JPH06325616A - Conductive paste - Google Patents

Abstract

PURPOSE:To increase conductivity, enhance the cost effectiveness, prevent or reduce short-circuiting between electrodes or wirings even under the atmosphere of high temperature and high wetness by including approximately globular particles having specific value or less of a particle diameter and flake-like silver powder. CONSTITUTION:Conductive paste is made of plastic or an inorganic material having an approximately globular shape and including particles having a long diameter of at least 30mum or less and flake-like silver powder. The particle may be a non-conductive or conductive particle, and does not require high conductivity such as silver, gold or the like. An aspect ratio of the flake-like silver powder is preferably almost 3 or more and, more preferably, 10 or more. Consequently, it is possible to obtain high conductive paste where resistance of a through hole 1 formed on a wiring board is low despite of the small content of silver, to reduce a decrease in insulative resistance between the through holes 1 after a load test in the wet atmosphere, and to reduce a using quantity of silver by the use of silver plating particles so as to enhance the cost effectiveness.

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 has a particle size of 30 μm.
The present invention relates to a conductive paste containing substantially spherical fine particles and flake silver powder.

The substantially spherical fine particles in the present invention are made of plastic or an inorganic material, and the shape thereof is substantially spherical and at least the major axis thereof is 30 μm or less, and the conductivity is not limited. That is, it may be non-conductive fine particles or conductive fine particles, and does not require high conductivity such as silver and gold. It should be noted that the use of substantially spherical fine particles having a particle size of more than 30 μm causes defects such as clogging of the screen during printing, poor elongation of the paste and poor printability.

The shape of the flaky silver powder is not particularly limited, but the aspect ratio is preferably about 3 or more, more preferably 10 or more. Also,
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-shaped silver powder is preferably 5: 1 to 1: 5 (substantially spherical fine particles: flake-shaped silver powder). When the flake-shaped silver powder is more than this range, the amount of silver used increases, so that the conductive paste becomes expensive and silver migration easily occurs.

In addition to the above materials, the conductive paste may contain a liquid organic adhesive component and, if necessary, a solvent, a fine graphite powder, a corrosion inhibitor and the like. The content of the substantially spherical fine particles and the flake-shaped silver powder is preferably 20 to 60% by weight based on the solid content of the conductive paste, and 30
More preferably, it is from about 60% by weight. If the content is less than this range, the resistance of the conductor is high, and if it is more than this range, it is economically disadvantageous.

[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 prepared by uniformly mixing and 145 g of this resin composition had an average particle size of 20 μm.
40 g of polystyrene-made spherical fine particles (manufactured by Hitachi Chemical Co., Ltd.) having a maximum diameter of 28 μm and 110 g of flake-shaped silver powder (manufactured by Tokuriki Kagaku Kenkyusho, product name TCG-1) are added, and an agitator and a three-roll mill are added. Was evenly dispersed 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 silver foil was 24 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 31 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 To 145 g of the resin composition obtained in Example 1, 65 g of the substantially spherical fine particles used in Example 1 and 200 g of silver powder were added, and the mixture was uniformly mixed and dispersed in the same manner as in Example 1 to conduct electricity. I got a 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 23 mΩ / hole, and the insulation resistance between the through holes is 1
Was 0 ⁸ Ω or more. As a result of the thermal shock test of the wiring board, the resistance of the through holes was 29 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 To 145 g of the resin composition obtained in Example 1, 30 g of the substantially spherical fine particles used in Example 1 and 800 g of silver powder were added and uniformly mixed and dispersed in the same manner as in Example 1 to conduct electricity. I got a 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 19 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 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 Ω or more.

Comparative Example 1 To 145 g of the resin composition obtained in Example 1, 1000 g of the 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.

[0016]

EFFECT OF THE INVENTION The conductive paste according to the present invention is a highly conductive paste having a low through-hole resistance in a wiring board even if the content of silver is low, and the insulation resistance between the through-holes after a wet and medium load test. Is a conductive paste that is economically excellent in that the amount of silver used can be reduced by using silver-plated fine particles.

[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 substantially spherical fine particles having a particle diameter of 30 μm or less and flaky silver powder.