The surface of electroless nickel-gold plating on fpc is red.

ENIG, the surface of gold is red, which is actually a popular oxidation. There may be many reasons. However, in many cases, the back surface of molten gold is not thoroughly cleaned, which may be the residue of pharmaceutical industry-incomplete cleaning or incomplete cleaning and drying, leaving water on the gold surface. Of course, in order to prevent the oxidation of gold, such as keyboard oxidation, some companies usually carry out pickling and antioxidant treatment, so that oxidation is unlikely to occur.