Effects of rare earth Ce addition on the microstructure, wettability and interfacial reactions of eutectic Sn–0.7Cu solder

The effects of trace RE Ce addition on the microstructure, melting point and wettability of eutectic Sn–0.7Cu solder as well as on the interfacial reactions of Sn–0.7Cu–xCe/Cu(Ni) during soldering were investigated. The Ce bearing solders owned slightly higher melting temperatures than eutectic Sn–0.7Cu solder, with small melting intervals. The addition of trace RE Ce had a diverse effect on the wettability of the solders, and better wettability was obtained on Cu substrate than on Ni substrate. Due to the metamorphism of RE elements, the β-Sn dentrites were refined and the eutectic regions became more uniform in the Sn–0.7Cu–xCe solders with the increase of Ce addition. The intermetallic compound (IMC) formed at Sn–0.7Cu–xCe/Cu interfaces during soldering was scallop-like Cu₆Sn₅, and those formed at Sn–0.7Cu–xCe/Ni interfaces were (Ni,Cu)₃Sn₄ and (Cu,Ni)₆Sn₅. With the increase of Ce addition, the average size, the aspect ratio and the thickness of the Cu₆Sn₅ grains on the Cu substrate decreased, while those of the IMC grains on the Ni substrate increased. The different growth behavior of the interfacial IMCs on Cu and Ni substrates were discussed.