Norm - this there any published data on this degradation mechanism?
     
     
     Dave Hillman
     Rockwell Collins
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______________________________ Reply Separator _________________________________
Subject: Re: GEN: Heat - Sealing?
Author:  [log in to unmask] at ccmgw1
Date:    5/13/96 2:52 PM


Heat sealing of plastic bags creates a gas.  This gas gets trapped in 
the bag and adversely works on the tin (not the lead).  Doesn't help 
popcorning because once you open the bag, moisture is back into the 
board material in less than 24 hours.  Baking the boards within 3 to 
4 hours just prior to soldering would help this.  However, I don't 
advocate baking as this will diminish solderability.  I don't 
advocate heal sealing either as this shortens solerability.  Simply 
fold over the end of the bag and tape it shut.
     
As for components losing solderability due to heat sealing, I would 
suspect you have the same problem here as the leads have a tin 
coating.  Requires investigative work on someone out there.
     
Regards,
     
Norm Einarson