Pool boiling interactions between multiple heat sources in an array of silicon chips

Increasing electronic chip densities encountered in the computer industry in the past have initiated the recent research of immersion cooling of microelectronics. Pool boiling of dielectric fluids appears to be an excellent way of dissipating the high heat fluxes generated by microelectronics devices. As package densities and heat fluxes continue to increase, new methods to enhance the boiling characteristics are needed. One of these methods consists of etching microcavities on a heat sink which is bonded to the substrate on which the chip is mounted. Previous studies have shown that these microcavities provide ideal nucleation sites which promote boiling at low superheat temperatures while virtually eliminating the overshoot associated with the transition from single-phase natural convection to established pool boiling. These pool boiling characteristics can also be affected by the heat dissipated from neighboring electronic chips. These effects have been studied by observing the boiling curves obtained from an array of heaters that simulate electronic chips. The heater array consists of five heaters arranged in perpendicular axes each having three heaters and sharing a common center heater. The heaters are constructed of a thin aluminum film and mounted to a silicon wafer bonded to a heat sink surface accommodating microcavities as described above. Saturated pool boiling results were obtained for the central heater in the array while neighboring heaters were dissipating a set constant heat flux. The dielectric fluid used was FC-72. Nearby heat dissipation affects natural convection performance. Heat dissipating neighbors located below the test heater promote incipience at lower heat fluxes and delay transition to film boiling to higher heat fluxes when compared to single heater results