On quantifying interfacial thermal resistance and surface energy during molten microdroplet surface deposition

Understanding and controlling the deposition of a molten microdroplet on a colder substrate with simultaneous beat transfer and solidification is of central importance to a host of technologies, exemplified by novel methods of electronic microchip manufacturing. The physics of the interfacial phenomena involved are to date only partially understood. For instance, the transient resistance to heat transfer at the droplet-substrate interface cannot be quantified theoretically, and adequate experimental data are lacking. Serious obstacles to experimental determination are the very short time and length scales involved (of the order of micrometerss and microseconds). In the present article, a numerical modeling for droplet impact and solidification based on the Navier-Stokes and energy equations is used in order to reproduce transient measurements of the deposition of a eutectic Pb-Sn microdroplet on a multilayer wafer. The resistance to beat transfer at the droplet-wafer interface and the surface energy of the molten microdroplet are determined by matching numerical and experimental results. This successfully demonstrated indirect method is of interest if direct transient thermal resistance data are not available (as is very often the case).