| There is significant current interest in new technologies for IC cooling; this interest is driven by the rapid increase in power densities in ICs and the trend towards high-density electronic packaging for applications throughout civilian and military markets. In accordance with the Moore's Law, the number of transistors on Intel Pentium processors increased from 7.5 × 10 6 in 1997 (Pentium II) to 42 × 106 in 2000 (Pentium 4). Accordingly, thermal management must be well designed to ensure proper functioning of these high-speed, high-power chips. Forced air convection has been traditionally used to remove the heat through a large heat sink and fan module. Currently, with 75 W power dissipation rate, or approximately 45 W/cm 2 heat flux, from a Pentium 4 processor with 2 GHz core frequency, the noise generated from high rotating speed fans is approaching the limit of acceptable level for human operation. However, the power dissipation level from a single high performance chip is expected to exceed 100 W/cm 2 by the year 2005, when the air cooling has to be replaced by new cooling technologies.; Among alternative cooling methods, pumped liquid loop cooling with phase change is one of the most promising solutions. A closed-loop silicon microchannel two-phase cooler with an electroosmotic pump has been proposed at Stanford University. This dissertation focuses on the heat transfer and phase change phenomena in sub-150 μm diameter microchannels. Single silicon channels formed on a freestanding beam with integrated heaters and thermometers have been designed and fabricated. These instrumented microchannels represent the first opportunity to carry out detailed, quantitative experiments on the boiling regimes in sub-150 μm diameter microchannels with the capability for simultaneous optical observation, thermal measurement, and pressure transient measurement. Wall temperature measurements and phase change visualizations show that the overall behavior of the two-phase flow in silicon microchannels does not apparently depart from traditional theories in either heat transfer or nucleation mechanisms. On the basis of experimental results and theoretical modeling, general design rules for two-phase microchannel heat sinks are proposed, with an example of a 200 W microchannel heat sink for future high-power IC chips. |
