 PCBs are plated with solder, tin, or gold over nickel and a resist for etching away the unneeded underlying copper.After PCBs are etched and then rinsed with water, the solder mask is applied, and then any exposed copper is coated with solder, nickel/gold, or some other anti-corrosion coating.Matte solder is usually fused to provide a better bonding surface for bare copper.