JP7751386B2 - magnetic paste - Google Patents

Description

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

Inductor substrates that can be included in circuit boards such as printed wiring boards are formed using resin compositions containing magnetic powder. Inductor substrates are formed by processing resin compositions containing magnetic powder using methods such as printing and pressing. Pressing allows for high loading of magnetic powder, making it one method of improving the performance of inductor substrates.

Pressing methods include the WIP method, the CIP method, and the compression molding method. Among these, the compression molding method allows for large-area processing and allows for the formation of an inductor substrate directly on the top surface of a substrate.

Patent Documents 1 and 2, for example, describe magnetic resin compositions that can be formed using compression molding.

Japanese Patent Application Laid-Open No. 2017-199896 Japanese Patent Application Laid-Open No. 2019-210447

The magnetic resin composition described in Patent Document 1 is produced by kneading solid resin in a kneader, which results in high viscosity and poor workability in the production of inductor substrates. Furthermore, the magnetic resin composition described in Patent Document 2 is intended for EMI shielding applications, and its corresponding frequency band and relative permeability are not suitable for use in inductor substrates.

The present invention was made in consideration of the above circumstances, and aims to provide a low-viscosity magnetic paste that can produce a cured product with high relative magnetic permeability, as well as a circuit board, inductor board, and circuit board manufacturing method that use this magnetic paste.

As a result of extensive research to achieve the above objective, the inventors discovered that by incorporating a specific liquid epoxy resin, the viscosity of the paste can be reduced and the relative permeability of the cured product can be increased, leading to the completion of the present invention.

That is, the present invention includes the following.
[1] A magnetic paste for forming an inductor substrate using a compression mold, comprising: (A) a magnetic powder; and (B) a liquid epoxy resin represented by the following general formula (1):
(In general formula (1), R represents a hydrogen atom or a methyl group.)
[2] The magnetic paste according to [1], having a relative permeability of 5 or more at a frequency of 10 MHz.
[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] The 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] The magnetic paste according to any one of [1] to [4], wherein R in general formula (1) represents a methyl group.
[6] A circuit board comprising a magnetic layer formed from 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, comprising the steps of supplying the magnetic paste according to any one of [1] to [5] onto an inner layer substrate, and molding the magnetic paste using a compression mold to form a magnetic layer.

The present invention provides a low-viscosity magnetic paste that can produce a cured product with high relative magnetic permeability, as well as a circuit board, inductor board, and method for manufacturing an inductor board that use the magnetic paste.

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

Embodiments of the present invention will now 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 enable understanding of the invention. The present invention is not limited by the following description, and each component may be modified as appropriate. In the drawings used in the following description, similar components will be designated by the same reference numerals, and duplicate explanations may be omitted. Furthermore, the configuration of the embodiments of the present invention will not necessarily be manufactured or used in the arrangement shown in the illustrations.

[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.
(In general formula (1), R represents a hydrogen atom or a methyl group.)

In the present invention, by including component (B), the viscosity of the magnetic paste can be reduced, improving the productivity of inductor substrates, and the cured product of the magnetic paste can have an improved relative permeability at a frequency of 10 MHz. Furthermore, preferably, the cured product can also have reduced magnetic loss and improved mechanical properties.

The magnetic paste may further contain (C) a dispersant, (D) a hardener, and (E) other additives as needed. Each component contained in the magnetic paste of the present invention is described in detail below.

<(A) Magnetic powder>
The magnetic paste contains (A) magnetic powder as component (A). The (A) magnetic powder is preferably either a nanocrystalline magnetic material or an amorphous magnetic material, from the viewpoint of improving the relative permeability of the cured product of the magnetic paste and reducing magnetic loss. It is more preferable that the (A) magnetic powder contains both a nanocrystalline magnetic material and an amorphous magnetic material, from the viewpoint of reducing the magnetic anisotropy of the crystals, thereby reducing magnetic loss. In this specification, a nanocrystalline magnetic material refers to a magnetic material containing crystal grains, and the crystal grains of the magnetic powder have a particle size of 100 nm or less. A nanocrystalline magnetic material preferably refers to a material having a maximum crystal grain size of 100 nm or less. Typically, each particle of the (A) magnetic powder contains multiple crystal grains, and the particles can be polycrystalline. The size of the crystal grains can be observed, for example, using a transmission electron microscope (TEM). Because nanocrystalline magnetic materials contain crystal grains, they typically exhibit peaks indicating crystallinity in an X-ray diffraction pattern. An amorphous magnetic material is a non-crystalline magnetic material that does not exhibit a specific peak indicating crystallinity in its X-ray diffraction pattern. Typically, the X-ray diffraction pattern of an amorphous magnetic material shows a broad pattern without any peaks indicating crystallinity. (A) By using either a nanocrystalline magnetic material or an amorphous magnetic material as the magnetic powder, the magnetic flux density increases, which is thought to effectively achieve both an improvement in relative permeability and a reduction in magnetic loss.

(A) The magnetic powder may be either soft magnetic powder or hard magnetic powder, but soft magnetic powder is preferred from the standpoint of preventing uneven distribution of the magnetic powder.

(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, and Fe-Ni-Co alloy powder.

Among these, iron alloy metal powder is preferred as the magnetic powder (A) from the viewpoint of achieving the effects of the present invention more significantly. The iron alloy metal powder preferably includes an iron alloy metal powder containing at least one selected from Fe, Si, Cr, Al, Ni, and Co, and more preferably includes an iron alloy metal powder containing Fe, Si, and Cr. Furthermore, either a nanocrystalline magnetic material or an amorphous magnetic material containing at least one selected from Fe, Si, Cr, Al, Ni, and Co is more preferred, and either a nanocrystalline magnetic material or an amorphous magnetic material containing Fe, Si, or Cr is even more preferred. Either an Fe-based nanocrystalline magnetic material or an Fe-based amorphous magnetic material is preferred, and an Fe-based nanocrystalline magnetic material is more preferred. Here, "Fe-based" means containing Fe atoms.

The magnetic powder (A) 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 component (A) contained in the magnetic paste. Therefore, component (A), which is a mixture of 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 the predetermined particle size distribution may be mixed, so that the entire component (A) has the predetermined particle size distribution.

(A) The particle size distribution of magnetic powder can be measured using a laser diffraction/scattering method based on Mie scattering theory. Specifically, a particle size distribution of the magnetic powder is created on a volume basis using a laser diffraction/scattering particle size distribution analyzer, and the median diameter is used as the average particle size. A preferred measurement sample is magnetic powder dispersed in pure water using ultrasonic waves. Examples of laser diffraction/scattering particle size distribution analyzers that can be used include the "MT3000II" manufactured by Microtrackbell, the "LA-960" manufactured by Horiba, Ltd., and the "SALD-2200" manufactured by Shimadzu Corporation.

(A) The magnetic powder may be used alone or in combination with two or more types. However, from the perspective of achieving the most pronounced 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.

When two or more types of magnetic powders with different average particle sizes are used in combination, where the average particle size of one magnetic powder is a1 and the average particle size of the other magnetic powder is a2, a1/a2 is preferably 1 or more, more preferably 3 or more, and even more preferably 5 or more, and preferably 20 or less, more preferably 15 or less, and even more preferably 10 or less. However, a1 > a2. By adjusting a1/a2 so that it is within this range, the effects of the present invention can be significantly achieved.

(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 Epson Atmix's "Kuamet NC1" and "ATFINE NC1" (nanocrystalline magnetic materials); Epson Atmix's "Kuamet 6B2" and "AW02-08PF3F" (amorphous magnetic materials), etc.

(A) The magnetic powder is preferably spherical. The aspect ratio, calculated 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, and even more preferably 1.2 or less, and is preferably greater than 1, more preferably 1.05 or greater. Generally, it is easier to improve the relative magnetic permeability when the magnetic powder is flat rather than spherical. However, in the present invention, it is preferable to use spherical magnetic powder from the viewpoint of reducing magnetic loss and obtaining a magnetic property with a desirable viscosity.

From the viewpoint of improving the relative magnetic permeability, the specific surface area of the (A) magnetic powder is preferably 0.05 ^{m 2} /g or more, more preferably 0.1 m ² /g or more, and even more preferably 0.3 m ² /g or more. Also, it is preferably 15 m ² /g or less, more preferably 12 m ² /g or less, and even more preferably 10 m ² /g or less. The specific surface area of the (A) magnetic powder can be measured by the BET method.

(A) From the perspective of improving the relative magnetic permeability and reducing the loss factor, the content (volume %) of the magnetic powder is preferably 40% by volume or more, more preferably 50% by volume or more, and even more preferably 60% by volume or more, assuming that the non-volatile components in the magnetic paste are 100% by volume. 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.

From the viewpoint of improving the relative magnetic permeability and reducing the loss factor, the content (mass %) of the (A) magnetic powder is preferably 70 mass % or more, more preferably 75 mass % or more, and even more preferably 80 mass % or more, when the nonvolatile components in the magnetic paste are taken as 100 mass %, and is also preferably 99 mass % or less, more preferably 98 mass % or less, and even more preferably 97 mass % or less.
In the present invention, the content of each component in the magnetic paste is a value when the non-volatile components in the magnetic paste are taken as 100 mass %, unless otherwise specified.

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

By including component (B), the viscosity of the magnetic paste can be reduced, improving the productivity of inductor substrates. It also makes it possible to improve the mechanical strength of the cured product.

The epoxy resin represented by general formula (1) is liquid at a temperature of 25°C, which reduces the viscosity of the magnetic paste.

In general formula (1), R represents a hydrogen atom or a methyl group, and a methyl group is preferred from the perspective of achieving the most pronounced 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 magnetic paste can also be effectively improved.

The bonding position of R in general formula (1) is preferably the ortho position relative to the position where the benzene ring is bonded to the nitrogen atom.

The liquid epoxy resin represented by the general formula (1) is preferably a liquid epoxy resin represented by the general formula (2).
(In general formula (2), ^R1 is the same as R in general formula (1).)

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

The epoxy equivalent of component (B) is preferably 50 g/eq. to 5,000 g/eq., more preferably 50 g/eq. to 3,000 g/eq., even more preferably 80 g/eq. to 2,000 g/eq., and even more preferably 90 g/eq. to 1,000 g/eq. This range ensures sufficient crosslink density in the cured product, resulting in a magnetic layer with low surface roughness. The epoxy equivalent can be measured in accordance with JIS K7236 and is the mass of the resin containing one equivalent of epoxy groups.

The weight-average molecular weight of component (B) is preferably 100 to 5,000, more preferably 150 to 3,000, and even more preferably 250 to 1,500. 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).

From the perspective of obtaining a magnetic layer exhibiting good mechanical strength, 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, assuming that the non-volatile components in the magnetic paste are 100% by mass. There is no particular upper limit to the content of component (B) as long as the effects of the present invention are achieved, but it is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less.

The content (vol %) of component (B) is preferably 1 vol % or more, more preferably 3 vol % or more, and even more preferably 5 vol % or more, assuming that the non-volatile components in the magnetic paste account for 100 vol %. The upper limit is not particularly limited as long as the effects of the present invention are achieved, but is preferably 25 vol % or less, more preferably 20 vol % or less, and even more preferably 15 vol % or less.

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

(C) Examples of dispersants include phosphate ester-based dispersants such as polyoxyethylene alkyl ether phosphate; anionic dispersants such as sodium dodecyl benzelsulfonate, sodium laurate, and ammonium salts of polyoxyethylene alkyl ether sulfate; and nonionic dispersants such as organosiloxane-based dispersants, acetylene glycol, polyoxyethylene alkyl ethers, polyoxyethylene alkyl esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene alkyl phenyl ethers, polyoxyethylene alkyl amines, and polyoxyethylene alkyl amides. Among these, anionic dispersants are preferred. Dispersants may be used alone or in combination of two or more.

Commercially available phosphate ester dispersants 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.

Commercially available organosiloxane dispersants include "BYK347" and "BYK348" manufactured by BYK-Chemie.

Commercially available polyoxyalkylene dispersants include NOF Corporation's "Marialim" series products such as "AKM-0531," "AFB-1521," "SC-0505K," "SC-1015F," "SC-0708A," and "HKM-50A."

Commercially available acetylene glycols include "82," "104," "440," "465," and "485" from the "Surfynol" series manufactured by Air Products and Chemicals Inc., as well as "Olefin Y."

In order to achieve the most pronounced effects of the present invention, the content of (C) the dispersant, when the non-volatile components in the magnetic paste are taken as 100% by mass, 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, with the upper limit being preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less.

<(D) Curing Agent>
The magnetic paste may contain a curing agent (D) as an optional component. The curing agent (D) 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). The magnetic paste preferably contains a curing accelerator as the curing agent (D).

-Epoxy resin hardener-
The epoxy resin curing agent typically reacts with the epoxy resin to harden the magnetic paste. 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. As the epoxy resin curing agent, acid anhydride-based epoxy resin curing agents and imidazole-based epoxy resin curing agents are preferred from the viewpoint of reducing the viscosity of the magnetic paste, and imidazole-based epoxy resin curing agents are more preferred from the viewpoint of the mechanical strength of the resulting cured product. The epoxy resin curing agents may be used alone or in combination of two or more.

As for phenolic epoxy resin curing agents and naphthol-based epoxy resin curing agents, from the viewpoint of heat resistance and water resistance, phenolic epoxy resin curing agents having a novolac structure or naphthol-based epoxy resin curing agents having a novolac structure are preferred. As for phenolic epoxy resin curing agents, nitrogen-containing phenolic epoxy resin curing agents are preferred, triazine skeleton-containing phenolic epoxy resin curing agents are more preferred, and triazine skeleton-containing phenolic novolac epoxy resin curing agents are even more preferred.

Specific examples of phenol-based epoxy resin curing agents and naphthol-based epoxy resin curing agents 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," and "SN495V" manufactured by Nippon Steel & Sumikin Chemical Co., Ltd. Examples include "SN375", "SN395", DIC Corporation's "TD-2090", "LA-7052", "LA-7054", "LA-1356", "LA-3018-50P", "EXB-9500", "HPC-9500", "KA-1160", "KA-1163", and "KA-1165", and Gun-ei Chemical Co., Ltd.'s "GDP-6115L" and "GDP-6115H".

While there are no particular limitations on the active ester-based epoxy resin curing agent, compounds with two or more highly reactive ester groups per molecule, such as phenol esters, thiophenol esters, N-hydroxyamine esters, and esters of heterocyclic hydroxy compounds, are generally preferred. Such active ester-based epoxy resin curing agents are preferably those obtained by the condensation reaction of a carboxylic acid compound and/or a thiocarboxylic acid compound with a hydroxy compound and/or a thiol compound. From the perspective of improving heat resistance, active ester-based epoxy resin curing agents obtained from a carboxylic acid compound and a hydroxy compound are preferred, and active ester-based epoxy resin curing agents obtained from a carboxylic acid compound and a phenol compound and/or a naphthol compound are 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, phenolphthalene, 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 dicyclopentadiene molecule with two phenol molecules.

Specific examples include active ester-based epoxy resin curing agents containing a dicyclopentadiene-type diphenol structure, active ester-based epoxy resin curing agents containing a naphthalene structure, active ester-based epoxy resin curing agents containing an acetylated phenol novolac, and active ester-based epoxy resin curing agents containing a benzoylated phenol novolac. A "dicyclopentadiene-type diphenol structure" refers to a divalent structure consisting of phenylene-dicyclopentylene-phenylene.

Commercially available active ester epoxy resin curing agents include DIC Corporation'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 Corporation's "EXB9416-70BK" as an active ester compound containing a naphthalene structure; Mitsubishi Chemical Corporation's "DC808" as an active ester epoxy resin curing agent containing an acetylated phenol novolac; Mitsubishi Chemical Corporation's "YLH1026," "YLH1030," and "YLH1048" as active ester epoxy resin curing agents containing a benzoylated phenol novolac; and Mitsubishi Chemical Corporation's "DC808" as an active ester epoxy resin curing agent that is an acetylated phenol novolac.

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-cyclohexene-1,2-dicarboxylic anhydride, trimellitic anhydride, pyromellitic anhydride, and benzophenone tetracarbohydrate. Examples of such anhydrides include carboxylic acid dianhydride, biphenyltetracarboxylic acid dianhydride, naphthalenetetracarboxylic acid dianhydride, oxydiphthalic acid dianhydride, 3,3'-4,4'-diphenylsulfonetetracarboxylic acid dianhydride, 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 polymeric acid anhydrides such as styrene-maleic acid resin, which is a copolymer of styrene and maleic acid.

Commercially available acid anhydride-based epoxy resin curing agents include "HNA-100" and "MH-700" manufactured by New Japan Chemical Co., Ltd.

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

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-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; multifunctional cyanate resins derived from phenol novolac and cresol novolac; and prepolymers of these cyanate resins partially converted to triazine. Specific examples of cyanate ester-based epoxy resin curing agents include Lonza Japan's "PT30" and "PT60" (both phenol novolac-type multifunctional cyanate ester resins), "BA230" and "BA230S75" (prepolymers in which part or all of bisphenol A dicyanate has been triazinated to form a trimer).

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-phenylimidazoline. 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- 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.

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

The ratio of the amount of epoxy resin to the amount of epoxy resin curing agent, expressed as the ratio of the total number of epoxy groups in the epoxy resin to the total number of reactive groups in the 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. Here, the reactive groups in the epoxy resin curing agent include active hydroxyl groups, active 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 mass of the nonvolatile components of each epoxy resin divided by the epoxy equivalent weight for all epoxy resins, and the total number of reactive groups in the epoxy resin curing agent is the sum of the mass of the nonvolatile components of each epoxy resin curing agent divided by the reactive group equivalent weight for all epoxy resin curing agents. Maintaining the ratio of epoxy resin to epoxy resin curing agent within this range further improves the heat resistance of the cured product.

-Curing accelerator-
The curing accelerator typically acts as a catalyst in the curing reaction of the epoxy resin, thereby accelerating the curing reaction. Examples of the curing accelerator 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 more preferred. The curing accelerators may be used alone or in combination of two or more.

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.

Commercially available amine-based curing accelerators may be used, such as "PN-50," "PN-23," and "MY-25" manufactured by Ajinomoto Fine-Techno Co., Inc.

Imidazole-based curing accelerators are similar to the imidazole-based epoxy resin curing agents 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.

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.

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 2[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, with dicyandiamide and 1,5,7-triazabicyclo[4.4.0]dec-5-ene being 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. Examples of organometallic salts include zinc octoate, tin octoate, zinc naphthenate, cobalt naphthenate, tin stearate, and zinc stearate.

(D) When the non-volatile components in the magnetic paste are taken as 100% by mass, from the viewpoint of reducing the viscosity of the magnetic paste, the content of the hardener 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 resin components in the magnetic paste are taken as 100% by mass. 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.

<(E) Other Additives>
The magnetic paste may further contain (E) other additives as needed. Examples of such other additives include curing retarders such as triethyl borate; inorganic fillers (excluding those corresponding to magnetic powder); 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; antifoaming agents; leveling agents; adhesion promoters; and colorants.

The content of organic solvent 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 can be 0.001% by mass or more, or none at all. Even if the magnetic paste does not contain an organic solvent, its viscosity can be reduced because it contains component (B). A small amount of organic solvent in the magnetic paste can suppress the generation of voids due to the evaporation of the organic solvent.

<Method of manufacturing magnetic paste>
The magnetic paste can be produced, for example, by a method in which the ingredients are stirred using a stirring device such as a three-roll mixer or a rotary mixer.

<Physical properties of magnetic paste>
The magnetic paste exhibits the characteristic of low viscosity. Therefore, the magnetic paste has excellent workability in producing inductor substrates. 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, or 300 Pa·s or less, and is preferably 30 Pa·s or more, preferably 50 Pa·s or more, and more preferably 60 Pa·s or more. The viscosity can be measured, for example, using an E-type viscometer (RE-80U manufactured by Toki Sangyo Co., Ltd.), and details can be measured by the method described in the examples below.

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

The cured product obtained by heating the magnetic paste at 190°C for 90 minutes typically exhibits the characteristic of low magnetic loss at a frequency of 10 MHz. Therefore, the cured product produces 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. Magnetic loss can be measured using the method described in the examples below.

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

The cured product obtained by heating the magnetic paste at 190°C for 90 minutes typically exhibits elongation characteristics. 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. Elongation can be measured by the method described in the examples below.

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

Furthermore, it is preferable that the circuit board includes the following steps (B) to (D) in addition to step (A).
(B) a step of drilling holes in the magnetic layer;
(C) a step of roughening the surface of the magnetic layer, and (D) a step of forming a conductive layer on the polished surface of the magnetic layer.
The above steps (A) to (D) for manufacturing a circuit board will be described in detail below.

<Process (A)>
Step (A) is a step of supplying a magnetic paste onto an inner layer substrate and compressing the magnetic paste using a compression mold to form a magnetic layer. In one embodiment of step (A), the magnetic paste is supplied onto the inner layer substrate, and the supplied magnetic paste is compressed in a mold such as a die, heated as needed, and compressed into a magnetic paste. After compression molding, the magnetic paste is thermally cured as needed to form a magnetic layer.

An insulating substrate can be used as the inner layer substrate. Examples of materials for the inner layer substrate 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 may also be an inner layer circuit board with wiring and the like built into its thickness.

As shown in FIG. 1, 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 multiple traces. In the illustrated example, only the traces that make up the coil-shaped conductive structure 400 of the inductor element are shown.

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. Among these, from the standpoints of versatility, cost, ease of patterning, and the like, chromium, nickel, titanium, aluminum, zinc, gold, palladium, silver, or copper, or nickel-chromium alloys, copper-nickel alloys, and copper-titanium alloys are preferred. Chromium, nickel, titanium, aluminum, zinc, gold, palladium, silver, or copper, or nickel-chromium alloys are more preferred, and copper is even more preferred. Methods for forming the first conductor layer 420 include plating, sputtering, and vapor deposition, with plating being preferred. In a preferred embodiment, the surface of the cured product is plated using an appropriate method such as a semi-additive method or a full-additive method to form a patterned conductor layer with the desired wiring pattern.

The first conductor layer 420 may have a single-layer structure, or 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.

As shown in an example in Figure 2, 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. Specific compression molding operations typically include supplying magnetic paste (not shown) onto the inner layer substrate 200 and compressing and molding the magnetic paste using a mold such as a metal die. After molding the magnetic paste, it is typically subjected to thermal curing in the mold, as described below.

Specific compression molding operations can be performed, for example, as follows: An upper mold and a lower mold are prepared as molds for compression molding. 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 also be placed on the inner layer substrate before the inner layer substrate is placed in the lower mold, or after the inner layer substrate is placed in the lower mold. The upper and lower molds are then clamped together so that the upper mold is in contact with the magnetic paste, and heat and pressure are applied to perform molding.

Specific compression molding operations may be performed, for example, 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 on the lower mold. The upper and lower molds are then 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.

The compression molding conditions 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, and preferably 50 MPa or less, more preferably 30 MPa or less, and even more preferably 20 MPa or less. The pressure application time is preferably 1 minute or more, more preferably 2 minutes or more, even more preferably 5 minutes or more, and preferably 60 minutes or less, more preferably 30 minutes or less, and even more preferably 20 minutes or less.

In addition, the compression mold may be heated, if necessary, while being pressed, in order to ensure good moldability. The heating temperature is preferably 80°C or higher, more preferably 100°C or higher, and even more preferably 120°C or higher, and is preferably 220°C or lower, more preferably 200°C or lower, and even more preferably 170°C or lower.

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

Before thermally curing the molded magnetic paste, the magnetic paste may be subjected to a preheating treatment in which the magnetic paste is heated at a temperature lower than the curing temperature. For example, prior to thermally curing the magnetic paste, the resin composition layer may be preheated for typically 5 minutes or more (preferably 5 to 150 minutes, more preferably 15 to 120 minutes) at a temperature typically between 50°C and 120°C (preferably between 60°C and 115°C, more preferably between 70°C and 110°C).

After forming the magnetic layer, a plurality of through holes 220 may be formed through the inner layer substrate 200, penetrating from the first main surface 200a to the second main surface 200b of the inner layer substrate 200, as shown in an example in FIG. 3. The through holes 220 may be formed using, for example, a drill, a laser, plasma, etc. The dimensions and shape of the through holes may be determined appropriately depending on the design of the printed wiring board.

Through-hole wiring 220a may be formed in the through-hole 220. The through-hole wiring 220a may be formed by a method such as plating, sputtering, or vapor deposition. Typically, an external terminal 240 is formed on the inner layer substrate 200 before, after, or simultaneously with the formation of the through-hole wiring 220a. The through-hole wiring 220a may electrically connect the first conductor layer 420 and the external terminal 240.

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 typically 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 ensuring good embedding of the magnetic layer into the spaces, it is preferably 1/1 μm or more.

<Process (B)>
In step (B), as shown in an example in Fig. 4, the first magnetic layer 320 is drilled to form via holes 360. The via holes 360 serve as paths for electrically connecting the first conductor layer 420 and the second conductor layer 440 described below. The via holes 360 may be formed using, for example, a drill, a laser, plasma, or the like, 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 appropriately depending on the design of the circuit board.

<Step (C)>
In step (C), the surface of the magnetic layer in which the via holes are formed is roughened. The procedure and conditions for the roughening step are not particularly limited, and known procedures and conditions commonly used in the manufacturing method of multilayer printed wiring boards can be adopted. For example, the roughening step can roughen the first magnetic layer 32 by performing a swelling treatment with a swelling liquid, a roughening treatment with an oxidizing agent, and a neutralization treatment with a neutralizing liquid in this order.

The swelling liquid that can be used in the roughening process is not particularly limited, but examples include alkaline solutions and surfactant solutions, with alkaline solutions being preferred. As alkaline solutions that serve as swelling liquids, sodium hydroxide solutions and potassium hydroxide solutions are more preferred. 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 200 provided with the first magnetic layer 320 in a swelling liquid at 30°C to 90°C for 1 to 20 minutes. From the perspective of keeping swelling of the resin that makes up the first magnetic layer 32 to an appropriate level, it is preferable to immerse the first magnetic layer 32 in a swelling liquid at 40°C to 80°C for 5 to 15 minutes.

The oxidizing agent that can be used in the roughening treatment with an oxidizing agent is not particularly limited, but examples include alkaline permanganate solutions prepared by dissolving potassium permanganate or sodium permanganate in an aqueous solution of sodium hydroxide. Roughening treatment with an oxidizing agent such as 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. The concentration of permanganate in the alkaline permanganate solution is preferably 5% to 10% by mass. Commercially available oxidizing agents include alkaline permanganate solutions such as "Concentrate Compact P" and "Dosing Solution Securigans P" manufactured by Atotech Japan.

An acidic aqueous solution is preferably used as the neutralizing solution for the neutralization treatment; a commercially available product such as "Reduction Solution Securigance P" manufactured by Atotech Japan is one example. Neutralization using a neutralizing solution can be performed by immersing the surface that has been roughened with an oxidizing solution in the neutralizing solution at 30°C to 80°C for 5 to 30 minutes. From the standpoint of workability, etc., a method in which the first magnetic layer 320 that has been roughened with an oxidizing solution is immersed in the neutralizing solution at 40°C to 70°C for 5 to 20 minutes is preferred.

From the viewpoint of improving adhesion with the plating, 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. 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.

In step (C), polishing may be performed instead of roughening to remove any protruding or adhering excess magnetic layer and achieve flattening.

<Step (D)>
In step (D), as shown in FIG. 5, a second conductor layer 440 is formed on the first magnetic layer 320 .

The conductive material that can be used to form the second conductive layer 440 is the same as the material for the first conductive layer described in step (A).

From the perspective of achieving a thinner design, 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.

The second conductor layer 440 can be formed by plating. The second conductor layer 440 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 440 using a wet plating method, it is possible to form a second conductor layer 440 that includes the desired wiring pattern. Note that this process also forms via hole wiring 360a within the via hole 360.

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 described below. In one example, one central end of the spiral wiring portion of the second conductor layer 440 is electrically connected to one central end of the spiral wiring portion of the first conductor layer 420 by via-hole wiring 360a. The other outer peripheral end of the spiral wiring portion of the second conductor layer 440 is electrically connected to the land 420a of the first conductor layer 42 by via-hole wiring 360a. Therefore, the other outer peripheral end of the spiral wiring portion of the second conductor layer 440 is electrically connected to the external terminal 240 via the via-hole wiring 360a, the land 420a, and the through-hole wiring 220a.

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

After step (D), a step of forming a magnetic layer on the conductor layer may be performed. In detail, as shown in an example in Figure 7, 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 a process similar to that already described.

[Inductor board]
The inductor substrate includes the circuit board of the present invention. When the inductor substrate includes a circuit board obtained by the circuit board manufacturing method of the present invention, the inductor substrate has a magnetic layer and a conductive structure at least partially embedded in the magnetic layer, and includes an inductor element formed by the conductive structure and a portion of the magnetic layer extending in the thickness direction of the magnetic layer and surrounded by the conductive structure. Here, Fig. 6 is a schematic plan view of the inductor substrate incorporating the inductor element, as seen from one side in the thickness direction. Fig. 7 is a schematic view showing the cut end surface of the inductor substrate cut at the position indicated by the dashed dotted line II-II in Fig. 6. Fig. 8 is a schematic plan view illustrating the configuration of a first conductor layer of the inductor substrate.

As shown by way of example in Figures 6 and 7, the inductor substrate 100 is a build-up wiring board having multiple magnetic layers (first magnetic layer 320, second magnetic layer 340) and multiple conductor layers (first conductor layer 420, second conductor layer 440), i.e., having build-up magnetic layers and build-up conductor layers. The inductor substrate 100 also includes an inner layer substrate 200.

As can be seen from Figure 7, the first magnetic layer 320 and the second magnetic layer 340 constitute the magnetic section 300, which can be viewed as an integrated magnetic layer. Therefore, the coiled conductive structure 400 is provided so that at least a portion of it is embedded in the magnetic section 300. That is, in the inductor substrate 100 of this embodiment, the inductor element is composed of the coiled conductive structure 400 and a core portion that extends in the thickness direction of the magnetic section 300 and is a portion of the magnetic section 300 surrounded by the coiled conductive structure 400.

As shown as an example in Figure 8, the first conductor layer 420 includes a spiral wiring portion for forming the 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 portion includes a straight portion, a bent portion that bends at a right angle, and a detour portion that detours around the land 420a. In the illustrated example, the spiral wiring portion of the first conductor layer 420 has an overall outline that is approximately rectangular, and has a shape that winds counterclockwise from the center to the outside.

Similarly, a second conductor layer 440 is provided on the first magnetic layer 320. The second conductor layer 440 includes a spiral wiring portion for forming the coil-shaped conductive structure 400. In Figures 6 and 7, the spiral wiring portion includes a straight portion and a bent portion that bends at a right angle. In Figures 6 and 7, the spiral wiring portion of the second conductor layer 44 has an overall outline that is approximately rectangular, and has a shape that winds clockwise from the center toward the outside.

Such an inductor substrate 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. Furthermore, such a wiring board can be singulated and used as a chip inductor substrate, and such a chip inductor substrate can also be used as a surface-mounted printed wiring board.

Furthermore, such wiring boards can be used to manufacture various types of semiconductor devices. Semiconductor devices including such wiring boards can be suitably used in electrical appliances (e.g., computers, mobile phones, digital cameras, and televisions) and vehicles (e.g., motorcycles, automobiles, trains, ships, and aircraft).

The present invention will be explained in more detail below using examples, but the present invention is not limited to these examples. In the following description, "parts" and "%" used to express amounts mean "parts by mass" and "% by mass," respectively, unless otherwise specified.

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

Example 2
In Example 1, 4 parts by mass of epoxy resin ("ELM-100H", amine-based epoxy resin, manufactured by Sumitomo Chemical Co., Ltd.) was changed to 4 parts by mass of epoxy resin ("630", 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. The structural formula of epoxy resin "630" is shown below.

<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.) was changed to 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 the epoxy resin "EP3980S" is shown below.

<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.) was changed to 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.

<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.) was changed to 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 the epoxy resin "EX201IM" is shown below.

<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.) was changed to 4 parts by mass of epoxy resin ("828", bisphenol A-type epoxy resin, manufactured by Mitsubishi Chemical Corporation). Apart from the above, magnetic paste 6 was prepared in the same manner as in Example 1. The structural formula of epoxy resin "828" is shown below.

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.) was changed to 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 the epoxy resin "ED-523" is shown below.

<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.) was changed to 4 parts by mass of epoxy resin ("YX4000HK", biphenyl-type epoxy resin, manufactured by Mitsubishi Chemical Corporation). Apart from the above, magnetic paste 8 was prepared in the same manner as in Example 1. The structural formula of epoxy resin "YX4000HK" is shown below.

<Viscosity measurement>
The temperature of magnetic pastes 1 to 8 was kept at 25±2° C., and the viscosity at 25° C. was measured using an E-type viscometer (Toki Sangyo Co., Ltd. "RE-80U", 3°×R9.7 cone, rotation speed 0.5 rpm).

<Measurement of relative permeability and magnetic loss>
A polyethylene terephthalate (PET) film ("PET501010" manufactured by Lintec Corporation, thickness 50 μm) treated with a silicone-based release agent was prepared as a support. 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 paste layer would be 100 μm thick after drying, thereby obtaining a resin sheet. The resulting resin sheet was heated at 190°C for 90 minutes to thermally cure the paste layer, and the support was peeled off to obtain a sheet-like cured product. The resulting cured product was cut into test pieces measuring 5 mm wide and 18 mm long to prepare evaluation samples. The evaluation samples were measured for relative permeability (μ') and magnetic loss (μ'') at a measurement frequency of 10 MHz using a 3-turn coil method at room temperature of 23°C using an Agilent Technologies ("HP8362B" manufactured by Agilent Technologies), and the loss factor was obtained. The loss factor was calculated using the following formula:
tan δ=μ′/μ″

<Measurement of maximum strength and elongation>
A polyethylene terephthalate (PET) film ("PET501010" manufactured by Lintec Corporation, thickness 50 μm) treated with a silicone-based release agent was prepared as a support. 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 paste layer was 100 μm thick after drying, yielding a resin sheet. The resulting resin sheet was heated at 190°C for 90 minutes to thermally cure the paste layer, and the support was peeled off to obtain a sheet-like cured product. The resulting cured product was subjected to a tensile test using a Tensilon universal testing machine (manufactured by A&D Co., Ltd.) in accordance with Japanese Industrial Standards (JIS K7127), and the maximum strength and elongation were measured.

It was found that Examples 1 and 2, which contain component (B), have superior magnetic properties and good maximum strength and elongation compared to Comparative Examples 1 to 6, which do not contain component (B). Furthermore, it was found that the low viscosity of the components allows for excellent workability in the fabrication of inductor substrates.

Comparative Example 1, which used a component similar to component (B), produced a brittle cured product, 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, viscosity, and mechanical properties. Comparative Example 4, which used an epoxy resin with a bisphenol A skeleton, had too high a viscosity to measure its viscosity. Comparative Example 5, which used a low-viscosity epoxy resin, produced a brittle cured product, 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, viscosity, and mechanical properties.

100 Inductor substrate 200 Inner layer substrate 200a First main surface 200b Second main surface 220 Through hole 220a Wiring inside through hole 240 External terminal 300 Magnetic portion 310 Magnetic sheet 320a Resin composition layer 320 First insulating layer 330 Support 340 Second insulating layer 360 Via hole 360a Wiring inside via hole 400 Coil-shaped conductive structure 420 First conductor layer 420a Land 440 Second conductor layer

Claims (8)

A magnetic paste for forming an inductor substrate using a compression mold, comprising: (A) a magnetic powder; and (B) a liquid epoxy resin represented by the following general formula (1):
(A) The magnetic powder is a combination of two types of magnetic powders having different average particle sizes, one of which has an average particle size of 0.01 μm or more and less than 10 μm, and the other has an average particle size of 10 μm or more;
(A) A magnetic paste in which the content of magnetic powder is 70% by mass or more, assuming that the non-volatile components in the magnetic paste are 100% by mass.
(In general formula (1), R represents a hydrogen atom or a methyl group.) The magnetic paste according to claim 1, having a relative permeability of 5 or greater at a frequency of 10 MHz. The magnetic paste according to claim 1 or 2, wherein the magnetic loss at a frequency of 10 MHz is 0.1 or less. The magnetic paste according to any one of claims 1 to 3, having a viscosity of 30 Pa·s or more and 600 Pa·s or less at 0.5 rpm at 25°C. The magnetic paste according to any one of claims 1 to 4, wherein R in general formula (1) represents a methyl group. A circuit board comprising a magnetic layer formed from a cured product of the magnetic paste described in any one of claims 1 to 5. An inductor substrate comprising the circuit board described in claim 6. A method for manufacturing a circuit board, comprising the steps of supplying the magnetic paste described in any one of claims 1 to 5 onto an inner layer substrate, and compressing the magnetic paste using a compression mold to form a magnetic layer.