Max,

We also are sensitive to EMI problems and are aware of the problems
caused by excessive anti-pad sizes, namely reducing the integrity
of the ground and power planes.  

There is a IPC spec concerning
clearance area in planes in IPC-D-275 section 5.3.2.4.
According to this spec, there is a .010" minimum clearance between
the edge of the land and the plane.  A fabrication allowance should
be added to this also.  For us, we use a .035" via pad with a .018"
finished drill size.  If we were to follow this spec, we should have a 
.020" clearance using the Level C fabrication allowance.  This would
translate to a anti-pad of .075", (pad size + .040" for .020" clearance).

Having said this, we don't follow the spec.  We use a much smaller anti-pad, .055" 
which gives us a .010" clearance.  I have asked our board fabricators about
this reduced clearance and they told me this is not a problem.

Hope this helps.

Danny Gross
PCB Designer
E-Mu Systems, Inc.
Scotts Valley, CA

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