The solder surface electroless nickel-gold (chem. NiAu) is also called ENIG (Electroless Nickel Immersion Gold). In a wet chemical process, a 3 to 6 µm thin layer of nickel (phosphorus-doped) is first deposited on the copper surfaces of the component connections. The nickel layer forms a barrier for the 0.05 to 0.125 µm thin gold