John S. Fitch

Packaging a 150-W bipolar ECL microprocessor

Recent developments in computer-aided design have made possible the highly automated layout of custom ECL (emitter coupled logic) circuits. These layouts have a much higher circuit and power density than gate array designs. It is now possible to place an entire ECL microprocessor, including floating point unit and cache memory, on one large die. To demonstrate the capability of supporting such a die, the authors built and tested low-cost, air-cooled single-chip packaging for a 12.6-mm*15.4-mm die. The PPGA (plastic pin grid array) package supplied the required current and maintained junction temperatures at less than 100 degrees C while dissipating 150 W. This required innovation in five areas: die metalization, bondwire layout, PPGA package design, die attach, and cooling by a thermosiphon.<<ETX>>

Boiling binary mixtures at subatmospheric pressures

The authors present a study of boiling binary mixtures of water with methanol or 2-propanol at subatmospheric pressures. Liquid-phase equilibrium vapor pressures, binary phase equilibrium thermodynamic properties, heat transfer characteristics, and the critical heat flux (CHF) condition are determined for saturated pool boiling from a localized heat source while varying the concentrations of methanol and 2-propanol in water. The heat source is an upward-facing copper surface submerged in a laterally confined, finite pool. Low-pressure boiling of aqueous mixtures provides a means of removing high heat fluxes while maintaining low surface temperatures. Small additions of alcohol to water increase the CHF condition above that of pure water. Higher concentrations of alcohol begin decreasing the CHF condition to that of the pure alcohol. While single-component correlations using mole weighted binary liquid thermodynamic properties have been shown to predict ideal binary mixture boiling behavior, they are unsuccessful in predicting the characteristics of aqueous mixtures. The significance of the results obtained to the use of binary coolants for electronics cooling applications is discussed.<<ETX>>

Thermap: a thermal model for microprocessors

Thermap is a numerical model which predicts the temperature of a multilayered stack of materials. Heat flux and temperature may be prescribed at any node. Thermap may gather the heat flux boundary descriptions from a VLSI CAD tool in order to simulate a microprocessor. This can be done with very fine spatial resolution. The thermal conductivities may be temperature dependent. Residual iteration, grid refinement, and efficient use of data structures allow Thermap to converge quickly. A graphical server called ezd is used to view the resulting images of power or temperature. Thermaps temperature predictions agree well with an infrared measurement of a real microprocessor.<<ETX>>