An approach to thermal analysis of PCB with components having cyclic electrical loading

Thermal transient analysis of an electronic packaging system is often cumbersome, even with today´s sophisticated numerical software. This paper presents an efficient numerical approach to thermal transient analysis of an electronic packaging,system under electrical cyclic loading conditions. A numerical solution of temperature as function of time is formulated upon which a simple computer code is written to obtain transient behavior of a system or components. Based on the lumped capacitance (LC) model, a general average power concept is presented to obtain a steady state solution from finite element modeling (FEM). The steady state solution is then used to evaluate the time constant for analysis of transient heat transfer. The transient solutions from the proposed model and those obtained from FEA show good agreement at component level. Time to transient solution of a wire resistor only takes a couple of seconds via the proposed approach while it took four hours on HP735 for the first 120 cycles. The proposed approach is demonstrated through an example of an automotive control module PCB with resistors having cyclic current input. Thermal measurements from an IR scanner are also presented to correlate with analytical results