Cu foil to spread the heat better on the inner backside of PBP would be even better. Magnesium alloys are not particularly great thermal conductors, so just the

Cu foil to spread the heat better on the inner backside of PBP would be even better. Magnesium alloys are not particularly great thermal conductors, so just the spot under the SoC is heated disproportionately to the rest of the backside.