JPH06349323A - Conductive paste - Google Patents

Abstract

PURPOSE:To reduce the insulating resistance between through holes, and to reduce the using amount of silver, by including a specific almost spherical form of minute particles, a copper powder, zeolite, and a thiazole genus, to a conductive paste. CONSTITUTION:(A) 20 to 60wt.% of almost spherical form of particles which consist of a plastic or an inorganic material with the particle size less than 30mum, on whose surface a nickel plating with the thickness 1 to 2mum is applied, and a silver plating with the thickness 0.5 to 1mum is applied thereover, and (B) a copper powder whose particle size is less than 20mum, are mixed at the volume ratio 10:1 to 1:5 to form a mixture. The resultant mixture (A+B), (C) zeolite, (D) 0.05 to 2.0wt.% of a thiazole genus, and (E) an organic adhesive component, and when necessary, a solvent, a minute graphite power, a corrosion depressor, and the like, are mixed to form this conductive paste.

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 includes substantially spherical fine particles having a particle diameter of 30 μm or less, copper particles, zeolite, and thiazoles, the surfaces of which are nickel-plated and whose upper surfaces are silver-plated. Regarding conductive paste.

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 smaller the particle size of the copper powder is, the more preferable it is, for example, 20 μm or less is preferable, and the particle size of 10 μm or less is more preferable because it is likely to be uniformly dispersed among the particles of the substantially spherical fine particles. The ratio of the substantially spherical fine particles to the copper powder is 1 by volume in terms of resistance of the conductor and prevention of migration.
It is preferably from 0: 1 to 1: 5 (substantially spherical fine particles: copper powder). As the thiazole, it is preferable to use one kind of thiazole, 2-aminothiazole, 2-mercaptothiazole, benzothiazole, 2-aminobenzothiazole, 2-mercaptobenzothiazole or a mixture thereof. The content of the thiazoles is preferably 0.05 to 2.0 wt% with respect to the solid content of the conductive paste from the viewpoint of preventing migration and economy.

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 is preferably 20 to 60% by weight in terms of the resistance of the conductor and economical efficiency with respect to the solid content of the conductive paste.

[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.

100 parts by weight of zeolite (manufactured by Wako Pure Chemicals, reagent), 10 parts by weight of benzothiazole (manufactured by Wako Pure Chemicals, reagent) and 100 parts of methyl ethyl ketone (manufactured by Wako Pure Chemicals, reagent)
Part by weight was placed in a beaker and uniformly mixed, and then gradually heated to evaporate methyl ethyl ketone to obtain a benzothiazole-treated zeolite.

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, the mixture was uniformly mixed to obtain a resin composition, and to 145 g of this resin composition, 500 g of the nickel-plated silver-plated substantially spherical fine particles obtained above was treated with benzothiazole-treated zeolite 4
4g and copper powder (Fukuda metal foil powder, trade name SPC4-8)
200 g was added and uniformly dispersed with a stirrer and a triple roll 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 36 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 48 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 A resin composition 145 obtained through the same steps as in Example 1 except that 33 g of zeolite treated with 2-aminothiazole (manufactured by Wako Pure Chemical Industries, reagent) was used in place of benzothiazole.
To g, 450 g of nickel-plated silver-plated substantially spherical fine particles and 350 g of copper powder used in Example 1 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 holes is 28 mΩ / hole, and the insulation resistance between the through holes is 1
Was 0 ⁸ Ω or more. As a result of a thermal shock test of the wiring board, the resistance of the through holes was 33 mΩ / hole, and the result of the wet and medium load test showed that the insulation resistance between the through holes was 10 ⁸ Ω or more.

Example 3 33% of the zeolite treated with 2-mercaptobenzothiazole (manufactured by Wako Pure Chemical Industries, Ltd.) in place of benzothiazole was used.
In the same manner as in Example 1, except that 145 g of the resin composition obtained in Example 1 was used, 320 g of nickel-plated silver-plated substantially spherical fine particles used in Example 1 and 200 g of copper powder were added. Was mixed and dispersed into 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 40
mΩ / hole, insulation resistance between through holes is 10 ⁸ Ω
That was all. As a result of the thermal shock test of the wiring board, the resistance of the through hole was 52 mΩ / hole, and the result of the wet and medium load test showed that the insulation resistance between the through holes was 10%.
It was more than ⁸ Ω.

Comparative Example 1 145 g of a resin composition obtained by the same method as in Example 1 except that zeolite and thiazoles were not added, and 250 flakes of silver powder (trade name TCG-1 manufactured by Tokuriki Kagaku Kenkyusho) were added.
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 48 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 67 m.
In some cases, the insulation resistance between the through holes was reduced to the order of 10 ⁷ Ω per 5 wiring boards as a result of the wet and medium load test.

Comparative Example 2 170 g of nickel-plated silver-plated substantially spherical fine particles used in Example 1 were added to 145 g of a resin composition obtained in the same manner as in Example 1 except that zeolite and thiazoles were not added. A conductive paste was obtained by uniformly mixing and dispersing in the same manner as in Example 1. 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 a thermal shock test of the wiring board, the resistance of the through hole was 450 mΩ / hole, which was 2.5 times as much as that before the thermal shock test. Further, according to the results of the wet and medium load test, the insulation resistance between the through holes was lowered to the order of 10 ⁷ Ω per one of the five wiring plates.

[0018]

INDUSTRIAL APPLICABILITY The conductive paste according to the present invention is a conductive paste in which the resistance of the through holes in the wiring board is at a practical level, the insulation resistance between the through holes after the wet and medium load test is small, and the nickel plating This conductive paste is economically excellent in that the amount of silver used can be reduced by using silver-plated substantially spherical fine particles and copper powder.

[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

Claims (2)

[Claims] 1. A conductive paste comprising nickel particles on the surface and silver particles on the upper surface, and substantially spherical fine particles having a particle diameter of 30 μm or less, copper powder, zeolite and thiazoles. 2. The conductive paste according to claim 1, wherein the thiazole is one of thiazole, 2-aminothiazole, 2-mercaptothiazole, benzothiazole, 2-aminobenzothiazole, 2-mercaptobenzothiazole or a mixture thereof.