Introduction

Faster and More Powerful Electronic Packages

Increase Demands on Active Thermal Management In the microelectronics industry, advances in technology have brought about an increase in transistor density and faster electronic chips. As electronic packages increase in speed and capability, the heat flux that must be dissipated through hot spot thermal management has also increased.

Abstract

Spot Cooling of High-Heat Flux Microelectronics

Two technologies for spot cooling of high-heat flux microelectronics based on enhanced phase-change are described. The first technology is based on a submerged vibration-induced bubble ejection process in which small vapor bubbles that form on and are attached to a submerged heated solid surface are dislodged and propelled into the cooler bulk liquid.

This ejection technique involves forced removal of the attached vapor bubbles using a submerged turbulent surface jet generated by a vibrating piezoelectric diaphragm operating at resonance. A small-scale vibration-induced bubble ejection module that produces a submerged liquid jet directed to a boiling heated surface was constructed. Initial test data described in this study include the operating characteristics of the jet as well as its hot spot thermal management capabilities.

The efficacy of this cooling approach is demonstrated using an active thermal management test die which normally dissipates 83 W/cm2 at 120°C in the absence of the jet. When the jet is active, the heat dissipation increases to 220 W/cm2 (i.e., improvement of 165%) at the same surface temperature.

Hot Spot Thermal Management for Desktop Microprocessors

The second technology consists of a gravity-independent, two-phase closed heat transfer cell, in which heat is removed from the hot surface by the evaporation of a thin liquid film that is produced by the impact of self-propelled atomized droplets. Surface atomization is achieved within the sealed heat transfer cell using a vibration-induced droplet atomization (VIDA) process. The present paper describes the operation of a small-scale VIDA heat transfer cell for cooling desktop microprocessors with particular emphasis on its operating characteristics and cooling capabilities. The effects of internal flow regulation and of geometry and surface characteristics of the heated surface on the cell performance are investigated. Heatfluxes as high as 420 W/cm2 have been dissipated at die temperatures below 135°C.

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