A Phase Change Study of Electroplated Copper Wick Structures

Abstract

Electroplating has been implemented in the fabrication of RF circuits for many years. Combined with a photolithography process, this technology can be employed to precisely define both the particle size and geometry of copper wick structures in a phase change heat transfer system. In this article, two electroplated copper wick structures are developed to investigate characteristics of phase change heat transfer at the early stage when applied heat flux is below 250W/cm. Using subcooled operating fluid, both visualization and heat transfer characterization indicate that the appearance of the onset of nucleation boiling (ONB) plays a critical role in determining the heat transfer model. Before the ONB is triggered, heat transfer is dictated by the heat conduction of the wick, as well as evaporation on the meniscus interface. After the ONB, the heat transfer coefficient is rapidly enhanced by phase change within the wick structures. On the characterization curves of heat flux versus the substrate temperature, the wick properties, such as porosity, directly affect the position of the ONB. Submicron porous structures on electroplated copper pillars accelerate the ONB and enhance the heat transfer coefficients of the phase change.