Thermally conductive sheet

Abstract

A thermally conductive sheet comprising an epoxy resin A and a thermally conductive filler, the thermally conductive sheet exhibiting two or more peaks when the temperature thereof is raised at a rate of 10°C / min from 23°C to 270°C using a differential scanning calorimeter.

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 that is bonded to the insulating layer is specified.

[0005] Japanese Patent Publication No. 2022-173751

[0006] The insulating layer as described above can be formed by sandwiching a thermally conductive sheet between a metal plate and a metal layer and hot-pressing the sheet. The thermally conductive sheet is required to be easy to handle as a sheet and to be further hardened by hot-pressing, so it is preferably 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.

[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] A thermally conductive sheet comprising an epoxy resin A and a thermally conductive filler, which has two or more peaks when heated from 23°C to 270°C at 10°C / min using a differential scanning calorimeter. [2] The thermally conductive sheet according to [1], wherein, when the peak located at the lowest temperature among the two or more peaks is defined as a first peak and the peak located at the next lowest temperature is defined as a second peak, the peak top heat generation value W1 of the first peak is smaller than the peak top heat generation value W2 of the second peak. [3] The thermally conductive sheet according to [1] or [2], wherein, when the peak located at the lowest temperature among the two or more peaks is defined as a first peak and the peak located at the highest temperature is defined as a second peak, the temperature T1 of the first peak is 75°C or higher and lower than 145°C. [4] The thermally conductive sheet according to any one of [1] to [3], wherein, when the lowest peak among the two or more peaks is defined as a first peak and the highest peak is defined as a second peak, the temperature T2 of the second peak is higher than 145°C and 200°C or lower. [5] The thermally conductive sheet according to any one of [1] to [4], wherein, when the lowest peak among the two or more peaks is defined as a first peak and the highest peak is defined as a second peak, the difference |T2 - T1| between the temperature T1 of the first peak and the temperature T2 of the second peak is 3°C or higher and 50°C or lower. [6] The thermally conductive sheet according to any one of [1] to [5], wherein the epoxy equivalent of the epoxy resin A is 136 g / eq or higher and 183 g / eq or lower. [7] The thermally conductive sheet according to any one of [1] to [6], further comprising a curing agent. [8] The thermally conductive sheet according to any one of [1] to [7], wherein the thermally conductive filler comprises a boron nitride aggregate. [9] 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 [8].

[10] A method for producing a laminate, comprising the steps of: preparing the thermally conductive sheet according to any one of [1] to [8]; and press-heating the thermally conductive sheet while sandwiching it between a metal foil and a metal substrate to obtain a laminate.

[11] 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 includes the thermally conductive sheet according to any one of [1] to [8], and the second metal layer is a circuit portion.

[12] A method for manufacturing a circuit board, comprising the steps of: preparing the laminate according to [9]; 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.

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

[0012] Fig. 1 is a cross-sectional view showing a laminate for a metal base circuit board of the present embodiment. Fig. 2 is a cross-sectional view showing a laminate for a metal core circuit board of the present embodiment. Fig. 3 is a cross-sectional view showing a circuit board of the present embodiment. Fig. 4 shows an example of a DSC curve of the thermally conductive sheet of the present embodiment.

[0013] Hereinafter, an embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described in detail, 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 by the symbol "to" includes the numerical values ​​placed before and after the symbol. 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, the sheet hardens further to form an insulating layer having 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 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.

[0018] 1.1. DSC Figure 4 shows an example of a DSC curve for the thermally conductive sheet of this embodiment. The DSC curve shown in Figure 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 Figure 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 heating from room temperature to a temperature (270°C) sufficient for the curing reaction to proceed in order to convert a thermally conductive sheet in a B-stage state into a C-stage. Therefore, the peaks observed by DSC during the temperature increase process from 23°C to 270°C include endothermic or exothermic peaks in the curing reaction when the thermally 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. And, being able to undergo at least two curing stages in different temperature ranges means, for example, that even if the curing reaction of the A-stage thermally conductive composition proceeds excessively and causes all of the curing reaction on the low temperature side to proceed, the curing reaction on the high temperature side can remain in a state where it does not proceed. Therefore, it is possible to avoid the deterioration of adhesion between the metal plate and the metal layer due to excessive curing reaction. On the other hand, since the problem of reduced adhesion does not occur even if the curing reaction on the low temperature side proceeds sufficiently, it is also possible to avoid the deterioration of handleability of the sheet due to insufficient curing reaction on the low temperature side.

[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," which 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 larger than the peak top calorific value W2 of the second peak, or 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 top of the first peak is smaller than the calorific value W2 at the top of the second peak, the calorific value W1 at the 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 top of the first peak is smaller than the calorific value W2 at the top of the second peak, the calorific value W2 at the 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 first peak temperature T1 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 second peak temperature 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.

[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 easily 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 |T2-T1| 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 |T2-T1| is within the above range, it becomes easier to control the reaction by adjusting the temperature in the B-staging step, and the reaction on the high-temperature side tends to proceed less easily.

[0030] The exotherm 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 exotherm 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 exotherm 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] In addition, the total heat generation amount C of the thermal conductive sheet of this embodiment obtained from the DSC curve from 23°C to 270°C １ (J / g) is preferably 50 J / g or more and 170 J / g or less, 55 J / g or more and 160 J / g or less, 60 J / g or more and 150 J / g or less, or 65 J / g or more and 140 J / g or less. １ When (J / g) is within the above range, the reaction can be easily controlled by adjusting the temperature in the B-staging step, and the reaction at high 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 temperature T2-T1 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 a hydroxyl group, 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 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.

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

[0040] 1.3 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.

[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 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.

[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 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.

[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 Curing Agent 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, 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.

[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. 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, 2-phenyl-4-methyl-5-hydroxymethylimidazole, and the like.

[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. 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.

[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. 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.

[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 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 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 scavenger is not particularly limited, but examples thereof include conventionally known ion scavenger 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, per 100 parts by mass of the resin component of the thermally conductive sheet.

[0063] 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.

[0064] 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.

[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 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.

[0068] 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."

[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. Furthermore, 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 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.

[0079] 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.

[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 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.

[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 agglomerated 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 (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.

[0086] 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.

[0087] 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.

[0088] 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 replaced with 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.

[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) 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 (manufactured by TA Instruments, "Q2000"), the thermally conductive sheet after heat drying was heated to 25 to 300 ° C. at a heating rate of 10 ° C. / min in a nitrogen atmosphere to obtain a DSC curve. From the obtained DSC curve, the number of peaks between 23 ° C. and 270 ° C. was counted, 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. In addition, the heat generation initiation temperature was calculated from the intersection of the tangent at the inflection point of the first peak on the low temperature side and the baseline.

[0091] From the integral value of the range surrounded by the tangent line, the baseline, and the DSC curve, the total heat generation amount C of the thermal conductive sheet after heating and drying is calculated. １ (J / g) was calculated.

[0092] [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 (J / g) was measured. Then, the curing rate was calculated by the following formula: Curing rate = (C ０ -C １ ) / C ０ ×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] 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] [Variation in Peel Strength] The peel strength of any four samples produced in the same process was measured as described above, and the deviation was determined.

[0096] [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

[0097] The specific heat Cp was calculated from differential scanning calorimetry. 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) x (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.)

[0098]

[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.

[0100] 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. A thermally conductive sheet having an epoxy resin A and a thermally conductive filler, and having two or more peaks when the temperature is raised from 23°C to 270°C at a rate of 10°C / min using a differential scanning calorimeter.

2. Among the two or more peaks, when the peak located on the low-temperature side from the lower peak temperature is defined as the first peak and the peak located on the next lower-temperature side is defined as the second peak, the peak-top exothermic amount W1 of the first peak is smaller than the peak-top exothermic amount W2 of the second peak. The thermally conductive sheet according to claim 1.

3. Among the two or more peaks, when the peak on the low-temperature side is defined as the first peak and the peak on the high-temperature side is defined as the second peak, the temperature T1 of the first peak is 75°C or higher and less than 145°C. The thermally conductive sheet according to claim 1.

4. Among the two or more peaks, when the peak on the low-temperature side is defined as the first peak and the peak on the high-temperature side is defined as the second peak, the temperature T2 of the second peak is more than 145°C and 200°C or lower. The thermally conductive sheet according to claim 1.

5. Among the two or more peaks, when the peak on the low-temperature side is defined as the first peak and the peak on the high-temperature side is defined as the second peak, the difference |T2 - T1| between the temperature T1 of the first peak and the temperature T2 of the second peak is 3°C or higher and 50°C or lower. 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 includes a boron nitride aggregate. The thermally conductive sheet according to claim 1.

9. 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 includes the thermally conductive sheet according to any one of claims 1 to 8.

10. A method for manufacturing a laminate, comprising: 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.

11. 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 includes the heat-conductive sheet according to any one of claims 1 to 8, and the second metal layer is a circuit portion.

12. A method for manufacturing a circuit board, comprising the step of preparing the laminate according to claim 9, and the 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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