JPS63190204A - Conducting fine pellet - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] (Industrial application field) The present invention has excellent compression resistance under high temperature and high humidity conditions.

The present invention also relates to conductive microspheres that have good conductivity even under these conditions.

(Prior art) For conductive materials such as conductive paste, conductive adhesive, conductive adhesive or anisotropic conductive film.

A composition consisting of conductive particles and a resin is used.

The conductive particles generally include metal particles such as gold, silver, and nickel. However, such metal particles have a higher specific gravity than the resin and are irregular in shape, so they tend to exist non-uniformly in the resin. This causes uneven conductivity. In order to solve these drawbacks, Japanese Patent Application Laid-open No. 59-28185 discloses that instead of metal particles, non-conductive particles such as glass beads, glass fibers, and plastic balls with two uniform particle diameters are coated on the surface. Gold, 11. Tin.

Conductive particles coated with copper, nickel, cobalt, etc. by plating are disclosed. especially.

If nickel or cobalt is plated, the plating layer is not easily affected by oxidation, so that the conductivity of the conductive particles is maintained at a good level under normal conditions. Furthermore, these conductive particles can be obtained at low cost.

However, if conductive particles plated with nickel or cobalt are left in a high temperature state for a long time or exposed to water vapor for a long time, the plating layer will be corroded and the quality will change.

Therefore, the electrical resistance of the conductive particles increases and the conductivity decreases. Moreover, since the plating layer of the conductive particles is too hard and lacks flexibility, the adhesion between the non-conductive particles and the conductive plating layer is lacking.

Therefore, when a compressive load is applied to this conductive particle.

The conductive plating layer easily separates from the non-conductive particles.

Since the conductive plating layer is brittle, there is a risk that it will be destroyed by compressive load.

(Problems to be Solved by the Invention) The present invention solves the above-mentioned conventional problems, and its purpose is to prevent the conductive thin film layer from deteriorating under high temperature and high humidity conditions. Therefore.

An object of the present invention is to provide conductive microspheres with good conductivity. Another object of the invention is that even when compressive loads are applied.

An object of the present invention is to provide conductive microspheres in which a conductive thin film layer is difficult to peel off from resin microspheres. Still another object of the present invention is to provide conductive microspheres whose conductive thin film layer is less likely to be destroyed by compressive loads.

(Means for Solving the Problems) The present invention makes it possible by limiting the phosphorus content incorporated into nickel to a certain range when nickel plating is applied to resin microspheres by an electroless nickel plating method. A conductive plating layer that has flexibility and is resistant to deterioration even under high temperature or high humidity can be obtained. Moreover, the above method can also be applied to a cobalt plating method. It was completed based on the inventor's knowledge.

The conductive microspheres of the present invention are conductive microspheres in which a conductive thin film layer made of nickel and/or cobalt is formed on the surface of a resin microsphere, and the conductive thin film layer contains 1.5 phosphorus.
4% by weight, thereby achieving the above object.

Examples of resin microspheres include polyethylene.

Linear polymers include polypropylene, methylpentene polymer, polystyrene, polymethyl methacrylate, polyvinyl chloride, polyvinyl fluoride, polytetrafluoroethylene, polyethylene terephthalate, polybutylene terephthalate, polysulfone, polycarbonate, polyacrylonitrile, polyacetal, polyamide, etc. . The resin microspheres include, for example, divinylbenzene, hexatriene, divinyl ether, and divinyl sulfone.

Diallylcarbinol, alkylene diacrylate, alkylene dimethacrylate, oligo or poly(alkylene glycol) diacrylate.

Oligo or poly(alkylene glycol) dimethacrylate, alkylene triacrylate, alkylene trimethacrylate, alkylene tetraacrylate, alkylene tetramethacrylate.

A network polymer obtained by polymerizing a crosslinking reactive monomer such as alkylene bisacrylamide or alkylene bismethacrylamide alone or with other polymerizable monomers may also be used. Preferred monomers include divinylbenzene, hexatriene, divinyl ether, divinyl sulfone, alkylene triacrylate, and alkylene tetraacrylate.

These resin microspheres are formed by pearl polymerization using a radical initiator and a suspension stabilizer.

The radical initiator is lauroyl peroxide.

benzoyl peroxide, acetyl peroxide,
Dicumyl peroxide, di-t-butyl peroxide, t-butyl peroxybenzoate, t-butyl peroxyoctoate, t-butyl peroxy acetate-1
-, t-butylbaroxyisobutyrate azobisisobutyronitrile.

Any known initiator can be used, such as azobisisovaleronitrile. The radical initiator is added in an amount of 0.5 to 15 parts by weight based on 100 parts by weight of the monomer. 0
．． When the amount is less than 5 parts by weight, the polymerization rate of the monomer decreases significantly. Amounts of initiator in excess of 15 parts by weight are not necessary. A suspension stabilizer is an additive that allows the resin microspheres formed by the polymerization reaction to exist stably in the reaction system.
Examples include polyvinyl alcohol, polyacrylic acid, polymethacrylic acid, gelatin, methylcellulose, polymethacrylamide, polyethylene glycol, polyethylene oxide monostearate sorbicune tetraoleate, and glyceryl monooleate.

A mixture containing these monomers, an initiator, and a suspension stabilizer is dispersed in a suitable liquid medium, atomized with vigorous stirring, and heated to form a polymer. The liquid medium 2 is usually water. The polymerization reaction is continued until unreacted monomers disappear. The obtained polymer becomes resin microspheres.

The particle size of the resin microspheres is controlled by the stirring speed and stirring time of the mixture in the above step.

The particle size is preferably 1 to 100 μI. More preferably 3
~20 μm is used. More preferably, the thickness is 5 to 15 μm. Because there is a distribution in particle size.

It is preferable to carry out one classification using a conventional method. or,
Classification may be performed after forming the conductive thin film layer.

A conductive thin film layer is formed on the surface of such resin microspheres by metal vapor deposition, plating, or the like. The conductive thin film layer is formed, for example, as follows (hereinafter, the conductive thin film layer of the resin microspheres in the present invention will be explained using a conductive plating layer as an example).

The process of forming the conductive plating layer is divided into etching, activation, and chemical plating processes.

The etching process is a process for forming irregularities on the surface of the resin microspheres and imparting adhesion to the conductive plating layer.
The etching solution may include, for example, a caustic soda aqueous solution.
Ji hydrochloric acid, tM sulfuric acid or chromic anhydride are used. However, the etching step is not always necessary and can be omitted depending on the case.

The acquisition step is a step of forming a catalyst layer on the surface of the etched resin microspheres and activating this catalyst layer. Activation of the catalyst layer promotes metal deposition in the chemical plating process described below. As catalysts, Pd'' and Sn'' are adsorbed on the surface of the resin microspheres. Concentrated sulfuric acid or concentrated hydrochloric acid is applied to this catalyst layer.

The metallized palladium, which undergoes metallization of Pd'' by the reaction Sn''+Pd''-=Sn''+Pd, is activated and degraded by a palladium activator such as a concentrated solution of caustic soda.

The chemical plating process is a process in which a conductive plating layer is further formed on the surface of the resin microspheres on which the catalyst layer has been formed.For example, in the case of nickel plating.

Nickel sulfate is used as a nickel ion supply material, and sodium hypophosphite is added as a reducing agent. During the activation step, palladium adsorbed on the surface of the resin microspheres serves as a catalyst, and the reduction reaction of nickel sulfate progresses, causing nickel metal to precipitate on the surface of the resin microspheres. In this case, phosphorus is incorporated in the form of an alloy into the nickel of the resulting conductive plating layer. What is this phosphorus content?

The present inventor has found that the physical properties of the conductive microspheres are greatly affected. If the phosphorus content exceeds 4% by weight, the initial conductive performance of the conductive microspheres will deteriorate, and if left for a long time under high temperature or high humidity, the conductive plating layer will be corroded and deteriorated. , the conductivity tends to decrease. When the phosphorus content is 4% by weight or less, not only the initial conductivity performance is improved, but also almost no change in conductivity is observed even when left at high temperature or high humidity. However, when the phosphorus content is less than 1.5% by weight, the crystallinity of the nickel plating layer becomes too high.
Since the hardness increases and the flexibility becomes insufficient, the adhesion between the resin microspheres and the conductive plating layer decreases.

Therefore, when a compressive load is applied to this conductive particle.

The conductive plating layer easily peels off from the resin microspheres. Since the conductive plating layer is brittle, there is a risk that it will be destroyed by compressive load. From these facts, the phosphorus content of the conductive plating layer is
1.5 to 4% by weight is preferred.

The phosphorus content is determined by controlling the pH of the plating reactor. When the amount of sodium hypophosphite added increases, the pH of the two reaction vessels increases and the phosphorus content increases.

On the other hand, ammonium hydroxide may be added to increase the pH of the reactor and increase the phosphorus content. The temperature of the plating reaction tank can be set at any level within the range of 100° C. or lower and room temperature or higher. The thickness of the conductive plating layer is preferably in the range of 0.01 to 5 μm. When the thickness is less than 0.01 μm, it is difficult to obtain the desired conductivity. When it exceeds 5 μm, the conductive plating layer tends to peel off from the surface of the resin microspheres due to the difference in thermal expansion coefficient between the resin microspheres and the conductive plating layer.

In the case of cobalt plating, it is carried out in exactly the same manner except that cobalt sulfate is used in place of the above-mentioned nickel sulfate.

The conductive microspheres obtained in this way have good conductivity and are not easily deteriorated even if left for a long time under high temperature or high humidity. Therefore, the conductivity is good even under these conditions. These conductive microspheres.

The conductive plating layer does not easily peel off from the resin microspheres even under compressive load. The conductive plating layer is also less likely to be destroyed by compressive loads. Therefore, these conductive microspheres are suitable for use in applications such as conductive pastes, conductive adhesives, conductive adhesives, anisotropic conductive films, fillers for electromagnetic shielding resins, and magnetic materials. It is particularly suitable for NL conductive adhesives, conductive adhesives, and anisotropic conductive films.

These are used as conductive materials for electrode transition between upper and lower electrodes, conductive bonding materials between external drive circuits and display electrodes, and the like in liquid crystal display cells.

(Example) The present invention will be described below with reference to examples.

Implementation Flaming (11 Preparation of conductive microspheres As resin microspheres, a spherical polymer obtained by suspension polymerization of divinylbenzene (average particle size 10 μm, standard deviation 0.35
) was used.

10 g of the resin microspheres were immersed in a powder plating pre-dip solution (manufactured by Okuno Pharmaceutical Co., Ltd.) for 30 minutes at room temperature for etching. It was washed with water, then activated by immersing it in Catalyst C solution (manufactured by Okuno Pharmaceutical Co., Ltd.) 1□+ffi, 37% hydrochloric acid 10-, methanol 1Qml at room temperature for 30 minutes.

Further, the resin microspheres were washed with 5% sulfuric acid and then thoroughly washed with water. Nickel sulfate 17g/100ml1. pH 9 consisting of the composition of sodium hypophosphite 17 g/100- and sodium birophosphate 34 g/100-
, 4 was prepared. The resin microspheres were placed in this electroless nickel plating solution.

A conductive plating layer was formed by dipping at 70°C for 10 minutes.

Next, this was thoroughly washed with water and then dried to obtain conductive microspheres.

(2) Quantitative analysis of conductive microspheres Weigh a predetermined amount of the conductive microspheres obtained in section (1).

This was dissolved in a 5% nitric acid aqueous solution. Add this solution to ICr
'Quantitative analysis was performed using a luminescence spectrometer (manufactured by Seiko Electronics Industries, Ltd.). As a result, 0.27 g of nickel and 0.010 g of phosphorus were contained per 1 g of the conductive microspheres. Therefore, the phosphorus content in the conductive plating layer is 3.
It was 6% by weight.

(3) Evaluation of conductive microspheres Regarding the conductive microspheres obtained in section (1), conductivity (normal state, after high temperature treatment, and after high temperature treatment) was evaluated as follows.
And compression resistance against compressive load was measured. These results are shown in the table below.

(A) Conductive epoxy adhesive 5E-4500 (manufactured by Yoshikawa Kako Co., Ltd.),
4 parts by weight of the conductive microspheres obtained in section (1) were mixed with 100 parts by weight to prepare a paste.

As an anisotropic conductivity test board, a 34μm thick copper plate was used as a 50μ
A substrate was used that was bonded to a polyimide film of m thickness and etched so that the electrode portion had a pinch of 400 μm. These two anisotropically conductive test substrates are placed facing each other so that the overlapping parts form two dragons,
The conductive microspheres were glued together using a dispersed paste. The bonding conditions were heating at 140° C. for 1 hour with a press pressure of 10 kg/cl. The resistance value (Ω) between each opposing electrode of the substrate bonded in this way was measured. moreover.

The resistance value of this substrate was measured after heating it at 150°C for 500 hours (after high temperature treatment) and after leaving it in an aquatic atmosphere at 121°C and 2 atm for 50 hours (after high humidity treatment). These resistance values were measured for 15 samples, and the average value and standard deviation of the resistance values were calculated. the result.

The average resistance value under normal conditions is 0.50Ω, and the standard deviation is 0.12
．． The average resistance value after high temperature treatment is 0.60Ω.

The standard deviation is 0.10. The average resistance value after high temperature treatment was 0.93Ω, and the standard deviation was 0.35.

(B) Compression resistance In item (8), when bonding substrates together, 10k
The conductive microspheres after being subjected to a press pressure of g/cnl were taken out and observed under a scanning electron microscope at a magnification of 10,000 times. As a result, almost no peeling or destruction of the conductive plating layer was observed.

17g of nickel sulfate as electroless nickel plating solution
100mf, sodium hypophosphite 10.3 g/l
oOml and sodium pyrophosphate 34g/100m
Conductive microspheres were produced in the same manner as in Example 1, except that a plating solution having pHio of 1 and 0 was used. 0.26 nickel per gram of these conductive microspheres. and 0.008 g of phosphorus, and the phosphorus content in the conductive plating layer was 2.0% by weight.

Using these conductive microspheres, the conductivity (normal state, after high temperature treatment, after high humidity treatment) and compression resistance were measured by the same method as in Example 1. As a result, the average resistance value under normal conditions is 0
．． 35Ω, standard deviation 0.06. The average resistance value after high temperature treatment is 0.38Ω, and the standard deviation is 0.0? .

The average resistance value after high temperature treatment was 0.72Ω, and the standard deviation was 0.36. Compression resistance: 10kg/cf
Almost no peeling or destruction of the conductive plating layer was observed after being subjected to the press pressure of 1I.

18 g of cobalt sulfate as electroless cobalt plating solution
/100++1. Sodium hypophosphite 25 g /
100- and sodium pyrophosphate 34g/100+
Conductive microspheres were produced in the same manner as in Example 1, except that a plating solution having a pH of 10.5 and having a composition of ++ffi was used. per gram of these conductive microspheres, 0.
23g and 0.006g of phosphorus were contained, and the content of phosphorus in the conductive plating layer was 2.5% by weight.

Using these conductive microspheres, the conductivity (normal state, after high temperature treatment, after high humidity treatment) and compression resistance were measured by the same method as in Example 1. As a result, the average resistance value under normal conditions is 0
．． 67Ω, standard deviation 0.29. The average resistance value after high temperature treatment was 0.75Ω, standard deviation 0.30°, and the average resistance value after high temperature treatment was 1.03Ω, standard deviation 0.40. Regarding compression resistance, almost no peeling or destruction of the conductive plating layer was observed after being subjected to a press pressure of 10 kg/a.

17 g of nickel sulfate as electroless nickel plating solution
/Loom, sodium hypophosphite 24 g /10
0mf and sodium pyrophosphate 34 g/100
Conductive microspheres were produced in the same manner as in Example 1, except that a plating solution having a pH of 8.5 and having a composition of - was used.

Each gram of the conductive microspheres contained 0.27 g of nickel and 0.013 g of phosphorus, and the content of phosphorus in the conductive plating layer was 4.6% by weight.

Using these conductive microspheres, the conductivity (normal state, after high temperature treatment, after high humidity treatment) and compression resistance were measured by the same method as in Example 1. As a result, the average resistance value under normal conditions is 0
．． 75Ω, standard deviation is 0.24. The average resistance value after high temperature treatment was 1.60Ω, standard deviation 0.42°, and the average resistance value after high temperature treatment was 7.80Ω, standard deviation 1.20. Regarding compression resistance, peeling of the conductive plating layer was observed after being subjected to a press pressure of 10 kg/cni.

As the electroless cobalt plating solution, 18g of cobalt sulfate/
100Wd, sodium hypophosphite 45g/ioa
Conductive microspheres were produced in the same manner as in Example 1, except that a plating solution having a pH of 9.0 and a composition of 34 g/100 d of sodium pyrophosphate was used. Each gram of the conductive microspheres contained 0.24 g of Kobal and 0.013 g of phosphorus, and the phosphorus content in the conductive plating layer was 5.1% by weight.

Using these conductive microspheres, the conductivity (normal state, after high temperature treatment, after high temperature treatment) and compression resistance were measured by the same method as in Example 1. As a result, the average resistance value under normal conditions is 0
．． 80Ω, standard deviation is 0.46. The average resistance value after high temperature treatment was 1.55Ω, standard deviation 0.75°, and the average resistance value after high temperature treatment was 5.70Ω, standard deviation 2.00. Regarding compression resistance, after being subjected to a press pressure of 10 kg/-, the conductive plating layer was observed to be axially off-axis.

17 g of nickel sulfate as electroless nickel plating solution
/100d, sodium hypophosphite 3.5g/100
Conductive microspheres were produced in the same manner as in Example 1, except that a plating solution having a pH of 14.0 and having a composition of 34 g/100 of sodium pyrophosphate was used. Each gram of the conductive microspheres contained 0.24 g of nickel and 0.002 g of phosphorus, and the phosphorus content in the yA electroplating layer was 0.8% by weight.

Using these conductive microspheres, the conductivity (normal state, after high temperature treatment, after high temperature treatment) and compression resistance were measured by the same method as in Example 1. As a result, under normal conditions, the average resistance value of ' is 0.53Ω, and the standard deviation is 0.1? The average resistance value after high temperature treatment was 2.75Ω, standard deviation 0.44°, and the average resistance value after high temperature treatment was 0.65Ω, standard deviation 0.40. Regarding compression resistance, peeling and destruction of the conductive plating layer were observed after being subjected to a press pressure of 10 kg/cd.

Comparison ■ 18 g of cobalt sulfate as electroless cobalt plating solution
/100m, sodium hypophosphite 10 g /10
0- and sodium pyrophosphate 34 g/100-
Conductive microspheres were produced in the same manner as in Example 1, except that a plating solution having the composition of ρ<3.0 was used. Each gram of the conductive microspheres contained 0.25 g of Kobal and 0.002 g of phosphorus, and the content of phosphorus in the conductive plating layer was 0.8% by weight.

Using these conductive microspheres, the same method as in Example 1 was carried out! X-electricity (normal state, after high temperature treatment, after high temperature treatment) and compression resistance were measured. As a result, the average resistance value under normal conditions was 0.70Ω, and the standard deviation was 0.21. The average resistance value after high temperature treatment was 3.54Ω, standard deviation 0.38°, and the average resistance value after high temperature treatment was 1.03Ω, standard deviation 0.47. Compression resistance: 10kg/cs! After being subjected to press pressure, peeling and destruction of the conductive plating layer were observed.

As is clear from the Examples and Comparative Examples, the conductive microspheres of the present invention are excellent not only in normal conductivity but also in high temperature and high temperature conductivity. Even when subjected to compressive loads, there is almost no peeling or destruction of the conductive plating layer.The conductive microspheres, whose conductive plating layer has a phosphorus content of more than 4% by weight, have a low resistance value under high temperature and high humidity conditions. conductivity decreases. The compressive load also causes peeling of the conductive plating layer. When the phosphorus content is less than 1.5% by weight, although the conductivity is good, peeling or destruction of the conductive plating layer is observed due to compressive load.

(The following is a blank space) (Effects of the Invention) As described above, the conductive microspheres of the present invention have good conductivity even under high temperature and high humidity conditions because the conductive thin film layer is difficult to deteriorate. Furthermore, even when a compressive load is applied, the conductive thin film layer is difficult to peel off from the resin microspheres. The conductive thin film layer is also less likely to be destroyed by compressive loads. As a result, the conductive microspheres of the present invention can be suitably used in applications such as conductive pastes, conductive adhesives, conductive adhesives, anisotropic conductive films, fillers for electromagnetic shielding resins, and magnetic materials.

that's all

Claims (1)

[Scope of Claims] 1. A conductive microsphere in which a conductive thin film layer made of nickel and/or cobalt is formed on the surface of a resin microsphere, the conductive thin film layer containing 1.5 to 4% by weight of phosphorus. conductive microspheres in a proportion of . 2. The resin microspheres are polyethylene, polypropylene, methylpentene polymer, polystyrene, polymethyl methacrylate, polyvinyl chloride, polyvinyl fluoride,
The conductive microspheres according to claim 1, which are a linear polymer of at least one of polytetrafluoroethylene, polyethylene terephthalate, polybutylene terephthalate, polysulfone, polycarbonate, polyacrylonitrile, polyacetal, and polyamide. 3. The resin microspheres contain divinylbenzene, hexatriene, divinyl ether, divinyl sulfone, diallyl carbinol, alkylene diacrylate, alkylene dimethacrylate, oligo or poly(alkylene glycol) diacrylate, oligo or poly(alkylene glycol) diacrylate, At least one monomer selected from methacrylate, alkylene triacrylate, alkylene trimethacrylate, alkylene tetraacrylate, alkylene tetramethacrylate, alkylene bisacrylamide, and alkylene bismethacrylamide,
The conductive microspheres according to claim 1, which are network polymers obtained by polymerizing alone or with other polymerizable monomers. 4. The conductive microspheres according to claim 1, wherein the thickness of the conductive thin film layer is in the range of 0.01 to 5 μm.