Silicon micromachined heat exchanger for MCMs with high temperature superconductors

The goal of this work was to develop a heat exchanger for a nine chip multi-chip module (MCM) with high temperature superconductor (HTS) interconnects, which was capable of removing 50 W/cm² and maintain a temperature of 80°K. This was accomplished by forming anisotropically etched 45 μm wide by 240 to 290 μm deep by 5 mm long channels into a <110> orientation silicon wafer. These channels were spaced 40 μm apart to form an efficient cooling fin structure. The silicon wafer was covered with a pyrex plate and anodically bonded to form parallel channels. Kovar fittings were attached to the pyrex plate to flow liquid nitrogen (LN₂) into the holes made in the pyrex and then through the silicon micro channel structure. This heat exchanger design is very similar to one previously developed by Tuckermann and Pease (1981), with the exceptions of the use of cryogenic temperatures, improved alignment accuracy to the {111} planes, and the HTS interconnect application. The module has been tested with polysilicon resistors as the heat source, and with a 30 W source the measured thermal resistance was well below 1°K/W