Membrane Keypads

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.

Technical characteristics

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.

LAYERS

Panel overlay or graphic overlay

The graphic overlay is the visible top part of the keypad (detailed in other product sheets).

Membrane Overlay

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.

Spacer

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.

Adhesive

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.

Usage

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.

Installation and options

We offer a wide range of options adapted to your needs.

Surface treatment

Polyesters come in an array of finishes, including grained, standard, fine-grained, crystal (smooth) anti-scratch, anti-reflection, brushed (brushed metal plate), and Softouch. 
Surface treatment is applied when necessary on the windows/cutouts to improve display visibility. On crystal materials, the graphic overlay can be selectively textured (grain) to produce different surface effects on the same product.

Keys/buttons

The overlay buttons can be embossed through thermoforming. “Finger guides” can be added with rim embossing around the buttons. Keypad construction depends on the shape selected for the keys.

Shielding

Shielding is an additional silver screen-printed layer on 125µm stabilised polyester. The purpose is to create an Electromagnetic Compatibility (EMC) shield. Shielding can also be applied to transparent areas (displays, LEDS, etc.) by integrating an Indium Tin Oxide (ITO) film into the layers of the keypad.

Backlighting

We are able to light up specific areas on your membrane keypads, including key rims, key surfaces, logos and pictograms. We use electroluminescent lighting, phosphorescent inks or LEDS/diffusers for backlighting.

Connectors

Male and female standard connectors can be installed on ribbon cables. If necessary, these connectors can be equipped with locks and keyed connections.

Extension cables

If the control unit to which the keypad ribbon cable is connected is too far away or if there is not enough room or a proper “path” for the ribbon cable, we offer extension cables compatible with keypad connectors, with no limit on the length and number of wires.

Surfaces / casings

Your keypads can be installed on any kind of surface, from plastic to steel, stainless steel and aluminium plaques. The keypads are cut out and equipped according to your specifications and can be fitted to any type of casing. 
Surfaces can also be treated (anodising, sandblasting, etc.).