Finite element modeling and experimental validation of conventional and high speed shear testing in Pb-free environment

With the extensive use of Pb-free solder in electronic assemblies, there is a growing concern about the reliability of the solder joint. The need to identify the capability of high speed shear, to reveal brittle fracture failures, was the driving force behind this study. Shearing of 0603 resistors mounted on a PCB with Pb-free solder was considered as the test process setup for modeling and experimentation. Finite element analysis (FEA) was employed to replicate the process of shearing the solder joint. A comparison was drawn between the FEA results and the results obtained through the actual lab testing. The FEA results for the low speed shear test suggest that the failure would have a very high probability of occurrence in the bulk of the solder with the shear force ranging from 20-28 N. This range, predicted by FEA, was found to be 20% lower than the actual test results. Furthermore, FEA provides reasonable assurance about the capability of high speed shear to demonstrate brittle fracture at the intermetallic. Application of force in the range of 56-65 N would be required for this failure mode at the interface. Moreover, the results establish Finite Element Analysis as a reasonable approach to illustrate the changing stress patterns that a component undergoes when subjected to shear. On the whole, the results of the analysis substantiate high speed (high force) shear being a promising test to predict and detect the brittle fracture failure of the Pb-free interconnects.