Lyle We experienced the same problem with polyimide. We added copper pads around the NPTH drill diameter OR Drill NPTH while copper is still on the board prior to etch. This eliminates the haloing. Roxanne Tovey ______________________________ Reply Separator _________________________________ Subject: FAB:haloing Author: [log in to unmask] at esdigate Date: 6/6/96 8:20 AM 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 [log in to unmask]