Surface failure mechanism of PCB-ENIG in typical outdoor atmospheric environments

Electroless nickel/immersion gold (ENIG)-plated printed circuit boards (PCBs) were exposed to typical atmospheric environments in China for prolonged periods to understand the mechanism of corrosion failure. Results showed that the corrosion products that covered PCB-ENIG played a protective role by filling, covering, and coating surface defects. Under Turpan atmospheric environment, the plating layer was prone to damage easily, resulting in loss of protective properties. The corrosion mechanism was mainly microporous corrosion, in which halo-shaped macropores with a raised nucleus in the center were formed. When electrical bias was applied, PCB-ENIG was prone to electrochemical migration (ECM) caused by galvanic effects in the form of localized corrosion. Both Ni and Cu elements were involved in the ECM process. The synergistic effect of contaminated medium and high humidity is the critical factor of the ECM-induced PCB-ENIG corrosion.