Novel heat spreader for the optical probing of PC board mounted flip chips [microprocessor debug]

Operating at high frequencies, microprocessors can consume significant power, up to 150 W - they generate a lot of heat. Even so, the internal debug of these IC devices requires removal of their heat sinks as well as thinning their silicon substrates (<100 μm remaining Si thickness). Thinning is necessary for optical probing to access individual transistor information. For through-silicon optical probing of these ICs, the heat has to be removed efficiently to maintain junction temperatures at a reasonable level. Transparent diamond enables this because it has the required transparency for optical probing and the highest thermal conductivity. Cooling a thinned microprocessor while under functional system test on its motherboard was further complicated by space and accessibility limitations due to other motherboard components, some of which required air-cooling. The optimized design enabled the microprocessor temperature to be regulated and the thermal gradients across the die to be minimized. Dissipating the generated heat has been successful. Further, the thermal system was mathematically modeled and after its characterization both the temperature of the microprocessor and the wattage produced can be determined while under functional system test.