Influence of Under Bump Metalization dimensions on passivation nitride stress

Cracks in die passivation adjacent to solder bumps due to thermal stress can lead to a multitude of failures including bond pad lifting. Modifying the solder reflow temperature-time profile is not trivial as this may impact the metallurgical properties of the solder ball. In this work, Under Bump Metalization (UBM) dimensions were optimized using finite element analysis (FEA) and response surface methodology (RSM) to obtain the lowest first principal stress for the Silicon Nitride (Si₃N₄) passivation layer. The optimized minimum stress value using FEA was well within the confidence interval predicted using RSM.