A viscoplastic-fatigue-creep damage model for tin-based solder alloy

During the past decade the demand for high performance automotive electronics is steadily increasing. An efficient development of such products requires the use of durability assessment techniques throughout the whole design optimization process. Since typical components comprise a large number of different materials and complex geometrical structures, Finite Element (FE) analysis is preferably used for durability evaluation and continuously replaces analytical calculations. However, a direct lifetime calculation by means of FE-techniques is still not achieved, partly due to the lack of material models capable of mapping the intrinsic material degradation under the relevant thermo-mechanical loads. Here, we propose a material model for a tin-based solder alloy which describes the non-linear mechanical behavior at the beginning of deformation as well as during continuous cyclic aging. We investigated the evolution of the mechanical properties and microstructure of the solder alloy Sn96:5Ag3:5 by cyclic strain-rate controlled fatigue- and creep-tests on as-casted standardized specimens. Material modeling is focused on the description of the complex interplay between viscoplastic, fatigue and creep processes observed in the experiment. Finally, a very good agreement is obtained between the measurements and the numerical model, which can offer new opportunities for lifetime simulations of lead-free solder joints.