COOLING TECHNIQUE BASED ON EVAPORATION OF THIN LIQUID FILMS IN MICROGAP CHANNELS

摘要

The forced flow of dielectric liquids, undergoing phase change while flowing in a narrow channel, is a promising candidate for the thermal management of advanced semiconductor devices in terrestrial and space applications. Such channels may be created by the spacing between silicon ribs in a microchannel cooler, between stacked silicon chips in a three-dimensional logic or heterogeneous microsystem, narrowly-spaced organic or ceramic substrates, and between a chip and a non-silicon polymer cover in a microgap cooler. These microgap configurations provide direct contact - and hence cooling - between a chemically-inert, dielectric liquid and the back surface of an active electronic component, thus eliminating the significant thermal resistance associated with a thermal interface material or the solid-solid contact resulting from the attachment of a microchannel coldplate to the chip. While direct contact cooling is thermally very efficient, in such configurations, it is the poorly understood two-phase flow phenomena that establish the upper bound on the heat removal capability. A detailed map of the flow sub-regimes in the stratified thin film flow of FC-72 liquid and nitrogen gas has been obtained for 2 mm flat mini-channel operating at room temperature. For shear-driven liquid films the critical heat flux is up to 10 times higher than that for a falling liquid film, which makes shear driven films (annular two-phase flow) more suitable for cooling applications than falling liquid films.