Effect of Ni solute on grain boundary diffusivity and structure of bSn

The effect of Ni impurity on the self-diffusivity of bSn in the (1 0 1) symmetric tilt grain boundary is investigated. Using molecular dynamics simulations over a temperature range of 300–450 K. It is shown that Ni solute decreases the grain boundary self-diffusivity of bSn as the amount of solute in grain boundary increases. We also study the solute effect on the diffusive width of grain boundary and observe that low concentrations of Ni solute lead to shrinking of the grain boundary width relative to the pure bSn grain boundary. Reliability of lead-free solder joints is a very important issue in electronic packaging such as high power electronics, nanoelectron-ics, and single deployment electronics used in military. Pb–Sn alloy was one of the most popular materials for solder joints in electronics due to its excellent properties such as low melting temperature and wetting behavior. However, current demand for lead-free solder joints requires a new alloy. The most commonly used lead-free solder alloys are Sn based alloys SAC405 (94.5Sn, 4.0Ag, 0.5Cu by weight). Reliability of solder joints requires fundamental understanding of solder alloys' thermo-electro-mechanical behavior. As a result, there are a large number of studies on Sn based lead-free solder alloys [1–12]. In [1–6], numerical simulations were used to investigate the atomic behavior or material properties of lead-free solder alloys. In [7–12], experimental approach was used to study the deformation behavior and material properties of pure Sn or Sn based solder alloys. Past studies of Sn-based solder alloys with addition of nickel (Ni) element have shown that ppm-level additions of nickel (Ni) have significant effects on the properties of the solder alloys, such as wettability, mechanical strength, and preventing the growth of intermetallic compound (IMC) [13,14]. However, most studies on Ni solute additions to bSn-based solder alloy are experimental. When considering that mass transport is one of the main failure mechanisms of solder alloys, especially diffusivity of solder alloy is an important property under electromigration, thermomigra-tion, and creep. Nevertheless, a study on the atomic level effect of Ni addition to bSn's self-diffusivity has never been published. In this present work, the effect of Ni solute segregation on bSn grain boundary diffusivity is studied at atomic level using molecular dynamics simulations (MDS). In 1982, Bernardini et al. [15] investigated solutes effects on mass transport in polycrystalline Fe. They showed that the self-diffusivity of Fe decreases as Sn solute atoms are added at the …