Effect of Ag on Sn-Cu Lead Free Solders

Abstract

Lead free solders are expected to replace the traditional Sn-Pb alloys due to environmental concern. The Sn-Cu lead free solder alloys are found to be a potential alternative to the Sn-Pb alloys compared to other solders. Eutectic Sn-0.7Cu (wt.%) solder has been used for interconnecting and packaging electronic component due to the good wettability between the Sn-Cu solder and the Cu substrates. Three compositions Sn-0.7Cu, Sn-1Cu and Sn-2Cu and three compositions containing Ag, Sn-2Ag-0.7Cu, Sn-2.5Ag-0.7Cu and Sn-4.5Ag-0.7Cu were considered here for the study. Ag was added to the eutectic Sn-0.7Cu composition in order to decrease the melting temperature of the eutectic alloy and to enhance the mechanical properties of the alloy such as hardness. But the amount of Ag was more increases hardness was decreases. The wettability of the Sn-Cu solder on the Cu substrate was also enhanced by the addition of Ag. Structure and morphology of the solder alloys were analyzed using a SEM, XRD and EDX. The microstructural observation reveals the formation of â-Sn matrix and presence of intermetallic phases like Cu6Sn5 and Ag3Sn. Furnace cooling was employed for solidifying the lead free solder alloys. Thermal analysis of the solder alloys were done with the help of a differential scanning calorimeter (DSC). Trace additions of Ag have been found to significantly reduce the melting temperature of these alloys.