A simple response is that there are several possible causes for uneven 
     etching. First examination may well reveal improperly set up etching 
     equipment or plugged nozzles.  Other process defects could be in poor 
     light distribution in an exposure machine, poor phototools, etc, 
     
     The design relationship can be significant also.  For Example, 
     isolated traces in open circuit areas can be overetched.  Also the 
     outside conductors in a group of tightly spaced traces may etch 
     differently.
     
     First action should be a process audit of the board fab supplier.
     
     Marshall Gurian
     Coates ASI        


______________________________ Reply Separator _________________________________
Subject: FAB: Etchback
Author:  [log in to unmask] at internet
Date:    7/26/96 8:13 AM


We are having a significant problem with quickturn cards coming in 
overetched, and we're trying to understand some things about the process of 
etching.
     One question that has come up is:  Is it possible for etching to be 
greater in one area of the card over another? If so, how is this possible, 
and what are the design considerations for this?
     Some here contend that every feature should etch down by the same 
nominal amount, say .002 inch, whether the feature is an .008 trace or a 
large ground plane, since the whole PCB is exposed to etchant at the same 
time.  Is there fault in this thinking?
     Thanks in advance.
     
Jim Ennis
Adtran Inc
[log in to unmask]
     
*************************************************************************** 
* TechNet mail list is provided as a service by IPC using SmartList v3.05 * 
*************************************************************************** 
* To unsubscribe from this list at any time, send a message to:           * 
* [log in to unmask] with <subject: unsubscribe> and no text.        * 
***************************************************************************
     

***************************************************************************
* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
***************************************************************************
* To unsubscribe from this list at any time, send a message to:           *
* [log in to unmask] with <subject: unsubscribe> and no text.        *
***************************************************************************