Effect of dilute H₂SO₄ droplets on initial corrosion behavior of PCB

The electrochemical impedance spectroscopy (EIS) and scanning Kelvin probe (SKP) testing techniques were used to study the corrosion behavior of four kinds of printed circuit boards (PCB) under dilute H₂SO₄ droplets with different pH values. Meanwhile, the corrosion morphology was observed and analyzed. The results show that general corrosion occurs on the printed circuit board PCB (PCB-Cu) surface under the droplet. The corrosion behavior of electroless nickel immersion gold finishing PCB (PCB-ENIG) is mainly in form of microporous corrosion, and the corroded micropores develop from the edge of droplet to the center, while the corrosion regions of immersion silver finishing PCB (PCB-ImAg) are confined at the edge region of droplet, the substrate metals for PCB-ENIG and PCB-ImAg are both corroded to some extent. Among four PCB materials, the hot air solder leveling PCB (PCB-HASL) corrodes the most mildly. EIS and SKP results show that the dilute sulfuric acid droplets can activate the sample surface and form a large potential difference on the whole droplet region, contributing to the further corrosion process. Overall, the corrosion resistance and protection performance of PCB-ENIG is better than that of PCB-ImAg, while PCB-HASL is the best without any corrosion occurring on the substrate.