Plastic Strain Based Criterion for Reliability Assessment of CSP Packages Subjected to Dynamic Shock Loads

Drop impact induced crack in ball grid array (BGA) solder joint is one of the most dominant failure modes found in BGA package under mechanical load. The failure in BGA due to its excess stress resulting from over bended deformation in a PCB board during shock event is not only a function of solder material but a board and package structure as well. Due to extremely difficult and infeasible in directly measuring responses in BGA solder joint during drop shock event, computer modeling approach has been increasingly played an important role in evaluating product reliability performance during product development. Modeling technique with a comprehensive failure criterion and metric including high strain rate effect is necessary to be developed to quantitatively evaluate and benchmark BGA package reliability performance for different board designs. In this paper, dynamic responses in CSP/BGA in different boards and product phone have been characterized by using nonlinear dynamic finite element software, LS-Dyna. Different failure criteria, such as plastic strain and stress based are investigated and compared. It is shown that a good correlation between validation test and numerical result can be achieved by using proposed plastic strain based criterion only and thus it can be used in cross comparisons between different board designs.