Membrane keypads are used in nearly every commercial industry, including automotive/aerospace, retail, telecommunications, medical, informations technology, and more. Unlike standard mechanical keypads, they are comprised of pressure pads with printed letters and symbols on the surface. When you press down on one of these printed pressure pads, the respective key press is registered. While the exact construction of a membrane keypad varies from model to model, they are typically made of multiple layers, each of which has its own purpose.
As you can see in the illustration presented below, a typical membrane keypad consists of three different layers: a top membrane layer, a bottom membrane layer, and a “holes” layer. Both the top and bottom membrane layers contain conductive tracers which are used to register key presses. The middle, “holes” layer, is simply a filler layer, usually with nothing more than air or inert gas. Without this middle layer in place, the top and bottom membrane layers would be sandwiched together; thus, registering a key press 24/7.
Normally, the keys are left in the open position, meaning the holes layer separates the top membrane and bottom membrane layers. When you press down on a membrane key, however, it squishes the top and bottom membrane layers together, causing them to make contact. The conductive electrical current from the top membrane layer travels down to the bottom layer, at which point the key press is registered. Sounds simple enough, right?
Membrane keypads with this three-layer design have become increasingly popular over the past few years, and for good reason: they are highly accurate, reliable, easy to operate, and require minimal cleaning. As long as the top and bottom membrane layers remain separated — and there’s conductive traces flowing through them — it should continue to operate.
It’s important to note that membrane keypads may or may not contain tactile feedback. Membrane keypads with tactile feedback provide some sort of notification when a key press is registered, such as a snap action. When a conductive steel dome is used, it eliminates the need for a flexible upper circuit layer while improving the accuracy of the keypad.