Electroplated nickel gold is more generally made use of on IC substrates (including PBGA), primarily for binding gold wires and copper wires; but when electroplating C substrates, additional conductive wires have to be built in the gold finger binding place right before electroplating. The metal layers within the multilayer PCB https://rivercprsu.bleepblogs.com/31739456/6-layer-central-control-pcb-board-for-dummies