JPH06338216A - Conductive paste - Google Patents

Abstract

PURPOSE:To improve conductivity and prevent the short circuit between electrodes or wirings by using nearly spherical fine particles plated with nickel and silver for conductive paste. CONSTITUTION:For conductive paste, nickel plating is applied on the surface, and further silver plating is applied on its topside, and it contains nearly spherical fine particles 30mum or under in diameter and flake-shaped silver powder. Hereby, high conductive paste, where the resistance of the through hole in a wiring board is low, can be gotten. Moreover, the drop in the insulation resistance between through holes after test of load in humidity is small, and further, the quantity of used silver can be lessened by using nearly spherical fine particles plated with nickel and silver.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Conventionally, as a method for forming a wiring conductor of a printed wiring board, an electronic component or the like, a method of applying or printing a paste containing silver powder having excellent conductivity is generally known. .

[0003]

Since a conductive paste using silver powder has good conductivity, it is used as a wiring conductor or an electrode for printed wiring boards, electronic parts, etc., but these are used under a high temperature and high humidity atmosphere. When an electric field is applied, there is a drawback that a wiring conductor or an electrode is electro-deposited with silver called migration and a short circuit occurs between electrodes or between wirings. Several measures have been taken to prevent this migration, and measures such as applying a moisture-proof coating to the surface of the conductor or adding a corrosion inhibitor such as a nitrogen compound to the conductive paste have been studied, but it is sufficient. It was not possible to obtain such an effect.

Further, in order to obtain a conductor having good conduction resistance, it is necessary to increase the amount of silver powder blended, and the silver paste is expensive, so that the conductive paste is also expensive.

The present invention provides a conductive paste that does not have such drawbacks.

[0006]

The present invention relates to a conductive paste containing substantially spherical fine particles having a particle size of 30 μm or less and flake-shaped silver powder, the surface of which is nickel plated and the upper surface of which is silver plated.

The substantially spherical fine particles in the present invention are made of a plastic or an inorganic material, and the shape thereof is a substantially spherical shape, and the major axis thereof may be at least 30 μm or less, and it is more preferable if it is conductive. The particle size is 30 μm
The use of substantially spherical fine particles exceeding the range causes drawbacks such as clogging of the screen during printing, poor elongation of the paste and poor printability. The thickness of the nickel plating applied to the surface of the substantially spherical fine particles is not particularly limited, but may be 1 to 2 μm, and the thicker the silver plating applied to the upper surface of the nickel plating, the easier it is to increase the conductivity, but the cost is low. The thickness is 0.5 to 1 μm, which is sufficient. The nickel plating and silver plating treatment methods are well known and are not particularly limited.

The flake silver powder is not limited in its shape, but the aspect ratio is preferably about 3 or more, more preferably 10 or more. In addition, the particle diameter is preferably 40 μm or less because the printability is not deteriorated. The volume ratio of the substantially spherical fine particles to the flake-like silver powder is 5: 1 to 1: 5 (substantially spherical fine particles: flake-like silver powder) in terms of resistance and migration prevention of the conductor.
Is preferred.

In addition to the above materials, the conductive paste is an organic adhesive component such as liquid epoxy resin, phenol resin and unsaturated polyester resin, and if necessary, a solvent such as terpineol, ethyl carbitol and carbitol acetate, and fine graphite. It contains powders, corrosion inhibitors such as benzothiazole and benzimidazole. The content of the substantially spherical fine particles and the flake silver powder is preferably 20 to 60% by weight, more preferably 30 to 60% by weight, based on the solid content of the conductive paste, from the viewpoint of the resistance of the conductor and economy.

[0010]

EXAMPLES Examples of the present invention will be described below. Example 1 100 g of polystyrene substantially spherical fine particles (made by Hitachi Chemical Co., Ltd.) having an average particle diameter of 20 μm and a maximum diameter of 28 μm, 400 g / liter of chromic anhydride and 350 g / liter of sulfuric acid.
The surface treatment was carried out for 10 minutes in a mixed acid containing 65 liters at 65 ° C.
Next, the substantially spherical fine particles are washed with water, dried, immersed in an aqueous solution of stannous chloride of 10 g / liter and hydrochloric acid of 5 ml / liter at 23 ° C. for 3 minutes and then washed with ion-exchanged water, and further palladium chloride is added. Immersion in an aqueous solution containing 0.2 g / liter and 2 ml / liter of hydrochloric acid at 30 ° C. for 3 minutes, followed by washing with ion-exchanged water, then 8
It was immersed in a nickel plating bath (manufactured by Nippon Kanigen, trade name S680) heated to 0 ° C. for 15 minutes to apply a nickel plating having a thickness of 1.5 μm. After this, the nickel-plated substantially spherical fine particles are washed with water, dried, and then added with an aqueous ammonia solution to make the silver nitrate transparent and contain 50 g / liter of silver nitrate.
While stirring and dispersing in an aqueous solution of 1 liter, the aqueous solution is heated weakly with a gas burner, and nickel-plated silver-plated substantially spherical fine particles having silver plating of 0.6 μm thick on the upper surface of nickel plating are formed. Obtained.

On the other hand, 60 parts by weight of bisphenol A type epoxy resin (made by oiled shell epoxy, trade name Epicoat 834) and 40 parts by weight of bisphenol A type epoxy resin (made by oiled shell epoxy, trade name Epicoat 828) are heated and dissolved in advance. Then, after cooling to room temperature, 5 parts by weight of 2 ethyl 4-methylimidazole (manufactured by Shikoku Kasei), 20 parts by weight of ethyl carbitol (manufactured by Wako Pure Chemicals, reagent) and 20 parts by weight of butyl cellosolve (manufactured by Wako Pure Chemicals, reagent) In addition, a resin composition was prepared by uniformly mixing the 145 g of the resin composition with 160 g of the nickel-plated silver-plated substantially spherical fine particles and flaky silver powder (manufactured by Tokuriki Kagaku Kenkyusho,
210 g of product name TCG-1) was added and uniformly dispersed with a stirrer and a three-roll mill to obtain a conductive paste.

Next, the conductive paste obtained above has a thickness of 1.
The test pattern shown in FIG. 1 is printed on a paper phenol copper clad laminate (Hitachi Chemical Co., Ltd., trade name MCL-437F) in which a through hole having a diameter of 6 mm and a diameter of 0.8 mm (φ) is formed. The wiring board was obtained by heat-treating the material filled in the above in the atmosphere under the conditions of 60 ° C. for 30 minutes and 160 ° C. for 30 minutes. In FIG. 1, 2 is a paper phenol copper clad laminate. Next, the resistance of the obtained wiring board was measured. As a result, the resistance of the through hole 1 excluding the resistance of the copper foil was 19 mΩ / hole, and the insulation resistance between adjacent through holes was 10 ⁸ Ω or more. As a result of the thermal shock test of the wiring board, the resistance of the through hole 1 is 24 mΩ.
/ It was a hole. Moreover, as a result of performing a wet and medium load test on the wiring board, the insulation resistance between the through holes was 10 ⁸ Ω or more. The cold heat test conditions are 125 ° C. 30 minutes to −65 ° C. 3
100 cycles of 0 minutes, 90 ° C for humidity and medium load test
In% RH, a voltage of 50 V was applied between adjacent lines and held for 1000 hours.

Example 2 To 145 g of the resin composition obtained in Example 1, 360 particles of substantially spherical particles adhered to nickel plating-silver plating used in Example 1 were applied.
g and 200 g of flaky silver powder were added and uniformly mixed and dispersed in the same manner as in Example 1 to obtain a conductive paste. A wiring board was manufactured through the same steps as in Example 1 and the characteristics thereof were evaluated. As a result, the resistance of the through hole is 18 mΩ.
/ Hole, and the insulation resistance between through holes was 10 ⁸ Ω or more. As a result of a thermal shock test of the wiring board, the resistance of the through holes was 23 mΩ / hole, and the result of the wet and medium load test showed that the insulation resistance between the through holes was 10 ^8.
It was more than Ω.

Example 3 To 145 g of the resin composition obtained in Example 1, 100 particles of substantially spherical particles adhered to nickel plating-silver plating used in Example 1 were added.
g and 800 g of flaky silver powder were added and uniformly mixed and dispersed in the same manner as in Example 1 to obtain a conductive paste. A wiring board was manufactured through the same steps as in Example 1 and the characteristics thereof were evaluated. As a result, the resistance of the through hole is 17 mΩ.
/ Hole, and the insulation resistance between through holes was 10 ⁸ Ω or more. As a result of a thermal shock test of the wiring board, the resistance of the through holes was 23 mΩ / hole, and the result of the wet and medium load test showed that the insulation resistance between the through holes was 10 ^8.
It was more than Ω.

Example 4 To 145 g of the resin composition obtained in Example 1, 100 particles of substantially spherical particles adhered to nickel plating-silver plating used in Example 1 were added.
g and 210 g of flaky silver powder were added and uniformly mixed and dispersed in the same manner as in Example 1 to obtain a conductive paste. A wiring board was manufactured through the same steps as in Example 1 and the characteristics thereof were evaluated. As a result, the resistance of the through hole is 20 mΩ.
/ Hole, and the insulation resistance between through holes was 10 ⁸ Ω or more. As a result of the thermal shock test of the wiring board, the resistance between the through holes was 25 mΩ / hole, and the result of the wet and medium load test showed that the insulation resistance between the through holes was 10 mΩ / hole.
It was more than ⁸ Ω.

Comparative Example 1 To 145 g of the resin composition obtained in Example 1, 1000 g of the flake silver powder used in Example 1 was added and uniformly mixed and dispersed in the same manner as in Example 1 to obtain a conductive paste. A wiring board was manufactured through the same steps as in Example 1 and the characteristics thereof were evaluated. As a result, the resistance of the through holes was 18 mΩ / hole, and the insulation resistance between the through holes was 10 ⁸ Ω or more. As a result of the thermal shock test of the wiring board, the resistance of the through hole was 24 mΩ / hole, and in the result of the wet and medium load test, the insulation resistance between the through holes was 10 ⁷ Ω per 5 wiring boards. There was something that was falling on the table.

COMPARATIVE EXAMPLE 2 145 g of the resin composition obtained in Example 1 was mixed with 170 particles of substantially spherical fine particles adhered to nickel plating-silver plating used in Example 1.
g and uniformly mixed and dispersed in the same manner as in Example 1 to obtain a conductive paste. A wiring board was manufactured through the same steps as in Example 1 and the characteristics thereof were evaluated. As a result, the resistance of the through holes was 180 mΩ / hole, and the insulation resistance between the through holes was 10 ⁸ Ω or more. As a result of the thermal shock test of the wiring board, the resistance between the through holes was 4
50mΩ / hole, 2.5 compared to before the thermal shock test
It has doubled. In addition, as a result of the wet and medium load test, the insulation resistance between the through holes was 10 ⁸ Ω or more.

[0018]

The conductive paste according to the present invention is a highly conductive conductive paste having a low resistance of through holes in a wiring board, and has a small decrease in insulation resistance between through holes after a wet and medium load test. This conductive paste is economically excellent in that the amount of silver used can be reduced by using the substantially spherical fine particles deposited by plating-silver plating.

[Brief description of drawings]

FIG. 1 is a plan view showing a state in which a conductive paste is printed on a paper phenol copper clad laminate and the through holes are filled.

[Explanation of symbols]

 1 Through hole 2 Paper phenol copper clad laminate

 ─────────────────────────────────────────────────── ─── Continued front page (72) Inventor Hideyuki Fujita 1-1-1, Nishishinjuku, Shinjuku-ku, Tokyo Hitachi Chemical Co., Ltd. (72) Inventor Toshikazu Ono 3-chome, Ayukawa-cho, Hitachi, Ibaraki No. 1 Sakuragawa Sangyo Co., Ltd.

Claims (1)

[Claims] 1. A conductive paste comprising substantially spherical fine particles having a particle size of 30 μm or less and flake-shaped silver powder, the surface of which is nickel-plated and the upper surface of which is silver-plated.