Resin sheet, composite molding and semiconductor device

Abstract

To provide a resin sheet containing nitride ceramics which can enhance thermal conductivity while maintaining moldability.SOLUTION: A resin sheet contains nitride ceramics, wherein when the sheet surface is observed, 30 pieces or more of colored particles are observed per 10 cm2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a resin sheet that can be suitably used as a heat dissipation member, an insulating member, etc. in, for example, a semiconductor device, and to a composite molded product and a semiconductor device using the same. [Background technology]

[0002] In recent years, heat generation due to the increasing density of integrated circuits has become a major problem in the electrical and electronic fields, and how to dissipate heat has become an urgent issue. For example, to ensure stable operation of semiconductor devices used to control the central processing unit of a personal computer or the motor of an electric vehicle, heat sinks, heat dissipation fins, etc. are essential for heat dissipation, and materials that can combine thermal conductivity and insulation are required to connect semiconductor devices to heat sinks, etc.

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

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

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

[0006] Nitride ceramics are widely used as heat dissipation materials due to their high thermal conductivity, as mentioned above. However, when mixing such nitride ceramics with resin to produce a cured resin, there is a limit to how much nitride ceramic can be added due to moldability considerations, making it difficult to sufficiently improve heat dissipation performance. In order to improve the heat dissipation performance of nitride ceramics, it is possible to remove impurities from the nitride ceramics by firing them in a non-oxidizing gas atmosphere or to increase the grain size of the nitride ceramics, but this has the problem of worsening formability.

[0007] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a resin sheet containing nitride ceramics that can maintain formability while increasing thermal conductivity. [Means for solving the problem]

[0008] In order to solve the above problems, the resin sheet proposed by the present invention has the following configuration.

[0009] [1] The first aspect of the present invention is a resin sheet containing nitride ceramics, and when observing the surface of the sheet, 2 This is a resin sheet in which more than 30 colored particles are observed per sheet. [2] A second aspect of the present invention is a thermosetting resin sheet made of a resin composition containing nitride ceramics and a thermosetting resin, wherein when the surface of the sheet is observed, 2 This is a resin sheet in which more than 30 colored particles are observed per sheet. [3] A third aspect of the present invention is a resin sheet made of a cured resin composition containing nitride ceramics and a thermosetting resin, wherein when the surface of the sheet is observed, 2 This is a resin sheet in which more than 30 colored particles are observed per sheet.

[0010] [4] A fourth aspect of the present invention is the resin sheet according to any one of the first to third aspects, wherein the colored particles are nitrides. [5] A fifth aspect of the present invention is the resin sheet according to any one of the first to fourth aspects, wherein the total mass content of the solvent and water in the resin sheet is 0.1 ppm or more and 50,000 ppm or less. [6] A sixth aspect of the present invention is the resin sheet according to any one of the first to fifth aspects, wherein the content of the thermosetting resin in the resin sheet is 60 mass % or less.

[0011] [7] A seventh aspect of the present invention is a resin sheet according to any one of the first to sixth aspects, wherein the nitride ceramic is one or more of boron nitride, aluminum nitride, silicon nitride, and titanium nitride. [8] An eighth aspect of the present invention is a resin sheet according to any one of the first to seventh aspects, wherein the cumulative volume 50% particle diameter (D50) of the nitride ceramic in a volume-based particle size distribution obtained by measurement using a laser diffraction / scattering particle size distribution measurement method is D50≧10 μm. [9] A ninth aspect of the present invention is the resin sheet according to any one of the first to eighth aspects, wherein the nitride ceramic contains agglomerated particles of boron nitride.

[0012]

[10] A tenth aspect of the present invention is a resin sheet according to any one of the third to ninth aspects, wherein when the resin sheet is subjected to a step voltage increase of 0.5 kV / 1 min using a 25 mmφ cylindrical electrode, the measured breakdown voltage BDV is 4 kV or more when the resin sheet has a thickness of 150 μm.

[11] An eleventh aspect of the present invention is a resin sheet according to any one of the third to tenth aspects, wherein when a resin sheet having two or more of the colored particles observed on its surface is subjected to a step voltage increase of 0.5 kV / 1 min using a 25 mmφ cylindrical electrode and placed below the 25 mmφ cylindrical electrode, the measured breakdown voltage BDV is 4 kV or more when the resin sheet has a thickness of 150 μm.

[0013]

[12] A twelfth aspect of the present invention is a resin sheet according to any one of the first to eleventh aspects, wherein, when the sheet surface is observed, the proportion of the total colored area due to colored particles on the sheet surface (100%) is 20% or less.

[13] A thirteenth aspect of the present invention is a resin sheet according to any one of the second to twelfth aspects, wherein the thermosetting resin is any one or more of an epoxy resin, a cyanate resin, a benzoxazine resin, a phenolic resin, and a maleimide resin.

[0014]

[14] A fourteenth aspect of the present invention is a composite molded product having the resin sheet of any one of the first to thirteenth aspects and a metal part.

[15] A fifteenth aspect of the present invention is a semiconductor device having the composite compact of the fourteenth aspect. [Effects of the Invention]

[0015] When observing the surface of the resin sheet proposed by this invention, 2 By including colored particles in the sheet to the extent that 30 or more colored particles are observed per unit area, it is possible to increase the thermal conductivity while maintaining moldability. [Brief explanation of the drawings]

[0016] [Figure 1] This is a reflection image (pixel count: 1280 x 960) of an arbitrary field of view (1 field of view 11.8 mm x 15.76 mm) obtained by observing the surface of the thermally conductive resin sheet (sample) obtained in Example 1 with a stereo microscope (SMZ 745T) while shining an LED light from the eyepiece side. DETAILED DESCRIPTION OF THE INVENTION

[0017] An example of an embodiment of the present invention will be described below, but the present invention is not limited to the embodiment described below.

[0018] <<Resin sheet of the present invention>> A resin sheet according to an embodiment of the present invention (also referred to as "the resin sheet of the present invention") is a resin sheet containing nitride ceramics, and is characterized by containing colored particles. Preferably, the resin sheet of the present invention is a resin sheet containing nitride ceramics, and when observing the surface of the sheet, 2 More than 30 colored particles are observed per particle.

[0019] The resin sheet of the present invention may be a thermosetting resin sheet (also referred to as "the present thermosetting resin sheet") made of a resin composition containing nitride ceramics and a thermosetting resin, or may be a resin sheet (also referred to as "the present cured resin sheet") made of a cured product of a resin composition containing nitride ceramics and a thermosetting resin. Preferably, the resin sheet of the present invention is a thermosetting resin sheet, and when the surface of the sheet is observed, the sheet has a thickness of 10 cm 2 The resin sheet may be a resin sheet in which 30 or more colored particles are observed per 10 cm or a cured resin sheet in which 30 or more colored particles are observed per 10 cm when observing the surface of the sheet. 2 The resin sheet may have 30 or more colored particles observed per unit area.

[0020] In the present invention, the term "resin sheet" refers to a sheet in which the component forming the continuous phase (matrix) of the sheet is a resin, and the "resin" includes thermoplastic resins, thermosetting resins, and cured products thereof, regardless of molecular weight.

[0021] <Thermosetting resin sheet> The "thermosetting resin sheet" refers to a sheet formed from a resin composition containing a resin that has the property of being cured by heat. The "resin composition containing a resin that has the property of being cured by heat" may be a resin composition that has the property of being cured by heat and that has the ability to be cured by heat, and may be one that has already been cured (also referred to as "temporarily cured") and has still the ability to be cured, or one that has not yet been cured (also referred to as "uncured").

[0022] <Colored particles> When observing the surface of the resin sheet of the present invention, 2 It is preferable that 30 or more colored particles are observed per pixel. The resin sheet of the present invention contains colored particles, which increases the thermal conductivity. 2 Preferably, 30 or more colored particles are observed per 10 cm, more preferably 40 or more, more preferably 50 or more, more preferably 60 or more, and even more preferably 70 or more. On the other hand, if the content of colored particles is too high, the insulating properties will decrease, so 2 The number of colored particles observed per unit area is preferably 20,000 or less, more preferably 10,000 or less, even more preferably 8,000 or less, even more preferably 5,000 or less, and even more preferably 2,000 or less.

[0023] Here, the colored particles contained in the resin sheet of the present invention (also referred to as "the present colored particles") are nitrides, and are by-products derived from nitride ceramics that are produced when processing is performed to remove impurities (e.g., carbon, oxygen) from nitride ceramics. By improving the purity of nitride ceramics, the crystallinity of the nitride ceramics increases, improving the thermal conductivity of resin sheets containing the nitride ceramics. As a result of extensive research into further improving thermal conductivity, we discovered that by further improving the crystallinity of nitride ceramics, metallic bonds are formed, causing coloration in parts of the nitride ceramics, resulting in the generation of colored particles, further increasing the desired thermal conductivity. It is presumed that these colored particles act to further increase thermal conductivity by incorporating metallic bonds into defects in the crystal lattice of nitride ceramics.

[0024] As described above, the colored particles of the present invention are substances derived from nitride ceramics, and therefore contain, for example, boron nitride, aluminum nitride, silicon nitride, or titanium nitride, but do not contain carbides such as graphite. The colored particles may be colored entirely or partially. The insulating properties of these colored particles are as follows: volume resistivity 1.0×10 8 It is preferable that the resistance is Ω·cm or more. The colored particles preferably have an average particle size of 1 μm or more and 5000 μm or less. The average particle size here is determined by observing 10 or more colored particles with an optical microscope or an electron microscope, measuring the particle size as the average of the longest and shortest diameters of each particle, and averaging the particle size.

[0025] From the viewpoint of improving thermal conductivity, the content of the coloring particles is preferably 0.2% by mass or more, more preferably 0.4% by mass or more, and even more preferably 0.6% by mass or more, relative to 100% by mass of the nitride ceramic. On the other hand, from the viewpoint of maintaining good formability, the content is preferably less than 3% by mass, more preferably 2.8% by mass or less.

[0026] A specific method for observing the sheet surface and counting the number of colored particles, as implemented in the examples described below, involves observing the sheet surface with an electron microscope while shining an LED light, obtaining reflected images in any 10 fields of view, converting the reflected images to grayscale (standard: ITU-R Rec BT.601), adjusting the center value to 130 to 140, extracting points with a grayscale of 100 or less by binarization, labeling the points obtained by binarization (connecting four), and calculating the number of parts with a circular equivalent diameter of 16 μm or more as the number of colored particles. If a circuit board is laminated on a resin sheet containing nitride ceramics, the circuit board can be removed, or the surface of the sheet in the area where no circuit is formed can be observed as above, and the area can be divided by the area of ​​the observed field of view to obtain a 10 cm 2 The number of colored particles per particle can be measured.

[0027] Furthermore, when observing the surface of the resin sheet of the present invention, if the total colored area due to colored particles is large, the large number of colored particles with poor wettability tends to result in poor coating properties, resulting in reduced formability, such as unevenness on the sheet surface and bubbles trapped within the film. Therefore, from the viewpoint of maintaining formability, the total colored area due to colored particles on the sheet surface (100%) is preferably 20% (200,000 ppm) or less, more preferably 5% (50,000 ppm) or less, even more preferably 1% (10,000 ppm) or less, and even more preferably 0.5% (5,000 ppm) or less. On the other hand, from the viewpoint of improving heat dissipation, it is preferably 0.00001% (0.1 ppm) or more, even more preferably 0.00005% (0.5 ppm) or more, even more preferably 0.0005% (5 ppm) or more, and even more preferably 0.001% (10 ppm) or more.

[0028] A specific method for measuring the percentage of the total colored area on the sheet surface caused by colored particles, as performed in the examples described below, is to observe the sheet surface with an electron microscope while shining LED light on it, obtain reflected images in any 10 fields of view, convert the reflected images to grayscale (standard: ITU-R Rec BT.601), adjust the center value to 130 to 140, extract points below grayscale 100 by binarization, measure the total area below grayscale 100, and calculate the percentage of the total sheet area.

[0029] <Nitride ceramics> Examples of the nitride ceramic contained in the resin sheet of the present invention (also referred to as "the present nitride ceramic") include boron nitride, aluminum nitride, silicon nitride, titanium nitride, etc. The present nitride ceramic may contain any one of these, or may contain two or more of them.

[0030] The present nitride ceramic preferably has a cumulative volume 50% particle diameter (D50) in the volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method, of D50≧10 μm. Regarding D50 of the present nitride ceramic, if the D50 is large to a certain extent, the number of particles in the resin sheet of the present invention will be relatively small, and the number of interparticle interfaces will be reduced, thereby reducing contact thermal resistance and increasing thermal conductivity, so it is preferably 10 μm or more, more preferably 15 μm or more, even more preferably 20 μm or more, and even more preferably 25 μm or more. On the other hand, because the surface smoothness of the resin sheet of the present invention tends to be obtained, it is preferably 150 μm or less, even more preferably 120 μm or less, and even more preferably 90 μm or less.

[0031] The D50 of the present nitride ceramic can be measured, for example, by the following method. A sample of the nitride ceramic dispersed in a solvent, specifically a sample of the nitride ceramic dispersed in a pure water medium containing a dispersion stabilizer, is measured for its volumetric particle size distribution using a laser diffraction / scattering particle size distribution analyzer, and D50 can be calculated from the particle size distribution obtained. Here, D50 is the particle size at 50% cumulative volume in the volume-based particle size distribution obtained by measurement using a laser diffraction / scattering particle size distribution measurement method. The resin sheet of the present invention (including the cured product) may be fired to remove the resin component and separate the present nitride ceramic, i.e., subjected to an ashing treatment, and the laser diffraction D50 of the present nitride ceramic contained in the resulting ashing residue may be measured.

[0032] The present nitride ceramic is preferably uncolored, for example, white.

[0033] The content of the present nitride ceramic in the resin sheet of the present invention is preferably 50% by mass or more, more preferably 53% by mass or more, and even more preferably 55% by mass or more, relative to 100% by mass of the resin sheet of the present invention, from the viewpoint of improving insulation and thermal conductivity. On the other hand, from the viewpoint of maintaining good handleability (brittleness), the content is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 88% by mass or less.

[0034] (Boron nitride agglomerated particles) Among these nitride ceramics, it is preferable to use boron nitride (also referred to as "BN"), as it has excellent insulating properties, thermal conductivity, solid lubricity, chemical stability, and heat resistance. Among these, boron nitride agglomerated particles (also referred to as "BN agglomerated particles") formed by agglomeration of plate-, scale-, or needle-shaped primary particles of boron nitride are particularly preferred because of their excellent insulating properties, thermal conductivity, solid lubricity, chemical stability, and heat resistance.

[0035] The boron nitride agglomerated particles include those formed by agglomerating plate-like, scale-like or needle-like primary particles into a spherical shape. Here, "spherical" means that the aspect ratio (ratio of major axis to minor axis) is from 1 to 2, and preferably from 1 to 1.5. The aspect ratio of the boron nitride agglomerated particles is determined by randomly selecting 200 or more particles from an image taken with an SEM, determining the ratio of the major axis to the minor axis of each particle, and calculating the average value.

[0036] Examples of boron nitride agglomerated particles include those having a conventionally known form in which crystals of scale-like or needle-like primary particles grow radially from the center to the surface of the agglomerated particle, a spherical form in which plate-like primary particles are sintered and agglomerated, and a house-of-card structure made up of plate-like primary particles. Here, the "house of card structure" refers to a structure in which plate-like particles are layered in a complex manner without being oriented, as described in, for example, Ceramics 43 No. 2 (published by the Ceramic Society of Japan in 2008). More specifically, boron nitride agglomerated particles having a house of card structure are aggregates of boron nitride primary particles, and have a structure in which the flat surfaces and edge surfaces of the primary particles are in contact with each other.

[0037] From the viewpoint of improving insulation and thermal conductivity, the content of the boron nitride agglomerated particles is preferably 50% by mass or more, more preferably 53% by mass or more, and even more preferably 55% by mass or more, relative to 100% by mass of the resin sheet of the present invention. On the other hand, from the viewpoint of maintaining good handleability (brittleness), it is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 88% by mass or less.

[0038] <Inorganic filler> The resin sheet of the present invention may contain other inorganic fillers in combination with the nitride ceramics. In this case, the "other inorganic filler" preferably has a thermal conductivity of 10 W / m·K or more, and examples thereof include particles of aluminum oxide (alumina), silica, magnesium oxide, and the like. When the "other inorganic filler" is contained, it is preferable that the "other inorganic filler" contains alumina particles, particularly spherical alumina particles, from the viewpoint of filling properties, water resistance, and thermal conductivity. The other inorganic filler is preferably not colored, for example, white.

[0039] When the "other inorganic filler" is contained, the mass proportion of the nitride ceramic in the total content (100 mass%) of the nitride ceramic and the other inorganic filler is preferably 50 mass% or more, more preferably 53 mass% or more, even more preferably 55 mass% or more, and even more preferably 60 mass% or more, from the viewpoint of increasing thermal conductivity. On the other hand, the upper limit may be 99.5 mass% or less, and preferably 98 mass% or less, from the viewpoint of increasing packing properties.

[0040] <Resin> The "resin" in the resin sheet of the present invention is a matrix resin, i.e., a component that forms the continuous phase (matrix) of the resin sheet of the present invention, and is preferably a thermoplastic resin or a thermosetting resin, with thermosetting resin being preferred from the standpoints of heat durability, adhesion to metals, and ease of handling. In the present invention, the term "resin" includes compounds, monomers, oligomers, and polymers regardless of molecular weight.

[0041] Examples of thermoplastic resins for the resin sheet of the present invention include polyolefin resins, polyester resins, polycarbonate resins, polystyrene resins, polyvinyl alcohol resins, acrylic resins, polyurethane resins, polyphenylene ether resins, polysulfone resins, polyphenylsulfone resins, polyethersulfone resins, polyetherimide resins, polyamide resins, polyetherketone resins, polytetrafluoroethylene resins, tetrafluoroethylene-perfluoroalkoxyethylene copolymer resins, tetrafluoroethylene-hexafluoropropylene copolymer resins, etc. Any one of these may be contained, or two or more may be contained.

[0042] The thermosetting resin of the resin sheet of the present invention may be any compound (including polymer) that has the property of being cured by heat. Examples include epoxy resin, cyanate resin, benzoxazine resin, phenol resin, maleimide resin, (meth)acrylic resin, etc. Any one of these may be contained, or two or more may be contained. Among these, it is preferable to contain an epoxy resin from the viewpoints of viscosity, heat resistance, moisture absorption, and ease of handling.

[0043] From the viewpoint of improving heat dissipation, the content of the thermosetting resin is preferably 60% by mass or less, more preferably 55% by mass or less, even more preferably 50% by mass or less, and even more preferably 45% by mass or less, based on 100% by mass of the resin sheet of the present invention (including volatile components such as solvents). On the other hand, from the viewpoint of reducing voids inside the sheet and at the adhesive interface, the content is preferably 10% by mass or more, more preferably 13% by mass or more, and even more preferably 15% by mass or more.

[0044] (epoxy resin) The epoxy resin may be any compound having one or more oxirane rings (epoxy groups) in the molecule. The oxirane ring (epoxy group) contained in the epoxy resin may be either an alicyclic epoxy group or a glycidyl group, but from the viewpoint of reaction rate or heat resistance, a glycidyl group is more preferable.

[0045] Examples of epoxy resins include epoxy group-containing silicon resins, aliphatic epoxy resins, bisphenol A or F epoxy resins, novolac epoxy resins, alicyclic epoxy resins, glycidyl ester epoxy resins, polyfunctional epoxy resins, and polymeric epoxy resins. The epoxy resin may be a resin containing an aromatic oxirane ring (epoxy group). Specific examples thereof include bisphenol-type epoxy resins obtained by glycidylating bisphenols such as bisphenol A, bisphenol F, bisphenol AD, bisphenol S, tetramethylbisphenol A, tetramethylbisphenol F, tetramethylbisphenol AD, tetramethylbisphenol S, and tetrafluorobisphenol A; biphenyl-type epoxy resins; epoxy resins obtained by glycidylating dihydric phenols such as dihydroxynaphthalene and 9,9-bis(4-hydroxyphenyl)fluorene; epoxy resins obtained by glycidylating trisphenols such as 1,1,1-tris(4-hydroxyphenyl)methane; epoxy resins obtained by glycidylating tetrakisphenols such as 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane; and novolac-type epoxy resins obtained by glycidylating novolacs such as phenol novolac, cresol novolac, bisphenol A novolac, and brominated bisphenol A novolac.

[0046] Among epoxy resins, polyfunctional epoxy resins are a particularly preferred example. The polyfunctional epoxy resin may be an epoxy resin having two or more oxirane rings (epoxy groups) in one molecule, and among these, an epoxy resin having three or more oxirane rings (epoxy groups) in one molecule is preferred, and an epoxy resin having four or more glycidyl groups in one molecule is even more preferred. The molecular weight of the polyfunctional epoxy resin is preferably 600 or less, particularly 100 or more or 590 or less, and more preferably 200 or more or 580 or less. Furthermore, from the viewpoint of achieving lower moisture absorption and higher crosslinking, it is preferable that the polyfunctional epoxy resin does not contain an amine-based or amide-based structure containing a nitrogen atom.

[0047] Furthermore, a high molecular weight epoxy compound (also referred to as an "epoxy polymer") having a mass average molecular weight of more than 5,000 may be contained. The inclusion of an epoxy polymer allows for the formation of a tougher crosslinked structure. On the other hand, the curing reaction rate of a resin composition containing a nitride ceramic and a thermosetting resin can be slowed, improving stability, for example, shelf life. Furthermore, even when the content of the nitride ceramic, preferably boron nitride agglomerated particles, is increased, good handleability (brittleness) can be maintained. The mass average molecular weight is a value calculated as polystyrene measured by gel permeation chromatography.

[0048] Examples of the epoxy polymer include phenoxy resins having at least one skeleton selected from the group consisting of a bisphenol A type skeleton, a bisphenol F type skeleton, a bisphenol A / F mixed type skeleton, a naphthalene skeleton, a fluorene skeleton, a biphenyl skeleton, an anthracene skeleton, a pyrene skeleton, a xanthene skeleton, an adamantane skeleton, and a dicyclopentadiene skeleton.

[0049] <Thickness> The thickness of the resin sheet of the present invention is not particularly limited. The thickness of the resin sheet of the present invention is preferably 80 μm or more, more preferably 100 μm or more, and even more preferably 110 μm or more, while the upper limit of the thickness is preferably 300 μm or less, more preferably 250 μm or less, even more preferably 220 μm or less, and even more preferably 200 μm or less. By making the thickness of the resin sheet of the present invention 80 μm or more, not only can high heat dissipation properties be ensured but also sufficient voltage resistance properties can be ensured. On the other hand, by making the thickness 300 μm or less, the resin sheet of the present invention and a composite molded body using the same can be made smaller or thinner, and the thinner film can have a reduced thermal resistance in the thickness direction compared to an insulating thermally conductive layer made of a ceramic material.

[0050] <Physical Properties of the Resin Sheet of the Present Invention> The physical properties that the resin sheet of the present invention can have will be described.

[0051] (Residual solvent amount) The resin sheet of the present invention (both before and after curing) can contain a solvent in the resin, which is the continuous phase that forms the resin sheet, and therefore the total mass content of the solvent and water in the resin sheet of the present invention (also referred to as the "residual solvent amount") can be 0.1 ppm or more and 50,000 ppm or less. If the total mass content of the solvent and water in the resin sheet of the present invention is 0.1 ppm or more, the effect of improving the toughness of the resin sheet of the present invention can be obtained, so the total mass content of the solvent and water in the resin sheet of the present invention is preferably 0.1 ppm or more, more preferably 0.2 ppm or more, even more preferably 0.5 ppm or more, and even more preferably 1 ppm or more. On the other hand, if the total mass content of the solvent and water in the resin sheet of the present invention is 50,000 ppm or less, in order to maintain the formability of the resin sheet of the present invention, the total mass content of the solvent and water in the resin sheet of the present invention is preferably 50,000 ppm or less, more preferably 40,000 ppm or less, even more preferably 20,000 ppm or less, and even more preferably 10,000 ppm or less.

[0052] The amount of residual solvent can be measured by holding the resin sheet of the present invention at 180° C. for 120 minutes in a nitrogen atmosphere, and measuring the amount of mass loss as the amount of residual solvent.

[0053] (thermal conductivity) The cured resin sheet of the present invention, i.e., the present cured resin sheet, preferably has a thermal conductivity in the thickness direction at 25°C of more than 15.3 W / m K, more preferably 15.5 W / m K or more, and particularly preferably 16 W / m K or more. When the thermal conductivity in the thickness direction is equal to or greater than the above lower limit, the resin sheet can be suitably used in power semiconductor devices that operate at high temperatures.

[0054] The thermal conductivity of the present cured resin sheet in the thickness direction can be measured by the following method. For example, the thermal conductivity can be determined from the slope of a graph obtained by plotting the thermal resistance value against the thickness using a thermal resistance measuring device.

[0055] (Breakdown voltage (BDV)) The cured resin sheet of the present invention, i.e., the present cured resin sheet, preferably has a breakdown voltage BDV of 4 kV or more, more preferably 5 kV or more, and even more preferably 6 kV or more, as measured when the resin sheet is subjected to a stepwise voltage increase of 0.5 kV / 1 min using a 25 mmφ cylindrical electrode, when the resin sheet has a thickness of 150 μm. If the thickness of the resin sheet for measuring the breakdown voltage BDV is not 150 μm, the breakdown voltage BDV can be converted into the BDV for a thickness of 150 μm and evaluated as follows: That is, if the thickness of the resin sheet for measuring the breakdown voltage BDV is T μm (T ≠ 150), the breakdown voltage BDV is preferably 4 × (T / 150) kV or more, more preferably 5 × (T / 150) kV or more, and even more preferably 6 × (T / 150) kV or more. For the method for measuring the BDV of the cured resin sheet, see the method described in the Examples below. In the case of the present cured resin sheet, two or more of the present colored particles are observed on the surface of the resin sheet below the 25 mmφ cylindrical electrode.

[0056] <<Method of manufacturing the cured resin sheet>> Next, an example of a method for producing the resin sheet of the present invention as a cured product, i.e., the present cured resin sheet, will be described.

[0057] The present cured resin sheet can be produced by preparing a resin composition (hereinafter referred to as "the present resin composition") containing the present nitride ceramics, the present colored particles, and a resin (preferably a thermosetting resin) (this process will be referred to as the "composition preparation process"), forming the present resin composition into a sheet (this process will be referred to as the "film formation process"), drying (this process will be referred to as the "drying process"), pressing to produce the present thermosetting resin sheet (this process will be referred to as the "pressing process"), optionally low-temperature aging (this process will be referred to as the "low-temperature aging process"), and then thermally curing (this process will be referred to as the "thermosetting process"). However, the present invention is not limited to this production method.

[0058] <Composition preparation process> A raw material containing the present nitride ceramic and the present coloring particles is prepared. The coloring particles are nitrides, and are by-products derived from nitride ceramics that are produced when processing is performed to remove impurities (e.g., carbon, oxygen) from nitride ceramics, and therefore can be produced together with the present nitride ceramics during the process of producing the present nitride ceramics.

[0059] Specifically, the raw material containing the present nitride ceramic and the present colored particles can be obtained by the following production method. It is preferable that the nitride ceramic is not colored, for example, white.

[0060] (Method of manufacturing BN agglomerated particles) There are no particular limitations on the method for producing the BN agglomerated particles of the present invention, but it is particularly preferred to pulverize the raw material boron nitride (also referred to as "raw BN powder" together with the pulverized form of boron nitride) in a pulverization step, then granulate by agglomeration in a granulation step, and then subject the resulting powder to a heating step for heat treatment. Furthermore, it is also preferred to re-fire the powder to further increase its purity. More specifically, it is preferred to first disperse the raw BN powder in a medium to form a raw BN powder slurry (also referred to as "BN slurry"), then subject the dispersion treatment, and then granulate the resulting slurry into spherical particles, followed by a heat treatment to crystallize the granulated BN agglomerated particles.

[0061] [Raw material BN powder] As the raw BN powder, any of commercially available h-BN, commercially available α- and β-BN, BN produced by the reduction-nitridation method of a boron compound and ammonia, BN synthesized from a boron compound and a nitrogen-containing compound such as melamine, etc. can be used without limitation. h-BN is particularly preferred because it more effectively exerts the effects of the present invention.

[0062] The preferred form of the raw BN powder is powdered BN particles with a wide peak half-width obtained by powder X-ray diffraction measurement and low crystallinity. While plate-shaped h-BN can be used as the raw material, non-plate-shaped nanoparticles are also suitable. As a measure of crystallinity, the peak half-width of the (002) plane obtained by powder X-ray diffraction measurement is typically 0.4° or more, preferably 0.45° or more, and more preferably 0.5° or more, in 2θ angle. Furthermore, it is typically 2.0° or less, preferably 1.5° or less, and even more preferably 1° or less. When the peak half-width of the (002) plane is below the upper limit, crystal growth is easily controlled, which tends to improve productivity. When the peak half-width of the (002) plane is above the lower limit, primary particle size can be easily controlled within an appropriate range, making it easier to control the compressive displacement, compressive strength, and elastic modulus of the BN agglomerated particles to the desired distribution. Furthermore, dispersion stability during slurry preparation tends to be improved.

[0063] From the viewpoint of BN crystal growth, it is preferable that a certain amount of oxygen atoms be present in the raw BN powder. In the present invention, the total oxygen concentration in the raw BN powder is preferably 1 mass% or more, more preferably 2 mass% or more, even more preferably 3 mass% or more, and particularly preferably 4 mass% or more, and is preferably 10 mass% or less, more preferably 9 mass% or less. By keeping the total oxygen concentration at or below the upper limit, excessive crystal growth is prevented, and the compressive displacement, compressive strength, and elastic modulus of the BN agglomerated particles can be controlled within appropriate ranges. By keeping the total oxygen concentration at or above the lower limit, residual oxygen after heat treatment is suppressed, resulting in a greater improvement in thermal conductivity.

[0064] Methods for adjusting the total oxygen concentration of the raw BN powder to fall within the above range include, for example, synthesizing BN at a low temperature of 1500°C or less, or heat-treating the raw BN powder in an oxidizing atmosphere at a low temperature of 500°C to 900°C. The total oxygen concentration of the raw BN powder can be measured by the inert gas fusion-infrared absorption method using an oxygen / nitrogen analyzer manufactured by Horiba, Ltd.

[0065] The total pore volume of the raw BN powder is preferably 1.5 cm 3 / g or less, and more preferably 0.3 cm 3 / g or more 1.5cm 3 / g or less, more preferably 0.5 cm 3 / g or more 1.5cm 3 / g or less. Total pore volume is 1.5 cm 3 When the particle size is 0.5 cm / g or less, the raw material BN powder is dense, and granulation with high sphericity is possible. 3 / g or more.

[0066] The specific surface area of ​​the raw material BN powder is preferably 50 m 2 / g or more, more preferably 60m 2 / g or more, more preferably 70m 2 / g or more. On the other hand, it is preferably 1000m 2 / g or less, more preferably 500m 2 / g or less, and more preferably 300m 2 / g or less. The specific surface area of ​​the raw material BN powder is 50m 2 / g or more, the dispersed particle diameter in the BN slurry used for spheroidization by granulation can be made small, which is preferable. 2 / g or less is preferable because it is possible to suppress an increase in the viscosity of the slurry. The total pore volume of the raw material BN powder can be measured by nitrogen adsorption method and mercury intrusion method, and the specific surface area can be measured by the BET one-point method (adsorption gas: nitrogen).

[0067] [Medium] The medium used to prepare the BN slurry is not particularly limited, and water and / or various organic solvents can be used. Among them, water is preferred, and pure water is more preferred, from the viewpoints of ease of spray drying and simplification of the equipment. The medium used to prepare the BN slurry is preferably added in an amount that gives the BN slurry a viscosity of 200 mPa·s or more and 5000 mPa·s or less.

[0068] Specifically, the amount of the medium used in preparing the BN slurry is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more, relative to the BN slurry, and is preferably 70% by mass or less, more preferably 65% ​​by mass or less, and even more preferably 60% by mass or less. When the amount of medium used is equal to or less than the upper limit, the slurry viscosity does not become too low, so that sedimentation and the like are suppressed, and the BN slurry tends to be uniform. Therefore, the tap density of the obtained BN agglomerated particles tends to be within the desired range. When the amount of medium used is equal to or more than the lower limit, the slurry viscosity does not become excessively high, and granulation tends to be easy.

[0069] [Surfactants] Various surfactants may be added to the BN slurry to adjust the viscosity of the slurry and to improve the dispersion stability (suppression of aggregation) of the raw BN powder in the slurry. As the surfactant, anionic surfactants, cationic surfactants, nonionic surfactants, etc. can be used, and these may be used alone or in combination of two or more.

[0070] [binder] The BN slurry may contain a binder to effectively granulate the raw BN powder into particles. The binder acts to firmly bind the BN primary particles together and stabilize the granulated particles. The binder used in the BN slurry may be any material that can enhance the adhesiveness between BN particles. In the present invention, since the granulated particles are heat-treated after granulation, it is preferable that the binder be heat-resistant to the high temperature conditions in this heat-treatment step.

[0071] As such a binder, metal oxides such as aluminum oxide, magnesium oxide, yttrium oxide, calcium oxide, silicon oxide, boron oxide, cerium oxide, zirconium oxide, titanium oxide, etc. are preferably used. Among these, aluminum oxide and yttrium oxide are preferred from the viewpoints of thermal conductivity and heat resistance as oxides, and the bonding strength for bonding BN particles together. The binder may be a liquid binder such as alumina sol, or may be one that reacts during heat treatment and is converted into other inorganic components. These binders may be used alone or in combination of two or more.

[0072] The amount of binder used (in the case of a liquid binder, the amount used as solid content) is preferably 0% by mass or more and 30% by mass or less, more preferably 0% by mass or more and 20% by mass or less, and even more preferably 0% by mass or more and 15% by mass or less, relative to the raw material BN powder in the BN slurry. When the amount of binder used is equal to or less than the above upper limit, crystal growth is obtained, and when used as a thermally conductive nitride ceramic, the effect of improving thermal conductivity tends to be obtained.

[0073] [BN slurry preparation method] The method for preparing the BN slurry is not particularly limited as long as the raw material BN powder, medium, and, if necessary, binder and surfactant are uniformly dispersed and the viscosity is adjusted to the desired range. When the raw material BN powder, medium, and, if necessary, binder and surfactant are used, the slurry is preferably prepared as follows.

[0074] A predetermined amount of raw BN powder is weighed into a resin bottle, and then a predetermined amount of binder is added. Furthermore, a predetermined amount of surfactant is added as needed, and then zirconia ceramic balls are added and the mixture is stirred on a pot mill rotating table for approximately 0.5 to 5 hours until the desired viscosity is achieved. The order of addition is not particularly limited, but when a large amount of raw BN powder is slurried, agglomerates such as lumps are likely to form. Therefore, an aqueous solution may be prepared by adding surfactant and binder to water, and then a predetermined amount of raw BN powder is added little by little. The zirconia ceramic balls are then added and the mixture is dispersed and slurried on a pot mill rotating table.

[0075] For dispersion, a dispersing device such as a bead mill or a planetary mixer may be used in addition to a pot mill. When forming the slurry, the temperature of the slurry is preferably 10° C. or higher and 60° C. or lower. When the slurry temperature is equal to or higher than the lower limit, an increase in the viscosity of the slurry tends to be suppressed, and when the slurry temperature is equal to or lower than the upper limit, the raw material BN powder can be suppressed from decomposing into ammonia in the slurry. The temperature of the slurry is more preferably 15°C or higher and 50°C or lower, even more preferably 15°C or higher and 40°C or lower, and particularly preferably 15°C or higher and 35°C or lower.

[0076] [Granulation] To obtain granulated particles from the BN slurry, a general granulation method such as spray drying, tumbling, fluidized bed, or stirring can be used, with the spray drying method being preferred. In the spray drying method, it is possible to produce granulated particles of a desired size and also to obtain spherical granulated particles by adjusting the concentration of the raw material slurry, the amount of liquid fed into the device per unit time, and the compressed air pressure and amount of compressed air used when spraying the fed slurry. There are no restrictions on the spray drying device used, but in order to obtain larger spherical granulated particles, a rotary disk type device is optimal. Examples of such devices include the spray dryer F series manufactured by Okawara Kakoki Co., Ltd., the spray dryer "MDL-050M" manufactured by Fujisaki Electric Co., Ltd., and the spray dryer "P260" manufactured by Pliss Co., Ltd.

[0077] When the volume-based average particle size (D50) of the BN agglomerated particles of the present invention is set to, for example, 10 μm or more and 150 μm or less, the volume-based average particle size (D50) of the granulated particles obtained by granulation is preferably set to 10 μm or more and 150 μm or less. Here, the volume-based average particle size D50 of the granulated particles can be measured using a "Morphorogi" manufactured by Malvern or the like.

[0078] [Heat treatment] The above BN agglomerated particles can be further heat-treated in a non-oxidizing gas atmosphere to produce BN agglomerated particles. Here, the non-oxidizing gas atmosphere refers to an atmosphere of nitrogen gas, helium gas, argon gas, ammonia gas, hydrogen gas, methane gas, propane gas, carbon monoxide gas, etc. The crystallization speed of the BN agglomerated particles varies depending on the type of atmospheric gas used. In order to perform crystallization in a short time, nitrogen gas or a mixed gas containing nitrogen gas and other gases is particularly suitable.

[0079] The heat treatment temperature is preferably 1400°C or higher and 2300°C or lower, more preferably 1500°C or higher or 2000°C or lower, and even more preferably 1600°C or higher or 2000°C or lower. When the heat treatment temperature is equal to or higher than the lower limit, the growth of the BN primary particles is sufficient, and the thermal conductivity of the BN agglomerated particles tends to be increased. When the heat treatment temperature is equal to or lower than the upper limit, the decomposition of the BN agglomerated particles tends to be suppressed.

[0080] The heat treatment time is preferably from 5 hours to 20 hours, more preferably from 5 hours to 15 hours. A heat treatment time of at least the lower limit mentioned above tends to ensure sufficient growth of BN primary particles, while a heat treatment time of at most the upper limit mentioned above tends to suppress decomposition of BN, thereby allowing the compressive deformation, compressive strength, and elastic modulus of the BN agglomerated particles to be controlled within the desired ranges.

[0081] Since the heat treatment is carried out in a non-oxidizing gas atmosphere, the inside of the firing furnace is preferably evacuated with a vacuum pump, and then heated to a desired temperature while introducing a non-oxidizing gas. If the inside of the firing furnace can be sufficiently replaced with a non-oxidizing gas, the temperature may be raised by heating while introducing a non-oxidizing gas under normal pressure. Examples of the calcination furnace include batch furnaces such as muffle furnaces, tubular furnaces, and atmosphere furnaces, and continuous furnaces such as rotary kilns, screw conveyor furnaces, tunnel furnaces, belt furnaces, pusher furnaces, and vertical continuous furnaces, and these can be used depending on the purpose.

[0082] Typically, the BN agglomerate particles to be heat-treated are placed in a graphite crucible with a lid and heated and fired in order to reduce non-uniformity in composition during firing. At this time, a graphite partition may be inserted to suppress sintering of the BN agglomerate particles during firing in addition to reducing non-uniformity in composition. The number of divisions by the partitions is not particularly limited as long as it can suppress sintering, but is usually 2 to 16 divisions. By setting the number of divisions to the upper limit or less and the lower limit or more, sintering can be suppressed and the growth of the h-BN primary particles can be controlled, thereby controlling the compressive deformation, compressive strength, and elastic modulus of the BN agglomerated particles within desired ranges.

[0083] [Re-firing] The BN agglomerated particles obtained as described above are preferably subjected to a single heat treatment, and the resulting powder is then filled into a boron nitride crucible and re-fired in order to enhance purity and crystallinity. Re-firing removes impurities and enhances purity, while also generating colored particles. In this case, it is preferable to adjust the firing conditions for the re-firing so that the "crucible mass reduction rate" described below falls within a predetermined range.

[0084] The re-firing is preferably carried out in a non-oxidizing gas atmosphere. The non-oxidizing gas atmosphere refers to an atmosphere of nitrogen gas, helium gas, argon gas, ammonia gas, hydrogen gas, methane gas, propane gas, carbon monoxide gas, or the like. The heat treatment temperature for re-firing is preferably 1400°C or higher and 2300°C or lower, more preferably 1500°C or higher or 2000°C or lower, and even more preferably 1600°C or higher or 2000°C or lower. If the heat treatment temperature is 1400°C or higher, impurities can be sufficiently removed and thermal conductivity can be maintained. On the other hand, if the heat treatment temperature is 2300°C or lower, decomposition of BN can be suppressed.

[0085] The heat treatment time is usually 1 hour or longer, preferably 2 hours or longer, more preferably 3 hours or longer, and usually 72 hours or shorter, preferably 48 hours or shorter. If the heat treatment time is 1 hour or more, impurities can be sufficiently removed, while if it is 72 hours or less, partial decomposition of BN can be suppressed.

[0086] Examples of the calcination furnace include batch furnaces such as muffle furnaces, tubular furnaces, and atmosphere furnaces, and continuous furnaces such as rotary kilns, screw conveyor furnaces, tunnel furnaces, belt furnaces, pusher furnaces, and vertical continuous furnaces, and these can be used depending on the purpose.

[0087] The BN agglomerated particles obtained by re-firing may contain metal elements derived from the binder. The amount of metal elements contained is preferably 10% by mass or less, more preferably 6% by mass or less, even more preferably 3% by mass or less, and even more preferably 2% by mass or less. By keeping the amount below the upper limit, the insulating properties resulting from the metal elements can be suppressed.

[0088] [Classification] The BN agglomerated particles after the heat treatment are preferably classified to narrow the particle size distribution and suppress an increase in viscosity when blended into a resin composition containing the BN agglomerated particles. This classification is usually performed after the heat treatment, but it may also be performed on the granulated particles before the heat treatment and then subjected to the heat treatment.

[0089] The classification may be either wet or dry. From the viewpoint of suppressing decomposition of the BN agglomerated particles, dry classification is preferred. In particular, when the binder is water-soluble, dry classification is preferably used. Dry classification includes classification using a sieve as well as air classification, which classifies particles by the difference between centrifugal force and fluid drag, and can also be performed using classifiers such as a swirling air classifier, a forced vortex centrifugal classifier, a semi-free vortex centrifugal classifier, etc. Among these, a swirling air classifier is used to classify small particles in the submicron to single micron range, and a semi-free vortex centrifugal classifier is used to classify relatively larger particles, etc., depending on the particle size of the particles to be classified.

[0090] However, the manufacturing method is not limited to the above.

[0091] [Crucible mass reduction rate] The BN agglomerated particles obtained as described above can have impurities volatilized by re-firing, so the "crucible mass reduction rate" described below, in other words, the volatilization rate of impurities, can be set within a predetermined range. Here, the "crucible mass reduction rate" can be calculated by the following formula. Crucible mass reduction rate = ((volatilization amount during re-firing) ÷ (filled amount before re-firing)) × 100 As will be described in detail in the Examples below, the amount of volatilization during re-firing was calculated by measuring the mass of a crucible filled with BN agglomerated particles before and after re-firing, and the amount of mass loss after re-firing was defined as the "amount of volatilization during re-firing."

[0092] The rate of mass reduction of the crucible can be controlled by adjusting the reducing atmosphere, temperature, time, and amount of material filled into the crucible.

[0093] The results of the study showed that this "crucible mass reduction rate" is strongly correlated with the generation of colored particles and the improvement of thermal conductivity. In other words, if the crucible mass reduction rate is small, the purity of the BN agglomerated particles cannot be sufficiently improved, and thermal conductivity tends to remain unchanged. On the other hand, if the crucible mass reduction rate is large, excessive reduction occurs, causing a decrease in wettability due to changes in the surface energy of the BN agglomerated particle surface, and sheet formability tends to decrease. From this viewpoint, it was found that the crucible mass reduction rate is preferably 0.7% or more and 3% or less.

[0094] (Preparation of the Resin Composition) The resin composition can be prepared by mixing raw materials containing the present nitride ceramic and colored particles, a resin, preferably a thermosetting resin, a solvent, and, if necessary, the other inorganic fillers, other polymers, curing agents, curing catalysts, and other components.

[0095] Examples of the organic solvent include methyl ethyl ketone, cyclohexanone, propylene glycol monomethyl ether acetate, butyl acetate, isobutyl acetate, propylene glycol monomethyl ether, etc. These organic solvents may be used alone or in combination of two or more.

[0096] Examples of the "other components" include dispersants, silane coupling agents, insulating carbon components such as reducing agents, viscosity modifiers, thixotropy-imparting agents, flame retardants, various antioxidants such as phosphorus-based and phenol-based, phenol acrylate-based and other process stabilizers, heat stabilizers, hindered amine radical scavengers (HAAS), impact modifiers, processing aids, metal deactivators, copper inhibitors, antistatic agents, extenders, etc. When these additives are used, the amount added may be within the range normally used for the purpose.

[0097] <Film forming process> For example, the present resin composition in a slurry state can be formed into a sheet by a coating method such as a blade method, a solvent casting method, or an extrusion film forming method.

[0098] When forming a sheet-like film by the above coating method, a coating film is formed by first coating the surface of a substrate with the present resin composition in a slurry form, i.e., by dipping, spin coating, spray coating, blade coating, or any other method using the present resin composition in a slurry form. The present resin composition in a slurry form can be applied using a coating device such as a spin coater, a slit coater, a die coater, a blade coater, etc. Such a coating device makes it possible to form a uniform coating film of a predetermined thickness on a substrate. The substrate is generally a copper plate or copper foil or a PET film, as described below, but is not limited thereto.

[0099] <Drying process> In the drying step, in order to remove the solvent and low molecular weight components, it is preferable to dry at a temperature of usually 10°C or higher and 150°C or lower, particularly 25°C or higher or 140°C or lower, particularly 30°C or higher or 130°C or lower. When the drying temperature is equal to or lower than the upper limit, curing of the resin in the resin composition is suppressed, and the resin in the sheet-shaped composition tends to flow in the subsequent pressurizing step, making it easier to remove voids.When the drying temperature is equal to or higher than the lower limit, the solvent can be effectively removed, and productivity tends to improve.

[0100] The drying time is not particularly limited, and is preferably adjusted appropriately depending on the state of the resin composition, the drying environment, etc. The drying time is preferably 1 minute or more, more preferably 2 minutes or more, and even more preferably 5 minutes or more. The drying time is preferably 24 hours or less, more preferably 10 hours or less, even more preferably 4 hours or less, and particularly preferably 2 hours or less. When the drying time is equal to or greater than the lower limit, the solvent can be sufficiently removed, and the residual solvent tends to be prevented from forming voids in the cured resin. When the drying time is equal to or less than the upper limit, productivity tends to be improved, and production costs tend to be reduced.

[0101] <Pressure process> After the drying step, the resin composition formed into a sheet is preferably pressed in a temperature range where the thermosetting resin does not harden to form the thermosetting resin sheet, for the purposes of bonding the nitride ceramics together to form a heat conduction path and eliminating voids and gaps within the sheet. However, depending on the purpose, pressing may not be necessary.

[0102] In the pressurizing step, it is desirable to apply a load of 2 MPa or more to the sheet-like present resin composition on the substrate. The load is preferably 5 MPa or more, more preferably 7 MPa or more, and even more preferably 9 MPa or more. The load is preferably 1500 MPa or less, more preferably 1000 MPa or less, and even more preferably 800 MPa or less. By setting the load during pressing to the upper limit or less, the nitride ceramic is not broken, and voids in the thermosetting resin sheet are reduced, resulting in a sheet with high thermal conductivity. By setting the load to the lower limit or more, contact between the nitride ceramic particles is improved, making it easier to form thermal conduction paths, ultimately resulting in a cured resin sheet with high thermal conductivity.

[0103] The temperature in the processing step is preferably 10° C. or higher, more preferably 20° C. or higher, and even more preferably 30° C. or higher. The heating temperature is preferably 300° C. or lower, more preferably 250° C. or lower, even more preferably 200° C. or lower, still more preferably 100° C. or lower, and particularly preferably 90° C. or lower. By carrying out the pressurization step within this temperature range, the melt viscosity of the resin in the thermosetting resin sheet can be reduced, and voids and gaps in the thermosetting resin sheet can be further reduced. Furthermore, by heating at or below the upper limit, decomposition of organic components in the thermosetting resin sheet and voids caused by residual solvent tend to be suppressed.

[0104] The time for the pressurizing step is not particularly limited. The time for the pressurizing step is preferably 30 seconds or more, more preferably 1 minute or more, even more preferably 3 minutes or more, and particularly preferably 5 minutes or more. The time for the pressurizing step is preferably 1 hour or less, more preferably 30 minutes or less, and even more preferably 20 minutes or less. When the pressing time is equal to or less than the upper limit, the manufacturing time of the thermosetting resin sheet can be reduced, and production costs tend to be reduced.When the pressing time is equal to or more than the lower limit, voids and gaps in the thermosetting resin sheet can be sufficiently removed, and heat transfer performance and voltage resistance characteristics tend to be improved.

[0105] Examples of the pressurizing method include a vacuum press, a calendar press, a belt press, a hydrostatic press, a heat press, and a servo press, but the press is not limited to these methods. For example, in the calender press method, the linear pressure on the sheet is preferably 20 kgf / cm or more and 200 kgf / cm or less, more preferably 25 kgf / cm or more and 150 kgf / cm or less, and even more preferably 30 kgf / cm or more and 125 kgf / cm or less. The temperature of the roller is preferably 0°C or higher and 50°C or lower, more preferably 5°C or higher or 45°C or lower, and even more preferably 10°C or higher or 40°C or lower. A normal calendar roll machine with one (2) or more pairs of rollers through which the sheet passes can be used. Note that one (2) means one pair and two rollers. The pressing time is 10 seconds or less due to the characteristics of the calendar press method.

[0106] For example, in the case of plate pressing, the pressure on the sheet (also called "hot press load") is preferably 1 MPa or more and 200 MPa or less, more preferably 5 MPa or more or 100 MPa or less, and even more preferably 7.5 MPa or more or 50 MPa or less. The temperature of the metal plate (also referred to as "hot pressing temperature") is preferably 0°C or higher and 100°C or lower, more preferably 5°C or higher or 80°C or lower, and even more preferably 15°C or higher or 50°C or lower. The pressing time (also referred to as "hot press pressing time") is preferably 1 second or more and 1500 seconds or less, more preferably 2 seconds or more or 1000 seconds or less, and even more preferably 3 seconds or more or 500 seconds or less.

[0107] <Low temperature aging process> The thermosetting resin sheet is preferably subjected to low-temperature aging as needed. For low-temperature aging, for example, the thermosetting resin sheet may be placed in an environment of preferably -50°C or higher and 0°C or lower, more preferably -30°C or higher or -5°C or lower, for preferably 5 minutes or longer and 365 days or shorter, more preferably 1 hour or longer or 7 days or shorter. The pressure during aging is preferably 0 kPa, but a minute pressure of 0.1 kPa or less may also be applied. The timing for aging can be after coating, after heat drying, after pressure application, etc. Among these, after pressure application is preferred.

[0108] By subjecting the thermosetting resin sheet to such low-temperature aging, the resin relaxation during the aging process can be expected to reduce voids at the resin / nitride ceramic interface without promoting the crosslinking reaction of the resin, thereby improving the insulation properties of the thermosetting resin sheet and its cured product, the cured resin sheet. Furthermore, the reduction in voids can also be expected to improve the adhesive strength at the resin / nitride ceramic interface, thereby improving the toughness of the thermosetting resin sheet and its cured product, the cured resin sheet.

[0109] <Curing process> The present thermosetting resin sheet obtained as described above can be heated and cured to produce the present cured resin sheet. In this case, the heating temperature is preferably 30° C. or higher and 400° C. or lower, more preferably 50° C. or higher, and even more preferably 90° C. or higher. On the other hand, it is preferably 300° C. or lower, and even more preferably 250° C. or lower.

[0110] The curing step for finally curing the thermosetting resin sheet may be performed under pressure or without pressure. When pressure is applied, it is desirable to perform the same conditions as the above-mentioned pressurizing step for the same reasons. The pressurizing step and the curing step may be performed simultaneously. In particular, in the sheet forming process which involves a pressing step and a curing step, it is preferable to apply a load within the above range to carry out pressing and curing.

[0111] The load applied when the pressing step and the curing step are performed simultaneously is not particularly limited. In this case, the thermosetting resin sheet is preferably subjected to a load of 5 MPa or more, more preferably 7 MPa or more, even more preferably 9 MPa or more, and particularly preferably 20 MPa or more. The load is preferably 2000 MPa or less, more preferably 1500 MPa or less. By setting the load when the pressing step and the curing step are performed simultaneously to the above upper limit or less, the nitride ceramics are not broken, voids in the sheet can be reduced, and a cured resin sheet with higher thermal conductivity can be obtained. On the other hand, by setting the load to the above lower limit or more, contact between the nitride ceramics is improved, making it easier to form heat conduction paths, and a cured resin sheet with higher thermal conductivity can be obtained.

[0112] When the pressing step and the curing step are performed simultaneously, the pressing time is not particularly limited. The pressing time is preferably 30 seconds or more, more preferably 1 minute or more, even more preferably 3 minutes or more, and particularly preferably 5 minutes or more. The pressing time is preferably 4 hours or less, more preferably 3 hours or less, and even more preferably 2.5 hours or less. By keeping the pressurizing time at or below the upper limit, the production time for the cured resin sheet can be reduced, and production costs tend to be reduced. By keeping the pressurizing time at or above the lower limit, voids and gaps in the cured resin sheet can be sufficiently removed, and heat transfer performance and voltage resistance tend to be improved.

[0113] <<Uses of the resin sheet of the present invention>> The resin sheet of the present invention (including the present thermosetting resin sheet and the present cured resin sheet) can be used in various applications requiring thermal conductivity. For example, a heat dissipating laminate, a heat dissipating circuit board, and a semiconductor device will be described as examples of a composite molded product having the present cured resin sheet and a metal part, although the uses of the resin sheet of the present invention are not limited to these.

[0114] (heat dissipation laminate) The heat dissipation laminate according to one embodiment of the present invention (also referred to as the "present heat dissipation laminate") may be any laminate including the present cured resin sheet. An example of the present heat-dissipating laminate is one in which a heat-dissipating metal layer containing a heat-dissipating material is laminated on at least one surface of the present cured resin sheet. The heat dissipating material is not particularly limited as long as it is made of a material with good thermal conductivity. In particular, in order to increase the thermal conductivity in the laminated structure, it is preferable to use a heat dissipating metal material, and it is more preferable to use a flat metal material. The metal material is not particularly limited, but among them, copper plate, aluminum plate, aluminum alloy plate, etc. are preferred because they have good thermal conductivity and are relatively inexpensive.

[0115] The cured resin sheet and the heat dissipation metal layer can be laminated and integrated by press molding, which is a batch process. In this case, the press equipment and press conditions are the same as those for obtaining the thermally conductive resin sheet.

[0116] (heat dissipation circuit board) A heat dissipation circuit board according to one embodiment of the present invention (also referred to as the "present heat dissipation circuit board") may be any circuit board provided with the present cured resin sheet. An example of the present heat dissipating circuit board is one having a configuration in which the above-mentioned heat dissipating metal layer is laminated on one surface of the present cured resin sheet, and a circuit board is formed on the surface of the thermally conductive resin sheet opposite the heat dissipating metal layer, for example, by etching or the like. Specifically, an integrated structure of "heat dissipating metal layer / present cured resin sheet / conductive circuit" is more preferable. The state before circuit etching includes, for example, an integrated structure of "heat dissipating metal layer / present cured resin sheet / conductive circuit-forming metal layer" in which the conductive circuit-forming metal layer is flat and formed on the entire surface of one side of the present cured resin sheet, or formed on a partial area.

[0117] The material of the conductive circuit-forming metal layer is not particularly limited, but it is generally preferable to form it from a copper thin plate having a thickness of 0.05 mm to 1.2 mm in terms of electrical conductivity, etching properties, cost, etc.

[0118] (Semiconductor Devices) A semiconductor device according to an example of an embodiment of the present invention (also referred to as "the present semiconductor device") may be any device that includes the present heat dissipation circuit board. An example of the present semiconductor device is one having a configuration in which a silicon wafer or a rewiring layer on which pre-diced semiconductor chips are mounted is formed on the present heat dissipation circuit substrate.

[0119] (power module) A power module according to an embodiment of the present invention (also referred to as "the present power module") may be any module provided with the present cured resin sheet. An example of the present power module is one in which the present cured resin sheet is mounted as a heat dissipating circuit board on a power semiconductor device. In this power semiconductor device, conventionally known materials can be used as appropriate for the aluminum wiring, sealing material, packaging material, heat sink, thermal paste, solder, and other materials other than the cured resin sheet.

[0120] <<Explanation of terms, etc.>> In the present invention, the term "film" includes the term "sheet", and the term "sheet" includes the term "film".

[0121] Furthermore, when it is stated that "α or more" or "α≦" (α is any number), it also means "preferably greater than α" unless otherwise specified, and when it is stated that "β or less" or "≦β" (β is any number), it also means "preferably smaller than β" unless otherwise specified. [Example]

[0122] An example of an embodiment of the present invention will be described below, but the present invention is not limited to the embodiment described below.

[0123] <Raw materials> Nitride ceramic powder A (boron nitride agglomerated particles containing colored particles) Boron nitride agglomerated particles (agglomerated particles formed by agglomeration of plate-like primary particles, spherical boron nitride agglomerated particles with a house-of-card structure (average particle size (D50) 45 μm, maximum particle size (Dmax) 90 μm), filled into a boron nitride crucible and re-fired, crucible mass reduction rate 1.1% by mass, white excluding colored particles) Nitride ceramic powder B (boron nitride agglomerated particles containing colored particles) Boron nitride agglomerated particles (agglomerated particles formed by agglomeration of plate-like primary particles, spherical boron nitride agglomerated particles with a house-of-card structure (average particle size (D50) 45 μm, maximum particle size (Dmax) 90 μm), filled into a boron nitride crucible and re-fired, crucible mass reduction rate 1.9 mass%, white excluding colored particles) Nitride ceramic powder C (boron nitride agglomerated particles containing colored particles) Boron nitride agglomerated particles (agglomerated particles formed by agglomeration of plate-like primary particles, spherical boron nitride agglomerated particles with a house-of-card structure (average particle size (D50) 45 μm, maximum particle size (Dmax) 90 μm), filled into a boron nitride crucible and re-fired, crucible mass reduction rate 1.3 mass%, white excluding colored particles)

[0124] ●Nitride ceramic powder D (boron nitride agglomerated particles) Boron nitride agglomerated particles (agglomerated particles formed by agglomeration of plate-like primary particles, spherical boron nitride agglomerated particles with a house-of-card structure (average particle size (D50) 45 μm, maximum particle size (Dmax) 90 μm), filled into a boron nitride crucible and re-fired, crucible mass reduction rate 0.3 mass%, white except for colored particles)

[0125] Spherical alumina particles 1 Average particle size (D50) 6.5 μm, Thermal conductivity: 20 W / m·K or more and 30 W / m·K or less

[0126] The average particle size (D50) and maximum particle size (Dmax) of boron nitride agglomerated particles were determined by dispersing boron nitride agglomerated particles in a pure water medium containing naphthalenesulfonate-formalin condensate as a dispersion stabilizer, measuring the volumetric particle size distribution using a laser diffraction / scattering particle size distribution analyzer LA-300 (manufactured by Horiba, Ltd.), and calculating the particle size distribution at 50% cumulative volume (average particle size D50) and the maximum particle size Dmax.

[0127] The mass loss rate of the crucible was calculated from the change in mass before and after re-firing. 2 The boron nitride agglomerated particles after the first firing were filled into a 6.5 cm high boron nitride crucible, and the filling amount (filling amount before re-firing) was measured. The boron nitride crucible was placed in a non-oxidizing gas atmosphere firing furnace and heated to 2000°C at a heating rate of 1200°C / hr in a N2 flow. It was then heat-treated at 2000°C for 2 hours. After natural cooling, the mass of the heat-treated crucible was measured to calculate the mass loss after re-firing, i.e., the amount of volatilization during re-firing, and the crucible mass loss rate was calculated using the following formula. Crucible mass reduction rate (%) = (volatilization amount during re-firing (g) ÷ amount filled before re-firing (g)) × 100

[0128] Epoxy resin 1: High molecular weight epoxy resin (mass average molecular weight in polystyrene equivalent: 30,000, epoxy equivalent: 9,000 g / equivalent, density: approximately 1.2 g / cm 3 ) Epoxy resin 2: Multifunctional epoxy resin: A multifunctional epoxy resin containing a structure with four or more glycidyl groups per molecule (molecular weight of 500 or less, density of approximately 1.2 g / cm 3 ) Epoxy resin 3: Biphenyl-type solid epoxy resin (molecular weight approximately 400, density approximately 1.2 g / cm 3 )

[0129] Hardener: Phenolic resin hardener Curing catalyst 1: 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(17')]-ethyl-s-triazine, molecular weight: 247, properties: solid, melting point: 215-225°C Curing catalyst 2: 2-phenyl-4,5-dihydroxymethylimidazole, molecular weight: 204, properties: solid, melting point: dec. 230, so the melting point is 230°C or higher

[0130] Example 1 A slurry-like resin composition was prepared by adding 54.1 parts by mass of nitride ceramic powder A, 20.4 parts by mass of spherical alumina particles 1, 6.2 parts by mass of epoxy resin 1, 5.1 parts by mass of epoxy resin 2, 10.2 parts by mass of epoxy resin 3, 3.5 parts by mass of a phenolic resin-based curing agent, 0.25 parts by mass of curing catalyst 1, and 0.25 parts by mass of curing catalyst 2 to methyl ethyl ketone and cyclohexanone and mixing them using a planetary centrifugal stirrer to give a solids concentration of 63% by mass.

[0131] The slurry-like resin composition prepared as described above was applied onto a polyethylene terephthalate (PET) film using an applicator with a gap of 400 μm, and then dried on a hot plate at 60°C for 60 minutes to produce a thermosetting resin sheet (sample) with a thickness of 240 μm. The thermosetting resin sheet (sample) was placed in a vacuum-packed bag, the air inside the bag was removed, and the opening of the bag was heat-sealed. The bag was then stored in a freezer at -20°C for 48 hours to perform low-temperature aging.

[0132] After low-temperature aging, the thermosetting resin sheet was removed from the vacuum pack bag and heated at 175°C for 30 minutes, and then at 200°C for 30 minutes to obtain a cured resin sheet (sample) with a thickness of 240 µm. This cured resin sheet was placed in a pressure press and heat-pressed at 41.5°C under a load of 150 MPa for 15 minutes. The thickness was 155 μm. Furthermore, this cured resin sheet was cut into a piece of 100 mm × 300 mm, and the mass was measured. The mass of the polyethylene terephthalate film was subtracted to determine the basis weight, which was found to be 0.282 kg / m 2 This is what happened.

[0133] <Examples 2 and 3, Comparative Example 1> As shown in Table 1, a thermosetting resin sheet (sample) and a cured resin sheet (sample) were produced in the same manner as in Example 1, except that nitride ceramic powder B to D were used instead of nitride ceramic powder A.

[0134] <Evaluation> The physical properties and characteristics of the thermosetting resin sheets (samples) and cured resin sheets (samples) obtained in Examples 1 to 3 and Comparative Example 1 were evaluated as follows.

[0135] (Moldability) The thermosetting resin sheets (samples) obtained in the examples and comparative examples were visually inspected to see if there were any holes or if there were any irregularities on the surface. If there were no such problems, the sample was evaluated as "Good (pass)", and if there were any such problems, the sample was evaluated as "Poor (fail)".

[0136] (Measurement of the amount of colored particles) The surfaces of the cured resin sheets (samples) obtained in the Examples and Comparative Examples were observed using a stereo microscope SMZ 745T. At 10x magnification, an LED light was shone from the eyepiece side, and reflection images (1280 x 960 pixels) were acquired from 10 random fields of view within the sheet surface (11.8 mm x 15.76 mm per field). The resulting reflection image was analyzed using the following procedure to obtain a 10cm 2 The number of colored particles per field was counted, and the average values ​​for 10 fields are shown in Table 1.

[0137] The reflected image was analyzed based on the following method. 1) The obtained reflection image was converted into a grayscale (standard: ITU-R Rec BT.601) and adjusted so that the center value was 130 to 140. 2) Grayscale: Points below 100 were extracted by binarization. 3) The points obtained by binarization were subjected to labeling processing (4-way connection), and parts with a circle-equivalent diameter of 16 μm or more were calculated as colored particles.

[0138] (Measurement of colored area ratio) For the cured resin sheets (samples) obtained in the Examples and Comparative Examples, reflection images were taken from any 10 fields of view in the same manner as above, converted to grayscale (standard: ITU-R Rec BT.601), and adjusted so that the center value was 130 to 140. Points with a grayscale value of 100 or less were extracted by binarization, and the total area of ​​those with a grayscale value of 100 or less was measured and calculated as a percentage of the total area of ​​the sheet. The average values ​​for the 10 fields of view are shown in Table 1.

[0139] (Measurement of dielectric breakdown voltage (BDV)) The thermosetting resin sheets (samples) prepared in the Examples and Comparative Examples were placed on a 2 mm thick copper plate with the surface of the thermosetting resin sheet in contact with the plate. The top and bottom plates were placed in a press preheated to 175°C and subjected to a heat press at 175°C and a load of 10 MPa for 40 minutes to produce 150 μm thick cured resin sheets (samples). The samples were then immersed in insulating oil (Fluorinert FC-40, manufactured by 3M Corporation) and tested using an ultra-high voltage tester 7470 (manufactured by Keisoku Gijutsu Kenkyusho Co., Ltd.) with a cylindrical electrode placed on the patterned 25 mm diameter copper plate. A voltage of 0.5 kV was applied, increasing by 0.5 kV every minute, and the breakdown voltage (BDV) was measured. In addition, for the thermally conductive resin sheet samples produced from at least the thermally conductive resin sheets (samples) of Examples 1 to 3, at least two or more colored particles were observed on the surface of the resin sheet below the 25 mmφ cylindrical electrode.

[0140] (Measurement of thermal conductivity (λ)) In addition to one cured resin sheet (sample) prepared in each of the examples and comparative examples, five types of sheets with different thicknesses were prepared by stacking two to five of these cured resin sheets (samples). Measurements were carried out under the conditions (1) to (4) below, and the thermal conductivity at 25°C in the sheet thickness direction in a steady state method was measured from the slope represented by the thermal resistance value relative to the sheet thickness (in accordance with ASTM D5470). The probe size during measurement was φ12.8 mm, the fixing pressure was 3400 kPa, and the measurement time was 300 seconds. To improve the adhesion between the sample and the probe, Shin-Etsu Chemical Co., Ltd.'s "OIL COMPOUND (himei: G-747)" was used.

[0141] (1) Thickness: Thickness (μm) when pressed at a pressure of 3400 kPa using a Mentor Graphics T3Ster-DynTIM. (2) Measurement area: The area (cm) of the heat transfer part when measuring using a Mentor Graphics T3Ster-DynTIM. 2 ) (3) Thermal resistance: Thermal resistance (K / W) when pressed at a pressure of 3400 kPa using a Mentor Graphics T3Ster-DynTIM. (4) Thermal conductivity: The thermal resistance of five types of cured resin sheets with different thicknesses was measured, and the thermal conductivity (W / m·K) was calculated using the following formula. Formula: Thermal conductivity (W / m K) = 1 / ((Slope (thermal resistance value / thickness): K / (W μm)) × (area: cm 2 ))×10 -2

[0142] [Table 1]

[0143] (Consideration) From the above examples and comparative examples, as well as the results of tests conducted by the inventors, it has been found that the thermal conductivity of resin sheets containing nitride ceramics increases when colored particles are included. The content of the colored particles is determined by the ratio of the colored particles to the surface of the sheet when observed at a depth of 10cm. 2 It was found that by including colored particles in the sheet to the extent that 30 or more colored particles were observed per unit area, it was possible to increase the thermal conductivity while maintaining moldability. These colored particles have been confirmed to be by-products derived from nitride ceramics that are produced when processing is carried out to remove impurities (e.g., carbon, oxygen) from the nitride ceramics. They are defects in the crystal lattice of the nitride ceramics, and because they contain metallic bonds, they are thought to contribute to thermal conductivity.

Claims

1. A resin sheet containing nitride ceramics, and when observing the surface of the sheet, ２ A resin sheet in which 30 or more colored particles are observed per sheet.

2. A thermosetting resin sheet made of a resin composition containing nitride ceramics and a thermosetting resin, wherein when the surface of the sheet is observed, the sheet has a thickness of 10 cm ２ A resin sheet in which 30 or more colored particles are observed per sheet.

3. A resin sheet made of a cured resin composition containing nitride ceramics and a thermosetting resin, wherein when the surface of the sheet is observed, the resin sheet has a thickness of 10 cm ２ A resin sheet in which 30 or more colored particles are observed per sheet.

4. 4. The resin sheet according to claim 1, wherein the coloring particles are nitride particles.

5. The resin sheet according to any one of claims 1 to 3, wherein the total mass content of the solvent and water in the resin sheet is 0.1 ppm or more and 50,000 ppm or less.

6. The resin sheet according to any one of claims 1 to 3, wherein the content of the thermosetting resin in the resin sheet is 60 mass% or less.

7. The resin sheet according to any one of claims 1 to 3, wherein the nitride ceramic contains one or more of boron nitride, aluminum nitride, silicon nitride, and titanium nitride.

8. The nitride ceramic has a cumulative volume 50% particle diameter (D50) in a volume-based particle size distribution obtained by measuring by a laser diffraction scattering particle size distribution measurement method, D50 ≧ 10 μm. The resin sheet according to any one of claims 1 to 3.

9. The resin sheet according to any one of claims 1 to 3, wherein the nitride ceramic contains boron nitride agglomerated particles.

10. 4. The resin sheet according to claim 3, wherein the measured breakdown voltage BDV is 4 kV or more when the resin sheet has a thickness of 150 μm, when the resin sheet is subjected to a step voltage increase of 0.5 kV / 1 min using a 25 mmφ cylindrical electrode.

11. 4. The resin sheet according to claim 3, wherein when a resin sheet having two or more colored particles observed on its surface is subjected to a stepwise voltage increase of 0.5 kV / 1 min under a 25 mmφ cylindrical electrode, the measured breakdown voltage BDV is 4 kV or more when the resin sheet has a thickness of 150 μm.

12. 4. The resin sheet according to claim 1, wherein, when the surface of the sheet is observed, the proportion of the total area colored by the colored particles to the surface of the sheet (100%) is 20% or less.

13. The resin sheet according to claim 2 or 3, wherein the thermosetting resin comprises one or more of an epoxy resin, a cyanate resin, a benzoxazine resin, a phenolic resin, and a maleimide resin.

14. A composite molded product comprising the resin sheet according to any one of claims 1 to 3 and a metal part.

15. A semiconductor device comprising the composite compact of claim 14.

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