Brett,
Set up your AOI to inspect the dishdowns.  If it is a reflective AOI unit it 
should be able to detect these defects without affecting other inspection 
parameters such opens/shorts/etc.  You can then keep track of frequency and 
note any patterns or repeatability of occurrance.

I don't know if there is any industry data supporting dishdowns, however, 
there may be some information in the IPC Operator Awareness Videos for PWB 
etching(IPC-OA-111) or PWB Inspection(IPC-OA-117.)

George Murray
Gerber Systems
 ----------
From: TechNet-request
To: TechNet
Subject: FAB-Dish downs in copper circuits
Date: Monday, January 27, 1997 10:24AM

Good Morning,

      Recently  a customer had a field failure in which and internal circuit
trace
burned through. After a failure analysis was done, a cross-section 
determined
that at the point of failure there was a dish-down or vertical thinning of
the trace.

     This defect was not picked up at innerlayer inspection as the primary
focus
is on shorts, breaks and mouse-bites. The customer would like to know if
there
is any industry data showing the possible frequency of such a defect.

    How do I give a cause/corrective action for a defect Im not sure I can
consistantly
detect?

Thank you for your help.

Brett Austin
Nationwide Circuits Inc




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