Feedback strategies to decrease droplet variability in drop-on-demand deposition of complex fluids.

Sammanfattning: Mycronic AB is a high-tech Swedish company that, among other things, makes production solutions for electronic manufacturing. Focusing on Surface Mounted Equipment produces equipment, such as jet printers and pick-and-place machines. Mycronic's jet printer deposits solder paste onto Printed Circuit Boards. To dispense the solder paste, the jet printer has an ejector that jets the paste out with a piezo-powered piston. At present, the statistical repeatability of deposition volume and droplet diameter of the ejector is efficient over a large number of depositions. But the precision of individual droplets or the long-term trend of volume and diameter needs to be improved. This thesis examined where to best sense temperature fluctuations in the ejector and current over the piezo to gain insight into possibilities of temperature and actuation control for more precise deposition repeatability, especially in relation to differences in ambient temperatures and with different frequencies in jetting. The conclusions were twofold. Firstly, to improve the temperature control in the ejector, it would be better to have the temperature sensor close to the jetting chamber of the ejector. Secondly, the method to sense the current over the piezo, is a viable option to look more into for implementing actuation control on the ejector.