We have had a problem in the past with OSP/bare copper boards with 
     gold fingers.  It might be related.  It occurs along the gold/copper 
     interface.  When the board goes through the microetch prior to the OSP 
     coating the bare copper traces entering the gold fingers were over 
     etched at the gold/copper interface.  
     
     For some reason, the term the "experts" used was "galvonic etch", the 
     microetch at the interface becomes too agressive resulting in etch 
     outs at the interface.  Very difficult to see.  Since electrical test 
     is before the OSP treatment we have had opens in final product as a 
     result of this..
     
     Our design solution was to make sure the soldermask overlaps the gold 
     fingers and also that there was enough room to insure the taping prior 
     to gold plating completely covered any bare copper. 
     
     Never saw this in HASL boards with gold fingers.  The exposed 
     copper/nickel/gold interface seemed to be the cause.  
     
     Someone else will have to explain the chemistry.
     
     [log in to unmask]
______________________________ Reply Separator _________________________________
Subject: Re:FAB gold plating problem
Author:  [log in to unmask] at Dell_UNIX
Date:    4/25/96 11:25 AM


     I'm in the same boat! Identical process. Tried everything under the 
     Sun. No go - No way. <For me> The gold lands must be completely 
     isolated with no outerlayer traces. (Solder to gold demarcation line) 
     The gold plating basically poisons the solder which disappears in
     the etcher (or is it itcher?) and wul-ah, an open.
     
     Groovy
     
     BTW-Isn't the itcher located next to the board stretcher?
        Or was it the on the shelf by the box of tooling holes? 
        <Poor guy. I guess everybody gets initiated into the buis
          one way or another.>
______________________________ Reply Separator _________________________________
Subject: gold plating problem
Author:  [log in to unmask] at SMTPLINK-HADCO 
Date:    4/24/96 8:18 PM
     
     
     Our Process
     Isolated tabs in the center of the board to be gold plated are defined 
     by a primary layer of resist.  After copper and tin-lead plating them, 
     we vacuum laminate 3 mil dry film resist.(over the plated tin-lead and 
     over the primary layer or resist)  This top layer of resist is 
     selectively imaged to produce an opening exposing the area to be gold 
     plated (which now has tin-lead on it). Then the tin-lead is stripped, 
     and the nickel and gold are plated using our usual sulfamate 
     nickel/soft gold process. 
     
     The Problem
     The plated nickel peels from the copper surface.  The peeling is 
     always near traces connecting to the tabs.
     Therefore I suspect that tin-lead stripper is being trapped under the 
     top layer of resist and coming out during plating. 
     
     Solutions?
     I don't suspect the nickel/gold process is the problem, as the usual 
     yield on products without this tin-lead stripping step is nearly 100%. 
     
     We have no option to change the design of the board to facilitate 
     manufacturing. ie: No bussing of the tabs is possible therefore base 
     copper must be used as a conductive path prior to etching.
     
     We've tried: 140 degree F water rinse after stripping, conveyorized 
     nitric tin-lead stripper, immersion and conveyorized peroxide tin-lead 
     strip, a second strip cycle, UV bump (160mJ), among other things.
     
     Any help would be appreciated.