MICROMACHINED SPRAY COOLING

The use of an aerosol spray to transport liquid droplets that subsequently undergo a liquid to vapor phase change can conformably and efficiently carry heat away from microelectronic circuits and packages. Through the use of microminiaturized spray nozzles and miniaturized pumps and condensers, very small, lightweight, and extremely efficient cooling systems have been built and deployed.

The objective of this effort is to achieve a breakthrough in cooling performance for power semiconductors, high performance computing engines, and advanced state-of-the-art packaging concepts. The liquid used is a fluorinert that is commonly used in the cleaning of semiconductor wafers, so it is perfectly compatible with contact to integrated circuit surfaces. It is also ozone safe in the environment.

A typical application uses an aerosol spray to conformably coat the object to be cooled with a very thin liquid film. The hot object causes the liquid thin film to evaporate and thereby remove heat from the object. A mass balance of arriving liquid aerosol droplets and the evaporating vapor forms the basis of this closed cycle cooling system. The total quantity of liquid fluorinert is only a few ounces in a system that is capable of extracting 20 kilowatts of heat! These systems are theoretically capable of extracting 250 watts of heat and depositing into the ambient at a cost of one watt of power out of a wall plug. Systems have demonstrated the capacity of extracting 250 watts of heat from one square centimeter of surface area on a continuous basis.

Other systems, in conjunction with extraordinary thermal conductivity of synthetic diamond heat spreaders, have extracted over 120 watts of heat from ceramic pin grid array packages similar in size to a 486 processor. In addition, all of this capability comes in a cooling system package that is typically 15 to 20 times smaller that standard militarized systems. These smaller systems are also 15 to 18 times lighter in weight than their military format cousins while still outperforming them.