Effects of aging treatment on reliability of SnZn soldered joints

The interface morphology and mechanical property of Sn-9Zn-0.06Nd/Cu soldered joints after aging treatment at 150℃ were investigated with scanning electronic microscope(SEM) and STR-1000 joint strength tester.The experimental results indicated that a planar Cu₅Zn₈ intermetallic layer(IMC) formed in the soldered joint interface,whose thickness increased with increasing aging time,and the rare earth element Nd migrated towards the interface and reacted with Sn forming Nd₃Sn near the interface.While increasing the aging time,the tensile stress of the Sn-9Zn-0.06Nd/Cu micro-joints decreased,and it even reduced by 50% after aging for 720 h.The fracture mode of the soldered joints turned from ductile fracture before aging treatment to both ductile and brittle fracture after aging for 720 h.