Optimal design of drop impact for TFBGA by concept of average stress within finite grid region

This study describes board-level drop reliability of TFBGA subjected to JEDEC drop test condition which features an impact pulse profile with a peak acceleration of 1500G and a pulse duration of 0.5 ms. The solder ball is assumed as an elastoplastic model, and the other components are assumed to be linear elastic models. Both the global/local finite element method and the finite grid region method are introduced to improve the accuracy and the convergence during the meshing process. Meanwhile the contact impact process during the dropping test is translated into the effective support excitation load on the PCB through the support excitation scheme to simplify the analysis. By means of optimal parameters of the Taguchi robust design, the average stress of the solder ball at PCB side surface becomes 80.9Mpa which shows a 57% reduction compared to the original stress of 189.7Mpa. As a result, the impact reliability of the TFBGA package has been significantly improved.