Impact of RDL polymer on reliability of flip chip interconnects in thermal cycling — Correlation of experiments with finite element simulations

For WLP (Wafer Level Packaging) thin film polymers play a key role in respect to board level reliability. This paper introduces a reliability indicator giving a tendency of the polymer material to crack initiation around the UBM pad. This indicator derived from Finite Element simulated maximum stress in polymer layer and the material specific tensile strength. Comparing the simulation results with the experimental data we see the same impact of the mechanical material properties on the reliability. This proves the described reliability indicator as suitable for estimating thermal cycle reliability of RDL polymer materials gives application engineers and manufacturers a new tool for selecting the most suitable RDL material for e.g. flip chip and WLP applications.