Rough Tin Plate after Soldering

What causes bright acid tin plate to become gritty after soldering?


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Q. What causes bright acid tin plate to become gritty after soldering? The parts look beautiful after plating but the surface turns gritty after our customer applies solder to the parts. –A.B.

A. A bright tin bath can contain surface-active agents, oxidation inhibitors, grain refiners and brighteners. Most of these additives are organic and are heat sensitive. Whether you have one or more than one of theses additives in your bath depends on whose chemistry you use. These additives are incorporated in the plated deposit and you get a very attractive finish. When the bright tin is heated, tin plate becomes molten and the additives can decompose and migrates to the surface, hence the gritty appearance. Try reducing your additive level in the plating bath and by all means, talk to your chemical vendor about this problem.