Brett / All,
     
        One possible cause for Dish-Downs is a mouse bite or pinhole in the 
     rubber of the Resist Laminator roll . A small vacancy in the rubber 
     will look like a bubble on the laminated panel surface. If a circuit 
     falls on the bubble etchant will under cut and cause a dish down.
        Typically , rollers with this condition are damaged when 2 panels 
     are overlapped in the cleaning cycle and Sulfuric acid is trapped 
     between them . The acid is squeezed out and deposited on the rollers 
     during resist lamination. Sulfuric acid will eat a hole in silicon of 
     the rollers leaving a small holes.
      
     
                                                Mike Covel 
                                                HMSC ,Tucson


______________________________ Reply Separator _________________________________
Subject: FAB-Dish downs in copper circuits
Author:  [log in to unmask] at CCGATE
Date:    1/27/97 8:58 AM


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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