One thing I've learned from using standard CNC mills to do this sort of thing over the years is that the V bit has to be brutally sharp to avoid tearing up the

One thing I've learned from using standard CNC mills to do this sort of thing over the years is that the V bit has to be brutally sharp to avoid tearing up the fine traces as it cuts. A high quality cutting bit makes the difference. Also be careful of the dust. Especially from the fiberglass substrates. Its nasty stuff.