Updated Life Prediction Models for Solder Joints with Removal of Modeling Assumptions and Effect of Constitutive Equations

There are two sources of errors in any finite element based life prediction model: the finite element mesh and assumptions, and the material properties used -specifically the constitutive model used to describe the behavior of solder joints during temperature cycling. The use of these assumptions may prohibit the application of life prediction model to conditions beyond the ones used to develop the model. The author has previously proposed life prediction models for SnPb and SnAgCu solder joints using advanced finite element modeling techniques such as sub-structuring and multi-point constraints. The assumptions were necessary to increase the efficiency of solution with available computing power. With the advances in computing technology, these assumptions are no longer necessary, and more accurate life prediction can be achieved by eliminating most of the modeling assumptions. In this paper, the updated life prediction model parameters for SnAgCu solder joints are presented without the use of sub-structuring and multi-point constraints. All joints for a particular package-board interconnection are modeled as having non-linear properties. In addition, a detailed mesh refinement study is done to determine the minimum mesh density required to yield near mesh-independent results. In addition to modeling assumptions, the constitutive equation used for solder joints may also influence the life prediction model parameters. To investigate this further, the creep behavior of SnAgCu solder joints is represented by using published constitutive equations (double power law creep and hyperbolic sine equation). The results show a significant influence of constitutive equation on creep strain based life prediction model but minimum impact when energy density based approach is used