Cycle time reduction methods for transient thermal simulations

A transient thermal analysis was performed on an electronic module to determine the maximum temperature of a number of transistors´ silicon dies during cyclic electrical loading. The computational-fluid-dynamics (CFD) software - Icepak® - was used to model system-level transient thermal behavior. An initial and lengthy full-CFD transient thermal analysis was performed, until periodic-steady-state was achieved. This analysis uses the finite volume method, solving for mass, momentum, and energy and is based on Navier Stokes and energy equations. A simplified Icepak® model was developed, which uses 1/2 of the full-CFD mesh size, by collapsing the computation domain to the boundaries of the solid-model, and imposing heat-transfer-coefficients, as a piece-wise-linear function of the surface temperature, coincident to the outer surface of this model, and solving only for the energy equation. This simplified heat-transfer-coefficient model (h-model) results in a 10 times reduction in cycle-time compared to the full-CFD. An R-C network system level model of this module was designed using PSpice™ software. Inputs were obtained from the Icepak® full-CFD model, and incorporated into the R-C network, resulting in near instantaneous temperature results. The full-CFD, simplified h-model, and R-C network simulation results were validated by experimental measurements, and were found to be within 15% of the overall temperature rise. This methodology can be used to solve for transient thermal analysis problems with various duty-cycles.