Mechanical properties of laser-jetted SAC305 solder on coated optical surfaces

Micro-optical packaging methods using laser-based Solderjet Bumping are a versatile alternative to established adhesive bonding, featuring the advantages of metallic solder in optical systems. Yet, aging properties have often been studied only for certain use cases. To examine application independent, long-term material properties of SAC305, square substrates of two widely used soda-lime glasses and the ceramic Al2O3 have been coated with a thin metallic layer system to be receptive for metallic solder. Using Solderjet Bumping, SAC305 balls of 400 mm diameter have been processed with different parameters to form an array of solder bumps on each substrate. While aging for two months at elevated temperature and for over a year at room temperature, shear strengths and failure modes of the individual bumps have been measured and compared. The results show that the mechanical stability of such bumps will stabilize on a level known from research by the electronics industry while observing a considerable dependency on the used substrate material.