Magnetic paste

Abstract

To provide, e.g., a low-viscosity magnetic paste capable of forming a cured product with high relative permeability and low magnetic loss.SOLUTION: A magnetic paste for inductor substrate formation using compression molding comprises (A) a magnetic powder and (B) a liquid epoxy resin represented by the general formula (1) in the figure, where R represents a hydrogen atom or methyl group.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a magnetic paste, a circuit board and an inductor board using the magnetic paste, and a method for manufacturing a circuit board. [Background technology]

[0002] Inductor substrates, which may be included in circuit boards such as printed wiring boards, are formed using a resin composition containing magnetic powder. Inductor substrates are formed by processing the resin composition containing magnetic powder using methods such as printing and pressing. The pressing method allows for high density of magnetic powder, and is therefore one of the methods for improving the performance of inductor substrates.

[0003] Pressing methods include WIP (Wipe-in-Plate), CIP (Cleaning-in-Plate), and compression molding. Among these, compression molding allows for large-area processing and direct formation of inductor substrates on the top surface of the substrate.

[0004] Patent documents 1 and 2 describe, for example, magnetic resin compositions that can be formed by the compression molding method. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2017-199896 [Patent Document 2] Japanese Patent Publication No. 2019-210447 [Overview of the project] [Problems that the invention aims to solve]

[0006] The magnetic resin composition described in Patent Document 1 is manufactured by kneading solid resin in a kneader, resulting in high viscosity and poor workability for inductor substrate production. Furthermore, the magnetic resin composition described in Patent Document 2 is intended for EMI shielding applications, and therefore its corresponding frequency band and relative permeability are not suitable for use in inductor substrates.

[0007] The present invention has been made in view of the above circumstances, and aims to provide a low-viscosity magnetic paste that can produce a cured product with high relative permeability, a circuit board, an inductor board using the magnetic paste, and a method for manufacturing a circuit board. [Means for solving the problem]

[0008] As a result of diligent research to achieve the above objective, the inventors discovered that by incorporating a specific liquid epoxy resin, the viscosity of the paste can be lowered and the relative permeability of the cured product can be increased, thus completing the present invention.

[0009] In other words, the present invention includes the following: [1] (A) Magnetic powder, and (B) A magnetic paste for forming an inductor substrate using a compression mold, comprising a liquid epoxy resin represented by the following general formula (1). [ka] (In general formula (1), R represents a hydrogen atom or a methyl group.) [2] The magnetic paste according to [1], wherein the relative permeability at a frequency of 10 MHz is 5 or more. [3] The magnetic paste according to [1] or [2], wherein the magnetic loss at a frequency of 10 MHz is 0.1 or less. [4] A magnetic paste according to any one of [1] to [3], wherein the viscosity at 0.5 rpm at 25°C is 30 Pa·s or more and 600 Pa·s or less. [5] A magnetic paste as described in any of [1] to [4], wherein R in general formula (1) represents a methyl group. [6] A circuit board including a magnetic layer formed of a cured product of the magnetic paste according to any one of [1] to [5]. [7] An inductor substrate including the circuit board according to [6]. [8] A method for manufacturing a circuit board, including the steps of supplying the magnetic paste according to any one of [1] to [5] onto an inner layer substrate, molding the magnetic paste by compression molding, and forming a magnetic layer. [Advantages of the Invention]

[0010] According to the present invention, it is possible to provide a magnetic paste having a low viscosity, a circuit board, an inductor substrate, and a method for manufacturing an inductor substrate, which can obtain a cured product having a high relative permeability. [Brief Description of the Drawings]

[0011] [Figure 1] FIG. 1 is a schematic cross-sectional view for explaining an example of an inner layer substrate. [Figure 2] FIG. 2 is a schematic cross-sectional view for explaining step (A) included in an example of a method for manufacturing a circuit board. [Figure 3] FIG. 3 is a schematic cross-sectional view for explaining step (A) included in an example of a method for manufacturing a circuit board. [Figure 4] FIG. 4 is a schematic cross-sectional view for explaining step (B) included in an example of a method for manufacturing a circuit board. [Figure 5] FIG. 5 is a schematic cross-sectional view for explaining step (D) included in an example of a method for manufacturing a circuit board. [Figure 6] FIG. 6 is a schematic plan view of an inductor substrate including a circuit board obtained by a method for manufacturing a circuit board as an example, as viewed from one side in the thickness direction. [Figure 7] FIG. 7 is a schematic view showing a cut end face of an inductor substrate including a circuit board obtained by a method for manufacturing a circuit board cut at a position indicated by a II-II chain line shown in FIG. 5 as an example. [Figure 8]FIG. 8 is a schematic plan view for explaining the configuration of a first conductor layer in an inductor substrate including a circuit substrate obtained by a method for manufacturing a circuit substrate as an example.

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that in each drawing, the shape, size, and arrangement of the components are only schematically shown to the extent that the invention can be understood. The present invention is not limited by the following description, and each component can be appropriately changed. In the drawings used in the following description, the same components are denoted by the same reference numerals, and redundant descriptions may be omitted. In addition, the configuration according to the embodiment of the present invention is not necessarily manufactured or used in the arrangement shown in the drawing examples.

[0013] [Magnetic Paste] The magnetic paste of the present invention contains (A) magnetic powder and (B) a liquid epoxy resin represented by the following general formula (1). The magnetic paste of the present invention is used for forming an inductor substrate using a compression mold. [Chemical Formula] (In the general formula (1), R represents a hydrogen atom or a methyl group.)

[0014] In the present invention, by containing the component (B), the viscosity of the magnetic paste can be reduced, so that the productivity of the inductor substrate is excellent, and the cured product of the magnetic paste can improve the relative permeability at a frequency of 10 MHz. Further, preferably, it is also possible to reduce the magnetic loss and improve the mechanical properties of the cured product.

[0015] The magnetic paste may further contain (C) a dispersant, (D) a curing agent, and (E) other additives as necessary. Hereinafter, each component contained in the magnetic paste of the present invention will be described in detail.

[0016] <(A) Magnetic powder> The magnetic paste contains (A) magnetic powder as component (A). From the viewpoint of achieving both improved relative permeability and reduced magnetic loss of the cured product of the magnetic paste, (A) magnetic powder is preferably either a nanocrystalline magnetic material or an amorphous magnetic material, and more preferably contains both a nanocrystalline magnetic material and an amorphous magnetic material from the viewpoint of reducing magnetic loss by reducing the magnetic anisotropy of the crystals. In this specification, a nanocrystalline magnetic material is a magnetic material containing crystal grains, wherein the particle size of the crystal grains of the magnetic powder is 100 nm or less. A nanocrystalline magnetic material is preferably one in which the maximum particle size of the crystal grains is 100 nm or less. Typically, one particle of (A) magnetic powder contains multiple crystal grains, and these particles may be polycrystalline. The size of the crystal grains can be observed, for example, by TEM (transmission electron microscope). Since nanocrystalline magnetic materials contain crystal grains, they typically show peaks indicating crystallinity in the X-ray diffraction pattern. Furthermore, amorphous magnetic materials are non-crystalline magnetic materials that do not exhibit specific peaks indicating crystallinity in their X-ray diffraction patterns. Typically, the X-ray diffraction patterns of amorphous magnetic materials show a broad pattern without peaks indicating crystallinity. (A) By using either nanocrystalline magnetic materials or amorphous magnetic materials for the magnetic powder, the magnetic flux density is increased, and as a result, it is thought that both an improvement in relative permeability and a reduction in magnetic loss can be effectively achieved.

[0017] (A) The magnetic powder may be either soft magnetic powder or hard magnetic powder, but soft magnetic powder is preferred from the viewpoint of suppressing the uneven distribution of the magnetic powder.

[0018] (A) Examples of magnetic powders include iron alloy metal powders (Fe-based metal powders) such as Fe-Si alloy powder, Fe-Si-Al alloy powder, Fe-Cr alloy powder, Fe-Cr-Si alloy powder, Fe-Ni-Cr alloy powder, Fe-Cr-Al alloy powder, Fe-Ni alloy powder, Fe-Ni-Mo alloy powder, Fe-Ni-Mo-Cu alloy powder, Fe-Co alloy powder, or Fe-Ni-Co alloy powder.

[0019] In particular, (A) as the magnetic powder, iron alloy-based metal powder is preferred from the viewpoint of significantly obtaining the effects of the present invention. The iron alloy-based metal powder preferably contains iron alloy-based metal powder containing at least one selected from Fe, Si, Cr, Al, Ni, and Co, and more preferably contains iron alloy-based metal powder containing Fe, Si, and Cr. Furthermore, it is more preferable to be either a nanocrystalline magnetic material or an amorphous magnetic material containing at least one selected from Fe, Si, Cr, Al, Ni, and Co, even more preferable to be either a nanocrystalline magnetic material or an amorphous magnetic material containing Fe, Si, and Cr, and it is preferable to be either an Fe-based nanocrystalline magnetic material or an Fe-based amorphous magnetic material, and more preferably an Fe-based nanocrystalline magnetic material. Here, Fe-based means containing Fe atoms.

[0020] (A) The magnetic powder can be adjusted to a predetermined particle size distribution, for example, by classification. Furthermore, the above particle size distribution represents the particle size distribution of the entire (A) component contained in the magnetic paste. Therefore, the (A) component, which is made by mixing two or more types of magnetic powder, may be adjusted to have a predetermined particle size distribution. For example, multiple magnetic powders that do not have a predetermined particle size distribution may be mixed, and the (A) component as a whole may have a predetermined particle size distribution.

[0021] (A) The particle size distribution of magnetic powder can be measured by the laser diffraction-scattering method based on Mie scattering theory. Specifically, the particle size distribution of magnetic powder can be prepared on a volume basis using a laser diffraction-scattering particle size distribution analyzer, and the median diameter can be used as the average particle size for measurement. Preferably, the sample used for measurement is magnetic powder dispersed in pure water using ultrasound. Suitable laser diffraction-scattering particle size distribution analyzers include the "MT3000II" from Microtrac-Bel, the "LA-960" from Horiba, Ltd., and the "SALD-2200" from Shimadzu Corporation.

[0022] (A) The magnetic powder may be used alone or in combination of two or more types, but from the viewpoint of obtaining the effects of the present invention, it is preferable to use two or more types of magnetic powder in combination, and it is even more preferable to use two or more types of magnetic powder with different average particle sizes. In one embodiment, when two types of magnetic powder with different average particle sizes are used in combination, the average particle size of one of the magnetic powders 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 less than 10 μm, more preferably 9 μm or less, and even more preferably 8 μm or less. The average particle size of the other magnetic powder is preferably 10 μm or more, more preferably 15 μm or more, and even more preferably 20 μm or more. It is also preferably 40 μm or less, more preferably 35 μm or less, and even more preferably 30 μm or less.

[0023] When using two or more magnetic powders with different average particle sizes, if the average particle size of one magnetic powder is a1 and the average particle size of the other magnetic powder is a2, then the ratio a1 / a2 is preferably 1 or more, more preferably 3 or more, even more preferably 5 or more, preferably 20 or less, more preferably 15 or less, and even more preferably 10 or less. However, a1 > a2. By adjusting a1 / a2 to fall within this range, the effects of the present invention can be significantly obtained.

[0024] (A) Commercially available magnetic powders can be used, and two or more types may be used in combination. Specific examples of commercially available magnetic powders that can be used include "KUAMET NC1" and "ATFINE NC1" (nanocrystalline magnetic materials) from Epson Atomics; and "KUAMET 6B2" and "AW02-08PF3F" (amorphous magnetic materials) from Epson Atomics.

[0025] (A) The magnetic powder is preferably spherical. The aspect ratio obtained by dividing the length of the major axis of the magnetic powder by the length of the minor axis is preferably 2 or less, more preferably 1.5 or less, even more preferably 1.2 or less, preferably greater than 1, and more preferably 1.05 or more. Generally, a flattened shape rather than a spherical shape of magnetic powder makes it easier to improve the relative permeability, but in the present invention, it is preferable to use spherical magnetic powder from the viewpoint of reducing magnetic loss and obtaining magnetism with a desirable viscosity.

[0026] (A) The specific surface area of ​​the magnetic powder is preferably 0.05 m² from the viewpoint of improving the relative permeability. 2 / g or more, more preferably 0.1m 2 / g or more, more preferably 0.3m 2 It is 15m or more. 2 / g or less, more preferably 12m 2 / g or less, more preferably 10m 2 It is less than / g. (A) The specific surface area of ​​magnetic powder can be measured by the BET method.

[0027] (A) The magnetic powder content (volume %) is preferably 40% by volume or more, more preferably 50% by volume or more, and even more preferably 60% by volume or more, when the non-volatile components in the magnetic paste are considered to be 100% by volume, from the viewpoint of improving the relative permeability and reducing the loss coefficient. It is also preferably 95% by volume or less, more preferably 90% by volume or less, and even more preferably 80% by volume or less.

[0028] (A) From the viewpoint of improving relative permeability and reducing the loss coefficient, the content (mass%) of magnetic powder is preferably 70% by mass or more, more preferably 75% by mass or more, and even more preferably 80% by mass or more, when the nonvolatile components in the magnetic paste are considered to be 100% by mass. Also preferably 99% by mass or less, more preferably 98% by mass or less, and even more preferably 97% by mass or less. In this invention, unless otherwise specified, the content of each component in the magnetic paste is the value when the non-volatile component in the magnetic paste is considered to be 100% by mass.

[0029] <(B) Liquid epoxy resin represented by general formula (1)> The magnetic paste contains, as component (B), a liquid epoxy resin represented by general formula (1). [ka] (In general formula (1), R represents a hydrogen atom or a methyl group.)

[0030] By incorporating component (B) into the magnetic paste, its viscosity can be reduced, resulting in improved productivity for inductor substrates. Furthermore, it becomes possible to improve the mechanical strength of the cured product.

[0031] The epoxy resin represented by general formula (1) is liquid at 25°C, from the viewpoint of reducing the viscosity of the magnetic paste.

[0032] In general formula (1), R represents a hydrogen atom or a methyl group, and a methyl group is preferred from the viewpoint of significantly obtaining the effects of the present invention. In particular, when R is a methyl group, not only can the viscosity of the magnetic paste be effectively reduced, but surprisingly, the relative permeability and magnetic loss of the cured product of the magnetic paste can also be effectively improved.

[0033] In general formula (1), the bond position of R is preferably at the ortho position relative to the site where the benzene ring is bonded to the nitrogen atom.

[0034] The liquid epoxy resin represented by general formula (1) is preferably the liquid epoxy resin represented by general formula (2). [ka] (In general formula (2), R 1 This is the same as R in general formula (1).

[0035] (B) Component can be a commercially available product. Examples of commercially available products include "ELM-100H" from Sumitomo Chemical Co., Ltd. and "630" from Mitsubishi Chemical Corporation. Component (B) may be used alone or in combination of two or more types.

[0036] The epoxy equivalent of component (B) is preferably 50 g / eq. to 5000 g / eq., more preferably 50 g / eq. to 3000 g / eq., even more preferably 80 g / eq. to 2000 g / eq., and even more preferably 90 g / eq. to 1000 g / eq. This range ensures sufficient crosslinking density in the cured product, resulting in a magnetic layer with low surface roughness. The epoxy equivalent can be measured according to JIS K7236 and is the mass of resin containing one equivalent of epoxy groups.

[0037] The weight-average molecular weight of component (B) is preferably 100 to 5000, more preferably 150 to 3000, and even more preferably 250 to 1500. Here, the weight-average molecular weight of component (B) is the weight-average molecular weight in terms of polystyrene, measured by gel permeation chromatography (GPC).

[0038] (B) The content of component (B) is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more, when the nonvolatile components in the magnetic paste are considered to be 100% by mass, from the viewpoint of obtaining a magnetic layer that exhibits good mechanical strength. The upper limit of the content of component (B) is not particularly limited as long as the effects of the present invention are achieved, but is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less.

[0039] The content (volume %) of component (B) is preferably 1 volume% or more, more preferably 3 volume% or more, and even more preferably 5 volume% or more, when the non-volatile components in the magnetic paste are considered to be 100 volume%. The upper limit is not particularly limited as long as the effects of the present invention are achieved, but is preferably 25 volume% or less, more preferably 20 volume% or less, and even more preferably 15 volume% or less.

[0040] <(C) Dispersant> The magnetic paste may contain (C) a dispersant as an optional component.

[0041] (C) Examples of dispersants include phosphate ester dispersants such as polyoxyethylene alkyl ether phosphate; anionic dispersants such as sodium dodecyl benzyl sulfonate, sodium lauryl phosphate, and ammonium salts of polyoxyethylene alkyl ether sulfate; and nonionic dispersants such as organosiloxane dispersants, acetylene glycol, polyoxyethylene alkyl ether, polyoxyethylene alkyl ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene alkylphenyl ether, polyoxyethylene alkylamine, and polyoxyethylene alkylamide. Among these, anionic dispersants are preferred. Dispersants may be used alone or in combination of two or more.

[0042] A commercially available phosphate ester dispersant can be used. Examples of commercially available products include "RS-410," "RS-610," and "RS-710" from the "Phosphanol" series manufactured by Toho Chemical Industry Co., Ltd.

[0043] Examples of commercially available organosiloxane-based dispersants include "BYK347" and "BYK348" manufactured by BIC Chemie.

[0044] Examples of commercially available polyoxyalkylene dispersants include NOF Corporation's "Marialim" series, specifically "AKM-0531," "AFB-1521," "SC-0505K," "SC-1015F," "SC-0708A," and "HKM-50A."

[0045] Examples of commercially available acetylene glycols include Air Products and Chemicals Inc.'s "Surfinol" series, specifically "82," "104," "440," "465," and "485," as well as "Olefin Y."

[0046] (C) From the viewpoint of significantly exhibiting the effects of the present invention, the content of the dispersant is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.1% by mass or more, when the nonvolatile components in the magnetic paste are considered to be 100% by mass, and the upper limit is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less.

[0047] <(D) Hardener> The magnetic paste may contain (D) a curing agent as an optional component. The (D) curing agent includes an epoxy resin curing agent that has the function of curing component (B) and a curing accelerator that has the function of accelerating the curing rate of component (B). It is preferable that the magnetic paste contains a curing accelerator as the (D) curing agent.

[0048] -Epoxy resin hardener- Epoxy resin curing agents typically react with epoxy resins to cure magnetic pastes. Examples of epoxy resin curing agents include phenol-based epoxy resin curing agents, naphthol-based epoxy resin curing agents, active ester-based epoxy resin curing agents, acid anhydride-based epoxy resin curing agents, benzoxazine-based epoxy resin curing agents, cyanate ester-based epoxy resin curing agents, and imidazole-based epoxy resin curing agents. From the viewpoint of reducing the viscosity of the magnetic paste, acid anhydride-based epoxy resin curing agents and imidazole-based epoxy resin curing agents are preferred, and from the viewpoint of the mechanical strength of the resulting cured product, imidazole-based epoxy resin curing agents are even more preferred. Epoxy resin curing agents may be used alone or in combination of two or more types.

[0049] From the viewpoint of heat resistance and water resistance, phenol-based epoxy resin curing agents and naphthol-based epoxy resin curing agents are preferred if they have a novolac structure or a naphthol-based epoxy resin curing agent having a novolac structure. Among phenol-based epoxy resin curing agents, nitrogen-containing phenol-based epoxy resin curing agents are preferred, triazine skeleton-containing phenol-based epoxy resin curing agents are more preferred, and triazine skeleton-containing phenol novolac epoxy resin curing agents are even more preferred.

[0050] Specific examples of phenol-based epoxy resin curing agents and naphthol-based epoxy resin curing agents include "MEH-7700," "MEH-7810," and "MEH-7851" from Meiwa Kasei Co., Ltd., "NHN," "CBN," and "GPH" from Nippon Kayaku Co., Ltd., "SN170," "SN180," "SN190," "SN475," "SN485," "SN495V," "SN375," and "SN395" from Nippon Steel & Sumitomo Metal Chemical Co., Ltd., "TD-2090," "LA-7052," "LA-7054," "LA-1356," "LA-3018-50P," "EXB-9500," "HPC-9500," "KA-1160," "KA-1163," and "KA-1165" from DIC Corporation, and "GDP-6115L" and "GDP-6115H" from Gun-ei Chemical Co., Ltd.

[0051] There are no particular restrictions on the active ester-based epoxy resin curing agent, but 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 preferred. The active ester-based epoxy resin curing agent is preferably 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. Particularly from the viewpoint of improving heat resistance, an active ester-based epoxy resin curing agent obtained from a carboxylic acid compound and a hydroxy compound is preferred, and an active ester-based epoxy resin curing agent obtained from a carboxylic acid compound and / or a naphthol compound is more preferred. Examples of carboxylic acid compounds 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, resorcinol, bisphenol A, bisphenol F, bisphenol S, phenolphthalein, 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 novolac. Here, "dicyclopentadiene-type diphenol compounds" refers to diphenol compounds obtained by the condensation of two phenol molecules with one dicyclopentadiene molecule.

[0052] Specifically, preferred active ester-based epoxy resin curing agents include a dicyclopentadiene-type diphenol structure, an active ester-based epoxy resin curing agent includes a naphthalene structure, an active ester-based epoxy resin curing agent includes an acetylated phenol novolac, and an active ester-based epoxy resin curing agent includes a benzoylated phenol novolac. The term "dicyclopentadiene-type diphenol structure" refers to a divalent structure consisting of phenylene-dicyclopentylene-phenylene.

[0053] Commercially available active ester epoxy resin curing agents include: DIC's "EXB9451," "EXB9460," "EXB9460S," "HPC-8000-65T," "HPC-8000H-65TM," and "EXB-8000L-65TM" as active ester epoxy resin curing agents containing a dicyclopentadiene-type diphenol structure; DIC's "EXB9416-70BK" as an active ester compound containing a naphthalene structure; Mitsubishi Chemical's "DC808" as an active ester epoxy resin curing agent containing an acetylated phenol novolac; Mitsubishi Chemical's "YLH1026," "YLH1030," and "YLH1048" as active ester epoxy resin curing agents containing a benzoylated phenol novolac; and Mitsubishi Chemical's "DC808" as an active ester epoxy resin curing agent that is an acetylated phenol novolac.

[0054] Examples of acid anhydride-based epoxy resin curing agents include epoxy resin curing agents having one or more acid anhydride groups in one molecule. Specific examples of acid anhydride-based epoxy resin curing agents include phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, methylnadic anhydride, hydrogenated methylnadic anhydride, trialkyltetrahydrophthalic anhydride, dodecenyl succinic anhydride, 5-(2,5-dioxotetrahydro-3-furanyl)-3-methyl-3-cyclohexen-1,2-dicarboxylic acid anhydride, trimellitic anhydride, pyromellitic anhydride, and benzophenone tetracarbone. Examples include dianhydrides of nitrates, dianhydrides of biphenyltetracarboxylic acid, dianhydrides of naphthalenetetracarboxylic acid, dianhydrides of oxydiphthalic acid, dianhydrides of 3,3'-4,4'-diphenylsulfonetetracarboxylic acid, dianhydrides of 1,3,3a,4,5,9b-hexahydro-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-C]furan-1,3-dione, ethylene glycol bis(anhydrotrimellitate), and polymer-type acid anhydrides such as styrene-maleic acid resins obtained by copolymerizing styrene and maleic acid.

[0055] Examples of commercially available acid anhydride-based epoxy resin curing agents include "HNA-100" and "MH-700" manufactured by Shin Nippon Rika Co., Ltd.

[0056] Specific examples of benzoxazine-based epoxy resin curing agents include "HFB2006M" manufactured by Showa Polymer Co., Ltd., and "Pd" and "Fa" manufactured by Shikoku Chemicals Co., Ltd.

[0057] Examples of cyanate ester-based epoxy resin 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-cyanatephenylmethane), bis(4-cyanate-3,5-dimethylphenyl)methane, 1,3-bis(4-cyanatephenyl-1-(methylethylidene))benzene, bis(4-cyanatephenyl) thioether, and bis(4-cyanatephenyl) ether; polyfunctional cyanate resins derived from phenol novolacs and cresol novolacs; and prepolymers in which these cyanate resins are partially triazined. Specific examples of cyanate ester-based epoxy resin curing agents include "PT30" and "PT60" (both phenol novolac type polyfunctional cyanate ester resins) manufactured by Lonza Japan, "BA230", and "BA230S75" (prepolymers in which part or all of bisphenol A dicyanate is triazined and trimerized).

[0058] Examples of imidazole-based epoxy resin curing agents 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, and 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 isocyanurate adduct, 2-phenylimidazole isocyanurate adduct, 2-phenyl-4,5-dihydroxymethylimidazole, 2- Examples include imidazole compounds such as phenyl-4-methyl-5-hydroxymethylimidazole, 2,3-dihydro-1H-pyrrolo[1,2-a]benzimidazole, 1-dodecyl-2-methyl-3-benzylimidazolium chloride, 2-methylimidazoline, and 2-phenylimidazoline, as well as adducts of imidazole compounds with epoxy resins, with 2-ethyl-4-methylimidazole and 1-benzyl-2-phenylimidazole being preferred.

[0059] Commercially available imidazole-based epoxy resin curing agents may be used, such as "2MZA-PW" and "2PHZ-PW" from Shikoku Chemicals, and "P200-H50" from Mitsubishi Chemical Corporation.

[0060] The ratio of epoxy resin to epoxy resin curing agent is preferably in the range of 1:0.2 to 1:2, more preferably in the range of 1:0.3 to 1:1.5, and even more preferably in the range of 1:0.4 to 1:1, expressed as [total number of epoxy groups in epoxy resin]:[total number of reactive groups in epoxy resin curing agent]. Here, the reactive groups of the epoxy resin curing agent are activated hydroxyl groups, activated ester groups, etc., and vary depending on the type of epoxy resin curing agent. The total number of epoxy groups in the epoxy resin is the sum of the values ​​obtained by dividing the mass of the non-volatile component of each epoxy resin by the epoxy equivalent for all epoxy resins, and the total number of reactive groups in the epoxy resin curing agent is the sum of the values ​​obtained by dividing the mass of the non-volatile component of each epoxy resin curing agent by the reactive group equivalent for all epoxy resin curing agents. By setting the ratio of epoxy resin to epoxy resin curing agent within this range, the heat resistance of the cured product is further improved.

[0061] -Curing accelerator- Curing accelerators typically act as catalysts in the curing reaction of epoxy resins, thereby accelerating the curing reaction. Examples of curing accelerators include amine-based curing accelerators, imidazole-based curing accelerators, phosphorus-based curing accelerators, guanidine-based curing accelerators, and metal-based curing accelerators. From the viewpoint of reducing the viscosity of the magnetic paste, amine-based curing accelerators, imidazole-based curing accelerators, and guanidine-based curing accelerators are preferred, and from the viewpoint of improving the mechanical strength of the resulting cured product, imidazole-based curing accelerators are even more preferred. Curing accelerators may be used individually or in combination of two or more types.

[0062] 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.

[0063] As the amine-based curing accelerator, commercially available products may be used, such as "PN-50," "PN-23," and "MY-25" manufactured by Ajinomoto Fine Techno Co., Ltd.

[0064] The imidazole-based curing accelerator is the same as that of the imidazole-based epoxy resin curing agent described above. When used in combination with other epoxy resin curing agents, the imidazole-based epoxy resin curing agent may function as a curing accelerator.

[0065] Examples of phosphorus-based curing accelerators include triphenylphosphine, phosphonium borate compounds, tetraphenylphosphonium tetraphenylborate, n-butylphosphonium tetraphenylborate, tetrabutylphosphonium decanoate, (4-methylphenyl)triphenylphosphonium thiocyanate, tetraphenylphosphonium thiocyanate, and butyltriphenylphosphonium thiocyanate, with triphenylphosphine and tetrabutylphosphonium decanoate being preferred.

[0066] 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]deca-5-ene, and 7-methyl-1,5,7-triazabicyclo[4.4.0]deca-5-ene. Examples include ro[4.4.0]deca-5-ene, 1-methyl biguanide, 1-ethyl biguanide, 1-n-butyl biguanide, 1-n-octadecyl biguanide, 1,1-dimethyl biguanide, 1,1-diethyl biguanide, 1-cyclohexyl biguanide, 1-allyl biguanide, 1-phenyl biguanide, 1-(o-tolyl) biguanide, and the like, with dicyandiamide and 1,5,7-triazabicyclo[4.4.0]deca-5-ene being preferred.

[0067] Examples of metal-based hardening accelerators include 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. Examples of organometallic salts include zinc octoate, tin octoate, zinc naphthenate, cobalt naphthenate, tin stearate, and zinc stearate.

[0068] (D) The content of the curing agent is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.1% by mass or more, when the nonvolatile components in the magnetic paste are considered to be 100% by mass, and when the resin components in the magnetic paste are considered to be 100% by mass, from the viewpoint of reducing the viscosity of the magnetic paste, and the upper limit is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less.

[0069] <(E) Other additives> The magnetic paste may further contain (E) other additives as needed, such as curing retarders such as triethyl borate; inorganic fillers (excluding those corresponding to magnetic powders); thermosetting resins (excluding those corresponding to components (B) and (D)); thermoplastic resins; flame retardants; organic fillers; organometallic compounds such as organocopper compounds, organozinc compounds and organocobalt compounds; and resin additives such as thickeners; defoamers; leveling agents; adhesion promoters; and colorants.

[0070] The amount of organic solvent contained in the magnetic paste described above is preferably less than 1.0% by mass, more preferably 0.8% by mass or less, even more preferably 0.5% by mass or less, and particularly preferably 0.1% by mass or less, relative to the total mass of the magnetic paste. There is no particular lower limit, but it should be 0.001% by mass or more, or not contained at all. Even without containing organic solvent, the viscosity of the magnetic paste can be reduced because it contains component (B). By using a small amount of organic solvent in the magnetic paste, the generation of voids due to the volatilization of the organic solvent can be suppressed.

[0071] <Method for manufacturing magnetic paste> Magnetic paste can be manufactured, for example, by stirring the ingredients using a stirring device such as a three-roll mixer or a rotary mixer.

[0072] <Physical properties of magnetic paste> Magnetic paste exhibits the characteristic of low viscosity. Therefore, magnetic paste offers excellent workability for inductor substrate production. The viscosity at 25°C is preferably 600 Pa·s or less, more preferably 550 Pa·s or less, even more preferably 500 Pa·s or less, 400 Pa·s or less, and 300 Pa·s or less, preferably 30 Pa·s or more, preferably 50 Pa·s or more, and more preferably 60 Pa·s or more. Viscosity can be measured, for example, using an E-type viscometer (RE-80U manufactured by Toki Sangyo Co., Ltd.), and details can be found in the methods described in the examples below.

[0073] The cured product obtained by heating the magnetic paste at 190°C for 90 minutes exhibits the characteristic of high relative permeability at a frequency of 10 MHz. Therefore, the cured product provides a magnetic layer with high relative permeability. The relative permeability of this cured product at a frequency of 10 MHz is preferably 5 or higher, more preferably 10 or higher, and even more preferably 15 or higher. There is no particular upper limit, but it can be 50 or lower, for example. The relative permeability can be measured by the method described in the examples below.

[0074] A cured product obtained by heating a magnetic paste at 190°C for 90 minutes typically exhibits low magnetic loss at a frequency of 10 MHz. Therefore, the cured product provides a magnetic layer with low magnetic loss. The magnetic loss of this cured product at a frequency of 10 MHz is preferably 0.1 or less, more preferably 0.09 or less, and even more preferably 0.08 or less. The lower limit is not particularly limited but can be 0.001 or more. The magnetic loss can be measured by the method described in the examples below.

[0075] A cured product obtained by heating a magnetic paste at 190°C for 90 minutes typically exhibits excellent mechanical strength (maximum point strength). Therefore, the cured product provides a magnetic layer with excellent maximum point strength. The maximum point strength is preferably 10 MPa or higher, more preferably 20 MPa or higher, and even more preferably 30 MPa or higher. There is no particular upper limit, but it can be 100 MPa or lower. The maximum point strength can be measured by the method described in the examples below.

[0076] The cured product obtained by heating the magnetic paste at 190°C for 90 minutes typically exhibits elongation properties. The elongation is preferably 0.001% or more, more preferably 0.01% or less, and even more preferably 0.1% or more. There is no particular upper limit. The elongation can be measured by the method described in the examples below.

[0077] [Circuit board, method for manufacturing a circuit board] The circuit board of the present invention includes a magnetic layer formed from a cured magnetic paste. The circuit board is manufactured, for example, by a manufacturing method including the following step (A). (A) A step of supplying magnetic paste onto an inner layer substrate, molding the magnetic paste using a compression mold, and forming a magnetic layer.

[0078] Furthermore, it is preferable that the circuit board includes the following steps (B) to (D) in addition to step (A). (B) A process of drilling holes in the magnetic layer, (C) A step of roughening the surface of the magnetic layer, (D) A step of forming a conductive layer on the polished surface of the magnetic layer. The following provides a detailed explanation of the above-mentioned processes (A) to (D) in the manufacturing of the circuit board.

[0079] <Process (A)> Step (A) is a step of supplying magnetic paste onto an inner layer substrate and forming a magnetic layer by compression molding of the magnetic paste. In one embodiment of step (A), magnetic paste is supplied onto an inner layer substrate, the supplied magnetic paste is pressurized in a mold such as a die, heated as necessary, and the magnetic paste is compressed molded. After compression molding, the magnetic layer is formed by heat curing the magnetic paste as necessary.

[0080] An insulating substrate can be used as the inner layer substrate. Examples of insulating substrate materials for the inner layer substrate include glass epoxy substrates, metal substrates, polyester substrates, polyimide substrates, BT resin substrates, and thermosetting polyphenylene ether substrates. The inner layer substrate may also be an inner layer circuit board in which wiring and other structures are fabricated within its thickness.

[0081] As shown in Figure 1 as an example, the inner layer substrate 200 has a first conductor layer 420 provided on the first main surface 200a. The first conductor layer 420 may include a plurality of wirings. In the illustrated example, only the wirings constituting the coil-shaped conductive structure 400 of the inductor element are shown.

[0082] Examples of materials for the first conductor layer 420 include single metals such as gold, platinum, palladium, silver, copper, aluminum, cobalt, chromium, zinc, nickel, titanium, tungsten, iron, tin, and indium; and alloys of two 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. In particular, from the viewpoint of versatility, cost, and ease of patterning, it is preferable to use chromium, nickel, titanium, aluminum, zinc, gold, palladium, silver, or copper, or nickel-chromium alloys, copper-nickel alloys, or copper-titanium alloys; it is more preferable to use chromium, nickel, titanium, aluminum, zinc, gold, palladium, silver, or copper, or nickel-chromium alloys; and it is even more preferable to use copper. Examples of methods for forming the first conductor layer 420 include plating, sputtering, and vapor deposition, with plating being the preferred method. In a preferred embodiment, a patterned conductor layer having a desired wiring pattern is formed by plating the surface of the cured material using an appropriate method such as a semi-additive method or a fully additive method.

[0083] The first conductor layer 420 may be a single-layer structure, or it may be a multi-layer structure in which two or more single-metal or alloy layers made of different types of metals or alloys are stacked. The thickness of the first conductor layer 420 is the same as that of the second conductor layer 440, which will be described later.

[0084] As shown in Figure 2 as an example, after preparing the inner layer substrate 200, the magnetic paste is molded using a compression mold to form the first magnetic layer 320 on the inner layer substrate 200. The specific operation of the compression mold usually includes supplying magnetic paste (not shown) onto the inner layer substrate 200 and molding the magnetic paste by applying pressure using a mold or the like. Usually, after molding the magnetic paste, thermal curing is performed inside the mold, as described later.

[0085] The specific operation of a compression mold can be carried out as follows: An upper mold and a lower mold are prepared as molds for the compression mold. An inner layer substrate is placed in the lower mold, and magnetic paste is placed on the inner layer substrate. The placed inner layer substrate may be fixed to the lower mold by vacuum suction. The magnetic paste may be placed on the inner layer substrate before it is placed in the lower mold, or it may be placed on the inner layer substrate after it has been placed in the lower mold. Then, the upper and lower molds are clamped together so that the upper mold is in contact with the magnetic paste, and heat and pressure are applied to perform molding.

[0086] Furthermore, the specific operation of the compression mold may be carried out as follows: An inner layer substrate is placed in the upper mold. The placed inner layer substrate may be fixed to the upper mold by vacuum suction. Magnetic paste is then placed in the lower mold. After that, the upper and lower molds are clamped together so that the magnetic paste on the lower mold is in contact with the inner layer substrate attached to the upper mold, and heat and pressure are applied to perform molding.

[0087] The molding conditions for compression molds vary depending on the composition of the magnetic paste. The pressure applied during molding is preferably 1 MPa or more, more preferably 3 MPa or more, even more preferably 5 MPa or more, preferably 50 MPa or less, more preferably 30 MPa or less, and even more preferably 20 MPa or less. The pressurizing time is preferably 1 minute or more, more preferably 2 minutes or more, even more preferably 5 minutes or more, preferably 60 minutes or less, more preferably 30 minutes or less, and even more preferably 20 minutes or less.

[0088] Furthermore, the compression mold may be heated simultaneously with the pressurization as needed, from the viewpoint of exhibiting moldability. The heating temperature is preferably 80°C or higher, more preferably 100°C or higher, even more preferably 120°C or higher, preferably 220°C or lower, more preferably 200°C or lower, and even more preferably 170°C or lower.

[0089] After forming a magnetic paste on an inner layer substrate using a compression mold, the magnetic paste is heat-cured to form a first magnetic layer 320, as shown in an example in Figure 2. The heat-curing conditions for the magnetic paste vary depending on the type of magnetic paste, but the curing temperature is usually in the range of 120°C to 240°C (preferably in the range of 150°C to 220°C, more preferably in the range of 170°C to 210°C), and the curing time is in the range of 5 minutes to 120 minutes (preferably in the range of 10 minutes to 100 minutes, more preferably in the range of 15 minutes to 100 minutes).

[0090] Before the magnetic paste is heat-cured after molding, it may be subjected to a preheating treatment by heating it at a temperature lower than the curing temperature. For example, prior to heat-curing the magnetic paste, the resin composition layer may be preheated at a temperature of 50°C or higher but less than 120°C (preferably 60°C or higher but 115°C or lower, more preferably 70°C or higher but 110°C or lower) for 5 minutes or more (preferably 5 minutes to 150 minutes, more preferably 15 minutes to 120 minutes).

[0091] After forming the magnetic layer, a plurality of through-holes 220 may be formed through the inner layer substrate 200, extending from the first main surface 200a to the second main surface 200b, as shown in an example in Figure 3. The through-holes 220 may be formed using, for example, a drill, laser, plasma, etc. The dimensions and shape of the through-holes may be determined as appropriate according to the design of the printed circuit board.

[0092] Through-hole wiring 220a may be formed in the through-hole 220. Through-hole wiring 220a can be formed by methods such as plating, sputtering, or vapor deposition. Typically, external terminals 240 are formed on the inner layer substrate 200 before, after, or simultaneously with the formation of through-hole wiring 220a. Through-hole wiring 220a can electrically connect the first conductor layer 420 and the external terminals 240.

[0093] The line (L) / space (S) ratio of the first conductor layer 420 and the external terminal 240 is not particularly limited, but from the viewpoint of reducing surface irregularities and obtaining a magnetic 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. The lower limit of the line / space ratio is not particularly limited, but from the viewpoint of good embedding of the magnetic layer into the space, it is preferably 1 / 1 μm or more.

[0094] <Process (B)> In step (B), as shown in Figure 4 as an example, holes are drilled in the first magnetic layer 320 to form via holes 360. The via holes 360 serve as pathways for electrically connecting the first conductor layer 420 and the second conductor layer 440, which will be described later. The via holes 360 may be formed using, for example, a drill, laser, plasma, etc., depending on the composition of the magnetic paste used to form the magnetic layer. The dimensions and shape of the via holes may be determined as appropriate according to the design of the circuit board.

[0095] <Process (C)> In step (C), the surface of the magnetic layer in which via holes are formed is roughened. The procedure and conditions of the roughening process are not particularly limited, and known procedures and conditions that are normally used in the manufacturing of multilayer printed circuit boards can be adopted. For example, the first magnetic layer 32 can be roughened by performing a swelling treatment with a swelling solution, a roughening treatment with an oxidizing agent, and a neutralization treatment with a neutralizing solution in this order.

[0096] The swelling solution that can be used in the roughening process is not particularly limited, but examples include alkaline solutions and surfactant solutions, and an alkaline solution is preferred. As the alkaline solution used as the swelling solution, sodium hydroxide solution and potassium hydroxide solution are more preferred. Examples of commercially available swelling solutions include "Swelling Dip Securing P" and "Swelling Dip Securing SBU" manufactured by Atotech Japan Co., Ltd.

[0097] The swelling treatment with a swelling solution is not particularly limited, but for example, it can be carried out by immersing the inner layer substrate 200, on which the first magnetic layer 320 is provided, in a swelling solution at 30°C to 90°C for 1 to 20 minutes. From the viewpoint of suppressing the swelling of the resin constituting the first magnetic layer 32 to an appropriate level, it is preferable to immerse the first magnetic layer 32 in a swelling solution at 40°C to 80°C for 5 to 15 minutes.

[0098] The oxidizing agent that can be used for roughening treatment with an oxidizing agent is not particularly limited, but examples include alkaline permanganate solutions obtained by dissolving potassium permanganate or sodium permanganate in an aqueous solution of sodium hydroxide. The roughening treatment with an oxidizing agent such as an alkaline permanganate solution is preferably carried out by immersing the first magnetic layer 32 in an oxidizing agent solution heated to 60°C to 80°C for 10 to 30 minutes. Furthermore, the concentration of permanganate in the alkaline permanganate solution is preferably 5% to 10% by mass. Examples of commercially available oxidizing agents include alkaline permanganate solutions such as "Concentrate Compact P" and "Dosing Solution Securigans P" manufactured by Atotec Japan.

[0099] As a neutralizing solution that can be used for neutralization treatment, an acidic aqueous solution is preferred, and a commercially available product is, for example, "Reduction Solution Securigans P" manufactured by Attec Japan. Neutralization treatment with a neutralizing solution can be carried out by immersing the treated surface, which has been roughened with an oxidizing agent solution, in a neutralizing solution at 30°C to 80°C for 5 to 30 minutes. From the viewpoint of workability, it is preferable to immerse the first magnetic layer 320, which has been roughened with an oxidizing agent solution, in a neutralizing solution at 40°C to 70°C for 5 to 20 minutes.

[0100] The arithmetic mean roughness (Ra) of the magnetic layer after roughening treatment is preferably 300 nm or more, more preferably 350 nm or more, and even more preferably 400 nm or more, from the viewpoint of improving adhesion with the plating. The upper limit is preferably 1500 nm or less, more preferably 1200 nm or less, and even more preferably 1000 nm or less. The surface roughness (Ra) can be measured, for example, using a non-contact surface roughness meter.

[0101] In step (C), polishing may be performed instead of roughening to remove any protruding or adhering excess magnetic layer and flatten the surface.

[0102] <Process (D)> In step (D), a second conductive layer 440 is formed on the first magnetic layer 320, as shown in Figure 5 as an example.

[0103] The conductive material that can constitute the second conductive layer 440 is the same as the material of the first conductive layer described in step (A).

[0104] The thickness of the second conductor layer 440 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 is preferably 1 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more.

[0105] The second conductor layer 440 can be formed by plating. Preferably, the second conductor layer 440 is formed by a wet plating method such as a semi-additive method or a fully additive method, which includes an electroless plating step, a mask pattern formation step, an electrolytic plating step, and a flash etching step. By forming the second conductor layer 440 using a wet plating method, it is possible to form a second conductor layer 440 that includes a desired wiring pattern. In addition, this process also forms via hole wiring 360a within the via hole 360.

[0106] The first conductor layer 420 and the second conductor layer 440 may be arranged in a spiral shape, for example, as shown in Figures 6 to 8, which will be described later. In one example, one end of the spiral wiring portion of the second conductor layer 440, on the central side, is electrically connected to one end of the spiral wiring portion of the first conductor layer 420 by via hole wiring 360a. The other end of the spiral wiring portion of the second conductor layer 440, on the outer circumference side, is electrically connected to the land 420a of the first conductor layer 42 by via hole wiring 360a. Thus, the other end of the spiral wiring portion of the second conductor layer 440, on the outer circumference side, is electrically connected to the external terminal 240 via via hole wiring 360a, land 420a, and through-hole wiring 220a.

[0107] The coil-shaped conductive structure 400 is composed of a spiral wiring section which is part of the first conductor layer 420, a spiral wiring section which is part of the second conductor layer 440, and via-hole wiring 360a which electrically connects the spiral wiring section of the first conductor layer 420 and the spiral wiring section of the second conductor layer 440.

[0108] After step (D), a further step of forming a magnetic layer on the conductor layer may be performed. In detail, as shown in Figure 7 as an example, the second magnetic layer 340 is formed on the first magnetic layer 320 on which the second conductor layer 440 and via hole wiring 360a are formed. The second magnetic layer may be formed by the same process as described above.

[0109] [Inductor board] The inductor substrate includes the circuit board of the present invention. When the circuit board is obtained by the manufacturing method of the circuit board of the present invention, the inductor substrate has a magnetic layer and a conductive structure in which at least a portion is embedded in the magnetic layer, and includes an inductor element composed of the conductive structure and a portion of the magnetic layer that extends in the thickness direction of the magnetic layer and is surrounded by the conductive structure. Here, Figure 6 is a schematic plan view of an inductor substrate containing an inductor element, viewed from one side in its thickness direction. Figure 7 is a schematic diagram showing the cut end face of the inductor substrate cut at the position indicated by the dashed line II-II shown in Figure 6. Figure 8 is a schematic plan view for explaining the configuration of the first conductor layer of the inductor substrate.

[0110] As shown as an example in Figures 6 and 7, the inductor substrate 100 has a plurality of magnetic layers (first magnetic layer 320, second magnetic layer 340) and a plurality of conductor layers (first conductor layer 420, second conductor layer 440), that is, it is a build-up wiring board having build-up magnetic layers and build-up conductor layers. The inductor substrate 100 also includes an inner layer substrate 200.

[0111] As shown in Figure 7, the first magnetic layer 320 and the second magnetic layer 340 constitute a magnetic portion 300 that can be viewed as an integrated magnetic layer. Therefore, the coil-shaped conductive structure 400 is provided such that at least a portion of it is embedded in the magnetic portion 300. In other words, in the inductor substrate 100 of this embodiment, the inductor element is composed of a coil-shaped conductive structure 400 and a core portion which is a part of the magnetic portion 300 that extends in the thickness direction of the magnetic portion 300 and is surrounded by the coil-shaped conductive structure 400.

[0112] As shown in Figure 8 as an example, the first conductor layer 420 includes a spiral wiring section for forming a coil-shaped conductive structure 400 and a rectangular land 420a that is electrically connected to the through-hole wiring 220a. In the illustrated example, the spiral wiring section includes a straight section, a bent section that bends at a right angle, and a bypass section that bypasses the land 420a. In the illustrated example, the spiral wiring section of the first conductor layer 420 has an overall outline that is approximately rectangular and has a shape that is wound counterclockwise from the center outwards.

[0113] Similarly, a second conductor layer 440 is provided on the first magnetic layer 320. The second conductor layer 440 includes a spiral wiring section for forming a coil-shaped conductive structure 400. In Figure 6 or Figure 7, the spiral wiring section includes a straight section and a bent section that bends at a right angle. In Figure 6 or Figure 7, the spiral wiring section of the second conductor layer 44 has an overall outline that is roughly rectangular and has a shape that is wound clockwise from the center outwards.

[0114] Such inductor substrates can be used as wiring boards for mounting electronic components such as semiconductor chips, and can also be used as (multilayer) printed wiring boards using such wiring boards as inner layer substrates. Furthermore, such wiring boards can be used as individual chip inductor substrates, and can also be used as printed wiring boards on which these chip inductor substrates are surface-mounted.

[0115] Furthermore, 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). [Examples]

[0116] Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples. In the following description, "parts" and "%" representing amounts mean "parts by mass" and "mass%" respectively, unless otherwise specified.

[0117] <Example 1> 4 parts by mass of an epoxy resin ("ELM-100H", an amine-based epoxy resin, manufactured by Sumitomo Chemical Co., Ltd.), 0.5 parts by mass of a dispersant ("RS-710", a phosphate ester-based dispersant, manufactured by Toho Chemical Co., Ltd.), 0.25 parts by mass of a curing accelerator ("2P4MZ", an imidazole-based curing accelerator, manufactured by Shikoku Kasei Co., Ltd.), 58 parts by mass of magnetic powder ("KUAMET NC1", an Fe-based nanocrystalline magnetic material, D 50 : 25 μm, manufactured by Epson Atmix Corporation), 24 parts by mass of magnetic powder ("AW02-08PF3F", an Fe-based amorphous magnetic material, D 50 : 3 μm, manufactured by Epson Atmix Corporation) were mixed and uniformly dispersed with a three-roll mill to prepare Magnetic Paste 1. The structural formula of the epoxy resin "ELM-100H" is shown below.

Chemical formula

[0118] <Example 2> In Example 1, 4 parts by mass of an epoxy resin ("ELM-100H", an amine-based epoxy resin, manufactured by Sumitomo Chemical Co., Ltd.) were changed to 4 parts by mass of an epoxy resin ("630", an amine-based epoxy resin, manufactured by Mitsubishi Chemical Corporation). Magnetic Paste 2 was prepared in the same manner as in Example 1 except for the above matters. The structural formula of the epoxy resin "630" is shown below.

Chemical formula

[0119] <Comparative Example 1> In Example 1, 4 parts by mass of epoxy resin ("ELM-100H", amine-based epoxy resin, manufactured by Sumitomo Chemical Co., Ltd.) were replaced with 4 parts by mass of epoxy resin ("EP-3980S", amine-based epoxy resin, manufactured by ADEKA Corporation). Magnetic paste 3 was prepared in the same manner as in Example 1, except for the above. The structural formula of epoxy resin "EP3980S" is shown below. [ka]

[0120] <Comparative Example 2> In Example 1, 4 parts by mass of epoxy resin ("ELM-100H", amine-based epoxy resin, manufactured by Sumitomo Chemical Co., Ltd.) were replaced with 4 parts by mass of epoxy resin ("604", amine-based epoxy resin, manufactured by Mitsubishi Chemical Corporation). Magnetic paste 4 was prepared in the same manner as in Example 1, except for the above. The structural formula of epoxy resin "604" is shown below. [ka]

[0121] <Comparative Example 3> In Example 1, 4 parts by mass of epoxy resin ("ELM-100H", amine-based epoxy resin, manufactured by Sumitomo Chemical Co., Ltd.) were replaced with 4 parts by mass of epoxy resin ("EX201IM", phenyl-based epoxy resin, manufactured by Nagase ChemteX Corporation). Magnetic paste 5 was prepared in the same manner as in Example 1, except for the above. The structural formula of epoxy resin "EX201IM" is shown below. [ka]

[0122] <Comparative Example 4> In Example 1, 4 parts by mass of epoxy resin ("ELM-100H", amine-based epoxy resin, manufactured by Sumitomo Chemical Co., Ltd.) were replaced with 4 parts by mass of epoxy resin ("828", bisphenol A type epoxy resin, manufactured by Mitsubishi Chemical Corporation). Magnetic paste 6 was prepared in the same manner as in Example 1, except for the above. The structural formula of epoxy resin "828" is shown below. [ka]

[0123] <Comparative Example 5> In Example 1, 4 parts by mass of epoxy resin ("ELM-100H", amine-based epoxy resin, manufactured by Sumitomo Chemical Co., Ltd.) were replaced with 4 parts by mass of epoxy resin ("ED-523", bifunctional dilutable epoxy resin, manufactured by ADEKA Corporation). Magnetic paste 7 was prepared in the same manner as in Example 1, except for the above. The structural formula of epoxy resin "ED-523" is shown below. [ka]

[0124] <Comparative Example 6> In Example 1, 4 parts by mass of epoxy resin ("ELM-100H", amine-based epoxy resin, manufactured by Sumitomo Chemical Co., Ltd.) were replaced with 4 parts by mass of epoxy resin ("YX4000HK", biphenyl-type epoxy resin, manufactured by Mitsubishi Chemical Corporation). Magnetic paste 8 was prepared in the same manner as in Example 1, except for the above. The structural formula of epoxy resin "YX4000HK" is shown below. [ka]

[0125] <Viscosity Measurement> The temperature of magnetic pastes 1-8 was maintained at 25±2℃, and the viscosity at 25℃ was measured using an E-type viscometer (RE-80U, manufactured by Toki Sangyo Co., Ltd., 3°×R9.7 cone, rotation speed 0.5 rpm).

[0126] <Measurement of relative permeability and magnetic loss> As a support, a polyethylene terephthalate (PET) film (Lintec Corporation, "PET501010", 50 μm thick) treated with a silicone-based release agent was prepared. Magnetic pastes 1 to 8 prepared in each example and comparative example were uniformly applied to the release surface of the PET film using a doctor blade so that the thickness of the paste layer after drying was 100 μm, and a resin sheet was obtained. The paste layer of the obtained resin sheet was heat-cured by heating it at 190°C for 90 minutes, and a sheet-like cured product was obtained by peeling off the support. The obtained cured product was cut into test pieces with a width of 5 mm and a length of 18 mm to be used as evaluation samples. Using Agilent Technologies ("HP8362B"), the relative permeability (μ') and magnetic loss (μ'') were measured using the 3-turn coil method at a measurement frequency of 10 MHz at room temperature of 23°C, and the loss coefficient was obtained. The loss coefficient was calculated using the following formula. tanδ = μ' / μ''

[0127] <Measurement of maximum point strength and elongation> As a support, a polyethylene terephthalate (PET) film (Lintec Corporation's "PET501010", 50 μm thick) treated with a silicone-based release agent was prepared. Magnetic pastes 1 to 8 prepared in each example and comparative example were uniformly applied to the release surface of the PET film using a doctor blade so that the thickness of the paste layer after drying was 100 μm, thereby obtaining a resin sheet. The paste layer of the obtained resin sheet was heat-cured by heating it at 190°C for 90 minutes, and a sheet-like cured product was obtained by peeling off the support. The obtained cured product was subjected to a tensile test using a Tensilon universal tester (A&D Company, Limited) in accordance with Japanese Industrial Standards (JIS K7127), and the maximum point strength and elongation were measured.

[0128] [Table 1]

[0129] Examples 1 and 2, which contain component (B), were found to have superior magnetic properties, as well as better maximum point strength and elongation, compared to Comparative Examples 1 to 6, which do not contain component (B). Furthermore, it was found that their low viscosity resulted in excellent workability in the fabrication of inductor substrates.

[0130] Comparative Example 1, which used a component similar to component (B), did not produce a paste, making it impossible to measure its magnetic and mechanical properties. Comparative Example 2, which used a component similar to component (B), did not form a paste, making it impossible to measure its magnetic properties, viscosity, and mechanical properties. Comparative Example 4, which used an epoxy resin having a bisphenol A skeleton, had too high a viscosity to measure. Comparative Example 5, which used a low-viscosity epoxy resin, did not produce a paste, making it impossible to measure its magnetic and mechanical properties. Comparative Example 6, which used a solid epoxy resin (an epoxy resin that is solid at 25°C), did not form a paste, making it impossible to measure its magnetic properties, viscosity, and mechanical properties. [Explanation of Symbols]

[0131] 100 Inductor Board 200 Inner layer substrate 200a 1st main surface 200b 2nd main surface 220 Through Hole 220a Through-hole wiring 240 External terminals 300 Magnetic part 310 Magnetic Sheet 320a Resin composition layer 320 First insulating layer 330 Support 340 Second insulating layer 360 Beer Hall 360a Wiring inside a via hall 400 Coil-shaped conductive structure 420 First Conductor Layer 420a Land 440 Second Conductor Layer

Claims

1. (A) magnetic powder, (B) A liquid epoxy resin represented by the following general formula (1), and (C) A magnetic paste for forming an inductor substrate using a compression mold, comprising a dispersant, (A) The magnetic powder is made by using two types of magnetic powder with different average particle sizes, where the average particle size of one magnetic powder is 0.01 μm or more and less than 10 μm, and the average particle size of the other magnetic powder is 10 μm or more. (A) The magnetic powder content is 70% by mass or more, when the non-volatile components in the magnetic paste are considered to be 100% by mass. (B) The content of component (B) is 1% by mass or more and 15% by mass or less, when the non-volatile components in the magnetic paste are considered to be 100% by mass. A magnetic paste in which the content of component (C) is 0.1% by mass or more and 5% by mass or less, when the nonvolatile components in the magnetic paste are taken as 100% by mass. 【Chemistry 1】 (In general formula (1), R represents a hydrogen atom or a methyl group.)

2. The magnetic paste according to claim 1, wherein component (A) is a soft magnetic powder.

3. The magnetic paste according to claim 1, wherein component (A) is spherical.

4. The magnetic paste according to claim 1, wherein component (B) is a liquid epoxy resin represented by general formula (2). 【Chemistry 2】 (In general formula (2), R １ (This represents a hydrogen atom or a methyl group.)

5. The magnetic paste according to claim 1, wherein component (C) contains an anionic dispersant.

6. Furthermore, the magnetic paste according to claim 1, wherein it contains (D) a curing agent, and the content of component (D) is 0.01% by mass or more and 5% by mass or less, when the nonvolatile components in the magnetic paste are considered to be 100% by mass.

7. A circuit board comprising a magnetic layer formed by a cured product of a magnetic paste according to any one of claims 1 to 6.

8. An inductor board including the circuit board described in claim 7.

9. A method for manufacturing a circuit board, comprising the steps of supplying a magnetic paste according to any one of claims 1 to 6 onto an inner layer substrate, molding the magnetic paste with a compression mold to form a magnetic layer.

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