PRODUCTION AND CHARACTERIZATION OF MONO SIZED SN-PB ALLOY BALLS

Mono-sized balls of the eutectic Sn-38w/o Pb alloy were produced by co ntrolling the break-up of a continuous laminar jet into uniform drople ts and by rapidly solidifying the droplets in a silicone oil bath. Tho ugh other sizes are possible, the process parameters were selected to produce droplets of a fixed diameter between 700 and 800 mu m. The use of silicone oil assured fast cooling and minimum droplet merging. The balls showed high sphericity; narrow size distribution (within +/- 5% of the target diameter), and a uniform, rapidly solidified microstruc ture. They also showed uniform re-melting characteristics due to their homogeneous microstructures. The present study suggests that the mono -sized Sn-Pb alloy balls, produced by the Uniform-Droplet Spray (UDS) process, may be applicable to the manufacture of ball grid array (EGA) type multimodule integrated-circuit (IC) packaging.