Another way to make a circuit board is to use a mill. A mill is a drill that moves in many directions. The drill removes a small amount of copper each time it moves across the board. The mill removes the copper around the wires on the board. This leaves extra copper on the board. Other methods do not leave the extra copper on the board. This method is cheaper per board, but the equipment to make it is expensive. This method is not used often, because the other two methods are easier.