Mcgean-rohco, Inc.

Atotech Deutschland Gmbh

Americus C Vitale

Randal D King

George S Bokisa

John R Dodd

Craig V Bishop

Anthony J Arduengo, Iii

Gary W Loar

Dickson L Whitney, Jr

Carl W Reinbold

Adhesion of polymeric materials to metal surfaces

A novel, environmentally innocuous, post-etch, pre-soldering cleaner and cleaning process is disclosed for removing contaminants from plated surfaces of printed circuit boards manufactured by the pattern plating method. The post-etch, cleaning process of this invention, for removing contaminants from plated surfaces of an etched printed circuit, comprises treating the plated surfaces with a cleaning solution which comprises an aqueous solution of (i) an imidazole-2-thione compound and (ii) an acid. The imidazole-2-thione compound has the formula: ##STR1## wherein A and B are the same or different --R--Y groups, wherein R is a linear, branched or cyclic alkenyl group containing 1 to 12 carbon atoms and Y is a hydrogen, halogen, cyano, vinyl, phenyl or ether moiety. Of this class of compounds, 1-methyl-3-propylimidazole-2-thione is preferred. The novel aqueous cleaners of this invention are effective replacements for conventional cleaners containing the toxic material thiourea and are superior to cleaners free of thiourea.

Post-etch, printed circuit board cleaning process

An efficient spray displacement tin plating process of copper printed circuit innerlayers is disclosed for the manufacture of multilayer printed circuit boards. The displacement tin plating solution is stabilized and replenished by incorporating free tin metal in the plating solution reservoir. Unwanted tin(IV) ions which are produced by aerial oxidation during the spray process, are reacted with tin metal in the reservoir to produce sufficient tin(II) ions to compensate for losses due to plating, oxidation and the like. Not only is the plating bath stabilized, but its useful life is extended dramatically.

Stabilized spray displacement plating process

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.

Process for extending the life of a displacement plating bath

An environmentally innocuous effective replacement for thiourea is disclosed for use as a complexing agent in displacement plating processes in which the plating solution is applied to the substrate surface to be plated by immersion or by spraying, cascading, pouring and the like. The replacement complexing agent is an imidazole-2-thione compound having the formula: ##STR1## wherein A and B are the same or different --R--Y groups, wherein R is linear, branched or cyclic alkenyl group containing 1 to 12 carbon atoms and Y is a hydrogen, halogen, cyano, vinyl, phenyl, or ether moiety. Of this class of compounds, 1-methyl-3-propyl-imidazole-2-thione is preferred for immersion tin plating. This class of complexing agents is particularly useful in spray displacement tin plating for the manufacture of printed circuit boards wherein free tin metal is added to the plating solution.

Complexing agent for displacement tin plating

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West Chester, PA, United States of America

Americus C Vitale