Board level solder joint reliability modeling of LFBGA package

Abstract

In this paper, a 3D FEA sliced model is built for LFBGA (low profile fine pitch BGA) on board to predict the fatigue life of solder joints during thermal cycling tests. The fatigue model applied is based on Darveaux's approach with nonlinear viscoplastic analysis of solder balls. The FEA fatigue model can be applied effectively as a design guide to determine the best package configuration in terms of ball geometry, pitch, die size, substrate size, material combination, etc. The model is first correlated with 3 sets of thermal cycling data to establish a connection between the strain energy density (SED) obtained from FEA models and the actual characteristic life during the thermal cycling test. Modified correlation constants based on Darveaux's method are extracted. The FEA-thermal cycling correlation is within /spl plusmn/10% error limit. In future, when more thermal cycling test data are available, the FEA model can be fine-tuned accordingly for more confident life prediction. Then, the validated model is applied to predict the fatigue life for LFBGA and TFBGA (thin fine pitch BGA) packages. Design analysis is performed to study the effect of key package parameters such as die size, substrate size, and solder ball size. Comparison between peripheral and full arrays and the effect of thermal balls are also investigated.