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

Abstract

Provided is a thermally conductive resin sheet having sufficient withstand voltage performance and excellent moisture absorption reflow tolerance that comprises a resin composition containing a crystalline thermoplastic resin having a fusing point of 300°C or higher and a thermally conductive filler, the thermally conductive filler containing aggregated boron nitride particles.　In addition, the thermally conductive resin sheet according to another mode of the present invention comprises a resin composition containing between 15% by mass and 40% by mass inclusive of the crystalline thermoplastic resin having a fusing point of 300°C or higher, and between 60% by mass and 85% by mass inclusive of the thermally conductive filler, the thermal conductivity in the thickness direction being 5.0 W / m·K or higher at 25°C.

Description

[Technical Field]

[0001] The present invention relates to a thermally conductive resin sheet, a laminated heat-dissipating sheet in which a metal plate material is laminated on a thermally conductive resin sheet, and a heat-dissipating circuit board in which a conductive circuit is further laminated on top of the sheet. [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 which is the issue of heat generation from the devices. Although high output and high density are possible when power semiconductor devices are operated at high temperatures, there are concerns that the heat generated by device switching will reduce the reliability of the power semiconductor devices.

[0004] In recent years, heat generation due to the increasing density of integrated circuits has become a major problem, particularly in the electrical and electronics fields, 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 drawbacks such as being easily cracked by impact, and being difficult to make thin and compact.

[0005] Therefore, heat dissipation sheets using thermosetting resins such as epoxy resins and inorganic fillers have been proposed. For example, Patent Document 1 proposes a heat dissipation resin sheet containing an epoxy resin with a Tg of 60°C or less and boron nitride, in which the boron nitride content is 30% by volume or more and 60% by volume or less.

[0006] Patent Document 2 proposes a film for metal substrates, which is characterized by containing an inorganic filler having an average major axis of 1 to 50 μm in a polyether ketone resin.

[0007] Patent Document 3 proposes a heat-resistant and heat-conductive packing made of polyether ether ketone (PEEK) filled with a heat-conductive filler.

[0008] Furthermore, Patent Document 4 proposes a polymer composition in which at least one oxide having an electronegativity within a specific range and at least one nitride having an electronegativity within a specific range are added to a semicrystalline polymer.

[0009] On the other hand, Patent Document 5 proposes an inorganic-organic composite material having a structure in which boron nitride particles serving as a highly thermally conductive filler are dispersed in a resin matrix, and the boron nitride particles are dispersed in the resin in the form of "exfoliated flat particles" that are produced through a process of interlaminar delamination of secondary particles, which are laminates of primary particles. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-036415 [Patent Document 2] Japanese Patent Application Publication No. 03-020354 [Patent Document 3] Japanese Patent Application Publication No. 07-157569 [Patent Document 4] Special Publication No. 2008-524362 [Patent Document 5] Japanese Patent Application Laid-Open No. 2012-255055 Summary of the Invention [Problem to be solved by the invention]

[0011] One of the processes for assembling power semiconductor modules is the reflow process. In this reflow process, the components are rapidly heated 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, when mounting a power semiconductor device on a module, heating and cooling are repeated in the same manner.

[0012] When using a circuit board in which a metal plate or the like is bonded to a conventional heat dissipation resin sheet, repeated temperature changes during the reflow process or the like cause thermal expansion and contraction, and the difference in the thermal expansion coefficients of the resin and the metal plate can cause interfacial peeling between the heat dissipation resin sheet and the metal plate, resulting in a decrease in the performance of the power semiconductor module. In addition, the components may absorb moisture during storage before the reflow process, which significantly accelerates the deterioration of the components during the reflow process, further deteriorating the performance of the power semiconductor module.

[0013] Furthermore, conventional heat dissipation resin sheets sometimes lack sufficient voltage resistance for use in power semiconductor devices, which require high voltages and large currents.

[0014] Therefore, an object of the present invention is to provide a thermally conductive resin sheet that has sufficient voltage resistance and excellent 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]

[0015] A thermally conductive resin sheet according to one embodiment of the present invention comprises a resin composition containing a crystalline thermoplastic resin having a melting point of 300°C or higher and a thermally conductive filler, wherein the thermally conductive filler contains agglomerated particles of boron nitride. Furthermore, a thermally conductive resin sheet according to another embodiment of the present invention comprises a resin composition containing 15% by mass or more and 40% by mass or less of a crystalline thermoplastic resin having a melting point of 300°C or more and 60% by mass or more and 85% by mass or less of a thermally conductive filler, and has a thermal conductivity in the thickness direction at 25°C of 5.0 W / m K or more. [Effects of the Invention]

[0016] The thermally conductive resin sheet of the present invention has sufficient voltage resistance and is also excellent in moisture absorption and reflow resistance. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a cross-sectional SEM image according to an example embodiment of the present invention. [Figure 2] FIG. 10 is a schematic diagram according to another example of an embodiment of the present invention. [Figure 3] 10 is a cross-sectional SEM image according to another example of the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] The following describes in detail the embodiments of the present invention, but the present invention is not limited to the following embodiments and can be practiced in various modified forms within the scope of the gist thereof.

[0019] <Summary of the Invention> First, an outline of the present invention will be described.

[0020] As mentioned above, conventional heat dissipation substrates made of ceramic materials have the problems of being easily cracked by impact, and being difficult to make thin and compact. It is also known that the thermal conductivity of ordinary ceramic substrates decreases as the temperature rises (see NETZSCH's "Manufacturer's Certification" (certificate for the "Pyroceram 9696" sample for calibration of xenon flash method measurements in accordance with ASTM-E1416). For this reason, there is concern that high thermal conductivity may not be achieved if ceramic substrates are used in power semiconductor devices, whose operating temperatures have been rising in recent years.

[0021] In order to solve the above-mentioned problems with ceramic materials, a heat dissipation sheet using a thermosetting resin such as an epoxy resin and an inorganic filler has been proposed (Patent Document 1). However, when such a heat dissipation sheet using a thermosetting resin is laminated with a metal plate, there are problems such as thermal expansion and contraction caused by temperature changes during the reflow process or when using a power semiconductor device, resulting in interfacial peeling and insufficient voltage resistance performance.

[0022] To improve this interfacial peeling, attempts have been made to increase the degree of crosslinking of epoxy resins to enhance the strength of the cured resin. However, increasing the degree of crosslinking requires increasing the number of epoxy functional groups per unit molecular weight. The addition reaction between the epoxy groups in the epoxy resin and active hydrogen increases the hydroxyl group concentration, which increases the moisture absorption rate of the epoxy resin. This increase in moisture absorption rate of the epoxy resin reduces the insulating properties of the cured resin and also reduces the voltage resistance under high-temperature and high-humidity conditions. Therefore, it was considered undesirable to use such resins as thermally conductive sheets for power semiconductor devices.

[0023] In addition, attempts have been made to improve the heat resistance of cured resins and lower the linear expansion coefficient by using epoxy resin monomers with rigid molecular structures or thermosetting polyimide resins. However, these resins have problems such as high temperature and long curing times, and the cured resins become brittle, making it difficult to add a large amount of inorganic filler to achieve high thermal conductivity.

[0024] Therefore, in order to solve the above-mentioned problems associated with thermosetting resins, heat dissipation sheets using thermoplastic resins (Patent Documents 2 to 4) have also been investigated.

[0025] In Patent Document 2, glass powder or the like is used as an inorganic filler, but because the thermal conductivity of glass particles is generally less than 1 W / m K, it is thought that it would be difficult to obtain high thermal conductivity even if a large amount of glass particles were added to a polyether ketone resin.

[0026] Furthermore, Patent Document 3 describes that spherical alumina is suitable as a thermally conductive filler, but in an example in which spherical alumina was added to polyether ether ketone resin, the thermal conductivity was 1.5 W / m K, and it is thought that it would be difficult to obtain a higher thermal conductivity using this technology.

[0027] Furthermore, Patent Document 4 lists polycarbonate and the like as examples of semi-crystalline polymers, but since the glass transition temperature of typical polycarbonate-based resins is 150°C, it is thought that they are not expected to be able to withstand a reflow process that can reach temperatures as high as 290°C.

[0028] On the other hand, in order to increase the thermal conductivity of the heat dissipation sheet, thermally conductive fillers to be combined with resins are also being investigated (Patent Document 5). In Patent Document 5, high thermal conductivity is achieved by using specially treated boron nitride particles, but examples of resins given include polycarbonate and epoxy resin, and the moisture absorption and reflow resistance problem when using these resins is not resolved.

[0029] Therefore, the present inventors have investigated various types of resins and thermally conductive fillers to be used in thermally conductive resin sheets, and have found that it is possible to obtain thermally conductive resin sheets that are excellent in moisture absorption and reflow resistance.

[0030] The thermally conductive resin sheet of the present invention, and the laminated heat dissipation sheet and heat dissipation circuit board using the thermally conductive resin sheet can be suitably used as a heat dissipation sheet for power semiconductor devices, and can realize a highly reliable power semiconductor module. Furthermore, the thermally conductive resin sheet of the present invention does not require high temperature and long curing times as is the case with thermosetting resins, and therefore can be produced easily.

[0031] <Configuration of the present invention> Next, the configuration of the present invention will be described.

[0032] 1.Resin composition The thermally conductive resin sheet of the present invention comprises a resin composition containing a crystalline thermoplastic resin having a melting point of 300° C. or higher and a thermally conductive filler. Each component will be described in detail below.

[0033] (1)Thermoplastic resin It is preferable that the thermoplastic resin used in the thermally conductive resin sheet does not cause any abnormalities even when subjected to the reflow conditions for heat dissipation circuit boards at 290°C for 5 minutes. To satisfy this condition, it is preferable to use a non-crystalline thermoplastic resin with a glass transition temperature (Tg) of at least 300°C or higher, or a crystalline thermoplastic resin with a melting point (Tm) of at least 300°C or higher.

[0034] 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.

[0035] 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 thermally conductive filler. 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.

[0036] For these reasons, the thermoplastic resin used as the matrix resin in the present invention is preferably a crystalline thermoplastic resin having a melting point of 300° C. or higher.

[0037] The melting point of the crystalline thermoplastic resin can be measured by the method specified in ISO 1183. Specifically, it can be determined from the crystalline melting peak temperature during the second heating period when the crystalline thermoplastic resin is measured using a differential scanning calorimeter (DSC). The crystalline thermoplastic resin used in the present invention is one in which at least an endothermic peak due to crystalline melting is clearly observed and the peak top temperature is 300°C or higher. Furthermore, when a resin composition containing a thermally conductive filler is measured using a differential scanning calorimeter (DSC), there is no significant difference in the melting point, except in cases where the addition of the thermally conductive filler accelerates the deterioration of the matrix resin during heat molding.

[0038] The melting point of the crystalline thermoplastic resin in the present invention is preferably 310°C or higher, more preferably 320°C or higher, and even more preferably 330°C or higher, from the viewpoint of moisture absorption reflow resistance at 290°C. On the other hand, the upper limit of the melting point is not particularly limited. Among these, from the viewpoint of moldability and productivity, it is preferably 380°C or lower, more preferably 370°C or lower, and even more preferably 360°C or lower. If the melting point is less than 300°C, the elastic modulus of the resin raw material may decrease during moisture absorption reflow at 290°C, causing the resin to flow and deform, or the elastic strain of the resin layer may be restored, which may result in a deterioration in the surface appearance of the thermally conductive resin sheet, an uneven thickness of the thermally conductive resin sheet, and an insufficient adhesive strength with the metal substrate. In addition, the expansion of moisture absorbed by the resin composition in a humid and hot environment may cause foaming in the thermally conductive resin sheet. Foaming inside the thermally conductive resin sheet may result in a significant decrease in breakdown voltage. When a heat-dissipating metal material is laminated on one surface of the thermally conductive resin sheet, foaming near the interface between the heat-dissipating metal material and the thermally conductive resin sheet may cause the heat-dissipating metal material to peel off, resulting in a significant decrease in thermal conductivity. Furthermore, when a conductive circuit pattern is formed on the other surface of the thermally conductive resin sheet, foaming near the interface between the conductive circuit pattern and the thermally conductive resin sheet may cause the conductive circuit pattern to peel off or fall off, resulting in electrical circuit problems or a significant decrease in the thermal conductivity of the thermally conductive resin sheet.

[0039] 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). Among these, the crystalline thermoplastic resins used in the present invention include liquid crystal polymers, polyether ketone resins, PTFE, and PFA, because they have a melting point of 300° C. or higher.

[0040] Among crystalline thermoplastic resins having a melting point of 300° C. or higher, liquid crystal polymers and / or polyether ketone resins are preferred from the viewpoint of moldability and the like. Furthermore, among the above, polyether ketone resins are preferred from the viewpoint of adhesiveness to heat-dissipating metal materials such as copper plates.

[0041] 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 formula (1) (wherein m and n are 1 or 2).

[0042] [ka]

[0043] 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.

[0044] Among polyether ketone resins, polyether ether ketone (PEEK) can be particularly preferably used, taking into consideration the following points in total: 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.

[0045] When polyether ether ketone (PEEK) is used as the crystalline thermoplastic resin of the present invention, it may be blended with other thermoplastic resins. The type of other thermoplastic resin is not particularly limited. Among them, as the other thermoplastic resin, 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 is preferable. When other thermoplastic resins are blended, the melting point of the blended resins should be 300° C. or higher.

[0046] Polyetherimide (PEI) is more preferable as the compatible resin. 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 and increases 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). Note that because 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.

[0047] 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, it is possible to maintain heat resistance in a moisture absorption reflow test due to the crystallinity of PEEK, while improving adhesion to heat-dissipating metal materials.

[0048] 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.

[0049] The melt viscosity of the crystalline thermoplastic resin in the present invention is not particularly limited. Since a relatively large amount of thermally conductive filler is blended, a melt viscosity of 0.60 kPa·s or less is preferred, and 0.30 kPa·s or less is more preferred, in order to facilitate heat molding. Having a melt viscosity within the above range eliminates the need to set the molding machine temperature 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 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.

[0050] 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. 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 the prevention of void formation between the resin and the added thermally conductive filler. 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).

[0051] (2) Thermally conductive filler The thermally conductive resin sheet of the present invention preferably contains an electrically insulating, thermally conductive filler in order to improve thermal conductivity, suppress the linear expansion coefficient, and ensure insulating performance. By suppressing the linear expansion coefficient of the thermally conductive resin sheet of the present invention, for example, in a configuration in which the thermally conductive resin sheet of the present invention is laminated and integrated with a different material such as a copper plate, interfacial peeling between the thermally conductive resin sheet and the different material can be suppressed even when the temperature changes repeatedly between low temperatures (e.g., -40°C) and high temperatures (e.g., 200°C). In the present invention, the thermally conductive filler refers to particles having a thermal conductivity of 1.0 W / m·K or more, preferably 1.2 W / m·K or more.

[0052] Examples of the thermally conductive filler include electrically insulating fillers made only of carbon, metal carbides or semi-metal carbides, metal oxides or semi-metal oxides, and metal nitrides or semi-metal nitrides.

[0053] An example of an electrically insulating filler made only of carbon is diamond (thermal conductivity: approximately 2000 W / m·K). Examples of metal carbides or semi-metal carbides include silicon carbide (thermal conductivity: approximately 60 to 270 W / m·K), titanium carbide (thermal conductivity: approximately 21 W / m·K), and tungsten carbide (thermal conductivity: approximately 120 W / m·K).

[0054] Examples of metal oxides or semi-metal oxides include magnesium oxide (thermal conductivity: approximately 40 W / m·K), aluminum oxide (thermal conductivity: approximately 20 to 35 W / m·K), silicon oxide (thermal conductivity: approximately 1.2 W / m·K), zinc oxide (thermal conductivity: approximately 54 W / m·K), yttrium oxide (thermal conductivity: approximately 27 W / m·K), zirconium oxide (thermal conductivity: approximately 3 W / m·K), ytterbium oxide (thermal conductivity: approximately 38.5 W / m·K), beryllium oxide (thermal conductivity: approximately 250 W / m·K), and "sialon" (ceramics composed of silicon, aluminum, oxygen, and nitrogen, thermal conductivity: approximately 21 W / m·K). Examples of metal nitrides or semi-metal nitrides include boron nitride (thermal conductivity in the plane direction of plate-like particles of hexagonal boron nitride (h-BN): approximately 200 to 500 W / m·K), aluminum nitride (thermal conductivity: approximately 160 to 285 W / m·K), and silicon nitride (thermal conductivity: approximately 30 to 80 W / m·K).

[0055] These thermally conductive fillers may be used alone or in combination of two or more.

[0056] Furthermore, when the thermally conductive resin sheet of the present invention is used for a power semiconductor device, electrical insulation is required, and therefore, it is preferable that the thermally conductive filler be an inorganic compound having excellent insulation properties. From this viewpoint, the volume resistivity of the thermally conductive filler at 20° C. is 10 13 Ω·cm or more is preferable, and 10 14 Ω·cm or more is more preferable. Among these, metal oxides, semi-metal oxides, metal nitrides, or semi-metal nitrides are preferred because they can easily provide sufficient electrical insulation for the thermally conductive resin sheet. Specific examples of such thermally conductive fillers include aluminum oxide (Al2O3, volume resistivity: >10 14 Ω·cm), aluminum nitride (AlN, volume resistivity: >10 14 Ω·cm), boron nitride (BN, volume resistivity: >10 14 Ω·cm), silicon nitride (Si3N4, volume resistivity:>10 14 Ω·cm), silica (SiO2, volume resistivity: >10 14 Ω·cm). Among these, aluminum oxide, aluminum nitride, boron nitride, and silica are preferred, with aluminum oxide and boron nitride being particularly preferred since they can impart high insulating properties to the thermally conductive resin sheet.

[0057] Among the above, it is preferable that the thermally conductive filler of the present invention contains boron nitride, because it has fewer problems with moisture absorption during heat molding, is low in toxicity, can efficiently increase thermal conductivity, and can impart high insulating properties to the thermally conductive resin sheet. The boron nitride preferably contains, as a main component, boron nitride agglomerated particles formed by agglomeration of primary particles of boron nitride. "Containing boron nitride agglomerated particles as a main component" means that the boron nitride agglomerated particles account for 50 mass% or more of the boron nitride, particularly 70 mass% or more, particularly 80 mass% or more, particularly 90 mass% or more (including 100 mass%).

[0058] In addition, boron nitride may be used in combination with other thermally conductive fillers. However, as described below, the heat transfer behavior in a thermally conductive resin sheet does not depend solely on the thermal conductivity within the thermally conductive filler. Therefore, even if diamond particles, which have extremely high thermal conductivity but are also extremely expensive, are used among the particles exemplified above, the thermal conductivity of the thermally conductive resin sheet in the thickness direction will not increase significantly. Therefore, when using boron nitride in combination with other thermally conductive fillers, the main focus is on reducing the cost of the composition. Therefore, because of their relatively low cost and relatively high thermal conductivity, it is preferable to appropriately select the thermally conductive filler to be used in combination with boron nitride from magnesium oxide, aluminum oxide, tungsten carbide, silicon carbide, aluminum nitride, etc.

[0059] The thermally conductive filler may be in the form of irregular particles, spheres, whiskers, fibers, plates, or an aggregate or mixture thereof. In particular, the thermally conductive filler of the present invention preferably has a spherical shape. The term "spherical" generally refers to an aspect ratio (ratio of major axis to minor axis) of 1 to 2, preferably 1 to 1.75, more preferably 1 to 1.5, and even more preferably 1 to 1.4. The aspect ratio can be determined by randomly selecting 200 or more particles from an image of the cross section of a thermally conductive resin sheet taken with an SEM, determining the ratio of the long diameter to the short diameter of each particle, and calculating the average value.

[0060] The thermally conductive filler of the present invention preferably contains agglomerated particles of boron nitride (also referred to as "secondary particles") formed by agglomeration of tabular boron nitride particles (also referred to as "primary particles"). Examples of the primary particles include cubic boron nitride, hexagonal boron nitride (h-BN), etc. Among these, hexagonal boron nitride is preferred from the viewpoint of improving thermal conductivity.

[0061] Hexagonal boron nitride particles have a flat or scale-like shape and are characterized by extremely high thermal conductivity in the planar plane direction (approximately 200–500 W / m·K). However, due to this shape, when resin sheets are produced using conventional thermoplastic resin molding methods (e.g., sheet extrusion using a twin-screw extruder and a T-die), most of the added boron nitride particles are oriented parallel to the surface of the resin sheet. As a result, the thermal conductivity of the resin sheet in the thickness direction may be lower than when spherical fillers with comparable thermal conductivity are added. Therefore, by agglomerating the flat primary particles oriented parallel to the thickness direction and disrupting the plane orientation, the thermal conductivity in the thickness direction can be improved.

[0062] Examples of the agglomerated structure of the boron nitride agglomerated particles include a cabbage structure and a card house structure, with the card house structure being preferred 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).

[0063] The cabbage structure refers to a spherical agglomeration of flat primary particles resembling a cabbage. When the cabbage-structured agglomerated particles are added to a resin sheet, the boron nitride primary particles constituting the boron nitride agglomerated particles are not oriented only in the plane direction of the thermally conductive resin sheet. Therefore, the thermal conductivity in the thickness direction of the sheet can be more easily increased than when boron nitride primary particles are simply added. However, when viewed radially from approximately the center of the cabbage-structured agglomerated particles, most of the primary particles have their flat surfaces oriented perpendicular to the radial direction. Therefore, although some primary particles are indeed oriented in the thickness direction of the sheet or oriented closer to the thickness direction, only a limited portion of the particles can effectively conduct heat in the thickness direction. Figure 1 shows a cross-sectional SEM image of a thermoplastic resin containing cabbage-structured agglomerated boron nitride particles, which were then hot-press molded. Referring to Figure 1, it can be seen that many of the primary boron nitride particles are oriented at a shallow angle relative to the surface of the resin sheet.

[0064] On the other hand, 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 an agglomerate are in contact with the edge surfaces of other primary particles present within the agglomerate. A schematic diagram of the house-of-cards structure is shown in Figure 2. The card-house structure of the aggregated particles has extremely high fracture strength due to its structure, and does not collapse even during the pressure process used in molding the heat-dissipating resin sheet. Therefore, primary particles that are normally oriented in the longitudinal direction of the heat-dissipating resin sheet can be made to exist in random directions. This allows the heat-dissipating resin sheet to achieve high thermal conductivity not only in the longitudinal direction but also in the thickness direction. Figure 3 shows a cross-sectional SEM image of a thermoplastic resin that has been added with house-of-card-structured boron nitride agglomerated particles and then hot-press molded. Compared to Figure 1, in which the same mass of cabbage-structured boron nitride agglomerated particles is added, it can be seen that there are more particles oriented at a shallow angle to the thickness direction of the thermally conductive resin sheet. As such, the house-of-card-structured boron nitride agglomerated particles have more primary particles oriented in the thickness direction than the cabbage-structured boron nitride agglomerated particles, and therefore can conduct heat more effectively in the thickness direction, further increasing the thermal conductivity in the thickness direction. The boron nitride agglomerated particles having a house-of-card structure can be produced, for example, by the method described in WO 2015 / 119198.

[0065] When using boron nitride agglomerated particles having a house-of-card structure, the particles may be surface-treated with a surface treatment agent. Examples of surface treatment agents that can be used include known surface treatments such as silane coupling treatment. Generally, direct affinity or adhesion between a thermally conductive filler and a thermoplastic resin is often not observed, and this is also true when boron nitride agglomerated particles having a house-of-card structure are used as the thermally conductive filler. It is believed that increasing the adhesion at the interface between the thermally conductive filler and the matrix resin through chemical treatment can further reduce thermal conductivity attenuation at the interface.

[0066] By using agglomerated particles of boron nitride as the thermally conductive filler of the present invention, the particle size can be made larger than that of a thermally conductive filler that uses primary particles as is. By increasing the particle size of the thermally conductive filler, the heat transfer path between the thermally conductive fillers via the thermoplastic resin with low thermal conductivity can be reduced, and therefore the increase in thermal resistance in the heat transfer path in the thickness direction can be reduced.

[0067] From the above viewpoints, the lower limit of the volumetric maximum particle diameter Dmax (hereinafter also referred to as "maximum particle diameter") of the thermally conductive filler 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 even more preferably 90 μm or less.

[0068] The lower limit of the volume-based average particle diameter D50 of the thermally conductive filler is preferably 2 μm or more, more preferably 5 μm or more, even more preferably 10 μm or more, and still more preferably 20 μm or more, while the upper limit of the average particle diameter D50 is preferably 300 μm or less, more preferably 200 μm or less, even more preferably 100 μm or less, and still more preferably 80 μm or less.

[0069] By having the maximum particle size of the thermally conductive filler be equal to or less than the above upper limit, when the thermally conductive filler is contained in a matrix resin, the interface between the matrix resin and the thermally conductive filler is reduced, resulting in lower thermal resistance, achieving high thermal conductivity, and forming a high-quality film without surface roughness, etc. By having the maximum particle size be equal to or greater than the above lower limit, a sufficient thermal conductivity improvement effect as a thermally conductive filler required for power semiconductor devices can be obtained.

[0070] Furthermore, it is believed that the influence of the thermal resistance at the interface between the matrix resin and the thermally conductive filler on the thickness of the thermally conductive resin sheet becomes significant when the size of the thermally conductive filler relative to the thickness of the thermally conductive resin sheet is 1 / 10 or less. In particular, in the case of power semiconductor devices, thermally conductive resin sheets with a thickness 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 thermally conductive filler be larger than the above lower limit. Furthermore, by having the maximum particle diameter Dmax of the thermally conductive filler be equal to or greater than the above lower limit, not only is the attenuation of thermal conductivity caused by the interface between the thermally conductive filler and the matrix resin suppressed, but the number of required thermal conduction paths between particles is reduced, increasing the probability that they will connect from one side to the other in the thickness direction of the thermally conductive resin sheet. Furthermore, when the maximum particle diameter Dmax of the thermally conductive filler is equal to or greater than the above lower limit, the interface area between the matrix resin and the thermally conductive filler 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 thermally conductive filler in the thermally conductive resin sheet, making it easier to obtain excellent voltage resistance characteristics. On the other hand, by having the volume-based maximum particle diameter Dmax of the thermally conductive filler be equal to or less than the above upper limit, the thermally conductive filler is prevented from protruding onto the surface of the thermally conductive resin sheet, and a good surface shape without surface roughness is obtained. Therefore, when a sheet is produced by bonding it to a copper substrate, sufficient adhesion can be obtained, and excellent voltage resistance characteristics can be obtained.

[0071] The ratio (Dmax / thickness) of the size (Dmax) of the thermally conductive filler 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.

[0072] The maximum particle size Dmax and the average particle size D50 of the thermally conductive filler can be measured, for example, by the following method. A sample in which a thermally conductive filler is dispersed in a solvent, specifically, a sample in which a thermally conductive filler is 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 thermally conductive filler 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 G3 (manufactured by Malvern Instruments). The maximum particle size Dmax and average particle size D50 of the thermally conductive filler 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 with the thermally conductive filler and then physically removing it, and then heating the resin component in air to incinerate it and remove it.

[0073] (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 thermally conductive filler 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 thermally conductive filler is preferably 85% by mass or less, more preferably 80% by mass or less. When the content of the thermally conductive filler is equal to or greater than the lower limit, the thermal conductivity improving effect and the linear expansion coefficient controlling effect of the thermally conductive filler are satisfactorily exhibited, whereas when the content of the thermally conductive filler is equal to or less than the upper limit, the moldability of the resin composition and the interfacial adhesion with different materials are improved.

[0074] Generally, the compounding ratio of a thermally conductive resin composition is often specified by the volume fraction of the matrix resin and the thermally conductive filler (hence, the area ratio in the cross section of the thermally conductive resin sheet). The thermal conductivity in the thickness direction of the thermally conductive resin sheet 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 house-of-card-structured boron nitride agglomerated particles are used as a thermally conductive filler, the particles are not only characterized by their house-of-card-structure internal structure, but also by the formation of numerous radially oriented, flat, plate-like boron nitride primary particles on the particle surface in a protrusion pattern known as a burr or confetti-like shape. The protrusions of adjacent house-of-card-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 thermally conductive filler by observation with a conventional scanning electron microscope (SEM). Furthermore, as the amount of house-of-card-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 at points. The observed contact areas then become linear, i.e., planar. In this contact state, the addition of house-of-card-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 thermally conductive filler by SEM observation.

[0075] The thermally conductive filler of the present invention preferably contains 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and even more preferably 80% by mass or more of agglomerated particles of boron nitride per 100% by mass of the thermally conductive filler. The entire amount (100% by mass) of the thermally conductive filler may be agglomerated particles of boron nitride. When the content of the boron nitride agglomerated particles is equal to or greater than the above lower limit, the thermal conductivity of the thermally conductive resin sheet in the thickness direction is increased.

[0076] The resin composition of the present invention may contain other components in addition to the crystalline thermoplastic resin and the thermally conductive filler, although from the viewpoint of increasing thermal conductivity, it is preferable that no other components are contained. 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 that improve the interfacial affinity between the thermally conductive filler and the thermoplastic resin, such as silane coupling agents, as well as additives that can be expected to increase the adhesive strength between the resin sheet and metal sheet material, such as silane coupling agents, extenders, etc. When these additives are used, the amount added may generally be within the range used for the purpose.

[0077] (4) Particularly preferred embodiment A resin composition according to a preferred embodiment of the present invention contains a crystalline thermoplastic resin having a melting point of 300° C. or higher and a thermally conductive filler, and the thermally conductive filler contains agglomerated particles of boron nitride. Furthermore, a resin composition according to another preferred embodiment of the present invention contains 15% by mass or more and 40% by mass or less of a crystalline thermoplastic resin having a melting point of 300°C or more, and 60% by mass or more and 85% by mass or less of a thermally conductive filler.

[0078] 2.Thermal conductive resin sheet The thermally conductive resin sheet of the present invention is made of the above resin composition, has excellent moisture absorption reflow resistance, and is less susceptible to interfacial peeling due to thermal expansion and shrinkage when laminated with a metal plate.

[0079] The thermal conductivity of the thermal conductive resin sheet in the thickness direction at 25°C is preferably 5.0 W / m K or more, more preferably 7.0 W / m K or more, even more preferably 9.0 W / m K or more, even more preferably 10.0 W / m K or more, and particularly preferably 15.0 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 and its physical properties such as melt viscosity, the type and content of the thermally conductive filler, the method of mixing the thermoplastic resin and the thermally conductive filler, the conditions in the heating and kneading process described below, and the like.

[0080] Furthermore, the thermal conductive resin sheet of the present invention preferably has a thermal conductivity in the thickness direction at 200° C. of 90% or more, and more preferably 92% or more, of the thermal conductivity in the thickness direction at 25° C. Since the thermal conductivity in the thickness direction at 200° C. 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.

[0081] 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. On the other hand, the upper limit of the thickness 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, particularly when using the thermally conductive resin sheet in a power semiconductor device or the like, miniaturization and thinning can be achieved, and further, compared to insulating thermally conductive layers made of ceramic materials, the thinning can achieve the effect of reducing thermal resistance in the thickness direction.

[0082] In the thermally conductive resin sheet of the present invention, it is preferable to reduce the orientation of the primary particles of the thermally conductive filler in order to reduce the anisotropy of the thermal conductivity and increase the thermal conductivity in the thickness direction. 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 20.0 or less, more preferably 17.0 or less, and even more preferably 15.0 or less. If the ratio exceeds 20.0, the thermally conductive filler collapses during the melt-kneading process or is excessively crushed during the pressing process, resulting in a large amount of thermally conductive filler that is parallel to or forms a small angle with the surface direction of the thermally conductive resin sheet. In this case, even if the content of the thermally conductive filler is increased, it is difficult to increase the thermal conductivity in the thickness direction. The lower limit of the ratio "I(002) / I(100)" is not particularly limited. For example, when boron nitride agglomerated particles having a house-of-card structure are used as the thermally conductive filler, 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.

[0083] From the viewpoint of simplifying the production process, it is preferable to adjust the orientation of the primary particles of the thermally conductive filler without intentionally performing an orientation operation. The orientation can be adjusted, for example, by appropriately changing the type and physical properties such as melt viscosity of the thermoplastic resin, the type and content of the thermally conductive filler, the method of mixing the thermoplastic resin and the thermally conductive filler, the conditions in the heating and kneading step described below, etc.

[0084] 3. Manufacturing method of thermally conductive resin sheet Hereinafter, a first production method and a second production method will be described as examples of the production method for the thermally conductive resin sheet of the present invention, although the production method for the thermally conductive resin sheet of the present invention is not limited to these production methods.

[0085] <First manufacturing method> A first manufacturing method of the thermally conductive resin sheet of the present invention is a method comprising a heating and kneading step of heating and kneading a crystalline thermoplastic resin having a melting point of 300°C or higher and a thermally conductive filler to prepare a resin composition, and a press molding step of pressing the resin composition with a heating body to form it into a sheet.

[0086] (1) Heat-kneading process In the heat-kneading step, the crystalline thermoplastic resin and the thermally conductive filler are melt-kneaded by heating. In the heat-kneading step, the crystalline thermoplastic resin and the thermally conductive filler can be put into a processing machine and melt-kneaded. The processing machine used in the heat-kneading step may be one generally used for the purpose of kneading a thermally conductive filler or various additives into a resin, such as a continuous kneader, a plastomill kneader, a co-rotating twin-screw extruder kneader, a counter-rotating twin-screw extruder kneader, or a single-screw extruder kneader. The melt-kneading temperature is set in the molding machine (e.g., in the case of an extruder-type melt-kneading device, the set temperature of the cylinder heater) preferably between 370°C and 430°C, more preferably between 380°C and 420°C. By setting the melt-kneading temperature at 370°C or higher, the resin viscosity is sufficiently reduced, and an increase in the load on the molding machine can be suppressed. Furthermore, shear fracture of the thermally conductive filler during kneading can be suppressed, resulting in good thermal conductivity of the resulting thermally conductive resin sheet. On the other hand, by setting the melt-kneading temperature at 450°C or lower, deterioration of the resin itself and deterioration of the physical properties of the molded thermally conductive resin sheet can be suppressed.

[0087] (2) Press molding process Because the resin composition of the present invention, which has been heated and melt-kneaded, contains a large amount of thermally conductive filler, it often remains in a lumpy or powdery form even after the heating and kneading process. Therefore, it is often difficult to use a manufacturing method in which the resulting mixture is molded into a sheet in a process subsequent to the melt-kneading process and then wound up, as is the case with conventional thermoplastic resin compositions. Therefore, in the present invention, it is preferable to form the resulting lumpy or powdery mixture into a sheet by press molding, a batch process. However, the manufacturing method for the thermally conductive resin sheet of the present invention is not limited to batch pressing; continuous sheet production is also possible if a sheet forming device using a steel belt method capable of continuous molding at a certain level of high temperature and pressure is available.

[0088] In the press molding, which is a batch process, various known press machines for molding thermoplastic resins can be used. From the viewpoint of preventing resin deterioration during heat pressing, it is particularly preferable to use a vacuum press machine that can reduce the amount of oxygen inside the press machine during heating, or a press machine equipped with a nitrogen substitution device. In the pressing step, it is preferable to set the applied pressure not only to form a sheet of uniform thickness from the melt-kneaded product, but also to bond the added thermally conductive filler particles together to form heat paths and eliminate voids and gaps within the sheet. From this perspective, the pressure applied to the sample in the pressing step is typically 8 MPa or higher, preferably 9 MPa or higher, and more preferably 10 MPa or higher. It is also preferably 50 MPa or lower, more preferably 40 MPa or lower, and even more preferably 30 MPa or lower. By setting the pressure at or below the upper limit, crushing of the thermally conductive filler particles can be prevented, resulting in a thermally conductive resin sheet with high thermal conductivity. Furthermore, setting the pressing pressure at or above the lower limit improves contact between the thermally conductive filler particles, facilitating the formation of heat conduction paths and resulting in a sheet with high thermal conductivity. Furthermore, by reducing the number of gaps in the resin sheet, a thermally conductive resin sheet with high breakdown voltage can be obtained, even after a moisture absorption reflow test.

[0089] In the press molding step, the temperature of the resin press machine is preferably set to 370°C to 440°C, and more preferably 380°C or higher or 420°C or lower. By performing press molding within this temperature range, the resulting thermally conductive resin sheet can be given good thickness uniformity and high thermal conductivity due to good contact between the added thermally conductive fillers. If the molding temperature is 370°C or higher, the resin viscosity is reduced to a level sufficient for shaping processing, and the molded thermally conductive resin sheet can be given sufficient thickness uniformity. On the other hand, if the press temperature is set to 440°C or lower, deterioration of the resin itself and deterioration of the physical properties of the molded thermally conductive resin sheet can be suppressed.

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

[0091] <Second manufacturing method> A second method for producing a thermally conductive resin sheet of the present invention includes mixing a powder of a crystalline thermoplastic resin having a melting point of 300°C or higher with a powder of a thermally conductive filler to prepare a resin composition, and pressing the resin composition with a heating element to form a sheet.

[0092] In the second production method, the resin composition may be charged into a processing machine, melt-kneaded, and then pressed, similarly to the melt-kneading step in the first production method. On the other hand, from the viewpoint of improving the thermal conductivity of the resulting thermally conductive resin sheet, it is preferable in the second production method to prepare the resin composition by stirring and mixing the thermoplastic resin powder and the thermally conductive filler powder at room temperature without performing the above-mentioned heat-kneading step. By using this method, it is possible to prevent the thermally conductive filler from being shear-fractured during melt-kneading.

[0093] In particular, when the thermally conductive filler contains boron nitride, particularly when the thermally conductive filler contains agglomerated particles of boron nitride, melt-kneading according to the first production method may result in shear fracture of the thermally conductive filler. On the other hand, in the second production method, the resin composition can be prepared without carrying out a heat-kneading step, so that shear fracture due to melt-kneading can be suppressed and excellent thermal conductivity can be maintained. From the above viewpoints, the second production method is particularly suitable when the thermally conductive filler used is one containing boron nitride, and in particular one containing agglomerated particles of boron nitride.

[0094] Furthermore, the ratio of D50 of the thermally conductive filler powder to D50 of the crystalline thermoplastic resin powder (filler / thermoplastic resin) is preferably 0.3 or more and 6.0 or less. When the ratio (filler / thermoplastic resin) is 0.3 or higher, the density of the thermally conductive filler is prevented from varying within the thermally conductive resin sheet, which is thought to reduce the occurrence of spatial unevenness in thermal conductivity. On the other hand, when the ratio (filler / thermoplastic resin) is 6.0 or lower, the thermally conductive filler is prevented from being excessively exposed on the surface of the thermally conductive resin sheet, which is thought to improve the adhesive strength when the thermally conductive resin sheet is laminated with a metal plate and reduce the occurrence of voids at the lamination interface with the metal plate.

[0095] In the second manufacturing method, from the viewpoints of improving thermal conductivity and controlling the linear expansion coefficient, the resin composition contains preferably 60% by mass or more, and more preferably 65% by mass or more, of the thermally conductive filler powder in 100% by mass of the resin composition. On the other hand, from the viewpoints of moldability and interfacial adhesion with metal materials, the resin composition contains preferably 85% by mass or less, and more preferably 80% by mass or less, of the thermally conductive filler powder in 100% by mass of the resin composition.

[0096] The pressing temperature and pressing pressure in the second manufacturing method may be the same as those in the above-mentioned press molding step.

[0097] 4.Laminated heat dissipation sheet The laminated heat-dissipating sheet of the present invention is obtained by laminating a heat-dissipating material on one surface of the above-described 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. Among them, 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., which have good thermal conductivity and are relatively inexpensive, are preferable.

[0098] 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.

[0099] 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.

[0100] 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 processes 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.

[0101] 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 the press molding conditions for obtaining the thermally conductive resin sheet described above.

[0102] 5. Heat dissipation circuit board The heat-dissipating circuit board of the present invention includes the laminated heat-dissipating sheet. The heat-dissipating circuit board has a configuration in which a heat-dissipating metal material is laminated on one surface of the thermally conductive resin sheet of the present invention. Among these, a configuration in which a conductive circuit is laminated by a post-processing etching process or the like on the surface of the thermally conductive resin sheet opposite the surface on which the heat-dissipating metal material is laminated may be used. The heat dissipation circuit board is preferably configured as an integrated structure of "heat dissipation metal material / thermally conductive resin sheet / conductive circuit." The state before circuit etching is, for example, an integrated structure of "heat dissipation metal material / thermally conductive resin sheet / conductive circuit forming metal material," in which the conductive circuit forming metal material is flat and formed on the entire surface of one side of the thermally conductive resin sheet, or on a partial area.

[0103] The metal material for forming the conductive circuit is not particularly limited, but is preferably formed from a copper thin plate having a thickness of 0.05 mm to 1.2 mm, in view of good electrical conductivity, etching properties, cost, etc.

[0104] 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.

[0105] 6. Power Semiconductor Devices The thermally conductive resin sheet of the present invention can be suitably used as a heat dissipation sheet for power semiconductor devices, 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.

[0106] <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]

[0107] 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 it does not depart from the gist of the invention.

[0108] <Examples 1 to 14, Comparative Examples 1 and 2, and Reference Examples 1 and 2> The materials used and the manufacturing methods for the thermally conductive sheets of Examples 1 to 14, Comparative Examples 1 and 2, and Reference Examples 1 and 2 are as follows.

[0109] [Materials used] (matrix resin) As the matrix resins in Examples 1 to 14, Comparative Examples 1 and 2, and Reference Examples 1 and 2, the following were used.

[0110] Polyether ether ketone "Vestakeep 1000G" (manufactured by Daicel-Evonik, melting point: 343°C, melt viscosity: 0.14 kPa·s (400°C), MFR: 158 g / 10 min, mass average molecular weight (Mw): 52,000) Polyetheretherketone "KetaSpire KT-880FP" (manufactured by Solvay, melting point: 343°C, melt viscosity: 0.15 kPa·s (400°C), average particle size (D50): 30.0-45.0 μm, MFR: 86 g / 10 min, mass average molecular weight (Mw): 58,000) Homopolybutylene terephthalate "NovaDuran 5010R" (manufactured by Mitsubishi Engineering Plastics Corporation, melting point: 224°C, melt viscosity: 0.12 kPa·s (300°C), MFR: 16 g / 10 min (MVR (cm 3 / 10 min) converted value 250℃ 2.16 kg, mass average molecular weight: 88000 Epoxy resin composition (8.74 parts by mass of bisphenol F epoxy resin (manufactured by Mitsubishi Chemical Corporation, polystyrene-equivalent mass average molecular weight: 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)

[0111] The melt viscosity of each resin was measured at a shear rate of 1000 s in accordance with ASTM D3835. -1 , the melt viscosity at a temperature of 400°C. The melt viscosity of homopolybutylene terephthalate is measured at a shear rate of 1000 s -1 is the melt viscosity at a temperature of 300°C.

[0112] (thermal conductive filler) The thermally conductive fillers used in Examples 1 to 14, Comparative Examples 1 and 2, and Reference Examples 1 and 2 were as follows.

[0113] Thermally conductive filler 1: PTX25 boron nitride agglomerated particles (secondary particles) with a so-called "cabbage" structure, formed by aggregating flat-plate-shaped boron nitride particles (primary particles) into a spherical shape (manufactured by Momentive, average particle diameter (D50) 25 μm, specific surface area 7 m 2 / g) Thermally conductive filler 2: boron nitride agglomerated particles with a house-of-cards structure manufactured based on International Publication No. 2015 / 119198 (average particle size (D50) 35 μm, Dmax: 90 μm) Thermally conductive filler 3: Plate-shaped boron nitride primary particles "AP-10S" (MARUKA Co., Ltd., average particle diameter (D50) 3.0 μm, specific surface area 10 m 2 / g)

[0114] [Creating a thermally conductive resin sheet] The types and amounts of matrix resin and thermally conductive filler added were as shown in Tables 1 and 2, and thermally conductive resin sheets were prepared by the following method.

[0115] (Examples 1 to 8 and Reference Example 1) The matrix resin and the thermally conductive filler were kneaded in a Labo Plastomill ("4C150", manufactured by Toyo Seiki Co., Ltd.) at 380°C for 5 minutes to obtain a melt-kneaded product of the matrix resin and the thermally conductive filler. In Example 5, a melt-kneaded product was obtained in the same manner as above, except that the melt-kneading temperature was changed to 395°C. The above-mentioned 5 minutes means that the total amount of the compounded matrix resin and thermally conductive filler was 80 g, and from that, a small amount of the matrix resin was first added to the Labo Plastomill. After confirming that it was plasticized, a similar small amount of the thermally conductive filler was added, and this procedure was repeated until the entire 80 g compounded amount had been added, after which the melt-kneading was continued for another 5 minutes.

[0116] Next, the melt-kneaded mixture was pressed for 10 minutes using a high-temperature vacuum press (Kitagawa Seiki Co., Ltd.) at a press temperature of 395°C and a press surface pressure of 10 MPa to obtain a thermally conductive resin sheet 15 cm square and 150 μm thick. Here, the above-mentioned 10 minutes means that the inside of a vacuum press was preheated to 150 ° C, the molten kneaded material was introduced therein as a press-loaded composition, and while operating the vacuum pump, a light pressure of several MPa was applied to the molten kneaded material, the internal temperature of the press was set to 395 ° C, and after 40 minutes of heating, the press surface pressure was set to 10 MPa and pressed for 10 minutes. After 10 minutes, the internal temperature of the press was again set to 150 ° C, and when the internal temperature approached 150 ° C, the vacuum was released, and the press-loaded composition was removed to obtain a thermally conductive resin sheet.

[0117] The press-loaded structure described above is a structure necessary for one batch press, in which a metal spacer 6 mm thick and 20 cm long and wide, with a frame-like opening measuring 15 cm x 15 cm in inner length, is placed on a lower plated plate measuring 30 cm long and wide, the molten mixture described above in an amount sufficient to obtain a pressed sheet 150 μm thick is dispersed into the spacer, and a drop lid 5.85 mm thick and measuring 14.6 cm x 14.6 cm long and wide is fitted into the 15 cm x 15 cm opening, and an upper plated plate of the same size as the lower plated plate is placed on top.

[0118] (Examples 9 to 14 and Reference Example 2) A thermally conductive resin sheet was obtained in the same manner as in Examples 1 to 8 and Reference Example 1, except that the matrix resin and the thermally conductive filler were not melt-kneaded, but were mixed at room temperature and used as the press-loaded composition.

[0119] (Comparative Example 1) A thermally conductive resin sheet was obtained in the same manner as in Examples 1 to 8 and Reference Example 1, except that the melt-kneading temperature in the Laboplastomill was set to 290°C and the press molding temperature was set to 300°C.

[0120] (Comparative Example 2) Thermally conductive filler 2 was added so that the total amount of the epoxy resin composition and thermally conductive filler 2 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 thermally conductive filler 2 was 62.8% by mass, thereby obtaining a coating slurry (sheet coating liquid). When mixing these, after manual stirring, stirring was carried out for 2 minutes using a planetary mixer "Awatori Rentaro AR-250". The coating slurry obtained above was applied onto a 38 μm thick polyethylene terephthalate film (hereinafter also referred to as "PET film") using the doctor blade method, and after heating and drying at 60°C for 120 minutes, it was pressed at a press temperature of 42°C and a press surface pressure of 15 MPa for 10 minutes to obtain an uncured epoxy resin sheet-shaped molding. Thereafter, the sheet-like molded article obtained above was further placed together with the PET film in a hot air oven at 170°C for 1 hour to harden the sheet-like molded article, and then the PET film was peeled off to obtain a thermally conductive resin sheet with a thickness of 150 μm.

[0121] [Creating a heat-dissipating circuit board] Using the thermally conductive resin sheets obtained in Examples 7, 13, and Comparative Examples 1 and 2, heat dissipation circuit boards were produced by the following method.

[0122] (Examples 7 and 13) The thermally conductive resin sheet was cut to a size of 40 mm x 80 mm, and one side of each of a 40 mm x 80 mm copper plate with a thickness of 2000 μm, which would serve as the metal plate material for heat dissipation, and a 40 mm x 80 mm copper plate with a thickness of 500 μm, which would serve as the copper plate for forming the conductive circuit, was pre-polished with #100 sandpaper to roughen the surface.The thermally conductive resin sheet was then sandwiched between the copper plates so that the roughened surface of each copper plate faced the thermally conductive resin sheet, and 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 dissipation metal material (copper plate) / thermally conductive resin sheet / copper plate for forming the conductive circuit." The copper plate for forming the conductive circuit was then subjected to etching treatment by a predetermined method and patterned to obtain a heat dissipation circuit board. The pattern was such that two circular patterns of φ25 mm copper plate for forming the conductive circuit remained on a 40 mm × 80 mm thermally conductive resin sheet.

[0123] (Comparative Example 1) A heat dissipation circuit board was obtained in the same manner as in Examples 7 and 13, except that the pressing temperature was set to 300°C.

[0124] (Comparative Example 2) A heat dissipation circuit board was obtained in the same manner as in Examples 7 and 13, except that the pressing temperature was set to 175°C.

[0125] <Measurement conditions and evaluation methods> The thermally conductive resin sheets of Examples 1 to 14, Comparative Examples 1 and 2, and Reference Examples 1 and 2 were measured and evaluated by the following methods.

[0126] [Thermal conductivity at 25℃] A thermally conductive resin sheet measuring 15 cm square and 500 μm thick was prepared using the same manufacturing method as in Example 1, and cut into 10 mm square pieces to serve as measurement samples. After a thin layer of laser light absorbing spray (Fine Chemical Japan's "Black Guard Spray FC-153") was applied to both sides of the measurement sample and allowed to dry, 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] In addition, the density ρ (g / m) of the resin sheet was measured using a specific gravity measuring instrument (manufactured by A&D Co., Ltd.). 3 ) was measured, and the specific heat capacity c (J / (g·K)) at 25°C was measured using a DSC measuring device (ThermoPlusEvo DSC8230, manufactured by Rigaku Corporation). 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 Since there are no JIS standards for the thermal diffusivity and thermal conductivity of resin-based materials, JIS R1611-2010 (Method for measuring thermal diffusivity, specific heat capacity, and thermal conductivity of fine ceramics by the flash method) was used as a reference. Since the standard stipulates that the sample thickness must be between 0.5 mm and 5 mm, only samples used for thermal conductivity measurements were measured at a thickness of 0.5 mm. Furthermore, density ρ was determined using the Archimedes method in accordance with JIS K6268. Furthermore, specific heat capacity c was determined using a DSC measuring device in accordance with JIS K7123.

[0129] [Evaluation of thermal conductivity retention at 200℃] The thermal conductive resin sheets of Examples 11, 13 and 14 were evaluated for thermal conductivity retention at 200° C. by the following method, and the results are shown in Table 3.

[0130] The laser flash method measurement was performed using the xenon flash analyzer (NETZSCH LFA447 NanoFlash300) used in the "Evaluation of thermal conductivity at 25°C" with the step measurement mode, with the starting temperature set at 25°C, the interval temperature set at 25°C, and the temperature raised to 200°C to measure the thermal diffusivity a at each temperature. These temperatures are the temperatures inside the chamber of the measurement device.

[0131] The specific heat capacity c was measured up to 250°C using a DSC measuring device, and the specific heat was determined at a temperature corresponding to the measurement temperature of the thermal diffusivity. Regarding density ρ, measurements could not be taken at any temperature other than 25°C. However, since the linear expansion coefficient in the planar direction of the thermally conductive resin sheet was a relatively small value of 27 ppm between 180°C and 200°C, it was considered that the volume change of the thermally conductive resin sheet of the present invention between 25°C and 200°C was not large, and the measurement value at 25°C was used as is. The linear expansion coefficient was measured in accordance with JIS K7197·1991, using a thermally conductive resin sheet with a thickness of 150 μm in a tensile mode. Furthermore, the linear expansion coefficient of neat PEEK resin, in the case of "KetaSpire KT-880FP" used in this example, is listed in the catalog as 50 ppm (-50°C to 50°C, ASTM E831), and the linear expansion coefficient of PEEK alone is small. From these measured values, the thermal conductivity in the sheet thickness direction up to 200°C was calculated using "H = a × ρ × c", and the thermal conductivity at each temperature was taken as the retention rate (%) when the thermal conductivity at 25°C was taken as 100%.

[0132] Furthermore, for Reference Example 3, the thermal conductivity of the ceramic material "Pyroceram 9696" at each of the above temperatures was recorded using the values listed in NETZSCH's "Manufacturer's Certification" (certificate for the calibration "Pyroceram 9696" sample for xenon flash method measurements in accordance with ASTM-E1416).

[0133] [Breakdown voltage (BDV) before moisture absorption reflow test] The heat dissipative circuit boards prepared in Examples 7, 13, and Comparative Examples 1 and 2 were immersed in Fluorinert FC-40 (manufactured by 3M), and an ultra-high voltage withstand voltage tester 7470 (manufactured by Keisoku Gijutsu Kenkyusho) was used to place a φ25 mm electrode on a φ25 mm copper plate patterned by etching on the heat dissipative circuit board, and a voltage of 0.5 kV was applied. The voltage was increased by 0.5 kV every 60 seconds, and measurements were taken until dielectric breakdown occurred. The measurements were carried out at a frequency of 60 Hz and a voltage increase rate of 1000 V / sec.

[0134] For specimens with a breakdown voltage of 40 kV / mm or more per unit thickness (equivalent to a thickness of 1 mm), the BDV was measured after the moisture absorption reflow test. On the other hand, specimens with a breakdown voltage of less than 40 kV / mm per unit thickness are marked with "ND" in Table 3. 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.

[0135] [Breakdown voltage (BDV) after moisture absorption reflow test] The heat-dissipating circuit boards of Examples 7, 13, and Comparative Example 1, which had a breakdown voltage of 40 kV / mm or higher before the moisture absorption reflow test, were stored in an environment of 85°C and 85% RH using a thermo-hygrostat SH-221 (manufactured by Espec Corporation) for 3 days. Within 30 minutes, the boards were heated from room temperature to 290°C in 12 minutes under a nitrogen atmosphere, held at 290°C for 10 minutes, and then cooled to room temperature (moisture absorption reflow test). The breakdown voltage was then measured in the same manner as above. Breakdown voltages per unit thickness (equivalent to a 1 mm thickness) of 40 kV / mm or higher were marked "good," while those below 40 kV / mm were marked "poor." The measurement results are shown in Table 3. 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] [Interface observation after moisture absorption reflow test] The heat-dissipating circuit boards produced in Examples 7, 13, and Comparative Examples 1 and 2 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 electrode 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 probe with a gain of 30 dB and a pitch of 0.2 mm, with the sample placed in water. The evaluation results are shown in Table 3. The evaluation of the interface observation after the moisture absorption reflow test can be used 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] [Orientation degree of primary particles of thermally conductive filler] Using the same manufacturing method as in Examples 7 and 13, a thermally conductive resin sheet measuring 15 cm square and 150 μm thick was prepared and cut into a 40 mm square to serve as a measurement sample. The measurement sample was measured using X-ray diffraction, and the ratio "I(002) / I(100)" was calculated, where the diffraction peak intensity of the (002) plane was defined as I(002) and the diffraction peak intensity of the (100) plane was defined as I(100). The evaluation results are shown in Tables 1 and 2.

[0138] [Table 1]

[0139] [Table 2]

[0140] [Table 3]

[0141] Comparing Examples 7 and 13 with Comparative Examples 1 and 2, the heat dissipation circuit boards using the thermally conductive resin sheets of Examples 7 and 13 maintained a breakdown voltage of 40 kV / mm or more both before and after the moisture absorption reflow test. Furthermore, when the interface between the thermally conductive resin sheet and the copper electrode after the moisture absorption reflow test was observed, no peeling, lifting, or void formation was observed.

[0142] On the other hand, in Comparative Example 1, which used PBT, a crystalline thermoplastic resin with a melting point of 224°C, as the matrix resin, a relatively high breakdown voltage was obtained before the moisture absorption reflow test, but the value after the moisture absorption reflow test was below 40 kV / mm. Furthermore, when the interface between the thermally conductive resin sheet and the copper electrode was observed after the moisture absorption reflow test, peeling, lifting, and the occurrence of relatively significant voids were observed. This indicates that when a thermoplastic resin with a melting point lower than the range of the present invention, such as PBT, is used, it cannot withstand the moisture absorption reflow test and interfacial peeling occurs when it is laminated with a metal plate.

[0143] In Comparative Example 2, which used an epoxy resin composition, a thermosetting resin, as the matrix resin, the breakdown voltage was below 40 kV / mm even before the moisture absorption reflow test. The reason for this is unclear, but it is thought that the solvent used in coating remained in the resin composition, foamed during thermal curing, and formed defects such as voids. Furthermore, when the interface between the thermally conductive resin sheet and the copper electrode was observed after the moisture absorption reflow test, significant peeling, lifting, and the occurrence of voids were observed.It is generally believed that thermosetting resins exhibit good heat resistance even when used at temperatures above their glass transition temperature due to their three-dimensional cross-linked structure, but the moisture absorption reflow test described above is also considered to be a severe condition for thermosetting resins.

[0144] From the above, it was found that the thermally conductive resin sheet of the present invention has good moisture absorption reflow resistance by using a crystalline thermoplastic resin with a melting point of 300°C or higher as the matrix resin, and when laminated with a metal plate, interfacial peeling due to thermal expansion and thermal contraction is less likely to occur.

[0145] Furthermore, when Examples 1 to 14 are compared with Reference Examples 1 and 2, when boron nitride is used as the thermally conductive filler, the thermal conductivity is higher when boron nitride agglomerated particles are used than when flat boron nitride primary particles are used, and in particular, the thermal conductivity is higher when card-house structured boron nitride agglomerated particles are used than when cabbage-structured boron nitride agglomerated particles are used.

[0146] More specifically, when comparing Example 9, Example 13 and Reference Example 2, when the same amounts of boron nitride agglomerated particles and tabular boron nitride primary particles were used, the thermal conductive resin sheets of Example 9 and Example 13, which used boron nitride agglomerated particles, had higher thermal conductivity. Furthermore, when Examples 2, 8 and Reference Example 1 are compared, even when the content of the tabular boron nitride primary particles is increased, the thermal conductivity does not reach that obtained when agglomerated particles of boron nitride are used. Furthermore, when Examples 1 and 7, Examples 2 and 8, and Examples 9 and 13 were compared, when the same amounts of cabbage-structured boron nitride agglomerated particles and card-house-structured boron nitride agglomerated particles were used, the thermally conductive resin sheets of Examples 7, 8, and 13, which used card-house-structured boron nitride agglomerated particles, had higher thermal conductivity.

[0147] From the above, it has been found that the thermal conductivity of the thermally conductive resin sheet of the present invention is improved by using boron nitride agglomerated particles as a thermally conductive filler, and that the thermal conductivity is further improved by using boron nitride agglomerated particles with a card-house structure.

[0148] Furthermore, when comparing Examples 11, 13, and 14 with Reference Example 3, the thermal conductivity in the thickness direction of the thermal conductive resin sheets of Examples 11, 13, and 14 at 200°C was 90% or more of the thermal conductivity in the thickness direction at 25°C, whereas the thermal conductivity in the thickness direction of the ceramic material of Reference Example 3 at 200°C was reduced to 87% of the thermal conductivity in the thickness direction at 25°C.

[0149] From the above, it was found that the thermally conductive resin sheet of the present invention can maintain high thermal conductivity even at 200°C.

[0150] Furthermore, when Example 4 and Example 5 are compared, the thermal conductivity of the thermally conductive resin sheet of Example 5, in which the melt-kneading temperature was set to 395° C., was higher. This is thought to be because increasing the melt-kneading temperature reduced the viscosity of the matrix resin, which reduced the shear stress applied to the thermally conductive filler and prevented the thermally conductive filler from being crushed.

[0151] Furthermore, when Examples 1 to 8 are compared with Examples 9 to 14, the thermally conductive resin sheets of Examples 9 to 14, which were produced by stirring and mixing the matrix resin powder raw material and the thermally conductive filler powder at room temperature and then press-molding without going through the heat-kneading step, had higher thermal conductivities. This is thought to be because shear fracture of the thermally conductive filler was suppressed by kneading.

[0152] From the above, it has been found that the thermal conductivity of the thermally conductive resin sheet of the present invention can be increased by changing the type of matrix resin, the type and content of the thermally conductive filler, the method of mixing the matrix resin and the thermally conductive filler, the conditions in the heating and kneading process, etc.

Claims

1. A heat-dissipating circuit board having a laminated heat-dissipating sheet in which a heat-dissipating metal material is laminated on one surface of a thermally conductive resin sheet, the laminated heat-dissipating sheet comprising a resin composition containing a crystalline thermoplastic resin having a melting point of 300°C or higher and a thermally conductive filler, the crystalline thermoplastic resin containing polyether ether ketone, the thermally conductive filler consisting of only spherical agglomerated particles of boron nitride, or consisting of spherical agglomerated particles of boron nitride and a thermally conductive filler consisting of particles other than boron nitride, the thermally conductive filler consisting of particles other than boron nitride consisting of irregular particles, spherical particles, plate-like particles, or aggregates thereof, or a mixture thereof.

2. 2. The heat dissipation circuit board according to claim 1, wherein the resin composition contains 15% by mass or more and 40% by mass or less of the crystalline thermoplastic resin and 60% by mass or more and 85% by mass or less of the thermally conductive filler.

3. 3. The heat dissipation circuit board according to claim 1, wherein the boron nitride agglomerated particles are contained in a proportion of 50% by mass or more and 100% by mass or less relative to 100% by mass of the thermally conductive filler.

4. 4. The heat dissipative circuit board according to claim 1, wherein the boron nitride agglomerated particles have a house-of-cards structure.

5. 5. The heat dissipation circuit board according to claim 1, wherein the thermal conductive resin sheet has a thermal conductivity in the thickness direction at 25° C. of 15.0 W / m·K or more.

6. 6. The heat dissipation circuit board according to claim 5, wherein the thermal conductivity of the thermal conductive resin sheet in the thickness direction at 200°C is 90% or more of the thermal conductivity in the thickness direction at 25°C.

7. 7. The heat dissipation circuit board according to claim 1, wherein the thermally conductive resin sheet has a thickness of 50 μm or more and 300 μm or less.

8. The heat dissipation circuit board according to any one of claims 1 to 7, wherein the spherical agglomerated particles of boron nitride are particles formed by spherical agglomeration of primary particles of boron nitride, and have an aspect ratio (ratio of major axis to minor axis) of 1 or more and 2 or less.

9. 9. The heat dissipative circuit board according to claim 1, wherein the crystalline thermoplastic resin has an MFR of 8 g / 10 min or more and less than 158 g / 10 min.

10. The heat dissipation circuit board according to any one of claims 1 to 9, wherein the boron nitride contained in the thermally conductive resin sheet is composed of spherical boron nitride particles and flat boron nitride particles, and the volume ratio of the spherical boron nitride particles to the total amount of the boron nitride is 75% by volume to 99% by volume, excluding those in which the volume ratio of the spherical boron nitride particles to the total amount of the boron nitride is 75% by volume to 99% by volume.

11. The heat dissipation circuit board according to any one of claims 1 to 10, wherein the thermal conductive resin sheet has a breakdown voltage (BDV) of 40 kV / mm or more per unit thickness after a moisture absorption reflow test measured by the following method for a heat dissipation circuit board manufactured by the following method. <Method for manufacturing a heat dissipation circuit board> A thermally conductive resin sheet having a thickness of 150 μm is cut to a size of 40 mm × 80 mm, and one side of each of a 2000 μm thick copper plate having a size of 40 mm × 80 mm that will become the heat dissipating metal plate material and a 500 μm thick copper plate having a size of 40 mm × 80 mm that will become the copper plate for forming the conductive circuit is polished in advance with #100 sandpaper to roughen the surface, and the thermally conductive resin sheet is sandwiched so that the roughened surface of each copper plate faces the thermally conductive resin sheet, and pressed at a press temperature of 390 ° C. and a press surface pressure of 13 MPa for 10 minutes to obtain a laminated heat dissipation sheet consisting of a heat dissipating metal material (copper plate) / a thermally conductive resin sheet / a copper plate for forming the conductive circuit. The copper plate for forming the conductive circuit is further etched and patterned to obtain a heat dissipation circuit board. In this case, the pattern is formed so that two copper plates for forming conductive circuits with a φ25 mm circular pattern remain on a 40 mm×80 mm thermally conductive resin sheet. <Method for measuring BDV after moisture absorption reflow test> The heat dissipative circuit board was stored in an environment of 85°C and 85% RH using a thermo-hygrostat for 3 days, and then within 30 minutes, the temperature was raised from room temperature to 290°C in 12 minutes in a nitrogen atmosphere, and the board was held at 290°C for 10 minutes, and then cooled to room temperature (moisture absorption reflow test). The heat-dissipating circuit board after the moisture absorption reflow test is immersed in a fluorine-based inert liquid, and using an ultra-high voltage withstand voltage tester, a φ25 mm electrode is placed on a φ25 mm copper plate patterned by etching on the heat-dissipating circuit board, and a voltage of 0.5 kV is applied, increasing the voltage by 0.5 kV every 60 seconds until breakdown occurs. The measurement is performed at a frequency of 60 Hz and a voltage increase rate of 1000 V / sec. At this time, if the breakdown voltage per unit thickness (equivalent to a thickness of 1 mm) is 40 kV / mm or more, the BDV after the moisture absorption reflow test is subsequently measured.

12. 12. The heat dissipation circuit board according to claim 1, wherein a conductive circuit is laminated on the other surface of the thermally conductive resin sheet.

13. The heat dissipative circuit board according to any one of claims 1 to 12, wherein the dielectric breakdown voltage is 40 kV / mm or more.

14. A power semiconductor device comprising the heat dissipation circuit board according to any one of claims 1 to 13.

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