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Eutectic solders are prone to cold flow and creep in thermal cycle process and therefore prone to fatigue failures. In this paper, eutectic solder fatigue in a molded board level BGA module was studied through finite element analysis. Particularly, the effects of underfilling molding compounds to the stresses and fatigue life of solder balls were investigated. A global finite element model was built to map out the most likely first-fail solder ball. The life cycle of this solder ball was further studied through a more detailed localized finite element model. Improvement of the fatigue life of this solder ball was investigated through optimizing materials properties of the underfilling molding compound.