Al,

   In my own experience, I try to adhere to a 100 mil copper free
edge to the board outline. But in some PC Boards I did have to 
go to a minimum of 25 mils away from the board edge.  I suppose if
you had your gnd plane out to the edge and your pwr plane to the edge
also, a possibility of a short could exist.  I think this would be a
bad Design practice.  I like all of my pc boards to work long term, so
I try to increase all of my clearances whenever possible.

Karl Bates
Zenith Electronics
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