Enhancing capillary performance of copper wicks by electrodeposition of superhydrophilic dendritic structures

Abstract

Capillary wick is a critical component that sustains working fluid circulation in heat-spreading vapor chambers. A preferred wick layer requires a porous structure of multiscale porosity to meet the requirements of high liquid permeability (K) and large capillary pressure (ΔP). In this study, we controlled the etched substrate topography to modulate the morphology and capillary dynamics of the electrodeposited porous films on a specifically treated Cu substrate. The effective pore radius (Reff) of porous Cu films depends on the size and density of the dendritic bushes grown on Cu substrates treated with sodium persulfate/sulfuric acid (SPS) solution. An analytical approach was used to quantitatively analyze the dendritic deposits grown on the SPS-treated Cu substrates. The surface profile and roughness of Cu substrates were investigated by alpha-step profilometer. Scanning electron microscopy, contact angle analyzer and x-ray diffractometer were used to characterize the surface morphology, wetting behavior and oxide formation of the electrodeposited Cu films, respectively. The capillary performance (K/Reff) of the electrodeposited Cu film was measured using the capillary rate-of-rise test. The effect of dendritic bush distribution on fluid transport properties was investigated. A high K/Reff value of 0.975 μm was obtained for the electrodeposited Cu film on a Cu substrate with an optimal SPS etching treatment.