Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Displacement or replacement coating
Patent
1991-11-27
1993-05-18
Niebling, John
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Displacement or replacement coating
205101, 427 98, 427345, 427436, B05D 512, B05D 118
Patent
active
052118312
ABSTRACT:
A stabilized spray displacement tin plating process of copper printed circuit innerlayers is disclosed for the manufacture of multilayer printed circuit boards. During prolonged use of spray tin plating, the plating solution becomes saturated with cupurous thiourea complex which precipitates interfering with spray nozzles and other mechanical components. The tin plating solution is stabilized by removing portions from the reservoir before saturation is reached, selectively precipitating the thiourea complex, and returning the remaining solution back to the reservoir. The precipitated cupurous thiourea complex is redissolved in acid and either disposed of by conventional waste treatment or the acid solution can be electrowinned to reclaim copper and oxidize thiourea to form a more acceptable acid solution for waste treatment. Preferably, the thiourea is isolated from the anode during electrowinning, so that the acid thiourea solution formed may be used to partially replenish the tin plating solution in the reservoir. By such periodic removal of the complex, the plating bath is stabilized and its useful life is extended dramatically.
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Dodd John R.
King Randal D.
Reinbold Carl W.
Vitale Americus C.
Bolam Brian M.
Hauser William P.
Lucas James A.
McGean-Rohco, Inc.
Niebling John
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