Resin composition for wiring board materials, prepregs, resin-coated films, resin-coated metal foils, metal-clad laminates, and wiring boards using the same

Abstract

One aspect of the present invention pertains to a resin composition for a wiring board material including a thermosetting resin and a thermally expandable microcapsule, wherein the dielectric constant (10 GHz) of a cured product of said resin composition is greater than 1.0 and no more than 2.2.

Description

Technical Field

[0001] The present invention relates to a resin composition for a wiring board material, and a prepreg, a resin film, a metal foil with resin, a metal-clad laminate, and a wiring board using the same.

Background Art

[0002] In recent years, with the increase in the amount of information processing in various electronic devices, mounting technologies such as high integration of semiconductor devices, high density of wiring, and multilayerization have been rapidly progressing. For the substrate material constituting the base material of the wiring board used in various electronic devices, it is required to have a low dielectric constant and a low dielectric tangent in order to increase the signal transmission speed and reduce the loss during signal transmission.

[0003] On the other hand, although thermally expandable microcapsules are known to be used, for example, for peeling in a method for manufacturing a package for mounting a semiconductor element (Patent Document 1), recently, it has also been reported that they are used for reducing the dielectric constant by using a foaming technique using thermally expandable microcapsules or the like. For example, in the technique described in Patent Document 2, by using a curable resin composition containing microcapsules in which a core material is encapsulated in a shell in a thermosetting resin, a low dielectric constant additive (core material) can be well dispersed in the cured product, bleeding out can be suppressed, and a reduction in the dielectric constant of the cured product can be achieved.

[0004] However, the well-known foaming technique centered on thermoplastic resins requires various hardware and the like in the foaming process, and since there are many resins with a large expansion coefficient among thermoplastic resins, there are many restrictions on the application to printed board materials and it could not be easily realized.

[0005] In some inventions, like the technology described in Patent Document 2, the foaming technology is used for substrate applications. The foaming technology is considered an effective means to obtain low dielectric properties. However, conventional thermally expandable microcapsules have a problem of weak heat resistance. That is, it has been found that in the curing process of the thermosetting resin, the thermally expandable microcapsules cannot withstand the curing temperature (above 100°C) and rupture. Then, not only can the low dielectric effect not be expected in the cured product of the resin composition for a wiring board containing the thermosetting resin, but there is also a risk of impairing the properties of some substrates. Therefore, it has been found by the research of the present inventors that the conventional foaming technology is not suitable for wiring board applications.

[0006] From the above, there has been a demand for the development of a resin composition for a wiring board containing a thermosetting resin that applies thermally expandable microcapsules and has extremely excellent low dielectric properties in its cured product.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

[0008] The present invention has been made in view of such circumstances, and an object thereof is to provide a resin composition for a wiring board material that can make the relative permittivity of the cured product extremely low while maintaining properties such as heat resistance. Another object is to provide a prepreg, a film with resin, a metal foil with resin, a metal-clad laminate, and a wiring board using the resin composition.

[0009] The resin composition for a wiring board material according to one aspect of the present invention contains a thermosetting resin and thermally expandable microcapsules, and is characterized in that the relative permittivity (10 GHz) of its cured product is more than 1.0 and 2.2 or less.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

MODE FOR CARRYING OUT THE INVENTION

[0011] The resin composition for a wiring board material according to an embodiment of the present invention (hereinafter, also simply referred to as a resin composition) contains a thermosetting resin and thermally expandable microcapsules, and is characterized in that the relative dielectric constant (10 GHz) of the cured product is more than 1.0 and 2.2 or less.

[0012] According to the above configuration, it is possible to provide a resin composition for a wiring board material that can make the relative dielectric constant of the cured product extremely low while maintaining characteristics such as heat resistance. Further, by using the resin composition, it is possible to provide a prepreg, a resin film with resin, a metal foil with resin, a metal-clad laminate, and a wiring board having excellent low dielectric characteristics.

[0013] <Relative Dielectric Constant> The resin composition of this embodiment has a relative dielectric constant (10 GHz) of the cured product of more than 1.0 and 2.2 or less, and has very low dielectric characteristics even compared with conventional thermosetting low dielectric constant substrate materials.

[0014] In this specification, the value of the relative permittivity (Dk) is a value obtained by measuring the relative permittivity at 10 GHz at a temperature of 23 ± 2°C and a humidity of 50 ± 5% RH using a cavity resonator perturbation method conforming to ASTM D2520 for a test piece prepared by the method described in the examples below.

[0015] In a more preferred embodiment, the relative permittivity (10 GHz) of the cured product of the resin composition of this embodiment is 1.5 to 2.0.

[0016] Also, although not limited, the dielectric loss tangent (Df) of the cured product of the resin composition of this embodiment is preferably about 0.0001 to 0.004, and more preferably 0.001 to 0.004. The dielectric loss tangent in this specification is a value measured by the same method as the above relative permittivity.

[0017] <Density of the cured product> Furthermore, for the resin composition of this embodiment, it is preferable that the density of its cured product is 0.3 to 1.0 g / cm3.

[0018] Previously, in order to suppress the influence of height variations that may exist in the electrodes of electronic components and circuit boards, a technique has been reported in which thermally expandable microcapsules are incorporated into an insulating base material in an electronic device to form a thermally expandable insulating base material (see, for example, Japanese Patent Application Laid-Open No. 2013-41905). Therefore, the present inventors considered using thermally expandable microcapsules in a substrate material for constructing a base material of a wiring board used in various electronic devices as described above, in order to achieve weight reduction in addition to the above low dielectric characteristics.

[0019] However, the conventional foaming technology centered around well-known thermoplastic resins requires various hardware and the like in the foaming process, and since many thermoplastic resins have a large expansion coefficient, there are many restrictions on the application to printed circuit board materials and it could not be easily realized.

[0020] In addition, most of the maximum expansion temperatures of conventional thermally expandable microcapsules are around 100°C. In the curing process of generally thermosetting resins heated at 100°C or higher for 1 hour or more, as the thin film of the shell of the thermally expandable microcapsules becomes thinner, the vaporized volatile substances escape from the thin film part or the broken part of the shell, and the microcapsules often shrink. In this case, in the cured product of the resin composition for a wiring board containing a thermosetting resin, there is a risk of impairing the characteristics of some substrates including molding defects of the substrate. Therefore, it has been found by the research of the present inventors that the foaming technology using conventional thermally expandable microcapsules is not suitable for wiring board applications.

[0021] Therefore, the present inventors have found that in a resin composition for a wiring board containing a thermosetting resin, it is possible to realize weight reduction of the substrate material by applying thermally expandable microcapsules. Therefore, the resin composition for a wiring board of the present embodiment has excellent advantages also in that its cured product is very light compared with conventional substrate materials.

[0022] In this specification, the density of the cured product of the resin composition was measured by the following operation. First, a cured resin plate with a thickness of 300 μm was cut out with a punching cutter to obtain a 10 cm × 10 cm piece. Let the result of measuring the weight of the cut piece with a precision balance be M (g). Also, the volume V of the resin piece is calculated by the area S (10 × 10 cm 2 ) × thickness H (0.03 cm). Then, for the density, the density of each resin cured product piece is calculated using the formula ρ = M / V.

[0023] Since the cured product has a density within the above range, by using the resin composition of the present embodiment as a substrate material, weight reduction of more than half compared with conventional printed boards can be realized. In addition, since it can be handled in the same way as the printed wiring boards using thermosetting resins so far, no special processing process is required, and it is considered that it can greatly contribute to weight reduction and thinning of electronic devices including future personal mobile devices.

[0024] Hereinafter, each component of the resin composition according to this embodiment will be specifically described.

[0025] <Thermosetting resin> The thermosetting resin used in this embodiment is not particularly limited as long as it is a thermosetting resin that can be used as a wiring board material, but it preferably contains at least one selected from the group consisting of polyphenylene ether compounds, hydrocarbon resins, epoxy resins, maleimide compounds, phenolic resins, oxetane resins, benzoxazine compounds, liquid crystal polymers, and compounds having polymerizable unsaturated groups.

[0026] Among these, it is more preferable to use a resin that can obtain low dielectric constant and low dielectric tangent and high heat resistance. Specifically, polyphenylene ether compounds, hydrocarbon resins, maleimide compounds, etc. are preferably exemplified.

[0027] (Polyphenylene ether compound) As the polyphenylene ether compound, for example, it is preferable to use a terminally modified polyphenylene ether compound that can exhibit excellent low dielectric properties when cured, and more preferably, a modified polyphenylene ether compound terminally modified with a substituent having a carbon-carbon unsaturated double bond is used.

[0028] Examples of the modified polyphenylene ether compound include modified polyphenylene ether compounds represented by the following formulas (1) to (3).

[0029]

Chemical formula

[0030]

Chemical formula

[0031]

Chemical formula

[0032] In the above formulas (1) to (3), R1 to R8, R9 to R 16 as well as R 17 ~R 20 are each independent. That is, R1 to R8, R9 to R 16 as well as R 17 ~R 20 may be the same group or different groups. Also, R1 to R8, R9 to R 16 as well as R 17 ~R 20 represent a hydrogen atom, an alkyl group, an alkenyl group, an alkynyl group, a formyl group, an alkylcarbonyl group, an alkenylcarbonyl group, or an alkynylcarbonyl group. Among these, a hydrogen atom and an alkyl group are preferred.

[0033] For R1 to R8, R9 to R 16 as well as R 17 ~R 20 as each of the functional groups listed above, specifically, the following can be mentioned.

[0034] The alkyl group is not particularly limited, but for example, an alkyl group having 1 to 18 carbon atoms is preferred, and an alkyl group having 1 to 10 carbon atoms is more preferred. Specifically, for example, a methyl group, an ethyl group, a propyl group, a hexyl group, and a decyl group, etc. can be mentioned.

[0035] Also, the alkenyl group is not particularly limited, but for example, an alkenyl group having 2 to 18 carbon atoms is preferred, and an alkenyl group having 2 to 10 carbon atoms is more preferred. Specifically, for example, a vinyl group, an allyl group, and a 3-butenyl group, etc. can be mentioned.

[0036] Also, the alkynyl group is not particularly limited, but for example, an alkynyl group having 2 to 18 carbon atoms is preferred, and an alkynyl group having 2 to 10 carbon atoms is more preferred. Specifically, for example, an ethynyl group, and a prop-2-yn-1-yl group (propargyl group), etc. can be mentioned.

[0037] In addition, the alkylcarbonyl group is not particularly limited as long as it is a carbonyl group substituted with an alkyl group. For example, an alkylcarbonyl group having 2 to 18 carbon atoms is preferable, and an alkylcarbonyl group having 2 to 10 carbon atoms is more preferable. Specifically, for example, an acetyl group, a propionyl group, a butyryl group, an isobutyryl group, a pivaloyl group, a hexanoyl group, an octanoyl group, and a cyclohexylcarbonyl group can be mentioned.

[0038] In addition, the alkenylcarbonyl group is not particularly limited as long as it is a carbonyl group substituted with an alkenyl group. For example, an alkenylcarbonyl group having 3 to 18 carbon atoms is preferable, and an alkenylcarbonyl group having 3 to 10 carbon atoms is more preferable. Specifically, for example, an acryloyl group, a methacryloyl group, and a crotonoyl group can be mentioned.

[0039] In addition, the alkynylcarbonyl group is not particularly limited as long as it is a carbonyl group substituted with an alkynyl group. For example, an alkynylcarbonyl group having 3 to 18 carbon atoms is preferable, and an alkynylcarbonyl group having 3 to 10 carbon atoms is more preferable. Specifically, for example, a propioloyl group can be mentioned.

[0040] In addition, in the above formulas (1) and (2), as described above, A has the structure represented by the following formula (4), and B has the structure represented by the following formula (5):

[0041]

Chemical formula

[0042]

Chemical formula

[0043] In formulas (4) and (5), m and n, which are repeating units, each represent an integer of 1 to 50.

[0044] R 21 ~R 24 And R 25 ~R28 are independent of each other. That is, R 21 ~R 24 as well as R 25 ~R 28 may be the same group or different groups respectively. Also, in the present embodiment, R 21 ~R 24 as well as R 25 ~R 28 is a hydrogen atom or an alkyl group.

[0045] Also, in the above formula (3), s represents an integer from 1 to 100.

[0046] Furthermore, in the above formula (2), examples of Y include linear, branched or cyclic hydrocarbons having 20 or less carbon atoms. More specifically, for example, it is a structure represented by the following formula (6):

[0047]

Chemical formula

[0048] In formula (6), R 29 and R 30 each independently represent a hydrogen atom or an alkyl group. Examples of the alkyl group include a methyl group and the like. Also, examples of the group represented by formula (6) include a methylene group, a methylmethylene group, and a dimethylmethylene group and the like.

[0049] In the above formulas (1) to (3), X1 to X3 each independently represent a styrene structure or a (meth)acrylate structure as shown by the following formula (7) or (8), for example. X1 and X2 may be the same or different.

[0050]

Chemical formula

[0051]

Chemical formula

[0052] In formula (8), R 31 represents a hydrogen atom or an alkyl group. The alkyl group is not particularly limited, and for example, an alkyl group having 1 to 18 carbon atoms is preferable, and an alkyl group having 1 to 10 carbon atoms is more preferable. Specifically, for example, a methyl group, an ethyl group, a propyl group, a hexyl group, a decyl group, and the like can be mentioned.

[0053] More specifically, examples of the substituents X1 to X3 in the present embodiment include vinylbenzyl groups (ethenylbenzyl groups) such as p-ethenylbenzyl group and m-ethenylbenzyl group, vinylphenyl group, acrylate group, and methacrylate group.

[0054] By using such a modified polyphenylene ether compound represented by the above formulas (1) to (3), it is considered that high Tg and adhesion can be improved while maintaining low dielectric properties such as low dielectric constant and low dielectric tangent and excellent heat resistance.

[0055] The modified polyphenylene ether compounds represented by the above formulas (1) to (3) can be used alone or in combination of two or more.

[0056] In the present embodiment, the weight average molecular weight (Mw) of the modified polyphenylene ether compound used as the thermosetting resin is not particularly limited, but for example, it is preferably 1000 to 5000, and more preferably 1000 to 4000. Here, the weight average molecular weight may be measured by a general molecular weight measurement method. Specifically, values measured using gel permeation chromatography (GPC) and the like can be mentioned. Further, when the modified polyphenylene ether compound has repeating units (s, m, n) in the molecule, these repeating units preferably have numerical values such that the weight average molecular weight of the modified polyphenylene ether compound is within such a range.

[0057] When the weight-average molecular weight of the modified polyphenylene ether compound is within such a range, it has excellent low dielectric properties of the polyphenylene ether backbone, and not only is the heat resistance of the cured product excellent, but the moldability is also excellent. This is considered to be due to the following. Compared with ordinary polyphenylene ether, if the weight-average molecular weight is within the range described above, since it is a relatively low molecular weight one, the heat resistance of the cured product tends to decrease. In this regard, since the modified polyphenylene ether compound according to this embodiment has a styrene structure or a (meth)acrylate structure at the terminal, it has high reactivity, and it is considered that a cured product with sufficiently high heat resistance can be obtained. Also, when the weight-average molecular weight of the modified polyphenylene ether compound is within such a range, although it has a higher molecular weight compared to styrene or divinylbenzene, it is a relatively low molecular weight one compared to general polyphenylene ether, so it is considered to have excellent moldability. Therefore, it is considered that such a modified polyphenylene ether compound not only has excellent heat resistance of the cured product, but also has excellent moldability.

[0058] In addition, in the modified polyphenylene ether compound used as the thermosetting resin in this embodiment, the average number (terminal functional group number) of the X1 to X3 substituents at the molecular terminals per molecule of the modified polyphenylene ether is not particularly limited. Specifically, it is preferably 1 to 5, and more preferably 1 to 3. If the number of terminal functional groups is too small, it tends to be difficult to obtain a cured product with sufficient heat resistance. Also, if the number of terminal functional groups is too large, the reactivity becomes too high, and for example, problems such as a decrease in the storage stability of the resin composition or a decrease in the fluidity of the resin composition may occur. That is, when using such a modified polyphenylene ether, due to insufficient fluidity, etc., molding defects such as the generation of voids during multi-layer molding may occur, and there may be a problem of moldability that it is difficult to obtain a highly reliable printed wiring board.

[0059] In addition, the number of terminal functional groups of the modified polyphenylene ether compound includes numerical values representing the average value of the substituents per molecule of all the modified polyphenylene ether compounds present in 1 mol of the modified polyphenylene ether compound. This number of terminal functional groups can be measured, for example, by measuring the number of hydroxyl groups remaining in the obtained modified polyphenylene ether compound and calculating the decrease from the number of hydroxyl groups of the polyphenylene ether before modification. The decrease from the number of hydroxyl groups of the polyphenylene ether before modification is the number of terminal functional groups. And the measuring method of the number of hydroxyl groups remaining in the modified polyphenylene ether compound can be determined by adding a quaternary ammonium salt (tetraethylammonium hydroxide) that associates with the hydroxyl group to the solution of the modified polyphenylene ether compound and measuring the UV absorbance of the mixed solution.

[0060] Also, the intrinsic viscosity of the modified polyphenylene ether compound used in this embodiment is not particularly limited. Specifically, it may be 0.03 to 0.12 dl / g, preferably 0.04 to 0.11 dl / g, and more preferably 0.06 to 0.095 dl / g. If this intrinsic viscosity is too low, the molecular weight tends to be low, and it tends to be difficult to obtain low dielectric properties such as low dielectric constant and low dielectric tangent. Also, if the intrinsic viscosity is too high, the viscosity is high, sufficient fluidity cannot be obtained, and the moldability of the cured product tends to decrease. Therefore, if the intrinsic viscosity of the modified polyphenylene ether compound is within the above range, excellent heat resistance and moldability of the cured product can be realized.

[0061] Here, the intrinsic viscosity is the intrinsic viscosity measured in methylene chloride at 25°C. More specifically, for example, it is a value measured with a viscometer for a methylene chloride solution (liquid temperature 25°C) of 0.18 g / 45 ml. Examples of this viscometer include the AVS500 Visco System manufactured by Schott.

[0062] In addition, the method for synthesizing the modified polyphenylene ether compound preferably used in the present embodiment is not particularly limited as long as a modified polyphenylene ether compound end-modified with the substituents X1 to X3 as described above can be synthesized. Specifically, examples include a method of reacting a polyphenylene ether with a compound in which the substituents X1 to X3 and a halogen atom are bonded.

[0063] The polyphenylene ether as a raw material is not particularly limited as long as it can finally synthesize a predetermined modified polyphenylene ether. Specifically, examples include polyphenylene ethers mainly composed of polyphenylene ethers such as those composed of 2,6-dimethylphenol and at least one of a bifunctional phenol and a trifunctional phenol, and poly(2,6-dimethyl-1,4-phenylene oxide). The bifunctional phenol is a phenol compound having two phenolic hydroxyl groups in the molecule, and examples thereof include tetramethyl bisphenol A. The trifunctional phenol is a phenol compound having three phenolic hydroxyl groups in the molecule.

[0064] As an example of the method for synthesizing the modified polyphenylene ether compound, for example, in the case of the modified polyphenylene ether compound represented by the above formula (2), specifically, the above-described polyphenylene ether and a compound in which the substituents X1 and X2 and a halogen atom are bonded (a compound having the substituents X1 and X2) are dissolved in a solvent and stirred. By doing so, the polyphenylene ether reacts with the compound having the substituents X1 and X2, and the modified polyphenylene ether represented by the above formula (2) of the present embodiment is obtained.

[0065] Also, during this reaction, it is preferably carried out in the presence of an alkali metal hydroxide. By doing so, it is considered that this reaction proceeds favorably. This is presumably because the alkali metal hydroxide functions as a dehydrohalogenating agent, specifically, a dehydrochlorinating agent. That is, the alkali metal hydroxide causes hydrogen halide to be eliminated from the phenol group of the polyphenylene ether and the compound having substituent X, and by doing so, it is considered that substituents X1 and X2 are bonded to the oxygen atom of the phenol group instead of the hydrogen atom of the phenol group of the polyphenylene ether.

[0066] Also, the alkali metal hydroxide is not particularly limited as long as it can function as a dehalogenating agent, and examples thereof include sodium hydroxide and the like. Further, the alkali metal hydroxide is usually used in an aqueous solution state, and specifically, it is used as an aqueous sodium hydroxide solution.

[0067] Also, the reaction conditions such as the reaction time and reaction temperature vary depending on the compound having substituents X1 and X2 and the like, and are not particularly limited as long as the reaction proceeds favorably under the conditions as described above. Specifically, the reaction temperature is preferably from room temperature to 100°C, more preferably from 30 to 100°C. Also, the reaction time is preferably from 0.5 to 20 hours, more preferably from 0.5 to 10 hours.

[0068] Also, the solvent used during the reaction is not particularly limited as long as it can dissolve the polyphenylene ether and the compound having substituents X1 and X2 and does not inhibit the reaction between the polyphenylene ether and the compound having substituents X1 and X2. Specific examples include toluene and the like.

[0069] Further, the above reaction is preferably carried out in the presence of not only an alkali metal hydroxide but also a phase transfer catalyst. That is, the above reaction is preferably carried out in the presence of an alkali metal hydroxide and a phase transfer catalyst. By doing so, it is considered that the above reaction proceeds more suitably. This is considered to be due to the following reasons. A phase transfer catalyst has a function of incorporating an alkali metal hydroxide, is soluble in both a phase of a polar solvent such as water and a phase of a nonpolar solvent such as an organic solvent, and can move between these phases. Specifically, when an aqueous sodium hydroxide solution is used as the alkali metal hydroxide and an organic solvent such as toluene that is immiscible with water is used as the solvent, even if the aqueous sodium hydroxide solution is dropped into the solvent used in the reaction, the solvent and the aqueous sodium hydroxide solution are separated, and it is considered that sodium hydroxide hardly migrates into the solvent. Then, it is considered that the aqueous sodium hydroxide solution added as the alkali metal hydroxide hardly contributes to the promotion of the reaction. On the other hand, when the reaction is carried out in the presence of an alkali metal hydroxide and a phase transfer catalyst, it is considered that the alkali metal hydroxide migrates into the solvent in a state of being incorporated into the phase transfer catalyst, and the aqueous sodium hydroxide solution easily contributes to the promotion of the reaction. Therefore, when the reaction is carried out in the presence of an alkali metal hydroxide and a phase transfer catalyst, it is considered that the above reaction proceeds more suitably.

[0070] Also, the phase transfer catalyst is not particularly limited, and examples thereof include quaternary ammonium salts such as tetra-n-butylammonium bromide.

[0071] The resin composition according to this embodiment preferably contains, as the modified polyphenylene ether, the modified polyphenylene ether obtained as described above.

[0072] (Hydrocarbon resin) Examples of hydrocarbon resins that can be used in this embodiment preferably include polyfunctional vinyl aromatic polymers, cyclic polyolefin resins, and hydrocarbon resins of vinyl aromatic compound-conjugated diene compound copolymers. The type of hydrocarbon resin and the like are not particularly limited, but considering moldability, appearance, and mechanical properties, it is preferable to use a hydrocarbon resin having a weight average molecular weight of 1000 to 500000.

[0073] The polyfunctional vinyl aromatic polymer preferably includes a polymer obtained by polymerizing at least a polyfunctional vinyl aromatic compound or / and its derivative, and is not particularly limited as long as it is a polymer containing a structure derived from a polyfunctional vinyl aromatic compound or / and its derivative, and may be a polymer containing a structure derived from one or more polyfunctional vinyl aromatic compounds or / and their derivatives. The polyfunctional vinyl aromatic compound or / and its derivative contains two or more vinyl groups and an aromatic ring as a monocyclic or condensed ring. For example, compounds such as divinylbenzene, divinylnaphthalene, 9,10-divinylanthracene, 9,9-bis(4-allyloxyphenyl)fluorene, triallyl trimesate, 1,4-diisopropenylbenzene, 1,3-diisopropenylbenzene and their derivatives and the like are included. Furthermore, in addition to the above, the polyfunctional vinyl aromatic polymer of this embodiment may further contain a monovinyl aromatic compound or other compounds polymerized, and may also be a copolymer containing a structure derived from a monovinyl aromatic compound or other compounds. The monovinyl aromatic compound contains one vinyl group and an aromatic ring as a monocyclic or condensed ring. For example, styrene compounds in which a part of the hydrogen atoms of the aromatic ring such as styrene and methylstyrene are substituted with substituents such as alkyl groups, styrene derivatives, and the like are included. The polyfunctional vinyl aromatic polymer may be a copolymer or the like containing one or more structures derived from a monovinyl aromatic compound or other monomers.

[0074] The cyclic polyolefin resin used in this embodiment refers to a polyolefin resin having a cyclic aliphatic main chain in the main chain or side chain, or having a cyclic aliphatic hydrocarbon in the side chain. Examples of the cyclic aliphatic hydrocarbon include those having structures represented by the following structural formulas (9) to (17).

[0075]

Chemical formula

[0076] The cyclic polyolefin resin includes a cycloolefin copolymer (COC) type obtained by copolymerizing norbornene and ethylene using a metallocene catalyst and a COP type of metathesis ring-opening polymerization type. It may be used alone or in combination of two or more. Examples of commercially available cyclic polyolefin resins include Zeonex (registered trademark) and Zeonor (registered trademark) manufactured by Nippon Zeon Co., Ltd., Arton (registered trademark) manufactured by JSR Corporation, Apel (registered trademark) manufactured by Mitsui Chemicals, Inc., and Topas (registered trademark) manufactured by Polyplastics Co., Ltd.

[0077] As the vinyl aromatic compound-conjugated diene compound copolymer used in this embodiment, any copolymer containing a structure derived from a vinyl aromatic compound (a compound containing one or more vinyl groups and having an aromatic ring) and a structure derived from a conjugated diene compound (a compound having a conjugated diene) is not particularly limited. Further, it may contain a structure derived from one or more vinyl aromatic compounds and their derivatives, and may also contain a structure derived from one or more conjugated diene compounds. The copolymer of the vinyl aromatic compound-conjugated diene compound may be a hydrogenated product in which a part thereof is hydrogenated. Examples of the vinyl aromatic compound include styrene compounds in which a part of the hydrogen atoms of the aromatic ring is substituted with an alkyl group, such as styrene, α-methylstyrene, and p-methylstyrene, and styrene derivatives such as 2-vinylnaphthalene and divinylbenzene. The conjugated diene compound is not particularly limited, and examples thereof include 1,3-butadiene, isoprene, 1,3-pentadiene, 1,4-pentadiene, 1,3-heptadiene, cyclopentadiene, 2,3-dimethyl-1,3-butadiene, 1,4-hexadiene, 1,5-hexadiene, 1,3-cyclohexadiene, 1,4-cyclohexadiene, and their polymers. Further, in the vinyl aromatic compound-conjugated diene compound copolymer, the content of the structural unit derived from the vinyl aromatic compound is preferably 5 to 95% by mass, more preferably 10 to 80% by mass, and even more preferably 20 to 50% by mass.

[0078] (Maleimide compound) As the maleimide compound that can be used in this embodiment, any compound having a maleimide group in the molecule can be used without particular limitation. Specifically, examples of the maleimide compound include monofunctional maleimide compounds having one maleimide group in the molecule, polyfunctional maleimide compounds having two or more maleimide groups in the molecule, and modified maleimide compounds. Examples of the modified maleimide compound include modified maleimide compounds in which a part of the molecule is modified with an amine compound, modified maleimide compounds in which a part of the molecule is modified with a silicone compound, and modified maleimide compounds in which a part of the molecule is modified with an amine compound and a silicone compound.

[0079] (Other resin components) In addition to the above, in the resin composition of the present embodiment, a thermosetting resin different from the above thermosetting resin can also be used as the resin component. For example, phenolic resins, benzoxazine compounds, liquid crystal polymers, styrene, styrene derivatives, compounds having an acryloyl group in the molecule, compounds having a methacryloyl group in the molecule, compounds having a vinyl group in the molecule, compounds having an allyl group in the molecule, compounds having an acenaphthylene structure in the molecule, and isocyanurate compounds having an isocyanurate group in the molecule are exemplified. These can be used alone or in combination of two or more with the thermosetting resin as described above.

[0080] Examples of the styrene derivative include bromostyrene and dibromostyrene.

[0081] The compound having an acryloyl group in the molecule is an acrylate compound. Examples of the acrylate compound include monofunctional acrylate compounds having one acryloyl group in the molecule and polyfunctional acrylate compounds having two or more acryloyl groups in the molecule. Examples of the monofunctional acrylate compound include methyl acrylate, ethyl acrylate, propyl acrylate, and butyl acrylate. Examples of the polyfunctional acrylate compound include tricyclodecane dimethanol diacrylate.

[0082] The compound having a methacryloyl group in the molecule is a methacrylate compound. Examples of the methacrylate compound include a monofunctional methacrylate compound having one methacryloyl group in the molecule and a polyfunctional methacrylate compound having two or more methacryloyl groups in the molecule. Examples of the monofunctional methacrylate compound include methyl methacrylate, ethyl methacrylate, propyl methacrylate, and butyl methacrylate. Examples of the polyfunctional methacrylate compound include tricyclodecane dimethanol dimethacrylate.

[0083] The compound having a vinyl group in the molecule is a vinyl compound. Examples of the vinyl compound include a monofunctional vinyl compound (monovinyl compound) having one vinyl group in the molecule and a polyfunctional vinyl compound having two or more vinyl groups in the molecule. Examples of the polyfunctional vinyl compound include divinylbenzene, divinylnaphthalene, and polybutadiene.

[0084] The compound having an allyl group in the molecule is an allyl compound. Examples of the allyl compound include a monofunctional allyl compound having one allyl group in the molecule and a polyfunctional allyl compound having two or more allyl groups in the molecule. Examples of the polyfunctional allyl compound include diallyl phthalate (DAP).

[0085] The compound having an acenaphthylene structure in the molecule is an acenaphthylene compound. Examples of the acenaphthylene compound include acenaphthylene, alkyl acenaphthylenes, halogenated acenaphthylenes, phenyl acenaphthylenes, and the like. Examples of the alkyl acenaphthylenes include 1-methylacenaphthylene, 3-methylacenaphthylene, 4-methylacenaphthylene, 5-methylacenaphthylene, 1-ethylacenaphthylene, 3-ethylacenaphthylene, 4-ethylacenaphthylene, 5-ethylacenaphthylene, and the like. Examples of the halogenated acenaphthylenes include 1-chloroacenaphthylene, 3-chloroacenaphthylene, 4-chloroacenaphthylene, 5-chloroacenaphthylene, 1-bromoacenaphthylene, 3-bromoacenaphthylene, 4-bromoacenaphthylene, 5-bromoacenaphthylene, and the like. Examples of the phenyl acenaphthylenes include 1-phenylacenaphthylene, 3-phenylacenaphthylene, 4-phenylacenaphthylene, 5-phenylacenaphthylene, and the like. The acenaphthylene compound may be a monofunctional acenaphthylene compound having one acenaphthylene structure in the molecule as described above, or a polyfunctional acenaphthylene compound having two or more acenaphthylene structures in the molecule.

[0086] The compound having an isocyanurate group in the molecule is an isocyanurate compound. Examples of the isocyanurate compound include compounds further having an alkenyl group in the molecule (alkenyl isocyanurate compounds), and for example, trialkenyl isocyanurate compounds such as triallyl isocyanurate (TAIC).

[0087] Among these, for example, a polyfunctional acrylate compound having two or more acryloyl groups in the molecule, a polyfunctional methacrylate compound having two or more methacryloyl groups in the molecule, a polyfunctional vinyl compound having two or more vinyl groups in the molecule, a styrene derivative, an allyl compound having an allyl group in the molecule, a maleimide compound having a maleimide group in the molecule, an acenaphthylene compound having an acenaphthylene structure in the molecule, and an isocyanurate compound having an isocyanurate group in the molecule are preferable.

[0088] Any of the thermosetting resins as described above may be used alone or in combination of two or more.

[0089] The thermosetting resin preferably has a weight average molecular weight of 100 to 5000, more preferably 100 to 4000, and even more preferably 100 to 3000. If the weight average molecular weight of the thermosetting resin is too low, there is a risk of being easily volatilized from the blending component system of the resin composition. Also, if the weight average molecular weight of the thermosetting resin is too high, there is a risk that the viscosity of the varnish of the resin composition and the melt viscosity during heat molding become too high. Therefore, when the weight average molecular weight of the thermosetting resin is within such a range, a resin composition with more excellent heat resistance of the cured product can be obtained. Here, the weight average molecular weight may be measured by a general molecular weight measurement method, and specifically, values measured using gel permeation chromatography (GPC) and the like can be mentioned.

[0090] (Ratio) The thermosetting resin as described above preferably contains 10 to 70% by mass, more preferably 10 to 50% by mass, based on the total solid content of the resin composition.

[0091] Although not particularly limited, the resin composition of the present embodiment preferably contains at least one low dielectric resin selected from a polyphenylene ether compound, a hydrocarbon resin, and a maleimide compound as the thermosetting resin.

[0092] When a polyphenylene ether compound is included, it is preferably included in an amount of 10 to 90 parts by mass, more preferably 30 to 90 parts by mass, per 100 parts by mass of the thermosetting resin. When a hydrocarbon resin is included, it is preferably included in an amount of 10 to 90 parts by mass, more preferably 30 to 90 parts by mass, per 100 parts by mass of the thermosetting resin. When a maleimide compound is included, it is preferably included in an amount of 10 to 90 parts by mass, more preferably 10 to 70 parts by mass, per 100 parts by mass of the thermosetting resin.

[0093] In addition to the above low-dielectric resin, when the thermosetting resin further contains at least one selected from the group consisting of a phenol resin, an oxetane resin, a benzoxazine compound, a liquid crystal polymer, a compound having a polymerizable unsaturated group, styrene, a styrene derivative, a compound having an acryloyl group in the molecule, a compound having a methacryloyl group in the molecule, a compound having a vinyl group in the molecule, a compound having an allyl group in the molecule, a compound having an acenaphthylene structure in the molecule, and an isocyanurate compound having an isocyanurate group in the molecule, it is preferable to include one or more of them in an amount of 10 to 90 parts by mass per 100 parts by mass of the low-dielectric resin.

[0094] <Thermally expandable microcapsules> The thermally expandable microcapsules contained in the resin composition of this embodiment are fine particles that expand (foam) when heated.

[0095] Specifically, the thermally expandable microcapsules of this embodiment are preferably hollow particles having a core-shell structure in which a liquid compound (core) that vaporizes by heat is coated with an outer shell (shell) containing a thermoplastic resin.

[0096] By including such thermally expandable microcapsules, when the resin composition of the present embodiment is thermally cured, the liquid compound inside the thermally expandable microcapsules contained in the resin composition vaporizes due to heat, and the capsules expand. After the resin composition has cured, since the resin covering the periphery of the outer shell of the thermally expandable microcapsules has cured and solidified, the capsules are maintained in the expanded state.

[0097] By including the thermally expandable microcapsules in the resin composition of the present embodiment, it becomes possible to obtain a cured product having extremely low dielectric properties while maintaining properties such as heat resistance.

[0098] The thermoplastic polymer contained in the outer shell of the thermally expandable microcapsules of the present embodiment is preferably a polymer containing a structure derived from at least one selected from the group consisting of nitrile monomers, monomers having a carboxyl group, (meth)acrylate monomers, styrene monomers, and monomers having an amide group. That is, it is preferably a polymer obtained by polymerizing one kind or a combination of two or more kinds of the above-described monomers.

[0099] Among these, in particular, it is preferably a polymer containing a structure derived from at least one selected from the group consisting of nitrile monomers, monomers having a carboxyl group, and (meth)acrylate monomers.

[0100] Examples of specific monomers include, for example, nitrile monomers such as acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile, fumaronitrile; carboxylic acid monomers such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid; vinylidene chloride; vinyl acetate; (meth)acrylate esters such as methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, isobornyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, β-carboxyethyl acrylate; styrene monomers such as styrene, α-methylstyrene, chlorostyrene; amide monomers such as acrylamide, substituted acrylamide, methacrylamide, substituted methacrylamide, or mixtures thereof, etc. are exemplified.

[0101] Among these, in particular, it is preferable to use nitrile-based monomers such as acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile, and fumaronitrile, and monomers having a carboxyl group such as methacrylic acid monomer. Thereby, a thermally expandable microcapsule having more excellent heat resistance can be obtained.

[0102] In the thermoplastic polymer composition constituting the outer shell of the thermally expandable microcapsule, the content of the monomer is preferably 80% by mass or more. More preferably, it is 90% by mass or more.

[0103] In order to polymerize the above-mentioned monomers alone or as a mixture of two or more, it is preferable to use them in combination with a polymerizable monomer or a cross-linking agent having two or more polymerizable double bonds.

[0104] Examples of the polymerizable monomer or crosslinking agent include aromatic divinyl compounds such as divinylbenzene and divinylnaphthalene; allyl methacrylate, triacrylic formal, triallyl isocyanate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, PEG#200 di(meth)acrylate, PEG#400 di(meth)acrylate, PEG#600 di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,4-butanediol dimethacrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, trimethylolpropane trimethacrylate, glycerin dimethacrylate, dimethylol-tricyclodecane diacrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate, neopentyl glycol acrylate benzoate, trimethylolpropane acrylate benzoate, 2-hydroxy-3-acryloyloxypropyl methacrylate, neopentyl glycol hydroxypivalate diacrylate, ditrimethylolpropane tetraacrylate, 2-butyl-2-ethyl-1,3-propanediol diacrylate, and the like. These may be used alone or in combination of two or more.

[0105] The blending amount of the polymerizable monomer or crosslinking agent is preferably about 0.01 to 5% by mass in the thermoplastic polymer composition forming the outer shell.

[0106] In order to obtain the thermoplastic polymer by polymerizing the monomer as described above, a polymerization initiator may be appropriately blended. The polymerization initiator is not particularly limited as long as it does not inhibit the effects of the present invention. For example, polymerization initiators such as peroxides and azo compounds can be used. Such a polymerization initiator may be appropriately selected according to the monomer to be used.

[0107] Next, the liquid compound serving as the core in the thermally expandable microcapsules of the present embodiment will be described.

[0108] The liquid compound used in the present embodiment is not particularly limited as long as it vaporizes by heat, but is preferably a liquid compound having a boiling point equal to or lower than the softening temperature of the thermoplastic polymer. That is, the liquid compound used in the present embodiment is preferably a compound that vaporizes into a gas state at a temperature equal to or lower than the softening point of the thermoplastic polymer constituting the outer shell (shell) of the thermally expandable microcapsule.

[0109] Specific examples of the liquid compound preferably include at least one selected from the group consisting of hydrocarbon-based compounds, hydrogen halide-based compounds, alcohol-based compounds, ether-based compounds, and ketone-based compounds.

[0110] Among them, low-boiling liquid compounds such as propane, propylene, butene, normal butane, isobutane, isopentane, neopentane, normal pentane, normal hexane, isohexane, heptane, octane, petroleum ether, halides of methane, tetraalkylsilane, or azodicarbonamide that becomes gaseous by thermal decomposition upon heating are preferably exemplified. The liquid compound of the present embodiment can be appropriately selected from the compounds as described above according to the temperature range in which the thermally expandable microcapsule is desired to expand (foam).

[0111] In addition, in the thermally expandable microcapsules of the present embodiment, it is preferable that the outer shell is not dissolved in the liquid compound. Since the thermoplastic polymer contained in the outer shell as described above is not dissolved in the liquid compound, the liquid compound can be confined in the shell, enabling the formation of microspheres and providing sufficient foaming performance.

[0112] Since the resin composition of the present embodiment is for a wiring board material, it is used for the purpose of creating a substrate by thermosetting a thermosetting resin. Therefore, in the temperature range in which the resin composition is thermoset, it is preferable that the thermoexpansive microcapsules expand (foam). Thus, it is preferable that the maximum thermoexpansion temperature of the thermoexpansive microcapsules is 100 to 280°C. More preferably, the maximum thermoexpansion temperature is 150 to 260°C, and even more preferably, 180 to 230°C.

[0113] If the thermoexpansive microcapsules have a maximum thermoexpansion temperature of less than 100°C, since it is considerably lower than the curing temperature of the resin, when heat treatment is performed at a high temperature for a long time, problems such as shrinkage of the thermoexpansive microcapsules due to gas leakage may occur. On the other hand, when the thermoexpansive microcapsules exceed 280°C, it is considered that a cured product with poor low dielectric characteristics may be obtained because foaming cannot be achieved at a high foaming ratio.

[0114] It is preferable that the average thickness of the outer shell of the thermoexpansive microcapsules is about 1 to 8 μm. It is considered that with an outer shell having such a thickness, breakage during expansion can be further suppressed. Further, it is preferable that the volume at the maximum expansion at the maximum thermoexpansion temperature of the thermoexpansive microcapsules is 3 times or more the volume at room temperature (25°C). Thereby, it is considered that excellent low dielectric characteristics can be more reliably obtained.

[0115] Furthermore, it is preferable that the thermoexpansive microcapsules of the present embodiment can maintain the expanded volume, which is 3 times or more the volume at room temperature (25°C), for 10 minutes or more at the maximum expansion. By being able to maintain the expanded volume for a certain period of time or more, the expanded state can be maintained during the curing of the resin composition. Therefore, it is considered that rupture of the capsules and swelling during molding can be suppressed when molding a substrate using the resin composition of the present embodiment.

[0116] In the resin composition of this embodiment, the content of the above-described thermally expandable microcapsules is preferably about 1 to 50 parts by mass with respect to 100 parts by mass of the resin component containing the thermosetting resin. More preferably, it is 10 to 30 parts by mass. Further, when the thermosetting resin contains at least one low dielectric resin selected from polyphenylene ether compounds, hydrocarbon resins, and maleimide compounds, the thermally expandable microcapsules are preferably contained in an amount of 1 to 50 parts by mass with respect to 100 parts by mass of these low dielectric resins.

[0117] The average particle diameter of the thermally expandable microcapsules at room temperature (25 °C) is not particularly limited, but the volume-based cumulative 50% particle diameter (D50) is preferably about 1 to 100 μm. Thereby, it is considered that there is an advantage that the strength of the shell becomes sufficient during foaming. Also, the true specific gravity of the thermally expandable microcapsules at room temperature (25 °C) is not particularly limited, but is preferably about 0.01 to 0.5.

[0118] Note that the true specific gravity in this embodiment is a value measured by the liquid displacement method (displacement liquid isopropyl alcohol).

[0119] And the above-mentioned expansion volume ratio is obtained by measuring the true specific gravity of the thermally expandable microcapsules obtained by putting the thermally expandable microcapsules of this embodiment in an oven and heating them at the expansion temperature (foaming temperature) for 2 minutes to expand, and dividing the true specific gravity of the microcapsules after expansion by the true specific gravity of the thermally expandable microcapsules as the raw material.

[0120] The thermally expandable microcapsules of this embodiment can be produced using the production method of conventionally used thermally expandable microcapsules.

[0121] As the thermally expandable microcapsules used in the resin composition of this embodiment, commercially available products can also be used. For example, "EML-101", "EM403", "EM504", etc. manufactured by Sekisui Chemical Co., Ltd., "920DU80", "920DU120", "980DU120", etc. manufactured by Nippon Fillite Co., Ltd., "F-190D", "F-230D", "F-260D", "F-80DE", etc. of Matsumoto Yushi Seiyaku Co., Ltd., "H850D" manufactured by Kureha Corporation, and the like can be mentioned.

[0122] <Other components> In addition, the resin composition according to this embodiment may further contain other components in addition to the thermosetting resin component and the thermally expandable microcapsules.

[0123] For example, the resin composition according to this embodiment may further contain a filler. Examples of the filler include those added to enhance the heat resistance and flame retardancy of the cured product of the resin composition, and are not particularly limited. In addition, by containing a filler, the heat resistance, flame retardancy, etc. can be further enhanced. Specific examples of the filler include silica such as spherical silica, metal oxides such as alumina, titanium oxide, and mica, metal hydroxides such as aluminum hydroxide and magnesium hydroxide, talc, aluminum borate, barium sulfate, and calcium carbonate. Among these, silica, mica, and talc are preferable as the filler, and spherical silica is more preferable. The filler may be used alone or in combination of two or more. Also, the filler may be used as it is, or may be used after surface treatment with a silane coupling agent of epoxy silane type, vinyl silane type, methacrylic silane type, or amino silane type. As this silane coupling agent, it may be added and used by the integral blend method instead of the method of surface treating the filler in advance.

[0124] When containing a filler, the content is preferably 1 to 300 parts by mass, more preferably 50 to 200 parts by mass, based on 100 parts by mass in total of the resin components.

[0125] Furthermore, the resin composition of the present embodiment may contain a flame retardant. Examples of the flame retardant include halogen-based flame retardants such as bromine-based flame retardants and phosphorus-based flame retardants. Specific examples of the halogen-based flame retardants include bromine-based flame retardants such as pentabromodiphenyl ether, octabromodiphenyl ether, decabromodiphenyl ether, tetrabromobisphenol A, and hexabromocyclododecane, and chlorine-based flame retardants such as chlorinated paraffin. Specific examples of the phosphorus-based flame retardants include phosphate esters such as condensed phosphate esters and cyclic phosphate esters, phosphazene compounds such as cyclic phosphazene compounds, phosphinate-based flame retardants such as aluminum dialkylphosphinate salts, melamine-based flame retardants such as melamine phosphate and polyphosphoric acid melamine, and phosphine oxide compounds having a diphenylphosphine oxide group. As the flame retardant, each of the exemplified flame retardants may be used alone, or two or more of them may be used in combination.

[0126] Furthermore, the resin composition according to the present embodiment may contain various additives other than those described above. Examples of the additives include defoaming agents such as silicone-based defoaming agents and acrylate-based defoaming agents, heat stabilizers, antistatic agents, ultraviolet absorbers, dyes and pigments, lubricants, and dispersants such as wetting dispersants.

[0127] In addition, the resin composition according to this embodiment may further contain a reaction initiator. Although the curing reaction can proceed with only the resin component, depending on the process conditions, it may be difficult to raise the temperature to a high level until the curing progresses. Therefore, a reaction initiator may be added. The reaction initiator is not particularly limited as long as it can accelerate the curing reaction of the thermosetting resin as described above. Specifically, for example, oxidizing agents such as α,α'-bis(t-butylperoxy-m-isopropyl)benzene, 2,5-dimethyl-2,5-di(t-butylperoxy)-3-hexyne, benzoyl peroxide, 3,3',5,5'-tetramethyl-1,4-diphenoquinone, chloranil, 2,4,6-tri-t-butylphenoxyl, t-butylperoxyisopropyl monocarbonate, and azobisisobutyronitrile can be mentioned. Further, if necessary, a metal carboxylate salt or the like can be used in combination. By doing so, the curing reaction can be further promoted. Among these, α,α'-bis(t-butylperoxy-m-isopropyl)benzene is preferably used. Since α,α'-bis(t-butylperoxy-m-isopropyl)benzene has a relatively high reaction start temperature, it can suppress the acceleration of the curing reaction at the time when curing is not required, such as during prepreg drying, and can suppress the deterioration of the storage stability of the resin composition. Further, since α,α'-bis(t-butylperoxy-m-isopropyl)benzene has low volatility, it does not volatilize during drying or storage of prepregs, films, etc., and has good stability. Also, the reaction initiator may be used alone or in combination of two or more. As the content, preferably, the reaction initiator is used so that the addition amount is 0.1 to 20 parts by mass with respect to 100 parts by mass in total of the resin components.

[0128] (Prepreg, resin-coated film, metal-clad laminate, wiring board, and metal foil with resin) Next, the prepreg for a wiring board, metal-clad laminate, wiring board, and metal foil with resin using the resin composition of the present embodiment will be described. The reference numerals in each drawing indicate the following: 1 prepreg, 2 resin composition or semi-cured product of the resin composition, 3 fibrous substrate, 4 thermally expandable microcapsule, 11 metal-clad laminate, 12 insulating layer, 13 metal foil, 14 wiring, 21 wiring board, 31 metal foil with resin, 32, 42 resin layer, 41 resin film with resin, 43 support film.

[0129] FIG. 1 is a schematic cross-sectional view showing an example of the prepreg 1 according to an embodiment of the present invention.

[0130] As shown in FIG. 1, the prepreg 1 according to the present embodiment includes the resin composition containing the thermally expandable microcapsule 4 or the semi-cured product 2 of the resin composition, and the fibrous substrate 3. Examples of this prepreg 1 include those in which the fibrous substrate 3 is present in the resin composition or its semi-cured product 2. That is, this prepreg 1 includes the resin composition or its semi-cured product, and the fibrous substrate 3 present in the resin composition or its semi-cured product 2.

[0131] In the present embodiment, the "semi-cured product" refers to a state in which the resin composition is cured halfway to such an extent that it can be further cured. That is, the semi-cured product is one in a state where the resin composition is semi-cured (B-staged). For example, when the resin composition is heated, first, the viscosity gradually decreases, and then, curing starts and the viscosity gradually increases. In such a case, examples of semi-curing include the state after the viscosity starts to increase and before complete curing.

[0132] As the prepreg obtained by using the resin composition according to this embodiment, those having a semi-cured product of the resin composition as described above may be used, or those having the resin composition itself that has not been cured may also be used. That is, it may be a prepreg including a semi-cured product (the resin composition in the B stage) of the resin composition and a fibrous substrate, or a prepreg including the resin composition before curing (the resin composition in the A stage) and a fibrous substrate. Specifically, for example, those in which a fibrous substrate exists in the resin composition can be mentioned. Note that the resin composition or its semi-cured product may be obtained by heating and drying the resin composition.

[0133] When manufacturing the prepreg, the resin foil with resin, the metal-clad laminate described later, etc. using the resin composition according to this embodiment, it is often prepared in a varnish form and used as a resin varnish. Such a resin varnish is prepared, for example, as follows.

[0134] First, each component that can be dissolved in an organic solvent such as a thermosetting resin and a reaction initiator is put into the organic solvent and dissolved. At this time, heating may be performed as necessary. Then, components that are insoluble in the organic solvent, thermally expandable microcapsules, inorganic fillers, etc. are added, and a varnish-like resin composition is prepared by dispersing them using a ball mill, bead mill, planetary mixer, roll mill, etc. until a predetermined dispersed state is achieved as necessary. The organic solvent used here is not particularly limited as long as it can dissolve the modified polyphenylene ether compound, the maleimide compound, the styrene-butadiene copolymer, etc. and does not inhibit the curing reaction. Specifically, for example, toluene, methyl ethyl ketone, cyclohexanone, propylene glycol monomethyl ether acetate, etc. can be mentioned. These may be used alone or in combination of two or more.

[0135] As a method for manufacturing the prepreg 1 of this embodiment using the varnish-like resin composition of this embodiment, for example, a method of impregnating a fibrous substrate 3 with a resin composition 2 in the form of a resin varnish and then drying it can be mentioned.

[0136] Examples of the fibrous base material used in manufacturing the prepreg include, specifically, glass cloth, aramid cloth, polyester cloth, LCP (liquid crystal polymer) non-woven fabric, glass non-woven fabric, aramid non-woven fabric, polyester non-woven fabric, pulp paper, and linter paper. When using glass cloth, a laminate with excellent mechanical strength can be obtained, and particularly, flattened glass cloth is preferred. The glass cloth used in this embodiment is not particularly limited, and examples include low dielectric constant glass cloth such as E glass, S glass, NE glass, Q glass, L glass, and L2 glass. The flattening process can be specifically performed, for example, by continuously pressing the glass cloth with a press roll at an appropriate pressure to compress the yarns flat. Note that as the thickness of the fibrous base material, for example, those with a thickness of 0.01 to 0.3 mm can generally be used.

[0137] The impregnation of the resin varnish (resin composition 2) into the fibrous base material 3 is performed by dipping, coating, etc. This impregnation can be repeated a plurality of times as necessary. Also, at this time, it is possible to repeat the impregnation using a plurality of resin varnishes with different compositions and concentrations and finally adjust to the desired composition (content ratio) and resin amount.

[0138] The fibrous base material 3 impregnated with the resin varnish (resin composition 2) is heated under desired heating conditions, for example, at 80°C or higher and 180°C or lower for 1 minute or longer and 10 minutes or shorter. By heating, the solvent is volatilized from the varnish, and the solvent is reduced or removed to obtain a prepreg 1 in a pre-cured (A stage) or semi-cured state (B stage).

[0139] Further, as shown in FIG. 4, the metal foil with resin 31 of the present embodiment has a structure in which a resin layer 32 containing the above-described resin composition or a semi-cured product of the resin composition and a metal foil 13 are laminated. That is, the metal foil with resin of the present embodiment may be a metal foil with resin including a resin layer containing the resin composition before curing (the resin composition in the A stage) and a metal foil, or a resin layer containing a semi-cured product of the resin composition (the resin composition in the B stage) and a metal foil.

[0140] As a method for manufacturing such a metal foil with resin 31, for example, a method of applying a resin varnish-like resin composition as described above onto the surface of a metal foil 13 such as a copper foil and then drying it can be mentioned. Examples of the coating method include a bar coater, a comma coater, a die coater, a roll coater, a gravure coater, etc.

[0141] As the metal foil 13, metal foils used in metal-clad laminates, wiring boards, etc. can be used without limitation, and examples include copper foil and aluminum foil.

[0142] Furthermore, as shown in FIG. 5, the resin film 41 of the present embodiment has a structure in which a resin layer 42 containing the above-described resin composition or a semi-cured product of the resin composition and a film support substrate 43 are laminated. That is, the resin film of the present embodiment may be a resin film including the resin composition before curing (the resin composition in the A stage) and a film support substrate, or a resin film including a semi-cured product of the resin composition (the resin composition in the B stage) and a film support substrate.

[0143] As a method for manufacturing such a resin film 41, for example, a resin varnish-like resin composition as described above is applied onto the surface of a film support substrate 43, and then the solvent is volatilized from the varnish to reduce or remove the solvent, whereby a resin film in a state before curing (A stage) or a semi-cured state (B stage) can be obtained.

[0144] Examples of the film support base material include electrically insulating films such as polyimide films, PET (polyethylene terephthalate) films, polyester films, polyparabanic acid films, polyether ether ketone films, polyphenylene sulfide films, aramid films, polycarbonate films, and polyarylate films.

[0145] In addition, in the resin-coated film and resin-coated metal foil of this embodiment, similar to the prepreg described above, the resin composition or its semi-cured product may be the resin composition dried or heat-dried.

[0146] The thicknesses of the metal foil 13 and the film support base material 43 can be appropriately set according to the desired purpose. For example, as the metal foil 13, those with a thickness of about 0.2 to 70 μm can be used. When the thickness of the metal foil is, for example, 10 μm or less, a copper foil with a release layer and a carrier may be used to improve handling properties. The application of the resin varnish to the metal foil 13 and the film support base material 43 is performed by coating or the like, and this can be repeated a plurality of times as necessary. At this time, it is also possible to repeat the coating using a plurality of resin varnishes with different compositions and concentrations, and finally adjust to the desired composition (content ratio) and resin amount.

[0147] The drying or heat-drying conditions in the manufacturing method of the resin-coated metal foil 31 and the resin film 41 are not particularly limited. After applying the resin composition in the form of a resin varnish to the metal foil 13 and the film support base material 43, it is heated under desired heating conditions, for example, at 80 to 170 °C for about 1 to 10 minutes to volatilize the solvent from the varnish and reduce or remove the solvent, thereby obtaining the resin-coated metal foil 31 and the resin film 41 in the pre-cured (A stage) or semi-cured state (B stage).

[0148] The metal foil with resin 31 and the resin film 41 may be provided with a cover film or the like as necessary. By providing a cover film, it is possible to prevent the entry of foreign substances and the like. The cover film is not particularly limited as long as it can be peeled off without impairing the form of the resin composition. For example, a polyolefin film, a polyester film, a TPX film, a film formed by providing a release agent layer on these films, or a paper obtained by laminating these films on a paper base material can be used.

[0149] As shown in FIG. 2, the metal-clad laminate 11 of the present embodiment is characterized by having an insulating layer 12 containing a cured product of the above-described resin composition or a cured product of the above-described prepreg, and a metal foil 13. As the metal foil 13 used in the metal-clad laminate 11, the same one as the above-described metal foil 13 can be used.

[0150] Further, the metal-clad laminate 13 of the present embodiment can also be produced using the above-described metal foil with resin 31 or resin film 41.

[0151] As a method for producing a metal-clad laminate using the prepreg 1, the metal foil with resin 31, and the resin film 41 obtained as described above, the prepreg 1, the metal foil with resin 31, and the resin film 41 are stacked in one or more layers, and further, a metal foil 13 such as a copper foil is stacked on both or one side of the upper and lower surfaces thereof, and this is heated and pressure-molded to be laminated and integrated, whereby a laminate with both sides metal foil-clad or one side metal foil-clad can be produced. The heating and pressure conditions can be appropriately set according to the thickness of the laminate to be produced, the type of the resin composition, etc. For example, the temperature can be 170 to 220 °C, the pressure can be 1.5 to 5.0 MPa, and the time can be 60 to 150 minutes.

[0152] Further, the metal-clad laminate 11 may be produced by forming a film-like resin composition on the metal foil 13 and heating and pressurizing it without using the prepreg 1 or the like.

[0153] Then, as shown in FIG. 3, the wiring board 21 of the present embodiment has an insulating layer 12 containing a cured product of the above-described resin composition or a cured product of the above-described prepreg, and a wiring 14.

[0154] The resin composition of the present embodiment is suitably used as a material for an interlayer insulating layer of a wiring board. As a method for manufacturing the wiring board 21, for example, by etching the metal foil 13 on the surface of the metal-clad laminate 11 obtained above to form a circuit (wiring), a wiring board 21 provided with a conductor pattern (wiring 14) as a circuit on the surface of the laminate can be obtained. As a method for forming a circuit, in addition to the method described above, for example, circuit formation by a semi-additive process (SAP: Semi Additive Process) or a modified semi-additive process (MSAP: Modified Semi Additive Process) can be mentioned.

[0155] The prepreg, resin film with resin, and metal foil with resin obtained using the resin composition for a wiring board material of the present embodiment have very excellent low dielectric characteristics, high Tg, heat resistance, etc. in their cured products, and are therefore very useful in industrial applications. Further, the metal-clad laminate and the wiring board obtained by curing them have high heat resistance, high Tg, and very excellent low dielectric characteristics.

[0156] Hereinafter, the present invention will be described more specifically with reference to examples, but the scope of the present invention is not limited thereto.

Examples

[0157] First, in this example, the components used when preparing the resin composition will be described.

[0158] <Thermosetting resin> · Modified PPE-1: Bifunctional vinylbenzyl-modified PPE (Mw: 1900) First, a modified polyphenylene ether (modified PPE-1) was synthesized. The average number of phenolic hydroxyl groups at the molecular terminals per molecule of polyphenylene ether is referred to as the number of terminal hydroxyl groups.

[0159] Polyphenylene ether and chloromethylstyrene were reacted to obtain modified polyphenylene ether 1 (modified PPE-1). Specifically, first, 200 g of polyphenylene ether (SA90 manufactured by SABIC Innovative Plastics, intrinsic viscosity (IV) 0.083 dl / g, number of terminal hydroxyl groups 1.9, weight-average molecular weight Mw 1700), 30 g of a mixture of p-chloromethylstyrene and m-chloromethylstyrene with a mass ratio of 50:50 (chloromethylstyrene: CMS manufactured by Tokyo Chemical Industry Co., Ltd.), 1.227 g of tetra-n-butylammonium bromide as a phase transfer catalyst, and 400 g of toluene were charged into a 1-liter three-necked flask equipped with a temperature controller, a stirrer, a cooling facility, and a dropping funnel, and stirred. Then, the polyphenylene ether, chloromethylstyrene, and tetra-n-butylammonium bromide were stirred until dissolved in toluene. At that time, it was gradually heated and finally heated until the liquid temperature reached 75°C. Then, an aqueous sodium hydroxide solution (20 g of sodium hydroxide / 20 g of water) was dropped into the solution over 20 minutes as an alkali metal hydroxide. Then, it was further stirred at 75°C for 4 hours. Next, after neutralizing the contents of the flask with 10% by mass hydrochloric acid, a large amount of methanol was added. By doing so, a precipitate was formed in the liquid in the flask. That is, the product contained in the reaction solution in the flask was reprecipitated. Then, this precipitate was taken out by filtration, washed three times with a mixed solution of methanol and water with a mass ratio of 80:20, and then dried under reduced pressure at 80°C for 3 hours.

[0160] The obtained solid was 1 analyzed by 1H-NMR (400 MHz, CDCl3, TMS). As a result of measuring the NMR, a peak derived from ethenylbenzyl was confirmed at 5 to 7 ppm. From this, it was confirmed that the obtained solid was polyphenylene ether ethenylbenzylated at the molecular terminal.

[0161] Also, the molecular weight distribution of the modified polyphenylene ether was measured using GPC. As a result of calculating the weight average molecular weight (Mw) from the obtained molecular weight distribution, Mw was 1900.

[0162] Also, the number of terminal functional groups of the modified polyphenylene ether was measured as follows.

[0163] First, the modified polyphenylene ether was accurately weighed. Let the weight at that time be X (mg). Then, this weighed modified polyphenylene ether was dissolved in 25 mL of methylene chloride, and 100 μL of a 10 mass% ethanol solution of tetraethylammonium hydroxide (TEAH) (TEAH:ethanol (volume ratio) = 15:85) was added to the solution. Then, using a UV spectrophotometer (UV-1600 manufactured by Shimadzu Corporation), the absorbance (Abs) at 318 nm was measured. Then, from the measurement result, the number of terminal hydroxyl groups of the modified polyphenylene ether was calculated using the following formula.

[0164] Residual OH amount (μmol / g) = [(25 × Abs) / (ε × OPL × X)] × 106 Here, ε represents the extinction coefficient and is 4700 L / mol·cm. Also, OPL is the cell optical path length and is 1 cm.

[0165] And since the calculated residual OH amount (number of terminal hydroxyl groups) of the modified polyphenylene ether was almost zero, it was found that the hydroxyl groups of the polyphenylene ether before modification were almost completely modified. From this, it was found that the decrease from the number of terminal hydroxyl groups of the polyphenylene ether before modification was the number of terminal hydroxyl groups of the polyphenylene ether before modification. That is, it was found that the number of terminal hydroxyl groups of the polyphenylene ether before modification was the number of terminal functional groups of the modified polyphenylene ether. That is, the number of terminal functional groups was 1.8. This is designated as "modified PPE-1".

[0166] · Modified PPE-2: Monofunctional vinylbenzyl-modified PPE (Mw: 3300) As the polyphenylene ether, the polyphenylene ether described below was used, and it was synthesized in the same manner as the synthesis of the modified PPE1 except that the conditions described below were satisfied.

[0167] The polyphenylene ether used had a structure represented by the formula (5) (SA120 manufactured by SABIC Innovative Plastics, intrinsic viscosity (IV) 0.125 dl / g, and the number of terminal hydroxyl groups was 1.

[0168] Next, the reaction between the polyphenylene ether and chloromethylstyrene was carried out in the same manner as the synthesis of the modified PPE1, except that 200 g of the polyphenylene ether (SA120), 15 g of CMS, and 0.92 g of a phase transfer catalyst (tetra-n-butylammonium bromide) were used, and an aqueous sodium hydroxide solution (10 g of sodium hydroxide / 10 g of water) was used instead of the aqueous sodium hydroxide solution (20 g of sodium hydroxide / 20 g of water).

[0169] And the obtained solid was 1 Analyzed by 1H-NMR (400 MHz, CDCl3, TMS). As a result of measuring the NMR, a peak derived from ethenylbenzyl was confirmed at 5 to 7 ppm. From this, it was confirmed that the obtained solid was a modified polyphenylene ether having a group represented by the formula (1) at the molecular terminal. Specifically, it was confirmed that it was an ethenylbenzylated polyphenylene ether.

[0170] Also, the number of terminal functional groups of the modified polyphenylene ether was measured in the same manner as above. As a result, the number of terminal functional groups was 0.9.

[0171] Also, the intrinsic viscosity (IV) of the modified polyphenylene ether in methylene chloride at 25 °C was measured in the same manner as the above method. As a result, the intrinsic viscosity (IV) of the modified polyphenylene ether was 0.125 dl / g. ·DVB: Divinylbenzene (manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.) ·TAIC: Triallyl isocyanurate (manufactured by Nippon Kasei Co., Ltd.) · B-1000: Polybutadiene oligomer (manufactured by Nippon Soda Co., Ltd.)

[0172] <Thermally expandable microcapsules> · EM403 (manufactured by Sekisui Chemical Co., Ltd., thermal expansion start temperature 150 - 170 °C, maximum expansion temperature 200 - 220 °C) · EM504 (manufactured by Sekisui Chemical Co., Ltd., thermal expansion start temperature 160 - 180 °C, maximum expansion temperature 190 - 210 °C) · 980DU120 (manufactured by Nippon Fillite Co., Ltd., thermal expansion start temperature 158 - 173 °C, maximum expansion temperature 215 - 235 °C) · F-230D (manufactured by Matsumoto Yushi-Seiyaku Co., Ltd., thermal expansion start temperature 180 - 190 °C, maximum expansion temperature 220 - 240 °C) · F-260D (manufactured by Matsumoto Yushi-Seiyaku Co., Ltd., thermal expansion start temperature 190 - 200 °C, maximum expansion temperature 250 - 260 °C)

[0173] <Other components> (Reaction initiator) · Peroxide: "Perbutyl P", 1,3-bis(butylperoxyisopropyl)benzene (manufactured by NOF Corporation) (Inorganic filler) · SO-C2: Spherical silica (manufactured by Admatechs Co., Ltd.) (Blowing agent) · Neocelbone N#5000: Chemical blowing agent (manufactured by Eimei Kasei Kogyo Co., Ltd.) · Spansel ST#44: Chemical blowing agent (manufactured by Eimei Kasei Kogyo Co., Ltd.)

[0174] <Examples 1 - 15, Comparative Examples 1 - 5> [Preparation method] (Resin varnish) First, each component was added to toluene at the blending ratios shown in Tables 1 and 2, and modified PPE and other thermosetting resins were added so that the solid content concentration became 50% by mass. The mixture was heated and stirred at 80 °C for 60 minutes to be mixed and dissolved. The mixture was allowed to cool to 25 °C, and then thermally expandable microcapsules, peroxide, inorganic filler, etc. were added, stirred, and dispersed with a bead mill to obtain a resin varnish (toluene solution resin varnish).

[0175] (Copper foil with resin) Using the resin varnishes of each of the examples and comparative examples prepared above, a resin-coated copper foil (RCC) was created and used for subsequent evaluations.

[0176] For the RCC, copper foils with a thickness of 18 μm or 36 μm (「FV-WS」manufactured by Furukawa Electric Co., Ltd.) were used. Then, the above resin varnish was applied to the surface of the copper foil so that the cured thickness would be 50 μm or more, and this was heated and dried at 130 °C for 3 minutes until it reached a semi-cured state to obtain the RCC.

[0177] (Metal-clad laminate) Two sheets of the above RCC were laminated together, and under vacuum conditions, at a temperature of 200 °C and a pressure of 5 - 10 kg / cm 2 it was heated and pressed for 120 minutes to obtain a 100-μm-thick copper-clad laminate (CCL) (evaluation substrate) with copper foils adhered to both sides.

[0178] <Evaluation Test 1> (Substrate formability) The above-prepared laminate (CCL) was visually evaluated. Those without swelling and with good adhesion were rated as ○, and those with swelling or no adhesion were rated as ×.

[0179] (Glass transition temperature (Tg)) The outer-layer copper foil of the above copper-clad laminate (CCL) was etched over the entire surface, and for the obtained sample, the Tg was measured using a viscoelastic spectrometer 「DMS100」manufactured by Seiko Instruments Inc. At this time, dynamic viscoelastic measurement (DMA) was performed with a tensile modulus and a frequency of 10 Hz, and the temperature at which tanδ showed a maximum when the temperature was raised from room temperature to 300 °C at a heating rate of 5 °C / min was defined as the Tg.

[0180] (Dielectric properties: relative permittivity (Dk) and dissipation factor (Df)) The laminate obtained by removing the copper foil from the above copper-clad laminate (CCL) was used as a test piece, and the relative permittivity (Dk) and dielectric loss tangent (Df) of the test piece were measured by the cavity resonator perturbation method. Specifically, using a network analyzer (N5230A manufactured by Agilent Technologies), the relative permittivity (Dk) and dielectric loss tangent (Df) of the test piece at 10 GHz were measured.

[0181] (Oven heat resistance) The heat resistance was evaluated according to the standard of JIS C 6481 (1996). The above copper-clad laminate cut to a predetermined size was left in a thermostatic bath set at 240 °C, 260 °C, and 280 °C for 1 hour, and then taken out. Then, the test pieces heat-treated at each temperature were visually observed, and when no swelling occurred, it was evaluated as ○, and when swelling occurred, it was evaluated as ×.

[0182] The above results are shown in Tables 1 and 2.

[0183]

Table 1

[0184]

Table 2

[0185] (Discussion) As is clear from the results shown in Tables 1 and 2, it was confirmed that, according to the present invention, a very low relative permittivity (2.2 or less) can be achieved. Furthermore, the dielectric loss tangent was also less than 0.004, and it was found that a cured product having low dielectric properties was obtained. And in the examples of the present invention, the Tg was high, the oven heat resistance was also high, and the moldability was excellent. Also, it was found that by selecting an appropriate thermally expandable microcapsule depending on the maximum expansion temperature, etc., a resin composition capable of obtaining a cured product excellent in the balance between heat resistance and low dielectric properties can be obtained. In particular, Examples 10 to 15 showed very excellent oven heat resistance.

[0186] On the other hand, in Comparative Examples 1 to 3 where the thermally expandable microcapsules of the present invention were not used, sufficient low dielectric characteristics aimed at by the present invention could not be obtained. Further, in Comparative Examples 4 and 5 where a chemical foaming agent was used instead of the thermally expandable microcapsules, violent foaming occurred even with a small addition, so that a laminate (substrate) could not be produced and the performance as a substrate could not be measured.

[0187] <Evaluation Test 2> Regarding Examples 2, 5, 6, 9 and 12, and Comparative Examples 2 and 3, the density of the cured resin was also evaluated by the method described below.

[0188] (Density) From the cured resin plate (thickness 300 μm), a 10 cm × 10 cm piece was cut out with a punching cutter. The result of measuring the weight of the piece with a precision balance was taken as M (g). Also, the volume V of the resin piece was calculated by the area S (10 × 10 cm 2 ) × thickness H (0.03 cm). The density was calculated by using the formula ρ = M / V to calculate the density of each cured resin piece.

[0189] The above results are shown in Table 3.

[0190]

Table 3

[0191] (Discussion) As is clear from the results shown in Table 3, it was confirmed that the resin composition of the present invention can achieve weight reduction in addition to low dielectric characteristics and heat resistance in its cured product.

[0192] On the other hand, in Comparative Examples 2 and 3 where inorganic fillers were added without using the thermally expandable microcapsules of the present invention, weight reduction as in the examples could not be achieved.

[0193] This application is based on Japanese Patent Application Nos. 2020-94229 and 2020-94230, filed on May 29, 2020, the contents of which are incorporated herein by reference.

[0194] In order to describe the present invention, the embodiments have been appropriately and fully described through specific examples, drawings, etc. in the foregoing. However, it should be recognized that those skilled in the art can easily make changes and / or improvements to the foregoing embodiments. Therefore, as long as the modified or improved forms implemented by those skilled in the art do not depart from the scope of the claims recited in the claims, such modified or improved forms are construed as being included within the scope of the claims.

Industrial Applicability

[0195] The present invention has broad industrial applicability in the technical field related to electronic materials and various devices using the same.

Claims

1. A resin composition for a wiring board material, comprising a thermosetting resin and thermally expandable microcapsules, wherein the thermosetting resin contains at least one selected from the group consisting of a modified polyphenylene ether compound, a hydrocarbon resin, a maleimide compound, an oxetane resin, a benzoxazine compound, and a compound having a polymerizable unsaturated group, and a resin composition for a wiring board material, wherein the relative dielectric constant (10 GHz) of the cured product of the resin composition is more than 1.0 and 2.2 or less.

2. The density of the cured product of the resin composition is 0.3 to 1.0 g / cm ３ The resin composition for a wiring board material according to claim 1, which is such.

3. The resin composition for a wiring board material according to claim 1 or 2, wherein the thermally expandable microcapsules are hollow particles obtained by coating a liquid compound that vaporizes by heat with an outer shell containing a thermoplastic polymer.

4. The resin composition for a wiring board material according to claim 3, wherein the thermoplastic polymer is a polymer containing a structure derived from at least one selected from the group consisting of a nitrile monomer, a monomer having a carboxyl group, a (meth)acrylate monomer, a styrene monomer, and a monomer having an amide group.

5. The resin composition for a wiring board material according to claim 4, wherein the thermoplastic polymer is a polymer containing a structure derived from at least one selected from the group consisting of a nitrile monomer, a monomer having a carboxyl group, and a (meth)acrylate monomer.

6. The resin composition for a wiring board material according to claim 5, wherein the nitrile monomer contains at least one selected from acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile, and fumaronitrile.

7. The resin composition for a wiring board material according to any one of claims 3 to 6, wherein the liquid compound contains at least one selected from the group consisting of a hydrocarbon compound, a hydrogen halide compound, an alcohol compound, an ether compound, and a ketone compound, and has a boiling point that is equal to or lower than the softening temperature of the thermoplastic polymer.

8. The resin composition for a wiring board material according to any one of claims 3 to 7, wherein the outer shell is insoluble in the liquid compound.

9. The resin composition for a wiring board material according to any one of claims 3 to 8, wherein the average thickness of the outer shell of the thermally expandable microcapsules is 1 to 8 μm.

10. The resin composition for a wiring board material according to any one of claims 1 to 9, wherein the maximum thermal expansion temperature of the thermally expandable microcapsules is 100 to 280°C.

11. The resin composition for a wiring board material according to any one of Claims 1 to 10, wherein the volume at maximum expansion at the maximum thermal expansion temperature of the thermally expandable microcapsules is 3 times or more the volume at normal temperature (25°C).

12. The resin composition for a wiring board material according to Claim 11, wherein the thermally expandable microcapsules can hold the expansion volume at maximum expansion, which is 3 times or more the volume at normal temperature (25°C), for 10 minutes or more.

13. The resin composition for a wiring board material according to any one of Claims 1 to 12, which contains 1 to 50 parts by mass of the thermally expandable microcapsules with respect to 100 parts by mass of the resin component containing the thermosetting resin.

14. The resin composition for a wiring board material according to any one of Claims 1 to 13, which further contains 1 to 300 parts by mass of an inorganic filler with respect to 100 parts by mass of the resin component containing the thermosetting resin.

15. A prepreg for a wiring board, which has the resin composition according to any one of Claims 1 to 14 or a semi-cured product of the resin composition and a fibrous base material.

16. A film with a resin for a wiring board, which has a resin layer containing the resin composition according to any one of Claims 1 to 14 or a semi-cured product of the resin composition and a support film.

17. A metal foil with a resin for a wiring board, which has a resin layer containing the resin composition according to any one of Claims 1 to 14 or a semi-cured product of the resin composition and a metal foil.

18. A metal-clad laminate for a wiring board, which has an insulating layer containing the resin composition according to any one of Claims 1 to 14 or a cured product of the prepreg according to Claim 15 and a metal foil.

19. A wiring board, which has an insulating layer containing the resin composition according to any one of Claims 1 to 14 or a cured product of the prepreg according to Claim 15 and a wiring.

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