Liquid resin composition and resin-encapsulated power module

Abstract

This liquid resin composition is used to encapsulate, by casting, a power module comprising a power module substrate with a circuit layer formed thereon and a power semiconductor element mounted on the circuit layer of the power module substrate. The liquid resin composition includes (A) an epoxy resin, (B) an acid anhydride, (C) a hardening accelerator, (D) an inorganic filler, and (E) a sedimentation preventing agent. The epoxy resin (A) includes an alicyclic epoxy resin. The viscosity of the liquid resin composition at 25°C is 75 Pa•s or less.

Description

Liquid resin composition and resin-sealed power module

[0001] The present invention relates to a liquid resin composition and a resin-encapsulated power module. More specifically, the present invention relates to a liquid resin composition for casting used to encapsulate power semiconductor elements, and a power module manufactured using the same.

[0002] Epoxy resins have excellent heat resistance, chemical resistance, insulating properties, etc., and are used as liquid encapsulants for molding to seal substrates and semiconductor elements in semiconductor devices and the like.

[0003] In recent years, power semiconductor elements capable of operating at high temperatures have been developed, and the epoxy resins used as their encapsulants are required to have higher levels of heat resistance. Furthermore, encapsulants for power modules are required to have low linear expansion in addition to insulation and heat resistance. This is to prevent cracks and peeling in the encapsulating resin due to expansion caused by heat generated by the power semiconductor elements. To reduce the linear expansion coefficient, inorganic fillers are commonly added to the encapsulating resin (see, for example, Patent Document 1).

[0004] However, the incorporation of inorganic fillers can increase the viscosity of the encapsulating material, making it difficult to cast. Furthermore, the inorganic fillers settle during curing, creating a difference in the linear expansion coefficient between the top and bottom surfaces of the cured product, which can lead to cracks forming in the cured encapsulating resin and reduce the reliability of the resulting device.

[0005] JP 2009-67890 A

[0006] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a liquid resin composition for encapsulating power semiconductor elements, which has low viscosity and reduces sedimentation of inorganic filler during storage, thereby making it easy to cast, reduces sedimentation of inorganic filler during curing, and has excellent heat resistance, as well as a power device that includes the liquid resin composition as an encapsulant and has excellent crack resistance, electrical properties, mechanical properties, and heat resistance.

[0007] According to the present invention, there are provided the following liquid resin composition and power device. [1] A liquid resin composition used for encapsulating, by a casting method, a power module including a power module substrate having a circuit layer formed thereon and a power semiconductor element mounted on the circuit layer of the power module substrate, the liquid resin composition comprising: (A) an epoxy resin; (B) an acid anhydride; (C) a curing accelerator; (D) an inorganic filler; and (E) an anti-settling agent; the epoxy resin (A) comprises an alicyclic epoxy resin; and the liquid resin composition has a viscosity of 75 Pa s or less at 25°C. [2] The liquid resin composition according to item [1], wherein the content of the inorganic filler (D) is 65% by mass or more and 85% by mass or less, based on the total solid content of the liquid resin composition. [3] The liquid resin composition according to item [1] or [2], further comprising core-shell rubber particles. [4] The liquid resin composition according to item [3], wherein the content of the core-shell rubber particles is 0.1% by mass or more and 10% by mass or less, based on the total solid content of the liquid resin composition. [5] The liquid resin composition according to any one of items [1] to [4], further comprising a flame retardant. [6] The liquid resin composition according to any one of items [1] to [5], wherein the flow distance measured under the following conditions is 20 mm or more. Conditions: 0.05 ml of the liquid resin composition is applied to a glass plate so that the diameter of the liquid resin composition is 1 cm or less. The glass plate is then held at a tilt angle of 45° and a temperature of 60°C for 3 minutes, and the distance traveled by the liquid resin composition during this period is defined as the flow distance (mm). [7] The liquid resin composition according to any one of items [1] to [6], wherein the amount of the alicyclic epoxy resin contained in the epoxy resin (A) is 75% by mass or more, based on the total amount of the epoxy resin (A). [8] The liquid resin composition according to any one of items [1] to [7], wherein the epoxy resin (A) further contains a liquid bisphenol A type epoxy resin or a liquid bisphenol F type epoxy resin.[9] The liquid resin composition according to item [8], wherein the amount of the liquid bisphenol A epoxy resin or the liquid bisphenol F epoxy resin contained in the epoxy resin (A) is 25 mass% or less based on the total amount of the epoxy resin (A).

[10] The liquid resin composition according to any one of items [1] to [9], wherein the acid anhydride (B) comprises at least one selected from methyl-5-norbornene-2,3-dicarboxylic anhydride, methylcyclohexane-1,2-dicarboxylic anhydride, and methyltetrahydrophthalic anhydride.

[11] The liquid resin composition according to item

[10] , wherein the viscosity of the methyltetrahydrophthalic anhydride at 25°C is 30 mPa·s or more and 50 mPa·s or less.

[12] The liquid resin composition according to any one of items [1] to

[11] , wherein the curing accelerator (C) comprises an organic acid salt of diazabicycloundecene.

[13] The liquid resin composition according to any one of items [1] to

[12] , wherein the sedimentation inhibitor (E) comprises bentonite or a polyhydroxycarboxylic acid ester.

[14] A resin-sealed power module comprising: a power module substrate having a circuit layer formed thereon, a power semiconductor element mounted on the circuit layer of the power module substrate, and an encapsulant covering the power module substrate and the power semiconductor element, wherein the encapsulant is made of a cured product of the liquid resin composition according to any one of items [1] to

[13] .

[0008] According to the present invention, there are provided a liquid resin composition for encapsulating power semiconductor elements, which has low viscosity, excellent casting workability, reduced sedimentation of inorganic filler during curing, and excellent heat resistance, as well as a power device which includes the liquid resin composition as an encapsulant and has excellent crack resistance, electrical properties, mechanical properties, and heat resistance.

[0009] Hereinafter, embodiments of the present invention will be described. In this specification, a numerical range indicated using "to" indicates a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this specification, the upper or lower limit of a certain numerical range can be arbitrarily combined with the upper or lower limit of another numerical range. In the numerical ranges described in this specification, the upper or lower limit of the numerical range may be replaced with a value shown in the examples. "A or B" may include either A or B, or may include both. Unless otherwise specified, the materials exemplified in this specification can be used alone or in combination of two or more. In this specification, when multiple substances corresponding to each component are present in the composition, the content of each component in the composition refers to the total amount of the multiple substances present in the composition, unless otherwise specified.

[0010] [Liquid Resin Composition] The resin composition of this embodiment is a liquid resin composition for casting used to encapsulate power semiconductor elements. More specifically, the resin composition of this embodiment is used to encapsulate a power module, which includes a power module substrate on which a circuit layer is formed and a power semiconductor element mounted on the circuit layer of the power module substrate, by a casting method. The liquid resin composition for casting power modules of this embodiment (sometimes simply referred to as the "resin composition" in this specification) contains (A) an epoxy resin, (B) an acid anhydride, (C) a curing accelerator, (D) an inorganic filler, and (E) an anti-settling agent. In this embodiment, the epoxy resin (A) contains an alicyclic epoxy resin. The viscosity of the resin composition of this embodiment at 25°C is 75 Pa·s or less.

[0011] The resin composition of this embodiment has a viscosity of 75 Pa·s or less at 25°C, which results in excellent casting workability. The resin composition of this embodiment also contains the above-mentioned components (A) to (E), and the epoxy resin (A) contains an alicyclic epoxy resin. By using an alicyclic epoxy resin, the resulting resin composition has excellent heat resistance.

[0012] The components used in the resin composition of this embodiment are described in detail below. (Epoxy Resin (A)) The epoxy resin (A) blended in the resin composition of this embodiment contains an alicyclic epoxy resin. By using an alicyclic epoxy resin, the cured product of the obtained resin composition has a high glass transition temperature of 200°C or higher, and therefore has sufficient heat resistance for use as an encapsulant for power modules.

[0013] As the alicyclic epoxy resin used in this embodiment, it is preferable to use an alicyclic epoxy resin that is liquid at 25°C. Examples of such liquid alicyclic epoxy resins include epoxy-[epoxy-oxaspiro C] such as vinylcyclopentadiene dioxide, vinylcyclohexene monodioxide, vinylcyclohexene dioxide, dicyclopentadiene oxide, and 3,4-epoxy-1-[8,9-epoxy-2,4-dioxaspiro[5.5]undecan-3-yl]-cyclohexane. ８－１５ Alkyl]-cycloC ５－１２ Alkanes, epoxy C such as 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate, 4,5-epoxycyclooctylmethyl-4',5'-epoxycyclooctanecarboxylate ５－１２ Cycloalkyl C １－３ Alkyl-epoxy C ５－１２ cycloalkane carboxylates, bis(C) such as bis(2-methyl-3,4-epoxycyclohexylmethyl) adipate; １－３ Alkyl Epoxy C ５－１２ Cycloalkyl C １－３ A commercially available product of 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate is preferably CELLOXIDE #2021P (epoxy equivalent: 128 to 140) manufactured by Daicel Corporation.

[0014] The amount of the alicyclic epoxy resin contained in the epoxy resin (A) is, for example, 70 mass% or more, preferably 75 mass% or more, and more preferably 80 mass% or more, based on the total amount of the epoxy resin (A).

[0015] In a preferred embodiment, the epoxy resin (A) contains, in addition to the above-mentioned alicyclic epoxy resin, a bisphenol A epoxy resin or a bisphenol F epoxy resin. By using these epoxy resins, the heat resistance of the cured product of the obtained resin composition can be further improved, and the insulation reliability can also be improved.

[0016] When the epoxy resin (A) contains a bisphenol A type epoxy resin or a bisphenol F type epoxy resin, the amount thereof is, for example, 30 mass% or less, preferably 25 mass% or less, and more preferably 20 mass% or less, based on the entire epoxy resin (A).

[0017] The epoxy resin (A) may contain other epoxy resins different from the above-mentioned epoxy resins, as long as the physical properties such as heat resistance and insulating properties of the cured product of the resulting resin composition are not impaired. Examples of other epoxy resins include bisphenol-type epoxy resins such as bisphenol E-type epoxy resin, bisphenol S-type epoxy resin, bisphenol M-type epoxy resin (4,4'-(1,3-phenylenediisopridiene)bisphenol-type epoxy resin), bisphenol P-type epoxy resin (4,4'-(1,4-phenylenediisopridiene)bisphenol-type epoxy resin), and bisphenol Z-type epoxy resin (4,4'-cyclohexidienebisphenol-type epoxy resin); phenol novolac-type epoxy resin, cresol novolac-type epoxy resin, trisphenol-group methane-type novolac-type epoxy resin, tetraphenol-group ethane-type novolac-type epoxy resin; Examples of epoxy resins include novolac-type epoxy resins such as novolac-type epoxy resins having a condensed ring aromatic hydrocarbon structure; biphenyl-type epoxy resins; aryl alkylene-type epoxy resins such as xylylene-type epoxy resins and biphenyl aralkyl-type epoxy resins; naphthalene-type epoxy resins such as naphthylene ether-type epoxy resins, naphthol-type epoxy resins, naphthalene diol-type epoxy resins, difunctional to tetrafunctional epoxy naphthalene resins, binaphthyl-type epoxy resins, and naphthalene aralkyl-type epoxy resins; anthracene-type epoxy resins; phenoxy-type epoxy resins; dicyclopentadiene-type epoxy resins; norbornene-type epoxy resins; adamantane-type epoxy resins; and fluorene-type epoxy resins. When these epoxy resins are used, the amount thereof is, for example, 10% by mass or less, and preferably 5% by mass or less, based on the total amount of the epoxy resin (A).

[0018] The amount of the epoxy resin (A) in the resin composition of this embodiment is, for example, 2 to 30% by mass, and preferably 4 to 25% by mass, based on the total mass of the resin composition. The amount of the epoxy resin (A) in the resin composition refers to the total amount of the above-mentioned alicyclic epoxy resin and the bisphenol A epoxy resin or bisphenol F epoxy resin, or other epoxy resin, which is used as needed.

[0019] (Acid Anhydride (B)) The resin composition of this embodiment contains an acid anhydride (B). The acid anhydride (B) functions as a curing agent for the epoxy resin (A). Examples of the acid anhydride (B) that can be used include dodecenyl succinic anhydride, polyadipic anhydride, polyazelaic anhydride, polysebacic anhydride, poly(ethyloctadecanedioic) anhydride, poly(phenylhexadecanedioic) anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, hexahydrophthalic anhydride, methylhimic anhydride, tetrahydrophthalic anhydride, trialkyltetrahydrophthalic anhydride, methylcyclohexene dicarboxylic anhydride, phthalic anhydride, trimellitic anhydride, and pyromellitic anhydride. acid, benzophenone tetracarboxylic anhydride, ethylene glycol bistrimellitate, HET acid anhydride, tetrahydrophthalic anhydride, methyl nadic anhydride (methyl-5-norbornene-2,3-dicarboxylic anhydride), methyl himic anhydride (methyl-3,6-endomethylene-1,2,3,6-tetrahydrophthalic anhydride), 4-methylcyclohexane-1,2-dicarboxylic anhydride, 5-(2,5-dioxotetrahydro-3-furanyl)-3-methyl-3-cyclohexane-1,2-dicarboxylic anhydride, and the like. Among these, as the acid anhydride (B), it is preferable to use acid anhydrides that are liquid at 25°C, such as methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, methyl-5-norbornene-2,3-dicarboxylic anhydride, and methylcyclohexane-1,2-dicarboxylic anhydride, because they are easily mixed uniformly with other components such as the epoxy resin (A). Among these, it is particularly preferable to use methyl-5-norbornene-2,3-dicarboxylic anhydride, methylcyclohexane-1,2-dicarboxylic anhydride, and methyltetrahydrophthalic anhydride. Furthermore, when using methyltetrahydrophthalic anhydride, it is preferable to use one having a viscosity of 30 to 50 mPa·s at 25°C. By using such an acid anhydride, it is possible to further reduce the viscosity of the resulting resin composition. Commercially available acid anhydrides include the HN series manufactured by Showa Denko Materials KK. The acid anhydride (B) may be used alone or in combination of two or more.

[0020] From the viewpoints of workability and curability, the amount of acid anhydride (B) in the resin composition of this embodiment is preferably 10% by mass to 60% by mass, and more preferably 15% by mass to 50% by mass, based on the total resin composition. Furthermore, the ratio of the total number of functional groups of the acid anhydride to the total number of epoxy groups in the epoxy resin (A) is preferably 0.7 to 1.2, and more preferably 0.8 to 1.1. By using the acid anhydride (B) in an amount within the above range, the mechanical strength and insulating properties of the cured product of the resulting resin composition can be improved.

[0021] (Curing Accelerator (C)) The resin composition of this embodiment contains a curing accelerator (C). The curing accelerator (C) has the effect of accelerating the reaction between the epoxy resin (A) and the acid anhydride (B) that serves as a curing agent. Examples of the curing accelerator (C) that can be used include tertiary amines, quaternary ammonium salts, imidazoles, organic phosphines, and Lewis acid catalysts. Among these, quaternary ammonium salts are preferably used.

[0022] Examples of tertiary amines include trimethylamine, triethylamine, tripropylamine, tributylamine, and benzyldimethylamine.

[0023] Examples of quaternary ammonium salts include organic acid salts of diazabicycloundecene such as octylate salt of DBU [1,8-diazabicyclo[5.4.0]undecene-7] (manufactured by San-Apro Ltd., trade name: SA102), DBN [1,5-diazabicyclo[4.3.0]-5-nonene], quaternary ammonium salts which are salts of tertiary amines and carboxylic acids (manufactured by San-Apro Ltd., trade name: U-CAT2313), octadecyltrimethylammonium chloride (manufactured by NOF Corporation, trade name: NissanCation), and tetraalkyl ammonium salts (each alkyl group having 1 to 18 carbon atoms) (e.g., tetraethylammonium bromide, tetrabutylammonium bromide, tetraalkylammonium carboxylates (carboxylic acid having 1 to 12 carbon atoms)).

[0024] Examples of imidazoles include 1-benzyl-2-methylimidazole, 2-ethyl-4-methylimidazole, 2-undecylimidazole, 1,2-dimethylimidazole, and 1-benzyl-2-phenylimidazole.

[0025] Examples of organic phosphines include triphenylphosphine, triphenylphosphine-triphenylborate, tris(p-methoxyphenyl)phosphine, and tetraphenylphosphonium tetraphenylborate.

[0026] Examples of the Lewis acid catalyst include boron trifluoride amine complex, boron trichloride amine complex, boron trifluoride ethylamine complex, etc. These may be used alone or in combination of two or more.

[0027] The amount of the curing accelerator (C) in the resin composition of this embodiment is, for example, 0.03 mass% or more, preferably 0.05 mass% or more, and more preferably 0.08 mass% or more, based on the entire resin composition. This can improve the curability of the resin composition. On the other hand, the upper limit of the content of the curing accelerator (C) is, for example, 1 mass% or less, preferably 0.8 mass% or less, and more preferably 0.5 mass% or less, based on the entire resin composition. This can improve the casting workability.

[0028] (Inorganic Filler (D)) The resin composition of this embodiment contains an inorganic filler (D). Examples of the inorganic filler (D) include silica fillers such as quartz, fumed silica, precipitated silica, silicic anhydride, fused silica, crystalline silica, and ultrafine amorphous silica, alumina, zircon, iron oxide, zinc oxide, titanium oxide, silicon nitride, boron nitride, aluminum nitride, silicon carbide, glass fiber, glass flakes, alumina fiber, carbon fiber, mica, graphite, carbon black, ferrite, graphite, diatomaceous earth, clay, clay, talc, aluminum hydroxide, magnesium hydroxide, calcium carbonate, manganese carbonate, magnesium carbonate, barium sulfate, potassium titanate, calcium silicate, inorganic balloons, and silver powder. These may be used alone or in combination of two or more. The inorganic filler may also be surface-treated. Examples of surface treatments include, but are not limited to, alkylation treatment, trimethylsilylation treatment, silicone treatment, and treatment with a silane coupling agent.

[0029] By using the inorganic filler (D), the viscosity of the resulting resin composition can be adjusted to an appropriate range, and various physical properties of the cured product of the resin composition, such as strength, hardness, elastic modulus, thermal expansion coefficient, thermal conductivity, heat dissipation, and electrical properties, can be improved.

[0030] Among the inorganic fillers (D), silica fillers are preferred. Silica fillers refer to silica-based fillers such as quartz, fumed silica, precipitated silica, silicic anhydride, fused silica, crystalline silica, and ultrafine amorphous silica. In typical resin compositions, increasing the amount of filler significantly increases the viscosity of the resin composition containing the filler. From the perspective of viscosity control, spherical shapes are preferred over fibrous or amorphous shapes. Here, "spherical" refers to shapes that are either perfectly spherical or elliptical, including oval shapes. Specifically, the aspect ratio (ratio of major axis to minor axis) is typically 1.3 or less, preferably 1.2 or less, and more preferably 1.1 or less. Furthermore, from the perspective of blending, it is preferable for the filler to have hydroxyl groups on its surface. Hydroxyl groups improve the polarity of the filler surface, making it easier to mix organic polymers, which have higher polarity than inorganic materials. Furthermore, the amount of filler added can be increased by controlling the particle size distribution. In other words, mixing fillers with different particle sizes can achieve a higher filling rate. The average particle size of the filler is measured using a Particle Size Analyzer (CILAS 1064) and is preferably 0.1 μm or more, more preferably 1 μm or more, and is preferably 100 μm or less, more preferably 50 μm or less.

[0031] The amount of inorganic filler (D) in the resin composition of this embodiment is, for example, 65% to 85% by mass, based on the entire resin composition. The lower limit of the amount of inorganic filler (D) is preferably 68% by mass or more, more preferably 70% by mass or more, and even more preferably 75% by mass or more, based on the entire resin composition. The upper limit of the amount of inorganic filler (D) is preferably 82% by mass or less, more preferably 80% by mass or less, based on the entire resin composition. By using the inorganic filler (D) in an amount within the above range, the resulting resin composition has a viscosity appropriate for casting, thereby providing excellent casting workability, and the cured product of the resin composition has low thermal expansion and high heat resistance. This can improve the curability of the resin composition.

[0032] (Anti-settling agent (E)) The resin composition of this embodiment contains an anti-settling agent (E). By using the anti-settling agent (E), it is possible to suppress the settling of the inorganic filler (D) in the resin composition. Examples of the anti-settling agent (E) that can be used include fine particle silica, asbestos powder, acicular magnesium, polyhydroxycarboxylic acid ester, synthetic wax, ultrafine precipitated calcium carbonate, clay, talc, organic bentonite, metal soaps, vegetable polymerized oil, and polyethylene oxide surfactants.

[0033] The amount of the anti-settling agent (E) in the resin composition of this embodiment is, for example, 0.01% by mass to 1.00% by mass, based on the entire resin composition. The lower limit of the amount of the anti-settling agent (E) is preferably 0.05% by mass or more, and more preferably 0.10% by mass or more, based on the entire resin composition. The upper limit of the amount of the anti-settling agent (E) is preferably 0.80% by mass or less, and more preferably 0.50% by mass or less, based on the entire resin composition. By using the anti-settling agent (E) in an amount within the above range, the resulting resin composition is inhibited from settling the filler during storage and curing, and can maintain viscosity and fluidity appropriate for casting workability.

[0034] (Core-shell rubber particles) The resin composition of this embodiment may contain core-shell rubber particles. By using core-shell rubber particles, the flexural modulus of the cured product can be reduced without significantly increasing the viscosity of the liquid resin composition. Therefore, a resin composition can be obtained that has good workability and can form a cured product with high strength and a low modulus.

[0035] Core-shell type rubber particles refer to rubber particles in which a particulate core component, mainly composed of a crosslinked rubbery polymer, is coated with a shell component by graft polymerizing a polymer different from the core component onto the surface of the particulate core component.

[0036] Examples of the core component include crosslinked rubber particles. Examples of crosslinked rubber particles include diene rubber, acrylic rubber, and polysiloxane rubber. More specifically, examples include butadiene rubber, acrylic rubber, silicone rubber, butyl rubber, nitrile rubber, styrene rubber, synthetic natural rubber, and ethylene propylene rubber.

[0037] Examples of the shell component include diene rubber, acrylic rubber, and polysiloxane rubber.Preferably, a polymer polymerized from one or more monomers selected from the group consisting of acrylic acid esters, methacrylic acid esters, and aromatic vinyl compounds is used.The shell component is preferably graft-polymerized to the core component and chemically bonded to the polymer constituting the core component.When a crosslinked rubbery polymer composed of a polymer of styrene and butadiene is used as the core component, it is preferable to use a polymer of methyl methacrylate, which is a methacrylic acid ester, and styrene, which is an aromatic vinyl compound, as the shell component.

[0038] Examples of commercially available core-shell rubber particles include "PARALOID (registered trademark)" EXL-2655 (manufactured by Kureha Chemical Industry Co., Ltd.) made of a butadiene-alkyl methacrylate-styrene copolymer, "STAFILOID (registered trademark)" AC-3355, TR-2122 (manufactured by Takeda Pharmaceutical Co., Ltd.) made of an acrylic acid ester-methacrylic acid ester copolymer, "PARALOID (registered trademark)" EXL-2611, EXL-3387 (manufactured by Rohm & Haas) made of a butyl acrylate-methyl methacrylate copolymer, and "KANE ACE (registered trademark)" MX series (manufactured by Kaneka Corporation).

[0039] Core-shell rubber particles are also available as masterbatch-type epoxy resins in which they are pre-dispersed in an epoxy resin, and examples of such core-shell rubber particle-dispersed epoxy resins include "Kane Ace (registered trademark)" (manufactured by Kaneka Corporation) and "Acryset (registered trademark) BP Series" (manufactured by Nippon Shokubai Co., Ltd.) By using such masterbatch-type core-shell rubber particle-dispersed epoxy resins, the core-shell rubber particles can be well dispersed in the resulting resin composition. Commercially available core-shell type rubber particle-dispersed epoxy resins include the MX series of Kane Ace manufactured by Kaneka Corporation, such as MX-113, MX-120, MX-125, MX-128, MX-130, MX-135, MX-136, MX-156, MX-153, MX-257, MX-150, MX-154, MX-960, MX-170, MX-267, MX-965, MX-217, MX-416, MX-451, MX-553, MX-710, and MX-714.

[0040] The content of the core-shell rubber particles is preferably 0.1 to 10 mass %, more preferably 0.5 to 5 mass %, based on the total solid content of the resin composition, since a resin composition capable of forming a cured product having high strength and a low elastic modulus can be obtained.

[0041] The average particle size of the primary particles of the core-shell rubber particles is preferably in the range of 50 to 500 nm, more preferably in the range of 50 to 300 nm, since a resin composition capable of forming a cured product having high strength and a low elastic modulus can be obtained.

[0042] The resin composition of this embodiment may contain a flame retardant. By using a flame retardant, it is possible to obtain a resin composition that can form a highly flame-retardant composite. Examples of flame retardants that can be used in the resin composition of this embodiment include aluminum hydroxide, magnesium hydroxide, zinc borate, zinc molybdate, antimony trioxide, antimony pentoxide, phosphazene, brominated epoxy resin, and brominated polycarbonate. One type of flame retardant may be used alone, or two or more types may be used in combination.

[0043] When a flame retardant is used, the amount thereof is, for example, 1 to 50 mass %, preferably 5 to 30 mass %, based on the total mass of the resin composition. By using the flame retardant in the above range, it is possible to improve the flame retardancy of the resulting cured product while maintaining the viscosity and fluidity of the resulting liquid resin composition suitable for casting workability.

[0044] (Coupling Agent) The resin composition of the present embodiment may contain a coupling agent. Use of the coupling agent can improve the compatibility between the epoxy resin (A) and the inorganic filler (D). Examples of the coupling agent that can be used include silane coupling agents such as epoxy silane, amino silane, ureido silane, and mercapto silane.

[0045] Examples of the epoxy silane include γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, and β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane. Examples of aminosilanes include γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-β(aminoethyl)γ-aminopropyltrimethoxysilane, N-β(aminoethyl)γ-aminopropylmethyldimethoxysilane, N-phenyl-γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, N-β(aminoethyl)γ-aminopropyltriethoxysilane, N-(6-aminohexyl)3-aminopropyltrimethoxysilane, and N-(3-(trimethoxysilylpropyl)-1,3-benzenedimethanane. Examples of ureidosilanes include γ-ureidopropyltriethoxysilane and hexamethyldisilazane. These may be used alone or in combination of two or more.

[0046] The lower limit of the content of the coupling agent is, for example, 0.05% by mass or more, preferably 0.02% by mass or more, and more preferably 0.05% by mass or more, based on the entire resin composition. The upper limit of the content of the coupling agent is, for example, 1% by mass or less, preferably 0.8% by mass or less, and more preferably 0.6% by mass or less, based on the entire resin composition. This makes it possible to suppress a decrease in the interfacial strength between the epoxy resin (A) and the inorganic filler (D), and therefore the resulting resin composition has excellent durability.

[0047] (Other Additives) The resin composition of the present embodiment may contain, as necessary, a colorant such as carbon black, an antifoaming agent such as a silicone antifoaming agent, and the like.

[0048] (Method for producing liquid resin composition) A method for producing the liquid resin composition of this embodiment will now be described in detail. The resin composition of this embodiment can be produced by adding the above-mentioned components, i.e., the epoxy resin (A), the acid anhydride (B), the curing accelerator (C), the inorganic filler (D), the anti-settling agent (E), and other components, and thoroughly mixing and stirring them in a conventional manner.

[0049] In one embodiment, the resin composition of the present invention can be obtained by mixing and / or kneading a main component and a curing agent component. More specifically, for example, the main component is produced by mixing an epoxy resin (A) with a portion of the inorganic filler (D), an anti-settling agent (E), and various other components as needed. The curing agent component is produced by mixing an acid anhydride (B) as a curing agent with a curing accelerator (C), the remainder of the inorganic filler (D), an anti-settling agent (E), and various other components as needed. The main component and the curing agent component are then mixed and / or kneaded using a mixer or other mixer, or a kneader or roll mill, to obtain a liquid resin composition.

[0050] (Physical Properties of Liquid Resin Composition) The resin composition of this embodiment is characterized by being liquid at 25°C, at which point casting can be easily performed and thermal curing does not proceed easily. The viscosity of the liquid resin composition of this embodiment containing the above components at 25°C is 75 Pa·s or less, preferably 70 Pa·s or less, more preferably 65 Pa·s or less, even more preferably 60 Pa·s or less, and even more preferably 55 Pa·s or less. The lower limit of the viscosity of the resin composition at 25°C is not particularly limited, but is, for example, 5 Pa·s or more. A liquid resin composition having a viscosity within the above range has excellent casting workability.

[0051] The liquid resin composition of this embodiment has a flow distance of preferably 20 mm or more, more preferably 25 mm or more, even more preferably 30 mm or more, and even more preferably 35 mm or more under the following conditions. The upper limit of the flow distance of the resin composition is, for example, 80 mm or less. A liquid composition having a flow distance within this range has excellent casting workability. (Conditions) 0.05 ml of the liquid resin composition of this embodiment is applied to a glass plate so that the diameter of the liquid resin composition is 1 cm or less. Next, the glass plate is held at a tilt angle of 45° and a temperature of 60°C for 3 minutes, and the distance the liquid resin composition flows during this time is taken as the flow distance (mm).

[0052] (Method for curing resin composition) The heating method for curing the resin composition of this embodiment is not particularly limited, and can be, for example, a conventionally known method such as hot air circulation heating, infrared heating, high-frequency heating, etc. The heat treatment conditions are not particularly limited as long as they can bring the resin composition to a desired cured state, but for example, a temperature of 100°C to 200°C is applied.

[0053] (Physical Properties of Cured Product of Resin Composition) The cured product of the liquid resin composition of this embodiment has a glass transition temperature of 180°C or higher, preferably 190°C or higher, more preferably 200°C or higher, even more preferably 205°C or higher, and particularly preferably 210°C or higher. This gives the cured product of the liquid resin composition excellent heat resistance, and therefore makes it suitable for use as an encapsulant for power modules. The upper limit of the glass transition temperature of the cured product of the resin composition of this embodiment is, for example, 250°C or lower.

[0054] The cured product of the liquid resin composition of this embodiment has a linear expansion coefficient of 25 ppm / K or less, preferably 20 ppm / K or less, and more preferably 15 ppm / K or less. As a result, the cured product of the liquid resin composition has excellent crack resistance. The lower limit of the linear expansion coefficient of the cured product of the liquid resin composition of this embodiment is, for example, 10 ppm / K or more.

[0055] The flexural modulus of the cured product of the liquid resin composition of this embodiment at 25° C. is, for example, 20 GGPa or less, preferably 18 GPa or less, and more preferably 16 GPa or less. The lower limit of the flexural modulus of the cured product of the resin composition of this embodiment at 25° C. is, for example, 10 GPa or more.

[0056] [Power Module] A cured product of the resin composition of this embodiment has a low coefficient of thermal expansion at high temperatures and high heat resistance, and is therefore suitable for use as an encapsulant for power modules. Examples of power modules include rectifiers, frequency converters, regulators, inverters, and the like. The resin composition of the present invention has fluidity as a resin composition, and therefore has good casting workability. Furthermore, a cured product of the resin composition of this embodiment has a low coefficient of linear expansion, and is therefore suitable for use in power modules of a wide range of sizes. The cured product can be used in power modules for home appliances, computers, and the like, as well as in large power modules for controlling automobiles, railway vehicles, and substations.

[0057] The power module of this embodiment can be obtained by casting the above-mentioned resin composition onto a power semiconductor element mounted on a power module substrate on which a circuit layer has been formed, so as to cover the substrate and the power semiconductor element, and then curing the composition. It is preferable to vacuum degas the resin composition during casting and / or before and after casting. Vacuum degassing removes air and the like contained in the resin composition, thereby obtaining a resin-sealed power module with few voids in the cured product of the epoxy resin composition. The power module of this embodiment has excellent reliability by using the cured product of the above-mentioned resin composition as an encapsulant.

[0058] Although the embodiments of the present invention have been described above, these are merely examples of the present invention, and various other configurations can also be adopted.

[0059] EXAMPLES The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these.

[0060] The raw materials used in the examples and comparative examples are as follows. <(A) Epoxy Resins> Epoxy resin 1: alicyclic epoxy resin (Celloxide 2021P, manufactured by Daicel Corporation) Epoxy resin 2: bisphenol A epoxy resin (jER828EL, manufactured by Mitsubishi Chemical Corporation) <(B) Acid Anhydrides (Curing Agents)> Acid Anhydride 1: methyl nadic anhydride (MHAC-P, manufactured by Showa Denko Materials) Acid Anhydride 2: methylhexahydrophthalic anhydride (HN-5500, manufactured by Showa Denko Materials) Acid Anhydride 3: methyltetrahydrophthalic anhydride (HN-2000, manufactured by Showa Denko Materials) <(C) Curing Accelerators> Curing Accelerators 1: DBU-octylate (U-CAT SA102, manufactured by San-Apro) Curing Accelerators 2: DBU-phenolate (U-CAT SA1, manufactured by San-Apro) <(D) Inorganic Filler> Inorganic filler 1: spherical fused silica (manufactured by Denka Company, FB-950, volume average particle size 23 μm) <(E) Sedimentation inhibitor> Sedimentation inhibitor 1: organic bentonite (manufactured by Hojun Co., Ltd., Esben N-400) Sedimentation inhibitor 2: polyhydroxycarboxylic acid ester (manufactured by BYK Japan KK, BYK-R606) <(F) Flame retardant> Flame retardant 1: brominated epoxy resin (manufactured by DIC Corporation, EPICLON 153) Flame retardant 2: antimony trioxide (manufactured by Nippon Seiko Co., Ltd., PATOX-K) Flame retardant 3: aluminum hydroxide (manufactured by Sumitomo Chemical Co., Ltd., CWL-325J) <Other additives> Stress reducing agent 1: core-shell type rubber particles (MX-553, manufactured by Kaneka Corporation, alicyclic epoxy resin (Celloxide 2021P):core-shell type rubber particles (mass ratio) of 7:3, core-shell type rubber particle dispersed epoxy resin) Colorant 1: carbon black (Carbon #5, manufactured by Mitsubishi Chemical Corporation) Coupling agent 1: epoxy silane coupling agent (A-187, manufactured by Momentive Performance Materials) Defoamer 1: silicone defoamer (KS603, manufactured by Shin-Etsu Chemical Co., Ltd.)

[0061] (Examples 1 to 20, Comparative Examples 1 and 2) <Production of Liquid Resin Composition> The components shown in "Main Agent" in Table 1 were mixed in the amounts shown in Table 1 to obtain main agent (I). Separately, the components shown in "Curing Agent" in Table 1 were mixed in the amounts shown in Table 1 to obtain curing agent (II). A liquid resin composition was produced by mixing 100 parts by mass of the main agent (I) and 100 parts by mass of curing agent (II).

[0062] <Evaluation of Physical Properties of Liquid Resin Composition> The liquid resin compositions obtained in each of the Examples and Comparative Examples were measured for the following physical properties. The results are shown in Table 1. (Viscosity at 25°C) The viscosity of the liquid resin composition was measured using an E-type viscometer with a rotor No. 4 at a rotation speed of 10 rpm, at a temperature of 25°C, and for a measurement time of 1 minute. The results are shown in Table 1.

[0063] (Flowability) 0.05 ml of the liquid resin composition was applied to a glass plate so that the diameter of the liquid resin composition was 1 cm or less. The glass plate was then held at a tilt angle of 45° and a temperature of 60°C for 3 minutes, and the distance the liquid resin composition flowed during this period was measured as the flow distance (mm). The flow distance is shown in Table 1.

[0064] (Storage stability) The storage stability of the main agent (I) and the curing agent (II) was evaluated by the following method. First, the main agent (I) was poured into a 120 mL plastic container with a lid to a height of 50 to 55 mm, and the lid was placed on the container. After 24 hours at 60°C, the height of the filler sedimentation (hard cake) deposited at the bottom was measured. The height of the hard cake was rated as "A" if it was 0 mm but less than 3 mm, "B" if it was more than 0 mm but less than 3 mm, and "C" if it was 3 mm or more, and these are shown in Table 1. The storage stability of the curing agent (II) was also evaluated in the same manner as the main agent (I). The results are shown in Table 1.

[0065] (Casting Workability) The casting workability of the liquid resin composition was evaluated based on the following evaluation criteria. A: All of the following (Requirement 1) to (Requirement 3) are met. B: Any two of the following (Requirement 1) to (Requirement 3) are met. C: Any one of the following (Requirement 1) to (Requirement 3) are met, or none of them are met. Requirement 1: The viscosity of the above-mentioned liquid resin composition at 25°C is 75 Pa·s or less. Requirement 2: The flow distance in the fluidity evaluation of the above-mentioned liquid resin composition is 30 mm or more. Requirement 3: The result of the above-mentioned storage stability evaluation is "A" for both the main agent (I) and the curing agent (II).

[0066] <Evaluation of Physical Properties of Cured Resin Products> The following physical properties were measured for the cured products obtained by curing the liquid resin compositions obtained in each Example and Comparative Example. (Glass Transition Temperature) The liquid resin compositions were poured into aluminum cups and cured at 160°C for 1 hour, then at 180°C for 2 hours. After slowly cooling to room temperature, test pieces measuring 10 mm x 5 mm x 5 mm were cut out. These were measured using a thermomechanical analyzer (TMA7100, manufactured by Hitachi High-Tech Science) under conditions of a measurement temperature range of 0°C to 320°C and a heating rate of 10°C / min. The glass transition temperature (°C) was then calculated from the measurement results. A higher glass transition temperature indicates better heat resistance of the cured product.

[0067] (Linear expansion coefficient) The cured product of the resin composition obtained in each example was placed in a thermomechanical analyzer (TMA7100, manufactured by Hitachi High-Tech Science) and measured under conditions of a temperature range of 0°C to 320°C and a heating rate of 10°C / min. The measurement data was analyzed to determine the average linear expansion coefficient in a temperature range from 50°C to 70°C. The unit of the average linear expansion coefficient is [ppm / K]. A smaller value for the average linear expansion coefficient indicates a cured product with lower expansibility.

[0068] (Flexural Modulus) The resin composition obtained in each example was poured into a mold having a hole (width 4 mm, length 100 mm, height 120 mm) and cured at 160°C for 1 hour and then at 180°C for 2 hours. After slowly cooling to room temperature, a specimen measuring 4 mm x 10 mm x 100 mm was cut out and the flexural modulus at 25°C was measured in accordance with JIS 6911. A smaller flexural modulus value indicates a lower elasticity of the cured product.

[0069] (Flame Retardancy) The resin compositions obtained in Examples 16 to 20 were poured into a mold with a hole (width 1.5 to 6.0 mm, length 100 mm, height 140 mm) and cured at 160°C for 1 hour, then at 180°C for 2 hours. After slowly cooling to room temperature, specimens were cut into pieces measuring 1.5 to 6.0 mm x 12.5 mm x 125 mm and evaluated by the burning time according to the UL-94 vertical test. Table 1 shows the flame retardancy. A maximum burning time of 10 seconds or less and a total burning time of 50 seconds or less was assigned a rating of "V-0," and a maximum burning time of 30 seconds or less and a total burning time of 250 seconds or less was assigned a rating of "V-1."

[0070]

[0071]

[0072]

[0073] The resin compositions of the Examples had low viscosity and were therefore excellent in casting workability. The cured products of the resin compositions of the Examples had high glass transition temperatures and low thermal expansion, and were therefore materials suitable for use as sealing materials with excellent heat resistance and crack resistance. In particular, the resin compositions of Examples 12 to 15, which contained core-shell rubber particles, had low viscosity and their cured products had low elasticity. Furthermore, the resin compositions of Examples 16 to 20, which contained a flame retardant, had low viscosity and were easy to handle, and their cured products had excellent flame retardancy.

[0074] This application claims priority based on Japanese Patent Application No. 2022-090311 filed on June 2, 2022, and Japanese Patent Application No. 2023-016277 filed on February 6, 2023, the disclosures of which are incorporated herein in their entireties.

Claims

1. A liquid resin composition used for sealing a power module by a casting method, the power module including a power module substrate having a circuit layer formed thereon and a power semiconductor element mounted on the circuit layer of the power module substrate, The liquid resin composition comprises: (A) an epoxy resin, (B) acid anhydride, (C) a curing accelerator, (D) an inorganic filler, and (E) an anti-settling agent, The epoxy resin (A) contains an alicyclic epoxy resin, The viscosity of the liquid resin composition at 25°C is 75 Pa s or less. A liquid resin composition.

2. 2. The liquid resin composition according to claim 1, wherein the content of the inorganic filler (D) is 65% by mass or more and 85% by mass or less based on the total solid content of the liquid resin composition.

3. The liquid resin composition according to claim 1 , further comprising core-shell type rubber particles.

4. 4. The liquid resin composition according to claim 3, wherein the content of the core-shell type rubber particles is 0.1% by mass or more and 10% by mass or less based on the total solid content of the liquid resin composition.

5. The liquid resin composition according to claim 1 , further comprising a flame retardant.

6. 2. The liquid resin composition according to claim 1, wherein the flow distance measured under the following conditions is 20 mm or more. Conditions: 0.05 ml of the liquid resin composition is applied onto a glass plate so that the diameter of the liquid resin composition is 1 cm or less. The glass plate is then held at an inclination angle of 45° and at a temperature of 60° C. for 3 minutes, and the distance that the liquid resin composition flows during that time is recorded as the flow distance (mm).

7. 2. The liquid resin composition according to claim 1, wherein the amount of the alicyclic epoxy resin contained in the epoxy resin (A) is 75 mass % or more based on the total amount of the epoxy resin (A).

8. The liquid resin composition according to claim 1 , wherein the epoxy resin (A) further comprises a liquid bisphenol A type epoxy resin or a liquid bisphenol F type epoxy resin.

9. 9. The liquid resin composition according to claim 8, wherein the amount of the liquid bisphenol A type epoxy resin or the liquid bisphenol F type epoxy resin contained in the epoxy resin (A) is 25 mass% or less based on the total amount of the epoxy resin (A).

10. The liquid resin composition according to claim 1, wherein the acid anhydride (B) includes at least one selected from methyl-5-norbornene-2,3-dicarboxylic anhydride, methylcyclohexane-1,2-dicarboxylic anhydride, and methyltetrahydrophthalic anhydride.

11. The liquid resin composition according to claim 10, wherein the viscosity of the methyltetrahydrophthalic anhydride at 25°C is 30 mPa·s or more and 50 mPa·s or less.

12. The liquid resin composition according to claim 1 , wherein the curing accelerator (C) comprises an organic acid salt of diazabicycloundecene.

13. The liquid resin composition according to claim 1 , wherein the sedimentation inhibitor (E) comprises bentonite or a polyhydroxycarboxylic acid ester.

14. A resin-sealed power module comprising: a power module substrate having a circuit layer formed thereon; a power semiconductor element mounted on the circuit layer of the power module substrate; and a sealing material that covers the power module substrate and the power semiconductor element, A resin-sealed power module, wherein the sealing material is a cured product of the liquid resin composition according to any one of claims 1 to 13.