Membrane keypads

Silver conductive technology is the most widely used technique for the production of membrane switches. The conductor tracks are screen-printed onto polyester films. The contact surfaces for plugs and snap domes are additionally overprinted with carbon to protect against corrosion.

With this method, crossings using bridges are also possible without any problems. This results in maximum flexibility with regard to the arrangement of all components, including connection assignment.

If LEDs are used, they are connected with electrically conductive adhesive.

The flexible foil cable is also part of the switching foil. The cable must not be kinked and the bending radius should not be less than 2 mm. In practice, however, this is usually easy to comply with.
For applications where this is not the case, a higher quality polyimide switching foil (= flexprint) can be used.

You can find more information on this under "Flexible or rigid PCB"

In order to meet the highest quality requirements in terms of temperature, humidity and mechanical stress, a copper-clad flexible printed circuit board with a thickness of 0.15 mm or a rigid FR4 printed circuit board is used as a carrier instead of the switching foil in silver conductive technology.

The contact points are tin-plated or gold-plated. When using 2-layer PCBs, it is also possible to cross conductor paths.
The connection cables of the flexible PCBs are very resistant and can be bent with a minimum radius of just 1 mm.

In contrast to silver conduction technology, components such as LEDs, resistors or ICs can be soldered on and are therefore also mechanically robustly connected.

For applications in hygienically sensitive areas such as medical technology or the food industry, films with antimicrobial technology are used to improve hygiene standards and reduce the spread of infection.

This protection serves to contain the growth of potentially harmful bacteria, mold and mildew and remains effective for the entire service life of the film.

Outdoor applications pose a particular challenge. The keyboards not only have to withstand high temperatures and moisture, but also UV radiation. To ensure this, UV-resistant film material specially developed for this application is used.

This also enables applications on building facades, boats and construction machinery, etc.

Surface like brushed metal

If you want the surface of a keyboard to look like brushed metal, or to match similarly treated housing parts, you can use a correspondingly textured foil material, which is printed silver-grey on the back. The effect is amazing, the front looks as elegant as aluminum or steel.

Shadow printing and 3D effect

In order to design the printed surface independently and give it a special look, the gradient of a screened screen print can be used. This can be used to create shadows or 3D effects, for example, even though the surface is completely flat.

A light guide foil can now be used to illuminate membrane keypads. This very thin foil allows for wide-area illumination in various colors. The light is scattered laterally into the light guide foil by tiny LEDs. By cleverly arranging the LEDs and boundaries in the light guide foil, the keypad can be selectively illuminated in defined areas and even in different colors.

This also enables user guidance if the LEDs are controlled accordingly.

If the desired key height cannot be achieved by embossing the decorative foil, it is possible to integrate an additional silicone mat into the keyboard.

The silicone mat is laminated onto the switch package and can be covered with a decorative foil punched out in the area of the keys. This sandwich construction significantly increases input reliability, the keys are easy to feel and the tactile feedback is very pleasant.

The silicone mat itself can be dyed in different colors, the button surfaces can be printed in different colors and provided with symbols. To protect the symbols against abrasion, a transparent coating is sprayed on as abrasion protection. The decorative foil can also be individually printed with additional symbols or logos.

To protect a display behind the transparent window of the decorative film from contact, it is possible to laminate a PC pane to the back of the decorative film. The use of OCA (= optical clear adhesive) means that the adhesion is full-surface and invisible. This technique also prevents the formation of unsightly "clouds" or Newton rings.

The solution also has the advantage that the window in the decorative film does not need to be punched out. The front is completely closed and therefore sealed. There is neither an offset nor edges that can easily become dirty.

The function of electronic devices can be disrupted by electrostatic discharges (ESD) from outside. Other devices can also be disturbed by unwanted electrical or electromagnetic effects that are emitted.

To suppress these effects, conductive foils, which have a separate earthing connection, can be integrated into the keyboard.

Another option is to integrate a polyester film printed with a conductive grid structure into the keypad. The connection to earth can simply be established via the foil cable.

To avoid edges and gaps that could collect dirt when using a resistive touch panel, the touch panel can be glued behind the transparent window in the decorative film. Depending on the size of the touch panel, this can be done over the entire surface with invisible adhesive (OCA) or around the edge. This results in a closed front that is easy to clean if necessary. The touch panel is also extremely easy to install, as the front film including the touch panel is simply stuck on.

The capacitive keyboards meet the highest quality requirements in terms of durability, as there are no moving parts that can wear out. The keyboards are also ideally suited to high mechanical stresses and are currently very much in vogue.

The surface can be made of up to 3 mm thick polyester, PC, acrylic glass, glass or other non-conductive materials, is easy to clean and, if glass is used, is also resistant to chemicals.

This makes the keyboards ideal for use in medical and hospital technology, the food industry, laboratory technology, mechanical engineering and public areas at risk of vandalism, for example.

In addition to normal buttons with freely selectable shapes, slide and rotary controls can also be realized.

The keyboards can be supplied with a controller and are then controlled via a USB interface. I2C, UART and SPI interfaces are also available as options.

To facilitate the installation of a membrane keypad, it can be supplied bonded to an aluminum carrier plate.

The carrier plate can be provided with holes, threaded bolts or bushes that can be used for fastening or mounting other elements such as a display.