Conductive Adhesive Composition and Method for Manufacturing a Connection Structure

Abstract

Disclosed is a conductive adhesive composition containing (A) conductive particles, (B) a thermosetting resin, and (C) a flux activator. The conductive particles include a metal having a melting point of 200°C or lower. In a volume-based cumulative particle size distribution of the conductive particles, the cumulative 50% particle diameter D50 is 3-10 μm and the cumulative 10% particle diameter D10 is 2.4 μm or larger. The flux activator contains a compound having a hydroxyl group and a carboxyl group. The conductive adhesive composition is used to electrically connect a circuit board 2 and an electronic component 3 mounted on the circuit board.

Description

Technical Field

[0001] The present disclosure relates to a conductive adhesive composition used for electrically connecting an electronic component and a circuit board, and a method for manufacturing a connection structure using the conductive adhesive composition.

Background Art

[0002] As a material for connecting an electronic component to a circuit board, a paste-like conductive adhesive in which metal particles are dispersed in a thermosetting resin may be used (see, for example, Patent Document 1).

[0003] When applying a conductive adhesive composition for connecting minute electrode pads or connection terminals arranged at a narrow pitch, in order to prevent a short circuit due to an inter-electrode bridge and to achieve sufficient electrical conduction with a small amount of application, the application of a conductive adhesive containing conductive particles having a small particle size is somewhat effective. However, in the case of conductive particles having a small particle size of about 10 μm or less in average particle diameter, since the specific surface area is large, the amount of the oxide film formed on the surface increases, and as a result, the meltability and joinability tend to be significantly reduced. When the meltability and joinability are reduced, the conductivity of the conductive adhesive is reduced. Further, un-melted conductive particles may float to a region outside the electrode pad, which may cause a short circuit between the electrodes.

[0004] Therefore, a conductive adhesive composition has been proposed in which the connection property is improved and the resistance to a temperature cycle test is improved by increasing the amount of the flux active material to some extent (see Patent Document 2).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, when the amount of the flux activator is large, the curability of the conductive adhesive decreases, and as a result, the adhesive strength after curing tends to decrease significantly. In addition, a connection structure in which an electronic component and a circuit board are connected is required to have resistance to a reflow test at 260°C. However, since the physical properties of the resin portion formed from the conductive adhesive are deteriorated by a large amount of the flux activator, in the reflow resistance test at 260°C, the resin portion may be broken due to the thermal expansion of the metal portion, which may cause poor conductivity.

[0007] Therefore, one aspect of the present disclosure aims to improve the resistance to a temperature cycle test and the resistance to a reflow test at 260°C while mounting an electronic component on a circuit board with sufficient adhesive strength and good conductivity when used to electrically connect a circuit board and an electronic component mounted on the circuit board, with respect to a conductive adhesive composition containing conductive particles having a relatively small particle size.

Means for Solving the Problems

[0008] One aspect of the present disclosure provides a conductive adhesive composition used for electrically connecting a circuit board and an electronic component mounted on the circuit board. In other words, one aspect of the present disclosure provides an application of the conductive adhesive composition for electrically connecting a circuit board and an electronic component mounted on the circuit board. The conductive adhesive composition contains (A) conductive particles, (B) a thermosetting resin, and (C) a flux activator. The conductive particles contain a metal having a melting point of 200°C or lower. In the cumulative particle size distribution based on volume of the conductive particles, D50 is 3 to 10 μm, and D10 is 2.4 μm or more. The flux activator contains a compound having a hydroxyl group and a carboxyl group.

[0009] In the conductive adhesive composition according to the present invention, the conductive particles have a relatively small particle size with D50 being 3 to 30 μm, and since D10 is 2.4 μm or more, the proportion of fine particles with a particle size of 2.4 μm or less having a large specific surface area is small. Therefore, a decrease in conductivity due to the influence of the oxide film on the surface of the conductive particles hardly occurs, and thereby good conductivity is ensured while maintaining sufficient adhesive strength. In addition, in the temperature cycle test and the reflow test at 260°C, the initial low connection resistance is maintained.

[0010] Another aspect of the present invention provides a method for manufacturing a connection structure. The method according to one aspect of the present invention includes preparing a circuit board having two or more connection terminals and an electronic component having two or more connection terminals, disposing the conductive adhesive composition on the connection terminals of the circuit board or on the connection terminals of the electronic component, disposing the electronic component on the circuit board so that the connection terminals of the circuit board and the connection terminals of the electronic component face each other through the conductive adhesive composition to obtain a temporary connection body having the circuit board, the conductive adhesive composition, and the electronic component, and heating the temporary connection body to form a connection portion having a conductive portion formed from the conductive particles in the conductive adhesive composition, the conductive portion electrically connecting the connection terminals of the circuit board and the connection terminals of the electronic component, and a resin portion formed around the conductive portion, thereby obtaining a connection structure in which the circuit board and the electronic component are joined.

Effects of the Invention

[0011] According to one aspect of the present disclosure, there is provided a conductive adhesive composition containing conductive particles having a relatively small particle size, which can improve the resistance to temperature cycle tests and the resistance to reflow tests at 260°C while mounting an electronic component on a circuit board with sufficient adhesive strength and good electrical conductivity when used for electrically connecting the circuit board and the electronic component mounted on the circuit board. The conductive adhesive composition according to one aspect of the present disclosure can improve the adhesive strength and electrical conductivity to a level that can meet the required characteristics regarding the reflow test at 260°C while suppressing short circuits due to bridges between connection terminals arranged at a narrow pitch. The conductive adhesive composition according to one aspect of the present disclosure is also advantageous in terms of lowering the connection temperature and suppressing warping of small and thin devices in the process of mounting an electronic component on a circuit board. The conductive adhesive composition according to the present disclosure is also suitable for connecting fine connection terminals because it can reduce the flux content that causes voids in the connection part.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0013] Hereinafter, some embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments.

[0014] The conductive adhesive composition according to one embodiment contains (A) conductive particles, (B) a thermosetting resin, and (C) a flux activator.

[0015] (A) The conductive particles contain a metal having a melting point of 200°C or lower. The melting point of the metal contained in the conductive particles may be 180°C or lower, or 150°C or lower. The lower limit of the melting point of the metal in the conductive particles is not particularly limited, but is about 100°C. When such conductive particles are used in a conductive adhesive composition, it is considered that they melt and aggregate at a relatively low temperature, and this aggregate contributes to the electrical connection of the connection terminals. When the metal contained in the conductive particles is an alloy containing two or more metal species, it is sufficient that the melting point of the alloy is 200°C or lower.

[0016] From the viewpoint of reducing environmental load, the metal in the conductive particles may be composed of metals other than lead. Examples of the metal contained in the conductive particles include a single metal selected from tin (Sn), bismuth (Bi), indium (In), and zinc (Zn), or an alloy composed of two or more metal species. The alloy may further contain a high-melting-point component selected from platinum (Pt), gold (Au), silver (Ag), copper (Cu), nickel (Ni), palladium (Pd), aluminum (Al), etc., within a range where the melting point of the entire metal in the conductive particles is 200°C or lower, from the viewpoint of obtaining better connection reliability.

[0017] Specific examples of the metal constituting the conductive particles include Sn42-Bi58 solder (melting point 138°C), Sn48-In52 solder (melting point 117°C), Sn42-Bi57-Ag1 solder (melting point 139°C), Sn90-Ag2-Cu0.5-Bi7.5 solder (melting point 189°C), Sn96-Zn8-Bi3 solder (melting point 190°C), and Sn91-Zn9 solder (melting point 197°C). These show a clear solidification behavior after melting. The solidification behavior means that the metal cools and solidifies after melting. From the viewpoints of easy availability and effectiveness, the conductive particles may contain Sn42-Bi58 solder. These are used alone or in combination of two or more.

[0018] In the volume-based cumulative particle size distribution of the conductive particles, the cumulative 50% particle size D50 may be 3 to 10 μm. The cumulative particle size distribution here is measured by the laser diffraction / scattering method. When D50 is 3 μm or more, the conductive adhesive composition is likely to have a moderately low viscosity, and good workability can be ensured. Also, the amount of the flux activator required to obtain sufficient fusibility of the conductive particles tends to be small. When the amount of the flux activator is small, the resin cured product formed from the conductive adhesive composition is likely to maintain good physical properties (such as adhesiveness at high temperatures). Further, in the reflow test at 260°C, it is difficult for the resin part to be broken due to the expansion of the conductive part containing metal. When the D50 of the conductive particles is 10 μm or less, when connecting the connection terminals arranged at the pitch and the electronic component, a short circuit between the adjacent connection terminals due to bridging of the adjacent connection terminals is less likely to occur. In addition, the conductive adhesive composition can be easily applied to the connection terminals with a small area by any of the printing method, the transfer method, and the dispensing method. From the viewpoint of further improving the coatability and workability of the conductive adhesive composition, the D50 of the conductive particles may be 4 to 9 μm. From the viewpoints of improving the storage stability of the conductive adhesive composition and the mounting reliability of the cured product, the D50 of the conductive particles may be 5 to 8 μm.

[0019] In the volume-based cumulative particle size distribution of the conductive particles, the cumulative 10% particle size D10 may be 2.4 μm or more. When D10 is 2.4 μm or more, for the same reasons as above, the amount of the required flux activator tends to be small, and therefore, for example, it is easy to maintain a high level of reflow resistance at 260°C. From the same viewpoint, the minimum particle size Dmin in the cumulative particle size distribution may be 1.0 μm or more. D10 may be 2.9 μm or less, and Dmin may be 2.5 μm or less.

[0020] In the volume-based cumulative particle size distribution of the conductive particles, the cumulative 90% particle size D90 may be 12 μm or less. When D90 is 12 μm or less, the occurrence of a short circuit due to a bridge between the connection terminals tends to be suppressed. From the same perspective, the maximum particle size Dmax may be 20 μm or less. D90 may be 10 μm or more, and Dmax may be 13 μm or more.

[0021] The specific surface area of the conductive particles is 1.45×10 -4 ~8.45×10 -4 cm 2 / g may also be acceptable.

[0022] The conductive particles may be metal particles composed only of metal, or composite particles having core particles made of solid materials other than metal such as ceramics, silica, and resin materials, and a metal film covering the surface of the core particles and made of a metal with a melting point of 200°C or less, or a combination thereof may also be acceptable.

[0023] The content of the conductive particles may be 5 to 95% by mass based on the total mass of the conductive adhesive composition. When the content of the conductive particles is less than 5% by mass, the conductivity of the cured product of the conductive adhesive composition tends to decrease. When the content of the conductive particles exceeds 95% by mass, the viscosity of the conductive adhesive composition increases, resulting in a tendency for workability to decrease. Also, since the proportion of the thermosetting adhesive component in the conductive adhesive composition relatively decreases, the mounting reliability also tends to decrease. From the perspective of improving workability or conductivity, the content of the conductive particles may be 30 to 90% by mass, and from the perspective of enhancing the mounting reliability of the conductive adhesive composition, it may be 40 to 85% by mass.

[0024] In addition to the conductive particles containing a metal with a melting point of 200°C or lower, the conductive adhesive composition may contain (a1) high-melting-point conductive particles containing a metal with a melting point exceeding 200°C. Examples of the metal with a melting point higher than 200°C include a single metal selected from Pt, Au, Ag, Cu, Ni, Pd, Al, and Sn, or an alloy composed of two or more metal species. Specific examples of the high-melting-point conductive particles include Au powder, Ag powder, Cu powder, Ag-plated Cu powder, Sn powder, and SnAgCu powder. As a commercially available product of the high-melting-point conductive particles, "MA05K" (trade name, manufactured by Hitachi Chemical Co., Ltd.), which is silver-plated copper powder, is available.

[0025] (A) When combining (A) conductive particles containing a metal with a melting point of 200°C or lower and (a1) conductive particles containing a metal with a melting point exceeding 200°C, the mass ratio of (A) conductive particles containing a metal with a melting point of 200°C or lower to (a1) conductive particles containing a metal with a melting point exceeding 200°C ((A):(a1)) may be in the range of 99:1 to 50:50, or 99:1 to 60:40.

[0026] (B) The thermosetting resin has the function of adhering to the adherend and acts as a binder component that binds the conductive particles in the conductive adhesive composition and the filler added as necessary to each other. Examples of the thermosetting resin include thermosetting organic polymer compounds such as epoxy resins, (meth)acrylic resins, maleimide resins, and cyanate resins, and their precursors. The (meth)acrylic resin indicates a methacrylic resin and an acrylic resin. The thermosetting resin may be a compound having a polymerizable carbon-carbon double bond represented by the (meth)acrylic resin and the maleimide resin, or an epoxy resin. These thermosetting resins are excellent in heat resistance and adhesiveness, and can also be handled in a liquid state if dissolved or dispersed in an organic solvent as necessary, so they are also excellent in workability. From the viewpoints of easy availability and reliability, the thermosetting resin may be an epoxy resin. These thermosetting resins are used alone or in combination of two or more.

[0027] Here, the epoxy resin is a compound having two or more epoxy groups. Examples of the epoxy resin include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol AD type epoxy resin, and amine type epoxy resin.

[0028] Specific examples of commercially available epoxy resins include AER-X8501 (trade name, manufactured by Asahi Kasei Corporation), R-301 (trade name, manufactured by Mitsubishi Chemical Corporation), and YL-980 (trade name, manufactured by Mitsubishi Chemical Corporation), which are bisphenol A type epoxy resins; YDF-170 (trade name, manufactured by Tohto Kasei Co., Ltd.) and YL-983U (trade name, manufactured by Mitsubishi Chemical Corporation), which are bisphenol F type epoxy resins; R-1710 (trade name, manufactured by Mitsui Petrochemical Industries, Ltd.), which is bisphenol AD type epoxy resin; N-730S (trade name, manufactured by Dainippon Ink and Chemicals, Inc.) and Quatrex-2010 (trade name, manufactured by The Dow Chemical Company), which are phenol novolac type epoxy resins; YDCN-702S (trade name, manufactured by Tohto Kasei Co., Ltd.) and EOCN-100 (trade name, manufactured by Nippon Kayaku Co., Ltd.), which are cresol novolac type epoxy resins; EPPN-501 (trade name, manufactured by Nippon Kayaku Co., Ltd.), TACTIX-742 (trade name, manufactured by The Dow Chemical Company), VG-3010 (trade name, manufactured by Mitsui Petrochemical Industries, Ltd.), and 1032S (trade name, manufactured by Mitsubishi Chemical Corporation), which are polyfunctional epoxy resins; HP-4032 (trade name, manufactured by Dainippon Ink and Chemicals, Inc.), which is an epoxy resin having a naphthalene skeleton, EHPE-3150, CEL-3000 (both trade names, manufactured by Daicel Chemical Industries, Ltd.), DME-100 (trade name, manufactured by Shin Nippon Rika Co., Ltd.), and EX-216L (trade name, manufactured by Nagase ChemteX Corporation), which are alicyclic epoxy resins; W-100 (trade name, manufactured by Shin Nippon Rika Co., Ltd.), which is an aliphatic epoxy resin; ELM-100 (trade name, manufactured by Sumitomo Chemical Co., Ltd.), YH-434L (trade name, manufactured by Tohto Kasei Co., Ltd.), TETRAD-X, TETRAD-C (both trade names, manufactured by Mitsubishi Gas Chemical Company, Inc.), 630, 630LSD (both trade names, manufactured by Mitsubishi Chemical Corporation), which are amine type epoxy resins; Denacol EX-201 (trade name, manufactured by Nagase ChemteX Corporation), which is a resorcin type epoxy resin; Denacol EX-211 (trade name, manufactured by Nagase ChemteX Corporation), which is a neopentyl glycol type epoxy resin; Denacol EX-212 (trade name, manufactured by Nagase ChemteX Corporation), which is 1,6-hexanediol diglycidyl ether;Denacol EX series (EX-810, 811, 850, 851, 821, 830, 832, 841, 861, all manufactured by Nagase Kasei Kogyo Co., Ltd., trade names), which are ethylene-propylene glycol type epoxy resins; E-XL-24 and E-XL-3L (both manufactured by Mitsui Chemicals, Inc., trade names), which are epoxy resins represented by the following general formula (I).;

[0029]

Chemical formula

[0030] When the thermosetting resin contains an epoxy resin, the conductive adhesive composition may further contain an epoxy compound having one epoxy group as a reactive diluent. Specific examples of commercially available products of the epoxy compound having one epoxy group include PGE (manufactured by Nippon Kayaku Co., Ltd., trade name), PP-101 (manufactured by Tohto Kasei Co., Ltd., trade name), ED-502, ED-509, ED-509S (manufactured by Asahi Denka Kogyo KK, trade name), YED-122 (manufactured by Yuka Shell Epoxy Co., Ltd., trade name), KBM-403 (manufactured by Shin-Etsu Chemical Co., Ltd., trade name), TSL-8350, TSL-8355, TSL-9905 (manufactured by Toshiba Silicone Co., Ltd., trade name). These may be used alone or in combination of two or more.

[0031] When the conductive adhesive composition contains a reactive diluent, its content may be in the range that does not significantly inhibit the effects of the present invention, and may be 0.1 to 30% by mass based on the total amount of the epoxy resin.

[0032] The thermosetting resin may contain a (meth)acrylic resin. The (meth)acrylic resin is composed of a compound having a polymerizable carbon-carbon double bond (acryloyl group or methacryloyl group). Such compounds include, for example, monoacrylate compounds, monomethacrylate compounds, diacrylate compounds, and dimethacrylate compounds.

[0033] Examples of the monoacrylate compound include methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, amyl acrylate, isoamyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, isodecyl acrylate, lauryl acrylate, tridecyl acrylate, hexadecyl acrylate, stearyl acrylate, isostearyl acrylate, cyclohexyl acrylate, isobornyl acrylate, diethylene glycol acrylate, polyethylene glycol acrylate, polypropylene glycol acrylate, 2-methoxyethyl acrylate, 2-ethoxyethyl acrylate, 2-butoxyethyl acrylate, methoxydiethylene glycol acrylate, methoxypolyethylene glycol acrylate, dicyclopentenyl oxyethyl acrylate, 2-phenoxyethyl acrylate, phenoxydiethylene glycol acrylate, phenoxypolyethylene glycol acrylate, 2-benzoyloxyethyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, benzyl acrylate, 2-cyanoethyl acrylate, γ-acryloxyethyl trimethoxysilane, glycidyl acrylate, tetrahydrofurfuryl acrylate, dimethylaminoethyl acrylate, diethylaminoethyl acrylate, acryloxyethyl phosphate, and acryloxyethyl phenyl acid phosphate.

[0034] Examples of the monomer methacrylate compounds include methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, amyl methacrylate, isoamyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, isodecyl methacrylate, lauryl methacrylate, tridecyl methacrylate, hexadecyl methacrylate, stearyl methacrylate, isostearyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, diethylene glycol methacrylate, polyethylene glycol methacrylate, polypropylene glycol methacrylate, 2-methoxyethyl methacrylate, 2-ethoxyethyl methacrylate, 2-butoxyethyl methacrylate, methoxydiethylene glycol methacrylate, methoxypolyethylene glycol methacrylate, dicyclopentenyl oxyethyl methacrylate, 2-phenoxyethyl methacrylate, phenoxydiethylene glycol methacrylate, phenoxypolyethylene glycol methacrylate, 2-benzoyloxyethyl methacrylate, 2-hydroxy-3-phenoxypropyl methacrylate, benzyl methacrylate, 2-cyanoethyl methacrylate, γ-methacryloxyethyltrimethoxysilane, glycidyl methacrylate, tetrahydrofurfuryl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, methacryloxyethyl phosphate, and methacryloxyethyl phenyl acid phosphate.

[0035] Examples of the diacrylate compound include ethylene glycol diacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, 1,9-nonanediol diacrylate, 1,3-butanediol diacrylate, neopentyl glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, tripropylene glycol diacrylate, polypropylene glycol diacrylate, the reaction product of 1 mol of bisphenol A, bisphenol F or bisphenol AD and 2 mol of glycidyl acrylate, the diacrylate of the polyethylene oxide adduct of bisphenol A, bisphenol F or bisphenol AD, the diacrylate of the polypropylene oxide adduct of bisphenol A, bisphenol F or bisphenol AD, bis(acryloxypropyl)polydimethylsiloxane, and bis(acryloxypropyl)methylsiloxane-dimethylsiloxane copolymer.

[0036] Examples of the dimethacrylate compound include ethylene glycol dimethacrylate, 1,4-butanediol dimethacrylate, 1,6-hexanediol dimethacrylate, 1,9-nonanediol dimethacrylate, 1,3-butanediol dimethacrylate, neopentyl glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, tripropylene glycol dimethacrylate, polypropylene glycol dimethacrylate, the reaction product of 1 mol of bisphenol A, bisphenol F or bisphenol AD and 2 mol of glycidyl methacrylate, the dimethacrylate of the polyethylene oxide adduct of bisphenol A, bisphenol F or bisphenol AD, the dimethacrylate of the polypropylene oxide adduct of bisphenol F or bisphenol AD, bis(acryloxypropyl)polydimethylsiloxane, and bis(acryloxypropyl)methylsiloxane-dimethylsiloxane copolymer.

[0037] These compounds are used singly or in combination of two or more. When the thermosetting resin contains a (meth)acrylic resin, these compounds may be polymerized in advance before use, or these compounds may be mixed together with conductive particles, flux activators, etc., and polymerization may be carried out simultaneously with the mixing. Compounds having polymerizable carbon-carbon double bonds in these molecules are used singly or in combination of two or more.

[0038] When the thermosetting resin contains a (meth)acrylic resin, the conductive adhesive composition may further contain a radical polymerization initiator. From the viewpoint of effectively suppressing voids, etc., an organic peroxide is suitable as the radical polymerization initiator. From the viewpoint of improving the curability and viscosity stability of the adhesive component, the decomposition temperature of the organic peroxide may be 130°C to 200°C.

[0039] As the radical polymerization initiator, those commonly used can be used. Examples thereof include peroxides such as benzoyl peroxide and t-butyl peroxy-2-ethylhexanoate, and azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile.

[0040] The content of the radical polymerization initiator may be 0.01 to 20% by mass, 0.1 to 10% by mass, or 0.5 to 5% by mass based on the total amount of the conductive adhesive composition.

[0041] Commercially available products can be used as the (meth)acrylic resin. Specific examples thereof include FINEDIC A-261 (manufactured by Dainippon Ink and Chemicals, Incorporated, trade name), and FINEDIC A-229-30 (manufactured by Dainippon Ink and Chemicals, Incorporated, trade name).

[0042] The content of the thermosetting resin in the conductive adhesive composition may be 1 to 60% by mass, 5 to 40% by mass, or 10 to 30% by mass based on the total mass of the conductive adhesive composition.

[0043] (C) The flux activator is a component that exhibits the function of removing the oxide film formed on the surface of the conductive particles. By using such a flux activator, the oxide film that hinders the melting and aggregation of the conductive particles is removed. The flux activator according to one embodiment includes a compound containing a hydroxyl group and a carboxyl group. This compound exhibits good flux activity and can react with an epoxy resin that can be used as a thermosetting resin. A compound having a hydroxyl group and a carboxyl group may be an aliphatic dihydroxycarboxylic acid in that it exhibits good oxide film removal ability even when the particle size of the conductive particles is small and the amount of the oxide film is large. Specifically, the flux activator may include a compound represented by the following general formula (V), tartaric acid, or a combination thereof.

[0044] [Chemical formula]

[0045] In formula (V), R5 represents an alkyl group having 1 to 5 carbon atoms. From the viewpoint of more effectively exerting the above-described effects of the present invention, R5 may be a methyl group, an ethyl group, or a propyl group. n and m each independently represent an integer of 0 to 5. From the viewpoint of more effectively exerting the above-described effects of the present invention, n may be 0 and m may be 1, or both n and m may be 1.

[0046] Examples of the compound represented by the above general formula (V) include 2,2-bis(hydroxymethyl)propionic acid, 2,2-bis(hydroxymethyl)butanoic acid, and 2,2-bis(hydroxymethyl)pentanoic acid. The flux activator may contain at least one compound selected from these.

[0047] From the perspective of more effectively exerting the effects of the present invention such as the resistance to the reflow test at 260°C, the content of the flux activator may be 1.0 to 3.9% by mass, 1.8 to 3.9% by mass, or 1.5 to 3.5% by mass based on the amount of the conductive particles. From the perspectives of the curability of the conductive adhesive composition and void suppression, the content of the flux activator may be 2.5 to 3.5% by mass based on the amount of the conductive particles.

[0048] When the thermosetting resin is an epoxy resin, the conductive adhesive composition may further contain (D) a curing catalyst. (D) The curing catalyst is a component that promotes the curing of the epoxy resin. From the perspectives of curability, the length of the pot life, and the heat resistance of the cured product, the curing catalyst may include a compound having an imidazole group. Examples of commercially available products of the compound having an imidazole group include 2P4MHZ-PW (2-phenyl-4-methyl-5-hydroxymethylimidazole), 2PHZ-PW (2-phenyl-4,5-dihydroxymethylimidazole), C11Z-CN (1-cyanoethyl-2-undecylimidazole), 2E4MZ-CN (1-cyanoethyl-2-ethyl-4-methylimidazole), 2PZ-CN (1-cyanoethyl-2-phenylimidazole), 2MZ-A (2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine), 2E4MZ-A (2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-s-triazine), 2MAOK-PW (2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanurate adduct) (all are products of Shikoku Kasei Co., Ltd., trade names). These curing catalysts are used alone or in combination of two or more.

[0049] The content of the curing catalyst may be 0.01 to 90 parts by mass or 0.1 to 50 parts by mass based on 100 parts by mass of the epoxy resin. When the content of the curing catalyst is less than 0.01 part by mass, the curability tends to decrease. When the content of the curing catalyst exceeds 90 parts by mass, the viscosity increases, and the workability tends to decrease when handling the conductive adhesive composition.

[0050] The conductive adhesive composition may further contain a curing agent to adjust the curing rate of the epoxy resin.

[0051] The curing agent is not particularly limited as long as it is conventionally used, and commercially available products are available. Examples of commercially available curing agents include H-1 (trade name, manufactured by Meiko Kasei Co., Ltd.) and VR-9300 (trade name, manufactured by Mitsui Toatsu Chemicals, Inc.), which are phenol novolak resins, XL-225 (trade name, manufactured by Mitsui Toatsu Chemicals, Inc.), which is a phenol aralkyl resin, MTPC (trade name, manufactured by Honshu Chemical Industry Co., Ltd.), which is a p-cresol novolak resin represented by the following general formula (II), AL-VR-9300 (trade name, manufactured by Mitsui Toatsu Chemicals, Inc.), which is an allylated phenol novolak resin, and PP-700-300 (trade name, manufactured by Nippon Petrochemical Co., Ltd.), which is a special phenol resin represented by the following general formula (III).

[0052]

Chemical formula

[0053] In formula (II), a plurality of R1 each independently represents a monovalent hydrocarbon group, which may be a methyl group or an allyl group. q represents an integer of 1 to 5. In formula (III), R2 represents an alkyl group, which may be a methyl group or an ethyl group. R3 represents a hydrogen atom or a monovalent hydrocarbon group, and p represents an integer of 2 to 4.

[0054] As the curing agent, dicyandiamide and the like, which have been conventionally used as curing agents, can also be used, and commercially available products are available. Examples of commercially available products include ADH, PDH, and SDH (all trade names, manufactured by Nippon Hydrazine Industry Co., Ltd.), which are dibasic acid dihydrazides represented by the following general formula (IV), and Novacure (trade name, manufactured by Asahi Kasei Corporation), which is a microcapsule type curing agent composed of a reaction product of an epoxy resin and an amine compound. These curing agents are used alone or in combination of two or more.

[0055]

Chemical formula

[0056] In formula (IV), R4 represents a divalent aromatic group or a linear or branched alkylene group having 1 to 12 carbon atoms, and may be an m-phenylene group or a p-phenylene group.

[0057] From the viewpoints of storage stability and curing time, the conductive adhesive composition may not substantially contain a curing agent. "Not substantially containing" means that the content is 0.05% by mass or less based on the total mass of the conductive adhesive composition.

[0058] The conductive adhesive composition may contain a filler. Examples of the filler include polymer particles such as acrylic rubber and polystyrene; inorganic particles such as diamond, boron nitride, aluminum nitride, alumina, and silica. These fillers may be used alone or in combination of two or more.

[0059] In addition to the above-described components, the conductive adhesive composition may optionally contain one or more additives selected from the group consisting of a flexibilizer for stress relaxation, a diluent for improving workability, an adhesion improver, a wettability improver, and an antifoaming agent.

[0060] Examples of the flexibilizer include liquid polybutadiene (manufactured by Ube Industries, Ltd., trade names "CTBN-1300×31" and "CTBN-1300×9", manufactured by Nippon Soda Co., Ltd., trade name "NISSO-PB-C-2000"). The content of the flexibilizer may be 0.1 to 500 parts by mass based on 100 parts by mass of the thermosetting resin.

[0061] Examples of diluents include relatively high-boiling organic solvents such as butyl carbitol, butyl carbitol acetate, butyl cellosolve, carbitol, butyl cellosolve acetate, carbitol acetate, dipropylene glycol monomethyl ether, ethylene glycol diethyl ether, and α-terpineol. The content of the diluent may be 0.1 to 30% by mass based on the total mass of the conductive adhesive composition.

[0062] The adhesion improver may be a coupling agent such as a silane coupling agent or a titanium coupling agent. Examples of the silane coupling agent include, for example, "KBM-573" manufactured by Shin-Etsu Chemical Co., Ltd. under the trade name. The wetting improver may be, for example, an anionic surfactant or a fluorine-based surfactant. The antifoaming agent may be, for example, silicone oil. The adhesion improver, wetting improver, and antifoaming agent are each used alone or in combination of two or more. Their contents may be 0.1 to 10% by mass based on the total mass of the conductive adhesive composition.

[0063] Any combination of the exemplified components described above may be used.

[0064] The conductive adhesive composition can be obtained by heating the above-described components once or in multiple portions as needed, and mixing, dissolving, deflocculating and kneading, or dispersing them. The conductive adhesive composition may be in the form of a paste in which each component is uniformly dispersed. Examples of the dispersion / dissolution apparatus used at this time include known stirrers, homogenizers, three-roll mills, planetary mixers, etc. The conductive adhesive composition may be in the form of a paste at 25°C, and its viscosity may be 5 to 400 Pa·s.

[0065] According to the conductive adhesive composition of the present embodiment described above, it is possible to connect the mounted components with good conductivity to a circuit board having small-area electrode pads or electrodes arranged at a pitch, without causing a short circuit between the electrodes. The conductive adhesive composition of the present embodiment can lower the reflow heating temperature and suppress warping of the circuit board in the process of mounting electronic components on a circuit board having electrodes arranged at a pitch. The connection portion formed by the conductive adhesive composition of the present embodiment can have a conductive portion containing conductive particles and a resin portion formed from an insulating adhesive component. The reinforcement by the resin portion can contribute to improving the temperature cycle test resistance of the connection structure. Furthermore, even in the 260°C reflow process, the connection can be maintained without the reinforcing resin portion breaking.

[0066] Next, an electronic component mounting substrate as an example of the connection structure will be described with reference to FIGS. 1 and 2.

[0067] FIG. 1 is a schematic cross-sectional view showing an embodiment of the connection structure. The connection structure 1 shown in FIG. 1 includes a circuit board 2 having a base material 5 and two or more connection terminals 7 formed on the main surface of the base material 5, an electronic component 3 having a main body portion 4 and two or more connection terminals 6 facing the circuit board 2, and a connection portion 8 disposed between the circuit board 2 and the electronic component 3 and joining them, which is an electronic component mounting substrate. The connection portion 8 is disposed between the connection terminal 7 of the circuit board 2 and the connection terminal 6 of the electronic component 3 and is composed of a conductive portion 8a that electrically connects them and a resin portion 8b formed around the conductive portion 8a. The connection portion 8 is a cured product of the conductive adhesive composition according to the above-described embodiment. The conductive portion 8a mainly includes an aggregate of conductive particles contained in the conductive adhesive composition. The resin portion 8b mainly includes a cured product of an adhesive component containing a thermosetting resin and a curing catalyst contained in the conductive adhesive composition. However, the resin portion 8b may contain a small amount of conductive particles as long as appropriate insulation is maintained. The circuit board 2 and the electronic component 3 are joined to each other and electrically connected by the connection portion 8.

[0068] The connection structure 1 can be manufactured, for example, by a method including the steps of preparing a circuit board 2 and an electronic component 3 each having two or more connection terminals 7, 6, respectively, disposing a conductive adhesive composition on the connection terminal 7 of the circuit board 2 or the connection terminal 6 of the electronic component 3, disposing the electronic component 3 on the circuit board 2 so that the connection terminal 7 of the circuit board 2 and the connection terminal 6 of the electronic component 3 face each other through the conductive adhesive composition disposed on the connection terminal 7 or the connection terminal 6, to obtain a temporary connection body having the circuit board 2, the conductive adhesive composition, and the electronic component 3, and heating the temporary connection body to form a connection portion 8 having a conductive portion 8a that electrically connects the connection terminal 7 of the circuit board 2 and the connection terminal 6 of the electronic component 3, formed from conductive particles in the conductive adhesive composition, and a resin portion 8b formed around the conductive portion 8a, thereby obtaining the connection structure 1.

[0069] The conductive adhesive composition can be applied to the connection terminals of the circuit board or the electronic component by methods such as the dispensing method, the screen printing method, the stamping method, etc. The heating of the temporary connection body can be performed using a heating device such as an oven or a reflow furnace. If necessary, the temporary connection body may be heated under pressure. During the heat curing process of the conductive adhesive composition, usually, the connection portion 8 having the conductive portion 8a and the resin portion 8b is formed. The conductive portion 8a includes an aggregate formed by the fusion of the conductive particles melted by heating. This aggregate joins with the connection terminals of the circuit board and the electronic component to form a metal connection path.

[0070] In the case of the connection structure 1 shown in FIG. 2, a solder ball 10 is provided on the connection terminal 6 of the electronic component 3 and the conductive portion 8a formed from the conductive adhesive composition, and the solder ball 10 and the connection terminal 7 of the circuit board 2 are electrically connected by the conductive portion 8a. That is, the connection terminal 7 of the circuit board 2 and the connection terminal 6 of the electronic component 3 are electrically connected through the conductive portion 8a and the solder ball 10. The connection terminals 7 of the circuit board 2 may be arranged on the main surface of the base material 2 with a distance of 200 μm or less from each other.

[0071] In these connection structures, the conductive part 8a is reinforced by the resin part 8b. When the connection structure undergoes a thermal history due to a temperature cycle test, large strains are applied to the connection part and other component members due to warping or the like. Since the conductive part 8a is reinforced by the resin part 8b, the deformation of the base material is stopped by the resin part 7b, and the generation of cracks in the connection part is suppressed.

[0072] When a cross-section along the thickness direction of the connection structure is viewed at the position where the connection terminal of the electronic component shows the maximum width, the area ratio of the conductive part to the resin part may be 5:95 to 80:20.

[0073] The electronic component may be a solid-state imaging device such as a CMOS.

[0074] As described above, the preferred embodiments of the present invention have been described, but the present invention is not limited to the above embodiments. The present invention can be variously modified without departing from the gist thereof.

Example

[0075] Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.

[0076] 1. Materials (A) Conductive particles · STC-7: Sn42-Bi58 particles (D50: 8.0 μm, D10: 5.3 μm, D90: 10.3 μm, Dmin: 2.8 μm, Dmax: 20 μm, manufactured by Mitsui Mining & Smelting Co., Ltd., melting point 138 °C) · STC-5: Sn42-Bi58 particles (D50: 6.4 μm, D10: 4.6 μm, D90: 8.7 μm, Dmin: 1.7 μm, Dmax: 13 μm, manufactured by Mitsui Mining & Smelting Co., Ltd., melting point 138 °C) · STC-3: Sn42-Bi58 particles (D50: 4.1 μm, D10: 2.7 μm, D90: 6.0 μm, Dmin: 1.0 μm, Dmax: 11 μm, manufactured by Mitsui Mining & Smelting Co., Ltd., melting point 138 °C) · ST-5: Sn42-Bi58 particles (D50: 5.3 μm, D10: 2.3 μm, D90: 8.5 μm, Dmin: 0.7 μm, Dmax: 14 μm, manufactured by Mitsui Mining & Smelting Co., Ltd., melting point 138 °C) · ST-3: Sn42-Bi58 particles (D50: 3.1 μm, D10: 1.7 μm, D90: 5.0 μm, Dmin: 0.6 μm, Dmax: 11 μm, manufactured by Mitsui Mining & Smelting Co., Ltd., melting point 138 °C) · Sn42-Bi57-Ag1 particles (D50: approximately 5 μm, D10: 2.2 μm, D90: 8.6 μm, Dmin: 0.7 μm, Dmax: 14 μm) (B) Thermosetting resin · YL980 (trade name of bisphenol A type epoxy resin, manufactured by Mitsubishi Chemical Corporation) (C) Flux activator · BHPA: 2,2-bis(hydroxymethyl)propionic acid · BHBA: 2,2-bis(hydroxymethyl)butanoic acid · Tartaric acid (D) Curing catalyst · 2P4MHZ-PW (trade name of imidazole compound, manufactured by Shikoku Chemicals Corporation)

[0077] 2. Conductive adhesive composition Example 1 15.2 parts by mass of YL980, 0.8 part by mass of 2P4MHZ-PW, and 3.0 parts by mass of BHPA as a flux activator were mixed, and the mixture was passed through a three-roll mill three times. Subsequently, 81 parts by mass of STC-7, which is Sn42-Bi58 particles, was added to 19 parts by mass of the mixture. The mixture was stirred using a planetary mixer and degassed at 500 Pa or less for 10 minutes to obtain a conductive adhesive composition.

[0078] Examples 2 to 16, Comparative Examples 1 to 20 Conductive adhesive compositions of Examples 2 to 16 and Comparative Examples 1 to 20 were obtained in the same manner as in Example 1, except that the mixing ratios (parts by mass) were changed as shown in Table 1, Table 2, or Table 3.

[0079] Comparative Examples 21 to 23 The following commercially available conductive adhesives were prepared. Comparative Example 21: Ag paste (manufactured by Fujikura Kasei Co., Ltd., Dotite (trade name)) Comparative Example 22: Sn42-Bi58 cream solder (manufactured by Senju Metal Industry Co., Ltd., Eco Solder (trade name)) Comparative Example 23: Sn96.5-Ag3-Cu0.5 cream solder (manufactured by Senju Metal Industry Co., Ltd., Eco Solder)

[0080] 3. Evaluation of Adhesion, Conductivity, and Resistance to TCT The properties of the conductive adhesive compositions of each example and comparative example were evaluated by the following methods. The results are summarized in Tables 1, 2, and 3. In the tables, "flux / metal ratio (%)" means the ratio (mass %) of the flux activator to the conductive particles.

[0081] (1) Adhesion (Adhesive Strength) Approximately 0.5 mg of the conductive adhesive composition was applied onto a copper plate with silver plating, and a rectangular flat copper plate with tin plating having dimensions of 2 mm × 2 mm × 0.25 mm was pressure-bonded thereon to obtain a test piece. A thermal history of 150°C for 10 minutes was applied to the obtained test piece. However, for the test piece of Comparative Example 23, a thermal history of 260°C for 10 minutes was applied. The adhesive strength (shear strength) at 25°C of each test piece after applying the thermal history was measured using a bond tester (DAGE, model 2400) under the conditions of a shear rate of 500 μm / sec and a clearance of 100 μm.

[0082] (2) Conductivity (Volume Resistivity) Two strip-shaped copper plates with gold plating having dimensions of 1 mm × 50 mm × 0.03 mm were bonded to each other orthogonally via the conductive adhesive composition to obtain a test piece. The dimensions of the adhesive at the orthogonal part of the copper plates were 1 mm × 1 mm × 0.03 mm. Subsequently, a thermal history similar to the evaluation method of "(1) Adhesion" was applied to the test piece. Thereafter, the volume resistivity of each test piece was measured by the four-terminal method.

[0083] (3) Resistance to TCT A thin FR4 substrate in the shape of a rectangular flat plate with dimensions of 100 mm × 50 mm × 0.5 mm was prepared, which had two adjacent copper foil lands (0.2 mm × 0.4 mm) with a distance of 100 μm between the copper foil lands. A conductive adhesive composition was printed on the copper foil lands using a metal mask (thickness 100 μm, opening dimension 0.2 mm × 0.3 mm). On top of that, a small chip resistor (0.2 mm × 0.4 mm) with an electrode distance of 100 μm was placed such that the electrodes and the copper foil lands faced each other through the conductive adhesive composition. The obtained component-mounted substrate was given the same thermal history as the evaluation of "(1) Adhesion" to obtain a test substrate for the TCT resistance evaluation. The initial resistance of this test substrate was confirmed using a simple tester. Then, the test substrate was subjected to a thermal shock test using a thermal shock tester, with a temperature change sequence of holding at -55°C for 30 minutes, heating to 125°C in 5 minutes, holding at 125°C for 30 minutes, and cooling to -55°C in 5 minutes as one cycle. The connection resistance of the test substrate after the thermal shock test was measured. The connection resistance of the test substrate was measured while increasing the number of cycles, and the maximum number of cycles showing a resistance change rate within ±10% of the initial resistance was used as an index for the TCT resistance.

[0084] (4) Reflow resistance at 260°C A thin FR4 substrate in the shape of a rectangular flat plate with dimensions of 100 mm × 50 mm × 0.5 mm was prepared, which had two adjacent copper foil lands (0.2 mm × 0.4 mm) with a distance of 100 μm between the copper foil lands. A conductive adhesive composition was printed on the copper foil lands using a metal mask (thickness 100 μm, opening dimension 0.2 mm × 0.3 mm). On top of that, a small chip resistor (0.2 mm × 0.4 mm) with an electrode distance of 100 μm was placed such that the electrodes and the copper foil lands faced each other through the conductive adhesive composition. The obtained component-mounted substrate was given the same thermal history as the evaluation of "(1) Adhesion" to obtain a test substrate for the reflow resistance at 260°C evaluation.

[0085] The initial resistance of this test substrate was measured using a simple tester. Subsequently, the test substrate was subjected to a reflow test in which it was heated at a 260°C reflow profile (heating at a maximum temperature of 260°C for 30 seconds) using a reflow simulator device (manufactured by Sanyo Seiko Co., Ltd., high-temperature observation device SK-5000). After conducting the reflow test three times, the connection resistance of the test substrate was measured, and the ratio of the connection resistance after the reflow test to the connection resistance before the reflow test was defined as the resistance change rate. In the table, "good" means that the resistance change rate was within ±10%, and "bad" means that the resistance change rate exceeded ±10%.

[0086]

Table 1

[0087]

Table 2

[0088]

Table 3

[0089] Examples 1 to 16 all showed good adhesive strength, volume resistivity, TCT resistance, and 260°C reflow resistance. Almost no warping of the test substrate was observed. In Comparative Examples 1 to 8, it was confirmed that the 260°C reflow resistance decreased and the TCT resistance decreased compared to Examples 1 to 16. In Comparative Examples 9 to 20, although the 260°C reflow resistance was good, the volume resistivity increased, and the adhesive strength and TCT resistance decreased. This suggested that the fusibility of the solder particles decreased and connection failures occurred. In Comparative Example 21, the 260°C reflow resistance was good, but the adhesive strength and TCT resistance decreased compared to Examples 1 to 16. In Comparative Example 22, the adhesive strength, volume resistivity, TCT resistance, and 260°C reflow resistance deteriorated compared to Examples 1 to 16. In Comparative Example 23, when heating and connecting at 260°C, the substrate warped significantly and the connection part was damaged. Therefore, the TCT resistance and 260°C reflow resistance could not be measured.

Description of Symbols

[0090] 1... Connection structure, 2... Circuit board, 3... Electronic component, 4... Main body of the electronic component, 5... Base material, 6... Connection terminal of the electronic component, 7... Connection terminal of the circuit board, 8... Connection part, 8a... Conductive part, 8b... Resin part, 10... Solder ball.

Claims

1. (A) conductive particles, (B) a thermosetting resin, and (C) a flux activator, and the conductive particles contain a metal having a melting point of 200°C or lower, in the volume-based cumulative particle size distribution of the conductive particles, the cumulative 50% particle size D50 is 3 to 10 μm, and the cumulative 10% particle size D10 is 2.4 μm or more, the flux activator contains a compound having a hydroxyl group and a carboxyl group, the content of the flux activator is 1.0 to 3.9% by mass based on the amount of the conductive particles, used for electrically connecting a circuit board and an electronic component mounted on the circuit board, a conductive adhesive composition, wherein the content of the conductive particles is 30 to 95% by mass based on the total mass of the conductive adhesive composition.

2. The conductive adhesive composition according to claim 1, wherein in the volume-based cumulative particle size distribution of the conductive particles, the cumulative 90% particle size D90 is 12 μm or less.

3. The conductive adhesive composition according to claim 1 or 2, wherein in the volume-based cumulative particle size distribution of the conductive particles, the minimum particle size Dmin is 1.0 μm or more.

4. The conductive adhesive composition according to any one of claims 1 to 3, wherein in the volume-based cumulative particle size distribution of the conductive particles, the maximum particle size Dmax is 20 μm or less.

5. The conductive adhesive composition according to any one of claims 1 to 4, wherein the metal having a melting point of 200°C or lower contained in the conductive particles contains at least one selected from bismuth, indium, tin, and zinc.

6. The conductive adhesive composition according to any one of claims 1 to 5, wherein the thermosetting resin contains an epoxy resin.

7. The conductive adhesive composition according to claim 6, further containing (D) a curing catalyst.

8. The circuit board has a base material and two or more connection terminals disposed on a main surface of the base material, and is used for electrically connecting the two or more connection terminals and connection terminals of the electronic component. The conductive adhesive composition according to any one of claims 1 to 7.

9. Preparing a circuit board having two or more connection terminals and an electronic component having two or more connection terminals, and disposing the conductive adhesive composition according to any one of claims 1 to 8 on the connection terminals of the circuit board or the connection terminals of the electronic component. A step of disposing the electronic component on the circuit board such that the connection terminal of the circuit board and the connection terminal of the electronic component face each other through the conductive adhesive composition, to obtain a temporary connection body having the circuit board, the conductive adhesive composition, and the electronic component; A step of heating the temporary connection body to form a connection portion having a conductive portion formed from conductive particles in the conductive adhesive composition, the conductive portion electrically connecting the connection terminal of the circuit board and the connection terminal of the electronic component, and a resin portion formed around the conductive portion, and obtaining a connection structure in which the circuit board and the electronic component are joined by the connection portion; A method for manufacturing a connection structure, including the above steps.

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