Dr. Marc Hodes, Ph.D., Tufts University

Key Note Speaker: Galinstan-Based Cooling of Microelectronics: Beyond Tuckerman and Pease? . by Dr. Marc Hodes, Ph.D., Tufts University, Ph.D.

In 1981 in perhaps the most cited study in the thermal management of electronics literature, Tuckerman and Pease at Stanford University pumped water through a bank of 50 microchannels etched into 1 cm x 1 cm footprint, 400 mm-thick silicon block.  A heater sputtered onto the silicon dissipated 791 W/cm2 and the pressure difference across the microchannels was 2 atmospheres.  The measured thermal resistance based upon the maximum heater temperature and inlet water temperature was 0.09oC/W and it has been subsequently been shown that it may be reduced to 0.07oC/W by refining the microchannel geometry.  Such a resistance implies that a microprocessor uniformly dissipating 1000 W/cm2, currently the heat flux at “hot spots” on high-end microprocessors, could be accommodated by single-phase liquid cooling.

Galinstan is a eutectic alloy of gallium, indium and tin developed as a non-toxic liquid metal replacement for mercury in oral thermometry.  It is a viable candidate for single-phase liquid cooling of microelectronics because it melts at -19oC.  The key advantage of galinstan relative to water as a coolant is that its thermal conductivity is 28 times larger as this results in extremely high heat transfer coefficients.  In this talk we justify the claim that by using galinstan rather than water as the coolant a thermal resistance of 0.05oC/W, i.e., 30% less than possible with water, may be achieved under precisely the same constraints by Tuckerman and Pease.

We also show that in galinstan-based cooling, the dominant contribution to thermal resistance is caloric rather than convective.  Indeed, on account of the thermophysical properties of galinstan, the increase in the bulk temperature of it across microchannels exceeds wall-to-bulk temperature differences.  Based upon this notion we will show that the thermal resistance of galinstan-based cooling can be further reduced by utilizing engineered structured surfaces to suspend galinstan on roughness features etched into the microchannel walls.  This introduces a lubricating-air layer between the galinstan and microchannel walls thereby reducing flow resistance.  The net result of the air layer is decreased caloric resistance, increased convective resistance and, most importantly, decreased total resistance