Development of an anodically-bonded test surface to obtain fundamental liquid immersion thermal management data for electronic devices

The study described in this paper aims at designing and developing the fabrication technique for an enhanced surface heat sink to document one dimensional pool boiling heat transfer data. The heat sink was designed to simulate a multichip module and symmetry was incorporated to eliminate back heat loss. Anodic bonding, a commonly used technique in the fabrication of sensors and actuators, was used to create silicon-to-glass and aluminum-to-glass bonds. Using glass, a low conductivity substrate, minimized spreading losses. Surface enhancement was achieved by fabricating micro-pyramidal surface structures using tetra methyl ammonium hydroxide (TMAH) anisotropic etch of 100 silicon. The micro-pyramidal cavities were 149mum tall, with a 40mum square mouth opening, arranged in a square array. Elimination of the back side heat loss and spreading ensured one dimensional heat transfer and also yielded a more realistic number for the critical heat flux (CHF). The dielectric fluid, FC 72, a popular choice for direct immersion cooling systems was the test fluid. The paper compares the results of the fabricated heat sink with a similar enhanced heat sink etched in silicon.