Kinetic study of eutectic Sn-3.5Ag and Electroplated Ni metallization in flip-chip solder joints

It is well known that Ni and its alloys possess a lower reaction rate with Sn than Cu and Cu alloys. Therefore Ni-based under bump metallization have attracted attention in recent years. In this study, the diffusion-control led reaction between eutectic Sn-3.5Ag flip chip solder joints between electroplated-Ni (EP-Ni) and electroless-Ni (EL-Ni) has been investigated. Morphology and growth kinetics of the formed Ni3Sn4 are study under different reflow temperatures, durations and times. The growth rates and the formation activation energy of Ni3Sn4 IMC were estimated with EP-Ni and EL-Ni, respectively. The obtained data showed that the Ni3Sn4 in the Sn-3.5Ag filp chip solder grow much faster with EP-Ni than EL-Ni UBM under the same condition. In summary, we can conclude that the slow reaction rate of EP-Ni provided a well-attached contact at the interface after 20 minutes reflow process and is better compare with EL-Ni UBM at the substrate.