (Malvern Instruments, Morphologi Circularity was measured using a G3S. It is possible that for all of the boron nitride agglomerated particles mentioned above, there may have been boron nitride particles that did not form agglomerates but remained as primary particles, or particles that had once formed agglomerates but then dropped off during subsequent handling to become primary boron nitride particles. Therefore, classification was performed using air dispersion at 1 bar, followed by image analysis to measure circularity. Circularity was measured using Morphologi by measuring and calculating the particle perimeter and the perimeter of a circle with an area equal to the particle area, with the former used as the denominator and the latter used as the numerator. Measurements were made on 10,000 particles, and the average value was taken as circularity. Since no measurement was performed for Filler 1, it is indicated as "-" in Table 1.

[0123] [Physical properties of agglomerated particles (sheet ash)] (Intraparticle pore volume A2, interparticle volume B2, A2 / A1 and B2 / B1) The intraparticle pore volume A2 (mL / g) and interparticle volume B2 (mL / g) of the boron nitride agglomerated particles contained in the residual ash when the thermally conductive resin sheet was heated to 700°C were measured by mercury intrusion porosimetry as follows. First, a 150 μm-thick thermally conductive resin layer was laminated with a copper plate (prepared for the moisture absorption reflow test described below). The laminated heat-dissipating sheet consisted of a 2 mm thick copper plate, a 0.15 mm thick thermally conductive resin sheet, and a 0.5 mm thick copper plate for forming conductive circuits. The copper plate was then removed by etching, leaving only the resin sheet. A 400 mg sample (resin sheet area approximately 3.6 cm × 3.6 cm) was taken and heated in a heating furnace in air at 700°C for 5 hours to decompose and remove the resin, resulting in the heated ash. The sheet before heating and the ash content after heating were weighed, and it was confirmed that the mass of the ash content roughly matched the calculated mass of the blended boron nitride agglomerated particles. Next, a Micromeritics Autopore IV mercury porosimeter was used, and 200 mg of sample was filled into the measurement cell. A pore size distribution curve was created in the same manner as in the measurements of A1 and B1 described above, and the interparticle void volume B2 (ml / g) and intraparticle pore volume A2 (ml / g) of the boron nitride agglomerated particles in the sheet ash were determined. The residual ratios A2 / A1 and B2 / B1 were calculated from the intra-particle pore volume A1 and inter-particle volume B1 of the filler used in Examples 1 to 3 and Comparative Examples 1 to 4, and the intra-particle pore volume A2 and inter-particle volume B2 of the ash content of the thermally conductive resin sheet.

[0124] (Peak top height and peak top diameter) From the pore size distribution curve of the sheet ash obtained above, the first peak top height, the first peak top diameter, the second peak top height, and the second peak top diameter were determined.

[0125] (Circularity) For Examples 2 and 3 and Comparative Examples 1 to 3, the circularity of the ash of the thermally conductive resin sheets was measured using a particle image analyzer (Malvern Instruments, Morphologi G3S). It is possible that the ash in each sheet consisted of boron nitride particles that did not form agglomerates but remained as primary particles, or particles that had once formed agglomerates but then shed from the agglomerates during subsequent handling or the pressurization process for sheet formation to become primary boron nitride particles. Therefore, classification was performed using airflow dispersion at 1 bar, followed by image analysis to measure the circularity. The circularity was measured using Morphologi by measuring and calculating the particle perimeter and the perimeter of a circle with an area equal to the particle area, with the former as the denominator and the latter as the numerator. Measurements were made on 10,000 particles, and the average value was taken as the circularity. Note that no measurement was performed on the thermally conductive resin sheet of Example 1, and therefore this is indicated as "-" in Table 1. The circularity of the thermally conductive resin sheet of Comparative Example 3 could not be measured because the aggregated particles had collapsed.

[0126] [Thermal conductivity at 25℃] Measurement samples were cut into 10 mm squares from the 500 μm thick thermally conductive resin sheets (specimens) obtained in Examples 1 to 3 and Comparative Examples 1 to 4. After a thin layer of laser light absorbing spray (Fine Chemical Japan's "Black Guard Spray FC-153") was applied to both sides and dried, the thermal diffusivity a (mm in the thickness direction of the resin sheet at a measurement temperature of 25°C was measured by laser flash method using a xenon flash analyzer (NETZSCH's "LFA447 NanoFlash300"). 2 The measurement was carried out on five points cut out from the same sheet, and the arithmetic mean value was calculated.

[0127] Next, the density ρ (g / m) of the resin sheet was measured using a specific gravity measuring instrument (manufactured by A&D Co., Ltd.) using the Archimedes method in accordance with JIS K6268. 3 In addition, the specific heat capacity c (J / (g·K)) at 25°C was measured using a DSC measuring device (ThermoPlusEvo DSC8230, manufactured by Rigaku Corporation) in accordance with JIS K7123. From these measured values, the thermal conductivity in the sheet thickness direction at 25°C was calculated as "H=a×ρ×c".

[0128] The thermal diffusivity a (mm 2 / sec) was measured with reference to JIS R1611:2010 (Method for measuring thermal diffusivity, specific heat capacity and thermal conductivity of fine ceramics by the flash method) because there are no JIS standards regarding the thermal diffusivity and thermal conductivity of resin-based materials. Since this standard specifies that "the thickness of the sample must be between 0.5 mm and 5 mm," only the thickness of the sample used for thermal conductivity measurement was adjusted to 0.5 mm.

[0129] [Breakdown voltage (BDV) before moisture absorption reflow test] (Making a heat dissipation circuit board) The thermally conductive resin sheets having a thickness of 150 μm produced in Examples 1 to 3 and Comparative Examples 1 to 4 were cut into a size of 40 mm×80 mm to prepare thermally conductive resin sheets for circuit boards. On the other hand, one copper plate measuring 40 mm x 80 mm and having a thickness of 2000 μm was prepared as a metal plate material for heat dissipation, and one copper plate measuring 40 mm x 80 mm and having a thickness of 500 μm was prepared as a copper plate for forming a conductive circuit, for each thermally conductive resin sheet for the circuit board. One side of a 2000 μm thick copper plate and one side of a 500 μm thick copper plate were each polished with #100 sandpaper to roughen the surface, and the thermally conductive resin sheet for circuit boards was sandwiched between the copper plates so that the roughened surface of each of the copper plates of different thicknesses faced the thermally conductive resin sheet for circuit boards.The copper plates were pressed at a press temperature of 390°C and a press pressure of 13 MPa for 10 minutes to obtain a laminated heat dissipation sheet consisting of ``heat dissipating metal plate material (copper plate) / thermal conductive resin sheet / copper plate for forming conductive circuits.''

[0130] On the other hand, for Comparative Example 4, which was a thermally conductive resin sheet made of a thermosetting resin, a 150 μm thick epoxy resin sheet molded body that was uncured or had only slightly progressed in the curing reaction was sandwiched between the above-mentioned roughened metal plate material for heat dissipation (copper plate) and a copper plate for forming a conductive circuit, and vacuum pressed for 30 minutes at a press temperature of 175°C and a press surface pressure of 10 MPa to complete the curing reaction of the thermosetting resin, thereby obtaining a laminated heat dissipation sheet consisting of "metal plate material for heat dissipation (copper plate) / thermally conductive resin sheet / copper plate for forming a conductive circuit."

[0131] The copper plate for forming the conductive circuit of each laminated heat dissipation sheet was then etched and patterned to obtain a heat dissipation circuit board. The pattern was such that two φ25 mm circular copper plates for the conductive circuit remained on a 40 mm × 80 mm thermally conductive resin sheet.

[0132] (Measurement of dielectric breakdown voltage (BDV)) The heat-dissipating circuit boards fabricated using the thermally conductive resin sheets obtained in Examples 1 to 3 and Comparative Examples 1 to 4 using the above-mentioned method were immersed in Fluorinert FC-40 (manufactured by 3M), and using an ultra-high voltage withstand voltage tester 7470 (manufactured by Keisoku Gijutsu Kenkyusho Co., Ltd.), a φ25 mm electrode was placed on a φ25 mm copper plate patterned by etching on the heat-dissipating circuit board, and a voltage of 0.5 kV was applied, and the voltage was increased by 0.5 kV every 60 seconds until dielectric breakdown occurred. The measurements were carried out at a frequency of 60 Hz and a voltage increase rate of 1000 V / sec.

[0133] If the breakdown voltage per unit thickness (equivalent value for a thickness of 1 mm) was 60 kV / mm or more, it was marked as "〇 (good)", if it was 40 kV / mm or more but less than 60 kV / mm, it was marked as "△ (not good)", and if it was less than 40 kV / mm, it was marked as "× (poor)". The measurement results are shown in Table 1. The evaluation of the dielectric breakdown voltage (BDV) before the moisture absorption reflow test can be used as an evaluation of the voltage resistance performance.

[0134] [Breakdown voltage (BDV) after moisture absorption reflow test] (Measurement of dielectric breakdown voltage (BDV)) Heat-dissipating circuit boards fabricated using the thermally conductive resin sheets obtained in Examples 1 to 3 and Comparative Examples 1 to 4 in the same manner as in the above [Breakdown voltage (BDV) before moisture absorption reflow test] were stored in an environment of 85°C and 85% RH using a thermo-hygrostat SH-221 (manufactured by Espec Corp.) for 3 days, then heated from room temperature to 290°C in 12 minutes in a nitrogen atmosphere within 30 minutes, held at 290°C for 10 minutes, and cooled to room temperature (moisture absorption reflow test). The heat-dissipating circuit boards were then immersed in Fluorinert FC-40 (manufactured by 3M Co.), and a 0.5 kV voltage was applied and increased by 0.5 kV every 60 seconds using an ultra-high voltage withstand voltage tester 7470 (manufactured by Keisoku Giken Kenkyusho Co., Ltd.) to measure the breakdown voltage until a 25 mm diameter electrode was placed on a 25 mm diameter copper plate patterned by etching on the heat-dissipating circuit board. The measurements were carried out at a frequency of 60 Hz and a voltage increase rate of 1000 V / sec.

[0135] If the breakdown voltage per unit thickness (equivalent value for a thickness of 1 mm) was 60 kV / mm or more, it was marked as "〇 (good)", if it was 40 kV / mm or more but less than 60 kV / mm, it was marked as "△ (not good)", and if it was less than 40 kV / mm, it was marked as "× (poor)". The measurement results are shown in Table 1. The evaluation of the dielectric breakdown voltage (BDV) after the moisture absorption reflow test can be used to evaluate the moisture absorption reflow resistance.

[0136] [Observation of sample condition after moisture absorption reflow test] The heat-dissipating circuit boards produced in Examples 1 to 3 and Comparative Examples 1 to 4 were subjected to a moisture absorption reflow test in the same manner as described above, and then the interface between the 25 mm diameter copper electrodes patterned by etching and the thermally conductive resin sheet was observed using an ultrasonic imaging device, FinSAT (FS300III) (manufactured by Hitachi Power Solutions). Measurements were performed using a 50 MHz frequency probe with a gain of 30 dB and a pitch of 0.2 mm, with the sample placed in water. Those for which no peeling, lifting, or voids were observed at the interface were marked with a "○ (good)" and those for which peeling, lifting, or voids were observed at the interface were marked with a "× (poor)." The evaluation results are also shown in Table 1. The evaluation of interfacial peeling after the moisture absorption reflow test can be performed to evaluate whether or not interfacial peeling due to thermal expansion and thermal contraction and deformation due to foaming of the thermal conductive resin sheet are likely to occur when the thermal conductive resin sheet is laminated with a metal plate and subjected to a reflow process.

[0137] [Table 1]

[0138] Comparing Examples 1 to 3 with Comparative Examples 1 to 3, it was found that when the second peak top height and second peak top diameter of the sheet ash content are within the range of the present invention, a heat dissipation sheet with significantly high thermal conductivity can be obtained. Furthermore, from the first peak, second peak, and circularity of the sheet ash of Examples 1 to 3, it is believed that the boron nitride agglomerated particles used in these examples maintain their internal structure even after sheet formation, thereby maintaining high thermal conductivity within the agglomerated particles, and at the same time, the surfaces of the contact areas between adjacent particles are moderately deformed, thereby keeping the thermal resistance between particles low.The SEM photograph of the boron nitride agglomerated particles contained in the ash of the thermal conductive resin sheet of Example 2 shown in Figure 9 also confirms that the internal structure of the agglomerated particles is maintained, while the surfaces of the contact areas between adjacent particles are moderately deformed. Furthermore, when comparing the breakdown voltage values ​​before and after the moisture absorption reflow test between Examples 1 to 3 and Comparative Example 4, it was found that the use of a thermoplastic resin having a melting point of 300°C or higher as the matrix resin resulted in good voltage resistance and moisture absorption reflow resistance. Furthermore, in Examples 1 to 3, the manufacturing method includes a mixing step of mixing a powder made of a thermoplastic resin with boron nitride agglomerated particles, and a press molding step of pressing the mixture to form a sheet. This makes it possible to achieve both high voltage resistance and high thermal conductivity without impairing the inherent properties of the boron nitride agglomerated particles, which have high thermal conductivity, and also suppresses the formation of voids in the sheet during molding. In Comparative Example 4, an epoxy resin and the boron nitride agglomerated particles of Example 1 were used to form a sheet by a conventional wet coating method. The interparticle volume of the boron nitride agglomerated particles was estimated to be too large for use in a wet coating method, resulting in the formation of streaks when the film was coated and the inclusion of many air bubbles within the sheet, which is thought to have reduced the voltage resistance performance. Due to the influence of these air bubbles within the sheet, the thermal conductivity was also inferior to that of Example 1, which contained the same amount of the same boron nitride agglomerated particles.

Claims

1. A thermally conductive resin sheet made of a resin composition containing a thermoplastic resin and agglomerated particles of boron nitride, The main component of the thermoplastic resin is a crystalline thermoplastic resin having a melting point of 300°C or higher, the resin composition contains 15% by mass or more and 40% by mass or less of the thermoplastic resin and 60% by mass or more and 85% by mass or less of the boron nitride agglomerated particles, based on 100% by mass of the resin composition; In a pore size distribution curve obtained by measuring the residual ash content when the thermal conductive resin sheet is heated at 700°C for 5 hours by mercury intrusion porosimetry, a peak having a maximum value at a pore size of less than 5 µm is defined as a first peak, and a peak having a maximum value at a pore size of 5 µm or more is defined as a second peak, A thermally conductive resin sheet having a second peak top height of 1.0 mL / g or more and a second peak top diameter of 15 μm or more.

2. 2. The thermally conductive resin sheet according to claim 1, wherein the crystalline thermoplastic resin having a melting point of 300°C or higher is a polyether ketone resin.

3. The thermally conductive resin sheet according to claim 2 , wherein the polyether ketone-based resin is polyether ether ketone.

4. The thermally conductive resin sheet according to any one of claims 1 to 3, wherein the boron nitride agglomerated particles have a house-of-card structure.

5. The thermally conductive resin sheet according to any one of claims 1 to 4, wherein the volume-based average particle diameter D50 of the boron nitride agglomerated particles is 10 µm or more and 200 µm or less.

6. The thermally conductive resin sheet according to any one of claims 1 to 5, wherein the first peak top diameter is 0.4 µm or less.

7. The thermally conductive resin sheet according to any one of claims 1 to 6, wherein the first peak top height is 0.25 mL / g or more and 0.7 mL / g or less.

8. The thermal conductive resin sheet according to any one of claims 1 to 7, wherein the circularity of boron nitride agglomerated particles contained in the residual ash when the thermal conductive resin sheet is heated at 700 ° C. for 5 hours exceeds 0.

945.

9. The thermally conductive resin sheet according to any one of claims 1 to 8, having a thickness of 50 µm or more and 300 µm or less.

10. The thermal conductive resin sheet according to any one of claims 1 to 9, having a thermal conductivity in the thickness direction at 25 ° C. of 18 W / m K or more.

11. A laminated heat dissipation sheet having a configuration in which a heat dissipation metal layer is laminated on one surface of the thermally conductive resin sheet according to any one of claims 1 to 10.

12. A heat-dissipating circuit board comprising the laminated heat-dissipating sheet according to claim 11.

13. 13. The heat dissipation circuit board according to claim 12, further comprising a conductive circuit formed on the other surface of the thermally conductive resin sheet.

14. A power semiconductor device comprising the heat dissipation circuit board according to claim 12 or 13.

15. a mixing step of obtaining a mixture of powder made of a thermoplastic resin and agglomerated particles of boron nitride; a press molding step of heating and pressurizing the mixture to form it into a sheet, The main component of the thermoplastic resin is a crystalline thermoplastic resin having a melting point of 300°C or higher, the mixture contains 15% by mass or more and 40% by mass or less of the thermoplastic resin and 60% by mass or more and 85% by mass or less of the boron nitride agglomerated particles, based on 100% by mass of the mixture; In a pore size distribution curve obtained by measuring the residual ash content when the sheet is heated at 700°C for 5 hours by mercury intrusion porosimetry, a peak having a maximum value at a pore size of less than 5 µm is defined as a first peak, and a peak having a maximum value at a pore size of 5 µm or more is defined as a second peak. A method for producing a thermally conductive resin sheet, wherein the second peak top height is 1.0 mL / g or more and the second peak top diameter is 15 μm or more.

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