From microwaves and smart appliances to TV remotes and human machine interfaces (HMIs), membrane switches are used in a variety of common electronics. Like other electrical switches, they are designed to control an electrical circuit. When you press a switch’s button, the circuit closes. When you release the button, the circuit reverts back to its default open position. Only membrane switches, however, feature a contact that’s either on or made of a flexible material. So, how exactly does a membrane switch work?
The Design of Membrane Switches
To better understand how membrane switches work, you must first look at their design. Normally, membrane switches feature a graphic overlay layer featuring its keys and buttons. Below the graphic overlay layer is a circuit layer, followed by a spacer layer and then another circuit layer.
Both circuit layers are made of a conductive material, such as copper or graphite. Of course, the circuit layers are separated by a spacer layer of either air or inert gas. When you press a key, the top circuit layer presses past the spacer layer and into the underlying circuit layer, thereby completing the electrical circuit. Releasing the key, on the other hand, allowing the two circuit layers to separate, thus reopening the electrical circuit.
While membrane switches are designed in different ways, they all feature a flexible substrate for the graphic overlay layer on which the circuit is printed using conductive ink. The graphic overlay layer isn’t made of hard plastic. Rather, it’s made of a soft and flexible material like polyethylene terephthalate (PET).
How Backlighting Works for Membrane Switches
Some membrane switches are able to produce illumination with the help of backlighting. Some of the most common backlighting solutions for membrane switches include light-emitting diodes (LEDs), optical fiber and electroluminescent (EL). Optical fiber backlighting is particularly effective because of its ability to withstand extreme temperatures and humidity levels. With that said, any of these three backlighting solutions can illuminate a membrane switch.
What About Tactile Feedback?
In addition to backlighting, some membrane switches also produce tactile feedback. Tactile feedback is accomplished through either embossing the graphic overlay layer or by integrating metal “snap” keys. Snap keys offer a simple and effective form of tactile feedback. They don’t change the way in which a membrane switch works. Rather, they simply create a physical sensation of “snapping” when you press and release a key.