JP2024052152A - Conductive composition, cured product thereof, and method for manufacturing electronic components using the conductive composition - Google Patents

Abstract

[Problem] To provide a conductive composition that can suppress microcracks in a conductor circuit that occur when a substrate on which a conductive layer (conductor circuit) is formed using the conductive composition is three-dimensionally molded, and that allows easy visual inspection to determine whether or not cracks exist. [Means] The conductive composition is characterized in that it contains at least an epoxy resin, a thermoplastic resin, and a conductive filler, and that the thermoplastic resin has a glass transition temperature of 80°C or higher. [Selected Figures] None

Description

The present invention relates to a conductive composition, and more specifically to a conductive composition that can be suitably used to form conductor circuits such as three-dimensional circuit boards, a cured product thereof, and a method for manufacturing electronic components using the conductive composition.

As electronic devices such as mobile phones and copiers become smaller and more multifunctional, there is a demand for compactly accommodating circuit boards on the inside and outside of their housings. Three-dimensional circuit boards form conductive wiring three-dimensionally, rather than flatly, on the inside and outside of housings and electronic components that have a three-dimensional structure, and are superior in terms of space efficiency, improved design, and reduced number of parts through the integration of parts and circuits.

Methods for directly forming a circuit on a three-dimensional substrate include, for example, a method in which a circuit is formed by physically masking the surface of a resin molded product and printing with a conductive composition; a method in which a metal thin film is formed on the surface of a molded product by deposition or the like and then unnecessary metal thin film is removed to form a circuit; a method in which a metal foil is attached to a molded product by hot stamping to form a circuit; a method in which a resin containing a non-conductive metal complex is injection molded to obtain a molded product, metal nuclei are generated by laser irradiation or the like, and the locations where the metal nuclei are generated are plated to form a circuit; a method in which a resin coating is formed on the surface of a molded product made of a resin containing an electroless plating catalyst or the like, the resin coating is removed by laser irradiation or the like while simultaneously cutting and roughening the surface of the molded product, and then electroless plating is applied to the openings where the resin coating has been removed to form a wiring pattern on the surface of the molded product.

In recent years, it has also been proposed to form a three-dimensional circuit board by forming a conductor circuit on a film-like substrate using a conductive composition, and then molding the film-like substrate on which the conductor circuit has been formed into a desired shape by thermoforming or the like (Patent Document 1). As a conductive composition for use in the manufacture of such three-dimensional circuit boards, a conductive composition capable of forming a stretchable conductor circuit that can follow the deformation during three-dimensional molding of the circuit board has also been proposed (Patent Document 2).

JP 2018-198133 A International Publication No. 2017/026420

Even when using a conductive composition that can follow the deformation of the substrate as described above, cracks may occur in the circuit when the substrate is molded into a three-dimensional shape after the circuit is formed, which is a major issue. The occurrence of cracks can lead to disconnections in the circuit or a significant increase in resistance, so it is necessary to check that there is no change in resistance for all three-dimensional circuit substrates manufactured.

On the other hand, when cracks can be confirmed by visual inspection in a circuit, product defects can be detected without inspection using a measuring device such as a resistance meter. However, cracks that occur in circuits come in different shapes and sizes, and there are not only relatively large cracks that can be confirmed by visual inspection, but also microcracks that are fine in shape and difficult to confirm by visual inspection. Even in cases where cracks cannot be confirmed by visual inspection in the case of microcracks, there is a possibility of a disconnection, so it is necessary to inspect using a resistance meter or the like, or to check for the presence or absence of microcracks using a magnifying glass or microscope. This makes it complicated to detect product defects caused by cracks.

Therefore, the object of the present invention is to provide a conductive composition that can suppress microcracks in the conductor circuit that occur when a substrate having a conductive layer (conductor circuit) formed thereon using the conductive composition is three-dimensionally molded, and that allows the presence or absence of cracks to be easily determined by visual inspection.

The present inventors have found that by incorporating a thermoplastic resin having a glass transition temperature equal to or higher than a predetermined temperature in addition to an epoxy resin, which is a curing component in a conductive composition, it is possible to suppress the occurrence of microcracks, which are among the cracks and breaks in a circuit (conductive layer) that occur during molding of a circuit board in a predetermined temperature environment, and as a result, it is possible to easily determine the presence or absence of cracks by visual inspection without performing a resistance value test using a complicated device. The present invention is based on this finding. That is, the gist of the present invention is as follows.
[1] A conductive composition comprising at least an epoxy resin, a thermoplastic resin, and a conductive filler,
The conductive composition, wherein the thermoplastic resin has a glass transition temperature of 80° C. or higher.
[2] The conductive composition according to [1], wherein the epoxy resin is contained in an amount of 5 to 100 parts by mass, calculated as a solid content, per 100 parts by mass of the thermoplastic resin.
[3] The conductive composition according to [1], wherein the epoxy resin contains an epoxy resin having an epoxy equivalent of 500 g/eq or more.
[4] The conductive composition according to [1], wherein the epoxy resin includes two types of epoxy resins: an epoxy resin having an epoxy equivalent of 500 g/eq or more; and an epoxy resin having an epoxy equivalent of less than 500 g/eq.
[5] The conductive composition according to [1], wherein the conductive filler comprises one or more conductive agglomerated powders selected from the group consisting of silver powder, copper powder, silver-coated copper powder, copper alloy powder, conductive oxide powder, and carbon particles.
[6] A cured product of the conductive composition according to any one of [1] to [5].
[7] The cured product according to [6], which has a storage modulus at 160° C. of 1.0×10 ⁵ Pa or more.
[8] An electronic component having a circuit formed on a surface of a three-dimensional substrate,
An electronic component, wherein the circuit comprises the cured product according to [6].
[9] A method for producing an electronic component using the conductive composition according to any one of [1] to [5],
The conductive composition is applied onto a substrate to form a coating film having a desired pattern;
The coating film is dried and cured to form a conductor circuit on the substrate;
The substrate on which the conductor circuit is formed is molded into a three-dimensional shape to produce a three-dimensional circuit substrate.
Including,
A method for producing an electronic component, characterized in that the molding is carried out within a temperature range of ±80° C. of the glass transition temperature of the cured product of the conductive composition.

The present invention provides a conductive composition that can suppress microcracks in a conductor circuit that occur when a substrate on which a conductor circuit is formed using a conductive composition is three-dimensionally molded, and that allows the presence or absence of cracks to be easily determined by visual inspection.

[Conductive composition]
The conductive composition according to the present invention contains, as essential components, an epoxy resin, a thermoplastic resin, and a conductive filler. Each component constituting the conductive composition according to the present invention will be described below.

<Epoxy resin>
The conductive composition according to the present invention contains an epoxy resin as an essential component. As the epoxy resin, any epoxy resin having two or more epoxy groups in one molecule can be used without limitation. For example, bisphenol A type epoxy resin, bisphenol F type epoxy resin, hydrogenated bisphenol A type epoxy resin, brominated bisphenol A type epoxy resin, bisphenol S type epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin, bisphenol A novolac type epoxy resin, biphenyl type epoxy resin, naphthol type epoxy resin, naphthalene type epoxy resin, dicyclopentadiene type epoxy resin, triphenylmethane type epoxy resin, alicyclic epoxy resin, aliphatic chain epoxy resin, phosphorus-containing epoxy resin, anthracene type epoxy resin, norbornene type epoxy resin, adamantane type epoxy resin, fluorene type epoxy resin, aminophenol type epoxy resin, aminocresol type epoxy resin, alkylphenol type epoxy resin, etc. can be mentioned. The above-mentioned epoxy resins can be used alone or in combination of two or more kinds.

The above-mentioned epoxy resins are available in solid, semi-solid, and liquid forms before curing. These can be used alone or in combination of two or more. Note that liquid means that the resin is in a liquid state that has fluidity at 20°C, and semi-solid means that the resin is in a solid state that has no fluidity at 20°C, but is in a liquid state that has fluidity at 40°C.

Examples of solid epoxy resins include epoxidized products of condensation products of phenols and aromatic aldehydes having a phenolic hydroxyl group (trisphenol type epoxy resins), such as EPPN-502H (trisphenol epoxy resin) manufactured by Nippon Kayaku Co., Ltd.; dicyclopentadiene aralkyl type epoxy resins, such as EPICLON HP-7200H (dicyclopentadiene skeleton-containing multifunctional solid epoxy resin) manufactured by DIC Corporation; novolac type epoxy resins, such as EPICLON N660 and EPICLON N690 manufactured by DIC Corporation and EOCN-104S manufactured by Nippon Kayaku Co., Ltd.; and D.E.N. manufactured by Dow Chemical Japan Ltd. Examples include phenol novolac type epoxy resins such as 431; biphenyl type epoxy resins such as YX-4000 manufactured by Mitsubishi Chemical Corporation; phosphorus-containing epoxy resins such as TX0712 manufactured by Nippon Steel Chemical & Material Co., Ltd.; tris(2,3-epoxypropyl)isocyanurates such as TEPIC manufactured by Nissan Chemical Co., Ltd.; and bisphenol A type epoxy resins such as jER1001 manufactured by Mitsubishi Chemical Corporation.

Examples of semi-solid epoxy resins include bisphenol A type epoxy resins such as EPICLON 860, EPICLON 900-IM, EPICLON EXA-4816, and EPICLON EXA-4822 manufactured by DIC Corporation, Epotohto YD-134 manufactured by Nippon Steel Chemical & Material Co., Ltd., jER834 and jER872 manufactured by Mitsubishi Chemical Corporation, and ELA-134 manufactured by Sumitomo Chemical Co., Ltd.; and phenol novolac type epoxy resins such as EPICLON N-740 manufactured by DIC Corporation.

Examples of liquid epoxy resins include ZX-1059 (a mixture of bisphenol A and bisphenol F epoxy resins) manufactured by Nippon Steel Chemical & Material Co., Ltd., jER 828 (bisphenol A epoxy resin), jER 807, and jER 4004P (bisphenol F epoxy resin) manufactured by Mitsubishi Chemical Corporation, and R710 (bisphenol E epoxy resin) manufactured by Air Water Inc.

In the present invention, among the above-mentioned epoxy resins, bisphenol A type epoxy resin, bisphenol S type epoxy resin, bisphenol F type epoxy resin, and novolac type epoxy resin can be preferably used.

From the viewpoint of suppressing the occurrence of microcracks, the epoxy resin preferably contains an epoxy resin with an epoxy equivalent of 500 g/eq or more, and more preferably contains an epoxy resin with an epoxy equivalent of 700 to 2500 g/eq.

In addition, in the present invention, it is preferable that the epoxy resin contains two types of epoxy resin: an epoxy resin with an epoxy equivalent of 500 g/eq or more, and an epoxy resin with an epoxy equivalent of less than 500 g/eq. By using two types of epoxy resins with different epoxy equivalents in combination, the storage modulus of the cured product can be increased, and as a result, the occurrence of cracks when the conductive composition is heated and deformed after being cured to form a conductive layer (circuit) can be suppressed.

When two types of epoxy resins with different epoxy equivalents are used in combination, it is preferable that the epoxy resin with an epoxy equivalent of 500 g/eq or more is contained in a proportion of 25 to 60 mass% relative to the total epoxy resin. Also, it is preferable that the epoxy resin with an epoxy equivalent of less than 500 g/eq is contained in a proportion of 40 to 75 mass%.

The mixing ratio of epoxy resins with an epoxy equivalent of 500 g/eq or more to epoxy resins with an epoxy equivalent of less than 500 g/eq is preferably 15:85 to 70:30 by mass, and more preferably 25:75 to 60:40.

As the novolac type epoxy resin, commercially available products may be used, such as YDCN-704 and YDPN-638 manufactured by Nippon Steel Chemical & Material Co., Ltd., D.E.N. 431 and D.E.N. 439 manufactured by Dow Chemical Japan, Araldite EPN-1138 and ECN-1299 manufactured by Huntsman, EPICLON N-730, N-770, N-865, N-665, N-673 and N-695 manufactured by DIC Corporation, and EOCN-104 and EOCN-1020 manufactured by Nippon Kayaku Co., Ltd. These may be used alone or in combination of two or more types according to the required properties.

In the present invention, from the viewpoint of imparting flexibility derived from the thermoplastic resin component to the cured product while suppressing the occurrence of microcracks derived from the thermoplastic resin component and imparting heat resistance to the cured product, the epoxy resin is preferably contained in a ratio of 5 to 100 parts by mass, and more preferably 5 to 30 parts by mass, calculated as solid content, per 100 parts by mass of the thermoplastic resin described below.

<Curing Agent>
The conductive composition according to the present invention preferably contains a curing agent for curing the epoxy resin. The curing agent is not particularly limited, and a suitable curing agent can be selected and used depending on the epoxy resin to be used. The curing agent can be a known agent, such as amines, imidazoles, phenols, acid anhydrides, isocyanates, and polymers containing these functional groups, and a plurality of these may be used as necessary. The amines include dicyandiamide, diaminodiphenylmethane, and the like. The imidazoles include alkyl-substituted imidazoles, benzimidazoles, and the like, and may be imidazole latent curing agents such as imidazole adducts such as reaction products of epoxy resins and imidazoles. The phenols include hydroquinone, resorcinol, bisphenol A and its halogen compounds, and further, novolacs and resol resins which are condensates of bisphenol A and aldehydes. The acid anhydrides include phthalic anhydride, hexahydrophthalic anhydride, methylnadic anhydride, and benzophenonetetracarboxylic acid. The isocyanates include tolylene diisocyanate, isophorone diisocyanate, etc., and these isocyanates may be used after being masked with phenols, etc. These curing agents may be used alone or in combination of two or more kinds.

Among the above-mentioned curing agents, amines, imidazoles and phenols can be preferably used from the viewpoints of dispersibility of the conductive filler, storage stability, heat resistance, etc., and imidazoles and phenols can be particularly preferably used.

Examples of imidazoles include 2-methylimidazole, 4-methyl-2-ethylimidazole, 2-phenylimidazole, 4-methyl-2-phenylimidazole, 1-benzyl-2-methylimidazole, 2-ethylimidazole, 2-isopropylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-undecylimidazole, and 2-phenyl-4,5-dihydroxymethylimidazole. Commercially available imidazole compounds include, for example, imidazoles such as 2E4MZ, C11Z, C17Z, and 2PZ, imidazole azine compounds such as 2MZ-A and 2E4MZ-A, imidazole isocyanurates such as 2MZ-OK and 2PZ-OK, and imidazole hydroxymethyl compounds such as 2PHZ and 2P4MHZ (all manufactured by Shikoku Chemical Industry Co., Ltd.). Commercially available imidazole-type latent curing agents include, for example, Curesol P-0505 (manufactured by Shikoku Chemical Industry Co., Ltd.).

The amount of the curing agent is preferably 0.5 to 200 parts by mass, and more preferably 1 to 100 parts by mass, calculated as solid content per 100 parts by mass of epoxy resin.

<Thermoplastic resin>
The conductive composition according to the present invention contains, as a resin component, a thermoplastic resin having a glass transition temperature of 80°C or higher in addition to the epoxy resin described above. By using such a thermoplastic resin having a relatively high heat resistance in combination with an epoxy resin, the heat resistance of the cured product (conductive layer) obtained by curing the conductive composition can be improved, and the occurrence of microcracks, which are cracks or breaks in the circuit (conductive layer) that occur during molding of a circuit board performed in a high-temperature environment, can be suppressed. That is, by making the composition such that the cured product is less likely to follow deformation during molding processing performed in a high-temperature environment, relatively large cracks are generated. As a result, it is possible to easily determine the presence or absence of cracks by visual inspection without performing a resistance value inspection using a complicated device. If the glass transition temperature of the thermoplastic resin is less than 80°C, it becomes difficult to suppress the occurrence of microcracks that cannot be confirmed by visual inspection. The preferred range of the glass transition temperature of the thermoplastic resin is 100 to 140°C. The glass transition temperature (Tg) may be measured by a standard method using a differential scanning calorimeter, or may be measured by thermomechanical analysis using a dynamic viscoelasticity measuring device.

Thermoplastic resins can be used without any particular restrictions as long as they have a glass transition temperature of 80°C or higher. Examples include polyester resins, polyether resins, polyamide resins, polyamideimide resins, polyimide resins, butyral resins (e.g., polyvinyl butyral resins, etc.), polyvinyl formal resins, phenoxy resins, polyhydroxypolyether resins, acrylic resins, polystyrene resins, butadiene resins, polyurethane resins, polyesterurethane resins, polyetheresteramides, copolymers having vinyl acetate as a structural unit (vinyl acetate copolymers, e.g., ethylene-vinyl acetate copolymers), acrylonitrile-butadiene copolymers, acrylonitrile-butadiene-styrene copolymers, styrene-butadiene copolymers, acrylic acid copolymers, etc. These thermoplastic resins may be used alone or in combination of two or more types.

Among the above, acrylic resin, polyurethane resin, and polyester resin can be preferably used. By using these resins, flexibility can be imparted to the cured product (circuit) at the temperature when the circuit-formed substrate is molded into a three-dimensional shape, making it easier to follow the deformation of the substrate.

<Conductive filler>
As the conductive filler contained in the conductive composition according to the present invention, metal particles, carbon particles, conductive oxide particles, etc. can be used.

Examples of metal particles include powders of simple metals such as gold, silver, copper, nickel, chromium, palladium, rhodium, ruthenium, indium, aluminum, tungsten, molbutene, and platinum, as well as alloy powders such as copper-nickel alloys, silver-palladium alloys, copper-tin alloys, silver-copper alloys, and copper-manganese alloys, metal particles, or metal-coated particles in which the surface of alloy powder is coated with silver or the like. Examples of carbon particles include carbon black, graphite, and carbon nanotubes. Examples of conductive oxide particles include silver oxide, indium oxide, tin oxide, zinc oxide, and ruthenium oxide. These conductive fillers may be used alone or in combination of two or more types.

Among the above, silver powder, copper powder, silver-coated copper powder, copper alloy powder, conductive oxide powder, and carbon particles can be preferably used.

The shape of the conductive filler is not particularly limited, but is preferably in the form of an agglomerated powder or flake powder. The form of an agglomerated powder refers to an indefinite shape formed by the settling of spherical particles, which are called, for example, a bound sphere, a chain sphere, or an agglomerated shape. The form of a flake powder refers to a two-dimensional flat shape such as a scale-like, scale-like, plate-like, flat, or sheet-like shape. In the present invention, it is preferable to use silver powder, copper powder, silver-coated copper powder, copper alloy powder, conductive oxide powder, or carbon particles in the form of an agglomerated powder.

The average particle size of the conductive agglomerate powder is not particularly limited, but from the viewpoints of maintaining dispersibility and printability in the conductive composition, maintaining conductivity during molding, etc., it is preferably in the range of 0.5 to 30 μm, and more preferably in the range of 1 to 10 μm. The average particle size refers to the median value (D50 value) of the particle size distribution on a volume basis, and can be determined by a laser diffraction particle size distribution measuring device or dynamic light scattering method.

From the viewpoint of electrical conductivity and dispersibility when cured, the conductive filler is preferably contained in an amount of 50 to 95 parts by mass, and more preferably 65 to 85 parts by mass, per 100 parts by mass of the solid content of the conductive composition.

<Other ingredients>
The conductive composition of the present invention may contain an organic solvent for adjusting the composition or for adjusting the viscosity for application to a substrate.

Examples of such organic solvents include ketones, aromatic hydrocarbons, glycol ethers, glycol ether acetates, esters, alcohols, aliphatic hydrocarbons, and petroleum-based solvents. More specifically, ketones such as methyl ethyl ketone and cyclohexanone; aromatic hydrocarbons such as toluene, xylene, and tetramethylbenzene; glycol ethers such as cellosolve, methyl cellosolve, butyl cellosolve, carbitol, methyl carbitol, butyl carbitol, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol diethyl ether, and triethylene glycol monoethyl ether; ethyl acetate, butyl acetate, carbitol acetate, and diethylene glycol monoethyl ether acetate. Examples of suitable organic solvents include esters such as propylene glycol methyl ether acetate, dipropylene glycol methyl ether acetate, propylene glycol ethyl ether acetate, propylene glycol butyl ether acetate, and 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate; alcohols such as ethanol, propanol, ethylene glycol, propylene glycol, butylene glycol, and terpineol; aliphatic hydrocarbons such as octane and decane; and petroleum solvents such as petroleum ether, petroleum naphtha, hydrogenated petroleum naphtha, and solvent naphtha. These organic solvents are used alone or as a mixture of two or more kinds. Among these, when forming a circuit on a substrate made of a thermoformable thermoplastic resin, the solvent can be appropriately selected in consideration of the erosion of the conductive composition into the substrate. For example, when polycarbonate is used as a three-dimensionally moldable circuit substrate, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate is preferred as the solvent from the viewpoint of the erosion of the circuit substrate.

The conductive composition of the present invention may contain other components as long as the effects of the present invention are not impaired. Examples include coupling agents, thermal polymerization inhibitors, plasticizers, flame retardants, antistatic agents, antiaging agents, antibacterial and antifungal agents, defoamers, leveling agents, thickeners, adhesion agents, thixotropy agents, curing accelerators, dispersants, wetting dispersants, dispersion aids, surface modifiers, stabilizers, and phosphors.

The conductive composition of the present invention can be produced, for example, by kneading a resin component, such as an epoxy resin or a thermoplastic resin, dissolved in a solvent with a conductive filler. Kneading methods include, for example, a method using a stirring and mixing device such as a roll mill. Depending on the type of resin component and the blending ratio of the solvent used, a liquid conductive composition or a paste-like (semi-solid) conductive composition can be produced.

The conductive composition of the present invention has no particular limit to its viscosity, but it is preferably 100 to 5000 dPa·s, and more preferably 200 to 1000 dPa·s. By keeping the viscosity within this range, a conductive composition with excellent printability and processability required for device manufacturing processes can be obtained.

[Cured product, electronic component, and method for producing same]
In the present invention, the conductive composition as described above can be applied in a pattern on a substrate and heat-treated to cure the resin component to form a cured product. Examples of the heat treatment include drying and heat-curing. When manufacturing a conductor circuit, the conductive composition is printed or applied on a substrate to form a desired conductor circuit pattern, the patterned coating is dried and solidified, and then heat-treated to cure the resin component of the coating to form a cured product, thereby forming a conductor circuit. A masking method or a method using a resist can be used to form the coating pattern.

Examples of the pattern formation process include printing and dispensing. Examples of printing methods include gravure printing, offset printing, and screen printing. When forming fine circuits, screen printing is preferred. Gravure printing and offset printing are suitable for large-area coating methods. The dispensing method is a method in which the amount of conductive composition applied is controlled to form an extrusion pattern from a needle, and is suitable for forming partial patterns such as earth wiring, and for forming patterns in uneven areas. There are no particular restrictions on the coating thickness, but it is generally selected appropriately in the range of 1 to 200 μm, preferably 10 to 150 μm, in terms of the thickness of the resin layer after drying.

The coating is dried at a temperature of 40 to 100°C for 1 to 30 minutes, depending on the solvent used. Heat treatment to harden the resin component of the coating is usually performed at a temperature of 60 to 180°C for 1 to 30 minutes, depending on the type of epoxy resin and hardener used. The coating of the conductive composition may be dried and the resin component may be hardened at the same time, for example by heat treatment at a temperature of 60 to 180°C for 5 to 60 minutes.

The substrate to which the conductive composition is applied can be any electrically insulating material without any particular limitations. Examples of such substrates include paper-phenolic resin, paper-epoxy resin, glass cloth-epoxy resin, glass-polyimide, glass cloth/nonwoven cloth-epoxy resin, glass cloth/paper-epoxy resin, synthetic fiber-epoxy resin, copper-clad laminates of all grades (such as FR-4) using composite materials such as fluororesin, polyethylene, polyphenylene ether, and polyphenylene oxide-cyanate ester, sheets or films made of plastics such as polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate, and polyethylene naphthalate, polyimide, polyphenylene sulfide, and polyamide, sheets or films made of crosslinked rubbers such as urethane, silicone rubber, acrylic rubber, and butadiene rubber, and sheets or films made of thermoplastic elastomers such as polyesters, polyurethanes, polyolefins, and styrene-based block copolymers.

It can be used not only for flat film-like substrates, but also for three-dimensional structures whose coated surfaces have a three-dimensional structure. Three-dimensional structures include polyhedrons and spheres. Examples of such substrates include flexible printed wiring boards and three-dimensional circuit boards, and it can be used particularly well for three-dimensional circuit boards. A three-dimensional circuit board is a plastic molded product in which electrical circuit wiring is formed three-dimensionally, having both mechanical and electrical functions, and an example of such a substrate is a three-dimensional circuit board in which a circuit is formed directly on a three-dimensional substrate. As a molding material for a three-dimensional substrate, a known material can be used, and an example of such a molding material can be a mixture of an organic material using resin and an inorganic material.

In the case of a three-dimensional circuit board, the three-dimensional board is preferably made of a resin molded product, and a circuit is preferably formed on the resin molded product. It is preferable to use a thermoplastic resin that is light in mass and easy to mold. In particular, since the electronic components are mounted on the three-dimensional circuit board by soldering, fluororesins, polycarbonate, polyacetal, polyamide, polyphenylene ether, amorphous polyarylate, polysulfone, polyethersulfone, polyphenylene sulfide, polyether ether ketone, polyimide, polyetherimide, and liquid crystal polymers, which are called engineering plastics and have excellent heat resistance, are suitable. Furthermore, when the solder resist composition of the present invention is applied to a three-dimensional circuit board, from the viewpoint of being able to withstand the heat when curing the epoxy resin (A), polyphenylene sulfide, polyether ether ketone, polycarbonate, polyamide, and polyacetal can be preferably used among the above.

As an embodiment of the method for manufacturing electronic components using the conductive composition according to the present invention, an example of a method for manufacturing a three-dimensional circuit board will be described. First, the conductive composition is applied to the surface of a film-like substrate to form a coating film of the desired pattern. Next, the coating film on the substrate surface is dried and the resin component is cured to form a conductor circuit. Next, the substrate provided with the conductor circuit of the desired pattern is molded into a predetermined three-dimensional shape. Examples of molding methods include vacuum molding, pressure molding, vacuum pressure molding, vacuum thermocompression molding, press molding, plug-assisted molding, and other heat molding methods.

In the molding process, the molding temperature is adjusted to a temperature at which the substrate can be deformed, but in the present invention, it is preferable to perform molding at a temperature within ±80°C of the glass transition temperature (Tg) of the cured product obtained by curing the conductive composition. A more preferable molding temperature is +50°C to +80°C of the Tg of the cured product. By setting the molding temperature within the above range, it is possible to further suppress the occurrence of microcracks in the conductor circuit, which is the cured product of the conductive composition. The glass transition temperature of the cured product is the peak top of tan δ obtained by cutting the cured product into a specified test piece and measuring it by thermomechanical analysis using a tensile load method using a dynamic viscoelasticity measuring device.

The conductive circuit is deformed, such as by stretching or bending, depending on the three-dimensional shape during molding, but according to the conductive composition of the present invention, as described above, the storage modulus of the cured product can be increased, and as a result, the occurrence of cracks when the conductive composition is cured to form a conductive layer (circuit) and then deformed by heating can be suppressed. Furthermore, according to the present invention, the occurrence of microcracks can be effectively suppressed, so that the presence or absence of cracks can be easily determined by visual inspection. The storage modulus of the cured product of the conductive composition at 160°C is preferably 1.0 x 10 ⁵ Pa or more, and more preferably 1.0 x 10 ⁶ Pa to 1.0 x 10 ⁹ Pa.

The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples. Note that in the following, "parts" and "%" are all by weight unless otherwise specified.

<Preparation of epoxy resin solution>
The following four types of epoxy resins were prepared and dissolved in carbitol acetate to prepare epoxy resin solutions having a solid content of 50 mass %.
Resin A: jER 828 (bisphenol A type epoxy resin, manufactured by Mitsubishi Chemical Corporation, epoxy equivalent: 184 to 194 g/eq)
Resin B: EPOX-MK R710 (bisphenol F type epoxy resin, manufactured by Printec Co., Ltd., epoxy equivalent 170 g/eq)
Resin C: jER 1004 (bisphenol A type epoxy resin, manufactured by Mitsubishi Chemical Corporation, epoxy equivalent: 875 to 975 g/eq)
Resin D: jER 1007 (bisphenol A type epoxy resin, manufactured by Mitsubishi Chemical Corporation, epoxy equivalent: 1750 to 2200 g/eq)

<Preparation of Thermoplastic Resin Solution>
The following four types of acrylic resins were prepared and dissolved in a solvent containing carbitol acetate or a 1:1 mixture of carbitol acetate and 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate to prepare acrylic resin solutions having a solid content of 35% by mass.
Resin E: Dianale MB-7948 (acrylic resin, manufactured by Mitsubishi Chemical Corporation, glass transition temperature 126°C)
Resin F: Elitel UE-9900 (polyester resin, manufactured by Unitika Ltd., glass transition temperature 101° C.)
Resin G: BR-115 (acrylic resin, manufactured by Mitsubishi Chemical Corporation, glass transition temperature 48°C)
Resin H: Clarity LA2250 (acrylic resin, manufactured by Kuraray Co., Ltd., glass transition temperature -25°C)

<Preparation of Conductive Composition>
The components shown in Table 1 below were blended in the ratios (parts by mass) shown in the table, premixed with a stirrer, and then dispersed with a three-roll mill to prepare the conductive compositions of Examples 1 to 11 and Comparative Examples 1 to 4. Note that the values shown in Table 1 refer to the solid content (parts by mass) for the epoxy resin and thermoplastic resin.

In addition, *1 to *9 in Table 1 represent the following components.
*1: Silver powder 1 (Silcoat AgC-G, manufactured by Fukuda Metal Foil Industry Co., Ltd., silver particle agglomerated powder, average particle diameter 4.2 μm)
*2: Silver powder 2 (K0082P, manufactured by METALOR, spherical silver powder, average particle diameter 1.68 μm)
*3: Silver powder 3 (Silcoat AgC-A, manufactured by Fukuda Metal Foil Industry Co., Ltd., silver flake powder, average particle size 3.5 μm)
*4: Curing agent 1 (Cureduct P-0505, manufactured by Shikoku Chemical Industry Co., Ltd.)
*5: Hardener 2 (2P4MZ, manufactured by Shikoku Chemical Industry Co., Ltd.)
*6: Boric acid ester compound (Cureduct L-07N, manufactured by Shikoku Chemical Industry Co., Ltd.)
* 7: Fine silica (Aerosil 200, manufactured by Nippon Aerosil Co., Ltd.)
*8: Carbitol acetate *9: 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate

<Storage modulus>
Each of the conductive compositions obtained as described above was applied to the release-treated surface of a 50 μm-thick polyethylene terephthalate film with a release treatment applied thereto using an applicator so that the film thickness after drying was about 20 μm, forming a coating film. The coating film was then heat-treated at 120° C. for 30 minutes using a hot air drying oven, and then allowed to cool to room temperature to dry and harden the coating film, forming a hardened coating film.
The cured coating was then peeled off from the polyethylene terephthalate film to prepare a rectangular test piece measuring 5 mm x 10 cm. The storage modulus of the test piece was measured at 30 to 200°C and a frequency of 1 Hz using a dynamic viscoelasticity measuring device (RSAIII (TA Instruments Japan, Inc.)). The storage modulus at 160°C was as shown in Table 1 below.

<Glass Transition Temperature of Cured Product>
The glass transition temperature (Tg) of test pieces of the cured coating prepared in the same manner as above was measured using a dynamic viscoelasticity measuring device (RSAIII (TA Instruments Japan, Inc.)). Tg was taken as the peak top temperature of tan δ obtained by thermomechanical analysis using the tensile load method (measurement conditions: load 0.1-0.5 N, heating rate 5°C/min). The measured Tg values were as shown in Table 1 below.

<Crack evaluation during molding>
Each of the conductive compositions obtained as described above was applied to the surface of a 0.15 mm thick polycarbonate film by screen printing to form a coating film in a 1 mm x 10 cm pattern, and a substrate having a cured coating (conductor circuit) was obtained in the same manner as described above.
Next, using a hemispherical mold in which the film had an elongation rate of 60%, vacuum molding was performed at a temperature of 140 to 170°C to produce a molded product. The conductor circuit on the surface of the obtained molded product was observed visually and with a magnifying glass (5x) to confirm the presence or absence of cracks. The evaluation criteria were as follows.
⊚: No cracks were visible to the naked eye or with a magnifying glass. ◯: Cracks larger than 0.5 mm were visible to the naked eye. △: Small cracks of about 40 μm, the limit of what can be seen with the naked eye, were present. ×: Small cracks less than 40 μm that could only be seen with a magnifying glass were present. The evaluation results are shown in Table 1 below.

<Conductivity evaluation>
Each conductive composition obtained as described above was screen printed on the surface of a 1 mm thick glass substrate to form a coating film in a pattern of 1 mm x 40 cm, and a substrate with a cured coating (conductor circuit) was obtained in the same manner as described above. The coating film was then heated at 120°C for 30 minutes using a hot air drying oven, and the coating film was dried and cured by cooling to room temperature to form a cured coating. The thickness of the cured coating was 5 μm.
The resistance of each of the cured films was then measured by a four-terminal method, and the line width, line length and thickness were also measured to determine the specific resistance (volume resistivity). The measurement results are shown in Table 1 below.

As is clear from the evaluation results in Table 1, the conductive compositions (Examples 1 to 11) containing an epoxy resin and a thermoplastic resin having a glass transition temperature of 80°C or higher can suppress the microcracks that occur when a substrate having a conductor circuit formed thereon is three-dimensionally molded using the conductive composition, and it can also be seen that the presence or absence of cracks can be easily determined by visual inspection.
In contrast, it is seen that the conductive composition containing a thermoplastic resin having a glass transition temperature of 80° C. or higher but not an epoxy resin (Comparative Example 1) tends to develop microcracks that are difficult to confirm with the naked eye. Similarly, it is seen that the conductive compositions containing a thermoplastic resin but having a glass transition temperature of less than 80° C. (Comparative Examples 2 and 3) also develop microcracks that are difficult to confirm with the naked eye.

Claims (9)

A conductive composition comprising at least an epoxy resin, a thermoplastic resin, and a conductive filler,
The conductive composition, wherein the thermoplastic resin has a glass transition temperature of 80° C. or higher. The conductive composition according to claim 1, wherein the epoxy resin is contained in an amount of 5 to 100 parts by mass, calculated as solid content, per 100 parts by mass of the thermoplastic resin. The conductive composition according to claim 1, wherein the epoxy resin includes an epoxy resin having an epoxy equivalent of 500 g/eq or more. The conductive composition according to claim 1, wherein the epoxy resin includes two types of epoxy resin: an epoxy resin having an epoxy equivalent of 500 g/eq or more, and an epoxy resin having an epoxy equivalent of less than 500 g/eq. The conductive composition according to claim 1, wherein the conductive filler comprises one or more conductive agglomerated powders selected from the group consisting of silver powder, copper powder, silver-coated copper powder, copper alloy powder, conductive oxide powder, and carbon particles. A cured product of the conductive composition according to any one of claims 1 to 5. The cured product according to claim 6, which has a storage modulus at 160°C of 1.0 x ¹⁰⁵ Pa or more. An electronic component having a circuit formed on a surface of a three-dimensional substrate,
An electronic component, wherein the circuit comprises the cured product according to claim 6. A method for producing an electronic component using the conductive composition according to any one of claims 1 to 5,
The conductive composition is applied onto a substrate to form a coating film having a desired pattern;
The coating film is dried and cured to form a conductor circuit on the substrate;
The substrate on which the conductor circuit is formed is molded into a three-dimensional shape to produce a three-dimensional circuit substrate.
Including,
A method for producing an electronic component, characterized in that the molding is carried out within a temperature range of ±80° C. of the glass transition temperature of the cured product of the conductive composition.