Well...I have seen post separation on boards with 0.0003" 
          etchback, so I think your PWB supplier is off base.  Post 
          separation has many causes that cannot be solved with 
          providing a three sided lock (which is my guess as to why 
          they recommended etchback).
          
          Your supplier has a post separation problem and will not 
          acknowledge it.  They are being unresponsive.  I know what I 
          do with suppliers like this.
          
          If you want to call out etchback, remember it is more 
          expensive.  There are plenty of suppliers out there who 
          desmear and have NO post separation.
          
          Regards,
          
          Dave Sullivan
          Rockwell Collins, Inc.
          
          [log in to unmask]


______________________________ Reply Separator _________________________________
Subject: Etchback 
Author:  [log in to unmask] at ccmgw1
Date:    4/8/97 7:44 PM


The purpose of this request is to solicited some opinions as to the 
merits of etchback.
          
          
My company has recently had some field returns which analysis has 
disclosed that the failures are a result of post separation. The PWB 
supplier ,when contacted, suggested that if our drawing had required 
etchback there would have been a less of a chance for a failure of this 
nature to occur.
          
          
My company uses both IPC-RB-276 (IPC-6011&IPC-6012) and 
MIL-STD-55110E as procurement specifications and it so happens we 
have experienced failures in PWB's procured using both 
specifications. The guidance furnished by either is not definitive 
just if the Master Drawing say do it the etchback has to fall within 
certain limits.
          
          
We have always gone with only a chemical desmear (permanganate) with 
no apparent epoxy removal. We have never specified a chemical 
etchback for fear of latent defects from residual chemicals. Our PWB 
supplier tells us there is now available plasma etchback/chemical 
desmear (permanganate) which we are told eliminates the potential 
for the latent defect problem.
          
          
Does anyone have data which would provide information as to which 
process would make the more reliable product. Any and all replies and 
opinions welcome.  
          
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