Constitutive relation and creep-fatigue life model for eutectic tin-lead solder

A constitutive equation for a typical SnPb eutectic or near-eutectic solder joint is developed, based on empirical data in shear and generalized to three dimensions. Three strain components are considered: elastic, time independent plastic, and steady-state creep. A continuum mechanics rather than a metallurgical approach is taken with emphasis on the formulation of an equation useful for predicting solder behavior under a variety of conditions. Solutions of the constitutive equation predict the experimental hysteresis data for the loading histories available. Solutions of the equation for the test conditions of three independent sets of solder fatigue data show that the equation, together with the matrix creep failure indicator, can give an estimate of fatigue life