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Tin plating for solderability rust after storage

October 26, 2011

I have been given a problem to solve in relation to tin plated flanged pins made of S28D steel.
They have 0.0002" of tin plate that is scratch brushed and then soldered onto a beryllium copper component at the flanged end.
After storage for about 1 year the pins are corroding with a dark stain on the exposed side of the flange section.
After soldering the whole assembly is cleaned with abrasive green pad, to give a bright finish.
I suspect that this action is removing enough tin to cause the substrate to be exposed and therefore the corrosion can take place.
What I would like to know is the 0.0002" of tin sufficient in itself to give corrosion protection as well as solderability?

Mark Lees
Chemist - Ballasalla, Isle of Man, Great Britain

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October 26, 2011

Gut feeling is that it is not even close. That is so thin that there are pores to allow moisture and other stuff to attack the "nail". Next, without a nickel coat, the copper will migrate thru the tin. Add any moisture and you have a wonderful battery.
Thin you take this thin coat and mechanically abrade it. No wonder it rusts.
Consider using electroless nickel and that may not work either because it is so thin.

James Watts
- Navarre, Florida