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- mum (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 mum, which is much smaller than the 35 mum of a conventional minimum droplet. As the relative positioning accuracy, a standard deviation of 0.81 mum was achieved when the diameter of the solder droplets was 13 mum. Furthermore, by changing the drive waveform of the conventional head, we enlarged the diameter of the solder droplets to 450 mum, which was much larger than 200 mum of a conventional maximum droplet. In this case, the standard deviation of 26 mum as the relative positioning accuracy was also achieved when the diameter of the solder droplets was 450 mum.