Experimental and Simulative Correlations of the Influence of Solder Volume and Receptor Size on the Capillary Self-Alignment of Micro Solar Cells

Surface tension-driven self-alignment is a promising technique to align millimeter-scale components with a high accuracy of a few microns. It is based on liquid capillary forces moving and aligning a solid component on its receiving pad. Using molten solders as the liquid is a promising way to bond, connect and align a chip with its substrate. Micro-solar cells soldering experiments for micro-concentrator photovoltaics have been carried out. It has been found experimentally that the solder volume, the receiving pad size and the initial placement of the chip have an impact on the placement accuracy. In this work, an analytical and a numerical model of the capillary forces during self-alignment are built to improve the understanding of the experimental results. Guidelines to reach a high placement accuracy are presented. In practice, low solder volumes, receiving pads smaller than the chip and an initial chip displacement of about 10% of the chip size yield a higher placement accuracy.