Wetting reaction of Sn-Ag based solder systems on Cu substrates plated with Au and/or Pd layer

The wetting behavior of SnAg based Pb-free solders on Cu and Cu substrates plated with Au, Pd, and Au/Pd thin films have been studied. The wetting ang le and kinetics of interfacial reaction were measured. The Au-plated substr ates exhibit better wetting than the Pd-plated substrates. In the case of S nAg on Pd-plated Cu, SEM observation revealed that the solder cap was surro unded by an inner ring of Cu-Sn compound and an outer ring of Pd-Sn compoun d. This implies that the molten SnAg solder had removed the Pd and wetted t he Cu directly in the equilibrium state. The effects of pre-doping Cu in th e SnAg solder on wetting behavior were also investigated. We found that wet tability decreases with increasing Cu content in the solder. We also observ ed that the SnAgCu solders have a lower Cu consumption rate than the SnAg s older.