The ramifications of the definition of failure on solder joint fatigue life are discussed in terms of two considerations: (1) the dependence of the measured damage parameter (load drop or resistance increase) on the solder joint area and (2) the time profile of solder joint area. The latter is influenced by the applied displacement profile, the assembly stiffness, the deformation properties of the solder joint, and the dependence of rate of fatigue damage accumulation on its driving force. Experimental data are presented to illustrate the influence of these considerations on failure criterion. An integral methodology is used for the description of damage accumulation. Representative simulations are performed that demonstrate failure criterion effects on apparent fatigue life. Isothermal mechanical displacement controlled cyclic loading is emphasized. The principles presented may also be applied to thermal cycling of solder interconnects.

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