Silver effect on the intermetallic growth in the Sn-8Zn-3Bi lead-free solder

Due to the health concerns, the demand for Pb-free solder is greater than before. In the past, Sn-Pb solders were widely used in soldering process due to their excellent soldering characteristics and reliability. Pb-free solder, the Sn-8Zn-3Bi eutectic alloy is regarded as one of the best potential candidates. This study investigated the effect of silver (Ag) addition on the morphology and growth rate of Cu5Zn8, Cu6Sn5 and Cu3Sn intermetallics in the Sn-8Zn-3Bi solder. The reflow was done at 220 degrees C, 230 degrees C, 250 degrees C, 270 degrees C and 290 degrees C at various soldering times. The Sn-8Zn-3Bi solder reacting with Cu substrate formed a single Cu5Zn8 intermetallic layer with a flat structure. On the other hand, the reaction between (Sn-8Zn-3Bi)-1Ag solder and Cu substrate produces Cu6Sn5 and Cu3Sn intermetallics. The addition of Ag into the Sn-8Zn-3Bi solder has significantly suppressed the formation of Cu5Zn8 intermetallic, and promoted the growth of Cu6Sn5 and Cu3Sn intermetallics. The growth rate constants of Cu5Zn8 phase is lower at low temperature and increases at high temperature. Meanwhile the growth rate constants of Cu6Sn5 is higher than Cu3Sn phase, thus providing an opportunity for Cu6Sn5 phase to predominate the total intermetallic compounds in this liquid-state aging study. (C) 2018 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of Materials Processing and characterization.