Thermally conductive sheet

Abstract

A thermally conductive sheet containing: an epoxy resin A having a prescribed repeating unit; and a thermally conductive filler.

Description

Thermally conductive sheet

[0001] The present invention relates to a thermally conductive sheet.

[0002] A variety of circuit boards have been put to practical use as circuit boards for mounting electronic and electrical components such as semiconductor elements to form hybrid integrated circuits. Circuit boards are classified based on the board material, such as resin circuit boards, ceramic circuit boards, and metal-based circuit boards.

[0003] Resin circuit boards are inexpensive, but due to the low thermal conductivity of the substrate, they are limited to applications requiring relatively low power. Ceramic circuit boards, due to the high insulation reliability and heat resistance characteristics of ceramics, are suitable for applications requiring relatively high power, but have the disadvantage of being expensive. On the other hand, metal-based circuit boards have properties intermediate between the two, and are suitable for general-purpose applications requiring relatively high power, such as refrigerator inverters, commercial air conditioner inverters, power supplies for industrial robots, and automotive power supplies.

[0004] For example, Patent Document 1 discloses a laminate for a metal base circuit board having a structure in which two metal layers are bonded together by an insulating layer, in order to address the issue of reduced adhesive reliability of insulating layers during high-temperature treatment, in which the surface roughness of the metal layer to be bonded to the insulating layer is specified.

[0005] Japanese Patent Publication No. 2022-173751

[0006] If ceramic circuit boards could be replaced with metal-based circuit boards, productivity could be improved. Ceramic circuit boards also have the problem of prone to solder cracks on the board during heat cycles. Substituting metal-based circuit boards for these boards is expected to reduce the occurrence of solder cracks. Meanwhile, in fields such as industrial modules where ceramic circuit boards are used, high-temperature processes such as solder reflow treatments are performed. With conventional metal-based circuit boards, the adhesive reliability of the insulating layer that bonds the metal layer may decrease after high-temperature treatment. Therefore, there has been a demand for an insulating, thermally conductive sheet with a high glass transition temperature that can be used as an insulating layer in laminates for metal-based circuit boards.

[0007] The present invention has been made in view of the above problems, and has as its object to provide an insulating, heat-conductive sheet that can give a cured product having a high glass transition temperature.

[0008] The present inventors have conducted extensive research to solve the above problems, and as a result have found that the above problems can be solved by using a specific epoxy resin, which has led to the completion of the present invention.

[0009] That is, the present invention is as follows: [1] An epoxy resin A having a repeating unit represented by the following formula (1), and a thermally conductive filler, (In the formula, each R is independently a hydrogen atom or a group represented by the following formula (2), and at least one R represents a group represented by the following formula (2).) (wherein X represents a divalent aryl group or a divalent bisphenol skeleton.) Thermally conductive sheet. [2] The thermally conductive sheet according to [1], wherein R is represented by the following formula (2a): [3] The thermally conductive sheet according to [1], wherein the epoxy equivalent a of the epoxy resin A is 170 to 195 g / eq. [4] The thermally conductive sheet according to [1], wherein the OH equivalent b of the epoxy resin A is 100 to 120 g / eq. [5] The thermally conductive sheet according to [1], wherein the ratio (b / a) of the OH equivalent b to the epoxy equivalent a of the epoxy resin A is 0.15 to 0.90. [6] The thermally conductive sheet according to [1], wherein the thermally conductive filler comprises a boron nitride aggregate. [7] A laminate comprising: a first metal layer; an insulating layer disposed on the first metal layer; and a second metal layer disposed on the insulating layer, wherein the insulating layer comprises the thermally conductive sheet according to any one of [1] to [6]. [8] A method for manufacturing a laminate, comprising the steps of preparing the thermally conductive sheet according to any one of [1] to [6], and press-heating the thermally conductive sheet while sandwiching it between a metal foil and a metal substrate to obtain a laminate. [9] A circuit board comprising: a first metal layer, an insulating layer disposed on the first metal layer, and a second metal layer disposed on the insulating layer, wherein the insulating layer comprises the thermally conductive sheet according to any one of [1] to [6], and the second metal layer is a circuit portion.

[10] A method for manufacturing a circuit board, comprising the steps of preparing the laminate according to [7], and removing a portion of the first metal layer or a portion of the second metal layer of the laminate to form a circuit portion.

[0010] According to the present invention, it is possible to provide an insulating thermally conductive sheet that can give a cured product having a high glass transition temperature.

[0011] 1A and 1B are cross-sectional views showing a laminate for a metal base circuit board according to the present embodiment, a laminate for a metal core circuit board according to the present embodiment, and a circuit board according to the present embodiment.

[0012] The following describes in detail an embodiment of the present invention (hereinafter referred to as "the present embodiment"); however, the present invention is not limited to this embodiment, and various modifications are possible without departing from the spirit of the present invention.

[0013] 1. Thermally conductive sheet The thermally conductive sheet of this embodiment contains an epoxy resin A having a repeating unit represented by the following formula (1), and a thermally conductive filler, and may also contain a curing agent, a curing accelerator, an ion trapping material, a solvent, and a surfactant, as necessary. Each component will be described in detail below. (In the formula, each R is independently a hydrogen atom or a group represented by the following formula (2), and at least one R represents a group represented by the following formula (2).) (In the formula, X represents a divalent aryl group or a divalent bisphenol skeleton.)

[0014] The thermally conductive sheet of this embodiment is preferably in a B-stage state, which allows the thermally conductive sheet to be easily handled as a sheet, and when sandwiched between a metal plate and a metal layer and heated and pressed, the sheet hardens further to form an insulating layer having thermal conductivity and heat resistance.

[0015] In this embodiment, B-stage refers to an intermediate stage in the reaction of certain thermosetting resins, in accordance with JIS K6900:1994, where the material swells when in contact with certain liquids and softens when heated, but does not completely dissolve or melt. In contrast to B-stage, A-stage refers to an early stage in the preparation of certain thermosetting resins, where the material is still soluble in certain liquids and fusible. Furthermore, C-stage refers to the final stage in the reaction of certain thermosetting resins, where the material is virtually insoluble and infusible. The resin in a fully cured thermosetting molded product is in C-stage.

[0016] Whether the thermally conductive sheet is in a B-stage state can also be evaluated by the cure rate of the thermally conductive sheet. In this embodiment, the B-stage state refers to a cure rate of the thermally conductive sheet of preferably 20 to 80%, 30 to 70%, or 40 to 60%. The cure rate is a value representing the amount of heat generated from the uncured state to the fully cured state, with the total heat generated being 100% when the sheet is converted from an uncured state to a fully cured state. The cure rate can be determined using a thermal analyzer such as a differential scanning calorimeter.

[0017] 1.1. Epoxy Resin A This embodiment contains an epoxy resin A having a repeating unit represented by formula (1) above. Such epoxy resin A is not particularly limited, but examples include compounds in which at least a portion of the hydrogen atoms of the hydroxyl groups of a bisphenol A novolak resin, such as that represented by formula (1') below, have been substituted with groups represented by formula (2). By including such an epoxy resin A, the glass transition temperature of the resulting cured product tends to be further improved. (In the formula, each R is independently a hydrogen atom or a group represented by the following formula (2), at least one R represents a group represented by the following formula (2), and n represents an integer of 1 to 10.)

[0018] In the above formula (1) or (1′), each R is independently a hydrogen atom or a group represented by the following formula (2), and at least one R represents a group represented by the following formula (2).

[0019] In the above formula (2), examples of X include divalent aryl groups such as a phenylene group, a naphthylene group, and an anthracene group; and divalent bisphenol skeletons derived from bisphenol A, bisphenol AP, bisphenol AF, bisphenol B, bisphenol BP, bisphenol C, bisphenol E, bisphenol F, bisphenol G, bisphenol M, bisphenol S, bisphenol P, bisphenol PH, bisphenol TMC, bisphenol Z, etc.

[0020] Among these, a divalent bisphenol skeleton is preferred, and it is more preferred to contain at least a repeating unit represented by the following formula (2a) having a divalent bisphenol skeleton derived from bisphenol A. The presence of such a side chain tends to further improve the glass transition temperature, insulating reliability, and peel strength. Furthermore, the presence of a repeating unit represented by formula (2a) tends to suppress deterioration over time in peel strength and insulating reliability at room temperature and at cold temperatures, and to further improve storage stability.

[0021] The term "divalent bisphenol skeleton" refers to a residue of bisphenol excluding two hydroxyl groups. Therefore, the term "divalent bisphenol skeleton derived from bisphenol A" refers to a structure represented by the following formula:

[0022] Among the above, it is preferred that the skeleton other than the R group in the repeating unit represented by formula (1) of the epoxy resin A is derived from a bisphenol A novolac resin A1, and the R group represented by formula (2) is derived from an epoxy resin A2 having a divalent aryl group or a divalent bisphenol skeleton. This tends to further improve the glass transition temperature, insulating reliability, and peel strength, and also tends to inhibit deterioration over time in peel strength and insulating reliability at room temperature and cold temperatures, thereby further improving storage stability.

[0023] The epoxy equivalent a of epoxy resin A2 is preferably 130 g / eq or more, 140 g / eq or more, 150 g / eq or more, 160 g / eq or more, or 170 g / eq or more. The epoxy equivalent a of epoxy resin A is preferably 205 g / eq or less, 200 g / eq or less, 195 g / eq or less, or 190 g / eq or less. When the epoxy equivalent a is within the above range, the glass transition temperature of the resulting cured product tends to be further improved.

[0024] The OH equivalent b of the bisphenol A novolak resin A1 is preferably 90 to 135 g / eq, 95 to 130 g / eq, 100 to 125 g / eq, or 100 to 120 g / eq. When the OH equivalent b is within the above range, the glass transition temperature of the resulting cured product tends to be further improved.

[0025] The ratio (b / a) of the bisphenol A novolac resin A1 to the epoxy equivalent a of the epoxy resin A2 is preferably 0.05 or more, 0.10 or more, 0.15 or more, 0.20 or more, 0.25 or more, or 0.35 or more. Furthermore, the ratio (b / a) is preferably 0.95 or less, 0.85 or less, 0.80 or less, 0.75 or less, 0.70 or less, or 0.65 or less. By keeping the ratio (b / a) within the above range, the glass transition temperature of the resulting cured product tends to be further improved.

[0026] The weight average molecular weight of the epoxy resin A is preferably 300 to 2000, 300 to 1500, 300 to 1000, 400 to 900, or 500 to 850. When the weight average molecular weight of the epoxy resin A is within the above range, the glass transition temperature of the obtained cured product tends to be further improved.

[0027] The content of epoxy resin A is preferably 50 to 95 parts by mass, 55 to 90 parts by mass, 60 to 87.5 parts by mass, or 62.5 to 85 parts by mass, relative to 100 parts by mass of the resin component of the thermal conductive sheet. When the content of epoxy resin A is within the above range, the glass transition temperature of the obtained cured product tends to be further improved.

[0028] In this embodiment, the "resin component" refers to the amount of components excluding the thermally conductive filler and the solvent.

[0029] 1.2 Thermally Conductive Filler The thermally conductive filler is not particularly limited, but examples thereof include boron nitride, aluminum nitride, aluminum oxide, silicon nitride, silicon oxide, magnesium oxide, metallic aluminum, and zinc oxide.

[0030] Among these, boron nitride is preferred, and boron nitride aggregates are more preferred. Here, "boron nitride aggregates" refers to aggregated particles formed by aggregating primary particles of boron nitride. Use of such thermally conductive fillers tends to further improve thermal conductivity and insulation reliability.

[0031] The average particle size of the thermally conductive filler is preferably 10 to 100 μm, 20 to 80 μm, 25 to 70 μm, or 30 to 60 μm. When the average particle size of the thermally conductive filler is 10 μm or more, high thermal conductivity tends to be achieved with a smaller amount. Furthermore, when the average particle size of the thermally conductive filler is 25 μm or more, insulation reliability and peel strength against the metal layer tend to be further improved. Furthermore, when the average particle size of the thermally conductive filler is 100 μm or less, viscosity tends to be reduced, and entrapment of air bubbles during sheet molding tends to be reduced. Therefore, partial discharge due to air bubbles is reduced, electric field concentration is less likely to occur, and insulation performance tends to be further improved.

[0032] When the thermally conductive filler is in the form of aggregated particles formed by aggregating primary particles, the average particle size refers to the particle size of the aggregated particles, which is also called the secondary particle size.

[0033] In this embodiment, the average particle size of the thermally conductive filler refers to the particle size at 50% of the cumulative value of the cumulative particle size distribution. The average particle size of the thermally conductive filler can be measured by laser diffraction light scattering. An example of a particle size distribution analyzer is the "MT3300EX" (manufactured by Nikkiso Co., Ltd.). For the measurement, water is used as the solvent and hexametaphosphoric acid is used as the dispersant. As a pretreatment, a dispersion treatment is performed using a homogenizer at 20 W output for 30 seconds. The refractive index of water is 1.33. When the measurement target is boron nitride powder, the refractive index can be 1.80. The measurement time per measurement is not particularly limited, but is, for example, 30 seconds.

[0034] The content of the thermally conductive filler is preferably 25 to 55 volume %, 30 to 50 volume %, or 35 to 45 volume % relative to the total amount of the thermally conductive sheet. When the content of the thermally conductive filler is 25 volume % or more, the thermal conductivity tends to be further improved due to the action of the thermally conductive filler. When the content of the thermally conductive filler is 55 volume % or less, voids and the like are less likely to occur, and the thermal conductivity and insulation reliability tend to be further improved.

[0035] 1.3. Other Epoxy Resin B The thermally conductive sheet of this embodiment may contain an epoxy resin other than the epoxy resin A (hereinafter referred to as "epoxy resin B" for convenience).

[0036] The epoxy resin B is not particularly limited, but examples thereof include bisphenol A type epoxy resins, bisphenol AP type epoxy resins, bisphenol AF type epoxy resins, bisphenol B type epoxy resins, bisphenol BP type epoxy resins, bisphenol C type epoxy resins, bisphenol E type epoxy resins, bisphenol F type epoxy resins, bisphenol G type epoxy resins, bisphenol M type epoxy resins, bisphenol S type epoxy resins, bisphenol P type epoxy resins, bisphenol PH type epoxy resins, bisphenol TMC type epoxy resins, bisphenol Z type epoxy resins, polypropylene glycol type epoxy resins, polytetramethylene glycol type epoxy resins, naphthalene type epoxy resins such as 1,6-naphthalenediol type epoxy resins, anthracene type epoxy resins such as 9,10-anthracenediol type epoxy resins, phenylmethane type epoxy resins, tetrakisphenolmethane type epoxy resins, biphenyl type epoxy resins, epoxy resins having a triazine skeleton, and bisphenol A alkylene oxide adduct type epoxy resins.

[0037] The thermally conductive sheet of this embodiment may contain a curing agent. The curing agent is not particularly limited, but examples thereof include phenol-based curing agents, amine-based curing agents, acid anhydride-based curing agents, and thiol-based curing agents.

[0038] The phenol-based curing agent is not particularly limited, but examples thereof include phenol novolac, xylylene novolac, and bisphenol A novolac.

[0039] The amine-based curing agent is not particularly limited, but examples thereof include aromatic amine-based curing agents, aliphatic amine-based curing agents, and dicyandiamide.

[0040] The acid anhydride curing agent is not particularly limited, but examples thereof include aliphatic acid anhydrides such as phthalic anhydride derivatives, and aromatic acid anhydrides such as maleic anhydride.

[0041] The thiol-based curing agent is not particularly limited, but examples thereof include aliphatic polythioethers, aliphatic polythioesters, and aromatic-containing polythioethers.

[0042] The content of the curing agent is preferably 2.5 to 30 parts by mass, 5.0 to 25 parts by mass, 7.5 to 20 parts by mass, or 10 to 15 parts by mass, per 100 parts by mass of the resin component of the thermal conductive sheet. When the content of the curing agent is 2.5 parts by mass or more, the glass transition temperature and strength of the B-stage sheet tend to be further improved. Furthermore, when the amount of curing agent used is 30 parts by mass or less, embrittlement due to the B-stage sheet becoming too hard tends to be further suppressed.

[0043] 1.5 Curing Accelerator The thermally conductive sheet of this embodiment may contain a curing accelerator for the epoxy resin A. Note that while a curing agent forms the main skeleton of the cured product, a curing accelerator does not form the main skeleton of the cured product but contributes to the curing speed and curing temperature.

[0044] Such a curing accelerator is not particularly limited, but examples thereof include imidazole-based curing accelerators and phosphorus-based curing accelerators.

[0045] The imidazole curing accelerator is not particularly limited, but examples thereof include 2-methylimidazole, 2-ethylimidazole, 2-undecylimidazole, 2,4-dimethylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole, 1,2-diethylimidazole, 2-phenyl-4-methylimidazole, 2,4,5-triphenylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-undecylimidazole, and 1-benzyl-2-methylimidazole. Examples thereof include imidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 2,3-dihydro-1H-pyrrolo[1,2-a]benzimidazole, 2-aryl-4,5-diphenylimidazole, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-S-triazine, 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-S-triazine, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-S-triazine isocyanuric acid adduct, and 2-phenyl-4-methyl-5-hydroxymethylimidazole.

[0046] The phosphorus-based curing accelerator is not particularly limited, but examples thereof include tetraphenylphosphonium tetra-p-tolylborate, tetraphenylphosphonium tetraphenylborate, triphenylphosphine, tri-p-tolylphosphine, tris(4-chlorophenyl)phosphine, tris(2,6-dimethoxyphenyl)phosphine, triphenylphosphine triphenylborane, tetraphenylphosphonium dicyanamide, and tetraphenylphosphonium tetra(4-methylphenyl)borate.

[0047] Among these, it is preferable to use a phosphorus-based curing accelerator in combination with an imidazole-based curing accelerator, as this tends to further improve curability and further increase the glass transition temperature of the resulting cured product.

[0048] The content of the phosphorus-based curing accelerator is preferably 0.01 to 2.5 parts by mass, 0.03 to 1.5 parts by mass, 0.05 to 0.80 parts by mass, or 0.10 to 0.60 parts by mass, relative to 100 parts by mass of the resin component of the thermal conductive sheet. By having the content of the phosphorus-based curing accelerator within the above range, the glass transition temperature and strength of the B-stage sheet tend to be further improved.

[0049] The content of the imidazole curing accelerator is preferably 0.01 to 2.5 parts by mass, 0.03 to 1.5 parts by mass, 0.05 to 0.80 parts by mass, or 0.10 to 0.60 parts by mass, relative to 100 parts by mass of the resin component of the thermal conductive sheet. By having the content of the imidazole curing accelerator within the above range, embrittlement due to excessive hardness of the B-stage sheet tends to be further suppressed.

[0050] The ratio of the content of the imidazole curing accelerator to the content of the phosphorus curing accelerator is preferably 0.50 to 2.00 parts by mass, 0.65 to 1.50 parts by mass, or 0.80 to 1.25 parts by mass. When the ratio of the content of the imidazole curing accelerator to the content of the phosphorus curing accelerator is within the above range, the glass transition temperature and strength of the B-stage sheet are further improved, and embrittlement due to the B-stage sheet becoming too hard tends to be further suppressed.

[0051] The total content of the curing accelerator is preferably 0.01 to 10 parts by mass, 0.03 to 7.5 parts by mass, 0.05 to 5.0 parts by mass, 0.10 to 2.5 parts by mass, or 0.15 to 1.5 parts by mass, relative to 100 parts by mass of the resin component of the thermal conductive sheet. When the total content of the curing accelerator is 0.01 parts by mass or more, the glass transition temperature and strength of the B-stage sheet tend to be further improved. Furthermore, when the total content of the curing accelerator is 10 parts by mass or less, embrittlement due to excessive hardness of the B-stage sheet tends to be further suppressed.

[0052] 1.6 Ion Scavenger The ion scavenger is not particularly limited, but examples thereof include conventionally known ion scavenger such as hydrotalcite.

[0053] The content of the ion scavenger is preferably 0.01 to 3.5 parts by mass, 0.10 to 2.5 parts by mass, or 0.50 to 1.5 parts by mass, relative to 100 parts by mass of the resin component of the thermally conductive sheet.

[0054] 1.7. Solvent The composition before preparation of the thermally conductive sheet may contain a solvent. The solvent is not particularly limited, but examples thereof include alcohol-based solvents, glycol ether-based solvents, aromatic solvents, and ketone-based solvents. Examples of alcohol-based solvents include isopropyl alcohol and diacetone alcohol. Examples of glycol ether-based solvents include ethyl cellosolve and butyl cellosolve. Examples of aromatic solvents include toluene and xylene. Examples of ketone-based solvents include methyl ethyl ketone and methyl isobutyl ketone.

[0055] 1.8. Surfactant The surfactant is not particularly limited as long as it improves the dispersibility of the thermally conductive filler. Examples of surfactants include copolymers having (meth)acrylic monomer units α having an anionic group, (meth)acrylic monomer units β having a cationic group, and silicone (meth)acrylic monomer units γ. Use of such surfactants tends to further improve the dispersibility of the thermally conductive filler.

[0056] The amount of the surfactant used is preferably 0.01 to 10 parts by mass, 0.02 to 8 parts by mass, or 0.03 to 6 parts by mass, relative to 100 parts by mass of the resin component of the thermal conductive sheet. When the amount of the surfactant used is within the above range, dispersibility tends to be further improved.

[0057] 2. Laminate The laminate of this embodiment includes a first metal layer, an insulating layer disposed on the first metal layer, and a second metal layer disposed on the insulating layer, and the insulating layer includes the thermally conductive sheet. Note that in this state, the thermally conductive sheet may be in an A-stage state due to hot pressing during the manufacturing process of the laminate.

[0058] A cross-sectional view of a laminate for a metal base circuit board according to this embodiment is shown in Fig. 1. As shown in Fig. 1, one aspect of the laminate 10 according to this embodiment comprises a first metal layer 13 as a base, a thermally conductive sheet 12 as an insulating layer, and a second metal layer 11, in this order, on one surface of the first metal layer 13.

[0059] 2 shows a cross-sectional view of a laminate for a metal core circuit board according to this embodiment. As shown in FIG. 2, another aspect of the laminate 10 according to this embodiment has a thermally conductive sheet 12 as an insulating layer and a second metal layer 11, in this order, on both surfaces of a first metal layer 13 that forms the core. Hereinafter, when there is no need to distinguish between a metal base circuit board and a metal core circuit board, they will simply be referred to as a "circuit board."

[0060] In this way, by using the first metal layer 13 as the base or core, heat generated by the electronic components formed on the second metal layer 11 can be conducted to the housing or heat sink via the thermally conductive sheet 12. The thermally conductive sheet used in such a laminate is required to have high insulation properties and high heat resistance.

[0061] The first metal layer serves as the base or core of the circuit board. The metal material constituting the first metal layer is not particularly limited, but examples thereof include aluminum, copper, iron, silver, gold, zinc, nickel, tin, and alloys containing these metals. Among these, aluminum, copper, and iron are preferred. The use of such metal materials can improve heat dissipation and further reduce the thermal expansion coefficient of the laminate.

[0062] The thickness of the first metal layer differs depending on whether it is the base or the core, but is preferably 0.01 to 10 mm, 0.1 to 5.0 mm, or 1.0 to 3.0 mm.

[0063] The second metal layer becomes the circuit portion of the circuit board. The metal material constituting the second metal layer is not particularly limited, and may be, for example, aluminum, copper, iron, silver, gold, zinc, nickel, tin, or an alloy containing these metals.

[0064] The thickness of the second metal layer is preferably 0.01 to 5.0 mm, 0.02 to 3.0 mm, or 0.03 to 1.0 mm.

[0065] The insulating layer includes the above-mentioned thermally conductive sheet, and specifically may be a thermally conductive sheet that has been heated in A-stage or B-stage to become C-stage.

[0066] The thickness of the insulating layer varies depending on the thickness of the thermally conductive sheet, but is preferably 30 to 500 μm, 50 to 300 μm, or 80 to 200 μm. When the thickness of the insulating layer is 30 μm or more, insulation reliability tends to be further improved. Furthermore, when the thickness of the insulating layer is 500 μm or less, thermal resistance tends to be further reduced.

[0067] The method for producing the laminate of this embodiment includes the steps of preparing the thermally conductive sheet and pressing and heating the thermally conductive sheet while sandwiching it between a metal foil and a metal substrate to obtain a laminate.

[0068] The temperature in the press heating is not particularly limited, but is, for example, 0.5 to 9 hours, or 1 to 6 hours. The time in the press heating is not particularly limited, but is, for example, 70 to 250° C., or 120 to 180° C. The pressure in the press heating is not particularly limited, but is, for example, 1 to 30 MPa, 5 to 25 MPa, or 8 to 20 MPa.

[0069] 3. Circuit Board The circuit board of this embodiment is a printed circuit board that uses a metal for the base or core, and includes a first metal layer, an insulating layer disposed on the first metal layer, and a second metal layer disposed on the insulating layer, the insulating layer including the thermally conductive sheet, and the second metal layer being a circuit portion.

[0070] A cross-sectional view of the circuit board of this embodiment is shown in Figure 3. As shown in Figure 3, the circuit board 20 of this embodiment includes, in this order, an electric circuit 21, a thermally conductive sheet 22, and a first metal layer 23. While Figure 3 shows a circuit board using a laminate for a metal base circuit board, the circuit board of this embodiment is not limited to this and includes circuit boards using a laminate for a metal core circuit board.

[0071] The thermally conductive sheet 22 and the first metal layer 23 in FIG. 3 may be the same as the thermally conductive sheet 12 and the first metal layer 13 in FIGS.

[0072] The method for manufacturing a circuit board of this embodiment includes the steps of preparing the above-mentioned laminate and removing a portion of the first metal layer or a portion of the second metal layer of the laminate to form a circuit portion.

[0073] The present invention will be described in more detail below using examples and comparative examples, but the present invention is not limited to the following examples.

[0074] Example 1 30 parts by mass of bisphenol A epoxy resin (manufactured by DIC Corporation, EXA850CRP, epoxy equivalent 170 to 175 g / eq, hereinafter also referred to as "Bis-A-Ep"), 12 parts by mass of bisphenol A novolak resin (manufactured by DIC Corporation, VH4170, OH equivalent 118 g / eq, hereinafter also referred to as "Bis-A-Nv"), 0.2 parts by mass of triphenylphosphine, 0.2 parts by mass of 1-benzyl-2-phenylimidazole (1B2PZ), 40 parts by mass of diacetone alcohol (DAA), 2.3 parts by mass of a surfactant (manufactured by Denka Company, iSE-Z2), 1.2 parts by mass of an ion trapping material (iXEPLAS-B1), and 40% by volume of boron nitride aggregates (BN agglomerated powder (T40), average particle size 40 μm) were mixed together.

[0075] The resulting mixture was applied to a 0.038 mm thick polyethylene terephthalate (PET) film so that the thickness after semi-curing was 0.080 mm, and then heated and dried at 100°C for 30 minutes to produce a semi-cured (B-stage) thermally conductive sheet. The curing rate of the resulting thermally conductive sheet was 20%.

[0076] The thermally conductive sheet obtained as described above contains an epoxy resin A-bis in which X is a bisphenol A-type skeleton. Specifically, in the epoxy resin A-bis, the skeleton represented by the repeating unit represented by formula (1) other than the R group is derived from a bisphenol A-type novolac resin, and the R group represented by formula (2) is derived from a bisphenol A-type epoxy resin, and the ratio (b / a) of the OH equivalent (g / eq) of the bisphenol A-type novolac to the epoxy equivalent (g / eq) of the bisphenol A-type epoxy was 0.60.

[0077] The resulting semi-cured body was peeled off from the PET film and placed on a metal plate (a copper plate having a thickness of 2.0 mm) that would become the first metal layer. Next, a metal foil (a copper foil having a thickness of 0.5 mm) that would become the second metal layer was placed on the semi-cured body, and then the semi-cured body was pressed with a press at a surface pressure of 30 kgf / cm. ２ The laminate was heated and cured at 180° C. for 410 minutes while applying a pressure of 3 MPa to the insulating layer to obtain a laminate. The thickness of the insulating layer in the laminate was 80 μm.

[0078] Next, predetermined positions on the metal foil (second metal layer) of the laminate were masked with an etching resist, and the copper foil was then etched using a sulfuric acid-hydrogen peroxide mixed solution as an etching solution. The etching resist was removed, and the substrate was washed and dried to obtain a metal base circuit board having a circular electrode (copper foil) with a diameter of 20 mm.

[0079] Example 2 A thermally conductive sheet was obtained in the same manner as in Example 1, except that the bisphenol A epoxy resin (Bis-A-Ep) in Example 1 was replaced with 29 parts by mass of a 1,6-naphthalenediol epoxy resin (manufactured by DIC Corporation, product name HP-4032D, epoxy equivalent 136 to 148 g / eq, hereinafter also referred to as "Np-Ep") The curing rate of the obtained thermally conductive sheet was 20%. Furthermore, a laminate and a metal base circuit board were obtained using the obtained thermally conductive sheet.

[0080] The thermally conductive sheet obtained in Example 2 contains an epoxy resin A-Np in which X is a naphthalene skeleton. Specifically, in the epoxy resin A-Np, the skeleton other than the R group in the repeating unit represented by formula (1) is derived from a bisphenol A novolac resin, and the R group represented by formula (2) is derived from a 1,6-naphthalenediol epoxy resin, and the ratio (b / a) of the OH equivalent (g / eq) of the bisphenol A novolac to the epoxy equivalent (g / eq) of the bisphenol A epoxy was 0.60.

[0081] Example 3 A thermally conductive sheet was obtained in the same manner as in Example 1, except that the bisphenol A epoxy resin (Bis-A-Ep) in Example 1 was changed to 38.6 parts by mass of a 1,6-naphthalenediol epoxy resin (Np-Ep) and the amount of bisphenol A novolak (Bis-A-Nv) used was changed to 3.2 parts by mass. The curing rate of the obtained thermally conductive sheet was 20%. Furthermore, a laminate and a metal base circuit board were obtained using the obtained thermally conductive sheet.

[0082] The thermally conductive sheet obtained in Example 3 contains an epoxy resin A-Np in which X is a naphthalene skeleton. Specifically, in the epoxy resin A-Np, the skeleton other than the R group in the repeating unit represented by formula (1) is derived from a bisphenol A novolac resin, and the R group represented by formula (2) is derived from a 1,6-naphthalenediol epoxy resin, and the ratio (b / a) of the OH equivalent (g / eq) of the bisphenol A novolac to the epoxy equivalent (g / eq) of the bisphenol A epoxy was 0.10.

[0083] Example 4 A thermally conductive sheet was obtained in the same manner as in Example 1, except that the bisphenol A epoxy resin (Bis-A-Ep) in Example 1 was changed to 40 parts by mass of a 1,6-naphthalenediol epoxy resin (manufactured by DIC Corporation, product name HP-4032D, epoxy equivalent 136 to 148 g / eq, hereinafter also referred to as "Np-Ep") and the amount of bisphenol A novolak (Bis-A-Nv) used was changed to 3 parts by mass. The curing rate of the obtained thermally conductive sheet was 20%. Furthermore, a laminate and a metal base circuit board were obtained using the obtained thermally conductive sheet.

[0084] The thermally conductive sheet obtained in Example 4 contains an epoxy resin A-Np in which X is a naphthalene skeleton. Specifically, in the epoxy resin A-Np, the skeleton other than the R group in the repeating unit represented by formula (1) is derived from a bisphenol A novolac resin, and the R group represented by formula (2) is derived from a 1,6-naphthalenediol epoxy resin, and the ratio (b / a) of the OH equivalent (g / eq) of the bisphenol A novolac to the epoxy equivalent (g / eq) of the bisphenol A epoxy was 0.15.

[0085] Example 5 A thermally conductive sheet was obtained in the same manner as in Example 1, except that the bisphenol A epoxy (Bis-A-Ep) in Example 1 was replaced with 40 parts by mass of a 9,10-anthracenediol epoxy resin (manufactured by Mitsubishi Chemical Corporation, product name YX8800, epoxy equivalent 174 to 183 g / eq, hereinafter also referred to as "An-Ep") and the amount of bisphenol A novolak (Bis-A-Nv) used was changed to 4 parts by mass. The curing rate of the obtained thermally conductive sheet was 20%. Furthermore, a laminate and a metal base circuit board were obtained using the obtained thermally conductive sheet.

[0086] The thermally conductive sheet obtained in Example 5 contains epoxy resin A-An in which X is an anthracene skeleton. Specifically, in epoxy resin A-An, the skeleton represented by the repeating unit represented by formula (1) other than the R group is derived from a bisphenol A novolac resin, and the R group represented by formula (2) is derived from a 9,10-anthracene diol epoxy resin, and the ratio (b / a) of the bisphenol A novolac to the epoxy equivalent (g / eq) of the bisphenol A epoxy was 0.15.

[0087] Example 6 A thermally conductive sheet was obtained in the same manner as in Example 1, except that the amount of bisphenol A epoxy resin (Bis-A-Ep) used in Example 1 was changed to 45 parts by mass and the amount of bisphenol A novolak resin (Bis-A-Nv) used in Example 1 was changed to 30 parts by mass. The curing rate of the obtained thermally conductive sheet was 20%. Furthermore, a laminate and a metal base circuit board were obtained using the obtained thermally conductive sheet.

[0088] The thermally conductive sheet obtained in Example 6 contains an epoxy resin A-bis in which X is a bisphenol A-type skeleton. Specifically, in the epoxy resin A-bis, the skeleton other than the R group in the repeating unit represented by formula (1) is derived from a bisphenol A-type novolac resin, and the R group represented by formula (2) is derived from a bisphenol A-type epoxy resin, and the ratio (b / a) of the bisphenol A-type novolac to the epoxy equivalent (g / eq) of the bisphenol A-type epoxy was 1.00.

[0089] Comparative Example 1 A thermally conductive sheet was obtained in the same manner as in Example 1, except that the bisphenol A novolak resin in Example 1 was replaced with 10 parts by mass of an aliphatic amine ("D-400" manufactured by Huntsman, amine equivalent 200). The curing rate of the obtained thermally conductive sheet was 20%. Furthermore, a laminate and a metal base circuit board were obtained using the obtained thermally conductive sheet.

[0090] The epoxy resin contained in the thermally conductive sheet obtained in Comparative Example 1 has a skeleton derived from an aliphatic amine, and is derived from a structure in which a bisphenol A type epoxy resin is added to the amine group by ring-opening addition. The ratio (b / a) of the amine equivalent (g / eq) of the aliphatic amine to the epoxy equivalent (g / eq) of the bisphenol A type epoxy was 0.15.

[0091] [Curing rate] Confirmation of a semi-cured body (B stage) was carried out by measuring the curing rate using a differential scanning calorimeter (manufactured by TA Instruments, "Q2000"). Specifically, the thermally conductive sheet after the heat drying was heated to 25 to 300°C at a heating rate of 10°C / min in a nitrogen atmosphere using a differential scanning calorimeter, and the total heat generation amount C １ Next, the heat conductive sheet before heat drying (solvent evaporated) was used as a sample and measured with a differential scanning calorimeter under the same conditions to determine the total calorific value C ０ The curing rate was calculated using the following formula: Curing rate = (C ０ -C １ ) / C ０ ×100 (%)

[0092] [Glass Transition Temperature] A measurement sample was prepared by cutting the semi-cured (B-stage) thermally conductive sheet into a plate-like size of 0.1 mm × 5 mm × 40 mm. The loss tangent (tan δ) was measured in the temperature range of 30°C to +300°C using a dynamic viscoelasticity measuring device ("RSA 3" manufactured by T&A Instruments) under conditions of a frequency of 10 Hz and a heating rate of 10°C / min, and the temperature at which the loss tangent value was maximized was defined as the glass transition point.

[0093] [Insulation Reliability] The insulation strength of the produced laminate was measured in accordance with JIS C 6481 using TOS 8650 (manufactured by Kikusui Electronics Co., Ltd.).

[0094] [Peel Strength] A copper foil of 10 mm × 100 mm was cut out from the produced laminate, and the 90° peel strength between the copper foil and the thermally conductive sheet was measured under conditions of 23±2°C and a relative humidity of 50% according to the method specified in JIS C 6481. The measurement was repeated five times, and the arithmetic mean value was taken as the peel strength.

[0095] [Thermal Conductivity] The thermal conductive sheets were laminated and press-molded to prepare samples measuring 10 mm in length, 10 mm in width, and 0.5 mm in thickness. The thermal diffusivity α was measured by a laser flash method, and the thermal conductivity λ was evaluated using the following formula: λ = α × Cp × ρ

[0096] The specific heat Cp was calculated from DSC measurement. The specific gravity ρ of the sample was calculated by measuring the weight of the sample in air and in distilled water at a temperature of 25°C and an atmospheric pressure of 1013 hPa using a specific gravity measurement kit AD-1653 (trade name) manufactured by A&D Co., Ltd., and then calculating it using the following formula: ρ=A / (A-B)×(ρ0-d)+d (where A is the mass of the sample in air, B is the mass of the sample in distilled water, ρ0 is the density of distilled water, and d is the density of air.)

[0097] [Storage stability 1: Insulation reliability] The insulation reliability I of the laminate produced after storing the thermal conductive sheet at 25°C for one week was １ and the insulation reliability I of the laminate produced immediately after producing the thermal conductive sheet. ０Then, the storage stability 1 of the insulation reliability was evaluated by the following formula: Storage stability 1 = I １ / I ０ ×100

[0098] [Storage Stability 2 Peel Strength] The peel strength P of the laminate produced after storing the thermal conductive sheet at 25°C for one week was １ and the peel strength P of the laminate produced immediately after producing the thermal conductive sheet. ０ The peel strength storage stability 2 was then evaluated using the following formula: Storage stability 2 = P １ / P ０ ×100

[0099] *The ratio (b / a) in Comparative Example 1 is the ratio of amino equivalent (g / eq) to epoxy equivalent (g / eq).

[0100] The thermally conductive sheet of the present invention has industrial applicability as a material for forming an insulating layer of a circuit board, for example.

[0101] DESCRIPTION OF SYMBOLS 10...Laminate, 11...Second metal layer, 12...Thermal conductive sheet, 13...First metal layer, 20...Circuit board, 21...Electrical circuit, 22...Thermal conductive sheet, 23...First metal layer

Claims

1. An epoxy resin A having a repeating unit represented by the following formula (1), and a thermal conductivity filler. (In the formula, each R is independently a hydrogen atom or a group represented by the following formula (2), and at least one R represents a group represented by the following formula (2).) (In the formula, X represents a divalent aryl group or a divalent bisphenol skeleton.) A thermal conductivity sheet.

2. The heat conductive sheet according to claim 1, wherein R is represented by the following formula (2a).

3. The skeleton represented other than the R group in the repeating unit represented by the formula (1) is derived from a bisphenol A type novolak resin A1, and the R group represented by the formula (2) is derived from an epoxy resin A2 having a divalent aryl group or a divalent bisphenol skeleton. The thermally conductive sheet according to claim 1.

4. The epoxy equivalent a of the epoxy resin A2 is 130 to 195 g / eq. The thermally conductive sheet according to claim 3.

5. The OH equivalent b of the bisphenol A type novolak resin A1 is 100 to 120 g / eq. The thermally conductive sheet according to claim 3.

6. The ratio (b / a) of the OH equivalent b of the bisphenol A type novolak resin A1 to the epoxy equivalent a of the epoxy resin A2 is 0.15 to 0.

90. The thermally conductive sheet according to claim 3.

7. The thermally conductive filler contains a boron nitride aggregate. The thermally conductive sheet according to claim 1.

8. A laminate comprising a first metal layer, an insulating layer disposed on the first metal layer, and a second metal layer disposed on the insulating layer, wherein the insulating layer contains the thermally conductive sheet according to any one of claims 1 to 7.

9. A method for manufacturing a laminate, comprising a step of preparing the thermally conductive sheet according to any one of claims 1 to 7, and a step of obtaining a laminate by press-heating while sandwiching the thermally conductive sheet between a metal foil and a metal substrate.

10. A circuit board comprising a first metal layer, an insulating layer disposed on the first metal layer, and a second metal layer disposed on the insulating layer, wherein the insulating layer contains the thermally conductive sheet according to any one of claims 1 to 6, and the second metal layer is a circuit portion.

11. A method for manufacturing a circuit board, comprising a step of preparing the laminate according to claim 8, and a step of removing a part of the first metal layer or a part of the second metal layer of the laminate to form a circuit portion.

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