Effect of Bi Additions on the Creep Behaviour of SAC Solder Alloys
Microstructural evolution resulting from long-term thermal exposure and creep behaviour of cast Sn-0.6Ag-0.7Cu-xBi solder alloys for electronic packaging applications are investigated. Deformation mechanisms are determined via creep tests conducted at a temperature range of 25–150°C using 7.5–12.5 MPa stress and in-depth scanning electron microscopy analysis. In all compositions, dislocation based processes are responsible for creep deformation. The creep strengthening of the 1.5–2.5 wt.% Bi alloys is from Cu6Sn5/Ag3Sn intermetallic phases. The higher coarsening rate of the Cu6Sn5 phase compared to Ag3Sn leads to loss of creep resistance. The low creep resistance of Sn-0.6Ag-0.7Cu-5Bi solder alloy is attributed to the presence of the Bi phase with polygonal morphology causing earlier failure in creep.