Multi-parameters optimization for electromigration in WLCSP solder bumps

In this study, we combined finite element method (FEM) based on Ansys and Noesis Optimus software to investigate the effect of bump structures and loading conditions on the electromigration properties of solder bumps in WLCSP. A numerical model considering current density, vacancy concentration, stress and temperature was utilized to calculate the vacancy concentration in solder bumps. The Optimus is an optimization software which can be used to perform the design of experiment (DOE) and sensitivity analysis. To optimize the bump structure, the DOE and response surface modeling (RSM) analysis were performed by using Noesis Optimus. The design optimization based on Noesis Optimus has three main advantages. First, the sensitivity analysis based on DOE results helps to find the most contributing factors. Second, it saves huge time because hundreds of experiments can be executed automatically. Third, it is able to perform evolutionary design optimization directly on RSM to identify the design’s optimal performance point. The maximum and concentration around solder were selected as the index to evaluate the effect of parameter combination on electromigration properties.