Conductive resin composition

Abstract

To provide a conductive resin composition from which an electronic element mounting substrate that facilitates repair work and has high connection reliability after repair work can be obtained.SOLUTION: A conductive resin composition contains at least (A) a thermosetting resin, (B) a curing agent for curing the thermosetting resin, (C) solder particles, and (D) a flux, wherein when the conductive resin composition is cured and converted into a cured film having thickness of 30 μm, reflectances of light at a wavelength of 1,064 nm or a wavelength of 532 nm in the cured film are 20% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a conductive resin composition, and more particularly to a conductive resin composition used when mounting electronic elements on a wiring board. [Background technology]

[0002] Electro-optical devices such as liquid crystal display devices are used as display units for computers, mobile phones, and various other electronic devices, and liquid crystal display devices in particular are widely used as display units for various electronic devices because they are lightweight, thin, and consume little power. Many of these liquid crystal display devices are equipped with a so-called backlight on the back side of the electro-optical component such as a liquid crystal panel.

[0003] In recent years, LED array substrates have come to be used as backlights for electro-optical devices and the like. An LED array substrate has multiple LED chips mounted in a matrix on a wiring board, with each LED chip electrically connected to the wiring board via solder or other means. Recently, to reduce the size and improve the efficiency of backlights, LED array substrates have begun to use smaller LED chips, which are integrated and mounted on the wiring board. Accordingly, in mounting LED chips, conductive pastes and films known as anisotropic conductive materials have begun to be used instead of the traditional solder-based electrical connection. Anisotropic conductive materials are insulating curable resin binders with conductive particles dispersed therein. By thermocompressing the electrodes of electronic components (here, the wiring board and the LED chips) together, the electronic components are electrically connected via the conductive particles only in the direction of pressure. The electronic components can be fixed by hardening the curable resin binder while maintaining insulation between adjacent electrodes (see, for example, Patent Document 1).

[0004] The advantage of using anisotropic conductive materials instead of solder is that it allows multiple LED chips to be mounted simultaneously and quickly on a wiring board. However, anisotropic conductive materials have the drawback of being less reworkable than solder connections. While solder connections allow components to be easily removed from the wiring board and remounted by heating them, connections using anisotropic conductive materials, such as those mentioned above, do not allow for easy removal because the electronic components are firmly bonded together by a resin binder. Even if the electronic components can be removed, the hardened resin binder remains on the wiring board, requiring removal using a special solvent or other method.

[0005] To address these issues, Patent Document 2 describes a technology that allows electronic components to be re-pressurized without using a repair agent by attaching a new anisotropic conductive film while leaving the cured anisotropic conductive material on the wiring board. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 8-003529 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-272545 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the method proposed in Patent Document 2 requires a design in which the modulus of elasticity of the cured anisotropic conductive film at 150°C is 10 MPa or less, making it difficult to obtain connection reliability (heat resistance) between electronic components. In addition, pressure is required when remounting electronic components, so if an FPC (flexible printed circuit) or the like is used as the wiring board, damage to the wiring board is unavoidable.

[0008] Furthermore, LED chips have become increasingly miniaturized in recent years. For example, LED array substrates have been commercialized in which LED chips with external dimensions of only a few tens of microns are mounted on a wiring board with adjacent chips spaced less than 1 mm apart. This makes it increasingly difficult to remove LED chips from the wiring board for repair. Furthermore, the area where a defective LED chip is removed is narrow, making it extremely difficult to remove the hardened resin binder remaining on the wiring board. While the repair area can be heated to melt the resin binder and solder and remove the LED chip, this can affect surrounding LED chips and other mounted components that do not require repair. While lasers and other methods capable of localized heating are also considered, even in this case, the insulating film and electrodes on the surface of the wiring board on which the LED chip is mounted will inevitably be heated.

[0009] The present invention has been made in light of the above-mentioned problems, and an object of the present invention is to provide a conductive resin composition that allows for easy repair work and that provides an electronic element mounting board with high connection reliability after the repair work. [Means for solving the problem]

[0010] In response to the above-mentioned problems, the present inventors have discovered that, when removing an electronic element from an electronic element mounting substrate in which an electrode of a wiring board and an electronic element are connected by a conductive resin composition, if a cured product of the conductive resin composition has specific optical properties, the electronic element can be easily removed by irradiation with a laser or the like, the impact on the surrounding area of ​​the electronic element to be removed can be reduced, and the connection reliability of the electronic element mounting substrate after repair work can be improved. The present invention has been completed based on this discovery. Specifically, the gist of the present invention is as follows.

[0011] [1] A conductive resin composition comprising at least (A) a thermosetting resin, (B) a curing agent for curing the thermosetting resin, (C) solder particles, and (D) a flux, The conductive resin composition, when cured to form a cured film having a thickness of 30 μm, has a reflectance of 20% or less at a wavelength of 1064 nm for light. [2] The conductive resin composition according to [1], wherein when the conductive resin composition is cured to form a cured film having a thickness of 30 μm, the cured film has a transmittance of 55% or less at a wavelength of 1064 nm. [3] A conductive resin composition comprising at least (A) a thermosetting resin, (B) a curing agent for curing the thermosetting resin, (C) solder particles, and (D) a flux, The conductive resin composition, when cured to form a cured film having a thickness of 30 μm, has a reflectance of 20% or less at a wavelength of 532 nm. [4] The conductive resin composition according to [3], wherein when the conductive resin composition is cured to form a cured film having a thickness of 30 μm, the cured film has a transmittance of 55% or less at a wavelength of 532 nm. [5] The conductive resin composition according to any one of [1] to [4], further comprising (E) a light absorber capable of absorbing light energy and converting a part or all of the absorbed light energy into heat energy. [6] The conductive resin composition according to [5], wherein the (E) light absorber capable of absorbing light energy and converting part or all of it into thermal energy does not denature or thermally decompose at a temperature 100°C higher than the melting point of the (C) solder particles. [7] The conductive resin composition according to [5] or [6], wherein the (E) light absorber capable of absorbing light energy and converting a part or all of it into heat energy is contained in an amount of 0.5 to 8 mass % relative to the solid content of the conductive resin composition. [8] The conductive resin composition according to any one of [1] to [7], wherein the (C) solder particles are contained in an amount of 20 to 70 mass % relative to the solid content of the conductive resin composition. [9] The conductive resin composition according to any one of [5] to [8], wherein the (E) light absorber capable of absorbing light energy and converting a part or all of it into heat energy is at least one selected from the group consisting of carbon black, titanium black, and near-infrared absorbers. [Effects of the Invention]

[0012] According to the present invention, when removing an electronic element from an electronic element mounting substrate, the electronic element can be easily removed by irradiating it with a laser or the like, and the impact on the surrounding area of ​​the electronic element to be removed can be reduced, and the connection reliability of the electronic element mounting substrate can be improved after repair work. The present invention is particularly effective when repairing miniaturized LED chips.

[0013] The conductive resin composition of the present invention contains as essential components (A) a thermosetting resin, (B) a curing agent for curing the thermosetting resin, (C) solder particles, and (D) a flux. When the conductive resin composition is applied between opposing electrodes, such as when mounting electronic devices on a wiring board, the opposing electrodes are electrically connected while maintaining insulation between adjacent electrodes. When the conductive resin composition of the present invention is cured to form a 30 μm-thick cured film, the cured film has a reflectance of 20% or less at light with a wavelength of 1064 nm or 532 nm. By using a conductive resin composition with these properties, when a cured product of the conductive resin composition (e.g., a cured film) is irradiated with a laser or the like and heated, the laser-irradiated area can be efficiently heated, thereby facilitating the removal of electronic devices from electronic device-mounted substrates during repair work. Furthermore, even when localized heating is achieved by laser irradiation, the diffusion of heat to non-irradiated areas can be suppressed, thereby reducing the impact on the surrounding area of ​​the electronic device to be removed and improving the connection reliability of the electronic device-mounted substrate after repair work. The reflectance of the cured coating at 1064 nm or 532 nm wavelength is preferably 15% or less, more preferably 10% or less, and particularly preferably 5% or less. From the viewpoint of further exerting the effects of the present invention, it is more preferable that the reflectance at both 1064 nm and 532 nm wavelengths is 20% or less.

[0014] The conductive resin composition of the present invention has the property that, when cured to form a 30 μm-thick cured film, the cured film has a reflectance of 20% or less at 1064 nm or 532 nm, preferably a transmittance of 55% or less at 1064 nm or 532 nm. When the conductive resin composition produces a cured film with the above optical properties, the resin components and solder particles constituting the conductive resin composition absorb light energy and convert some or all of it into thermal energy, thereby further improving the removability of the resin components in the cured product during repair work. The conductive resin composition does not necessarily require the use of (E) a light absorber capable of absorbing light energy and converting some or all of it into thermal energy (hereinafter also referred to as (E) light absorber) to achieve these properties. The selection of the (A) thermosetting resin, (B) curing agent, and other optional components is not particularly limited as long as they impart optical properties. In addition to containing the (E) light absorber, the above characteristics may be satisfied by, for example, combining the components so that the cured resin is colored. Furthermore, the (C) solder particles may have the function of absorbing light energy and converting some or all of it into thermal energy, or the cured resin itself may absorb light energy and convert some or all of it into thermal energy. In either case, a conductive resin composition that, when formed into a cured film, has a reflectance of 20% or less, and preferably a transmittance of 55% or less, for light with a wavelength of 1064 nm or 532 nm, improves the removability of resin components in the cured product during repair work. The transmittance of the cured film is preferably 30% or less, more preferably 20% or less, and particularly preferably 10% or less.

[0015] The reflectance and transmittance defined in the present invention can be specifically measured as follows. First, a conductive resin composition is applied to one side of a glass substrate (product name S1112, manufactured by Matsunami Glass Industrial Co., Ltd.), and the conductive resin composition is cured to form a cured coating having a thickness of 30 μm. The conductive resin composition is cured (the cured coating is formed) using a hot plate at 180°C for 30 minutes. Next, the reflectance and transmittance of the substrate on which the resulting cured coating is formed are measured for light having a wavelength of 1064 nm or 532 nm using, for example, a V-570 UV-Visible-Infrared Spectrophotometer (manufactured by JASCO Corporation) equipped with an ISN-470 integrating sphere unit.

[0016] The conductive resin composition of the present invention provides a cured coating film having the above-mentioned optical properties. Each component constituting the conductive resin composition will now be described in detail.

[0017] <(A) Thermosetting resin> The thermosetting resin (A) functions as a binder for the solder particles (C) described below, and also hardens to bond the wiring board and the electronic element. Examples of the thermosetting resin include epoxy resin, phenol resin, melamine resin, unsaturated polyester resin, maleimide resin, polyurethane resin, silicone resin, cyanate resin, and acrylic resin. Of these, epoxy resin and acrylic resin are preferred, with epoxy resin being particularly preferred.

[0018] Any epoxy resin having two or more epoxy groups per molecule can be used without limitation. Examples include epoxy resins having a bisphenol skeleton, such as bisphenol A epoxy resin, bisphenol F epoxy resin, bisphenol E epoxy resin, hydrogenated bisphenol A epoxy resin, brominated bisphenol A epoxy resin, and bisphenol S epoxy resin; the phenol novolac epoxy resin, cresol novolac epoxy resin, bisphenol A novolac epoxy resin, biphenyl epoxy resin, naphthol epoxy resin, naphthalene epoxy resin, dicyclopentadiene epoxy resin, triphenylmethane epoxy resin, alicyclic epoxy resin, aliphatic linear epoxy resin, phosphorus-containing epoxy resin, anthracene epoxy resin, norbornene epoxy resin, adamantane epoxy resin, fluorene epoxy resin, and the aminophenol epoxy resin, aminocresol epoxy resin, and alkylphenol epoxy resin, which will be described later. The above epoxy resins can be used alone or in combination of two or more.

[0019] Examples of polyfunctional epoxy resins include hydroxybenzophenone-type liquid epoxy resins such as EP-3300E manufactured by ADEKA Corporation, aminophenol-type liquid epoxy resins (paraaminophenol-type liquid epoxy resins) such as jER 630 manufactured by Mitsubishi Chemical Corporation and ELM-100 manufactured by Sumitomo Chemical Co., Ltd., glycidylamine-type epoxy resins such as jER 604 manufactured by Mitsubishi Chemical Corporation, YH-434 manufactured by Nippon Steel Chemical & Material Co., Ltd., and Sumiepoxy ELM-120 manufactured by Sumitomo Chemical Co., Ltd., and phenol novolac-type epoxy resins such as DEN431 manufactured by Dow Chemical Co. These polyfunctional epoxy resins can be used alone or in combination of two or more.

[0020] Among the epoxy resins mentioned above, liquid is preferable to solid in terms of forming the conductive resin composition into a paste form. Specifically, epoxy resins having a bisphenol skeleton are preferred, with bisphenol A epoxy resin, bisphenol F epoxy resin, and bisphenol E epoxy resin being more preferred. Commercially available products include ZX-1059 (a mixture of bisphenol A and bisphenol F epoxy resins) manufactured by Nippon Steel Chemical & Material Co., Ltd., jER 828, jER 834, jER 1001 (bisphenol A epoxy resins), jER 807, and jER 4004P (bisphenol F epoxy resins) manufactured by Mitsubishi Chemical Corporation, and R710 (bisphenol E epoxy resin) manufactured by Air Water Inc.

[0021] The acrylic resin is not particularly limited as long as it is a resin having a (meth)acrylic group, and examples thereof include trifunctional methacrylate monomers such as trimethylolpropane trimethacrylate and epoxy acrylate having a trimethylpropane skeleton. Among these, monofunctional (meth)acrylates, bifunctional (meth)acrylates, trifunctional or higher polyfunctional (meth)acrylates, epoxy (meth)acrylates, urethane (meth)acrylates, and bifunctional or higher polyester (meth)acrylates can be preferably used.

[0022] Examples of monofunctional (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, butoxyethyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, heptyl (meth)acrylate, and octylheptyl (meth)acrylate. Nonyl (meth)acrylate, decyl (meth)acrylate, undecyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, stearyl (meth)acrylate, behenyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-chloro-2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate aliphatic (meth)acrylates such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cyclopentyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, isobornyl (meth)acrylate, 3-methyl-3-oxetanylmethyl (meth)acrylate, alicyclic (meth)acrylates such as 1-adamantyl (meth)acrylate, phenyl (meth)acrylate, nonylphenyl (meth)acrylate, p-cumylphenyl (meth)acrylate aromatic (meth)acrylates such as o-biphenyl (meth)acrylate, 1-naphthyl (meth)acrylate, 2-naphthyl (meth)acrylate, benzyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 2-hydroxy-3-(o-phenylphenoxy)propyl (meth)acrylate, 2-hydroxy-3-(1-naphthoxy)propyl (meth)acrylate, and 2-hydroxy-3-(2-naphthoxy)propyl (meth)acrylate, 2-tetrahydrofurfuryl (meth)acrylate,Examples of heterocyclic (meth)acrylates include N-(meth)acryloyloxyethyl hexahydrophthalimide and 2-(meth)acryloyloxyethyl-N-carbazole.

[0023] Examples of bifunctional (meth)acrylates include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, tetrapropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, 1,3-butanediol di(meth)acrylate, 2-methyl-1,3-propanediol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 3-methyl-1,5-pentanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 2-butyl cycloaliphatic (meth)acrylates such as 2-ethyl-1,3-propanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, glycerin di(meth)acrylate, and tricyclodecane dimethanol (meth)acrylate; cyclohexanedimethanol (meth)acrylate, tricyclodecane dimethanol (meth)acrylate, hydrogenated bisphenol A di(meth)acrylate, and hydrogenated bisphenol F di(meth)acrylate; aromatic (meth)acrylates such as bisphenol A di(meth)acrylate, bisphenol F di(meth)acrylate, bisphenol AF di(meth)acrylate, ethoxylated bisphenol A di(meth)acrylate, and fluorene di(meth)acrylate; and heterocyclic (meth)acrylates such as isocyanuric acid di(meth)acrylate.

[0024] Examples of the tri- or higher functional (meth)acrylate include aliphatic (meth)acrylates such as trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and ethoxylated glycerin tri(meth)acrylate, and heterocyclic (meth)acrylates such as isocyanuric acid tri(meth)acrylate.

[0025] <(B) Hardener> The conductive resin composition includes a (B) curing agent for curing the (A) curable resin. The (B) curing agent can be any known curing agent commonly used to cure the (A) thermosetting resin. Examples of the (B) curing agent include amines, imidazoles, polyfunctional phenols, acid anhydrides, isocyanates, and polymers containing these functional groups. Multiple curing agents may be used as needed. Examples of amines include dicyandiamide and diaminodiphenylmethane. Examples of imidazoles include alkyl-substituted imidazoles and benzimidazoles. The imidazole compound may also be an imidazole latent curing agent, such as an imidazole adduct. Examples of polyfunctional phenols include hydroquinone, resorcinol, bisphenol A and its halogen compounds, as well as condensates of these with aldehydes, such as novolaks and resol resins. Examples of acid anhydrides include phthalic anhydride, hexahydrophthalic anhydride, methylnadic anhydride, and benzophenonetetracarboxylic acid. Examples of isocyanates include tolylene diisocyanate and isophorone diisocyanate, and these isocyanates may be masked with phenols, etc. These curing agents may be used alone or in combination of two or more.

[0026] From the viewpoints of the curing speed of the conductive resin composition and the strength of the cured product after curing, the blending amount of the (B) curing agent is preferably 3 to 15 parts by mass, more preferably 4 to 10 parts by mass, and particularly preferably 5 to 8 parts by mass, per 100 parts by mass of the (A) thermosetting resin, calculated as solid content.

[0027] The curing rate of the conductive resin composition can be controlled by adjusting the type and amount of the (B) curing agent and optional curing accelerator. However, to impart anisotropy to the conductive resin composition, the reaction temperature (curing temperature) of the resin is preferably higher than the melting point of the (C) solder particles (described below), more preferably by 5°C or more. An "anisotropic" conductive resin composition refers to a composition in which solder particles dispersed in a fluid curable resin melt and self-assemble on the electrodes, utilizing the solder particles' tendency to gather on electrodes when melted. This allows solder to be placed only between the electrodes to be connected, while maintaining insulation between adjacent electrodes. As mentioned above, by having the reaction temperature (curing temperature) of the (A) thermosetting resin higher than the melting point of the (C) solder, the (C) solder particles dispersed in the composition can self-aggregate before the thermosetting resin cures.

[0028] <(C) Solder particles> The (C) solder particles can be any conventionally known material without particular limitations, including gold, silver, nickel, copper, lead, and the low-melting-point solder particles described below. The (C) solder particles may be composite particles in which non-conductive particles such as glass, ceramic, or plastic are coated with solder as core particles, or composite particles containing the non-conductive particles and solder particles. When the (C) solder particles are the composite particles or heat-fusible metal particles, the (C) solder particles melt and deform when heated, increasing the contact area with the electrode during connection and achieving particularly high reliability.

[0029] The (C) solder particles are preferably solder particles that melt when heated at 170°C or less, and low-melting-point solder particles are more preferred, with Sn-Pb and Sn-Bi low-melting-point solder particles being more preferred. Low-melting-point solder particles refer to solder particles with a melting point of 200°C or less, preferably 170°C or less, and more preferably 150°C or less. In particular, from the viewpoint of facilitating removal of the defective electronic elements in the aforementioned step of removing the electronic elements, the melting point of the (C) solder particles may be higher or lower than the glass transition temperature of the cured product of the aforementioned curable resin.

[0030] Furthermore, lead-free solder particles are preferred as low-melting point solder particles, and lead-free solder particles refer to solder particles with a lead content of 0.10 mass% or less as specified in JIS Z 3282:2017 (Solder - Chemical composition and shape).

[0031] As the lead-free solder particles, low-melting-point solder particles composed of one or more metals selected from tin, bismuth, indium, copper, silver, and antimony are preferably used. In particular, an alloy of tin (Sn) and bismuth (Bi) is preferably used from the viewpoint of the balance between cost, ease of handling, and bonding strength.

[0032] The content of Bi in such low melting point solder particles is appropriately selected within the range of 15 to 65 mass %, preferably 35 to 65 mass %, and more preferably 55 to 60 mass %.

[0033] By setting the Bi content to 15% by mass or more, the alloy begins to melt at approximately 160°C. As the Bi content increases further, the melting initiation temperature decreases, reaching 139°C at 20% by mass or more and forming a eutectic composition at 58% by mass. Therefore, by setting the Bi content in the range of 15 to 65% by mass, the effect of lowering the melting point is sufficiently achieved, resulting in sufficient electrical connection even at low temperatures.

[0034] The (C) solder particles are preferably spherical. Here, "spherical" means that at a magnification at which the shape of the (C) solder can be confirmed, 90% or more of the spherical powder has a ratio of major axis to minor axis of 1 to 1.5. The (C) solder particles also preferably have an average particle diameter of 1 to 100 μm, more preferably 3 to 80 μm, and even more preferably 5 to 60 μm. In this specification, the average particle diameter refers to the median diameter (D50) measured using a laser diffraction particle size distribution analyzer.

[0035] In addition, (C) solder particles have a specific surface area of ​​300 cm 2 / g~2000cm 2 / g, and 500 cm 2 / g~1500cm 2 / g is more preferable. By using solder particles having a specific surface area within the above range, the stability of the conductive connection between the electrodes of the wiring board and the electronic element is improved. The specific surface area of ​​the solder particles means a value measured by the BET method. Specifically, an inert gas (e.g., nitrogen gas) with a known molecular size is adsorbed onto the surface of a measurement sample, and the specific surface area can be calculated from the amount of adsorption and the area occupied by the inert gas.

[0036] The amount of (C) solder particles is preferably 20 to 70 mass % of the solid content in the conductive resin composition, more preferably 30 to 60 mass %, and particularly preferably 35 to 55 mass %. By setting the amount of (C) solder particles to 20 mass % or more, it is possible to ensure sufficient electrical connection while ensuring adhesion between the wiring board and electronic elements. Furthermore, by setting the amount of (C) solder particles to 70 mass % or less, it is possible to ensure sufficient adhesion while ensuring electrical connection.

[0037] <(D) Flux> The conductive resin composition of the present invention contains (D) a flux in addition to (A) a thermosetting resin, (B) a curing agent, and (C) solder particles in order to enhance the stability of conductive connection. (D) The flux may be any known flux used in conductive resin compositions, such as zinc chloride, a mixture of zinc chloride and an inorganic halide, a mixture of zinc chloride and an inorganic acid, a molten salt, phosphoric acid, a phosphoric acid derivative, an organic halide, hydrazine, an organic acid, or rosin. These fluxes may be used alone or in combination of two or more.

[0038] Among the fluxes described above, organic acids are suitable for use. Preferred organic acids include monocarboxylic acids as well as polycarboxylic acids such as dicarboxylic acids, tricarboxylic acids, and tetracarboxylic acids. Examples of monocarboxylic acids include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, capric acid, lauric acid, myristic acid, pentadecylic acid, palmitic acid, margaric acid, stearic acid, tuberculostearic acid, arachidic acid, behenic acid, lignoceric acid, and glycolic acid. Examples of dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, fumaric acid, maleic acid, tartaric acid, and diglycolic acid. Examples of tricarboxylic acids include benzene-1,2,5-tricarboxylic acid, 1,2,4-benzenetricarboxylic acid, and 1,2,3-propanetricarboxylic acid. Further, examples of the tetracarboxylic acid include benzophenonetetracarboxylic acid, 1,2,3,4-butanetetracarboxylic acid, etc. Among these carboxylic acids, dicarboxylic acids are preferred, glutaric acid and adipic acid are more preferred, and adipic acid is particularly preferred.

[0039] The content of the (D) flux in the conductive resin composition is preferably 1 to 15 mass % and more preferably 3 to 10 mass % based on the solid content of the composition. By making the conductive resin composition have a flux content within the above range, the conductive connectability can be further improved.

[0040] In order to adjust the activity of the flux (D), a basic organic compound may be contained, such as aniline hydrochloride and hydrazine hydrochloride.

[0041] <(E) Light absorber capable of absorbing light energy and converting a part or all of it into heat energy> The conductive resin composition of the present invention preferably contains a light absorber capable of absorbing light energy and converting a portion or all of it into heat energy, so that the reflectance and transmittance of the cured coating having a thickness of 30 μm can be easily adjusted within the above-mentioned ranges when the cured coating is formed. The inclusion of (E) a light absorber in the conductive resin composition further improves connection reliability after repair work. Note that the light referred to here is not limited to electromagnetic waves in the heat ray band but also includes various wavelengths, for example, from 300 nm to 10.6 μm. However, a light absorber capable of absorbing electromagnetic waves in the visible light band to the near-infrared band and converting a portion or all of it into heat energy is particularly preferred.

[0042] Examples of the (E) light absorber that can be used in the present invention include various colorants, carbon black, titanium black, near-infrared absorbers, and the like. Known colorants, such as red, blue, green, and yellow, can be used as colorants, and they may be any of pigments, dyes, and coloring matter. The near-infrared absorber is not particularly limited as long as it has absorption in the near-infrared band (700 to 1800 nm). Examples include metal complex compounds such as nickel dithiolene complexes with a planar tetracoordinate structure, cyanine dyes with an extended polymethine skeleton, phthalocyanine dyes with aluminum or zinc at the center, anthraquinones, naphthoquinones, squarium dyes, quinone compounds, diimmonium compounds, and azo compounds. Among these, those that do not denature or thermally decompose at temperatures 100°C higher than the melting point of the (C) solder particles are preferred. Carbon black, titanium black, and phthalocyanines are preferred as (E) light absorbers with these properties. Specifically, Mitsubishi Chemical Corporation's MA11, MA100, MA600, #900, MA7, MA77, MA14, and MA8 (all carbon blacks), Resino Color Industries Co., Ltd.'s Black SD-TT2259 (carbon black), Mitsubishi Materials Electronic Chemicals Co., Ltd.'s 12S, 13M, 13M-C, 13M-T, UF-8, and FB15M (all titanium blacks), and Ako Kasei Co., Ltd.'s TilackD. Examples of such near-infrared absorbers include TM-F (titanium black), FDN-010, FDN-007, and FDN-008 (phthalocyanine-based near-infrared absorbers) manufactured by Yamada Chemical Co., Ltd., OPTLION (registered trademark) (near-infrared absorber) manufactured by Toyo Visual Solutions Co., Ltd., LaB6 (lanthanum hexaboride) and CWO (registered trademark (cesium-doped tungsten oxide)) manufactured by Sumitomo Metal Mining Co., Ltd., IR-915, IR-924, and HA-1 (all near-infrared absorbers) manufactured by Nippon Shokubai Co., Ltd., IR-001 (near-infrared absorber) manufactured by Fujifilm Corporation, IR-813 (p-toluenesulfonate), indocyanine green, and Copper(II) 5,9,14,18,23,27,32,36-octabutoxy-2,3-naphthalocyanine manufactured by Tokyo Chemical Industry Co., Ltd., and OIL Blue 613 manufactured by Orient Chemical Industry Co., Ltd.

[0043] The size and shape of the (E) light absorber are not limited as long as they do not inhibit the dispersibility of the (C) solder particles or their self-aggregation during heating. However, if the (E) light absorber is a material that does not dissolve in the conductive resin composition, the average particle size is preferably 1 μm or less from the viewpoint of further reducing the reflectance of the cured coating of the conductive resin composition. The average particle size refers to the median diameter (D50) measured using a laser diffraction particle size analyzer. Alternatively, the (E) light absorber may be one that dissolves when blended into the conductive resin composition.

[0044] The content of the (E) light absorber in the conductive resin composition can be adjusted as appropriate depending on the type of (A) thermosetting resin used and the amount of (C) solder particles blended, but from the viewpoint of the effects of the present invention, it is preferably 0.5 to 8 mass % relative to the solid content in the composition, and more preferably 0.6 to 6 mass %.

[0045] Furthermore, a filler can be blended into the conductive resin composition as needed to increase the physical strength of the cured product. Known inorganic or organic fillers can be used as the filler, with barium sulfate, spherical silica, hydrotalcite, and talc being particularly preferred. Furthermore, to achieve flame retardancy, metal oxides and metal hydroxides such as aluminum hydroxide can be used as extender pigment fillers. Among these fillers, those having a wavelength band capable of absorbing at least a portion of the wavelength band of laser light are preferably used.

[0046] Furthermore, when a filler is blended, the filler may be surface-treated to enhance dispersibility in the conductive resin composition. By using a surface-treated filler, aggregation can be suppressed. The surface treatment method is not particularly limited, and any known or commonly used method may be used. However, it is preferable to treat the surface of the inorganic filler with a surface treatment agent having a curable reactive group, for example, a coupling agent having a curable reactive group as an organic group.

[0047] Examples of the coupling agent include silane-based, titanate-based, aluminate-based, and zircoaluminate-based coupling agents. Among these, silane-based coupling agents are preferred. Examples of such silane-based coupling agents include vinyltrimethoxysilane, vinyltriethoxysilane, N-(2-aminomethyl)-3-aminopropylmethyldimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-anilinopropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, and 3-mercaptopropyltrimethoxysilane. These can be used alone or in combination of two or more.

[0048] The conductive resin composition may contain an organic solvent from the viewpoint of ease of preparation and coating properties. Examples of the organic solvent include 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, diethylene glycol monomethyl ether acetate, and tripropylene glycol monomethyl ether; esters such as ethyl acetate, butyl acetate, butyl lactate, cellosolve acetate, butyl cellosolve acetate, carbitol acetate, butyl carbitol acetate, propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl ether acetate, and propylene carbonate; aliphatic hydrocarbons such as octane and decane; and petroleum-based solvents such as petroleum ether, petroleum naphtha, and solvent naphtha. These organic solvents can be used alone or in combination of two or more.

[0049] The conductive resin composition of the present invention can be produced by mixing and stirring the above-mentioned components in a predetermined mixing ratio using a known, commonly used method.

[0050] The conductive resin composition of the present invention can be used for electrical connection between components in electronic components. For example, it can be used for electrical connection between a printed wiring board and an electronic element, or for electrical connection between printed wiring boards. In particular, it can be suitably used for electronic element mounting substrates such as chip-on-board (COB) in which electronic elements such as bare chips and LED chips are directly mounted and connected on a substrate. In particular, it can be suitably used for applications in which multiple elements are mounted on a wiring board with a fine-pitch spacing between adjacent electrodes and electrically connected together.

[0051] <Repair work> The identified defective portion in the electronic element mounting substrate is heated to remove the identified electronic element from the wiring substrate. The area to be heated need only include the identified defective portion, and if there is only one defective portion, only that defective portion can be heated to remove the identified electronic element. If there are multiple defective portions in the electronic element mounting substrate, each defective portion can be heated, or the entire wiring substrate can be heated to remove the identified electronic element.

[0052] The heating temperature is not particularly limited as long as it allows removal of electronic elements mounted on the wiring board, but is preferably higher than the glass transition point of the cured product of the conductive resin composition and higher than the melting point of the molten and solidified product of the solder particles (i.e., the (C) solder particles contained in the conductive resin composition). Depending on the (A) thermosetting resin and (C) solder particles contained in the conductive resin composition used, heating is preferably carried out at 100 to 240°C, more preferably 120 to 200°C, and even more preferably 140 to 170°C. The heating time is preferably 1 to 60 seconds, more preferably 1 to 30 seconds, and even more preferably 1 to 15 seconds.

[0053] Heating may be performed from the side of the wiring board on which the electronic elements are mounted, or from the opposite side, but from the viewpoint of minimizing thermal damage to the electronic elements, it is preferable to heat from the side of the wiring board opposite to the side on which the electronic elements are mounted. Furthermore, the heating means is not particularly limited, and various methods can be used. For example, when only the defective portion is to be heated locally, heating means such as a spot heater or a heat dryer can be applied, and when the entire wiring board is to be heated, planar heating means such as a hot plate can be applied.

[0054] By heating, the cured product of the conductive resin composition that fixes (adheres) the wiring board and the electronic element is softened, and the molten and solidified solder particles in the cured product are remelted, allowing the electronic element to be removed from the electronic element mounting board without applying unnecessary stress. The electronic element may be removed manually using tweezers or the like, or a removal device equipped with a dedicated gripping tool may be used.

[0055] Next, after removing the specific electronic elements as described above, the cured conductive resin composition remaining on the surface of the electronic element mounting substrate is removed. Such residues may cause poor connection or misalignment of the electronic elements when a new electronic element is remounted. The conductive resin composition of the present invention allows for easy localized removal of the remaining cured material by laser light irradiation or other methods, while also reducing the thermal impact on the surrounding area. The laser light to be irradiated can be of any wavelength or type, and may be a continuous wave laser or a pulsed wave laser. Examples of continuous wave lasers that can be used include YVO4 lasers, fiber lasers, excimer lasers, green lasers, carbon dioxide lasers, ultraviolet lasers, YAG lasers, semiconductor lasers, glass lasers, ruby ​​lasers, He-Ne lasers, nitrogen lasers, chelate lasers, and dye lasers. Examples of pulsed wave lasers that can be used include nanosecond pulsed lasers and millisecond pulsed lasers. Among these, from the viewpoint of removability and handling of the cured product, it is preferable to use a fiber laser (wavelength 1064 nm), a carbon dioxide laser (wavelength 10.6 μm), a YAG laser (wavelength 1064 nm), or a green laser (wavelength 532 nm).

[0056] There are no particular limitations on the output of the laser light, as long as it is sufficient to remove the resin components in the cured product; however, high output may generate excessive heat, potentially damaging the substrate. Therefore, repeated laser irradiation is preferably performed at an average output of approximately 0.2 to 1.0 W. The number of repetitions is not particularly limited, but approximately 5 to 50 times is preferred to balance the risk of substrate damage and practicality. Repeated laser irradiation may be performed using a continuous wave laser, or a pulsed wave laser may also be used. The beam diameter of the laser light is, for example, approximately 5 μm to 200 μm. [Example]

[0057] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the following, "parts" and "%" are all by mass unless otherwise specified.

[0058] <Preparation of Conductive Resin Composition> Each conductive resin composition (Examples 1 to 6 and Comparative Example 1) was prepared by blending the components shown in Table 1 below in the prescribed ratio and mixing them for 10 minutes at 400 rpm using a stirrer (FBLh600M, manufactured by Tokyo Glass Instruments Co., Ltd.) Note that *1 to *10 in Table 1 represent the following components. *1: Epoxy resin (jER 828, manufactured by Mitsubishi Chemical Corporation) *2: Hardener (DICY, dicyandiamide) *3: Low melting point solder particles (DS10, melting point 139°C, manufactured by Mitsui Mining & Smelting Co., Ltd., spherical, specific surface area: 541 cm 2 / g) *4: Flux (glutaric acid) *5: Carbon black (MA11, average particle size 29 nm, manufactured by Mitsubishi Chemical Corporation) *6: Titanium black (12S, primary particle size: 80-100 nm, manufactured by Mitsubishi Materials Electronic Chemicals Co., Ltd.) *7: Titanium black (13M, primary particle size: 80-100 nm, manufactured by Mitsubishi Materials Electronic Chemicals Co., Ltd.) *8: Near-infrared absorber (FDN-010, manufactured by Yamada Chemical Industry Co., Ltd.) *9: Blue dye (OIL Blue 613, manufactured by Orient Chemical Industries Co., Ltd.) *10 White pigment (CR-58, titanium oxide, average particle size: 0.28 μm, manufactured by Ishihara Sangyo Kaisha, Ltd.)

[0059] Each of the obtained conductive resin compositions was applied to one side of a glass substrate (product name S1112, manufactured by Matsunami Glass Industry Co., Ltd.) and cured using a hot plate at 180°C for 30 minutes to form a cured coating having a thickness of 30 μm. The substrate on which the cured coating was formed was then measured for reflectance and transmittance at wavelengths of 1064 nm and 532 nm using a V-570 UV-Visible-Infrared Spectrophotometer (manufactured by JASCO Corporation) equipped with an ISN-470 integrating sphere unit. The measurement conditions were: measurement response: Fast, bandwidth: 2 nm, scanning speed: 400 nm / min, starting wavelength: 1100 nm, ending wavelength: 350 nm, data acquisition interval: 2 nm. A glass substrate (product name S1112, manufactured by Matsunami Glass Industrial Co., Ltd.) was used as the reference, and Spectralon (registered trademark) was used as the reflector. Other conditions were measured in accordance with JIS K 7375:2008. The measurement results are shown in Table 1 below.

[0060] <Evaluation> (Connection reliability after mounting) Each of the obtained conductive resin compositions was applied to a PCB substrate (electrode width: 120 μm, electrode length: 200 μm, pitch width: 0.6 mm, number of electrodes: 10, flash Au treatment) using a scraper through a metal mask (mask thickness: 100 μm, opening: 200 μm × 100 μm) to a thickness of 80 μm. Next, the electrodes of individual LED chips (125 μm x 75 μm) were placed on each electrode position of the PCB substrate coated with the conductive resin composition so that they overlapped with each other, and the LED chip side was heated at 180°C for 10 minutes to produce an evaluation board mounted with 10 LED chips. A voltage of 2.5 V was applied to the electrodes of each evaluation board using a 7011 DC signal source (manufactured by Hioki E.E. Corporation), and the ability of the LEDs to light up was confirmed. The ability of the LEDs to light up was evaluated according to the following criteria. ◎: 9 or more of the 10 LEDs on the evaluation board are lit ○: 6 to 8 of the 10 LEDs on the evaluation board are lit △: 3 to 5 of the 10 LEDs on the evaluation board are lit ×: Less than 2 out of 10 LEDs on the evaluation board are lit The evaluation results are shown in Table 1.

[0061] <Connection reliability after repair> Of the evaluation boards described above, a board on which all 10 LEDs were lit was selected, and the backside of the board was heated at 170°C for 1 minute using a hot plate with the heating surface partially masked with insulating material. After removing the 10 LEDs from the board, the board was cooled to room temperature. Each area where the LEDs had been removed was visually observed, and it was confirmed that the cured conductive resin composition remained on the electrodes on the board surface in all 10 areas. Next, the area where the LED had been removed was irradiated with laser light for 1 second using a fiber laser (wavelength: 1064 μm, beam diameter: 40 μm) at an output of 0.4 W. This operation was repeated 10 times. Next, 300 mg of each conductive resin composition was applied using a dispenser to the area where the LED had been removed (area of ​​one area: approximately 120 μm x 200 μm). The same LED as used on the LED-mounted board was then placed on the applied area, and the positions of the board's electrodes and the LED's electrodes were adjusted so that they overlapped. The LED was then remounted by heating from the LED chip side at 180°C for 10 minutes. A voltage of 2.5 V was applied to the electrodes of the remounted board using a 7011 DC signal source (manufactured by Hioki E.E. Corporation) to check whether the LED could be lit. The ability of the LED to light was evaluated according to the following criteria. ◎: 9 or more of the 10 LEDs on the evaluation board are lit ○: 6 to 8 of the 10 LEDs on the evaluation board are lit △: 3 to 5 of the 10 LEDs on the evaluation board are lit ×: Less than 2 out of 10 LEDs on the evaluation board are lit The evaluation results are shown in Table 1.

[0062] <Impact on surrounding insulating film during repair> The insulating film around the mounted LED on the remounted board was observed with an OM microscope. The insulating film was evaluated for any deterioration according to the following criteria. ◎: No change in shape or color was observed ○: No change in shape can be seen, but some color changes can be seen △: Changes in shape and color can be seen in some areas ×: Changes in shape and color can be seen throughout the specimen. The evaluation results are shown in Table 1.

[0063] [Table 1]

[0064] As is clear from the evaluation results in Table 1, the conductive resin compositions (Examples 1 to 6) in which the reflectance of the cured coating for light with a wavelength of 1064 nm and light with a wavelength of 532 nm were both 20% or less maintained connection reliability when an electronic element such as an LED was mounted on a circuit board, and even after repair work in which the electronic element was removed from the electronic element mounting board and then remounted, they had excellent connection reliability without affecting the insulating portion surrounding the electronic element. Furthermore, it can be seen that the conductive resin compositions (Examples 1 to 4) in which the transmittance of light with a wavelength of 1064 nm and the transmittance of light with a wavelength of 532 nm in the cured coating are both 55% or less further suppress the influence of the surrounding insulating parts and also improve connection reliability. On the other hand, in the conductive resin composition (Comparative Example 1) in which the reflectance of the cured coating for both light with a wavelength of 1064 nm and light with a wavelength of 532 nm exceeds 20%, connection reliability can be maintained when an electronic element is mounted on a circuit board, but the peripheral insulating portion of the circuit board from which the electronic element has been removed is altered, and connection reliability is not maintained after remounting.

Claims

1. A conductive resin composition comprising at least (A) a thermosetting resin, (B) a curing agent for curing the thermosetting resin, (C) solder particles, (D) a flux, and (E) a light absorber (excluding leuco dyes) capable of absorbing light energy and converting a part or all of the absorbed light energy into thermal energy, the (A) thermosetting resin is an epoxy resin, the (B) curing agent for curing the thermosetting resin is dicyandiamide, and is contained in an amount of 3 to 15 parts by mass, calculated as a solid content, per 100 parts by mass of the (A) thermosetting resin; The conductive resin composition, when cured to form a cured film having a thickness of 30 μm, has a reflectance of 20% or less at a wavelength of 1064 nm.

2. 2. The conductive resin composition according to claim 1, wherein when the conductive resin composition is cured to form a cured film having a thickness of 30 μm, the cured film has a transmittance of 55% or less at a wavelength of 1064 nm.

3. A conductive resin composition comprising at least (A) a thermosetting resin, (B) a curing agent for curing the thermosetting resin, (C) solder particles, (D) a flux, and (E) a light absorber (excluding leuco dyes) capable of absorbing light energy and converting a part or all of the absorbed light energy into thermal energy, the (A) thermosetting resin is an epoxy resin, the (B) curing agent for curing the thermosetting resin is dicyandiamide, and is contained in an amount of 3 to 15 parts by mass, calculated as a solid content, per 100 parts by mass of the (A) thermosetting resin; The conductive resin composition, when cured to form a cured film having a thickness of 30 μm, has a reflectance of 20% or less at a wavelength of 532 nm.

4. 4. The conductive resin composition according to claim 3, wherein when the conductive resin composition is cured to form a cured film having a thickness of 30 μm, the cured film has a transmittance of 55% or less for light having a wavelength of 532 nm.

5. 5. The conductive resin composition according to claim 1, wherein the (E) light absorber capable of absorbing light energy and converting a part or all of the light energy into thermal energy does not denature or thermally decompose at a temperature 100° C. higher than the melting point of the (C) solder particles.

6. 6. The conductive resin composition according to claim 1, wherein the (E) light absorber capable of absorbing light energy and converting a part or all of the light energy into heat energy is contained in an amount of 0.5 to 8 mass% relative to the solid content of the conductive resin composition.

7. 7. The conductive resin composition according to claim 1, wherein the (C) solder particles are contained in an amount of 20 to 70 mass % relative to the solid content of the conductive resin composition.

8. The conductive resin composition according to any one of claims 1 to 7, wherein the (E) light absorber capable of absorbing light energy and converting a part or all of the light energy into heat energy is at least one selected from the group consisting of carbon black, titanium black, and near-infrared absorbers.

9. The conductive resin composition according to any one of claims 1 to 8, wherein the (E) light absorber capable of absorbing light energy and converting a part or all of it into heat energy has an average particle size of 1 µm or less.

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