Boron nitride aggregate powder, resin composition, heat dissipation sheet, and semiconductor device

Abstract

The present invention aims to provide a boron nitride aggregate powder that exhibits good coatability during the manufacturing of heat dissipation sheets, further reduces cracking of the heat dissipation sheets, and improves the voltage resistance characteristics of the heat dissipation sheets; a resin composition containing this boron nitride aggregate powder; a heat dissipation sheet; and a semiconductor device using this heat dissipation sheet. [Solution] A boron nitride aggregate powder containing hexagonal boron nitride aggregate particles, wherein the shear adhesion force after being conditioned for 4 hours at a temperature of 25°C and 70% humidity is 0.40 kPa or more and 1.5 kPa or less.

Description

[Technical Field]

[0001] The present invention relates to boron nitride aggregate powder suitably used in heat dissipation sheets for semiconductor devices, a resin composition containing the boron nitride aggregate powder and a resin, a heat dissipation sheet formed by molding the resin composition, and a semiconductor device using this heat dissipation sheet. [Background technology]

[0002] Boron nitride (BN) is an insulating ceramic, and various crystal forms are known, including c-BN with a diamond structure, h-BN (hexagonal boron nitride) with a graphite structure, and α-BN and β-BN with a random layered structure. Among these, h-BN has the same layered structure as graphite, is relatively easy to synthesize, and possesses excellent thermal conductivity, solid lubricity, chemical stability, and heat resistance, making it widely used in the field of electrical and electronic materials.

[0003] In recent years, heat generation associated with the increasing density of integrated circuits has become a major problem, particularly in the electrical and electronic fields, making heat dissipation an urgent issue. h-BN is attracting attention as a thermally conductive filler for such heat dissipation materials, leveraging its characteristic of possessing high thermal conductivity despite being an insulating material. However, it is known that h-BN particles exhibit thermal conductivity anisotropy in the direction of the crystal axis. To suppress the anisotropy of properties due to orientation, studies have been conducted to obtain heat dissipation members with higher thermal conductivity and dielectric strength by using aggregated particles of h-BN that satisfy specific conditions.

[0004] Patent Document 1 proposes a boron nitride aggregate powder that exhibits excellent isotropic thermal conductivity, resistance to disintegration, and kneadability with resins. Patent Document 2 proposes hexagonal boron nitride aggregate particles and hexagonal boron nitride powder containing said aggregate particles, which provide a resin composition that exhibits high thermal conductivity, is less prone to retaining air bubbles, and has high dielectric strength. Patent document 3 proposes a boron nitride powder with excellent insulating properties and a method for producing the same.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] The boron nitride agglomerated powder of Patent Document 1 has low cohesive force between boron nitride agglomerated particles and adhesive force with resin. During continuous coating, peeling at the boron nitride agglomerated powder - resin interface occurs due to bending stress at the roll part, and there is a concern that the heat - radiating sheet is likely to crack.

[0007] The boron nitride powder of Patent Document 2 removes impurities by acid treatment to improve insulation, but there is a concern about poor coating property because primary particles are generated in the pulverization process. Also, since the primary particles have a large specific surface area, there is a concern that peeling at the boron nitride agglomerated powder - resin interface occurs and the heat - radiating sheet is likely to crack.

[0008] The boron nitride powder of Patent Document 3 removes carbon by heating at a temperature of 500°C or higher and lower than 1000°C in an oxidizing atmosphere to improve insulation. However, the cohesive force between boron nitride agglomerated particles on the surface of boron nitride primary particles and the adhesive force with resin are small. During continuous coating, peeling at the boron nitride agglomerated powder - resin interface occurs due to bending stress at the roll part, and there is a concern that the heat - radiating sheet is likely to crack.

[0009] An object of the present invention is to provide a boron nitride agglomerated powder that has good coating property during the production of a heat - radiating sheet, is less likely to crack in the heat - radiating sheet, and can also have good withstand - voltage characteristics of the heat - radiating sheet, a resin composition and a heat - radiating sheet containing this boron nitride agglomerated powder, and a semiconductor device using this heat - radiating sheet. [Means for solving the problem]

[0010] The inventors of the present invention have conducted diligent studies to solve the above problems and have found that the above problems can be solved by having the following configuration. In other words, the gist of this invention is as follows:

[0011] [1] Boron nitride aggregate powder containing hexagonal boron nitride aggregate particles, wherein the shear adhesion force after being conditioned for 4 hours at a temperature of 25°C and 70% humidity is 0.40 kPa or more and 1.5 kPa or less.

[0012] [2] The boron nitride aggregate powder according to [1] above, wherein the shear adhesion force is 1.0 kPa or less. [3] Boron nitride aggregate powder as described in [1] or [2] above, wherein the average particle size (D50) is 20 μm or more and 100 μm or less. [4] The boron nitride aggregate powder according to any one of [1] to [3] above, wherein the hexagonal boron nitride aggregate particles have a cardhouse structure.

[0013] [5] A resin composition comprising the boron nitride aggregate powder described in any one of [1] to [4] above and a resin. [6] The resin composition according to [5] above, wherein the resin comprises an epoxy resin. [7] A heat dissipation sheet obtained by molding the resin composition described in [5] or [6] above. [8] A semiconductor device including the heat dissipation sheet described in [7] above. [Effects of the Invention]

[0014] The boron nitride aggregate powder of the present invention provides a heat dissipation sheet that exhibits good coatability during manufacturing, is resistant to cracking, and has good voltage resistance. Using a heat dissipation sheet containing the boron nitride aggregate powder of the present invention, it is possible to realize a highly reliable semiconductor device with good handling properties and voltage resistance. [Modes for carrying out the invention]

[0015] The embodiments of the present invention will be described in detail below, but the present invention is not limited to the embodiments described below and can be implemented in various ways within the scope of its gist. The "~" symbol, which indicates a numerical range, means that the numbers before and after it are included as the lower and upper limits, respectively. For example, "A~B" is equivalent to "A or greater, B or less." The percentages (contents), various physical properties, and numerical ranges disclosed herein can be arbitrarily combined with their lower and upper limits to create new numerical ranges.

[0016] [Boron nitride aggregated powder] In the present invention, boron nitride aggregate powder (hereinafter sometimes simply referred to as "BN aggregate powder") refers to a powder that is an aggregate of boron nitride aggregate particles (hereinafter sometimes simply referred to as "BN aggregate particles"). In other words, BN aggregate powder is an aggregate of BN aggregate particles. The BN aggregated particles constituting the BN aggregated powder include hexagonal boron nitride aggregated particles. The BN aggregated particles may also include BN aggregated particles other than hexagonal boron nitride aggregated particles. The content ratio of hexagonal boron nitride aggregated particles relative to the total mass (100% by mass) of the BN aggregated particles may be, for example, 95% by mass or more, 96% by mass or more, 97% by mass or more, 98% by mass or more, or 99% by mass or more, and may also be 100% by mass.

[0017] The BN aggregate powder of the present invention contains hexagonal boron nitride aggregate particles, and the shear adhesion force (hereinafter sometimes simply referred to as "shear adhesion force") measured after conditioning at a temperature of 25°C and a humidity of 70% for 4 hours is 0.40 kPa or more and 1.5 kPa or less. The mechanism by which the BN aggregate powder of the present invention can provide a heat dissipation sheet that has good applicability during heat dissipation sheet manufacturing, is resistant to cracking, and has good voltage resistance characteristics is presumed to be as follows. Since the shear adhesion force of the BN agglomerated powder of the present invention is 0.40 kPa or more, the adhesion force between the BN agglomerated particles and the resin increases, and resin peeling from the interface between the BN agglomerated particles and the resin is suppressed, so that the coated dry film (heat dissipation sheet) is less likely to crack, and the mandrel test results described later are improved. On the other hand, since the shear adhesion force of the BN agglomerated powder of the present invention is 1.5 kPa or less, aggregation between BN agglomerated particles is suppressed during the preparation of the coating liquid during the production of the heat dissipation sheet, and the coating property becomes good. In addition, during the pressing of the heat dissipation sheet, the movement and deformation of the BN agglomerated particles are likely to occur, and the voids in the heat dissipation sheet are reduced, so that the withstand voltage characteristics become good.

[0018] [Hexagonal boron nitride agglomerated particles] The hexagonal boron nitride agglomerated particles according to the present invention are those formed by aggregating h-BN primary particles (that is, h-BN agglomerated particles), and may contain components other than h-BN primary particles as long as the effects of the present invention are not impaired. Examples of components other than h-BN primary particles include binders, surfactants, and components derived from solvents (media) that may be added to the slurry, as described in the [Method for Producing BN Agglomerated Powder] described later. The content of h-BN primary particles in the h-BN agglomerated particles is preferably 93% by mass or more, more preferably 95% by mass or more, still more preferably 97% by mass or more, based on the total mass (100% by mass) of the h-BN agglomerated particles, and may be 100% by mass or less, 99% by mass or less, or 98% by mass or less.

[0019] [Shape of BN Agglomerated Particles in BN Agglomerated Powder] The shape of the BN agglomerated particles in the BN agglomerated powder of the present invention is not particularly limited. For example, it may be any shape of agglomerated particles that can be produced by aggregating BN primary particles, such as spherical, ellipsoidal, cylindrical, hexagonal columnar, etc. In particular, in order to obtain high thermal conductivity, the BN aggregated particles are preferably card house-type BN aggregated particles having a card house structure, and more preferably card house-type h-BN aggregated particles having a card house structure. The card house structure is described, for example, in Ceramics 43 NO.2 (published by the Ceramic Society of Japan in 2008), and is a structure in which plate-like particles are stacked complexly without orientation. More specifically, the BN aggregated particles having a card house structure are an aggregate of BN primary particles, and are BN aggregated particles having a structure in which the plane portion and the end face portion of the BN primary particles are in contact, and are preferably spherical. Also, the card house structure is preferably the same structure inside the particles. The aggregation morphology and internal structure of these BN aggregated particles can be confirmed by a scanning electron microscope (SEM).

[0020] In addition, the hexagonal boron nitride aggregated particles according to the present invention preferably have a card house structure. That is, the BN aggregated powder of the present invention is preferably an aggregate of BN aggregated particles containing hexagonal boron nitride aggregated particles having a card house structure, and more preferably an aggregate of BN aggregated particles having a card house structure.

[0021] (Physical properties of BN aggregated powder) (Shearing adhesion force) The shear adhesion force of the BN aggregate powder of the present invention after being conditioned for 4 hours at a temperature of 25°C and 70% humidity is 0.40 kPa or more, preferably 0.43 kPa or more, more preferably 0.46 kPa or more, and even more preferably 0.50 kPa or more. On the other hand, the shear adhesion force of the BN aggregate powder after being conditioned for 4 hours at a temperature of 25°C and 70% humidity is 1.5 kPa or less, preferably 1.35 kPa or less, more preferably 1.2 kPa or less, even more preferably 1.0 kPa or less, even more preferably 0.80 kPa or less, and even more preferably 0.70 kPa or less. When the shear adhesion force of the BN aggregate powder is above the above lower limit, the adhesion force between the BN aggregate particles and the resin is increased, and resin peeling from the BN aggregate particle-resin interface is suppressed, making the coated and dried film (heat dissipation sheet) less prone to cracking, and the mandrel test results described later are improved. Furthermore, because the shear adhesion force of the BN aggregated powder is below the above upper limit, aggregation of BN aggregated particles is suppressed during the preparation of the coating solution when manufacturing the heat dissipation sheet, resulting in good coating properties. In addition, the movement and deformation of BN aggregated particles become easier when the heat dissipation sheet is pressed, and the number of voids in the heat dissipation sheet is reduced, resulting in good dielectric strength. To achieve the above-mentioned shear adhesion, methods such as firing in an atmospheric environment or decomposition with an oxidizing agent can be employed. Firing in an atmospheric environment tends to increase shear adhesion. Decomposition with an oxidizing agent also tends to increase shear adhesion. The "shear adhesion force" is a value calculated from the powder layer failure envelope obtained by a powder layer shear force measurement test, and can be measured using a powder layer shear force measuring device. For example, it can be measured using the "Powder Rheometer FT4" (product name) manufactured by Spectris, in accordance with JIS Z 8835:2016.

[0022] (Average particle diameter (D50)) The average particle size (D50) of the BN aggregate powder of the present invention is not particularly limited, but is preferably 20 μm or more, more preferably 25 μm or more, even more preferably 30 μm or more, and particularly preferably 40 μm or more. On the other hand, the D50 of the BN aggregate powder is preferably 100 μm or less, more preferably 90 μm or less, even more preferably 80 μm or less, and particularly preferably 60 μm or less. When the D50 of the BN aggregate powder is above the lower limit, the thermal conductivity of the BN aggregate powder itself is increased. Furthermore, when it is below the upper limit, the surface smoothness is improved when used as a heat dissipation sheet, the contact between the heat dissipation sheet and the substrate is improved, and the thermal conductivity is improved. To bring D50 within the above range, for example, adjustments can be made to the atomizer rotation speed and slurry supply amount in the spray-dry granulation process, and the resulting BN granulated powder can be classified.

[0023] Here, the average particle size (D50) of the BN agglomerated powder refers to the particle size at which the cumulative volume reaches 50% in a cumulative curve where the volume of the BN agglomerated powder used for measurement is set to 100% (50% cumulative volume particle size). Particle size measurement methods include, as a wet measurement method, a method in which BN aggregated particles are dispersed in a pure water medium containing sodium hexametaphosphate or naphthalene sulfonate-formaldehyde condensate as a dispersion stabilizer, and then measured using a laser diffraction / scattering particle size distribution analyzer, etc., as a dry measurement method, a method using MALVERN's "MORPHOLOGI" is used. This specification employs a wet measurement method. Specifically, the average particle size (D50) of the BN aggregated powder in this invention is the cumulative volume 50% particle size in the particle size distribution obtained by measuring the particle size distribution of a sample in which BN aggregated particles are dispersed in a pure water medium containing a dispersion stabilizer using a laser diffraction / scattering particle size distribution measurement method.

[0024] [Method for producing BN aggregated powder] There are no limitations on the method for producing the BN aggregated powder of the present invention, but it is particularly preferable to grind the raw material boron nitride (hereinafter, together with the ground boron nitride, it may be referred to as "raw material BN powder") in a grinding step, then aggregate it in a granulation step to form granules, and then further to a heating step in which it is heated in a non-oxidizing atmosphere and a heating oxidation step in which it is heated in an air atmosphere. More specifically, it is preferable to first disperse the raw material BN powder in a medium to form a slurry of raw material BN powder (hereinafter, it may be referred to as "BN slurry"), then perform a dispersion treatment, then granulate the obtained slurry into spherical particles, and then heat treat the granulated BN granulated particles in a non-oxidizing atmosphere to crystallize them, followed by a heating oxidation treatment in an air atmosphere. The BN granulated powder is an aggregate of BN granulated particles.

[0025] <Raw material BN powder> The raw material BN powder contains h-BN. Commercially available h-BN can be used. The raw material BN powder may further contain other BN, such as commercially available α-BN and β-BN, BN produced by the reduction nitridation method of boron compounds and ammonia, and BN synthesized from boron compounds and nitrogen-containing compounds such as melamine, to the extent that it does not impair the effects of the present invention. The h-BN content relative to BN in the raw material BN powder may be, for example, 95% by mass or more, 96% by mass or more, 97% by mass or more, 98% by mass or more, or 99% by mass or more, and may also be 100% by mass.

[0026] As for the form of the raw material BN powder, powdered BN particles with a wide peak width at half maximum (FWHM) obtained by powder X-ray diffraction measurement and low crystallinity are preferred. That is, plate-shaped h-BN can also be used as a raw material, but non-plate-shaped nanoparticles are also suitably used. As a guideline for crystallinity, the peak FWHM of the (002) plane obtained by powder X-ray diffraction measurement is usually 0.4° or more, preferably 0.45° or more, and more preferably 0.5° or more at an angle of 2θ. Also, it is usually 2.0° or less, preferably 1.5° or less, and more preferably 1° or less. When the peak FWHM of the (002) plane is below the above upper limit, crystal growth is easier to control and productivity tends to improve. When the peak FWHM of the (002) plane is above the above lower limit, the primary particle size is easier to control within an appropriate range, making it easier to control the shear adhesion force of the resulting BN aggregated powder within a desired range. In addition, dispersion stability during slurry preparation tends to improve.

[0027] From the viewpoint of BN crystal growth, it is preferable that a certain amount of oxygen atoms be present in the raw material BN powder. In the present invention, the total oxygen concentration in the raw material BN powder is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, particularly preferably 4% by mass or more, preferably 10% by mass or less, and more preferably 9% by mass or less. By keeping the total oxygen concentration below the above upper limit, crystal growth does not become excessive, and the shear adhesion force of the resulting BN aggregated powder can be controlled within an appropriate range. By keeping the total oxygen concentration above the above lower limit, residual oxygen after heat treatment is suppressed, and the effect of improving thermal conductivity is enhanced.

[0028] Methods for adjusting the total oxygen concentration of the raw material BN powder to the above range include, for example, performing the synthesis at a low temperature of 1500°C or less during BN synthesis, or heat-treating the raw material BN powder in a low-temperature oxidizing atmosphere of 500°C to 900°C. The total oxygen concentration of the raw material BN powder can be measured using an oxygen / nitrogen analyzer manufactured by Horiba, Ltd., by the inert gas fusion-infrared absorption method.

[0029] The total pore volume of the raw material BN powder is preferably 1.5 cm³. 3It is below / g, more preferably 0.3 cm 3 / g or more and 1.5 cm or less 3 / g or less, still more preferably 0.5 cm 3 / g or more and 1.5 cm or less 3 / g or less. Since the raw material BN powder is dense when the total pore volume is below the above upper limit value, granulation with a high sphericity can be achieved. When the total pore volume is above the above lower limit value, the BN agglomerated powder is appropriately deformed during the pressing of the heat dissipation sheet, and the voids in the heat dissipation sheet are reduced, so that the withstand voltage characteristics are improved.

[0030] The specific surface area of the raw material BN powder is preferably 50 m 2 / g or more, more preferably 60 m 2 / g or more, still more preferably 70 m 2 / g or more. On the other hand, it is preferably 1000 m 2 / g or less, more preferably 500 m 2 / g or less, still more preferably 300 m 2 / g or less. When the specific surface area is above the above lower limit value, it is preferable because the dispersed particle diameter in the BN slurry used for spheroidization by granulation can be reduced. Also, when the specific surface area is below the above upper limit value, it is preferable because an increase in the slurry viscosity can be suppressed.

[0031] The total pore volume of the raw material BN powder can be measured by the nitrogen adsorption method and the mercury intrusion method, and the specific surface area can be measured by the BET one-point method (adsorption gas: nitrogen).

[0032] <Medium> There is no particular limitation on the medium used for preparing the BN slurry, and water and / or various organic solvents can be used. From the viewpoints of ease of spray drying and simplification of the apparatus, it is preferable to use water, and pure water is more preferable. It is preferable to add the medium used for preparing the BN slurry in an amount such that the viscosity of the BN slurry at 25 °C is 200 to 5000 mPa·s.

[0033] Specifically, the amount of media used in preparing the BN slurry is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, preferably 70% by mass or less, more preferably 65% ​​by mass or less, and even more preferably 60% by mass or less, relative to the BN slurry. When the amount of media used is below the above upper limit, the slurry viscosity does not become too low, which suppresses sedimentation and tends to result in a more uniform BN slurry. As a result, the shear adhesion force of the resulting BN aggregated powder tends to be within the desired range. When the amount of media used is above the above lower limit, the slurry viscosity does not become excessively high, which tends to facilitate granulation.

[0034] <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 material BN powder in the slurry. As surfactants, anionic surfactants, cationic surfactants, nonionic surfactants, etc., can be used, and these may be used individually or in combination of two or more types.

[0035] When a surfactant is added, the amount of surfactant used is preferably 0.1 parts by mass or more and 5 parts by mass or less, more preferably 0.3 parts by mass or more and 4 parts by mass or less, and even more preferably 0.5 parts by mass or more and 3 parts by mass or less, per 100 parts by mass of raw material BN powder in the BN slurry. While BN slurry does not necessarily need to contain surfactants, adding surfactants to the BN slurry not only adjusts the viscosity of the BN slurry to a range suitable for granulation, but also improves the dispersion stability of the raw BN powder, making it easier to stably obtain spherical BN granulated powder of the desired size. By keeping the amount of surfactant used below the above upper limit, the viscosity of the BN slurry can be adjusted to a range suitable for granulation, while preventing the residue of surfactant during heat treatment, and resulting in high-purity agglomerated BN powder.

[0036] <Binder> The BN slurry may contain a binder in order to effectively granulate the raw material BN powder into particles. The binder acts to firmly bind the BN primary particles and stabilize the BN granulated particles. The binder used for the BN slurry may be any binder that can enhance the adhesiveness between the BN primary particles. However, in the present invention, since the BN granulated particles are heat-treated after granulation, it is preferable that the binder has heat resistance against the high-temperature conditions in this heat-treatment step.

[0037] 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 preferable from the viewpoints of thermal conductivity and heat resistance as oxides, and the binding force for binding the BN primary particles together. Note that a liquid binder such as alumina sol may be used as the binder, and it may react during the heat treatment and be converted into other inorganic components. These binders may be used alone or in combination of two or more.

[0038] The amount of the binder used (in the case of a liquid binder, the amount used as the solid content) is preferably 0 parts by mass or more and 30 parts by mass or less, more preferably 0 parts by mass or more and 20 parts by mass or less, and still more preferably 0 parts by mass or more and 15 parts by mass or less, based on 100 parts by mass of the raw material BN powder in the BN slurry. When the amount of the binder used is below the above upper limit value, crystal growth can be obtained, and when used as a filler for improving thermal conductivity, a tendency to obtain an effect of improving thermal conductivity can be obtained. When the amount of the binder used is above the above lower limit value, the binding force between the BN primary particles increases, and the withstand voltage characteristics become good because the BN agglomerated powder does not collapse and is appropriately deformed during the pressing of the heat dissipation sheet.

[0039] <BN Slurry Preparation Method> The method for preparing the BN slurry is not particularly limited as long as the raw material BN powder and medium, and optionally a binder and surfactant, are uniformly dispersed and adjusted to the desired viscosity range. However, when using raw material BN powder and medium, and optionally a binder and surfactant, it is preferably prepared as follows.

[0040] A predetermined amount of raw material 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. The mixture is stirred on a pot mill turntable for about 0.5 to 5 hours until the desired viscosity is reached. There are no particular restrictions on the order of addition, but when slurrying a large amount of raw material BN powder, agglomerates such as lumps tend to form. Therefore, an aqueous solution can be prepared by adding a surfactant and binder to water, then adding a predetermined amount of raw material BN powder in small amounts, and finally adding zirconia ceramic balls to this solution. The mixture can then be dispersed and slurryed using a pot mill turntable.

[0041] In addition to a pot mill, other dispersion devices such as a bead mill or planetary mixer may also be used for dispersion. When forming the slurry, the slurry temperature is preferably between 10°C and 60°C. Keeping the slurry temperature above the lower limit tends to suppress an increase in slurry viscosity, while keeping it below the upper limit suppresses the decomposition of the raw material BN powder into ammonia in the slurry. The slurry temperature is more preferably 15°C to 50°C, even more preferably 15°C to 40°C, and particularly preferably 15°C to 35°C.

[0042] <Granulation> To obtain BN granulated particles from BN slurry, general granulation methods such as spray drying, rolling, fluidized bed, and stirring can be used, with the spray drying method being preferred among these. In the spray drying method, BN granulated particles of a desired size can be produced by adjusting the concentration of the raw material slurry, the amount of liquid supplied per unit time to the apparatus, and the compressed air pressure and volume used when spraying the supplied slurry. It is also possible to obtain spherical BN granulated particles. There are no restrictions on the spray drying apparatus used, but for larger spherical BN granulated particles, a rotary disc type is optimal. Examples of such apparatus include the Okawara Chemical Machinery Co., Ltd. spray dryer F series, the Fujisaki Electric Co., Ltd. spray dryer "MDL-050M", and the Priss Co., Ltd. spray dryer "P260".

[0043] When the volume-based average particle size (D50) range of the BN aggregated powder of the present invention is set to be 20 μm or more and 100 μm or less, it is preferable that the volume-based average particle size (D50) of the BN granulated powder obtained by granulation be 20 μm or more and 100 μm or less. Here, the volume-based average particle size (D50) of the BN granulated powder can be measured with a device such as "Morphorogi" manufactured by Malvern.

[0044] <Heat treatment> BN aggregated powder can be produced by further heating the above-mentioned BN granulated powder under a non-oxidizing gas atmosphere. Here, a non-oxidizing gas atmosphere refers to atmospheres such as nitrogen gas, helium gas, argon gas, ammonia gas, hydrogen gas, methane gas, propane gas, and carbon monoxide gas. The crystallization rate of BN aggregated particles will differ depending on the type of atmospheric gas used. To achieve crystallization in a short time, nitrogen gas, or a mixed gas of nitrogen gas and another gas, is particularly suitable.

[0045] The heat treatment temperature is preferably 1400°C to 2300°C, more preferably 1500°C to 2000°C, and even more preferably 1600°C to 2000°C. When the heat treatment temperature is above the lower limit, sufficient growth of BN primary particles is obtained, and the thermal conductivity of the BN aggregated powder tends to increase. When the heat treatment temperature is below the upper limit, decomposition of the BN aggregated powder tends to be suppressed.

[0046] The heat treatment time is preferably 1 hour to 20 hours, and more preferably 2 hours to 15 hours. A heat treatment time above the lower limit tends to allow sufficient growth of primary BN particles, while a heat treatment time below the upper limit tends to suppress the decomposition of BN. The heat treatment is carried out under a non-oxidizing gas atmosphere, and preferably, after evacuating the furnace with a vacuum pump, the furnace is heated to the desired temperature while introducing a non-oxidizing gas. If the furnace can be sufficiently replaced with a non-oxidizing gas, the heating may be carried out under atmospheric pressure while introducing the non-oxidizing gas. Examples of furnaces include batch-type furnaces such as muffle furnaces, tubular furnaces, and atmosphere furnaces, as well as continuous furnaces such as rotary kilns, screw conveyor furnaces, tunnel furnaces, belt furnaces, pusher furnaces, and vertical continuous furnaces, which are used according to the purpose.

[0047] Typically, BN granulated powder that is heat-treated is heated and calcined in a circular crucible with a lid to reduce non-uniformity of composition during calcination. Crucible materials include boron nitride and graphite, with boron nitride being preferred from the standpoint of reducing the risk of carbon contamination.

[0048] <Classification> The BN aggregated powder after the heat treatment described above is preferably subjected to classification in order to reduce the particle size distribution and suppress the increase in viscosity when it is blended into a resin composition containing BN aggregated powder. This classification is usually performed after the heat treatment, but it may also be performed on the BN granulated particles before the heat treatment and then subjected to the heat treatment.

[0049] Classification can be performed using either a wet or dry method, but dry classification is preferred from the viewpoint of suppressing the decomposition of BN. In particular, dry classification is preferred when the binder is water-soluble. Dry classification methods include sieving classification and wind classification, which classifies particles based on the difference between centrifugal force and fluid drag. Classification can also be performed using classifiers such as swirling airflow classifiers, forced vortex centrifugal classifiers, and semi-free vortex centrifugal classifiers. Among these, a swirling airflow classifier is suitable for classifying small particles in the submicron to single-micron range, while a semi-free vortex centrifugal classifier is suitable for classifying larger particles. The appropriate classifier should be selected according to the particle size of the particles to be classified.

[0050] <Heat oxidation treatment> The BN aggregated powder after the above heat treatment may also include a step to change its surface state by reacting boron nitride with oxygen through heat oxidation treatment in an atmospheric environment. By increasing the amount of hydroxyl groups on the surface of the BN aggregated particles, the shear adhesion force increases after conditioning at a temperature of 25°C and 70% humidity for 4 hours. Therefore, the shear adhesion force of the resulting BN aggregated powder can be controlled to a desired range.

[0051] The heating oxidation treatment temperature is preferably 1000°C or higher. By setting the heating oxidation treatment temperature above the lower limit, boron nitride reacts with oxygen, changing the surface state of the BN aggregated particles. On the other hand, the heating oxidation treatment temperature is preferably less than 1200°C, more preferably 1150°C or lower, and even more preferably 1100°C or lower. By setting the heating oxidation treatment temperature below the upper limit, excessive oxidation of boron nitride can be prevented, and excessive aggregation of BN aggregated particles can be suppressed.

[0052] [BN agglomerated powder-containing resin composition] To produce the heat dissipation sheet of the present invention containing the BN agglutinated powder of the present invention, a resin composition containing at least the BN agglutinated powder of the present invention and a resin as an inorganic filler (hereinafter sometimes referred to as "the BN agglutinated powder-containing resin composition of the present invention" or "the composition of the present invention") is prepared, and the prepared composition of the present invention is formed into a sheet to produce the heat dissipation sheet of the present invention. That is, the BN agglutinated powder-containing resin composition of the present invention contains the BN agglutinated powder of the present invention. The BN agglutinated powder-containing resin composition of the present invention will be described below.

[0053] The BN aggregate powder-containing resin composition of the present invention typically comprises a resin component, preferably a thermosetting resin component, an inorganic filler containing the BN aggregate powder of the present invention, a curing agent, a curing catalyst, other components used as needed, and a solvent for forming a coating slurry. Furthermore, when forming a composite molded article as described later, the composition of the present invention preferably contains a compound having a heterocyclic structure containing nitrogen atoms, from the viewpoint of improving adhesion to metals.

[0054] [Ingredients other than BN aggregate powder] <Thermosetting resin component> The thermosetting resin included in the composition of the present invention is not particularly limited, as long as it cures in the presence of a curing agent or curing catalyst. Specific examples of thermosetting resins include epoxy resins, phenolic resins, polycarbonate resins, unsaturated polyester resins, urethane resins, melamine resins, urea resins, and the like. Among these, epoxy resins are preferred from the viewpoint of viscosity, heat resistance, hygroscopicity, and ease of handling. Examples of epoxy resins include epoxy group-containing silicon compounds, aliphatic epoxy resins, bisphenol A or F type epoxy resins, novolac type epoxy resins, alicyclic epoxy resins, glycidyl ester type epoxy resins, polyfunctional epoxy resins, and polymeric epoxy resins. The density of thermosetting resins is 0.9 to 2.0 g / cm³. 3 Preferably, 1.0 to 1.8 g / cm³ 3 More preferably, 1.1 to 1.5 g / cm³ 3This is even more preferable. If the density of the thermosetting resin is above the lower limit of the above range, the thermal conductivity of the resin is maintained and the thermal resistance at the interface with the filler is reduced, and if it is below the upper limit, the dispersibility of the filler in the resin is maintained.

[0055] (Epoxy resin) Epoxy resins are a general term for compounds that have one or more oxirane rings (epoxy groups) in their molecule. The oxirane rings (epoxy groups) in epoxy resins can be either alicyclic epoxy groups or glycidyl groups, but glycidyl groups are more preferable from the viewpoint of reaction rate or heat resistance.

[0056] The epoxy resin used in the present invention may be an aromatic oxirane ring (epoxy group) containing compound. Specific examples include bisphenol-type epoxy resins obtained by glycidly fermenting bisphenols such as bisphenol A, bisphenol F, bisphenol AD, bisphenol S, tetramethylbisphenol A, tetramethylbisphenol F, tetramethylbisphenol AD, tetramethylbisphenol S, and tetrafluorobisphenol A; biphenyl-type epoxy resins; epoxy resins obtained by glycidly fermenting divalent phenols such as dihydroxynaphthalene and 9,9-bis(4-hydroxyphenyl)fluorene; epoxy resins obtained by glycidly fermenting trisphenols such as 1,1,1-tris(4-hydroxyphenyl)methane; epoxy resins obtained by glycidly fermenting tetrakisphenols such as 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane; and novolac-type epoxy resins obtained by glycidly fermenting novolacs such as phenol novolac, cresol novolac, bisphenol A, novolac, and brominated bisphenol A novolac.

[0057] The following describes epoxy resins suitable for use in the present invention (hereinafter sometimes referred to as "high molecular weight epoxy resins") and polyfunctional epoxy resins that are preferably used in combination with these high molecular weight epoxy resins. In the following, "organic group" refers to any group containing a carbon atom, specifically including alkyl groups, alkenyl groups, aryl groups, etc., which may be substituted with halogen atoms, heteroatoms, or other hydrocarbon groups.

[0058] (High molecular weight epoxy resin) Examples of high molecular weight epoxy resins include epoxy resins having at least one structure selected from the structure represented by the following structural formula (1) (hereinafter sometimes referred to as "structure (1)") and the structure represented by the following structural formula (2) (hereinafter sometimes referred to as "structure (2)").

[0059] [ka]

[0060] (In structure (1), R 1 and R 2 Each represents an organic group, and at least one of them is an organic group with a molecular weight of 16 or more, and in structure (2), R 3 (This represents a divalent cyclic organic group.) Furthermore, examples of high molecular weight epoxy resins include epoxy resins having a structure represented by the following structural formula (3) (hereinafter sometimes referred to as "structure (3)").

[0061] [ka]

[0062] (In structure (3), R 4 , R 5 , R 6 , R 7 (Each of these represents an organic group with a molecular weight of 15 or more.)

[0063] In the above structure (1), R 1 and R 2At least one of these represents an organic group with a molecular weight of 16 or more, preferably 16 to 1000, such as alkyl groups like ethyl, propyl, butyl, pentyl, hexyl, and heptyl groups, or aryl groups like phenyl, tolyl, xylyl, naphthyl, and fluorenyl groups. 1 and R 2 Both may be organic groups with a molecular weight of 16 or more, or one may be an organic group with a molecular weight of 16 or more and the other may be an organic group or hydrogen atom with a molecular weight of 15 or less. Preferably, one is an organic group with a molecular weight of 16 or more and the other is an organic group with a molecular weight of 15 or less, and in particular, it is preferable that one is a methyl group and the other is a phenyl group, as this makes it easier to control handling properties such as resin viscosity and is preferable from the viewpoint of the strength of the resulting cured product, the heat dissipation sheet.

[0064] In structure (2), R 3 The group is a divalent cyclic organic group, and may be an aromatic ring structure such as a benzene ring structure, a naphthalene ring structure, or a fluorene ring structure, or an aliphatic ring structure such as cyclobutane, cyclopentane, or cyclohexane. Furthermore, these may independently have substituents such as hydrocarbon groups or halogen atoms. The divalent bond may be a divalent group located on a single carbon atom or on different carbon atoms. Preferably, divalent aromatic groups with 6 to 100 carbon atoms, or groups derived from cycloalkanes with 2 to 100 carbon atoms such as cyclopropane and cyclohexane are used, but the 3,3,5-trimethyl-1,1-cyclohexylene group represented by the following structural formula (4) is particularly preferred from the viewpoint of controlling handling properties such as resin viscosity and the strength of the resulting cured product, the heat dissipation sheet.

[0065] [ka]

[0066] In structure (3), R 4 , R 5 , R 6 , R 7Each of these is an organic group with a molecular weight of 15 or more, but preferably an alkyl group with a molecular weight of 15 to 1000, and especially R 4 , R 5 , R 6 , R 7 It is preferable that all of them are methyl groups from the viewpoint of controlling handling properties such as resin viscosity and the strength of the resulting cured product, the heat dissipation sheet.

[0067] The high molecular weight epoxy resin is preferably an epoxy resin that includes either structure (1) or structure (2) and structure (3) from the viewpoint of achieving both reduced hygroscopicity and strength retention of the resulting cured product, the heat dissipation sheet. Compared to typical epoxy resins with bisphenol A and bisphenol F skeletons, these high molecular weight epoxy resins contain more hydrophobic hydrocarbons and aromatic structures. By incorporating high molecular weight epoxy resins, the moisture absorption of the resulting cured heat dissipation sheet can be reduced.

[0068] Furthermore, from the viewpoint of reducing moisture absorption, it is preferable that the high molecular weight epoxy resin contains a large amount of hydrophobic structures (1), (2), and (3). Specifically, it is preferable that the epoxy resin has a mass average molecular weight of 10,000 or more, more preferably 20,000 or more, and even more preferably 30,000 to 40,000.

[0069] Furthermore, it is preferable that the high molecular weight epoxy resin is more hydrophobic. Specifically, it is preferable that the epoxy equivalent of the high molecular weight epoxy resin be large, preferably 5,000 g / equivalent or more, and more preferably 7,000 g / equivalent or more, for example, 8,000 to 15,000 g / equivalent. Here, the mass-average molecular weight of the epoxy resin is the polystyrene-equivalent value measured by gel permeation chromatography. Furthermore, epoxy equivalent is defined as "the mass of epoxy resin containing one equivalent of epoxy groups" and can be measured in accordance with JIS K7236. Such high molecular weight epoxy resins may be used individually or in combination of two or more types.

[0070] (Polyfunctional epoxy resin) A polyfunctional epoxy resin is an epoxy resin that has three or more oxirane rings (epoxy groups) per molecule. From the viewpoint of increasing the storage modulus of the heat dissipation sheet after thermosetting, and especially the storage modulus at high temperatures which is important in cases of high heat generation such as semiconductor devices, epoxy resins having three or more oxirane rings (epoxy groups) in the molecule are preferred, and epoxy resins having four or more oxirane rings (epoxy groups) in the molecule are even more preferred. Having multiple oxirane rings (epoxy groups), especially glycidyl groups, in the molecule improves the crosslinking density of the cured product, resulting in a higher strength heat dissipation sheet. As a result, when internal stress occurs in the heat dissipation sheet during processes such as reflow, the heat dissipation sheet maintains its shape without deforming or breaking, thereby suppressing the generation of voids and other air pockets within the heat dissipation sheet.

[0071] Furthermore, from the viewpoint of increasing the storage modulus of the heat dissipation sheet after thermosetting, the molecular weight of the polyfunctional epoxy resin is preferably 1,000 or less, and particularly preferably 100 to 800. Furthermore, by adding a polyfunctional epoxy resin, it is possible to introduce highly polar oxirane rings (epoxy groups) at high density, thereby increasing the effects of physical interactions such as van der Waals forces and hydrogen bonds, and improving the adhesion between the metal and the heat dissipation sheet, which is the cured product, in the composite molded body described later. In addition, by adding a polyfunctional epoxy resin, the storage modulus of the heat dissipation sheet after heat curing can be increased, so that after the cured product of the composition of the present invention penetrates the irregularities of the metal adherend, it exhibits a strong anchoring effect and improves the adhesion between the metal and the heat dissipation sheet.

[0072] On the other hand, while the introduction of a polyfunctional epoxy resin tends to increase the hygroscopicity of the composition of the present invention, improving the reactivity of the oxirane ring (epoxy group) can reduce the amount of hydroxyl groups during the reaction and suppress the increase in hygroscopicity. Furthermore, by combining the aforementioned high molecular weight epoxy resin and polyfunctional epoxy resin to produce the composition of the present invention, it becomes possible to achieve both high elasticity and low hygroscopicity in the resulting cured product, the heat dissipation sheet.

[0073] As for polyfunctional epoxy resins, specifically, for example, EX321L, DLC301, DLC402, etc., manufactured by Nagase ChemteX Corporation can be used. These polyfunctional epoxy resins may be used individually or in combination of two or more.

[0074] The composition of the present invention preferably contains a thermosetting resin component in an amount of 5 to 99% by mass, particularly 50 to 98% by mass, of 100% by mass of the composition of the present invention excluding the solvent and inorganic filler. If the content of the thermosetting resin component is above the lower limit, moldability is good, and if it is below the upper limit, the content of other components can be ensured and thermal conductivity can be improved. Furthermore, the composition of the present invention preferably contains 20 to 100% by mass, particularly 45 to 100% by mass, of epoxy resin in the thermosetting resin component.

[0075] Furthermore, the composition of the present invention preferably contains a high molecular weight epoxy resin, which is the aforementioned preferred epoxy resin, in an amount of 50% by mass or less, for example, 5 to 50% by mass, and particularly 10 to 40% by mass, of 100% by mass of the total epoxy resin. When the content of the high molecular weight epoxy resin is above the lower limit, the aforementioned effects due to the inclusion of the high molecular weight epoxy resin can be effectively obtained. On the other hand, if there is too much high molecular weight epoxy resin, the crosslinking density decreases, and the cured heat dissipation sheet becomes brittle. By keeping the content of the high molecular weight epoxy resin below the upper limit, it is possible to suppress the hygroscopicity of the cured heat dissipation sheet and improve the strength performance of the cured heat dissipation sheet, thereby achieving both performances.

[0076] Furthermore, the composition of the present invention preferably contains 5 to 50% by mass, particularly 10 to 40% by mass, of the aforementioned suitable epoxy resin, a polyfunctional epoxy resin, in the total epoxy resin by mass of 100%. When the content of the polyfunctional epoxy resin is above the lower limit, the aforementioned effects due to the inclusion of the polyfunctional epoxy resin can be effectively obtained. On the other hand, when the content of the polyfunctional epoxy resin is below the upper limit, it is possible to suppress the hygroscopicity of the cured heat dissipation sheet and improve the strength performance of the cured heat dissipation sheet, thereby achieving both of these performances.

[0077] In particular, the composition of the present invention preferably contains both a high molecular weight epoxy resin and a polyfunctional epoxy resin as the epoxy resin, in order to obtain both high elasticity and low moisture absorption of the resulting cured product, the heat dissipation sheet. In this case, the content ratio of the high molecular weight epoxy resin to the polyfunctional epoxy resin is preferably high molecular weight epoxy resin:polyfunctional epoxy resin = 10-90:90-10, and particularly preferably 20-80:80-20 (by mass).

[0078] In addition, there are no particular restrictions on the epoxy resins other than the high molecular weight epoxy resin and polyfunctional epoxy resin included in the composition of the present invention. However, one or more of the following are preferred: various bisphenol-type epoxy resins obtained by glycidly modifying bisphenols such as bisphenol A-type epoxy resin and bisphenol F-type epoxy resin; various biphenyl-type epoxy resins obtained by glycidly modifying biphenyls; epoxy resins obtained by glycidly modifying aromatic compounds having two hydroxyl groups such as dihydroxynaphthalene and 9,9-bis(4-hydroxyphenyl)fluorene; epoxy resins obtained by glycidly modifying trisphenols such as 1,1,1-tris(4-hydroxyphenyl)methane; epoxy resins obtained by glycidly modifying tetrakisphenols such as 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane; novolac-type epoxy resins obtained by glycidly modifying novolacs such as phenol novolac, cresol novolac, bisphenol A novolac, and brominated bisphenol A novolac; and silicone-containing epoxy resins. When the epoxy resin includes high molecular weight epoxy resin, polyfunctional epoxy resin, and other epoxy resins, the total content of high molecular weight epoxy resin and polyfunctional epoxy resin relative to the total epoxy resin is preferably, for example, 10 to 90% by mass, more preferably 20 to 80% by mass, even more preferably 25 to 70% by mass, and particularly preferably 30 to 60% by mass.

[0079] <Compounds having a heterocyclic structure containing nitrogen atoms> Compounds having a heterocyclic structure containing nitrogen atoms (hereinafter sometimes referred to as "nitrogen-containing heterocyclic compounds") exhibit the effect of improving the adhesion between the cured product of the composition of the present invention and the metal. That is, when the composition of the present invention and the metal are compounded, the nitrogen-containing heterocyclic compound is located at their interface, thereby improving the adhesion between the composition of the present invention and the metal. From this viewpoint, in order to facilitate the retention of the nitrogen-containing heterocyclic compound at the interface between the composition of the present invention and the metal, it is preferable that the nitrogen-containing heterocyclic compound has a low molecular weight, more preferably 1,000 or less, and even more preferably 500 or less.

[0080] Examples of heterocyclic structures that nitrogen-containing heterocyclic compounds may have include structures derived from imidazole, triazine, triazole, pyrimidine, pyrazine, pyridine, and azole. However, from the viewpoint of improving the insulating properties and adhesion to metals of the composition of the present invention, imidazole-based compounds and triazine-based compounds are preferred. Preferred imidazole and triazine compounds include, for example, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 2-phenyl-4-methylimidazole, 1-cyanoethyl-2-phenylimidazolium trimellitate, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-undecylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl- Examples include s-triazine, 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(17')]-ethyl-s-triazine, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanurate adduct, 2-phenylimidazole isocyanurate adduct, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2,4-diamino-6-vinyl-s-triazine, 2,4-diamino-6-vinyl-s-triazine isocyanurate adduct, 2,4-diamino-6-methacryloyloxyethyl-s-triazine, and 2,4-diamino-6-methacryloyloxyethyl-s-triazine isocyanurate adduct.

[0081] Among these, those with high resin compatibility and a high reaction activation temperature allow for easy adjustment of the curing speed and the physical properties of the heat dissipation sheet after curing, thereby improving the storage stability of the composition of the present invention and further improving the adhesive strength after heat molding. For this reason, those having a structure derived from imidazole and those having a structure derived from triazine are particularly preferred, and those having a structure derived from triazine are especially preferred. As for the heterocyclic structure of the nitrogen-containing heterocyclic compound, the structure derived from 1,3,5-triazine is particularly preferred. Furthermore, it is acceptable for a structure to have multiple of these exemplified structural components.

[0082] Furthermore, depending on the structure, nitrogen-containing heterocyclic compounds may contain curing catalysts as described later, and therefore, the compositions of the present invention may contain nitrogen-containing heterocyclic compounds as curing catalysts. Nitrogen-containing heterocyclic compounds may be used individually or in combination of two or more. Furthermore, a single molecule may simultaneously contain multiple heterocyclic structures.

[0083] The nitrogen-containing heterocyclic compound is preferably present in an amount of 0.001 to 10% by mass, particularly 0.1 to 5% by mass, of 100% by mass of the composition of the present invention, excluding the solvent and inorganic filler. If the curing catalyst described later is included in the nitrogen-containing heterocyclic compound due to its molecular structure, it is preferable that the total amount, including the content of the curing catalyst, is included within the above range. If the content of the nitrogen-containing heterocyclic compound is above the lower limit, the above effects due to the inclusion of this compound can be fully obtained, and if it is below the upper limit, the reaction proceeds effectively, the crosslinking density can be improved, the strength can be increased, and storage stability can be further improved.

[0084] <Hardening agent> The curing agent is not particularly limited, but preferred curing agents are phenolic resins, acid anhydrides having an aromatic or alicyclic skeleton, or aqueous additives of said acid anhydrides or modified products of said acid anhydrides. By using these preferred curing agents, a heat dissipation sheet can be obtained that has an excellent balance of heat resistance, moisture resistance, and electrical properties. The curing agent may be used alone or in combination of two or more types.

[0085] The phenolic resin is not particularly limited. Specific examples of phenolic resins include phenol novolac, o-cresol novolac, p-cresol novolac, t-butylphenol novolac, dicyclopentadiene cresol, poly-p-vinylphenol, bisphenol A type novolac, xylylene-modified novolac, decalin-modified novolac, poly(di-o-hydroxyphenyl)methane, poly(di-m-hydroxyphenyl)methane, or poly(di-p-hydroxyphenyl)methane. In particular, for further improvement of the flexibility and flame retardancy of the composition of the present invention, and for improvement of the mechanical properties and heat resistance of the cured heat dissipation sheet, novolac-type phenolic resins having a rigid main chain skeleton or phenolic resins having a triazine skeleton are preferred. Furthermore, for improvement of the flexibility of the uncured composition of the present invention and the toughness of the cured heat dissipation sheet, phenolic resins having allyl groups are preferred.

[0086] Commercially available phenolic resins include MEH-8005, MEH-8000H, and NEH-8015 (all manufactured by Meiwa Kasei Co., Ltd.), YLH903 (manufactured by Mitsubishi Chemical Corporation), LA-7052, LA-7054, LA-7751, LA-1356, and LA-3018-50P (all manufactured by Dainippon Ink & Chemicals Inc.), as well as PSM6200, PS6313, and PS6492 (manufactured by Gun-ei Chemical Industry Co., Ltd.).

[0087] Acid anhydrides having an aromatic skeleton, aqueous additives of said acid anhydrides, or modified products of said acid anhydrides are not particularly limited. Specific examples include SMA resin EF30 and SMA resin EF60 (both manufactured by Sartomer Japan), ODPA-M and PEPA (both manufactured by Manac), Ricajit MTA-10, Ricajit TMTA, Ricajit TMEG-200, Ricajit TMEG-500, Ricajit TMEG-S, Ricajit TH, Ricajit MH-700, Ricajit MT-500, Ricajit DSDA and Ricajit TDA-100 (all manufactured by Shin Nippon Rika), EPICLON B4400 and EPICLON B570 (all manufactured by Dainippon Ink and Chemicals).

[0088] The acid anhydride having an alicyclic skeleton, the aqueous additive of the acid anhydride, or the modified acid anhydride is preferably an acid anhydride having a polyalicyclic skeleton, the aqueous additive of the acid anhydride, or the modified acid anhydride, or an acid anhydride having an alicyclic skeleton obtained by an addition reaction between a terpene compound and maleic anhydride, the aqueous additive of the acid anhydride, or the modified acid anhydride. Specific examples include Ricasit HNA and Ricasit HNA-100 (both manufactured by Shin-Nippon Rika Co., Ltd.), and Epicure YH306 and Epicure YH309 (both manufactured by Mitsubishi Chemical Corporation).

[0089] The curing agent is preferably present in an amount of 0 to 70% by mass, particularly 0 to 55% by mass, of 100% by mass of the composition of the present invention, excluding the solvent and inorganic filler. If the curing agent content is above the lower limit, sufficient curing performance can be obtained, and if it is below the upper limit, the reaction proceeds effectively, improving the crosslinking density, increasing the strength, and further improving film-forming properties.

[0090] <Curing catalyst> The composition of the present invention preferably contains a curing catalyst together with the curing agent in order to adjust the curing speed and the physical properties of the cured product. The curing catalyst is not particularly limited, but is appropriately selected depending on the type of thermosetting resin component and curing agent used. Specific examples of curing catalysts include linear or cyclic tertiary amines, organophosphorus compounds, diazabicycloalkenes such as quaternary phosphonium salts or organic acid salts, and imidazole compounds. Organometallic compounds, quaternary ammonium salts, or metal halides can also be used. Examples of the above-mentioned organometallic compounds include zinc octoate, tin octoate, or aluminum acetylacetone complexes.

[0091] These may be used individually or in combination of two or more types. The curing catalyst is preferably present in an amount of 0.1 to 10% by mass, particularly 0.1 to 5% by mass, of 100% by mass of the composition of the present invention, excluding the solvent and inorganic filler. If the content of the curing catalyst is above the lower limit, the curing reaction can be sufficiently promoted to achieve good curing, and if it is below the upper limit, the curing rate will not be too fast, and therefore the storage stability of the composition of the present invention can be improved.

[0092] <Other ingredients> The composition of the present invention may contain other components besides the inorganic filler, to the extent that they do not impair the effects of the present invention. Other components include surface treatment agents such as silane coupling agents that improve the interfacial adhesion strength between the inorganic filler and the resin component when manufacturing a heat dissipation sheet, which is a cured product, using the composition of the present invention; insulating carbon components such as reducing agents; viscosity modifiers; dispersants; thixotropic agents; flame retardants; colorants; organic fillers; organic solvents; and thermoplastic resins.

[0093] Among these, the inclusion of a dispersant makes it possible to form a uniformly cured heat dissipation sheet, and in some cases improves the thermal conductivity and dielectric strength of the resulting heat dissipation sheet. Furthermore, the inclusion of organic fillers or thermoplastic resins can impart appropriate elongation to the composition of the present invention, alleviate the resulting stress, and suppress the occurrence of cracks during temperature cycling tests.

[0094] The dispersant preferably has a functional group containing hydrogen atoms that have hydrogen bonding properties. By having a functional group containing hydrogen atoms that have hydrogen bonding properties in the dispersant, the thermal conductivity and dielectric strength of the resulting cured product, the heat dissipation sheet, can be further improved. Examples of the functional group containing hydrogen atoms that have hydrogen bonding properties include a carboxyl group (pKa=4), a phosphate group (pKa=7), or a phenol group (pKa=10).

[0095] The pKa of the functional group containing hydrogen atoms with hydrogen bonding properties is preferably in the range of 2 to 10, and more preferably in the range of 3 to 9. When the pKa is above the lower limit, the acidity of the dispersant is within an appropriate range, and the reaction of the epoxy resin in the thermosetting resin component may be suppressed. Therefore, when the molded product is stored in an uncured state, the storage stability tends to improve. When the pKa is 10 or less, the function as a dispersant is fully performed, and the thermal conductivity and dielectric strength characteristics of the resulting cured product, the heat dissipation sheet, tend to be sufficiently enhanced.

[0096] The functional group containing hydrogen atoms that have hydrogen bonding properties is preferably a carboxyl group or a phosphate group. In this case, the thermal conductivity and dielectric strength characteristics of the heat dissipation sheet can be further improved. Examples of dispersants include polyester carboxylic acids, polyether carboxylic acids, polyacrylic carboxylic acids, aliphatic carboxylic acids, polysiloxane carboxylic acids, polyester phosphoric acids, polyether phosphoric acids, polyacrylic phosphoric acids, aliphatic phosphoric acids, polysiloxane phosphoric acids, polyester phenols, polyether phenols, polyacrylic phenols, or polysiloxane phenols. A single dispersant may be used, or two or more may be used in combination.

[0097] Any thermoplastic resin that is generally known can be used as the thermoplastic resin, but specifically, for example, it may be polyethylene, polypropylene, polystyrene, polyvinyl chloride, (meth)acrylic resin, vinyl polymers such as ethylene-vinyl acetate copolymer and ethylene-vinyl alcohol copolymer, polylactic acid resin, polyesters such as polyethylene terephthalate and polybutylene terephthalate, nylon, polyamides such as polyamidoamine, polyvinyl acetal resins such as polyvinyl acetal, polyvinyl benzal and polyvinyl butyral resin, ionomer resin, polyphenylene ether, polyphenylene sulfide, polycarbonate, polyether ether ketone, polyacetal, ABS resin, LCP (liquid crystal polymer), fluororesin, urethane resin, silicone resin, various elastomers, or modified products of these resins.

[0098] These thermoplastic resins may be uniform in the resin phase of the heat dissipation sheet, or they may undergo phase separation and their shape may be recognizable. If they undergo phase separation, the shape of the thermoplastic resin in the heat dissipation sheet may be particulate or fibrous. In this way, when the shape of the thermoplastic resin is recognizable in the heat dissipation sheet, the thermoplastic resin may be recognized as an organic filler. However, in this invention, organic fillers refer to natural products such as wood flour, modified cellulose, starch, various organic pigments, etc., and thermoplastic resins are not included in organic fillers.

[0099] The inclusion of thermoplastic resins and organic fillers can impart appropriate elongation to the composition of the present invention, alleviate the resulting stress, and suppress the occurrence of cracks during temperature cycling tests. When thermoplastic resins or organic fillers are insoluble in thermosetting resins, the viscosity of the composition of the present invention does not increase, and the smoothness of the sheet surface can be improved, for example, when it is molded into a sheet as described later. In this case, by mixing thermoplastic resins and organic fillers insoluble in thermosetting resins with a large amount of inorganic fillers at the same time, the thermoplastic component phase that improves elongation can be efficiently dispersed in the heat dissipation sheet, which is the cured product, and stress can be easily relieved. Therefore, it is possible to suppress the occurrence of cracks in the heat dissipation sheet, which is the cured product, without lowering the elastic modulus of the heat dissipation sheet, which is the cured product. For these reasons, polyamide resins such as nylon and cellulose resins are preferred as thermoplastic resins, and polyamide resins such as nylon are particularly preferred.

[0100] When the thermoplastic resin observed in the cured heat dissipation sheet is particulate, the upper limit of its average particle diameter is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 30 μm or less. By keeping the average particle diameter below the above upper limit, heat dissipation sheets of various thicknesses can be manufactured without the risk of a decrease in thermal conductivity. The average particle diameter of the particulate thermoplastic resin is determined by observing the cross-section of the cured heat dissipation sheet and using the average value of the longest diameters of any 20 particles.

[0101] <Solvent> The composition of the present invention may contain a solvent, for example, to improve the applicability when forming a heat dissipation sheet, which is a cured product, through a coating process. Examples of solvents that may be contained in the composition of the present invention include organic solvents such as methyl ethyl ketone, cyclohexanone, propylene glycol monomethyl ether acetate, butyl acetate, isobutyl acetate, and propylene glycol monomethyl ether. These organic solvents may be used individually or in combination of two or more.

[0102] If the composition of the present invention contains an organic solvent, its content is appropriately determined according to factors such as ease of handling during the production of the heat dissipation sheet. Generally, it is preferable to use the organic solvent such that the solid content (total of components other than the solvent) concentration in 100% by mass of the composition of the present invention is 10 to 90% by mass, and particularly 40 to 80% by mass.

[0103] [Inorganic filler] The composition of the present invention contains at least the BN aggregate powder of the present invention as an inorganic filler. The composition of the present invention may contain inorganic fillers other than the BN aggregate powder of the present invention, in which case spherical fillers are preferred as inorganic fillers other than the BN aggregate powder of the present invention.

[0104] The spherical filler used with the BN aggregated powder of the present invention preferably has a thermal conductivity of 10 W / m·K or higher, more preferably 15 W / m·K or higher, and even more preferably 20 W / m·K or higher. Furthermore, its new Mohs hardness is preferably 3.1 or higher, more preferably 5 or higher. In particular, a thermal conductivity of 20-30 W / m·K and a new Mohs hardness of 5-10 are preferred. By using such a spherical filler in combination with the BN aggregated powder of the present invention, the adhesion strength to metal and heat dissipation properties of the resulting heat dissipation sheet can be improved.

[0105] Here, "spherical" simply means something that is generally recognized as spherical. For example, an object with an average circularity of 0.4 or higher may be considered spherical, or an object with an average circularity of 0.6 or higher may be considered spherical. The upper limit for average circularity is usually 1. Circularity can be measured by image processing of its projected image, for example, using Sysmex's FPIA series. The spherical filler is preferably at least one selected from the group consisting of alumina, synthetic magnesite, crystalline silica, aluminum nitride, silicon nitride, silicon carbide, zinc oxide, and magnesium oxide, and more preferably alumina. The use of these preferred spherical fillers can further enhance the heat dissipation performance of the resulting heat dissipation sheet.

[0106] The average particle size (D50) of the spherical filler is preferably within the range of 0.5 μm to 40 μm. A D50 average particle size above the lower limit allows the resin and inorganic filler to flow easily during heat molding, thereby improving the interfacial adhesion of the heat dissipation sheet. Furthermore, a D50 average particle size below the upper limit makes it easier to maintain the dielectric strength of the heat dissipation sheet.

[0107] Other inorganic fillers that are electrically insulating can be used, and include at least one particle selected from the group consisting of carbon, metal carbides, metal oxides, and metal nitrides. An example of carbon is diamond. Examples of metal carbides include silicon carbide, titanium carbide, and tungsten carbide. Examples of metal oxides include magnesium oxide, aluminum oxide, silicon oxide, calcium oxide, zinc oxide, yttrium oxide, zirconium oxide, cerium oxide, ytterbium oxide, and SiAlON (ceramics composed of silicon, aluminum, oxygen, and nitrogen). Examples of metal nitrides include boron nitride, aluminum nitride, and silicon nitride, other than the BN aggregated particles of the present invention.

[0108] There are no restrictions on the shape of other inorganic fillers; they may be particulate, whisker-like, fibrous, plate-like, or aggregates thereof. These inorganic fillers may be surface-treated with a surface treatment agent. Any known surface treatment agent can be used. These inorganic fillers may be used individually or mixed in any combination and ratio of two or more types.

[0109] The inorganic filler content in the composition of the present invention is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more, based on 100% by mass of the composition of the present invention excluding the solvent. Furthermore, it is preferably 99% by mass or less, more preferably 90% by mass or less, and even more preferably 80% by mass or less. By having an inorganic filler content above the lower limit mentioned above, the effects of improved thermal conductivity and control of the coefficient of linear expansion due to the inclusion of inorganic fillers can be fully obtained. Furthermore, by having an inorganic filler content below the upper limit mentioned above, the moldability of the cured heat dissipation sheet and the interfacial adhesion of the composite molded product described later tend to be obtained.

[0110] When using the BN aggregated powder of the present invention in combination with a spherical filler such as alumina as an inorganic filler, the content ratio of the BN aggregated powder of the present invention to the spherical filler in the composition of the present invention is not particularly limited, but it is preferably 90:10 to 10:90 by mass ratio, and preferably 80:20 to 20:80. Furthermore, in order to effectively obtain the effects of using the BN aggregated powder of the present invention, it is preferable that 30% by mass or more, and particularly 40% by mass or more, of the inorganic filler used is the BN aggregated powder of the present invention. In the present invention, it is preferable to use only the BN aggregated powder of the present invention or only the BN aggregated powder of the present invention and the above-mentioned spherical filler as the inorganic filler.

[0111] <Method for producing the composition of the present invention> The composition of the present invention can be obtained by uniformly mixing, for example, an inorganic filler containing the BN aggregate powder of the present invention, a resin component such as a thermosetting resin, and other components added as needed, by stirring or kneading. For mixing, a general kneading device such as a mixer, kneader, single-screw or twin-screw kneader can be used, and heating may be used during mixing as needed.

[0112] The mixing order of each component is arbitrary as long as there are no particular problems such as reactions or precipitate formation. For example, one method involves mixing and dissolving a thermosetting resin component in an organic solvent (e.g., methyl ethyl ketone) to prepare a resin solution, then adding a thoroughly mixed inorganic filler and other components as needed to the resulting resin solution and mixing it. After that, an organic solvent is added and mixed to adjust the viscosity, and finally, additives such as a curing agent, curing catalyst, nitrogen-containing heterocyclic compound, or dispersant are added and mixed.

[0113] [Heat dissipation sheet] The heat dissipation sheet of the present invention is made of the BN aggregate powder-containing resin composition of the present invention. A method for producing the heat dissipation sheet of the present invention as a sheet-like cured product using the composition of the present invention is described below. Sheet-like cured products can be manufactured by commonly used methods. For example, they can be obtained by forming the composition of the present invention into a sheet and curing it.

[0114] The composition of the present invention can be formed into a sheet using a generally accepted method. For example, if the composition of the present invention has plasticity or fluidity, it can be molded into a desired shape by curing it, for example, while it is contained in a mold. In this case, injection molding, injection compression molding, extrusion molding, compression molding, and vacuum compression molding can be used.

[0115] The solvent in the composition of the present invention can be removed by known heating methods such as a hot plate, hot air furnace, IR heating furnace, vacuum dryer, or high-frequency heater. Furthermore, a sheet-like cured product can also be obtained by cutting the cured product of the composition of the present invention into a desired shape. Sheet-like cured products can also be obtained by forming a slurry of the composition of the present invention (hereinafter sometimes referred to as "sheet slurry") into a sheet using methods such as the doctor blade method, solvent casting method, or extrusion film formation method. The following describes an example of a method for producing a sheet-like cured product using this sheet slurry.

[0116] <Coating process> First, a coating film is formed on the surface of the substrate using a sheet slurry. Specifically, a coating film is formed on the substrate using a sheet slurry by a dip method, spin coating method, spray coating method, blade method, or any other method. For applying the sheet slurry, coating equipment such as a spin coater, slit coater, die coater, or blade coater can be used, making it possible to uniformly form a coating film of a predetermined thickness on the substrate. While metal plates and polyethylene terephthalate (PET) films, as described later, are commonly used as substrates, they are not limited to these materials.

[0117] <Drying process> The coating film formed by applying the sheet slurry is typically dried at a temperature of 10 to 150°C, preferably 25 to 120°C, and more preferably 30 to 110°C, to remove solvents and low molecular weight components. A drying temperature below the upper limit suppresses the hardening of the thermosetting resin in the slurry, allowing the resin to flow more easily during the subsequent pressing process and facilitating the removal of voids. A drying temperature above the lower limit effectively removes the solvent. The drying time is typically 5 minutes to 10 days, preferably 10 minutes to 3 days, more preferably 20 minutes to 1 day, and even more preferably 30 minutes to 4 hours. A drying time above the lower limit tends to allow for sufficient removal of the solvent and suppress the formation of voids in the sheet-like cured product by residual solvent. A drying time below the upper limit tends to improve productivity and reduce manufacturing costs.

[0118] <Pressurization process> After the drying process, it is desirable to perform a pressurization process for the purposes of bonding inorganic fillers together to form heat paths, eliminating voids and air gaps within the sheet, and improving adhesion to the substrate. The pressurization process involves applying 10 kgf / cm² to the dried film on the substrate. 2 It is desirable to carry out the process with the above load. The load is preferably 20 kgf / cm². 2 The above is a more favorable 50 kgf / cm². 2 That concludes the explanation. Furthermore, a load of 2000 kgf / cm² is preferable. 2The following, and more preferably 1000 kgf / cm² 2 More preferably 800 kgf / cm² 2 The following applies: By keeping the applied pressure below the upper limit, the secondary particles of the inorganic filler do not break, and a sheet with high thermal conductivity and no voids can be obtained. Furthermore, by keeping the pressure above the lower limit, contact between the inorganic fillers improves, making it easier to form heat conduction paths, thus resulting in a sheet with high thermal conductivity.

[0119] In the pressurizing process, it is desirable to heat the dry film on the substrate to 25°C or higher. This heating temperature is preferably 40°C or higher, more preferably 50°C or higher, and even more preferably 60°C or higher. It is also desirable to heat it to 300°C or lower, preferably 250°C or lower, more preferably 200°C or lower, and even more preferably 180°C or lower. By performing the pressurizing process within this temperature range, the melt viscosity of the resin in the coating can be reduced, eliminating voids and air pockets within the sheet. If the temperature is below the upper limit of this temperature range, there is a risk that organic components may decompose or residual solvents may vaporize and form voids.

[0120] The pressurization process typically lasts 30 seconds or more, preferably 1 minute or more, more preferably 3 minutes or more, and even more preferably 5 minutes or more. It is also preferably 4 hours or less, more preferably 2 hours or less, even more preferably 1 hour or less, and particularly preferably 45 minutes or less. A pressurization time below the above upper limit tends to reduce the manufacturing time of the sheet-like cured product and lower production costs. On the other hand, a pressurization time above the above lower limit tends to sufficiently remove voids and air pockets within the sheet-like cured product, improving heat transfer performance and dielectric strength.

[0121] <Curing process> The curing process, which involves a complete hardening reaction, may be carried out under pressure or without pressure. However, if pressure is used, it is desirable to carry it out under the same conditions as the pressure process described above, for the same reasons as above. The pressure process and the curing process may also be carried out simultaneously. In particular, in the sheet formation process which involves a pressurizing process and a curing process, it is preferable to apply a load within the above range when performing the pressurizing and curing.

[0122] There are no particular restrictions on the thickness of the heat dissipation sheet of the present invention, which is a sheet-like cured product formed in this manner, but it is preferably 50 μm or more, more preferably 100 μm or more. It is also preferably 400 μm or less, and more preferably 300 μm or less. When the thickness of the heat dissipation sheet is above the lower limit, dielectric strength characteristics are obtained and the dielectric breakdown voltage tends to improve. When the thickness is below the upper limit, miniaturization and thinning of the device can be achieved and the thermal resistance of the resulting heat dissipation sheet tends to be suppressed.

[0123] [Composite molded body] The heat dissipation sheet of the present invention can be used as a composite molded body formed by laminating and integrating the heat dissipation sheet of the present invention with a metal part. In this case, the metal part may be provided on only one surface of the heat dissipation sheet of the present invention, or on two or more surfaces. For example, the heat dissipation sheet of the present invention may have a metal part on only one surface, or it may have metal parts on both surfaces. Furthermore, the metal part may be patterned.

[0124] Such a composite molded body can be manufactured by using the metal part as the base material and forming a sheet-like cured material made of the composition of the present invention on this base material according to the method described above. Alternatively, it can also be manufactured by peeling off a sheet-like cured material formed on a base material separate from the metal part, and then heat-pressing it onto a metal member that will become the metal part. In this case, a sheet-like cured product made of the composition of the present invention can be formed in the same manner as described above, except that it is applied to a substrate such as a PET film which may have been treated with a release agent. After that, the sheet-like cured product can be peeled off the substrate, placed on another metal plate, or sandwiched between two metal plates and pressed together to form a single unit.

[0125] In this case, as the metal plate, a metal plate having a thickness of about 10 to 10,000 μm made of copper, aluminum, nickel-plated metal, or the like can be used. The surface of the metal plate may be physically roughened or chemically treated with a surface treatment agent or the like. From the viewpoint of adhesion between the resin composition and the metal plate, it is more preferable that these treatments are performed.

[0126] 〔Semiconductor device〕 The semiconductor device of the present invention is one in which the heat dissipation sheet of the present invention is mounted as a heat dissipation substrate, that is, it includes the heat dissipation sheet of the present invention. Due to its high heat conduction and breakdown voltage characteristics, high output and high density can be achieved with high reliability. In the semiconductor device, members such as aluminum wiring, encapsulant, package material, heat sink, thermal paste, and solder other than the heat dissipation sheet of the present invention can be appropriately adopted as conventionally known members.

Examples

[0127] Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples as long as the gist thereof is not exceeded. Note that the various conditions and the values of the evaluation results in the following examples indicate the preferable ranges in the embodiments of the present invention, and the preferable range of the present invention can be determined in consideration of the preferable ranges in the above-described embodiments and the ranges indicated by the values in the following examples or combinations of the values of the examples.

[0128] [Measurement conditions] The various characteristics and physical properties in the following examples and comparative examples were measured by the methods described below.

[0129] <Shearing adhesion force of BN agglomerated powder> The BN agglomerated powder obtained in the examples and comparative examples was placed in a thermo-hygrostat (KCL-2000 manufactured by Tokyo Rikakikai Co., Ltd.) and left standing at 25 °C and 70% humidity for 4 hours, and this was used as a measurement sample. The shear test evaluation of this measurement sample was carried out using the "Powder Rheometer FT4" manufactured by Spectris. Specifically, this measurement sample was filled into a measurement container with an outer diameter of 25 mm and a volume of 10 mL. After flattening the upper surface of the powder layer, shear was started under the condition of a pre-pressure of 15 kPa, and the powder layer failure envelope was measured. Then, the shear adhesion force was calculated from the intersection of the powder layer failure envelope and the shear stress axis.

[0130] <Average particle diameter (D50) of BN agglomerated powder> 0.05 g of BN agglomerated particles were dispersed in 20 mL of a pure water medium containing naphthalene sulfonate - formalin condensate as a dispersion stabilizer. At this time, ultrasonic treatment was performed for 30 seconds at 15 W using an ultrasonic disperser (homogenizer). For this dispersed sample, the volume - based particle size distribution was measured in a batch cell type of a laser diffraction / scattering type particle size distribution measuring device "LA - 300" (manufactured by Horiba, Ltd.), and the cumulative volume 50% particle diameter (average particle diameter (D50)) was determined from the obtained particle size distribution.

[0131] <Evaluation of coating property of coating slurry> Regarding the coating slurry prepared to a solid content concentration of 62.8% by mass (the same as the coating slurry described in Example 5 below), the presence or absence of fluidity and the presence or absence of lumps were visually evaluated, and evaluated as the coating property during the production of the heat - dissipation sheet according to the following criteria. ◎(very good): It has fluidity, and there is no or little lump, so it can be coated without dilution. The coating property of the slurry is good. ○(good): It has fluidity, but there are some lumps. It cannot be coated without dilution, but it can be coated when the solid content concentration in the coating slurry is diluted to 52% by mass. The coating property of the slurry is good. △(fair): It has poor fluidity and many lumps. It cannot be coated when the solid content concentration in the coating slurry is diluted to 52% by mass, but it can be coated when diluted to 43% by mass. The coating property of the slurry is good. ×(poor): It has no fluidity or many lumps. It cannot be coated when the solid content concentration in the coating slurry is diluted to 43% by mass. The coating property of the slurry is poor.

[0132] <Mandrel Test of Heat Dissipation Sheet> The sheet-shaped molded bodies obtained in the examples and comparative examples were cut into strips of 2 cm × 15 cm, and these were used as measurement samples. Regarding this measurement sample, in accordance with JIS K 5600-5-1, the flexibility was evaluated using a cylindrical mandrel bending tester. When the measurement sample was wound around the test bar, the maximum diameter (integer value, mm) at which cracking or peeling occurred was measured.

[0133] <Breakdown Voltage (BDV) of Heat Dissipation Sheet> The sheet-shaped molded bodies obtained in the examples and comparative examples were placed on a copper plate with a thickness of 2 mm, and temporarily adhered to the copper plate under the pressing conditions of 20 kgf / cm 2 , 80 °C, and 5 minutes. Then, a sheet-shaped cured product (heat dissipation sheet) was obtained by thermally curing the sheet-shaped molded body under the pressing conditions of 100 kgf / cm 2 , 175 °C, and 40 minutes. The withstand voltage of the heat dissipation sheet was measured in a fluorine-based inert liquid (manufactured by 3M, product name "Fluorinert FC-40") using a cylindrical electrode. The withstand voltage characteristics were obtained by increasing the voltage by 500 V every minute, and the characteristic value was taken when a current of 10 mA or more flowed through the heat dissipation sheet.

[0134] [Preparation of BN Agglomerated Powder from BN Slurry] The BN agglomerated powder used in the following examples and comparative examples was prepared by the following method.

[0135] [Preparation of BN Slurry] [Examples 1 to 4 and Comparative Examples 1 to 6] Raw material h-BN powder (the half-value width of the (002) plane peak obtained by powder X-ray diffraction measurement is 2θ = 0.67°, total oxygen concentration = 7.5 mass%, specific surface area 116 m 2 / g, total pore volume 0.754 cm 3 / g). Usage amount: 10000 g. Binder ("Taxelam M160L" manufactured by Takagi Chemical Co., Ltd., basic aluminum lactate aqueous solution, solid content concentration 21 mass%). Usage amount: 11496 g. Surfactant (surfactant "ammonium lauryl sulfate" manufactured by Kao Corporation, aqueous solution with a solid content concentration of 14% by mass). Usage amount: 250 g.

[0136] (Preparation of slurry) Weighed a predetermined amount of raw material h-BN powder into a resin bottle, and then added a predetermined amount of binder (solid content 21% by mass). Furthermore, after adding a predetermined amount of surfactant, zirconia ceramic balls were added, and it was stirred on a pot mill turntable for 1 hour to prepare a BN slurry with a viscosity of 200 - 2000 mPa·s at 25°C. Note that pure water was added as necessary to adjust the viscosity.

[0137] <Granulation> BN granulated powder was produced from the BN slurry using the spray drying method. Specifically, using "spray dryer P260" manufactured by Pulvis Co., Ltd., granulation was carried out at a disk rotation speed of 8000 - 20000 rpm and a drying temperature of 85°C.

[0138] <Production of BN agglomerated powder> After pre-firing (700°C, 5 hours) the above BN granulated powder, the powder after pre-firing was heat-treated by the following method. In Examples 1 - 4 and Comparative Examples 3 - 6, after the first firing and re-firing were carried out under N2 flow, firing in an air atmosphere (air firing) was carried out to obtain BN agglomerated powder. In Comparative Examples 1 and 2, the first firing and re-firing were carried out under N2 flow to obtain BN agglomerated powder. Firing in an air atmosphere was not carried out.

[0139] [First firing] Firing was carried out under N2 flow using a vacuum firing furnace. 50 g of the powder after pre-firing was filled into a graphite crucible (φ60 mm with lid) and placed inside a BN inner crucible. The BN inner crucible was set in the vacuum firing furnace and heated at a heating rate of 450°C / hr to the first firing temperature under N2 flow. Then, after heat treatment at the firing temperature shown in Table 1 for 20 hours, it was heated at a heating rate of 90°C / hr to 2000°C, held for 5 hours, and after natural cooling, the powder in the crucible was recovered.

[0140] [Classification] The powder after the above heat treatment was subjected to air classification. Air classification was performed using an AC-15 manufactured by Nisshin Engineering Co., Ltd., and the powder was classified into particles smaller than 100 μm and particles larger than 100 μm.

[0141] [Re-firing] After the classification described above, 30 g of powder smaller than 100 μm was packed into a newly prepared BN crucible (φ60 mm with lid) and placed inside a BN internal crucible. The BN internal crucible was set in a vacuum firing furnace and heated under N2 flow at a heating rate of 1200 °C / hr until it reached the re-firing temperature shown in Table 1. Subsequently, heat treatment was performed at the re-firing temperature shown in Table 1 for 2 hours. After natural cooling, the powder in the crucible was recovered.

[0142] [Air firing] The BN agglomerated powders used in Examples 1-4 and Comparative Examples 3-6 were calcined in an air atmosphere. The re-calcined powder was filled into the calcination containers shown in Table 1 (alumina calcination dish (φ70mm with lid, purity 99.5% or higher) or BN crucible (φ60mm with lid)) by the weights (amount of powder to be added, in units: g) shown in Table 1. These containers were then placed in a small electric furnace (Motoyama "Super Burn RH2035D") and heated to the air calcination temperature shown in Table 1 at a heating rate of 5°C / min while circulating air at a flow rate of 5 L / min. After that, heat treatment was carried out at the air calcination temperature shown in Table 1 for 2 hours. After natural cooling, the powder in the calcination containers was recovered.

[0143] The conditions for preparing the BN aggregated powder are summarized in Table 1. Scanning electron microscopy (SEM) observation confirmed that the BN aggregated powders of Examples 1-4 and Comparative Examples 1-6 were all aggregates of BN aggregated particles having a cardhouse structure.

[0144] [Table 1]

[0145] [Fabrication and evaluation of sheet-like molded bodies] In the following Examples and Comparative Examples, the BN agglomerated powder obtained above was used as an inorganic filler, respectively, and a resin composition containing the BN agglomerated powder was prepared by the following method, and a sheet-shaped molded body was produced.

[0146] <Preparation of Resin Composition Containing BN Agglomerated Powder> The raw materials used were as follows.

[0147] (Thermosetting resin component) · Resin component 1: A high molecular weight epoxy resin disclosed as resin component 1 in JP-A-2020-63438, manufactured by Mitsubishi Chemical Corporation, mass average molecular weight in terms of polystyrene: 30,000, epoxy equivalent: 9,000 g / equivalent, density: about 1.2 g / cm 3 . Having the structural formula (2) and the structural formula (3), R in the structural formula (2) 3 is the structural formula (4), and R in the structural formula (3) 4 , R 5 , R 6 , R 7 are all methyl groups, an epoxy resin. · Resin component 2: A polyfunctional epoxy resin containing a structure having 4 or more glycidyl groups per molecule, manufactured by Nagase ChemteX Corporation, molecular weight: about 400, epoxy equivalent: 100 g / equivalent, density: about 1.2 g / cm 3 . · Resin component 3: A biphenyl-type solid epoxy resin manufactured by Mitsubishi Chemical Corporation, having 2 glycidyl groups per molecule, molecular weight: about 400, epoxy equivalent: 200 g / equivalent, density: about 1.2 g / cm 3 .

[0148] (Inorganic filler component) · Inorganic filler 1: BN agglomerated powder obtained in each example. · Inorganic filler 2: Aluminum oxide particles, spherical alumina, volume average particle diameter (D50): 8.8 μm, thermal conductivity: 20 - 30 W / m·K.

[0149] (Hardener component) · Hardener 1: "MEH-8000H" manufactured by Meiwa Kasei Co., Ltd., a phenolic resin-based hardener.

[0150] (Curing catalyst component) • Curing catalyst 1: "2E4MZ-A" manufactured by Shikoku Chemicals, 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(17')]-ethyl-s-triazine (having both structures derived from imidazole and structures derived from triazine in one molecule), molecular weight: 247, properties: solid, melting point: 215-225℃. • Curing catalyst 2: "2PHZ-PW" manufactured by Shikoku Chemicals, 2-phenyl-4,5-dihydroxymethylimidazole, molecular weight: 204, properties: solid, melting point: dec. 230, therefore the melting point is 230°C or higher.

[0151] <Example 5> Using a rotation-and-revolving stirring device, a mixture was prepared with the following proportions: 6 parts by mass of resin component 1, 5 parts by mass of resin component 2, 10 parts by mass of resin component 3, 3.5 parts by mass of curing agent 1, 0.25 parts by mass of curing catalyst 1, 0.25 parts by mass of curing catalyst 2, 54 parts by mass of inorganic filler 1 (BN aggregated powder obtained in Example 1), and 20 parts by mass of inorganic filler 2. In addition, when preparing the above mixture, methyl ethyl ketone and cyclohexanone were added so that the above mixture constituted 62.8% by mass (solid content concentration) of the coating slurry, and the mixture was mixed using a rotation-and-revolving stirring device to prepare the coating slurry.

[0152] The resulting coating slurry (sheet slurry) was applied to a PET substrate using the doctor blade method, then heated and dried at 60°C for 120 minutes, followed by drying at 42°C and 1500 kgf / cm². 2 The mixture was pressed for 10 minutes to obtain a sheet-like molded body with a thickness of 150 μm. The total content of methyl ethyl ketone and cyclohexanone in the sheet-like molded body was 1% by mass or less. Table 2 shows the shear adhesion strength and average particle size (D50) of the BN aggregated powder used. Table 2 also shows the coatability, mandrel test results, and dielectric breakdown voltage (BDV) of the heat dissipation sheet obtained using the BN aggregated powder. In the mandrel test results in Table 2, "<4" means that neither cracking nor delamination occurred even when the diameter of the test rod was reduced to 4 mm.

[0153] <Example 6 and Comparative Examples 7-8> Table 2 shows the evaluation results of heat dissipation sheets prepared according to the method of Example 5, but with only the BN aggregated powder replaced with the one shown in Table 2. The shear adhesion force of the BN aggregated powder used is also shown in Table 2.

[0154] <Example 7> Table 2 shows the evaluation results of a heat dissipation sheet prepared by diluting the solid content concentration to 52% by mass, with only the BN aggregated powder being replaced with the one shown in Table 2, in accordance with the method of Example 5. The shear adhesion strength of the BN aggregated powder used is also shown in Table 2.

[0155] <Example 8> Table 2 shows the evaluation results of a heat dissipation sheet prepared by diluting the solid content concentration to 43% by mass, with only the BN aggregated powder being replaced with the one shown in Table 2, in accordance with the method of Example 5. The shear adhesion strength of the BN aggregated powder used is also shown in Table 2.

[0156] <Comparative Examples 9-12> Table 2 shows the evaluation results of a heat dissipation sheet prepared by diluting the solid content concentration to 40% by mass, with only the BN aggregated powder being replaced with the one shown in Table 2, in accordance with the method of Example 5. The shear adhesion strength of the BN aggregated powder used is also shown in Table 2.

[0157] [Table 2]

[0158] Table 2 shows that in Examples 5-8, which used BN aggregated powder from Examples 1-4 with a shear adhesion force of 0.40-1.5 kPa, the coating properties during the manufacture of the heat dissipation sheets were good. Furthermore, the heat dissipation sheets from Examples 5-8, which used BN aggregated powder from Examples 1-4, showed a small maximum diameter (mm) at which cracking or peeling occurred in the mandrel test, indicating that they were less prone to cracking and had excellent handling properties. In addition, the high dielectric breakdown voltage (BDV) indicates that these heat dissipation sheets had good dielectric strength characteristics. On the other hand, in Comparative Examples 7 and 8, which used BN aggregate powder in Comparative Examples 1 and 2 with a shear adhesion force of less than 0.40 kPa, although the coating properties during the production of the heat dissipation sheet were good, the mandrel test results showed that the heat dissipation sheet was prone to cracking. Furthermore, in Comparative Examples 9-12, which used BN aggregate powder with a shear adhesion force exceeding 1.5 kPa, it was found that the coating properties during the manufacture of the heat dissipation sheet were poor. Therefore, by using BN aggregate powder with a specific range of shear adhesion, it is possible to realize a heat dissipation sheet that has good coating properties during manufacturing, is resistant to cracking, and has good voltage resistance characteristics.

Claims

1. It contains hexagonal boron nitride aggregate particles, Boron nitride aggregate powder having a shear adhesion force of 0.40 kPa or more and 1.5 kPa or less after being conditioned for 4 hours at a temperature of 25°C and 70% humidity.

2. The boron nitride aggregate powder according to claim 1, wherein the shear adhesion force is 1.0 kPa or less.

3. The boron nitride aggregate powder according to claim 1, wherein the average particle size (D50) is 20 μm or more and 100 μm or less.

4. The boron nitride aggregate powder according to claim 1, wherein the hexagonal boron nitride aggregate particles have a cardhouse structure.

5. A resin composition comprising boron nitride aggregate powder according to any one of claims 1 to 4 and a resin.

6. The resin composition according to claim 5, wherein the resin comprises an epoxy resin.

7. A heat dissipation sheet obtained by molding the resin composition described in claim 5.

8. A semiconductor device comprising the heat dissipation sheet described in claim 7.

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