Kevin,

It's not clear if the laminate in question is an FR-4. Looks like a
composite? If this is the case, then it may absorb more moisture and
possibly chemicals which in turn may leave residues on the surface which
in turn oxidises when heat is applied to the material. The heat is
probably from the solder resist and /or ident curing stage.

I also note that the resist colour is black. It is possible that the
dense pigments from the resist, if a photo-imageable resist type have
been left behind on the surface after developing, which would account
for the staining. 

If the product is sensitive, then get your fab shop to analyse the
stain, by Mass spectrometer or similar to determine make-up.

Colin W.T. McVean M.Inst.C.T                                
Production Manager
 
 
Artetch Circuits Ltd  (www.artetch.co.uk)
Direct Dial      01903 712926
Switch Board  01903 725365
Skype: colin.artetch                                           
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Kevin Glidden
Sent: 28 September 2007 14:06
To: [log in to unmask]
Subject: [TN] Copper Staining in PCB laminate

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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