We recently received a shipment of PCBs where the exposed outer layer
laminate has staining that looks like copper. I have a photo -
<http://tinyurl.com/yp9za2> http://tinyurl.com/yp9za2
My question is what would cause this?  I've never seen it before, but I am
thinking something in the Copper plating process.  The vendor is telling us
it is staining but it is an asthetic issue only. What would cause it?  Is it
an asthetic issue only?  It seems to me if the staining was caused by some
plating chemistry, then it would effect the laminate properties,
particularly the insulation resistance.
 
Thanks!
 
Kevin Glidden
Manufacturing Engineer
Luminescent Systems Inc.
 
 
 

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