Membrane Switches, Overview
A membrane switch is very simple in concept:
In its simplest form, layers of plastic, normally polyester, are printed with various inks, and laminated with other layers of
plastic with holes cut in them to selectively allow circuits to be made when areas of the front of the keypad are pressed.
Obviously the top layer, or Graphic Overlay, is reverse printed with all the legend and graphics that will show through to the front
of the label, and be visible to the user.
The next layer that is printed, (either onto the reverse of Graphic Overlay, or a separate layer), is an electrically conductive
layer, which will act as an electrical bridge over the lower circuit when the key is pushed.
A spacer is then inserted, between this layer, and the lower circuit which is placed on after the spacer. However, holes are punched
out in the spacer so that some areas will allow the 2 circuits to touch when the keypad is pressed.
This next layer has the electrical circuit printed onto it, the lower circuit.
All layers are bonded together with adhesive, and a final adhesive added with a protective backing, which the user then peels off,
just prior to fixing it onto his equipment.
There are of course many variations, and enhancements that can be made to this basic type of switch. Indeed, the non tactile membrane
switch has been all but replaced by the tactile membrane switch, due to its greatly preferred performance in feeding back to the user that it has been pressed.
The following 3 sections cover the 3 most commonly used types of keypad, and are followed by a rundown of other techniques
They include, the
Non Tactile Membrane Switch, the Tactile Membrane Switch, and the Membrane Switch with LED.