Resin composition, dry film, and cured product

Abstract

Provided are: a resin composition capable of securing insulation reliability and suppressing bleeding and warpage after curing while having magnetic characteristics; a dry film; and a cured product. This resin composition contains a solid epoxy resin having a weight average molecular weight of 20,000 or more and an epoxy equivalent of 2,500-9,000, a liquid epoxy resin, a magnetic filler, and an epoxy curing agent.

Description

Resin composition, dry film, and cured product

[0001] The present invention relates to a resin composition, a dry film, and a cured product.

[0002] Along with the recent reduction in size and thickness of electronic devices, demands for reducing the size and thickness of printed wiring boards and inductor components mounted on printed wiring boards are increasing. For this reason, for inductor components, there are demands for thinner substrates (core materials), and even inductor components having a coreless structure.

[0003] In such inductor components, since the substrate is thin, if warpage occurs when the component is formed on the substrate and cured, it becomes difficult to form the component. Additionally, in order to improve the performance of an inductor, the number of turns of the coil is sometimes increased, which shortens the distance between coiled circuits. As a result, the magnetic material used is required to have both insulation reliability and magnetic properties. A technique of incorporating a magnetic filler into a resin composition to impart magnetic properties is known (for example, Patent Document 1).

[0004] Japanese Patent Application Laid-Open No. 2016-172790

[0005] However, since magnetic fillers have low insulating properties, when a magnetic filler is contained in a resin composition, it becomes difficult to ensure the insulation reliability of the cured product. Additionally, when a thermoplastic resin having a relatively large molecular weight is used in the resin composition to maintain the strength of the cured product, warpage may occur after curing due to bleeding, a phenomenon in which part of the resin composition oozes out from the coated surface, and uneven physical properties of the cured product.

[0006] Accordingly, an object of the present invention is to provide a resin composition, a dry film, and a cured product that have magnetic properties, ensure insulation reliability, and can suppress bleeding and warpage after curing.

[0007] One aspect of the present invention is a resin composition. The resin composition includes a solid epoxy resin having a weight average molecular weight of 20,000 or more and an epoxy equivalent of 2,500 to 9,000, a liquid epoxy resin, a magnetic filler, and an epoxy curing agent.

[0008] In the resin composition according to the above embodiment, it is preferable that the viscosity of the liquid epoxy resin is 10,000 mPa·s or less.

[0009] In the resin composition according to the above embodiment, it is preferable that the magnetic filler includes one or more selected from the group consisting of ferrite and alloy.

[0010] In the resin composition according to the above embodiment, it is preferable that the epoxy curing agent includes a phenolic curing agent.

[0011] Another aspect of the present invention is a dry film. This dry film is obtained by applying the resin composition of the above aspect to a first film.

[0012] Another aspect of the present invention is a cured product. The cured product is obtained using the resin composition of the above aspect or the dry film of the above aspect.

[0013] The present invention provides a resin composition, a dry film, and a cured product that have magnetic properties while ensuring insulation reliability and suppressing bleeding and warping after curing.

[0014] In this specification, if isomers exist for the compounds described, all possible isomers are usable in the present invention unless otherwise specified.

[0015] Where the upper and lower limits of a numerical range are described separately in this specification, all combinations of each lower limit and each upper limit shall be substantially described to the extent that they are not inconsistent.

[0016] In this specification, unless otherwise specified, all measurements shall be performed with an ambient temperature of room temperature (25°C).

[0017] In this specification, the number-average molecular weight and weight-average molecular weight are measured by gel permeation chromatography (GPC) and converted using a calibration curve prepared with standard polystyrene.

[0018] In this specification, "solids content" refers to components of the resin composition or each raw material other than solvents (especially organic solvents), and unless otherwise specified, it is based on mass.

[0019] 1. Resin Composition The resin composition of this embodiment comprises a solid epoxy resin, a liquid epoxy resin, a magnetic filler, and an epoxy curing agent. The resin composition may also contain other components as long as they do not hinder the effects of the present invention. Each component will be described below.

[0020] 1-1. Solid epoxy resins are epoxy resins that are solid at room temperature (25°C), i.e., in a solid state. Solid epoxy resins include solid epoxy resins having a weight-average molecular weight of 20,000 or more and an epoxy equivalent of 2,500 to 9,000.

[0021] The weight-average molecular weight of the solid epoxy resin is 20,000 or more, preferably 25,000 or more, 30,000 or more, 35,000 or more, and preferably 100,000 or less, 95,000 or less, 90,000 or less.

[0022] The epoxy equivalent of the solid epoxy resin is 2,500 or more, preferably 2,800 or more, 3,000 or more, 3,500 or more, and preferably 8,500 or less, 8,000 or less, 7,800 or less.

[0023] By setting the weight-average molecular weight and epoxy equivalent of the solid epoxy resin within the above range, it is possible to suppress bleeding while maintaining insulation reliability when combined with the liquid epoxy resin described later.

[0024] Examples of the solid epoxy resins include bisphenol A type epoxy resin, bisphenol F type epoxy resin, phenol novolac epoxy resin, cresol novolac epoxy resin, triphenylmethane type epoxy resin, dicyclopentadiene type epoxy resin, phenol aralkyl epoxy resin, biphenol aralkyl epoxy resin, trisphenol type epoxy resin, and the like. These may be used individually or in combination of two or more types.

[0025] The solid epoxy resin can be a commercially available product and is not particularly limited as long as its weight-average molecular weight and epoxy equivalent are within the above-mentioned range. For example, as a bisphenol A type epoxy resin, jER1256 (manufactured by Mitsubishi Chemical Corporation, weight-average molecular weight 50,000, epoxy equivalent 7,700) and jER1010 (manufactured by Mitsubishi Chemical Corporation, weight-average molecular weight 38,000, epoxy equivalent 3,700) are preferred.

[0026] As described above, the resin composition of this embodiment includes a solid epoxy resin having a weight-average molecular weight of 20,000 or more and an epoxy equivalent of 2,500 to 9,000, but may further include other solid epoxy resins whose weight-average molecular weight and epoxy equivalent are outside the above-mentioned range.

[0027] The content of solid epoxy resin having a weight-average molecular weight of 20,000 or more and an epoxy equivalent of 2,500 to 9,000 is preferably 10 to 80% by mass, and more preferably 20 to 60% by mass, when the total amount of all solid epoxy resins and liquid epoxy resins contained in the composition is 100% by mass.

[0028] The ratio of the solid content of a solid epoxy resin having a weight-average molecular weight of 20,000 or more and an epoxy equivalent of 2,500 to 9,000 to the solid content of the liquid epoxy resin described later is preferably 0.1 to 2.5, and more preferably 0.5 to 2.0.

[0029] 1-2. Liquid Epoxy Resins Liquid epoxy resins are fluid at room temperature (25°C), and more specifically, they are those with a viscosity in the range of 100 to 20,000 mPa·s at 25°C. In this respect, liquid epoxy resins are distinguished from the solid epoxy resins described above.

[0030] The viscosity of the liquid epoxy resin is preferably 10,000 mPa·s or less, 8,000 mPa·s or less, 5,000 mPa·s or less, 3,000 mPa·s or less, 1,500 mPa·s or less, etc. By setting the viscosity of the liquid epoxy resin within the above range, warping of the resin composition after curing can be suppressed.

[0031] The viscosity of the resin in this disclosure is measured as follows: In accordance with JIS-Z8803:2011, section 10, "Method for measuring viscosity using a cone-plate type rotational viscometer," a cone-plate type rotational viscometer (TVE-33H, manufactured by Toki Sangyo Co., Ltd.) was used, and the 30-second value measured under conditions of 25°C and a rotation speed of 5 rpm was taken as the viscosity. For resins with a viscosity of 1,000 mPa·s or more, a cone-plate type rotational viscometer with a rotor of 3° × R9.7 was used, and for resins with a viscosity of less than 1,000 mPa·s, a rotor of 1° 34 × R24 was used.

[0032] The epoxy equivalent of the liquid epoxy resin is preferably 100 or more, 150 or more, 170 or more, and preferably 800 or less, 700 or less, 500 or less.

[0033] Liquid epoxy resins preferably have a flexible skeleton. Having a flexible skeleton in the liquid epoxy resin helps to suppress warping after curing.

[0034] The flexible skeleton is not particularly limited as long as it is a structure that imparts flexibility to the main chain or side chains of the epoxy resin. Specifically, examples include aliphatic structures having linear or branched C1-C20 alkyl chains, ether bonds, aliphatic cyclic structures such as cyclohexane, and polyol skeletons. These structures enhance flexibility by improving the mobility of the molecular chains.

[0035] The type of liquid epoxy resin is not particularly limited, and known types can be used. Examples include liquid bisphenol A type epoxy resin, liquid bisphenol F type epoxy resin, liquid phenol novolac type epoxy resin, liquid bisphenol AD ​​type epoxy resin, liquid naphthalene type epoxy resin, liquid glycidyl ester type epoxy resin, liquid glycidyl ether type epoxy resin, liquid glycidylamine type epoxy resin, liquid heterocyclic epoxy resin, liquid diarylsulfone type epoxy resin, and modified liquids thereof. These may be used individually or in combination of two or more types.

[0036] The solid content of the liquid epoxy resin is preferably 5 to 80% by mass, and more preferably 10 to 60% by mass, when the total mass of all solid epoxy resins and liquid epoxy resins contained in the resin composition is 100% by mass.

[0037] 1-3. Magnetic Fillers Magnetic fillers are used to ensure the magnetic properties of the cured product. There are no particular limitations on the magnetic fillers, and known ones can be used. Preferably, the magnetic fillers include one or more selected from the group consisting of ferrite and alloys.

[0038] More specifically, as magnetic fillers, Fe-Mn ferrite, Fe-Mn-Zn ferrite, Mg-Zn ferrite, Mn-Zn ferrite, Mn-Mg ferrite, Cu-Zn ferrite, Mg-Mn-Sr ferrite, Ni-Zn ferrite, Ba-Zn ferrite, Ba-Mg ferrite, Ba-Ni ferrite, Ba-Co ferrite, Ba-Ni-Co ferrite, Y ferrite, iron oxide powder (III), four Examples include iron oxide powder such as triiron oxide; pure iron powder; iron alloy metal powders such as Fe-Si alloy powder, Fe-Si-Al alloy powder, Fe-Cr alloy powder, Fe-Cr-Si alloy powder, Fe-Ni-Cr alloy powder, Fe-Cr-Al alloy powder, Fe-Ni alloy powder, Fe-Ni-Mo alloy powder, Fe-Ni-Mo-Cu alloy powder, Fe-Co alloy powder, or Fe-Ni-Co alloy powder; and amorphous alloys such as Co-based amorphous alloys.

[0039] The shape of the magnetic filler is not particularly limited as long as it does not impair the effects of the present invention. Examples include spherical, needle-shaped, plate-shaped, scaly, hollow, irregularly shaped, hexagonal, cubic, and flake-shaped fillers. Among the above, a spherical shape is preferred from the viewpoint of high packing and high dispersibility.

[0040] From the viewpoint of improving the dispersibility of the magnetic filler, its ability to fill the gaps in the circuit, and its magnetic properties, the average particle size of the magnetic filler is preferably in the range of 0.1 μm to 25 μm, and more preferably in the range of 0.1 μm to 5 μm.

[0041] The average particle diameter of the magnetic filler is the median particle diameter D50 (volume basis) measured by a laser diffraction particle size distribution analyzer.

[0042] The magnetic filler may be subjected to surface treatment. Examples of the surface treatment agent include vinylsilane coupling agents, (meth)acrylic coupling agents, fluorine-containing silane coupling agents, aminosilane coupling agents, epoxysilane coupling agents, mercaptosilane coupling agents, silane coupling agents, alkoxysilanes, organosilazane compounds, titanate coupling agents, and the like. One type of the surface treatment agent may be used alone, or two or more types may be used in any combination.

[0043] The content of the magnetic filler is preferably 40 to 85% by mass, and more preferably 50 to 85% by mass, when the total mass of the solid content of the resin composition is taken as 100% by mass.

[0044] 1-4. Epoxy curing agent The epoxy curing agent is formulated to cure the above-mentioned solid epoxy resin and liquid epoxy resin through a crosslinking reaction. The epoxy curing agent is not particularly limited, and any known one can be used. Examples thereof include phenolic curing agents, polyamine curing agents, polyamide curing agents, acid anhydride curing agents, imidazole curing agents, thiol curing agents, catechol curing agents, photocurable curing agents, diamine curing agents, and the like. One of these may be used alone, or two or more of these may be used in combination.

[0045] Among the above-mentioned options, the epoxy curing agent preferably contains a phenolic curing agent or an imidazole curing agent, and more preferably contains a phenolic curing agent, from the viewpoint of ensuring insulation reliability.

[0046] The phenolic curing agent is not particularly limited, and conventionally known ones such as phenol novolac resins, alkylphenol novolac resins, bisphenol A novolac resins, dicyclopentadiene type phenolic resins, Xylok type phenolic resins, terpene-modified phenolic resins, cresol / naphthol resins, polyvinylphenols, phenol / naphthol resins, α-naphthol skeleton-containing phenolic resins, triazine skeleton-containing cresol novolac resins, biphenyl aralkyl type phenolic resins, and Xylok type phenol novolac resins can be used.

[0047] The imidazole-based curing agent is not particularly limited, and examples include 2-methylimidazole, 4-methyl-2-ethylimidazole, 2-phenylimidazole, 4-methyl-2-phenylimidazole, 1-benzyl-2-methylimidazole, 2-ethylimidazole, 2-isopropylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, and 1-cyanoethyl-2-undecylimidazole.

[0048] The epoxy curing agent content is preferably 1 to 100% by mass, and more preferably 4 to 50% by mass, when calculated on a solid content basis, with the total of all solid epoxy resins and liquid epoxy resins contained in the resin composition being 100% by mass.

[0049] 1-5. Other Components Other components include additives such as crosslinking agents, crosslinking aids, defoaming agents, rust inhibitors, catalysts (reaction catalysts for epoxy resins, thermosetting catalysts), antioxidants, leveling agents, inorganic fillers such as silica, sensitizers, adhesion aids, surfactants, plasticizers, flame retardants, cellulose nanofibers, dispersants, and adhesion-improving agents, to the extent that they do not hinder the effects of the present invention.

[0050] Other components may include organic solvents. Examples of organic solvents include ketones such as acetone, methyl ethyl ketone, and cyclohexanone; acetic acid esters such as ethyl acetate, butyl acetate, cellosolve acetate, propylene glycol monomethyl ether acetate, and carbitol acetate; cellosolves such as cellosolve and butyl cellosolve, and carbitols such as carbitol and butyl carbitol; aromatic hydrocarbons such as toluene and xylene; and other organic solvents such as dimethylformamide and dimethylacetamide.

[0051] The other components may be used individually or in combination of two or more.

[0052] The total content of other components (excluding organic solvents) in the resin composition may be 1% by mass or more, 5% by mass or more, or 10% by mass or more, and may be 40% by mass or less, 30% by mass or less, or 20% by mass or less, based on the total mass of the solids in the resin composition.

[0053] The resin composition of this embodiment can be manufactured, for example, by mixing the above-mentioned components simultaneously or sequentially and kneading them appropriately using conventionally known methods. Each component may be prepared in advance as a solution or dispersion before mixing.

[0054] 2. Uses / Methods of Use of Resin Compositions Below, we will describe the uses / methods of use of the resin composition, specifically dry films using the resin composition and cured products obtained using the resin composition.

[0055] 2-1. Dry Film The dry film has a resin layer obtained by applying the resin composition of this embodiment to at least one surface of a first film (carrier film) and then drying it. The dry film is used by laminating the resin layer so that it is in contact with a substrate.

[0056] A dry film can be manufactured by uniformly applying a resin composition onto a first film using an appropriate method such as a blade coater, lip coater, comma coater, or film coater, and then drying it to form the aforementioned resin layer. Preferably, the dry film has a second film (protective film) laminated on top of the resin layer. The first film and the second film may be made of the same film material or different film materials.

[0057] The first film is one that serves to support the resin layer of the dry film, and when it is laminated onto a substrate by heating or other means so that the resin layer side of the dry film is in contact with the substrate, it refers to a film that is at least adhered to the resin layer.

[0058] The second film is provided on the side of the resin layer opposite the first film to the dry film, with the purpose of preventing dust and other debris from adhering to the surface of the resin layer and improving handling. When the second film is laminated onto the substrate by heating or other means so that the resin layer side of the dry film is in contact with it, it is peeled off from the resin layer before lamination.

[0059] The film materials for the first and second films can be any materials known to be used for dry films.

[0060] As the first film, for example, a thermoplastic film such as a polyester film like polyethylene terephthalate with a thickness of 2 to 150 μm is used.

[0061] As the second film, polyethylene film, polypropylene film, etc., can be used, but it is preferable that the adhesive strength to the resin layer is weaker than that of the first film.

[0062] The thickness of the resin layer on the first film is preferably 100 μm or less, and more preferably in the range of 5 to 50 μm.

[0063] 2-2. Cured Products A cured product can be obtained using the resin composition of this embodiment, or a dry film having a resin layer obtained from the resin composition of this embodiment. The method for producing the cured product and its uses will be described below.

[0064] (Method for manufacturing the cured product) An example of a method for manufacturing the cured product according to this disclosure is described below.

[0065] Step 1 involves applying a resin composition to the substrate and drying it to form a resin layer. When using a dry film, the resin layer is formed on the substrate by laminating it onto the substrate using a laminator or the like so that the resin layer is in contact with the substrate.

[0066] Methods for applying the resin composition onto a substrate include conventional methods used for applying resin compositions, such as application using a spin coater, bar coater, blade coater, curtain coater, screen printing machine, spray application using a spray coater, and inkjet methods.

[0067] The dry film is preferably bonded to the substrate using a vacuum laminator or the like under pressure and heat. By using such a vacuum laminator, even if the circuit-formed substrate has irregularities on its surface, the dry film adheres closely to the circuit board, preventing the inclusion of air bubbles and improving the ability to fill in depressions on the substrate surface. The pressure is preferably around 0.1 to 2.0 MPa, and the heating is preferably around 40 to 120°C.

[0068] Drying methods after coating the resin composition include air drying, heating and drying in an oven or on a hot plate, and vacuum drying. The drying conditions are not particularly limited, and can be performed by natural drying, forced-air drying, or heating and drying at 60 to 130°C for 1 to 30 minutes.

[0069] There are no particular limitations on the substrate on which the resin layer is formed. Examples include printed circuit boards and flexible printed circuit boards with circuits pre-formed using copper, etc., copper-clad laminates using materials such as paper phenol, paper epoxy, glass cloth epoxy, glass polyimide, glass cloth / nonwoven fabric epoxy, glass cloth / paper epoxy, synthetic fiber epoxy, fluororesin / polyethylene / polyphenylene ether, polyphenylene oxide / cyanate, metal substrates, glass substrates, ceramic substrates, wafers, etc. In this disclosure, films such as polyimide film, polyethylene terephthalate film, and polyethylene naphthalate (PEN) film can also be used as substrates.

[0070] Step 2 involves heat curing the resin layer formed on the substrate. If a dry film is used, the first film is peeled off from the dry film before curing. The heating temperature is not particularly limited, but for example, it can be heated at 100 to 220°C for 30 to 120 minutes. The atmosphere (gas) at this time may be air, or an inert gas such as nitrogen or argon may be used.

[0071] Heat curing may be carried out in two stages. That is, the curable resin composition can be pre-cured at a lower temperature, and then fully cured (final curing) can be performed. The conditions for pre-curing are preferably heating at 80 to 120°C for about 30 to 120 minutes. After that, heating is performed to fully cure. The conditions for full curing are preferably heating at 160 to 180°C for about 30 to 180 minutes.

[0072] (Applications of the cured product) The cured product of this embodiment can be used in various electronic components, including inductor components. The cured product of this embodiment has magnetic properties while ensuring insulation reliability and suppressing bleeding and warping after curing, so it can also be used to miniaturize and thin the electronic components mentioned above.

[0073] <<Preparation of Resin Compositions>> Using the raw materials listed below, resin compositions according to Examples 1 to 14 and Comparative Examples 1 to 5 were prepared to the proportions shown in Tables 1 and 2. Tables 1 and 2 show the solid content (parts by mass) of each raw material.

[0074] <Solid Epoxy Resin (A)> Solid epoxy resin (A) is a solid epoxy resin having a weight-average molecular weight of 20,000 or more and an epoxy equivalent of 2,500 to 9,000. • jER1256 (manufactured by Mitsubishi Chemical Corporation) (weight-average molecular weight: 50,000, epoxy equivalent: 7,700) • jER1010 (manufactured by Mitsubishi Chemical Corporation) (weight-average molecular weight: 38,000, epoxy equivalent: 3,700) • jER1009 (manufactured by Mitsubishi Chemical Corporation) (weight-average molecular weight: 20,000, epoxy equivalent: 2,600)

[0075] <Other Solid Epoxy Resins> Other solid epoxy resins are solid epoxy resins whose weight-average molecular weight and epoxy equivalent are outside the range of solid epoxy resin (A) described above. • jER1004F (manufactured by Mitsubishi Chemical Corporation) (weight-average molecular weight: 6,200, epoxy equivalent: 930) • YX6954 (manufactured by Mitsubishi Chemical Corporation) (weight-average molecular weight: 38,000, epoxy equivalent: 12,000) • XD-1000 (manufactured by Nippon Kayaku Co., Ltd.) (weight-average molecular weight: 1,000, epoxy equivalent: 245-260)

[0076] <Liquid epoxy resin (B)> ・EP-4040L (manufactured by ADEKA Corporation) (Viscosity: 220 mPa·s, epoxy equivalent: 310) ・AER-9000 (manufactured by Asahi Kasei Corporation) (Viscosity: 1200 mPa·s, epoxy equivalent: 350-400) ・jER828 (manufactured by Mitsubishi Chemical Corporation) (Viscosity: 12,000 mPa·s, epoxy equivalent: 184-194)

[0077] <Magnetic Fillers> ・M03S (Ferrite, manufactured by Powdertec Co., Ltd.) ・AW02-08 PF-3F (Amorphous alloy, manufactured by Epson Atomics Co., Ltd.)

[0078] <Epoxy hardeners> ・HF4MH55 (manufactured by Meiwa Kasei Co., Ltd.) (phenol-based hardener) ・2E4MZ (manufactured by Shikoku Kasei Holdings Co., Ltd.) (imidazole-based hardener) ・1BPZ (manufactured by Shikoku Kasei Holdings Co., Ltd.) (imidazole-based hardener)

[0079] <<Preparation of Dry Film>> The resin compositions of Examples 1 to 14 and Comparative Examples 1 to 5 were each appropriately diluted with cyclohexanone, and then applied to a carrier film (PET film; manufactured by Toyobo Co., Ltd., TN-200, 38 μm thick) using an applicator so that the thickness of the resin layer after drying was 80 μm. Next, the resin layer was dried in an IR drying oven at 100 to 110°C for 5 to 10 minutes so that the residual solvent in the resin layer was 0.5 to 2.0% by mass, thereby forming a resin layer on the carrier film.

[0080] <<Evaluation>> For each example and comparative example below, the resin compositions were evaluated for magnetic permeability, post-lamination bleeding, warping, and insulation reliability based on the following evaluation method. The evaluation results are shown in Tables 1 and 2.

[0081] <Measurement of Magnetic Permeability> The dry film obtained by the above method was attached to the glossy side of copper foil attached to an etch-out board using a vacuum laminator (Nikko Materials Co., Ltd., CVP-600) under the following conditions: vacuum pressure: 4 hPa, pressure: 0.4 MPa, temperature: 60°C, and lamination pressure time: 60 seconds. Next, a cured coating film was formed by heat treatment in a hot air circulation drying oven (Yamato Scientific Co., Ltd., DF610) at 100°C for 60 minutes, followed by 180°C for 30 minutes. After peeling off the carrier film, the cured coating film was peeled off the copper foil, and the peeled cured coating film was cut into strips with an outer diameter of 1 cm and an inner diameter of 3 cm to prepare evaluation test pieces. For each evaluation test piece obtained as described above, the relative magnetic permeability (μ') was measured at a temperature of 25°C and 100 MHz using an impedance analyzer (Keysight, Inc., E4291B).

[0082] <Bleeding after Lamination> The dry film obtained by the above method was cut to a size of 3 cm x 3 cm and attached to the copper of a copper-clad laminate treated with CZ8101 (manufactured by MEC Corporation) using a vacuum laminator (manufactured by Nikko Materials Co., Ltd., CVP-600) under the following conditions: vacuum pressure: 4 hPa, pressure: 0.4 MPa, temperature: 110°C, lamination time: 60 seconds. Next, it was heat-pressed under atmospheric pressure at a temperature of 110°C, pressure of 0.5 MPa, and time: 60 seconds to obtain an evaluation substrate. For each of the four sides of the evaluation substrate, the length of the bleed from the original size (3 cm x 3 cm) was measured using an optical microscope and evaluated according to the following criteria. (Evaluation Criteria) A: Average value of bleed on all four sides is less than 2 mm B: Average value of bleed on all four sides is 2 mm or more and less than 4 mm C: Average value of bleed on all four sides is 4 mm or more and less than 6 mm D: Average value of bleed on all four sides is 6 mm or more

[0083] <Warpage> The dry film prepared by the above method was placed on the glossy surface of 35 μm electrolytic copper foil (product name: FV-WS) manufactured by Furukawa Electric Co., Ltd., and laminated using a vacuum laminator (Nikko Materials Co., Ltd., CVP-600) under the following conditions: vacuum pressure: 4 hPa, pressure: 0.4 MPa, temperature: 60°C, lamination pressure time: 60 seconds. This copper foil was heated in a hot air circulation drying oven (Yamato Scientific Co., Ltd., DF610) at 100°C for 30 minutes, and then at 180°C for 60 minutes to cure the resin layer. A 5 cm x 5 cm piece was cut out, and the amount of warpage on each of the four sides was measured and evaluated according to the following criteria. (Evaluation Criteria) A: Average curvature of all four sides is less than 2 mm B: Average curvature of all four sides is 2 mm or more and less than 4 mm C: Average curvature of all four sides is 4 mm or more and less than 10 mm D: Average curvature of all four sides is 10 mm or more

[0084] <Insulation Reliability> After acid treatment, a substrate with a Cu thickness of 18 μm and a circuit pattern with L / S = 13 μm / 12 μm was laminated with the dry film prepared by the above method, in the same manner as the <Warpage> evaluation above. The resin was cured by heat treatment in a hot air circulation type drying oven (DF610, manufactured by Yamato Scientific Co., Ltd.) at 100°C for 60 minutes, followed by 180°C for 30 minutes. The carrier film was peeled off to obtain the evaluation substrate. In a highly accelerated life test apparatus (HAST apparatus, manufactured by Hirayama Seisakusho Co., Ltd.) PC-R8D, the insulation resistance value was 10 under the conditions of 130 RH°C, 85 RH%, and applied voltage of 2 V. ６ The time it took for the resistance to drop below Ω was measured. (Evaluation criteria) A: 168 hours or more, resistance value 10 ６ Maintained a resistance of Ω or higher. B: 96 hours or more but less than 168 hours, resistance value 10 ６ Maintaining a resistance of Ω or higher: C: 48 hours or more but less than 96 hours, resistance value 10 ６ D: Resistance value remained above Ω for less than 48 hours ６ It became less than Ω

[0085]

[0086]

[0087] The resin composition, dry film, and cured product of this disclosure can be used in electronic components, including inductor components, because they possess magnetic properties while ensuring insulation reliability and suppressing bleeding and warping after curing. Cross-reference of related applications

[0088] This application claims priority based on Japanese Patent Application No. 2025-029034, filed with the Japan Patent Office on 26 February 2025, all of which disclosures are incorporated herein by reference in their entirety.

Claims

1. A resin composition comprising: a solid epoxy resin having a weight-average molecular weight of 20,000 or more and an epoxy equivalent of 2,500 to 9,000; a liquid epoxy resin; a magnetic filler; and an epoxy curing agent.

2. The resin composition according to claim 1, wherein the viscosity of the liquid epoxy resin is 10,000 mPa·s or less.

3. The resin composition according to claim 1, wherein the magnetic filler comprises one or more selected from the group consisting of ferrite and alloy.

4. The resin composition according to claim 1, wherein the epoxy curing agent comprises a phenolic curing agent.

5. A dry film obtained by applying the resin composition according to claim 1 to a first film.

6. A cured product obtained using the resin composition according to claim 1 or the dry film according to claim 5.

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