Analysis of Heat Transfer from a Heat Dissipating Device on a Substrate

Increasing trends of heat dissipation rate combined with high packaging density of heat dissipating devices in automotive electronics requires simple methods to estimate the heat transfer characteristics from the devices to the ambient. Especially, the heat dissipation rate of such devices is under serious considerations for the rigorous prediction of the operation temperature, which is a crucial parameter for the device reliability. As for the first step, this work aims at formulating the heat transfer from a heat dissipating device mounted on a flat plate, imitating an IC on a PCB (printed circuit board), to the ambient by using a simple heat transfer model. The model considers the heat transfer from the device to the ambient through two heat transfer paths: one directly from the device surface to the ambient, and the other through the solder into the PCB, and lastly from the PCB to the ambient. The heat transfer through the PCB is modeled by using a simple 1D fin model in cylindrical coordinates. The model prediction is evaluated with experimental results showing good agreement. Three-dimensional heat transfer analysis is also preformed to investigate the parameters essential to heat transfer in the described system.