Thermal and mechanical stability of Ce-containing Sn-3.9Ag-0.7Cu lead-free solder on Cu and electroless Ni-P metallizations

Rare earth (RE)-containing solders have been shown to exhibit improvements in both physical and mechanical properties. However, the reactive nature of RE elements with oxygen may degrade the mechanical properties even under room-temperature aging. In this article, we report on the microstructure and mechanical properties of as-processed and thermally aged Ce-containing Sn-3.9Ag-0.7Cu solder reflowed on electroless Ni-P and Cu metallizations. The microstructure of both as-reflowed and thermally aged Ce-containing Sn-3.9Ag-0.7Cu solder joints is more refined compared with conventional Sn-3.9Ag-0.7Cu solder joints. The (Cu,Ni)₆Sn₅ intermetallic layer formed at the Cu/Ce-containing solder interface is thinner than that of Sn-3.9Ag-0.7Cu solder. The monotonic shear behavior of as-reflowed and thermally aged Sn-3.9Ag-0.7Cu-0.5Ce/Cu and electroless Ni-P lap shear joints was studied, and compared with Sn-3.9Ag-0.7Cu. It was found that both as-reflowed and thermally aged Ce-containing Sn-3.9Ag-0.7Cu exhibit higher strain to failure compared with Sn-3.9Ag-0.7Cu solder joints.