The influence of PBGAs post-manufacturing warpage simulation, viscoelastic material properties and evaluation methodology on accuracy of solder joints damage prediction

Two Plastic Ball Grid Array (PBGA) designs were stressed with Temperature Cycles (TC) in the Board Level Reliability (BLR) test, and simulated using FEM. The test result for one of the PBGAs was not in line with original expectation, but it was confirmed by FE-simulation. The simulation incorporated manufacturing process (the real post-cure shape verified by measurement) and viscoelastic material properties. The impact of model simplifications (i.e. omitting manufacturing process simulation or viscoelastic material properties) on the thermo-mechanical load of the solder joints was investigated. The opportunities and restrictions of these simplifications are shown and discussed. The current work also describes an improvement of the strategy for evaluation of the simulation results. The correlation between the test result (crack lengths observed via cross sections) and the local damage-related state variables from the FE-simulation was improved when effects of hydrostatic stress and cross section direction were included in the evaluation.