Membrane switches are self-contained printed keyboards. They are basically a wafer thin, three-layer component. On top is a clean polycarbonate film with the graphics and conductive pads printed under the surface. In the middle layer of the membrane switches are polyester films which act as a spacer with cut outs. On the bottom, there is either another polyester film with contacts and interconnections printed in conductive ink on the top surface, or a printed circuit board with the contact and interconnections etched into the membrane switches.