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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