Fabrication and characterization of novel rectangular cross-sectional microchannel wicks for ultrathin flat heat pipes

Ultra-thin flat heat pipes (UFHPs) with extremely low thickness have become critical in the thermal management solution to highly integration of electronic devices. Improving the thermal performance of the UFHP requires a thinner wick to maintain vapor space inside, while the capillary performance of the wick cannot deteriorate. In this work, a novel rectangular cross-sectional microchannel wick (RCMW) featuring an array of radially closed micro-capillary tubes is proposed to improve the thermal performance of UFHPs. Five RCMW samples with different cross-sectional sizes are fabricated with a novel template-assisted electrochemical deposition-based method. The effect of the RCMW cross-sectional dimension on the capillary performance is investigated. A capillary rise test is performed to quantitatively characterize the capillary performance of the RCMW. The height of RCMW has a more significant effect on the capillary performance than the width. The capillary performance of RCMWs outstands those from most of the previously reported works. Among these samples, the optimal capillary performance parameter κ/r_eff = 2.982 μm is obtained with only 60 μm in thickness. The capillary limit of RCMW is also predicted theoretically, with a critical heat flux of 17.6 W/cm² obtained. These experimental and theoretical studies demonstrate the superiority of RCMW in terms of reducing wick thickness and improving UFHP capillary limit, as well as indicating the direction for further optimization.