|M.Sc Student||Avital Alon|
|Subject||Fluidic Self Assembly of Micro-Parts|
|Department||Department of Mechanical Engineering||Supervisor||Professor Eyal Zussman|
A growing number of designs in optoelectronics and MEMS require alignment of matched components during the assembly process. Soldering is a common choice for assembly, enabling connecting and maintaining precision alignment through a batch process in a cost-effective way. The mechanism of solder self-alignment can be visualized by considering two chips with two sessile drops of molten solder between them. If the lower chip is horizontal and fixed, then the upper chip movement is driven by gravity, capillary and viscous forces. Intuitively, it is clear that when the liquid capillary forces are the dominant forces it can be equilibrated horizontally parallel and aligned to the lower chip, with its position locked by cooling of the solder joint. The aim of the present work is to provide insight into the alignment mechanism, namely, the motion of the upper chip after it has been placed initially over the solder drop. Minimizing external net forces is accomplished in this work, by reducing the weight of the upper chip through a new design. The lower chip is attached to a fixture submerged in a liquid, and the upper chip is floating to be in contact with the lower chip. Self-alignment is achieved through heating, thus melting the solder. Quantitative characterization of the solder joint formation was carried out in this work, in terms of the minimum energy of the joint in a quasi-stationary situation. The self-assembly mechanism was demonstrated by assembling a microsystem equipped with single mode optical fibers. Insertion loss, passing through the fiber in the first chip to the fiber in the second chip, reached levels of 0.3 dB which demonstrate alignment in the order of 0.2 micron.