Metal treatment – Stock – Noble metal base
Patent
1991-10-18
1993-09-07
Dean, R.
Metal treatment
Stock
Noble metal base
148432, 148442, 252511, 252514, 420497, 420502, 420587, C22C 500, H01B 106
Patent
active
052425118
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to copper alloy composition pastes having high electroconductivity, oxidation resistance and electromigration resistance, and to electric conductors obtained by the use of the pastes. The pastes are useful for electromagnetic shielding, and as electrically conductive adhesives, pastes for conductive circuits, pastes for electrodes, pastes for screen printing, pastes for printing resistance terminals, pastes for through holes, materials for contact, etc.
BACKGROUND ART
As electrically conductive pastes or electrically conductive compositions, dispersions have been obtained by adding an organic binder and optionally a solvent and additives to powder of, for example, any of the following metals: noble metals, such as gold, platinum, palladium, silver, and silver-palladium [for instance, Jap. Pat. Appln. Kokai (Laid-Open) Nos. SHO 56 (1981)-70064, SHO 51 (1976)-124655, SHO 59 (1984)-45355, and HEI 1 (1989)-98674], nickel [for instance, Jap. Pat. Appln. Kokai (Laid-Open) SHO 58 (1983)-53966], silver-plated copper [for instance, Jap. Pat. Appln. Kokai (Laid-Open) Nos. SHO 56 (1981)-8892 and HEI 1 (1989)-231208], and copper [for instance, Jap. Pat. Appln. Kokai (Laid-Open) Nos. SHO 56 (1981)-163166, SHO 62 (1987)-74967, SHO 63 (1988)-89577, SHO 57 (1982)-55974 and HEI 2 (1990)-16172].
The conventional electrically conductive pastes have the following defects. Copper is not expensive but oxidation tends to decrease its electroconductivity. Addition of an antioxidant to paste obtained with copper powder has also been tried. In such case, in an early stage, copper oxide is removed from particle surfaces and electroconductivity can be attained. But, after the paste is made into a coating film, the contact resistance is gradually increased at high temperatures or high humidities, resulting in low electroconductivity. Electrically conductive pastes obtained by the use of silver powder are well known but involve an electromigration problem. Electrically conductive pastes obtained by the use of powder produced by plating copper powder with silver are also well known, but it is difficult to plate fine powder uniformly with silver and these pastes encounter a problem when a plated silver film comes off and an electromigration problem. Furthermore, a local battery cell tends to form between silver and copper, so that copper is easily oxidized. Processes for mechanically alloying silver with, copper forcedly have been disclosed [for example, Jap. Pat. Appln. Kokai (Laid-Open) Nos. SHO 56 (1981)-155259 and SHO 57 (1982 )-98572], but are disadvantageous in that because of the mechanical alloying, the processes are not sufficiently effective in preventing the electromigration of silver.
BEST MODE FOR CONDUCTING THE INVENTION
The present invention relates to inexpensive electrically conductive pastes which have an excellent electroconductivity, a high oxidation resistance for a long period of time, and a high electromigration resistance.
One aspect of the present invention is directed to a method for stabilizing an electrically conductive paste for a long period of time, particularly by improving the oxidation resistance and the migration resistance.
Copper alloy powder used in the present invention is produced by atomization. Gas atomization and water atomization are preferable. In particular, inert gas atomization is preferable. For inert gas atomization used in the present invention, the process disclosed by the present inventors in U.S. patent application Ser. No. 07/395531 is preferably employed. This process is as follows. For example, a copper-silver mixture or alloy having a specified composition is melted in a crucible by high-frequency induction heating in an inert atmosphere or in vacuo. In this case, the term "inert atmosphere" means an atmosphere which does not react with the melt at all or reacts therewith very slowly. For instance, an atmosphere composed mainly of nitrogen, helium, hydrogen or argon is preferable. The melt is jetted into an inert gas atmosphere
REFERENCES:
patent: 3583930 (1971-06-01), Ehrreich et al.
patent: 5064469 (1991-11-01), Mack
patent: 5091114 (1992-02-01), Nakajima et al.
Katsumata Tsutomu
Nakajima Hitoshi
Yokoyama Akinori
Asahi Kasei Kogyo Kabushiki Kaisha
Dean R.
Koehler Robert R.
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