Thermally conductive liquid epoxy resin composition and die attach material for semiconductor device

Abstract

The present invention is a thermally conductive liquid epoxy resin composition comprising (A) 100 parts by mass of an epoxy resin, (B) 0.5 to 20 parts by mass of a silicone‑modified epoxy resin, (C) 0.05 to 20 parts by mass of an imidazole‑based curing accelerator, and (D) 400 to 1,200 parts by mass of a flake‑shaped thermally conductive filler having an average particle diameter (D50) of 3 μm or greater and a tapped density of 4.0 to 10.0 g / cm3, the thermally conductive liquid epoxy resin composition being characterized in that: the epoxy resin (A) includes 20 to 90 parts by mass of an aminophenol‑type epoxy resin per 100 parts by mass of the epoxy resin; and the viscosity of the thermally conductive liquid epoxy resin composition at 25°C is in the range of 1 to 100 Pa·s. As a result of this configuration, the present invention provides: a resin composition that has excellent workability and little volatile content during curing, and that achieves a cured product having good adhesive force retention after being left in high temperatures; and a die attach material for semiconductor devices.

Description

Thermally conductive liquid epoxy resin composition and die attach material for semiconductor devices

[0001] The present invention relates to a thermally conductive liquid epoxy resin composition and a die attach material for semiconductor devices.

[0002] Epoxy resins and acrylic resins are used as die attach materials in the field of electronic materials. In recent years, particularly in CMOS image sensors, the increasing heat generation due to the larger chip size has made thermal conductivity required in die attach materials. When imparting thermal conductivity to die attach materials, it is common to fill epoxy resins with a high concentration of thermal conductive fillers, but this raises concerns about increased resin viscosity and reduced workability. Therefore, compositions incorporating solvents or reactive diluents can reduce viscosity, but there are concerns about volatilization during curing, leading to voids and contamination of wire pads (Patent Documents 1 and 2).

[0003] Furthermore, due to their recent use in automotive applications, reliability test conditions such as temperature cycling tests and high-temperature storage tests are higher than those for conventional consumer semiconductor applications. Therefore, there is a demand for high heat resistance and low stress properties in thermally conductive liquid epoxy resins.

[0004] International Publication No. 2021 / 039794, International Publication No. 2022 / 030089

[0005] Conventional techniques involve adding reactive diluents, solvents, or other components to a thermally conductive liquid epoxy resin composition to reduce its viscosity, which leads to the problem of these components volatilizing during curing.

[0006] The present invention has been made to solve the above problems, and aims to provide a thermally conductive liquid epoxy resin composition that has excellent workability and low volatile content during curing, and that maintains good adhesive strength after being left at high temperatures, as well as a die attach material for semiconductor devices.

[0007] To solve the above problems, the present invention provides: (A) epoxy resin: 100 parts by mass (B) silicone-modified epoxy resin: 0.5 to 20 parts by mass (C) imidazole-based curing accelerator: 0.05 to 20 parts by mass (D) average particle size (D50) of 3 μm or more, tap density of 4.0 to 10.0 g / cm ３ The present invention provides a thermally conductive liquid epoxy resin composition comprising 400 to 1,200 parts by mass of a flake-shaped thermally conductive filler, wherein the epoxy resin (A) contains 20 to 90 parts by mass of an aminophenol-type epoxy resin per 100 parts by mass, and the viscosity of the thermally conductive liquid epoxy resin composition at 25°C is in the range of 1 to 100 Pa·s.

[0008] Such a thermally conductive liquid epoxy resin composition offers excellent workability, low volatile content during curing, and good adhesion retention after being left at high temperatures.

[0009] Furthermore, it is preferable that the aminophenol-type epoxy resin in component (A) contains an aminophenol-type epoxy resin having three or more epoxy groups in one molecule.

[0010] The component (A) of the above-mentioned thermally conductive liquid epoxy resin composition is preferably such a component (A).

[0011] Furthermore, it is preferable that the aminophenol-type epoxy resin in component (A) is an aminophenol-type epoxy resin having one or more aromatic rings in one molecule.

[0012] The component (A) of the above-mentioned thermally conductive liquid epoxy resin composition is preferably such a component (A).

[0013] Furthermore, it is preferable that component (B) is a silicone-modified epoxy resin having one or more aromatic rings in one molecule.

[0014] The component (B) of the above-mentioned thermally conductive liquid epoxy resin composition is preferably such a component (B).

[0015] Furthermore, it is possible to provide a die attach material for a semiconductor device comprising the thermally conductive liquid epoxy resin composition, wherein the volatile content of the thermally conductive liquid epoxy resin composition after heating at 120°C for 3 hours is 1% by mass or less.

[0016] The thermally conductive liquid epoxy resin composition of the present invention can be suitably used as a die attach material for semiconductor devices.

[0017] As described above, the thermally conductive liquid epoxy resin composition of the present invention is liquid without the need to add reactive diluents, solvents, or other components to reduce the viscosity of the composition, thus offering excellent workability and adhesion to the substrate. Furthermore, the cured product retains its resin reliability even after thermal cycling.

[0018] As described above, there has been a need for the development of a thermally conductive liquid epoxy resin composition that offers excellent workability, low volatile content during curing, and good adhesion retention after high-temperature storage of the cured product, as well as a die attach material for semiconductor devices.

[0019] The inventors of the present invention conducted extensive research to solve the above problems and, as a result, discovered that the thermally conductive liquid epoxy resin composition of the present invention can achieve the above objectives, thus completing the present invention.

[0020] In other words, the present invention comprises: (A) epoxy resin: 100 parts by mass (B) silicone-modified epoxy resin: 0.5 to 20 parts by mass (C) imidazole-based curing accelerator: 0.05 to 20 parts by mass (D) average particle size (D50) of 3 μm or more, and tap density of 4.0 to 10.0 g / cm ３ A thermally conductive liquid epoxy resin composition comprising 400 to 1,200 parts by mass of a flake-shaped thermally conductive filler, wherein the epoxy resin (A) contains 20 to 90 parts by mass of an aminophenol-type epoxy resin per 100 parts by mass, and the viscosity of the thermally conductive liquid epoxy resin composition at 25°C is in the range of 1 to 100 Pa·s.

[0021] The present invention will be described in detail below, but the present invention is not limited to these descriptions.

[0022] [Thermally conductive liquid epoxy resin composition] (A) Epoxy resin The epoxy resin, which is component (A) of the present invention, is the main component of the thermally conductive liquid epoxy resin composition of the present invention. Examples of epoxy resins include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin, bisphenol A novolac type epoxy resin, bisphenol F novolac type epoxy resin, stilbene type epoxy resin, triazine skeleton-containing epoxy resin, fluorene skeleton-containing epoxy resin, triphenol alkane type epoxy resin, biphenyl type epoxy resin, xylylene type epoxy resin, biphenyl aralkyl type epoxy resin, naphthalene type epoxy resin, dicyclopentadiene type epoxy resin, alicyclic epoxy resin, aminophenol type epoxy resin, hydrogenated bisphenol type epoxy resin, alcohol ether type epoxy resin, diglycidyl ether compounds of polycyclic aromatics such as polyfunctional phenols and anthracenes, and phosphorus-containing epoxy resins obtained by introducing phosphorus compounds into these. Among these, liquid bisphenol A type epoxy resin, liquid bisphenol F type epoxy resin, liquid naphthalene type epoxy resin, liquid aminophenol type epoxy resin, liquid hydrogenated bisphenol type epoxy resin, liquid alcohol ether type epoxy resin, liquid cyclic aliphatic type epoxy resin, and liquid fluorene type epoxy resin are preferred from the viewpoint of workability. Among these, aminophenol type epoxy resins having three or more epoxy groups in one molecule, or aminophenol type epoxy resins having one or more aromatic rings in one molecule are preferred. In particular, aminophenol type epoxy resins having three or more epoxy groups in one molecule, and more specifically, aminophenol type epoxy resins having one or more aromatic rings in one molecule are preferred. There is no particular upper limit to the number of epoxy groups contained in one molecule of the aminophenol type epoxy resin, but it can be, for example, 10 or less. Similarly, there is no particular upper limit to the number of aromatic rings contained in one molecule of the aminophenol type epoxy resin, but it can be, for example, 10 or less.

[0023] The epoxy resin, which is component (A) of the present invention, contains 20 to 90 parts by mass of an aminophenol-type epoxy resin per 100 parts by mass. If the amount is less than 20 parts by mass, the viscosity of the resin composition will be high, and if it exceeds 90 parts by mass, the resulting cured product may become brittle. Epoxy resins other than the aminophenol-type epoxy resin can be used individually or in combination of two or more types.

[0024] In the thermally conductive liquid epoxy resin composition of the present invention, (A) epoxy resin is preferably contained in an amount of 5 to 20% by mass, more preferably in an amount of 6 to 19% by mass, and even more preferably in an amount of 7 to 18% by mass.

[0025] (B) Silicone-modified epoxy resin The silicone-modified epoxy resin, which is component (B) of the present invention, is a component that improves the curability and moisture resistance reliability of a thermally conductive liquid epoxy resin composition when included. Examples of the silicone-modified epoxy resin include copolymers obtained by reacting an alkenyl group-containing epoxy resin with an organohydrogen polysiloxane. Examples of the alkenyl group-containing epoxy resin include those shown in the following general formulas (1) to (3).

[0026] In the above general formulas (1) to (3), R １ is a glycidyl group (2,3-epoxypropyl group), X is a hydrogen atom or a bromine atom, n is an integer of 0 or more, preferably 0 to 50, more preferably 1 to 20, and m is an integer of 1 or more, preferably 1 to 5, more preferably 1.

[0027] Examples of the above organohydrogen polysiloxanes include the compounds shown in the following average composition formula (4). ａ (R ２ ) ｂ SiO （４－ａ－ｂ）／２ (4)

[0028] In the above average composition formula (4), R ２is a monovalent hydrocarbon group having 1 to 10 carbon atoms, a hydroxy group, an alkoxy group having 1 to 10 carbon atoms, or an alkenyloxy group having 2 to 10 carbon atoms. Examples of the monovalent hydrocarbon group include alkyl groups such as methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, tert-butyl group, pentyl group, neopentyl group, hexyl group, cyclohexyl group, octyl group, decyl group, etc., aryl groups such as phenyl group, tolyl group, etc., and aralkyl groups such as benzyl group, phenylethyl group, etc. Examples of the alkoxy group include methoxy group, ethoxy group, propoxy group, isopropoxy group, n-hexyloxy group, etc. Examples of the alkenyloxy group include vinyloxy group, propenoxy group, isopropenoxy group, etc.

[0029] In the above average composition formula (4), a and b are numbers satisfying 0.001 ≦ a ≦ 1, 1 ≦ b ≦ 3, and 1 < a + b ≦ 4, preferably 0.01 ≦ a ≦ 0.1, 1.8 ≦ b ≦ 2, and 1.85 ≦ a + b ≦ 2.1. The organohydrogenpolysiloxane preferably has 1 to 1,000 silicon atoms, more preferably 2 to 400 silicon atoms, and still more preferably 5 to 200 silicon atoms in one molecule.

[0030] Examples of the organohydrogenpolysiloxane include compounds represented by the following general formula (5).

[0031] In the above general formula (5), R ２ is as described above, preferably a methyl group or a phenyl group. p is an integer from 0 to 1,000, preferably an integer from 3 to 400, q is an integer from 0 to 20, preferably an integer from 0 to 5, and more preferably q = 0. Further, p + q satisfies 1 < p + q < 1,000, preferably 2 < p + q < 400, and still more preferably 5 < p + q < 200.

[0032] Examples of such organohydrogenpolysiloxane include compounds having the following structural formulas.

[0033] The above organohydrogenpolysiloxane preferably has a weight-average molecular weight of 100 to 100,000, and more preferably 500 to 20,000. When the weight-average molecular weight of the organohydrogenpolysiloxane is within the above range, depending on the structure or weight-average molecular weight of the alkenyl group-containing epoxy resin reacted with the organohydrogenpolysiloxane, a uniform structure in which the organohydrogenpolysiloxane is uniformly dispersed in the matrix, or a sea-island structure in which the organohydrogenpolysiloxane forms fine layer separations in the matrix will appear.

[0034] When the weight-average molecular weight of the organohydrogenpolysiloxane is relatively small, especially between 100 and 10,000, a uniform structure is formed. Conversely, when the weight-average molecular weight of the organohydrogenpolysiloxane is relatively large, especially between 10,000 and 100,000, a sea-island structure is formed. Either a uniform structure or a sea-island structure can be selected depending on the application. If the weight-average molecular weight of the organohydrogenpolysiloxane is 100 or more, the resulting cured product will not be rigid and will not be brittle. If the weight-average molecular weight of the organohydrogenpolysiloxane is 100,000 or less, the sea-island structure will not be large, and there will be no risk of localized stress occurring in the resulting cured product.

[0035] In this invention, the weight-average molecular weight is the weight-average molecular weight using polystyrene as the standard substance, measured by gel permeation chromatography (GPC), and can be measured under the following conditions.

[0036] [GPC Measurement Conditions] Developing solvent: Tetrahydrofuran Flow rate: 0.6 mL / min Column: TSK Guardcolumn SuperH-L TSKgel SuperH4000 (6.0 mm I.D. × 15 cm × 1) TSKgel SuperH3000 (6.0 mm I.D. × 15 cm × 1) TSKgel SuperH2000 (6.0 mm I.D. × 15 cm × 2) (All manufactured by Tosoh Corporation) Column temperature: 40°C Sample injection volume: 20 μL (Sample concentration: 0.5 mass% - tetrahydrofuran solution) Detector: Differential refractometer (RI)

[0037] The method for obtaining the silicone-modified epoxy resin by reacting an alkenyl group-containing epoxy resin with an organohydrogenpolysiloxane can use a known method. For example, a method of adding an alkenyl group-containing epoxy resin and an organohydrogenpolysiloxane in the presence of a platinum-based catalyst can be mentioned. In this way, a silicone-modified epoxy resin can be obtained. The organohydrogenpolysiloxane is preferably copolymerized in an amount such that the amount of SiH groups in the organohydrogenpolysiloxane is 0.1 to 1 mol per 1 mol of the alkenyl groups in the alkenyl group-containing epoxy resin.

[0038] In the thermally conductive liquid epoxy resin composition of the present invention, the above-mentioned (B) silicone-modified epoxy resin is contained in an amount of 0.5 to 20 parts by mass, preferably 1 to 15 parts by mass, more preferably 2 to 10 parts by mass, based on 100 parts by mass of the (A) epoxy resin.

[0039] Further, it is preferable that the component (B) is a silicone-modified epoxy resin having one or more aromatic rings in one molecule. The upper limit of the number of aromatic rings contained in one molecule of the silicone-modified epoxy resin is not particularly limited, but can be, for example, 30 or less.

[0040] (C) Imidazole-based curing accelerators Examples of the imidazole-based curing accelerators that are component (C) of the present invention include 2-methylimidazole, 2-ethylimidazole, 4-methylimidazole, 4-ethylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 2-phenyl-4-hydroxymethylimidazole, 2-ethyl-4-methylimidazole, 1-cyanoethyl-2-methylimidazole, 2-phenyl-4-methyl-5-hydroxy Examples include xymethylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 2-undecylimidazole, 1-decyl-2-phenylimidazole, 1-cyanomethyl-2-undecylimidazole, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanurate adduct, 2-methylimidazole isocyanurate adduct, and 2,3-dihydro-1H-pyrrolo(1,2-a)benzimidazole. These may be used individually or in combination of two or more.

[0041] In the thermally conductive liquid epoxy resin composition of the present invention, (C) imidazole-based curing accelerator is present in an amount of 0.05 to 20 parts by mass, preferably 0.1 to 10 parts by mass, and more preferably 0.5 to 10 parts by mass, per 100 parts by mass of (A) epoxy resin. If the amount is less than 0.05 parts by mass, the curing speed during curing is very slow, and if it exceeds 20 parts by mass, the moisture resistance deteriorates.

[0042] (D) Thermally conductive filler The thermally conductive filler, which is component (D) of the present invention, has an average particle size (D50) of 3 μm or more and a tap density of 4.0 to 10.0 g / cm³. ３ This is a flake-shaped thermally conductive filler. It is added to improve the thermal conductivity of the thermally conductive liquid epoxy resin composition of the present invention, and specifically, it is preferable that the filler has a thermal conductivity of 20 W / m·K or higher. Inorganic substances or metals can be selected as the material of the thermally conductive filler. It is more preferable to use flake-shaped silver particles or aluminum particles because they can keep the storage modulus of the cured product obtained from the thermally conductive liquid epoxy resin composition low and have high thermal conductivity.

[0043] The particle size of the above-mentioned thermally conductive filler has an average particle size (D50) of 3 μm or more, but can be selected according to the film thickness at the time of mounting, depending on the intended application. When used as a die attach material for semiconductor devices, the average particle size is preferably 3 to 10 μm, and more preferably 4 to 8 μm. In this invention, the average particle size (D50) refers to the median diameter based on volume measured by laser diffraction.

[0044] The tap density of the above thermally conductive filler is 4.0 to 10.0 g / cm³. ３ The concentration is preferably 4.2 to 10.0 g / cm³. ３ In this invention, the tap density is measured and calculated according to the metal powder-tap density measurement method described in JIS Z2512:2012.

[0045] The amount of the thermally conductive filler is in the range of 400 to 1,200 parts by mass, preferably 500 to 1,100 parts by mass, per 100 parts by mass of epoxy resin (A). If the amount is less than 400 parts by mass, the thermal conductivity of the cured product obtained by curing the thermally conductive liquid epoxy resin composition will be low, and if it exceeds 1,200 parts by mass, the viscosity of the composition will become too high, resulting in poor workability.

[0046] (E) Other Additives The thermally conductive liquid epoxy resin composition of the present invention is obtained by blending predetermined amounts of components (A), (B), (C), and (D) above, but other additives, component (E), can be added as needed according to the purpose of the present invention. Examples of such additives include inorganic fillers, ion trapping agents, antioxidants, adhesion promoters, stress reducers, etc.

[0047] Inorganic fillers are added to the thermally conductive liquid epoxy resin composition to reduce its thermal expansion coefficient and improve its moisture resistance reliability, and are different from the thermally conductive filler of component (D) mentioned above. Examples of inorganic fillers include silica (fused silica, crystalline silica, cristobalite, etc.), titanium oxide, and glass fibers. The average particle size and shape of these inorganic fillers can be selected according to the application. Among these, spherical alumina, spherical fused silica, and glass fibers are preferred.

[0048] Ion trapping agents are added to thermally conductive liquid epoxy resin compositions to capture ionic impurities and prevent thermal and hygroscopic degradation. Any known ion trapping agent can be used and is not particularly limited. Examples of ion trapping agents include hydrotalcites, bismuth hydroxide compounds, and rare earth oxides.

[0049] Antioxidants are added to prevent oxidative degradation of the cured product of a thermally conductive liquid epoxy resin composition when stored at high temperatures. There are no particular restrictions on the antioxidant, but examples include n-octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, n-octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)acetate, neododecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, dodecyl-β-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, and ethyl acetate. 2-α-(4-hydroxy-3,5-di-t-butylphenyl) isobutyrate, octadecyl-α-(4-hydroxy-3,5-di-t-butylphenyl) isobutyrate, octadecyl-α-(4-hydroxy-3,5-di-t-butyl-4-hydroxyphenyl) propionate, 2-(n-octylthio)ethyl-3,5-di-t-butyl-4-hydroxyphenyl acetate, 2-(n-octadecylthio)ethyl-3, 5-di-t-butyl-4-hydroxyphenyl acetate, 2-(n-octadecylthio)ethyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 2-(2-stearoyloxyethylthio)ethyl-7-(3-methyl-5-t-butyl-4-hydroxyphenyl)heptanoate, 2-hydroxyethyl-7-(3-methyl-5-t-butyl-4-hydroxyphenyl)propionate, pentae Phenolic antioxidants such as lysritol tetrakiss [3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]; sulfur-based antioxidants such as dilauryl-3,3'-thiodipropionate, dimyristyl-3,3'-thiodipropionate, distearyl-3,3'-thiodipropionate, ditridecyl-3,3'-thiodipropionate, and pentaerythrityl tetrakiss (3-laurylthiopropionate);Examples of phosphorus-based antioxidants include tridecyl phosphite, triphenyl phosphite, tris(2,4-di-t-butylphenyl) phosphite, 2-ethylhexyl diphenyl phosphite, diphenyl tridecyl phosphite, 2,2-methylenebis(4,6-di-t-butylphenyl)octyl phosphite, distearyl pentaerythritol diphosphite, bis(2,6-di-t-butyl-4-methylphenyl) pentaerythritol diphosphite, and 2-[[2,4,8,10-tetrakis(1,1-dimethylethyl)dibenzo[d,f][1,3,2]dioxaphosfepin-6-yl]oxy]-N,N-bis[2-[[2,4,8,10-tetrakis(1,1-dimethylethyl)dibenzo[d,f][1,3,2]dioxaphosfepin-6-yl]oxy]-ethyl]ethanamine. These can be used individually or in combination of two or more types.

[0050] Adhesion-improving agents are added to enhance adhesion to silicon wafers, metal substrates, and organic substrates. There are no particular limitations, and known agents can be used. For example, coupling agents such as silane coupling agents and titanate coupling agents can be added, with silane coupling agents being preferred.

[0051] Examples of such coupling agents include epoxy-functional alkoxysilanes such as γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, and β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; amino-functional alkoxysilanes such as N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, and N-phenyl-γ-aminopropyltrimethoxysilane; and mercapto-functional alkoxysilanes such as γ-mercaptopropyltrimethoxysilane. These may be used individually or in combination of two or more.

[0052] Stress-reducing agents are added to thermally conductive liquid epoxy resin compositions to reduce stress, and all known agents can be used without particular limitations. Examples of stress-reducing agents include silicone compounds such as silicone oil, silicone resin, and silicone-modified phenolic resin; and thermoplastic elastomers such as styrene resin and acrylic resin. These may be used individually or in combination of two or more.

[0053] The amount of component (E) varies depending on the intended use of the thermally conductive liquid epoxy resin composition, but it is preferable that component (E) other than the inorganic filler be in an amount of 5% by mass or less of the total thermally conductive liquid epoxy resin composition. If the inorganic filler is component (E), it is preferable that it be 90% by mass or less.

[0054] [Method for preparing a thermally conductive liquid epoxy resin composition] The thermally conductive liquid epoxy resin composition of the present invention can be prepared, for example, by the following method.

[0055] A mixture of components (A) to (D) is obtained by mixing components (A) to (D) simultaneously or separately, subjecting them to heat treatment as necessary, and then stirring, dissolving, and / or dispersing them. Preferably, a mixture of components (A) to (D) is obtained by adding an imidazole-based curing accelerator (C) to the mixture of components (A), (B), and (D), and stirring, dissolving, and / or dispersing it. Alternatively, depending on the intended use, one or more of the inorganic fillers, ion trappers, adhesion promoters, and stress reducers that constitute component (E) may be added and mixed with the mixture of components (A) to (D).

[0056] There are no particular limitations on the apparatus used for mixing, stirring, and dispersion. For example, a mixing machine equipped with stirring and heating devices, a two-roll mill, a three-roll mill, a ball mill, a planetary mixer, or a muscoloider can be used, and these devices may be used in appropriate combinations.

[0057] The thermally conductive liquid epoxy resin composition of the present invention has a viscosity at 25°C in the range of 1 to 100 Pa·s, preferably in the range of 2 to 85 Pa·s. If it is outside this range, the thermally conductive liquid epoxy resin composition will have poor coatability. There are several methods for measuring viscosity, but for example, it can be measured using a cone-to-plate rotational viscometer (E-type viscometer) in accordance with JIS Z8803:2011.

[0058] The thermally conductive liquid epoxy resin composition of the present invention can be used as a cured epoxy resin product after curing. The curing conditions for the epoxy resin composition of the present invention are not particularly limited, but for example, it may be heated at a temperature in the range of 60 to 200°C, preferably 80 to 180°C, for 30 minutes to 10 hours, preferably 1 to 5 hours.

[0059] [Die Attach Material for Semiconductor Devices] The thermally conductive liquid epoxy resin composition of the present invention can be suitably used as a die attach material for semiconductor devices. In this case, it is preferable that the volatile content of the thermally conductive liquid epoxy resin composition after heating at 120°C for 3 hours is 1% by mass or less, and more preferably 0.01 to 0.5% by mass.

[0060] The present invention will be specifically described below using examples and comparative examples, but the present invention is not limited to these.

[0061] The components listed below (components (A) to (D)) were mixed at 25°C using a planetary mixer in the composition shown in Table 1, then kneaded and mixed using a three-roll mill to prepare a thermally conductive liquid epoxy resin composition. The amounts of each component in Table 1 are in parts by mass.

[0062] The prepared thermally conductive liquid epoxy resin compositions were evaluated using the evaluation method described below. The results are shown in Table 1.

[0063] (A) Epoxy resins (A1) Mixture of bisphenol A type epoxy resin and bisphenol F type epoxy resin (ZX1059, viscosity 2,000 mPa·s at 25°C, manufactured by Nippon Steel Chemical & Material Co., Ltd.) (A2) Aminophenol type trifunctional epoxy resin (jER630, viscosity 1,000 mPa·s at 25°C, manufactured by Mitsubishi Chemical Corporation) (A3) Amine type tetrafunctional epoxy resin (ELM-434VL, viscosity 5,000 mPa·s at 50°C, manufactured by Sumitomo Chemical Co., Ltd.)

[0064] (B) A four-necked flask with an internal volume of 1 liter, equipped with a silicone-modified epoxy resin reflux condenser, thermometer, stirrer and dropping funnel, contains the following structural formula (6) 200 g of phenol novolac resin (phenol equivalent 125, allyl equivalent 1,100) modified with allyl glycidyl ether represented by [formula], 800 g of chloromethyloxirane, and 0.6 g of cetyltrimethylammonium bromide were added to each of these and heated, stirring and mixing at 110°C for 3 hours. This was cooled to 70°C, and the pressure was reduced to 160 mmHg. Then, 128 g of a 50% aqueous solution of sodium hydroxide was added dropwise over 3 hours while azeotropically dehydrating. The resulting contents were reduced in pressure to remove the solvent, then dissolved in a mixed solvent of 300 g of methyl isobutyl ketone and 300 g of acetone, washed with water, and the solvent was removed under reduced pressure to obtain the following structural formula (7). An epoxy resin containing allyl groups (allyl equivalent 1590, epoxy equivalent 190) represented by [formula] was obtained. This epoxy resin was mixed with 170 g of methyl isobutyl ketone, 330 g of toluene, and 0.07 g of a 2-ethylhexanol-modified chloroplatinic acid solution with a platinum concentration of 2% by mass. Azeotropic dehydration was carried out for 1 hour, and the following structural formula (8) was obtained at reflux temperature. 133 g of organohydrogenpolysiloxane represented by was added dropwise over a dropwise time of 30 minutes. Structural formula (8) is R in the average empirical formula (4). ２ =methyl group, a=0.02, b=1.98. Furthermore, after stirring and reacting at the same temperature for 4 hours, the obtained contents were washed with water and the solvent was removed under reduced pressure to obtain a yellowish-white opaque solid copolymer represented by the following structural formula (9). The epoxy equivalent was 280, and the ICI melt viscosity at 150°C, measured using a cone / plate viscometer according to ASTM D4287, was 800 mPa·s, with a silicon content of 31% by mass.

[0065] (C) Imidazole-based curing accelerator (C1) 2-phenyl-4-methyl-5-hydroxymethylimidazole (2P4MHz, melting point 193°C, manufactured by Shikoku Chemicals Co., Ltd.)

[0066] (D) Thermally conductive filler (D1) Flake-shaped silver powder (AgC237, average particle size 6.5 μm, tap density 4.8 g / cm²) ３ (Manufactured by Fukuda Metal Co., Ltd.) (D2) Flake-type silver powder (TC-466, average particle size 4.0 μm, tap density 6.7 g / cm³) ３ (Manufactured by Tokuriki Honten Co., Ltd.) (D3) Spherical silver powder for comparative example (average particle size 4.0 μm, tap density 4.8 g / cm³) ３ (D4) Flake silver powder for comparative example (AgC239, average particle size 2.4 μm, tap density 5.7 g / cm³) ３ (Manufactured by Fukuda Metal Co., Ltd.)

[0067] [Viscosity] The viscosity of the thermally conductive liquid epoxy resin composition at 25°C was measured in accordance with JIS Z8803:2011. Specifically, at a measurement temperature of 25°C, the viscosity was measured 2 minutes after setting the sample using a cone-plate type rotational viscometer (Type E viscometer).

[0068] [Volatile Content] The initial weight of the thermally conductive liquid epoxy resin composition was weighed into a φ60 mm aluminum container using an analytical balance (product name: METTLER AT201 (Mettler Toledo Co., Ltd.)). After storage in an oven at 120°C for 3 hours, the mixture was cooled to 25°C and weighed again using an analytical balance (product name: METTLER AT201 (Mettler Toledo Co., Ltd.)). The volatile content (%) was calculated using the following formula: Volatile content = ([Initial weight] - [Weight after storage at 120°C for 3 hours]) / [Initial weight] × 100 (%)

[0069] [Thermal Conductivity] A 2 mm thick epoxy resin cured product was prepared by heating a thermally conductive liquid epoxy resin composition at 120°C for 1 hour and then at 180°C for 3 hours using a hot air circulation dryer. The thermal conductivity of the above epoxy resin cured product was measured using the laser flash method (equipment used: "LFA467 HyperFlash" manufactured by Netch Japan Co., Ltd.).

[0070] [Adhesive strength retention rate after high-temperature storage] On a copper frame measuring 10 mm x 10 mm, the adherend area was 4 mm. ２ A thermally conductive liquid epoxy resin composition was applied, a silicone chip was placed on top, and the sample was heated at 120°C for 1 hour, then at 180°C for 3 hours to prepare a test specimen. Using this test specimen, the shear adhesive strength at room temperature (25°C) was measured using a Bond Tester DAGE-SERIES-4000PXY (manufactured by DAGE Corporation) to evaluate the adhesive strength. The obtained test specimen was also stored in an oven at 180°C for 150 hours, cooled to 25°C, and the shear adhesive strength was measured again. The adhesive strength retention rate after high-temperature storage was calculated in more detail using the following formula: Adhesion strength retention rate = [Shear adhesive strength after 150 hours of storage at 180°C] / [Shear adhesive strength before storage] × 100 (%)

[0071] [Heat Cycle Test] A heat-conductive liquid epoxy resin composition was applied to a copper frame measuring 30 mm x 30 mm. A 20 mm x 20 mm silicon chip was placed on top of the resin, and the frame was heated at 120°C for 1 hour, and then at 180°C for 3 hours to prepare a test specimen. Using this test specimen, a heat cycle test was performed for 1,000 cycles, with each cycle consisting of raising the temperature from -55°C to 150°C and then cooling to -55°C. Defects were defined as the occurrence of delamination of the silicon chip or resin cracks after the test. A defect rate of less than 10% was classified as A, a defect rate of 10% or more but less than 50% as B, and a defect rate of 50% or more as C.

[0072]

[0073] From the results in Table 1 above, the examples (Examples 1 to 7) using the thermally conductive liquid epoxy resin composition of the present invention showed low volatile content during curing, and good results in adhesive strength retention after high-temperature storage and heat cycle tests. On the other hand, Comparative Example 1, which does not contain component (B), showed low adhesive strength retention during high-temperature storage and a high failure rate in the heat cycle test, indicating that the composition is inferior in terms of curability and moisture resistance reliability. Furthermore, Comparative Examples 2 and 3, which use components (D3) and (D4) different from component (D) of the present invention, showed low thermal conductivity and inferior thermal conductivity.

[0074] This specification includes the following embodiments: [1]: (A) Epoxy resin: 100 parts by mass (B) Silicone-modified epoxy resin: 0.5 to 20 parts by mass (C) Imidazole-based curing accelerator: 0.05 to 20 parts by mass (D) Average particle size (D50) of 3 μm or more, tap density of 4.0 to 10.0 g / cm ３A thermally conductive liquid epoxy resin composition comprising 400 to 1,200 parts by mass of a flake-shaped thermally conductive filler, wherein the epoxy resin (A) contains 20 to 90 parts by mass of an aminophenol-type epoxy resin per 100 parts by mass, and the viscosity of the thermally conductive liquid epoxy resin composition at 25°C is in the range of 1 to 100 Pa·s. [2]: The thermally conductive liquid epoxy resin composition according to [1], wherein the aminophenol-type epoxy resin in component (A) contains an aminophenol-type epoxy resin having three or more epoxy groups in one molecule. [3]: The thermally conductive liquid epoxy resin composition according to [1] or [2], wherein the aminophenol-type epoxy resin in component (A) is an aminophenol-type epoxy resin having one or more aromatic rings in one molecule. [4]: The thermally conductive liquid epoxy resin composition according to any one of [1] to [3], characterized in that the (B) component is a silicone-modified epoxy resin having one or more aromatic rings in one molecule. [5]: A die attach material for a semiconductor device comprising the thermally conductive liquid epoxy resin composition according to any one of [1] to [4], characterized in that the amount of volatile matter of the thermally conductive liquid epoxy resin composition after heating at 120°C for 3 hours is 1% by mass or less.

[0075] It should be noted that the present invention is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of the present invention and achieves similar effects is included within the technical scope of the present invention.

Claims

1. (A) Epoxy resin: 100 parts by mass (B) Silicone-modified epoxy resin: 0.5 to 20 parts by mass (C) Imidazole-based curing accelerator: 0.05 to 20 parts by mass (D) Average particle size (D50) of 3 μm or more, tap density of 4.0 to 10.0 g / cm ３ A thermally conductive liquid epoxy resin composition comprising 400 to 1,200 parts by mass of a flake-shaped thermally conductive filler, wherein the epoxy resin (A) contains 20 to 90 parts by mass of an aminophenol-type epoxy resin per 100 parts by mass, and the viscosity of the thermally conductive liquid epoxy resin composition at 25°C is in the range of 1 to 100 Pa·s.

2. The thermally conductive liquid epoxy resin composition according to claim 1, characterized in that the aminophenol-type epoxy resin in component (A) contains an aminophenol-type epoxy resin having three or more epoxy groups in one molecule.

3. The thermally conductive liquid epoxy resin composition according to claim 1, characterized in that the aminophenol-type epoxy resin in component (A) is an aminophenol-type epoxy resin having one or more aromatic rings in one molecule.

4. The thermally conductive liquid epoxy resin composition according to claim 1, characterized in that the component (B) is a silicone-modified epoxy resin having one or more aromatic rings in one molecule.

5. A die attach material for a semiconductor device comprising the thermally conductive liquid epoxy resin composition described in any one of claims 1 to 4, characterized in that the amount of volatile matter of the thermally conductive liquid epoxy resin composition after heating at 120°C for 3 hours is 1% by mass or less.

Images