Variable-Size Solder Droplets by a Molten-Solder Ejection Method

We have developed a molten-solder ejection method by which molten-solder droplets from a 13- (1 pL) to 450- $\mu\hbox{m}$ (48 nL) diameter could be realized. This method has been developed as a technique to supply small solder balls. The authors have developed a newly designed solder ejection head and confirmed that solder balls with almost no surface oxidation can be formed by using this method. The diameter of the molten-solder droplets using an advanced head is 13 $\mu \hbox{m}$, which is much smaller than the 35 $\mu\hbox{m}$ of a conventional minimum droplet. As the relative positioning accuracy, a standard deviation of 0.81 $\mu\hbox{m}$ was achieved when the diameter of the solder droplets was 13 $\mu\hbox{m}$. Furthermore, by changing the drive waveform of the conventional head, we enlarged the diameter of the solder droplets to 450 $\mu\hbox{m}$, which was much larger than 200 $\mu\hbox{m}$ of a conventional maximum droplet. In this case, the standard deviation of 26 $\mu\hbox{m}$ as the relative positioning accuracy was also achieved when the diameter of the solder droplets was 450 $\mu\hbox{m}$.$\hfill$ [2008-0068]