JPH0992029A - Conductive paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a decrease in heat history for a board and energy savings by enabling a conductive paste for use in making a circuit connection between the layers of a printed wiring board to be cured at low temperatures. SOLUTION: In order to lower a curing temperature, a phenoxy resin and a higher fatty acid are added to a material composed chiefly of an epoxy resin as a binder for a conductive paste, thereby curing and contraction are promoted to enhance conductivity of the 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 which can be used for connecting circuits between layers in a printed wiring board.

[0002]

2. Description of the Related Art In recent years, with the rapid development of the field of information equipment, there has been a strong demand for higher density and higher precision of printed wiring boards. Among them, a silver paste for through holes is often used as a means for electrically connecting layers. This is due to the excellent conductivity of silver, and a countermeasure against migration is taken by a resin coat. Therefore, it is expected that the amount used will increase in the future. Among them, for binder, the degree of cure shrinkage,
From the viewpoint of coating film hardness, phenol resin systems are the mainstream. On the other hand, the curing of the phenol resin system is a condensation reaction, and therefore a temperature of 160 ° C. or higher is required. Further, further improvement in adhesive strength with the substrate is desired. Further, there has been a strong demand for the construction of a low-temperature curing type binder system from the viewpoint of reducing the heat history of the printed wiring board to improve the accuracy of the printed wiring board and saving energy. Further, when a phenolic resin-based conductive paste is used for through-hole interlayer connection, there is a problem that solvent desorption does not easily occur in a thick portion of the coating film. From this point of view, at present, the phenolic resin-based conductive paste has not yet been in a satisfactory state.

[0003]

Epoxy resin has the advantages that it has good adhesion to metals, has a smaller curing shrinkage than other resins, and that the curing temperature can be adjusted by selecting a curing agent. Many. However, when it is considered as a binder of a curable conductive paste, it has a disadvantage that the curing shrinkage is small. This is because in the conductive paste, the conductive particles are dispersed in the binder, and conduction is obtained based on an increase in the contact area due to contraction of the binder during curing. That is, if the curing shrinkage is small, the conduction becomes poor and it becomes unsuitable as a binder for the conductive paste.

An object of the present invention is to provide an epoxy resin-based conductive paste having excellent conductivity while taking advantage of the fact that the curing temperature of the epoxy resin can be lowered and the adhesive strength is strong.

[0005]

In order to achieve the above-mentioned object, a conductive paste using an electrically conductive metal powder and an epoxy resin as a binder for the metal powder is used. I examined it in detail. The present invention is based on the fact that the addition of a phenoxy resin to an epoxy resin increases the curing shrinkage to improve conduction, and the inclusion of a higher fatty acid further improves conduction. According to the present invention, the curing temperature can be lowered without impairing the characteristics of the epoxy resin.

In the above construction, when silver powder is selected as the conductive particles, it is desirable that the silver powder has a scaly shape with an average particle size of 1 to 2 μm. If desired, dendritic silver powder may be added. The proportion of silver powder in the coating film is preferably 77 to 80% by weight. If it is less than 77% by weight, the conductivity is low, and if it exceeds 80% by weight, the adhesive strength and fluidity are poor. The reason why conduction is improved by adding a phenoxy resin or a higher fatty acid is not clear at present, but it is considered that a hydroxyl group or the like has an action of promoting conduction improvement during the reaction between the epoxy resin and the curing agent. If the addition amount of either the phenoxy resin or the higher fatty acid is too small, the effect of promoting conduction improvement is small, and if it is too large, it may be liberated from the paste during long-term storage, which is not desirable. Therefore, a preferable addition amount range exists. Myristic acid as higher fatty acid,
Palmitic acid, stearic acid, oleic acid, etc. can be used. It is also possible to add other resin components such as butyral resin in order to improve paint properties such as thixotropy.
Although various types of latent curing agents for epoxy resins have been proposed, Amicure (R), which is commercially available as an epoxy resin amine adduct, is preferable from the viewpoints of storage stability and curing temperature.

[0007]

According to the above-mentioned structure of the present invention, the curing temperature can be arbitrarily lowered and the solvent can be easily removed smoothly. Therefore, the epoxy resin type conductive paste suitable for the through-hole interlayer connection can be obtained. Is obtained. By using this conductive paste, it is possible to reduce the heat history on the substrate and realize a highly accurate printed wiring board. Further, it contributes to energy saving from the viewpoint of heat quantity.

[0008]

【Example】

(Example 1) Hereinafter, the present invention will be described in more detail. 100 parts by weight of scaly silver powder having an average particle size of 1.5 μm, 20 parts by weight of an epoxy resin (trade name Epicoat 828 manufactured by Yuka Shell Epoxy Co., Ltd.), and phenoxy resin (trade name YP-50).
A mixture of 2.4 parts by weight of Toto Kasei Co., Ltd., 0.4 parts by weight of oleic acid, and 42 parts by weight of ethyl cellosolve is sufficiently kneaded and dispersed by a three-roll mill. Next, 5.5 parts by weight of a curing agent (trade name Amicure PN-23 manufactured by Ajinomoto Co., Inc.) was added,
Three rolls were kneaded to obtain a silver paste. The obtained silver paste was applied to a glass plate with an applicator and cured at 130 ° C. for 1 hour. The sheet resistance of the coating film after curing is 0.1Ω / □
Met. The cross-cut peeling test for evaluating the adhesive strength to the copper foil was 100/100, and there was no problem.

Comparative Example 1 A cured film was obtained in the same manner as in Example 1 except that the phenoxy resin was not added and the amount of the epoxy resin added was 22.4 parts by weight. The sheet resistance value was 0.2 Ω / □. The crosscut peel test was 100/100.

Comparative Example 2 A cured film was obtained in the same manner as in Example 1 except that oleic acid was removed. The sheet resistance value was 0.3Ω / □. The crosscut peel test was 100/100.

Comparative Example 3 A cured film was obtained in the same manner as in Example 1 except that the binder was changed to phenol resin and the curing agent was changed to dicyandiamide to set the curing temperature to 160 ° C. The sheet resistance value was 0.1Ω / □. The cross-cut peel test was 90/100 (decrease in adhesive strength).

Comparative Example 4 A cured film was obtained in the same manner as in Comparative Example 3 except that the curing temperature was 130 ° C. The sheet resistance value was 0.2 Ω / □. The cross-cut peel test was 93/100.

Example 2 100 parts by weight of scaly silver powder having an average particle size of 1 μm, 20 parts by weight of an epoxy resin (Epicote 828 Yuka Shell Epoxy Co., Ltd.), and a phenoxy resin (YP).
-50S manufactured by Toto Kasei Co., Ltd.) 1.2 parts by weight, butyral resin (S-REC BM-S manufactured by Sekisui Chemical Co., Ltd.)
A mixture of 2 parts by weight, 0.5 parts by weight of stearic acid, and 42 parts by weight of ethyl cellosolve is sufficiently kneaded and dispersed by a three-roll mill. Next, 5 parts by weight of a curing agent (trade name, Amicure MY-H, manufactured by Ajinomoto Co., Inc.) was added and kneaded with three rolls to obtain a silver paste. The obtained silver paste was applied to a glass plate with an applicator and cured at 130 ° C. for 1 hour. The sheet resistance of the coating film after curing was 0.1 Ω / □. The cross-peel test was 100/100. As is clear from the above examples and comparative examples, the coating temperature of 160 ° C. of the phenol resin system was changed to another coating by the binder design mainly composed of the epoxy resin of the present invention. The physical properties of the film can be lowered to 130 ° C. without changing.
Also, the adhesive strength to various printed circuit boards was sufficient.

Then, the through holes were filled by printing and various reliability tests as a printed wiring board were conducted. Thermal shock test (125 ℃, 30 minutes ← → -65 ℃, 30 minutes) 1
00 cycle, humidity resistance test (55 ℃, 95% RH) 100
There was no problem at 0 hours, high temperature storage (100 ° C.) 1000 hours, and low temperature storage (−55 ° C.) 1000 hours.

Although the present invention has been described with reference to the metal powder,
It goes without saying that carbon powder can also be used.

[0016]

According to the present invention, the adhesive strength to a copper substrate is sufficient and the curing temperature can be lowered by selecting a curing agent, which contributes to higher precision of printed boards and improved productivity. can do.

Claims (5)

[Claims] 1. A conductive paste comprising a conductive metal powder and an epoxy resin as a binder for the metal powder. 2. The conductive paste according to claim 1, which contains a phenoxy resin in an amount of 3 to 10% by weight based on the epoxy resin. 3. The conductive paste according to claim 2, which contains a higher fatty acid in addition to the epoxy resin and the phenoxy resin. 4. The conductive paste according to claim 3, wherein the amount of the higher fatty acid added is 0.7 to 1.5% by weight based on the total amount of resin. 5. The conductive paste according to claim 1, wherein the curing agent for the epoxy resin is a latent curing agent.