Membrane keyboard

A membrane keyboard is a flexible keyboard that is permanently suitable for use under special conditions. The surface consists of polyester films which are often thermally deformed or have embossments.

Often they have elastic " spring zones " that allow a keystroke of about half a millimeter. Occur essentially the same ergonomic features on as standard mechanical push buttons, in addition they meet specific criteria such as dust tightness, water tightness and resistance to chemicals. Furthermore, the production is inexpensive, since no separate push buttons are required and the keystroke mechanics omitted.

For use in dusty environment (eg workshops ) films and normal keyboards are sometimes combined such that the keys on a normal keyboard use an underlying membrane keypad. The keypad is the conclusion of a dust-protected outer housing.

The layers of the circuits are printed using special silver, carbon and insulating inks on polyester substrates. Additional protection against oxidation is achieved by overprinting with carbon.

There are various techniques, such as metal domes, which are mounted under the film, or the so-called polydome technique, the whole consists only of an embossed film. There are other techniques, such as without embossing and without the metal dome.

The design of the buttons is usually printed on the back with the screen printing process.

Areas of application

The keypad is used especially where their dirt - and water -resistance or the ease of cleaning required and are indispensable, or where a compact design and low-cost production for only occasional use are desired. They can be found to control machinery in the industry or as a keyboard in industrial PCs as well as in medical devices, disinfectant-ready applications and household appliances, but also in peripheral devices for computers, remote controls and mobile phones.

In the classic inexpensive design of the keypad ( for structure see schematic drawing above ), there is inevitably a result of wear or mechanical stress at some point to cracks in the film. The top film breaks at the position over the hole edges of the middle film, where their mechanical stress due to the pressure is the greatest. He can plasticizers ( which gradually outgas ) delayed and friendly service, but shall not be finally prevented.

• Keyboard ( input device )