JP2011113804A - Conductive particulate, anisotropic conductive material, and connection structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide conductive fine particles capable of achieving high connection reliability, and capable of simplifying a connection process of an electrode, to provide an anisotropic conductive material with the use of the conductive fine particles, and to provide a connection structure. <P>SOLUTION: The conductive fine particles include conductive base material particles with a low-melting-point metal layer formed on a surface of the base fine particles, and a microcapsule containing solder flux which has a polar group on an outer surface of a shell, the microcapsule containing solder flux is firmly fixed to a surface of the low-melting-point metal layer, and a content of the microcapsule containing solder flux is to be 0.04 to 4 vol%. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention provides conductive fine particles that can realize high connection reliability and can simplify the electrode connection process, an anisotropic conductive material using the conductive fine particles, and connection Concerning the structure.

Conventionally, in an electronic circuit board, ICs and LSIs are connected by soldering electrodes to a printed circuit board. However, soldering cannot efficiently connect the printed circuit board to the IC or LSI. In addition, it is difficult to improve the mounting density of ICs and LSIs by soldering.
In order to solve this problem, a BGA (ball grid array) has been developed in which the solder is made into a spherical shape, so-called “solder balls” that connect the IC or LSI to the substrate. According to this technology, an electronic circuit that achieves both high productivity and high connection reliability can be manufactured by melting a solder ball mounted on a chip or a substrate at a high temperature and connecting the substrate and the chip.

As another method for connecting between electronic circuit boards, an anisotropic conductive material in which conductive fine particles are dispersed in an insulating resin binder is applied to the electrode surface and thermocompression bonded, so that adjacent electrodes can be connected to each other. It is also possible to manufacture an electronic circuit that achieves both high productivity and high connection reliability by connecting a plurality of electrodes together while ensuring insulation.

However, in recent years, since the number of substrates has been increased and multilayer substrates are easily affected by the use environment, there has been a problem that distortion and expansion / contraction occur in the substrates and disconnection occurs in the connection portion between the substrates.

For such a problem, Patent Document 1 discloses that a metal layer containing a highly conductive metal is formed on the surface of resin fine particles, and further, a low melting point metal made of a metal such as tin on the surface of the metal layer. A conductive fine particle having a layer formed therein is disclosed. If such conductive fine particles are used, the stress applied to the conductive fine particles by the flexible resin fine particles can be relaxed, and the low melting point metal layer is formed on the outermost surface, so that the electrodes can be easily conductive. Can be connected.

On the other hand, when joining by soldering, flux is usually applied to the electrode surface which is a joint for the purpose of improving the wettability of the solder.
However, in the connection by BGA, the flux applied to the electrode becomes unnecessary after the electrode is connected, and the excess flux may cause various harmful effects. There was a need to do. Therefore, there is a problem that a process for cleaning the flux is required separately and an organic solvent must be used for the cleaning process.
In addition, when connecting between electrodes as an anisotropic conductive material, there is a problem that flux cannot be applied to the electrodes because the adhesion of the binder resin is hindered.

In order to solve these problems, Patent Document 2 describes conductive fine particles obtained by combining microcapsules encapsulating a flux on the outer surface of a fine particle of a substrate having a metal layer using a hot melt adhesive. . By using a microcapsule containing such a flux, a minimum amount of flux can be eluted only at the periphery of the substrate fine particles during heating.
However, with such conductive fine particles, there has been a problem that the microcapsules and the conductive fine particles are aggregated in the step of combining the microcapsules with the base fine particles. Further, regarding the case where the electrodes are connected as an anisotropic conductive material, the adhesive is volatilized when heated, causing problems such as voids.

In addition, regarding the case of connecting electrodes as an anisotropic conductive material, Patent Document 3 discloses a solder composition containing a lead-free SnZn-based alloy and a soldering flux containing at least an epoxy resin and an organic carboxylic acid. By using such a solder composition, it is said that it is not necessary to wash the flux, and it is possible to prevent changes over time such as printability and solderability.
However, when the flux is directly mixed in the solder composition, there has been a problem that the deterioration of the binder resin proceeds. In addition, in order for each conductive fine particle contained in the solder composition to exhibit sufficient wettability, it is necessary to add a large amount of flux.

JP 2001-220691 A Japanese Patent Laid-Open No. 2003-247083 JP 2003-010997 A

The present invention provides conductive fine particles that can realize high connection reliability and can simplify the electrode connection process, an anisotropic conductive material using the conductive fine particles, and connection An object is to provide a structure.

The present invention relates to conductive fine particles comprising conductive base particles having a low melting point metal layer formed on the surface of the base fine particles, and flux-encapsulating microcapsules having polar groups on the outer surface of the shell, wherein the flux The encapsulated microcapsules are conductive fine particles that are fixed to the surface of the low-melting-point metal layer, and the content of the flux-encapsulated microcapsules is 0.04 to 4 vol%.
The present invention is described in detail below.

The conductive fine particles of the present invention are conductive fine particles having conductive base material particles having a low melting point metal layer formed on the surface of the base material fine particles, and flux-encapsulating microcapsules having polar groups on the outer surface of the shell. The flux-encapsulating microcapsules are fixed to the surface of the low melting point metal layer.
In the conductive fine particles of the present invention, the flux-encapsulated microcapsules are fixed to the surface of the low melting point metal layer, so that when the low melting point metal layer is melted to conduct conductive connection, the encapsulated flux is externally exposed. Elute. This eliminates the need for a flux application process that has been performed in the past, and further eliminates a minimum required flux, thereby eliminating the need for a surplus flux cleaning process. As a result, the electrode connection process can be greatly simplified. Further, the generation of extra flux does not cause deterioration of the working environment.
Furthermore, as compared with the case where the microcapsules enclosing the flux are fixed to the surface with a hot melt adhesive, not only can they be manufactured easily, but also the occurrence of problems such as detachment of the microcapsules can be prevented.
In addition, unlike the case where the flux is directly mixed into the solder composition, the binder resin is hardly contaminated.

FIG. 1 is a cross-sectional view showing an example of conductive fine particles of the present invention. As shown in FIG. 1, the conductive fine particles of the present invention are composed of base material fine particles 1, a low melting point metal layer 2, and flux-encapsulating microcapsules 5 that enclose a flux 3 in a shell 4. The structure is such that the flux-encapsulating microcapsules 5 are fixed to the surface of the melting point metal layer 2.
FIG. 2 is a cross-sectional view showing a state where the conductive fine particles of the present invention are connected to an electrode. As shown in FIG. 2, when the low melting point metal layer 2 is melted by heat, the shell 4 of the flux-encapsulating microcapsule 5 is also destroyed by heat, so that the flux 3 ′ is eluted on the electrode 6. In this case, the amount of flux 3 ′ is the minimum necessary, and the structure exists only on the vicinity of the electrode 6.

The substrate fine particles are not particularly limited, and examples thereof include resin fine particles, inorganic fine particles, organic-inorganic hybrid fine particles, and metal fine particles. As the substrate fine particles, resin fine particles are particularly preferable.

The resin fine particles are not particularly limited, and include, for example, polyolefin resin, acrylic resin, polyalkylene terephthalate resin, polysulfone resin, polycarbonate resin, polyamide resin, phenol formaldehyde resin, melamine formaldehyde resin, benzoguanamine formaldehyde resin, urea formaldehyde resin, and the like. Resin fine particles.
The polyolefin resin is not particularly limited, and examples thereof include polyethylene resin, polypropylene resin, polystyrene resin, polyisobutylene resin, and polybutadiene resin. The acrylic resin is not particularly limited, and examples thereof include polymethyl methacrylate resin and polymethyl acrylate resin. These resins may be used alone or in combination of two or more.

The method for producing the resin fine particles is not particularly limited, and examples thereof include a polymerization method, a method using a polymer protective agent, and a method using a surfactant.
The polymerization method is not particularly limited, and examples thereof include emulsion polymerization, suspension polymerization, seed polymerization, dispersion polymerization, and dispersion seed polymerization.

The inorganic fine particles are not particularly limited, and examples thereof include fine particles composed of metal oxides such as silica and alumina. The organic-inorganic hybrid fine particles are not particularly limited, and examples thereof include hybrid fine particles containing an acrylic polymer in an organosiloxane skeleton.
The metal fine particles are not particularly limited, and examples thereof include fine particles made of metals such as aluminum, copper, nickel, iron, gold, and silver. Of these, copper fine particles are preferred. The copper fine particles may be copper fine particles formed substantially only of copper metal, or may be copper fine particles containing copper metal. In addition, when the said base material microparticles | fine-particles are copper microparticles | fine-particles, it is not necessary to form the conductive layer mentioned later.

When the substrate fine particles are resin fine particles, the preferred lower limit of the 10% K value of the fine resin particles is 1000 MPa, and the preferred upper limit is 15000 MPa. If the 10% K value is less than 1000 MPa, the resin fine particles may be destroyed when the resin fine particles are compressed and deformed. When the 10% K value exceeds 15000 MPa, the conductive fine particles may damage the electrode. The more preferable lower limit of the 10% K value is 2000 MPa, and the more preferable upper limit is 10,000 MPa.

The 10% K value is obtained by using a micro compression tester (for example, “PCT-200” manufactured by Shimadzu Corporation), and using a smooth indenter end face of a diamond cylinder having a diameter of 50 μm and a compression speed of 2.6 mN / The compression displacement (mm) when compressed under conditions of seconds and a maximum test load of 10 g can be measured and determined by the following equation.
K value ^{(N / mm 2) = (} 3 / √2) · F · S -3/2 · R -1/2
F: Load value at 10% compression deformation of resin fine particles (N)
S: Compression displacement (mm) in 10% compression deformation of resin fine particles
R: radius of resin fine particles (mm)

The average particle diameter of the substrate fine particles is not particularly limited, but a preferable lower limit is 1 μm and a preferable upper limit is 2000 μm. When the average particle diameter of the above-mentioned substrate fine particles is less than 1 μm, the substrate fine particles are likely to aggregate. When conductive fine particles in which a low melting point metal layer is formed on the surface of the aggregated substrate fine particles are used, a gap between adjacent electrodes can be obtained. May cause a short circuit. When the average particle diameter of the base material fine particles exceeds 2000 μm, the range suitable for connection between electrodes such as a circuit board may be exceeded. The more preferable lower limit of the average particle diameter of the substrate fine particles is 3 μm, and the more preferable upper limit is 1000 μm.
The average particle size of the above-mentioned substrate fine particles is obtained by measuring the particle size of 50 randomly selected substrate fine particles using an optical microscope or an electron microscope and arithmetically averaging the measured particle sizes. Can do.

The coefficient of variation of the average particle diameter of the substrate fine particles is not particularly limited, but is preferably 10% or less. If the coefficient of variation exceeds 10%, the connection reliability of the conductive fine particles may be lowered. The coefficient of variation is a numerical value obtained by dividing the standard deviation obtained from the particle size distribution by the average particle size and expressed as a percentage (%).

The shape of the substrate fine particles is not particularly limited as long as the distance between the opposing electrodes can be maintained, but a true spherical shape is preferable. Further, the surface of the substrate fine particles may be smooth or may have a protrusion.

In the conductive fine particles of the present invention, a flux-encapsulating microcapsule that encloses a flux is fixed to the surface of the low melting point metal layer. In the present invention, since the flux-encapsulated microcapsules are directly bonded to the low melting point metal layer, there is no problem as in the case of bonding using an adhesive, and the microcapsules are detached when mounting or mixing the binder. Defects caused by the are less likely to occur.

The flux-encapsulating microcapsule is composed of a shell and a flux.
The flux used for the above-mentioned capsule containing the flux is not particularly limited. For example, an inactive rosin flux mainly composed of rosins such as rosin and rosin derivatives, and an active rosin mainly composed of the above rosins and an activator. Examples thereof include flux, carboxylic acid, and flux mainly composed of dicarboxylic acid.
The activator is not particularly limited, and examples thereof include organic acid or inorganic acid salts of amine compounds such as triethanolamine hydrochloride, triethylenetetramine hydrochloride, cyclohexylamine hydrochloride, and aniline hydrochloride.
The carboxylic acid is not particularly limited, and examples thereof include stearic acid, adipic acid, anthranilic acid, lauric acid, glycolic acid, azelaic acid, succinic acid, and sebacic acid.

Moreover, in the electroconductive fine particle of this invention, a commercially available flux can be used as it is as a flux by using a flux inclusion microcapsule. Therefore, it has an advantage that a commercially available flux that has been activated in advance can be suitably used.
Furthermore, a wide range of fluxes can be used regardless of the form of flux such as liquid or paste.

As the shell of the flux-encapsulating microcapsule, a material having a polar group on the outer surface and capable of encapsulating the flux inside thereof and being melted or broken by heating below the melting point of the low melting point metal layer is particularly used. For example, polymers such as methyl (meth) acrylate, ethyl (meth) acrylate, (meth) acrylic acid, acrylonitrile, methacrylonitrile, vinylidene chloride, copolymers thereof, polyvinyl alcohol (Poval), Examples include ethylene-vinyl alcohol copolymer (eval), polystyrene, polyvinyl pyrrolidone, polyvinyl ether, urea resin, urethane resin, melamine resin, and cellulose derivatives.

When the shell part is a polymer or copolymer obtained by polymerizing a polymerizable monomer such as acrylonitrile, methacrylonitrile, vinylidene chloride, etc., a crosslinked product crosslinked using a polyfunctional polymerizable monomer as a crosslinking agent It is preferable that

Examples of the polyfunctional polymerizable monomer include trimethylolpropane triacrylate, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, 1.6-hexanediol di (meth) ) Acrylate, trimethylolpropane di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, divinylbenzene, butadiene and the like.

The flux-encapsulating microcapsule has a polar group on the outer surface of the shell. By having the said polar group, it adheres to a low melting-point metal layer by hetero-aggregation, and can detach | leave the flux inclusion microcapsule.
As the polar group, for example, at least one functional group selected from the group consisting of a sulfonic acid group, a phosphoric acid group, a carboxylic acid group, and a hydroxyl group is preferable.

The flux-encapsulating microcapsules are produced, for example, by dispersing a flux in a solvent, adding a polymerizable monomer such as ethyl (meth) acrylate, acrylonitrile, methacrylonitrile, and polymerizing these polymerizable monomers. be able to.

The lower limit of the content of the flux-encapsulating microcapsules with respect to the total volume of the conductive fine particles of the present invention is 0.04 vol%, and the upper limit is 4 vol%. When the content of the above-described flux-encapsulating microcapsules is less than 0.04 vol%, the amount of flux to be eluted decreases, and the wettability of solder becomes insufficient. If the content of the above-mentioned flux-encapsulating microcapsules exceeds 4 vol%, excessive flux increases, and a cleaning process is required, or when an interelectrode connection is performed as an anisotropic conductive material, excess flux and capsules The volatile content of the shell causes voids. The minimum with preferable content of the said flux inclusion microcapsule is 0.1 vol%, and a preferable upper limit is 2.5 vol%.

A preferable lower limit of 0.1 μm and a preferable upper limit of the average particle size of the flux-encapsulating microcapsules are 100 μm.

Moreover, it is preferable that the average particle diameter of the said flux inclusion | inner_cover microcapsule is 1/10 or less of the average particle diameter of electroconductive base material particle | grains. If it exceeds 1/10 of the average particle diameter of the conductive substrate particles, the flux-encapsulated microcapsules may be easily detached from the surface of the conductive fine particles due to external force.

In the conductive fine particles of the present invention, a low melting point metal layer is formed on the surface of the base fine particles. Since the low-melting-point metal layer is melted and bonded to the electrode by a heating process, connection reliability can be improved.

The low melting point metal layer is made of tin or an alloy of tin and another metal. The said alloy is not specifically limited, For example, a tin-copper alloy, a tin-silver alloy, a tin-bismuth alloy, a tin-zinc alloy, a tin-indium alloy etc. are mentioned. Among these, a tin-silver alloy is preferable because the melting point of the low melting point metal layer to be formed can be lowered.

Further, in order to improve the bonding strength between the low-melting-point metal layer and the electrode, the low-melting-point metal layer includes nickel, antimony, aluminum, iron, gold, titanium, phosphorus, germanium, tellurium, gallium, cobalt, manganese, A metal such as chromium, molybdenum, palladium, or indium may be contained. Especially, since it is excellent in the effect which improves the joining strength of the said low melting metal layer and an electrode, it is suitable to make the said low melting metal fine particle contain nickel, antimony, and aluminum.
The content of the metal in the total of metals contained in the low melting point metal layer is not particularly limited, but a preferred lower limit is 0.0001% by weight and a preferred upper limit is 2% by weight. When the content of the metal is less than 0.0001% by weight, the bonding strength between the low melting point metal layer and the electrode may not be sufficiently obtained. If the metal content exceeds 2% by weight, the melting point of the conductive fine particles may change.

Although the thickness of the said low melting metal layer is not specifically limited, A preferable minimum is 0.1 micrometer and a preferable upper limit is 200 micrometers. When the thickness of the low-melting-point metal layer is less than 0.1 μm, it may not be able to be sufficiently bonded to the electrode even when reflowed and melted. When the thickness of the low-melting-point metal layer exceeds 200 μm, Aggregation tends to occur when the melting point metal layer is formed, and the aggregated conductive fine particles may cause a short circuit between adjacent electrodes. The minimum with more preferable thickness of the said low melting metal layer is 0.2 micrometer, and a more preferable upper limit is 50 micrometers.
The thickness of the low-melting-point metal layer is a thickness obtained by observing and measuring the cross section of 10 randomly selected conductive fine particles with a scanning electron microscope (SEM) and arithmetically averaging the measured values. .

The low melting point metal layer may be formed directly on the surface of the substrate fine particles. In the low melting point metal layer, a conductive layer (underlying metal layer) may be further formed between the low melting point metal layer and the base particle.
The metal forming the conductive layer is not particularly limited, and examples thereof include gold, silver, copper, zinc, iron, lead, tin, aluminum, cobalt, indium, nickel, chromium, antimony, bismuth, germanium, and cadmium. . Especially, since it is excellent in electroconductivity, it is preferable that the metal which forms the said conductive layer is gold, copper, or nickel.

The method for forming the conductive layer on the surface of the substrate fine particles is not particularly limited, and examples thereof include an electroless plating method, an electrolytic plating method, a vacuum deposition method, an ion plating method, and an ion sputtering method.

Although the thickness of the said conductive layer is not specifically limited, A preferable minimum is 0.1 micrometer and a preferable upper limit is 100 micrometers. If the thickness of the conductive layer is less than 0.1 μm, sufficient conductivity may not be obtained. When the thickness of the conductive layer exceeds 100 μm, the flexibility of the conductive fine particles may be lowered. A more preferable lower limit of the thickness of the conductive layer is 0.2 μm, and a more preferable upper limit is 50 μm.
The thickness of the conductive layer is a thickness obtained by observing and measuring a section of 10 randomly selected conductive fine particles with a scanning electron microscope (SEM) and arithmetically averaging them.

The method for producing conductive fine particles of the present invention is not particularly limited as long as the conductive fine particles having the above-described configuration can be obtained. For example, a conductive layer and a low melting point metal layer are formed on the surface of the resin fine particles. In the case of using conductive substrate particles, it can be produced by the following method.

First, in order to form a conductive layer on the surface of the resin fine particles, a nickel layer (hereinafter also referred to as a base nickel plating layer) is formed on the surface of the resin fine particles by an electroless plating method. Next, a conductive layer such as copper is formed on the surface of the underlying nickel plating layer.
The method for forming the conductive layer is not particularly limited, and examples thereof include a method using an electrolytic plating method, an electroless plating method, or the like.

Next, conductive base material particles are produced by forming a low melting point metal layer containing tin on the surface of the conductive layer.
The method for forming the low melting point metal layer is not particularly limited, and examples thereof include a method using an electrolytic plating method.

Next, a flux-encapsulating microcapsule having a polar group on the outer surface of the shell is fixed to the surface of the low melting point metal layer.
The method for fixing the flux-encapsulating microcapsules to the surface of the low melting point metal layer is not particularly limited. For example, the conductive base material particles and the flux-encapsulating microcapsules are mixed in water and mixed by heteroaggregation. Methods and the like.
In the above method, the amount of the flux-encapsulating microcapsules can be controlled by changing the mixing conditions.

The conductive fine particles obtained by such a production method are such that flux-encapsulated microcapsules are fixed to the surface of the low melting point metal layer. Thereby, in the connection by BGA, when conducting the conductive connection by melting the low melting point metal layer, the flux contained therein is eluted to the outside, so that the flux application step which has been conventionally performed is not necessary. Moreover, since only the minimum necessary flux is eluted, the cleaning process of the surplus flux becomes unnecessary, and the electrode connecting process can be greatly simplified. Furthermore, it is possible to prevent the working environment from deteriorating due to the extra flux.

An anisotropic conductive material can be produced by dispersing the conductive fine particles of the present invention in a binder resin. Such an anisotropic conductive material is also one aspect of the present invention.

Examples of the anisotropic conductive material of the present invention include anisotropic conductive paste, anisotropic conductive ink, anisotropic conductive adhesive, anisotropic conductive film, and anisotropic conductive sheet.

The binder resin is not particularly limited, but an insulating resin is used, and examples thereof include a vinyl resin, a thermoplastic resin, a curable resin, a thermoplastic block copolymer, and an elastomer.
Although the said vinyl resin is not specifically limited, For example, a vinyl acetate resin, an acrylic resin, a styrene resin etc. are mentioned.
Although the said thermoplastic resin is not specifically limited, For example, polyolefin resin, ethylene-vinyl acetate copolymer, a polyamide resin etc. are mentioned.
Although the said curable resin is not specifically limited, For example, an epoxy resin, a urethane resin, a polyimide resin, an unsaturated polyester resin etc. are mentioned. The curable resin may be a room temperature curable resin, a thermosetting resin, a photocurable resin, or a moisture curable resin. The curable resin may be used in combination with a curing agent.
The thermoplastic block copolymer is not particularly limited. For example, styrene-butadiene-styrene block copolymer, styrene-isoprene-styrene block copolymer, hydrogenated product of styrene-butadiene-styrene block copolymer, styrene -Hydrogenated product of isoprene-styrene block copolymer.
The elastomer is not particularly limited, and examples thereof include styrene-butadiene copolymer rubber and acrylonitrile-styrene block copolymer rubber.
These resins may be used alone or in combination of two or more.

In addition to the conductive fine particles of the present invention and the above-mentioned binder resin, the anisotropic conductive material of the present invention is, for example, an extender, a plasticizer, and improved adhesiveness within a range that does not hinder the achievement of the present invention. Agents, antioxidants, heat stabilizers, light stabilizers, ultraviolet absorbers, colorants, flame retardants, organic solvents, and the like.

The method for producing the anisotropic conductive material of the present invention is not particularly limited. For example, the conductive fine particles of the present invention are added to the binder resin, and the mixture is uniformly mixed and dispersed. Examples thereof include a method for producing an anisotropic conductive ink, an anisotropic conductive adhesive, and the like. Further, the conductive fine particles of the present invention are added to the binder resin and uniformly dispersed or dissolved by heating, and a predetermined film thickness is applied to a release treatment surface of a release material such as release paper or release film. For example, a method for producing an anisotropic conductive film, an anisotropic conductive sheet or the like by coating may be used.
Moreover, it is good also as an anisotropic conductive material by using separately the said binder resin and the electroconductive fine particles of this invention, without mixing.

A connection structure using the conductive fine particles of the present invention or the anisotropic conductive material of the present invention is also one aspect of the present invention.

The connection structure of the present invention is a conductive connection structure in which a pair of circuit boards are connected by filling the pair of circuit boards with the conductive fine particles of the present invention or the anisotropic conductive material of the present invention. is there.

According to the present invention, conductive fine particles that can realize high connection reliability and can simplify the electrode connection step, an anisotropic conductive material using the conductive fine particles, and A connection structure can be provided.

It is sectional drawing which shows an example of the electroconductive fine particles of this invention. It is sectional drawing which shows the state at the time of connecting the electroconductive fine particles of this invention to an electrode.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

Example 1
(Preparation of conductive fine particles)
A copper layer having a thickness of 1 μm was formed by electroplating on the surface of resin fine particles (average particle diameter 10 μm) made of a copolymer of tetramethylolmethane tetraacrylate and divinylbenzene, to obtain copper layer-forming resin fine particles. A 1.5 μm thick tin layer was formed on the obtained copper layer-forming resin fine particles by electroplating to obtain conductive base particles.
Next, a mixed solution of methyl methacrylate, trimethylolpropane triacrylate, dibutyl ether, azobisisobutyronitrile, flux (Deltalux 523H, manufactured by Senju Metal Industry Co., Ltd.), water, sodium p-styrenesulfonate, GM-14 (Partially saponified polyvinyl alcohol) and a mixed solution of sodium nitrite were prepared, and mixed and emulsified using a homogenizer to prepare an emulsion solution.
Flux-encapsulated microcapsules with an average particle diameter of 1 μm encapsulating the flux were prepared by heating and polymerizing the emulsion while stirring.
Thereafter, 50 g of the obtained conductive substrate particles and 0.0125 g of the flux-encapsulated microcapsules are added to water and mixed using a chemical stirrer, whereby the conductive fine particles having the flux-encapsulated microcapsules fixed to the surface are obtained. Obtained. The amount of the flux-encapsulating microcapsules attached to the entire conductive fine particles was 0.1 vol%.

(Preparation of anisotropic conductive paste)
20 g of the obtained conductive fine particles, 100 g of an epoxy resin (“Epicoat 828” manufactured by Yuka Shell Epoxy Co., Ltd.) as binder resin, 2 g of trisdimethylaminoethylphenol, and 100 g of toluene are sufficiently mixed using a planetary stirrer. An anisotropic conductive paste was obtained.

(Example 2)
Conductive fine particles and anisotropic conductive paste were produced in the same manner as in Example 1 except that the amount of the flux-encapsulating microcapsules was 0.05 vol%.

(Example 3)
Conductive fine particles and anisotropic conductive paste were prepared in the same manner as in Example 1 except that the amount of the flux-encapsulated microcapsules was 2 vol%.

(Comparative Example 1)
Conductive fine particles and anisotropic conductive paste were produced in the same manner as in Example 1, except that the amount of the flux-encapsulating microcapsules was 0.01 vol%.

(Comparative Example 2)
Conductive fine particles and anisotropic conductive paste were produced in the same manner as in Example 1 except that the amount of the flux-encapsulating microcapsules was 5 vol%.

(Comparative Example 3)
Conductive fine particles and anisotropic conductive paste were prepared in the same manner as in Example 1 except that the flux-encapsulating capsule was not fixed to the surface.

(Comparative Example 4)
After applying a hot melt adhesive (Aron Melt PES120L, manufactured by Toa Gosei Co., Ltd.) to the surface of the flux-encapsulating capsule, 50 g of the conductive fine particles and 0.0125 g of the flux-encapsulating microcapsule are mixed while heating, Conductive fine particles and anisotropic conductive paste were prepared in the same manner as in Example 1 except that the flux-encapsulating capsule was fixed.

(Comparative Example 5)
50 g of conductive fine particles obtained in Comparative Example 3, 100 g of epoxy resin (“Epicoat 828” manufactured by Yuka Shell Epoxy Co., Ltd.) as binder resin, 2 g of trisdimethylaminoethylphenol, flux (“Delta Lux 523H” manufactured by Senju Metal Industry Co., Ltd.) ) 0.125 g and 100 g of toluene were sufficiently mixed using a planetary stirrer to obtain an anisotropic conductive paste.

<Evaluation>
The following evaluation was performed about the electroconductive fine particles obtained by the Example and the comparative example. The results are shown in Table 1.

(1) Viscosity increase rate The viscosity of the obtained anisotropic conductive paste is 25 ° C. and 50% environment under an E-type viscometer (trade name: VISCOMETER TV-22, manufactured by TOKI SANGYO CO. LTD, rotor used: (φ15 mm). Then, after leaving it for 2 days under the same conditions, the viscosity was further measured, and the viscosity increase rate was measured from the obtained value.

(2) Leakage confirmation The anisotropic conductive paste obtained was applied to a glass substrate having 10 aluminum electrodes having a line width of 50 μm and a line spacing of 50 μm on the line, and a glass substrate having the same aluminum electrode was applied to each glass substrate. The connection structure was obtained by aligning the electrodes so that the electrodes face each other and overlap, and bonding them together.
This connection structure was subjected to thermocompression bonding at 250 ° C. from both bottom surfaces of the glass substrate, interelectrode bonding by melting of the low melting point metal layer, and thermosetting of the binder resin.
Next, the obtained connection structure was subjected to a thermal fatigue test at 125 ° C. for 250 hours to confirm the continuity between the electrodes after the test and the presence or absence of leakage between the adjacent electrodes.

According to the present invention, conductive fine particles that can realize high connection reliability and can simplify the electrode connection step, an anisotropic conductive material using the conductive fine particles, and A connection structure can be provided.

Claims (10)

Conductive fine particles having conductive base particles in which a low melting point metal layer is formed on the surface of the base fine particles, and flux-encapsulating microcapsules having polar groups on the outer surface of the shell,
The flux-encapsulating microcapsule is fixed to the surface of the low melting point metal layer,
And the content of the said flux inclusion | inner_cover microcapsule is 0.04-4 vol%, The electroconductive fine particles characterized by the above-mentioned. The conductive fine particle according to claim 1, wherein the polar group is at least one functional group selected from the group consisting of a sulfonic acid group, a phosphoric acid group, a carboxylic acid group, and a hydroxyl group. The conductive fine particles according to claim 1 or 2, wherein the average particle size of the flux-encapsulating microcapsules is 1/10 or less of the average particle size of the conductive base particles. The conductive fine particles according to claim 1, 2 or 3, wherein the flux-encapsulating microcapsules are melted or broken by heating below the melting point of the low melting point metal layer. 5. The conductive fine particles according to claim 1, 2, 3, or 4, wherein the low melting point metal layer is made of tin or an alloy of tin and another metal. The conductive fine particles according to claim 1, wherein the base fine particles are resin fine particles. 6. The conductive fine particles according to claim 1, wherein the base fine particles are copper fine particles. The conductive fine particles according to claim 1, 2, 3, 4, 5, 6 or 7, further comprising a conductive layer between the substrate fine particles and the low melting point metal layer. An anisotropic conductive material, wherein the conductive fine particles according to claim 1, 2, 3, 4, 5, 6, 7 or 8 are dispersed in a binder resin. A connection structure comprising the conductive fine particles according to claim 1, 2, 3, 4, 5, 6, 7 or 8, or the anisotropic conductive material according to claim 9.

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