Louh,
     
     At a previous employer we did not accept this type of defect, 
     especially where conductors were impedance controlled and on 
     component pads near the knee of holes.  I would say >90% of all 
     incidences are not related to the copper chemistries.  The operators 
     and/or plating shop managers are very knowledgable about their plating 
     bathes (this case Electrolytic Plating).  They insure that chemistries 
     are balance through set and random sampling for each shift (based
     on volume).  Although a sceince, the electrolytic plating chemistries 
     are pretty much defined.  
     
     Most burnt copper cases, as with my previous employer, where related 
     to the external PWB layouts.  
     
     When calculating the total current per side, an operator is supplying 
     current via rectifiers to exposed copper regardless of its 
     geographical location.  So low density areas with thin conductors will 
     tend to overplate and eventually burn due to the supplied current, 
     whereas high density areas will tend to plate evenly.  By re-routing 
     your pads or conductors closer to the body of copper will minimize if 
     not eliminate this condition.  Also provide deviations to suppliers by 
     allowing theiving patterns to isolated conductors.  Other than 
     cosmetics, the theiving does not affect fit, form and function.
     
     Due to the topography of burnt copper it will leave an impression on 
     solder dewetting on pads or lands.
     
     Although slow, this is ONE reason why Japanese PWB shops still use 
     Electroless Plating as the major copper depositor following a quick 
     electrolytic.  There are other benefits for using Electroless Copper.
     
     General, but I hope it helps.
     
     John Gulley - QA
     Inet Inc. - A Smarter Vision
     Plano, TX 
     972-578-3928
     
     
     
     
______________________________ Reply Separator _________________________________
Subject: FAB, ASSY:  "Copper Burning" during plating
Author:  <[log in to unmask]> at Internet 
Date:    10/21/96 11:54 AM
     
     
This morning, I was looking at some boards that had pads covered with 
copper bumps, blisters, pimples, or whatever you want to call them.  I've 
been told this was a product of copper "burning", resulting when boards 
are plated with current too high.  Is this burnt copper unacceptable?  I 
didn't see any pictures in IPC-A-600 to suggest it wasn't, but don't like 
the looks of the plating.  Any comments?  Thoughts from assemblers would 
be welcome, too.
Lou Hart 
Compunetics Quality Assurance
412-858-6117
     
     
.
     
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