Influence of alloying elements on stability and electronic structures of Cu6Sn5(010) surface by first principles calculations

Due to the reliability problem and high melting point, the development of lead-free solders is hindered. Alloying is considered to be a promising approach to design new Sn-based solders. Cu6Sn5 plays an important role in the quality of microelectronic packaging that formed at the interface of solder and Cu substrate. In the present study, first principles calculations were employed to study the occupation properties of alloying elements (A = P, Zn, Ag, In, Sb, Ce, Pb, and Bi) and anti-site defects (Cu and Sn) in (0 1 0) surface of Cu6Sn5 and their influence on the electronic structures of Cu6Sn5(0 1 0) surface. Formation energies were calculated to evaluate the occupation preferences of alloying elements in considered eight sites of Cu6Sn5(0 1 0) surface. Different alloying elements show different occupation preferences. The occupations of alloying elements in Cu6Sn5 surface show negative formation energies comparing the positive formation energies in bulk Sn. Therefore, the alloying elements will easily occur in the Cu6Sn5 compound during soldering process. Electronic structures were studied to reveal the occupation mechanisms of alloying elements, and the interactions between them and Cu6Sn5 surface. Large values of density of states appear around the Fermi energy level for Ce contained system. In terms of the lowest work function, the electrons in Ce contained systems will be much easier to lose than that in other contained systems. Therefore, alloying of Ce will greatly affect the stability and electrical properties of solder joints in microelectronic packaging. (C) 2016 Elsevier B.V. All rights reserved.