Impact of aluminium addition on the corrosion behaviour of Sn-1.0Ag-0.5Cu lead-free solder

The effect of Al on the corrosion resistance behaviour of Pb-free Sn-1.0Ag-0.5Cu- x Al solder ( x = 0.2 wt%, 0.5 wt% and 1.0 wt%) in 5% NaCl solution was investigated by using potentiodynamic polarization and salt spray exposure. Passivation behaviour was evident in all the solder formulations containing Al, compared to the base SAC solder. FESEM and XRD results revealed that more dense passive films were formed on the solder containing Al, compared to the base solder. These passivation films contained intermetallic compounds such as Al 2 O 3 , AlCuO 4 , SnO and SnO 2 served to prevent further reaction on the material surface. Polarization studies showed that the corrosion rate was 30% and 6% lower for alloys with 0.5 wt% and 0.2 wt% Al content, respectively, even though the corrosion potential shifted towards more negative values. The Al-added solder alloys exhibit more refined surface after exposure in the salt spray chamber and revealed no visible infiltration of aggressive ions at the solder-substrate joint. This work suggests a corrosion mitigation strategy for SAC 105 solder through doping of Al. (a) Al provides an enhanced passivation capability over SAC105 solder alloy. (b) Corrosion products on the surface consist of Al 2 CuO 4 , Al 2 O 3 , SnO and SnO 2 . (c) Al-added SAC105 is less susceptible to corrosion.