Sealing resin composition

Abstract

A sealing resin composition including an epoxy resin, a curing agent, an inorganic filler, and rubber particles, in which a toughness index of a cured product of the sealing resin composition at 25°C is equal to or more than 80 and equal to or less than 100.

Description

Sealing resin composition

[0001] The present invention relates to an encapsulating resin composition used for encapsulating electronic components.

[0002] Resin encapsulation using thermosetting resins, such as epoxy resins, has been widely used as a method for encapsulating semiconductor devices. In particular, resin compositions primarily composed of multifunctional epoxy resins, novolac-type phenolic resin curing agents, and inorganic fillers have become the mainstream encapsulation resins due to their excellent heat resistance, moldability, and electrical properties.

[0003] One of the performance requirements for encapsulants for semiconductor devices is stress relief within the semiconductor device. Typically, semiconductor devices have a chip primarily made of single-crystal silicon bonded to a substrate primarily made of metal or plastic via a die-bonding agent primarily made of epoxy resin or the like, and these are then protected by an encapsulant primarily made of epoxy resin and inorganic filler. Therefore, large stresses are generated within the encapsulant or at the interface between the encapsulant and surrounding components due to the characteristics of these components, i.e., differences in thermal expansion and elastic modulus. Therefore, it is necessary to absorb or dissipate this stress to relieve it.

[0004] One of the means for alleviating the stress is to incorporate a silicone component into the resin composition. For example, Patent Document 1 describes a method for reducing stress by using a specific polyfunctional phenolic resin as a curing agent and adding silicone rubber particles.

[0005] Japanese Patent Application Laid-Open No. 2005-264037

[0006] However, epoxy resins and silicone rubbers are inherently poorly compatible, and external impacts, for example, can easily cause defects in the cured product at their interface. That is, although the modulus of elasticity of the cured product decreases in proportion to the amount of silicone rubber particles added, mechanical properties such as flexural strength may also decrease.

[0007] The present invention has been made in view of the above problems, and an object of the present invention is to provide a semiconductor encapsulation composition that can achieve both low elasticity and high strength, and a method for producing the same.

[0008] According to the present invention, there is provided an encapsulating resin composition comprising: an epoxy resin; a curing agent; an inorganic filler; and rubber particles, wherein a cured product of the encapsulating resin composition has a toughness index at 25°C of 80 or more and 100 or less.

[0009] The present invention also provides a method for producing the encapsulating resin composition, comprising: a step of mixing an epoxy resin with rubber particles to obtain a masterbatch; and a step of mixing the masterbatch with a curing agent and an inorganic filler to obtain a resin composition.

[0010] According to the present invention, there are provided a semiconductor encapsulation composition that can achieve both low elasticity and high strength, and a method for producing the same.

[0011] Hereinafter, embodiments of the present invention will be described. In this specification, the expression "a to b" in the description of a numerical range means a to b, unless otherwise specified. For example, "1 to 5% by mass" means "1% by mass or more and 5% by mass or less."

[0012] In the description of groups (atomic groups) in this specification, when a notation does not specify whether the group is substituted or unsubstituted, it encompasses both groups that have no substituents and groups that have a substituent. For example, the term "alkyl group" encompasses not only alkyl groups that have no substituents (unsubstituted alkyl groups) but also alkyl groups that have a substituent (substituted alkyl groups). Unless otherwise specified, the term "organic group" in this specification refers to an atomic group obtained by removing one or more hydrogen atoms from an organic compound. For example, the term "monovalent organic group" refers to an atomic group obtained by removing one hydrogen atom from any organic compound.

[0013] [Encapsulating Resin Composition] The encapsulating resin composition of the present embodiment (sometimes referred to as "resin composition" in this specification) contains an epoxy resin (A), a curing agent (B), an inorganic filler (C), and rubber particles (D). The encapsulating resin composition of the present embodiment has a toughness index at 25°C of 80 or more and 100 or less.

[0014] By including the above components, the resin composition of this embodiment has a cured product with a highly favorable balance of low elasticity and high strength. The balance between the elastic modulus and strength of the cured product of the resin composition can be confirmed using the toughness index value as an indicator. In this specification, the "toughness index" is defined as the flexural modulus of the cured product at 25°C divided by the flexural strength of the cured product at 25°C, multiplied by 10,000. Toughness index = flexural modulus / flexural strength × 10,000. Resin compositions with a cured product toughness index in the range of 80 to 100 have low elasticity and high strength, and therefore electronic devices obtained using this as an encapsulant have excellent reliability. In this embodiment, the flexural modulus at 25°C refers to the elastic modulus measured at 25°C in accordance with JIS 6911, and the flexural strength at 25°C refers to the strength measured at 25°C in accordance with JIS 6911.

[0015] The toughness index of the resin composition of this embodiment can be adjusted by selecting the type and amount of component (A) and the method for producing the resin composition. Each component used in the resin composition of this embodiment will be described below.

[0016] (Epoxy Resin (A)) The encapsulating resin composition of the present embodiment contains an epoxy resin (A). As the epoxy resin, any monomer, oligomer, or polymer having two or more epoxy groups in one molecule (in other words, polyfunctional) can be used. As the epoxy resin, a non-halogenated epoxy resin is particularly preferred.

[0017] stilbene-type epoxy resins; novolac-type epoxy resins such as phenol novolac-type epoxy resins and cresol novolac-type epoxy resins; polyfunctional epoxy resins such as triphenolmethane-type epoxy resins and alkyl-modified triphenolmethane-type epoxy resins; phenol aralkyl-type epoxy resins such as phenol aralkyl-type epoxy resins having a phenylene skeleton and phenol aralkyl-type epoxy resins having a biphenylene skeleton; naphthol-type epoxy resins such as dihydroxynaphthalene-type epoxy resins and epoxy resins obtained by glycidyl etherifying a dihydroxynaphthalene dimer; triazine-nucleus-containing epoxy resins such as triglycidyl isocyanurate and monoallyl diglycidyl isocyanurate; and bridged cyclic hydrocarbon compound-modified phenol-type epoxy resins such as dicyclopentadiene-modified phenol-type epoxy resins.

[0018] The epoxy resin (A) preferably contains at least one of a bisphenol-type epoxy resin, a biphenyl-type epoxy resin, a novolac-type epoxy resin (e.g., an o-cresol novolac epoxy resin), a phenol aralkyl-type epoxy resin, and a triphenol methane-type epoxy resin. In order to control the high-temperature elastic modulus, a phenol aralkyl-type epoxy resin having a biphenylene skeleton is particularly preferred.

[0019] As the epoxy resin (A), for example, at least one selected from the group consisting of epoxy resins represented by the following general formula (1), epoxy resins represented by the following general formula (2), epoxy resins represented by the following general formula (3), epoxy resins represented by the following general formula (4), and epoxy resins represented by the following general formula (5) can be used. Among these, the epoxy resins represented by the following general formula (1) and the epoxy resins represented by the following general formula (4) are cited as more preferred embodiments.

[0020]

[0021] In general formula (1), Ar １ represents a phenylene group or a naphthylene group, Ar １ When Ar is a naphthylene group, the glycidyl ether group may be bonded to either the α-position or the β-position. ２ represents any one of a phenylene group, a biphenylene group, and a naphthylene group. ａ and R ｂ each independently represents a hydrocarbon group having 1 to 10 carbon atoms, g is an integer of 0 to 5, and h is an integer of 0 to 8. ３ represents the degree of polymerization, the average value of which is 1 to 3.

[0022]

[0023] In the general formula (2), each of the plural Rc's independently represents a hydrogen atom or a hydrocarbon group having 1 to 4 carbon atoms. ５ represents the degree of polymerization, the average value of which is 0 to 4.

[0024]

[0025] In the general formula (3), there are a plurality of R ｄ and R ｅ each independently represents a hydrogen atom or a hydrocarbon group having 1 to 4 carbon atoms. ６ represents the degree of polymerization, the average value of which is 0 to 4.

[0026]

[0027] In the general formula (4), ｆ each independently represents a hydrogen atom or a hydrocarbon group having 1 to 4 carbon atoms. ７ represents the degree of polymerization, the average value of which is 0 to 4.

[0028]

[0029] In the general formula (5), ｇ each independently represents a hydrogen atom or a hydrocarbon group having 1 to 4 carbon atoms. ８ represents the degree of polymerization, the average value of which is 0 to 4.

[0030] The number molecular weight of the epoxy resin (A) is not particularly limited and may be appropriately selected from the viewpoints of flowability, curability, etc. For example, the number molecular weight is about 100 to 700. From the viewpoint of flowability, etc., the ICI viscosity of the epoxy resin (A) at 150°C is preferably 0.1 to 5.0 poise.

[0031] The encapsulating resin composition may contain only one type of epoxy resin (A), or may contain two or more types of epoxy resin (A).

[0032] The epoxy equivalent of the epoxy resin (A) is preferably 100 to 400 g / eq, more preferably 150 to 350 g / eq. When the encapsulating resin composition contains a plurality of epoxy resins (A), it is preferable that the epoxy equivalent of the plurality of epoxy resins (A) as a whole is within the above range.

[0033] The lower limit of the amount of epoxy resin (A) in the encapsulating resin composition is, for example, preferably 3% by mass or more, more preferably 4% by mass or more, and particularly preferably 5% by mass or more, based on the total amount of the encapsulating resin composition. By setting the content of epoxy resin (A) to the above-mentioned lower limit or more, the fluidity of the encapsulating resin composition can be improved, thereby improving moldability. On the other hand, the upper limit of the amount of epoxy resin (A) is, for example, preferably 50% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less, based on the total amount of the encapsulating resin composition. By setting the content of epoxy resin (A) to the above-mentioned upper limit or less, the moisture resistance reliability and reflow resistance of electronic devices such as power devices equipped with an encapsulant formed using the encapsulating resin composition can be improved.

[0034] By appropriately selecting the epoxy equivalent of the epoxy resin (A) or by appropriately adjusting the amount of the epoxy resin (A) in the encapsulating resin composition, the curing reaction in the composition can be easily optimized. In addition, by appropriately adjusting the epoxy equivalent or the amount of the epoxy resin, the curing / flow properties of the composition can be appropriately adjusted.

[0035] (Curing Agent (B)) The encapsulating resin composition of the present embodiment contains a curing agent (B). The curing agent (B) is not particularly limited as long as it can react with the epoxy resin (A). Examples of the curing agent (B) include phenol-based curing agents, amine-based curing agents, acid anhydride-based curing agents, and mercaptan-based curing agents. Among these, phenol-based curing agents are preferred in terms of the balance of flame resistance, moisture resistance, electrical properties, curability, storage stability, and the like.

[0036] Phenolic Curing Agents The phenolic curing agent is not particularly limited as long as it is one commonly used in encapsulating resin compositions. Examples include novolak resins obtained by condensing or co-condensing phenols such as phenol novolak resins and cresol novolak resins with formaldehyde or ketones under an acidic catalyst; phenol aralkyl resins having a biphenylene skeleton synthesized from the above-mentioned phenols with dimethoxyparaxylene or bis(methoxymethyl)biphenyl; and phenol aralkyl resins such as phenol aralkyl resins having a phenylene skeleton; and phenolic resins having a trisphenylmethane skeleton. These curing agents may be used alone or in combination of two or more.

[0037] Amine-based curing agents include aliphatic polyamines such as diethylenetriamine (DETA), triethylenetetramine (TETA), and metaxylylenediamine (MXDA), aromatic polyamines such as diaminodiphenylmethane (DDM), m-phenylenediamine (MPDA), and diaminodiphenylsulfone (DDS), as well as polyamine compounds including dicyandiamide (DICY) and organic acid dihydralazides. These may be used alone or in combination of two or more.

[0038] Acid anhydride curing agents include alicyclic acid anhydrides such as hexahydrophthalic anhydride (HHPA), methyltetrahydrophthalic anhydride (MTHPA), and maleic anhydride, and aromatic acid anhydrides such as trimellitic anhydride (TMA), pyromellitic anhydride (PMDA), benzophenonetetracarboxylic acid (BTDA), and phthalic anhydride. These may be used alone or in combination of two or more.

[0039] Mercaptan-based curing agents include trimethylolpropane tris(3-mercaptobutyrate), trimethylolethane tris(3-mercaptobutyrate), etc. These may be used alone or in combination of two or more.

[0040] Other curing agents include isocyanate compounds such as isocyanate prepolymers and blocked isocyanates, and organic acids such as carboxylic acid-containing polyester resins. These may be used alone or in combination of two or more.

[0041] The curing agent (B) may be a combination of two or more different types. For example, the present embodiment also includes the use of a phenol-based curing agent and an amine-based curing agent in combination.

[0042] The amount of curing agent (B) is preferably 0.5% by mass or more, more preferably 1% by mass or more, and particularly preferably 1.5% by mass or more, based on the total encapsulating resin composition. On the other hand, the content of curing agent (B) is preferably 9% by mass or less, more preferably 8% by mass or less, and particularly preferably 7% by mass or less, based on the total encapsulating resin composition. By appropriately adjusting the amount of curing agent (B), the curing / flow properties of the composition can be appropriately adjusted.

[0043] From another perspective, it is preferable that the amount of curing agent (B) is appropriately adjusted in relation to the amount of epoxy resin (A). Specifically, it is preferable that the so-called "molar equivalent" (molar ratio of reactive groups) is appropriately adjusted. For example, when the curing agent (B) is a phenolic curing agent, the amount of epoxy resin (A) relative to the phenolic curing agent is preferably 0.9 to 1.5, more preferably 1.0 to 1.4, even more preferably 1.0 to 1.3, and particularly preferably 1.01 to 1.20, in terms of molar equivalent of functional groups (epoxy group / hydroxy group).

[0044] (Inorganic Filler (C)) The encapsulating resin composition of the present embodiment contains an inorganic filler (C). Specific examples of the inorganic filler (C) include silica, alumina, titanium white, aluminum hydroxide, magnesium hydroxide, zinc borate, and silicon nitride.

[0045] As the inorganic filler (C), silica is preferred. Examples of silica include fused crushed silica, fused spherical silica, crystalline silica, finely divided silica, and secondary agglomerated silica. Of these, fused spherical silica is particularly preferred.

[0046] The inorganic filler (C) is usually in the form of particles. The particle shape is preferably approximately spherical. The average particle size of the inorganic filler (C) is not particularly limited, but is typically 1 to 100 μm, preferably 1 to 50 μm, and more preferably 1 to 20 μm. An appropriate average particle size can ensure appropriate fluidity during curing, etc. The average particle size of the inorganic filler (C) can be determined by acquiring volume-based particle size distribution data using a laser diffraction / scattering particle size distribution measuring device (e.g., a wet particle size distribution measuring device LA-950 manufactured by Horiba, Ltd.) and processing the data. The measurement is usually performed in a dry state.

[0047] The inorganic filler (C) such as silica may be surface-modified in advance (before mixing all components to prepare the encapsulating resin composition) with a coupling agent such as a silane coupling agent. This suppresses aggregation of the inorganic filler (C) and allows for better fluidity. Furthermore, the affinity of the inorganic filler (C) with other components is increased, improving the dispersibility of the inorganic filler (C). This is believed to contribute to improving the mechanical strength of the cured product and suppressing the occurrence of microcracks.

[0048] As the coupling agent used for the surface treatment of the inorganic filler (C), those listed as coupling agents (E) described below can be used. Among these, aminosilanes such as γ-aminopropyltriethoxysilane and γ-aminopropyltrimethoxysilane can be preferably used. By modifying the surface of the inorganic filler (C) with a group (such as an amino group) that can react with the epoxy resin (A), the dispersibility of the inorganic filler (C) in the encapsulating resin composition can be improved. Furthermore, by appropriately selecting the type of coupling agent used for the surface treatment of the inorganic filler (C) or by appropriately adjusting the amount of the coupling agent added, the flowability and post-curing strength of the encapsulating resin composition can be controlled.

[0049] The surface treatment of the inorganic filler (C) with a coupling agent can be carried out, for example, as follows. First, the inorganic filler (C) and the coupling agent are mixed and stirred using a mixer. A known mixer, such as a ribbon mixer, can be used for mixing and stirring. The mixer can be operated in the following ways: (i) the inorganic filler (C) and the coupling agent are charged into the mixer in advance and the blades are then rotated, or (ii) only the inorganic filler (C) is first charged and the coupling agent is gradually added to the mixer using a spray nozzle or the like while the blades are rotated.

[0050] During mixing and stirring, it is preferable to maintain a low humidity (for example, 50% or less) inside the mixer. By maintaining a low humidity, it is possible to prevent moisture from adhering to the surface of the inorganic filler (C). Furthermore, it is possible to prevent moisture from being mixed into the coupling agent, which would cause the coupling agents to react with each other.

[0051] The resulting mixture is then removed from the mixer and subjected to an aging treatment to promote the coupling reaction. The aging treatment is carried out, for example, by leaving the mixture under conditions of 20±5°C and 40 to 50% RH for at least one day (preferably 1 to 7 days). By carrying out the aging treatment under these conditions, the coupling agent can be uniformly bonded to the surface of the inorganic filler (C). After the aging treatment, the mixture is sieved to remove coarse particles, thereby obtaining an inorganic filler (C) that has been subjected to a surface treatment (coupling treatment).

[0052] The encapsulating resin composition may contain only one type of inorganic filler (C), or may contain two or more types. The lower limit of the content of the inorganic filler (C) is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 65% ​​by mass or more, based on the total amount of the encapsulating resin composition. The upper limit of the content of the inorganic filler (C) is, for example, preferably 95% by mass or less, more preferably 93% by mass or less, and even more preferably 90% by mass or less. By appropriately adjusting the amount of the inorganic filler (C), the curing / flow properties of the resin composition can be appropriately adjusted.

[0053] (Rubber particles (D)) The encapsulating resin composition of this embodiment contains rubber particles (D). A resin composition containing the rubber particles (D) has high strength and a low elastic modulus, and therefore has high toughness. As the rubber particles, core-shell type rubber particles are preferably used because they have an excellent toughening effect.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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).

[0058] The content of the rubber particles (D) is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, based on the total encapsulating resin composition, since a resin composition capable of forming a cured product having high strength and a low elastic modulus can be obtained. The upper limit of the content of the rubber particles is preferably 10% by mass or less, more preferably 5% by mass or less.

[0059] The average particle size of the primary particles of the rubber particles (D) 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.

[0060] (Coupling Agent (E)) The encapsulating resin composition of the present embodiment preferably contains a coupling agent (E). The coupling agent (E) here is contained in the encapsulating resin composition as the coupling agent (E) alone. For example, the above-mentioned coupling agent used in the surface treatment of the inorganic filler (B) (bonded to the inorganic filler (B)) does not fall under the category of the coupling agent (E) here.

[0061] As the coupling agent (E), known coupling agents such as various silane-based compounds such as epoxysilane, mercaptosilane, aminosilane, alkylsilane, ureidosilane, vinylsilane, methacrylsilane, titanium-based compounds, aluminum chelates, aluminum / zirconium-based compounds, etc. can be used. More specifically, the following can be exemplified:

[0062] Silane coupling agents: vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(β-methoxyethoxy)silane, γ-methacryloxypropyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, γ-methacryloxypropyltriethoxysilane, vinyltriacetoxysilane, γ-mercaptopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-anilinopropyltrimethoxysilane, γ-anilinopropylmethyldimethoxysilane, γ-[bis(β-hydroxyethyl)]aminopropyltriethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, N-β-(amino N-beta-(ethyl)-γ-aminopropyltriethoxysilane, N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane, phenylaminopropyltrimethoxysilane, γ-(β-aminoethyl)aminopropyldimethoxymethylsilane, N-(trimethoxysilylpropyl)ethylenediamine, N-(dimethoxymethylsilylisopropyl)ethylenediamine, methyltrimethoxysilane, dimethyldimethoxysilane, methyltriethoxysilane, N-β-(N-vinylbenzylaminoethyl)-γ-aminopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, hexamethyldisilane, vinyltrimethoxysilane, γ-mercaptopropylmethyldimethoxysilane, 3-isocyanatopropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, hydrolyzate of 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, and the like.

[0063] Titanate coupling agent Isopropyl triisostearoyl titanate, isopropyl tris(dioctyl pyrophosphate) titanate, isopropyl tri(N-aminoethyl-aminoethyl) titanate, tetraoctyl bis(ditridecyl phosphite) titanate, tetra(2,2-diallyloxymethyl-1-butyl)bis(ditridecyl)phosphite titanate, bis(dioctyl pyrophosphate)oxyacetate titanate, bis(dioctyl pyrophosphate)ethylene titanate, isopropyl trioctanoyl titanate, isopropyl dimethacrylisostearoyl titanate, isopropyl tridodecylbenzenesulfonyl titanate, isopropyl isostearoyl diacryl titanate, isopropyl tri(dioctyl phosphate) titanate, isopropyl tricumylphenyl titanate, tetraisopropyl bis(dioctyl phosphite) titanate, and the like.

[0064] When the encapsulating resin composition contains a coupling agent (E), it may contain only one type of coupling agent (E), or may contain two or more types of coupling agents (E). The content of the coupling agent (E) is preferably 0.1 mass% or more, and more preferably 0.15 mass% or more, based on the total encapsulating resin composition. By setting the content of the coupling agent (E) to the above-mentioned lower limit or more, the dispersibility of the inorganic filler can be improved. On the other hand, the content of the coupling agent (E) is preferably 1 mass% or less, and more preferably 0.5 mass% or less, based on the total encapsulating resin composition. By setting the content of the coupling agent (E) to the above-mentioned upper limit or less, the fluidity of the encapsulating resin composition during encapsulation molding can be improved, and filling properties and moldability can be improved.

[0065] (Curing Accelerator (F)) In an embodiment, the encapsulating resin composition may contain a curing accelerator (F). The curing accelerator (F) may be any accelerator that accelerates the reaction (typically, a crosslinking reaction) between the epoxy resin (A) and the curing agent (B).

[0066] The curing accelerator (F) may include one or more compounds selected from phosphorus atom-containing compounds such as organic phosphines, tetra-substituted phosphonium compounds, phosphobetaine compounds, adducts of phosphine compounds and quinone compounds, and adducts of phosphonium compounds and silane compounds; and nitrogen atom-containing compounds such as amidines and tertiary amines, exemplified by 1,8-diazabicyclo[5.4.0]-7-undecene, benzyldimethylamine, and 2-methylimidazole, and quaternary salts of amidines and amines. Among these, from the viewpoint of improving the curability of the resin composition, it is more preferable to include a phosphorus atom-containing compound. Furthermore, from the viewpoint of improving the balance between moldability and curability, it is more preferable to include a compound having latency, such as a tetra-substituted phosphonium compound, phosphobetaine compound, adducts of phosphine compounds and quinone compounds, or adducts of phosphonium compounds and silane compounds.

[0067] Examples of organic phosphines include primary phosphines such as ethylphosphine and phenylphosphine; secondary phosphines such as dimethylphosphine and diphenylphosphine; and tertiary phosphines such as trimethylphosphine, triethylphosphine, tributylphosphine and triphenylphosphine.

[0068] Examples of the tetra-substituted phosphonium compound include compounds represented by the following general formula (6).

[0069]

[0070] In the general formula (6), P represents a phosphorus atom. ４ , R ５ , R ６ and R ７ each independently represents an aromatic group or an alkyl group. A represents the anion of an aromatic organic acid having at least one functional group selected from a hydroxyl group, a carboxyl group, and a thiol group on the aromatic ring. AH represents an aromatic organic acid having at least one functional group selected from a hydroxyl group, a carboxyl group, and a thiol group on the aromatic ring. x and y are 1 to 3, z is 0 to 3, and x=y.

[0071] The compound represented by general formula (6) can be obtained, for example, as follows. First, a tetra-substituted phosphonium halide, an aromatic organic acid, and a base are mixed uniformly in an organic solvent, and an aromatic organic acid anion is generated in the solution system. Then, water is added to precipitate the compound represented by general formula (6). In the compound represented by general formula (6), R bonded to the phosphorus atom ４ , R ５ , R ６ and R ７ is preferably a phenyl group, AH is a compound having a hydroxyl group on an aromatic ring, i.e., a phenol, and A is an anion of the phenol. Examples of the phenol include monocyclic phenols such as phenol, cresol, resorcinol, and catechol, condensed polycyclic phenols such as naphthol, dihydroxynaphthalene, and anthraquinol, bisphenols such as bisphenol A, bisphenol F, and bisphenol S, and polycyclic phenols such as phenylphenol and biphenol.

[0072] Examples of the phosphobetaine compound include compounds represented by the following general formula (7).

[0073]

[0074] In the general formula (7), P represents a phosphorus atom. ８ is an alkyl group having 1 to 3 carbon atoms, R ９ represents a hydroxyl group, f is 0 to 5, and g is 0 to 3.

[0075] The compound represented by general formula (7) can be obtained, for example, as follows: First, a triaromatic-substituted phosphine, which is a tertiary phosphine, is brought into contact with a diazonium salt to substitute the diazonium group of the diazonium salt with the triaromatic-substituted phosphine.

[0076] Examples of the adduct of a phosphine compound and a quinone compound include compounds represented by the following general formula (8).

[0077]

[0078] In the general formula (8), P represents a phosphorus atom. １０ , R １１ and R １２ represents an alkyl group having 1 to 12 carbon atoms or an aryl group having 6 to 12 carbon atoms, and may be the same or different. １３ , R １４ and R １５ represent a hydrogen atom or a hydrocarbon group having 1 to 12 carbon atoms, and may be the same or different from each other; R １４ and R １５ may be bonded to form a cyclic structure.

[0079] The phosphine compound used in the adduct of a phosphine compound and a quinone compound is preferably, for example, triphenylphosphine, tris(alkylphenyl)phosphine, tris(alkoxyphenyl)phosphine, trinaphthylphosphine, tris(benzyl)phosphine, etc., which is unsubstituted or has a substituent such as an alkyl group or alkoxy group on the aromatic ring, and the substituent such as the alkyl group or alkoxy group has a carbon number of 1 to 6. From the viewpoint of availability, triphenylphosphine is preferred.

[0080] The quinone compound used in the adduct of a phosphine compound and a quinone compound includes benzoquinone and anthraquinones, and among these, p-benzoquinone is preferred from the viewpoint of storage stability.

[0081] The adduct of a phosphine compound and a quinone compound can be produced by contacting and mixing the organic tertiary phosphine and the benzoquinone in a solvent that can dissolve both of them. The solvent is preferably a ketone such as acetone or methyl ethyl ketone, which has low solubility in the adduct, but is not limited thereto.

[0082] In the compound represented by the general formula (8), R bonded to the phosphorus atom １０ , R １１ and R １２ is a phenyl group, and R １３ , R １４ and R １５is a hydrogen atom, that is, a compound obtained by adding 1,4-benzoquinone and triphenylphosphine, is preferred in that it reduces the modulus of elasticity of the cured product of the encapsulating resin composition when heated.

[0083] Examples of the adduct of a phosphonium compound and a silane compound include compounds represented by the following general formula (9).

[0084]

[0085] In the general formula (9), P represents a phosphorus atom, and Si represents a silicon atom. １６ , R １７ , R １８ and R １９ R each represents an organic group having an aromatic ring or a heterocyclic ring, or an aliphatic group, and may be the same or different from each other. ２０ is the group Y ２ and Y ３ R is an organic group that bonds to ２１ is the group Y ４ and Y ５ is an organic group that bonds to ２ and Y ３ represents a group formed by releasing a proton from a proton-donating group, and a group Y ２ and Y ３ is bonded to a silicon atom to form a chelate structure. ４ and Y ５ represents a group formed by releasing a proton from a proton-donating group, and a group Y ４ and Y ５ is bonded to a silicon atom to form a chelate structure. ２０ , and R ２１ may be the same or different, and Y ２ , Y ３ , Y ４ and Y ５ may be the same or different. １ is an organic group having an aromatic ring or a heterocyclic ring, or an aliphatic group.

[0086] In general formula (9), R １６ , R１７ , R １８ and R １９ Examples of the alkyl group include a phenyl group, a methylphenyl group, a methoxyphenyl group, a hydroxyphenyl group, a naphthyl group, a hydroxynaphthyl group, a benzyl group, a methyl group, an ethyl group, an n-butyl group, an n-octyl group, and a cyclohexyl group. Among these, an aromatic group having a substituent such as an alkyl group, an alkoxy group, or a hydroxyl group, such as a phenyl group, a methylphenyl group, a methoxyphenyl group, a hydroxyphenyl group, or a hydroxynaphthyl group, or an unsubstituted aromatic group is more preferred.

[0087] In general formula (9), R ２０ Is Y ２ and Y ３ Similarly, R ２１ is the group Y ４ and Y ５ is an organic group that bonds to ２ and Y ３ is a group formed by releasing a proton from a proton-donating group, and the group Y ２ and Y ３ is bonded to a silicon atom to form a chelate structure. ４ and Y ５ is a group formed by releasing a proton from a proton-donating group, and the group Y ４ and Y ５ is bonded to a silicon atom to form a chelate structure. ２０ and R ２１ may be the same or different, and the group Y ２ , Y ３ , Y ４ , and Y ５ may be the same or different. ２ -R ２０ -Y ３ -, and Y ４ -R ２１ -Y ５The group represented by - is constituted by a group formed by a proton donor releasing two protons, and as the proton donor, an organic acid having at least two carboxyl groups or hydroxyl groups in the molecule is preferred, and an aromatic compound having at least two carboxyl groups or hydroxyl groups on adjacent carbons constituting an aromatic ring is more preferred, and an aromatic compound having at least two hydroxyl groups on adjacent carbons constituting an aromatic ring is more preferred, and examples thereof include catechol, pyrogallol, 1,2-dihydro- Examples of the dihydroxynaphthalene include xynaphthalene, 2,3-dihydroxynaphthalene, 2,2'-biphenol, 1,1'-bi-2-naphthol, salicylic acid, 1-hydroxy-2-naphthoic acid, 3-hydroxy-2-naphthoic acid, chloranilic acid, tannic acid, 2-hydroxybenzyl alcohol, 1,2-cyclohexanediol, 1,2-propanediol, and glycerin. Of these, catechol, 1,2-dihydroxynaphthalene, and 2,3-dihydroxynaphthalene are more preferred.

[0088] Z in general formula (9) １ represents an organic group or an aliphatic group having an aromatic ring or a heterocyclic ring, and specific examples thereof include aliphatic hydrocarbon groups such as methyl, ethyl, propyl, butyl, hexyl, and octyl groups; aromatic hydrocarbon groups such as phenyl, benzyl, naphthyl, and biphenyl groups; glycidyloxy groups such as glycidyloxypropyl, mercaptopropyl, and aminopropyl groups; mercapto groups; alkyl groups having amino groups; and reactive substituents such as vinyl groups. Among these, methyl, ethyl, phenyl, naphthyl, and biphenyl groups are more preferred in terms of thermal stability.

[0089] An example of a method for producing an adduct of a phosphonium compound and a silane compound is as follows. A silane compound such as phenyltrimethoxysilane and a proton donor such as 2,3-dihydroxynaphthalene are dissolved in a flask containing methanol, and then a sodium methoxide-methanol solution is added dropwise to the solution with stirring at room temperature. A previously prepared solution of a tetra-substituted phosphonium halide such as tetraphenylphosphonium bromide dissolved in methanol is then added dropwise to the solution with stirring at room temperature, resulting in the precipitation of crystals. The precipitated crystals are filtered, washed with water, and vacuum dried to obtain an adduct of a phosphonium compound and a silane compound.

[0090] The encapsulating resin composition may contain only one type of curing accelerator (F), or may contain two or more types. The content of the curing accelerator (F) is preferably 0.01 mass% or more, more preferably 0.05 mass% or more, and even more preferably 0.10 mass% or more, based on the entire encapsulating resin composition. On the other hand, the content of the curing accelerator (F) is preferably 2.0 mass% or less, more preferably 1.5 mass% or less, and even more preferably 1.0 mass% or less, based on the entire encapsulating resin composition. By appropriately adjusting the amount of the curing accelerator (F), it is also possible to appropriately adjust the curing / flow properties of the resin composition.

[0091] (Other ingredients)

[0092] (Other Components) The encapsulating resin composition of the present embodiment may further contain various additives, such as an ion scavenger, a flame retardant, a colorant, a release agent, a stress reducing agent, an antioxidant, and a heavy metal deactivator, as necessary.

[0093] As the ion trapping agent (also called an ion catcher or an ion trapping agent), for example, hydrotalcite can be used. Bismuth oxide and yttrium oxide are also known as ion trapping agents. When an ion trapping agent is used, only one type may be used, or two or more types may be used in combination. When an ion trapping agent is used, the amount thereof is, for example, 0.01 to 0.5 mass %, preferably 0.05 to 0.3 mass %, based on the total mass of the encapsulating resin composition.

[0094] Examples of flame retardants include inorganic flame retardants (e.g., hydrated metal compounds such as aluminum hydroxide, available from Sumitomo Chemical Co., Ltd., etc.), halogen-based flame retardants, phosphorus-based flame retardants, and organic metal salt-based flame retardants. When a flame retardant is used, only one type may be used, or two or more types may be used in combination. The amount of the flame retardant is, for example, 0 to 15% by mass, preferably 0 to 10% by mass, based on the total mass of the encapsulating resin composition.

[0095] Specific examples of colorants include carbon black, red iron oxide, and titanium oxide. When a colorant is used, one colorant may be used alone or two or more colorants may be used in combination. When a colorant is used, the amount thereof is, for example, 0.1 to 0.8 mass %, and preferably 0.2 to 0.5 mass %, based on the total mass of the encapsulating resin composition.

[0096] Examples of the release agent include natural wax, synthetic wax such as montanic acid ester, higher fatty acid or metal salts thereof, paraffin, polyethylene oxide, etc. When a release agent is used, only one type may be used, or two or more types may be used in combination. When a release agent is used, the amount thereof is, for example, 0.1 to 0.8 mass %, preferably 0.2 to 0.5 mass %, based on the total mass of the encapsulating resin composition.

[0097] Examples of low-stress agents include silicone oil, silicone rubber, polyisoprene, polybutadienes such as 1,2-polybutadiene and 1,4-polybutadiene, thermoplastic elastomers such as styrene-butadiene rubber, acrylonitrile-butadiene rubber, polychloroprene, poly(oxypropylene), poly(oxytetramethylene) glycol, polyolefin glycol, and poly-ε-caprolactone, polysulfide rubber, and fluororubber. Among these, silicone rubber, silicone oil, and acrylonitrile-butadiene rubber are particularly preferred from the viewpoint of controlling the flexural modulus and shrinkage rate within the desired range and suppressing warpage in the resulting power device. When a low-stress agent is used, a single agent may be used, or two or more agents may be used in combination. The amount of the low-stress agent is, for example, 0 to 5% by mass, preferably 0 to 3% by mass, based on the total mass of the encapsulating resin composition.

[0098] Examples of antioxidants include phenol-based antioxidants (dibutylhydroxytoluene, etc.), sulfur-based antioxidants (mercaptopropionic acid derivatives, etc.), and phosphorus-based antioxidants (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, etc.). When antioxidants are used, they may be used alone or in combination of two or more. When antioxidants are used, the amount thereof is, for example, 0 to 3 mass %, and preferably 0 to 2 mass %, based on the total mass of the encapsulating resin composition.

[0099] Examples of heavy metal deactivators include the ADK STAB CDA series (manufactured by ADEKA Corporation). When a heavy metal deactivator is used, only one type may be used, or two or more types may be used in combination. The amount of the heavy metal deactivator is, for example, 0 to 1 mass %, preferably 0 to 0.5 mass %, based on the total mass of the encapsulating resin composition.

[0100] [Method for Producing Encapsulating Resin Composition] As described above, in the encapsulating resin composition of the present embodiment, in order to make the toughness index at 25°C of the cured product thereof fall within the range of 80 or more and 100 or less, the method for producing (preparing) the encapsulating resin composition is very important.

[0101] For example, the encapsulating resin composition can be obtained by mixing the above-mentioned components in a known mixer or the like, melt-kneading the mixture in a kneading machine such as a roll, kneader, or extruder, and then cooling and pulverizing the mixture. The encapsulating resin composition may be in the form of a powder or granule as pulverized, a tablet-formed product after pulverization, a pulverized product that has been sieved, or a granule produced by a granulation method in which the degree of dispersion, fluidity, etc. are appropriately adjusted by a centrifugal milling method, a hot-cut method, or the like.

[0102] The resin composition of the present embodiment is preferably produced by the following procedure: first, the epoxy resin (A) and the rubber particles (D) are mixed together to form a master batch; and then, this master batch is mixed with other components (such as the curing agent (B) and the inorganic filler (C)).

[0103] By employing such a production method, the dispersibility of the rubber particles (D) in the encapsulating resin composition can be made highly uniform, and the toughness index, strength, and elastic modulus of the cured product can be adjusted to fall within the desired ranges.

[0104] The resin composition of this embodiment obtained by the above method has a toughness index at 25°C of 80 or more and 100 or less. The cured product of the resin composition of this embodiment obtained by the above method has a flexural modulus at 25°C of, for example, 12,000 MPa or less, preferably 11,000 MPa or less. The lower limit of the flexural modulus at 25°C of the cured product of the resin composition of this embodiment is, for example, 9,000 MPa or more. The flexural strength at 25°C of the cured product of the resin composition of this embodiment is, for example, 95 MPa or more, preferably 98 MPa or more. The upper limit of the flexural strength at 25°C of the cured product of the resin composition is, for example, 120 MPa or less.

[0105] The toughness index at 260°C of the cured product of the resin composition of this embodiment is, for example, 100 or more and 160 or less. The flexural modulus at 260°C of the cured product of the resin composition of this embodiment is, for example, 3000 MPa or less, preferably 2500 MPa or less. The lower limit of the flexural modulus at 260°C of the cured product of the resin composition of this embodiment is, for example, 1000 MPa or more. The flexural strength at 260°C of the cured product of the resin composition of this embodiment is, for example, 20 MPa or more, preferably 25 MPa or more. The upper limit of the flexural strength at 260°C of the cured product of the resin composition is, for example, 40 MPa or less.

[0106] By using the above-mentioned components in specific blending amounts or by preparing the resin composition of the present embodiment by a specific method, high strength and low elasticity can be achieved in the cured product, particularly at room temperature, and as a result, high toughness can be achieved.

[0107] [Uses] The resin composition of the present embodiment is suitable for use in sealing semiconductor devices, and is particularly suitable as a sealing material for power devices due to its excellent toughness.

[0108] 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.

[0109] EXAMPLES The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these.

[0110] [Examples 1 to 6, Comparative Examples 1 to 3] (Preparation of encapsulating resin composition) The components shown in Table 1 were mixed in the amounts (parts by weight) shown in the table at room temperature using a Henschel mixer to obtain a mixture. The mixture was then roll-kneaded at 70 to 100°C to obtain a kneaded product. The kneaded product was cooled and then pulverized to obtain an encapsulating resin composition.

[0111] The ratio of the amounts (parts by mass) of the components is as shown in Table 1. Details of the components shown in Table 1 are shown below.

[0112] (Epoxy resins) Epoxy resin 1: Triphenolmethane type epoxy resin (manufactured by Mitsubishi Chemical Corporation, 1032H60) Epoxy resin 2: Orthocresol novolac type epoxy resin (manufactured by Nippon Kayaku Co., Ltd., EOCN-1020-55) (Curing agents) Curing agent 1: Triphenolmethane type phenolic resin (manufactured by Meiwa Kasei Co., Ltd., MEH-7500) Curing agent 2: Novolac type phenolic resin (manufactured by Sumitomo Bakelite Co., Ltd., PR-HF-3) (Rubber particles) Rubber particle 1: Core-shell rubber (butadiene rubber) (manufactured by Mitsubishi Chemical Corporation, S-2030) Rubber particle 2: Core-shell rubber (acrylic rubber) (manufactured by Aica Kogyo Co., Ltd., AC-3832SD) Rubber particle 3: Core-shell rubber (acrylic rubber) (manufactured by Aica Kogyo Co., Ltd., AC-4030) Rubber particle 4: core-shell rubber (core: butadiene rubber, shell: acrylic rubber) (manufactured by The Dow Chemical Company, EXL-2655) Rubber particle 5: core-shell rubber (core: butadiene rubber, shell: acrylic rubber) (manufactured by The Dow Chemical Company, TMS-2670J) Rubber particle 6: silicone rubber (manufactured by Dow Corning Toray Co., Ltd., CF-2152) (inorganic fillers) Inorganic filler 1: fused spherical silica (manufactured by Denka Company, Ltd., FB-105) Inorganic filler 2: fused spherical silica (manufactured by Admatechs Co., Ltd., SC-2500-SQ) Inorganic filler 3: fused spherical silica (manufactured by Admatechs Co., Ltd., SC-5500-SQ) (curing accelerators) Curing accelerator 1: tetraphenylphosphonium 4,4'-sulfonyldiphenolate Curing accelerator 2: 2,3-dihydroxynaphthalene (colorant) Colorant 1: Carbon black (Carbon #5, manufactured by Mitsubishi Chemical Corporation) (coupling agent) Coupling agent 1: N-phenyl-3-aminopropyltrimethoxysilane (CF-4083, manufactured by Dow Corning Toray Co., Ltd.) (mold release agent) Mold release agent 1: Oxidized polyethylene wax (Licowax PED191, manufactured by Clariant Japan Co., Ltd.) (stress reduction agent) Stress reduction agent 1: Epoxy polyether modified silicone oil (FZ-3730, manufactured by Dow Corning Toray Co., Ltd.) Stress reduction agent 2: Silicone resin (KR-480, manufactured by Shin-Etsu Chemical Co., Ltd.)

[0113] (Evaluation of Physical Properties of Encapsulating Resin Composition) The encapsulating 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.

[0114] (Spiral flow) A spiral flow test was carried out using the resin composition obtained in each example. The test was carried out by injecting the resin molding material into a mold for spiral flow measurement conforming to EMMI-1-66 using a low-pressure transfer molding machine ("KTS-15" manufactured by Kotaki Seiki Co., Ltd.) under conditions of a mold temperature of 175°C, an injection pressure of 6.9 MPa, and a curing time of 120 seconds, and measuring the flow length.

[0115] (Gel time) The gel time of the resin composition obtained in each example was measured by melting the resin composition on a hot plate heated to 120°C, and then measuring the time (gel time: seconds) until the resin composition hardened while kneading with a spatula.

[0116] (Flexural Modulus) The resin composition was transfer molded at 180°C for 3 minutes and then cured at 180°C for 4 hours, and the flexural modulus was measured at 25°C and 260°C in accordance with JIS 6911. (Flexural Strength) A cured product was prepared in the same manner as in the measurement of the flexural modulus above, and the flexural strength was measured at 25°C and 260°C in accordance with JIS 6911.

[0117] (Toughness Index) The toughness index at 25°C and 260°C was calculated using the following formula: Toughness index = flexural modulus / flexural strength × 10000

[0118]

[0119] All of the resin compositions in the examples can be used as sealing materials, and in particular, the resin compositions in the examples had a toughness index at 25°C of the cured product within a specified range, and thus possessed both low elasticity and high strength.

[0120] This application claims priority based on Japanese Patent Application No. 2021-089965, filed on May 28, 2021, the disclosure of which is incorporated herein in its entirety.

Claims

1. An encapsulating resin composition comprising an epoxy resin, a curing agent, an inorganic filler, and rubber particles, wherein the toughness index of a cured product of the encapsulating resin composition at 25°C is 80 or more and 100 or less.

2. The encapsulating resin composition according to claim 1, wherein the flexural modulus of the cured product at 25°C is 12,000 MPa or less.

3. The encapsulating resin composition according to claim 1 or 2, wherein the flexural strength of the cured product of the encapsulating resin composition at 25°C is 95 MPa or more.

4. The encapsulating resin composition according to any one of claims 1 to 3, wherein the toughness index of the cured product of the encapsulating resin composition at 260°C is 100 or more and 160 or less.

5. The encapsulating resin composition according to any one of claims 1 to 4, wherein the flexural modulus of the cured product of the encapsulating resin composition at 260°C is 3000 MPa or less.

6. The encapsulating resin composition according to any one of claims 1 to 5, wherein the flexural strength of the cured product of the encapsulating resin composition at 260°C is 20 MPa or more.

7. The encapsulating resin composition according to any one of claims 1 to 6, wherein the encapsulating resin composition has a glass transition temperature of 150°C or higher and 270°C or lower.

8. The encapsulating resin composition according to any one of claims 1 to 7, wherein the average particle size of the primary particles of the rubber particles is 10 nm or more and 500 nm or less.

9. The encapsulating resin composition according to any one of claims 1 to 8, wherein the rubber particles include core-shell type rubber particles.

10. The encapsulating resin composition according to claim 9, wherein the core layer of the core-shell type rubber particle comprises at least one selected from diene-based rubber, acrylic-based rubber, and polysiloxane-based rubber.

11. The encapsulating resin composition according to any one of claims 1 to 10, wherein the shell layer of the core-shell rubber particles contains at least one selected from diene-based rubber, acrylic-based rubber, and polysiloxane-based rubber.

12. The encapsulating resin composition according to any one of claims 1 to 11, wherein the rubber particles are contained in an amount of 0.1 mass % or more and 10 mass % or less based on the total solid content of the encapsulating resin composition.

13. The encapsulating resin composition according to any one of claims 1 to 12, wherein the epoxy resin is at least one selected from the group consisting of bisphenol F type epoxy resins, bisphenol A type epoxy resins, phenol novolac type epoxy resins, cresol novolac type epoxy resins, naphthalene type epoxy resins, and biphenyl type epoxy resins.

14. The encapsulating resin composition according to any one of claims 1 to 13, wherein the inorganic filler is at least one selected from the group consisting of silica, talc, alumina, titanium white, aluminum nitride, aluminum hydroxide, magnesium hydroxide, zinc borate, zinc molybdate, and silicon nitride.

15. The encapsulating resin composition according to any one of claims 1 to 14, further comprising a curing accelerator.

16. The encapsulating resin composition according to any one of claims 1 to 15, which is used to encapsulate a power semiconductor.

17. A method for producing an encapsulating resin composition according to any one of claims 1 to 16, comprising: a step of mixing an epoxy resin with rubber particles to obtain a master batch; and a step of mixing the master batch with a curing agent and an inorganic filler to obtain a resin composition.