Effects of alloying elements on the dissolution and diffusion of Bi in Sn: A first-principles study

Abstract

Interfacial Bi segregation in Sn-based solders is a critical issue that affects the reliability of solder joints. Doping alloying elements into Sn-Bi solders is considered as a potential way to improve the Bi precipitation. We provided insights into the mechanism of Bi segregation at the atomic scale, by calculating the dissolution and diffusion energies of Bi in the Sn bulk. Importantly, we investigated the effects of alloying elements on the Bi dissolution and diffusion, which varies much with element species. The addition of elements such as Pt, Pd, and Au could enhance the dissolution and weaken the diffusion of Bi in the Sn bulk, thus suppressing the interfacial Bi segregation to some extent. However, other elements such as In, Ag, Sb, and Ga have slight impacts on the dissolution and diffusion of Bi. The bonding characters between the third elements, Bi, and Sn atoms explain different influences of alloying elements on Bi segregation in Sn-based solders.

Partial Segregation of Bi and Microvoid Formation on a Pure Cu Substrate After Solid–Solid Reactions

“…According to the Sn-Bi phase diagram, the solubility of Bi in Sn is approximately 9 wt% and 18 wt% at 200 and 160°C, respectively. 12 The solubility of Bi in Sn was increased twofold in this study. A large amount of Bi dissolved in the solder, which means that a small amount of Bi could segregate at the interface.…”

“…First, a Bi content less than 10 wt% (Sn-xBi, x < 10 wt%) or alloying element addition inhibits Bi segregation at the interface. 6,12,13 Second, adding Au, Pd, or Pt increases the dissolution and reduces the diffusion of Bi in Sn. These elements have positive effects in inhibiting Bi segregation.…”

“…These elements have positive effects in inhibiting Bi segregation. 12 Third, Bi segregation and void formation are restrained with the addition of Ag, Al, Sn, or Zn into a Cu substrate.…”