Ken,

I usually take the other approach and specify thermal relief ONLY ON PIN
THROUGH PARTS. (No thermal relief is needed on press fit parts). Vias to
power and ground planes do not usually need thermal relief and it makes for
a much more continuous plane which give better electrical characteristics
and are easier for the PWB designer to route (vias can be closer together).
I've also had dense designs which would have had large gaps in the power
and ground planes if I'd used thermal relief on the hundreds of vias that
connected to these planes.

Problems with lack of thermal reliefs may occur if a very short and wide
(>.025 in) trace is used to connect a SMT part to a via to a gnd/pwr plane.

Ray Klein

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