TWI720290B - Conductive adhesive - Google Patents

Abstract

The subject of the present invention is to realize a conductive adhesive having both embedding and adhesion properties. The solution of the present invention is to provide a conductive adhesive, which contains: acrylic resin having a weight average molecular weight of 500,000 or more and 1 million or less and having an epoxy group; and a thermosetting resin having a glass transition temperature of 0 The temperature is above 50℃, the number average molecular weight is above 10,000 and below 50,000, and it has functional groups that can react with epoxy groups; and conductive fillers. The ratio of the acrylic resin to the total amount of the acrylic resin and the thermosetting resin is 15% by mass or more and 95% by mass or less.

Description

Conductive adhesive

The present disclosure relates to a conductive adhesive.

BACKGROUND OF THE INVENTION In flexible printed wiring boards, conductive adhesives are often used. For example, a reinforcing metal plate made of stainless steel can be attached to a flexible printed wiring board. By using a conductive adhesive when attaching the metal reinforcing plate, the reinforcing metal plate can be used as a shield against electromagnetic waves. The function of shielding. In this case, the conductive adhesive system requires that the insulating film (covering layer) provided on the surface of the flexible printed circuit board and the metal reinforcing plate be firmly bonded, and at the same time, it can be ensured and exposed from the opening provided in the insulating film The grounding circuit is well conducted.

In recent years, with the miniaturization of electrical equipment, it is required to embed a conductive adhesive in a minute opening to ensure conductivity. Therefore, the improvement of the embedding property of the conductive adhesive has been under discussion (for example, refer to Patent Document 1).

Prior Art Documents Patent Documents Patent Document 1: International Publication No. 2014/010524

Summary of the Invention Problems to be Solved by the Invention However, conductive adhesives require not only embedding properties but also adhesion properties. Specifically, the adhesion between the polyimide used in the flexible printed wiring board and the conductive adhesive is emphasized, and the adhesion between the gold plating layer and the conductive adhesive provided on the surface of the ground circuit is emphasized.

The subject of the present disclosure is to realize a conductive adhesive that has both embedding and adhesion properties.

Means to Solve the Problem The conductive adhesive of the present disclosure includes: acrylic resin with a weight average molecular weight of 500,000 to 1 million and an epoxy group; thermosetting resin with a glass transition temperature of 5°C or more and 100°C or less, with a number average molecular weight of 10,000 or more and 50,000 or less, and have functional groups that can react with epoxy groups; and conductive fillers; and, acrylic resins have thermosetting properties relative to acrylic resins The ratio of the total amount of resin is 15% by mass or more and 95% by mass or less.

In one aspect of the conductive adhesive of the present disclosure, the glass transition temperature of the acrylic resin can be set to 0°C or more and 50°C or less.

In one aspect of the conductive adhesive of the present disclosure, the thermosetting resin can be a urethane modified polyester resin.

In one aspect of the conductive adhesive of the present disclosure, the epoxy equivalent of the acrylic resin can be set to 1000 g/eq or more and 10000 g/eq or less.

In one aspect of the conductive adhesive of the present disclosure, the acid value of the thermosetting resin can be set to 5 mgKOH/g or more and 50 mgKOH/g or less.

Effects of the Invention According to the conductive adhesive of the present disclosure, it is possible to have both embedding properties and adhesion properties.

The conductive adhesive used to implement the first embodiment of the invention contains an acrylic resin (A) having an epoxy group, a thermosetting resin (B) having a functional group that reacts with the epoxy group, and a conductive filler ( C). The weight average molecular weight (Mw) of the acrylic resin (A) is 500,000 or more and 1 million or less. The glass transition temperature of the thermosetting resin (B) is 5° C. or more and 100° C. or less, and the number average molecular weight (Mn) is 10,000 or more and 50,000 or less. The ratio of the acrylic resin (A) to the total amount of the acrylic resin (A) and the thermosetting resin (B) is 15% by mass or more and 95% by mass or less.

Acrylic resin (A) The acrylic resin in this disclosure is a polymer mainly composed of alkyl acrylate or alkyl methacrylate. Hereinafter, acrylate and methacrylate are collectively referred to as (meth)acrylate. The alkyl (meth)acrylate is not particularly limited. For example, it can be a (meth)acrylate having a linear or branched alkyl group having a carbon number of about 1 to 18. Specifically, it can be set as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, tertiary butyl (meth)acrylate, pentyl (meth)acrylate, (meth) )Hexyl acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isopropyl (meth)acrylate, isobutyl (meth)acrylate, isodecyl (meth)acrylate Esters, lauryl (meth)acrylate and stearyl (meth)acrylate, etc. These alkyl (meth)acrylates may be used alone or in combination of two or more kinds.

The acrylic resin of this disclosure has an epoxy group. The epoxy group can be obtained by polymerizing an acrylic resin by adding a polymerizable monomer having an epoxy group to an alkyl (meth)acrylate. The polymerizable monomer having an epoxy group can be, for example, a (meth)acrylate having an epoxy group such as glycidyl (meth)acrylate. It can also be obtained by polymerizing an acrylic resin by adding a polymerizable (meth)acrylate oligomer having an epoxy group. It can also be obtained by polymerizing acrylic resin by adding other polymerizable monomers or oligomers with epoxy groups.

The acrylic resin of the present disclosure may also contain other monomer components. Other monomer components may include: aromatic vinyl compounds, (meth)acrylic acid, β-carboxyethyl acrylate, itaconic acid, crotonic acid, maleic acid, fumaric acid, maleic anhydride and other carboxyl-containing monomers; Monomers containing aliphatic ester groups other than alkyl groups such as cyclohexyl meth)acrylate and isobornyl (meth)acrylate; containing aromatic esters such as phenyl (meth)acrylate and benzyl (meth)acrylate Monomer; 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, chloro-2-hydroxypropyl acrylate, diethylene glycol mono(meth)acrylate, allyl Alcohols and other hydroxyl-containing monomers; aminomethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate and other amine-containing monomers; acrylamide, methylol (meth)acrylic acid Amine, methoxyethyl (meth)acrylamide and other amine group-containing monomers; methacryloxypropyl methoxysilane and other alkoxy-containing monomers; acetyl acetoxyethyl ( Acetylacetate group-containing monomers such as meth)acrylate; vinyl-based monomers other than styrene such as vinyl acetate and vinyl chloride; (meth)acrylonitrile, etc. These can be used individually or in combination of 2 or more types.

The epoxy equivalent of acrylic resin especially affects heat resistance. Therefore, it is preferably 10000g/eq or less, more preferably 9000g/eq or less, and more preferably 8000g/eq or less. Moreover, it is preferably 1000 g/eq or more, more preferably 2000 g/eq or more, and more preferably 3000 g/eq or more. In addition, the epoxy equivalent can be measured in accordance with JIS K7236:2001.

The Mw of the acrylic resin (A) of the present disclosure is 500,000 or more and 1 million or less. From the standpoint of embedding properties, the Mw of the acrylic resin (A) is 500,000 or more, preferably 700,000 or more, and more preferably 750,000 or more. On the other hand, from the viewpoint of ensuring liquidity, Mw is 1 million or less, preferably 950,000 or less, and more preferably 900,000 or less. In addition, Mw can be a styrene conversion value measured by gel permeation chromatography (GPC).

From the viewpoint of embedding property, the glass transition temperature of acrylic resin is preferably 0°C or higher, more preferably 5°C or higher, and more preferably 10°C or higher. Furthermore, it is preferably 50°C or less, more preferably 30°C or less, and more preferably 20°C or less. In addition, the glass transition temperature can be measured using a differential scanning calorimetry (DSC).

The polymerization method of the acrylic resin is not particularly limited, and a known polymerization method can be used. For example, if suspension polymerization is used, acrylic resins with epoxy groups with Mw of 500,000 or more and 1,000,000 or less can be easily obtained.

Commercially available acrylic resins satisfying such characteristics include, for example, Teisanresin series (SG-70L, SG-708-6, SG-P3) manufactured by Nagase ChemteX Co., and the like.

Thermosetting resin (B) From the viewpoint of embedding properties, the glass transition temperature of the thermosetting resin of this embodiment is 5°C or higher, preferably 10°C or higher, and more preferably 30°C or higher. In addition, it is below 100°C, preferably below 90°C, and more preferably below 80°C. In addition, the glass transition temperature can be measured using a differential scanning calorimetry (DSC).

From the viewpoint of embedding properties, the Mn of the thermosetting resin of this embodiment is preferably 10,000 or more. And it should be less than 50,000, more preferably less than 30,000. In addition, Mn can be set as a styrene conversion value measured by gel permeation chromatography (GPC).

The thermosetting resin of this embodiment has a functional group which can react with an epoxy group. The functional group that can react with the epoxy group is not particularly limited, and examples include a hydroxyl group, a carboxyl group, an epoxy group, and an amino group. Among them, hydroxyl group and carboxyl group are suitable.

When the thermosetting resin has a carboxyl group, from the viewpoint of heat resistance, the acid value is preferably 5 mgKOH/g or more, more preferably 10 mgKOH/g or more, and more preferably 15 mgKOH/g or more. And it is preferably 50mgKOH/g or less, more preferably 45mgKOH/g or less, and more preferably 40mgKOH/g or less. In addition, the acid value can be measured in accordance with JIS K0070: 1992.

The thermosetting resin in this embodiment is not particularly limited, but it is preferably a urethane modified polyester resin. The modified urethane polyester resin is a polyester resin containing urethane resin as a copolymer component. Urethane-modified polyester resin can be prepared by, for example, polycarboxylic acid or its anhydride, acid component and diol component undergoing condensation polymerization to obtain a polyester resin, and then the terminal hydroxyl group of the polyester resin reacts with the isocyanate component. Got. In addition, the acid component, the diol component, and the isocyanate component can be simultaneously reacted to obtain a urethane modified polyester resin.

The acid component is not particularly limited. For example, terephthalic acid, isophthalic acid, phthalic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid can be used. Formic acid, 2,2'-diphenyl dicarboxylic acid, 4,4'-diphenyl ether dicarboxylic acid, adipic acid, azelaic acid, sebacic acid, 1,4-cyclohexane dicarboxylic acid, 1, 3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 4-methyl-1,2-cyclohexanedicarboxylic acid, dimer acid, trimellitic anhydride, 1,2,4 , 5-pyromellitic anhydride, 5-(2,5-dioxotetrahydro-3-furyl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride, etc.

The glycol component is not particularly limited. For example, ethylene glycol, propylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,2-butanediol, 1,3-butanediol can be used , 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, neopentyl glycol, diethylene glycol, dipropylene glycol , 2,2,4-Trimethyl-1,5-pentanediol, cyclohexanedimethanol, neopentyl hydroxytrimethyl acetate, ethylene oxide adduct of bisphenol A and epoxy Propane adduct, hydrogenated bisphenol A ethylene oxide adduct and propylene oxide adduct, 1,9-nonanediol, 2-methyloctanediol, 1,10-decanediol, 2 -Butyl-2-ethyl-1,3-propanediol, tricyclodecane dimethanol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol and other glycols; or trimethylolpropane, Trimethylolethane, neopentylerythritol and other polyhydric alcohols with more than three valence

The isocyanate component is not particularly limited. For example, 2,4-tolylphenyl diisocyanate, 2,6-tolylphenyl diisocyanate, p-phenylene diisocyanate, diphenylmethane diisocyanate, m-phenylene diisocyanate can be used , Hexamethylene diisocyanate, tetramethylene diisocyanate, 3,3'-dimethoxy-4,4'-biphenylene diisocyanate, 1,5-naphthalene diisocyanate, 2,6-naphthalene Diisocyanate, 3,3'-dimethyl-4,4'-diisocyanate, 4,4'-diisocyanate diphenyl ether, 1,5-diisocyanate, 1,3 diisocyanate methyl ring Hexane, 1,4-diisocyanate methyl cyclohexane, isophorone diisocyanate, etc.

The thermosetting resin is not limited to urethane modified polyester resin, and acid anhydride modified polyester resin, epoxy resin, etc. may also be used.

In the conductive adhesive of this embodiment, the ratio of the mass of acrylic resin (A) to the total mass of acrylic resin (A) and thermosetting resin (B) (A/(A+B)) can be set as : 15% by mass or more, preferably 20% by mass or more, more preferably 30% by mass or more, and 95% by mass or less, preferably 90% by mass or less, more preferably 80% by mass or less. By setting the acrylic resin (A) and the thermosetting resin (B) to such a ratio, it is possible to achieve both embedding properties and adhesion to the insulating film and the gold plating layer.

Conductive filler (C) In the conductive adhesive of this embodiment, the conductive filler is not particularly limited. For example, metal fillers, metal-coated resin fillers, carbon fillers, and mixtures thereof can be used. Metal fillers can include copper powder, silver powder, nickel powder, silver-coated copper powder, gold-coated copper powder, silver-coated nickel powder, and gold-coated nickel powder. The metal powders can be produced by electrolysis, atomization, reduction, or the like. Among them, any one of silver powder, silver-clad copper powder and copper powder is suitable.

The conductive filler is not particularly limited. From the viewpoint of contact between fillers, the average particle size is preferably 1 μm or more, more preferably 3 μm or more, and preferably 50 μm or less, and more preferably 40 μm or less. The shape of the conductive filler is not particularly limited, and it can be spherical, flake, dendritic, or fibrous. From the viewpoint of obtaining a good connection resistance value, it is preferably dendritic.

In the conductive adhesive of this embodiment, the content of the conductive filler can be appropriately selected depending on the application, but the total solid content is preferably 5% by mass or more, more preferably 10% by mass or more, and preferably 95% by mass or less And it is more preferably 90% by mass or less. From the viewpoint of embedding property, it is preferably 70% by mass or less, and more preferably 60% by mass or less. In addition, when anisotropy is to be realized, it is preferably 40% by mass or less, and more preferably 35% by mass or less.

(Other curable resin components) In the conductive adhesive of this embodiment, it is also possible to add curable resins other than the above-mentioned acrylic resin with epoxy groups and thermosetting resins with functional groups that react with epoxy groups. ingredient. As such a curable resin component, an epoxy resin that is solid at normal temperature or an epoxy resin that is liquid at normal temperature can be used. In addition, regarding epoxy resin, "solid at room temperature" means a state that does not have fluidity at 25°C and a solvent-free state, and "liquid at room temperature" means a state that has fluidity under the same conditions.

Examples of epoxy resins that are solid or liquid at room temperature include: bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin and other bisphenol type epoxy resins; spiro ring type epoxy resin Oxygen resin, naphthalene type epoxy resin, biphenyl type epoxy resin, terpene type epoxy resin, ginseng (glycidoxy phenyl) methane, tetra (glycidoxy phenyl) ethane, etc. Propyl ether type epoxy resin; epoxy propyl amine type epoxy resin such as tetraglycidyl diamino diphenylmethane, tetrabromobisphenol A type epoxy resin, cresol novolac type epoxy resin, phenol phenolic aldehyde Novolac epoxy resin, α-naphthol novolac epoxy resin, brominated phenol novolac epoxy resin, etc.; rubber-modified epoxy resin, etc. These may be used individually by 1 type, and may use 2 or more types together. When other curable resin components are added to the conductive adhesive of this embodiment, it is preferable to blend 100 parts by mass of the acrylic resin having epoxy groups and the thermosetting resin having functional groups that react with epoxy groups in total Combined 1.0 to 10.0 parts by mass.

(Curing compound) In the conductive adhesive of this embodiment, in order to promote acrylic resins with epoxy groups, thermosetting resins with functional groups that react with epoxy groups, and other curing resins on demand The reaction of the components can also be blended with a curable compound. As such a hardening compound, imidazole hardeners, phenol hardeners, cationic hardeners, etc. can be used. These may be used individually by 1 type, and may use 2 or more types together.

等的化合物等，諸如：2-苯基-4,5-二羥基甲基咪唑、2-十七基咪唑、2,4-二胺基-6-(2′-十一基咪唑基)乙基-S-三吖

、1-氰乙基-2-苯基咪唑、2-苯基咪唑、5-氰基-2-苯基咪唑、2,4-二胺基-6-[2′甲基咪唑基-(1′)]-乙基-S-三吖

異三聚氰酸加成物、2-苯基咪唑異三聚氰酸加成物、2-甲基咪唑異三聚氰酸加成物、1-氰乙基-2-苯基-4,5-二(2-氰乙氧基)甲基咪唑等。Examples of imidazole hardeners include alkyl, ethyl cyano, hydroxyl, and acridine added to the imidazole ring.

And other compounds, such as: 2-phenyl-4,5-dihydroxymethylimidazole, 2-heptadecylimidazole, 2,4-diamino-6-(2'-undecylimidazolyl) ethyl Base-S-three acridine

, 1-cyanoethyl-2-phenylimidazole, 2-phenylimidazole, 5-cyano-2-phenylimidazole, 2,4-diamino-6-[2'methylimidazolyl-(1 ′)]-Ethyl-S-Triacrine

Isocyanuric acid adduct, 2-phenylimidazole isocyanuric acid adduct, 2-methylimidazole isocyanuric acid adduct, 1-cyanoethyl-2-phenyl-4, 5-bis(2-cyanoethoxy)methylimidazole and the like.

Examples of phenolic hardeners include novolac phenol and naphthol-based compounds.

Examples of cationic hardeners include amine salts of boron trifluoride, antimony pentachloride-acetyl chloride complexes, and sulfonium salts having phenethyl or allyl groups.

(Optional component) In the conductive adhesive of this embodiment, defoamers, antioxidants, viscosity modifiers, diluents, anti-settling agents, leveling agents, coupling agents, colorants, flame retardants, etc. can be added. Among these, in order to impart flame retardancy to the conductive adhesive, it is also preferable to add a flame retardant.

Examples of such flame retardants include: nitrogen-based flame retardants such as melamine cyanurate or melamine polyphosphate; metal hydrates such as magnesium hydroxide and aluminum hydroxide; and phosphate, red phosphorus and phosphate compounds, etc. Phosphorus flame retardant, etc. Among these, phosphate compounds are preferred.

When a flame retardant is added to the conductive adhesive of this embodiment, it is different from acrylic resin with epoxy groups and thermosetting resins with functional groups that react with epoxy groups (and other curable resins as required). Ingredients) are 100 parts by mass in total, and it is preferable to blend 10 parts by mass to 60 parts by mass.

(Method of use) As an example of the method of use of the conductive adhesive of the present embodiment, a method of mounting a metal reinforcing plate on a flexible printed wiring board will be described below. First, as shown in FIG. 1, a flexible printed wiring board 110 and a metal reinforcing plate 135 are prepared, and the metal reinforcing plate 135 is provided with a conductive adhesive layer 130 made of the conductive adhesive of this embodiment on one surface.

The method of disposing a conductive adhesive layer 130 on the surface of the metal reinforcing plate 135, for example, as shown in FIG. 2, firstly, a conductive adhesive is coated on the release substrate (separation film) 142 to form a conductive adhesive layer The conductivity of 130 is attached to the film 141. Then, the conductive adhesive film 141 and the metal reinforcing plate 135 are pressurized to adhere to each other, and the metal reinforcing plate 135 with the conductive adhesive layer 130 can be made. The peeling substrate 142 may be peeled off before use.

The peeling substrate 142 can be used on a base film such as polyethylene terephthalate, polyethylene naphthalate, etc., and is coated with silicon or non-silicon on the surface where the conductive adhesive layer 130 is to be formed. The thing of the release agent. In addition, the thickness of the peeling substrate 142 is not particularly limited, and can be determined in consideration of the ease of use.

The thickness of the conductive adhesive layer 130 is preferably 15 μm to 100 μm. By setting it to 15μm or more, sufficient embedding can be achieved, and sufficient connection with the ground circuit can be obtained. In addition, if it is set to 100 μm or less, it can respond to the requirement of thinning, and it is also advantageous in terms of cost.

The flexible printed wiring board 110 has, for example, a base member 112 and an insulating film 111, and the insulating film 111 is adhered to the base member 112 through the adhesive layer 113. The insulating film 111 is provided with an opening 160 through which the ground circuit 115 is exposed. The surface layer 116 which is a gold plating layer is provided on the exposed part of the ground circuit 115. In addition, the flexible printed wiring board 110 may be changed to a rigid board.

Next, as shown in FIG. 3, the metal reinforcing plate 135 is placed on the flexible printed wiring board 110 so that the conductive adhesive layer 130 is positioned above the opening 160. Then, two heating plates (not shown) heated to a predetermined temperature (for example, 120°C) sandwich the metal reinforcing plate 135 and the flexible printed wiring board 110 from the top and bottom, and press them at a predetermined pressure (for example, 0.5 MPa) A short time (for example, 5 seconds). Thereby, the metal reinforcing plate 135 can be temporarily fixed to the flexible printed wiring board 110.

Next, set the temperature of the two hot plates to a predetermined temperature (for example, 170° C.) higher than the above-mentioned temporary fixing, and pressurize at a predetermined pressure (for example, 3 MPa) for a predetermined time (for example, 30 minutes). Thereby, the conductive adhesive layer 130 can be filled in the opening 160, and the metal reinforcing plate 135 can be fixed to the flexible printed wiring board 110 in this state.

Then, a solder reflow step for mounting the parts is performed. In the reflow step, the flexible printed wiring board 110 is exposed to a high temperature of about 260°C. The parts to be mounted are not particularly limited. Examples include connectors or integrated circuits, as well as chip parts such as resistors and capacitors.

The conductive adhesive of this embodiment has high embedding properties, so even when the diameter of the opening 160 is as small as 1 mm or less, the opening 160 can be fully embedded and the metal reinforcing plate 135 and the ground circuit 115 can be secured Good connection. If the embedding property is not sufficient, fine air bubbles will enter between the surface layer 116 and the insulating film 111 and the conductive adhesive layer 130. Therefore, when exposed to a high temperature in the reflow step, the bubbles will become larger, which may cause the conductive adhesive layer 130 to peel off. However, the conductive adhesive layer 130 of this embodiment has good adhesion with the surface layer 116 and the insulating film 111, and good adhesion can be maintained after the reflow step.

From the viewpoint of firmly adhering to the metal reinforcing plate 135, the peeling strength between the conductive adhesive layer 130 and the metal reinforcing plate 135 should be high, specifically, 4N/10mm or more, and more preferably 5N/10mm or more. In addition, the peeling strength between the conductive adhesive layer 130 and the surface layer 116 is preferably high, and specifically, it is preferably 2N/10mm or more, and more preferably 3N/10mm or more. In addition, the peeling strength of the conductive adhesive layer 130 and the metal reinforcing plate 135 or the surface layer 116 can be measured by the method shown in the embodiment.

The metal reinforcing plate 135 may be formed of a conductive material with appropriate strength. For example, it can be a conductive material containing nickel, copper, silver, tin, gold, palladium, aluminum, chromium, titanium, and zinc. Among them, stainless steel is suitable from the viewpoint of corrosion resistance and strength.

The thickness of the metal reinforcing plate 135 is not particularly limited, but from the viewpoint of reinforcement, it is preferably 0.05 mm or more, more preferably 0.1 mm or more, and preferably 1.0 mm or less, and more preferably 0.3 mm or less.

In addition, it is preferable that a nickel layer is formed on the surface of the metal reinforcing plate 135. The method of forming the nickel layer is not particularly limited, and it can be formed by electroless plating, electroplating, or the like. If a nickel layer is formed, the adhesion between the metal reinforcing plate and the conductive adhesive can be improved.

The base member 112 can be, for example, a resin film, etc., specifically, it can be made of polypropylene, cross-linked polyethylene, polyester, polybenzimidazole, polyimide, polyimide, and polyetherimide. Or a film made of resin such as polyphenylene sulfide.

The insulating film 111 is not particularly limited. For example, polyethylene terephthalate, polypropylene, cross-linked polyethylene, polyester, polybenzimidazole, polyimide, polyimide amide, and polyether can be used. Formation of resins such as imide and polyphenylene sulfide. The thickness of the insulating film is not particularly limited, and can be about 10 μm to 30 μm.

The surface layer 116 is not limited to a gold plating layer, and may be a layer composed of copper, nickel, silver, tin, and the like. In addition, the surface layer 116 may be provided as required, or it may be configured without the surface layer 116.

The conductive adhesive of this embodiment has excellent embedding properties and adhesion to the surface layer and insulating film composed of gold plating, etc., and is particularly ideal for attaching a metal reinforcing plate to a flexible printed wiring board. Effect. However, it is also quite useful in other applications where conductive adhesives can be used. For example, it can be used for the adhesive layer of electromagnetic wave shielding film. Example

The following examples further illustrate the conductive adhesive of the present disclosure in detail. The following examples are examples and are not intended to limit the present invention.

<Preparation of a conductive adhesive film> The conductive adhesive films of Examples 1 to 13 and Comparative Examples 1 to 7 having the compositions shown in Tables 1 to 5 were produced by the following manufacturing method.

A planetary stirring and degassing device is used to mix and stir predetermined materials to produce a paste-like conductive adhesive composition. Next, use a plate-shaped spatula (doctor blade) to manually apply the manufactured conductive adhesive composition onto the release-treated polyethylene terephthalate film (separation film), and perform 100 Dried at ℃×3 minutes to produce a conductive adhesive film. In addition, the squeegee blade is based on the thickness of the conductive adhesive film to be produced, and the item of 1mil~5mil is appropriately selected (1mil=1/1000 inch=25.4μm). In addition, in each Example and each Comparative Example, each conductive adhesive film was produced to the predetermined thickness shown in Table 1. In addition, the thickness of the conductive adhesive film is measured with a micrometer.

<Adhesion to gold plating and polyimide> The adhesion between gold plating or polyimide and conductive adhesive was measured by a 90° peel test. Specifically, first, the conductive adhesive film and the metal reinforcing plate made of SUS plate with a thickness of 200 μm are temporarily attached using a pressing machine under the conditions of temperature: 120°C, time: 5 seconds, and pressure: 0.5 MPa to produce A conductive adhesive film 201 with a metal reinforcement plate with a conductive adhesive layer 212 is provided on the surface of the metal reinforcement plate 211. Next, on the surface of the copper foil 222 of the copper foil laminate film 203 in which the copper foil 222 is formed on the surface of the polyimide film 221, a gold plating layer 224 is formed. Next, the gold plating layer 224 of the copper foil laminate film 203 and the conductive adhesive film 201 with a metal reinforcing plate were bonded together using a pressing machine under the conditions of temperature: 120° C., time: 5 seconds, and pressure: 0.5 MPa. Then use a pressing machine to follow the conditions of temperature: 170°C, time: 3 minutes, and pressure: 2~3MPa to produce a copper foil laminate film with a metal reinforcing plate, and perform the post-treatment at 150°C for 1 hour. Hardening (after cure). Next, as shown in Fig. 4, at room temperature, the copper foil laminated film 203 was peeled off using a tensile tester (manufactured by Shimadzu Corporation, trade name AGS-X50S) at a tensile speed of 50 mm/min and a peeling angle of 90°. And take the maximum value at break as the peel strength to the gold plating.

The polyimide film 221 surface of the copper foil laminate film 203 and the conductive adhesive film 201 were adhered under the same conditions as the gold plating layer 224 to form a sample, and the sample was subjected to a 90° peel test under the same conditions to obtain Peel strength to polyimide.

<Preparation of a circuit board with a metal reinforcing plate> Next, the conductive adhesive films prepared in the examples and comparative examples were combined using a press machine under the conditions of temperature: 120°C, time: 5 seconds, and pressure: 0.5 MPa (With a separation film) and a metal reinforcement plate (the surface of the SUS plate is Ni-plated, thickness: 200μm) heat and press to produce a conductive adhesive film with a metal reinforcement plate. Then, peel off the separation film on the conductive adhesive film, and bond the conductive adhesive film with the metal reinforcing plate on the flexible substrate under the same conditions as the above-mentioned thermocompression bonding. Then, use a press to set the temperature: 170 ℃, time: 3 minutes, pressure: 2~3MPa, then make the circuit board with metal reinforcement board.

In addition, a flexible substrate is used as shown in Figure 1, that is: on the base member 112 composed of a polyimide film, a copper foil pattern 115 of a virtual ground circuit is formed, and an insulating adhesive layer is formed thereon 113 and a cover layer (insulating film) 111 made of a polyimide film. A gold plating layer is provided on the surface of the copper foil pattern 115 as the surface layer 116. In addition, an opening 160 that simulates a ground connection portion with a diameter of 0.8 mm is formed in the cover layer 111.

<Measurement of connection resistance> Using the circuit boards with metal reinforcement plates prepared in the examples and comparative examples, as shown in FIG. 5, the resistance meter 205 was used to measure two copper foil patterns with a gold plating layer on the surface, which is a surface layer 116. The resistance value between 115 is used to evaluate the connectivity between the copper foil pattern 115 and the metal reinforcing plate 135 and is used as the initial connection resistance value (connection resistance value before reflow).

Then, after 5 times of hot-air reflow of the prepared circuit boards with metal reinforcing plates of the examples and comparative examples, the connection resistance value after reflow was measured by the above-mentioned method. The reflow conditions are assumed to be lead-free solder, and the temperature profile of the polyimide film in the circuit board with metal reinforcement board is set to be exposed to 265°C for 5 seconds.

In addition, the case where the connection resistance value after reflow is 0.1Ω/1 hole or less is evaluated as the one with excellent conductivity after reflow.

(Example 1) For the acrylic resin (A), a resin (SG-P3, manufactured by Nagase ChemteX Co.) having an Mw of 850,000, an epoxy equivalent of 4700 g/eq, and a glass transition temperature of 12°C was used. For the thermosetting resin (B), a polyurethane modified polyester resin (UR3600, manufactured by Toyobo Co., Ltd.) having an Mn of 18000, an acid value of 20 mgKOH/g, and a glass transition temperature of 40°C was used. The blending amount is based on the acrylic resin (A) being 30 parts by mass and the thermosetting resin (B) being 70 parts by mass (A/(A+B)=30% by mass). As the conductive filler, a dendrite-like silver-coated copper powder (D-1) having an average particle diameter of 6 μm and a silver coverage rate of 9% by mass was used. The conductive filler is set to be 150 parts by mass with respect to 100 parts by mass of the resin component.

The peel strength of the obtained conductive adhesive to polyimide was 8N/10mm, and the peel strength to gold plating was 3N/10mm. In addition, the initial connection resistance when the hole diameter is 0.8mmφ is 40mΩ/1 hole, and the connection resistance after reflow is 28mΩ/1 hole.

(Example 2) The same as in Example 1 except that the acrylic resin was 50 parts by mass and the thermosetting resin was 50 parts by mass (A/(A+B)=50% by mass).

The peeling strength of the obtained conductive adhesive to polyimide was 9N/10mm, and the peeling strength to the gold plating layer was 4N/10mm. Also, the initial connection resistance is 39mΩ/1 hole, and the connection resistance after reflow is 30mΩ/1 hole.

(Example 3) The same as in Example 1 except that the acrylic resin was 70 parts by mass and the thermosetting resin was 30 parts by mass (A/(A+B)=70% by mass).

The peeling strength of the obtained conductive adhesive to polyimide was 19N/10mm, and the peeling strength to the gold plating layer was 5N/10mm. In addition, the initial connection resistance is 32mΩ/1 hole, and the connection resistance after reflow is 26mΩ/1 hole.

(Example 4) Except that the thermosetting resin is set to a polyurethane modified polyester resin (BX-39SS, manufactured by Toyobo Co., Ltd.) with an Mn of 16000, an acid value of 17 mgKOH/g, and a glass transition temperature of 15°C Otherwise, the rest is the same as in Example 1.

The peeling strength of the obtained conductive adhesive to polyimide was 5N/10mm, and the peeling strength to the gold plating layer was 7N/10mm. Also, the initial connection resistance is 133mΩ/1 hole, and the connection resistance after reflow is 100mΩ/1 hole.

(Example 5) The same as Example 4 except that the acrylic resin was 50 parts by mass and the thermosetting resin was 50 parts by mass (A/(A+B)=50% by mass).

The peel strength of the obtained conductive adhesive to polyimide was 10N/10mm, and the peel strength to gold plating was 7N/10mm. In addition, the initial connection resistance is 91mΩ/1 hole, and the connection resistance after reflow is 58mΩ/1 hole.

(Example 6) The same as Example 4 except that the acrylic resin was 60 parts by mass and the thermosetting resin was 40 parts by mass (A/(A+B)=60% by mass).

The peeling strength of the obtained conductive adhesive to polyimide was 12N/10mm, and the peeling strength to the gold plating layer was 6N/10mm. In addition, the initial connection resistance is 83mΩ/1 hole, and the connection resistance after reflow is 62mΩ/1 hole.

(Example 7) The same as Example 4 except that the acrylic resin was 70 parts by mass and the thermosetting resin was 30 parts by mass (A/(A+B)=70% by mass).

The peel strength of the obtained conductive adhesive to polyimide was 10N/10mm, and the peel strength to gold plating was 6N/10mm. Also, the initial connection resistance is 71mΩ/1 hole, and the connection resistance after reflow is 67mΩ/1 hole.

(Example 8) The same as Example 4 except that the acrylic resin was set to 80 parts by mass and the thermosetting resin was set to 20 parts by mass (A/(A+B)=80% by mass).

The peel strength of the obtained conductive adhesive to polyimide was 7N/10mm, and the peel strength to gold plating was 6/10mm. In addition, the initial connection resistance is 72mΩ/1 hole, and the connection resistance after reflow is 54mΩ/1 hole.

(Example 9) In addition to acrylic resin (SG-P3, manufactured by Nagase ChemteX Co.) and thermosetting resin (Vylon BX-39SS, manufactured by Toyobo Co., Ltd.), bisphenol A type solid epoxy resin was added (JER1003, manufactured by Mitsubishi Chemical). The blending amount was 60 parts by mass of acrylic resin, 30 parts by mass of thermosetting resin, and 10 parts by mass of solid epoxy resin (A/(A+B)=66.6 mass %). In addition, the conductive filler was set to a dendritic silver-coated copper powder (D-2) having an average particle diameter of 12 μm and a silver coverage rate of 8% by mass.

The peel strength of the obtained conductive adhesive to polyimide was 10N/10mm, and the peel strength to gold plating was 7N/10mm. Also, the initial connection resistance is 99mΩ/1 hole, and the connection resistance after reflow is 42mΩ/1 hole.

(Example 10) Except that the conductive filler was set to a dendritic silver-coated copper powder (D-3) with an average particle size of 12 μm and a silver coverage rate of 9% by mass, the rest was the same as in Example 9 (A/(A+ B)=66.6 mass%).

The peeling strength of the obtained conductive adhesive to polyimide was 9N/10mm, and the peeling strength to the gold plating layer was 7N/10mm. In addition, the initial connection resistance is 179mΩ/1 hole, and the connection resistance after reflow is 93mΩ/1 hole.

(Example 11) In addition to acrylic resin (SG-P3, manufactured by Nagase ChemteX Co.) and thermosetting resin (UR3600, manufactured by Toyobo Co., Ltd.), bisphenol A type solid epoxy resin (JER1003, Mitsubishi Chemical Corporation). The blending amount was 85 parts by mass of acrylic resin, 10 parts by mass of thermosetting resin, and 5 parts by mass of solid epoxy resin (A/(A+B)=89.5% by mass). Furthermore, 3 parts by mass of 2-phenyl-1H-imidazole-4,5-dimethanol (2PHZPW, manufactured by Shikoku Kasei Co., Ltd.) was added as a curing agent relative to 100 parts by mass of the resin component, and relative to the resin component 100 parts by mass of 35 parts by mass of ginsenoside aluminum salt (OP935, manufactured by Clariant Japan KK) was used as a flame retardant. The conductive filler is set to dendritic silver-coated copper powder (D-1) with an average particle size of 6μm and a silver coverage rate of 9% by mass, and the blending amount is set to 150 parts by mass relative to 100 parts by mass of the resin component .

The peeling strength of the obtained conductive adhesive to polyimide was 14N/10mm, and the peeling strength to the gold plating layer was 7N/10mm. Also, the initial connection resistance is 20mΩ/1 hole, and the connection resistance after reflow is 12mΩ/1 hole.

(Example 12) Except that 35 parts by mass of ginseng diethylphosphonate aluminum salt (OP935, manufactured by Clariant Japan KK) was added as a flame retardant relative to 100 parts by mass of the resin component, the rest was the same as in Example 8 (A/ (A+B)=80% by mass).

The peel strength of the obtained conductive adhesive to polyimide was 14N/10mm, and the peel strength to the gold plating layer was 8N/10mm. In addition, the initial connection resistance is 32mΩ/1 hole, and the connection resistance after reflow is 23mΩ/1 hole.

(Example 13) Except that the thermosetting resin is set to have an Mn of 35000~45000, an acid value of 35mgKOH/g and a glass transition temperature of 5℃~15℃ polyurethane modified polyester resin (UR3500, Toyobo Except for the company system), the rest was the same as in Example 8 (A/(A+B)=80% by mass).

The peeling strength of the obtained conductive adhesive to polyimide was 8N/10mm, and the peeling strength to the gold plating layer was 6N/10mm. In addition, the initial connection resistance is 38mΩ/1 hole, and the connection resistance after reflow is 38mΩ/1 hole.

(Comparative Example 1) The same as in Example 1 except that only acrylic resin was used and no thermosetting resin was added (A/(A+B)=100% by mass).

The obtained conductive adhesive was not closely adhered to any one of the polyimide and the gold plating layer. In addition, the initial connection resistance is 27mΩ/1 hole, and the connection resistance after reflow is 64mΩ/1 hole.

(Comparative Example 2) The same as in Example 1 except that the acrylic resin was 10 parts by mass and the thermosetting resin was 90 parts by mass (A/(A+B)=10% by mass).

The peel strength of the obtained conductive adhesive to polyimide was 3N/10mm, and the peel strength to gold plating was 3N/10mm. In addition, the initial connection resistance is 34mΩ/1 hole, and the connection resistance after reflow is above the measurement limit (OL).

(Comparative Example 3) The same as in Example 1 except that only the thermosetting resin was used and the acrylic resin was not added (A/(A+B)=0% by mass).

The peeling strength of the obtained conductive adhesive to polyimide was 2N/10mm, and the peeling strength to the gold plating layer was 3N/10mm. In addition, the initial connection resistance is 30mΩ/1 hole, and the connection resistance after reflow is above the measured limit value.

(Comparative Example 4) Except that the acrylic resin is set to a resin (SG-P3-MW1, Nagase ChemteX Co.) (manufactured by Nagase ChemteX Co.) with an Mw of 300,000, an epoxy equivalent of 1680 g/eq, and a glass transition temperature of 11°C Comparative Example 1 (A/(A+B)=100% by mass).

The obtained conductive adhesive was not closely adhered to any one of the polyimide and the gold plating layer. In addition, the initial connection resistance is 50mΩ/1 hole, and the connection resistance after reflow is above the measured limit value.

(Comparative Example 5) Except that the acrylic resin is set to a resin (SG-P3-MW8, manufactured by Nagase ChemteX Co.) with an Mw of 600,000 and an epoxy equivalent of 3300 g/eq, the rest is the same as in Comparative Example 1 (A/( A+B)=100% by mass).

The obtained conductive adhesive was not closely adhered to any one of the polyimide and the gold plating layer. In addition, the initial connection resistance is 43mΩ/1 hole, and the connection resistance after reflow is 88mΩ/1 hole.

(Comparative Example 6) Except that the conductive filler was set to have an average particle diameter of 5 μm and a silver coating rate of 10% by mass of flake silver-coated copper powder (D-4), the rest was the same as in Example 7 (A/(A+ B)=70% by mass).

The peeling strength of the obtained conductive adhesive to polyimide was 12N/10mm, and the peeling strength to the gold plating layer was 8N/10mm. In addition, the initial connection resistance and the connection resistance after reflow are both above the measurement limit value.

(Comparative Example 7) Except that the conductive filler was set to an atomized silver-coated copper powder (D-5) with an average particle diameter of 5 μm and a silver coverage rate of 10% by mass, the rest was the same as in Example 7 (A/(A+ B)=70% by mass).

The peeling strength of the obtained conductive adhesive to the metal reinforcing plate was 10N/10mm, and the peeling strength to the gold plating layer was 8N/10mm. In addition, the initial connection resistance and the connection resistance after reflow are both above the measurement limit value.

The composition and measurement results of each example and comparative example are collectively listed in Tables 1 to 5.

[Table 1]

[Table 2]

[table 3]

[Table 4]

[table 5]

Industrial Applicability The conductive adhesive of this disclosure can have both embedding and adhesion properties, and can be used as a conductive adhesive for flexible printed wiring boards and the like.

110‧‧‧Flexible printed wiring board 111‧‧‧Insulation film (covering layer) 112‧‧‧Base member 113‧‧‧Adhesive layer 115‧‧‧Ground circuit (copper foil pattern) 116‧‧‧Surface layer 130 ‧‧‧Conductive Adhesive Layer 135‧‧‧Metal Reinforcing Plate 141‧‧‧Conductive Adhesive Film 142‧‧‧Peeling Substrate (Separation Film) 160‧‧‧ Opening 201‧‧‧Conductive Adhesive Film 203‧ ‧‧Copper foil laminated film 205‧‧‧Resistance meter 211‧‧‧Metal reinforcement plate 212‧‧‧Conductive adhesive layer 221‧‧‧Polyimide film 222‧‧‧Copper foil 224‧‧‧Gold plating

Fig. 1 is a cross-sectional view showing a step of attaching a reinforcing metal plate. Fig. 2 is a cross-sectional view showing a step of attaching a reinforcing metal plate. Fig. 3 is a cross-sectional view showing a step of attaching a reinforcing metal plate. Figure 4 is a diagram showing the method of measuring peel strength. Figure 5 is a diagram showing the method of measuring the connection resistance.

Claims (5)

A conductive adhesive containing: acrylic resin with a weight average molecular weight of 500,000 or more and 1 million or less and having epoxy groups; thermosetting resin with a glass transition temperature of 5°C or more and 100°C or less, and the number is average The molecular weight is 10,000 or more and 50,000 or less and has a functional group that can react with epoxy groups; and a conductive filler; and the ratio of the acrylic resin to the total amount of the acrylic resin and the thermosetting resin is 15 Mass% or more and 95 mass% or less; the conductive filler is dendritic; the thermosetting resin is a urethane modified polyester resin. The conductive adhesive of claim 1, wherein the glass transition temperature of the acrylic resin is 0°C or more and 50°C or less. The conductive adhesive of claim 1 or 2, wherein the epoxy equivalent of the acrylic resin is 1000 g/eq or more and 10000 g/eq or less. The conductive adhesive of claim 1 or 2, wherein the acid value of the thermosetting resin is 5 mgKOH/g or more and 50 mgKOH/g or less. The conductive adhesive of claim 3, wherein the acid value of the thermosetting resin is 5 mgKOH/g or more and 50 mgKOH/g or less.

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