Optimization of Extruded Type External Heat Sink for Multichip Module

Abstract

A three-dimensional finite element model of a multichip module (MCM) has been developed by using ANSYS™ finite element simulation code. The model has been used for thermal characterization of the module. In addition, optimum dimensions of an external heat sink, which maintains the specified device’s junction temperature within desired operating temperature limits, are determined as functions of air flow rate and power density of surrounding semiconductor devices. Parametric studies have been performed to study the effects of heat sink height, width and length on junction-to-ambient thermal resistance of a high power application specific integrated circuit (ASIC) device found in the MCM assembly. A set of curves are generated to select either heat sink dimensions or air speed for a given design requirements. Influence of the power output of surrounding devices on the thermal performance of the high power ASIC device is also assessed. The predicted results indicate that the ASIC device’s junction temperature as well as junction-to-ambient resistance increase as the power of the surrounding packages increases. This effect diminishes if a sufficiently large heat sink is used to cool the package.