Electroplated nickel gold is more typically utilised on IC substrates (including PBGA), predominantly for binding gold wires and copper wires; but when electroplating C substrates, added conductive wires must be produced at the gold finger binding place before electroplating. Nonetheless, there is just one layer of copper on one-sided board, https://beckettmqrsx.blogacep.com/36608689/the-basic-principles-of-4-layers-pcb-with-ic-carrier