General rule for low melting point plastics is to keep your feed rate high to avoid local heating and melting, use dust extraction to get the static-cling chips away too. Start with low depth of cut going fast (1500mm/min or more) and slowly increase the DoC based on how it sounds.
On the FR4, if that’s the glass fibre PCB material I believe that the dust from this can be very very bad for you, see this thread