"Roy Lewallen" wrote in message
...
Loss will be greater on the thicker board, because a greater fraction of
the fields surrounding traces and components will be in the board
material as opposed to being in the air. Having less field in the board

This is correct as far as dielectric loss is concerned, but copper resistive
loss decreases as the board gets thicker. Which one will dominate depends
on frequency and characteristic impedance. At low frequencies, dielectric
loss will probably dominate. At high enough frequencies,
copper loss will dominate. For low enough impedance traces, the
field will be mostly in the air for either board thickness. Complex
problem to analyze.

Rick N6RK