Inkjet Assisted Spray Cooling of Electronics

Increases in microprocessor power dissipation and the resulting effect on the cost and complexity of thermal management solutions has been well documented in recent years. Accompanying this increase in overall power dissipation has been a reduction in feature size due to process improvements resulting in a steady decrease in the size of the processing core where most of the power on a die is generated. This trend is expected to continue into the near future and will likely lead to a power dense core covering a fraction of the total die surface area surrounded by areas of reduced power density cache. Evaporative spray cooling has been long identified as a technology that can be used to manage very high power densities (> 100 W/cm²). Limitations in the controllability of individual spray droplets, however, have generally prevented its use in applications that contain marked variation in spatial power density. Since only a relatively uniform spray pattern is possible with existing spray delivery technologies, sections of lower power density become susceptible to pool boiling and thereby place limitations on bulk flow rates, which accordingly limit thermal performance. Conversely, variations in heat transfer coefficients caused by uncontrolled pool boiling across devices can create thermal stresses. In this paper we demonstrate how thermal inkjet technology can be effectively utilized to spray cool a heat source with non-uniform power density. Experimental data is presented for a water-cooled heat source and critical heat fluxes of up to 270 W/cm² are reported. Additionally, correlations are developed for the unique spray pattern afforded by the technology.