JPH08148035A - Conductive material and conductive paste using this conductive material - Google Patents

Abstract

PURPOSE: To provide a couductive material inexpensive and excellent in conductivity and migration resistance by using silver coated copper powder obtained by coating a specific amount of silver in a surface of flake-shaped copper powder having a specific grain size. CONSTITUTION: This conductive material contains silver coated copper powder coating a surface of flake-shaped copper powder of a 20μm or less mean grain size with 5 to 30wt.% silver relating to this copper powder. For instance, less than 30 to 100 pts.wt. this silver coated copper powder and 70 pts.wt. or less (except 0) flake-shaped silver powder of 30μm or less mean grain size are used so as to obtain 100 pts.wt. in total. It is preferable to coat the surface of copper powder with silver by an electroless plating method. Conductive paste is formed by mixing a binder and a solvent added to the conductive material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive material for forming an electric circuit and a conductive paste using the same.

[0002]

2. Description of the Related Art Conventionally, as a method for forming a wiring conductor such as a wiring board or an electronic component, a conductive material such as gold, silver, palladium, copper, aluminum or carbon has been used as a filler, and a binder and a solvent have been added thereto. , A method of forming by coating or printing a conductive paste obtained by mixing is generally known, in various conductive paste, in the field where particularly high conductivity is required among the conductive materials, Noble metals such as gold and silver are used.

[0003]

However, gold is extremely expensive and has limited applications. For this reason, conductive materials using silver powder are often used as wiring conductors and electrodes for wiring boards, electronic components and the like. However, silver is also more expensive than non-metals and other metals, and when an electric field is applied in a hot and humid atmosphere, silver electroplating called migration occurs on wiring conductors and electrodes, and it occurs between electrodes or between wirings. A short circuit occurs.

[0004] For the purpose of lowering the cost, studies have been made to mix copper, but when the conductive paste is heated and hardened, an oxide film is formed on the surfaces of the copper particles due to oxygen in the air and the binder, so that the conductive paste becomes conductive. Deteriorate. For this reason, measures such as applying a moisture-proof coating to the surface of the conductor or adding a corrosion inhibitor to the conductive material have been studied, but sufficient effects have not been obtained.

On the other hand, an alloy of silver and palladium is sometimes used for the purpose of preventing migration, but this also has the drawback of being expensive.

As a method for solving both the defects of copper's oxidation resistance and silver's migration resistance, JP-A-3-247 is known.
As disclosed in Japanese Patent Application Laid-Open No. 702, Japanese Patent Application Laid-Open No. 4-268381, etc., there is a method of dissolving copper and silver and coating the surface of copper with silver by an atomizing method, but this method involves complicated steps. Since the cost is high and the above-mentioned conductive material is substantially spherical particles, there is a drawback that the conductivity is inferior to that of a conductive material composed of flaky or dendritic particles.

The present invention provides a conductive material which does not cause the above-mentioned drawbacks, is inexpensive, and is excellent in conductivity and migration resistance, and a conductive paste using the same.

[0008]

The present invention has an average particle size of 20.
On the surface of flaky copper powder having a size of less than or equal to μm,
To 30% by weight of silver-coated copper powder coated with a conductive material, the copper-coated copper powder 30 to less than 100 parts by weight and an average particle size of 30 μm or less flaky silver powder 70 parts by weight or less (0 And a binder and a solvent are added to and mixed with the above-described conductive material.

In order to coat the surface of the flake-like copper powder with silver, it is preferable to coat it by an electroless plating method because the adhesion between copper and silver is high and the running cost is low. The silver coating amount is 5 with respect to the flake-shaped copper powder.
-30% by weight, preferably 10-30% by weight. When it is less than 5% by weight, the flaky copper powder is oxidized to lower the conductivity, and when it exceeds 30% by weight, migration occurs and particles are generated. Aggregate, which makes printing difficult.

The conductive material according to the present invention contains silver-coated copper powder, or the total amount of silver-coated copper powder and flaky silver powder is 1%.
The content of the silver-coated copper powder as 00 parts by weight is 30 to 100.
It is less than 30 parts by weight, preferably in the range of 30 to 50 parts by weight, while the content of the flake silver powder is 70 parts by weight or less (excluding 0), preferably 70 to 50 parts by weight. If the amount of silver-coated copper powder is less than 30 parts by weight and the amount of flaky silver powder exceeds 70 parts by weight, migration occurs, and the amount of silver increases, so that the cost becomes high.

The flaky copper powder and the flaky silver powder do not limit the shape, but the aspect ratio is preferably about 3 or more, and more preferably 10 or more. The average particle size of the flaky copper powder is 20 μm or less, preferably 15 μm or less, more preferably 10 μm or less, and if it exceeds 20 μm, printability and conductivity deteriorate. On the other hand, the average particle size of the flake silver powder is 30 μm or less,
The thickness is preferably 20 μm or less, more preferably 10 μm or less, and if it exceeds 30 μm, the printability deteriorates.

The conductive paste includes, in addition to the above-mentioned conductive materials, a binder such as epoxy resin, phenol resin, unsaturated polyester resin, hexamethylenetetramine, a solvent such as butyl cellosolve, terpineol, ethylene carbitol, carbitol acetate, and the like. It is obtained by adding fine graphite powder, a corrosion inhibitor such as benzothiazole or benzimidazole, etc., if necessary, and uniformly mixing. The content of the binder and the solvent is preferably 10 to 20% by weight of the binder and 10 to 30% by weight of the solvent with respect to the conductive paste.

[0013]

EXAMPLES Examples of the present invention will be described below. Example 1 Flake-shaped copper powder having an average particle diameter of 12 μm (flake-shaped copper powder manufactured by Fukuda Metal Foil Co., Ltd.) was degreased with an acidic cleaner (manufactured by Nippon MacDermid, trade name L-5B), washed with water, and AgCN20.
g / H the amount of silver in a mixed bath of ₂ O1 liters and NaCN40g / H ₂ O1 liter 10 relative to flaky copper powder
Electroless plating was performed so that the weight% was reached, followed by washing with water and drying to obtain silver-coated copper powder.

On the other hand, 70 parts by weight of novolac type phenol resin (manufactured by Gunei Chemical Industry Co., Ltd., trade name PS-2607), 20 parts by weight of bisphenol A type epoxy resin (manufactured by Yuka Shell Epoxy, trade name Epicoat 828), hexamethylenetetramine 10 Butyl cellosolve 1 as parts by weight and solvent
A resin composition was obtained by uniformly mixing 00 parts by weight.

Next, to 30 parts by weight of the resin composition obtained above,
50 parts by weight of the silver-coated copper powder obtained above and an average particle size of 8.
5 μm flaky silver powder (Tokuriki Chemical Laboratory, trade name T
50 parts by weight of CG-1) was added and uniformly mixed to obtain a conductive paste.

Next, the conductive paste is applied to a thickness of 1.6 mm.
Paper phenol copper clad laminate (Hitachi Chemical Co., Ltd., trade name M
A test pattern having a width of 0.4 mm and a length of 100 mm was printed on CL-437F) through a 200-mesh screen, and heat-treated in the atmosphere at 150 ° C. for 30 minutes to obtain a wiring board. The specific resistance of the paste cured product of the obtained wiring board was 0.95 × 10 ⁻⁴ Ωcm. Further, as a result of performing a humidity and medium load test on the wiring board, the resistance change rate was within a range of ± 1%. In the wet and medium load test, the specific resistance was measured after the sample was held at 60 ° C and 95% relative humidity for 1000 hours.

On the other hand, separately from the above, 6 pieces of the conductive paste were printed on the glass slide in the same manner as described above so that the electrodes having the width of 2 mm were spaced from each other by 3 mm, and the paste was printed at 150 in the atmosphere.
The electrode was cured by heat treatment at 30 ° C. for 30 minutes. After this, a filter paper cut into a width of 3 mm is placed between the electrodes, 0.01 cc of ion-exchanged water is dropped on the filter paper, a DC voltage of 5 V is applied between the electrodes, and the time required for a current of 100 μA to flow. It was 20 minutes when measured (hereinafter referred to as 100 μA arrival time).

Comparative Example 1 To 30 parts by weight of the resin composition obtained in Example 1, 100 parts by weight of the flake silver powder used in Example 1 was added, and the mixture was uniformly mixed in the same manner as in Example 1 to obtain electroconductivity. I got a paste. The characteristics were evaluated in the same manner as in Example 1 below. As a result, the specific resistance was as low as 1.0 × 10 ⁻⁴ Ωcm, but the arrival time at 100 μA was as short as 3 minutes, and migration was extremely easy to occur. The rate of resistance change was −10%.

Comparative Example 2 To 30 parts by weight of the resin composition obtained in Example 1, 20 parts by weight of the silver-coated copper powder obtained in Example 1 and 80 parts by weight of the flaky silver powder used in Example 1 were added. The mixture was uniformly mixed to obtain a conductive paste. The characteristics were evaluated in the same manner as in Example 1 below. As a result, the specific resistance was as low as 0.95 × 10 ^-4 Ωcm,
The rate of resistance change was −5%, but the time required to reach 100 μA was as short as 6 minutes.

Comparative Example 3 The procedure was carried out except that 30 parts by weight of the resin composition obtained in Example 1 had a silver content of 2% by weight based on the flake copper powder (flake copper powder manufactured by Fukuda Metal Foil Industry Co., Ltd.). 50 parts by weight of the silver-coated copper powder obtained through the same steps as in Example 1 and 50 parts by weight of the flaky silver powder used in Example 1 were added and uniformly mixed to obtain a conductive paste. The characteristics were evaluated in the same manner as in Example 1 below. As a result, the time required to reach 100 μA was as long as 30 minutes and the specific resistance was 1.0 × 10 ⁻⁴ Ωcm, but the resistance change rate exceeded + 20%, and the electrode was oxidized.

Example 2 The same as Example 1 except that the amount of the silver-coated copper powder obtained in Example 1 was 30 parts by weight and the amount of the flaky silver powder used in Example 1 was 70 parts by weight. A conductive paste was obtained through the steps. The characteristics were evaluated in the same manner as in Example 1 below.
As a result, the specific resistance was 1.0 × 10 ⁻⁴ Ωcm, the arrival time at 100 μA was 15 minutes, and the resistance change rate was + 1%.

Example 3 A conductive paste was obtained through the same steps as in Example 1 except that the amount of the silver-coated copper powder obtained in Example 1 was 100 parts by weight and the flake silver powder was not used. The characteristics were evaluated in the same manner as in Example 1 below. As a result, the specific resistance is 1.1.
× 10 ⁻⁴ Ωcm, arrival time at 100 μA was 40 minutes, and resistance change rate was + 5%, which were all favorable.

Example 4 Instead of the flaky copper powder used in Example 1, the flaky copper powder was classified, and the average particle size obtained by this was 3.
Properties were evaluated in the same manner as in Example 1 below, in which a conductive paste was obtained with the same composition as in Example 1 except that 5 μm flaky copper powder was used, and through the same steps as in Example 1.
As a result, the specific resistance was reduced to 0.6 × 10 ⁻⁴ Ωcm, and the other characteristics were substantially the same as those in Example 1.

Comparative Example 4 Instead of the flaky copper powder used in Example 1, the flaky copper powder was classified, and the average particle size obtained by this classification was 22.
A conductive paste was obtained in the same composition as in Example 1 except that the flaky copper powder of μm was used, and through the same steps as in Example 1. The characteristics were evaluated in the same manner as in Example 1 below. As a result, the specific resistance increased to 1.8 × 10 ⁻⁴ Ωcm. However, the other properties were almost the same as those in Example 1.

Comparative Example 5 Instead of the flaky silver powder used in Example 1, the flaky silver powder was classified, and the average particle size obtained by this classification was 35.
A conductive paste was obtained in the same composition as in Example 1 except that flake-shaped silver powder of μm was used, and through the same steps as in Example 1. When an attempt was made to print using this conductive paste, the mesh of the screen was clogged and printing could not be performed efficiently.

[0026]

According to the present invention, since the amount of silver used can be reduced and a complicated process is not required, the conductive material is inexpensive, excellent in conductivity and migration resistance, and industrially extremely suitable. And a conductive paste.

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Claims (4)

[Claims] 1. A conductive material comprising a silver-coated copper powder in which the surface of flaky copper powder having an average particle diameter of 20 μm or less is coated with 5 to 30% by weight of silver with respect to the copper powder. 2. A silver-coated copper powder in which the surface of flaky copper powder having an average particle size of 20 μm or less is coated with 5 to 30% by weight of silver with respect to the copper powder, 30 to less than 100 parts by weight, and an average particle size. A conductive material containing 70 parts by weight or less (excluding 0) of flake-shaped silver powder having a particle size of 30 μm or less in a total amount of 100 parts by weight. 3. The conductive material according to claim 1, wherein the surface of the copper powder is coated with silver by electroless plating. 4. A conductive paste obtained by adding and mixing a binder and a solvent to the conductive material according to claim 1, 2 or 3.