The Cooling Efficiency Concept — A Tool for Fast Thermal Analysis of PCBs Available to Purchase

Thermal analyses of printed circuit boards (PCBs) based on the finite element or finite difference methods are frequently used in the electronics industry, the major reason for this being the geometrical complexity of the thermal problems. Correctly used and with access to all relevant data, these methods are very accurate. In the early stages of the PCB design process, it is often necessary to make temperature estimations based on data which are very uncertain and sometimes mere guesswork. Any temperature prediction based on such assumptions will, regardless of the method used, always be of a preliminary nature. A fast and approximate method can then offer advantages over a complex but accurate method. The cooling efficiency for a PCB is defined as the heat dissipation for the PCB over the heat dissipation for a flat smooth isothermal plate of the same size and with a temperature which equals the maximum temperature of the PCB. This definition makes it possible to derive the maximum temperature on a PCB from the well‐defined isothermal case. The cooling efficiency for a particular PCB can be calculated or measured. The experience of the author is that the values for most multilayer PCBs are in the range 50–85%. For PCBs which have a few concentrated heat sources, the cooling efficiency could be considerably lower. For PCBs with any form of surface extension, the cooling efficiency could be higher. The cooling efficiency concept is particularly useful as a fast front‐end thermal analysis tool. The concept can also be used in conjunction with thermal specifications of PCBs and at the PCB enclosure level.