Localised aqueous corrosion of electroless nickel immersion gold-coated copper

Electroless nickel (Ni) immersion gold (Au), commonly referred to by the acronym ENIG, is most common protective coating applied on exposed copper (Cu) traces of printed circuit boards (PCBs). In this work, we elucidate local corrosion mechanism ENIG-Cu system applying microscopic, surface analysis and electrochemical techniques with high spatial resolution provide a comprehensive understanding complex system. The initiation highly localised associated pores or micro-defects in Au layer. initiates dissolution underlying Ni layer, being less noble than Au. propagates lateral perpendicular directions relative an elliptical fashion. With time, direction propagation changes predominantly attack process governed cathode/anode ratio Au/Ni galvanic couple.