Investigation on the efficiency of thermal relief shapes on different Printed Circuit Boards

As known, thermal relief is a technique used to separate soldering pads or plated through-hole vias from large copper planes in order to reduce soldering dwell time by providing thermal resistance during the process, thus minimizing the heat transfer to the plane. However, during normal operation, the same thermal resistance limits the heat transfer for power component dissipation. The narrower the thermal pad, the greater temperature increasing during power dissipation. Hence, the dimensions of the thermal pads are critical. The work presents the results of a practical approach not for a hole via or a pad for an ordinarily component connected to a large copper area, but a medium power Surface Mounting Device, SMD, using the Printed Circuit Board, PCB, as heat sink. There are taken into consideration different thermal pads and there are investigated by temperature measurements with thermocouples and thermovision. The variables are the thermal pad dimensions, the area of the radiant surface, the base material of PCB, and the reflow soldering process. It is analyzed the effect of the thermal pad versus the temperature on the soldering pad and beyond the thermal pad and on the case of the device during reflow soldering process and during operation