Study on Board-Level Drop Impact Reliability of Sn-Ag-Cu Solder Joint by Considering Strain Rate Dependent Properties of Solder

Board-level drop reliability test and analysis require dynamic characterization of the high strain-rate properties of the solder, along with solder joint failure tests. Relying on just the drop impact analysis of board-level dynamic response (i.e. G-levels and board bending strains) and an oversimplification of deformation response of solder joints (i.e., assuming elastic stress criteria) can lead to misleading conclusions in the physics-of-failure understanding in drop impact tests. In this paper, impact tests were conducted with a split Hopkinson pressure bar test system to study the dynamic response of bulk solder materials. A finite-element analysis of drop impact was conducted by considering different solder constitutive models such as the elastic and strain rate-dependent plastic model to investigate the effect of the solder constitutive model on the dynamic response of the solder joint. The important finding of this study is that the constitutive model used has a major impact on the dynamic response of solder joint stress and strain results. Theoretically, it is predicted that the strain rate-dependent plastic model gave better correlation results than the simple elastic model. A solder joint reliability characterization using the drop impact test with a clamped-clamped boundary condition was investigated for a plastic ball grid array assembly with Sn-Ag-Cu solder and two board surface finishes. In order to assess drop reliability of solder joint with different surface finishes, Charpy test was conducted to evaluate the dynamic strength of the soldered specimen using Sn-Ag-Cu solder and with or without Ni/Au plating.