2010 Volume 4 Issue 10 Pages 1530-1538
Hollow eutectic tin-lead solder spheres with diameters from 3.5 to 4.5 mm have been produced directly from the melt. Raw solder placed in a crucible was melted at a temperature of typically about 50 °C above its melting point. The molten solder was then extruded vertically downward into air at room temperature through the outer nozzle of a coaxial nozzle mounted at the crucible bottom. Capillary instability of the extruded hollow molten solder jet led to the formation of hollow solder spheres. This formation was assisted by a transverse nozzle placed close to the coaxial nozzle, which directed an inert gas past the hollow jet at position where sphere detached. The spheres were then quickly cooled and solidified by water mist prior to collection in a container filled with water. Most of these spheres were completely hermetic and had a relatively smooth surface. Hollow water spheres were also formed as a test of production of hollow solder spheres through the nozzle.