In its simplest form a membrane switch comprises of two flexible printed circuits, physically separated by a spacer, when the button is pressed, holes in the spacer allow the two circuits to contact completing the circuit. The printed top layer is known as the graphic overlay. It is normally made of clear polyester, and reverse printed to protect the image from wear, solvents, and abrasion. As membrane switches are momentary switches, it may be necessary to introduce a method of electronic latching to replicate the actions of mechanical switches.
There are many variations on this simple design, and by laminating further layers into the switch, it is possible to add additional features such as snap domes, ESD/RFI shielding films, lighting panels and embedded surface mount components.
The membrane switch is mounted on a flat enclosure, and typically a single ribbon cable connects the switch to the PCB though a single slot in the mounting panel. In contrast, an overlay requires cutouts in the enclosure beneath each switch adding to machining costs.