JP7304167B2 - Method for manufacturing insulating sheet, method for manufacturing metal-based circuit board, and insulating sheet - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing an insulating sheet, a method for manufacturing a metal-based circuit board, and an insulating sheet.

2. Description of the Related Art In recent years, there has been a demand for electronic components to be smaller and to have higher performance. Along with this, the amount of heat generated from semiconductor elements and the like in narrow spaces tends to increase, and methods for efficiently dissipating the heat generated from semiconductor elements and the like are being studied.

For example, in Patent Documents 1 and 2, a material with high thermal conductivity (for example, alumina, aluminum nitride, boron nitride, etc.) is used for the insulating layer of the substrate on which the semiconductor element or the like is mounted, and the heat generated by the semiconductor element or the like is dissipated. A method for efficiently releasing heat to a housing and cooling fins is disclosed.

In addition, Patent Document 3 discloses a thermally conductive sheet using aggregated particles in which particles of scale-like boron nitride are aggregated and having a porosity of 50% or less, and a power comprising the thermally conductive sheet A module is disclosed.

JP-A-6-44824 JP 2011-249606 A JP 2010-157563 A

Sheets used as insulating materials in electronic parts and the like are required to have high thermal conductivity and high insulating properties, and there is still room for improvement in this regard.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for producing an insulating sheet having sufficient thermal conductivity and insulating properties and particularly excellent in at least one of the thermal conductivity and insulating properties. Another object of the present invention is to provide a method for manufacturing a metal base circuit board using the insulating sheet.

In the present invention, a resin sheet having a porosity of 15% or more is obtained by applying a coating liquid containing an epoxy resin, a curing agent, agglomerated powder of boron nitride, and a solvent into a sheet and then heating the sheet. Provided is a method for manufacturing an insulating sheet, comprising a first step and a second step of hot-pressing a resin sheet to obtain an insulating sheet.

The crushing strength of the boron nitride agglomerated powder may be 1.0 to 15 MPa.

The content of the solvent in the coating liquid may be 30 to 100 parts by mass with respect to 100 parts by mass of the solid content in the coating liquid.

The porosity of the resin sheet may be 20-50%.

The temperature of the hot press may be 130-200° C., and the press pressure may be 3-20 MPa.

The hot press may be a laminate obtained by sandwiching a resin sheet between a first metal plate and a second metal plate.

The present invention also provides a resin sheet having a porosity of 15% or more by applying a coating liquid containing an epoxy resin, a curing agent, agglomerated powder of boron nitride, and a solvent into a sheet, followed by heating. A first step to obtain, and a laminate obtained by sandwiching a resin sheet between a first metal plate and a second metal plate is hot-pressed to obtain the first metal plate, the insulating sheet, and the second metal plate. a second step of obtaining a metal substrate comprising two metal plates in this order; and a third step of forming an electric circuit on at least one surface of the metal substrate. provide a way.

The present invention further provides an insulating sheet comprising boron nitride agglomerates having a porosity greater than 50%.

ADVANTAGE OF THE INVENTION According to this invention, it has sufficient thermal conductivity and insulation, and can provide the manufacturing method of the insulation sheet with which at least one of thermal conductivity and insulation was especially excellent. Further, according to the present invention, it is possible to provide a method for manufacturing a metal base circuit board using the insulating sheet.

It is a figure which shows the measurement principle of the porosity of boron nitride coherent powder. It is a sectional view showing a metal base circuit board concerning this embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments.

[Insulating sheet]
The insulating sheet according to the present embodiment includes a first step of applying a coating liquid in a sheet shape and then heating to obtain a resin sheet, and a second step of hot-pressing the resin sheet to obtain an insulating sheet. It can be manufactured by going through. Each step will be described below in order.

<First step>
The coating liquid used in the first step contains an epoxy resin, a curing agent, agglomerated powder of boron nitride, and a solvent.

Examples of solvents include, but are not limited to, hydroxyl group-containing aliphatic hydrocarbons such as alcohols, carbonyl group-containing aliphatic hydrocarbons such as ketones, halogenated aliphatic hydrocarbons, halogenated Examples include aromatic hydrocarbons, ethers, aromatic hydrocarbons, nitrogen-containing compounds, aprotic solvents, and the like. More specifically, for example, methanol, ethanol, propanol, isopropanol, acetone, methyl ethyl ketone, cyclohexanone, cyclopentanone, 1-acetoxy-2-methoxyethane, pentane, hexane, dichloromethane, chloroform, trichloroethane, chlorobenzene, dichlorobenzene ( ortho-dichlorobenzene, etc.), tetrahydrofuran, butyl cellosolve, benzene, toluene, xylene, N-methylpyrrolidone (NMP), pyridine, acetonitrile, dimethylformamide (DMF), dimethylsulfoxide (DMSO), dimethylformamide and the like. These solvents can be used singly or in combination of two or more.

The content of the solvent in the coating liquid is preferably 30 to 100 parts by mass, more preferably 40 to 90 parts by mass, and 50 to 70 parts by mass with respect to 100 parts by mass of the solid content of the coating liquid. It is even more preferable to have If the content of the solvent is 30 parts by mass or more with respect to 100 parts by mass of the solid content of the coating liquid, the dispersion of the boron nitride agglomerated powder can be promoted. When the content of the solvent is 100 parts by mass or less per 100 parts by mass of the solid content of the coating liquid, it is possible to reduce the inclusion of air bubbles in the coating liquid. In this specification, the solid content of the coating liquid means components other than volatile components such as water and solvent.

Examples of epoxy resins include bisphenol A type epoxy resin, bisphenol S type epoxy resin, bisphenol F type epoxy resin, bisphenol A type hydrogenated epoxy resin, polypropylene glycol type epoxy resin, polytetramethylene glycol type epoxy resin, naphthalene type Examples include epoxy resins, phenylmethane-type epoxy resins, tetrakisphenolmethane-type epoxy resins, biphenyl-type epoxy resins, epoxy resins having a triazine nucleus in the skeleton, and bisphenol A alkylene oxide adduct-type epoxy resins. These epoxy resins can be used singly or in combination of two or more. Among these, it is preferable to use a naphthalene type epoxy resin as the epoxy resin from the viewpoint of heat resistance.

Examples of curing agents include amine-based resins, acid anhydride-based resins, and phenol-based resins, and these can be used singly or in combination of two or more. Amine-based resins generally have high reactivity with epoxy resins, and can more effectively impart insulating properties to the cured insulating sheet. Acid anhydride-based resins and phenol-based resins generally have low reactivity with epoxy resins, and even if the time from mixing with epoxy resin to coating is long, the viscosity of the coating solution will increase due to the reaction. less and excellent workability.

The total content of the epoxy resin and the curing agent in the solid content of the coating liquid is preferably 5 to 50 parts by mass, more preferably 10 to 40 parts by mass, with respect to 100 parts by mass of the solid content of the coating liquid. More preferably, 15 to 35 parts by mass is even more preferable. If the total content of the epoxy resin and the curing agent is 5 parts by mass or more with respect to 100 parts by mass of the solid content of the coating liquid, it is possible to obtain an insulating sheet with better insulation. If the amount is 50 parts by mass or less based on the mass parts, an insulating sheet with more excellent thermal conductivity can be obtained.

Agglomerated boron nitride powder is particulate powder in which scaly boron nitride is aggregated into a spherical shape. The aggregated powder of boron nitride can be produced by producing scaly primary particles of boron nitride and then aggregating the primary particles. Further, agglomerated powder of boron nitride can be produced directly from a boron nitride precursor. The boron nitride aggregated powder according to the present embodiment preferably has voids, and more preferably has a porosity of more than 50%. By using the boron nitride agglomerated powder having voids, the agglomerated powder is easily deformed during press molding of the resin sheet, which makes it easier for the boron nitride agglomerated powder to come into contact with each other, thereby improving the thermal conductivity more efficiently. can. From this point of view, the boron nitride aggregated powder more preferably has a porosity of 60% or more. In addition, the boron nitride aggregated powder has a porosity of 90% or less from the viewpoint of suppressing an increase in the viscosity of the coating liquid due to the resin entering the voids of the aggregated powder and suppressing the occurrence of defects such as voids. It preferably has a porosity of 80% or less, and even more preferably has a porosity of 75% or less. The porosity of the boron nitride agglomerated powder can be adjusted by the method described in JP-A-2018-20932.

As used herein, the porosity of the boron nitride agglomerated powder means a value determined by measuring the total pore volume using a mercury porosimeter in accordance with JIS R 1655. More specifically, the total pore volume using a mercury porosimeter is measured using, for example, "PASCAL 140-440" (manufactured by FISONS INSTRUMENTS, trade name), and can be calculated based on the following formula. .
Formula ε _g =V _g /(V _g +1/ρ _t )×100
In the formula, ε _g is the porosity (%) of the boron nitride agglomerated powder, and V _g is the cumulative pore volume (cm ³ /g) of the intra-particle voids 12 (inter-particle voids 15 in FIG. 1). , ρ _t is the density of the primary hexagonal boron nitride particles, 2.34 (g/cm ³ ). In addition, V _g is a value (reference numeral 14 in FIG. 1) obtained by subtracting the cumulative pore volume of the interparticle voids (interparticle voids 11 in FIG. 1) from the total pore volume (total pore volume 13 in FIG. 1). can ask.

The average particle size of the aggregated boron nitride powder is preferably 20 to 100 μm at a cumulative value of 50% of the cumulative particle size distribution in particle size distribution measurement by a laser diffraction light scattering method in accordance with JIS Z8825. By making it 20 μm or more, it is possible to suppress a decrease in thermal conductivity due to an increase in the interface between the boron nitride aggregated powder and the resin. Further, by setting the particle size to 100 μm or less, it is possible to suppress breakage of the boron nitride aggregated powder due to shear stress during kneading. A commercially available particle size distribution analyzer can be used for the average particle size. In the measurement, water was used as a solvent and hexametaphosphoric acid was used as a dispersant. A refractive index of 1.33 was used for water, and a refractive index of 1.80 was used for the aggregate powder of boron nitride.

The crushing strength of the boron nitride agglomerated powder is not particularly limited, and may be, for example, 0.5 to 20 MPa. If the crushing strength of the boron nitride agglomerated powder is 0.5 MPa or more, it is possible to suppress the boron nitride agglomerated powder from collapsing when kneading with the resin, and it becomes easier to control the orientation, so it is easier to maintain thermal conductivity. Become. If the crushing strength of the boron nitride agglomerated powder is 20 MPa or less, the agglomerated powder is easily deformed during press molding of the resin sheet. be able to. From this point of view, the crushing strength of the aggregated boron nitride powder is preferably 1.0 to 15 MPa.

As used herein, the crushing strength of agglomerated boron nitride powder means a value obtained from a test force when the particles are deformed, which is measured according to JIS R 1639-5. More specifically, for example, the test force is measured using a microcompression tester "MCT-510" (manufactured by Shimadzu Corporation, trade name), and the crushing strength can be calculated based on the following formula.
Formula S _t =2.8P/πd ²
where _St is the crushing strength (MPa), P is the breaking test force (N), and d is the particle diameter (mm). In the formula, "2.8" is a coefficient, determined with reference to Japan Mining Association, 81, p1024 (1965). The test was performed by a compression test using a flat indenter with a diameter of 200 μm, and the test conditions were a set test force of 49 (mN) and a load speed of 0.25 (mN/sec). The measurement is performed 10 times, and the average value of the crushing strength calculated for each measurement is taken as the crushing strength of the boron nitride agglomerated powder.

The content of the boron nitride aggregated powder in the coating liquid is preferably 40 to 100 parts by mass, more preferably 50 to 80 parts by mass, based on 100 parts by mass of the solid content. Thermal conductivity can be improved by setting the content of the boron nitride cohesive powder to 40 parts by mass or more with respect to 100 parts by mass of the solid content. In addition, by setting the content of the boron nitride agglomerated powder to 100 parts by mass or less with respect to 100 parts by mass of the solid content, it is possible to improve the coating properties of the coating liquid and the gap between the insulating sheet and the metal plate during the production of the metal base circuit board. It is possible to efficiently suppress the occurrence of gaps in the gaps and effectively maintain the thermal conductivity.

In addition to the components described above, other components can be appropriately added to the coating liquid. Other components include, but are not limited to, curing accelerators, antioxidants, surfactants, coupling agents, coloring agents, viscosity modifiers, leveling agents, wetting and dispersing agents, and inorganic powders other than boron nitride aggregates. A filler etc. are mentioned. When the coating liquid contains the above other components, the content is not particularly limited, but may be, for example, 5 parts by mass or less, or 1 part by mass or less with respect to 100 parts by mass of the solid content of the coating liquid. good.

Examples of curing accelerators include imidazoles such as 2-ethyl-4-methylimidazole and 2-methylimidazole, and phosphorus compounds such as triphenylphosphine and tripparatolylphosphine.

Examples of antioxidants include phenol-based antioxidants, phosphite-based antioxidants, thioether-based antioxidants, and the like.

Examples of surfactants include anionic surfactants such as higher fatty acid potassium salts, rosin acid potassium salts, and sodium sulfonate salts, nonionic surfactants having an oxyalkylene chain in the molecule, quaternary ammonium salts, and the like. Examples include cationic surfactants.

Examples of silane coupling agents include vinyl-based silane coupling agents such as vinyltrimethoxysilane and vinyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, and 3-glycidoxypropylmethyldimethoxysilane. Epoxy silane coupling agents such as silane, 3-methacryloxypropylmethyldimethoxysilane, (meth)acrylic acid-modified silane coupling agents such as 3-methacryloxytrimethoxysilane, N-2-(aminoethyl)-3- Examples include amino-based silane coupling agents such as aminopropylmethyldimethoxysilane.

Examples of colorants include synthetic inorganic pigments, natural mineral pigments and organic pigments.

Examples of inorganic fillers other than the boron nitride agglomerated powder include boron nitride flake powder, alumina, crystalline silica, and magnesium oxide.

In the first step, a resin sheet can be obtained by applying the above-described coating liquid to a desired thickness in a sheet form using various coaters, followed by heating and drying. By appropriately adjusting the properties and amounts of the solid content and solvent in the coating liquid, and the amount of heat for them, the reaction rate of the coating liquid applied in the form of a sheet is controlled, and the semi-cured (B-stage state) resin sheet. can be obtained. As for the method of molding into a sheet, besides the method of coating on a base material such as a release film, a method such as extrusion molding, injection molding, or laminate molding may be used.

The reaction rate of the coating liquid applied in the form of a sheet may be, for example, 30% or more and 60% or less from the viewpoint of appropriately controlling the progress of the reaction of the epoxy resin.

The reaction rate can be calculated as follows using, for example, a differential scanning calorimeter (DSC) "Q2000" (manufactured by TA Instruments, trade name).

Using a differential scanning calorimeter, the obtained B-stage resin sheet was heated to 25 to 300° C. at a heating rate of 10° C./min in a nitrogen atmosphere, and the total calorific value C ₁ (cal/g) was measured. Measure. Next, a sample obtained by evaporating only the solvent from the uncured coating liquid is measured with a differential scanning calorimeter under the same conditions to measure the total calorific value C ₀ (cal/g). The cure rate is obtained from (C ₀ -C ₁ )/C ₀ ×100(%).

The resin sheet obtained by the first step has a porosity of 15% or more. By using a resin sheet having certain voids, deformation of the resin and movement of components such as boron nitride aggregated powder contained in the resin can be easily performed when the resin sheet is hot-pressed in the second step described later. can be done. As a result, it is considered that the boron nitride aggregated powder is less likely to be destroyed during hot pressing, and an effective heat conduction path can be formed while maintaining the orientation in the aggregated powder. For this reason, the resin sheet obtained in the first step preferably has a porosity of 20% or more, and more preferably has a porosity of 25% or more. Although the upper limit of the porosity of the resin sheet is not particularly limited, it may be, for example, 80% or less, 70% or less, or 50% or less.

The porosity of the resin sheet can be calculated from the measured specific gravity and the theoretical specific gravity of the resin sheet by the following formula.
Porosity (%) of resin sheet = {1-(measured specific gravity/theoretical specific gravity)} x 100
Here, the measured specific gravity of the resin sheet is obtained from the weight of the resin sheet in air, the weight in water, and the density of water using a specific gravity measurement kit "AD-1653" (manufactured by A&D Co., Ltd., trade name). can be calculated. The theoretical specific gravity of the resin sheet can be calculated from the specific gravity of each material constituting the solid content of the coating liquid and its composition ratio.

The orientation index of boron nitride in the resin sheet is preferably 1% or more, more preferably 5% or more, and even more preferably 10% or more. When the orientation index is within the above range, the boron nitride powder in the resin sheet is oriented in the direction perpendicular to the surface, and high thermal conductivity can be achieved. Although the upper limit of the orientation index of boron nitride in the resin sheet is not particularly limited, it may be, for example, 90% or less or 80% or less.

The orientation index of boron nitride in the resin sheet is the integrated value of the (100) plane peak among the peaks obtained from X-ray diffraction measurement using an X-ray diffractometer “XRD6100” (manufactured by Shimadzu Corporation, trade name). The integrated value P0 of the peaks of P and (002) planes can be calculated and obtained using the following formula.
Orientation index f={P/(P+P0)}×100

<Second step>
An insulating sheet can be obtained by hot-pressing the resin sheet obtained in the first step.

The conditions for the hot press are not particularly limited, and are appropriately set according to the type of resin sheet to be used and the use of the resulting insulating sheet. For example, the temperature of the hot press may be 130-200° C., and the pressure of the hot press may be 3-20 MPa.

When hot-pressing the resin sheet, the hot-pressing may be performed on a laminate obtained by sandwiching the resin sheet between the first metal plate and the second metal plate. As the first metal plate and the second metal plate, for example, those made of aluminum, copper, iron or the like and having a thickness of 0.1 to 5 mm or 0.035 to 2 mm may be appropriately used. . Also, the first metal plate and the second metal plate may be made of the same material or different materials.

[Metal base circuit board]
FIG. 2 is a cross-sectional view showing the metal base circuit board according to this embodiment. As shown in FIG. 2, the metal base circuit board 20 according to this embodiment includes a circuit board 21, an insulating sheet 22, and a base plate 23 in this order.

The metal base circuit board 20 according to the present embodiment is formed by applying a coating liquid containing an epoxy resin, a curing agent, a boron nitride aggregated powder, and a solvent in a sheet form, followed by heating to obtain a thickness of 15% or more. A first step of obtaining a resin sheet having a porosity, and heat-pressing a laminate obtained by sandwiching the resin sheet between the first metal plate and the second metal plate to form the first metal plate. , an insulating sheet, and a second metal plate in this order; a second step of obtaining a metal substrate; and a third step of forming an electric circuit on at least one surface of the metal substrate. can do.

The first step is the same as the first step described in the manufacturing method of the insulating sheet, and redundant description is omitted here.

In the second step, during the hot press, the laminate obtained by sandwiching the resin sheet between the first metal plate and the second metal plate is hot pressed. The conditions for the hot press may be the same as the conditions explained in the second step in the method for manufacturing the insulating sheet. As a result, a metal substrate having the first metal plate, the insulating sheet, and the second metal plate in this order can be obtained.

In the third step, an electric circuit is formed on at least one surface of the hot-pressed metal substrate to obtain the metal base circuit substrate. The method of forming the electric circuit is not particularly limited, and for example, it can be formed by subjecting a metal plate to a treatment such as an etching treatment. In the metal substrate, one or both of the first metal plate and the second metal plate may be used as the metal plate for forming the electric circuit. As the metal plate on which the electric circuit is formed (which becomes the circuit board 21), for example, a plate made of aluminum, copper, or the like and having a thickness of 0.035 to 2 mm can be used. As the metal plate on which the electric circuit is not formed (which becomes the base plate 23), for example, a plate made of aluminum, copper, iron, or the like and having a thickness of 0.1 to 5 mm can be used.

EXAMPLES 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.

(Examples 1 to 26, Comparative Examples 1 to 3)
[Preparation of coating liquid]
Each component shown below was mixed based on the compounding ratio (parts by mass) shown in Tables 1 to 5 to prepare a coating liquid.

<Epoxy resin>
A1: Bisphenol A type epoxy resin (manufactured by Mitsubishi Chemical Corporation, trade name "ep828", specific gravity: 1.2)
A2: Bisphenol F type epoxy resin (manufactured by Mitsubishi Chemical Corporation, trade name "YDF-170", specific gravity: 1.2)
A3: Naphthalene type epoxy resin (manufactured by DIC, trade name “HP-4032D”, specific gravity: 1.2)

<Curing agent>
B1: Phenol novolac resin (manufactured by Tohto Kasei Co., Ltd., trade name "TD2131", specific gravity: 1.1)
B2: Aromatic amine (manufactured by Nippon Gosei Kako Co., Ltd., trade name “H84B”, specific gravity: 1.1)
B3: Aliphatic amine (manufactured by Huntsman, trade name "D400", specific gravity: 1.1)

<Boron nitride aggregated powder>
The porosity of the boron nitride agglomerated powder was adjusted by the method described in JP-A-2018-20932.
C1: average particle size: 70 μm, porosity: 10%, crushing strength: 2 MPa
C2: Average particle size: 70 μm, porosity: 20%, crushing strength: 2 MPa
C3: Average particle size: 70 μm, porosity: 60%, crushing strength: 0.5 MPa
C4: average particle size: 70 μm, porosity: 60%, crushing strength: 1 MPa
C5: average particle size: 70 μm, porosity: 60%, crushing strength: 2 MPa
C6: average particle size: 70 μm, porosity: 60%, crushing strength: 15 MPa
C7: average particle size: 70 μm, porosity: 60%, crushing strength: 20 MPa
C8: average particle size: 70 μm, porosity: 70%, crushing strength: 2 MPa
C9: average particle size: 70 μm, porosity: 80%, crushing strength: 2 MPa

<Solvent>
D1: butyl cellosolve D2: 1-acetoxy-2-methoxyethane

<Others>
E1: Curing accelerator (manufactured by Shikoku Kasei Co., Ltd., 2E4MZ: 2-methyl-4-methylimidazole)
E2: Boron nitride scale powder (manufactured by Denka, trade name “SGP”)
E3: Alumina (manufactured by Showa Denko, trade name “AL-170”)

[Production of resin sheet]
Each of the coating solutions obtained above is applied to a polyethylene terephthalate (PET) film having a thickness of 0.05 mm so that the thickness after drying by heating is 0.20 mm, and the temperature is maintained at 100° C. for 15 minutes. It was dried by heating for 90 minutes to obtain a B-stage resin sheet. Tables 1 to 5 show the reaction rate in each coating liquid, the porosity of each resin sheet, and the orientation index of boron nitride in each resin sheet.

[Preparation of insulating sheet]
The resin sheet removed from the PET film is placed on an aluminum metal plate with a thickness of 1.5 mm, and a 0.035 mm copper foil "GTS-MP" (manufactured by Furukawa Circuit Foil Co., Ltd., trade name) is placed on the resin sheet. A metal substrate provided with an insulating sheet was obtained by placing the roughened surface and heat-curing for 180 minutes under the temperature and pressure conditions shown in Tables 1 to 5 while applying a surface pressure of 160 kgf/cm ² with a press.

[Production of metal base circuit board]
A circuit was formed by etching the copper foil on the metal substrate obtained above to produce a metal base circuit substrate.

(Evaluation of thermal conductivity of metal base circuit board)
Pour each coating liquid into a silicone sheet to prepare a cured body of 10 mm × 10 mm × 0.5 mm (thickness), measure the thermal diffusivity α2 by the laser flash method, and calculate the thermal conductivity λ from the following formula. bottom.
λ=α2× _Cp ×ρ
The specific heat _Cp was calculated from DSC measurement, and the specific gravity ρ was measured by the Archimedes method. The results are shown in Tables 1-5.

(Evaluation of insulating property of metal base circuit board)
The insulation properties of the obtained metal base circuit board were measured based on JIS C 6481 using a withstand voltage tester "TOS8650" (manufactured by Kikusui Electronics Co., Ltd., trade name). The results are shown in Tables 1-5.

Evaluation of the thermal conductivity and insulation of the metal base circuit board is performed according to the above method, and if the thermal conductivity is 9.5 W / mK or more, the metal base circuit It can be said that the insulating sheet in the substrate has particularly excellent thermal conductivity, and if the insulating property is 40 kV/mm or more, the insulating sheet can be said to have particularly excellent insulating property. However, even if it can be said that either thermal conductivity or insulation is excellent, if the other does not satisfy practically acceptable levels of thermal conductivity and insulation, performance as an insulation sheet. It is not superior to For example, if the thermal conductivity is less than 5 W/mK or the insulation is less than 30 kV/mm, it can be determined that the insulating sheet does not meet practically acceptable and sufficient performance.

All of the metal base circuit boards obtained in Examples 1 to 26 have sufficient thermal conductivity and insulation (thermal conductivity is 5 W/mK or more and insulation is 30 kV/mm or more). , at least one of thermal conductivity and insulation is particularly excellent (thermal conductivity is 9.5 W/mK or more and/or insulation is 40 kV/mm or more).

20... Metal base circuit board, 21... Circuit board, 22... Insulating sheet, 23... Base plate.

Claims (8)

A first step of obtaining a resin sheet having a porosity of 15% or more by applying a coating liquid containing an epoxy resin, a curing agent, agglomerated boron nitride powder, and a solvent in a sheet form and then heating the sheet. and,
a second step of hot-pressing the resin sheet to obtain an insulating sheet;
A method for manufacturing an insulating sheet. The production method according to claim 1, wherein the crushing strength of the boron nitride aggregated powder is 1.0 to 15 MPa. 3. The manufacturing method according to claim 1, wherein the content of the solvent in the coating liquid is 30 to 100 parts by mass with respect to 100 parts by mass of the solid content in the coating liquid. The manufacturing method according to any one of claims 1 to 3, wherein the resin sheet has a porosity of 20 to 50%. The manufacturing method according to any one of claims 1 to 4, wherein the temperature of the hot press is 130 to 200°C and the press pressure is 3 to 20 MPa. The production according to any one of claims 1 to 5, wherein the heat press heat-presses a laminate obtained by sandwiching the resin sheet between a first metal plate and a second metal plate. Method. A metal base circuit comprising a first metal plate, an insulating sheet, and a second metal plate in this order, wherein at least one of the first metal plate and the second metal plate forms an electric circuit. A method of manufacturing a substrate,
A first step of obtaining a resin sheet having a porosity of 15% or more by applying a coating liquid containing an epoxy resin, a curing agent, agglomerated boron nitride powder, and a solvent in a sheet form and then heating the sheet. and,
A laminate obtained by sandwiching the resin sheet between the first metal plate and the second metal plate is hot-pressed to form the first metal plate, the insulating sheet, and the second metal plate. a second step of obtaining a metal substrate provided in order;
a third step of forming an electric circuit on at least one of the first metal plate and the second metal plate of the metal substrate;
A method of manufacturing a metal-based circuit board, comprising: The production method according to any one of claims 1 to 6 , wherein the boron nitride cohesive powder contains a boron nitride cohesive powder having a porosity of more than 50% and 90% or less .

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