Effect of Er on Microstructure and Mechanical Properties of Sn58bi Based Lead-Free Solder

The influences of Er element on microstructure and properties of Sn58Bi based lead-free solder were investigated in this study. With Er element addition, the amount of primary Sn-rich phase increased in the Sn-Bi alloys. Sn-58Bi-xEr solder alloy not only is mainly composed of ß-Sn phase and Bi phase, also has trace Er phase, the added rare earth Er does not react with the Sn, Bi to form compounds. Tensile test results showed that the tensile strength changed slightly with increasing Er addition, while the elongation increased remarkably first and then decreased after adding 0.1% Er. With the addition of rare earth element Er, the Cu6Sn5 intermetallic compound layer formed Sn-58Bi-xEr/Cu the interface of welded joint can be refined, and the intermetallic compound layer tends to be flat. With the increase of Er (>0.5%), the oxidation slag will act as the external nucleation particle, which will promote the nucleation of the interface IMC, and then promote the formation of the IMC.