JP2001151894A - Electroconductive fine particle and electroconductive joint structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a monodispersion organic electroconductive fine particles having uniform shapes and a narrow particle diameter distribution, and further to provide an electroconductive joint structure by using the electroconductive fine particles. SOLUTION: This electroconductive fine particles are obtained by using polymer articles having 0.1-10 μm particle diameters as seed particles, allowing the seed particles to absorb a monomer in an amount of 10-500 times as much as that of the seed particles expressed in terms of weight, polymerizing the monomer to provide monodispersion fine particles, and subjecting the resultant monodispersion fine particles to a treatment for making the particles electroconductive. The electroconductive joint structure is obtained by using the electroconductive fine particles.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to conductive fine particles, and more particularly, to a conductive adhesive for mounting a micro element, an anisotropic conductive adhesive, or a conductive material for an anisotropic conductive sheet. The present invention relates to conductive fine particles used.

[0002]

2. Description of the Related Art In the field of electronic packaging, in order to connect opposing fine electrodes, a conductive paste is prepared by mixing metal particles such as gold, silver, and nickel and a binder resin, and the paste is mixed with the corresponding fine electrodes. The connection between the fine electrodes is performed by filling between the electrodes. However, it is difficult to uniformly disperse such metal particles in the binder resin because of their non-uniform shape and higher specific gravity than the binder resin.

On the other hand, it has been reported that fine particles are synthesized by polymerizing an organic polymer and a metal plating layer is formed on the surface of the fine particles to form conductive fine particles. Since particles having a wide diameter distribution were formed, they could not be directly used as a base material for conductive fine particles. Therefore, uniform fine particles were produced by a classifying process and used as a base material for the conductive fine particles. However, classification has drawbacks such as a long lead time when producing a product, and difficulty in obtaining monodispersed particles due to swelling and specific gravity depending on the base material.

[0004]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and is intended to provide monodispersed organic conductive fine particles having a uniform shape and a narrow particle size distribution, and the conductive fine particles. It is an object to provide a conductive connection structure used.

[0005]

SUMMARY OF THE INVENTION The present invention relates to conductive fine particles obtained by conducting conductive treatment on organic fine particles suitable for use as a base material for conductive fine particles, and a conductive connection structure using the conductive fine particles.

[0006] The invention according to claim 1 has a particle diameter of 0.1 to 0.1.
The polymer particles of 10 μm are used as seed particles, and the monodispersed fine particles obtained by polymerizing the monomers, in which the monomer and the initiator are absorbed in a weight ratio of 10 to 500 times the seed particles, are subjected to a conductive treatment. The conductive fine particles obtained by the above method.

According to a second aspect of the present invention, there is provided the conductive fine particles according to the first aspect, wherein the seed particles have a CV value of 8% or less.

[0008] The invention according to claim 3 is a method for preparing monodispersed fine particles of C
3. The conductive fine particles according to claim 1, having a V value of 8% or less.

According to a fourth aspect of the present invention, there is provided a conductive connection structure using the conductive fine particles according to any one of the first to third aspects.

In the present invention, the polymerizable monomer used for producing the seed particles is not particularly limited.
Styrene, α-methylstyrene, p-methylstyrene,
styrene derivatives such as p-chlorostyrene and chloromethylstyrene; vinyl chloride; vinyl esters such as vinyl acetate and vinyl propionate; unsaturated nitriles such as acrylonitrile; methyl (meth) acrylate, ethyl (meth) acrylate; Butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, stearyl (meth) acrylate, ethylene glycol (meth) acrylate, trifluoroethyl (meth) acrylate, pentafluoropropyl (meth) acrylate, cyclohexyl (meth) (Meth) acrylic acid ester derivatives such as acrylate and the like can be mentioned. These monomers may be used alone or in combination of two or more.

The particle size of the seed particles used in the present invention can be appropriately selected according to the finally required particle size.
0.1 to 10 μm. When the particle diameter of the seed particles is 0.1 to 1
If it is 10 μm, conductive fine particles suitably used for a conductive adhesive for mounting a micro element, an anisotropic conductive adhesive or an anisotropic conductive sheet can be obtained. The particle size of the seed particles is 0.
When the particle diameter is less than 1 μm, the particle diameter of the obtained conductive fine particles is too small, and when connecting between the electrodes, good connection is not obtained, and poor conduction is likely to occur.
If it exceeds 0 μm, the resulting conductive fine particles will have a too large particle diameter, causing a leak between adjacent electrodes, or causing a problem that when mixed with a binder, it is easy to settle and it is difficult to produce a uniform conductive adhesive. It will be easier. Furthermore, when producing the seed particles, if the particle diameter is in the range of 0.1 to 10 μm, monodisperse polymer particles can be easily obtained by soap-free polymerization and dispersion polymerization. If it deviates, it will be difficult to obtain particles having a narrow particle size distribution.

The particle size distribution of the seed particles is not particularly limited, but is reflected in the particle size distribution of fine particles obtained by absorbing and polymerizing a monomer (seed polymerization). As described above, the CV value of the seed particles is preferably 8% or less, more preferably 5% or less. The above CV value is represented by the following equation. CV (%) = (standard deviation (σ) / average particle diameter (Dn)) × 100

The above-mentioned seed particles can be synthesized by ordinary polymerization methods such as soap-free polymerization, dispersion polymerization, and emulsion polymerization. Among them, soap-free polymerization, dispersion polymerization, and dispersion polymerization suitable for synthesis of particles having a narrow particle distribution. Is desirable.

The type of the monomer to be absorbed by the seed particles is as follows:
There is no particular limitation, and it can be appropriately selected according to the physical properties of the conductive fine particles. Specifically, the following monomers are mentioned as examples. That is, styrene, α-methylstyrene, p-
Styrene derivatives such as methylstyrene, p-chlorostyrene, chloromethylstyrene; vinyl chloride; vinyl acetate;
Vinyl esters such as vinyl propionate; unsaturated nitriles such as acrylonitrile; methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, (meth) (Meth) such as stearyl acrylate, ethylene glycol (meth) acrylate, trifluoroethyl (meth) acrylate, pentafluoropropyl (meth) acrylate, and cyclohexyl (meth) acrylate
Acrylic ester derivatives may be mentioned.

The above monomers further include divinylbenzene, polyethylene glycol di (meth) acrylate such as 1,6-hexanediol di (meth) acrylate and ethylene glycol di (meth) acrylate, and propylene glycol di (meth) acrylate. Polypropylene glycol di (meth) acrylate such as acrylate, polytetramethylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, 1,3-butylene glycol di (meth) acrylate, 2,2-bis [4- 2,2-bis [4- (methacryloxypolyethoxy) phenyl] propanedi (meth) acrylate such as (methacryloxyethoxy) phenyl] propanedi (meth) acrylate, 2,2-hydrogenated bis [4- (acryloxypoly) Ethoxy) Nyl] propanedi (meth) acrylate, di (meth) acrylates such as 2,2-bis [4- (acryloxyethoxypolypropoxy) phenyl] propanedi (meth) acrylate; conjugated dienes such as butadiene and isoprene; diallyl phthalate And its isomers; trimethylolpropane tri (meth) acrylate and derivatives thereof, tetramethylolmethane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, tetramethylolpropane tetra (meth) acrylate, pentaerythritol tetra (meth) acrylate And trifunctional or more (meth) acrylates such as dipentaerythritol hexa (meth) acrylate; triallyl isocyanurate and derivatives thereof. These monomers may be used alone or in combination of two or more.

The amount of the monomer to be absorbed by the seed particles is 10 to 500 times, preferably 20 to 100 times, the weight ratio of the seed particles. Within this range, conductive fine particles suitable for use in conductive adhesives for mounting microelements, anisotropic conductive adhesives or anisotropic conductive sheets can be obtained. The body component undergoes phase separation, resulting in non-uniform particles such as porous and hollow,
If it exceeds twice, monomers that cannot be absorbed by the seed particles will be generated,
The particle size distribution is widened, and aggregation of particles occurs.

In the present invention, the above monomer is finely dispersed in water together with an initiator to prepare a monomer emulsion, which is then absorbed by seed particles. Specifically, for example, after dissolving an emulsifier in water, a monomer and an initiator are added to prepare a mixture. This mixture may be emulsified by a fine emulsifier such as a homogenizer, ultrasonic treatment, or a nanomizer. In the present invention, the above-mentioned monomer emulsion is mixed with an aqueous dispersion of seed particles, and polymerization is carried out after the monomer and the initiator are absorbed in the seed particles. This absorption process is usually achieved by mixing the seed particles and the monomer emulsion and stirring for 1 to 24 hours. The end of absorption can be confirmed by observing with an optical microscope.

The polymerization initiator added to the monomer emulsion and used at the time of seed polymerization includes, for example, benzoyl peroxide, lauroyl peroxide, orthochlorobenzoyl peroxide, orthomethoxybenzoyl peroxide, 3,5,5 Organic peroxides such as -trimethylhexanoyl peroxide, t-butylperoxy-2-ethylhexanoate, di-t-butyl peroxide, azobisisobutyronitrile, azobiscyclohexacarbonitrile, azobis ( Azo compounds such as 2,4-dimethylvaleronitrile). Usually, the amount of the polymerization initiator used is preferably 0.1 to 10 parts by weight based on 100 parts by weight of the monomer.

At the time of seed polymerization, a dispersion stabilizer can be used if necessary. Such a dispersion stabilizer is generally a polymer that is soluble in a medium, and examples thereof include polyvinyl alcohol, polyvinyl pyrrolidone, methyl cellulose, ethyl cellulose, polyacrylic acid, polyacrylamide, and polyethylene oxide. A nonionic or ionic surfactant is also used as appropriate.

The CV value of the monodisperse fine particles of the present invention is preferably 8% or less. When the CV value exceeds 8%, particles having an excessively large or small particle size are present, which is not preferable during use. That is, when particles having an excessively large particle diameter are present, a leak occurs between adjacent electrodes when the electrode gap is small, or a large press-press brush is used for connection, which easily damages the substrate. On the other hand, if particles having an excessively small particle size are present, particles not involved in conduction increase, which is not preferable.

There is no particular limitation on the method for imparting conductivity to the monodisperse fine particles of the present invention. For example, the monodisperse fine particles may be used as base particles, and the surface thereof may be coated with a conductive material to form a conductive layer. can get. The metal used for the conductive layer is not particularly limited, for example, nickel,
Examples include gold, silver, copper, cobalt, tin, indium, ITO, and alloys containing these as main components.

The method of forming a metal layer on the surface of the above-mentioned monodisperse fine particles is not particularly limited. For example, a method of electroless plating, a method of coating a fine particle with a paste obtained by mixing a metal fine powder alone or with a binder, or the like. And physical vapor deposition methods such as vacuum vapor deposition, ion plating, and ion sputtering. A method of forming a metal layer by the above-described electroless plating method will be described below, taking the case of gold displacement plating as an example.

This method is divided into the following etching step, activation step, chemical nickel plating step, and gold displacement plating step. The etching step is a pretreatment step for improving the adhesion of the plating layer to the fine particles by forming irregularities on the surface of the fine particles. Examples of the etching solution include caustic soda aqueous solution, concentrated hydrochloric acid, concentrated sulfuric acid, and chromic anhydride. Is included. The activation step is a step for forming a catalyst layer on the surface of the etched fine particles and activating the catalyst layer. The activation of the catalyst layer promotes the deposition of metallic nickel in a chemical nickel plating step described below.
By dispersing the fine particles in the catalyst solution, the catalyst layer containing Pd ²⁺ and Sn ²⁺ on the surface of the fine particles is treated with concentrated sulfuric acid or concentrated hydrochloric acid, and Pd ²⁺ is metallized and deposited on the surface of the fine particles.
The metallized palladium is activated and sensitized by a palladium activator such as a concentrated solution of sodium hydroxide.

In the chemical nickel plating step, a metal nickel layer is further formed on the surface of the fine particles on which the catalyst layer has been formed. For example, nickel chloride is reduced with sodium hypophosphite, and nickel is reduced on the surface of the fine particles. To precipitate. In the metal displacement plating step, the fine particles coated with nickel in this way are placed in a potassium gold cyanide solution, and while elevating the temperature, nickel is eluted to deposit gold on the surface of the fine particles. The thickness of the conductive layer (the combined layer of the nickel layer and the gold layer) is preferably 0.02 to 5 μm. When the thickness of the conductive layer is less than 0.02 μm, desired conductivity is hardly obtained. When the thickness exceeds 5 μm, aggregation of the conductive fine particles easily occurs at the time of manufacturing, and the conductive fine particles are disposed between the electrodes facing each other. When both electrodes are pressurized by sandwiching them, the flexibility of the conductive fine particles is hardly effectively exhibited.

The conductive fine particles are used as a conductive material such as a conductive adhesive for mounting a micro element, an anisotropic conductive adhesive, and an anisotropic conductive sheet, and are used for bonding substrates or parts. The method for joining the substrate or component is not particularly limited as long as it is a method of joining using conductive fine particles,
For example, the following method can be considered. A method in which an anisotropic conductive sheet is placed on a substrate or component having an electrode formed on the surface, and then a substrate or component having the other electrode surface is placed, and heated and pressed for joining. Instead of using an anisotropic conductive sheet, a method in which an anisotropic conductive adhesive is supplied by means of screen printing, a dispenser or the like, and joined. Further, for example, a method in which a liquid binder is supplied to a gap between two electrode portions bonded to each other with conductive particles interposed therebetween, followed by curing and bonding. In the present invention, the joined body of substrates or components obtained as described above is referred to as a conductive connection structure.

[0026]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. (Preparation of Seed Particle A) Polyvinylpyrrolidone (weight average molecular weight: 30,000, manufactured by Wako Pure Chemical Industries, Ltd .: K-30) in a separable flask reactor equipped with a cooling tube, a stirring blade, and a nitrogen introducing tube.
4 parts by weight, 0.6 parts by weight of anionic surfactant (Aerosol OT, manufactured by Wako Pure Chemical Industries, Ltd.), 2,2′-azobis-2,4
-Dimethylvaleronitrile (V-65, manufactured by Wako Pure Chemical Industries)
Parts by weight was dissolved in a mixture of 82 parts by weight of methanol and 2 parts by weight of ion-exchanged water, and a mixture of 18 parts by weight of styrene and 2 parts by weight of α-methylstyrene was added dropwise while stirring the solution under a nitrogen stream. did. Then, the temperature was raised to 60 ° C,
The reaction was performed for 24 hours. After the completion of the reaction, polymer fine particles were isolated by centrifugation, and washed with methanol several times to obtain seed particles A. When the particle size and the particle size distribution of the seed particles A were measured with a Coulter counter, the average particle size (D
n) was 2.1 μm, and the Cv value was 3.0%.

(Preparation of Seed Particle B)
Was changed to 3 parts by weight, and the same operation as in the preparation method of the seed particles A was performed except that the monomer was only 14 parts by weight of styrene. Dn
Was 1.4 μm and the Cv value was 3.2%.

(Preparation of Seed Particle C) In a separable flask reactor equipped with a cooling pipe, a stirring blade, and a nitrogen introducing pipe, 90 parts by weight of ion-exchanged water, 10 parts by weight of styrene, 2.5 parts by weight of octyl mercaptan, 0.02 parts by weight of sodium was charged, and nitrogen was supplied for 1 hour to replace the inside of the reactor with nitrogen. Then, with stirring, the temperature was raised to 70 ° C.,
The atmosphere was replaced with nitrogen for hours. Next, 0.1 part by weight of potassium persulfate was dissolved in 10 parts by weight of water and added. After this 7
The reaction was performed at 0 ° C. for 24 hours. After completion of the reaction, polymer fine particles were isolated by centrifugation, and washed several times with methanol to obtain seed particles C. Obtained particles were observed using a transmission electron microscope (TEM), and the particle diameter of 500 arbitrary particles in the photographed photograph was measured to determine the average particle diameter and the particle diameter distribution. Dn was 0.67 μm and Cv value was 3.0%.

(Preparation of Seed Particle D) The same operation as in the preparation method of seed particle A was performed except that the charged composition was changed to 14 parts by weight of methyl methacrylate instead of 14 parts by weight of styrene. Dn was 2.4 μm and Cv value was 3.2%.

Example 1 17.5 parts by weight of divinylbenzene, 1.2 parts by weight of benzoyl peroxide (containing 25% water), 175 parts by weight of ion-exchanged water, and 0.35 parts by weight of sodium lauryl sulfate were mixed and finely mixed with a homogenizer. The mixture was dispersed and emulsified to prepare a monomer emulsion. The seed particles A0.5 obtained in the above reaction were placed in a separable flask reactor equipped with a cooling pipe, a stirring blade, and a nitrogen introduction pipe.
Parts by weight, 50 parts by weight of ion-exchanged water and 0.05 parts by weight of sodium lauryl sulfate were added and dispersed uniformly, and a 3% by weight aqueous solution of polyvinyl alcohol (PVA) was added to 20 parts by weight.
A seed particle dispersion was prepared by adding parts by weight. Next, the monomer emulsion was added to the seed particle dispersion, and 25 ° C and 100 rpm.
For 24 hours to allow the monomer emulsion to be absorbed by the seed particles.

Next, nitrogen was purged by flowing nitrogen into the system for 1 hour, and then stirred at 200 rpm at 70 ° C. for 24 hours.
Polymerization was carried out for hours. After completion of the polymerization, fine particles were isolated by centrifugation. Subsequently, washing and centrifugation were performed twice each in the order of ethanol, a mixed medium of ethanol and water, and water to remove extra initiator, monomer, surfactant, and the like, thereby obtaining fine particles. About the obtained particles, the particle diameter and the particle diameter distribution were observed with an electron microscope using a Coulter counter. Table 1 shows the results.

Examples 2 to 6 and Comparative Examples 1 and 2 As shown in Table 1, the same operation as in Example 1 was carried out by changing the seed particles, the kind of the monomer, and the ratio of the monomer to the seed particles. Was. The results are shown in Table 1.

[0033]

[Table 1]

[0034]

According to the first aspect of the present invention, the conductive fine particles have polymer particles having a particle diameter of 0.1 to 10 .mu.m as seed particles, and a monomer and an initiator having a weight ratio of 10 to 500 times the seed particles. Monodisperse fine particles obtained by absorbing an agent and polymerizing a monomer are obtained by conducting treatment, so that the conductive fine particles have a uniform shape and a narrow particle size distribution. In the conductive fine particles according to the second aspect, since the CV value of the seed particles is 8% or less, the effect according to the first aspect can be more reliably achieved. In the conductive fine particles according to the third aspect, since the monodisperse fine particles have a CV value of 8% or less, the effect according to the first or second aspect can be more reliably achieved. The conductive connection structure according to claim 4 is a conductive connection structure excellent in conductivity and connection reliability since the conductive fine particles according to any one of claims 1 to 3 are used.

Claims (4)

[Claims] 1. Polymer particles having a particle size of 0.1 to 10 μm are used as seed particles, and the seed particles absorb a monomer and an initiator in a weight ratio of 10 to 500 times to polymerize the monomer. Conductive fine particles obtained by subjecting the monodispersed fine particles obtained to a conductive treatment. 2. The conductive fine particles according to claim 1, wherein the CV value of the seed particles is 8% or less. 3. The conductive fine particles according to claim 1, wherein the monodisperse fine particles have a CV value of 8% or less. 4. A conductive connection structure comprising the conductive fine particles according to claim 1.