Boron nitride sintered sheet

Abstract

To further improve thermal conductivity of a boron nitride sintered sheet.SOLUTION: A sintered sheet disclosed herein comprises boron nitride particles. In the boron nitride sintered sheet, in a number-based particle size distribution of the boron nitride particles present on a surface based on an electron microscope observation image, a D50 diameter, which is a particle diameter corresponding to cumulative 50% from a small-diameter side, is 8 μm or more and 15 μm or less. A D90 diameter, which is a particle diameter corresponding to cumulative 90% from the small-diameter side of the boron nitride particles present on the surface, is 15 μm or more and 30 μm or less. A density of the boron nitride sintered sheet is 0.9 g / cm3 or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a boron nitride sintered sheet. [Background technology]

[0002] Power semiconductor elements (so-called power devices) have become indispensable for the efficient use of electrical energy. Demand is also increasing for lighting semiconductor elements (so-called high-power LED devices) used in energy-saving, long-life, high-brightness, and power LED lamps. The use of power devices and high-power LED devices requires technology to dissipate the heat generated into the surroundings. The following patent documents disclose technology for producing heat-dissipating sheets (thermally conductive sheets) using boron nitride.

[0003] Japanese Patent Application Laid-Open Publication No. 2013-177562 discloses a thermally conductive sheet formed from a thermally conductive composition containing plate-shaped boron nitride particles, an epoxy resin, at least one of a curing agent and a curing accelerator, and a rubber component. This thermally conductive sheet contains 35% or more by volume of boron nitride particles. Its thermal conductivity in a direction perpendicular to the sheet thickness direction is 4 W / m·K or more. This thermally conductive sheet is formed from a rubber-containing composition in which the boron nitride particles have been removed from the thermally conductive composition. When the rubber-containing sheet is heated at a frequency of 1 Hz and a heating rate of 2°C / min, it exhibits a storage shear modulus of 5.5×10 at least at any temperature in the temperature range of 50 to 80°C. 3 ~7.0×10 4 Pa. The publication states that this structure provides excellent thermal conductivity in the direction perpendicular to the thickness direction (plane direction).

[0004] Japanese Patent Application Laid-Open Publication No. 2013-177564 discloses a thermally conductive sheet containing plate-shaped boron nitride particles and a resin component. The boron nitride particle content of this thermally conductive sheet is 60% by mass or more. The thermal conductivity of the thermally conductive sheet in the plane direction is 4 W / m·K or more. The thermally conductive sheet is characterized by a tack strength of 350 g / 2 cm diameter or more in a temperature range of 40°C or higher. The publication also states that a thermally conductive sheet with this configuration has excellent initial adhesion.

[0005] Japanese Patent Publication No. 6786778 discloses a heat-dissipating resin sheet containing a resin and a boron nitride filler. In this heat-dissipating resin sheet, the boron nitride filler is in the form of agglomerated particles, and the boron nitride filler content is 40 vol% to 60 vol%. The resin has a Tg of 60°C or less. The resin contains two or more epoxy resins. One of the resins is a phenoxy resin, and the phenoxy resin content is 18.0 mass% to 95 mass% of the total epoxy resin. This heat-dissipating resin sheet has a 90-degree peel test strength of 1.5 N / cm or more and a thermal conductivity of 10 W / mK or more. The publication also states that this heat-dissipating resin sheet has good thermal conductivity due to its high filler content, sufficient strength despite its high filler content, and sufficient adhesive strength.

[0006] The boron nitride agglomerated particles disclosed in JP 2016-135729 A are characterized by an average crystallite diameter of the primary particles of 375 angstroms or more, as determined from the (002) plane peak in powder X-ray diffraction measurement, and a volume-based average particle diameter (D50) of the agglomerated particles of 26 μm to 200 μm. The publication also states that the use of such particles makes it possible to produce a heat-dissipating sheet that exhibits high thermal conductivity.

[0007] The boron nitride agglomerated particles disclosed in JP 2016-135730 A are characterized in that the peak intensity ratio ((100) / (004)) of the (100) plane to the (004) plane in powder X-ray diffraction measurement is 3 or more, and the average crystallite diameter of the primary particles determined from the (002) plane peak in powder X-ray diffraction measurement of the agglomerated particles is 375 angstroms or more. The publication also states that the use of such particles can be used to produce a heat-dissipating sheet that exhibits high thermal conductivity.

[0008] JP 2013-176981 A discloses a method for producing a thermally conductive sheet, which includes the steps of preparing raw material components containing plate-shaped boron nitride particles and a polymer matrix, forming the raw material components into a long sheet using a calendar, and pressing the long sheet. The publication states that this production method allows for the production of a thermally conductive sheet with excellent production efficiency. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-177562 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-177564 [Patent Document 3] Patent No. 6786778 [Patent Document 4] Japanese Patent Application Laid-Open No. 2016-135729 [Patent Document 5] Japanese Patent Application Laid-Open No. 2016-135730 [Patent Document 6] Japanese Patent Application Laid-Open No. 2013-176981 Summary of the Invention [Problem to be solved by the invention]

[0010] Controlling the orientation of ceramic particles within the ceramic substrate is considered important for manufacturing substrates with high heat dissipation properties. Techniques for selectively orienting particles include, for example, applying an electric field to align particles or forcing alignment through extrusion molding, press molding, and other methods. When applying an electric field, the ceramic particles must be magnetic. Extrusion molding and press molding tend to orient the ceramic particles horizontally relative to the thickness direction, resulting in an orientation unfavorable for thermal conductivity. In contrast, a technique exists in which a block is formed in advance and then cut into sheets with a wire saw to form substrates with the ceramic particles aligned perpendicular to the thickness direction. However, these techniques have issues, such as damage to the ceramic particles, which can impair sinterability and thermal conductivity, or internal cracks caused by vibrations and stress during cutting, which can worsen thermal conductivity.

[0011] In view of these circumstances, the present inventors wish to further improve the thermal conductivity of boron nitride sintered sheets. [Means for solving the problem]

[0012] The sintered sheet disclosed herein is a boron nitride sintered sheet containing boron nitride particles. In the boron nitride sintered sheet, the boron nitride particles present on the surface have a particle diameter D 1 corresponding to a cumulative 50% from the smallest diameter side in a particle size distribution based on the number of particles based on an electron microscope observation image. 50 The diameter is 8 μm or more and 15 μm or less. D corresponds to the particle diameter of the smallest 90% of the boron nitride particles present on the surface. 90 The diameter is 15 μm or more and 30 μm or less. The density of the boron nitride sintered sheet is 0.9 g / cm 3 The boron nitride sintered sheet having such a configuration has further improved thermal conductivity.

[0013] In a preferred embodiment of the sintered sheet disclosed herein, when X-ray diffraction analysis is performed in the sheet thickness direction, the degree of orientation of the boron nitride particles, as indicated by the peak intensity ratio (I(002) / I(100)), is 20 or less. With this configuration, the orientation of the boron nitride particles along the sheet thickness direction is suppressed, and the effect of improving thermal conductivity can be more effectively achieved.

[0014] In another preferred embodiment of the sintered sheet disclosed herein, the thermal conductivity of the boron nitride sintered sheet in the thickness direction is 30 W / m K or more. With this configuration, the effect of improving the thermal conductivity of the boron nitride sintered sheet can be more effectively achieved.

[0015] In another preferred embodiment of the sintered sheet disclosed herein, the average thickness of the boron nitride sintered sheet is 200 μm or more and 1000 μm or less. With this configuration, the effect of improving the thermal conductivity of the boron nitride sintered sheet can be more effectively achieved. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic diagram of a dry powder rolling apparatus 5. [Figure 2] FIG. 2 is an SEM image of the surface of a sintered sheet of one example. [Figure 3] FIG. 3 is an SEM image of the surface of a sintered sheet of a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of the technology disclosed herein will be described. It should be noted that matters necessary for implementing the technology disclosed herein, other than those specifically mentioned in this specification, can be understood as design matters for a person skilled in the art based on the prior art in the relevant field. The technology disclosed herein can be implemented based on the contents disclosed in this specification and the technical common sense in the relevant field. In this specification, the notation "P to Q" indicating a numerical range includes "P or more and Q or less," "more than P but less than Q," "more than P but Q or less," and "P or more and less than Q." In this specification, "R contains S as a major component" means that, when the entire R is 100% by mass, the S content is, for example, 50% by mass or more, preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more (the closer to 100% by mass the better).

[0018] <Boron nitride sintered sheet> The boron nitride sintered sheet disclosed herein contains, for example, boron nitride particles (BN particles). In this embodiment, the boron nitride sintered sheet may contain BN particles as a main component, and may contain unavoidable impurities resulting from the manufacturing process of the BN particles, the manufacturing process of the boron nitride sintered sheet, etc. In the boron nitride sintered sheet, the BN particles may be bonded to each other by sintering and exist in agglomerated form. In the following description, the boron nitride sintered sheet may also be simply referred to as a "sintered sheet."

[0019] BN particles are, for example, a component that provides thermal conductivity in a sintered sheet. In a sintered sheet, BN particles can exist not only in the form of primary particles, but also in the form of secondary particles, where the particles are aggregated and fused together. Therefore, the BN particles to be measured in the calculation of the average aspect ratio (described below) and in the measurement of particle size refer to BN particles contained in a sintered sheet that are particulate and can be recognized as a single particle when observed with a scanning electron microscope (SEM). Therefore, the BN particles to be measured include not only primary particles but also secondary particles that are aggregated and fused together, and can be recognized as a single particle when observed with an SEM.

[0020] The average aspect ratio of BN particles is generally 1.2 or greater, for example, 1.5 or greater, preferably 2 or greater, more preferably 2.5 or greater, and even more preferably 3 or greater. The average aspect ratio of BN powder may be 10 or less, 7.5 or less, or even 5 or less. In this specification, the "average aspect ratio" of BN particles contained in a sintered sheet refers to the average ratio of the long dimension to the short dimension of multiple BN particles. For example, the aspect ratio of each BN particle can be obtained by drawing the smallest rectangle circumscribing the BN particle in an SEM image of the surface of the sintered sheet and calculating the ratio (A / B) of the long dimension A to the short dimension B of the rectangle. The average aspect ratio can be obtained by calculating the arithmetic mean of the aspect ratios of multiple (e.g., 100 to 300) BN particles.

[0021] In the sintered sheet disclosed herein, the D of the BN particles present on the surface 50 The diameter is preferably 8 μm or more. From the viewpoint of improving the thermal conductivity of the sintered sheet, D 50 The diameter is, for example, 15 μm or less, preferably 14 μm or less, more preferably 12 μm or less, and even more preferably 10 μm or less. 50"D diameter" refers to the particle diameter corresponding to the cumulative 50% from the small diameter side in the number-based particle size distribution based on the SEM observation image. The particle diameter of the BN particles measured in the SEM observation image is the circle-equivalent diameter of the BN particles. The circle-equivalent diameter may be determined from the SEM observation image that has been binarized using image analysis software. The number of BN particles to be measured may be, for example, 100 to 300. In this specification, the particle diameter corresponding to the cumulative 10% from the small diameter side in the number-based particle size distribution based on the SEM observation image is referred to as "D 10 The particle diameter corresponding to the cumulative 90% from the smallest diameter side is called "D 90 It is called the "diameter."

[0022] In the sintered sheet disclosed herein, the D of the BN particles present on the surface 90 The diameter is preferably 15 μm or more. From the viewpoint of improving the thermal conductivity of the sintered sheet, D 90 The diameter is more preferably 17.5 μm or more, and even more preferably 20 μm or more. 90 The diameter is preferably 30 μm or less.

[0023] In the sintered sheet disclosed herein, the D of the BN particles present on the surface 10 The diameter is not particularly limited, but it is preferable that it is approximately 2 μm to 5 μm. 10 The diameter is preferably 2.5 μm or more, and more preferably 3 μm or more. 10 The diameter is preferably 4.5 μm or less.

[0024] The density of the sintered sheet disclosed herein is 0.9 g / cm 3 The higher the density, the higher the thermal conductivity of the sintered sheet tends to be. From this viewpoint, the density is preferably 1.0 g / cm or more. 3 More preferably, 1.1 g / cm 3 More preferably, 1.2 g / cm 3 The above is particularly preferred. Although not particularly limited, the density is approximately 1.5 g / cm 3 Less than 1.4 g / cm is preferred 3 Less than 1.3 g / cm is more preferable.3 The following is more preferable: The density of the sintered sheet here is an actually measured density. The sintered sheet is processed into a test piece having predetermined dimensions, and the density can be calculated based on the dimensions and weight of the test piece.

[0025] The thermal conductivity of the sintered sheet disclosed herein in the thickness direction is preferably 30 W / m·K or more. The higher the thermal conductivity, the higher the thermal conductivity of the sintered sheet. The thermal conductivity is more preferably 35 W / m·K or more, and even more preferably 40 W / m·K or more. Although not particularly limited, the thermal conductivity is generally 100 W / m·K or less, and may be 90 W / m·K or less, 85 W / m·K or less, or 80 W / m·K or less. The thermal conductivity of the sintered sheet can be measured, for example, using a commercially available thermal conductivity measuring device.

[0026] The degree of orientation of BN particles in the sintered sheet disclosed herein is generally 20 or less. The degree of orientation of BN particles here is a parameter expressed by the peak intensity ratio (I(002) / I(100)) when the sintered sheet is subjected to X-ray diffraction analysis in the thickness direction. I(002) is the intensity of the X-ray diffraction line of the (002) plane. I(100) is the intensity of the X-ray diffraction line of the (100) plane. In this embodiment, the degree of orientation in the thickness direction of the sheet can be measured using a commercially available XRD device (e.g., Bruker AXS's "D8 ADVANCE Super Speed"). The X-ray source used in the measurement is preferably CuKα radiation, and the tube voltage and tube current are preferably set to 45 kV and 360 mA, respectively. In this embodiment, the test piece used for the measurement is a test piece having dimensions of 50 mm × 50 mm and a thickness of 0.5 mm. When the degree of orientation defined above is 7, the orientation of the BN particles in the sintered sheet can be said to be random. The higher the degree of orientation, the more the BN particles are oriented in the sheet thickness direction, and the thermal conductivity of the sintered sheet tends to decrease. Therefore, from the viewpoint of improving the thermal conductivity of the sintered sheet, the degree of orientation is, for example, 19 or less, preferably 18 or less, more preferably 17 or less, and even more preferably 16 or less. The degree of orientation is not particularly limited, but is generally 5 or more, for example, 7 or more.

[0027] The thickness of the sintered sheet is not particularly limited, but is generally 10 μm or more, preferably 50 μm or more, more preferably 100 μm or more, and even more preferably 200 μm or more. The thickness of the sintered sheet is, for example, 5000 μm or less, preferably 2000 μm or less, more preferably 1500 μm or less, and even more preferably 1000 μm or less.

[0028] The method for producing a sintered sheet disclosed herein includes, for example, a preparation step, a granulation step, a molding step, a drying step, a binder removal step, and a firing step. The preparation step is, for example, a step of preparing materials to be used in producing a sintered sheet. In this embodiment, the preparation step includes preparing raw materials such as BN powder, a resin binder, and a plasticizer. Furthermore, various additives such as a dispersant, a release agent, and an antifoaming agent are also prepared as needed.

[0029] The BN powder used as a raw material may be, for example, plate-shaped or needle-shaped. The average aspect ratio of the BN powder is generally 1.2 or more, for example, 2 or more, preferably 4 or more, more preferably 6 or more, even more preferably 7 or more, and particularly preferably 8 or more. From the viewpoint of improving the efficiency of the granulation described below, the average aspect ratio of the BN powder is, for example, 50 or less, preferably 30 or less, more preferably 20 or less, and even more preferably 10 or less. The larger the average aspect ratio of the BN powder, the more likely it is that the thermal conductivity in the direction of the major axis will be improved. The average aspect ratio of the BN powder used as a raw material can be measured, for example, by randomly selecting multiple particles (for example, 1,000 to 300) from an SEM observation image of the BN powder, calculating the aspect ratio (ratio of major axis to minor axis) based on the major axis and minor axis of each particle, and obtaining the arithmetic average value.

[0030] D of BN powder as raw material 50 The diameter is not particularly limited, but it is preferable that it is approximately 0.5 μm to 50 μm. 50 The diameter here is the particle diameter corresponding to the cumulative 50% from the smallest diameter side in the number-based particle size distribution based on the SEM observation image. The particle diameter of the BN powder measured in the SEM observation image is the circle-equivalent diameter of the BN powder. The circle-equivalent diameter may be determined, for example, from the SEM observation image that has been binarized using image analysis software. The number of particles to be measured may be, for example, 100 to 300.

[0031] The resin binder is a component that functions to bind BN powder particles together, for example, during part of the manufacturing process of the sintered sheet. For example, a resin material that has thermoplasticity and is burned off in the binder removal process described below can be preferably used as the resin binder. Examples of the resin binder include natural polymer compounds such as carrageenan and xanthan gum; celluloses such as carboxymethyl cellulose; acrylic resins; epoxy resins; phenolic resins; amine resins; and alkyl resins. One type of resin binder can be used alone, or two or more types can be used in combination.

[0032] A plasticizer is, for example, a component that has the function of weakening the intermolecular forces of the polymer that constitutes the resin binder and imparting flexibility to the polymer. A resin material that is not decomposed in the drying process but is decomposed and removed in the binder removal process or baking process can be preferably used as the plasticizer. Examples of the plasticizer include polyhydric alcohols such as glycerin and polyglycerin; polyethers such as polyethylene glycol; and the like. One type of plasticizer can be used alone, or two or more types can be used in combination. Additives such as dispersants, release agents, and antifoaming agents can be any conventional additives used in this type of application, without particular limitation.

[0033] The granulation step is a step of producing granulated powder (granulated particles) using, for example, the BN powder prepared in the preparation step. The granulation method for BN powder is not particularly limited, and examples thereof include tumbling granulation, fluidized bed granulation, stirring granulation, compression granulation, extrusion granulation, crushing granulation, and spray drying (atomization granulation). Considering the ease of handling of the raw powder, the spray drying method is preferably used. In the spray drying method, first, the raw materials prepared in the preparation step are mixed to prepare a mixture. Conventional mixing devices such as a ball mill, mixer, disperser, and kneader can be used to prepare the mixture. Next, the raw material mixture is dispersed in a dispersion medium to prepare a slurry. Water, for example, is preferably used as the dispersion medium. Next, the slurry is sprayed into droplets using a spray drying device and dried to obtain a BN granulated powder. The droplet size can be appropriately adjusted depending on the desired size, mass, etc. of the granulated powder.

[0034] Granulated powder D 50 The diameter is not particularly limited, but it is generally 3 μm to 20 μm (preferably 5 μm to 15 μm). 90 The diameter is not particularly limited, but it is generally 5 μm to 40 μm (preferably 10 μm to 35 μm). 10 The diameter is not particularly limited, but it is generally 0.5 μm to 5 μm (preferably 1 μm to 3.5 μm). 50 Here, the diameter is a particle diameter corresponding to 50% cumulatively from the small diameter side in the number-based particle size distribution based on the SEM observation image. The particle size of the granulated powder measured in the SEM observation image is the circle-equivalent diameter of the granulated powder. The circle-equivalent diameter may be determined from the SEM observation image that has been subjected to binarization processing using image analysis software. The number of granulated powder particles to be measured may be, for example, 100 to 300. In the number-based particle size distribution based on the SEM observation image, the particle diameter corresponding to 10% cumulatively from the small diameter side is called "D 10 The particle diameter corresponding to the cumulative 90% from the smallest diameter side is called "D 90 It is called the "diameter."

[0035] The molding step is, for example, a step of molding the granulated powder obtained in the granulation step into a sheet. FIG. 1 is a schematic diagram of a dry powder rolling apparatus 5. FIG. 1 schematically shows one embodiment of manufacturing a green sheet 100 using the dry powder rolling apparatus 5. As shown in FIG. 1, the dry powder rolling apparatus 5 has a storage tank 1, a feeder 1b, and a pair of rolls 2. The storage tank 1 is, for example, a portion for storing granulated powder 10. In this embodiment, the storage tank 1 is disposed at the top of the dry powder rolling apparatus 5. The feeder 1b is, for example, a portion for feeding granulated powder 10 from the storage tank 1 toward the rolls 2. In the embodiment shown in FIG. 1, the feeder 1b is disposed at the bottom of the storage tank 1. The pair of rolls 2 is, for example, a portion for rolling and molding the granulated powder 10 into a sheet. In this embodiment, the pair of rolls 2 is disposed below the feeder 1b so that their rotation axes are parallel to each other.

[0036] In the molding process, as shown in FIG. 1, first, granulated powder 10 obtained in the granulation process is charged into storage tank 1 of dry powder rolling apparatus 5. Granulated powder 10 charged into storage tank 1 is discharged to the outside through feeder 1b at the bottom. The discharged granulated powder 10 is supplied between a pair of rolls 2. Rolls 2 rotate at a predetermined rotation speed in the direction of the arrow in FIG. 1, thereby compressing the supplied BN granulated powder 10. At this time, it is preferable to heat the pair of rolls 2. The temperature of the pair of rolls 2 at this time is preferably higher than room temperature (25°C) and is a temperature at which the resin binder contained in granulated powder 10 is deformed, for example. The temperature can be set appropriately depending on the melting point of the resin binder. The rotation speed of rolls 2 can be set appropriately. In this process, granulated powder 10 is formed into a sheet shape to produce green sheet 100.

[0037] The binder removal step is, for example, a step of removing a resin binder contained in a green sheet. In this embodiment, in the binder removal step, the green sheet that has been subjected to the drying step is subjected to the binder removal treatment. The temperature of the binder removal treatment may be, for example, 200°C to 600°C. The time period of the binder removal treatment may be, for example, 15 minutes to 5 hours. In other embodiments, if the drying step is omitted, the binder removal step may be performed on the green sheet immediately after the molding step.

[0038] The firing step is, for example, a step of firing a green sheet. In this embodiment, by carrying out the firing step, the BN powder constituting the granulated powder contained in the green sheet is sintered to each other, and the sintered sheet disclosed herein is obtained. In this embodiment, in the firing step, the green sheet that has been subjected to the binder removal step is subjected to a firing treatment. The temperature of the firing treatment is preferably approximately above 600°C (1600°C to 2300°C). The time of the firing treatment is preferably, for example, 1 hour to 40 hours. The atmosphere in the firing treatment is preferably an inert atmosphere such as a nitrogen (N2) atmosphere, a helium (He) atmosphere, or an argon (Ar) atmosphere.

[0039] The uses of the sintered sheet disclosed herein are not particularly limited, but it can be used, for example, as a heat dissipation material. It can be interposed between a heat-generating component (e.g., a power device) and a heat-dissipating component (e.g., a heat dissipation fin, a heat sink, a heat dissipation plate, etc.), or can be used as a heat dissipation sheet to dissipate heat from the heat-generating component in place of the heat-dissipating component. Alternatively, the sintered sheet disclosed herein can be preferably used as a material for constituting a heat dissipation device combined with a heat-dissipating component.

[0040] The sintered sheet disclosed herein is a BN sintered sheet containing BN particles. In the sintered sheet, the D of the boron nitride particles present on the surface 50 The diameter is 8 μm or more and 15 μm or less, and D 90 The diameter is 15 μm or more and 30 μm or less. The density of the sintered sheet is 0.9 g / cm 3The sintered sheet disclosed herein has a D of boron nitride particles present on the surface of the sheet. 50 Diameter and D 90 By setting the diameter and thickness within the above range, the BN particles in the sintered sheet are prevented from being arranged along a plane perpendicular to the sheet thickness direction. This allows the BN particle content in the sintered sheet to be increased, and also increases the thermal conductivity in the sheet thickness direction. When the sheet density is 0.9 g / cm 3 By setting the above, the thermal conductivity of the sintered sheet can be increased.

[0041] Next, test examples relating to the technology disclosed herein will be described. Note that the test examples shown below are not intended to limit the technology disclosed herein.

[0042] <Preparing the sintered sheet> [Example 1 to Example 11] The BN powder was prepared from Denka Co., Ltd. The binder resin was a water-based acrylic resin, and the plasticizer was polyglycerin from Sakamoto Pharmaceutical Co., Ltd. Other ingredients included a release agent, a dispersant, and an antifoaming agent.

[0043] The above materials were mixed so that the total weight of the materials was 100 parts by mass, the amount of BN powder added was 75 parts by mass, and the total amount of the remaining additives (binder resin, plasticizer, release agent, dispersant, and antifoaming agent) was 25 parts by mass. A slurry containing BN powder was prepared by stirring while adding a dispersion medium (water) appropriately to ensure proper mixing of these materials. Subsequently, a granulated powder was produced from the above slurry by spray granulation using a spray granulation device (spray dryer). The granulated powder was then rolled using a dry powder rolling device to form a strip-shaped green sheet. The various conditions for green sheet formation using the dry powder rolling device (e.g., roll spacing, roll rotation speed) were appropriately set so that green sheets with thicknesses of 0.2 mm to 0.5 mm were produced.

[0044] Next, the green sheets were subjected to a binder removal treatment at 600°C for 2 hours. After the binder removal treatment, the green sheets were subjected to a firing treatment at 2000°C for 10 hours in an N2 atmosphere. In this way, sintered sheets (porous sheets) of each example were obtained.

[0045] [Examples 12 to 16] BN powder manufactured by Denka Co., Ltd. was used. Toluene was used as the organic solvent. Polyglycerin manufactured by Sakamoto Pharmaceutical Co., Ltd. was used as the plasticizer. The above materials were mixed so that the total weight of the materials was 100 parts by mass, the amount of BN powder added was 75 parts by mass, and the total amount of the remaining components was 25 parts by mass. These materials were mixed and stirred to prepare a clay containing BN powder. The prepared clay was then molded into a block using a press. The block dimensions were 100 mm length x 100 mm width x 100 mm height. The block was then dried at 120°C for 2 hours and debindered at 600°C for 2 hours. After the debindering process, the block was fired in a N2 atmosphere at 2000°C for 10 hours. The fired block was then cut using a wire saw to obtain sintered sheets for each example. The dimensions of the sintered sheet were 100 mm length x 100 mm width x 0.2 mm height.

[0046] <Measurement of particle size distribution> [Measuring particle size of raw materials] For Examples 1 to 11, the particle size distribution of the granulated powder prepared as described above was measured. For Examples 12 to 16, the particle size distribution of the boron nitride powder used as the raw material was measured. For the powder in each example, the image analysis software "ImageJ" was used to obtain the particle size distribution based on the SEM observation image, and the D 10 diameter and D 50 diameter and D 90 The results are shown in the corresponding columns in Table 1.

[0047] [Table 1]

[0048] [Particle size measurement for sintered sheets] SEM images of the surface of the sintered sheet for each example were taken. The particle size distribution of the boron nitride powder was obtained from these SEM images using the image analysis software "ImageJ." 10 diameter and D 50 diameter and D 90 The diameters of the particles were measured. The results are shown in the corresponding columns in Table 2. As a reference example, an SEM image of the surface of the sintered sheet of Example 1 is shown in Figure 2. An SEM image of the surface of the sintered sheet of Example 12 is shown in Figure 3. The magnification of each SEM was 1000x.

[0049] [Table 2]

[0050] [Thermal conductivity of sintered sheet] The thermal conductivity (W / m K) of each sintered sheet in the thickness direction was measured using a thermal conductivity measuring device (LFA 467 HyperFlash (registered trademark) (NETZSCH)) according to the device manual. The results are shown in the corresponding columns in Table 2.

[0051] [Sintered sheet density] The sintered sheet of each example was processed to a predetermined size to prepare a test piece. The outer diameter and weight of the test piece were measured, and the density (actual density) was calculated. The results are shown in the corresponding column in Table 2.

[0052] [Orientation degree] For each sample, a 50 mm x 50 mm, 0.5 mm thick specimen was prepared. The X-ray diffraction intensity of the (002) plane (I(002)) and the (100) plane (I(100)) were measured using an XRD instrument (Bruker AXS D8 ADVANCE Super Speed). The orientation of each specimen (the peak intensity ratio in the sheet thickness direction, I(002) / I(100)) was calculated. The X-ray source used for the measurement was CuKα radiation, with a tube voltage of 45 kV and a tube current of 360 mA. The results are shown in the corresponding columns in Table 2.

[0053] As shown in Table 2, the sintered sheets of Examples 1 to 11 have a D in the particle size distribution based on the number of BN powder particles present on the surface based on the SEM observation image. 50 The diameter is 8 μm or more and 15 μm or less, and D 90 The sintered sheets of Examples 1 to 11 had a density of 0.9 g / cm 3 The sintered sheets of Examples 1 to 11 all had a thermal conductivity of 30 W / m K or more, which indicated that they were sintered sheets with improved thermal conductivity. 50 Diameter and D 90 In the sintered sheets of Examples 12 to 16, in which at least one of the diameter and density did not satisfy the predetermined range, the thermal conductivity was less than 30 W / m·K, and no improvement in thermal conductivity was confirmed.

[0054] The technology disclosed herein has been described above, but these are merely examples and do not limit the scope of the claims. Various modifications can be made to the technology disclosed herein without departing from the spirit of the technology.

[0055] The techniques disclosed herein include the techniques described in the following sections. Section 1: A boron nitride sintered sheet containing boron nitride particles, The boron nitride particles present on the surface thereof, In the particle size distribution based on the number of particles observed by electron microscope, D is the particle size corresponding to the cumulative 50% from the smallest diameter side. 50 The diameter is 8 μm or more and 15 μm or less, In the particle size distribution, D corresponds to the particle diameter that is 90% cumulative from the smallest diameter side. 90 The diameter is 15 μm or more and 30 μm or less, Density is 0.9g / cm 3 That's it, sintered sheet. Section 2: Item 2. The sintered sheet according to item 1, wherein the degree of orientation of the boron nitride particles, as represented by the peak intensity ratio (I(002) / I(100)), when analyzed by X-ray diffraction in the sheet thickness direction is 20 or less. Section 3: Item 3. The sintered sheet according to item 1 or 2, having a thermal conductivity of 30 W / m·K or more in the sheet thickness direction. Section 4: 4. The sintered sheet according to any one of items 1 to 3, having an average thickness of 200 μm or more and 1000 μm or less. [Explanation of symbols]

[0056] 1. Storage tank 1b Feeder 2 rolls 5. Dry powder rolling equipment 10 Granulated powder 100 Green Sheet

Claims

1. A boron nitride sintered sheet containing boron nitride particles, The boron nitride particles present on the surface thereof, In the particle size distribution based on the number of particles observed by an electron microscope, D is the particle diameter corresponding to the cumulative 50% from the smallest diameter side. ５０ The diameter is 8 μm or more and 15 μm or less, In the particle size distribution, D corresponds to the particle diameter corresponding to the cumulative 90% from the smallest diameter side. ９０ The diameter is 15 μm or more and 30 μm or less, Density is 0.9 g / cm ３ That's it, sintered sheet.

2. 2. The sintered sheet according to claim 1, wherein, when X-ray diffraction analysis is performed in the thickness direction of the sheet, the degree of orientation of the boron nitride particles, as represented by the peak intensity ratio (I(002) / I(100)), is 20 or less.

3. 2. The sintered sheet according to claim 1, wherein the thermal conductivity in the thickness direction of the sheet is 30 W / m·K or more.

4. The sintered sheet according to claim 1, having an average thickness of 200 μm or more and 1000 μm or less.

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