Thermally conductive sheet with metal plate and method for manufacturing thermally conductive sheet

Abstract

A heat conductive sheet with a metal plate, comprising: a metal plate; and a heat conductive sheet laminated to the metal plate and containing a thermosetting resin and boron nitride particles, the boron nitride particles having an average particle diameter of 10 μm or more and 100 μm or less, the heat conductive sheet having a warping amount of 0.15 mm or more and 1.30 mm or less when the metal plate is removed.

Description

Technical Field

[0001] This invention relates to a thermally conductive sheet with a metal plate and a method for manufacturing the thermally conductive sheet. More specifically, this invention relates to a thermally conductive sheet with a metal plate used as a thermally conductive sheet for transferring heat from heat-generating components such as electrical / electronic devices to heat-dissipating components, and a method for manufacturing the thermally conductive sheet. Background Technology

[0002] In the past, by including inorganic fillers in resins, strength and thermal conductivity have been improved compared to resins alone. For example, polymer compositions obtained by dispersing inorganic fillers for improving thermal conductivity in a base resin using epoxy resin are widely used in electronic component applications, such as thermally conductive sheets, sealing of chip components, and forming insulating layers for metal-based circuit boards used in power modules.

[0003] Here, inorganic fillers with excellent thermal conductivity and electrical insulation properties include alumina, boron nitride, silicon dioxide, and aluminum nitride. Among them, boron nitride (BN) not only has excellent thermal conductivity and electrical insulation properties but also excellent chemical stability, and is non-toxic and relatively inexpensive, making it suitable for use in thermally conductive sheets. As a thermally conductive sheet containing boron nitride, a type of thermally conductive sheet has been proposed, in which secondary particles with isotropic thermal conductivity, such as secondary agglomerated particles formed by agglomerating flake-like boron nitride particles or secondary sintered particles formed by further sintering, are dispersed in a thermosetting resin (for example, see Patent Documents 1 and 2). This thermally conductive sheet improves the thermal conductivity in the thickness direction of the sheet through the secondary particles with isotropic thermal conductivity.

[0004] In recent years, with the increasing voltage and current requirements of electrical / electronic equipment, thermally conductive sheets have been exposed to higher temperatures. Therefore, in order to further improve the thermal conductivity of thermally conductive sheets, there is a tendency to increase the amount of inorganic filler. However, increasing the amount of inorganic filler can easily lead to defects such as voids or cracks in the thermally conductive sheets, which can sometimes reduce the electrical insulation of the sheets.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2003-60134

[0008] Patent Document 2: International Publication No. 2009 / 041300 Summary of the Invention

[0009] The technical problem that the invention aims to solve

[0010] The present invention was made in view of the above-mentioned technical problems, and its object is to provide a thermally conductive sheet with balanced improvement in heat resistance and crack resistance.

[0011] Technical solutions for solving technical problems

[0012] Through in-depth research, the inventors discovered that by controlling the warpage of the sheet within a specific range, a thermally conductive sheet that balances heat resistance and crack resistance can be obtained, thus completing this invention.

[0013] According to the present invention, a thermally conductive sheet with a metal plate is provided, comprising:

[0014] Metal plate; and

[0015] A thermally conductive sheet, laminated on the aforementioned metal plate, and containing thermosetting resin and boron nitride particles.

[0016] The average particle size of the aforementioned boron nitride particles is between 10 μm and 100 μm.

[0017] When the metal plate is removed, the warpage of the thermally conductive sheet is between 0.15 mm and 1.30 mm.

[0018] Furthermore, according to the present invention, a method for manufacturing a thermally conductive sheet is provided, comprising:

[0019] The process of forming a first thermally conductive resin layer in a stage B state by coating a first thermally conductive resin composition onto a first substrate film and heating it, and then separating the first thermally conductive resin layer from the first substrate film to obtain a first thermally conductive resin film.

[0020] The process of forming a first thermally conductive resin layer in stage B by coating a second thermally conductive resin composition onto a second substrate film and heating it, and then separating the first thermally conductive resin layer from the second substrate film to obtain a second thermally conductive resin film.

[0021] The process of laminating the second thermally conductive resin film onto the first thermally conductive resin film to obtain a laminated film; and

[0022] The process of hot-pressing and curing the above-mentioned laminated film to obtain a thermally conductive sheet.

[0023] The first thermally conductive resin composition and the second thermally conductive resin composition described above contain thermosetting resin and boron nitride particles.

[0024] The average particle size of the aforementioned boron nitride particles is between 10 μm and 100 μm.

[0025] Furthermore, according to the present invention, a method for manufacturing a thermally conductive sheet is provided, comprising:

[0026] The steps of coating a thermally conductive resin composition onto a substrate film and heating it to form a thermally conductive resin layer in stage B, and separating the thermally conductive resin layer from the substrate film to obtain a thermally conductive resin film; and

[0027] The process of hot-pressing and curing the above-mentioned thermally conductive resin film to obtain a thermally conductive sheet.

[0028] The above-mentioned thermally conductive resin composition contains a thermosetting resin composition and boron nitride particles.

[0029] The average particle size of the aforementioned boron nitride particles is between 10 μm and 100 μm.

[0030] Invention Effects

[0031] According to the present invention, a thermally conductive sheet that combines heat resistance and crack resistance, and a method for manufacturing such a thermally conductive sheet, are provided. Attached Figure Description

[0032] Figure 1 This is a schematic diagram illustrating the method for measuring the warpage of the thermally conductive sheet according to this embodiment. Detailed Implementation

[0033] The embodiments of the present invention will be described below.

[0034] The thermally conductive sheet involved in this embodiment is provided in the form of a thermally conductive sheet with a metal plate laminated on top of a metal plate. In this embodiment, the thermally conductive sheet with a metal plate includes a metal plate and a thermally conductive sheet laminated on top of the metal plate. Here, the thermally conductive sheet contains a thermosetting resin and boron nitride particles, and the average particle size of the boron nitride particles is 10 μm or more and 100 μm or less. The warpage of the thermally conductive sheet with a metal plate in this embodiment when the metal plate is removed is 0.15 mm or more and 1.30 mm or less. Here, the warpage of the thermally conductive sheet refers to the maximum value of the warpage (Z-axis) when the thermally conductive sheet is placed alone on a planar worktable (X, Y axis).

[0035] In the thermally conductive sheet of this embodiment, to ensure thermal conductivity, the thermosetting resin contains boron nitride particles in a high proportion. The inventors have discovered that by controlling the warpage of the thermally conductive sheet within a specific range, even when using a high proportion of boron nitride particles, the resulting thermally conductive sheet exhibits high heat resistance and excellent crack resistance. It is believed that the high heat resistance is achieved by using boron nitride in a high proportion. Furthermore, by using boron nitride particles with large particle sizes, the warpage of the thermally conductive sheet can be controlled. The reason is not necessarily clear, but when large-particle-size boron nitride particles form a film, the boron nitride particles settle, thus creating a boron nitride particle concentration gradient in the thickness direction of the resulting sheet. More specifically, as described below, the thermally conductive sheet of this embodiment is obtained through the following steps: coating (applying) a thermally conductive resin composition onto a substrate film, and forming a resin film (resin layer) by heating. When this thermally conductive composition is applied, a layer with a high resin concentration and a layer with a high boron nitride particle concentration are formed, and warping occurs due to this compositional difference. In this embodiment, it is believed that by using boron nitride particles with a larger particle size, the warping of the obtained thermally conductive sheet can be controlled to be below 1.30 mm. Thermally conductive sheets with a warping of less than 1.30 mm will hardly or not at all crack during use, thus exhibiting excellent moisture absorption and heat resistance, making them suitable as heat dissipation materials with excellent reliability, and possessing sufficient heat resistance to withstand high-temperature use. Furthermore, the warping of the thermally conductive sheet in this embodiment is 0.15 mm or more, thereby allowing identification of the resin coating surface of the thermally conductive sheet. Here, the thermally conductive sheet of this embodiment is obtained by applying (coating) a thermally conductive resin composition onto a substrate film, forming a resin film (resin layer) by heating, and then peeling the substrate film off from the resin film (resin layer). The resin-coated surface refers to the side of the thermally conductive sheet opposite to the surface that contacts the substrate film. During the resin film (resin layer) formation process in the manufacturing method of the thermally conductive sheet, impurities from the resin composition may be present on the surface of the resin film that adheres to the substrate sheet. Since the resin-coated surface and the substrate sheet side can be distinguished, impurities can be removed by cleaning only the substrate sheet side, thereby enabling the efficient manufacture of highly reliable thermally conductive sheets.

[0036] In this embodiment, "thermal conductive sheet" refers to a sheet-like resin composition in stage B state obtained by semi-curing a thermally conductive resin composition. Furthermore, the sheet obtained by curing a thermosetting resin sheet through heat treatment is referred to as "cured thermally conductive sheet".

[0037] The warpage of the thermally conductive sheet in this embodiment can be controlled by adjusting the materials contained in the thermally conductive resin composition used to make the sheet and their proportions, and can also be controlled by adjusting the manufacturing conditions of the thermally conductive sheet.

[0038] In one embodiment, from the viewpoint of improving thermal conductivity, the boron nitride particles used for the thermally conductive sheet are preferably agglomerated particles of flake-shaped boron nitride. By using such boron nitride particles, a cured product of a thermally conductive sheet with balanced thermal conductivity and insulation can be obtained.

[0039] In this embodiment, the average particle size of the condensed flake-like boron nitride particles is 10 μm to 100 μm, more preferably 20 μm to 100 μm, and even more preferably 30 μm to 100 μm. This reduces warpage, thereby enabling the realization of a thermally conductive sheet with improved thermal conductivity and crack resistance.

[0040] In one embodiment, the boron nitride particles are preferably contained in an amount of 50% to 95% by mass relative to the entire thermally conductive sheet, more preferably 55% to 90% by mass, even more preferably 60% to 88% by mass, and particularly preferably 70% to 85% by mass. By containing boron nitride particles in the above-mentioned range, the uniformity of the film thickness of the obtained thermally conductive sheet can be improved, and the cured thermally conductive sheet has high thermal conductivity.

[0041] The thermally conductive sheet of this embodiment contains a thermosetting resin. Epoxy resin is preferably used as the thermosetting resin. As the epoxy resin, resins commonly used in the art can be used, such as epoxy resins having a phenolic varnish backbone or a cresolic varnish backbone, epoxy resins having a dicyclopentadiene backbone, epoxy resins having a biphenyl backbone, epoxy resins having an adamantane backbone, epoxy resins having a phenolic aralkyl backbone, epoxy resins having a biphenyl aralkyl backbone, and epoxy resins having a naphthyl aralkyl backbone. Epoxy resins that are liquid at room temperature can be used. As such epoxy resins, epoxy resins having a biphenyl backbone that are liquid at room temperature are preferred. These can be used alone or in combination of two or more.

[0042] In one embodiment, the epoxy resin is preferably contained in an amount of 1% to 30% by mass relative to the entire thermally conductive sheet, more preferably in an amount of 5% to 28% by mass. By using an amount of epoxy resin within the above-mentioned range, the processability of the resin composition used as the sheet material is easily improved to form the thermally conductive sheet. Furthermore, by using an amount of epoxy resin within the above-mentioned range, a thermally conductive sheet with a smooth surface can be obtained without any unevenness caused by boron nitride particles appearing on the surface of the obtained thermally conductive sheet.

[0043] In one embodiment, the thermally conductive sheet may contain other thermosetting resins in addition to epoxy resin. Examples of other thermosetting resins include cyanate ester resins. Containing cyanate ester resins can improve the insulation properties of the cured thermally conductive sheet at high temperatures. Examples of cyanate ester resins include phenolic varnish-type cyanate ester resins; bisphenol A-type cyanate ester resins, bisphenol E-type cyanate ester resins, tetramethylbisphenol F-type cyanate ester resins, and other bisphenol-type cyanate ester resins; naphthol aralkyl-type cyanate ester resins obtained by reacting naphthol aralkyl-type phenolic resins with cyanide halides; dicyclopentadiene-type cyanate ester resins; biphenyl alkyl-type cyanate ester resins, etc., but are not limited to these. When using cyanate ester resins, the amount used is preferably 2% by mass or more and 25% by mass or less relative to the entire thermally conductive sheet, more preferably 5% by mass or more and 20% by mass or less.

[0044] The thermally conductive sheet involved in this embodiment preferably contains a phenolic curing agent or curing catalyst. Examples of phenolic curing agents include phenolic varnish resins such as phenol-formaldehyde resin, cresol-formaldehyde resin, naphthol-formaldehyde resin, aminotriazine-formaldehyde resin, phenolic resin, and triphenylmethane-type phenolic varnish resin; modified phenolic resins such as terpene-modified phenolic resin and dicyclopentadiene-modified phenolic resin; aralkyl resins such as phenolic aralkyl resins having a phenylene backbone and / or a biphenylene backbone, and naphthol aralkyl resins having a phenylene backbone and / or a biphenylene backbone; bisphenol compounds such as bisphenol A and bisphenol F; and methyl-type phenolic resins. These can be used alone or in combination of two or more. When using a phenolic curing agent, its usage amount relative to the entire thermally conductive sheet is preferably 0.1% by mass or more to 30% by mass, more preferably 0.3% by mass or more to 15% by mass or less.

[0045] Examples of organometallic salts that can be used as curing catalysts include zinc naphthenate, cobalt naphthenate, tin octoate, cobalt octoate, cobalt diacetylacetonate (II), and cobalt triacetylacetonate (III); tertiary amines such as triethylamine, tributylamine, and 1,4-diazabicyclo[2.2.2]octane; imidazoles such as 2-phenyl-4-methylimidazole, 2-ethyl-4-methylimidazole, 2,4-diethylimidazole, 2-phenyl-4-methyl-5-hydroxyimidazole, and 2-phenyl-4,5-dihydroxymethylimidazole; organophosphorus compounds such as triphenylphosphine, tri-p-tolylphosphine, tetraphenylphosphonium-tetraphenylborate, triphenylphosphine-triphenylborane, and 1,2-bis-(diphenylphosphino)ethane; phenolic compounds such as phenol, bisphenol A, and nonylphenol; organic acids such as acetic acid, benzoic acid, salicylic acid, and p-toluenesulfonic acid; and mixtures thereof. These can be used individually or in combination of two or more. When using a curing catalyst, its usage is preferably 0.001% by mass or more (1% by mass) relative to the entire thermally conductive sheet.

[0046] The thermally conductive sheet of this embodiment may also contain a coupling agent. By incorporating a coupling agent, the interfacial wettability between the epoxy resin and the boron nitride particles can be improved. As the coupling agent, epoxy silane coupling agents, cationic silane coupling agents, amino silane coupling agents, titanate-based coupling agents, and silicone oil-based coupling agents can be used, but the method is not limited to these. When using a coupling agent, it is preferable to use it in an amount of 0.1% to 10% by mass relative to the entire thermally conductive sheet, and more preferably in an amount of 0.5% to 7% by mass.

[0047] The thermally conductive sheet of this embodiment may also contain a phenoxy resin. By using a phenoxy resin, the flexural strength of the thermally conductive sheet can be improved. As the phenoxy resin, phenoxy resins having a bisphenol backbone, phenoxy resins having a naphthalene backbone, phenoxy resins having an anthracene backbone, phenoxy resins having a biphenyl backbone, etc., can be used, but the method is not limited to these. When using a phenoxy resin, it is preferable to use it in an amount of 2% to 15% by mass relative to the entire resin-conductive sheet.

[0048] The thermally conductive sheet of this embodiment may contain additives such as antioxidants, leveling agents, defoamers, and dispersants without compromising the effectiveness of the present invention.

[0049] The thermally conductive sheet with a metal plate according to this embodiment can be obtained by: preparing a varnish-like thermally conductive resin composition containing the above-mentioned materials, coating the thermally conductive resin composition onto a metal plate, performing heat treatment, and drying. More specifically, firstly, a resin varnish is prepared by adding the above-mentioned resin components to a solvent. A varnish-like thermally conductive resin composition is obtained by adding boron nitride particles to the resin varnish and kneading it. Next, the obtained varnish-like thermally conductive resin composition is coated onto a metal plate, dried to remove the solvent, and a sheet-like resin composition in a stage B state can be obtained as a thermally conductive sheet. Examples of metal plates include metal foils constituting peelable carrier materials, heat dissipation components, lead frames, etc. Furthermore, the heat treatment for drying the thermally conductive resin composition is performed, for example, at 80–150°C for 5 minutes to 1 hour. The film thickness of the obtained thermally conductive sheet is, for example, 100 μm or more and 400 μm or less.

[0050] In another embodiment, the thermally conductive sheet can be manufactured through the following process:

[0051] The process of obtaining a first thermally conductive resin film by coating a first thermally conductive resin composition onto a first substrate film and heating it to form a first thermally conductive resin layer in a stage B state, and separating the first thermally conductive resin layer from the first substrate film.

[0052] The steps include: forming a first thermally conductive resin layer in stage B by coating a second thermally conductive resin composition onto a second substrate film and heating it; and obtaining a second thermally conductive resin film by separating the first thermally conductive resin layer from the second substrate film; and

[0053] The process of laminating the second thermally conductive resin film onto the first thermally conductive resin film to obtain a laminated film.

[0054] Here, the first thermally conductive resin composition and the second thermally conductive resin composition can be manufactured by the same method as the method for manufacturing the varnish-like thermally conductive resin composition described above. Furthermore, the first thermally conductive composition and the second thermally conductive resin can be the same or have different compositions.

[0055] In the thermally conductive sheet with a double-layer laminated structure obtained by the above method, the thicknesses of the first and second thermally conductive resin layers are, for example, 50 μm or more and 200 μm or less, respectively, and the thickness of the thermally conductive sheet with a double-layer laminated structure obtained by stacking them is, for example, 100 μm or more and 400 μm or less. The thicknesses of the first and second thermally conductive resin layers may be the same or different, but from the viewpoint of easily controlling the amount of warpage, it is preferable that they are the same.

[0056] In yet another embodiment, the thermally conductive sheet can be manufactured through the following process:

[0057] The steps of coating a thermally conductive resin composition onto a substrate film and heating it to form a thermally conductive resin layer in a stage B state, and separating the thermally conductive resin layer from the substrate film to obtain a thermally conductive resin film; and

[0058] The process of hot-pressing and curing the thermally conductive resin film to obtain a thermally conductive sheet.

[0059] Here, the thermally conductive resin composition can be manufactured by the same method as the method for manufacturing the varnish-like thermally conductive resin composition described above. The thickness of the single-layer thermally conductive sheet obtained by the above method is, for example, 100 μm or more and 400 μm or less.

[0060] As for the substrate film, there are no particular limitations as long as it can withstand the above-mentioned heating and drying conditions. For example, polyester films, polypropylene films, polyimide films, polyamide films, polysulfone films, and polyetherketone films can be used. The surface of these substrate films can be treated with a release agent.

[0061] In one embodiment, the specific gravity of the thermally conductive sheet in the B-stage state obtained above is preferably 1.0 to 1.9 or less. If it is within the above range, then when the sheet resin composition is cured to form a thermally conductive component, it has sufficient thermal conductivity.

[0062] In this embodiment, the thermally conductive sheet is disposed, for example, between a heat-generating element such as a semiconductor chip and a substrate such as a lead frame or wiring board (intercalation board) on which the heat-generating element is mounted, or between the substrate and a heat dissipation component such as a heat sink. This allows heat generated from the heat-generating element to be effectively dissipated to the outside of the semiconductor device while maintaining its insulation.

[0063] The embodiments of the present invention have been described above, but these are merely examples of the present invention, and various structures other than those described above may also be used.

[0064] Example

[0065] The present invention will be described below through examples and comparative examples, but the present invention is not limited thereto.

[0066] (Examples 1-4, Comparative Examples 1-3)

[0067] <1. Preparation of thermosetting resin compositions>

[0068] According to the formulation shown in Table 1, thermosetting resin, curing agent, and curing catalyst were added to methyl ethyl ketone as a solvent and stirred to obtain a mixed solution. Next, boron nitride particles as an inorganic filler were added to this mixed solution for premixing, followed by kneading using a three-roll mill to obtain a varnish-like thermosetting resin composition with uniformly dispersed boron nitride particles. The obtained thermosetting resin composition was then aged at 60°C for 15 hours.

[0069] The components shown in Table 1 are as follows.

[0070] (Thermosetting resin)

[0071] • Epoxy Resin 1: Epoxy resin with a dicyclopentadiene backbone (XD-1000, manufactured by Nippon Kayaku Co., Ltd.)

[0072] • Cyanate ester resin 1: Phenolic varnish type cyanate ester resin (PT-30, manufactured by Lonza KK)

[0073] (Curing agent)

[0074] • Phenolic curing agent 1: Triphenylmethane type phenolic varnish resin (MEH-7500, manufactured by Meiwa Kasei Corporation)

[0075] (Catalyst solidification)

[0076] • Curing catalyst 1: 2-Phenyl-4,5-dihydroxymethylimidazolium (2PHZ-PW, manufactured by Shikoku Kasei Corporation)

[0077] (Inorganic filler)

[0078] Inorganic filler 1: Boron nitride particles (average particle size 40 μm)

[0079] Inorganic filler 2: Boron nitride particles (average particle size 7μm)

[0080] <2. Fabrication of Thermally Conductive Sheets>

[0081] Sheet manufacturing method A

[0082] The above-mentioned varnish-like thermally conductive resin composition was coated onto a PET film (100mm × 100mm) and dried at 80°C for 30 minutes to produce a thermally conductive sheet with a PET film, measuring 50mm × 50mm and 200μm in thickness. The PET film was peeled off from the obtained thermally conductive sheet with the PET film, and the sheet was placed between two copper foils, heated and pressurized, and then cured. After curing, the copper foils were removed by etching to obtain the cured thermally conductive sheet.

[0083] Sheet manufacturing method B

[0084] The aforementioned varnish-like thermally conductive resin composition was coated onto two PET films (100mm × 100mm in size) and dried at 80°C for 30 minutes to produce two thermally conductive sheets with PET films, each with a size of 50mm × 50mm and a thickness of 100μm. The PET films were then peeled off from the resulting thermally conductive sheets, and the sheets were stacked with the opposite sides of the PET film-contacting surfaces of one sheet and the other sheet facing each other. These were then placed between two copper foils, heated and pressurized, and cured. After curing, the copper foils were removed by etching to obtain a cured thermally conductive sheet with a size of 50mm × 50mm and a thickness of 200μm.

[0085] ·Sheet manufacturing method C

[0086] The aforementioned varnish-like thermally conductive resin composition was coated onto two PET films (100mm × 100mm in size) and dried at 80°C for 30 minutes to produce two thermally conductive sheets with PET films, each with a size of 50mm × 50mm and a thickness of 100μm. The PET films were then peeled off from the resulting thermally conductive sheets, and the sheets were laminated with the PET film-contacting surfaces of one and the other facing each other. These laminates were then placed between two copper foils, heated and pressurized, and cured. After curing, the copper foils were removed by etching to obtain a cured thermally conductive sheet with a size of 50mm × 50mm and a thickness of 200μm.

[0087] <3. Determination of physical properties of thermally conductive sheets>

[0088] The warpage of the cured thermally conductive sheet was measured. Specifically, as... Figure 1 As shown, the thermally conductive sheet obtained by the above method is placed such that the central portion of the thermally conductive sheet 10 contacts the plate 20, while the ends of the thermally conductive sheet 10 float above the plate. Figure 1 As shown, the vertical distance A from the end of the thermally conductive sheet 10 to the plate was measured as the warpage of the thermally conductive sheet. The results are shown in Table 1.

[0089] <4. Performance Evaluation of Thermally Conductive Sheets>

[0090] The following aspects of the thermally conductive sheet obtained above were evaluated.

[0091] (Crack resistance)

[0092] Regarding the crack resistance of the thermally conductive sheet, a power module substrate was fabricated using the aforementioned thermally conductive sheet. The resulting substrate was placed in a 300°C oven and left to stand for 5 minutes. Internal cracks were then confirmed non-destructively using SAT (Supersonic Aperture Test). After confirming the presence of cracks using SAT, the cross-section of the thermally conductive sheet was observed using a scanning electron microscope (SEM). The results are shown in Table 1 according to the following evaluation criteria.

[0093] ◎: No crack was detected by the SAT method.

[0094] ○: The presence of cracks was confirmed by SAT method, but no peeling of more than 10 μm was confirmed between the thermally conductive sheet and the support substrate by SEM.

[0095] ×: Using SEM, a peel of more than 10 μm was confirmed between the thermally conductive sheet and the support substrate.

[0096] (Heat resistance after moisture absorption treatment)

[0097] After curing a 50mm×50mm thermally conductive sheet and letting it stand for 2 days at 40℃ and 90% humidity, the copper foil side was suspended in a solder bath at 260℃~300℃, and the appearance was checked for any abnormalities after 30 seconds. The evaluation criteria are as follows. The results are shown in Table 1.

[0098] <Evaluation Criteria>

[0099] ○: No abnormalities

[0100] ×: There is expansion (parts that are expanded overall).

[0101] (thermal conductivity)

[0102] The thermally conductive sheet obtained above was heat-treated at 180°C and 10 MPa for 40 minutes to obtain a cured thermally conductive sheet. Then, the thermal conductivity in the thickness direction of the cured thermally conductive sheet was measured using a laser flash method. Specifically, the thermal conductivity was calculated using the following formula: the thermal diffusivity (α) measured by the laser flash method (half-life method), the specific heat (Cp) measured by the DSC method, and the density (ρ) measured based on JIS-K-6911. The unit of thermal conductivity is W / (m·K). The measurement temperature was 25°C. Thermal conductivity [W / (m·K)]=α[mm 2 / s]×Cp[J / kg·K]×ρ[g / cm 3 The results are presented in Table 1 based on the following evaluation criteria.

[0103] ○: Above 8W / (m·K)

[0104] ×: Less than 8 W / (m·K)

[0105] (Distinguishing features of resin-coated surfaces)

[0106] The degree of warpage of the cured thermally conductive sheet was visually observed to confirm whether the resin-coated surface could be identified. The resin-coated surface refers to the side of the thermally conductive sheet opposite to the surface in contact with the substrate film. The evaluation criteria are as follows.

[0107] ○: Able to visually identify resin-coated surfaces.

[0108] ×: The resin coating surface cannot be visually identified.

[0109] [Table 1]

[0110]

[0111] The thermally conductive sheet of the embodiment has balanced heat resistance and crack resistance, and the resin coating surface of the sheet can be identified.

[0112] Explanation of reference numerals in the attached figures

[0113] 10: Thermally conductive sheet; 20: Flat plate.

[0114] This application claims priority based on Japanese Application No. 2020-091379, filed on May 26, 2020, and incorporates all of its disclosure herein.

Claims

1. A method for manufacturing a thermally conductive sheet, characterized in that, include: The process of obtaining a first thermally conductive resin film by coating a first thermally conductive resin composition onto a first substrate film and heating it to form a first thermally conductive resin layer in a stage B state, and separating the first thermally conductive resin layer from the first substrate film. The process of forming a second thermally conductive resin layer in a stage B state by coating a second thermally conductive resin composition onto a second substrate film and heating it, and then separating the second thermally conductive resin layer from the second substrate film to obtain a second thermally conductive resin film. The process of laminating the second thermally conductive resin film onto the first thermally conductive resin film to obtain a laminated film, with the face of the first thermally conductive resin film in contact with the first substrate film and the face of the second thermally conductive resin film opposite to the face of the second substrate film facing each other. and The process of hot-pressing and curing the laminated film to obtain a thermally conductive sheet. The first thermally conductive resin composition and the second thermally conductive resin composition contain thermosetting resin and boron nitride particles. The thermosetting resin includes epoxy resin and cyanate ester resin. The boron nitride particles have an average particle size of 10 μm to 100 μm. The warpage of the thermally conductive sheet is between 0.15 mm and 1.30 mm.

2. The method for manufacturing the thermally conductive sheet according to claim 1, characterized in that: The thickness of the first thermally conductive resin layer is between 50 μm and 200 μm. The thickness of the second thermally conductive resin layer is more than 50 μm and less than 200 μm.

3. The method for manufacturing the thermally conductive sheet according to claim 1 or 2, characterized in that: The thickness of the thermally conductive sheet is between 100μm and 400μm.

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