Electrochemical noise analysis of corrosion sensitivity of Pb-free solders in 5 wt% citric acid solution

The corrosion behavior of pure Sn, Sn2Ag, Sn42In, and Sn58Bi alloys in 5 wt% citric acid solutions has been investigated using electrochemical noise analysis combined with potentiodynamic polarization, electrochemical impedance spectroscopy tests, and etching morphology observation. The Sn58Bi has shown the lowest corrosion rate, followed by Sn2Ag, Sn42In, and Sn. The corrosion evolution of the four alloys mainly consists of two stages as follows: for pure Sn, the first stage is local corrosion (corrosion pits growth) stage and the second stage is uniform corrosion with preferential dissolution of some grains on the sample surface. In contrast, for dual-phase alloys, Sn2Ag, Sn42In, and Sn58Bi alloys, all preferentially undergo a selective phase corrosion in the first stage, followed by the growth of uniform corrosion and selective phase corrosion in the second stage. The corrosion incubation rate for the four Sn-based alloys follows Sn42In > Sn > Sn2Ag > Sn58Bi for both uniform corrosion and local corrosion, while the probability of corrosion growth in sequence is Sn > Sn58Bi > Sn42In > Sn2Ag (uniform corrosion) and Sn58Bi > Sn > Sn42In > Sn2Ag (local corrosion). In this work, the corrosion behaviors are consistent with the observed corrosion morphology, which provides a guidance for understanding the interaction between solder alloys surfaces and acid in flux and further selecting organic acid activators compatible with new solder alloys.