JP2002289983A - Reinforced flexible printed board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reinforced flexible printed board in which the flexible printed board is not separated from a reinforcing board by the heat of soldering when mounted components are soldered. SOLUTION: The reinforced flexible printed board is made by placing the flexible printed board on the reinforcing board with a curing type adhesive which includes polyester resin, photocation polymeric compound having no boiling point and decomposed at 200 deg.C or more or having a boiling point of 200 deg.C or more, and a photocation polymerization starting agent and the weight of which is reduced by 10 weight % or less after curing. Preferably, to 100 parts by weight of polyester resin is added 10 to 100 parts by weight of the photocation polymeric compound.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flexible printed circuit board reinforced by a reinforcing plate, and more particularly, has a tackiness, that is, a pressure-sensitive adhesive property under normal conditions, and can be cured by irradiating light or an electron beam. The present invention relates to a reinforced flexible printed circuit board in which a flexible printed circuit board and a reinforcing plate are bonded using a curable adhesive.

[0002]

2. Description of the Related Art A flexible printed circuit board is formed by forming a conductor pattern on at least one surface of a film made of a synthetic resin such as polyimide, and has a flexibility so that it is widely used in various electronic and optical devices. Have been.

[0003] Since the flexible printed circuit board is joined to a connection portion of an electronic device or the like at its end, the connection portion of the flexible printed circuit board must be reinforced to have sufficient strength. Therefore, in the conventional flexible printed circuit board, a structure is adopted in which a reinforcing plate made of a synthetic resin or the like is bonded to the flexible printed circuit board in the vicinity of the end portion, or an adhesive is applied to the end portion and hardened by application. .

When bonding a reinforcing plate, an acrylic pressure-sensitive adhesive is used for the bonding of the reinforcing plate because the operation is simple. However, since the pressure-sensitive adhesive is used, the reinforcing plate is attached to a reinforcing surface of a flexible printed circuit board. Can be easily adhered, but sufficient adhesive strength could not be obtained, and the reinforcing plate sometimes peeled off when the product was used.

In order to solve these problems, Japanese Patent Application Laid-Open No. H10-140128 discloses a curable adhesive which contains a tacky polymer and a cationic photopolymerization initiator and can be cured by light irradiation. A method for reinforcing a flexible printed circuit board using an agent is disclosed.

[0006]

However, the reinforced flexible printed board obtained by the above method is left at room temperature for at least 5 minutes and then soldered to mount components to manufacture an electronic component mounting board. In this case, there is a problem that the flexible printed board and the reinforcing plate are separated from each other at the soldered portion due to heat of the solder.

Therefore, prior to the soldering step,
Providing a heating and drying process for the reinforced flexible printed circuit board, or using the fact that the flexible printed circuit board and the reinforcing agent are usually bonded by a heated press, and soldering is performed immediately after the heated press where the heated and dried state is maintained. In addition, the process is controlled so that heating and drying can be performed in the heating press process, and in order to solder the mounted component to the flexible printed circuit board, some drying and heating process is required in advance.

In view of the above, an object of the present invention is to provide a flexible printed circuit board and a reinforcing plate which are soldered at a room temperature for at least 5 minutes or more by the heat of the solder even when the mounted parts are soldered. An object of the present invention is to provide a reinforced flexible printed circuit board that does not peel off.

[0009]

The reinforced flexible printed circuit board according to claim 1 is a polyester resin, which has no boiling point and decomposes at 200 ° C. or higher or has a boiling point of 20 ° C.
A flexible printed circuit board and a reinforcing plate are formed by using a curable adhesive having a photocationic polymerizable compound of 0 ° C. or higher and a photocationic polymerization initiator and having a heating loss after curing of 10% by weight or less. It is characterized by being laminated. The reinforced flexible printed circuit board according to claim 2 is the reinforced flexible printed circuit board according to claim 1, wherein the compounding amount of the cationic photopolymerizable compound is 10 to 100 parts by weight based on 100 parts by weight of the polyester resin. Part.

Hereinafter, the present invention will be described in detail. The polyester resin in the present invention is not particularly limited, and may have any structure such as aliphatic, alicyclic, and aromatic. Specifically, the polyester resin may be a dicarboxylic acid (or a diester equivalent thereof) and a diol. Reaction products and the like. Dicarboxylic acids (or their diester equivalents)
Fatty acids containing 5 carbon atoms (unbranched, branched, or 5
And / or aromatic acids containing from 8 to 15 carbon atoms.

The fatty acids include succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, 1,12-dodecane diacid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexane Pentanedicarboxylic acid, 2-methylsuccinic acid, 2-methylpentanedioic acid, 3-methylhexanedioic acid, and the like. Suitable aromatic acids are terephthalic acid, isophthalic acid, phthalic acid,
4,4'-benzophenone dicarboxylic acid, 4,4'-diphenylmethane dicarboxylic acid, 4,4'-diphenyl ether dicarboxylic acid, 4,4'-diphenyl thioether dicarboxylic acid, and 4,4'-diphenylamine dicarboxylic acid, and the like. Can be

In these dicarboxylic acids, the structure between the two carboxyl groups preferably contains only carbon and hydrogen. The above dicarboxylic acids may be used alone or in combination of two or more. Usually, in order to increase the flexibility of the polyester resin, adipic acid, an aliphatic dicarboxylic acid such as sebacic acid is copolymerized, but when it is necessary to improve the wet heat resistance of the curable adhesive, this is used. It is preferable not to use such an aliphatic dicarboxylic acid.

Preferred diols include branched, unbranched and cyclic aliphatic diols having 2 to 12 carbon atoms. Specific examples of preferred diols include, for example, ethylene glycol, diethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,3-butanediol, 1,4-butanediol, α-methylbutanediol, α -Dimethylbutanediol, 1,5-pentanediol, 2-methyl-2,4-pentanediol, 3-methylpentanediol, 1,6-hexanediol, 1,8-octanediol, cyclobutane-1,3-di (2′-ethanol), 1,4-dihydroxycyclohexane, cyclohexane-1,4-dimethanol, 1,10-decanediol, 1,12-dodecanediol, neopentyl glycol, having 2 to 9 carbon atoms (preferably Is a polyoxyalkylene group containing 2 to 4) alkylene groups. Long chain diol comprising a call and polytetramethylene ether glycol, and the like. The above-mentioned diols may be used alone or in combination of two or more. In order to improve the flexibility of the polyester resin, it is more preferable to use a straight-chain alcohol having many carbon atoms as the diol.

When it is necessary to improve the wet heat resistance of the curable adhesive, as the polyester resin used in the present invention, a resin containing an ester bond of a dicarboxylic acid and a diol in an amount of 50 mol% or more of the whole. It is more preferable that the resin has a structure in which an ether bond is introduced in the molecule. One of the methods for introducing an ether bond is a method of polycondensing a polyether having a hydroxyl group at a terminal with a dicarboxylic acid or a diol. Examples of the polyether used include polytetramethylene ether glycol, polypropylene glycol, and polyethylene glycol. When it is necessary to improve the wet heat resistance of the curable adhesive, it is better to use a more hydrophobic resin, and among these, polytetramethylene ether glycol is preferable.

Further, the polyester resin in the present invention comprises:
The carboxyl group of the carboxylic acid compound may be esterified, or may be obtained by transesterification of the ester bond. Further, the hydroxyl group of the hydroxyl group-containing compound may be etherified or esterified, or may be a copolymerized polyether with an alkylene oxide. The above polyester resins may be used alone or in combination of two or more.

The polyester resin in the present invention is usually obtained by polycondensing the above dicarboxylic acid and diol using an appropriate catalyst. The preferred number average molecular weight is 10,000 to 100,000. Further, those having a softening temperature of 40 ° C. or higher according to a ring and ball measurement method are preferred.
When the softening temperature is lower than 40 ° C., the curable adhesive tends to flow easily and may not show a sheet shape.

The polyester resin of the present invention may have crystallinity at room temperature or may not have crystallinity. It is preferable that the polyester resin does not have a polyester resin, and when it is desired to promote curing at room temperature, the glass transition temperature of the polyester resin is preferably 25 ° C. or less. Further, when it is desired to improve the wet heat resistance, the glass transition temperature of the polyester resin is preferably 25 ° C. or higher, and in order to improve the curability, a material which sufficiently transmits light or an electron beam effective for the initiation of curing is used. Is preferred.

The polyester resin in the present invention preferably has an acid value of 3 mgKOH / g or less. When the acid value exceeds 3 mgKOH / g, a reaction with a photocationically polymerizable functional group occurs during storage of the curable adhesive,
It does not show pressure-sensitive adhesiveness or hardening progresses. Also, the moist heat resistance may decrease.

The photocationically polymerizable compound in the present invention must have no boiling point and decompose at 200 ° C. or higher, or have a boiling point of 200 ° C. or higher. If the decomposition temperature or boiling point of the photocationically polymerizable compound is less than 200 ° C, decomposition gas and evaporation and volatile components are likely to be generated at the time of heating, such as when performing normal soldering. It is easy to peel off from the board. The photocationically polymerizable compound in the present invention is not particularly limited as long as it satisfies the above conditions, and is composed of an organic compound having a photocationically polymerizable functional group that can be made high in molecular weight by cationic polymerization, and its structure is a fatty acid. The structure may be any of a group, an alicyclic, an aromatic and the like, and the form may be any of a monomer, an oligomer, a polymer and the like.

The photocationically polymerizable functional group may be present at any terminal in the molecular skeleton, in a side chain, or in the molecular skeleton. Specific examples thereof include an epoxy group, an oxetane group, a vinyl ether group, and an episulfide group. And an ethyleneimine group. The number of cationic photopolymerizable functional groups in the cationic photopolymerizable compound is preferably one or more per molecule, more preferably two or more per molecule. Here, the number of cationic photopolymerizable functional groups per molecule is determined by dividing the total number of cationic photopolymerizable functional groups in the cationic photopolymerizable compound by the total number of molecules in the cationic photopolymerizable compound.

The shape of the photocationically polymerizable compound may be any of liquid, semi-solid, and solid at room temperature, but is preferably liquid or semi-solid at room temperature. . If the cationic photopolymerizable compound is solid at room temperature, the resulting curable adhesive may not exhibit pressure-sensitive adhesive properties at room temperature. Further, it may have crystallinity at room temperature or may not have crystallinity. However, when it is desired to enhance pressure-sensitive adhesiveness at room temperature, a material having no crystallinity is preferable. In addition, when it is desired to promote curing at room temperature, the glass transition temperature of the cationic photopolymerizable compound is preferably 25 ° C. or lower, and sufficient light or electron beam effective for curing initiation is required to improve curability. Those that transmit light are preferred. Further, those having no structure (such as an amino group) that excessively suppresses the progress of cationic polymerization and makes the curing of the curable adhesive and adhesive incomplete are preferable. Further, as long as it does not cause macrophase separation with other components constituting the curable adhesive, it may be compatible with these or may be incompatible. Here, the macro phase separation means a state in which any or all of the components are completely separated in a transparent state, and a state different from a state in which the components are merely clouded by micro phase separation. .

The photocationically polymerizable compound is not particularly limited, and examples thereof include a cyclic ether compound such as an epoxy group-containing compound, an oxetane compound, and an oxolane compound, a cyclic ester compound, a vinyl ether compound, and the like. Propenyl ether compounds and the like are mentioned, and are preferably used. The above-mentioned cationic photopolymerizable compound may be used alone or in combination of two or more.

Among the above various cationic photopolymerizable compounds, epoxy group-containing compounds are more preferably used because of their high reactivity and short curing time. The epoxy group-containing compound refers to an organic compound having at least one oxirane ring that can be polymerized by cationic polymerization. The number of epoxy groups in the epoxy group-containing compound is preferably one or more per molecule, more preferably two or more per molecule. Here, the number of epoxy groups per molecule is determined by dividing the total number of epoxy groups in the epoxy group-containing compound by the total number of molecules in the epoxy group-containing compound.

The epoxy group-containing compound is not particularly limited. For example, bisphenol A
Novolak type epoxy resin such as bisphenol type epoxy resin such as type epoxy resin, bisphenol F type epoxy resin, bisphenol AD type epoxy resin, bisphenol S type epoxy resin, phenol novolak type epoxy resin, cresol novolak type epoxy resin, and trisphenol methane tri Aromatic epoxy resins such as glycidyl ether and the like, and hydrogenated and brominated products thereof; 3,4-epoxycyclohexylmethyl-3,4-
Epoxycyclohexanecarboxylate, 3,4-epoxy-2-methylcyclohexylmethyl 3,4-epoxy-2-methylcyclohexanecarboxylate, bis (3,4-epoxycyclohexyl) adipate, bis (3,4-epoxycyclohexylmethyl) Adipate, bis (3,4-epoxy-6-methylcyclohexylmethyl) adipate, 2- (3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy) cyclohexanone-meta-dioxane, bis (2 3-epoxycyclopentyl) ether, trade name "EHPE-31
Alicyclic epoxy resins such as "50" (softening temperature: 71C, manufactured by Daicel Chemical Industries, Ltd.); diglycidyl ether of 1,4-butanediol, diglycidyl ether of 1,6-hexanediol, triglycidyl of glycerin Ether, triglycidyl ether of trimethylolpropane, diglycidyl ether of polyethylene glycol,
Such as polyglycidyl ether of polypropylene glycol, polyoxyalkylene glycol having an alkylene group having 2 to 9 (preferably 2 to 4) carbon atoms, and polyglycidyl ether of a long-chain polyol including polytetramethylene ether glycol. Aliphatic epoxy resins;
Diglycidyl phthalate, diglycidyl tetrahydrophthalate, diglycidyl hexahydrophthalate, diglycidyl-p-oxybenzoic acid, glycidyl ether of salicylic acid-glycidyl ester,
Glycidyl ester type epoxy resins such as dimer acid glycidyl ester and the like and hydrogenated products thereof; triglycidyl isocyanurate, N, N of cyclic alkylene urea
Glycidylamine type epoxy resins such as N'-diglycidyl derivatives, N, N, O-triglycidyl derivatives of p-aminophenol, N, N, O-triglycidyl derivatives of m-aminophenol, and hydrogenated products thereof A copolymer of glycidyl (meth) acrylate and a radical polymerizable monomer such as ethylene, vinyl acetate, or (meth) acrylate; a polymer mainly composed of a conjugated diene compound such as epoxidized polybutadiene or the like Epoxidized unsaturated carbon double bond of partially hydrogenated polymer; "Polymer block mainly composed of vinyl aromatic compound" such as epoxidized SBS and "conjugated diene compound mainly" Of a block copolymer having the same polymer block or its partially hydrogenated polymer block in the same molecule. Epoxidized double bond of unsaturated carbon of epoxy compound; polyester resin having one or more (preferably two or more) epoxy groups per molecule; urethane bond or Urethane-modified epoxy resin or polycaprolactone-modified epoxy resin into which polycaprolactone bond is introduced;
Conventionally known various epoxy group-containing compounds such as a rubber-modified epoxy resin in which a rubber component such as NBR, CTBN, polybutadiene, and acrylic rubber is added to the various epoxy group-containing compounds. The epoxy group-containing compounds may be used alone or in combination of two or more.

The amount of the cationic photopolymerizable compound in the present invention is preferably 10 to 100 parts by weight based on 100 parts by weight of the polyester resin. When the amount of the cationic photopolymerizable compound exceeds 100 parts by weight, volatile components are generated from the curable adhesive due to the heat of the solder, and the flexible printed board and the reinforcing plate are separated at the soldered portion. If the amount is less than 10 parts by weight, the proportion of a crosslinking component due to cationic polymerization may decrease, and the heat resistance after curing may decrease.

The cationic photopolymerization initiator used in the present invention is not particularly limited, and may be an ionic photoacid generating type or a nonionic photoacid generating type. As the cationic photopolymerization initiator of the ionic photoacid generation type, for example, aromatic diazonium salt,
Onium salts such as aromatic halonium salts and aromatic sulfonium salts, and organic metal complexes such as iron-allene complex, titanocene complex, and arylsilanol-aluminum complex, and the like, more preferably aromatic iodonium salt,
Aromatic sulfonium salts and metallocene salts are exemplified. More preferably, it is an aromatic sulfonium salt. One or more of these are suitably used.

By containing these cationic photopolymerization initiators, the curable adhesive becomes 200 to 400 nm.
Curing can proceed rapidly by irradiation with light having a wavelength of, and the curable adhesive has excellent storage stability when stored. The aromatic iodonium salts, aromatic sulfonium salts and metallocene salts effective as photocationic polymerization initiators are described, for example, in US Pat.
No. 828, U.S. Pat. No. 5,089,536,
It is disclosed in JP-A-6-306346.

Among the above-mentioned cationic photopolymerization initiators, aromatic iodonium salts and aromatic sulfonium salts do not produce cations when exposed to light other than in the ultraviolet region, but they do not contain known cations such as aromatic amines and colored aromatic polycyclic hydrocarbons. By using the above sensitizer in combination, a cation can be generated even with light in the near ultraviolet region or the visible region. When a metallocene salt is used, a reaction accelerator such as an oxalate ester of tertiary alcohol may be used in combination.

Specific examples of the cationic photopolymerization initiator of the ionic photoacid generating type are not particularly limited. For example, a trade name of "ADEKA OPTOMER SP15"
0 "," ADEKA OPTOMER SP170 "(above, manufactured by Asahi Denka Kogyo), trade name" UVE-1014 "(manufactured by General Electronics), trade name" CD-1012 "(manufactured by Sartomer), and the like. One or more of these are suitably used.

The nonionic photoacid generator-type photocationic polymerization initiator is not particularly limited. Examples thereof include nitrobenzyl ester, sulfonic acid derivative, phosphoric acid ester, phenolsulfonic acid ester,
Examples thereof include diazonaphthoquinone and N-hydroxyimidosulfonate, and one or more of these are preferably used. The above cationic photopolymerization initiator may be used alone, or two or more kinds may be used in combination.

The amount of the above-mentioned cationic photopolymerization initiator is not particularly limited, but is based on 100 parts by weight of the total amount of the above-mentioned polyester resin and the cationic photopolymerizable compound.
0.1 to 10 parts by weight is preferred. If the amount of the cationic photopolymerization initiator is less than 0.1 part by weight, the cationic photopolymerization may not proceed sufficiently or the curing may be too slow. Conversely, if the amount is more than 10 parts by weight, the curing will be too fast, and it may be difficult to bond the flexible printed board and the reinforcing plate.

In the present invention, the activation energy applied for activating the above-mentioned cationic photopolymerization initiator is not particularly limited, but for example, light, electron beam and the like are used. Examples of the light include microwaves, infrared rays, visible light, ultraviolet rays, X-rays, γ-rays, and the like, and ultraviolet rays that are particularly easy to handle and can obtain relatively high energy are more preferably used. . Of these, wavelengths of 200 to 400 nm are particularly preferably used.
UV light.

As the ultraviolet rays, for example, carbon arc,
Mercury vapor arc, fluorescent lamp, argon glow lamp,
Halogen lamp, incandescent lamp, low-pressure mercury lamp, high-pressure mercury lamp, ultra-high-pressure mercury lamp, flash UV lamp, deep U
Irradiation can be performed using an appropriate light source such as a V lamp, a xenon lamp, a tungsten filament lamp, and sunlight.

Since the irradiation amount of the light or the electron beam or the like varies depending on the kind and amount of each component constituting the curable adhesive, the coating thickness, the irradiation source of the light or the electron beam, etc. The irradiation amount at a wavelength effective for generating cations from the photocationic polymerization initiator is 0.01 to 100 J / cm.
It is desirable to set the range of ² .

The curable adhesive according to the present invention may contain, if necessary, an aliphatic hydroxyl group-containing compound, a thermoplastic resin, an adhesion improver, a filler, a reinforcing agent as long as the object of the present invention is not hindered. One of various additives such as materials, softeners, plasticizers, viscosity modifiers, thixotropic agents, stabilizers, antioxidants, coloring agents, dehydrating agents, flame retardants, antistatic agents, foaming agents, and fungicides Alternatively, two or more kinds may be contained.

The aliphatic hydroxyl group-containing compound may be in any form such as monomeric, oligomeric, and polymeric forms. The aliphatic hydroxyl group may be any one of the terminal, side chain, and molecular skeleton of the molecular skeleton. It may be present at a site. or,
The number of the aliphatic hydroxyl groups is preferably one or more per molecule, more preferably two or more per molecule. Here, the number of aliphatic hydroxyl groups per molecule is determined by dividing the total number of aliphatic hydroxyl groups in the aliphatic hydroxyl group-containing compound by the total number of molecules in the aliphatic hydroxyl group-containing compound.

The aliphatic hydroxyl group-containing compound is not particularly restricted but includes, for example, polyhydroxyalkane, alkylene glycol and alkylene groups having 2 to 9 (preferably 2 to 4) carbon atoms. Long chain polyols containing polyoxyalkylene glycol, polytetramethylene ether glycol, etc., hydroxyl terminated polyalkadiene, hydroxyl terminated polyester not included in the polyester resin of the present invention, hydroxyl terminated polycaprolactone, hydroxyl terminated polycarbonate, acrylic polyol, ethylene- (Partial) saponification of vinyl acetate copolymer,
Examples thereof include polyvinyl alcohol, castor oil, ketone resin, xylene resin, and copolymers and modified products of these aliphatic hydroxyl group-containing compounds.
More than one species is preferably used.

The compounding amount of the aliphatic hydroxyl group-containing compound is as follows:
Although not particularly limited, the amount is preferably such that the ratio of the number of aliphatic hydroxyl groups to the number of photocationically polymerizable functional groups in the curable adhesive is 10 or less. When the ratio of the number of the aliphatic hydroxyl groups to the number of the photocationically polymerizable functional groups exceeds 10, the heat-resistant adhesiveness of the obtained curable adhesive may be insufficient.

The shape of the above-mentioned aliphatic hydroxyl group-containing compound may be any of liquid, semi-solid and solid at room temperature, but it has no boiling point and decomposes at 200 ° C. or more. Alternatively, it is preferable that the compound has a boiling point of 200 ° C. or higher and is liquid or semi-solid at room temperature. When the decomposition temperature or the boiling point of the aliphatic hydroxyl group-containing compound is lower than 200 ° C., the aliphatic hydroxyl group-containing compound is volatilized from the obtained curable adhesive, which may cause deterioration in performance and pollution of the atmosphere. If the aliphatic hydroxyl group-containing compound is solid at room temperature, the resulting curable adhesive may not exhibit pressure-sensitive adhesive properties at room temperature. When it is desired to accelerate the curing at room temperature, the aliphatic hydroxy group-containing compound preferably has a glass transition temperature of 25 ° C. or lower.

Examples of the thermoplastic resin include, but are not limited to, polyolefin resins such as ethylene-vinyl acetate copolymer; block polymers such as styrene-butadiene-styrene block copolymer; Acrylic copolymer; polycaprolactone resin;
Polycarbonate resins; tackifying resins such as rosin-based resins, terpene-based resins, styrene-based resins, petroleum-based resins, and the like; various commonly used thermoplastic resins such as waxes; Two or more are suitably used.

The above-mentioned adhesion improver is not particularly limited, and examples thereof include silane coupling agents, titanium coupling agents, aluminum coupling agents and the like.
Various types of conventionally known adhesion improvers are mentioned, and one or more of these are suitably used.

The filler is not particularly limited, but for example, calcium carbonate, magnesium carbonate,
Inorganic fillers such as clay, talc, titanium oxide, asbestos, etc .; fibers such as rayon, acrylic fiber, nylon fiber, glass fiber, carbon fiber, cellulose, etc .; glass balloons, shirasu balloons, vinylidene chloride balloons, acrylic balloons Hollow spherical fillers such as,, etc .; organic spheres such as nylon beads, acrylic beads, silicon beads, etc .; synthetic resin powders, such as urea melamine resin powder, acrylic resin powder, phenol resin powder, etc .;
Conventionally known various fillers such as natural powders such as wood flour and fruit husk powder and surface-treated products thereof are mentioned, and one or more of these fillers are suitably used.

The above-mentioned various components contained in the curable adhesive according to the present invention may be compatible with them or may be incompatible. More preferably, it does not cause macro phase separation with other components constituting the curable adhesive. Here, macro phase separation means
It refers to a state where any or all of the components are completely transparent and completely phase-separated, which is different from a state where the components are merely clouded by microphase separation.

The above-mentioned various components contained in the curable adhesive of the present invention are, for example, aromatic hydroxyl groups and (anhydrous) carboxyl groups which can react with a photocationically polymerizable functional group during storage. It is preferable that the compound does not have a functional group such as a group. In addition, the above-mentioned various components are preferably those which do not decompose or volatilize upon storage or irradiation with light or electron beam, and which can sufficiently transmit light or electron beam necessary for initiation of curing. Is preferred.

The above-mentioned various components may or may not have crystallinity at room temperature. However, if it is desired to increase the pressure-sensitive adhesiveness at room temperature, the crystallinity may be reduced. Are preferred. Furthermore, the above various components are
It is preferable that the resin does not have a functional group such as an amino group, which excessively suppresses the progress of the cationic polymerization and inhibits the curing of the curable adhesive.

The curable adhesive in the present invention must have a loss on heating of 10% by weight or less after curing. Here, the heating loss after curing means that the curing type adhesive is irradiated with light, an electron beam, or the like to start curing, and then left at 110 ° C. for 30 minutes to be cured, by TG / DTA. The weight loss was measured at a heating rate of 10 ° C./min, and the ratio of the weight loss at 220 ° C. to the weight before heating was determined. If the loss on heating after curing is greater than 10% by weight, volatiles are generated from the curable adhesive due to the heat of the solder,
The flexible printed circuit board and the reinforcing plate may peel off at the soldered portion.

The method for producing the curable adhesive according to the present invention is not particularly limited. For example, using a mixer such as a homodisper, a homomixer, a universal mixer, a planetarium mixer, a kneader, or a three-roll mixer, Alternatively, a desired curable adhesive can be obtained by uniformly mixing predetermined amounts of the components to be blended under heating.
It is desirable that the above-described manufacturing method is performed in a state where light, electron beams and the like are blocked. Kneading of each component at the time of production may be carried out without a solvent, for example, in an inert solvent such as aromatic hydrocarbon, acetate, ketone and the like.

In the above-mentioned production, if the water content of each component is large, the progress of curing after irradiating the obtained curable adhesive with light or an electron beam may be hindered. Accordingly, it is preferable to remove water in each component in advance. Examples of the method for removing water include dehydration by mixing with a molecular sieve or the like, heat dehydration with an oven or a heater, and dehydration under reduced pressure, all of which are suitably employed. The kneading of each component may be usually performed under atmospheric pressure, but it is preferable to perform kneading under a reduced pressure atmosphere or an inert gas atmosphere such as a nitrogen gas when it is particularly desired to avoid mixing of water.

The curable adhesive of the present invention obtained as described above may be applied as it is to a flexible printed circuit board and a reinforcing plate, photo-cationically polymerized and cured, but better handling is possible. In order to obtain workability and simplicity, it is preferable to use in the form of a curable pressure-sensitive adhesive sheet which has been previously processed into a pressure-sensitive adhesive sheet.

The method for processing the above-mentioned adhesive sheet is not particularly limited. For example, a bar-coating method, a roll-coating method, a gravure-coating method, an extrusion-coating method, etc. may be applied to a release-treated sheet-like support. A desired pressure-sensitive adhesive sheet can be obtained by protecting the surface of the curable pressure-sensitive adhesive sheet with a release sheet such as polyethylene by various coating methods and winding the sheet. By the above processing, the curable adhesive is solid, or semi-solid, or has a high viscosity even in a liquid state and is difficult to apply, for example, diluted with an organic solvent or heated and melted. The viscosity may be reduced.

The support and the release sheet are not particularly limited. For example, polyethylene terephthalate, polyethylene naphthalate, polyethylene, polypropylene, polycarbonate, nylon, polyarylate, polysulfone, polyethersulfone, polyetherether Ketone, polyphenylene sulfite,
Polystyrene, polyacryl, polyvinyl acetate, triacetyl cellulose, diacetyl cellulose, cellophane and the like can be mentioned. The support and release sheet are not particularly limited, but preferably have a thickness of 10 μm or more. When the thickness is less than 10 μm, the strength may be low, so that the support and the release sheet may be broken during use.

The coating thickness in the above is not particularly limited, but the thickness of the adhesive sheet itself is 1 to 2000.
The thickness is preferably such that the thickness is μm, more preferably 10 to 1000 μm. If the thickness of the adhesive sheet itself is too thin, the adhesiveness of the adhesive sheet may be affected by surface irregularities of the joining member. Conversely, if the thickness of the adhesive sheet itself is too thick, the curing time may be reduced. May be excessively long.

The reinforced flexible printed board of the present invention is obtained by bonding a flexible printed board and a reinforcing plate via a curable adhesive. As the flexible printed board, a conventionally known flexible printed board can be appropriately used.For example, a metal foil, a metal is deposited on a film made of an insulating resin such as polyester or polyimide, or a circuit is formed by a conductive resin or the like. Can be used.

As the reinforcing plate, those made of a material conventionally used for reinforcing a flexible printed circuit board can be appropriately used. For example, a glass-epoxy resin composite material, a paper phenol composite material, a paper polyester composite can be used. A material made of a material, polyester, polyimide, or the like can be used.

In order to manufacture such a reinforced flexible printed circuit board, for example, a curable adhesive is laminated on a portion of the flexible printed circuit board to be reinforced, and then the curable adhesive layer is applied to the curable adhesive layer. After irradiation with light or an electron beam, a reinforcing plate may be attached. Lamination of the curable adhesive may be performed by applying the curable adhesive, and a sheet made of the curable adhesive (hereinafter, also appropriately referred to as a “curable adhesive sheet”). May be laminated in advance, and then the use of a curable adhesive sheet is preferred because lamination is easy. In the case of laminating the curable adhesive sheet, the pressure-sensitive adhesive property may be used to apply the sheet while applying pressure by finger pressure, lamination, press or the like. Thereby, the curable adhesive sheet is securely adhered to the surface of the flexible printed circuit board.

The sticking temperature is not particularly limited.
It is carried out at an appropriate temperature from normal temperature to about 120 ° C. 12
Attachment at a temperature higher than 0 ° C. may cause wrinkles or deviation. On the other hand, if the temperature at the time of application is too low, the elastic modulus of the curable adhesive decreases, the pressure-sensitive adhesiveness decreases, and poor adhesion may occur.

Irradiation with light or an electron beam is performed by irradiating light or an electron beam having a wavelength capable of activating the above-mentioned cationic photopolymerization initiator by an appropriate method described above. In the irradiated curable adhesive, polymerization initiation species are generated, so that polymerization starts and curing progresses with time. Then, before the curing reaction proceeds and the pressure-sensitive adhesive property is lost, the reinforcing plate is pressed. Therefore, without necessarily requiring a hot press,
The reinforcing plate can be adhered to the curable adhesive, and the curing reaction proceeds with time, so that the reinforcing plate can be firmly bonded to the flexible printed circuit board.

In the present invention, the pot life of the curable adhesive is defined as the time from the start of irradiation with light or an electron beam to the loss of pressure-sensitive adhesiveness. The longer the pot life, the better the workability, but since the curing speed is slow, it takes time until the desired cured physical properties are obtained. Therefore, the pot life is 10
It is preferable to set the time from about minutes to half a day. Further, the loss of the pressure-sensitive adhesiveness can be confirmed by a change in the initial adhesive force at the application temperature. As a guide, when the adhesive strength at the time of attaching the reinforcing plate after irradiation decreases to 0 to 50% before irradiation, it can often be determined that the pressure-sensitive adhesive property has been lost. In any case, the process should be determined by the balance between the required initial tack and the adhesive strength after curing.

(Function) Since the curable adhesive according to the present invention contains a polyester resin, a cationic photopolymerizable compound and a cationic photopolymerization initiator, it usually has excellent adhesion to a flexible printed board and a reinforcing plate. Irradiation with light, an electron beam or the like can surely cure the resin, and the time until the initial adhesive force is lost can be made sufficiently long.

Also, when the obtained reinforced flexible printed circuit board is allowed to stand at room temperature for at least 5 minutes or more, and then the mounting parts are soldered to manufacture an electronic component mounting board, the curable adhesive bonding is also required. Since the adhesive property and heat resistance of the agent are excellent, the flexible printed circuit board and the reinforcing plate are not separated at the soldered portion by the heat of the solder.

Further, the cationic photopolymerizable compound has no boiling point and decomposes at 200 ° C. or higher, or has a boiling point of 200 ° C.
° C or higher, and the loss on heating after curing is 10% by weight or less, so that decomposition gas and evaporative volatiles are less likely to be generated during heating, such as when soldering, and the soldered part Thus, a reinforced flexible printed board in which the flexible printed board and the reinforcing plate are not separated can be obtained.

[0062]

The present invention will be clarified below by describing non-limiting examples of the present invention. (Example 1) <Polyester resin> Polyester resin was composed of 25 mol% of terephthalic acid, 25 mol% of isophthalic acid, 17.5 mol% of ethylene glycol, 17.5 mol% of an ethylene glycol adduct of bisphenol A, and polytetramethylene. A polyester resin obtained by copolymerizing 15 mol% of ether glycol was used. <Photocationic polymerizable compound> The photocationic polymerizable compound is an epoxy resin, bisphenol F diglycidyl ether (trade name "Epicoat 807" manufactured by Yuka Shell Epoxy Co., Ltd.), epoxy equivalent 170, no boiling point observed, decomposition temperature 200 ° C or higher ) Was used. <Photocationic polymerization initiator> The photocationic polymerization initiator is a mixture of aromatic sulfonium antimony hexafluoride and propylene carbonate (trade name "ADEKA OPTMER SP170" manufactured by Asahi Denka Kogyo Co., Ltd.) (Weight ratio: 50%).

<Preparation of Curable Adhesive Sheet> The composition was as follows. Polyester resin: 80 parts by weight of the prepared polyester resin Photocationic polymerizable compound: Epicoat 807 20 parts by weight Photocationic polymerization initiator: 1 part by weight of Adeka Optomer SP170 Solvent: 150 parts by weight of methyl ethyl ketone Homodisper type stirring mixer (Trade name: “Homodisper L type” manufactured by Tokushu Kika Co., Ltd.) was uniformly mixed with stirring at a stirring speed of 3000 rpm to prepare a curable adhesive solution. A 50 μm-thick PET film subjected to a mold release treatment was used as a support, and was coated and dried using a bar coater so that the thickness after coating was 20 μm. Next, the release-treated surface of the PET film which had been subjected to silicone release treatment as a protective film was laminated on the surface of the pressure-sensitive adhesive agent to prepare a curable pressure-sensitive adhesive sheet.

<Preparation of Reinforced Flexible Printed Board> While the protective film was peeled off, the curable adhesive sheet was coated with a 50 μm thick polyimide film (5 cm × 10 5
cm) at room temperature. Next, the release PET film is peeled off, and the adhesive surface of the curable adhesive sheet is irradiated with ultraviolet light having a wavelength of 365 nm using an ultrahigh pressure mercury lamp so that the irradiation amount becomes 2400 mJ / cm ^2, and immediately thereafter. A glass-epoxy resin composite reinforcing plate (5 cm × 10 cm) having a thickness of 0.3 mm was laminated on the surface of the adhesive agent at normal temperature. This was put into a gear oven at 110 ° C. for 30 minutes to be cured, thereby obtaining a reinforced flexible printed board.

<Evaluation of Heat Loss> The prepared curable adhesive sheet was irradiated with an ultraviolet ray having a wavelength of 365 nm using an ultra-high pressure mercury lamp so that the irradiation amount became 2,400 mJ / cm ^2, and then a gear oven at 110 ° C. for 30 minutes. And cured.
The temperature is raised from 23 ° C. to 35 ° C. by TG / DTA 6200 (manufactured by Seiko Instruments Inc.) at a rate of 10 ° C./min.
The weight loss when the temperature was raised to 0 ° C. was measured, and the weight loss at 220 ° C. with respect to the weight before the temperature was raised was determined. Table 1 shows the results. <Evaluation of solder heat resistance (peeling time)> Reinforced flexible printed circuit board at 23 ° C and 65% RH
Was placed on a solder surface of a solder bath set at 220 ° C., and the time until peeling occurred was measured. Table 1 shows the results.

Comparative Example 1 A copolymer of 90% by weight of butyl acrylate and 10% by weight of glycidyl methacrylate was used in place of the polyester resin, and bisphenol A diglycidyl, an epoxy resin, was used as the cationic photopolymerizable compound. Ether (made by Yuka Shell Epoxy)
(Product name "Epicoat 828", decomposition temperature 200 ° C or higher)
And a CTBN-modified epoxy resin (trade name “Epon 58901” manufactured by Yuka Shell Epoxy Co., Ltd., decomposition temperature of 200 ° C. or higher), and the composition was as follows. Copolymer: 100 parts by weight of the prepared copolymer Photocationic polymerizable compound : Epicoat 828 50 parts by weight Epon 58901 50 parts by weight Photocationic polymerization initiator: Adeka optomer SP170 3 parts by weight Solvent: ethyl acetate 100 parts by weight The same evaluation as in Example 1 was carried out. Table 1 shows the results.

[0067]

[Table 1] As is clear from Table 1, the heat loss in the comparative example is large and the solder heat resistance (peeling time) is inferior. In contrast, in the example, even after being left for one day in an atmosphere of 23 ° C. and 65% RH. It was found that the solder did not peel off due to the heat of the solder and the heat resistance of the solder was excellent.

[0068]

Since the curable adhesive according to the present invention contains a polyester resin, a specific cationic photopolymerizable compound and a cationic photopolymerization initiator, it usually has excellent adhesion to a flexible printed board and a reinforcing plate. Thus, curing can be surely performed by irradiating light, an electron beam, or the like, and the time until the initial adhesive strength is lost can be made sufficiently long.

Also, when the obtained reinforced flexible printed circuit board is allowed to stand at room temperature for at least 5 minutes or more to solder the mounted components to manufacture an electronic component mounted substrate, the decomposition gas and the evaporation and volatilization are also required. It does not easily occur, and does not peel off due to the heat of the solder.
Furthermore, when the compounding amount of the photocationically polymerizable compound is 10 to 100 parts by weight with respect to 100 parts by weight of the polyester resin, the above-described effect can be more reliably achieved.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4F100 AK41G AK49B AK53G AL05G BA02 CA02G CB00 EC04 GB43A JJ03 JL11 4J040 EC031 EC032 EC041 EC042 EC061 EC062 EC071 EC072 EC111 EC112 EC121 EC122 EC151 EC152 EC221 EC321 EC321 EC321 EC321 EC321 EC321 ED041 ED051 GA01 GA08 GA11 GA13 GA25 KA13 LA06 LA08 MA02 MA05 MA09 MA10 NA20 PA32 5E338 AA12 BB72 EE26

Claims (2)

[Claims] 1. A polyester resin having a boiling point of 200
Via a curable adhesive comprising a cationic photopolymerizable compound that decomposes at a temperature of at least 100 ° C. or has a boiling point of at least 200 ° C., and a photocationic polymerization initiator and has a weight loss after curing of 10% by weight or less. A reinforced flexible printed circuit board, wherein a flexible printed circuit board and a reinforcing plate are bonded together. 2. The reinforced flexible printed circuit board according to claim 1, wherein the amount of the cationic photopolymerizable compound is 10 to 100 parts by weight based on 100 parts by weight of the polyester resin.