The uniform droplets for lead-free solder balls fabricated by using the Droplet-Based Manufacturing(DBM) process. The DBM process generates uniform droplet from molten metal jets by the uniform vibration of the piezoelectric materials, and consists of a crucible, an orifice, a spray chamber system, a gas control system, a melt vibration system, a charging system, and a video monitoring system.
The Sn-Pb eutentic solder balls use make of the most widly in chip-packing technique. However the use of Pb have been resricted due to environment and toxicologic. Therefore lead-free solder alloys to make investigate Sn, Sn-3.5wt%Ag, Sn-3.8wt%Ag-0.6wt%Zn materials.
In order to observe the morphology and microstructure of the droplets, lead-free solder balls were collected at different levels of flight distance of 0.15m, 0.30m, 0.50m, and 0.65m, respectively. The collected solder balls were characterized by use of SEM, OM, AES, and XPS.
The sphericity of droplets decreased with increasing the flight distance due to oxidation effect of droplet surface. The microstructure of droplets changed from cell structure to dendrite structure with increasing orifice size due to effect of cooling effect. The microstructure of droplets showed that the arm spacing of dendrite increased with increasing the flight distance.