Try doing a copper purge.
     
     We purge copper from our solder wave by cooling the pot to just above 
     freezing for 12 (or more) hours. The copper forms 1-3 balls that we 
     scoop out. This generally reduces copper concentration from .2% to 
     less than measurable. 
     
     This can be done on a weekend.
     
     I don't see why you can't do something similar.
     
     Aric Parr
     United Technologies Electronic Controls


______________________________ Reply Separator _________________________________
Subject: FAB: HASL drossing
Author:  [log in to unmask] at internet
Date:    8/5/96 2:42 PM


     Hello Technet,
     We are having difficulty maintaining our HASL pot below 0.25% Cu, even 
     with 2x daily drossing.  The machine is an old vertical Electrovert 
     with less than easy access.
     - Is this 0.25% more critical at assembly than at fab? 
     - What is the practical USL for copper in HASL?
     - How often should metal contaminants be measured?
     - Should drossing be done at a constant frequency, or based on panel
       loading?
     - Are there any studies out there correlating HASL quality with Cu
       contamination level?
     - Any special recommended procedures or tools?
     
     As always, we appreciate any input.
     Joe Felts
     PC World, Toronto
     
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