Fractography and failure location evolution of Sn58Bi-Ag-Cu solder alloy during thermal aging

Eutectic Sn-Bi has long been regarded as one of the most promising alternates of Sn-Pb alloy for its low melting point and comprehensive mechanical properties. But during long time aging treatment, Bi-rich phase would coarsen, and the solder becomes brittle, which limits its large range application in electronic packaging. So many works have been carried out to figure out the essential reason of its brittleness and the strategies to eliminate it and so much data about improved mechanical properties has been reported. However, it's rare to find reports on the fracture morphology of eutectic Sn-Bi alloy itself. Herein, we present a study about details on fracture surfaces of modified eutectic Sn-Bi alloy. Characteristics on fracture surfaces from samples with different aging time have been well observed and the whole surface was divided into different regions by that. Failure mode was also determined by changes of these surface characteristics. Element analysis of different regions was done to identify the failure location of each joint. At last, the failure mode and location evolution with the prolonging of aging time was analyzed and concluded.