With most direct metalization process, one must first hit the hole holes
with a fairly high amps per square foot (asf) copper plating to "lock in"
the direct metalization, and then add the majority of the copper plating at
a lower asf application. The higher asf does not level very well, and tends
to exaggerate the wall condition as seen in these photos. The lower asf of
the second application allows the copper plating to fill in the topography
of the first plating application. In the example supplied, the amount of
copper plating applied in the first application may also have been too
much. Werner, take another look at photo DI, upper left corner, and you
will find a fold. And you are exactly right, not all holes will fail, but
some surely will.
Tom



             Werner Engelmaier
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             IPC-600-6012                                               cc
             <IPC-600-6012@ipc
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                                       Re: [IPC-600-6012] Cobblestone"
                                       appearance on via wall.
             08/05/2005 10:37
             AM


             Please respond to
             "(Combined Forum
               of D-33a and
                   7-31a
              Subcommittees)"
             <IPC-600-6012@IPC
                   .ORG>






Hi Constantino,
Your problem is a direct result of very poor drilling. The 'cobblestone'
appearance of the plating is a direct reflection of the underlying rough
hole wall
with protruding glass bundles, and glass bundles ripped out of the epoxy
matrix. These capillary gaps between the glass bundles and the resin allow
plating
into these spaces--causing possible CAF shorting--but more importantly rob
Cu
from plating a uniform hole wall. This creates this 'cobblestone'
appearance
which is only the visual clue of significant stress risers in the PTH hole
wall. I would suspect that the second plating run was done because bare
board
testing showed open PTH structures. I would also suspect you have cracked
PTH
barrels somewhere in these PCBs--you just have not found them yet.

Werner