Design, fabrication and test of an integrated multi-microchannel heat sink for electronics cooling

• A microchannel cooling device is designed and fabricated using microfabrication techniques for integrated heaters and sensors.
• Precise and interface-free heat flux imposition and temperature measurements are achieved.
• The importance of sensor and heater dimensions in the chip performance is assessed.
• The suitability of the design was investigated with particular attention given to the stability and accuracy of the boundary conditions.
• Scaling effects such as fluid properties, entrance effects and axial conduction are found to influence heat and momentum transfer at this scale.

In this paper, MEMS fabrication techniques are used to assemble a micro device which integrates a simulated heat source, a multi-microchannel heat sink and flow sensors.The front side of the silicon chip comprises one 1000 nm-thick Aluminum heater and six 400 Å-thick Ruthenium thermal sensors microfabricated to achieve precise and interface-free heat flux imposition and temperature measurements, respectively. The heat sink on the backside is made of 27 parallel rectangular channels with hydraulic diameter Dh = 96 μm, length to diameter ratio L/Dh = 104 and relative roughness of 2.4%. The channels are closed with glass to allow visualization of the flow, and sealed by anodic bonding, instead of using adhesives, thermal fusion or mechanical sealing, in order to guarantee resistant sealing over the entire range of operating pressures and temperatures while still preserving the depth of the microchannels.Primary fabrication tests are performed to evaluate the influence of geometrical parameters (thin film width and length) in thermal response and joule heating performance for surface temperatures in the range from 25 °C to 106 °C obtained with currents from 0 mA to 250 mA. The temperature coefficient of electrical resistivity, TCR, of the Ru thermal sensors is found to be (1.72 ± 0.45) × 10−3 K−1. The thermo-fluid-dynamic performance of the device is assessed with hydrofluoroether coolant (HFE-7000) with Reynolds numbers up to 640 (mass flux up to 2727 kg m−2 s−1) and constant wall heat fluxes q″ up to 10.8 W cm−2. Preliminary tests have shown that, without boiling, the temperature of the chip can be kept below 85 °C (Tw,avg = 65.4 °C) with a maximum heat flux of 10.8 W cm−2 and a flow rate of 3050 mL h−1. Boiling of the coolant fluid allows to increase the heat flux up to 26.6 W cm−2 with a flow rate of 1300 mL h−1 (Re = 277) with perfect robustness and reliability of the system.