A Finite Element Study of Factors Affecting Fatigue Life of Solder Joints

The elastic-plastic-creep characteristics of solder joints are implemented in a nonlinear finite element program ABAQUS by developing user defined material subroutines. An eutectic Pb-Sn solder joint of a resistor carrier under thermal cycling between 125°C and −55°C is modeled, and the effect of various parameters on the solder joint cycle life is evaluated. The strain range of the solder joint under thermal cycling loads is calculated, which is then converted into solder joint cycle life through a fatigue-life relationship proposed by Engelmaier (1983). The parameters studied include: ramp time, hold time, grain size, initial temperature, constitutive equations, material properties for solder alloys, and mesh refinement. The effects of these variations on the fatigue life of solder joints are illustrated. The described method can serve as a tool in the design and manufacturing of surface-mount (SMT) assemblies.