Splashing of Sn–Bi–Ag solder droplets

Abstract

In this paper, we study the behavior and spreading dynamics of molten metallic alloy droplets. Five solders, including three rare earth elements and a commercial alloy, were used to assess their splashing behavior in terms of the material and impact conditions. The metallic solders were melted down in a heated chamber (oven) and then dripped onto a smooth copper flat substrate as spherical droplets. The impact of each alloy droplet was recorded and analyzed by high-speed imaging and image analysis to obtain the impact speed, the droplet size, and the dynamic contact angle. Our results show that the impact behavior is well parameterized by the splashing ratio, a dimensionless number encompassing the impact and liquid properties, and the maximum dynamic spreading contact angle. Our results are useful to the industry as they provide a criterion to select the maximum soldering injection speed or the droplet size to avoid splashing during soldering or the jetting of molten metals.