Effect of Surface Roughness on Droplet Bouncing in Droplet-Based Manufacturing Processes

In droplet-based manufacturing processes, such as drop-wise rapid prototyping, solder bumping and spray forming, the bouncing phenomenon adversely affects the quality of the deposit. This study investigates the effect of surface roughness on bouncing of liquid metal droplets from the substrate. An analytical model was developed to correlate the surface roughness with a non-dimensional droplet bouncing potential. In addition, an experimental study was conducted to image the deposition behavior of Pb-37wt% Sn solder droplets, 280 μm in diameter, on Au-plated substrates with a wide range of surface roughness. The high-speed image data correlate well with the model prediction that droplet bouncing increases as the surface roughness increases.