Wetting characteristics of Cu–xZn layers for Sn–3.0Ag–0.5Cu solders

Abstract

Cu–xZn solder wetting layers for Pb-free solders were successfully electroplated in an eco-friendly non-cyanide bath. Wetting experiment for the Sn–3.0Ag–0.5Cu (SAC305) solder were performed on the four wetting layers; Cu, Cu–20wt.% Zn electroplated using cyanide solution, Cu–20wt.% Zn and Cu–30wt.% Zn layer electroplated using a non-cyanide solution. The effects of soldering temperature and flux type on wetting characteristics with SAC305 solder were also investigated. First, the wetting force and wetting time were measured from the wetting balance test to evaluate the wetting characteristics of SAC solder. The rosin mildly activated (RMA) and water soluble (WS) fluxes were used. The wettability of SAC solder on both the Cu and Cu–xZn layer was enhanced by increasing the soldering temperature and chemical cleaning of the wetting layers. When RMA type flux was applied, the Cu layer exhibited better wetting characteristics than the Cu–xZn layer. When WS flux was applied, the wettability of both the Cu and Cu–xZn layer was enhanced and the Cu and Cu–xZn layer showed similar wetting characteristics. Next, the spreading area and wetting angle were measured after SAC305 solder balls were placed on four wetting layers and reflowed at 250°C for 10s by using the WS flux. As the reflow temperature increased or after chemical etching, the spreading area of all the samples was increased and the wetting angle decreased. Applying the WS flux which includes higher activity has good wettability in the Cu–Zn layer. If the proper flux is used, the wettability of the Cu–xZn layer was as good as the Cu layer.