Letter 3025

Pitting in tin 

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We are processing components with 75 microns of tin from an acid bath and experiencing pittingin HCD areas. Our suppliers tell us that the solution is OK and should not pit. Has anyone had similar problems and any solutions to the problem.

Bob Lynch
     plating company
Sydney, Australia

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You didn't mention if this was a bright tin plating bath or not. However, if it is, there are two things that come to mind; One pitting problem specifically occurred in HCD areas and turned out to be related to the agitation in the bath. We were using mechanical agitation from the work bar and it was evidently insufficient by itself. The in-tank filter pump in the tank had not been working and unfortunately it had not been noticed by the operator. When it was repaired and there was vigorous circulation of the solution as well as the work bar movement, the pitting in the HCD areas disappeared. The other was a series of what looked like pitting problems, however when viewed under magnification, the pits actually looked like fish-eyes as in paint. That turned out to be a lack of wetting agent. That was over the entire surface including LCD areas.

Ward Barcafer, CEF
aerospace - Wichita, Kansas

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