Electrochemical corrosion behavior of Pcb-hasl in NaHSO₃/Na₂SO₃ solution

With the innovation of electronic technology, integration and miniaturization become the future developing direction of printed circuit board (PCB). Meanwhile, the corrosion problems of PCB also stand out more clearly, and even trace amounts of corrosion products will have a serious impact on the reliability of PCB. Under the actual condition for use, like sulfur-containing industrial environment, due to the diurnal temperature variations or/and the temperature field fluctuations for PCB itself, condensation phenomenon is likely to occur. Furthermore, as a result of the moisture absorption effect of granular deposit or supersaturated humidity, a layer of electrolyte solution will be formed on the surface of PCB, causing electrochemical corrosion. In this work, electrochemical impedance spectroscopy (EIS) and scanning Kelvin probe (SKP) techniques were used to study the corrosion behavior and mechanism of hot air solder leveling printed circuit boards (PCB-HASL) in a simulated electrolyte 0.1 mol/L NaHSO₃ and 0.1 mol/L NaHSO₃/Na₂SO₃ solutions with different pH values, and the influences of immersion time and pH value on the change of corrosion mechanism were discussed. Meanwhile, with the aids of OM, SEM combined with EDS, the nucleation and propagation processes of corrosion products on the surface of PCB-HASL were observed and analyzed. SEM and EDS results showed that the corrosion behavior of PCB-HASL in acid simulation solution was similar to pitting corrosion, and the corrosion pits were in a state of accelerated expansion at the early immersion stage. The corrosion products mainly consisted of oxides and sulfates of Sn. EIS and SKP analysis indicated that the PCB-HASL surface could be activated by NaHSO₃ solution and pitting nucleation process only occurred at the early immersion stage. In the neutral or alkaline solution system of NaHSO₃/Na₂SO₃, pitting corrosion couldn't occur, and the transmission of the electrolyte to the electrode interface through the oxide film was the control step of the corrosion reaction.