The copper component pads and holes have been left clear of soldermask. Now we apply a solderable surface finish to protect the copper until the components are soldered onto the board.
On this line we chemically deposit first nickel onto the copper and then a thin coating of gold over the nickel. This is a chemical process needing no electrical connections. The line is fully automated, moving the panels through a series of tanks which clean and sensitise the copper surface and then deposit about 5 microns of nickel and a tenth of a micron of gold.
Under the EU Reduction of Hazardous Substances (or “RoHS”) legislation we cannot not use lead in our finishes, so we offer gold over nickel as you see, chemical silver using a similar process to deposit a sterling silver finish, or lead-free hot-air levelling. For this the panel is lowered into a bath of molten tin. As it is lifted from the bath hot air jets blast the surplus molten metal from the panel to leave an overall coating of tin about 2 microns thick.