I have had exactly that conversation with suppliers of direct plate 
     chemistries:  
     If a large nailhead is present, then part of it can be removed after 
     microetch, which is done AFTER key steps in the process. Microetch is 
     done after the application of the carbon/graphite in the Blackhole/ 
     Shadow processes, & after the wetting agent conditioner in the 
     palladium systems.  These can leave circumferential voids.
     
     The recommendation was to perform a microetch before the key steps if 
     a Fab shop knows that it has nailheading.
     
     
     MB
______________________________ Reply Separator _________________________________
Subject: Fab-Re: More nailheading
Author:  [log in to unmask] at SMTPLINK-HADCO
Date:    5/2/96 05:07 PM


Other info on nailheading 
     
Received a note on nailheading to the effect: What if a direct-plate process 
was used and the undercutting that is required to remove the unwanted coating 
also etched away the thin layer of copper at the extension of the nailhead.
 Does this result in a circumferential void?. I believe it would; however, it
probably does not have have any relation to the often specified 150% of the 
base foil thickness, and may also happen with a 125% nailhead.      
     
Other incidental on nailheading:  It is remembered that Bob Lomerson-ex Gen 
Dynam-Ft. Worth  has a patent on a nail heading process wherein he imposed on 
the top of the drill stack during drilling a layer of another foil and 
nailheaded (smeared) it all the way through the the hole thus eliminating 
electroless processing.
     
Phil Hinton
hintpwb1.aol.com