John, 

Pertaining to the apparent contradictions contained in items #1 & #2, 
as can often happen in this business they are both correct.  Acid 
will indeed help finish crosslinking the polymers if they have not 
completely "kicked over".   However a acid cleaner with a strong 
oxidizer, such as free flouride or chloride ions,  will also help 
undercut and actually remove thin residues prior to surface 
finishing.  Because of this we have a chamber of solder stripper 
prior to our conventional  HASL micro-etch.  We run it only rarely 
when someone or some process up the line goes astray.  Such developer 
problems, excessive hold times, over tack curing, ambient U.V. light 
ETC.  

Robert E. Welch
Process Specialist
Email: [log in to unmask]
Modem: 804-239-9120
Fax:   804-237-3048

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