Method for manufacturing wiring board with protective material, curable composition, and wiring board with protective material

Abstract

This method for manufacturing a wiring board with a protective material includes a step for applying a curable composition to a space between conductors on a wiring board, which has a substrate and the conductors that are arranged in a pattern on the substrate, and then irradiating with an active energy ray so as to cure the curable composition. The curable composition includes a ring-opening polymerizable compound and a photo-cationic polymerization initiator.

Description

Method for producing a wiring board with protective material, curable composition, and wiring board with protective material

[0001] The present invention relates to a method for producing a wiring board with a protective material, a curable composition, and a wiring board with a protective material.

[0002] In recent years, with the increasing output of electronic devices such as solar cells used for photovoltaic power generation and high-power motors, high voltages and currents are sometimes applied to the conductor circuits of wiring boards. Accordingly, wiring boards having conductors with a thickness of 100 μm or more are being used. In such wiring boards, an insulating protective material is sometimes placed in the space between the conductors to ensure insulation between the conductors.

[0003] For example, Patent Document 1 discloses a method for manufacturing a wiring board in which a metal plate on which a conductor circuit is formed is sandwiched between two prepregs and thermocompression-bonded, in which a glass substrate impregnated with epoxy resin is used as the prepreg.

[0004] Patent Document 2 discloses a method for producing a wiring board with a protective material by applying a thermosetting composition containing an epoxy resin and an amine-based curing agent to the space between the conductors of a conductor circuit and then thermally curing the composition.

[0005] Patent Document 3 discloses a method for producing a wiring board with a protective material by applying a photocurable composition to spaces between conductors of a conductor circuit, then repeating the photocuring step multiple times to form a layer thicker than the conductors, and then scraping the surface of the obtained layer. The photocurable composition used is a photoradical polymerizable composition containing an acrylic resin and a photoradical polymerization initiator.

[0006] JP 2001-36201 A JP 2019-56077 A JP 2020-194877 A

[0007] In wiring boards having thick conductor circuits as described above, the spacing between conductors is becoming narrower as the conductor circuits become denser and smaller. Compositions for protective materials to be placed in such narrow spaces are desired to have viscosity stability sufficient to allow application using a dispenser, inkjet printer, or the like. However, thermosetting compositions such as those described in Patent Document 2 contain an amine-based curing agent, which is a thermosetting agent, and therefore have the problem of easily increasing viscosity even with a slight increase in temperature, resulting in poor application properties.

[0008] In contrast, the photo-radical polymerizable photocurable composition described in Patent Document 3 has good viscosity stability and good applicability. However, the inventors have newly discovered that the protective material obtained by applying and curing the photocurable composition has poor adhesion and heat resistance. In particular, in order to fill the space between thick conductors, it is necessary to form a thick cured product of the photocurable composition, and it has been revealed that in such cases, the adhesion and heat resistance of the protective material are particularly likely to decrease.

[0009] An object of the present invention is to provide a method for producing a wiring board with a protective material, a curable composition, and a wiring board with a protective material, which are capable of forming a protective material with good adhesion and heat resistance even between thick conductors.

[0010] [1] A method for producing a protective material-equipped wiring board, the method comprising the steps of applying a curable composition between conductors in a wiring board having a substrate and conductors arranged in a pattern on the substrate, and then irradiating active energy rays to cure the composition, thereby forming a layer containing a cured product of the curable composition, the curable composition containing a ring-opening polymerizable compound and a photocationic polymerization initiator. [2] The method for producing a protective material-equipped wiring board according to [1], wherein the conductor has a thickness of 100 to 1000 μm. [3] The method for producing a protective material-equipped wiring board according to [1], wherein the conductor has a thickness of 200 to 500 μm. [4] The method for producing a protective material-equipped wiring board according to [1], wherein the conductor has a thickness of 300 to 500 μm. [5] The method for producing a protective material-equipped wiring board according to any one of [1] to [4], further comprising the steps of applying the curable composition onto the layer containing the cured product of the curable composition, and then irradiating active energy rays to cure the composition, thereby obtaining a laminate of layers containing the cured product of the curable composition. [6] The method for producing a protective material-equipped wiring board according to any one of [1] to [5], wherein the thickness of the layer containing the cured product of the curable composition is thinner than the thickness of the conductor. [7] The method for producing a protective material-equipped wiring board according to any one of [1] to [6], wherein the thickness of the layer containing the cured product of the curable composition is 5 to 100 μm. [8] The method for producing a protective material-equipped wiring board according to [5], further comprising a step of heat-treating a laminate of layers containing the cured product of the curable composition. [9] The method for producing a protective material-equipped wiring board according to any one of [1] to [8], wherein the curable composition is applied by an inkjet method.

[10] A curable composition for protecting a wiring board, disposed between conductors having a thickness of 100 μm or more, the curable composition comprising a ring-opening polymerizable compound and a photocationic polymerization initiator.

[11] The curable composition according to

[10] , wherein the ring-opening polymerizable compound is a cationically polymerizable compound.

[12] The curable composition according to

[11] , wherein the cationically polymerizable compound is a compound having an oxetanyl group or an epoxy group.

[13] The curable composition according to

[11] or

[12] , wherein the cationically polymerizable compound further contains a radically polymerizable group.

[14] The curable composition according to any one of

[10] to

[13] , further containing a coupling agent.

[15] A wiring board with a protective material, the wiring board having a substrate and conductors arranged in a pattern thereon, and a protective material arranged between the conductors, wherein the protective material comprises a laminate of one or more layers containing a cured product of the curable composition according to any one of

[10] to

[14] .

[16] The wiring board with a protective material according to

[15] , wherein the protective material comprises a laminate of layers containing a cured product of the curable composition.

[0011] According to the present invention, it is possible to provide a method for manufacturing a wiring board with a protective material, a curable composition, and a wiring board with a protective material, which can form a protective material with good adhesion and heat resistance even between thick conductors.

[0012] 1A to 1F are schematic cross-sectional views showing a method for manufacturing a wiring board with a protective material according to one embodiment of the present invention, and FIG. 2 is a schematic cross-sectional view showing a wiring board with a protective material obtained by the above manufacturing method.

[0013] Hereinafter, a resin molded product according to one embodiment of the present invention and a resin composition used therein will be specifically described. In this specification, unless otherwise specified, the term "to" means a numerical range including a lower limit and an upper limit, which are endpoints.

[0014] As described above, when the photocurable composition of Patent Document 3 is applied thickly, adhesion and heat resistance tend to decrease. While the reason for this is unclear, it is presumed that the photocurable composition of Patent Document 3 contains an acrylic monomer, which is a photoradical polymerizable compound, resulting in increased cure shrinkage after photocuring. In particular, if the photocurable composition is applied thickly to form a thick protective film, it becomes difficult for light to reach the interior of the coating film. Therefore, it is conceivable to apply a thin layer of the photocurable composition and repeat the photocuring process to laminate multiple thin cured layers. However, as the number of photocurings increases, cure shrinkage after photocuring tends to increase, and adhesion between the wiring board and the cured layer and between the cured layer itself tends to decrease. Furthermore, the more significant the cure shrinkage, the more residual stress concentrates between the wiring board and the cured layer, making peeling more likely to occur at high temperatures, which also tends to reduce heat resistance.

[0015] In contrast, in the present invention, by cationic polymerization of the ring-opening polymerizable compound, it is possible to make it difficult for cure shrinkage to occur, and as a result, even when a thick protective material is formed by laminating multiple layers containing a cured product of the curable composition, peeling due to cure shrinkage can be suppressed, and a protective material with good adhesion and heat resistance can be formed.

[0016] That is, in one embodiment of the present invention, in a method for manufacturing a wiring board with a protective material, a curable composition containing a ring-opening polymerizable compound and a photocationic polymerization initiator is used as the protective material.

[0017] First, a curable composition for protecting a wiring board according to one embodiment of the present invention will be described.

[0018] 1. Curable Composition The curable composition according to this embodiment contains a ring-opening polymerizable compound and a photocationic polymerization initiator.

[0019] 1-1. Ring-opening polymerizable compound The ring-opening polymerizable compound is preferably a cationically polymerizable compound. The cationically polymerizable compound is preferably a compound having an oxetanyl group or an epoxy group as a ring-opening polymerizable group.

[0020] The ring-opening polymerizable compound may be a monofunctional compound having only one ring-opening polymerizable group in one molecule, or may be a polyfunctional compound having two or more ring-opening polymerizable groups in one molecule.

[0021] In addition, only one type of ring-opening polymerizable compound may be used, or two or more types may be used. For example, a monofunctional ring-opening polymerizable compound may be combined with a polyfunctional ring-opening polymerizable compound. When the content of the monofunctional ring-opening polymerizable compound is high, the cured product of the curable composition obtained tends to be more flexible, and when the content of the polyfunctional ring-opening polymerizable compound is high, the crosslink density of the cured product obtained tends to be higher and stronger. In addition, a compound having an oxetanyl group may be combined with a compound having an epoxy group.

[0022] The compound having an oxetanyl group (oxetane compound) is a compound having one or more oxetanyl groups. Examples of the oxetane compound include monofunctional oxetane compounds such as 3-ethyl-3-[(phenoxy)methyl]oxetane, 3-ethyl-3-(hexyloxymethyl)oxetane, 3-ethyl-3-(2-ethylhexyloxymethyl)oxetane, 3-ethyl-3-(hydroxymethyl)oxetane, and 3-ethyl-3-(chloromethyl)oxetane; Polyfunctional oxetane compounds such as 3,7-bis(3-oxetanyl)-5-oxa-nonane, 1,4-bis[(3-ethyl-3-oxetanylmethoxy)methyl]benzene, 1,2-bis[(3-ethyl-3-oxetanylmethoxy)methyl]ethane, 1,3-bis[(3-ethyl-3-oxetanylmethoxy)methyl]propane, ethylene glycol bis(3-ethyl-3-oxetanylmethyl)ether, triethylene glycol bis(3-ethyl-3-oxetanylmethyl)ether, tetraethylene glycol bis(3-ethyl-3-oxetanylmethyl)ether, 1,4-bis(3-ethyl-3-oxetanylmethoxy)butane, 1,6-bis(3-ethyl-3-oxetanylmethoxy)hexane, 3-ethyl-3-(3-ethyl-3-oxetanylmethyloxymethyl)oxetane, and xylylene bisoxetane are included. Among these, from the viewpoint of reactivity, polyfunctional oxetane compounds are preferred, and bifunctional oxetane compounds are more preferred. These may be used alone or in combination of two or more.

[0023] The compound having an epoxy group (epoxy compound) is a compound having one or more epoxy groups. Examples of the epoxy compound include alicyclic epoxy compounds, aliphatic epoxy compounds, and aromatic epoxy compounds.

[0024] Examples of the alicyclic epoxy compound include polyglycidyl ethers of polyhydric alcohols having an alicyclic ring, and cyclohexene oxide and cyclopentene oxide-containing compounds obtained by epoxidizing cyclohexene or cyclopentene ring-containing compounds with an oxidizing agent. Examples of the alicyclic epoxy compound include 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, 3,4-epoxy-1-methylcyclohexyl-3,4-epoxy-1-methylhexanecarboxylate, 6-methyl-3,4-epoxycyclohexylmethyl-6-methyl-3,4-epoxycyclohexanecarboxylate, 3,4-epoxy-3-methylcyclohexylmethyl-3,4-epoxy-3-methylcyclohexanecarboxylate, 3,4-epoxy-5-methylcyclohexylmethyl-3,4-epoxy-5-methylcyclohexanecarboxylate, bis(3,4-epoxycyclohexylmethyl)adipate, 3,4-epoxy-6-methylcyclohexanecarboxylate, methylene bicarbonate, and the like. bis(3,4-epoxycyclohexane), propane-2,2-diyl-bis(3,4-epoxycyclohexane), 2,2-bis(3,4-epoxycyclohexyl)propane, dicyclopentadiene diepoxide, ethylene bis(3,4-epoxycyclohexanecarboxylate), cyclohexene oxide, dioctyl epoxyhexahydrophthalate, di-2-ethylhexyl epoxyhexahydrophthalate, 1-epoxyethyl-3,4-epoxycyclohexane, 1,2-epoxy-2-epoxyethylcyclohexane, limonene dioxide, vinylcyclohexene dioxide, hydrogenated bisphenol A diglycidyl ether, hydrogenated bisphenol F diglycidyl ether, hydrogenated bisphenol S diglycidyl ether, and the like.

[0025] Aliphatic epoxy compounds are epoxy compounds that do not belong to alicyclic epoxy compounds or aromatic epoxy compounds. Examples of aliphatic epoxy compounds include glycidyl ethers of aliphatic alcohols such as allyl glycidyl ether, butyl glycidyl ether, 2-ethylhexyl glycidyl ether, and C12-13 mixed alkyl glycidyl ethers; and glycidyl ethers of aliphatic polyhydric alcohols or alkylene oxide adducts thereof such as ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, glycerin triglycidyl ether, trimethylolpropane triglycidyl ether, sorbitol tetraglycidyl ether, pentaerythritol tetraglycidyl ether, dipentaerythritol hexaglycidyl ether, polyethylene glycol diglycidyl ether, and polypropylene glycol diglycidyl ether.

[0026] The aromatic epoxy compound is an epoxy compound having an aromatic ring. Examples of the aromatic epoxy compound include glycidyl ethers of monohydric phenols having an aromatic ring, such as phenol, cresol, and butylphenol (e.g., phenyl glycidyl ether); glycidyl ethers of aromatic compounds having two or more phenolic hydroxyl groups, such as bisphenol A, bisphenol F, bisphenol E, resorcinol, hydroquinone, catechol, and phenol novolak, or alkylene oxide adducts thereof (e.g., bisphenol F diglycidyl ether, bisphenol A diglycidyl ether, bisphenol B diglycidyl ether, bisphenol AD ​​diglycidyl ether, bisphenol S diglycidyl ether, halogenated bisphenol A diglycidyl ether, tetrachlorobisphenol A diglycidyl ether, catechin diglycidyl ether, resorcinol diglycidyl ether, and hydroquinone diglycidyl ether); and styrene oxide.

[0027] Among these, from the viewpoint of further improving the adhesion of a cured product of the curable composition (hereinafter also simply referred to as "cured product") to a substrate, the cationically polymerizable compound preferably contains a cationically polymerizable compound having an aromatic ring. This is thought to be because the aromatic ring of the cationically polymerizable compound having an aromatic ring is more likely to be oriented at the interface with the substrate, thereby further improving adhesion.

[0028] Examples of the cationic polymerizable compound having an aromatic ring include the above-mentioned oxetane compound having an aromatic ring and the epoxy compound having an aromatic ring. Among them, glycidyl ethers having an aromatic ring (for example, glycidyl ethers of aromatic compounds having two or more phenolic hydroxyl groups or alkylene oxide adducts thereof) are preferred. Glycidyl ethers having an aromatic ring can further improve the curing reactivity and adhesion of the cured product from the viewpoint of the orientation of the aromatic ring and the degree of rotational freedom of the ether group.

[0029] When the cationically polymerizable compound includes a cationically polymerizable compound having an aromatic ring, the content of the cationically polymerizable compound having an aromatic ring is preferably 5 to 60 mass% relative to the total amount of the cationically polymerizable compound. When the content of the cationically polymerizable compound having an aromatic ring is 5 mass% or more, the adhesion of the cured product can be further improved. When the content of the cationically polymerizable compound having an aromatic ring is 60 mass% or less, the viscosity of the curable composition can be further reduced. From the same viewpoint, the content of the cationically polymerizable compound having an aromatic ring is more preferably 10 to 55 mass% relative to the total amount of the cationically polymerizable compound.

[0030] Furthermore, from the viewpoint of further improving the adhesion, heat resistance, and migration resistance of the cured product, it is preferable that the cationically polymerizable compound further contains a radically polymerizable group, i.e., a compound having both a ring-opening polymerizable group and a radically polymerizable group. The mechanism by which the adhesion and heat resistance of the cured product are improved by including a compound having both a ring-opening polymerizable group and a radically polymerizable group is unclear, but it is presumed that this is because radicals are generated during heat treatment, and some of the radically polymerizable groups undergo radical polymerization, thereby increasing the crosslink density.

[0031] Examples of compounds having a radical polymerizable group and a ring-opening polymerizable group include oxetane compounds or epoxy compounds having a (meth)acryloyl group, a vinyl group, or an allyl group. Examples of the oxetane compound include (3-ethyl-3-oxetanyl)methoxymethyl(meth)acrylate, (3-ethyloxetan-3-yl)methyl methacrylate, and 3-ethyl-3-((allyloxy)methyl)oxetane. Examples of the epoxy compound include 3-methacryloyloxymethylcyclohexene oxide, 3-acryloyloxymethylcyclohexene oxide, and 3-vinylcyclohexene oxide.

[0032] When the cationic polymerizable compound includes a compound having both a ring-opening polymerizable group and a radical polymerizable group, the content of the compound having both a ring-opening polymerizable group and a radical polymerizable group is preferably 5 to 30 mass% relative to the total amount of the cationic polymerizable compound. When the content of the compound having both a ring-opening polymerizable group and a radical polymerizable group is 5 mass% or more, the crosslinking density of the cured product can be further increased, thereby further improving adhesion and heat resistance. Migration resistance can also be further improved. When the content of the compound having both a ring-opening polymerizable group and a radical polymerizable group is 30 mass% or less, cure shrinkage can be further reduced. From the same perspective, the content of the compound having both a ring-opening polymerizable group and a radical polymerizable group is more preferably 10 to 20 mass% relative to the total amount of the cationic polymerizable compound.

[0033] Furthermore, from the viewpoint of enhancing photocurability, the cationic polymerizable compound preferably contains an alicyclic epoxy compound. When the cationic polymerizable compound contains an alicyclic epoxy compound, the content of the alicyclic epoxy compound is preferably 5 to 40 mass% relative to the total amount of the cationic polymerizable compounds. When the content of the alicyclic epoxy compound is 5 mass% or more, the photocurability can be further enhanced. When the content of the alicyclic epoxy compound is 40 mass% or less, the increase in viscosity of the curable composition can be further reduced. From the same viewpoint, the content of the alicyclic epoxy compound is more preferably 10 to 30 mass% relative to the total amount of the cationic polymerizable compounds.

[0034] The content of the ring-opening polymerizable compound is preferably 70% by mass or more, more preferably 90% by mass or more, relative to the curable composition. When the content of the ring-opening polymerizable compound is 70% by mass or more, photocuring is more excellent. The upper limit of the content of the ring-opening polymerizable compound is not particularly limited, but is preferably 100% by mass.

[0035] 1-2. Photocationic Polymerization Initiator A photocationic polymerization initiator is a compound that generates an acid capable of initiating cationic polymerization when irradiated with active energy rays such as ultraviolet rays.

[0036] Examples of the photocationic polymerization initiator include aromatic sulfonium salts, aromatic iodonium salts, aromatic diazonium salts, and aromatic ammonium salts. The anion portion of these salts is BF ４ － , P.F. ６ － , SbF ６ － , or BX ４ － (X is a phenyl group substituted with at least two fluorine or trifluoromethyl groups).

[0037] Examples of the aromatic sulfonium salt include bis[4-(diphenylsulfonio)phenyl]sulfide bishexafluorophosphate, bis[4-(diphenylsulfonio)phenyl]sulfide bishexafluoroantimonate, bis[4-(diphenylsulfonio)phenyl]sulfide bistetrafluoroborate, bis[4-(diphenylsulfonio)phenyl]sulfide tetrakis(pentafluorophenyl)borate, diphenyl-4-(phenylthio)phenylsulfonium hexafluorophosphate, diphenyl-4-(phenylthio)phenylsulfonium hexafluoroantimonate, diphenyl-4-(phenylthio)phenylsulfonium tetrafluoroborate, and the like.

[0038] Examples of aromatic iodonium salts include diphenyliodonium hexafluorophosphate, diphenyliodonium hexafluoroantimonate, diphenyliodonium tetrafluoroborate, diphenyliodonium tetrakis(pentafluorophenyl)borate, bis(dodecylphenyl)iodonium hexafluorophosphate, bis(dodecylphenyl)iodonium hexafluoroantimonate, bis(dodecylphenyl)iodonium tetrafluoroborate, bis(dodecylphenyl)iodonium tetrakis(pentafluorophenyl)borate, and the like.

[0039] Examples of aromatic diazonium salts include phenyldiazonium hexafluorophosphate, phenyldiazonium hexafluoroantimonate, phenyldiazonium tetrafluoroborate, and the like.

[0040] Examples of aromatic ammonium salts include 1-benzyl-2-cyanopyridinium hexafluorophosphate, 1-benzyl-2-cyanopyridinium hexafluoroantimonate, and the like.

[0041] Examples of the photocationic polymerization initiator include Irgacure 250, Irgacure 270, Irgacure 290 (manufactured by BASF), CPI-100P, CPI-101A, CPI-200K, CPI-210S, CPI-310B, CPI-400PG (manufactured by San-Apro Ltd.), SP-150, SP-170, SP-171, SP-056, SP-066, SP-130, SP-140, SP-601, SP-606, and SP-701 (manufactured by ADEKA Corporation). Of these, sulfonium salts such as Irgacure 270, Irgacure 290, CPI-100P, CPI-101A, CPI-200K, CPI-210S, CPI-310B, CPI-400PG, SP-150, SP-170, SP-171, SP-056, SP-066, SP-601, SP-606, and SP-701 are preferred.

[0042] The content of the cationic photopolymerization initiator is preferably 0.01 to 10 parts by mass, and more preferably 0.05 to 5 parts by mass, relative to 100 parts by mass of the ring-opening polymerizable compound. When the content of the cationic photopolymerization initiator is 0.01 part by mass or more, the resulting curable composition has better curability. When the content of the cationic photopolymerization initiator is 10 parts by mass or less, the curing reaction of the resulting curable composition does not become too fast, and the cured product can be made more uniform.

[0043] 1-3. Other Components The curable composition may further contain other components such as a sensitizer, a coupling agent, or other curable compounds, as needed, within the scope of not impairing the object of the present invention.

[0044] The sensitizer can further improve the polymerization initiation efficiency of the cationic polymerization initiator, and further accelerate the curing reaction of the ring-opening polymerizable compound.

[0045] Examples of the sensitizer include anthracene compounds such as 9,10-dibutoxyanthracene, thioxanthone compounds such as 2,4-diethylthioxanthone, 2,2-dimethoxy-1,2-diphenylethan-1-one, benzophenone, 2,4-dichlorobenzophenone, methyl o-benzoylbenzoate, 4,4'-bis(dimethylamino)benzophenone, 4-benzoyl-4'methyldiphenyl sulfide, and the like.

[0046] The content of the sensitizer is preferably 0.05 to 5 parts by weight relative to 100 parts by weight of the ring-opening polymerizable compound. When the content of the sensitizer is 0.05 parts by weight or more, the sensitizing effect is more pronounced. When the content of the sensitizer is 5 parts by weight or less, light can be transmitted to deep areas without excessive absorption. The content of the sensitizer is more preferably 0.1 to 3 parts by weight.

[0047] (Coupling Agent) A coupling agent can be added to further improve the adhesion and heat resistance between the cured product and the conductor. Examples of the coupling agent include silane coupling agents, titanium coupling agents, zirconium coupling agents, and aluminum coupling agents, and silane coupling agents are preferred.

[0048] The silane coupling agent may be one having a reactive group such as an epoxy group, a carboxy group, a methacryloyl group, an isocyanate group, etc. Examples of such silane coupling agents include trimethoxysilylbenzoic acid, 3-aminopropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-isocyanatopropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, vinyltriacetoxysilane, vinyltrimethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

[0049] Among these, epoxy-terminated silane coupling agents are preferred, with 3-glycidoxypropyltrimethoxysilane and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane being more preferred. The silanol groups react with copper, and the epoxy terminals react with monomers during photopolymerization, improving adhesion between the conductor and the cured product. Improved adhesion makes it possible to withstand interfacial peeling caused by differences in the thermal expansion coefficients of the conductor and the cured product at high temperatures.

[0050] The content of the coupling agent can be, for example, 0.1 to 10 parts by mass, preferably 0.5 to 5 parts by mass, relative to 100 parts by weight of the ring-opening polymerizable compound. When the content of the coupling agent is within this range, bleeding out of excess coupling agent can be further suppressed, and the adhesion and heat resistance of the resulting cured product can be further improved.

[0051] (Other Curable Compounds) Examples of other curable compounds include radical polymerizable compounds having no ring-opening polymerizable group. However, the content of the radical polymerizable compound is set to a level that does not impair the object of the present invention, and is, for example, preferably 20% by mass or less, more preferably 5% by mass or less, relative to the curable composition.

[0052] 1-4. Physical Properties The viscosity of the curable composition is preferably appropriately low from the viewpoint of facilitating filling of narrow spaces between conductors. Specifically, the viscosity of the curable composition measured at 25°C and 50 rpm using an E-type viscometer can be, for example, 5 to 200 mPa·s. When the viscosity is within this range, the resulting curable composition has superior inkjet applicability. From the same viewpoint, the viscosity is preferably 8 to 30 mPa·s.

[0053] The curable composition can be obtained by mixing a cationically polymerizable compound, a cationic polymerization initiator, and, if necessary, other components such as a coupling agent, using a mixer such as a homodisper, a homomixer, a universal mixer, a planetary mixer, a kneader, or a three-roll mill.

[0054] The curable composition can be widely used as an insulating protective material for electronic devices, particularly as a protective material for wiring boards such as thick copper substrates, preferably as a protective material disposed in the space between conductors of a wiring board, more preferably as a protective material disposed in the space between conductors having a thickness of 100 μm or more.

[0055] Next, a method for producing a wiring board with a protective material using the above curable composition will be described.

[0056] 2. Method for manufacturing a wiring board with a protective material The method for manufacturing a wiring board with a protective material includes a step of applying a curable composition between conductors of a wiring board having a substrate and conductors arranged in a pattern, and then irradiating the curable composition with active energy rays to cure the composition, thereby forming a layer containing a cured product of the curable composition. Furthermore, the method for manufacturing a wiring board with a protective material may further include a step of laminating a layer containing a cured product of the curable composition on the obtained layer containing the cured product of the curable composition, as necessary.

[0057] 1A to 1E are schematic cross-sectional views showing a method for manufacturing a wiring board with a protective material according to one embodiment of the present invention.

[0058] The method for manufacturing a wiring board with a protective material according to this embodiment includes the following steps: 1) applying a curable composition between conductors 12 of wiring board 10, which has substrate 11 and conductors 12 arranged in a pattern thereon, and then irradiating the curable composition with active energy rays to cure the composition, thereby forming layer 13A containing a cured product of the curable composition (see FIGS. 1A to 1C); 2) applying a curable composition onto layer 13A containing the cured product of the curable composition, and then irradiating the curable composition with active energy rays to cure the composition, thereby laminating layer 13B containing the cured product of the curable composition (see FIGS. 1D to 1E); and 3) heat-treating the resulting laminate (FIG. 1F).

[0059] Step 1) (Coating) First, a wiring board 10 having a substrate 11 and conductors 12 arranged in a pattern is prepared (see FIG. 1A). The curable composition M described above is coated into the spaces between the conductors 12 on this wiring board 10 (see FIG. 1B).

[0060] The method for applying the curable composition is not particularly limited, and may be, for example, inkjet coating, dispenser coating, spray coating, screen printing, coating with a bar coater, etc. Among these, inkjet coating, dispenser coating, and spray coating are preferred, with inkjet coating being more preferred, from the viewpoint of making it easy to fill spaces between narrowly spaced conductors arranged on a wiring board without generating voids or the like.

[0061] The coating thickness of the curable composition is not particularly limited, but a thinner thickness is preferable from the viewpoint of allowing active energy rays to easily reach the inside of the coating film. Specifically, the coating thickness of the curable composition is preferably set so that the thickness of the obtained layer containing the cured product of the curable composition is thinner than the thickness of the conductor, preferably to a thickness described below.

[0062] (Irradiation of Active Energy Rays) Next, the applied curable composition is irradiated with active energy rays to cure the curable composition (see FIG. 1C).

[0063] The active energy rays may be any energy rays that can trigger the above-mentioned cationic polymerization reaction or radical polymerization reaction, and may be any of light rays such as far ultraviolet rays, ultraviolet rays, near ultraviolet rays, infrared rays, electromagnetic waves such as X-rays and gamma rays, as well as electron beams, proton beams, neutron beams, etc. Among these, ultraviolet rays are preferred from the viewpoints of curing speed, ease of availability of irradiation equipment, etc. The irradiation conditions may be such that the first curable composition is cured, and may be, for example, 200 to 1500 mJ / cm. ２ It can be about.

[0064] (Layer Containing Cured Product of Curable Composition) By the irradiation with active energy rays as described above, a layer 13A containing a cured product of the curable composition is formed.

[0065] The thickness of the layer 13A containing the cured product of the curable composition is not particularly limited, but is preferably thinner than the thickness of the conductor 12, preferably 5 to 100 μm, and more preferably 50 to 100 μm. When the thickness of the layer is 50 μm or more, the number of laminations can be reduced, thereby further shortening the production time. When the thickness of the layer is 100 μm or less, the active energy rays can reach the interior more easily, making curing easier. For example, the thickness of the layer 13A containing the cured product of the curable composition is preferably the thickness of the conductor 12 divided by the number of laminations of layers containing the cured product of the curable composition (the number of times the process of applying the curable composition and then irradiating it with active energy rays to cure it is repeated).

[0066] Step 2) The curable composition is applied onto the layer 13A containing the cured product of the curable composition obtained in the step 1, and then the layer 13B containing the cured product of the curable composition is laminated thereon by irradiating it with active energy rays and, if necessary, heat-treating it (see FIGS. 1D and 1E ). As a result, a protective material 13 containing a laminate of two cured product layers 13A and 13B of the curable compositions is formed on the substrate 10 between the conductors 12.

[0067] The methods and conditions for applying the curable composition, irradiating with active energy rays, and heat treatment in this step may be the same as or similar to the methods and conditions for applying the curable composition, irradiating with active energy rays, and heat treatment in the above step 1). Furthermore, the thickness of the layer containing the cured product of the curable composition formed in this step may be the same as or similar to the thickness of the layer containing the cured product of the curable composition in the above step 1).

[0068] Step 3) When the curable composition contains a polymerizable compound having radical polymerizability, the resulting laminate of layers containing the cured product of the curable composition may be further heat-treated (post-cured) ( FIG. 1F ). By performing the heat treatment, the polymerizable compound having a radical polymerizable group can be thermally cured even in the absence of a thermal curing agent. This can further increase the crosslink density of the curable composition in the layer containing the cured product of the curable composition.

[0069] The temperature and time of the heat treatment may be such that the radically polymerizable polymerizable compound in the curable composition can be thermally cured. The heat treatment temperature can be, for example, 120 to 200° C. The heat treatment time can be, for example, 30 to 120 minutes.

[0070] The heat treatment method is not particularly limited, and may be performed using a hot air circulation dryer, an IR heater, a ceramic heater, or the like.

[0071] (Operation) According to the above embodiment, a curable composition containing the above-described ring-opening polymerizable compound and a photocationic polymerization initiator is used as the curable composition to fill the spaces between the conductors of the wiring board. Because the curable composition cures by photocationic polymerization, it is less likely to undergo cure shrinkage, as occurs in photoradical polymerization. Therefore, a protective material with good adhesion and heat resistance can be filled into the spaces between the conductors.

[0072] In particular, when layers of a cured material thinner than the thickness of a conductor are laminated as in the above embodiment, the adhesion between the layers is likely to decrease if there is cure shrinkage. Even in such cases, the use of the curable composition described above can make it difficult for the adhesion between the layers to decrease.

[0073] Furthermore, in wiring boards, such as thick copper substrates, it is desirable to be able to suppress short circuits between conductors due to migration. Migration is a phenomenon in which the metal material constituting a conductor ionizes, flows, and grows, resulting in connections between conductors and short circuits. Migration is likely to occur when the protective material surrounding the conductor contains a large amount of ionic species or when a curable compound that facilitates the growth and mobility of metal ions is used. Migration is also likely to occur when the protective material surrounding the conductor contains a large amount of residual monomer. In contrast, this embodiment uses a curable composition that undergoes a curing reaction via cationic polymerization. In cationic polymerization, light-generated acid acts within the coating film even after light irradiation to promote the curing reaction. This reduces the occurrence of phenomena such as insufficient curing due to radical deactivation in radical polymerization, and allows for the production of a coating film with minimal residual monomer. In particular, when the curable composition contains a cationically polymerizable compound with a radically polymerizable group, sufficient curing can be achieved by photocuring and thermal curing, thereby reducing residual monomer. This further reduces the risk of migration.

[0074] 3. Wiring Board with Protective Material Fig. 2 is a schematic cross-sectional view showing a wiring board with a protective material obtained by the above manufacturing method.

[0075] As shown in FIG. 2 , a protective material-attached wiring board 20 has a wiring board 10 having conductors 12 arranged in a pattern, and a protective material 13 arranged in the spaces between the conductors 12 .

[0076] The wiring board 10 has a substrate 11 and conductors 12 arranged in a pattern.

[0077] The conductors 12 arranged in a pattern can be, for example, conductor circuits. The material of the conductors 12 is not particularly limited, but is preferably copper. The cross-sectional shape of the conductors 12 is also not particularly limited, and can be, for example, rectangular or trapezoidal. The thickness of the conductors 12 is not particularly limited, but is preferably, for example, 100 to 1000 μm, more preferably 200 to 500 μm, and even more preferably 300 to 500 μm. The thickness of the conductors 12 refers to the height from the surface of the substrate 11.

[0078] The protective material 13 includes a layer containing the cured product of the curable composition. In this embodiment, the protective material 13 includes a layer 13A containing the cured product of the curable composition and a layer 13B containing the cured product of the curable composition disposed thereon (see FIG. 2 ). Whether the protective material 13 has such a laminated structure of layers containing the cured product of the curable composition can be confirmed, for example, by cutting a cross section and observing it with a microscope or the like.

[0079] The thickness of the protective material 13 may be the same as or different from the thickness of the conductor 12. For example, the thickness of the protective material 13 is preferably 80 to 120% of the thickness of the conductor 12, more preferably 90 to 110%, and even more preferably 95 to 105%.

[0080] 4. Modifications In the method for manufacturing a wiring board with a protective material according to the above embodiment, an example has been shown in which two layers containing a cured product of a curable composition are laminated in the space between conductors 12 of wiring board 10, but the present invention is not limited to this, and only one layer may be formed, or three or more layers may be laminated.

[0081] For example, when only one layer containing the cured product of the curable composition is formed, the above step 2) can be omitted. In this case, the thickness of the layer containing the cured product of the curable composition is preferably approximately the same as the thickness of the conductor 12.

[0082] On the other hand, when three or more layers containing the cured product of the curable composition are laminated, the process of applying the curable composition at the same position between the conductors of the wiring board and then irradiating with active energy rays to cure the curable composition may be repeated three or more times so that the total thickness of the finally obtained laminate of layers containing the cured product of the curable composition (thickness of the protective material 13) is approximately the same as the thickness of the conductor 12.

[0083] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0084] 1. Materials for Curable Composition 1-1. Polymerizable Compound 1-1-1. Ring-opening Polymerizable Compound (Oxetane Compound) OXT-121 (manufactured by Toagosei Co., Ltd., bifunctional, containing aromatic ring) OXT-221 (manufactured by Toagosei Co., Ltd., bifunctional)

[0085] (Oxetane compound having a radical polymerizable group) OXMA (manufactured by UBE, 3-ethyl-3-oxetanylmethyl methacrylate)

[0086] (Alicyclic epoxy compounds) Celloxide 2021P (manufactured by Daicel Corporation, alicyclic epoxy compound, bifunctional)

[0087] (Aliphatic epoxy compounds) Denacol EX-211 (manufactured by Nagase & Co., Ltd., neopentyl glycol diglycidyl ether, bifunctional)

[0088] (Aromatic epoxy compounds) Denacol EX-201 (manufactured by Nagase & Co., Ltd., resorcinol diglycidyl ether, bifunctional)

[0089] 1-1-2. Radical polymerizable compounds: Isobornyl acrylate, 1,6-hexanediol diacrylate, trimethylolpropane triacrylate

[0090] 1-2. Photopolymerization initiators: CPI-100P (manufactured by San-Apro Co., Ltd., aromatic sulfonium salt, photocationic polymerization initiator); Irgacure 379 (manufactured by IGM Co., Ltd., photoradical polymerization initiator)

[0091] 1-3. Other ingredients: KBM-402 (Shin-Etsu Silicones Co., Ltd., 3-glycidoxypropyltrimethoxysilane, silane coupling agent), 2,4-diethylthioxanthone (photosensitizer), UVS-1101 (Air Water Performance Chemicals Co., Ltd., photosensitizer)

[0092] 2. Preparation of Curable Compositions [Preparation of Compositions 1 to 6] The components were mixed using a stirrer so as to have the composition ratios shown in Table 1, to prepare curable compositions.

[0093] The formulation of the curable composition is shown in Table 1.

[0094] 3. Preparation and Evaluation of Wiring Board with Protective Material [Example 1] A wiring board having a conductor circuit with the thickness shown in Table 2 was prepared. The conductor width was 1 mm, the spacing between the conductors was 1 mm, and the conductor thickness was 200 μm. The conductors used were in a linear pattern extending linearly in one direction. Next, the curable composition prepared above was applied by inkjet printing to the spaces between the conductors of the wiring board. The apparatus used was a linear XY stage equipped with one inkjet head (KM1024iLHE-30, manufactured by Konica Minolta, Inc., nozzle resolution 360 dpi) and a control system (IJCS-1, manufactured by Konica Minolta, Inc.). The inkjet printing was performed at a resolution of 1440 dpi x 1440 dpi. Specifically, after one application at 360 dpi, the curable composition was applied by a UV-LED light source with a wavelength of 365 nm at an illuminance of 2 W / cm. ２ , irradiation energy 1000 mJ / cm ２ The head was then moved 18 μm (corresponding to the pixel spacing at 1440 dpi) in the nozzle row direction, and coating was repeated in four passes. These coating and UV irradiation processes were performed a total of two times (two laminations), and then heat treatment was performed in an oven at 150°C for 1 hour to form a protective material.

[0095] Examples 2 to 4, Comparative Example 1 Wiring boards were produced in the same manner as in Example 1, except that the type of curable composition was changed as shown in Table 2.

[0096] Examples 5 to 7 Wiring boards were produced in the same manner as in Example 1, except that the type of curable composition, the thickness of the conductor, and the number of laminations were changed as shown in Table 2.

[0097] Example 8 A wiring board was produced in the same manner as in Example 1, except that the method of applying the curable composition was changed to dispenser application and the number of laminations was changed to one.

[0098] [Evaluation] (1) Adhesion The adhesion between layers was evaluated by a cross-cut peeling method and was evaluated according to the following criteria: ⊚: no peeling at all; ◯: slight peeling at the intersections of the cross-cuts; Δ: peeling in 30% to less than 50% of the cross-cuts; ×: peeling in 50% or more of the cross-cuts.

[0099] (2) Solder Resistance Solder resistance (heat resistance) was evaluated by immersing the sample in a solder bath at 260°C for 20 seconds, repeating this process three times, and visually checking for the occurrence of peeling or cracking. Evaluation was then made according to the following criteria: ○: No peeling or cracking occurred △: Slight peeling or cracking occurred ×: Peeling or cracking occurred over the entire surface

[0100] (3) Photocuring: The curable composition was applied to a copper plate with an applicator to a thickness of 50 μm, and then exposed to a UV-LED light source with a wavelength of 365 nm at an illuminance of 2 W / cm. ２ , irradiation energy 1000 mJ / cm ２ The resulting cured film was evaluated by touch for tackiness on the surface.

[0101] The preparation conditions and evaluation results of Examples 1 to 8 and Comparative Example 1 are shown in Table 2.

[0102]

[0103] As shown in Table 2, it can be seen that in Comparative Example 1, which used a radically polymerizable curable composition, both the adhesion and solder resistance of the cured product were low. In contrast, it can be seen that in Examples 1 to 8, which used cationically polymerizable curable compositions, the adhesion and solder resistance of the cured product were all good.

[0104] These findings demonstrate that the use of a cationically polymerizable curable composition can improve adhesion and heat resistance even in the case of a thick coating film.

[0105] According to the present invention, it is possible to provide a method for manufacturing a wiring board with a protective material, which can form a protective material with good adhesion and heat resistance even between thick conductors, a curable composition for protecting a wiring board, and a wiring board with a protective material.

[0106] This application claims priority from Japanese Patent Application No. 2023-207775, filed December 8, 2023. The contents of the specification and drawings of that application are incorporated herein by reference in their entirety.

[0107] REFERENCE SIGNS LIST 10: Circuit board 11: Substrate 12: Conductor 13: Protective material 13A, 13B: Layer containing a cured product of a curable composition 20: Circuit board with protective material

Claims

1. A method for producing a wiring board with a protective material, comprising the steps of applying a curable composition between conductors of a wiring board having a substrate and conductors arranged in a pattern on the substrate, and then curing the composition by irradiating the composition with active energy rays to form a layer containing a cured product of the curable composition, wherein the curable composition contains a ring-opening polymerizable compound and a photocationic polymerization initiator.

2. The method for manufacturing a wiring board with a protective material according to claim 1, wherein the conductor has a thickness of 100 to 1000 μm.

3. The method for manufacturing a wiring board with a protective material according to claim 1, wherein the conductor has a thickness of 200 to 500 μm.

4. The method for manufacturing a wiring board with a protective material according to claim 1, wherein the conductor has a thickness of 300 to 500 μm.

5. A method for producing a wiring board with a protective material according to claim 1, further comprising the step of applying the curable composition onto a layer containing a cured product of the curable composition, and then curing the composition by irradiating with active energy rays to obtain a laminate of a layer containing a cured product of the curable composition.

6. The method for producing a wiring board with a protective material according to claim 1 or 5, wherein the thickness of the layer containing the cured product of the curable composition is thinner than the thickness of the conductor.

7. The method for producing a wiring board with a protective material according to claim 1 or 5, wherein the layer containing the cured product of the curable composition has a thickness of 5 to 100 μm.

8. The method for producing a wiring board with a protective material according to claim 5, further comprising a step of heat treating a laminate of layers containing the cured product of the curable composition.

9. The method for producing a wiring board with a protective material according to claim 1 or 5, wherein the curable composition is applied by an inkjet method.

10. A curable composition for protecting a wiring board disposed between conductors having a thickness of 100 μm or more, the curable composition comprising a ring-opening polymerizable compound and a photocationic polymerization initiator.

11. The curable composition according to claim 10, wherein the ring-opening polymerizable compound is a cationically polymerizable compound.

12. The curable composition according to claim 11, wherein the cationically polymerizable compound is a compound having an oxetanyl group or an epoxy group.

13. The curable composition according to claim 12, wherein the cationically polymerizable compound further comprises a radically polymerizable group.

14. The curable composition of claim 10, further comprising a coupling agent.

15. A wiring board with a protective material, comprising: a wiring board having a substrate and conductors arranged in a pattern on the substrate; and a protective material arranged between the conductors, wherein the protective material includes a layer containing a cured product of the curable composition according to any one of claims 10 to 14.

16. The wiring board with protective material according to claim 15, wherein the protective material comprises a laminate of layers containing a cured product of the curable composition.

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