Kelly,

Try this method which is recommended by a large pcb fabricator.
We are about to give it a try on one of our designs.

Create 2 sets of masking artwork; the LPI artwork, and the plug
artwork.  For the LPI artwork make the via aperture the same size
as the drilled hole (.005 larger then nom FHS) on the solder side,
and .006 larger than drilled hole on the component side.  For the
plug artwork, use a .012 aperture.

Specify "plugging" to be done from the solder side with a wet
solder mask, and after solder leveling.  Via reliability is enhanced
because the solder in the barrel acts as an oxide inhibitor.

By creating "via plug" artwork, you can define test and non-test
vias which are left open for probing.

Tom Hybiske
General Atronics Corp.
1200 E. Mermaid Lane
Wyndmoor, PA 19038

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