03. Electronics Packaging and Thermal Management

A vapor chamber is a plate-type heat pipe, and is used as a heat spreader. Since the latent heat of evaporation and condensation of a working fluid is used for heat transfer, heat is spread effectively from a heat source to a heat sink. Recently, an ultrathin vapor chamber has been developed for thermal management of thin electronic devices. The principle of operation of the ultrathin vapor chamber is essentially the same as that of conventional vapor chamber; however, the layout of a wick structure was different. Because of the limitation of inner height, a conventional wick layer cannot be used in the ultrathin heat pipe, which requires further investigations of a wick structure for rational thermal design of ultrathin vapor chambers. In the present study, three types (Type-1, 2, and 3) of wick structures were prepared, and comparative studies were conducted on the evaporation heat transfer characteristics of the wick structures. Type-1 was a wick structure with rectangular shape. Type-2 and 3 were trapezoidal shapes, but the side lengths on the evaporation side were different. In experiment, the wick structure was placed vertically, and the bottom was immersed in a working fluid. The top of the wick structure was heated, and the relation between the evaporation heat transfer rate and the superheat of the working fluid was obtained. Water was used as the working fluid. Pumping performance of the three wick structures were also compared, and the discussion was made on the effectiveness of trapezoidal shape.