Controllable fabrication of Sn-Bi alloy microspheres for improved lead-free solder

A ripening and growing method of Sn and Bi nanoseeds mixture was developed to synthesize the Sn-Bi alloy microspheres (Sn-Bi MSs) with adjustable diameter. Which played a vital role in bonding the Cu and Sn MSs fillers of ternary composite solder. Through careful investigations of the relationship between soldering per-formances and the proportion of different filler, the optimal conductivity (& rho; = 19.0 & mu;& omega; cm), bending strength (162.0 MPa) and peeling strength (9.8 N cm-1) were obtained. Meanwhile, the work temperature has been raised about 130 degrees C by the transform of low-melting Sn-Bi to high-melting intermetallic compounds (IMCs) during soldering process. The balance mechanisms of soldering quality and fillers properties have been unraveled and validated. This work suggests a new pathway toward the improvements of performance and high-temperature stability of lead-free Sn-Bi solder, which could be widely applied in the microelectronic and semiconductor packaging.