Design and fabrication of a metallic micro-heat pipe based on high-aspect-ratio microchannels

Abstract

The cooling capacity of a micro-heat pipe is mainly governed by the magnitude of capillary pressure induced in the wick structure. For microchannel wicks, a higher capillary pressure is achievable for narrower and deeper channels. In this study, a metallic micro-heat pipe adopting high-aspect-ratio microchannel wicks is fabricated. The micro-machining of highaspectratio microchannels is done using the laser-induced wet etching technique in which a focused laser beam irradiates the workpiece placed in a liquid etchant along a desired channel pattern. Because of the direct writing characteristic of the laser-induced wet etching method, no mask is necessary, and the fabrication procedure is relatively simple. Deep microchannels of an aspect ratio close to 10 can be readily fabricated with little heat damage to the workpiece. The laser-induced wet etching process for the fabrication of high-aspect-ratio microchannels in 0.5 mm thick stainless steel foil is presented in detail. The shape and size variations of microchannels with respect to the process variables, such as laser power, scanning speed, number of scans, and etchant concentration, are closely examined. Also, the fabrication of a flat micro-heat pipe based on the high-aspect-ratio microchannels is demonstrated.