I have ran into similar issues quite some time back. My issue was
     obviously connected to the design and my racking used. I had stainless
     Steel racks that either had a "galvanic" condition taking place or
     some sort of thermal absorption into the rack from the signal layer. 
     The whole thing was strange because some jobs had it and some didn't.
     (NahNu NahNu????) Anyways....We increased the agitation in the oxide 
     bath to something from nothing and plastisol coated our racks and the
     problem went away. (Poooof!)
     
     Good Luck!
     
     Stay in touch!
     
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______________________________ Reply Separator _________________________________
Subject: Periodic Problems With Oxiding
Author:  [log in to unmask] at SMTPLINK-HADCO
Date:    11/27/95 3:49 AM


Does anybody have a definitive Cause and Corrective Action for a problem that 
seems to occue infrequently with oxiding?  
     
Specifically a detail with a power or ground plane and a signal layer 
opposite will oxide fine on the power/ground side, but will occasionally 
oxide incompletely on the other side.
     
I've always thought it was basically a cleaning problem, and I know it has 
occurred on a variety of coppers and substrates.  But on occasion it has been 
very persistent, unable to be improved by strip and re-oxide for example.
     
Very frustrating to the PWB producer and both the laminator and the chemical 
supplier get accused of having something wrong with their products.
     
Any ideas?