Wetting interaction of Pb-free Sn-Zn-Al solders on metal plated substrate

A newly developed Pls-free Sn-9(Zn-5Al) solder was investigated for its wetting behavior on metal plated Cu substrate. The Cu substrate was plated with electroless nickel (EN) or with EN/Cu multilayer plating. The wetting behavior was investigated with a wetting balance which gave rise to a wetting curve. Fluxes including L-glutamic acid and dimethylammonium chloride were applied for enhancing the wetting behavior. The solder was unable to wet the EN plated Cu substrate without the assistance of flux until temperatures of 460 degrees C and above. The material interaction between the solder and the substrate at this high temperature was investigated with scanning electron microscope elemental analysis. The wetting temperature between solder and EN plated copper was lowered to 310 degrees C with the application of the above fluxes. The further incorporation of a layer of Cu plating with the EN layer further lowered the wetting temperature to 250 degrees C.