CALCE Webinar - Why Current Approaches for Solder Joint Modeling are Inadequate – and What to Do About It

Abhishek Deshpande
Thursday, August 5, 2021 11:00 am US EDT

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Functional SAC solder joints commonly consist of a few highly anisotropic grains. Due to the randomness of crystalline orientation and arrangement, even for joints in the same ball grid array (BGA), grains are subjected to different stress conditions. This piece-to-piece variability in solder joints leads to significant uncertainty in their thermo-mechanical performance, where numerical simulations based only on homogeneous isotropic material properties are insufficient, and a large number of repeated tests are needed to determine the statistical variability.

An alternative grain-scale modelling approach is proposed in the current work, where the discrete grain morphology of coarse-grain solder joints is explicitly modelled with anisotropic viscoplastic and plastic properties of SAC single crystal. The viscoplastic behavior is modelled based on dislocation mechanics and typical microstructural features of multiple length scales, and the plastic behavior is determined by the orientation-dependent stress-strain data. Both models are calibrated by combining the results of in-house testing and those provided in the literature. Hill’s anisotropic potential is then used to extract the continuum-scale compact models of viscoplasticity and plasticity, respectively. This methodology enables user-friendly computationally-efficient finite element simulations of multi-grain solder joints and facilitates parametric sensitivity studies of different grain configuration. This capability will provide numerical exploration for the best-case and worst-case microstructural configuration and corresponding margins of solder joints performance. Selected examples of SAC solder joints with triple crystals are presented, for modelling creep deformation under slow temperature cycling and plastic deformation under rapid mechanical cycling.

About the Presenter: Abhishek is advised by Professor Abhijit Dasgupta and works in the University of Maryland’s (UMD) Center for Advanced Life Cycle Engineering (CALCE). His research focuses on the effect of multiaxial stress states and interfacial roughness on mechanical fatigue degradation of solder joints in functional electronics, using a combination of microscale mechanical testing and grain-scale finite element analysis.