Kevin,
     
        The definition of wedge voiding that I'm familiar with is a defect
     located at the plated through hole where the oxided layer meets 
     perpendicular to the plated barrel of the hole. (I have never heard 
     of the ends <or tails> of nailheading called that before)
     
     --[===|    |===]--
           |    |                          |    |
     ======|<  >|=====            ========<|    |
           |    |                 ^Oxided  |    |
     ======|<  >|=====         InnerLayer
           |    |             Wedge void @ PTH interface
     --[===|    |===]--
     
       On this <crude> 4 lyr diagram 
     the "<" and ">" would indicate where the 
     wedge void could be.
     
     An improperly drilled hole may produce a small gap at that location
     as attempted to depict above.
     
     During <acidic> wet processing solution works it way up the innerlayer
     oxided copper area surrounding the drilled hole and can dissolve oxide
     <hence pink ring but lets leave that one alone>. If the size of the
     gap <or wedge> is sufficient to trap air bubbles or chemistries, there
     would not be ample coverage for proper copper plated through holes.
     Cross section analysis could produce circumferential voiding or copper 
     plated through hole thickness less than .0008" <isolated>.
     
     Are others calling the <absence of> ends of the nailheading not taking
     plating wedge voids?
     
     Groovy
     
     


______________________________ Reply Separator _________________________________
Subject: Re: Fab-Re: More nailheading
Author:  [log in to unmask] at SMTPLINK-HADCO
Date:    5/4/96 2:42 AM


Dear Phil:
     
As you indicated, the potential for circumferential voiding exists in any direct
plating process that would remove the underlying copper from the conductive 
deposit. This condition is commonly referred to as wedge voiding, as it exhibits
itself as a wedge shaped defect in cross sectional examinations. Further, this 
condition manifests itself typically on the oxide treated surface of the foil 
only.
     
Actual production using palladium based direct plating systems can occasionally 
exhibit this defect, but the liklihood is not very great. Further, because 
palladium systems can modify the process sequence to incorporate microetching 
prior to conditioning, the chance of the defect occuring is further reduced. 
Finally, substituting double treat foil for oxide treated foil will eliminate 
the chance of wedge voiding in all but the most severe cases.
     
Kevin H. Baranowski
Atotech USA Inc.