JPH09171714A - Conductive powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain conductivity excellent in durability by coating a spherical resin particle whose surface is coated with gold by dry coating method, further with a gold plating film by electroless plating method. SOLUTION: For example, gold coating is made in advance on the surface of, for example, polystyrene resin particles by dry coating method, setting the quantity of coating to the range of, preferably, 0.05-65wt.%. The surface of this power is further coated with gold by electroless coating. At the time, the principal components of gold salt, a complexing agent, and a reducing agent, and a very small quantity of additive are dissolved in water, and the gold is adjusted with electroless plating solution. As for the gold salt, gold cyanide, and as for the complexing agent, citric acid, and as for the reducing agent, a boric sodium hydroxide or the like, are used, for example. The conductive powder coated with metallic coating by electroless plating is close in coating metallic layer, and is made as a continuous film, so as to obtain conductivity excellent in covering force of the metallic film and excellent in durability.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an electroless plated powder capable of imparting excellent dispersibility, adhesiveness and high conductive performance when compounded in various matrix materials, especially in a plastic material. ACF (anisotropic conductive film), HSC that electrically connects minute parts of electronic devices
The present invention relates to a conductive electroless plated powder suitable for purposes such as (heat seal connector).

[0002]

2. Description of the Related Art Plastic materials with conductivity are
It is widely used as a material for static electricity prevention, electromagnetic wave absorption, electromagnetic wave shielding, etc. of electronic devices and parts. As a method of imparting conductivity to a plastic material, there has been a conventional method of dispersing and compounding a fine powdery conductive filler in a matrix resin component. As such a conductive filler,
For example, alloy powder such as Cu, Fe, Ni and stainless steel,
Metal-based substances such as fibers or foil pieces, carbon-based substances such as graphite powder, carbon black and carbon fibers are generally used.

Other inorganic conductive fillers such as titanium dioxide, silica, mica, silicate, alumina,
An electroless plated powder is known in which the surface of a base material of white powder such as barium sulfate is doped with antimony and coated with stannic oxide. (JP-A-56-41603, JP-A-62-181371, JP-A-2-218768)
Japanese Patent Application Laid-Open No. 5-116930, Japanese Patent Application Laid-Open No. 7-5
As the plated powder product, for example, base metal particles such as stainless steel or nickel coated with a noble metal such as palladium or gold (Japanese Patent Laid-Open No. 60-233166, Japanese Patent Laid-Open No. 2-66101), inorganic powder What is plated on the body (Japanese Patent Laid-Open Nos. 60-181294 and 5
9-182961), plated on various inorganic or organic base materials (JP-A-1-242782),
In addition, there are proposed those in which special resin particles such as benzoguanamine and styrene are plated with metal (JP-A-57-49632 and JP-A-60-12603).

The methods for producing these conductive metal-coated powders are roughly classified into the wet coating methods such as the electroless plating method and the dry coating methods such as the chemical vapor deposition method, the physical vapor deposition method, the alkoxide method and the mechanochemical method. it can. The wet coating method has advantages such as low manufacturing cost and excellent mass productivity, but the conductive performance is insufficient,
In the case of plating, there is a drawback that the choice of metals that can be plated is limited. In particular, when resin particles are coated with a noble metal such as gold by electroless plating, it is necessary to coat a base metal such as nickel in advance. However, since nickel is easily oxidized, the coating power of the plating film is large. Also, there is a problem of lack of durability. For this reason, it is necessary to increase the amount of gold to be used because of the need to compensate for the thickness of the gold plating film, resulting in high cost.

On the other hand, in the dry coating method, most metal materials can be used for the deposited metal, but this is also costly because the apparatus is complicated and the mass productivity is low in order to uniformly coat each particle. It has drawbacks.

[0006]

Recently, electrical connection of minute parts of electronic devices such as connection of electrodes of a liquid crystal display panel to a circuit board of a driving LSI chip and connection between electrode terminals of other minute pitches has been made. A plastic material with conductivity is used as a conductive material for
For these purposes, particularly high and reproducible conductive performance is required.

At present, carbon particles, metal particles of gold, nickel, solder or the like and metal-coated resin particles by electroless plating are used as the conductive fillers as these precision electronic materials. However, when higher conductivity is required, these conductive particles cannot sufficiently meet the demand.

The inventors of the present invention have conducted extensive studies on such unsolved problems, and conducted a conductive coating in which the surface of substantially spherical resin particles was coated with gold by a dry coating method, and further gold was coated by an electroless plating method. The present inventors have completed the present invention by finding that the conductive powder imparts high conductivity performance to the matrix component. The present inventor aims to provide a conductive powder that is particularly useful as a precision electronic member.

[0009]

That is, the electroconductive powder to be provided by the present invention comprises particles coated with gold on the surface of particles of substantially spherical resin by a dry coating method, and further electroless plating. It is characterized in that it is coated with a gold plating film by the method.

The present invention will be described in detail below. The resin particles applicable as a substrate in the present invention are not particularly limited, but usable resins include, for example, polystyrene, polyvinyl chloride, polypropylene, polyethylene, polyolefins such as polyisobutylene, styrene-
Acrylonitrile copolymer, acrylonitrile-butadiene-styrene terpolymer, acrylic acid derivatives such as polyacrylate, polymethylmethacrylate and polyacrylamide, polyvinyl compounds such as polyvinyl acetate and polyvinyl alcohol, ethers such as polyacetal, polyethylene glycol, polypropylene glycol and epoxy resin. Polymer, benzoguanamine, urea, thiourea, melamine, acetoguanamine, dicyanamide,
Examples thereof include amino resins made of amino compounds such as aniline and aldehydes such as formaldehyde, paraformaldehyde, acetaldehyde and glyoxal, polyurethanes, polyesters, fluorine-containing resins and nitrile resins.

The resin particles are substantially spherical particles, and the substantially spherical particles are, in addition to completely spherical particles,
It means that a shape close to a sphere such as an ellipse can be included, but a shape close to a sphere is preferable. It is not preferable that the powder form has sharp projections, because it causes the adhesion of the plating film to be impaired and the dispersibility to be reduced.

The particle size of the substantially spherical resin particles is not particularly limited, but the average particle size is 1 to 50 μm, preferably 4 to 20 μm. The reason for this is that if the particle size is out of this range, a sharp particle size distribution cannot be obtained, or the industrial production is not necessary in terms of practical use.

The characteristic of the conductive powder according to the present invention is that the particle surface of the above resin sphere powder is previously coated with gold by a dry coating method, and the particle shape is substantially spherical particles. . Here, the dry coating method is not particularly limited as long as it is conventionally known, and examples thereof include physical vapor deposition methods (PVD) such as vacuum vapor deposition, sputtering, ion beam mixing, and ion implantation, thermal It is a vapor deposition method represented by a chemical vapor deposition method (CVD) such as a CVD method, a photo CVD method, a plasma CVD method and the like.

The coating amount is not particularly limited because it varies depending on the particle size, but is usually 0.05 wt%.
All that is required is the above. The smaller the cost, the more preferable. In other words, at least the amount required for gold coating of the monolayer on the surface of the base resin spherical particles is sufficient, and the upper limit is naturally limited.

The second characteristic of the conductive powder according to the present invention is that
The surface of the powder is further coated with gold by an electroless plating method. That is, the feature is that the base can be coated with gold alone without using the nickel plating as in the conventional electroless nickel plating method. Therefore, not only high conductivity but also acid resistance and durability are excellent. It has a covering property. Further, as compared with the case where the same gold coating is applied by the conventional dry method, it is greatly advantageous in terms of manufacturing cost and mass production.

Note that all electroless plating reactions based on reactions such as substitution, chemical reduction, and disproportionation reaction can be applied to gold coating by electroless plating. Since such a gold plating coating is tightly adhered to the gold coating previously coated as an underlayer to form an electroless plating layer having good peeling resistance, the above effects can be provided. The metal coating weight is 0.03 to 65 as the content.
wt%, preferably 0.3 to 15 wt%.

In order to obtain the electroless plating powder, a substrate obtained by dry-coating substantially spherical resin particles with gold (hereinafter, referred to as
“Substrate particles”) is dispersed in an electroless gold plating solution prepared in advance, and gold is substituted or reduced and deposited. The electroless gold plating solution used here is not particularly limited as long as it can replace or reduce gold and is available.

The specific means of the electroless gold plating method is as follows, as an example. That is, a gold salt, a complexing agent, and a reducing agent are used as main components, and other trace amounts of additives are dissolved in water to prepare gold for an electroless gold plating solution. Here, examples of the gold salt include gold cyanide, gold cyanide, potassium cyanide, and other cyanide cyanides, gold chloride, gold bromide, and other halogenated gold salts, tetrachloroauric acid, and tetrabromoauric acid. Such as halogenauric acid and its sodium salt or potassium salt, ammonium gold sulfite, potassium gold sulfite, gold sulfite such as sodium gold sulfite, thiocyan gold, trimethyl gold, and the like, as long as it is soluble in water.

Examples of complexing agents include citric acid, hydroxyacetic acid, tartaric acid, malic acid, lactic acid, gluconic acid or carboxylic acids (salts) such as alkali metal salts or ammonium salts thereof, amino acids such as glycine, ethylenediamine,
Water-soluble amines or their derivatives such as triethanolamine, triethylenetetramine, dimethylamine, hydroxylamine hydrochloride, other ammonium, EDTA,
Pyrophosphate (salt), hydrazine compound thiosulfate, etc.
At least one compound having a complexing effect on gold ions is used.

As the reducing agent, borohydride compounds such as sodium borohydride and sodium borohydride,
An alkylamine borane such as dimethylamine borane (DMAB), hypophosphorous acid or a salt thereof, hydrazine, hydroxylamine, ascorbic acid or a salt thereof, and the like are used. Other additives include lead compounds for the purpose of stabilizing the plating bath and improving the characteristics of the deposited gold film.
Heavy metal compounds such as thallium compounds or various organic compounds are used.

The electroless gold plating solution thus prepared is adjusted to a predetermined pH and then heated, and the conductive particles of the base material are added thereto and dispersed sufficiently evenly, followed by separation after a predetermined time. to recover. The pH at this time is usually 5 to 14, and the temperature is 30 to
Although it is within the range of 100 ° C., the optimum value is usually determined by the composition of the electroless plating solution. This gold plating method is
In addition to using the gold plating solution at once as described above, the method of gradually adding the gold plating solution is less likely to cause secondary agglomeration,
preferable. Through the above steps, the metal film is formed as a dense and continuous thin film. Hereafter, it is collected as a product by post-processing in a conventional manner.

Since the coated metal layer is formed as a dense and continuous thin film in the conductive powder thus metal-coated by the electroless plating method, the particle property is base conductive particles. The particle size is slightly larger than
It does not make a substantial difference in the particle size distribution or the like.

[0023]

EXAMPLES The present invention will be described below based on examples. Examples 1 to 3, Comparative Examples 1 to 2 10 g of styrene spherical resin particle powder coated with gold by a dry coating method based on chemical vapor deposition having an average particle size of 8 μm and a gold content of 0.42 wt% was mixed with EDTA-4Na (10).
g / l), citrate-2Na (10 g / l) and potassium gold cyanide (3.0 g / l, 2.1 g / Au as Au).
l), and the pH of the aqueous solution of sodium hydroxide
The solution was added to the electroless plating solution having a solution temperature of 60 ° C. adjusted to 6 with stirring and subjected to plating treatment for 10 minutes. Table 1 shows the electroless plating solution at this time.

[0024]

[Table 1]

Subsequently, the liquid was filtered, and the filtered material was repulped and washed three times and then dried at a temperature of 100 ° C. with a hot air dryer to form a gold coating. The average particle diameter of the conductive powder thus obtained, the thickness of the gold coating, the metal content, and the conductivity were measured and evaluated, and the results are shown in Table 2. The gold content was measured by dissolving the obtained sample powder in aqua regia and quantifying it by ICP and chemical analysis. The conductivity was evaluated by placing 1.5 g of the sample powder vertically in a resin cylinder having an inner diameter of 10 mm and measuring the electrical resistance between the upper and lower electrodes while applying a weight of 5 kg. For comparison, Table 2 also shows powders obtained by electroless nickel plating as a base on the same base material with a film thickness of 0.1 μm and then gold plating by the same operation as above by the electroless plating method.

Further, FIG. 1 shows an SEM photograph of the electroconductive electroless plating powder obtained in Example 1. From the figure, it can be seen that the plating layer has a shape along the surface of the base material in the state of the plating powder.

(Acid resistance test) The plating powders obtained in Examples 1 to 3 and the plating powders of Comparative Examples 1 and 2 were stirred in 1: 1 nitric acid for 5 minutes, collected by filtration, and washed three times with demineralized water. Table 2 also shows the electric resistance measurement results of the post-dried powder.

[0028]

[Table 2]

As shown in Table 2, the electrical conductivity of the example products satisfying the requirements of the present invention is better than that of the comparative example, and in particular, the electrical resistance value after the acid resistance test is less deteriorated and the environmental resistance is improved. It turns out that it is excellent. When the particles of the comparative example after the test are observed with a microscope, it is observed that the plating film is completely peeled off. This is because the underlying nickel plating was dissolved by nitric acid, and the electroless plated powders of the examples were proved to have excellent chemical resistance because the coating was composed of gold alone.

[0030]

INDUSTRIAL APPLICABILITY The spherical resin powder gold-coated by the gold coating method by the dry coating method and the wet coating method based on the electroless plating according to the present invention is excellent in the covering power of the gold coating and is free from the dissimilar metal. Since it does not contain it, it has good conductivity and durability. Therefore, it is particularly suitable as a conductive material for precision electronic materials.

[0031]

[Brief description of the drawings]

FIG. 1 is an electron micrograph (magnification: about 1000 times) showing a particle structure of a conductive powder (average particle diameter; 8 μm) obtained in Example 1.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location // C23C 18/44 C23C 18/44 H05K 1/09 H05K 1/09 A

Claims (3)

[Claims] 1. A dry coating on the surface of substantially spherical resin particles.
A conductive powder characterized in that the surface of particles coated with gold by the coating method is further coated with a gold plating film by the electroless plating method. 2. The conductive powder according to claim 1, wherein the dry coating method is a physical vapor deposition method or a chemical vapor deposition method. 3. The conductive powder according to claim 1, wherein the gold content is in the range of 0.05 to 65 wt%.