I have been told by others with this experience that 
electro-tin plated or tin-dipped parts, such as RF 
screens or 'cans', may become unsolderable after a 
month or less on the stockroom shelf.  Apparently, the 
tarnishing of the tin results from the parts being 
improperly packaged in materials such as paper, 
cardboard or plastic which were made with sulfur- or 
acid- compounds. These parts are typically made from 
copper or aluminum, with a nickel overplating, then 
tinned.

Thus, I am tempted to instruct my vendor to assure 
that parts of this nature must be packaged in 
acid-free, sulfur-free packaging.  When the parts 
arrive, I would instruct the stockroom to store them 
at low temperatures (refrigerated) to also reduce 
electromigration.  

Does anyone have information that these assumptions 
are correct, and is there published material that 
might add validity to these assumptions? 

----------------------
Richard Huziak
Manufacturing Engineering
SED Systems
Saskatoon, SK, Canada
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