"220V AC Cooling Fan" thermal conductivity, thermal conductivity in the thickness direction of the surface area of PCB smaller. In order to improve the thermal conductivity in the thickness direction, can be thermal via. Through thermal vias are: PCB metallized holes (1.0mm-0.4mm). The effect is equivalent to a thin copper tubing along "220V AC Cooling Fan" PCB thickness direction from the surface to penetrate, so that the heat is the back of a short circuit PCB, heat the heating element to quickly escape or other heat conduction layer to the back of the PCB. Design as installed on the "220V AC Cooling Fan" PCB's IC die, setting numerous thermal holes directly below the PCB is universal. Therefore, when PCB traces the progress of cooling capacity, should adopt bold lines, thick copper foil, sheet, multilayer, large shop copper, plus thermal hole design.