Composite spreader for submersion cooling of a computer chip with non-uniform heat dissipation

Thermal analysis is performed which investigated using a composite spreader for removing the thermal power dissipated by a high power, 10 times 10 mm computer chip with a non-uniform surface heat flux. The composite spreader consists of a 0.4 mm top layer of porous graphite (PG) and a 1.6 mm copper (Cu) substrate. The exposed surface of PG is cooled by saturation or 30 K subcooled boiling of FC-72 liquid. The composite spreader takes advantage of the high nucleate boiling heat transfer coefficient of FC-72 on PG and the good heat spreading property of Cu. Assuming a cosine-like distribution, the chip peak-to-average heat flux ratio, Phi_max, varied from unity (uniform) to 2.467 and the spreader surface area, the total thermal power dissipated and the total thermal resistance are calculated and compared with those for PG and Cu spreaders of the same total thickness (2.0 mm). The calculated surface area and total thermal resistance of the composite spreader are smaller than the Cu spreader, while the removed power is similar or higher. With Phi_max = 2.467, a total of 39.48 W and 72.0 W could be removed by the composite spreader cooled with saturation and 30 K subcooled boiling, compared to 43.0 and 65.3 W for the Cu spreader. The corresponding surface area and the total thermal resistance of the composite spreader are 6.82 and 4.90 cm² and 0.284 and 0.68 degC/W. These values are much smaller than for the Cu spreader of 12.26 and 11.92 cm², and 0.51 and 0.83 degC/W. With a composite spreader cooled by saturation and 30 K subcooled boiling of FC-72, the calculated maximum chip temperatures of 62.37 and 72.2 K are lower than with a copper spreader (72.67 and 76.30 K). The PG spreader has the smallest surface areas, removes the smallest thermal power at higher thermal resistance, but the chip maximum surface temperature is lower than with a copper spreader