Thermally conductive composition

Abstract

The present invention provides a thermally conductive composition which has excellent thermal conductivity, processability, and long-term reliability.　The thermally conductive composition comprises: 100 parts by mass of an epoxy resin comprising 1-30 parts by mass of a dimer acid type epoxy resin and 1-40 parts by mass of a liquid epoxy resin (excluding the dimer acid type epoxy resin); and 700-1,700 parts by mass of an electrically conductive filler. The electrically conductive filler contains an electrically conductive filler (A) having a mean particle size (D50) of 5-20 μm, as measured by laser diffraction / scattering particle distribution measurement, and an electrically conductive filler (B) having a mean particle size (D50) of 1-8 μm. The ratio ((A) / (B)) of the mean particle size of the electrically conductive filler (A) to the mean particle size of the electrically conductive filler (B) is not less than 1.5. The ratio ((A) / (B)) of the content of the electrically conductive filler (A) to the content of the electrically conductive filler (B) is 1.0-50.0 by mass.

Description

[Technical Field]

[0001] The present invention relates to a thermally conductive composition that is excellent in thermal conductivity, processability, and long-term reliability. [Background technology]

[0002] As semiconductor chips become smaller and denser, the amount of heat generated within semiconductor components increases, which has become a problem. To address this problem, for example, Patent Document 1 describes the use of a thermally conductive composition.

[0003] However, there is an increasing demand in the market for compositions with better thermal conductivity.

[0004] One method for increasing thermal conductivity is to increase the content of conductive filler, but increasing the content of conductive filler increases the viscosity of the thermally conductive composition, which may worsen processability (printability). In contrast, adding a solvent is one method for decreasing the viscosity of the thermally conductive composition, but this may cause voids to form in the cured product due to the solvent volatilizing during curing of the thermally conductive composition. If voids form in the cured product, contact between the conductive fillers is prevented, which may result in a decrease in thermal conductivity.

[0005] In other words, thermal conductivity and processability (printability) are mutually exclusive properties, and there is a need to improve these properties in a balanced manner.

[0006] Furthermore, when the thermally conductive composition is used as a semiconductor material, it is required to obtain excellent results in a long-term reliability test. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-036931 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been made in view of the above, and an object of the present invention is to provide a thermally conductive composition that is excellent in thermal conductivity, processability, and long-term reliability. [Means for solving the problem]

[0009] The present invention includes the embodiments shown below. [1] 1 to 30 parts by mass of a dimer acid type epoxy resin; Viscosity at 25°C is 50 mPa·s or less The composition contains 700 to 1700 parts by mass of a conductive filler relative to 100 parts by mass of an epoxy resin containing 1 to 40 parts by mass of a liquid epoxy resin (excluding dimer acid type epoxy resin), and the conductive filler has an average particle diameter (D50) of 5 to 20 μm as measured by a laser diffraction scattering particle size distribution measurement method. spherical Conductive filler (A) and average particle size (D50) 2 ~8μm spherical and a conductive filler (B), wherein the ratio ((A) / (B)) of the average particle size of the conductive filler (A) to the average particle size of the conductive filler (B) is 1.5 or more, and the content ratio ((A) / (B)) of the conductive filler (A) to the conductive filler (B) is 1.0 to 50.0 in mass ratio. [2] The thermally conductive composition according to [1], wherein the dimer acid type epoxy resin is a glycidyl-modified compound of dimer acid. [3] The thermally conductive composition according to [1] or [2], wherein the liquid epoxy resin is a glycidyl ether type epoxy resin. [4] The thermally conductive composition according to any one of [1] to [3], wherein the epoxy resin contains a glycidylamine type epoxy resin. [Effects of the Invention]

[0010] The thermally conductive composition of the present invention provides excellent thermal conductivity, processability, and long-term reliability. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 2 is a schematic cross-sectional view of a sample substrate used in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0012] As described above, the thermally conductive composition according to the present invention contains 700 to 1,700 parts by mass of a conductive filler per 100 parts by mass of epoxy resin, which contains 1 to 30 parts by mass of a dimer acid type epoxy resin and 1 to 40 parts by mass of a liquid epoxy resin (excluding dimer acid type epoxy resins), wherein the conductive filler contains a conductive filler (A) having an average particle size (D50) of 5 to 20 μm and a conductive filler (B) having an average particle size (D50) of 1 to 8 μm, as measured by a laser diffraction / scattering particle size distribution measurement method, and the ratio ((A) / (B)) of the average particle size of the conductive filler (A) to the average particle size of the conductive filler (B) is 1.5 or more, and the content ratio ((A) / (B)) of the conductive filler (A) to the conductive filler (B) is 1.0 to 50.0 by mass.

[0013] The use of this thermally conductive composition is not particularly limited, but it is preferably used as a composition for filling vias formed in a multilayer substrate.

[0014] The dimer acid type epoxy resin is an epoxy resin having one or more epoxy groups in the molecule, and is obtained by modifying a dimer acid, and examples thereof include glycidyl-modified compounds of dimer acid, and two or more types can be used in combination. Examples of such resins include those represented by the following general formulas (1) and (2).

[0015] [ka]

[0016] In the formulas (1) and (2), n1 to n5 each independently represent an integer of 3 to 9.

[0017] n1 represents an integer of 3 to 9, preferably an integer of 4 to 8, more preferably 5 to 7, and particularly preferably 7. n2 represents an integer of 3 to 9, preferably an integer of 5 to 9, more preferably 7 or 8, and particularly preferably 7. n3 represents an integer of 3 to 9, preferably an integer of 4 to 8, more preferably 6 or 7, and particularly preferably 6. n4 represents an integer of 3 to 9. n5 represents an integer of 3 to 9, preferably an integer of 4 to 8, more preferably 5 or 6, and particularly preferably 5.

[0018] By including such a dimer acid type epoxy resin, the viscosity of the thermally conductive composition tends to be low, and excellent processability and excellent filling ability into vias formed in a multilayer substrate tend to be obtained.

[0019] The epoxy equivalent of the dimer acid epoxy resin is not particularly limited, but is preferably 80 to 1500 g / eq, and more preferably 200 to 1000 g / eq. When the epoxy equivalent is within the above range, a thermally conductive composition having a good balance of heat resistance, viscosity, and adhesion is easily obtained.

[0020] The content of the dimer acid type epoxy resin in 100 parts by mass of the epoxy resin is not particularly limited as long as it is 1 to 30 parts by mass, but is preferably 5 to 30 parts by mass. When the content of the dimer acid type epoxy resin is within the above range, excellent processability is likely to be obtained.

[0021] Liquid epoxy resins (excluding dimer acid epoxy resins) are not particularly limited as long as they contain one or more epoxy groups. However, from the viewpoint of forming a three-dimensional crosslinked structure upon curing, those containing two or more epoxy groups per molecule are preferred. Specific examples of liquid epoxy resins include bisphenol A epoxy resins, brominated epoxy resins, bisphenol F epoxy resins, novolac epoxy resins, alicyclic epoxy resins, glycidyl amine epoxy resins, glycidyl ether epoxy resins, glycidyl ester epoxy resins, and heterocyclic epoxy resins. Among these, glycidyl amine epoxy resins and glycidyl ether epoxy resins are preferred. These liquid epoxy resins may be used alone or in combination of two or more. Herein, the term "liquid" refers to a resin that has fluidity at 25°C.

[0022] The viscosity of the liquid epoxy resin (excluding dimer acid epoxy resin) at 25°C (viscosity of the mixture when two or more types are mixed) is not particularly limited, but is preferably 50 mPa·s or less, more preferably 30 mPa·s or less, and even more preferably 20 mPa·s or less. When the viscosity is within the above range, excellent printability is likely to be obtained.

[0023] The epoxy equivalent of the liquid epoxy resin (excluding dimer acid type epoxy resin) is not particularly limited, but is preferably 100 to 500 g / eq, and more preferably 110 to 300 g / eq. When the epoxy equivalent is within the above range, a thermally conductive composition excellent in heat resistance, viscosity, and thermal conductivity is easily obtained.

[0024] The content of the liquid epoxy resin (excluding dimer acid type epoxy resin) in 100 parts by mass of the epoxy resin is not particularly limited as long as it is 1 to 40 parts by mass, but is preferably 5 to 40 parts by mass. When the liquid epoxy resin is within the above range, excellent processability is likely to be obtained.

[0025] The epoxy resin other than the dimer acid type epoxy resin and the liquid epoxy resin (excluding the dimer acid type epoxy resin) may be any resin having one or more epoxy groups in the molecule, and two or more types may be used in combination. Specific examples include bisphenol A type epoxy resin, brominated epoxy resin, bisphenol F type epoxy resin, novolac type epoxy resin, alicyclic epoxy resin, glycidylamine type epoxy resin, glycidyl ester type epoxy resin, heterocyclic epoxy resin, etc., and among these, those containing glycidylamine type epoxy resin are preferred.

[0026] The epoxy equivalent of the epoxy resin other than the dimer acid type epoxy resin and the liquid epoxy resin (excluding the dimer acid type epoxy resin) is not particularly limited, but is preferably 1500 g / eq or less, and more preferably 20 to 1000 g / eq. When the epoxy equivalent is within the above range, a thermally conductive composition having a good balance of heat resistance, viscosity, and adhesion is easily obtained.

[0027] By using conductive filler (A) and conductive filler (B) having an average particle size ratio ((A) / (B)) of 1.5 or more, the conductive filler (B) can fill the gaps between the conductive fillers (A), making it easier to obtain a thermally conductive composition that has excellent thermal conductivity, low viscosity, and excellent processability.

[0028] The content of the conductive filler is not particularly limited as long as it is 700 to 1700 parts by mass relative to 100 parts by mass of the epoxy resin, but is preferably 1000 to 1700 parts by mass, and more preferably 1200 to 1700 parts by mass. When it is within the above range, it is easy to obtain a thermally conductive composition that has excellent thermal conductivity, low viscosity, and excellent processability.

[0029] The content ratio of the conductive filler (A) to the conductive filler (B) ((A) / (B)) is not particularly limited as long as it is 1.0 to 50.0 in mass ratio, but is preferably 1.5 to 30.0, and more preferably 2.0 to 25.0. When the content ratio of the conductive filler (A) to the conductive filler (B) is within the above range, excellent thermal conductivity is likely to be obtained.

[0030] The conductive filler (A) and the conductive filler (B) are preferably copper powder, silver powder, gold powder, silver-coated copper powder, or silver-coated copper alloy powder, and one of these may be used alone or two or more may be used in combination. From the viewpoint of cost reduction, copper powder, silver-coated copper powder, or silver-coated copper alloy powder is more preferred.

[0031] The silver-coated copper powder has copper powder and a silver layer or a silver-containing layer that coats at least a portion of the copper powder particles, and the silver-coated copper alloy powder has copper alloy powder and a silver layer or a silver-containing layer that coats at least a portion of the copper alloy particles. The copper alloy particles, for example, contain 0.5 to 20 mass% nickel and 1 to 20 mass% zinc, with the balance being copper, and the balance of copper may contain unavoidable impurities.

[0032] Examples of the shape of the conductive filler (A) include flake (scale), dendritic, spherical, fibrous, and amorphous (polyhedral) shapes. From the viewpoint of obtaining a composition with a lower resistance value and improved thermal conductivity, spherical shapes are preferred.

[0033] When the conductive filler (A) is spherical, the tap density of the conductive filler (A) is 3.5 to 7.0 g / cm 3 When the tap density is within the above range, the thermal conductivity tends to be better.

[0034] Examples of the shape of the conductive filler (B) include flake (scale), dendritic, spherical, fibrous, and amorphous (polyhedral) shapes. However, spherical shapes are preferred from the viewpoint of obtaining a composition with lower resistance and improved thermal conductivity.

[0035] When the conductive filler (B) is spherical, the tap density of the conductive filler (B) is 4.0 to 7.0 g / cm 3 When the tap density is within the above range, the thermal conductivity tends to be better.

[0036] The thermally conductive composition according to the present invention can contain an epoxy resin curing agent. Examples of the epoxy resin curing agent include phenolic curing agents, imidazole curing agents, amine curing agents, and cationic curing agents. These curing agents can be used alone or in combination of two or more.

[0037] Examples of phenol-based hardeners include phenol novolak and naphthol-based compounds.

[0038] Examples of imidazole curing agents include imidazole, 2-undecylimidazole, 2-heptadecylimidazole, 2-methylimidazole, 2-ethylimidazole, 2-phenylimidazole, 1-benzyl-2-phenylimidazole, 2-ethyl-4-methyl-imidazole, and 1-cyanoethyl-2-undecylimidazole.

[0039] Examples of the amine-based curing agent include aliphatic polyamines such as diethylenetriamine and triethylenetetramine, and aromatic polyamines such as metaphenylenediamine, diaminodiphenylmethane and diaminodiphenylsulfone.

[0040] Examples of cationic curing agents include onium compounds such as amine salts of boron trifluoride, p-methoxybenzenediazonium hexafluorophosphate, diphenyliodonium hexafluorophosphate, triphenylsulfonium, tetra-n-butylphosphonium tetraphenylborate, and tetra-n-butylphosphonium-o,o-diethylphosphorodithioate.

[0041] The content of the curing agent is preferably 0.3 to 40 parts by mass, and more preferably 0.5 to 35 parts by mass, relative to 100 parts by mass of the epoxy resin. When the content of the curing agent is 0.3 parts by mass or more, the thermally conductive composition is sufficiently cured, and a thermally conductive composition with excellent thermal conductivity is likely to be obtained, while when the content is 40 parts by mass or less, a thermally conductive composition with excellent storage stability is likely to be obtained.

[0042] The thermally conductive composition of the present invention may contain known additives such as antifoaming agents, thickeners, adhesives, fillers, flame retardants, colorants, etc., within the scope of the invention.

[0043] The thermally conductive composition according to the present invention preferably has a low viscosity so that it can be easily applied to vias formed in a multilayer substrate by a dispensing method, an atmospheric printing method, or a vacuum printing method.

[0044] Here, the dispensing method refers to a method of applying a thermally conductive composition by extruding it from the tip of a syringe-shaped nozzle. The atmospheric printing method refers to a method of printing a stencil printing plate by stretching a synthetic fiber screen on the plate, optically forming a printing film on the screen to block all pores except for the necessary image lines, creating a plate, and rubbing the thermally conductive composition through the pores of the printing film under atmospheric pressure onto the printing surface of a substrate placed below the plate. The vacuum printing method refers to a method of printing a stencil printing plate by stretching a synthetic fiber screen on the plate, optically forming a printing film on the screen to block all pores except for the necessary image lines, creating a plate, and rubbing the thermally conductive composition through the pores of the printing film under vacuum onto the printing surface of a substrate placed below the plate.

[0045] The viscosity of the thermally conductive composition according to the present invention is preferably adjusted appropriately depending on the application and the equipment used for application, and is not particularly limited. However, as a general guideline, at a temperature of 25°C, the thermally conductive composition preferably has a viscosity of 2800 dPa·s or less, more preferably 2500 dPa·s or less, and even more preferably 2000 dPa·s or less. A viscosity of 3000 dPa·s or less is less likely to clog nozzles in dispensing methods or screens in printing methods, and is likely to provide excellent filling of vias formed in multilayer substrates. The viscosity can be measured in accordance with JIS K7117-1 using a single-cylinder rotational viscometer (known as a B-type or BH-type viscometer) with a rotor No. 7 at 10 rpm. Note that a low viscosity is acceptable as long as it can be measured using a single-cylinder rotational viscometer.

[0046] From the viewpoint of preventing the occurrence of voids, it is preferable that the thermally conductive composition according to the present invention does not contain a solvent. [Example]

[0047] The present invention will be described in detail below based on examples, but the present invention is not limited to the following. In the following, "parts" and "%" are based on mass unless otherwise specified.

[0048] [Examples and Comparative Examples] A thermally conductive composition was obtained by mixing 100 parts by mass of the epoxy resin shown below with a conductive filler and a curing agent in the proportions shown in Tables 1 to 7. Details of each component used are as follows:

[0049] Dimer acid type epoxy resin: In the above formula (2), n1 = 7, n2 = 7, n4 = 4, and n5 = 5 was used. Epoxy resin: Glycidylamine type epoxy resin, ADEKA Corporation "EP-3905S", epoxy equivalent = 95g / eq Liquid epoxy resin: Glycidyl ether type epoxy resin, ADEKA Corporation "ED502", epoxy equivalent = 320g / eq

[0050] Conductive filler (a): Silver-coated copper particles, D50=22μm, spherical Conductive filler (b): Silver-coated copper particles, D50=20μm, spherical Conductive filler (c): Silver-coated copper particles, D50=18μm, spherical Conductive filler (d): Silver-coated copper particles, D50=15μm, spherical Conductive filler (e): Silver-coated copper particles, D50=14μm, spherical Conductive filler (f): Silver-coated copper particles, D50=12μm, spherical Conductive filler (g): Silver-coated copper particles, D50=10μm, spherical Conductive filler (h): Silver-coated copper particles, D50=8μm, spherical Conductive filler (i): Silver-coated copper particles, D50=6μm, spherical Conductive filler (j): Silver-coated copper particles, D50=5μm, spherical Conductive filler (k): Silver-coated copper particles, D50=4μm, spherical Conductive filler (l): Silver-coated copper particles, D50=3μm, spherical Conductive filler (m): silver-coated copper particles, D50=2μm, spherical Conductive filler (n): Silver-coated copper particles, D50=1μm, spherical

[0051] Curing agent (a): Imidazole-based curing agent, "2E4MZ" manufactured by Shikoku Chemical Industries, Ltd. Hardener (b): Phenol novolac hardener, "Tamanol 758" manufactured by Arakawa Chemical Industries, Ltd.

[0052] The thermally conductive compositions of the above Examples and Comparative Examples were evaluated as follows, and the results are shown in Tables 1 to 7.

[0053] <Viscosity of Thermally Conductive Composition> The viscosity of the thermally conductive compositions according to each Example and Comparative Example at 25° C. was measured in accordance with JIS K7117-1 using a single cylindrical rotational viscometer (a so-called B-type viscometer) with a rotor No. 7 at 10 rpm.

[0054] <Printability of thermally conductive compositions using printing methods> Measurement samples were prepared using the sample substrate shown in Figure 1 by a printing method. Specifically, through-holes with a diameter of 0.15 mm were drilled into a 1.0 mm thick copper-patterned glass epoxy substrate. Using a printing machine "LS-77A" manufactured by Newlong Precision Industries Co., Ltd., the thermally conductive composition prepared by the printing method was filled into the holes. The composition was then heated at 80°C for 30 minutes and then cured at 160°C for 30 minutes to produce the sample. The vias of the obtained samples were observed before and after curing using an X-ray transmission device "Y.Cheetah μHD" manufactured by Yxlon International under the following measurement conditions to confirm the presence of voids. Furthermore, the cross-sections of the vias after curing were observed for peeling from the wall and cracks. Samples without voids, peeling from the wall, or cracks were evaluated as having excellent printability and rated "Good." Furthermore, if any one of voids, peeling from the wall surface, or cracks was observed, the printability was deemed poor and the result was evaluated as "X."

[0055] <Printing conditions> Printing pressure: 0.3MPa Squeegee angle: 15° Squeegee speed: 10mm / sec Clearance: 1.0mm Urethane squeegee hardness: 70 degrees <Measurement conditions> Voltage: 50kV Current: 80μA Power: 4W

[0056] <Thermal conductivity of the cured product of the thermally conductive composition> The thermally conductive compositions according to each example and comparative example were printed onto a Teflon (registered trademark) sheet using a bar film applicator (manufactured by Byck-Gardner). The thermally conductive compositions were then cured by heating at 160°C for 60 minutes, and the compositions were peeled off from the Teflon (registered trademark) sheet to obtain cured samples with a thickness of approximately 100 μm. The thermal conductivity of the prepared cured samples was evaluated using a Thermowave Analyzer TA-35 (manufactured by BETHEL) certified to JIS R7240. The thermal diffusivity α (m 2 / S) and the density ρ (kg / m 3 The thermal conductivity K (W / m K) was calculated from the specific heat Cp (J / Kg K) using the following formula (1). A thermal conductivity of 30 W / m K or higher was determined to be excellent in heat dissipation. Thermal conductivity K = thermal diffusivity α × density ρ × specific heat Cp (1)

[0057] Next, the excess cured thermally conductive composition that had overflowed above and below the through-holes of the samples obtained by the printing method was polished off to prepare evaluation boards, and long-term reliability was evaluated.

[0058] <Initial resistance> Using a milliohm tester, the resistance value between both ends of the connection pattern of the sample board shown in Figure 1 was measured. The resistance value per hole was calculated by subtracting the wiring resistance from the resistance value and dividing by the number of holes. Note that the wiring resistance was measured on a circuit board with the same design but without holes.

[0059] <Long-term reliability 1 (solder dip test)> In the solder dip test, the evaluation board was immersed in molten solder heated to 260°C for 10 seconds. This was repeated three times. After the solder dip test, the vias and cross sections were observed using an X-ray transmission device, and the rate of change in resistance was calculated.

[0060] (i) Observation of vias and cross sections using an X-ray transmission device Using an X-ray transmission device "Y.Cheetah μHD" manufactured by YXLON International, the vias were observed under the following measurement conditions to check for the presence of voids. In addition, the cross section of the vias after curing was observed to check for peeling from the wall and cracks. Those that did not have voids, peeling from the wall, or cracks were evaluated as having excellent reliability and given a "Good" rating. Furthermore, those that had any of voids, peeling from the wall, or cracks after the reliability test were evaluated as having poor reliability and given a "Poor" rating.

[0061] <Measurement conditions> Voltage: 50kV Current: 80μA Power: 4W

[0062] (ii) Resistance change rate Similar to the measurement of the initial resistance value, the resistance value between both ends of the connecting pattern shown in Figure 1 was measured after the reliability test. The initial resistance value before the reliability test was designated as a, and the resistance value after the reliability test was designated as b. The rate of change in resistance value before and after the reliability test was calculated using the following formula. A rate of change in resistance value of +20% or less was evaluated as having excellent reliability. Resistance change rate (%) = (ba) × 100 / a

[0063] <Long-term reliability 2 (heat resistance test)> In the heat resistance test, the evaluation boards were left standing for 1000 hours in an environment with an environmental temperature of 100°C. After the heat resistance test, the vias were observed with an X-ray transmission device, cross sections were observed, and the rate of change in resistance was calculated, just as in the solder dip test.

[0064] <Long-term reliability 3 (moisture resistance test)> In the moisture resistance test, the evaluation boards were left standing for 1000 hours in an environment with an environmental temperature of 85°C and humidity of 85%. After the moisture resistance test, the vias and cross sections were observed using an X-ray transmission device, and the rate of change in resistance was calculated, just as in the solder dip test.

[0065] [Table 1]

[0066] [Table 2]

[0067] [Table 3]

[0068] [Table 4]

[0069] [Table 5]

[0070] [Table 6]

[0071] [Table 7]

[0072] From the results shown in Table 1, when the content of the dimer acid type epoxy resin was within the predetermined range, the printability, thermal conductivity, and long-term reliability test results were all excellent.

[0073] The results shown in Table 2 show that when the content of the liquid epoxy resin (excluding dimer acid type epoxy resin) was within the specified range, the printability, thermal conductivity, and long-term reliability test results were all excellent.

[0074] From the results shown in Table 3, when the total amount of the conductive filler was within the predetermined range, the printability, thermal conductivity, and long-term reliability test results were all excellent.

[0075] From the results shown in Table 4, when the average particle size of the conductive filler (A) was within the predetermined range, the printability, thermal conductivity, and long-term reliability test results were all excellent.

[0076] From the results shown in Table 5, when the average particle size of the conductive filler (B) was within the predetermined range, the printability, thermal conductivity, and long-term reliability test results were all excellent.

[0077] The results shown in Table 6 show that when the ratio of the average particle diameters of the conductive filler (A) and the conductive filler (B) is within a specified range, the printability, thermal conductivity, and long-term reliability test results were all excellent.

[0078] From the results shown in Table 7, when the content ratio of the conductive filler (A) and the conductive filler (B) was within the specified range, the printability, thermal conductivity, and long-term reliability test results were all excellent. [Explanation of symbols]

[0079] 1. Glass epoxy substrate 2...copper 3. Via

Claims

1. per 100 parts by mass of an epoxy resin containing 1 to 30 parts by mass of a dimer acid type epoxy resin and 1 to 40 parts by mass of a liquid epoxy resin (excluding dimer acid type epoxy resins) having a viscosity of 50 mPa s or less at 25°C, Contains 700 to 1700 parts by mass of a conductive filler, the conductive filler contains spherical conductive filler (A) having an average particle diameter (D50) of 5 to 20 μm measured by a laser diffraction scattering particle size distribution measurement method, and spherical conductive filler (B) having an average particle diameter (D50) of 2 to 8 μm; the ratio ((A) / (B)) of the average particle size of the conductive filler (A) to the average particle size of the conductive filler (B) is 1.5 or more; A thermally conductive composition, wherein the content ratio ((A) / (B)) of the conductive filler (A) to the conductive filler (B) is 1.0 to 50.0 in mass ratio.

2. The thermally conductive composition according to claim 1 , wherein the dimer acid type epoxy resin is a glycidyl-modified compound of a dimer acid.

3. 3. The thermally conductive composition according to claim 1, wherein the liquid epoxy resin is a glycidyl ether type epoxy resin.

4. The thermally conductive composition according to claim 1 or 2, wherein the epoxy resin contains a glycidyl amine type epoxy resin.

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