The thermal and mechanical responses of a 304-Pin, 0.5 mm pitch, 40 mm by 40 mm body size plastic quad flat pack (QFP) solder joints and leads have been determined in this study. The thermal stress and strain in the leads and solder joints have been obtained by a 3-D nonlinear finite element method and the thermal fatigue life of the QFP corner solder joint was then estimated based on the calculated plastic strains, Coffin-Manson law, and isothermal fatigue data of solders. The effects of overload environmental stress factors on the mechanical responses of the leads and solder joints have been determined by bending and twisting experiments.

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