EXPERIMENTAL INVESTIGATION OF MICRO HEAT PIPES FABRICATED IN SILICON-WAFERS

An experimental investigation was conducted to determine the thermal b ehavior of arrays Of Micro heat pipes fabricated in silicon wafers. Tw o types of micro heat pipe arrays were evaluated, one that utilized ma chined rectangular channels 45 mum wide and 80 um deep and the other t hat used an anisotropic etching process to produce triangular channels 120 mum wide and 80 mum deep. Once fabricated, a clear pyrex co ver p late was bonded to the top surface of each wafer using an ultraviolet bonding technique to form the micro heat pipe array. These micro heat pipe arrays were then evacuated and charged with a predetermined amoun t of methanol. Using an infrared thermal imaging unit, the temperature gradients and maximum localized temperatures were measured and an eff ective thermal conductivity was computed. The experimental results wer e compared with those obtainedfor a plain silicon wafer and indicated that incorporating an array of micro heat pipes as an integral part of semiconductor devices could significantly increase the effective ther mal conductiuity; decrease the temperature gradients occurring across the wafer, decrease the maximum wafer temperatures; and reduce the num ber and intensity of localized hot spots. A t an input power of 4 W, r eductions in the maximum chip temperature of 14.1-degrees-C and 24.9-d egrees-C and increases in the effective thermal conductivity of 31 and 81 percent were measuredfor the machined rectangular and etched trian gular heat pipe arrays, respectively. In addition to reducing the maxi mum wafer temperature and increasing the effective thermal conductivit y, the incorporation of the micro heat pipe arrays was found to improv e the transient thermal response of the silicon test wafers significan tly.