Comprising of one, two, or multiple layers, PCBs are built via alternating layers of a conductive metal–most always copper–and an insulating layer. The conductive pathways, or traces, are etched, layer by layer, into the copper metal. This is done in one of two ways. The first method has a full copper sheet being laid upon the board. Then, the desired paths for the traces are masked out and a machine is used to etch out the superfluous copper, leaving behind the conductive metal only in the places where the designer intended for there to be traces.

Alternatively, it is possible to leave only the paths of the traces exposed and dip the board into a copper solution. This method coats just the exposed portions of the layer in copper, leaving you with the same end result as the previous method. This second method is sometimes favored if you will be making a lot of PCBs or a many layered PCB as it can be more cost effective since there is less overall copper waste. Regardless of method, this process is repeated until you are left with the desired amount of layers on your board. The completed assembly of all layers of the PCB is often called a “layer stack” or “stackup.”