Background
Temperature variations within electronic equipment are a primary source of undesirable
stresses. These stresses are cyclic in nature based on power cycling of equipment and/or
variations in the external environment. As part of the CALCE EPRC's effort to characterize
failure mechanisms of components and printed wiring board, an effort has focused on
evaluating temperature distributions within electronic equipment. Currently, the thermal
analysis capability includes conduction, forced convection and passive cooling of vertically
oriented printed wiring boards. Traditionally, horizontally oriented heated boards have
received little attention. However, with increase in commercial applications and desire to
simplify cooling system, passive cooling is extremely attractive.
Work Accomplished
For the present study, three configurations of a horizontal PCB in increasing order of
complexity were selected. These include a uniformly heated PCB, a five by five array, and a
three by three array of equally sized heated components on a horizontal substrate. A design
of experiments study was carried out to identify the computational runs needed to examine
the thermal behavior of these horizontal boards in an enclosure. First, a simulation model for
a heated horizontal surface in an enclosure was developed using a computational fluid
dynamics code.
Thirty five detailed computational fluid dynamics (CFD) based runs to charac
terize
thermal behavior of horizontally placed PCBs were carried out.
Based on the results of these runs, a simpler empirical convection
correlation was derived and implemented within the existing CALCE Thermal Analysis Tool.
The empirical correlation was calibrated based on results from the CFD simulation.
