JPH06349319A - Conductive paste - Google Patents

Abstract

PURPOSE:To obtain a conductive paste which has a high conductivity and an excellent economy, and can improve a short circuit between electrodes and between wirings, when an electric field is applied in the ambiance of a high temperature and a high humidity, by including a silver powder, and a ceramics powder whose surface is covered with silver partially or overall, to the conductive paste. CONSTITUTION:This conductive paste includes a silver powder, and a ceramics powder whose surface is covered with silver partially or overall. The form of the ceramics powder is suitable to be undifined form, and the particle size is favorable to be less than 10mum in the longer diameter, and more favorable to be less than 5mum. And the ceramics powder is preferable to use an alumina powder. Furthermore, although the ceramics powder is favorable that the whole surface is covered with silver, there is no problem when about 1/2 or more of the surface is covered with the silver. As the covering method of the silver, a method to throw in the silver powder and the ceramics powder, together with balls for powdering, to a ball mill, and to cover the surface of the ceramics powder with the silver powder while rotating them to disperse the coagulated powders, for example, is favorable, because a large amount of powders can be process in such a method.

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 silver powder and a ceramic powder whose surface is partially or entirely covered with silver.

The shape of the silver powder in the present invention is not limited, but flake silver powder having an aspect ratio of about 3 or more is preferably used, and flake silver powder having an aspect ratio of 10 or more is more preferably used. The major axis of the particle diameter is preferably 20 μm or less, and more preferably 10 μm or less because printability is not deteriorated.

The shape of the ceramic powder is not limited, but an irregular shape is suitable. The major axis of the ceramic powder is preferably 10 μm or less, more preferably 5 μm or less. The type of ceramic powder is not particularly limited, but alumina powder is preferably used. Further, it is desirable that the entire surface of the ceramic powder is covered with silver, but if about 1/2 or more of the surface is covered, there will be no problem. The method of coating silver is not particularly limited, but for example, a method of charging silver powder and ceramics powder together with a ball for grinding into a ball mill, and rotating this to disperse the agglomerated powders and coating the surface of the ceramics powder with silver powder is a method. It is preferable because a large amount can be processed.

The volume ratio of the silver powder to the ceramic powder is 5: 1 from the viewpoint of resistance of the conductor and prevention of migration.
It is preferably 1: 5 (silver powder: ceramic powder).

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

[0011]

EXAMPLES Examples of the present invention will be described below. Example 1 60 parts by weight of bisphenol A type epoxy resin (Oilized shell epoxy, trade name Epicoat 834) and 40 parts by weight of bisphenol A type epoxy resin (Oilized shell epoxy, trade name Epicoat 828) were dissolved by heating in advance. ,
Then, after cooling to room temperature, 5 parts by weight of 2 ethyl 4-methyl imidazole (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) were added. The resin composition was mixed uniformly.

On the other hand, 110 g of flake silver powder (trade name TCG-1 manufactured by Tokuriki Kagaku Kenkyusho) and an average particle size of 0.4.
μm alumina powder (Sumitomo Chemical, trade name AES-12)
35 g was put into a ball mill together with a ball for grinding, and 10
A mixed powder of silver powder which was rotated for 0 hours and uniformly dispersed and alumina powder whose surface was coated with silver powder was prepared. When the coverage of silver powder was observed with an optical microscope, the coverage was about 70.
%Met. Then, 145 g of the above-mentioned mixed powder was added to 145 g of the resin composition obtained above and uniformly dispersed by 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 23 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 30 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
Apply a voltage of 50V between adjacent lines during% RH to set 1
Hold for 000 hours.

Example 2 A mixed powder of silver powder and alumina powder whose surface was coated with silver powder was produced through the same steps as in Example 1 except that 200 g of the flake silver powder used in Example 1 and 40 g of alumina powder were blended. Then, 240 g of the above mixed powder was added to 145 g of the resin composition obtained in Example 1, and the mixture was 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 22 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 holes was 28 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 A mixed powder of silver powder and alumina powder whose surface was coated with silver powder was produced through the same steps as in Example 1 except that 800 g of the flake silver powder used in Example 1 and 70 g of alumina powder were blended. Then, 870 g of the above-mentioned mixed powder was added to 145 g of the resin composition obtained in Example 1 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 19 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 holes was 26 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.

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 22 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 28 mΩ / hole, and the result of the wet and medium load test showed that the insulation resistance between the through holes was 10 ⁷ Ω per one of the five wiring boards. There was something that was falling on the table.

[0017]

EFFECT OF THE INVENTION The conductive paste of the present invention is a highly conductive paste having a low resistance of through holes in a wiring board, has a small decrease in insulation resistance between through holes after a humidity and medium load test, and has a silver powder content. The conductive paste is economically excellent in that the amount of silver used can be reduced by using a ceramic powder whose surface is partially or entirely covered with silver.

[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 (1)

[Claims] 1. A conductive paste containing silver powder and a ceramic powder whose surface is partially or entirely covered with silver.