The Impact of Heat Transfer Coefficient Value on Temperature of Hybrid Electronic Circuits Cooled by Natural Convection

This paper discusses the problem of modeling heat transfer coefficient values in electronic circuits cooled by natural convection. This coefficient represents the heat exchange between the outer circuit surfaces and the surrounding environment, and in thermal simulations, their value is quite often assumed to be constant. However, in reality, it depends on both the absolute temperature of a surface and the temperature difference between this surface and the ambient. Consequently, this assumption may lead to important simulation errors, especially when a heat source occupies only a small part of the circuit’s area. This issue is illustrated here based on the results of thermal simulations carried out for a hypothetical test structure containing a heat source that dissipates different amounts of power, has variable dimensions, and is placed in various locations. Moreover, the thermal coupling between two heat sources is also analyzed as a function of their spacing. The simulation results are compared and analyzed for cases when the heat transfer coefficient value is constant and when it is temperature-dependent. The main conclusions of the analyses are that the simulated circuit temperature values are much lower when temperature-dependent values of the coefficient used and that proper optimization of the circuit layout could substantially decrease the maximal and average circuit temperature values.