Interfacial Reaction of Lead-Free Solders with Lead-Free Finished Leadframes

Due to the implementation of the legislations to restrict the use of environmental unfriendly materials, the use of lead (Pb) in electronic products is banned. This includes the use of surface finishing materials such as that for integrated circuit (IC) leadframes. As these leadframes with Pb-free surface finishings will have their leads soldered with Pb-free solder alloys, the reaction between the surface finishing and the solder needs to be evaluated. In this study, comparisons between four types of Pb-free surface finishings of Matte Sn, Bright Sn, Sn-3Bi and Ni/Pd/Au, and a Pb-containing one were made. The wettability performance between the leadframes electroplated with these five surface finishings and three solder alloys was analyzed using a wetting balance to obtain the wetting force and wetting time. The leadframes soldered with the three types of solders were subjected to thermal aging at 150degC for 150 hours to study the growth of the intermetallic compounds (IMCs). The results showed that the Ni/Pd/Au surface finishing provided very good wetting performance among the five types of surface finishings. It also had comparable wetting force with lead-containing and Pb-free solder alloys. The wetting time of Ni/Pd/Au with Sn- 3.5Ag-0.7Cu-RE was the smallest among all cases investigated. It was also found that the growth of IMC between Sn-3.5Ag-0.7Cu-RE and Ni/Pd/Au was the slowest. Thus, the use of Sn-3.5Ag-0.7Cu-0.1RE on Ni/Pd/Au finished leadframes would provide the best combination of wetting and reliability performance in terms of the suppression of IMC growth.