Heat-conductive sheet

Abstract

To provide an insulating heat-conductive sheet in which a curing reaction is controlled.SOLUTION: A heat-conductive sheet has an epoxy resin A, and a heat-conductive filler, and has two or more peaks when the temperature is raised from 23°C to 270°C at 10°C / min by a differential scanning calorimeter.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

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

[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 addresses the issue of reduced adhesive reliability of insulating layers during high-temperature treatment and 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 which the surface roughness of the metal layer that bonds to the insulating layer is specified. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-173751 Summary of the Invention [Problem to be solved by the invention]

[0006] The insulating layer described above can be formed by sandwiching a thermally conductive sheet between a metal plate and a metal layer and hot-pressing them. The thermally conductive sheet is required to be easy to handle as a sheet and to have the property of being further hardened by hot-pressing, so it is desirable that it be a so-called B-stage thermally conductive sheet.

[0007] B-stage thermally conductive sheets can be produced by partially curing an A-stage thermally conductive composition in a sheet form. However, controlling this partial curing reaction is difficult, and quality variations can occur between product lots due to insufficient or excessive curing. If the curing reaction is insufficient, the sheet cannot be handled, and if the curing reaction is excessive, the adhesion between the metal plate and the metal layer is poor.

[0008] The present invention has been made in view of the above problems, and has an object to provide an insulating thermally conductive sheet in which the curing reaction is controlled. [Means for solving the problem]

[0009] 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.

[0010] That is, the present invention is as follows. [1] Epoxy resin A, a thermally conductive filler; When heated from 23°C to 270°C at a rate of 10°C / min using a differential scanning calorimeter, there are two or more peaks. Thermally conductive sheet. [2] When the peak located at the lowest temperature among the two or more peaks is defined as the first peak, and the peak located at the next lowest temperature is defined as the second peak, The calorific value W1 at the peak top of the first peak is smaller than the calorific value W2 at the peak top of the second peak. The thermally conductive sheet according to [1]. [3] When the peak on the lowest temperature side of the two or more peaks is defined as the first peak and the peak on the highest temperature side is defined as the second peak, The temperature T1 of the first peak is 75°C or higher and lower than 145°C. The thermally conductive sheet according to [1] or [2]. [4] When the peak on the lowest temperature side of the two or more peaks is defined as the first peak and the peak on the highest temperature side is defined as the second peak, The temperature T2 of the second peak is greater than 145°C and less than 200°C. The thermally conductive sheet according to any one of [1] to [3]. [5] When the peak on the lowest temperature side of the two or more peaks is defined as the first peak and the peak on the highest temperature side is defined as the second peak, the difference |T1-T2| between the temperature T1 of the first peak and the temperature T2 of the second peak is 3°C or more and 50°C or less; The thermally conductive sheet according to any one of [1] to [4]. [6] The epoxy equivalent of the epoxy resin A is 136 g / eq or more and 183 g / eq or less. The thermally conductive sheet according to any one of [1] to [5]. [7] further comprising a curing agent, The thermally conductive sheet according to any one of [1] to [6]. [8] the thermally conductive filler comprises boron nitride aggregates; The thermally conductive sheet according to any one of [1] to [7]. [9] a first metal layer; an insulating layer disposed on the first metal layer; a second metal layer disposed on the insulating layer; The insulating layer includes the thermally conductive sheet according to any one of [1] to [8]. Laminate.

[10] A step of preparing the thermally conductive sheet according to any one of [1] to [8]; and pressing and heating the thermally conductive sheet while sandwiching it between a metal foil and a metal substrate to obtain a laminate. A method for manufacturing a laminate.

[11] a first metal layer; an insulating layer disposed on the first metal layer; a second metal layer disposed on the insulating layer; The insulating layer includes the thermally conductive sheet according to any one of [1] to [8], The second metal layer is a circuit portion. Circuit board.

[12] A step of preparing the laminate according to [9]; removing a portion of the first metal layer or a portion of the second metal layer of the laminate to form a circuit portion; A method for manufacturing a circuit board. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide an insulating thermally conductive sheet in which the curing reaction is controlled. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a cross-sectional view showing a laminate for a metal base circuit board according to the present embodiment. [Figure 2] 1 is a cross-sectional view showing a laminate for a metal core circuit board according to an embodiment of the present invention. [Figure 3] FIG. 2 is a cross-sectional view showing the circuit board of the present embodiment. [Figure 4] 2 shows an example of a DSC curve of the thermally conductive sheet of the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] An embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described in detail below, but the present invention is not limited to this and various modifications are possible without departing from the spirit of the present invention. A numerical range expressed with the symbol "to" includes the numerical values placed before and after the symbol "to". For example, a numerical range expressed as "20 to 80%" is the same as a numerical range expressed as "20% or more and 80% or less".

[0014] 1. Thermally conductive sheet The thermally conductive sheet of this embodiment contains epoxy resin A and a thermally conductive filler, and has two or more peaks when heated from 23°C to 270°C at a rate of 10°C / min using a differential scanning calorimeter (hereinafter also referred to as "DSC"). The thermally conductive sheet of this embodiment may contain a curing agent, a curing accelerator, an ion trapping material, a solvent, and a surfactant, as necessary. The DSC peaks and each component are described in detail below.

[0015] 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, it hardens further to become an insulating layer with thermal conductivity and heat resistance.

[0016] 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.

[0017] Whether the thermally conductive sheet is in the B-stage state can also be evaluated by the cure rate of the thermally conductive sheet. In this embodiment, the B-stage state means that the cure rate of the thermally conductive sheet is preferably 20 to 80%, 30 to 70%, or 40 to 60%. The cure rate is a value representing the amount of heat generated until the sheet reaches a semi-cured (B-stage) state, with the total amount of heat generated when the sheet is converted from an uncured state to a fully cured state being 100%. The cure rate can be determined using a thermal analyzer such as a differential scanning calorimeter.

[0018] 1.1.DSC FIG. 4 shows an example of a DSC curve of the thermally conductive sheet of this embodiment. The DSC curve shown in FIG. 4 shows the change in calorific value when the temperature is increased from 23°C to 270°C at 10°C / min. As shown in FIG. 4, the thermally conductive sheet of this embodiment has two or more peaks when the temperature is increased from 23°C to 270°C at 10°C / min by DSC. The peaks may be endothermic peaks due to an endothermic reaction or exothermic peaks due to an exothermic reaction. Among these, exothermic peaks due to an exothermic reaction are preferred.

[0019] The temperature increase "from 23°C to 270°C" is a condition that assumes that the thermal conductive sheet in the B-stage state is heated from room temperature to a temperature (270°C) sufficient for the curing reaction to proceed in order to change the sheet to the C-stage. Therefore, the peaks observed by DSC during the temperature increase from 23°C to 270°C include endothermic or exothermic peaks in the curing reaction when the thermal conductive sheet transitions from the B-stage to the C-stage.

[0020] Therefore, "having two or more peaks" defines the property that the thermally conductive sheet of this embodiment can undergo at least two curing stages in at least different temperature ranges. The ability to undergo at least two curing stages in different temperature ranges means that, for example, even if the A-stage curing reaction of the thermally conductive composition proceeds excessively and causes all of the curing reaction at the low temperature to proceed, the curing reaction at the high temperature can be prevented from proceeding. This prevents the deterioration of adhesion between the metal plate and the metal layer due to excessive curing reaction. Furthermore, since the problem of reduced adhesion does not occur even if the curing reaction at the low temperature proceeds sufficiently, it is also possible to avoid the deterioration of sheet handleability due to insufficient curing reaction at the low temperature.

[0021] In this embodiment, it is desirable to prevent the curing reaction on the low temperature side from proceeding completely, but to allow the curing reaction on the low temperature side to proceed further, i.e., to have "two or more peaks." This tends to further improve the adhesion between the metal plate and the metal layer.

[0022] In this embodiment, the term "peak" refers to a maximum or minimum value, and a shape of a DSC curve that does not have a maximum or minimum value, such as a shoulder peak, does not qualify as a peak in this embodiment.

[0023] Hereinafter, of the two or more peaks, the peak located at the lowest temperature from the lowest peak temperature will be referred to as the first peak, and the peak located at the next lowest temperature will be referred to as the second peak. The number of peaks in the range of 23°C to 270°C of the thermal conductive sheet of this embodiment is not particularly limited as long as it is two or more, but two is preferred.

[0024] The peak top calorific value W1 of the first peak may be greater than the peak top calorific value W2 of the second peak, or the peak top calorific value W1 of the first peak may be smaller than the peak top calorific value W2 of the second peak. Among these, it is preferable that the peak top calorific value W1 of the first peak is smaller than the peak top calorific value W2 of the second peak. In other words, it is preferable that the peak on the high temperature side is large and the peak on the low temperature side is small. This tends to further improve peel strength.

[0025] When the calorific value W1 at the peak top of the first peak is smaller than the calorific value W2 at the peak top of the second peak, the calorific value W1 at the peak top of the first peak is preferably 0.010 to 0.100, 0.015 to 0.085, 0.020 to 0.070, or 0.025 to 0.055. When the calorific value W1 at the peak top of the first peak is smaller than the calorific value W2 at the peak top of the second peak, the calorific value W2 at the peak top of the second peak is preferably 0.110 to 0.400, 0.120 to 0.350, 0.130 to 0.300, or 0.140 to 0.250.

[0026] When the calorific value W1 of the first peak is larger than the calorific value W2 of the second peak, the calorific value W1 of the first peak is preferably 0.100 to 0.500, 0.110 to 0.450, or 0.120 to 0.400. When the calorific value W1 of the first peak is smaller than the calorific value W2 of the second peak, the calorific value W2 of the second peak is preferably 0.010 to 0.090, 0.015 to 0.070, or 0.020 to 0.055.

[0027] The temperature T1 of the first peak is preferably 75° C. or higher but lower than 145° C., 85° C. or higher but lower than 143° C., 95° C. or higher but lower than 140° C., or 105° C. or higher but lower than 138° C. When the temperature T2 of the second peak is within the above range, it becomes easier to control the reaction by adjusting the temperature in the B-staging step, and the reaction at higher temperatures tends to proceed less easily.

[0028] The second peak temperature T2 is preferably above 145°C and below 200°C, 148°C or above and 190°C or below, or 150°C or above and 180°C or below. When the second peak temperature T2 exceeds 145°C, the reaction at higher temperatures tends to proceed less smoothly in the B-stage conversion step. Furthermore, when the second peak temperature T2 is below 200°C, unreacted components are less likely to remain in the C-stage conversion step, and peel strength tends to be further improved.

[0029] Furthermore, the difference |T1-T2| between the temperature T1 of the first peak and the temperature T2 of the second peak is preferably 3° C. or more and 50° C. or less, 5° C. or more and 45° C. or less, or 10° C. or more and 40° C. or less. When the difference |T1-T2| is within the above range, it becomes easier to control the reaction by adjusting the temperature in the B-staging step, and the reaction at higher temperatures tends to proceed less easily.

[0030] The exothermic onset temperature of the first peak is preferably 90°C or higher and 175°C or lower, 95°C or higher and 165°C or lower, 100°C or higher and 155°C or lower, 105°C or higher and 145°C or lower, or 110°C or higher and 135°C or lower. When the exothermic onset temperature of the first peak is within the above range, reaction control by temperature adjustment becomes easier in the B-staging step, and the reaction on the high-temperature side tends to proceed less easily. The exothermic onset temperature can be determined as the temperature at the intersection of the tangent to the inflection point of the first peak and the DSC curve.

[0031] Furthermore, the total calorific value C1 (J / g) of the thermally conductive sheet of this embodiment, determined from a DSC curve from 23°C to 270°C, is preferably 50 J / g to 170 J / g, 55 J / g to 160 J / g, 60 J / g to 150 J / g, or 65 J / g to 140 J / g. When the total calorific value C1 (J / g) is within the above range, it becomes easier to control the reaction by adjusting the temperature in the B-staging step, and the reaction at higher temperatures tends to proceed less easily.

[0032] There are no particular limitations on the method for obtaining two or more peaks when the temperature is increased from 23°C to 270°C at 10°C / min by DSC. For example, the method may involve adjusting the components of the thermally conductive sheet so that two different curing reactions, one proceeding at a relatively low temperature and the other at a relatively high temperature, occur.

[0033] For example, such a method may involve allowing the reaction between the epoxy resin and the curing agent to proceed at a low temperature to form an epoxy prepolymer, and allowing the reaction between the epoxy groups of the epoxy prepolymer to proceed at a high temperature. Furthermore, in controlling such reactions, a curing accelerator that accelerates the reaction between the epoxy resin and the curing agent at a low temperature and another curing accelerator that accelerates the reaction between epoxy resins at a high temperature may be used.

[0034] The temperatures T1 and T2 may be adjusted by controlling the reaction as described above, or by controlling the reaction to bring the reaction into the B stage.

[0035] 1.2.Epoxy Resin A The epoxy resin A 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.

[0036] The epoxy resin A may also contain a prepolymer of the above-mentioned epoxy resin and a polyol. The polyol is not particularly limited, but examples thereof include aliphatic diols such as ethylene glycol, propanediol, butanediol, hexanediol, and decanediol; alicyclic diols such as cyclohexanediol; bisphenols such as bisphenol F, bisphenol A, bisphenol B, bisphenol AD, bisphenol S, and halogenated bisphenol A; and novolac resins having hydroxyl groups, such as phenol novolac resins and bisphenol novolac resins.

[0037] The epoxy equivalent of the epoxy resin A is preferably 120 to 200 g / eq, 125 to 195 g / eq, 130 to 190 g / eq, or 136 to 183 g / eq. When the epoxy equivalent a is within the above range, the glass transition temperature of the obtained cured product tends to be further improved.

[0038] The content of epoxy resin A is preferably 15 to 60 parts by mass, 20 to 55 parts by mass, 25 to 50 parts by mass, or 30 to 45 parts by mass, relative to 100 parts by mass of the resin component of the thermally 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.

[0039] In this embodiment, the "resin component" refers to the amount of components excluding the thermally conductive filler and the solvent.

[0040] 1.3.Thermal 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.

[0041] 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.

[0042] The thermally conductive filler preferably has an average particle size of 10 to 100 μm, 20 to 80 μm, 25 to 70 μm, or 30 to 60 μm. When the thermally conductive filler has an average particle size of 10 μm or more, high thermal conductivity tends to be achieved with a smaller amount. When the thermally conductive filler has an average particle size of 25 μm or more, insulation reliability and peel strength against the metal layer tend to be further improved. When the thermally conductive filler has an average particle size of 100 μm or less, viscosity tends to be reduced and entrapment of air bubbles during sheet molding tends to be reduced. As a result, partial discharge due to air bubbles is reduced, electric field concentration is less likely to occur, and insulation performance tends to be further improved.

[0043] When the thermally conductive filler is in the form of aggregated particles formed by aggregation of primary particles, the average particle size refers to the particle size of the aggregated particles, which is also called the secondary particle size.

[0044] 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 an output of 20 W 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.

[0045] 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.

[0046] 1.4. Hardener The thermally conductive sheet of this embodiment may further 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.

[0047] The phenol-based curing agent is not particularly limited, but examples thereof include phenol novolac, xylylene novolac, and bisphenol A novolac.

[0048] 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.

[0049] 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.

[0050] The thiol-based curing agent is not particularly limited, but examples thereof include aliphatic polythioethers, aliphatic polythioesters, and aromatic-containing polythioethers.

[0051] 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, relative to 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 the 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.

[0052] 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.

[0053] Such curing accelerators are not particularly limited, but examples thereof include imidazole-based curing agents and phosphorus-based curing agents.

[0054] The imidazole curing agent 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 of suitable hydroxymethylimidazoles 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.

[0055] The phosphorus-based curing agent 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.

[0056] Among these, it is preferable to use a phosphorus-based curing agent in combination with an imidazole-based compound, as this tends to further improve curability and further increase the glass transition temperature of the resulting cured product.

[0057] 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. When the content of the phosphorus-based curing accelerator is within the above range, the glass transition temperature and strength of the B-stage sheet tend to be further improved.

[0058] 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. When the content of the imidazole curing accelerator is within the above range, embrittlement due to excessive hardness of the B-stage sheet tends to be further suppressed.

[0059] 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.

[0060] The total content of the curing accelerator is preferably 0.03 to 4.5 parts by mass, 0.05 to 3.5 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 part 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 4.5 parts by mass or less, embrittlement due to excessive hardness of the B-stage sheet tends to be further suppressed.

[0061] 1.6. Ion Scavenger The ion trapping agent is not particularly limited, but examples thereof include conventionally known ion trapping agents such as hydrotalcite.

[0062] The amount of the ion scavenger used 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.

[0063] Solvents 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.

[0064] 1.8.Surfactants The surfactant is not particularly limited as long as it improves the dispersibility of the thermally conductive filler. For example, a copolymer having an anionic group-containing (meth)acrylic monomer unit α, a cationic group-containing (meth)acrylic monomer unit β, and a silicone (meth)acrylic monomer unit γ can be used as the surfactant. The use of such a surfactant tends to further improve the dispersibility of the thermally conductive filler.

[0065] 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.

[0066] 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.

[0067] A cross-sectional view of a laminate for a metal base circuit board of this embodiment is shown in Fig. 1. As shown in Fig. 1, one aspect of a laminate 10 of this embodiment has a first metal layer 13 serving as a base, on one surface of which a thermally conductive sheet 12 as an insulating layer and a second metal layer 11 are provided in this order.

[0068] 2 shows a cross-sectional view of a laminate for a metal core circuit board of this embodiment. As shown in FIG. 2, another aspect of the laminate 10 of this embodiment has a thermally conductive sheet 12 as an insulating layer and a second metal layer 11 provided 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."

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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. On the other hand, when the thickness of the insulating layer is 500 μm or less, thermal resistance tends to be further reduced.

[0076] 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.

[0077] 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.

[0078] 3. Circuit board The circuit board of this embodiment is a printed circuit board that uses metal for the base or core, and comprises a first metal layer, an insulating layer arranged on the first metal layer, and a second metal layer arranged on the insulating layer, the insulating layer including the above-mentioned thermally conductive sheet, and the second metal layer being a circuit portion.

[0079] A cross-sectional view of the circuit board of this embodiment is shown in Fig. 3. As shown in Fig. 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 Fig. 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.

[0080] 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.

[0081] The method for manufacturing a circuit board of this embodiment includes the steps of preparing the 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. [Example]

[0082] 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.

[0083] 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 aggregate powder (T40), average particle size 40 μm) were mixed together.

[0084] 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%.

[0085] The resulting semi-cured body was peeled off from the PET film and placed on a metal plate (2.0 mm thick copper plate) that would become the first metal layer. Next, a metal foil (0.5 mm thick copper foil) that would become the second metal layer was placed on the semi-cured body, and then the surface pressure was 30 kgf / cm using a press. 2 The laminate was heated and cured at 180°C for 410 minutes while applying a pressure of 3 MPa to the laminate. The thickness of the insulating layer in the laminate was 80 µm.

[0086] Next, after masking predetermined positions on the metal foil (second metal layer) of the laminate with an etching resist, the copper foil was etched using a sulfuric acid-hydrogen peroxide mixed solution as an etching solution. After removing the etching resist and washing and drying, a metal base circuit board with a circular electrode (copper foil) with a diameter of 20 mm was obtained.

[0087] Example 2 A thermally conductive sheet was obtained in the same manner as in Example 1, except that the bisphenol A-type epoxy resin (Bis-A-Ep) in Example 1 was replaced with 29 parts by mass of a 1,6-naphthalenediol-type epoxy resin (manufactured by DIC Corporation, product name HP-4032D, epoxy equivalent 136-148 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.

[0088] 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 replaced with 40 parts by mass of a 1,6-naphthalenediol epoxy resin (manufactured by DIC Corporation, product name HP-4032D, epoxy equivalent 136-148 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.

[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 (Huntsman's "D-400", amine equivalent 200) and triphenylphosphine (TPP) was not used. 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] [Differential scanning calorimeter (DSC)] Using a differential scanning calorimeter (TA Instruments, "Q2000"), the thermally conductive sheet after heat drying was heated from 25 to 300°C at a rate of 10°C / min in a nitrogen atmosphere to obtain a DSC curve. The number of peaks was counted from the obtained DSC curve, and the first peak on the low-temperature side and the second peak on the high-temperature side were identified to determine their respective peak temperatures. The exothermic onset temperature was calculated from the intersection of the tangent to the inflection point of the first peak on the low-temperature side and the baseline.

[0091] The total calorific value C1 (J / g) of the thermally conductive sheet after heat drying was calculated from the integral value of the range surrounded by the tangent line, the baseline, and the DSC curve.

[0092] [Curing rate] The semi-cured state (B stage) was confirmed by measuring the cure rate using a differential scanning calorimeter (TA Instruments, "Q2000"). Specifically, the thermally conductive sheet after heat drying was heated to 25-300°C at a rate of 10°C / min using a differential scanning calorimeter in a nitrogen atmosphere, and the total heat generation amount C1 (J / g) was measured as described above. Next, the thermally conductive sheet before heat drying (solvent volatilized product) was used as a sample and measured using a differential scanning calorimeter under the same conditions to measure the total heat generation amount C0 (J / g). The cure rate was then calculated using the following formula. Curing rate=(C0-C1) / C0×100(%)

[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] The copper foil was cut into a 10 mm × 100 mm piece from the prepared laminate, and the 90° peel strength between the copper foil and the thermally conductive sheet was measured at 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] [Peel strength variation] The peel strength was measured for any four samples produced by the same process as above, and the deviation was calculated.

[0096] [Thermal conductivity] The thermally conductive sheets were stacked 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 using the laser flash method, and the thermal conductivity λ was evaluated using the following formula. λ=α×Cp×ρ

[0097] The specific heat capacity Cp was calculated from differential scanning calorimetry. The specific gravity ρ of the sample was calculated using the following formula, based on the weight of the sample in air and in distilled water measured at 25°C and 1013 hPa using a specific gravity measurement kit AD-1653 (product name) manufactured by A&D Co., Ltd. ρ=A / (AB)×(ρ0-d)+d (In the formula, 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.)

[0098] [Table 1] [Industrial Applicability]

[0099] 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. [Explanation of symbols]

[0100] 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. Epoxy resin A, a thermally conductive filler; When heated from 23°C to 270°C at a rate of 10°C / min using a differential scanning calorimeter, it has two or more peaks. Thermally conductive sheet.

2. When the peak located at the lowest temperature side from the lowest peak temperature among the two or more peaks is defined as a first peak, and the peak located at the next lowest temperature side is defined as a second peak, The peak top calorific value W1 of the first peak is smaller than the peak top calorific value W2 of the second peak. The thermally conductive sheet according to claim 1 .

3. When the peak on the lowest temperature side of the two or more peaks is defined as a first peak and the peak on the highest temperature side is defined as a second peak, The first peak temperature T1 is 75°C or higher and lower than 145°C. The thermally conductive sheet according to claim 1 .

4. When the peak on the lowest temperature side of the two or more peaks is defined as a first peak and the peak on the highest temperature side is defined as a second peak, The temperature T2 of the second peak is greater than 145°C and less than 200°C. The thermally conductive sheet according to claim 1 .

5. When the peak on the lowest temperature side of the two or more peaks is defined as a first peak and the peak on the highest temperature side is defined as a second peak, a difference |T1-T2| between the first peak temperature T1 and the second peak temperature T2 is 3°C or more and 50°C or less; The thermally conductive sheet according to claim 1 .

6. The epoxy equivalent of the epoxy resin A is 136 g / eq or more and 183 g / eq or less. The thermally conductive sheet according to claim 1 .

7. further comprising a curing agent, The thermally conductive sheet according to claim 1 .

8. the thermally conductive filler comprises boron nitride aggregates; The thermally conductive sheet according to claim 1 .

9. a first metal layer; an insulating layer disposed on the first metal layer; a second metal layer disposed on the insulating layer; The insulating layer comprises the thermally conductive sheet according to any one of claims 1 to 8. Laminate.

10. A step of preparing the thermally conductive sheet according to any one of claims 1 to 8; and pressing and heating the thermally conductive sheet while sandwiching it between a metal foil and a metal substrate to obtain a laminate. A method for manufacturing a laminate.

11. a first metal layer; an insulating layer disposed on the first metal layer; a second metal layer disposed on the insulating layer; The insulating layer comprises the thermally conductive sheet according to any one of claims 1 to 8, The second metal layer is a circuit portion. Circuit board.

12. providing a laminate according to claim 9; removing a portion of the first metal layer or a portion of the second metal layer of the laminate to form a circuit portion; A method for manufacturing a circuit board.

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