Microstructure and properties of AgCu/2 wt% Ag-added Sn–Pb solder/CuBe joints fabricated by vapor phase soldering

The purpose of this paper is to investigate the effect of 2 wt% Ag addition in Sn–Pb eutectic solder on microstructure and mechanical properties of AgCu/solder/CuBe joint fabricated by vapor phase soldering. 63Sn37Pb and 62Sn36Pb2Ag solder pastes were used to join Cu(1.7 wt%–2.5 wt%)Be and Ag(2 wt%–5 wt%)Cu alloys. Two fracture modes are observed in 62Sn36Pb2Ag and 63Sn37Pb joints after lateral shear tests at room temperature or 120 °C, and shear forces of 62Sn36Pb2Ag joints are far higher than those of 63Sn37Pb joints. No obvious difference is observed in morphology and thickness of intermetallic compounds (IMCs) at interfaces of the 63Sn37Pb and 62Sn36Pb2Ag joints. Within the two kinds of joints, formation of big blocky or plate-like Ag₃Sn is restrained. However, many Ag₃Sn IMCs particles (1–3 μm in width) in isolated and dispersed distribution are observed within 62Sn36Pb2Ag joints. The Ag₃Sn particles are responsible for the better mechanical properties of 62Sn36Pb2Ag joints than those of 63Sn37Pb joints. The results present in this paper may provide a guide for restraining formation of big blocky or plate-like Ag₃Sn in joints with Ag pads or thick Ag surface finish on pads by utilizing vapor phase soldering process, and improving mechanical properties of Cu/SnPb/Ag joints by adding Ag in SnPb eutectic solder.