Membrane keypads are thin (around 1 mm) human-machine interfaces used to control all kinds of machines and computer devices. They are used in a number of environments, including the medical, industrial, rail, aeronautical, agricultural, machining and engineering sectors.
Membrane keypads generally include 4 to 5 different layers of polyester and adhesive of different thicknesses, depending on the type of keypad.
Available with up to 8 layers, depending on the options added to the keypad.
Panel overlay or graphic overlay
The graphic overlay is the visible top part of the keypad (detailed in other product sheets).
The membrane overlay is a polyester layer with adhesive on one side to keep the domes in place along the “Z” axis. The thickness will depend on the characteristics of the end keypad.
The spacer is a double-sided adhesive. Its thickness depends on the type of keypad and it has several functions. On a dome membrane keypad, it keeps the domes aligned along the “X” and “Y” axes. It also creates sufficient space to integrate surface mounted devices (SMD) such as LEDs and resistors.
Printed circuit board
The printed circuit is the functional part of the keypad. It is a screen printed with silver, graphite and dielectric insulating technical inks to provide the “electrical” connection between humans and machine intelligence. (PCB). It can be printed in several successive layers separated by dielectric insulation layers. The circuit is connected to the control unit via a ribbon cable or multi-wire planar cable.
Various domes can be mounted onto the circuits, along with SMDs such as LEDs, resistors, temperature probes, and phototransistors.
The adhesive is the bottom layer of the keypad and holds the keypad in place on the mounting surface. The choice of adhesive and thickness will depend on the type of surface on which the keypad will be bonded (metal, various plastics, glass, etc.) and the mounting surface finish (smooth, brushed, sandblasted, painted, etc.). These adhesives have a thickness of 50 µm or more, depending on the case. They can also serve as a spacer to raise the keypad in some cases.
The operator presses a keypad switch (key/button), which establishes contact between 2 parts of the circuit. Contact is made from pressing a conductive pad or adding a metal component called a dome, which closes the circuit. A signal is then sent to the machine.