Resin film, printed wiring board, and semiconductor package

Abstract

A resin film comprises a resin composition containing a curable resin and an inorganic filler, wherein the content of the inorganic filler is more than 50 vol %, and the minimum melt viscosity is 2000 Pa・s or less.

Description

Resin films, printed wiring boards and semiconductor packages

[0001] The present disclosure relates to a resin film, a printed wiring board, and a semiconductor package.

[0002] Insulating materials are used in electronic components such as printed wiring boards and semiconductor packages for the purpose of protecting elements, wiring, etc., and for electrical insulation. Resin compositions in various forms, such as liquid, tablet, and sheet, have been developed as such insulating materials. For example, Patent Document 1 describes a resin film containing a compound having an N-substituted maleimide group as a curable resin.

[0003] International Publication No. 2023 / 282313

[0004] Resin films containing curable resins are sometimes used to fill recesses in substrates with uneven surfaces. Specifically, a resin film is placed on a substrate with uneven surfaces and heated to soften it. In this state, the resin film is pressurized to deform the resin film so as to fill the recesses in the substrate. If the resin film does not deform sufficiently, defects such as void inclusions may occur. However, making a resin sheet more deformable generally tends to increase the thermal expansion coefficient after curing. An increase in the thermal expansion coefficient may cause other problems, such as increased warping of the substrate to which the resin sheet is attached.

[0005] In view of the above circumstances, one embodiment of the present disclosure aims to provide a resin film that has excellent deformability before curing and a low thermal expansion coefficient after curing, a printed wiring board obtained using this resin film, and a semiconductor package obtained using this resin film.

[0006] Specific means for solving the above problems include the following aspects. <1> A resin film made of a resin composition containing a curable resin and an inorganic filler, wherein the content of the inorganic filler is more than 50% by volume and the minimum melt viscosity is 2000 Pa s or less. <2> The resin film according to <1>, wherein the curable resin contains a radically polymerizable curable resin. <3> The resin film according to <1> or <2>, wherein the curable resin contains a curable resin having a molecular weight of 2000 or less. <4> The resin film according to any one of <1> to <3>, wherein the content of the inorganic filler is 70% by volume or less. <5> The resin film according to any one of <1> to <4>, wherein the resin film is used as an encapsulant for a semiconductor package. <6> The resin film according to any one of <1> to <4>, wherein the resin film is used to form an insulating layer of a printed wiring board. <7> A printed wiring board comprising a cured product of the resin film according to any one of <1> to <4>. <8> A semiconductor package comprising a cured product of the resin film according to any one of <1> to <4>.

[0007] According to one embodiment of the present disclosure, there are provided a resin film having excellent deformability before curing and a low thermal expansion coefficient after curing, a printed wiring board obtained using this resin film, and a semiconductor package obtained using this resin film.

[0008] In the present disclosure, the term "process" includes not only processes that are independent of other processes, but also processes that cannot be clearly distinguished from other processes as long as the purpose of the process is achieved. In the present disclosure, numerical ranges indicated using "to" include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in the present disclosure, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in the numerical ranges described in the present disclosure, the upper or lower limit of that numerical range may be replaced with a value shown in the examples. In the present disclosure, each component may contain multiple corresponding substances. When multiple substances corresponding to each component are present in a composition, the content or amount of each component refers to the total content or amount of the multiple substances present in the composition, unless otherwise specified.

[0009] In this disclosure, the term "resin composition" refers to a mixture of two or more components containing at least a resin. When a resin composition contains a curable component, the resin composition also includes a state in which at least a portion of the curable component has reacted. In this disclosure, the term "solid content" refers to components other than volatile components such as solvents. In this disclosure, "(meth)acrylate" refers to "acrylate" or "methacrylate," "(meth)acrylic" refers to "acrylic" or "methacrylic," and "(meth)acryloyl" refers to "acryloyl" or "methacryloyl." In this disclosure, the "molecular weight" of a compound refers to the molecular weight that can be calculated from the structural formula if the compound is not a polymer and the structural formula of the compound can be identified. In the case of a polymer, the "molecular weight" refers to the number-average molecular weight or weight-average molecular weight. The mechanism of action described herein is speculative and does not limit the mechanism by which the resin composition according to this embodiment exerts its effects. This embodiment also includes any combination of the descriptions herein.

[0010] <Resin Film> The resin film of the present disclosure is made of a resin composition containing a curable resin and an inorganic filler, the content of the inorganic filler being more than 50% by volume, and the minimum melt viscosity being 2000 Pa·s or less.

[0011] As shown in the examples described below, the resin film of the present disclosure has excellent deformability before curing and a low thermal expansion coefficient after curing. One possible way to make a resin sheet more deformable before curing is to reduce the amount of inorganic filler to increase the flexibility of the resin sheet. However, reducing the amount of inorganic filler increases the thermal expansion coefficient of the resin sheet after curing. An increase in the thermal expansion coefficient may cause other problems, such as increased warping of the substrate to which the resin sheet is attached. The resin film of the present disclosure has a minimum melt viscosity of 2000 Pa·s or less, making the resin film more deformable before curing without reducing the amount of inorganic filler. In other words, the resin film of the present disclosure can satisfy both the contradictory properties of ease of deformability before curing and a reduced thermal expansion coefficient after curing.

[0012] From the viewpoint of ease of deformation before curing, the minimum melt viscosity of the resin film is preferably 1800 Pa s or less, more preferably 1700 Pa s or less, and even more preferably 1600 Pa s or less. While the lower limit of the minimum melt viscosity of the resin film is not particularly limited, from the viewpoint of balance with other properties of the resin film, it is preferably 600 Pa s or more, more preferably 800 Pa s or more, and even more preferably 1000 Pa s or more. In the present disclosure, the minimum melt viscosity of the resin film is measured using a rheometer under the conditions described in the Examples.

[0013] From the viewpoint of suppressing warpage of the substrate, the lower the thermal expansion coefficient of the resin film after curing, the more preferable. The thermal expansion coefficient of the resin film after curing is, for example, preferably 25.0 ppm / K or less, and more preferably 20.0 ppm / K or less. In the present disclosure, the thermal expansion coefficient of the resin film after curing is measured by thermomechanical analysis (TMA) under the conditions described in the Examples.

[0014] The resin film of the present disclosure is made of a resin composition containing a curable resin and an inorganic filler. Hereinafter, each component that may be contained in the resin composition constituting the resin film of the present disclosure will be described.

[0015] (Curable Resin) The resin composition contains a curable resin. In the present disclosure, a curable resin refers to a resin that exhibits the property of undergoing a chemical reaction and curing upon treatment such as heating or actinic radiation exposure. Examples of curable resins that can be contained in the resin composition include compounds having functional groups such as N-substituted maleimide groups, vinyl groups, (meth)acryloyl groups, epoxy groups, hydroxyl groups, carboxy groups, and amino groups as reactive groups. From the viewpoints of compatibility with the manufacturing process of electronic components, heat resistance, and the like, the curable resin is preferably a thermosetting resin that exhibits the property of curing upon heating. One type of curable resin may be used alone, or two or more types may be used in combination.

[0016] From the viewpoint of the handleability of the resin film, it is preferable that at least one of the curable resins contained in the resin composition is solid at 25°C, and it is more preferable that at least one of the curable resins contained in the resin composition is solid at 25°C and at least one is liquid at 25°C.

[0017] The curable resin contained in the resin composition may be radically polymerizable. A resin composition containing a radically polymerizable curable resin is less likely to change in properties during storage than, for example, a resin composition containing an epoxy resin. Therefore, there is an advantage that the resin composition can be stored at room temperature, for example.

[0018] Among radically polymerizable curable resins, maleimide resins are preferred from the viewpoints of heat resistance and dielectric properties (low dielectric constant). In the present disclosure, maleimide resin refers to a compound having an N-substituted maleimide group as a reactive group. From the viewpoint of curing reactivity, the maleimide resin is preferably a compound having two N-substituted maleimide groups (hereinafter also referred to as a bismaleimide resin) or a compound having three or more N-substituted maleimide groups (hereinafter also referred to as a polymaleimide resin). From the viewpoint of heat resistance, the maleimide resin is preferably a compound having an N-substituted maleimide group directly bonded to an aromatic ring (hereinafter also referred to as an aromatic maleimide resin), and more preferably a compound having two or three or more N-substituted maleimide groups directly bonded to an aromatic ring (hereinafter also referred to as an aromatic bismaleimide resin or aromatic polymaleimide resin). The maleimide resin contained in the resin composition may be one type or two or more types.

[0019] The maleimide resin contained in the resin composition may be a compound having N-substituted maleimide groups at both ends of the molecule. Examples of the compound having N-substituted maleimide groups at both ends of the molecule include compounds represented by the following formula (A1):

[0020]

[0021] In the formula, X ａ１１ is a divalent organic group. ａ１１ The structure of the divalent organic group represented by X is not particularly limited. ａ１１ The divalent organic group represented by the formula (I) may contain a structure in which structural units of the same type are linked together, and may further contain an N-substituted maleimide group.

[0022] The maleimide resin may contain a fused ring of an aromatic ring and an aliphatic ring. A preferred example of the fused ring of an aromatic ring and an aliphatic ring is an indane ring. The indane ring refers to a fused bicyclic structure of an aromatic six-membered ring and a saturated aliphatic five-membered ring. The indane ring contained in the maleimide resin is preferably contained as a divalent group represented by the following general formula (A1-1):

[0023]

[0024] In the formula, R ａ１ is an alkyl group having 1 to 10 carbon atoms, an alkyloxy group having 1 to 10 carbon atoms, an alkylthio group having 1 to 10 carbon atoms, an aryl group having 6 to 10 carbon atoms, an aryloxy group having 6 to 10 carbon atoms, an arylthio group having 6 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, a halogen atom, a hydroxyl group, or a mercapto group. ａ１ is an integer from 0 to 3. ａ２ ~R ａ４ are each independently an alkyl group having 1 to 10 carbon atoms. * represents a bonding site (the same applies hereinafter).

[0025] R ａ１ Examples of the alkyl group having 1 to 10 carbon atoms represented by R include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, and a decyl group. These alkyl groups may be either linear or branched. ａ１ Examples of the alkyl group contained in the alkyloxy group having 1 to 10 carbon atoms and the alkylthio group having 1 to 10 carbon atoms represented by the formula (I) include the same alkyl groups as those having 1 to 10 carbon atoms described above. ａ１ Examples of the aryl group having 6 to 10 carbon atoms represented by R include a phenyl group and a naphthyl group. ａ１ Examples of the aryl group contained in the aryloxy group having 6 to 10 carbon atoms and the arylthio group having 6 to 10 carbon atoms represented by the formula (R) include the same as the aryl group having 6 to 10 carbon atoms described above. ａ１ Examples of the cycloalkyl group having 3 to 10 carbon atoms represented by the formula (I) include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a cyclononyl group, and a cyclodecyl group. From the viewpoint of solubility in a solvent and reactivity, R ａ１ is preferably an alkyl group having 1 to 4 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or an aryl group having 6 to 10 carbon atoms, and more preferably an alkyl group having 1 to 4 carbon atoms.

[0026] R ａ２ ~R ａ４Examples of the alkyl group having 1 to 10 carbon atoms represented by the formula (I) include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, and a decyl group. These alkyl groups may be either linear or branched. Among these, R ａ２ ~R ａ４ is preferably an alkyl group having 1 to 4 carbon atoms, more preferably a methyl group or an ethyl group, and even more preferably a methyl group. ａ１ is an integer from 0 to 3. ａ１ When R is 2 or 3, two or three R ａ１ may be the same or different.

[0027] From the viewpoint of ease of production, the divalent group represented by general formula (A1-1) is ａ１ is 0, and R ａ２ ~R ａ４ are each preferably a methyl group. Specifically, a divalent group represented by the following formula (A1-1a) is preferred, and a divalent group represented by the following formula (A1-1a') or a divalent group represented by the following formula (A1-1a'') is more preferred.

[0028]

[0029] The maleimide resin containing an indane ring is preferably an aromatic maleimide resin, more preferably an aromatic bismaleimide resin, and even more preferably a compound represented by the following general formula (A1-2).

[0030]

[0031] In the formula, R ａ１ ~R ａ４ and n ａ１ is the same as in general formula (A1-1). ａ５ are each independently an alkyl group having 1 to 10 carbon atoms, an alkyloxy group having 1 to 10 carbon atoms, an alkylthio group having 1 to 10 carbon atoms, an aryl group having 6 to 10 carbon atoms, an aryloxy group having 6 to 10 carbon atoms, an arylthio group having 6 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, a halogen atom, a nitro group, a hydroxyl group, or a mercapto group. ａ２are each independently an integer of 0 to 4. ａ３ is a number between 0.95 and 10.0.

[0032] In the formula, multiple R ａ１ , a plurality of n ａ１ , multiple R ａ５ or multiple n ａ２ may be the same or different. ａ３ If R exceeds 1, multiple R ａ２ , multiple R ａ３ or multiple R ａ４ may be the same or different.

[0033] R ａ５ Examples of the alkyl group having 1 to 10 carbon atoms represented by R include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, and a decyl group. These alkyl groups may be either linear or branched. ａ５ Examples of the alkyl group contained in the alkyloxy group having 1 to 10 carbon atoms and the alkylthio group having 1 to 10 carbon atoms represented by the formula (I) include the same alkyl groups as those having 1 to 10 carbon atoms described above. ａ５ Examples of the aryl group having 6 to 10 carbon atoms represented by R include a phenyl group and a naphthyl group. ａ５ Examples of the aryl group contained in the aryloxy group having 6 to 10 carbon atoms and the arylthio group having 6 to 10 carbon atoms represented by the formula (R) include the same as the aryl group having 6 to 10 carbon atoms described above. ａ５ Examples of the cycloalkyl group having 3 to 10 carbon atoms represented by the formula (I) include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a cyclononyl group, and a cyclodecyl group. From the viewpoint of solvent solubility and ease of production, R ａ５ is preferably an alkyl group having 1 to 4 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or an aryl group having 6 to 10 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms, and even more preferably a methyl group.

[0034] n in the formula ａ２is an integer of 0 to 4, and from the viewpoints of compatibility with other resins, dielectric properties, conductor adhesion and ease of production, is preferably an integer of 1 to 3, more preferably 2 or 3, and even more preferably 2. ａ２ When n is 1 or more, the benzene ring and the N-substituted maleimide group have a twisted conformation, and intermolecular stacking is suppressed, which tends to further improve solvent solubility. ａ２ When R is 1 or more, ａ５ The substitution position of is preferably the ortho position relative to the N-substituted maleimide group. ａ３ From the viewpoints of dielectric properties, conductor adhesion, solvent solubility, handling properties, and heat resistance, n is preferably a number from 0.98 to 8.0, more preferably a number from 1.0 to 7.0, and even more preferably a number from 1.1 to 6.0. ａ３ represents the average number of structural units containing an indane ring.

[0035] From the viewpoints of dielectric properties, conductor adhesion, solvent solubility, and ease of production, the maleimide resin represented by general formula (A1-2) is more preferably a maleimide resin represented by the following general formula (A1-3) or a maleimide resin represented by the following general formula (A1-4):

[0036]

[0037] In the formula, R ａ１ ~R ａ５ , n ａ１ and n ａ３ is the same as in general formula (A1-2).

[0038]

[0039] In the formula, R ａ１ ~R ａ４ , n ａ１ and n ａ３ is the same as in general formula (A1-2).

[0040] Examples of the maleimide resin represented by general formula (A1-3) include a maleimide resin represented by the following general formula (A1-3-1), a maleimide resin represented by the following general formula (A1-3-2), and a maleimide resin represented by the following general formula (A1-3-3).

[0041]

[0042] In the formula, n ａ３ is the same as in general formula (A1-2).

[0043] The maleimide resin (A1) represented by general formula (A1-4) is preferably represented by the following general formula (A1-4-1):

[0044] In the formula, n ａ３ is the same as in general formula (A1-2).

[0045] The maleimide resin containing an indane ring can be synthesized by a known method, for example, by the method described in WO 2023 / 282313.

[0046] When the resin composition contains a maleimide resin as the curable resin and a maleimide resin containing an indane ring as the maleimide resin, the content of the maleimide resin containing an indane ring is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more of the total maleimide resins. The content of the maleimide resin containing an indane ring may be 100% by mass of the total maleimide resins.

[0047] The number-average molecular weight of the maleimide resin containing an indane ring is not particularly limited. From the viewpoints of compatibility with other resins, adhesion to conductors, and heat resistance, the number-average molecular weight of the maleimide resin is preferably 600 to 3,000, more preferably 800 to 2,000, and even more preferably 1,000 to 1,500.

[0048] In the present disclosure, the number average molecular weight or weight average molecular weight of a compound is measured in terms of polystyrene by gel permeation chromatography (GPC). The measurement conditions for GPC are shown below. Apparatus: High-speed GPC apparatus HLC-8320GPC Detector: Ultraviolet absorption detector UV-8320 [manufactured by Tosoh Corporation] Column: Guard column; TSK Guard column SuperHZ-L + Column; TSKgel SuperHZM-N + TSKgel SuperHZM-M + TSKgel SuperH-RC (all manufactured by Tosoh Corporation, trade names) Column size: 4.6 x 20 mm (guard column), 4.6 x 150 mm (column), 6.0 x 150 mm (reference column) Eluent: Tetrahydrofuran Sample concentration: 10 mg / 5 mL Injection volume: 25 μL Flow rate: 1.00 mL / min Measurement temperature: 40°C Calibration curve: Standard polystyrene: TSKstandard Approximation is performed using a cubic equation using POLYSTYRENE (Type: A-2500, A-5000, F-1, F-2, F-4, F-10, F-20, F-40) (product name, manufactured by Tosoh Corporation).

[0049] When the resin composition contains a maleimide resin other than a maleimide resin containing an indane ring as a curable resin, the type thereof is not particularly limited. Specific examples of the maleimide resin other than a maleimide resin containing an indane ring include N,N'-ethylene bismaleimide, N,N'-hexamethylene bismaleimide, N,N'-(1,3-phenylene)bismaleimide, N,N'-[1,3-(2-methylphenylene)]bismaleimide, N,N'-[1,3-(4-methylphenylene)]bismaleimide, N,N'-(1,4-phenylene)bismaleimide, bis(4-maleimidophenyl)methane, bis(3-methyl-4-maleimidophenyl)methane, and 3,3'-dimethyl -5,5'-diethyl-4,4'-diphenylmethane bismaleimide, bis(4-maleimidophenyl)ether, bis(4-maleimidophenyl)sulfone, bis(4-maleimidophenyl)sulfide, bis(4-maleimidophenyl)ketone, bis(4-maleimidocyclohexyl)methane, 1,4-bis(4-maleimidophenyl)cyclohexane, 1,4-bis(maleimidomethyl)cyclohexane, 1,4-bis(maleimidomethyl)benzene, 1,3-bis(4-maleimidophenoxy)benzene, 1,3- Bis(3-maleimidophenoxy)benzene, bis[4-(3-maleimidophenoxy)phenyl]methane, bis[4-(4-maleimidophenoxy)phenyl]methane, 1,1-bis[4-(3-maleimidophenoxy)phenyl]ethane, 1,1-bis[4-(4-maleimidophenoxy)phenyl]ethane, 1,2-bis[4-(3-maleimidophenoxy)phenyl]ethane, 1,2-bis[4-(4-maleimidophenoxy)phenyl]ethane, 2,2-bis[4-(3-maleimidophenoxy)phenyl]propane propane, 2,2-bis[4-(4-maleimidophenoxy)phenyl]propane, 2,2-bis[4-(3-maleimidophenoxy)phenyl]butane, 2,2-bis[4-(4-maleimidophenoxy)phenyl]butane, 2,2-bis[4-(3-maleimidophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, 2,2-bis[4-(4-maleimidophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, 4,4-bis(3-maleimidophenoxy)biphenyl, 4,4-bis(4-maleimidophenoxy)biphenyl, bis[4-(3-maleimidophenoxy)phenyl]ketone, bis[4-(4-maleimidophenoxy)phenyl]ketone, bis(4-maleimidophenyl)disulfide, bis[4-(3-maleimidophenoxy)phenyl]sulfide, bis[4-(4-maleimidophenoxy)phenyl]sulfide, bis[4-(3-maleimidophenoxy)phenyl]sulfide sulfoxide, bis[4-(4-maleimidophenoxy)phenyl]sulfoxide, bis[4-(3-maleimidophenoxy)phenyl]sulfone, bis[4-(4-maleimidophenoxy)phenyl]sulfone, bis[4-(3-maleimidophenoxy)phenyl]ether, bis[4-(4-maleimidophenoxy)phenyl]ether, 1,4-bis[4-(4-maleimidophenoxy)-α,α-dimethylbenzene 1,3-bis[4-(4-maleimidophenoxy)-α,α-dimethylbenzyl]benzene, 1,4-bis[4-(3-maleimidophenoxy)-α,α-dimethylbenzyl]benzene, 1,3-bis[4-(3-maleimidophenoxy)-α,α-dimethylbenzyl]benzene, 1,4-bis[4-(4-maleimidophenoxy)-3,5-dimethyl-α,α-dimethylbenzyl]benzene, 1,3- Examples of the maleimide resin include bis[4-(4-maleimidophenoxy)-3,5-dimethyl-α,α-dimethylbenzyl]benzene, 1,4-bis[4-(3-maleimidophenoxy)-3,5-dimethyl-α,α-dimethylbenzyl]benzene, 1,3-bis[4-(3-maleimidophenoxy)-3,5-dimethyl-α,α-dimethylbenzyl]benzene, polyphenylmethane maleimide, and biphenylaralkyl maleimide. The resin composition may contain, as the maleimide resin, an aminomaleimide resin having structural units derived from a maleimide resin and structural units derived from a diamine compound.

[0050] When the resin composition contains a maleimide resin as a curable resin, the proportion of the maleimide resin in the entire curable resin is not particularly limited. The proportion of the maleimide resin in the entire curable resin may be, for example, 40% by volume or more, 45% by volume or more, or 50% by volume or more. The proportion of the maleimide resin in the entire curable resin may be, for example, 75% by volume or less, 70% by volume or less, or 65% by volume or less.

[0051] The resin composition may contain a compound having a (meth)acryloyl group as a curable resin. From the viewpoint of the balance of the properties of the resin film, the resin composition preferably contains, as curable resins, a compound having an N-substituted maleimide group and a compound having a (meth)acryloyl group. The resin composition may contain only one type of compound having a (meth)acryloyl group, or may contain two or more types of compounds having a (meth)acryloyl group.

[0052] Examples of the compound having a (meth)acryloyl group include (meth)acrylic acid esters such as di(meth)acrylic acid esters and tri- or higher functional (meth)acrylic acid esters.

[0053] Examples of di(meth)acrylic acid esters include 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, tricyclodecane di(meth)acrylate, 1,12-dodecanediol di(meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, and triethylene glycol di(meth)acrylate. Examples of the di(meth)acrylate include 2-[5-ethyl-5-[(acryloyloxy)methyl]-1,3-dioxane-2-yl]-2,2-dimethylethyl acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, ethoxylated bisphenol A di(meth)acrylate, ethoxylated bisphenol F di(meth)acrylate, dioxane glycol di(meth)acrylate, etc. Examples of the dioxane glycol di(meth)acrylate include 2-[5-ethyl-5-[(acryloyloxy)methyl]-1,3-dioxane-2-yl]-2,2-dimethylethyl acrylate, etc.

[0054] Examples of tri- or higher functional (meth)acrylic acid esters include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and dipentaerythritol hexa(meth)acrylate.

[0055] From the viewpoint of the balance of the properties of the resin film, the resin composition preferably contains a di(meth)acrylic acid ester, more preferably a di(meth)acrylic acid ester containing an alkylene group, and even more preferably a di(meth)acrylic acid ester in which (meth)acryloyl groups are bonded to both ends of the alkylene group. As the di(meth)acrylic acid ester containing an alkylene group, preferred are diacrylic acid esters represented by the following general formula (B-1) and dimethacrylic acid esters represented by the following general formula (B-2), and more preferably the dimethacrylic acid ester represented by the following general formula (B-2).

[0056]

[0057] In the formula, R ｂ１ is an alkylene group having 1 to 20 carbon atoms.

[0058] R in the above general formulas (B-1) and (B-2) ｂ１ The number of carbon atoms in the alkylene group having 1 to 20 carbon atoms represented by is preferably 4 to 18, more preferably 6 to 15, and even more preferably 8 to 12. Examples of the alkylene group having 1 to 20 carbon atoms include a methylene group, an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, a heptylene group, an octylene group, a nonylene group, a decylene group, an undecylene group, a dodecylene group, a tetradecylene group, and a pentadecylene group. The alkylene group may be linear, branched, or cyclic, but is preferably linear.

[0059] The resin composition may contain a compound having a vinyl group as a curable resin. From the viewpoint of the balance of the properties of the resin film, it is preferable that the resin composition contains, as curable resins, a compound having an N-substituted maleimide group and a compound having a vinyl group. The resin composition may contain only one type of compound having a vinyl group, or two or more types of compounds having a vinyl group.

[0060] Examples of compounds having a vinyl group include conjugated diene polymers. In the present disclosure, the term "conjugated diene polymer" refers to a polymer of a conjugated diene compound.

[0061] Examples of conjugated diene compounds include 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, 2-phenyl-1,3-butadiene, and 1,3-hexadiene. The conjugated diene polymer may be a homopolymer of one type of conjugated diene compound, or a copolymer of two or more types of conjugated diene compounds. The conjugated diene polymer may be a copolymer of one or more types of conjugated diene compounds and one or more types of monomers other than conjugated diene compounds. When the conjugated diene polymer is a copolymer, the polymerization mode is not particularly limited, and may be any of random polymerization, block polymerization, and graft polymerization.

[0062] From the viewpoints of compatibility with other resins contained in the resin composition and dielectric properties, the conjugated diene polymer is preferably a conjugated diene polymer having multiple vinyl groups in its side chains, and more preferably a conjugated diene polymer having multiple 1,2-vinyl groups in its side chains. The number of vinyl groups contained in one molecule of the conjugated diene polymer is not particularly limited, but from the viewpoints of compatibility with other resins and dielectric properties, it is preferably 3 or more, more preferably 5 or more, and even more preferably 10 or more. The upper limit of the number of vinyl groups contained in one molecule of the conjugated diene polymer is not particularly limited, but may be 100 or less, 80 or less, or 60 or less.

[0063] Examples of conjugated diene polymers include polybutadiene having a 1,2-vinyl group, butadiene-styrene copolymer having a 1,2-vinyl group, and polyisoprene having a 1,2-vinyl group. Among these, from the viewpoints of dielectric properties and heat resistance, polybutadiene having a 1,2-vinyl group and butadiene-styrene copolymer having a 1,2-vinyl group are preferred, and polybutadiene having a 1,2-vinyl group is more preferred. As polybutadiene having a 1,2-vinyl group, polybutadiene homopolymer having a 1,2-vinyl group is preferred.

[0064] When the conjugated diene polymer is a polybutadiene having a 1,2-vinyl group, the content of structural units having a 1,2-vinyl group relative to all structural units derived from butadiene constituting the polybutadiene [hereinafter, may be referred to as the "vinyl group content"] is not particularly limited. From the viewpoints of compatibility with other resins contained in the resin composition, dielectric properties, and heat resistance, the vinyl group content is preferably 50 mol% or more, more preferably 70 mol% or more, and even more preferably 85 mol% or more. There is no particular upper limit to the vinyl group content, and it may be 100 mol% or less, 95 mol% or less, or 90 mol% or less.

[0065] The number average molecular weight of the conjugated diene polymer is not particularly limited, but from the viewpoints of compatibility with other resins, dielectric properties, and heat resistance, it is preferably 1,000 to 3,000, more preferably 1,100 to 2,000, and even more preferably 1,150 to 1,500.

[0066] (Inorganic filler) The resin composition contains an inorganic filler. When the resin composition contains an inorganic filler, the thermal expansion coefficient of the cured product tends to be reduced, and the heat resistance and flame retardancy tend to be improved. The resin composition may contain only one type of inorganic filler or two or more types of inorganic fillers.

[0067] Examples of inorganic fillers include silica, alumina, titanium oxide, beryllia, barium titanate, potassium titanate, strontium titanate, calcium titanate, aluminum carbonate, magnesium hydroxide, aluminum hydroxide, aluminum silicate, calcium carbonate, calcium silicate, magnesium silicate, silicon nitride, boron nitride, aluminum borate, silicon carbide, etc. Among these, silica and alumina are preferred from the viewpoints of low thermal expansion, heat resistance, and flame retardancy.

[0068] The average particle size of the inorganic filler is not particularly limited, but from the viewpoint of dispersibility in the resin composition and compatibility with fine wiring, it is preferably 0.01 μm to 20 μm, more preferably 0.1 μm to 10 μm, and even more preferably 0.5 μm to 5 μm.

[0069] In the present disclosure, the average particle size of the inorganic filler refers to the particle size at which the cumulative volume reaches 50% in a volume-based particle size distribution curve (volume average particle size, D50). The volume-based particle size distribution curve can be obtained, for example, by a laser diffraction scattering method. The shape of the inorganic filler is not particularly limited, but is preferably spherical.

[0070] The inorganic filler may be surface-treated with a coupling agent to improve dispersibility and adhesion to organic components. Examples of the coupling agent include silane coupling agents and titanate coupling agents. Among these, silane coupling agents are preferred. Examples of the silane coupling agent include aminosilane coupling agents, vinylsilane coupling agents, and epoxysilane coupling agents.

[0071] (Elastomer) The resin composition may contain an elastomer. In the present disclosure, "elastomer" refers to a compound having a glass transition temperature of 25°C or less as measured by differential scanning calorimetry in accordance with JIS K 6240:2011, and having either a number average molecular weight or a weight average molecular weight of 10,000 or more. The number average molecular weight or weight average molecular weight of the elastomer can be selected, for example, from the range of 10,000 to 500,000. The resin composition may contain only one type of elastomer, or two or more types of elastomers.

[0072] The elastomer contained in the resin composition may have the properties of a curable resin (i.e., have reactive groups), or may not have the properties of a curable resin (i.e., do not have reactive groups).

[0073] Examples of the elastomer include polystyrene elastomers, polyolefin elastomers, polyurethane elastomers, polyphenylene ether elastomers, polyester elastomers, polyamide elastomers, and polyacrylic elastomers. From the viewpoint of the dielectric properties of the cured product, the resin composition preferably contains a polystyrene elastomer. Examples of the polystyrene elastomer include those having a structural unit derived from a styrene compound represented by the following general formula (D3-1):

[0074]

[0075] In the formula, R ｄ１ is a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and R ｄ２ is an alkyl group having 1 to 5 carbon atoms. ｄ１ is an integer from 0 to 5.

[0076] R in the formula ｄ１ and R ｄ２Examples of the alkyl group having 1 to 5 carbon atoms represented by the formula include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-butyl group, an n-pentyl group, etc. The alkyl group having 1 to 5 carbon atoms may be either linear or branched. Among these, an alkyl group having 1 to 3 carbon atoms is preferred, an alkyl group having 1 or 2 carbon atoms is more preferred, and a methyl group is even more preferred. ｄ１ is an integer of 0 to 5, preferably an integer of 0 to 2, more preferably 0 or 1, and even more preferably 0.

[0077] The polystyrene elastomer may contain structural units other than those derived from styrene compounds. Examples of structural units other than those derived from styrene compounds that the polystyrene elastomer may contain include butadiene-derived structural units, isoprene-derived structural units, maleic acid-derived structural units, and maleic anhydride-derived structural units. The butadiene-derived structural units and isoprene-derived structural units may be hydrogenated. When hydrogenated, the butadiene-derived structural units become structural units in which ethylene units and butylene units are mixed, and the isoprene-derived structural units become structural units in which ethylene units and propylene units are mixed.

[0078] Specific examples of polystyrene-based elastomers include hydrogenated styrene-butadiene-styrene block copolymers, hydrogenated styrene-isoprene-styrene block copolymers, and styrene-maleic anhydride copolymers. Examples of hydrogenated styrene-butadiene-styrene block copolymers include SEBS, which is obtained by completely hydrogenating the carbon-carbon double bonds in the butadiene block, and SBBS, which is obtained by partially hydrogenating the carbon-carbon double bonds at 1,2-bond sites in the butadiene block. In SEBS, complete hydrogenation typically refers to 90% or more of the total carbon-carbon double bonds, but may also be 95% or more, 99% or more, or even 100%. The partial hydrogenation rate in SBBS is, for example, 60% to 85% of the total carbon-carbon double bonds. That is, SBBS contains carbon-carbon double bonds as reactive groups in the molecular chain. Examples of hydrogenated styrene-isoprene-styrene block copolymers include SEPS, which is obtained by hydrogenating the polyisoprene portion.

[0079] The number average molecular weight of the elastomer is not particularly limited, but is preferably 10,000 to 500,000, more preferably 50,000 to 350,000, and even more preferably 100,000 to 200,000. The weight average molecular weight of the elastomer is not particularly limited, but is preferably 10,000 to 500,000, more preferably 50,000 to 350,000, and even more preferably 100,000 to 200,000.

[0080] (Curing Accelerator) The resin composition may contain a curing accelerator. When the resin composition contains a curing accelerator, the curability of the resin composition is improved, and the dielectric properties and heat resistance of the cured product tend to be improved.

[0081] The type of curing accelerator is not particularly limited and can be selected depending on the type of curable resin contained in the resin composition, etc. Examples of the curing accelerator include acidic catalysts such as p-toluenesulfonic acid; amine compounds such as triethylamine, pyridine, tributylamine, and dicyandiamide; imidazole compounds such as methylimidazole, phenylimidazole, and 1-cyanoethyl-2-phenylimidazole; isocyanate-masked imidazole compounds such as an addition reaction product of hexamethylene diisocyanate resin and 2-ethyl-4-methylimidazole; tertiary amine compounds; quaternary ammonium compounds; phosphorus compounds such as triphenylphosphine; dicumyl peroxide, 2,5-dimethyl-2,5-bis(t- Examples of peroxides include organic peroxides such as 2,5-dimethyl-2,5-bis(t-butylperoxy)hexyne-3, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane, t-butylperoxyisopropyl monocarbonate, and 1,3-di(t-butylperoxyisopropyl)benzene; inorganic peroxides such as potassium persulfate, sodium persulfate, and ammonium persulfate; azo compounds such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), and 2,2'-azobis(4-methoxy-2'-dimethylvaleronitrile); and carboxylates of manganese, cobalt, zinc, and the like.

[0082] When the resin composition contains a radically polymerizable curable resin, it is preferable to contain a radical polymerization initiator as a curing accelerator. Examples of the radical polymerization initiator include organic peroxides, inorganic peroxides, azo compounds, etc., among the above-mentioned curing accelerators. From the viewpoint of improving curability, organic peroxides are preferred.

[0083] The resin composition may contain one or more types of curing accelerators.

[0084] When the resin composition contains a curing accelerator, its content is not particularly limited, but is preferably 0.1 to 15 parts by mass, more preferably 1 to 10 parts by mass, and even more preferably 4 to 8 parts by mass relative to the total amount (100 parts by mass) of the resin components. When the content of the curing accelerator is 0.1 parts by mass or more, a sufficient curing acceleration effect tends to be obtained. When the content of the curing accelerator is 15 parts by mass or less, the storage stability of the resin composition tends to be better. When the resin composition contains a radical polymerization initiator as a curing accelerator, its content is not particularly limited, but is preferably 0.05 to 7 parts by mass, more preferably 0.5 to 5 parts by mass, and even more preferably 2 to 4 parts by mass relative to the total amount (100 parts by mass) of the resin components. When the content of the radical polymerization initiator is equal to or greater than the above lower limit, a sufficient curing acceleration effect tends to be easily obtained. Furthermore, when the content of the radical polymerization initiator is equal to or less than the above upper limit, the storage stability tends to be better.

[0085] (Other Components) The resin composition may contain components (other components) other than the above-mentioned components, as necessary. Examples of other components include flame retardants, antioxidants, heat stabilizers, antistatic agents, UV absorbers, colorants, lubricants, etc. The resin composition may contain only one or more other components.

[0086] (Content of Main Components) The content of the main components (curable resin, inorganic filler, and elastomer if necessary) contained in the resin composition is not particularly limited and can be selected depending on the application and desired properties of the resin film.

[0087] From the viewpoint of imparting sufficient curability to the resin film, the content of the curable resin contained in the resin composition is preferably 10% by volume or more, more preferably 15% by volume or more, and even more preferably 20% by volume or more. From the viewpoint of balance with other components, the content of the curable resin contained in the resin composition is preferably 45% by volume or less, more preferably 33% by volume or less, and even more preferably 30% by volume or less.

[0088] When the resin composition contains an elastomer, the content of the elastomer can be selected, for example, from the range of 1% by volume to 30% by volume. From the viewpoint of lowering the melt viscosity of the resin film before curing, the content of the elastomer may be 0% by volume or 10% by volume or less.

[0089] The content of the resin component contained in the resin composition is not particularly limited as long as it is less than 50% by volume. The content of the resin component can be selected, for example, from the range of 30% to 45% by volume.

[0090] From the viewpoint of reducing the melt viscosity of the resin film before curing, the resin composition preferably contains a curable resin having a small molecular weight. Specifically, for example, the proportion of the curable resin having a molecular weight of 2000 or less in the entire curable resin is preferably 70% by volume or more, 80% by volume or more, or 90% by volume or more. The proportion of the curable resin having a molecular weight of 2000 or less in the entire curable resin may be 100% by volume.

[0091] The content of the inorganic filler in the resin composition is not particularly limited as long as it is more than 50% by volume. From the viewpoint of keeping the thermal expansion coefficient after curing low, the content of the inorganic filler is preferably 52% by volume or more, more preferably 55% by volume or more. From the viewpoint of balance with other properties of the resin film, the content of the inorganic filler in the resin film is preferably 70% by volume or less, more preferably 65% ​​by volume or less.

[0092] The content of each component described above is based on the solid content contained in the resin composition. In the present disclosure, the resin component refers to a component corresponding to an organic substance among the solid content contained in the resin composition.

[0093] (Various characteristics of resin film) The thickness of the resin film is not particularly limited and can be selected depending on the application of the resin film. The thickness of the resin film may be, for example, 10 μm or more, 50 μm or more, 80 μm or more, or 100 μm or more. The thickness of the resin film may be, for example, 1,000 μm or less, 700 μm or less, or 500 μm or less.

[0094] From the viewpoint of ease of handling of the resin film, it is preferable that the resin film is disposed on a support. The material of the support is not particularly limited, and examples thereof include resin, metal, paper, etc. If necessary, a release treatment may be applied to the surface of the support that comes into contact with the resin film. The thickness of the support is not particularly limited, but from the viewpoint of ease of handling and economy, it is preferably 10 μm to 150 μm, more preferably 20 μm to 100 μm, and even more preferably 25 μm to 50 μm.

[0095] A resin film disposed on a support can be produced, for example, by applying a resin varnish obtained by adding an organic solvent to a resin composition onto a support and then drying to remove the organic solvent. The content of the organic solvent in the dried resin film is preferably 2% by mass or less, more preferably 1% by mass or less, and even more preferably 0.5% by mass or less, relative to the total amount (100% by mass) of the resin film, and may even be 0% by mass. When the content of the organic solvent in the resin film is within the above range, the amount of volatilization of the organic solvent during heat curing is sufficiently suppressed. The resin film may be in a state in which at least a portion of the curable component contained in the resin film has reacted.

[0096] The resin film may have a protective film disposed on its surface. For example, the resin film may have a support disposed on one side and a protective film disposed on the other side. The material of the protective film is not particularly limited, and examples thereof include resin, metal, paper, and the like. If necessary, a release treatment may be applied to the surface of the protective film that comes into contact with the resin film. The thickness of the protective film is not particularly limited, but from the viewpoints of handleability and economy, it is preferably 10 μm to 150 μm, more preferably 20 μm to 100 μm, and even more preferably 25 μm to 50 μm.

[0097] The use of the resin film of the present disclosure is not particularly limited. Preferred examples of uses include forming an insulating layer on a printed wiring board and sealing a semiconductor element included in a semiconductor package. The resin film of the present disclosure has excellent deformability before heating, and therefore can be suitably used, for example, in applications involving filling recesses formed in a substrate. The resin film of the present disclosure has excellent deformability before heating, and therefore is suitable for applications involving filling recesses with a large aspect ratio. For example, it is suitable for applications involving filling recesses with an aspect ratio of 5 or more. The aspect ratio of a recess is the value obtained by dividing the depth of the recess by the width or diameter of the recess.

[0098] <Printed Wiring Board> The printed wiring board of the present disclosure includes a cured product of the resin film described above. The cured product of the resin film may be, for example, an insulating layer disposed on a substrate included in the printed wiring board. The printed wiring board may be a multilayer printed wiring board.

[0099] An example of a method for manufacturing a printed wiring board using the resin film of the present disclosure will be described below. First, a resin film is placed on a substrate. The resin film may be placed while applying pressure and heat to the resin film. The resin film may be placed on only one side or both sides of the substrate. The substrate for the printed wiring board may be a circuit board having a patterned conductor layer formed on its surface as a circuit. The substrate may be selected without particular limitation from known substrates such as glass epoxy substrates, metal substrates, polyester substrates, polyimide substrates, BT resin substrates, and thermosetting polyphenylene ether substrates. Next, the resin film placed on the substrate is cured to form an insulating layer. The curing conditions are set taking into account the components contained in the resin film, etc. The insulating layer formed by curing the resin film may be subjected to drilling, roughening treatment, polishing, etc. as necessary. A conductor layer may be further placed on the insulating layer formed by curing the resin film. The conductor layer may be placed by a known method such as plating.

[0100] <Semiconductor Package> The semiconductor package of the present disclosure includes the cured resin film described above. The cured resin film may be, for example, a sealing portion disposed around an electronic component disposed on a substrate.

[0101] An example of a method for manufacturing a semiconductor package using the resin film of the present disclosure will be described below. First, the resin film is placed on an electronic component, such as a semiconductor chip, placed on a substrate. Next, the resin film is heated and pressurized as necessary to embed the electronic component in the resin film. Thereafter, the resin film with the embedded electronic component is cured, thereby manufacturing a semiconductor package in which the periphery of the electronic component is sealed with the cured resin film.

[0102] The present embodiment will be specifically described below with reference to examples, although the present embodiment is not limited to the following examples.

[0103] (Preparation of Resin Film) The components shown in Table 1 were mixed with a solvent (toluene) to prepare a resin varnish with a solids concentration of approximately 50% by mass. The blend amounts of the components listed in Table 1 are expressed in "volume percent" unless otherwise specified. The resin varnish was then applied to one side of a PET film to form a resin varnish layer. The resin varnish was then dried by heating at 105°C for 5 minutes to volatilize the solvent contained in the resin varnish layer, yielding a resin composition layer with a PET film disposed on one side. The resin composition layer with a PET film disposed on one side was then superimposed on another resin composition layer with a PET film disposed on the other side, facing each other. In this state, the resin composition layers were bonded together using a vacuum laminator at a temperature of 100°C and a pressure time of 5 seconds to obtain a resin film with PET films disposed on both sides.

[0104] (Curing treatment of resin film) The PET film of the resin film obtained above was peeled off and removed. Next, a 12 μm thick low-profile copper foil (manufactured by Mitsui Mining & Smelting Co., Ltd., product name "3EC-VLP-12") was placed on both sides of the resin film, with the S-side facing the resin film. In this state, the low-profile copper foil and the resin film were bonded together using a vacuum laminator to obtain a laminate. The bonding conditions were a temperature of 100°C, a vacuuming time of 30 seconds, a pressure time of 20 seconds, and a pressure of 0.1 MPa. This laminate was subjected to a curing treatment by heating at a temperature of 180°C for 1 hour to obtain a cured resin film (thickness: 120 μm).

[0105] (Measurement of Thermal Expansion Coefficient) A test specimen measuring 0.4 mm in width, 20 mm in length, and 0.12 mm in thickness was prepared from the cured resin film obtained by the curing treatment. The thermal expansion coefficient of this test specimen was measured by thermomechanical analysis (TMA). The measurement was performed using an SS6100 manufactured by Seiko Instruments Inc. under the following conditions: tension mode, temperature range 30°C to 300°C, heating rate 5°C / min, and load 4 g. Both ends of the long side of the test specimen were gripped with grippers, with a distance of 10 mm between the grippers. The average change in length per unit temperature from 30°C to 150°C was taken as the linear expansion coefficient (CTE, ppm / K). The results are shown in Table 1.

[0106] (Measurement of Melt Viscosity) A test piece measuring 30 mm x 30 mm was prepared from the resin film before the curing treatment. The shear viscosity of the test piece was measured using a rheometer (DHR-20 manufactured by TA Instruments, parallel plate diameter: 20 mm) under the following conditions: temperature range: 30°C to 300°C, heating rate: 5°C / min, load: 1 g. The minimum value of the measured shear viscosity was taken as the minimum melt viscosity (Pa s). The results are shown in Table 1.

[0107] (Evaluation of Embeddability) The embeddability of the resin film before curing was evaluated using the following test. A grid pattern consisting of 10 vertical and 5 horizontal grooves was formed on one side of the evaluation substrate by cutting. The grooves were 1 mm deep and 0.1 mm wide, with a 7 mm spacing between adjacent grooves. A resin film before curing was attached to the grid-patterned side of the evaluation substrate using a vacuum laminator. A vacuum was applied for 30 seconds in this state, and the resin film was embedded into the grooves at 0.1 MPa and 100°C. The surface of the substrate after embedding was visually inspected, and the number of voids observed in a 30 mm x 30 mm area was counted. The results are shown in Table 1. Furthermore, the surface roughness of the substrate after embedding was measured. A laser microscope was used for the measurement, and the measurement area was 20 mm x 10 mm. The results are shown in Table 1.

[0108]

[0109] Details of the components listed in Table 1 are as follows. Curable resin 1: aromatic bismaleimide resin containing an indane ring represented by general formula (A1-4-1), number average molecular weight: 1,300, solid at 25°C. Curable resin 2: polybutadiene homopolymer having 1,2-vinyl groups, vinyl group content: 85% or more, number average molecular weight: 1,200, liquid at 25°C. Curable resin 3: nonanediol dimethacrylate, molecular weight: 296.4, liquid at 25°C. Elastomer: SEBS. Inorganic filler 1: silica particles with a volume average particle size of 2.4 μm. Inorganic filler 2: silica particles with a volume average particle size of 1.0 μm. Coupling agent: 3-methacryloxypropyltrimethoxysilane. Curing accelerator 1: 1,3-di(t-butylperoxyisopropyl)benzene. Curing accelerator 2: imidazole-based curing accelerator.

[0110] As shown in Table 1, the resin films of Examples 1 and 2, which have an inorganic filler content of more than 50% by volume and a minimum melt viscosity of 2000 Pa s or less, have a smaller number of voids observed after the embedding process and a smaller surface roughness value than the resin films of Comparative Examples 1 and 2, which have a minimum melt viscosity of more than 2000 Pa s. Furthermore, the resin films of Examples 1 and 2 have a smaller CTE after curing than the resin film of Comparative Example 3, which has an inorganic filler content of 50% by volume. From the above results, it was found that resin films with an inorganic filler content of more than 50% by volume and a minimum melt viscosity of 2000 Pa s or less have excellent deformability before curing and a low thermal expansion coefficient after curing.

[0111] The disclosure of Japanese Patent Application No. 2024-013690 is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards mentioned herein are incorporated by reference into this specification to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. A resin film made of a resin composition containing a curable resin and an inorganic filler, wherein the content of the inorganic filler is more than 50% by volume and the minimum melt viscosity is 2000 Pa·s or less.

2. The resin film according to claim 1, wherein the curable resin includes a radically polymerizable curable resin.

3. The resin film according to claim 1, wherein the curable resin includes a curable resin having a molecular weight of 2000 or less.

4. The resin film according to claim 1, wherein the content of the inorganic filler is 70% by volume or less.

5. The resin film according to any one of claims 1 to 4, for use as a sealing material for semiconductor packages.

6. The resin film according to any one of claims 1 to 4, for forming an insulating layer of a printed wiring board.

7. A printed wiring board comprising a cured resin film according to any one of claims 1 to 4.

8. A semiconductor package comprising a cured resin film according to any one of claims 1 to 4.

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