Plasticity-creep separation method for viscoplastic deformation of lead-free solders

This paper applies a constitutive model proposed previously by the authors to three lead-free solder alloys of Sn/Ag, Sn/Bi and Sn/Zn. First, the material constants in the constitutive model are determined using the so-called "Plasticity-creep separation method" by simple tests such as pure tensile tests. The constitutive model is incorporated into a general purpose Finite Element Method program ANSYS using the stress integration method. The material constants for the lead-free solders could be simply determined using only the data obtained by the pure tensile tests with three strain rates. The basic mechanical deformation such as creep and cyclic deformation are simulated by the constitutive model using the material constants determined using the "plasticity-creep separation method". Thermal deformation during a reflow process with electronic packaging is also simulated by the constitutive model.