JP2012119470A - Wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wiring board that is lightweight, hardly cracks, suppresses generation of CAF and smear in a via formation process, and further has a low filler filling rate and low linear expansion.
[MEANS FOR SOLVING PROBLEMS] After removing impurities in a resin such as a thermoplastic resin, a thermosetting resin, and a light (active energy ray) curable resin from a substance containing cellulose obtained from a plant-derived raw material through purification, for example. A wiring substrate obtained by dispersing cellulose fibers having a number average fiber diameter of 4 to 1000 nm obtained by defibrating.
[Selection figure] None

Description

  The present invention relates to a wiring board such as a printed wiring board used as an electronic component.

  Wiring boards such as printed wiring boards are used in various applications, and various high characteristics are required. Insulating properties, high heat transfer, low linear expansion, and flame retardancy are required for the wiring board material. Examples of rigid board materials having no flexibility include paper phenol and glass epoxy boards, and examples of flexible board materials include: Examples include polyimide and polyester films. As electronic devices have become smaller and lighter in recent years, the mounting density of components and the density of wiring have been increased. However, these wiring board materials have the following problems and are becoming more dense. It was difficult to convert.

  For example, a glass epoxy substrate (FR-4) is a glass cloth made of glass fiber impregnated with epoxy resin and thermally cured, and is often used for surface mounting and multilayer substrates. However, as shown in Non-Patent Document 1, FR-4 has a problem of short circuit phenomenon (Conductive Anodic Filaments; CAF) due to contact between the copper electrode and the glass fiber. Further, since glass fiber has inherently hard and brittle properties, FR-4 has a problem of cracking the substrate. Such a crack is pointed out as a cause of the above-mentioned CAF. In addition, since the bending rigidity of FR-4 decreases when the film is thinned, the dimensional change and warpage in the circuit processing process tend to be large. For this reason, there is a problem that the dimensional accuracy is liable to be lowered, the deflection generated during the heating process is large, and the mounting accuracy of the components is liable to be lowered.

  In addition, among rigid substrates, a build-up substrate that has a higher mounting density and is required to be thinner employs a film obtained by filling an epoxy resin or polyimide with silica in order to reduce the coefficient of linear expansion. However, an inorganic material such as silica has a problem that unburned residue (smear) remains in the interlayer via formation process (laser processing). In addition, when a spherical filler such as silica is used, the linear expansion coefficient of the film only decreases linearly with respect to the filling rate, so that the filler is highly filled to achieve the required low linear expansion. There was a need.

Matsushita Electric Works Technical Report (Vol. 54 (2006), No. 3, pp.44-48)

  It is an object of the present invention to provide a wiring board that is light in weight, hardly cracks, suppresses the generation of CAF and smear in a via formation step, and further has a low filler filling rate and low linear expansion.

As a result of intensive studies by the present inventors, it has been found that the above problem can be solved by using a composite in which fine cellulose fibers are dispersed in a resin as a wiring board, and the present invention has been achieved.
That is, the present invention resides in a wiring board in which cellulose fibers having a number average fiber diameter of 4 to 1000 nm are dispersed in a resin.

  According to the present invention, it is possible to provide a wiring board that is light in weight, hardly cracks, suppresses generation of CAF and smear in a via formation process, and has a low filler filling rate and low linear expansion.

The description of the constituent requirements described below is an example (representative example) of the embodiment of the present invention, and the contents are not specified.
The wiring board of the present invention is a board in which cellulose fibers having an average fiber diameter of 4 to 1000 nm are uniformly dispersed in a resin.
The wiring board in the present invention is a board used as a rigid board (single-sided board, double-sided board, multilayer board, build-up board), flexible board, etc., for example, a mobile phone, a digital camera, a central processing unit. It can be used for electronic devices such as (CPU).

(1) Resin The resin contained in the wiring board of the present invention is not particularly limited, and examples thereof include a thermoplastic resin, a thermosetting resin, and a light (active energy ray) curable resin.
(Thermoplastic resin)
Examples of the thermoplastic resin include styrene resin, acrylic resin, aromatic polycarbonate resin, aliphatic polycarbonate resin, aromatic polyester resin, aliphatic polyester resin, aliphatic polyolefin resin, and cyclic olefin resin. And polyamide resins, polyphenylene ether resins, thermoplastic polyimide resins, polyacetal resins, polysulfone resins, and amorphous fluorine resins. These thermoplastic resins may be used individually by 1 type, and may use 2 or more types together.

(Curable resin)
The thermosetting resin and the light (active energy ray) curable resin mean a resin that is cured by heat or light. The precursor usually means a substance that is liquid, semi-solid or solid at room temperature and exhibits fluidity at room temperature or under heating. These can be insoluble and infusible resins formed by forming a network-like three-dimensional structure while increasing the molecular weight by causing a polymerization reaction or a crosslinking reaction by the action of a curing agent, a catalyst, heat or light.

(Thermosetting resin)
Although the thermosetting resin in the present invention is not particularly limited, for example, epoxy resin, acrylic resin, oxetane resin, phenol resin, urea resin, melamine resin, unsaturated polyester resin, silicon resin, polyurethane resin, diallyl phthalate resin, thermosetting Resin such as conductive polyimide resin.

(Photo-curing resin)
Although the photocurable resin in this invention is not specifically limited, For example, resin, such as an epoxy resin, an acrylic resin, an oxetane resin, or its precursor illustrated in the description of the above-mentioned thermosetting resin is mentioned.
In particular, an epoxy resin or an acrylic resin is preferable, and an epoxy resin is particularly preferable.
Examples of the epoxy resin include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, biphenol type epoxy resin, bisphenol AD type epoxy resin, bisphenol acetophenone type epoxy resin, bisphenol fluorenone type epoxy resin, and the like. Type epoxy resin, diglycidyl ether type epoxy resin of monocyclic dihydric phenol such as catechol, resorcin, hydroquinone, dihydroxy naphthalene type epoxy resin, dihydroxy dihydroanthracene type epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin , Glycidyl ether type epoxy resins such as bisphenol A novolac type epoxy resin, glycidyl ester Le epoxy resin, glycidyl amine type epoxy resins, linear aliphatic epoxy resins, alicyclic epoxy resins, various epoxy resins such as heterocyclic epoxy resins.

These epoxy resins may be substituted with a substituent having no adverse effect such as an alkyl group, an aryl group, an ether group or an ester group.
Among these epoxy resins, particularly preferable ones are bisphenol A type epoxy resins, bisphenol F type epoxy resins, crystalline resins which are easy to handle, and 4,4′-biphenol type epoxy resins which have a low viscosity above the melting point. , 3,3 ′, 5,5′-tetramethyl-4,4′-biphenol type epoxy resin, phenol novolac type epoxy resin which is multifunctional and has a high cross-linking density upon curing to obtain a cured product having high heat resistance, cresol novolak Type epoxy resin, bisphenol A novolac type epoxy resin and the like.

  The epoxy resin can be used from a monomer type having a low weight average molecular weight (for example, Mw = 200) to a polymer type having a high molecular weight (for example, Mw = 90,000). When the weight average molecular weight is 100,000 or more, it becomes difficult to handle the resin, which is not preferable. From the viewpoint of the handleability of the resin, the weight average molecular weight of the epoxy resin is preferably 200 to 80,000, more preferably 300 to 60,000.

Examples of the acrylic resin include polymers and copolymers such as (meth) acrylic acid, (meth) acrylonitrile, (meth) acrylic acid ester, and (meth) acrylamide. Especially, the polymer of a (meth) acrylic acid (meth) acrylic acid ester, a copolymer, etc. are mentioned preferably.
The weight average molecular weight of the acrylic resin is not particularly limited, but is preferably 300 to 3,000,000 and more preferably 400 to 2,500,000 from the viewpoint of handleability.

The wiring board of the present invention is preferably formed by curing the resin and / or a precursor of the resin and a composition containing cellulose fibers having an average fiber diameter of 4 to 1000 nm.
In this case, the precursor of the resin means a monomer or oligomer constituting the resin. For example, the epoxy resin precursor includes dihydric phenols, and any epoxy group may be used as long as a hydroxyl group is bonded to an aromatic ring. For example, bisphenols such as bisphenol A, bisphenol F, bisphenol B, bisphenol AD, 4-4′-biphenyl, 3,3 ′, 5,5′-tetramethyl-4,4′-biphenol, biphenol, catechol, resorcin , Hydroquinone, dihydroxynaphthalene and the like.

  Examples of the epoxy resin precursor include those in which these dihydric phenols are substituted with non-interfering substituents such as an alkyl group, an aryl group, an ether group, and an ester group. Among these dihydric phenols, preferred are bisphenol A, bisphenol F, 4,4'-biphenol, 3,3 ', 5,5'-tetramethyl-4,4'-biphenol. These dihydric phenols can be used in combination.

In addition to dihydric phenols, polyfunctional phenol resins may be mentioned, such as phenol novolac resins, bisphenol novolac resins, dicyclopentadiene phenol resins, Xylok phenol resins, terpene modified phenol resins, melamine modified phenol novolac resins. And a triazine structure-containing novolac resin.
Examples of the acrylic resin precursor include (meth) acrylic acid, (meth) acrylonitrile, (meth) acrylic acid ester, (meth) acrylamide, and the like. Especially, (meth) acrylic acid (meth) acrylic acid ester etc. are mentioned preferably.

  The content of the resin in the wiring board is usually 1% by weight or more, preferably 20% by weight or more, more preferably 30% by weight or more, usually 99.5% by weight or less, preferably 95% by weight or less, more preferably. Is 98 wt% or less.

(2) Cellulose fiber having an average fiber diameter of 4 to 1000 nm The number average fiber diameter of the cellulose fiber used in the present invention is usually preferably 1000 nm or less, 200 nm or less, more preferably 100 nm or less, and particularly preferably 80 nm or less. The lower limit of the number average fiber diameter is usually 4 nm or more.
The number average fiber diameter was observed with SEM, TEM, etc., a line was drawn on the diagonal line of the photograph, and 12 fibers in the vicinity were randomly extracted to remove the thickest and thinnest fibers. It is the value obtained by measuring points and averaging.
Cellulose fibers having an average fiber diameter of 4 to 1000 nm are not particularly limited, but are obtained by defibrating after removing impurities from a cellulose-containing substance (cellulose-containing material) through purification. It is preferable. In particular, it is preferable to use as a raw material a substance (cellulose-containing material) containing cellulose obtained from plant-derived raw materials.

The average aspect ratio of the cellulose fiber used is preferably 5 or more, and more preferably 10 or more. This is because, generally, the filler in the resin has a high aspect ratio, and the interaction between the fillers works at a low filling rate, thereby producing an effect.
Further, the cellulose fiber used may be one derived by chemical modification (chemically modified cellulose fiber). The chemical modification is a chemical modification in which a hydroxyl group in cellulose reacts with a chemical modifier.

  Substituents introduced into the hydroxyl group of cellulose by chemical modification (groups introduced by substituting hydrogen atoms in the hydroxyl group) are not particularly limited. For example, acetyl group, acryloyl group, methacryloyl group, propionyl group, propioroyl group, butyryl Group, 2-butyryl group, pentanoyl group, hexanoyl group, heptanoyl group, octanoyl group, nonanoyl group, decanoyl group, undecanoyl group, dodecanoyl group, myristoyl group, palmitoyl group, stearoyl group, pivaloyl group, benzoyl group, naphthoyl group, nicotinoyl Group, acyl group such as isonicotinoyl group, furoyl group, cinnamoyl group, isocyanate group such as 2-methacryloyloxyethylisocyanoyl group, methyl group, ethyl group, propyl group, 2-propyl group, butyl group, 2-butyl group, ter -Alkyl groups such as butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, undecyl group, dodecyl group, myristyl group, palmityl group, stearyl group, oxirane group, oxetane group, thiirane group, Examples include a thietane group. Among these, an acyl group having 2 to 12 carbon atoms such as an acetyl group, an acryloyl group, a methacryloyl group, a benzoyl group, and a naphthoyl group is particularly preferable.

  Moreover, it is preferable that this cellulose fiber has a cellulose I type crystal structure. Cellulose I-type crystals are preferable because they have higher crystal elastic modulus than other crystal structures, and thus have high elastic modulus, high strength, and low linear expansion coefficient. That the cellulose fiber has the I-type crystal structure is typical at two positions near 2θ = 14-17 ° and 2θ = 22-23 ° in the diffraction profile obtained by wide-angle X-ray diffraction image measurement. It can be identified from having a peak.

  The content of the cellulose fiber in the wiring board is not particularly limited, but the preferred content of the cellulose fiber is preferably 0.5% by weight or more, more preferably 1% by weight or more based on the total amount of the composite. 2% by weight or more is more preferable, 99% by weight or less is preferable, 80% by weight or less is more preferable, and 70% by weight or less is more preferable. When there is too little content of a cellulose fiber, there exists a tendency for the effect of the linear thermal expansion coefficient reduction of the wiring board by a cellulose fiber to become inadequate. If the cellulose fiber content is too large, adhesion between the fibers by the resin or filling of the spaces between the fibers becomes insufficient, and the strength of the substrate and the flatness of the surface when cured may be reduced.

The wiring board of the present invention is preferably substantially composed of cellulose fibers and a resin.
The content of the cellulose fibers and the resin in the wiring board can be determined from, for example, the weight of cellulose before being combined with the resin and the weight of cellulose after being combined. Alternatively, the wiring board can be immersed in a solvent in which the resin is soluble to remove only the resin, and the weight can be determined from the weight of the remaining cellulose fibers. In addition, the functional group of the resin or cellulose fiber can be quantified and determined using thermal analysis or specific gravity of the resin, or NMR or IR.

(3) Others In the wiring board of the present invention, in addition to the resin and cellulose fibers described above, a chain transfer agent, an ultraviolet absorber, a filler, a silane coupling agent, a photo / thermal polymerization initiator, A curing agent or the like may be contained.
In addition, when using an epoxy resin or its precursor as resin or a resin precursor, the epoxy resin hardening | curing agent may contain.
The epoxy resin curing agent is not particularly limited, and for example, polyhydric phenol compounds, amine compounds, acid anhydrides, and the following can be used.

  For example, bisphenol A, bisphenol F, bisphenol AD, hydroquinone, resorcin, methylresorcin, biphenol, tetramethylbiphenol, dihydroxynaphthalene, dihydroxydiphenyl ether, thiodiphenols, phenol novolac resin, cresol novolac resin, phenol aralkyl resin, terpene phenol resin Various polyphenols such as dicyclopentadiene phenol resin, bisphenol A novolak resin, naphthol novolak resin, biphenylphenol resin, brominated bisphenol A, brominated phenol novolac resin, various phenols and benzaldehyde, hydroxybenzaldehyde, Condensation with various aldehydes such as crotonaldehyde and glyoxal Of polyphenolic resins obtained by reaction, various phenol resins such as heavy oil or pitches, co-condensation resins of phenols and formaldehyde, and phenolic hydroxyl groups of these various phenols (resins) Active ester compounds obtained by esterifying all or part of them, such as benzoate or acetate, and acid anhydrides such as methyltetrahydrophthalic anhydride, hexahydrophthalic anhydride, pyromellitic anhydride, methylnadic acid And amines such as diethylenetriamine, isophoronediamine, diaminodiphenylmethane, diaminodiphenylsulfone, dicyandiamide, aliphatic polyamine, and polyamide.

Cationic polymerization initiators can also be used as curing agents for epoxy resins or their precursors. As the cationic polymerization initiator, an active energy ray cationic polymerization initiator that generates a cationic species or a Lewis acid by active energy rays or a thermal cationic polymerization initiator that generates a cationic species or a Lewis acid by heat is used. be able to.
For example, phosphine compounds such as triphenylphosphine, phosphonium salts such as tetraphenylphosphonium tetraphenylborate, 2-methylimidazole, 2-phenylimidazole, 2-ethyl-4-methylimidazole, 2-undecyl Imidazoles such as imidazole, 1-cyanoethyl-2-methylimidazole, 2,4-dicyano-6- [2-methylimidazolyl- (1)]-ethyl-S-triazine, 1-cyanoethyl- 2-undecylimidazolium trimellitate, 2-methylimidazolium isocyanurate, 2-ethyl-4-methylimidazolium tetraphenylborate, 2-ethyl-1,4-dimethylimidazolium tetraphenylborate Imidazolium salts such as 2,4-6-tris (dimethylaminomethy ) Amines such as phenol and benzyldimethylamine; ammonium salts such as triethylammonium tetraphenylborate; 1,5-diazabicyclo (5,4,0) -7-undecene; 1,5-diazabicyclo (4, And diazabicyclo compounds such as 3,0) -5-nonene.

Further, tetraphenylborate, phenol salt, phenol novolak salt, 2-ethylhexanoate and the like of these diazabicyclo compounds, triflic acid salt, boron trifluoride ether complex compound, metal fluoroboron complex salt, bis (perfluoroalkyl sulfonyl) methane metal salts, aryl diazonium compounds, aromatic onium salts, periodic table dicarbonyl chelate of a IIIa~Va group elements, thiopyrylium salts, MF ₆ ^- anion (where M is phosphorus, antimony Periodic group VIb elements, arylsulfonium complex salts, aromatic iodonium complex salts, aromatic sulfonium complex salts, bis [4- (diphenylsulfonio) phenyl] sulfide-bis-hexafluorometal salts (Eg phosphate, arsenate, antimonate, etc.), ants Or a sulfonium complex salt, an aromatic sulfonium or iodonium salt of a halogen-containing complex ion, or the like. In addition, mixed ligand metal salts of iron compounds and silanol-aluminum complexes can also be used. Some of these salts are FX-512 (3M), UVR-6990 and UVR-6974 (Union Carbide), UVE-1014 and UVE-1016 (General Electric) ), KI-85 (Degussa), SP-150 and SP-170 (Asahi Denka), and Sun Aid SI-60L, SI-80L and SI-100L (Sanshin Chemical Co., Ltd.) Available.

  A preferred thermal cationic polymerization initiator is triflate, for example, diethylammonium triflate, triethylammonium triflate, diisopropylammonium triflate, ethyl diisopropyl triflate available from 3M as FC-520. Ammonium, etc. (many of which are described in Modern Coatings published October 1980 by RR Alm).

On the other hand, among aromatic onium salts that are also used as active energy ray cationic polymerization initiators, there are those that generate cationic species by heat, and these can also be used as thermal cationic polymerization initiators.
These may be used alone or in combination of two or more.
Examples of the curing accelerator include amines such as benzyldimethylamine and various imidazole compounds, and phosphines such as triphenylphosphine.

  Examples of the filler include silica filled for the purpose of reducing the linear expansion coefficient, rubber components filled for the purpose of roughening the surface of the cured product (for example, described in Japanese Patent No. 378549), and a flame retardant.

(4) Manufacturing method of wiring board Although it does not specifically limit as a manufacturing method of the wiring board of this invention, The above-mentioned resin and / or the precursor of resin, and a cellulose fiber whose average fiber diameter is 4-1000 nm It is preferably formed by curing a composition comprising

The resin and / or resin precursor and a composition containing cellulose fibers having an average fiber diameter of 4 to 1000 nm usually have a resin and / or resin precursor and an average fiber diameter of 4 in a solvent. It is a dispersion liquid in which cellulose fibers of ˜1000 nm are dispersed.
Examples of the solvent include water and organic solvents. Specifically, the organic solvent is not particularly limited as long as the resin or resin precursor used is dissolved or dispersed. For example, aromatic hydrocarbon, aprotic polar solvent, alcohol solvent, ketone solvent, glycol Examples include ether solvents. Preferred are aprotic polar solvents (particularly amide solvents), alcohol solvents, and ketone solvents. These solvents may be used alone or in combination of two or more.

In addition, since the organic solvent used by this invention has the process of removing an organic solvent at a next process, it is preferable that a boiling point is not too high. The boiling point of the organic solvent is preferably 300 ° C. or less, preferably 200 ° C. or less, and more preferably 180 ° C. or less. Moreover, 70 degreeC or more is preferable from points, such as handleability.
The aromatic hydrocarbon is preferably an aromatic hydrocarbon having 6 to 12 carbon atoms, specifically, benzene, toluene, xylene and the like.

The alcohol solvent is preferably an alcohol solvent having 1 to 7 carbon atoms, specifically, methanol, ethanol, propanol, butanol and the like.
The ketone solvent (referring to a liquid having a ketone group) is preferably a ketone solvent having 3 to 9 carbon atoms, specifically, acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), diisopropyl. Examples include ketone, di-tert-butyl ketone, 2-heptanone, 4-heptanone, 2-octanone, cyclopentanone, cyclohexanone, cyclohexyl methyl ketone, acetophenone, acetylacetone, and dioxane. Among these, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), cyclopentanone, and cyclohexanone are preferable, and methyl ethyl ketone (MEK) and cyclohexanone are more preferable.

Examples of the aprotic polar solvent include sulfoxide solvents such as dimethyl sulfoxide (DMSO), formamide, N-methylformamide, N, N-dimethylformamide, acetamide, N-methylacetamide, N, N-dimethylacetamide, 2 Examples include amide solvents such as -pyrrolidone and N-methylpyrrolidone.
Preferred examples of the glycol ether solvent include glycol ether solvents having 3 to 9 carbon atoms. Specific examples include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono-n-butyl ether, and ethylene glycol dimethyl ether. , Ethylene glycol monoethyl ether acetate, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-butyl ether, diethylene glycol dimethyl ether, diethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether, propylene glycol mono-n-butyl ether, propylene glycol monomethyl ether Acetate etc. It is.

The content of the cellulose fiber in the composition is preferably 0.5% by weight or more, more preferably 1% by weight or more, and preferably 50% by weight or less based on the total amount of the dispersion from the viewpoint of the stability of the dispersion. 40% by weight or less is more preferable, and 30% by weight or less is more preferable.
The content of the organic solvent in the composition is not particularly limited, but is preferably 1% by weight or more, preferably 5% by weight with respect to the total amount of the composition from the viewpoint of handleability such that the viscosity and liquid stability are suitable. The above is more preferable, 97.5% by weight or less is preferable, and 95% by weight or less is more preferable.

The weight ratio of the resin and / or resin precursor to the organic solvent in the composition is not particularly limited, but in the same manner as described above, from the viewpoint of handleability such that viscosity and liquid stability are suitable, the organic solvent The content of is preferably 5 to 2000 parts by weight and more preferably 25 to 1000 parts by weight with respect to 100 parts by weight of the resin and / or resin precursor.
The composition may contain a chain transfer agent, an ultraviolet absorber, a filler, a silane coupling agent, a photo / thermal polymerization initiator, a curing agent, and the like as described above.

  By using this composition, a wiring board in which cellulose fibers are uniformly dispersed in the resin can be obtained. Although the manufacturing method of this wiring board is not specifically limited, For example, the composition is subjected to heat treatment and / or exposure treatment, and the solvent is removed to obtain a wiring board containing cellulose fibers and a resin. In addition, when a resin precursor is used, the precursor is cured through the step to become a resin.

When performing the heating and / or exposure treatment, the composition may be applied onto a substrate to form a coating film, or may be poured into a mold. When applying or pouring into a mold, the solvent may be removed by performing a drying treatment as necessary.
The conditions for the heat treatment are not particularly limited, and when a resin precursor is used, it may be at or above the temperature at which the precursor is cured. Among these, the heating temperature is preferably 60 ° C. or higher, more preferably 100 ° C. or higher, from the viewpoint that the solvent can be volatilized and removed. In addition, from the point which suppresses decomposition | disassembly of a cellulose fiber, 250 degrees C or less is preferable and 200 degrees C or less is more preferable. The heating time is preferably 60 to 180 minutes from the viewpoint of productivity.

  The heat treatment may be performed multiple times by changing the temperature and the heating time. Specifically, primary heating at 60 to 100 ° C. for 30 to 60 minutes, secondary heating at 130 to 160 ° C. for 30 to 60 minutes, and 150 to 200 ° C. which is 40 to 60 ° C. higher than the secondary heating temperature. It is preferable to carry out by three-stage treatment with tertiary heating for ˜60 minutes in that the solvent is completely removed, the surface shape of the substrate is reduced, and the substrate is completely cured. In addition, at least two stages of heating is preferable.

Examples of the exposure treatment include light such as infrared rays, visible rays, and ultraviolet rays, electron beams, and the like, preferably light. More preferred is light having a wavelength of about 200 to 450 nm, and more preferred is ultraviolet light having a wavelength of 300 to 400 nm.
The amount to be irradiated, or a resin precursor used, but suitably the optimum amount depending on the photopolymerization initiator is selected, the ultraviolet rays having a wavelength of 300 to 450 nm, preferably 0.1 J / cm ² or more 200 J / cm ² Irradiate within the following range. More preferably, irradiation is performed in a range of 1 J / cm ² or more and 20 J / cm ² or less. It is more preferable to irradiate by dividing into multiple times. That is, it is preferable to irradiate about 1/20 to 1/3 of the total irradiation amount at the first time and to irradiate the necessary remaining amount after the second time. Specific examples of the lamp to be used include a metal halide lamp, a high pressure mercury lamp lamp, an ultraviolet LED lamp and the like.

When an epoxy resin and / or precursor thereof is used as the resin and / or resin precursor, an epoxy resin curing agent and / or a curing accelerator may be added to the composition and cured to produce a composite. preferable.
When the weight average molecular weight (Mw) of the epoxy resin component in the composition is 200 to 6,000, the epoxy resin (equivalent): epoxy resin curing agent (equivalent) = 1: 0.8 to 1.2 It is preferable to do. Further, when the weight average molecular weight (Mw) of the epoxy resin component in the composition is more than 6,000 but not more than 90,000, it can be cured by adding an epoxy resin curing agent. It is preferable to add 2 to 20% by weight of the components and cure.

Since the high molecular weight epoxy resin has a low epoxy group concentration, it is preferable to add a polyfunctional epoxy resin to increase the epoxy group concentration and increase the crosslinking density in order to cure.
The curing accelerator is preferably blended in an amount of 0.1 to 5.0 parts by weight with respect to 100 parts by weight of the total epoxy resin.
As curing conditions, the following curing methods I and II are preferably exemplified.

  Curing Method I: When the weight average molecular weight (Mw) of the epoxy resin component in the composition is 200 to 6,000, an epoxy resin curing agent is added to the composition and heated and mixed at a temperature of 100 to 200 ° C. for 5 minutes. Then, a curing accelerator is quickly mixed to prepare a resin composition. The resin composition is defoamed after removing the solvent component under reduced pressure, and then poured into a mold and heated at 120 to 200 ° C. for 2 to 5 hours to obtain a wiring board.

  Curing method II: When the weight average molecular weight (Mw) of the epoxy resin component in the composition is more than 6,000 but not more than 90,000, a polyfunctional epoxy resin and a curing accelerator are mixed into the dispersion to prepare a varnish. Using an applicator having a slit width of 300 μm, a coating film was drawn on a PTFE tape (Chuko Kasei Kogyo Co., Ltd .: Chuko Flow Skived Tape MSF-100), held at 60 ° C. for 60 minutes with a hot air dryer, and 160 ° C. For 60 minutes, and further at 200 ° C. for 60 minutes to obtain a wiring board.

(Shape, thickness)
The shape of the wiring board of the present invention is not particularly limited, and may be a plate shape or a plate shape having a curved surface. Other irregular shapes may also be used. Further, the thickness is not necessarily uniform and may be partially different.
When the shape is a plate shape (sheet shape, film shape), the thickness (average thickness) is preferably 5 μm or more and 10 cm or less, and by using such a thickness, the strength as a structural material can be maintained. it can. Furthermore, it is more preferably 7 μm or more and 1 cm or less, and further preferably 10 μm or more and 250 μm or less.
In addition, in the said plate-shaped object, the film means the plate-shaped object whose thickness is generally 200 micrometers or less, and a sheet | seat means the plate-shaped object thicker than a film.
In addition, this thickness means the thickness of only the board | substrate of a wiring board, and an adhesive bond layer, copper foil, etc. are not included.

(Linear expansion coefficient)
The wiring board of the present invention exhibits a low coefficient of linear expansion (elongation rate per 1K). The linear expansion coefficient of the cellulose fiber composite is preferably 1 to 70 ppm / K, more preferably 1 to 60 ppm / K, and particularly preferably 1 to 50 ppm / K.
In particular, in wiring board applications, since the linear expansion coefficient of an inorganic thin film transistor is about 15 ppm / K, when the linear expansion coefficient of the wiring board exceeds 50 ppm / K, two layers are formed in the lamination composite with the inorganic film. There is a risk that cracks and the like may occur due to a large difference in linear expansion coefficient. Therefore, the linear expansion coefficient of the wiring board is particularly preferably 1 to 50 ppm / K.
In addition, a linear expansion coefficient is measured by the method described in the term of the below-mentioned Example.

(Glass-transition temperature)
In the wiring board of this invention, it has the effect of raising Tg (glass transition temperature) of resin, when a cellulose fiber disperse | distributes uniformly in resin. Due to this effect, a material having a high Tg suitable for the use described later can be obtained. In particular, when an epoxy resin is used, the effect becomes remarkable.

  The wiring board of the present invention is expected to be applied to the field of semiconductor mounting wiring boards, especially flip chip packages that will be required in the future, and technology for incorporating passive elements, and is particularly useful for high current wiring boards due to its excellent heat dissipation. It is.

Hereinafter, the present invention will be described more specifically with reference to production examples, examples, and comparative examples. However, the present invention is not limited to the following examples unless it exceeds the gist.
The measuring method of various physical properties in the wiring board is as follows.
[Number average fiber diameter of cellulose fibers in the wiring board]
The number average fiber diameter of the cellulose fibers was measured and determined by observing with an optical microscope, SEM, TEM or the like. Specifically, after removing the solvent from the composition for producing the wiring board by drying, a line is drawn on the diagonal line of the SEM photograph magnified 30,000 times, and 12 fibers in the vicinity are randomly extracted, The average of 10 measured values from which the thick fiber and the thinnest fiber were removed was defined as the number average fiber diameter.

[Linear expansion coefficient and Tg of wiring board]
The wiring board was cut into 2.5 mm width × 20 mm length. Using a TII “EXSTAR6000” manufactured by SII, this was stretched in a tension mode at 10 mm / min. From room temperature to 150 ° C. in a nitrogen atmosphere with a load of 30 mm and a load of 30 mN. And then from 150 ° C. to 20 ° C. at 10 ° C./min. At a temperature of 5 ° C./min. The linear expansion coefficient was determined from the measured values from 40 ° C. to 110 ° C. during the second temperature increase.
Moreover, Tg (glass transition temperature) was calculated | required from the measured value of 40 to 200 degreeC at the time of the 2nd temperature rise.

[Evaluation of CAF occurrence]
In order to evaluate the occurrence of CAF, the electrolytic corrosion test is performed as follows. The test substrate is a conductor pattern having a line / space of 100 μm / 100 μm formed from a copper foil of a copper-clad laminate, and an insulator layer made of an epoxy adhesive film is formed thereon. Under the environmental conditions of 85 ° C. and 85% RH, DC 15 V is applied for 1000 h between the conductor lines.

[Crack test]
The crack test is evaluated by a three-point bending test.
[Laser irradiation test]
The laser irradiation test is performed as follows.
Cut the film into 50 mm wide x 50 mm long. This is irradiated with a laser processing machine “Laserman A” manufactured by Comax, and the irradiated surface is observed with an SEM.

<Production Example 1>
Wood flour (Miyashita Wood Co., Ltd., Yonematsu 100, particle size 50-250 μm, average particle size 138 μm) was degreased with an aqueous solution of sodium carbonate 2% by weight at 80 ° C. for 6 hours. This was washed with demineralized water and then delignified with sodium chlorite under acetic acid acidity at 80 ° C. for 5.5 hours. This was washed with demineralized water and then immersed in a 5% by weight aqueous solution of potassium hydroxide for 16 hours for dehemicellulose treatment. This was washed with demineralized water and then dehydrated by filtration. The process of dispersing this in acetic acid and filtering was performed three times, and water was replaced with acetic acid. The cellulose fiber was added with 400 ml of acetic acid and 400 ml of acetic anhydride to a solid content of 40 g, and reacted at 115 ° C. for 5 hours. After the reaction, the reaction solution was filtered and washed with methanol and demineralized water in this order to obtain acetylated cellulose fibers (number average fiber diameter 60 μm).
It was 16 mol% when the chemical modification rate of the obtained acetylated cellulose fiber was calculated | required according to the following measuring method.

The term “chemical modification rate” as used herein refers to the proportion of all hydroxyl groups in cellulose that have been chemically modified, and the chemical modification rate can be measured by the following titration method.
0.05 g of dry cellulose is precisely weighed, and 1.5 ml of ethanol and 0.5 ml of distilled water are added thereto. This is left to stand in a hot water bath at 60 to 70 ° C. for 30 minutes, and then 2 ml of 0.5N aqueous sodium hydroxide solution is added. After leaving this in a 60-70 degreeC hot water bath for 3 hours, it ultrasonically shakes for 30 minutes with an ultrasonic cleaner. This is titrated with 0.2N hydrochloric acid standard solution using phenolphthalein as an indicator.

Here, from the amount Z (ml) of the 0.2N aqueous hydrochloric acid solution required for the titration, the number of moles Q of the substituent introduced by chemical modification is obtained by the following formula.
Q (mol) = 0.5 (N) × 2 (ml) / 1000
-0.2 (N) x Z (ml) / 1000

The relationship between the number of moles Q of the substituent and the chemical modification rate X (mol%) is calculated by the following formula (cellulose = (C ₆ O ₅ H ₁₀ ) _n = (162.14) _n , repetition Number of hydroxyl groups per unit = 3, molecular weight of OH = 17). In the following, T is the molecular weight of the substituent.

  Solving this, it is as follows.

<Example 1>
The water-containing acetylated cellulose fiber obtained in Production Example 1 (fiber content 7% by weight, the balance being mainly water) is dehydrated by filtration. The step of dispersing this in methyl ethyl ketone and filtering is carried out three times to replace water with methyl ethyl ketone.
On the other hand, methyl ethyl ketone and cyclohexanone were further added to a solution containing 30% by weight of a modified biphenol type epoxy resin, 35% by weight of methyl ethyl ketone, and 35% by weight of cyclohexanone (JER (registered trademark) YX6954BH30 manufactured by Mitsubishi Chemical Corporation), and the resin content was 20% by weight. % Prepared epoxy resin solution (modified biphenol type epoxy resin 20 wt%, methyl ethyl ketone 40 wt%, cyclohexanone 40 wt%).

Using the acetylated cellulose fiber substituted with methyl ethyl ketone and the epoxy resin solution, the content of the acetylated cellulose fiber is mixed to 5% by weight with respect to the total solid content, and the cellulose fiber dispersion is prepared. Prepare.
The obtained dispersion was treated with a bead mill (Ultra Apex Mill UAM-015 manufactured by Kotobuki Industries Co., Ltd.) at a bead diameter of 0.3 mm and a peripheral speed of 11.4 m / sec for 4 hours, and further a bead diameter of 0.05 mm and a peripheral speed of 11 The cellulose fiber is defibrated by treatment at 4 m / sec for 4 hours to obtain a cellulose fiber dispersion in which the cellulose fibers are dispersed. The number average fiber diameter of the cellulose fibers is estimated to be about 50 nm.

  A composition containing a special novolak-type epoxy resin and an epoxy resin curing agent in the cellulose fiber dispersion, based on the solid content of the epoxy resin in the cellulose fiber dispersion (jER (registered trademark) 157S65 manufactured by Mitsubishi Chemical Corporation), 5 weight %, A curing accelerator (jER Cure (registered trademark) EMI24 manufactured by Mitsubishi Chemical Corporation) of 0.05% by weight is added to the total amount of the epoxy resin solids and the composition, and mixed uniformly (resin , A composition containing cellulose fibers having a number average fiber diameter of 4 to 1000 nm).

  Thereafter, a part of the solvent is volatilized and a film is formed with an applicator to obtain a coating film (thickness: 200 μm). This coating film is heated at 60 ° C. for 1 hour, further heated at 160 ° C. for 1 hour, and further heated at 200 ° C. for 1 hour to be cured to obtain a wiring board. The number average fiber diameter of the cellulose fibers in the wiring board is estimated to be about 50 nm. The linear expansion coefficient is estimated to be 50 ppm / K and Tg is 142 ° C.

In the CAF generation evaluation, it is assumed that no short circuit or other defects occur, and that the insulation resistance between the lines after the 1000 h test is maintained.
In the cracking test, it is assumed that no cracking occurs.
It is presumed that smear is not observed in the laser irradiation test.

<Example 2>
The same as in Example 1 except that the acetylated cellulose fiber substituted with methyl ethyl ketone and the epoxy resin solution were mixed so that the content of acetylated cellulose fiber was 10% by weight with respect to the total solid content. Thus, a wiring board is obtained.
The number average fiber diameter of the cellulose fibers in the wiring board is estimated to be about 50 nm. The linear expansion coefficient is estimated to be 40 ppm / K and Tg is 142 ° C.
In the CAF generation evaluation, it is assumed that no short circuit or other defects occur, and that the insulation resistance between the lines after the 1000 h test is maintained.
In the cracking test, it is assumed that no cracking occurs.
It is presumed that smear is not observed in the laser irradiation test.

<Example 3>
The same as in Example 1 except that the acetylated cellulose fiber substituted with methyl ethyl ketone and the epoxy resin solution were mixed so that the content of acetylated cellulose fiber was 20% by weight with respect to the total solid content. Thus, a wiring board is obtained.
The number average fiber diameter of the cellulose fibers in the wiring board is estimated to be about 50 nm. The linear expansion coefficient is estimated to be 30 ppm / K and Tg is 142 ° C.
In the CAF generation evaluation, it is assumed that no short circuit or other defects occur, and that the insulation resistance between the lines after the 1000 h test is maintained.
In the cracking test, it is assumed that no cracking occurs.
It is presumed that smear is not observed in the laser irradiation test.

<Example 4>
The acetylated cellulose fiber obtained in Production Example 1 was made into a 0.5% by weight aqueous suspension, and subjected to 60-decomposition fiber treatment at 20000 rpm with a rotary high-speed homogenizer (Cleamix 0.8S manufactured by M Technique Co., Ltd.).
Further, ultrasonic treatment was performed using an ultrasonic homogenizer UH-600S (frequency 20 kHz, effective output density 22 W / cm ² ) manufactured by SMT.
Using a 36 mmφ straight tip (made of titanium alloy), tuning was performed with the output volume 8, and ultrasonic treatment was performed for 30 minutes at the optimum tuning position. The cellulose fiber raw material dispersion was cooled with cold water at 5 ° C. from the outside of the processing vessel, and was processed while stirring with a magnetic stirrer.

  The ultrasonically treated dispersion was centrifuged to obtain a supernatant. HimacCR22G manufactured by Hitachi Koki Co., Ltd. was used as the centrifuge, and R20A2 was used as the angle rotor. Eight 50 ml centrifuge tubes were installed at an angle of 34 degrees from the rotation axis. The amount of the cellulose dispersion put in one centrifuge tube was 30 ml. Centrifugation was performed at 18000 rpm for 30 minutes, and the supernatant was collected.

The obtained supernatant was diluted with water so that the solid content concentration was 0.13% by weight. Thereafter, 150 g was put into a 90 mm diameter filter using PTFE having a pore diameter of 1 μm, and when the solid content reached about 5% by weight, 30 ml of 2-propanol was added and replaced.
Thereafter, it was press-dried at 120 ° C. and 0.14 MPa for 5 minutes to obtain a white cellulose sheet.

  In this sheet, a special novolac type epoxy resin with respect to a solution containing 30% by weight of a modified biphenol type epoxy resin, 35% by weight of methyl ethyl ketone, and 35% by weight of cyclohexanone (jER (registered trademark) YX6954BH30 manufactured by Mitsubishi Chemical) and an epoxy resin solid content , A composition containing an epoxy resin curing agent (JER (registered trademark) 157S65 manufactured by Mitsubishi Chemical Corporation), 5% by weight, an epoxy resin solid content, and 0.05% by weight of a curing accelerator based on the total amount of the composition (JER Cure (registered trademark) EMI24 manufactured by Mitsubishi Chemical Corporation) is added and impregnated with the uniformly mixed solution.

  This epoxy impregnated sheet is heated at 60 ° C. for 1 hour, further heated at 160 ° C. for 1 hour, and further heated at 200 ° C. for 1 hour to be cured to obtain a wiring board. The filling rate of the cellulose fiber in this wiring board is 40 wt%. The number average fiber diameter of the cellulose fibers in the wiring board is estimated to be about 50 nm. Moreover, it is estimated that a linear expansion coefficient is 10 ppm / K and Tg is 142 degreeC.

In the CAF generation evaluation, it is assumed that no short circuit or other defects occur, and that the insulation resistance between the lines after the 1000 h test is maintained.
In the cracking test, it is assumed that no cracking occurs.
It is presumed that smear is not observed in the laser irradiation test.

<Comparative Example 1>
Special novolak-type epoxy resin and epoxy resin cured with a solution containing 30% by weight of modified biphenol-type epoxy resin, 35% by weight of methyl ethyl ketone, and 35% by weight of cyclohexanone (Mitsubishi Chemical Corporation jER (registered trademark) YX6954BH30) and epoxy resin solids 0.05% by weight based on the total amount of the composition containing the agent (Mitsubishi Chemical Corporation jER (registered trademark) 157S65) 5% by weight, epoxy resin solids and Mitsubishi Chemical Corporation jER (registered trademark) 157S65 A curing accelerator (JER Cure (registered trademark) EMI24 manufactured by Mitsubishi Chemical Co., Ltd.) was added to the epoxy solution uniformly mixed, and 20% by weight of colloidal silica (MEK-ST-L manufactured by Nissan Chemical Co., Ltd., based on the total solid content). ) And uniformly disperse with a high-speed rotating homogenizer.

Thereafter, a part of the solvent is volatilized and a film is formed with an applicator to obtain a coating film (thickness: 200 μm). This coating film is heated at 60 ° C. for 1 hour, further heated at 160 ° C. for 1 hour, and further heated at 200 ° C. for 1 hour to be cured to obtain a wiring board.
The linear expansion coefficient in the wiring board is estimated to be 60 ppm / K and Tg is 137 ° C.
In the CAF generation evaluation, it is assumed that no short circuit or other defects occur, and that the insulation resistance between the lines after the 1000 h test is maintained.
In the cracking test, it is assumed that no cracking occurs.
It is presumed that smear is observed in the laser irradiation test.

<Comparative example 2>
A wiring board is obtained in the same manner as in Comparative Example 1 except that the amount of colloidal silica added is 30% by weight.
The linear expansion coefficient in the wiring board is estimated to be 50 ppm / K and Tg is 137 ° C.
In the CAF generation evaluation, it is assumed that no short circuit or other defects occur, and that the insulation resistance between the lines after the 1000 h test is maintained.
In the cracking test, it is assumed that no cracking occurs.
It is presumed that smear is observed in the laser irradiation test.

<Comparative Example 3>
A film for a wiring board is obtained in the same manner as in Comparative Example 1 except that the colloidal silica to be added is 40% by weight.
The linear expansion coefficient in the wiring board film is estimated to be 40 ppm / K and Tg is 137 ° C.
In the CAF generation evaluation, it is assumed that no short circuit or other defects occur, and that the insulation resistance between the lines after the 1000 h test is maintained.
In the cracking test, it is assumed that no cracking occurs.
It is assumed that a large amount of smear is observed in the laser irradiation test.

<Comparative example 4>
A plain woven glass cloth made of E glass fibers having a mass per unit area of 48 g / m ² is impregnated with an epoxy resin varnish and dried to prepare a prepreg having a glass volume fraction of 38%. Two prepregs are laminated, and a single-side roughened electrolytic copper foil with a thickness of 18 μm is constructed so that the roughened surface is in contact with the prepreg on the top and bottom, and is integrated by hot pressing with a press. A copper-clad laminate having a glass volume fraction of 38% in a composite of glass cloth and resin is obtained.

The linear expansion coefficient in the wiring board is estimated to be 30 ppm / K and Tg is 137 ° C.
In the CAF generation evaluation, it is assumed that defects such as short-circuits occur and the insulation resistance between lines after the 1000 h test is not maintained.
In the crack test, it is assumed that cracking occurs.
It is presumed that smear is observed in the laser irradiation test.

In Examples 1 to 4, since the specific gravity is small with respect to silica or glass fiber by using cellulose fiber (cellulose fiber is about 1.5 or more with respect to silica or glass fiber), the wiring is lighter than before. A substrate can be provided.
Moreover, when glass fiber is used as a filler as shown in Comparative Example 4, it is assumed that the substrate is cracked or CAF is generated. In Comparative Examples 1 to 4, since inorganic silica or glass fiber is used as the filler, it is presumed that unburned residue (smear) in the via formation process is observed.

Moreover, since the cellulose fiber in this invention has a large aspect ratio, it is guessed that it is a low linear expansion with a low filler filling rate with respect to spherical silica.
On the other hand, in Comparative Examples 1 to 3, since the filler is filled with spherical silica, it is presumed that the linear expansion coefficient decreases linearly with respect to the filler filling rate.
Further, the Tg of the wiring board of the present invention is higher than that of a single resin sheet. This is probably due to the interaction between cellulose fibers and resin.

  From these results, the wiring board of the present invention is lighter than conventional, is less likely to crack, suppresses the generation of CAF, suppresses the occurrence of smear in the via formation process, and further has a low filler filling rate and low linear expansion. .

Claims (5)

A wiring board in which cellulose fibers having a number average fiber diameter of 4 to 1000 nm are dispersed in a resin. The wiring board according to claim 1, which is formed by curing a resin and / or a resin precursor and a composition containing cellulose fibers having a number average fiber diameter of 4 to 1000 nm. The wiring board according to claim 2, wherein the resin and / or resin precursor is an epoxy resin and / or a precursor thereof. The wiring board according to claim 1, wherein the cellulose fiber is a cellulose fiber obtained from a substance containing cellulose obtained from a plant-derived raw material. The electronic device using the wiring board as described in any one of Claims 1-4.