Optimization of Heat Sink Geometries for Impingement Air-Cooling of LSI Packages

This paper describes the use of our previous study's prediction procedures for thermal resistance and pressure drop in the optimization of heat sink geometries for impingement air-cooling of LSI packages. Two types of heat sink are considered : those having longitudinal fins and those with pin fins. We optimized the heat sink geometries by evaluating sixteen parameters simultaneously, including fin thickness, spacing and height. For the longitudinal fins, the optimal thickness was found to be 0.12-0.15 mm, depending on which of the four types of fans were used. For pin fins, optimal pin diameters were 0.39-0.40 mm. Under the conditions of constant pumping power, the optimal thermal resistance of the longitudinal fins was about 60% of that of the pin fins. For both types of heat sinks, the optimal thermal resistance by four off-the-shelf fans was only slightly (max. about 1%) higher than the theoretical optimum for the same pumping power. When manufacturing (cost-performance) is considered, the economically best fin thickness and diameter become about 5 to 10 times higher than the optimal values calculated without respect for manufacturing costs. Those values almost correspond to the actual limits of the extrusion and press heat-sink manufacturing processes.