We have experienced similar problems in the past.  The only way we 
     have determined to get around the haloing, is to drill the non-plated 
     through-holes before etching copper.
     
     The copper cladding prevents any chipping or delaminating of the 
     glass fibers.
     
     In board designs with only a few NPTHs, we tend to drill both PTH and 
     NPTH at the same time.  Plating in the NPTHs doesn't appear to be 
     much of a problem.
     
     In board designs with quite a few NPTHs, we still drill PTHs and 
     NPTHs in separate operations.  Drilling the NPTH after plating 
     reduces the occurrence of copper plating in the NPTH.
     
     We hope this information helps you out.
     
     Bob Penniston
     AlliedSignal Aerospace, Inc.
     Federal Manufacturing and Technologies 
     Kansas City, MO


______________________________ Reply Separator _________________________________
Subject: FAB:haloing
Author:  Mike McHenry at KCD-ELECTRONIC
Date:    6/6/96 2:44 PM


We are 2nd stage drilling .220" to .250" holes at NC rout and experiencing 
.020" to .030" haloing/delamination. The 2nd drill is in areas of bare 
laminate (no metal pad or ground plane).  Does anyone have suggestions to 
prevent this? Thanks for any input.

Lyle Anderson
Electrostar-Utah
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