Fabrication and pool boiling performance of stepped microgroove wicks for ceramic vapor chambers

To address the thermal-expansion coefficient mismatch between metal vapor chambers and semiconductor materials, multilayer laser processing was employed to fabricate a ceramic-based stepped microgroove wick (SMW) for a ceramic vapor chamber. The depth of the SMW ranged from 200 to 500 μm, and the surface of the grooves was characterized by micro/nano melt. The boiling heat transfer performance of the SMW under atmospheric pressure was investigated, revealing a maximum critical heat flux (CHF) increase in 64% compared with a smooth plate. The enhanced boiling performance is attributed to the stepped microgroove structures and the micro/nano melt layer, which provide a larger heat-transfer area and additional nucleation sites. However, the low thermal conductivity of the micro/nano melt results in increased wall superheat. An acid-washed stepped microgroove wick, which eliminates the micro/nano melt layer from the SMW, achieves a maximum CHF of 1938.4 kW/m2 and a heat-transfer coefficient of 156.8 kW/(m2·K), representing a decrease in 16.9% and an increase in 43.4%, respectively, compared with the SMW. A visualization study revealed that microgrooves can effectively separate bubbles and shorten the bubble detachment time, preventing large bubbles from covering the wick surface and thereby enhancing the CHF.