Hi Frank,

Not sure exactly what you mean by "tapered voids".  Could be a few things.

*  Voids that have a slow taper almost immediately from the knee of the hole
(on both sides of the board) usually come from a copper plate condition such
as low amperage or a chemistry related issue that causes poor throw.  If
you're using electroless copper it is unlikely that the problem started
there, however if you're using a direct plate it's possible that you had high
resistivity through the hole and/or poor coverage towards the hole center.
That would make subsequent plating difficult and would likely result in a
tapered effect.

* Voids that have a sharp taper, more like a scallop, can be caused by a few
things.  Most likely it occurred as a result of poor tin or tin/lead resist
plating alowing an etch void to result.  It can also be caused by air bubble
entrapment somewhere in the electroless line.  If you can find them before
etch (while they still have tin in the hole) then it usually easy to find
where they're originating.

* Resist residues would be my last suggestion.  If you have residues in the
holes that resist plating it's possible it could appear tapered.

Pictures and a description of your metalization and plating processes would
help.

Good luck

Mark Mazzoli

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