Printing solder droplets for micro devices packages using pneumatic drop-on-demand (DOD) technique

A pneumatic drop-on-demand (DOD) system has been applied to solder complex and dense interconnects of modern micro electronic devices. Initial parameters of uniform droplets were first measured. Then influences of experiment parameters, such as the crucible temperature, the substrate temperature and the droplet velocity on spread of solder droplets, were investigated experimentally and theoretically. The results showed that effects of impact velocity on the spreading could be negligible and the solder spreading process was driven by capillary forces because of the low Weber (We) number of depositing droplet. The influence of initial droplet temperature on the droplet spreading was not regular. The contact diameter of solder droplets on copper substrate increased when the substrate temperature increased from 443 K to 493 K. At last, copper cables were successfully soldered to pins of a flexible circuit using the direct solder deposition and re-melting process. The soldering results showed the feasibility of the data-driven soldering technique using the pneumatic DOD deposition technology.