Effects of tip clearance and fin density on the performance of heat sinks for VLSI packages

Motivated by the high heat dissipation requirements of the advanced VLSI packages, experiments were performed with several heat sinks to study their heat transfer characteristics. The thermal resistances and pressure drops of the heat sinks were measured for fin densities of 1.3, 4.6, and 5.6 fins/cm and tip clearances varying from 0 to 2 cm. The mass flow rate varied from 0.01 to 0.1 kg/s. For a fixed mass flow rate and zero tip clearance, the 1.3-fins/cm heat sink dissipated four times more heat than a heat sink without fins, and the 5.6-fins/cm heat sink dissipated seven times more. Accompanying this increased heat transfer, however, is an increase in pressure drop. With an increase in tip clearance, the pressure drop penalty is reduced, but the heat transfer gain is also lower. This information is presented for different fin densities and tip clearances and should be useful to packaging engineers for the optimal design of high-density finned heat sinks