On the Deposition of Monodispersed Molten Microdroplets in Industrial Jetting Processes
Thursday, January 11, 2001 - 5:00pm - 5:30pm
Dimos Poulikakos (Swiss Federal Institute of Technology)
The reliable and repeatable microdroplet generation and deposition of non-traditional liquids is of paramount importance to a plethora of emerging technologies. In this lecture the deposition of picoliter size droplets of molten materials will be discussed with emphasis on three dimensional phenomena and substrate melting phenomena. The three dimensinality of the phenomenon is induced by non axisymmetric impact or by the motion of the substrate upon which the microdroplet is deposited. The substrate melting is a result of the energy input from the impacting molten material. The novel solder jetting process for the manufacturing of microelectronics is used to underpin the industrial importance and relevance of the phenomena investigated. The numerical modelling is based on the Lagrangian Finite-Element formulation of the Navier-Stokes, energy and material transport equations. The model accounts for a host of complex thermofluidic phenomena, exemplified by surface tension effects and heat transfer with solidification in a severely deforming domain. The dependence of the molten volume on time is determined and discussed. The influence of the thermal and hydrodynamic initial conditions on the amount of remelting is discussed for a range of superheat, Biot and Reynolds numbers. Multidimensional and convective heat transfer effects, as well as material mixing between the droplet and the substrate are found and quantified and the underlying physics is discussed. . Good agreement in the main features of the maximum melting depth boundary between the present numerical results and published experiments of other investigators for larger (mm-size) droplets is obtained, and a complex mechanism was identified, showing the influence of the droplet fluid dynamics on the substrate melting and resolidification.