FEA based reliability prediction for different Sn-based solders subjected to fast shear and fatigue loadings

Abstract

Recent studies revealed that there is no simple ldquodrop inrdquo solution for the lead-free replacement of SnPb joints, instead different Sn-based solders are advantageous for different use conditions, which can be dominated either by drop loading or by thermal cyclic loading in harsh use conditions. By way of high-speed shear testing reliability assessments of components during drop and shock events can be studied in a simplified manner. Dynamic 3-D finite element simulations have been performed applying explicit FEA to replicate the shear tests virtually. It was shown in this way that SAC 1305 solder outperformed SAC 387 solder. The low cycle fatigue behavior of different SAC alloys is additionally of interest. Fatigue life predictions require both the constitutive description of the lead-free solders and a fatigue hypothesis linked to the material selected. Based on recently measured creep properties the solder joint creep strain and creep dissipation responses were analyzed for several components and thermal cycling conditions. The results based upon non-linear finite element calculations indicate different trends for creep strain and energy dissipation: while the first is clearly increasing with lowered alloying Ag-content, the latter is almost stable and does only slightly vary. Furthermore, these trends are different for different test- and field cycling conditions as well as the different components studied.