Characterization of interfacial IMCs in low-AgSn-Ag-xCu-Bi-Ni solder joints

This research investigated the effects of Cu content on the interfacial IMCs in low-Ag Sn-0.7Ag-xCu-3.5Bi-0.05Ni (x = 0.3, 0.5, 0.7, and 1.5 wt%, respectively) solder joints by deep-etching method and SEM observation. Experimental results indicated that as Cu content increased in the solder, the grain size of the IMCs increased and the thickness of the IMCs decreased on Cu substrate. When the concentration of Cu in the solder was 0.3 wt%, the IMC on the soldering interface was (Cu, Ni)(6)Sn-5. The concentration of Ni in (Cu, Ni)(6)Sn-5 IMC was significantly suppressed by the increase of Cu content in the solder. As Cu content increased to 1.5 wt%, the concentration of Ni in the IMC decreased to 0 and the IMC transformed from (Cu, Ni)(6)Sn-5 to Cu6Sn5. Due to the increase of Cu content, more and more (Cu, Ni)(6)Sn-5 grains nucleated on Ni substrate, and the morphology of (Cu, Ni)(6)Sn-5 transformed from polyhedrons to tiny prisms.