Addicted to Fun and Learning
- Nov 5, 2018
- Calgary, Canada
Yellow anyway... ENIG gold would be very, very thin and would look pretty on the board. It's standard practice these days to gold plate the boards, though the boards are usually only plated on the pads - which is where the gold matters. The purpose is that the gold provides a planar and clean (inert) surface to solder to. The gold actually dissolves in the solder joint. So the gold doesn't participate electrically in the connections between the components on the board.
ENIG gold is applied by first electroplating a layer of nickel on the copper of the PCB. The board is then dunked in a soup that displaces the surface nickel and replaces it with gold. The resulting gold layer is 0.1-0.2 µm thick. Silver can be deposited in the same way, but that wouldn't have much of a bling factor as it tarnishes quickly.
Another gold plating options commonly offered by PCB manufacturers is to apply relatively thick (0.1-1.3 µm) gold to the copper. This is commonly done to the fingers on PC expansion cards for example.
PCB traces are typically 35 µm thick ("1 oz copper"), though 70 µm is sometimes touted. So even if thick gold is used, it won't have much impact on the resistance of the PCB traces.