Hi Richard-
     
     I have not had any problems with the components you describe provided 
     the plating was done correctly to begin with. There have been some 
     discussions within the IPC solderability committees about the need to 
     have "clean" packaging materials to avoid some of the problems you 
     described (sulfur contamination/corrosion of a finish due to packaging 
     is an industry documented phenomena, especially for silver finishes). 
     Your packaging thoughts are an idea that many people would endorse but 
     I don't think the refrigeration theory would be supported. Again - 
     good plating should solve you problem. Good Luck.
     
     
     Dave Hillman
     Rockwell Collins
     [log in to unmask]
     


______________________________ Reply Separator _________________________________
Subject: ASSY: Solderability - Storage of Tin Plated Parts
Author:  [log in to unmask] at ccmgw1
Date:    10/14/96 1:58 PM


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
[log in to unmask]
     
     
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