Hi Blue Smurf:
     
     A couple of questions:
     
     a) was there tape on the fingers when this phenomena occurred (ie. did 
     the solder get under the tape)?
     
     b) did you do any FTIR or surface analysis on the gold to confirm that 
     there was no contamination?
     
     I have seen this happen on a couple of our assemblies but we traced 
     the phenomena to:
     
     1)the solder was "just" molten and therefore was not really 
     metallurgically joined to the gold fingers (ie. it solidified too fast 
     to attach).
     
     2) there was a residue on the gold fingers from the tape that didn't 
     allow for joining to occur.
     
     3) the nickel underplate had diffused up through the gold plating 
     porosity. But this also makes it nonsolderable too!
     
     
     Dave Hillman
     Rockwell Collins
     [log in to unmask]
     
     
     


______________________________ Reply Separator _________________________________
Subject: SOLDER SPLASH ON GOLD FINGER
Author:  [log in to unmask] at ccmgw1
Date:    6/26/96 3:40 PM


     
As  you know, gold dissolves extremely rapidly in molten solder compared 
with other metals. Some of you might have experienced the effect of solder 
splash or balls landing on gold plated surfaces which  contaminate the gold 
surface finish. Typically, tape or sheath is used to protect the gold plated 
surface (gold fingers) from solder contamination.  Recently, we found some 
gold plated assemblies that exhibited no contamination on the gold surface 
even when solder balls or splash landed on the surface.  The strange thing 
is that no solderability problem has been reported on any gold plated SMT 
pads. Can someone comment on this phenomenon!!
     
Thanks
     
Blue Smurf
Here is some additional info.
Electroplated Ni thickness: ~ 100 micro inch 
Electroplated  Gold thickness ~40 micro inch