Characterization of microstructural evolution of crept, aged and thermomechanically fatigued eutectic tin-silver solder joints using orientation imaging microscopy.

摘要

Single shear lap eutectic Sn-Ag solder joints with copper substrate were subjected to isothermal aging, creep at room and elevated temperature, and thermomechanical fatigue (TMF). Orientation Imaging Microscopy (OIM) studies reveal how the crystallographic orientations are correlated with microstructural features in the solder joints. Certain misorientations appear to be energetically favored during solidification, which have twin and Σ boundary type relationships. Changes in the crystallographic orientations, grain size and misorientation angles between grains, occurring due to subsequent heating and/or deformation were documented and analyzed. The gross texture components remained unchanged after creep and aging. High temperature processes caused some grain boundary motion and modest grain growth. Observations made in three different regions of a specimen that underwent 150 and 370 TMF cycles indicate that no significant changes occurred, though grain boundaries moved, resulting in slight grain growth. This study shows that the lead-free solder joints are multi-crystals, so that deformation is very heterogeneous and sensitive to crystal orientation, strain and the temperature history.