Indirect spray evaporative thermal management for semiconductor burn-in

Semiconductor bum-in testing is one of several quality assurance tests conducted during High Volume Manufacturing (HVM) of semiconductor logic devices. The goal of bum-in is to induce "infant mortality" component failures. To accelerate infant mortality defects, semiconductor devices are subjected to stressing techniques that induce heat levels, typically, 100%-300% greater than end use environment heat loads. For this work, an indirect spray cooling method was developed and experimentally evaluated. In the indirect method, sprays are sealed within a spraycap (evaporator) that is thermally connected with the heated surface by way of a thermal interface material. The test fluid is the perfluorocarbon HFE-7000 that has a boiling point of 34 degrees C at 1 atm. pressure. Experiments were run at a spraycap nominal pressure of I atm. with about 16 degrees C of liquid subcooling at the inlet. Tests were performed on a lidded Thermal Test Vehicle (TTV) device (1.2 cm(2) die size) to measure the thermal solution maximum power, dynamic control, repeatability, and the effect of applied force. Time varying test patterns (thermal loads) are simulated by changing TTV power in 20 W steps up to 200 W. The pertinent output measurements for performance evaluation are TTV power and junction temperatures (Tj), thermocouple measurements in the heat path, coolant flow rate, and applied force to the TTV. From these measurements, resultant parameters of thermal resistance and heat transfer coefficients are calculated. Maximum TTV power maintaining Tj at or below 105 degrees C was shown to approach 240 W. Thermal controllability of the system was demonstrated for a Tj of 105 degrees C over the TTV power range of 30 W to 200 W. Performance was extremely stable and very repeatable even when the spraycap exit quality was 100%. The thermal solution demonstrated good repeatability during a limited cycle test. Contact force of approximately 10 lb(f) (45 N) was found to minimize the thermal resistance of the solution, and no significant improvement is realized beyond that force level.