Multi-scale analysis of microstructural evolution and degradation in solder alloys


Geers, M.G.D., Ubachs, R.L.J.M., Erinc, M.E., Matin, M.A., Schreurs, P.J.G. & Vellinga, W.P. (2007). Multi-scale analysis of microstructural evolution and degradation in solder alloys. International Journal for Multiscale Computational Engineering, 5(2), 93-103. In Scopus Cited 9 times.

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The past years have triggered considerable scientific efforts towards the predictive analysis of the reliability of solder connections in micro-electronics. Evidently, the replacement of theclassical Sn-Pb solder alloy by a lead-free alternative constitutes the main motivation for this. This paper concentrates on the theoretical, computational and experimental multi-scale analysis ofthe microstructure evolution and degradation of the reference material Sn-Pb and the most promising alternative, a Sn-Ag-Cu (SAC) alloy. The microstructure evolution of Sn-Pb is analysed on thebasis of a representative volume element (RVE) of the underlying microstructure. At this level, a phase field model is used to incorporate the thermally driven diffusion, thereby accounting for anonlocal interfacial free energy. Starting from this phase field description of the microstructure, the intrinsic viscoplastic response and the damage developing in the phases and interfaces areanalysed. The correlation with experimentally found results is highlighted, whereby the microstructural dependence is the key issue. The lead-free SAC alloy is investigated at the material level by considering the mechanical and thermal anisotropy of theSn-rich grains. It is shown that experimental results indicate severe grain boundary damage upon thermal cycling. Using detailed microstructural information obtained through orientation imaging microscopy, the elaborated microstructural model reflects patternsof localized plastic strains and damage, that show remarkable correlation with the experimentally found patterns. At the meso-scale, the numerical-experimental analysis concentrates at theinternal and external interfaces in the material. A cohesive zone methodology is followed here, which represents the homogenized response of the underlying complex interfacial intermetallic microstructure. The motivation, qualification and quantification ofthe cohesive zone parameters are briefly addressed. The paper concludes by emphasizing the importance of collecting and exploiting different computational and experimental techniques in a multi-scale setting, for which the case studied here constitutes a relevantexample.