JP7600174B2 - Manufacturing method of inductor substrate - Google Patents

Description

The present invention relates to a method for manufacturing an inductor substrate, a resin composition used in the manufacturing method, and a resin sheet with a support.

Inductors known as power inductors, high-frequency inductors, and common mode choke coils are installed in large numbers in information terminals such as mobile phones and smartphones. Traditionally, independent inductor components were mounted on a printed wiring board, but in recent years, a method has been adopted in which coils are formed using the conductor pattern of a printed wiring board and the inductor is installed inside the printed wiring board.

For example, Patent Document 1 discloses a multilayer printed wiring board with an inductor built in, in which a spiral conductor pattern is formed with multiple turns on multiple layers of the multilayer board, and the ends of the conductor pattern on each layer are connected to the upper and lower layers to form a spiral coil as a whole. Patent Document 2 also discloses that an inductor board is built into the core board of a printed wiring board in order to make the printed wiring board thinner.

When manufacturing an inductor board in which an inductor is formed by a plurality of conductor patterns formed on an insulating layer in this way, it is conceivable that the material for forming the insulating layer is made by adding a magnetic material to a resin composition that has been used in the build-up method of multilayer printed wiring boards. By using an insulating layer formed using such a resin composition, the inductance value can be increased and leakage of magnetic lines of force to the outside of the inductor can be prevented. For example, Patent Document 2 discloses that a magnetic filler is added to the resin composition that constitutes the resin composition layer of a resin sheet with a support, and the insulating layer formed is made magnetic.

JP 2009-16504 A JP 2012-186440 A

The inventors have conducted extensive research and found that when a wet desmear process is carried out when forming a conductor layer on an insulating layer using a resin sheet with a support containing a magnetic filler in the resin composition layer in a build-up method, the oxidizing agent solution used in the wet desmear process dissolves the magnetic filler, causing the roughened shape of the insulating layer surface to deteriorate, resulting in swelling of the conductor layer that is formed, and thus reducing the adhesion (peel strength) between the insulating layer and the conductor layer. The inventors have also found that when a high content of magnetic filler is blended into the resin composition in order to increase the magnetic permeability (relative magnetic permeability) of the insulating layer that becomes a magnetic body, the reduction in adhesion is particularly noticeable.

The object of the present invention is therefore to provide a method for manufacturing an inductor substrate using a resin sheet with a support containing a magnetic filler in a resin composition layer, in which the decrease in adhesion between the insulating layer and the conductor layer is suppressed even when a wet desmear treatment using an oxidizing agent solution is performed, and a resin composition and a resin sheet with a support used in the manufacturing method.

As a result of intensive research into solving the above problems, the inventors discovered that the decrease in adhesion between the insulating layer and the conductor layer can be suppressed by adding a magnetic filler to a resin composition, the weight loss rate of which falls within a predetermined range when the resin composition is kept in an acidic solution of pH 1 at 20°C for 3 hours, and thus completed the present invention.

That is, the present invention includes the following.
[1] (A) a step of laminating a support-attached resin sheet including a support and a resin composition layer provided on the support onto an inner layer substrate such that the resin composition layer is bonded to the inner layer substrate;
(B) a step of thermally curing the resin composition layer to form an insulating layer;
(C) drilling holes in the insulating layer;
(D) performing a wet desmear treatment on the surface of the insulating layer using an oxidizing agent solution; and (E) forming a conductor layer on the surface of the insulating layer that has been subjected to the wet desmear treatment.
A method for manufacturing an inductor substrate, in which an inductor is formed by a plurality of insulating layers and a plurality of conductor layers, comprising the steps of:
The resin composition layer is formed from a resin composition containing a magnetic filler,
A method for manufacturing an inductor substrate, in which the weight loss rate of a magnetic filler is 0% or more and 40% or less when held in an acidic solution of pH 1 at 20° C. for 3 hours.
[2] The method for manufacturing an inductor substrate according to [1], wherein the magnetic filler has a magnetic powder and a coating layer that coats the magnetic powder.
[3] The method for producing an inductor substrate according to [2], wherein the coating layer is at least one of an acrylic resin and a silicon oxide compound.
[4] The method for manufacturing an inductor substrate according to any one of [1] to [3], wherein the content of the magnetic filler is 30% by mass or more and 95% by mass or less, when the non-volatile components in the resin composition are taken as 100% by mass.
[5] The method for manufacturing an inductor substrate according to any one of [1] to [4], wherein the content of the magnetic filler is 60% by mass or more and 95% by mass or less, when the non-volatile components in the resin composition are taken as 100% by mass.
[6] The method for producing an inductor substrate according to any one of [1] to [5], wherein the resin composition contains an epoxy resin.
[7] The method for producing an inductor substrate according to [6], wherein the content of the epoxy resin is 1% by mass or more and 40% by mass or less, when the non-volatile components of the resin composition are taken as 100% by mass.
[8] The method for producing an inductor substrate according to any one of [1] to [7], wherein the resin composition contains an active ester compound.
[9] The method for producing an inductor substrate according to [8], wherein the content of the active ester compound is 1% by mass or more and 40% by mass or less, when the non-volatile components in the resin composition are taken as 100% by mass.
[10] The method for producing an inductor substrate according to any one of [1] to [9], wherein the resin composition contains a thermoplastic resin.
[11] The method for manufacturing an inductor substrate according to [10], wherein the content of the thermoplastic resin is 0.1% by mass or more and 20% by mass or less, when the non-volatile content in the resin composition is 100% by mass.
[12] The method for manufacturing an inductor substrate according to any one of [1] to [11], wherein the support is peeled off between step (B) and step (C) or after step (C).
[13] The method for manufacturing an inductor substrate according to any one of [1] to [12], wherein the step (C) is performed by using a laser to perform hole drilling.
[14] The method for producing an inductor substrate according to any one of [1] to [13], wherein the step (E) is carried out by a wet plating method.
[15] The method for manufacturing an inductor substrate according to any one of [1] to [14], wherein the average particle size of the magnetic filler is 0.01 μm or more and 8 μm or less.
[16] The method for manufacturing an inductor substrate according to any one of [1] to [15], wherein the aspect ratio of the magnetic filler is 2 or less.
[17] The method for producing an inductor substrate according to any one of [1] to [16], wherein the magnetic filler contains an Fe alloy containing one or more elements selected from the group consisting of Si, Al, and Cr.
[18] The method for manufacturing an inductor substrate according to any one of [1] to [17], wherein the insulating layer has a relative permeability of greater than 1.
[19] The method for manufacturing an inductor substrate according to any one of [1] to [18], wherein the insulating layer has a loss factor of 0.07 or less.
[20] A resin composition for forming an insulating layer of an inductor substrate, the inductor being formed from a plurality of insulating layers and a plurality of conductor layers, comprising a magnetic filler having a weight loss rate of 0% or more and 40% or less when held at 20°C for 3 hours in an acidic solution of pH 1.
[21] A support-attached resin sheet comprising a support and a resin composition layer formed on the support using the resin composition according to [20].

The present invention provides a method for manufacturing an inductor substrate using a resin sheet with a support containing a magnetic filler in a resin composition layer, which prevents a decrease in adhesion between an insulating layer and a conductor layer even when a wet desmear treatment using an oxidizing agent solution is performed, as well as a resin composition and a resin sheet with a support used in the manufacturing method.

FIG. 1 is a schematic cross-sectional view for explaining a method for manufacturing a wiring board with a built-in inductor element as an example. FIG. 2 is a schematic cross-sectional view for explaining a method for manufacturing a wiring board with a built-in inductor element as an example. FIG. 3 is a schematic cross-sectional view for explaining a method for manufacturing a wiring board with a built-in inductor element as an example. FIG. 4 is a schematic cross-sectional view for explaining a method for manufacturing a wiring board with a built-in inductor element as an example. FIG. 5 is a schematic plan view of an example of a wiring board with a built-in inductor element, as viewed from one side in the thickness direction. FIG. 6 is a schematic diagram showing a cut end surface of an example of a wiring board with a built-in inductor element cut at the position indicated by the dashed dotted line II-II. FIG. 7 is a schematic plan view for explaining the configuration of a first conductor layer in a wiring board with a built-in inductor element as an example.

Below, an embodiment of the present invention will be described with reference to the drawings. Note that each drawing merely shows the shape, size, and arrangement of the components in a schematic manner to the extent that the invention can be understood. The present invention is not limited by the following description, and each component can be modified as appropriate without departing from the gist of the present invention. In the drawings used in the following description, similar components are indicated with the same reference numerals, and duplicated explanations may be omitted. Furthermore, the configuration according to the embodiment of the present invention is not necessarily manufactured or used according to the arrangement of the illustrated example.

Before describing the method for manufacturing an inductor substrate of the present invention, we will explain the resin composition and the resin sheet with a support that can be used in the method for manufacturing an inductor substrate.

[Resin composition]
The resin composition of the present invention contains a magnetic filler that has a weight loss rate of 0% or more and 40% or less when held at 20°C for 3 hours in an acidic solution of pH 1, and is used for forming an insulating layer of an inductor substrate in which an inductor is formed by multiple insulating layers and multiple conductor layers.

By including such a magnetic filler in the resin composition, it is possible to suppress a decrease in the peel strength between the insulating layer and the conductor layer. The resin composition may further include an epoxy resin, an active ester compound, a thermoplastic resin, a curing agent, a curing accelerator, a carbodiimide compound, and other additives, as necessary.

<Magnetic filler>
The resin composition contains a magnetic filler. The magnetic filler has a weight loss rate of 40% or less, preferably 38% or less, more preferably 35% or less, when held in an acidic solution of pH 1 at 20° C. for 3 hours. The lower limit can be 0% or more. By including a magnetic filler having a weight loss rate in such a range in the resin composition, it is possible to suppress a decrease in the peel strength between the insulating layer and the conductor layer even when a wet desmear treatment is performed using an oxidizing agent solution. The weight loss rate can be measured according to the method described in the examples below.

The material of the magnetic filler is not particularly limited as long as it has the above weight reduction rate. From the viewpoint of suppressing a decrease in peel strength, the magnetic filler is preferably a magnetic filler with a core-shell structure. Examples of magnetic fillers with a core-shell structure include those formed from a magnetic powder contained in a core and a coating layer (shell) that covers the magnetic powder. The magnetic filler with a core-shell structure may have a two-layer structure of a magnetic powder and a coating layer, but may also have a structure of three or more layers including an optional layer.

The magnetic powder contained in the core may be, for example, pure iron powder, 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 or other Fe alloys, Fe-based amorphous, Co-based amorphous, etc. Examples of the magnetic powder include amorphous alloys, spinel ferrites such as Mg-Zn ferrite, Mn-Zn ferrite, Mn-Mg ferrite, Cu-Zn ferrite, Mg-Mn-Sr ferrite, and Ni-Zn ferrite, hexagonal ferrites such as Ba-Zn ferrite, Ba-Mg ferrite, Ba-Ni ferrite, Ba-Co ferrite, and Ba-Ni-Co ferrite, and garnet ferrites such as Y ferrite. Among these, the magnetic powder is preferably an Fe alloy containing one or more elements selected from Si, Al, and Cr, such as an Fe-Si alloy powder, an Fe-Si-Al alloy powder, an Fe-Cr alloy powder, an Fe-Cr-Si alloy powder, an Fe-Ni-Cr alloy powder, and an Fe-Cr-Al alloy powder, and more preferably an Fe alloy containing Si and Cr.

As the magnetic powder, commercially available magnetic powders can be used. Specific examples of commercially available magnetic powders that can be used include "PST-S" manufactured by Sanyo Special Steel Co., Ltd., "AW2-08", "AW2-08PF20F", "AW2-08PF10F", "AW2-08PF3F", "Fe-3.5Si-4.5CrPF20F", "Fe-50NiPF20F", "Fe-80Ni-4MoPF20F" manufactured by Epson Atmix Corporation, "LD-M", "LD-MH", "KNI-106", "KNI-106GSM", "KNI-106GS", "KNI-109", " Examples of magnetic powders include "KNI-109GSM", "KNI-109GS", "KNS-415", "BSF-547", "BSF-029", "BSN-125", "BSN-714", "BSN-828", "S-1281", "S-1641", "S-1651", "S-1470", "S-1511", and "S-2430" manufactured by Toda Kogyo Co., Ltd., "JR09P2" manufactured by Japan Metals and Chemical Industries Co., Ltd., "Nanotek" manufactured by CIK Nanotech Co., Ltd., "JEMK-S" and "JEMK-H" manufactured by Kinsei Matec Co., Ltd., and "Yttrium iron oxide" manufactured by ALDRICH Co., Ltd. One type of magnetic powder may be used alone, or two or more types may be used in combination.

The material that constitutes the shell preferably contains a compound that can form a coating on the surface of the magnetic powder and is resistant to the oxidizing solution.

For example, such a compound is preferably at least one of an acrylic resin and a silicon oxide compound. By using an acrylic resin and/or a silicon oxide compound as the coating layer, it is possible to suppress a decrease in peel strength.

Acrylic resins can be obtained by polymerizing acrylic monomers. For the polymerization, it is preferable to use a polymerization initiator such as azobisisobutyronitrile. Examples of acrylic monomers that can constitute acrylic resins include (meth)acrylic acid; (meth)acrylates such as trimethylolpropane tri(meth)acrylate and tricyclodecane dimethanol di(meth)acrylate; hydroxy(meth)alkyl acrylates such as 2-hydroxyethyl (meth)acrylate and 2-hydroxybutyl (meth)acrylate; mono- or di(meth)acrylates of glycols such as ethylene glycol, methoxytetraethylene glycol, polyethylene glycol, and propylene glycol; (meth)acrylamides such as N,N-dimethyl(meth)acrylamide and N-methylol(meth)acrylamide; Examples of the methacrylates include aminoalkyl (meth)acrylates such as ethylaminoethyl (meth)acrylate; polyhydric alcohols such as pentaerythritol and dipentaerythritol, or polyhydric (meth)acrylates of their adducts with ethylene oxide, propylene oxide, or ε-caprolactone; phenols such as phenoxy (meth)acrylate and phenoxyethyl (meth)acrylate, or (meth)acrylates of their ethylene oxide or propylene oxide adducts; epoxy (meth)acrylates derived from glycidyl ethers such as trimethylolpropane triglycidyl ether; and melamine (meth)acrylates. Among these, (meth)acrylic acid, (meth)acrylates, and polyhydric (meth)acrylates are preferred, with (meth)acrylic acid and (meth)acrylates being more preferred.

Examples of trivalent (meth)acrylates in polyvalent (meth)acrylates include pentaerythritol tri(meth)acrylate, trimethylolpropane EO-added tri(meth)acrylate, glycerin PO-added tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, tetrafurfuryl alcohol oligo(meth)acrylate, ethyl carbitol oligo(meth)acrylate, 1,4-butanediol oligo(meth)acrylate, 1,6-hexanediol oligo(meth)acrylate, trimethylolpropane oligo(meth)acrylate, pentaerythritol oligo(meth)acrylate, tetramethylolmethane tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and (meth)acrylic acid ester of N,N,N',N'-tetrakis(β-hydroxyethyl)ethyldiamine. Examples of trivalent or higher (meth)acrylates include phosphate triester (meth)acrylates such as tri(2-(meth)acryloyloxyethyl)phosphate, tri(2-(meth)acryloyloxypropyl)phosphate, tri(3-(meth)acryloyloxypropyl)phosphate, tri(3-(meth)acryloyl-2-hydroxyloxypropyl)phosphate, di(3-(meth)acryloyl-2-hydroxyloxypropyl)(2-(meth)acryloyloxyethyl)phosphate, and (3-(meth)acryloyl-2-hydroxyloxypropyl)di(2-(meth)acryloyloxyethyl)phosphate. These acrylic monomers may be used alone or may be copolymerized by combining two or more types. "(meth)acrylic acid" refers to methacrylic acid and acrylic acid, and "(meth)acrylate" refers to methacrylate and acrylate. "EO" refers to ethylene oxide and "PO" refers to propylene oxide.

The silicon acid compound can be obtained by the so-called sol-gel method, in which a silica precursor is hydrolyzed and polycondensed under acidic or basic conditions. Examples of silica precursors that can form silicon acid compounds include silicate esters such as tetraethyl orthosilicate; silicates such as sodium silicate, etc. These may be used alone, or two or more types may be combined to form a sol.

When the magnetic filler is a core-shell magnetic filler, the mass ratio of the magnetic powder to the coating layer (magnetic powder/coating layer) is preferably 0.1 or more, more preferably 0.5 or more, and even more preferably 1 or more, and is preferably 20 or less, more preferably 15 or less, and even more preferably 10 or less. By setting the above mass ratio within this range, it is possible to suppress a decrease in peel strength between the insulating layer and the conductor layer even when a wet desmear treatment using an oxidizing agent solution is performed. The mass of the magnetic powder in the above mass ratio represents the amount of magnetic powder charged when manufacturing the core-shell magnetic filler, and the mass of the coating layer represents the total amount of monomers and silica precursors that form the coating layer when manufacturing the core-shell magnetic filler.

The thickness of the coating layer is preferably 3 nm or more, more preferably 5 nm or more, and even more preferably 10 nm or more, from the viewpoint of suppressing a decrease in the peel strength between the insulating layer and the conductor layer, and is preferably 200 nm or less, more preferably 150 nm or less, and even more preferably 100 nm or less. The thickness of the coating layer can be measured, for example, by observing the cross section with a SEM.

Magnetic fillers with a core-shell structure can be produced by adding the material that constitutes the shell to the magnetic powder and stirring to polymerize the material that constitutes the shell. When a silicon acid compound is used as the coating layer, the surface of the coating layer may be treated with a silane coupling agent.

The average particle size of the magnetic filler is preferably 0.01 μm or more, more preferably 0.5 μm or more, and even more preferably 1 μm or more. It is also preferably 8 μm or less, more preferably 5 μm or less, and even more preferably 4 μm or less. By setting the average particle size of the magnetic filler within this range, it is possible to maintain the relative magnetic permeability. When the magnetic filler is a magnetic filler with a core-shell structure, it is preferable that the average particle size of the magnetic powder is within this range.

The aspect ratio (the value obtained by dividing the length of the long side of the magnetic filler by the length of the short side) is preferably 2 or less, more preferably 1.5 or less, and even more preferably 1.2 or less. In general, it is easier to improve the relative magnetic permeability when the magnetic filler is flat rather than spherical. However, from the viewpoint of suppressing the decrease in peel strength between the insulating layer and the conductor layer and maintaining the relative magnetic permeability even when a wet desmear treatment is performed using an oxidizing agent solution, a resin composition having the desired characteristics can be easily obtained by using spherical (B) magnetic filler.

The average particle size of the magnetic filler can be measured by a laser diffraction/scattering method based on the Mie scattering theory. Specifically, a particle size distribution of the magnetic filler is created on a volume basis using a laser diffraction/scattering particle size distribution measuring device, and the median diameter is taken as the average particle size. A preferable measurement sample is one in which the magnetic filler is dispersed in methyl ethyl ketone using ultrasonic waves. Examples of laser diffraction/scattering particle size distribution measuring devices that can be used include the "LA-500" manufactured by Horiba, Ltd. and the "SALD-2200" manufactured by Shimadzu Corporation.

From the viewpoint of improving the relative magnetic permeability, the content (volume %) of the magnetic filler is preferably 10 vol% or more, more preferably 20 vol% or more, and even more preferably 30 vol% or more, assuming that the non-volatile components in the resin composition are 100 vol%. Also, it is preferably 85 vol% or less, more preferably 75 vol% or less, and even more preferably 65 vol% or less.

From the viewpoint of improving the relative magnetic permeability, the content of the magnetic filler is preferably 30% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, assuming that the non-volatile components in the resin composition are 100% by mass. Also, it is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 88% by mass or less.

<Epoxy resin>
The resin composition may contain an epoxy resin. Examples of the epoxy resin include epoxy resins having a condensed ring structure such as naphthalene type epoxy resins, naphthalene type tetrafunctional epoxy resins, naphthol type epoxy resins, naphthylene ether type epoxy resins, anthracene type epoxy resins, dicyclopentadiene type epoxy resins, naphthalene type epoxy resins, naphthalene type tetrafunctional epoxy resins, naphthol type epoxy resins, naphthylene ether type epoxy resins, and dicyclopentadiene type epoxy resins; bisphenol A type epoxy resins; bisphenol F type epoxy resins; bisphenol S type epoxy resins; bisphenol AF type epoxy resins; and trisphenol type epoxy resins. Resins; novolac type epoxy resins; naphthol novolac type epoxy resins; phenol novolac type epoxy resins; tert-butyl-catechol type epoxy resins; glycidylamine type epoxy resins; glycidyl ester type epoxy resins; cresol novolac type epoxy resins; biphenyl type epoxy resins; linear aliphatic epoxy resins; epoxy resins having a butadiene structure; alicyclic epoxy resins; heterocyclic epoxy resins; spiro ring-containing epoxy resins; cyclohexane dimethanol type epoxy resins; trimethylol type epoxy resins; tetraphenylethane type epoxy resins; bixylenol type epoxy resins, etc. The epoxy resins may be used alone or in combination of two or more.

The epoxy resin is preferably one or more selected from bisphenol A type epoxy resin, bisphenol F type epoxy resin, biphenyl type epoxy resin, cresol novolac type epoxy resin, and epoxy resin having a condensed ring structure. Among them, it is more preferable that the component (A) contains an epoxy resin having a condensed ring structure from the viewpoint of obtaining an insulating layer having excellent physical properties such as peel strength. As the epoxy resin having a condensed ring structure, among the above-mentioned examples, naphthalene type epoxy resin, naphthalene type tetrafunctional epoxy resin, naphthol type epoxy resin, naphthylene ether type epoxy resin, anthracene type epoxy resin, and dicyclopentadiene type epoxy resin are preferable, and naphthalene type epoxy resin and naphthol type epoxy resin are particularly preferable.

The epoxy resin preferably contains an epoxy resin having two or more epoxy groups in one molecule. When the non-volatile components of the epoxy resin are taken as 100% by mass, it is preferable that at least 50% by mass of the epoxy resin is an epoxy resin having two or more epoxy groups in one molecule. In particular, the resin composition preferably contains a combination of an epoxy resin that is liquid at a temperature of 20°C (hereinafter referred to as a "liquid epoxy resin") and an epoxy resin that is solid at a temperature of 20°C (hereinafter referred to as a "solid epoxy resin"). By using a liquid epoxy resin and a solid epoxy resin in combination as the epoxy resin, a resin composition having excellent flexibility can be obtained. In addition, the breaking strength of the cured product of the resin composition is also improved. The liquid epoxy resin is preferably a liquid epoxy resin having two or more epoxy groups in one molecule. The solid epoxy resin is preferably a solid epoxy resin having three or more epoxy groups in one molecule.

Preferred liquid epoxy resins are bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol AF type epoxy resins, naphthalene type epoxy resins, glycidyl ester type epoxy resins, glycidyl amine type epoxy resins, phenol novolac type epoxy resins, alicyclic epoxy resins having an ester skeleton, cyclohexane dimethanol type epoxy resins, glycidyl amine type epoxy resins, and epoxy resins having a butadiene structure, and more preferred are glycidyl amine type epoxy resins, bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol AF type epoxy resins, and naphthalene type epoxy resins. Specific examples of liquid epoxy resins include "HP4032", "HP4032D", and "HP4032SS" (naphthalene type epoxy resins) manufactured by DIC Corporation, "828US", "jER828EL" (bisphenol A type epoxy resin), "jER807" (bisphenol F type epoxy resin), "jER152" (phenol novolac type epoxy resin), "630", and "630LSD" (glycidylamine type epoxy resin) manufactured by Mitsubishi Chemical Corporation, and "ZX1059" (bisphenol A type epoxy resin and bisphenol F type epoxy resin) manufactured by Nippon Steel & Sumikin Chemical Co., Ltd. Examples of such epoxy resins include "EX-721" (glycidyl ester type epoxy resin) manufactured by Nagase ChemteX Corporation, "Celloxide 2021P" (alicyclic epoxy resin having an ester structure) and "PB-3600" (epoxy resin having a butadiene structure) manufactured by Daicel Corporation, "ZX1658" and "ZX1658GS" (liquid 1,4-glycidylcyclohexane) manufactured by Nippon Steel & Sumikin Chemical Co., Ltd., "630LSD" (glycidylamine type epoxy resin) manufactured by Mitsubishi Chemical Corporation, and "EP-3980S" (glycidylamine type epoxy resin) manufactured by ADEKA Corporation. These may be used alone or in combination of two or more types.

As solid epoxy resins, naphthalene-type tetrafunctional epoxy resins, cresol novolac-type epoxy resins, dicyclopentadiene-type epoxy resins, trisphenol-type epoxy resins, naphthol-type epoxy resins, biphenyl-type epoxy resins, naphthylene ether-type epoxy resins, anthracene-type epoxy resins, bisphenol A-type epoxy resins, and tetraphenylethane-type epoxy resins are preferred, and naphthalene-type tetrafunctional epoxy resins, naphthol-type epoxy resins, and biphenyl-type epoxy resins are more preferred. Specific examples of solid epoxy resins include "HP4032H" (naphthalene-type epoxy resin), "HP-4700", "HP-4710" (naphthalene-type tetrafunctional epoxy resin), "N-690" (cresol novolac-type epoxy resin), "N-695", "N-680" (cresol novolac-type epoxy resin), "HP-7200" (dicyclopentadiene-type epoxy resin), and "HP-7200" manufactured by DIC Corporation. HH", "HP-7200H", "EXA-7311", "EXA-7311-G3", "EXA-7311-G4", "EXA-7311-G4S", "HP6000" (naphthylene ether type epoxy resin), Nippon Kayaku's "EPPN-502H" (trisphenol type epoxy resin), "NC7000L" (naphthol novolac type epoxy resin), "NC3000H", "NC3000", "NC30 00L, "NC3100" (biphenyl type epoxy resin), "ESN475V" (naphthalene type epoxy resin), "ESN485" (naphthol novolac type epoxy resin) manufactured by Nippon Steel & Sumikin Chemical Co., Ltd., "YX4000H", "YL6121" (biphenyl type epoxy resin), "YX4000HK" (bixylenol type epoxy resin), "YX8800" (anthracene type epoxy resin) manufactured by Mitsubishi Chemical Corporation, "PG-100", "CG-500" manufactured by Osaka Gas Chemical Co., Ltd., "YL7760" (bisphenol AF type epoxy resin), "YL7800" (fluorene type epoxy resin) manufactured by Mitsubishi Chemical Corporation, "jER1010" (solid bisphenol A type epoxy resin), "jER1031S" (tetraphenylethane type epoxy resin), "157S70" (novolac type epoxy resin) manufactured by Mitsubishi Chemical Corporation, and the like. These may be used alone or in combination of two or more.

When liquid epoxy resin and solid epoxy resin are used in combination as epoxy resins, the ratio of the amounts (liquid epoxy resin:solid epoxy resin) is preferably in the range of 1:0.1 to 1:15 by mass. By setting the ratio of the liquid epoxy resin to the solid epoxy resin in this range, the following effects can be obtained: i) when used in the form of a resin sheet with a support, appropriate adhesion is obtained; ii) when used in the form of a resin sheet with a support, sufficient flexibility is obtained and handling is improved; and iii) a cured product having sufficient breaking strength can be obtained. From the viewpoint of the effects i) to iii) above, the ratio of the liquid epoxy resin to the solid epoxy resin (liquid epoxy resin:solid epoxy resin) is more preferably in the range of 1:0.3 to 1:10 by mass, and even more preferably in the range of 1:0.5 to 1:8.

When the resin composition contains an epoxy resin, the content of the epoxy resin is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more, based on 100% by mass of the non-volatile components in the resin composition, from the viewpoint of obtaining an insulating layer exhibiting good mechanical strength and insulating reliability. The upper limit of the content of the epoxy resin is not particularly limited as long as the effects of the present invention are achieved, but is preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less.

The epoxy equivalent of the epoxy resin is preferably 50 to 5,000, more preferably 50 to 3,000, even more preferably 80 to 2,000, and even more preferably 110 to 1,000. This range ensures that the crosslink density of the cured product is sufficient, resulting in an insulating layer with low surface roughness. The epoxy equivalent can be measured according to JIS K7236 and is the mass of the resin containing one equivalent of epoxy groups.

The weight average molecular weight of the epoxy resin is preferably 100 to 5000, more preferably 250 to 3000, and even more preferably 400 to 1500. Here, the weight average molecular weight of the epoxy resin is the weight average molecular weight in terms of polystyrene measured by gel permeation chromatography (GPC).

The number average molecular weight of the epoxy resin is preferably less than 5,000, more preferably 4,000 or less, and even more preferably 3,000 or less. The lower limit is preferably 100 or more, more preferably 300 or more, and even more preferably 500 or more. The number average molecular weight (Mn) is the number average molecular weight in terms of polystyrene measured using GPC (gel permeation chromatography).

The glass transition temperature (Tg) of the epoxy resin is preferably greater than 25°C, more preferably 30°C or higher, and even more preferably 35°C or higher. The upper limit is preferably 500°C or lower, more preferably 400°C or lower, and even more preferably 300°C or lower.

<Active ester compound>
The resin composition may contain an active ester compound. The active ester compound is an active ester compound having one or more active ester groups in one molecule. The active ester compound may be used alone or in combination of two or more.

As the active ester compound, generally, compounds having two or more highly reactive ester groups in one molecule, such as phenol esters, thiophenol esters, N-hydroxyamine esters, and esters of heterocyclic hydroxy compounds, are preferably used. The active ester compound is preferably one obtained by a condensation reaction between a carboxylic acid compound and/or a thiocarboxylic acid compound and a hydroxy compound and/or a thiol compound. In particular, from the viewpoint of improving heat resistance, an active ester compound obtained from a carboxylic acid compound and a hydroxy compound is preferred, and an active ester compound obtained from a carboxylic acid compound and a phenol compound and/or a naphthol compound is more preferred. Examples of the carboxylic acid compound include benzoic acid, acetic acid, succinic acid, maleic acid, itaconic acid, phthalic acid, isophthalic acid, terephthalic acid, and pyromellitic acid. Examples of phenol compounds or naphthol compounds include hydroquinone, resorcin, bisphenol A, bisphenol F, bisphenol S, phenolphthaline, methylated bisphenol A, methylated bisphenol F, methylated bisphenol S, phenol, o-cresol, m-cresol, p-cresol, catechol, α-naphthol, β-naphthol, 1,5-dihydroxynaphthalene, 1,6-dihydroxynaphthalene, 2,6-dihydroxynaphthalene, dihydroxybenzophenone, trihydroxybenzophenone, tetrahydroxybenzophenone, phloroglucin, benzenetriol, dicyclopentadiene-type diphenol compounds, and phenol novolak. Here, "dicyclopentadiene-type diphenol compounds" refer to diphenol compounds obtained by condensing one molecule of dicyclopentadiene with two molecules of phenol.

Specifically, active ester compounds containing a dicyclopentadiene-type diphenol structure, active ester compounds containing a naphthalene structure, active ester compounds containing an acetylated product of phenol novolac, and active ester compounds containing a benzoylated product of phenol novolac are preferred, and among these, active ester compounds containing a naphthalene structure and active ester compounds containing a dicyclopentadiene-type diphenol structure are more preferred. The term "dicyclopentadiene-type diphenol structure" refers to a divalent structural unit consisting of phenylene-dicyclopentylene-phenylene.

Commercially available active ester compounds include "EXB9451", "EXB9460", "EXB9460S", "HPC-8000-65T", "HPC-8000H-65TM", "EXB-8000L-65TM", and "EXB-8150-65T" (manufactured by DIC Corporation) as active ester compounds containing a dicyclopentadiene-type diphenol structure, "EXB9416-70BK" (manufactured by DIC Corporation) as an active ester compound containing a naphthalene structure, and "EXB9416-70BK" (manufactured by DIC Corporation) as an active ester compound containing an acetylated product of phenol novolac. Examples of active ester compounds that contain benzoyl phenol novolac include "DC808" (manufactured by Mitsubishi Chemical Corporation), active ester compounds that are acetylated phenol novolac include "DC808" (manufactured by Mitsubishi Chemical Corporation), and active ester-based curing agents that are benzoyl phenol novolac include "YLH1026" (manufactured by Mitsubishi Chemical Corporation), "YLH1030" (manufactured by Mitsubishi Chemical Corporation), and "YLH1048" (manufactured by Mitsubishi Chemical Corporation).

When the resin composition contains an active ester compound and an epoxy resin, the ratio of the amount of the epoxy resin to the active ester compound is preferably in the range of 1:0.01 to 1:5, more preferably 1:0.05 to 1:3, and even more preferably 1:0.1 to 1:1.5, in terms of the ratio of [total number of epoxy groups in the epoxy resin]:[total number of reactive groups in the active ester compound]. Here, the reactive groups in the active ester compound are active ester groups. The total number of epoxy groups in the epoxy resin is the total value of the solid content mass of each epoxy resin divided by the epoxy equivalent for all epoxy resins, and the total number of reactive groups in the active ester compound is the total value of the solid content mass of each active ester compound divided by the reactive group equivalent for all active ester compounds. By setting the ratio of the epoxy resin to the active ester compound in this range, the heat resistance of the cured product of the resin composition is further improved.

When the resin composition contains an active ester compound, the content of the active ester compound is preferably 1% by mass or more, more preferably 1.5% by mass or more, and even more preferably 2% by mass or more, assuming that the non-volatile components in the resin composition are 100% by mass. The upper limit is preferably 40% by mass or less, more preferably 30% by mass or less, even more preferably 20% by mass or less, 10% by mass or less, 8% by mass or less, or 5% by mass or less. By setting the content of the active ester compound within this range, it is possible to suppress a decrease in the peel strength between the insulating layer and the conductor layer.

<Thermoplastic resin>
The resin composition may contain a thermoplastic resin. Examples of the thermoplastic resin include phenoxy resin, polyvinyl acetal resin, polyolefin resin, polybutadiene resin, siloxane resin, poly(meth)acrylic resin, polyalkylene resin, polyalkyleneoxy resin, polyisoprene resin, polyisobutylene resin, polyimide resin, polyamideimide resin, polyetherimide resin, polysulfone resin, polyethersulfone resin, polyphenylene ether resin, polycarbonate resin, polyetheretherketone resin, and polyester resin. Poly(meth)acrylic resin refers to polyacrylic resin and polymethacrylic resin.

The polystyrene-equivalent weight average molecular weight of the phenoxy resin is preferably in the range of 8,000 to 70,000, more preferably in the range of 10,000 to 60,000, and even more preferably in the range of 20,000 to 60,000. The polystyrene-equivalent weight average molecular weight of the phenoxy resin is measured by gel permeation chromatography (GPC). Specifically, the polystyrene-equivalent weight average molecular weight of the phenoxy resin is measured at a column temperature of 40°C using a measuring device LC-9A/RID-6A manufactured by Shimadzu Corporation, a column Shodex K-800P/K-804L/K-804L manufactured by Showa Denko K.K., and chloroform or the like as the mobile phase, and can be calculated using the calibration curve of standard polystyrene.

Specific examples of phenoxy resins include Mitsubishi Chemical's "1256" and "4250" (both phenoxy resins containing a bisphenol A structure), "YX8100" (phenoxy resin containing a bisphenol S skeleton), and "YX6954" (phenoxy resin containing a bisphenol acetophenone structure). Other examples include Nippon Steel & Sumikin Chemical's "FX280" and "FX293," and Mitsubishi Chemical's "YX7180," "YX6954," "YX7553," "YX7553BH30," "YL7553BH30," "YL7769," "YL6794," "YL7213," "YL7290," "YL7891," and "YL7482." Among these, phenoxy resins with a polyalkyleneoxy structure are preferred, and specific examples include "YX-7180" and "YL7553BH30" manufactured by Mitsubishi Chemical Corporation.

The thermoplastic resin preferably has one or more structures selected from a polybutadiene structure, a polysiloxane structure, a poly(meth)acrylate structure, a polyalkylene structure, a polyalkyleneoxy structure, a polyisoprene structure, a polyisobutylene structure, and a polycarbonate structure in the molecule, more preferably has one or more structures selected from a polybutadiene structure, a poly(meth)acrylate structure, a polyalkyleneoxy structure, a polyisoprene structure, a polyisobutylene structure, and a polycarbonate structure, and further preferably has one or more structures selected from a polybutadiene structure and a polyalkyleneoxy structure. By including a resin having the above structure, the insulating layer has low elasticity, and is excellent in shear strength, bending strain at break, and cracking properties, and further can suppress the occurrence of warping. In addition, "(meth)acrylate" refers to methacrylate and acrylate. These structures may be included in the main chain or in the side chain.
The polybutadiene structure may be partially or completely hydrogenated.
The polyalkyleneoxy structure is preferably a polyalkyleneoxy structure having 2 to 15 carbon atoms, more preferably a polyalkyleneoxy structure having 3 to 10 carbon atoms, and even more preferably a polyalkyleneoxy structure having 5 or 6 carbon atoms.

The thermoplastic resin preferably has a high molecular weight in order to reduce warping when the resin composition is cured. The number average molecular weight (Mn) is preferably 1,000 or more, more preferably 1500 or more, even more preferably 3000 or more, and even more preferably 5000 or more. The upper limit is preferably 1,000,000 or less, more preferably 900,000 or less. The number average molecular weight (Mn) is the number average molecular weight in terms of polystyrene measured using GPC (gel permeation chromatography).

From the viewpoint of improving the mechanical strength of the cured product, it is preferable that the thermoplastic resin has a functional group capable of reacting with the epoxy resin. Note that the functional group capable of reacting with the epoxy resin also includes a functional group that appears upon heating.

In a preferred embodiment, the functional group capable of reacting with the epoxy resin is one or more functional groups selected from the group consisting of a hydroxy group, a carboxy group, an acid anhydride group, a phenolic hydroxyl group, an epoxy group, an isocyanate group, and a urethane group. Among these, the functional group is preferably a hydroxy group, an acid anhydride group, a phenolic hydroxyl group, an epoxy group, an isocyanate group, or a urethane group, more preferably a hydroxy group, an acid anhydride group, a phenolic hydroxyl group, or an epoxy group, and particularly preferably a phenolic hydroxyl group. However, when an epoxy group is included as a functional group, the number average molecular weight (Mn) is preferably 5,000 or more.

Specific examples of polybutadiene resins include Cray Valley's "Ricon 130MA8," "Ricon 130MA13," "Ricon 130MA20," "Ricon 131MA5," "Ricon 131MA10," "Ricon 131MA17," "Ricon 131MA20," and "Ricon 184MA6" (polybutadiene containing acid anhydride groups), Nippon Soda's "GQ-1000" (polybutadiene with hydroxyl and carboxyl groups introduced), "G-1000," "G-2000," and "G-3000" (polybutadiene with hydroxyl groups at both ends), "GI-1000," "GI-2000," and "GI-3000" (hydrogenated polybutadiene with hydroxyl groups at both ends), and Nagase ChemteX's "FCA-061L" (hydrogenated polybutadiene skeleton epoxy resin). As an embodiment, a linear polyimide (polyimides described in JP 2006-37083 A and WO 2008/153208 A) made from hydroxyl-terminated polybutadiene, a diisocyanate compound, and a tetrabasic acid anhydride can be mentioned. The content of the butadiene structure in the polyimide resin is preferably 60% by mass to 95% by mass, more preferably 75% by mass to 85% by mass. For details of the polyimide resin, please refer to the descriptions in JP 2006-37083 A and WO 2008/153208 A, the contents of which are incorporated herein by reference.

Examples of poly(meth)acrylic resins include Teisan Resin manufactured by Nagase ChemteX Corporation, and "ME-2000", "W-116.3", "W-197C", "KG-25", and "KG-3000" manufactured by Negami Chemical Industries, Ltd.
Examples of polycarbonate resins include "T6002" and "T6001" (polycarbonate diols) manufactured by Asahi Kasei Chemicals Corporation, and "C-1090", "C-2090", and "C-3090" (polycarbonate diols) manufactured by Kuraray Co., Ltd. In addition, linear polyimides made from hydroxyl-terminated polycarbonates, diisocyanate compounds, and tetrabasic acid anhydrides can also be used. The content of the carbonate structure in the polyimide resin is preferably 60% by mass to 95% by mass, more preferably 75% by mass to 85% by mass. For details of the polyimide resin, refer to the description in International Publication No. WO 2016/129541, the contents of which are incorporated herein by reference.

Other specific examples include "SMP-2006", "SMP-2003PGMEA", and "SMP-5005PGMEA" manufactured by Shin-Etsu Silicone Co., Ltd.; linear polyimides made from amine-terminated polysiloxane and tetrabasic acid anhydride (see, for example, International Publication No. 2010/053185, JP 2002-12667 A and JP 2000-319386 A); "PTXG-1000" and "PTXG-1800" manufactured by Asahi Kasei Fibers Corporation; "KL-610" and "KL613" manufactured by Kuraray Co., Ltd.; "SIBSTAR-073T" (styrene-isobutylene-styrene triblock copolymer) and "SIBSTAR-042D" (styrene-isobutylene diblock copolymer) manufactured by Kaneka Corporation; and "Denkabure" manufactured by Denki Kagaku Kogyo Co., Ltd. Examples include "Cyral 4000-2", "Denka Butyral 5000-A", "Denka Butyral 6000-C", "Denka Butyral 6000-EP", Sekisui Chemical's S-LEC BH series, BX series (e.g. BX-5Z), KS series (e.g. KS-1), BL series, and BM series, New Japan Chemical's "Rikacoat SN20" and "Rikacoat PN20", Toyobo's "Vilomax HR11NN" and "Vilomax HR16NN", Hitachi Chemical's "KS9100" and "KS9300", Sumitomo Chemical's "PES5003P", Solvay Advanced Polymers' polysulfone "P1700" and "P3500", and Ganz Chemical's "AC3832".

When the resin composition contains a thermoplastic resin, the content of the thermoplastic resin is, from the viewpoint of imparting flexibility, preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more, and is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less, or 3% by mass or less, when the non-volatile components in the resin composition are taken as 100% by mass. By keeping the content of the thermoplastic resin within this range, the relative magnetic permeability of the cured product can be maintained, and a decrease in peel strength can also be suppressed.

<Curing Agent>
The resin composition may contain a curing agent. However, the curing agent does not include an active ester compound. The curing agent is not particularly limited as long as it has the function of curing a resin such as an epoxy resin, and examples thereof include a phenol-based curing agent, a naphthol-based curing agent, a benzoxazine-based curing agent, and a cyanate ester-based curing agent. The curing agent may be used alone or in combination of two or more types. The curing agent is preferably one or more selected from a phenol-based curing agent, a naphthol-based curing agent, and a cyanate ester-based curing agent, and is preferably a phenol-based curing agent, and as one embodiment, it is more preferably one or more selected from a triazine skeleton-containing phenol-based curing agent and an active ester-based curing agent.

As for the phenol-based and naphthol-based curing agents, from the viewpoint of obtaining sufficient strength of the cured product, a phenol-based curing agent having a novolac structure or a naphthol-based curing agent having a novolac structure is preferred. Also, from the viewpoint of adhesion to the conductor layer, a nitrogen-containing phenol-based curing agent is preferred, and a triazine skeleton-containing phenol-based curing agent is more preferred.

Specific examples of phenol-based and naphthol-based hardeners include "MEH-7700", "MEH-7810", and "MEH-7851" manufactured by Meiwa Kasei Co., Ltd., "NHN", "CBN", and "GPH" manufactured by Nippon Kayaku Co., Ltd., "SN170", "SN180", "SN190", "SN475", "SN485", "SN495V", "SN375", and "SN395" manufactured by Nippon Steel & Sumikin Chemical Co., Ltd., and "SN170", "SN180", "SN190", "SN475", "SN485", "SN495V", "SN375", and "SN395" manufactured by DIC Corporation. Examples include "TD2090", "TD2090-60M", "LA-7052", "LA-7054", "LA-1356", "LA-3018", "LA-3018-50P", "EXB-9500", "HPC-9500", "KA-1160", "KA-1163", "KA-1165", and Gun-ei Chemical's "GDP-6115L", "GDP-6115H", and "ELPC75".

Specific examples of benzoxazine-based curing agents include "HFB2006M" manufactured by Showa Polymer Co., Ltd., and "P-d" and "F-a" manufactured by Shikoku Chemical Industries Co., Ltd.

Examples of cyanate ester curing agents include bifunctional cyanate resins such as bisphenol A dicyanate, polyphenol cyanate, oligo(3-methylene-1,5-phenylene cyanate), 4,4'-methylenebis(2,6-dimethylphenyl cyanate), 4,4'-ethylidene diphenyl dicyanate, hexafluorobisphenol A dicyanate, 2,2-bis(4-cyanate)phenylpropane, 1,1-bis(4-cyanate phenylmethane), bis(4-cyanate-3,5-dimethylphenyl)methane, 1,3-bis(4-cyanate phenyl-1-(methylethylidene))benzene, bis(4-cyanate phenyl)thioether, and bis(4-cyanate phenyl)ether; polyfunctional cyanate resins derived from phenol novolac and cresol novolac; and prepolymers in which these cyanate resins have been partially converted to triazine. Specific examples of cyanate ester-based hardeners include Lonza Japan's "PT30" and "PT60" (both of which are phenol novolac-type multifunctional cyanate ester resins), "BA230" and "BA230S75" (prepolymers in which part or all of bisphenol A dicyanate has been converted to triazine and turned into a trimer).

The content of the curing agent is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more, and is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 2% by mass or less, assuming that the resin component in the resin composition is 100% by mass. By keeping the content of the curing agent within this range, it is possible to suppress a decrease in peel strength.

<Curing accelerator>
The resin composition may contain a curing accelerator. Examples of the curing accelerator include phosphorus-based curing accelerators, amine-based curing accelerators, imidazole-based curing accelerators, guanidine-based curing accelerators, and metal-based curing accelerators. Phosphorus-based curing accelerators, amine-based curing accelerators, imidazole-based curing accelerators, and metal-based curing accelerators are preferred, and amine-based curing accelerators, imidazole-based curing accelerators, and metal-based curing accelerators are more preferred. The curing accelerator may be used alone or in combination of two or more.

Examples of phosphorus-based curing accelerators include triphenylphosphine, phosphonium borate compounds, tetraphenylphosphonium tetraphenylborate, n-butylphosphonium tetraphenylborate, tetrabutylphosphonium decanoate, (4-methylphenyl)triphenylphosphonium thiocyanate, tetraphenylphosphonium thiocyanate, butyltriphenylphosphonium thiocyanate, etc., with triphenylphosphine and tetrabutylphosphonium decanoate being preferred.

Examples of amine-based curing accelerators include trialkylamines such as triethylamine and tributylamine, 4-dimethylaminopyridine, benzyldimethylamine, 2,4,6-tris(dimethylaminomethyl)phenol, and 1,8-diazabicyclo(5,4,0)-undecene, with 4-dimethylaminopyridine and 1,8-diazabicyclo(5,4,0)-undecene being preferred.

Examples of imidazole-based curing accelerators include 2-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazolium trimellitate, 1-cyanoethyl-2-phenylimidazolium trimellitate, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine, 2,4 -diamino-6-[2'-undecylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanuric acid adduct, 2-phenylimidazole isocyanuric acid adduct, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl Examples of the imidazole compounds include 1-dodecyl-4-methyl-5-hydroxymethylimidazole, 2,3-dihydro-1H-pyrrolo[1,2-a]benzimidazole, 1-dodecyl-2-methyl-3-benzylimidazolium chloride, 2-methylimidazoline, 2-phenylimidazoline, and adducts of imidazole compounds and epoxy resins, with 2-ethyl-4-methylimidazole and 1-benzyl-2-phenylimidazole being preferred.

Commercially available imidazole curing accelerators may be used, such as "P200-H50" manufactured by Mitsubishi Chemical Corporation.

Examples of guanidine-based curing accelerators include dicyandiamide, 1-methylguanidine, 1-ethylguanidine, 1-cyclohexylguanidine, 1-phenylguanidine, 1-(o-tolyl)guanidine, dimethylguanidine, diphenylguanidine, trimethylguanidine, tetramethylguanidine, pentamethylguanidine, 1,5,7-triazabicyclo[4.4.0]dec-5-ene, and 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene. Examples include o[4.4.0]dec-5-ene, 1-methylbiguanide, 1-ethylbiguanide, 1-n-butylbiguanide, 1-n-octadecylbiguanide, 1,1-dimethylbiguanide, 1,1-diethylbiguanide, 1-cyclohexylbiguanide, 1-allylbiguanide, 1-phenylbiguanide, and 1-(o-tolyl)biguanide, and dicyandiamide and 1,5,7-triazabicyclo[4.4.0]dec-5-ene are preferred.

Metal-based curing accelerators include, for example, organometallic complexes or organometallic salts of metals such as cobalt, copper, zinc, iron, nickel, manganese, and tin. Specific examples of organometallic complexes include organocobalt complexes such as cobalt (II) acetylacetonate and cobalt (III) acetylacetonate, organocopper complexes such as copper (II) acetylacetonate, organozinc complexes such as zinc (II) acetylacetonate, organoiron complexes such as iron (III) acetylacetonate, organonickel complexes such as nickel (II) acetylacetonate, and organomanganese complexes such as manganese (II) acetylacetonate. Organometallic salts include, for example, zinc octylate, tin octylate, zinc naphthenate, cobalt naphthenate, tin stearate, and zinc stearate.

When the resin composition contains a curing accelerator, the content of the curing accelerator is preferably 0.001% by mass or more, more preferably 0.005% by mass or more, even more preferably 0.01% by mass or more, preferably 0.1% by mass or less, more preferably 0.08% by mass or less, and even more preferably 0.05% by mass or less, when the non-volatile components in the resin composition are taken as 100% by mass. By keeping the content of the curing accelerator within this range, it is possible to suppress a decrease in peel strength.

<Carbodiimide Compound>
The resin composition may contain a carbodiimide compound. The carbodiimide compound is a compound having one or more carbodiimide groups (-N=C=N-) in one molecule, and by containing the carbodiimide compound, an insulating layer having excellent adhesion to a conductor layer can be obtained. As the carbodiimide compound, a compound having two or more carbodiimide groups in one molecule is preferable. The carbodiimide compound may be used alone or in combination of two or more.

In one embodiment, the carbodiimide compound contained in the resin composition of the present invention contains a structure represented by the following formula (1):

（式中、Ｘは、アルキレン基、シクロアルキレン基又はアリーレン基を表し、これらは置換基を有していてもよい。ｐは１～５の整数を表す。Ｘが複数存在する場合、それらは同一でも相異なってもよい。＊は結合手を表す。）

(In the formula, X represents an alkylene group, a cycloalkylene group, or an arylene group, which may have a substituent. p represents an integer of 1 to 5. When there are multiple Xs, they may be the same or different. * represents a bond.)

The number of carbon atoms in the alkylene group represented by X is preferably 1 to 20, more preferably 1 to 10, and even more preferably 1 to 6, 1 to 4, or 1 to 3. The number of carbon atoms does not include the number of carbon atoms of the substituent. Suitable examples of the alkylene group include a methylene group, an ethylene group, a propylene group, and a butylene group.

The number of carbon atoms in the cycloalkylene group represented by X is preferably 3 to 20, more preferably 3 to 12, and even more preferably 3 to 6. The number of carbon atoms in the substituent is not included in the number of carbon atoms. Suitable examples of the cycloalkylene group include a cyclopropylene group, a cyclobutylene group, a cyclopentylene group, and a cyclohexylene group.

The arylene group represented by X is a group in which two hydrogen atoms on an aromatic ring have been removed from an aromatic hydrocarbon. The number of carbon atoms in the arylene group is preferably 6 to 24, more preferably 6 to 18, even more preferably 6 to 14, and even more preferably 6 to 10. The number of carbon atoms does not include the number of carbon atoms of the substituent. Suitable examples of the arylene group include a phenylene group, a naphthylene group, and an anthracenylene group.

The alkylene group, cycloalkylene group or aryl group represented by X may have a substituent. The substituent is not particularly limited, and examples thereof include a halogen atom, an alkyl group, an alkoxy group, a cycloalkyl group, a cycloalkyloxy group, an aryl group, an aryloxy group, an acyl group and an acyloxy group. Examples of the halogen atom used as a substituent include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom. The alkyl group and the alkoxy group used as a substituent may be either linear or branched, and the number of carbon atoms is preferably 1 to 20, more preferably 1 to 10, and even more preferably 1 to 6, 1 to 4, or 1 to 3. The number of carbon atoms of the cycloalkyl group and the cycloalkyloxy group used as a substituent is preferably 3 to 20, more preferably 3 to 12, and even more preferably 3 to 6. The aryl group used as a substituent is a group obtained by removing one hydrogen atom on the aromatic ring from an aromatic hydrocarbon, and the number of carbon atoms is preferably 6 to 24, more preferably 6 to 18, even more preferably 6 to 14, and even more preferably 6 to 10. The number of carbon atoms of the aryloxy group used as a substituent is preferably 6 to 24, more preferably 6 to 18, even more preferably 6 to 14, and even more preferably 6 to 10. The acyl group used as a substituent refers to a group represented by the formula: -C(=O)-R ¹ (wherein R ¹ represents an alkyl group or an aryl group). The alkyl group represented by R ¹ may be either linear or branched, and the number of carbon atoms is preferably 1 to 20, more preferably 1 to 10, even more preferably 1 to 6, 1 to 4, or 1 to 3. The number of carbon atoms of the aryl group represented by R ¹ is preferably 6 to 24, more preferably 6 to 18, even more preferably 6 to 14, and even more preferably 6 to 10. The acyloxy group used as a substituent refers to a group represented by the formula: -O-C(=O)-R ¹ (wherein R ¹ represents the same meaning as above). Among them, as the substituent, an alkyl group, an alkoxy group, and an acyloxy group are preferable, and an alkyl group is more preferable.

In formula (1), p represents an integer of 1 to 5. From the viewpoint of realizing an insulating layer having even better heat resistance, laser via reliability, and peel strength, p is preferably 1 to 4, more preferably 2 to 4, and even more preferably 2 or 3.

In formula (1), when there are multiple X's, they may be the same or different. In a preferred embodiment, at least one X is an alkylene group or a cycloalkylene group, which may have a substituent.

In a preferred embodiment, the carbodiimide compound contains the structure represented by formula (1) in an amount of preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and even more preferably 80% by mass or more or 90% by mass or more, when the mass of the entire molecule of the carbodiimide compound is taken as 100% by mass. The carbodiimide compound may essentially consist of the structure represented by formula (1), except for the terminal structure. The terminal structure of the carbodiimide compound is not particularly limited, and examples thereof include an alkyl group, a cycloalkyl group, and an aryl group, which may have a substituent. The alkyl group, cycloalkyl group, and aryl group used as the terminal structure may be the same as the alkyl group, cycloalkyl group, and aryl group described for the substituent that the group represented by X may have. In addition, the substituent that the group used as the terminal structure may have may be the same as the substituent that the group represented by X may have.

From the viewpoint of suppressing the generation of outgassing when the resin composition is cured, the weight average molecular weight of the carbodiimide compound is preferably 500 or more, more preferably 600 or more, even more preferably 700 or more, even more preferably 800 or more, and particularly preferably 900 or more or 1000 or more. From the viewpoint of obtaining good compatibility, the upper limit of the weight average molecular weight of the carbodiimide compound is preferably 5000 or less, more preferably 4500 or less, even more preferably 4000 or less, even more preferably 3500 or less, and particularly preferably 3000 or less. The weight average molecular weight of the carbodiimide compound can be measured, for example, by gel permeation chromatography (GPC) method (polystyrene equivalent).

The carbodiimide compound may contain an isocyanate group (-N=C=O) in the molecule due to the manufacturing method. From the viewpoint of obtaining a resin composition exhibiting good storage stability, and thus from the viewpoint of realizing an insulating layer exhibiting the desired characteristics, the content of isocyanate groups in the carbodiimide compound (also referred to as the "NCO content") is preferably 5% by mass or less, more preferably 4% by mass or less, even more preferably 3% by mass or less, even more preferably 2% by mass or less, and particularly preferably 1% by mass or less or 0.5% by mass or less.

Commercially available carbodiimide compounds may be used. Examples of commercially available carbodiimide compounds include Carbodilite (registered trademark) V-02B, V-03, V-04K, V-07, and V-09 manufactured by Nisshinbo Chemical Co., Ltd., and Stavaxol (registered trademark) P, P400, and Hi-Kasil 510 manufactured by Rhein Chemie.

When the resin composition contains a carbodiimide compound, the content of the carbodiimide compound is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more, based on 100% by mass of the non-volatile components in the resin composition, from the viewpoint of obtaining an insulating layer that is excellent in all properties of heat resistance, laser via reliability, and adhesion to the conductor layer. The upper limit of the content of the carbodiimide compound is not particularly limited, but is preferably 3% by mass or less, more preferably 2% by mass or less, and even more preferably 1.5% by mass or less.

<Optional Additives>
The resin composition may further contain other additives as necessary. Examples of such other additives include flame retardants, organometallic compounds such as organocopper compounds, organozinc compounds, and organocobalt compounds, as well as resin additives such as binders, thickeners, defoamers, leveling agents, adhesion promoters, and colorants.

Examples of flame retardants include phosphazene compounds, organic phosphorus flame retardants, organic nitrogen-containing phosphorus compounds, nitrogen compounds, silicone flame retardants, metal hydroxides, etc. Specific examples of phosphazene compounds include "SPH-100", "SPS-100", "SPB-100", and "SPE-100" manufactured by Otsuka Chemical Co., Ltd., and "FP-100", "FP-110", "FP-300", and "FP-400" manufactured by Fushimi Pharmaceutical Co., Ltd. Commercially available flame retardants other than phosphazene compounds may be used, such as "HCA-HQ" manufactured by Sankosha and "PX-200" manufactured by Daihachi Chemical Industry Co., Ltd.

<Physical Properties of Resin Composition>
The cured product obtained by thermally curing the resin composition of the present invention at 130°C for 30 minutes and then at 165°C for 30 minutes exhibits excellent peel strength with a metal layer, particularly a plated conductor layer formed by plating, even when the surface of the cured product is subjected to a wet desmear treatment. That is, an insulating layer with excellent peel strength is obtained. The peel strength is preferably 0.1 kgf/cm or more, more preferably 0.2 kgf/cm or more, and even more preferably 0.3 kgf/cm or more. On the other hand, the upper limit of the peel strength is not particularly limited, but may be 1.5 kgf/cm or less. The peel strength can be evaluated by measuring the peel strength according to the method described in the examples below.

The resin composition of the present invention is thermally cured at 130°C for 30 minutes and then at 165°C for 30 minutes, and the surface of the cured product is subjected to a wet desmear treatment. The cured product exhibits the characteristic of having a low arithmetic mean roughness (Ra). That is, even if the wet desmear treatment is performed, an insulating layer having a low arithmetic mean roughness is obtained. The arithmetic mean roughness is preferably 450 nm or less, more preferably 400 nm or less, even more preferably 350 nm or less, even more preferably 330 nm or less, and particularly preferably 300 nm or less. On the other hand, the lower limit of the arithmetic mean roughness is not particularly limited, and may be 1 nm or more. The arithmetic mean roughness can be measured according to the method described in the examples below.

The resin composition is thermally cured at 190°C for 90 minutes, and the cured product exhibits the characteristic of a high relative magnetic permeability at a frequency of 100 MHz. The relative magnetic permeability at a frequency of 100 MHz is preferably greater than 1, more preferably 2 or more, and even more preferably 3 or more. It is also preferably 20 or less, more preferably 18 or less, and even more preferably 15 or less. The relative magnetic permeability can be measured according to the method described in the examples below.

The resin composition is thermally cured at 190°C for 90 minutes, and the cured product exhibits the characteristic of a low loss factor at a frequency of 100 MHz. The loss factor at a frequency of 100 MHz is preferably 0.07 or less, more preferably 0.06 or less, and even more preferably 0.05 or less. The lower limit is not particularly limited, but may be 0.0001 or more. The loss factor can be measured according to the method described in the examples below.

The cured product obtained by thermally curing the resin composition at 190° C. for 90 minutes exhibits the characteristic of a high resistance value. That is, an insulating layer with a high resistance value is obtained. The resistance value is preferably 1×10 ¹⁰ Ω or more, more preferably 3×10 ¹⁰ Ω or more, and even more preferably 5×10 ¹⁰ Ω or more. The upper limit is not particularly limited, but may be 1×10 ¹⁵ Ω or less.

[Resin sheet with support]
The support-attached resin sheet includes a support and a resin composition layer formed from the resin composition of the present invention provided on the support.

From the viewpoint of thinning, the thickness of the resin composition layer is preferably 250 μm or less, more preferably 200 μm or less, and even more preferably 150 μm or less, 100 μm or less, 80 μm or less, 60 μm or less, or 40 μm or less. The lower limit of the thickness of the resin composition layer is not particularly limited, but can usually be 5 μm or more, 10 μm or more, 20 μm or more, etc.

Examples of the support include films made of plastic materials, metal foils, and release paper, with films made of plastic materials and metal foils being preferred.

When a film made of a plastic material is used as the support, examples of the plastic material include polyesters such as polyethylene terephthalate (hereinafter sometimes abbreviated as "PET") and polyethylene naphthalate (hereinafter sometimes abbreviated as "PEN"), polycarbonate (hereinafter sometimes abbreviated as "PC"), acrylics such as polymethyl methacrylate (PMMA), cyclic polyolefins, triacetyl cellulose (TAC), polyether sulfide (PES), polyether ketone, polyimide, etc. Among these, polyethylene terephthalate and polyethylene naphthalate are preferred, with inexpensive polyethylene terephthalate being particularly preferred.

When a metal foil is used as the support, examples of the metal foil include copper foil and aluminum foil, with copper foil being preferred. As the copper foil, a foil made of a single metal, copper, or an alloy of copper and another metal (e.g., tin, chromium, silver, magnesium, nickel, zirconium, silicon, titanium, etc.) may be used.

The support may be matte-treated or corona-treated on the surface that is to be bonded to the resin composition layer.

As the support, a support with a release layer having a release layer on the surface to be bonded to the resin composition layer may be used. Examples of the release agent used in the release layer of the support with a release layer include one or more release agents selected from the group consisting of alkyd resins, polyolefin resins, urethane resins, and silicone resins. The support with a release layer may be a commercially available product, such as "SK-1", "AL-5", and "AL-7" manufactured by Lintec Corporation, "Lumirror T60" manufactured by Toray Industries, "Purex" manufactured by Teijin Limited, and "Unipeel" manufactured by Unitika Limited, which are PET films having a release layer mainly composed of an alkyd resin-based release agent.

The thickness of the support is not particularly limited, but is preferably in the range of 5 μm to 75 μm, and more preferably in the range of 10 μm to 60 μm. When using a support with a release layer, it is preferable that the thickness of the entire support with the release layer is in the above range.

In the resin sheet with a support, a protective film similar to the support can be further laminated on the surface of the resin composition layer that is not bonded to the support (i.e., the surface opposite the support). The thickness of the protective film is not particularly limited, but is, for example, 1 μm to 40 μm. By laminating the protective film, it is possible to suppress adhesion of dirt and scratches on the surface of the resin composition layer. The resin sheet can be wound up in a roll and stored. When the resin sheet with a support has a protective film, it can be used by peeling off the protective film.

[Inductor Substrate and Method for Manufacturing Inductor Substrate]
Hereinafter, the inductor substrate and its manufacturing method will be described through the manufacturing method of the inductor substrate.

Figure 5 is a schematic plan view of an inductor substrate incorporating an inductor element, viewed from one side in the thickness direction. Figure 6 is a schematic diagram showing a cut end surface of the inductor substrate cut at the position indicated by the dashed line II-II. Figure 7 is a schematic plan view for explaining the configuration of the first conductor layer of the inductor substrate.

The inductor substrate has an insulating layer (magnetic layer) that is a hardened resin composition (resin composition layer) and a conductive structure at least partially embedded in the insulating layer, and includes an inductor formed by the conductive structure and a portion of the insulating layer that extends in the thickness direction of the insulating layer and is surrounded by the conductive structure.

As shown in Figs. 5 and 6 as an example, the inductor substrate 10 is a build-up wiring board having multiple insulating layers (first insulating layer 32, second insulating layer 34) and multiple conductor layers (first conductor layer 42, second conductor layer 44), i.e., having build-up insulating layers and build-up conductor layers. The inductor substrate 10 also includes an inner layer substrate 20.

As shown in FIG. 6, the first insulating layer 32 and the second insulating layer 34 constitute the insulating section 30, which can be seen as an integrated insulating layer. Therefore, the coil-shaped conductive structure 40 is provided so that at least a portion of it is embedded in the insulating section 30. That is, in the inductor substrate 10 of this embodiment, the inductor element is constituted by the coil-shaped conductive structure 40 and a core portion that extends in the thickness direction of the insulating section 30 and is a portion of the insulating section 30 surrounded by the coil-shaped conductive structure 40.

As shown as an example in FIG. 7, the first conductor layer 42 includes a spiral wiring portion for forming the coil-shaped conductive structure 40, and a rectangular land 42a electrically connected to the through-hole wiring 22a. In the illustrated example, the spiral wiring portion includes a bent portion that bends at a right angle to a straight portion, and a detour portion that detours around the land 42a. In the illustrated example, the spiral wiring portion of the first conductor layer 42 has an overall outline that is approximately rectangular, and has a shape that winds counterclockwise from the center toward the outside.

Similarly, a second conductor layer 44 is provided on the first insulating layer 32. The second conductor layer 44 includes a spiral wiring portion for forming the coil-shaped conductive structure 40. In FIG. 5 or FIG. 6, the spiral wiring portion includes a straight portion and a bent portion that is bent at a right angle. In FIG. 5 or FIG. 6, the spiral wiring portion of the second conductor layer 44 has an overall outline that is approximately rectangular, and has a shape that is wound clockwise from the center toward the outside.

The inductor element of the inductor substrate of this embodiment is expected to function at frequencies between 10 MHz and 200 MHz. In addition, the inductor element of the inductor substrate of this embodiment is expected to be a power supply system.

The method for manufacturing the inductor substrate according to the present embodiment includes the steps of:
(A) a step of laminating a support-attached resin sheet including a support and a resin composition layer provided on the support onto an inner layer substrate such that the resin composition layer is bonded to the inner layer substrate;
(B) a step of thermally curing the resin composition layer to form an insulating layer;
(C) drilling holes in the insulating layer;
(D) performing a wet desmear treatment on the surface of the insulating layer using an oxidizing agent solution; and (E) forming a conductor layer on the surface of the insulating layer.
in this order. The method for producing an inductor substrate includes forming an insulating layer using the supported resin sheet of the present invention. The resin composition layer in the supported resin sheet of the present invention contains a magnetic filler that exhibits a weight loss rate of 0% or more and 40% or less when held in an acidic solution of pH 1 at 20°C for 3 hours, so that even if a wet desmear treatment using an oxidizing agent solution is performed, a decrease in adhesion between the insulating layer and the conductor layer is suppressed.

The step (A) may include a step of preparing a resin sheet with a support, the resin sheet including a support and a resin composition layer provided on the support. The support and the resin composition layer are as described above in [Resin sheet with support].

A resin sheet with a support can be produced, for example, by preparing a resin varnish by dissolving a resin composition in an organic solvent, applying this resin varnish onto a support using a die coater or the like, and then drying the varnish to form a resin composition layer.

Examples of organic solvents include ketones such as acetone, methyl ethyl ketone (MEK), and cyclohexanone; acetate esters such as ethyl acetate, butyl acetate, cellosolve acetate, propylene glycol monomethyl ether acetate, and carbitol acetate; carbitols such as cellosolve and butyl carbitol; aromatic hydrocarbons such as toluene and xylene; and amide solvents such as dimethylformamide, dimethylacetamide (DMAc), and N-methylpyrrolidone. The organic solvents may be used alone or in combination of two or more.

Drying may be performed by known methods such as heating or blowing hot air. There are no particular limitations on the drying conditions, but drying is performed so that the content of organic solvent in the resin composition layer is 10% by mass or less, preferably 5% by mass or less. Although it varies depending on the boiling point of the organic solvent in the resin varnish, for example, when using a resin varnish containing 30% by mass to 60% by mass of organic solvent, the resin composition layer can be formed by drying at 50°C to 150°C for 3 to 10 minutes.

<Step (A)>
In step (A), as shown in an example in Figure 1, a resin sheet 31 with a support, which includes a support 33 and a resin composition layer 32a provided on the support 33, is laminated onto an inner layer substrate 20 so that the resin composition layer 32a is bonded to the inner layer substrate 20.

The inner layer substrate 20 is an insulating substrate. Examples of materials for the inner layer substrate 20 include insulating substrates such as glass epoxy substrates, metal substrates, polyester substrates, polyimide substrates, BT resin substrates, and thermosetting polyphenylene ether substrates. The inner layer substrate 20 may be an inner layer circuit substrate having wiring and the like built into its thickness.

The inner layer substrate 20 may be, for example, a Panasonic R1515A glass cloth epoxy resin double-sided copper-clad laminate, with the copper layer patterned to form a conductor layer.

As shown in FIG. 1, the inner layer substrate 20 has a first conductor layer 42 provided on the first main surface 20a and an external terminal 24 provided on the second main surface 20b. The first conductor layer 42 includes a plurality of wirings. In the illustrated example, only the wirings constituting the coil-shaped conductive structure 40 of the inductor element are shown. The external terminal 24 is a terminal for electrically connecting to an external device or the like (not shown). The external terminal 24 can be configured as part of the conductor layer provided on the second main surface 20b.

Examples of conductor materials that can be used to form the first conductor layer 42, the external terminal 24, and other conductor layers include one or more metals selected from the group consisting of gold, platinum, palladium, silver, copper, aluminum, cobalt, chromium, zinc, nickel, titanium, tungsten, iron, tin, and indium. The first conductor layer 42, the external terminal 24, and other wiring may be made of a single metal or an alloy, and examples of the alloy include alloys of two or more metals selected from the above group (e.g., nickel-chromium alloy, copper-nickel alloy, and copper-titanium alloy). Among these, from the viewpoints of versatility, cost, ease of patterning, etc., it is preferable to use chromium, nickel, titanium, aluminum, zinc, gold, palladium, silver, or copper, or a nickel-chromium alloy, a copper-nickel alloy, or a copper-titanium alloy, and it is more preferable to use chromium, nickel, titanium, aluminum, zinc, gold, palladium, silver, or copper, or a nickel-chromium alloy, and it is even more preferable to use copper.

The first conductor layer 42, the external terminal 24, and other conductor layers may have a single-layer structure or a multi-layer structure in which two or more single metal layers or alloy layers made of different types of metals or alloys are laminated. When the first conductor layer 42, the external terminal 24, and other conductor layers have a multi-layer structure, the layer in contact with the insulating layer is preferably a single metal layer of chromium, zinc, or titanium, or an alloy layer of a nickel-chromium alloy.

The thickness of the first conductor layer 42, the external terminal 24, and other conductor layers depends on the desired design of the multilayer printed wiring board, but is generally 3 μm to 35 μm, preferably 5 μm to 30 μm.

The thickness of the first conductor layer 42 and the external terminal 24 of the inner layer substrate 20 is not particularly limited. From the viewpoint of thinning, the thickness of the first conductor layer 42 and the external terminal 24 is preferably 70 μm or less, more preferably 60 μm or less, even more preferably 50 μm or less, even more preferably 40 μm or less, and particularly preferably 30 μm or less, 20 μm or less, 15 μm or less, or 10 μm or less. The lower limit of the thickness of the external terminal 24 is not particularly limited, but is preferably 1 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more.

The line (L)/space (S) ratio of the first conductor layer 42 and the external terminal 24 is not particularly limited, but from the viewpoint of reducing surface irregularities and obtaining an insulating layer with excellent smoothness, it is usually 900/900 μm or less, preferably 700/700 μm or less, more preferably 500/500 μm or less, even more preferably 300/300 μm or less, and even more preferably 200/200 μm or less. There is no particular lower limit to the line/space ratio, but from the viewpoint of improving the embedding of the resin composition in the space, it is preferably 1/1 μm or more.

The inner layer substrate 20 has a plurality of through holes 22 penetrating the inner layer substrate 20 from the first main surface 20a to the second main surface 20b. The through holes 22 are provided with through-hole wiring 22a. The through-hole wiring 22a electrically connects the first conductor layer 42 and the external terminal 24.

The resin composition layer 32a and the inner layer substrate 20 can be bonded, for example, by heat-pressing the support-attached resin sheet 31 to the inner layer substrate 20 from the support 33 side. Examples of the member for heat-pressing the support-attached resin sheet 31 to the inner layer substrate 20 (hereinafter also referred to as the "heat-pressing member") include a heated metal plate (such as a stainless steel (SUS) plate) or a metal roll (SUS roll). It is preferable to press the support-attached resin sheet 31 through a sheet made of an elastic material such as heat-resistant rubber so that the support-attached resin sheet 31 can sufficiently follow the unevenness of the surface of the inner layer substrate 20, rather than pressing the support-attached resin sheet 31 in direct contact with the heat-pressing member.

The temperature during heat-pressure bonding is preferably in the range of 80°C to 160°C, more preferably 90°C to 140°C, and even more preferably 100°C to 120°C, the pressure during heat-pressure bonding is preferably in the range of 0.098MPa to 1.77MPa, more preferably 0.29MPa to 1.47MPa, and the time during heat-pressure bonding is preferably in the range of 20 seconds to 400 seconds, and more preferably 30 seconds to 300 seconds. The bonding of the resin sheet with support and the inner layer substrate is preferably performed under reduced pressure conditions of 26.7hPa or less.

The resin composition layer 32a of the support-attached resin sheet 31 can be bonded to the inner layer substrate 20 by a commercially available vacuum laminator. Examples of commercially available vacuum laminators include a vacuum pressure laminator manufactured by Meiki Seisakusho Co., Ltd. and a vacuum applicator manufactured by Nikko Materials Co., Ltd.

After bonding the resin sheet 31 with the support and the inner layer substrate 20, the laminated resin sheet 31 with the support may be smoothed under normal pressure (atmospheric pressure), for example by pressing a thermocompression member from the support side. The pressing conditions for the smoothing treatment may be the same as the thermocompression conditions for the lamination. The smoothing treatment may be performed using a commercially available laminator. Note that the lamination and smoothing treatment may be performed consecutively using the commercially available vacuum laminator described above.

<Step (B)>
2, the resin composition layer 32a bonded to the inner layer substrate 20 is thermally cured to form the first insulating layer 32. The conditions for the thermal curing step are not particularly limited, and conditions that are typically employed when forming an insulating layer for a multilayer printed wiring board can be applied.

The first insulating layer 32 is formed using the resin sheet 31 with a support as already described, and therefore has excellent sealing properties for the first conductor layer 42. In addition, since the first insulating layer 32 is formed using the resin sheet 31 with a support, the relative permeability is improved in the frequency range of 10 MHz to 200 MHz, and furthermore, magnetic loss is usually reduced.

For example, the thermal curing conditions for the resin composition layer 32a vary depending on the type of resin composition, but the curing temperature is preferably 120°C to 240°C, more preferably 150°C to 220°C, and even more preferably 170°C to 190°C. The curing time is preferably 5 minutes to 90 minutes, more preferably 10 minutes to 75 minutes, and even more preferably 15 minutes to 60 minutes.

Before the resin composition layer 32a is thermally cured, the resin composition layer 32a may be preheated at a temperature lower than the curing temperature. For example, prior to thermally curing the resin composition layer 32a, the resin composition layer 32a may be preheated for 5 minutes or more (preferably 5 minutes to 150 minutes, more preferably 15 minutes to 120 minutes) at a temperature of 50°C or more and less than 120°C (preferably 60°C or more and 110°C or less, more preferably 70°C or more and 110°C or less). Preheating is preferably performed under atmospheric pressure (normal pressure).

The support 33 may be removed between steps (B) and (C), or may be peeled off after step (C).

<Step (C)>
In step (C), as shown in FIG. 3, the first insulating layer 32 is drilled to form a via hole 36. The via hole 36 serves as a path for electrically connecting the first conductor layer 42 and the second conductor layer 44 described later. The via hole 36 can be formed by a method using a drill, a laser, plasma, or the like, taking into consideration the characteristics of the first insulating layer 32. However, from the viewpoints of the small diameter and high accuracy of holes associated with the high density of printed wiring boards, and the versatility of processing equipment, it is preferable to perform the drilling process using a laser. For example, if the support (not shown) of the resin sheet with support remains at this point, the via hole 36 can also be formed by irradiating the first insulating layer 32 with a laser beam through the support.

Examples of laser light sources that can be used to form the via hole 36 include carbon dioxide lasers, YAG lasers, and excimer lasers. Among these, carbon dioxide lasers are preferred from the standpoint of processing speed and cost.

The via hole 36 can be formed using a commercially available laser device. Examples of commercially available carbon dioxide gas laser devices include the "LC-2E21B/1C" manufactured by Hitachi Via Mechanics, the "ML605GTWII" manufactured by Mitsubishi Electric, and a board drilling laser processing machine manufactured by Matsushita Welding Systems.

<Step (D)>
In step (D), the surface of the first insulating layer is subjected to a wet desmear treatment using an oxidizing agent solution. Conventionally, the magnetic filler contained in the insulating layer is dissolved by the oxidizing agent solution, and the peel strength between the first insulating layer and the second conductor layer 44 is reduced, so that the surface of the insulating layer is usually roughened by dry sputtering. However, in the present invention, the magnetic filler whose weight loss rate is 0% or more and 40% or less when held in an acidic solution of pH 1 at 20° C. for 3 hours is contained in the insulating layer, so that even if a wet desmear treatment using an oxidizing agent solution is performed, the peel strength can be prevented from decreasing. As a result, it is possible to manufacture a large-area inductor substrate.

The procedure and conditions for the wet desmear treatment are not particularly limited, and procedures and conditions that are normally used in the manufacturing method of multilayer printed wiring boards can be adopted. For example, the wet desmear treatment includes a swelling treatment using a swelling liquid, a roughening treatment using an oxidizing agent solution, and a neutralization treatment using a neutralizing liquid, in that order.

The swelling liquid that can be used in the wet desmear treatment is not particularly limited, but includes an alkaline solution, a surfactant solution, etc., and is preferably an alkaline solution. As the alkaline solution that is the swelling liquid, a sodium hydroxide solution or a potassium hydroxide solution is more preferable. Examples of commercially available swelling liquids include "Swelling Dip Securigans P" and "Swelling Dip Securigans SBU" manufactured by Atotech Japan.

The swelling treatment using the swelling liquid is not particularly limited, but can be carried out, for example, by immersing the inner layer substrate on which the insulating layer is provided in a swelling liquid at 30°C to 90°C for 1 to 20 minutes. From the viewpoint of suppressing the swelling of the resin constituting the insulating layer to an appropriate level, it is preferable to immerse the insulating layer in a swelling liquid at 40°C to 80°C for 5 to 15 minutes.

The oxidizing agent solution that can be used for the roughening treatment with an oxidizing agent solution is not particularly limited, but examples thereof include alkaline permanganate solutions in which potassium permanganate or sodium permanganate is dissolved in an aqueous solution of sodium hydroxide. Roughening treatment with an oxidizing agent such as an alkaline permanganate solution is preferably performed by immersing the insulating layer in an oxidizing agent solution heated to 60°C to 80°C for 10 to 30 minutes. The concentration of permanganate in the alkaline permanganate solution is preferably 5% by mass to 10% by mass. Examples of commercially available oxidizing agent solutions include alkaline permanganate solutions such as "Concentrate Compact P" and "Dosing Solution Securigans P" manufactured by Atotech Japan.

The neutralizing solution that can be used for the neutralization treatment is preferably an acidic aqueous solution, and a commercially available product is, for example, "Reduction Solution Securigans P" manufactured by Atotech Japan. Neutralization treatment with a neutralizing solution can be performed by immersing the treated surface that has been roughened with an oxidizing solution in a neutralizing solution at 30°C to 80°C for 5 to 30 minutes. From the viewpoint of workability, etc., a method in which the insulating layer that has been roughened with an oxidizing solution is immersed in a neutralizing solution at 40°C to 70°C for 5 to 20 minutes is preferred.

In one embodiment, the arithmetic mean roughness (Ra) of the insulating layer surface after step (D) is preferably 450 nm or less, more preferably 400 nm or less, even more preferably 350 nm or less, and even more preferably 330 nm or less. There is no particular limit to the lower limit, but it can be preferably 1 nm or more. The arithmetic mean roughness can be measured according to the method described in the examples below.

<Step (E)>
4, a second conductor layer 44 is formed on the surface of the first insulating layer 32 that has been subjected to the wet desmear treatment. The second conductor layer 44 includes a plurality of wirings.

The conductive material that may constitute the second conductor layer 44 is the same as that of the first conductor layer 42. The second conductor layer 44 may have a single-layer structure or a multi-layer structure in which two or more single metal layers or alloy layers made of different types of metals or alloys are laminated. When the second conductor layer 44 has a multi-layer structure, the layer in contact with the insulating layer is preferably a single metal layer of chromium, zinc, or titanium, or an alloy layer of a nickel-chromium alloy. The thickness of the second conductor layer 44 is the same as that of the first conductor layer 42.

The second conductor layer 44 can be formed by plating. The second conductor layer 44 is preferably formed by a wet plating method such as a semi-additive method or a full-additive method including an electroless plating process, a mask pattern formation process, an electrolytic plating process, and a flash etching process. By forming the second conductor layer 44 using a wet plating method, it is possible to form the second conductor layer 44 including the desired wiring pattern. Note that this process also forms the via hole wiring 36a in the via hole 36.

One end of the spiral wiring portion of the second conductor layer 44 on the central side is electrically connected to one end of the spiral wiring portion of the first conductor layer 42 on the central side by the via-hole wiring 36a. The other end of the spiral wiring portion of the second conductor layer 44 on the outer periphery is electrically connected to the land 42a of the first conductor layer 42 by the via-hole wiring 36a. Therefore, the other end of the spiral wiring portion of the second conductor layer 44 on the outer periphery is electrically connected to the external terminal 24 via the via-hole wiring 36a, the land 42a, and the through-hole wiring 22a.

The coil-shaped conductive structure 40 is composed of a spiral wiring portion that is part of the first conductor layer 42, a spiral wiring portion that is part of the second conductor layer 44, and via-hole wiring 36a that electrically connects the spiral wiring portion of the first conductor layer 42 and the spiral wiring portion of the second conductor layer 44.

Next, as shown in FIG. 6, the second insulating layer 34 is formed on the first insulating layer 32 on which the second conductor layer 44 and the via hole wiring 36a are formed. The second insulating layer 34 may be formed by a process similar to that already described.

The second insulating layer 34, like the first insulating layer 32, is a layer derived from a resin sheet with a support, and therefore has excellent sealing properties for the second conductor layer 44. In addition, since the second insulating layer 34 is formed using a resin sheet with a support, it usually has improved relative magnetic permeability and also usually has reduced magnetic loss.

In the inductor substrate 10 of the present invention, an inductor is formed by a plurality of insulating layers and a plurality of conductor layers. Therefore, the insulating layers are build-up insulating layers, and the conductor layers are build-up conductor layers. In the inductor substrate 10 of this embodiment, the series of steps already described from step (A) to step (E) may be repeated one or more times.

In this embodiment, an example has been described in which the coil-shaped conductive structure 40 includes two conductor layers, the first conductor layer 42 and the second conductor layer 44, but the coil-shaped conductive structure 40 can also be configured with three or more conductor layers (and three or more build-up insulating layers). In this case, the spiral wiring portion of the conductor layer (not shown) that is arranged so as to be sandwiched between the topmost conductor layer and the bottommost conductor layer has one end electrically connected to one of the ends of the spiral wiring portion of the conductor layer that is arranged closest to the topmost layer side, and the other end electrically connected to one of the ends of the spiral wiring portion of the conductor layer that is arranged closest to the bottommost layer side.

The inductor substrate according to this embodiment can be used as a wiring board for mounting electronic components such as semiconductor chips, and can also be used as a (multilayer) printed wiring board using such a wiring board as an inner layer substrate. In addition, such a wiring board can also be used as an individualized chip inductor component, and can also be used as a printed wiring board with the chip inductor component surface mounted.

In addition, if the printed wiring board has a cavity, the inductor substrate according to this embodiment may be embedded in the cavity, forming a printed wiring board with an embedded inductor substrate. For details of such a wiring board, refer to paragraphs 0011 to 0164 of Japanese Patent Application Laid-Open No. 2012-186440, the contents of which are incorporated herein by reference.

In addition, various types of semiconductor devices can be manufactured using such wiring boards. Semiconductor devices including such wiring boards can be suitably used in electrical products (e.g., computers, mobile phones, digital cameras, and televisions) and vehicles (e.g., motorcycles, automobiles, trains, ships, and aircraft).

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. In the following description, the terms "parts" and "%" used to indicate amounts refer to "parts by mass" and "% by mass", respectively, unless otherwise specified. The weight loss rate was measured by immersing the magnetic filler in a 5% by mass aqueous solution of sulfuric acid at pH 1, and then drying the magnetic filler.

[Measurement of peel strength and arithmetic mean roughness (Ra value)]
(1) Undercoat treatment of inner layer circuit board Both sides of a glass cloth-based epoxy resin double-sided copper-clad laminate (copper foil thickness 18 μm, substrate thickness 0.8 mm, Panasonic Corporation, R1515A) on which an inner layer circuit was formed were etched by 1 μm with an etching agent (MEC Corporation, CZ8101) to roughen the copper surface.

(2) Lamination of Resin Sheet with Support The resin sheet with support prepared in the Examples and Comparative Examples was laminated on both sides of a laminate using a batch type vacuum pressure laminator (MVLP-500, manufactured by Meiki Seisakusho Co., Ltd.) The lamination was performed by reducing the pressure for 30 seconds to 13 hPa or less, and then pressing for 30 seconds at 100°C and a pressure of 0.74 MPa.

(3) Curing of Resin Composition Layer The resin composition layer of the laminated resin sheet with the support was cured at 130° C. for 30 minutes and then at 165° C. for 30 minutes to form an insulating layer, and then the support was peeled off.

(4) Wet desmear treatment (roughening treatment)
For Examples 1 to 3, 5, and Comparative Example 1, the insulating layer surface of the laminate was immersed in a swelling liquid, Swelling Dip Securigant P (glycol ethers, aqueous solution of sodium hydroxide) made by Atotech Japan, which contains diethylene glycol monobutyl ether, at 60° C. for 5 minutes. Next, the laminate was immersed in a roughening liquid, Concentrate Compact P (aqueous solution of KMnO ₄ : 60 g/L, NaOH: 40 g/L) made by Atotech Japan, at 80° C. for 20 minutes. Finally, the laminate was immersed in a neutralizing liquid, Reduction Solution Securigant P (aqueous solution of sulfuric acid) made by Atotech Japan, at 40° C. for 5 minutes. Then, the laminate was dried at 80° C. for 30 minutes. The laminate after the roughening treatment is called Laminate A.

For Example 4, the insulating layer surface of the laminate was immersed in a swelling liquid, Swelling Dip Securigant P (glycol ethers, aqueous solution of sodium hydroxide) containing diethylene glycol monobutyl ether manufactured by Atotech Japan, at 60° C. for 3 minutes. Next, the laminate was immersed in a roughening liquid, Concentrate Compact P (aqueous solution of KMnO ₄ : 60 g/L, NaOH: 40 g/L) manufactured by Atotech Japan, at 80° C. for 10 minutes. Finally, the laminate was immersed in a neutralizing liquid, Reduction Solution Securigant P (aqueous solution of sulfuric acid) manufactured by Atotech Japan, at 40° C. for 5 minutes. Then, the laminate was dried at 80° C. for 30 minutes. The laminate after the roughening treatment is called Laminate A.

(5) Plating by semi-additive process The laminate A was immersed in an electroless plating solution containing _PdCl2 at 40 ° C for 5 minutes, and then immersed in an electroless copper plating solution at 25 ° C for 20 minutes. After heating at 150 ° C for 30 minutes to perform annealing treatment, an etching resist was formed, and after pattern formation by etching, copper sulfate electroplating was performed to form a conductor layer with a thickness of 25 μm. Next, annealing treatment was performed at 180 ° C for 60 minutes. This substrate was used as an evaluation substrate.

(6) Measurement of peel strength of plated conductor layer A cut was made in the conductor layer of the evaluation board, measuring 10 mm in width and 100 mm in length, and one end of the cut was peeled off and held with an Autocom type testing machine (manufactured by TSE, AC-50C-SL) as a gripping jig. The load (kgf/cm) when 35 mm was peeled off vertically at a speed of 50 mm/min at room temperature was measured. If the evaluation board blistered and the peel strength could not be measured, this was recorded as blister in the table below.

(7) Measurement of arithmetic mean roughness (Ra value) The Ra value of the laminate A that had been subjected to the wet desmearing process was determined using a non-contact surface roughness meter (WYKO NT3300 manufactured by B-CO Instruments) in VSI contact mode with a 50x lens over a measurement range of 121 μm×92 μm. The Ra value was determined by calculating the average value of three randomly selected points.

[Method of measuring relative permeability and permeability loss]
In each of the Examples and Comparative Examples, the release-treated polyethylene terephthalate film ("AL5" manufactured by Lintec Corporation, thickness 38 μm) was replaced with a PET film ("Fluorouge RL50KSE" manufactured by Mitsubishi Plastics, Inc.) treated with a fluororesin-based release agent (ETFE). Each resin sheet with a support was obtained in the same manner as in each of the Examples and Comparative Examples, except for the above points.

The obtained resin sheet with the support was heated at 190°C for 90 minutes to heat-cure the resin composition layer, and the support was peeled off to obtain a sheet-like cured body. The obtained cured body was cut into a test piece with a width of 5 mm and a length of 18 mm to be used as an evaluation sample. The evaluation sample was measured for relative permeability (μ') and permeability loss (μ'') at room temperature of 23°C using a short-circuit strip line method with a measurement frequency ranging from 1 MHz to 10 GHz using an Agilent Technologies "HP8362B", and the loss factor was obtained. The loss factor was calculated from the following formula.
tan δ=μ′/μ″
The magnetic permeability and loss factor when the measurement frequency is 100 MHz are shown in the table below.

[Resistance measurement]
Each of the resin sheets with a support obtained in each Example and Comparative Example was laminated on the wiring pattern side of a polyimide film having a thickness of 38 μm, in which the width of the line and space was set to L (line) / S (space) = 20 μm / 20 μm, the circuit (wiring pattern) was 8 μm thick, and a comb-shaped wiring pattern was formed. The support was peeled off from the resin sheet with a support formed by this lamination, and the insulating layer was formed by heat treatment at 190 ° C. for 90 minutes to heat cure the laminated structure. The obtained laminated structure was used as an evaluation sample. The resistance value was measured by applying a voltage of 3.3 V to the obtained evaluation sample. The average value was calculated from the obtained resistance values at seven points.

<Production Example 1: Preparation of magnetic filler>
300 g of magnetic powder (Epson Atmix "AW2-08PF3F", Fe-Cr-Si alloy (amorphous), average particle size 3.0 μm, specific gravity 7.0 g/cm ³ ) serving as core particles was placed in a 3-liter separable flask, and 1,400 g of mineral spirits was added and stirred to form a slurry. With continued stirring, nitrogen gas was purged into the system to create a nitrogen atmosphere, and the temperature was then raised to 80°C. The following operations were carried out while maintaining these conditions unless otherwise specified.

Next, 0.90 g of acrylic acid, 8.40 g of trimethylolpropane triacrylate, 7.90 g of tricyclodecane dimethanol dimethacrylate, and 1.0 g of azobisisobutyronitrile (AIBN) were added to the above slurry.

Then, stirring was continued for 8 hours to carry out the radical polymerization reaction. After that, the slurry was cooled to below 35°C to terminate the reaction, and then filtered and washed with 1 liter of mineral spirits to obtain a magnetic filler (core-shell structure magnetic filler A) in which an acrylic resin was formed as a coating layer on the surface of the magnetic powder. The core-shell structure magnetic filler A was a magnetic powder coated with a coating layer 120 nm thick.

When 1 g of the core-shell structured magnetic filler A was immersed in 50 g of a 5 mass % sulfuric acid aqueous solution of pH 1 at 20° C. for 3 hours, the weight loss rate was 5%. On the other hand, when 1 g of magnetic powder ("AW2-08PF3F" manufactured by Epson Atmix, Fe-Cr-Si alloy (amorphous), average particle size 3.0 μm, specific gravity 7.0 g/cm ³ ) was immersed in 50 g of a 5 mass % sulfuric acid aqueous solution of pH 1 at 20° C. for 3 hours, the weight loss rate was 100%.

<Production Example 2: Preparation of magnetic filler>
In Production Example 1,
1) The amount of acrylic acid was changed from 0.90 g to 0.45 g.
2) The amount of trimethylolpropane triacrylate was changed from 8.40 g to 4.20 g.
3) The amount of tricyclodecane dimethanol dimethacrylate was changed from 7.90 g to 3.95 g;
4) The amount of azobisisobutyronitrile (AIBN) was changed from 1.0 g to 0.50 g.
A core-shell structured magnetic filler B was produced in the same manner as in Production Example 1 except for the above points.

The core-shell structure magnetic filler B was a magnetic powder coated with a coating layer having a thickness of 60 nm. When 1 g of the core-shell structure magnetic filler B was immersed in 50 g of a 5% by weight aqueous sulfuric acid solution with a pH of 1 at 20°C for 3 hours, the weight loss rate was 8%.

<Production Example 3: Preparation of magnetic filler>
100 g of magnetic powder (Epson Atmix "AW2-08PF3F", Fe-Cr-Si alloy (amorphous), average particle size 3.0 μm, specific gravity 7.0 g/cm ³ ) was added as core particles to a 500 mL three-neck flask, 60 ml of ethanol was added, and ultrasonic dispersion was performed for 53 minutes. A nitrogen flow (60 ml/min) and a cooling tube were attached to the three-neck flask, and a mixed solution of 20 ml of ethanol and ammonia water (16 mass% ammonia water consisting of 23.7 g of water and 4.59 g of ammonia) was added, and the mixture was stirred at 300 rpm in an oil bath at 25 ° C. for 1 hour. Tetraethyl orthosilicate (5.6 g) diluted with 300 mL of ethanol was added using a dropping funnel, and the mixture was reacted at 25 ° C. for 3 hours while stirring at 500 rpm with a forced stirrer. 100 ml of methanol was added to stop the reaction. The particles were washed twice with ethanol, dried, and then treated with 1.0 g of a silane coupling agent (3-glycidoxypropyltrimethoxysilane, "KBM-403" manufactured by Shin-Etsu Chemical Co., Ltd.) to obtain a core-shell structure magnetic filler C in which silicic acid was formed as a coating layer on the surfaces of the magnetic core particles. The core-shell structure magnetic filler C was a particle powder coated with a coating layer having a thickness of 20 nm and treated with a silane coupling agent. When 1 g of the core-shell structure magnetic filler C was immersed in 50 g of a 5% by mass aqueous sulfuric acid solution with a pH of 1 at 20° C. for 3 hours, the weight loss rate was 35%.

Example 1
Three parts of a bisphenol A type epoxy resin ("828US" manufactured by Mitsubishi Chemical Corporation, epoxy equivalent: approximately 180), 10 parts of a biphenyl type epoxy resin ("NC3000L" manufactured by Nippon Kayaku Co., Ltd., epoxy equivalent: approximately 269), 2 parts of a naphthalene type epoxy resin ("HP-4032" manufactured by DIC Corporation, epoxy equivalent: approximately 150), and 4.4 parts of a phenoxy resin ("YL7553BH30" manufactured by Mitsubishi Chemical Corporation, a 1:1 solution of MEK and cyclohexanone with a solids content of 30%) were heated and dissolved in 8 parts of methyl ethyl ketone with stirring. After cooling to room temperature, 2 parts of a triazine skeleton-containing phenolic curing agent (DIC Corporation's "LA-3018-50P", a 2-methoxypropanol solution with a solid content of 50% and a hydroxyl group equivalent of about 151), 5 parts of an active ester type curing agent (DIC Corporation's "HPC8000-65T", a toluene solution with a solid content of 65% and an active group equivalent of about 223), 2.5 parts of a carbodiimide compound (Nisshinbo Chemical Corporation's "V-03", a toluene solution with a solid content of 50%), 0.4 parts of a curing accelerator (Wako Pure Chemical Industries, Ltd.'s "4-dimethylaminopyridine (DMAP)", a MEK solution with a solid content of 10%), and 89 parts of the core-shell structure magnetic filler A prepared in Production Example 1 were mixed therein and uniformly dispersed using a high-speed rotating mixer to prepare resin varnish 1.

Next, resin varnish 1 was evenly applied onto the release surface of a release-treated polyethylene terephthalate film ("AL5" manufactured by Lintec Corporation, thickness 38 μm) so that the thickness of the resin composition layer after drying would be 35 μm, and the film was dried at 75 to 92°C (average 83°C) for 3 minutes to produce a resin sheet 1 with a support.

Example 2
5.25 parts of a bisphenol A type epoxy resin ("828US" manufactured by Mitsubishi Chemical Corporation, epoxy equivalent: about 180), 5.25 parts of a biphenyl type epoxy resin ("NC3000L" manufactured by Nippon Kayaku Co., Ltd., epoxy equivalent: about 269), and 3.3 parts of a phenoxy resin ("YL7553BH30" manufactured by Mitsubishi Chemical Corporation, a 1:1 solution of MEK and cyclohexanone with a solid content of 30%) were heated and dissolved in 8 parts of methyl ethyl ketone with stirring. After cooling to room temperature, 1.5 parts of a triazine skeleton-containing phenolic curing agent (DIC Corporation's "LA-3018-50P", a 2-methoxypropanol solution with a solid content of 50% and a hydroxyl group equivalent of about 151), 3.75 parts of an active ester type curing agent (DIC Corporation's "HPC8000-65T", a toluene solution with a solid content of 65% and an active group equivalent of about 223), 2 parts of a carbodiimide compound (Nisshinbo Chemical Corporation's "V-03", a toluene solution with a solid content of 50%), 0.3 parts of a curing accelerator (Wako Pure Chemical Industries, Ltd.'s "4-dimethylaminopyridine (DMAP)", a MEK solution with a solid content of 10%), and 103 parts of the core-shell structure magnetic filler A prepared in Production Example 1 were mixed therein and uniformly dispersed using a high-speed rotating mixer to prepare resin varnish 2.

In Example 1, Resin Varnish 1 was changed to Resin Varnish 2. Other than the above, Resin Sheet 2 with Support was produced in the same manner as in Example 1.

Example 3
In Example 2, 103 parts of the core-shell structured magnetic filler A was changed to 103 parts of the core-shell structured magnetic filler B. Except for the above, a resin varnish 3 and a resin sheet 3 with a support were prepared in the same manner as in Example 2.

Example 4
In Example 2, 103 parts of the core-shell structured magnetic filler A was changed to 103 parts of the core-shell structured magnetic filler C. Except for the above, resin varnish 4 and resin sheet with support 4 were prepared in the same manner as in Example 2.

Example 5
Six parts of a bisphenol A type epoxy resin ("828US" manufactured by Mitsubishi Chemical Corporation, epoxy equivalent: about 180), three parts of a biphenyl type epoxy resin ("NC3000L" manufactured by Nippon Kayaku Co., Ltd., epoxy equivalent: about 269), one part of a biphenyl type epoxy resin ("YX4000HK" manufactured by Mitsubishi Chemical Corporation, epoxy equivalent: about 193), and 3.3 parts of a phenoxy resin ("YL7553BH30" manufactured by Mitsubishi Chemical Corporation, a 1:1 solution of MEK and cyclohexanone with a solids content of 30%) were heated and dissolved in 8 parts of methyl ethyl ketone with stirring. After cooling to room temperature, 3 parts of a triazine skeleton-containing phenolic curing agent (DIC Corporation's "LA-3018-50P", a 2-methoxypropanol solution with a solid content of 50% and a hydroxyl group equivalent of approximately 151), 4 parts of an active ester type curing agent (DIC Corporation's "HPC8000-65T", a toluene solution with a solid content of 65% and an active group equivalent of approximately 223), 0.3 parts of a curing accelerator (Wako Pure Chemical Industries, Ltd.'s "4-dimethylaminopyridine (DMAP)", a MEK solution with a solid content of 10%), and 103 parts of core-shell structure magnetic filler A were mixed and uniformly dispersed using a high-speed rotating mixer to prepare resin varnish 5.

In Example 1, Resin Varnish 1 was changed to Resin Varnish 5. Apart from the above, Resin Sheet 5 with Support was produced in the same manner as in Example 1.

<Comparative Example 1>
In Example 2, 103 parts of the core-shell structure magnetic filler A was changed to 103 parts of magnetic powder (Epson Atmix "AW2-08PF3F", average particle size 3.0 μm, specific gravity 7.0 g/cm ³ ). Aside from the above, a resin varnish 6 and a resin sheet with a support 6 were prepared in the same manner as in Example 2.

The results of the above-mentioned Examples and Comparative Examples are shown in the following table. In the table, the meanings of the abbreviations are as follows.
828US: Bisphenol A type epoxy resin (manufactured by Mitsubishi Chemical Corporation, epoxy equivalent: approximately 180)
NC3000L: Biphenyl type epoxy resin (manufactured by Nippon Kayaku Co., Ltd., epoxy equivalent: approximately 269)
YX4000HK: Biphenyl type epoxy resin (manufactured by Mitsubishi Chemical Corporation, epoxy equivalent weight: approx. 193)
HP-4032: Naphthalene type epoxy resin (DIC Corporation, epoxy equivalent: approx. 150)
LA-3018-50P: Triazine skeleton-containing phenolic curing agent (DIC Corporation, 2-methoxypropanol solution with a solid content of 50% and a hydroxyl equivalent of approximately 151)
HPC-8000-65T: Active ester curing agent (manufactured by DIC Corporation, toluene solution with a solid content of 65% and an active group equivalent of approximately 223)
V-03: Carbodiimide compound (manufactured by Nisshinbo Chemical Co., Ltd., toluene solution with 50% solids)
YL7553BH30: Phenoxy resin (manufactured by Mitsubishi Chemical Corporation, 1:1 solution of MEK with 30% solids and cyclohexanone)
DMAP: Amine-based curing accelerator ("4-dimethylaminopyridine" manufactured by Wako Pure Chemical Industries, Ltd., MEK solution with 10% solids)
AW2-08PF3F: magnetic powder (manufactured by Epson Atmix, average particle size 3.0 μm, specific gravity 7.0 g/cm ³ )

Reference Signs List 10 Inductor substrate 20 Inner layer substrate 20a First main surface 20b Second main surface 22 Through hole 22a Through hole internal wiring 24 External terminal 30 Magnetic portion 31 Resin sheet with support 32a Resin composition layer 32 First insulating layer 33 Support 34 Second insulating layer 36 Via hole 36a Via hole internal wiring 40 Coil-shaped conductive structure 42 First conductor layer 42a Land 44 Second conductor layer

Claims (19)

(A) a step of laminating a support-attached resin sheet including a support and a resin composition layer provided on the support onto an inner layer substrate such that the resin composition layer is bonded to the inner layer substrate;
(B) a step of thermally curing the resin composition layer to form an insulating layer;
(C) drilling holes in the insulating layer;
(D) performing a wet desmear treatment on the surface of the insulating layer using an oxidizing agent solution; and (E) forming a conductor layer on the surface of the insulating layer that has been subjected to the wet desmear treatment.
A method for manufacturing an inductor substrate, in which an inductor is formed by a plurality of insulating layers and a plurality of conductor layers, comprising the steps of:
the resin composition layer is formed from a resin composition containing a magnetic filler and a carbodiimide compound ;
the magnetic filler has a magnetic powder and a coating layer that coats the magnetic powder,
The coating layer is at least one of an acrylic resin and a silicon oxide compound,
A method for manufacturing an inductor substrate, in which the weight loss rate of a magnetic filler is 0% or more and 40% or less when held in an acidic solution of pH 1 at 20° C. for 3 hours. The method for manufacturing an inductor substrate according to claim 1, wherein the content of the magnetic filler is 30% by mass or more and 95% by mass or less, assuming that the non-volatile components in the resin composition are 100% by mass. The method for manufacturing an inductor substrate according to claim 1 or 2, wherein the content of the magnetic filler is 60% by mass or more and 95% by mass or less, assuming that the non-volatile components in the resin composition are 100% by mass. The method for manufacturing an inductor substrate according to any one of claims 1 to 3, wherein the resin composition contains an epoxy resin. The method for manufacturing an inductor substrate according to claim 4, wherein the content of the epoxy resin is 1% by mass or more and 40% by mass or less, assuming that the non-volatile components of the resin composition are 100% by mass. The method for manufacturing an inductor substrate according to any one of claims 1 to 5, wherein the resin composition contains an active ester compound. The method for producing an inductor substrate according to claim 6, wherein the content of the active ester compound is 1% by mass or more and 40% by mass or less, assuming that the non-volatile components in the resin composition are 100% by mass. The method for manufacturing an inductor substrate according to any one of claims 1 to 7, wherein the resin composition contains a thermoplastic resin. The method for manufacturing an inductor substrate according to claim 8, wherein the content of the thermoplastic resin is 0.1% by mass or more and 20% by mass or less, assuming that the non-volatile content in the resin composition is 100% by mass. The method for manufacturing an inductor substrate according to any one of claims 1 to 9, wherein the support is peeled off between steps (B) and (C) or after step (C). The method for manufacturing an inductor substrate according to any one of claims 1 to 10, wherein step (C) involves performing hole drilling using a laser. The method for manufacturing an inductor substrate according to any one of claims 1 to 11, wherein step (E) is performed by a wet plating method. The method for manufacturing an inductor substrate according to any one of claims 1 to 12, wherein the average particle size of the magnetic filler is 0.01 μm or more and 8 μm or less. The method for manufacturing an inductor substrate according to any one of claims 1 to 13, wherein the aspect ratio of the magnetic filler is 2 or less. The method for manufacturing an inductor substrate according to any one of claims 1 to 14, wherein the magnetic filler includes an Fe alloy containing one or more elements selected from Si, Al, and Cr. The method for manufacturing an inductor substrate according to any one of claims 1 to 15, wherein the insulating layer has a relative permeability of greater than 1 at a frequency of 100 MHz . The method for manufacturing an inductor substrate according to any one of claims 1 to 16, wherein the insulating layer has a loss factor of 0.07 or less at a frequency of 100 MHz . The magnetic filler and the carbodiimide compound have a weight loss rate of 0% or more and 40% or less when held at 20°C for 3 hours in an acidic solution of pH 1, and are used for forming an insulating layer of an inductor substrate in which an inductor is formed by a plurality of insulating layers and a plurality of conductor layers,
the magnetic filler has a magnetic powder and a coating layer that coats the magnetic powder,
The resin composition, wherein the coating layer is at least one of an acrylic resin and a silicon acid compound. A resin sheet with a support, comprising a support and a resin composition layer formed from the resin composition according to claim 18 provided on the support.

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