A demystifying study of thermal relief pads: Tradeoff between manufacturing and cooling

Thermal relief is a technique used by printed circuit board (PCB) designers to thermally decouple soldering pads from large copper areas, in order to avoid excessive heat transfer from the pads during the soldering process, which would result in late melting or even no melting at all of the soldering alloy. Although from the manufacturing point of view this is a clear and imperative requirement, we found out that many designers deem this technique with precaution because of the possible negative effects on the thermal management of the board. Since thermal relief implies poor thermal coupling between soldering pads and large copper areas, there is a concern that during operation, the heat spreading capability of such large copper areas will not be put at good use, thus localizing the heat at the component terminals. This paper presents the results of our investigation of this problem, based on computational fluid dynamics (CFD) simulations, with the goal to provide a clear answer to this question.