JP7467980B2 - Boron nitride agglomerated powder, heat dissipation sheet, and method for manufacturing semiconductor device - Google Patents

Description

The present invention relates to a boron nitride agglomerated powder suitable for use in heat dissipation sheets for semiconductor devices, a heat dissipation sheet containing the boron nitride agglomerated powder, and a semiconductor device using this heat dissipation sheet.

Boron nitride (BN) is an insulating ceramic, and various crystal types are known, such as c-BN with a diamond structure, h-BN with a graphite structure, α-BN with a turbostratic structure, and β-BN.
Among these, h-BN has the same layered structure as graphite, is relatively easy to synthesize, and has excellent thermal conductivity, solid lubricity, chemical stability, and heat resistance, and is therefore widely used in the field of electrical and electronic materials.

In recent years, heat generation due to the increasing density of integrated circuits has become a major problem, especially in the electrical and electronics fields, and how to dissipate heat has become an urgent issue. h-BN is attracting attention as a thermally conductive filler for such heat dissipation components, taking advantage of its characteristic of having high thermal conductivity despite being insulating.

However, h-BN has a plate-like particle shape and, although it exhibits high thermal conductivity (usually about 400 W/m·K in thermal conductivity) in the plate surface direction (in the ab plane or in the (002) plane), it only exhibits low thermal conductivity (usually about 2 to 3 W/m·K in thermal conductivity) in the plate thickness direction (C-axis direction). Therefore, when this is blended with a resin to form a BN particle-containing resin composition and, for example, a plate-like sheet-shaped molded product is molded, the plate-like h-BN will be oriented in the plate surface direction of the sheet-shaped molded product, which is the flow direction of the BN particle-containing resin composition during molding, and the obtained sheet-shaped molded product has a high thermal conductivity in the plate surface direction but only low thermal conductivity in the thickness direction.

In order to improve the anisotropy of the thermal conductivity of such h-BN particles, agglomerated particles of h-BN that have little orientation when filled into a resin and have shapes other than the scaly plate shape have been investigated.
For example, Patent Documents 1 and 2 describe BN agglomerated particles having a specific average particle size (D ₅₀ ), but make no mention of the fine powder ratio, and the thermal conductivity and voltage resistance of the particles when used in a heat dissipation sheet for a semiconductor device are still insufficient.

International Publication No. 2012/070289 JP 2018-104253 A

The present invention aims to provide a boron nitride agglomerated powder that can improve the thermal conductivity of a heat dissipation sheet while also providing good voltage resistance characteristics, a heat dissipation sheet containing this boron nitride agglomerated powder, and a semiconductor device that uses this heat dissipation sheet.

As a result of extensive research conducted by the inventors to solve the above problems, they discovered that boron nitride agglomerated powder with a fine powder ratio below a specific value can achieve high thermal conductivity and voltage resistance characteristics when used in a heat dissipation sheet.

That is, the gist of the present invention is as follows:

[1] A boron nitride agglomerated powder having a fine powder ratio, as defined below, of 27 volume % or less.
<Definition of fine powder rate>
The fine powder ratio is determined by dividing each peak obtained in the volume-based particle size distribution measurement by the mode and the least frequent point between the peaks centered on the mode, and the ratio (%) of the area of the region with the smallest particle size in the particle size distribution measurement chart among the divided regions to the total peak area in the particle size distribution measurement chart.
When there is one peak in the particle size distribution measurement chart, the fine powder ratio is the ratio (%) of the area of the region in the particle size distribution measurement chart where the particle size is 10 μm or less to the total peak area in the particle size distribution measurement chart.
[2] The boron nitride agglomerated powder according to [1], having a volume average particle diameter (D ₅₀ ) of 30 μm or more.
[3] The boron nitride agglomerated powder according to [1] or [2], wherein the boron nitride agglomerated particles in the boron nitride agglomerated powder have a house-of-cards structure.
[4] A heat dissipation sheet comprising the boron nitride agglomerated powder according to any one of [1] to [3].
[5] A semiconductor device using the heat dissipation sheet according to [4].

The boron nitride agglomerated powder of the present invention can provide a heat dissipation sheet that has excellent thermal conductivity and voltage resistance characteristics, and this heat dissipation sheet can be used to realize a high-quality, highly reliable power semiconductor module that has good heat dissipation performance and excellent thermal conductivity.

1 is an example of a particle size distribution measurement (volume) chart of a BN agglomerated powder to explain the definition of the fine powder ratio according to the present invention.

The following describes in detail the embodiments of the present invention, but the present invention is not limited to the following embodiments and can be modified in various ways within the scope of the gist of the invention.

[Boron nitride agglomerated powder]
The boron nitride agglomerated powder of the present invention (hereinafter sometimes simply referred to as "the BN agglomerated powder of the present invention") is characterized in that the fine powder ratio defined below (hereinafter sometimes simply referred to as "the fine powder ratio") is 27 volume % or less.
<Definition of fine powder rate>
The fine powder ratio is determined by dividing each peak obtained in the volume-based particle size distribution measurement by the mode and the least frequent point between the peaks centered on the mode, and the ratio (%) of the area of the region with the smallest particle size in the particle size distribution measurement chart among the divided regions to the total peak area in the particle size distribution measurement chart.
When there is one peak in the particle size distribution measurement chart, the fine powder ratio is the ratio (%) of the area of the region in the particle size distribution measurement chart where the particle size is 10 μm or less to the total peak area in the particle size distribution measurement chart.
As an example, the particle size distribution measurement (volume) of the BN agglomerated powder shown in Figure 1 will be described. The peak is divided at the most frequent value of the peak and the least frequent point between the peaks centered on the most frequent value (division point in Figure 1), and the area ratio of the area with the smallest particle size (area A) to the left of the division point in Figure 1 to the whole area (area A + B + C) is defined as the fine powder ratio. The fine powder ratio is expressed as A/(A + B + C) x 100 (%).
In the present invention, the boron nitride agglomerated powder refers to a powder that is an aggregate of boron nitride agglomerated particles (hereinafter, sometimes simply referred to as "BN agglomerated particles").

[mechanism]
Although the details of the mechanism by which a heat dissipation sheet excellent in thermal conductivity and voltage resistance characteristics can be obtained from the BN agglomerated powder of the present invention are not clear, it is presumed to be as follows.
When the fine powder ratio of the BN agglomerated powder added to prepare a heat dissipation sheet is high, the contact resistance between the BN particles increases, the thermal conductivity decreases, and the viscosity of the composition for preparing the heat dissipation sheet increases, which deteriorates moldability and makes it more likely to include voids. These voids deteriorate the voltage resistance.
The present invention was achieved by discovering that a material having a fine powder ratio of 27 volume % or less suppresses the inclusion of the above-mentioned voids and has excellent thermal conductivity and voltage resistance characteristics when used as a heat dissipation sheet.

The fine powder ratio in the present invention is defined as above, and is specifically measured by the method shown in the Examples section below.
The fine powder ratio according to the present invention is different from the average particle size ( _D50 ) described in Patent Documents 1 and 2, and represents the mode of each peak obtained in particle size distribution measurement of BN agglomerated powder after classifying the BN agglomerated powder, and the area ratio (%) of the region with the smallest particle size among the regions obtained by dividing the peaks at the least frequent point between the peaks centered on the mode, to the total region. Note that when there is one peak in the particle size distribution measurement chart, the fine powder ratio represents the ratio (%) of the area of the region with a particle size of 10 μm or less to the total peak area of the particle size distribution measurement chart.

[BN agglomerated powder]
The BN agglomerated powder of the present invention is an aggregate of BN agglomerated particles formed by agglomeration of BN primary particles, preferably h-BN primary particles, and the BN agglomerated particles may contain components other than the BN primary particles within a range that does not impair the effects of the present invention. Examples of components other than the h-BN primary particles include components derived from the binder, surfactant, and solvent that may be added to the slurry, which will be described later in [Method for producing BN agglomerated powder].

<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, and may be any shape that can be produced by agglomerating BN primary particles, such as a sphere, an ellipsoid, a cylinder, or a hexagonal cylinder.
In particular, in order to obtain high thermal conductivity, it is preferable to use a card-house type BN agglomerated particle 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-shaped particles are complexly stacked without being oriented. More specifically, the card-house structured BN agglomerated particle is an aggregate of BN primary particles, and is a BN agglomerated particle having a structure in which the flat surface and the end surface of the BN primary particles are in contact with each other, and is preferably spherical. In addition, the card-house structure may be a similar structure inside the particle. The agglomerated form and internal structure of these BN agglomerated particles can be confirmed by a scanning electron microscope (SEM).

<Physical properties of BN agglomerated powder>
(Fine powder rate)
The BN agglomerated powder of the present invention is characterized in that the fine powder ratio is 27 volume % or less.
If the fine powder ratio exceeds 27% by volume, the object of the present invention of improving the thermal conductivity and voltage resistance characteristics cannot be achieved.
The fine powder ratio is preferably 27 vol% or less, particularly 20 vol% or less, more preferably 15 vol% or less, and further preferably 13 vol% or less. There is no particular lower limit to the fine powder ratio, but it is usually 0.1 vol% or more from the viewpoints of the viscosity of the composition containing the BN agglomerated powder, the surface roughness of the sheet after molding, and the like.

(Volume average particle size ( _D50 ))
The volume average particle size (D ₅₀ ) of the BN agglomerated powder of the present invention is preferably 30 μm or more.
When _D50 is 30 μm or more, the contact resistance between the BN agglomerated particles becomes small when the heat dissipation sheet is formed, and the thermal conductivity of the BN agglomerated particles themselves tends to be high. From this viewpoint, _D50 of the BN agglomerated powder of the present invention is more preferably 35 μm or more, even more preferably 36 μm or more, and particularly preferably 40 μm or more. Moreover, _D50 of the BN agglomerated powder is preferably 200 μm or less, more preferably 150 μm or less, and even more preferably 100 μm or less. When it is less than the above upper limit, the surface is smooth when the heat dissipation sheet is formed, and the gaps between the BN agglomerated particles are suppressed, and the thermal conductivity tends to be improved.

The volume average particle size ( _D50 ) of the BN agglomerated powder means the particle size at which the cumulative volume is exactly 50% when a cumulative curve is drawn with the volume of the powder used for measurement being 100%. The measurement method includes, as a wet measurement method, a method in which a sample in which the BN agglomerated powder is dispersed in a pure water medium containing sodium hexametaphosphate as a dispersion stabilizer is measured using a laser diffraction/scattering type particle size distribution measurement device, and as a dry measurement method, a method in which the measurement is performed using "Morphologi" manufactured by Malvern.

[Method of manufacturing BN agglomerated powder]
There is no limitation on the method for producing the BN agglomerated powder of the present invention, but it is particularly preferable to pulverize the raw material boron nitride (hereinafter, together with the pulverized product thereof, may be referred to as "raw BN powder") in a pulverization step, granulate by agglomeration in a granulation step, and then pass through a heating step in which heat treatment is performed. More specifically, it is preferable to disperse the raw material BN powder in a medium once to obtain a raw material BN powder slurry (hereinafter, may be referred to as "BN slurry"), perform a pulverization treatment, and then granulate the obtained slurry into spherical particles, and perform a heat treatment to crystallize the granulated BN powder.

<Raw material BN powder>
As the raw BN powder, any of commercially available h-BN, commercially available α- and β-BN, BN produced by a reduction-nitridation method of a boron compound and ammonia, and BN synthesized from a boron compound and a nitrogen-containing compound such as melamine can be used without limitation, but h-BN is preferably used in that it more effectively exerts the effects of the present invention.

As the form of the raw material BN powder, powdered BN particles having a wide half-width of the peak obtained by powder X-ray diffraction measurement and low crystallinity are suitable. That is, it is possible to use plate-shaped h-BN as a raw material, but non-plate-shaped nanoparticles are also preferably used. As a guideline for crystallinity, the peak half-width of the (002) plane obtained by powder X-ray diffraction measurement is usually 0.4° or more, preferably 0.45° or more, more preferably 0.5° or more, in terms of 2θ angle. Also, it is usually 2.0° or less, preferably 1.5° or less, and even more preferably 1° or less. When the peak half-width of the (002) plane is equal to or less than the above upper limit, the crystallites tend to become sufficiently large, and productivity tends to improve. When the peak half-width of the (002) plane is equal to or more than the above lower limit, sufficient crystal growth can be expected, and the dispersion stability during slurry preparation tends to improve.
The method for producing the raw material BN powder is not particularly limited, but examples thereof include the method described in Microstructural Development with Crystallization of Hexagonal Boron Nitride (TSUYOSHI et al. JOURNAL OF MATERIALS SCIENCE LETTERS 16 (1997) 795-798).

From the viewpoint of BN crystal growth, it is preferable that a certain amount of oxygen atoms are present in the raw BN powder, and in the present invention, the total oxygen concentration in the raw BN powder is preferably 1 wt% or more, more preferably 2 wt% or more, even more preferably 3 wt% or more, particularly preferably 4 wt% or more, and preferably 10 wt% or less, more preferably 9 wt% or less. When the total oxygen concentration is below the above upper limit, oxygen is less likely to remain even after heat treatment, which tends to improve thermal conductivity. When the total oxygen concentration is above the above lower limit, crystal growth is more easily obtained.

Methods for adjusting the total oxygen concentration of the raw material BN powder to fall within the above range include, for example, a method in which the synthesis temperature during BN synthesis is set at a low temperature of 1500°C or lower, and a method in which the raw material BN powder is heat-treated in an oxidizing atmosphere at a low temperature of 500 to 900°C.
The total oxygen concentration of the raw material BN powder can be measured by an inert gas fusion-infrared absorption method using an oxygen/nitrogen analyzer manufactured by Horiba, Ltd.

The total pore volume of the raw BN powder is usually 1.0 ^cm3 /g or less, preferably 0.3 ^cm3 /g to 1.0 ^cm3 /g, more preferably 0.5 ^cm3 /g to 1.0 ^cm3 /g. When the total pore volume is 1.0 ^cm3 /g or less, the raw BN powder is dense, making it possible to produce granules with high sphericity.

The specific surface area of the raw BN powder is usually 50 m ² /g or more, preferably 60 m ² /g or more, more preferably 70 m ² /g or more, and usually 1000 m ² /g or less, preferably 500 m ² /g or less, more preferably 300 m ² /g or less. The specific surface area of the raw BN powder is preferably 50 m ² /g or more, since it is possible to reduce the dispersed particle size in the BN slurry used for spheroidization by granulation. In addition, it is preferable to set the specific surface area to 1000 m ² /g or less, since it is possible to suppress an increase in the slurry viscosity.
The total pore volume of the raw material BN powder can be measured by nitrogen adsorption method and mercury intrusion method.
The specific surface area of the raw BN powder can be measured by the BET one-point method (adsorption gas: nitrogen). The nitrogen adsorption method is performed according to JIS Z8830, and the measurement temperature is -196°C (liquid nitrogen temperature). The mercury intrusion method is performed according to JIS R1655, and the surface tension of BN is 485 dyn/ ^cm2 , the contact angle is 140°, and the measurement temperature is 23 to 26°C.

<Media>
The medium used in preparing the BN slurry is not particularly limited, 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.

The medium used in preparing the BN slurry is preferably added in an amount that gives the BN slurry a viscosity of 200 to 5000 mPa·s. Here, the viscosity of the BN slurry refers to the viscosity when the slurry temperature is 10° C. or higher and 60° C. or lower, and the above viscosity is preferably from 15° C. to 50° C., more preferably from 15° C. to 40° C., and even more preferably from 15° C. to 35° C.
Specifically, the amount of the medium used in preparing the BN slurry is usually 10% by weight or more, preferably 20% by weight or more, more preferably 30% by weight or more, and usually 70% by weight or less, preferably 65% by weight or less, more preferably 60% by weight or less, based on the BN slurry. By using an amount of the medium that is equal to or less than the upper limit, settling due to a decrease in the slurry viscosity is suppressed. Therefore, the uniformity of the BN slurry is obtained, and the fine powder ratio of the obtained BN agglomerated particles tends to be in the desired range. By using an amount of the medium that is equal to or more than the lower limit, the slurry viscosity is not too high, and granulation tends to be easy.

<Surfactant>
Various surfactants may be added to the BN slurry in order to adjust the viscosity of the slurry and to improve the dispersion stability (suppression of aggregation) of the raw BN powder in the slurry.
As the surfactant, anionic surfactants, cationic surfactants, nonionic surfactants, etc. can be used. These may be used alone or in combination of two or more.

In general, a surfactant can change the viscosity of a slurry. Therefore, when a surfactant is added to a BN slurry, the amount of the surfactant is adjusted so that the viscosity of the BN slurry is 200 to 5000 mPa·s. The viscosity of the BN slurry represents the viscosity in the temperature range described above for the medium used in the preparation of the BN slurry.
For example, when preparing a slurry with a solid content of 50% by weight using BN having a (002) plane peak half-width 2θ of 0.67° and a total oxygen concentration of 7.5% by weight obtained by powder X-ray diffraction measurement as the raw material BN, an anionic surfactant is usually added as an active ingredient in an amount of usually 0.01% by weight or more, preferably 0.05% by weight or more, more preferably 0.1% by weight or more, usually 10% by weight or less, preferably 7% by weight or less, more preferably 5% by weight or less, and even more preferably 3% by weight or less relative to the total amount of the slurry. By adding this amount below the upper limit, the slurry viscosity does not drop too much, and carbon components derived from the surfactant tend not to remain in the generated BN agglomerated particles. By adding the amount above the lower limit, the slurry viscosity does not become too high, and granulation tends to be easy.

<Binder>
The BN slurry may contain a binder to effectively granulate the raw BN powder into particles. The binder acts to firmly bind the BN primary particles together and stabilize the granulated particles.

The binder used in the BN slurry may be any material capable of increasing the adhesion between BN particles, but in the present invention, since the granulated particles are heat-treated after granulation, it is preferable that the binder has heat resistance to the high temperature conditions in this heat treatment process.

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

The BN slurry may or may not contain a binder, and may contain 0% by weight of the raw BN powder in the BN slurry. If a binder is contained, the amount used (in the case of a liquid binder, the amount used as solids) is preferably 0.1% by weight or more, more preferably 0.5% by weight or more, and even more preferably 1.0% by weight or more, and is preferably 30% by weight or less, more preferably 20% by weight or less, and even more preferably 15% by weight or less, of the raw BN powder in the BN slurry. By using an amount of binder that is equal to or less than the above upper limit, crystal growth is obtained, and when used as a thermally conductive filler, a thermal conductivity improvement effect tends to be obtained.

<Method of preparing BN slurry>
The method for preparing the BN slurry is not particularly limited as long as the raw material BN powder, a medium, and, if necessary, a binder and a surfactant are uniformly dispersed and the viscosity is adjusted to a desired range. However, when the raw material BN powder, a medium, and, if necessary, a binder and a surfactant are used, the slurry is preferably prepared as follows.

A prescribed amount of raw BN powder is weighed into a resin bottle, then a prescribed amount of binder is added, followed by a prescribed amount of surfactant, followed by adding zirconia ceramic balls, and stirring on a pot mill rotating platform for about 0.5 to 5 hours until the desired viscosity is reached.
The order of addition is not particularly limited, but when a large amount of raw BN powder is to be made into a slurry, in order to suppress agglomerations such as lumps, a surfactant and a binder may be added to water to prepare an aqueous solution, and then a predetermined amount of raw BN powder may be added little by little. Zirconia ceramic balls may then be added thereto, and the mixture may be dispersed and slurried on a pot mill rotating table.

In addition to a pot mill, dispersing devices such as a bead mill or planetary mixer may be used for dispersion.

When forming the slurry, the temperature of the slurry is usually 10°C or higher and 60°C or lower. By keeping the slurry temperature at or above the lower limit, the increase in the slurry viscosity is suppressed, and the desired viscosity range is easily obtained. In addition, by keeping the temperature below the upper limit, the raw BN powder is less likely to decompose into ammonia in the slurry. The temperature of the slurry is preferably 15°C or higher and 50°C or lower, more preferably 15°C or higher and 40°C or lower, and even more preferably 15°C or higher and 35°C or lower.

<Granulation>
To obtain a granulated powder from the BN slurry, a general granulation method such as a spray-drying method, a rolling method, a fluidized bed method, or a stirring method can be used, and among these, the spray-drying method is preferred.

In the spray drying method, it is possible to produce granulated powder of the desired size by adjusting the concentration of the raw material slurry, the amount of liquid fed into the device per unit time, and the compressed air pressure and amount of compressed air when spraying the fed slurry, and it is also possible to obtain spherical granulated powder. There are no restrictions on the spray drying device used, but to obtain larger spherical granulated powder, a device using a rotating disk is optimal. Examples of such devices include the spray dryer F series manufactured by Okawara Kakoki Co., Ltd., the spray dryer "MDL-050M" manufactured by Fujisaki Electric Co., Ltd., and the spray dryer "P260" manufactured by PRIS.

When the range of the volume-based average particle diameter _D50 of the BN agglomerated powder of the present invention is set to 30 μm or more and 200 μm or less, the volume-based average particle diameter _D50 of the granulated powder obtained by granulation is usually 30 μm or more and 200 μm or less, preferably 35 μm or more and 200 μm or less. Here, the volume-based average particle diameter _D50 of the granulated powder can be measured, for example, by using "LA920" manufactured by Horiba Ltd. in the wet method or "Morphorogi" manufactured by Malvern in the dry method.

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

The heat treatment temperature is preferably 1600°C or higher and 2300°C or lower, and more preferably 1800°C or higher and 2200°C or lower. When the heat treatment temperature is equal to or higher than the lower limit, the average crystallites of the BN primary particles can grow sufficiently, and the thermal conductivity of the BN agglomerated powder tends to increase. When the heat treatment temperature is equal to or lower than the upper limit, decomposition of the BN agglomerated powder tends to be suppressed.

The heat treatment time is preferably 5 hours or more and 20 hours or less, and more preferably 5 hours or more and 15 hours or less. A heat treatment time of at least the lower limit mentioned above tends to ensure sufficient crystal growth, while a heat treatment time of at most the upper limit mentioned above tends to suppress decomposition of BN.

To carry out the heat treatment in a non-oxidizing gas atmosphere, the inside of the calcination furnace is preferably evacuated using a vacuum pump, and then heated to the desired temperature while introducing a non-oxidizing gas. However, if the inside of the calcination furnace can be sufficiently replaced with a non-oxidizing gas, the temperature may be increased while introducing a non-oxidizing gas under normal pressure. Examples of calcination furnaces include batch furnaces such as muffle furnaces, tubular furnaces, and atmospheric furnaces, and continuous furnaces such as rotary kilns, screw conveyor furnaces, tunnel furnaces, belt furnaces, pusher furnaces, and vertical continuous furnaces, and these are used according to the purpose.

The granulated powder to be heat-treated is usually placed in a circular graphite crucible with a lid and heated and fired in order to reduce non-uniformity in the composition during firing. At this time, in addition to reducing non-uniformity in the composition, graphite partitions may be inserted to suppress sintering of BN aggregate particles during firing. There is no particular limit to the number of partitions as long as sintering can be suppressed, but it is usually between 2 and 16. If the number of partitions is less than the upper limit, sintering is suppressed and the crystals of the h-BN primary particles tend to grow sufficiently, and if the number of partitions is greater than or equal to the lower limit, sintering tends to be suppressed.

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

Classification can be done by either wet or dry method, but dry classification is preferred from the viewpoint of suppressing the decomposition of BN. Dry classification is particularly preferred when the binder is water-soluble.

Dry classification includes classification using sieves and air classification, which classifies based on the difference between centrifugal force and fluid drag, but it can also be done using a classifier such as a swirling air classifier, forced vortex centrifugal classifier, or semi-free vortex centrifugal classifier. Of these, a swirling air classifier is used to classify small particles in the submicron to single micron range, and a semi-free vortex centrifugal classifier is used to classify relatively larger particles, etc., depending on the particle size of the particles to be classified.

<Mechanism for obtaining the BN agglomerated powder of the present invention>
The method for producing the BN agglomerated powder of the present invention having a fine powder ratio of 27 volume % or less and a volume average particle diameter (D ₅₀ ) of preferably 20 μm or more is not particularly limited, but the following methods can be mentioned.

In the heat treatment process of the granulated particles during the production of the BN agglomerated powder, the temperature is increased at a rate of 100 to 200° C./hr, which is faster than the normal rate of 50 to 100° C./hr, and a holding step is provided in which the temperature is held at a temperature about 300 to 600° C. lower than the maximum heating temperature, specifically at a temperature of about 1400 to 1700° C., for about 5 to 20 hours before the maximum heating temperature (the maximum heating temperature is the above-mentioned heat treatment temperature) is reached, and then a two-stage firing is performed in which the temperature is increased at the above-mentioned heating rate up to the maximum heating temperature.
By carrying out stepwise firing in this manner, the oxygen concentration in the BN raw material can be controlled to a concentration suitable for crystal growth, which results in uniform growth of the BN primary particles and allows the degree of sintering to be controlled. This makes it possible to classify the BN agglomerated particles without destroying their shape, and tends to make it easier to obtain a BN agglomerated powder with a low fine powder ratio.

In addition, in order to keep the fine powder ratio within the range of the present invention, in addition to performing two-stage firing in the heat treatment, the oxygen concentration of the BN raw material used to prepare the BN agglomerated powder may be controlled during the heat treatment. Specific examples include a method of adding a powder of carbon or the like that reacts with oxygen to the crucible, a method of providing a graphite partition in the crucible, and a method of removing oxygen-containing compounds from the pre-fired granulated product to be subjected to the heat treatment under reduced pressure during the heat treatment. Among these, the method of providing a graphite partition in the crucible is preferable as a method suitable for mass production. For example, in Example 6 described below, one graphite partition (a strip of 10 mm thickness, 50 mm height, and 200 mm length) was placed in the center of the crucible.

[Resin composition containing BN agglomerated powder]
To manufacture the heat dissipation sheet of the present invention containing the BN agglomerated powder of the present invention, a resin composition containing at least the BN agglomerated powder of the present invention as an inorganic filler and a resin (hereinafter, sometimes referred to as the "composition containing the BN agglomerated powder of the present invention" or the "composition of the present invention") is prepared, and the prepared composition of the present invention is molded into a sheet to obtain the heat dissipation sheet of the present invention. The composition containing the BN agglomerated powder of the present invention will be described below.

The resin composition containing the BN agglomerated powder of the present invention is usually composed of a resin component, preferably a thermosetting resin component, an inorganic filler containing the BN agglomerated powder of the present invention, a curing agent, a curing catalyst, other components used as necessary, a solvent for forming a coating slurry, etc. Furthermore, when forming a composite molded product as described below, the composition of the present invention preferably contains a compound having a heterocyclic structure containing a nitrogen atom from the viewpoint of improving adhesion to metals.

[Components other than inorganic filler]
<Thermosetting resin component>
The thermosetting resin contained in the composition of the present invention is not particularly limited as long as it is cured in the presence of a curing agent or a curing catalyst.Specific examples of the thermosetting resin include epoxy resin, phenol resin, polycarbonate resin, unsaturated polyester resin, urethane resin, melamine resin, and urea resin.Among these, epoxy resin is preferred from the viewpoints of viscosity, heat resistance, moisture absorption, and handling.Examples of the epoxy resin include epoxy group-containing silicon compounds, aliphatic epoxy resins, bisphenol A or F epoxy resins, novolac epoxy resins, alicyclic epoxy resins, glycidyl ester epoxy resins, multifunctional epoxy resins, and polymeric epoxy resins.

(Epoxy resin)
Epoxy resin is a general term for compounds having one or more oxirane rings (epoxy groups) in the molecule. The oxirane rings (epoxy groups) contained in the epoxy resin may be either alicyclic epoxy groups or glycidyl groups, but are more preferably glycidyl groups from the viewpoint of reaction rate or heat resistance.

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 glycidylating bisphenols such as bisphenol A, bisphenol F, bisphenol AD, bisphenol S, tetramethyl bisphenol A, tetramethyl bisphenol F, tetramethyl bisphenol AD, tetramethyl bisphenol S, and tetrafluorobisphenol A; biphenyl-type epoxy resins; epoxy resins obtained by glycidylating divalent phenols such as dihydroxynaphthalene and 9,9-bis(4-hydroxyphenyl)fluorene; epoxy resins obtained by glycidylating trisphenols such as 1,1,1-tris(4-hydroxyphenyl)methane; epoxy resins obtained by glycidylating tetrakisphenols such as 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane; and novolac-type epoxy resins obtained by glycidylating novolacs such as phenol novolac, cresol novolac, bisphenol A novolac, and brominated bisphenol A novolac.

Hereinafter, an epoxy resin suitable for use in the present invention (hereinafter, sometimes referred to as a "specific epoxy resin") and a polyfunctional epoxy resin preferably used in combination with this specific epoxy resin will be described.
In the following, the term "organic group" includes any group containing a carbon atom, and specific examples thereof include an alkyl group, an alkenyl group, an aryl group, etc., which may be substituted with a halogen atom, a group having a heteroatom, or another hydrocarbon group.

(Specific epoxy resin)
The specific epoxy resin includes an epoxy resin having at least one structure selected from a structure represented by the following structural formula (1) (hereinafter, may be referred to as "Structure (1)") and a structure represented by the following structural formula (2) (hereinafter, may be referred to as "Structure (2)").

(In formula (1), ^R1 and ^R2 each represent an organic group, at least one of which is an organic group having a molecular weight of 16 or more, and in formula (2), ^R3 represents a divalent cyclic organic group.)

The specific epoxy resin may also be an epoxy resin having a structure represented by the following structural formula (3) (hereinafter, sometimes referred to as "structure (3)").

(In formula (3), R ⁴ , R ⁵ , R ⁶ , and R ⁷ each represent an organic group having a molecular weight of 15 or more.)

In the above formula (1), at least one of R ¹ and R ² represents an organic group having a molecular weight of 16 or more, preferably a molecular weight of 16 to 1000, and examples thereof include alkyl groups such as ethyl, propyl, butyl, pentyl, hexyl, and heptyl groups, and aryl groups such as phenyl, tolyl, xylyl, naphthyl, and fluorenyl groups. Both R ¹ and R ² may be organic groups having a molecular weight of 16 or more, or one may be an organic group having a molecular weight of 16 or more and the other may be an organic group having a molecular weight of 15 or less or a hydrogen atom, but preferably one is an organic group having a molecular weight of 16 or more and the other is an organic group having a molecular weight of 15 or less, and in particular, one of them being a methyl group and the other being a phenyl group is preferable from the viewpoint of easy control of handleability such as resin viscosity and strength of the cured product.

In formula (2), R ³ is a divalent cyclic organic group, which 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. They may also have a substituent, such as a hydrocarbon group or a halogen atom, independently. The divalent bond may be a divalent group on a single carbon atom, or a divalent group on different carbon atoms. Preferred examples include divalent aromatic groups having 6 to 100 carbon atoms, and groups derived from cycloalkanes having 2 to 100 carbon atoms such as cyclopropane and cyclohexane. In particular, the 3,3,5-trimethyl-1,1-cyclohexylene group represented by the following structural formula (4) is preferred from the viewpoints of controlling the handleability of the resin viscosity and the strength of the cured product.

In formula (3), R ⁴ , R ⁵ , R ⁶ , and R ⁷ are each an organic group having a molecular weight of 15 or more, preferably an alkyl group having a molecular weight of 15 to 1000, and it is particularly preferred that R ⁴ , R ⁵ , R ⁶ , and R ⁷ are all methyl groups from the viewpoints of controlling handleability such as resin viscosity and strength of the cured product.

The specific epoxy resin is preferably an epoxy resin containing either one of structure (1) and structure (2) and structure (3) from the viewpoint of achieving both reduced moisture absorption and strength retention performance of the resulting cured heat dissipation sheet.

Since such specific epoxy resins contain more hydrophobic hydrocarbon and aromatic structures than general epoxy resins having bisphenol A or bisphenol F skeletons, by blending the specific epoxy resins, it is possible to reduce the moisture absorption amount of the heat dissipation sheet obtained as a cured product.
From the viewpoint of reducing the amount of moisture absorption, the specific epoxy resin is preferably one that contains a large amount of structures (1), (2), and (3), which are hydrophobic structures. Specifically, the specific epoxy resin is preferably an epoxy resin having a weight-average molecular weight of 10,000 or more, more preferably an epoxy resin having a weight-average molecular weight of 20,000 or more, and even more preferably an epoxy resin having a weight-average molecular weight of 30,000 or more, for example, from 30,000 to 40,000.
In addition, the specific epoxy resin is preferably more hydrophobic. Specifically, the epoxy equivalent of the specific epoxy component is preferably larger, and is preferably 5,000 g/equivalent or more, more preferably 7,000 g/equivalent or more, for example, 8,000 to 15,000 g/equivalent.

Here, the weight average molecular weight of the epoxy resin is a value calculated in terms of polystyrene measured by gel permeation chromatography. The epoxy equivalent is defined as the weight of the epoxy resin containing one equivalent of epoxy groups, and can be measured in accordance with JIS K7236.

Such specific epoxy resins may be used alone or in combination of two or more types.

(Multifunctional epoxy resin)
A polyfunctional epoxy resin is an epoxy resin having three or more oxirane rings (epoxy groups) per molecule.

From the viewpoint of increasing the storage modulus of the cured product after thermal curing, particularly the storage modulus at high temperatures, which is important when a large amount of heat is generated, such as in power semiconductors, epoxy resins having two or more oxirane rings (epoxy groups) in the molecule are preferred, epoxy resins having three or more oxirane rings (epoxy groups) in the molecule are more preferred, and epoxy resins having four or more glycidyl groups in the molecule are even more preferred. By having multiple oxirane rings (epoxy groups), especially glycidyl groups, in the molecule, the crosslink density of the cured product is improved, and the heat dissipation sheet obtained as the cured product has a higher strength. As a result, when internal stress occurs in the heat dissipation sheet during a moisture absorption reflow test, the heat dissipation sheet does not deform or break, but maintains its shape, thereby suppressing the occurrence of voids and other voids in the heat dissipation sheet.
From the viewpoint of increasing the storage modulus of the heat dissipation sheet after thermal curing, the molecular weight of the polyfunctional epoxy resin is preferably 1,000 or less, and more preferably 100 to 800.

In addition, by adding a multifunctional epoxy resin, it is possible to introduce highly polar oxirane rings (epoxy groups) at a high density, which increases the effects of physical interactions such as van der Waals forces and hydrogen bonds, and improves the adhesion between the metal in the composite molded body described below and the heat dissipation sheet of the present invention, which is the resin cured product. In addition, by adding a multifunctional epoxy resin, it is possible to increase the storage modulus of the heat dissipation sheet after thermal curing, and as a result, after the cured product of the thermosetting resin composition penetrates into the unevenness of the metal to be adhered, a strong anchor effect is exerted, improving the adhesion between the metal and the heat dissipation sheet.

On the other hand, the introduction of a multifunctional epoxy resin tends to increase the hygroscopicity of the thermosetting resin composition, but by improving the reactivity of the oxirane ring (epoxy group), the amount of hydroxyl groups during the reaction can be reduced and the increase in hygroscopicity can be suppressed. In addition, by combining the specific epoxy resin and a multifunctional epoxy resin described above to produce a thermosetting resin composition, it is possible to achieve both high elasticity and low hygroscopicity in the resulting heat dissipation sheet.

Specifically, the polyfunctional epoxy resin is preferably an epoxy resin having three or more epoxy groups, and for example, EX321L, DLC301, DLC402, etc. manufactured by Nagase ChemteX Corporation can be used.
These polyfunctional epoxy resins may be used alone or in combination of two or more.

(Content)
The composition of the present invention preferably contains 5 to 99% by weight, particularly 50 to 98% by weight, of the thermosetting resin component based on 100% by weight of the composition of the present invention excluding the solvent and inorganic filler. When the content of the thermosetting resin component is equal to or higher than the lower limit, the moldability is good, and when the content is equal to or lower than the upper limit, the content of other components can be secured, and thermal conductivity can be increased.

The composition of the present invention preferably contains 20 to 100% by weight, and particularly 45 to 100% by weight, of epoxy resin in the thermosetting resin component.

In addition, the composition of the present invention preferably contains the specific epoxy resin, which is the above-mentioned preferred epoxy resin, in an amount of 50% by weight or less, for example 5 to 50% by weight, and particularly 10 to 40% by weight, based on the total epoxy resin. When the content of the specific epoxy resin is equal to or greater than the above-mentioned lower limit, the above-mentioned effects of containing the specific epoxy resin can be effectively obtained. On the other hand, if the content of the specific epoxy resin is too high, the crosslink density decreases and the cured product becomes brittle. By keeping the content of the specific epoxy resin equal to or less than the above-mentioned upper limit, it is possible to suppress the moisture absorption of the cured product and improve the strength performance of the cured product, thereby achieving both of these performances.

The composition of the present invention preferably contains 5 to 50% by weight, particularly 10 to 40% by weight, of the polyfunctional epoxy resin, which is the aforementioned preferred epoxy resin, based on the total epoxy resin. When the content of the polyfunctional epoxy resin is equal to or greater than the above lower limit, the aforementioned effects of containing the polyfunctional epoxy resin can be effectively obtained. On the other hand, when the content of the polyfunctional epoxy resin is equal to or less than the above upper limit, the moisture absorption of the cured product is suppressed and the strength performance of the cured product is excellent, making it possible to achieve both of these performances.

In particular, it is preferable that the composition of the present invention contains both a specific epoxy resin and a multifunctional epoxy resin as epoxy resins in order to obtain both high elasticity and low moisture absorption of the resulting cured product. In this case, the content ratio of the specific epoxy resin to the multifunctional epoxy resin is preferably specific epoxy resin:multifunctional epoxy resin = 10-90:90-10, particularly 20-80:80-20 (weight ratio).

The epoxy resin other than the specific epoxy resin and the polyfunctional epoxy resin contained in the composition of the present invention is not particularly limited, but is preferably one or more selected from various bisphenol-type epoxy resins obtained by glycidylating bisphenols such as bisphenol A-type epoxy resins and bisphenol F-type epoxy resins, various biphenyl-type epoxy resins obtained by glycidylating biphenyls, epoxy resins obtained by glycidylating aromatic compounds having two hydroxyl groups such as dihydroxynaphthalene and 9,9-bis(4-hydroxyphenyl)fluorene, epoxy resins obtained by glycidylating trisphenols such as 1,1,1-tris(4-hydroxyphenyl)methane, epoxy resins obtained by glycidylating tetrakisphenols such as 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane, novolac-type epoxy resins obtained by glycidylating novolacs such as phenol novolac, cresol novolac, bisphenol A novolac, and brominated bisphenol A novolac, and silicone-containing epoxy resins.

<Compound having a heterocyclic structure containing a nitrogen atom>
A compound having a heterocyclic structure containing a nitrogen atom (hereinafter, sometimes referred to as a "nitrogen-containing heterocyclic compound") has the effect of improving the adhesion between the cured product of the composition of the present invention and a metal. That is, when the composition of the present invention is composited with a metal, the nitrogen-containing heterocyclic compound is located at the interface between them, thereby improving the adhesion between the composition of the present invention and the metal. From this viewpoint, in order to make it easier for the nitrogen-containing heterocyclic compound to remain at the interface between the composition of the present invention and the metal, it is more preferable that the molecular weight is low, and the molecular weight of the nitrogen-containing heterocyclic compound is preferably 1,000 or less, more preferably 500 or less.

Examples of heterocyclic structures possessed by nitrogen-containing heterocyclic compounds include structures derived from imidazole, triazine, triazole, pyrimidine, pyrazine, pyridine, and azole. From the viewpoint of improving the insulating properties of the thermosetting resin composition and adhesion to metals, imidazole-based compounds and triazine-based compounds are preferred. Preferable imidazole compounds 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-imidazolyl ... ethyl-4'methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanuric acid adduct, 2-phenylimidazole isocyanuric acid 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 isocyanuric acid adduct, 2,4-diamino-6-methacryloyloxyethyl-s-triazine, 2,4-diamino-6-methacryloyloxyethyl-s-triazine isocyanuric acid adduct, etc.

Among these, those having a structure derived from imidazole and those having a structure derived from triazine are particularly preferred, since their high resin compatibility and high reaction activation temperature make it easy to adjust the curing speed and post-curing physical properties, thereby enabling the composition of the present invention to have improved storage stability and further improved adhesive strength after heat molding. As the heterocyclic structure of the nitrogen-containing heterocyclic compound, a structure derived from 1,3,5-triazine is particularly preferred. Moreover, it is acceptable for the compound to have a plurality of these exemplified structural portions.

Depending on the structure, the nitrogen-containing heterocyclic compound may contain a curing catalyst, which will be described later, and therefore the composition of the present invention may contain a nitrogen-containing heterocyclic compound as a curing catalyst.
The nitrogen-containing heterocyclic compound may be used alone or in combination of two or more kinds. Also, one molecule may simultaneously have a plurality of heterocyclic structures.

The nitrogen-containing heterocyclic compound is preferably contained in an amount of 0.001 to 10% by weight, particularly 0.1 to 5% by weight, based on 100% by weight of the composition of the present invention excluding the solvent and inorganic filler. When a curing catalyst, which will be described later, is contained 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 within the above range. When the content of the nitrogen-containing heterocyclic compound is equal to or higher than the above lower limit, the above effects of containing this compound can be sufficiently obtained, and when it is equal to or lower than the above upper limit, the reaction proceeds effectively, the crosslinking density is improved, the strength is increased, and storage stability is improved.

<Curing Agent>
The curing agent is not particularly limited, but the preferred curing agent is a phenol resin, an acid anhydride having an aromatic skeleton or an alicyclic skeleton, or a water additive of the acid anhydride or a modified product of the acid anhydride. By using these preferred curing agents, a resin cured product having an excellent balance of heat resistance, moisture resistance, and electrical properties can be obtained. The curing agent may be used alone or in combination of two or more kinds.

The phenolic resin is not particularly limited. Specific examples of the phenolic resin include phenol novolac, o-cresol novolac, p-cresol novolac, t-butylphenol novolac, dicyclopentadiene cresol, polyparavinylphenol, bisphenol A type novolac, xylylene modified novolac, decalin modified novolac, poly(di-o-hydroxyphenyl)methane, poly(di-m-hydroxyphenyl)methane, poly(di-p-hydroxyphenyl)methane, etc. Among them, in order to further improve the flexibility and flame retardancy of the thermosetting resin composition and to improve the mechanical properties and heat resistance of the cured resin, novolac type phenolic resins having a rigid main chain skeleton and phenolic resins having a triazine skeleton are preferred. In addition, phenolic resins having an allyl group are preferred to improve the flexibility of the uncured thermosetting resin composition and the toughness of the cured resin.

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 Co., Ltd.), as well as PSM6200, PS6313, and PS6492 (manufactured by Gun-ei Chemical Industry Co., Ltd.).

The acid anhydride having an aromatic skeleton, the water additive of the acid anhydride, or the modified product of the acid anhydride is 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), Ricadit MTA-10, Ricadit TMTA, Ricadit TMEG-200, Ricadit TMEG-500, Ricadit TMEG-S, Ricadit TH, Ricadit MH-700, Ricadit MT-500, Ricadit DSDA and Ricadit TDA-100 (all manufactured by New Japan Chemical), EPICLON B4400, and EPICLON B570 (all manufactured by Dainippon Ink and Chemicals).

The acid anhydride having an alicyclic skeleton, the water additive of the acid anhydride, or the modified product of the acid anhydride is preferably an acid anhydride having a polyalicyclic skeleton, the water additive of the acid anhydride, or the modified product of the acid anhydride, or an acid anhydride having an alicyclic skeleton obtained by an addition reaction between a terpene compound and maleic anhydride, the water additive of the acid anhydride, or the modified product of the acid anhydride. Specific examples include Ricadit HNA and Ricadit HNA-100 (both manufactured by New Japan Chemical Co., Ltd.), Epicure YH306 and Epicure YH309 (both manufactured by Mitsubishi Chemical Corporation), etc.

The hardener is preferably contained in an amount of 0 to 70% by weight, particularly 0 to 55% by weight, based on 100% by weight of the composition of the present invention excluding the solvent and inorganic filler. If the content of the hardener is equal to or greater than the lower limit, sufficient hardening performance can be obtained, and if the content is equal to or less than the upper limit, the reaction proceeds effectively, improving the crosslinking density, increasing the strength, and further improving the film formability.

<Curing catalyst>
The composition of the present invention preferably contains a curing catalyst together with the above-mentioned curing agent in order to adjust the curing rate and the physical properties of the cured product.

The curing catalyst is not particularly limited, but is appropriately selected according to the type of thermosetting resin component and curing agent used.Specific examples of the curing catalyst include chain or cyclic tertiary amines, organic phosphorus compounds, quaternary phosphonium salts, diazabicycloalkenes such as organic acid salts, etc.In addition, organic metal compounds, quaternary ammonium salts, metal halides, etc. can also be used.The above-mentioned organic metal compounds include zinc octylate, tin octylate, and aluminum acetylacetone complex.
These may be used alone or in combination of two or more.

The curing catalyst is preferably contained in an amount of 0.1 to 10% by weight, particularly 0.1 to 5% by weight, based on 100% by weight of the composition of the present invention excluding the solvent and inorganic filler. If the content of the curing catalyst is equal to or greater than the lower limit, the progress of the curing reaction can be sufficiently promoted to achieve good curing, and if the content is equal to or less than the upper limit, the curing speed is not too fast, and therefore the storage stability of the composition of the present invention can be improved.

<Other ingredients>
The composition of the present invention may contain other components other than the inorganic filler as long as the effects of the present invention are not impaired. Examples of other components include a surface treatment agent such as a silane coupling agent that improves the interfacial adhesive strength between the inorganic filler and the resin component when a resin cured product is produced using the composition of the present invention, an insulating carbon component such as a reducing agent, a viscosity adjuster, a dispersant, a thixotropy imparting agent, a flame retardant, a colorant, an organic filler, an organic solvent, and a thermoplastic resin.
Among these, the inclusion of a dispersant may enable the formation of a uniform resin cured product, and may improve the thermal conductivity and dielectric breakdown characteristics of the resulting resin cured product. Also, the inclusion of an organic filler or a thermoplastic resin may impart appropriate elongation to the composition, relieve the stress generated, and suppress the occurrence of cracks during a temperature cycle test.

The dispersant preferably has a functional group containing hydrogen atoms with hydrogen bonding properties. When the dispersant has a functional group containing hydrogen atoms with hydrogen bonding properties, the thermal conductivity and dielectric breakdown properties of the resulting cured heat dissipation sheet can be further improved. Examples of the functional group containing hydrogen atoms with hydrogen bonding properties include a carboxyl group (pKa = 4), a phosphate group (pKa = 7), and a phenol group (pKa = 10).

The pKa of the functional group containing a hydrogen atom capable of hydrogen bonding is preferably in the range of 2 to 10, and more preferably in the range of 3 to 9. With a pKa of 2 or more, the acidity of the dispersant is in an appropriate range, which may make it easier to suppress the reaction of the epoxy resin in the thermosetting resin component. Therefore, when the molded product in an uncured state is stored, the storage stability tends to be improved. With a pKa of 10 or less, the function of the dispersant is fully fulfilled, and the thermal conductivity and dielectric breakdown characteristics of the heat dissipation sheet, which is the resulting cured product, tend to be sufficiently improved.

The functional group containing a hydrogen atom capable of forming a hydrogen bond is preferably a carboxyl group or a phosphate group. In this case, the thermal conductivity and dielectric breakdown characteristics of the heat dissipation sheet can be further improved.

Specific examples of dispersants include polyester-based carboxylic acids, polyether-based carboxylic acids, polyacrylic-based carboxylic acids, aliphatic carboxylic acids, polysiloxane-based carboxylic acids, polyester-based phosphoric acids, polyether-based phosphoric acids, polyacrylic-based phosphoric acids, aliphatic phosphoric acids, polysiloxane-based phosphoric acids, polyester-based phenols, polyether-based phenols, polyacrylic-based phenols, and polysiloxane-based phenols. Only one type of dispersant may be used, or two or more types may be used in combination.

As the thermoplastic resin, any commonly known thermoplastic resin can be used, but specific examples include vinyl polymers such as polyethylene, polypropylene, polystyrene, polyvinyl chloride, (meth)acrylic resin, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, etc., polylactic acid resin, polyesters such as polyethylene terephthalate, polybutylene terephthalate, etc., polyamides such as nylon and polyamidoamine, polyvinyl acetal resins such as polyvinyl acetoacetal, polyvinyl benzal, polyvinyl butyral resin, ionomer resins, polyphenylene ether, polyphenylene sulfide, polycarbonate, polyether ether ketone, polyacetal, ABS resin, LCP (liquid crystal polymer), fluororesin, urethane resin, silicone resin, various elastomers, and modified products of these resins.

These thermoplastic resins may be uniform in the resin phase of the heat dissipation sheet, or may be phase-separated and have a recognizable shape. If they are phase-separated, the shape of the thermoplastic resin in the heat dissipation sheet may be particulate or fibrous. In this way, if the shape of the thermoplastic resin is recognizable in the heat dissipation sheet, the thermoplastic resin may be recognized as an organic filler, but in the present invention, organic fillers refer to natural products such as wood flour, cellulose that may be modified, starch, various organic pigments, etc., and thermoplastic resins are not included in organic fillers.

The inclusion of thermoplastic resins and organic fillers can impart appropriate elongation to the composition, reduce stress that occurs, and may help prevent cracks from occurring during temperature cycle testing.

When the thermoplastic resin or organic filler is insoluble in the thermosetting resin, the viscosity of the composition of the present invention is prevented from increasing, and when the composition is molded into a sheet as described below, the smoothness of the sheet surface can be improved. In this case, by simultaneously mixing a thermoplastic resin and an organic filler that are insoluble in the thermosetting resin with a large amount of inorganic filler, the component phase that is thermoplastic and has good elongation can be efficiently dispersed in the cured product, making it easy to relieve stress. Therefore, it is possible to suppress the occurrence of cracks in the cured product without reducing the elastic modulus of the cured product. For these reasons, polyamide resins such as nylon, cellulose resins, etc. are preferred as the thermoplastic resin, and polyamide resins such as nylon are particularly preferred.

When the shape of the thermoplastic resin that can be observed in the heat dissipation sheet that is the cured product is particulate, the upper limit of the average particle size is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 30 μm or less. By setting the average particle size to the above upper limit or less, it is possible to create sheet-shaped cured products of various thicknesses without risking a decrease in thermal conductivity. The average particle size of the particulate thermoplastic resin is determined by observing the cross section of the cured product and averaging the longest diameter of any 20 particles.

The composition of the present invention may contain an organic solvent, for example, to improve the coatability when forming a sheet-shaped cured product through a coating process.

Examples of organic solvents that may be contained in the composition of the present invention include methyl ethyl ketone, cyclohexanone, propylene glycol monomethyl ether acetate, butyl acetate, isobutyl acetate, propylene glycol monomethyl ether, etc. These organic solvents may be used alone or in combination of two or more.

When the composition of the present invention contains an organic solvent, its content is appropriately determined depending on the handleability during the production of the heat dissipation sheet, etc. Usually, it is preferable to use the organic solvent so that the solids concentration (total of components other than the solvent) in the composition of the present invention is 10 to 90% by weight, particularly 40 to 80% by weight.

[Inorganic filler]
The composition of the present invention contains at least the BN agglomerated powder of the present invention as an inorganic filler.

The composition of the present invention may contain an inorganic filler other than the BN agglomerated powder of the present invention. In that case, a preferred example of the inorganic filler other than the BN agglomerated powder of the present invention is a spherical filler.

The spherical filler used together with the BN agglomerated powder of the present invention preferably has a thermal conductivity of 10 W/m·K or more, more preferably 15 W/m·K or more, and even more preferably 20 W/m·K or more. The new Mohs hardness is preferably 3.1 or more, and more preferably 5 or more. In particular, it is preferable for the thermal conductivity to be 20 to 30 W/m·K and the new Mohs hardness to be 5 to 10. By using such a spherical filler together with the BN agglomerated powder of the present invention, the adhesive strength to metal and the heat dissipation properties of the obtained heat dissipation sheet can be improved.

Here, "spherical" refers to anything that is generally recognized as being spherical; for example, an average circularity of 0.4 or more may be considered spherical, or an average circularity of 0.6 or more may be considered spherical. Usually, the upper limit of the average circularity is 1. The circularity can be measured by performing image processing on the projected image, and can be measured, for example, with 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. By using these preferred spherical fillers, the heat dissipation properties of the resulting heat dissipation sheet can be further improved.

The average particle size of the spherical filler is preferably in the range of 0.5 μm or more and 40 μm or less. It is believed that an average particle size of 0.5 μm or more allows the resin and filler to flow easily during heat molding, thereby increasing the interfacial adhesive strength of the heat dissipation sheet. In addition, an average particle size of 40 μm or less makes it easier to maintain the insulation breakdown characteristics of the heat dissipation sheet.

Other inorganic fillers that can be used include electrically insulating ones, and include at least one type of particles selected from the group consisting of carbon, metal carbides, metal oxides, and metal nitrides. Examples of carbon include 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 consisting of silicon, aluminum, oxygen, and nitrogen). Examples of metal nitrides include boron nitride, aluminum nitride, and silicon nitride, other than the BN agglomerated particles of the present invention.

There are no limitations on the shape of other inorganic fillers, and they may be particles, whiskers, fibers, plates, 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 alone or in any combination and ratio of two or more.

The content of the inorganic filler in the composition of the present invention is preferably 30% by weight or more and 99% by weight or less, particularly preferably 40% by weight or more and 90% by weight or less, and even more preferably 50% by weight or more and 80% by weight or less, based on 100% by weight of the composition of the present invention excluding the solvent.
By making the content of the inorganic filler equal to or more than the lower limit, the effect of improving thermal conductivity and the effect of controlling the linear expansion coefficient due to the inclusion of the inorganic filler tend to be sufficiently obtained, while by making the content equal to or less than the upper limit, the moldability of the cured product and the interfacial adhesion in the composite molded product described below tend to be obtained.

When the BN agglomerated powder of the present invention is used in combination with a spherical filler such as alumina as an inorganic filler, the content ratio of the BN agglomerated powder of the present invention to the spherical filler in the composition of the present invention excluding the solvent is not particularly limited, but is preferably 90:10 to 10:90 by weight, and more preferably 80:20 to 20:80.

In order to effectively obtain the effects of using the BN agglomerated powder of the present invention, it is preferable that 10% by weight or more, particularly 20% by weight or more of the inorganic filler used is the BN agglomerated powder of the present invention. In the present invention, it is preferable to use only the BN agglomerated powder of the present invention or a combination of the BN agglomerated powder of the present invention and the above-mentioned spherical filler as the inorganic filler.

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

The order of mixing the various components can be arbitrary as long as there are no particular problems such as the occurrence of reactions or precipitation. For example, a method can be used in which the thermosetting resin components are mixed and dissolved in an organic solvent (e.g., methyl ethyl ketone) to create a resin liquid, and then a thoroughly mixed inorganic filler and other components are added to the resulting resin liquid and mixed, after which an organic solvent is further added to adjust the viscosity and mixed, and then additives such as a curing agent, a curing accelerator, or a dispersant are further added and mixed.

[Heat dissipation sheet]
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 will be described below.
The sheet-shaped cured product can be produced by a commonly used method, for example, by forming the composition of the present invention into a sheet and curing it.

The composition of the present invention can be formed into a sheet by any commonly used method.
For example, when the composition of the present invention has plasticity and flowability, the composition can be molded into a desired shape, for example, by curing the composition 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.
The solvent in the composition of the present invention can be removed by a known heating method such as a hot plate, a hot air oven, an IR heating oven, a vacuum dryer, or a high-frequency heater.
Alternatively, a sheet-like cured product can be obtained by cutting the cured product of the composition of the present invention into a desired shape.

A sheet-like cured product can also be obtained by forming a slurry of the composition of the present invention (hereinafter referred to as "sheet slurry") into a sheet by a doctor blade method, a solvent casting method, an extrusion film formation method or the like.
An example of a method for producing a sheet-like cured product using this sheet slurry will be described below.

<Coating process>
First, a coating film is formed on the surface of a substrate using a sheet slurry.
That is, the sheet slurry is used to form a coating film on a substrate by a dip method, a spin coat method, a spray coat method, a blade method, or any other method. A coating device such as a spin coater, a slit coater, a die coater, or a blade coater can be used to apply the sheet slurry, and this makes it possible to uniformly form a coating film of a predetermined thickness on the substrate.
As the substrate, copper foil or a PET film, which will be described later, is generally used, but there is no limitation thereto.

<Drying process>
The coating film formed by applying the sheet slurry is dried at a temperature of usually 10 to 150°C, preferably 25 to 120°C, more preferably 30 to 110°C in order to remove the solvent and low molecular weight components. By keeping the drying temperature below the upper limit, the curing of the thermosetting resin in the slurry is suppressed, and the resin flows in the subsequent pressing process, which tends to make it easier to remove voids. By keeping the drying temperature above the lower limit, the solvent can be effectively removed.

Drying time is usually 5 minutes to 10 days, preferably 10 minutes to 3 days, more preferably 20 minutes to 1 day, and particularly preferably 30 minutes to 4 hours. By keeping the drying time at or above the lower limit, the solvent can be sufficiently removed and the residual solvent tends to be prevented from forming voids in the sheet-like cured product. By keeping the drying time at or below the upper limit, productivity tends to be improved and production costs can be reduced.

<Pressing step>
After the drying step, it is desirable to carry out a pressurizing step for the purpose of bonding inorganic fillers together to form a heat path, eliminating voids and gaps in the sheet, improving adhesion to the substrate, etc. It is desirable to carry out the pressurizing step by applying a load of 10 kgf/cm2 or ^more to the dried film on the substrate. The load is preferably 20 kgf/ ^cm2 or more, more preferably 50 kgf/ ^cm2 or more. Also, it is preferably 2000 kgf/ ^cm2 or less, more preferably 1000 kgf/ ^cm2 , and even more preferably 800 kgf/ ^cm2 or less. By setting the load at the time of pressing to the above upper limit or less, it is possible to obtain a sheet having high thermal conductivity without destroying the secondary particles of the inorganic filler and without voids in the sheet. In addition, by setting the load to the above lower limit or more, the contact between the inorganic fillers becomes good, making it easier to form a heat conduction path, so that a sheet having high thermal conductivity can be obtained.

In the pressurizing step, it is desirable to heat the dried 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 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 carrying out the pressurizing step within this temperature range, the melt viscosity of the resin in the coating film can be reduced, and voids and air spaces within the sheet can be eliminated. If the film is heated at a temperature higher than this temperature range, there is a risk that the organic components will decompose or that the residual solvent will vaporize and form voids.

The time for the pressurization step is usually 30 seconds or more, preferably 1 minute or more, more preferably 3 minutes or more, and even more preferably 5 minutes or more. It is also preferably 4 hours or less, more preferably 2 hours or less, even more preferably 1 hour or less, and particularly preferably 45 minutes or less. By keeping the pressurization time below the upper limit, the production time for the sheet-shaped cured product can be reduced, and production costs tend to be reduced. On the other hand, by keeping the pressurization time above the lower limit, voids and gaps in the sheet-shaped cured product can be sufficiently removed, and heat transfer performance and voltage resistance characteristics tend to be improved.

<Curing process>
The curing step for completely carrying out the curing reaction may be carried out under pressure or without pressure, but when pressure is applied, it is preferable to carry out the same conditions as the above-mentioned pressurizing step for the same reasons as above. Note that the pressurizing step and the curing step may be carried out simultaneously.
In particular, in the sheet forming process which involves a pressing step and a hardening step, it is preferable to apply a load within the above range and carry out the pressing and hardening.

There is no particular limit to 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, more preferably 300 μm or less. When the thickness of the heat dissipation sheet is equal to or greater than the above lower limit, voltage resistance characteristics are obtained and the dielectric breakdown voltage tends to improve. When the thickness is equal to or less than the above upper limit, the device can be made smaller and thinner, and the thermal resistance of the obtained heat dissipation sheet tends to be suppressed.

[Composite Molded Body]
The heat dissipation sheet of the present invention can be used as a composite molded body in which the heat dissipation sheet of the present invention and a metal part are laminated together. 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 may have a metal part on both surfaces. The metal part may also be patterned.

Such a composite molded product can be produced by using a metal part as the substrate and forming a sheet-like product made of the composition of the present invention on this substrate according to the method described above. It can also be produced by peeling a sheet-like product formed on a substrate other than the metal part from the substrate, and then heat-pressing the sheet onto a metal member that will become the metal part.

In this case, a sheet-like material made of the composition of the present invention is formed in the same manner as above, except that the composition is applied to a substrate such as PET, which may be treated with a release agent, and then the sheet-like material is peeled off from the substrate and placed on another metal plate, or sandwiched between two metal plates, and pressed to be integrated.

In this case, the metal plate may be a metal plate of about 10 to 10,000 μm thick made of copper, aluminum, nickel-plated metal, or the like. The surface of the metal plate may be physically roughened or chemically treated with a surface treatment agent, and from the viewpoint of adhesion between the resin composition and the metal plate, it is more preferable that the surface of the metal plate is roughened or chemically treated with a surface treatment agent, and the like.

[Semiconductor Devices]
The semiconductor device of the present invention is mounted with the heat dissipation sheet of the present invention as a heat dissipation substrate, and the heat dissipation effect and voltage resistance characteristics due to its high thermal conductivity enable high output and high density with high reliability. In the semiconductor device, conventionally known materials such as aluminum wiring, sealing materials, packaging materials, heat sinks, thermal pastes, and solders other than the heat dissipation sheet of the present invention can be appropriately used.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as it does not deviate from the gist of the invention. Note that the various conditions and evaluation result values in the following examples indicate the preferred ranges of the present invention, just as the preferred ranges in the embodiments of the present invention, and the preferred ranges of the present invention can be determined by taking into account the preferred ranges in the above-mentioned embodiments and the ranges indicated by the values in the following examples or a combination of the values of the examples.

[Measurement condition]
Various characteristics and physical properties in the following examples and comparative examples were measured by the methods described below.

<Volume average particle size ( _D50 ) of BN agglomerated powder>
The D ₅₀ (μm) of the BN agglomerated powder was measured using "Morphologi" manufactured by Malvern.

<Fine powder ratio of BN agglomerated powder>
The BN agglomerated powder after heating and calcination and classification was added to 30 ml of a 0.2 wt % aqueous solution of sodium hexametaphosphate so that the transmittance of the dispersion was 90% or more, and the mixture was irradiated with ultrasonic waves of 150 W for 1 minute to prepare a dispersion for particle size distribution measurement. The particle size distribution of this dispersion was measured (volume) using a laser diffraction/scattering type particle size distribution measuring device "Microtrac MT3300EX" manufactured by Nikkiso Co., Ltd.
From the obtained particle size distribution curve, the peaks were divided at the least frequent point between the mode of each peak and the peaks centered on the mode, and the area ratio (%) of the area with the smallest particle diameter to the entire area obtained by dividing was calculated, and the calculated value was taken as the fine powder ratio (%). In addition, when there was one peak in the particle size distribution measurement chart, the ratio (%) of the area of the area with a particle diameter of 10 μm or less to the entire peak area of the particle size distribution measurement chart was taken as the fine powder ratio.

<Thermal conductivity in the thickness direction of the sheet-like molded body>
The thermal resistance values of four sheets of different thicknesses were measured using the following device and conditions, and the thermal conductivity in a steady state method was measured from the slope represented by the thermal resistance value versus the sheet thickness (in accordance with ASTM D5470).
(1) Thickness: Thickness (μm) when pressed at a pressure of 3400 kPa using a T3 Star-DynTIM manufactured by Mentor Graphics
(2) Measurement area: the area (cm ² ) of the part that transfers heat when measured using a T3Star-DynTIM manufactured by Mentor Graphics
(3) Thermal resistance value: Thermal resistance value (K/W) when pressed at a pressure of 3,400 kPa using a T3 Star-DynTIM manufactured by Mentor Graphics.
(4) Thermal conductivity: The thermal resistance values of four sheets of different thicknesses are measured, and the thermal conductivity (W/m·K) is calculated using the following formula.
Formula: Thermal conductivity (W/m·K)=1/((slope (thermal resistance value/thickness): K/(W·μm))×(area: cm ² ))×10 ⁻²

<Voltage resistance characteristics of sheet-shaped molded body>
A 150 μm thick sheet was placed on a 2 mm thick copper plate and temporarily attached to the copper plate under pressing conditions of 20 kgf/cm ² , 80° C., and 5 minutes. The sheet was then thermally cured under pressing conditions of 100 kgf/cm ² , 175° C., and 40 minutes to obtain a sheet-like molded product. The withstand voltage of the molded product was measured in Fluorinert using a cylindrical electrode. The withstand voltage characteristic was determined as the characteristic value when the voltage was increased by 500 V every minute and a current of 10 mA or more flowed through the molded product.

[Preparation and evaluation of BN agglomerated powder from BN slurry]
The BN agglomerated powders used in the following Examples and Comparative Examples were prepared and evaluated by the following method.

<Preparation of BN Slurry>
(material)
Raw material h-BN powder (half width of (002) plane peak obtained by powder X-ray diffraction measurement: 2θ=0.67°, total oxygen concentration=7.5% by weight, specific surface area: 116 m ² /g, total pore volume: 0.754 cm ³ /g): 10,000 g
Binder (Taki Chemical Co., Ltd. "Taxeram M160L", solid content concentration 21% by weight): 11,496 g
Surfactant (Kao Corporation surfactant "Ammonium Lauryl Sulfate", solid content concentration 14% by weight): 250 g

(Preparation of Slurry)
A predetermined amount of raw material h-BN powder was weighed into a resin bottle, a predetermined amount of binder was added, and a predetermined amount of surfactant was added, followed by adding zirconia ceramic balls and stirring for 1 hour on a pot mill rotating table to prepare a slurry.

<Granulation>
Granulation from the BN slurry was carried out using a spray dryer P260 manufactured by PRIS Co., Ltd. at a disk rotation speed of 15,000 to 20,000 rpm and a drying temperature of 85°C.

<Preparation of BN agglomerated powder>
The BN granulated particles were placed in a graphite crucible with a lid (a graphite crucible having a bottomed cylindrical shape with a diameter of 200 mm and a height of 50 mm, with a graphite lid), and the temperature was raised to 2000° C. while introducing nitrogen gas. After reaching 2000° C., the temperature was maintained at that temperature for 5 hours while introducing nitrogen gas. Thereafter, the temperature was cooled to room temperature to obtain a heat-treated sample.
At this time, the heat treatment conditions were changed for each example as shown in Table 1. That is, in Examples 1 to 6, the temperature was increased to the holding temperature shown in Table 1 at the heating rate shown in Table 1, and the temperature was held for the holding time shown in Table 1, and then the temperature was increased again to 2000° C. at the heating rate shown in Table 1 and held for 5 hours as described above.
In Example 6, the same heat treatment as in Examples 1 to 5 was carried out, but a rectangular graphite partition plate having a thickness of 10 mm, a height of 50 mm, and a length of 200 mm was placed in the crucible in the diametric direction to separate the center of the crucible.
In Comparative Example 1, the temperature was increased to 2000° C. at a rate of 63° C./hr, and was maintained at 200° C. for 5 hours.

<Classification>
The heat-treated BN agglomerated powder was air-classified using 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.

<Evaluation>
After classification, the fine powder ratio was measured for the powders with a particle size of less than 100 μm according to the above-mentioned method. The volume average particle size (D ₅₀ ) was also measured. The measurement results of the BN agglomerated powders obtained in each example are shown in Table 1.

SEM observation confirmed that all BN agglomerated powders had a house-of-cards structure.

[Preparation and evaluation of sheet-like molded body]
Using each of the BN agglomerated powders obtained above, a BN agglomerated powder-containing resin composition was prepared by the following method, and a sheet-like molded article was produced.

<Preparation of BN agglomerated powder-containing resin composition>
The raw materials used are as follows:

(Thermosetting Resin Component)
Resin component 1: A specific epoxy resin having structure (2) (R ³ = structure (4)) and structure (3) (R ⁴ , R ⁵ , R ⁶ , R ⁷ = methyl groups), produced in accordance with the epoxy resin production method disclosed in the examples of JP-A-2006-176658.
Weight average molecular weight in terms of polystyrene: 30,000
Epoxy equivalent: 9,000 g/equivalent Resin component 2: Bisphenol A type liquid epoxy resin manufactured by Mitsubishi Chemical Corporation Resin component 3: Multifunctional epoxy resin containing a structure having 4 or more glycidyl groups per molecule manufactured by Nagase ChemteX Corporation

(Inorganic Filler Component)
Inorganic filler 1: BN agglomerated powder obtained in each example Inorganic filler 2: Spherical alumina particles manufactured by Admatechs Co., Ltd.
New Mohs hardness: 9
Volume average particle size: 6.5 μm
Thermal conductivity: 20-30 W/mK

(Hardening agent)
Hardener 1: Meiwa Chemical Industries, Ltd. "MEH-8000H"
Phenol Resin Hardener

(Curing catalyst)
Curing catalyst 1: "2E4MZ-A" manufactured by Shikoku Kasei Corporation
2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(17')]-ethyl-s-triazine
(Compound having a triazine ring as a nitrogen atom-containing heterocyclic structure)
Molecular weight: 247

<Examples 1 to 6, Comparative Example 1>
Using a planetary stirring device, a mixture was prepared so that the composition was: resin component 1: 7.02% by weight, resin component 2: 7.02% by weight, resin component 3: 6.67% by weight, curing agent 1: 7.37% by weight, curing catalyst 1: 0.42% by weight, inorganic filler 1 (BN agglomerated powder): 51.14% by weight, inorganic filler 2 (spherical alumina particles): 20.35% by weight. In addition, when preparing the mixture, 18.6% by weight each of methyl ethyl ketone and cyclohexanone was used so that the mixture accounted for 62.8% by weight (solid concentration) of the coating slurry.

The obtained coating slurry (slurry for sheet) was applied to a PET substrate by the doctor blade method, and after heating and drying at 60°C for 120 minutes, it was pressed at 42°C and 1500 kgf/ ^cm2 for 10 minutes to obtain a sheet-like molded product having a thickness of 150 μm. The total content of methyl ethyl ketone and cyclohexanone in the sheet-like molded product was 1 wt% or less. The thermal conductivity and voltage resistance characteristics of the obtained sheet-like molded product were measured, and the results are shown in Table 1.

From Table 1, it can be seen that by using the BN agglomerated powder of the present invention, which has a fine powder ratio of 27 volume % or less, a heat dissipation sheet with excellent thermal conductivity and voltage resistance characteristics can be realized.

Claims (4)

A method for producing boron nitride agglomerated powder by pulverizing boron nitride having a total oxygen concentration of 1 to 10% by weight in a pulverizing step, agglomerating and granulating the raw material in a granulating step, and then heat-treating the raw material under a non-oxidizing gas atmosphere in a heating step and a classification step , in which the temperature is increased at a heating rate of 125 to 200°C/hr, and before reaching the maximum heating temperature, the temperature is held at a temperature of 1400 to 1700°C, which is 300 to 600°C lower than the maximum heating temperature, for 5 to 20 hours, and then the temperature is increased at a heating rate of 125 to 200°C/hr to the maximum heating temperature of 1600°C to 2300°C, and heating is performed at the maximum heating temperature for 5 to 20 hours . In the classification step, the boron nitride agglomerated powder obtained after the heat treatment is classified into particles less than 100 μm and particles greater than 100 μm, and the particles less than 100 μm are separated, thereby obtaining a fine powder ratio defined below of 15 vol% or less and a volume average particle diameter (D ₅₀ ) is 40 μm or more .
<Definition of fine powder rate>
The fine powder ratio is determined by dividing each peak obtained in the volume-based particle size distribution measurement by the mode and the least frequent point between the peaks centered on the mode, and the ratio (%) of the area of the region with the smallest particle size in the particle size distribution measurement chart among the divided regions to the total peak area in the particle size distribution measurement chart.
When there is one peak in the particle size distribution measurement chart, the fine powder ratio is the ratio (%) of the area of the region in the particle size distribution measurement chart where the particle size is 10 μm or less to the total peak area in the particle size distribution measurement chart. 2. The method for producing a boron nitride agglomerated powder according to claim 1 , wherein the boron nitride agglomerated particles in the boron nitride agglomerated powder have a house of cards structure. A method for producing a heat dissipation sheet, comprising producing boron nitride agglomerated powder by the method for producing boron nitride agglomerated powder according to claim 1 or 2 , and using the produced boron nitride agglomerated powder to produce a heat dissipation sheet containing the boron nitride agglomerated powder. A method for manufacturing a semiconductor device, comprising the steps of: manufacturing a heat dissipation sheet by the method for manufacturing a heat dissipation sheet according to claim 3 ; and manufacturing a semiconductor device by using the manufactured heat dissipation sheet.

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