Membrane keyboard
A membrane keyboard is a flexible keyboard that can be used permanently even under special operating conditions. The surface consists of polyester foils , which are usually thermally deformed or embossed.
They often have elastic "suspension zones" that allow a key travel of around half a millimeter. Essentially, the same ergonomic performance features occur as with standard mechanical pushbuttons, and they also meet special criteria such as dust-tightness, water-tightness or resistance to chemicals. Furthermore, the production is inexpensive, since no separate pushbuttons are required and the pushbutton mechanism is omitted.
For use in a dusty environment (e.g. factory halls), membrane and normal keyboards are occasionally combined in such a way that keys of a normal keyboard operate a membrane keyboard underneath. The membrane keyboard is the outer closure of a dust-protected housing.
The layers of the circuits are printed on polyester substrates using special silver, carbon and insulation inks. Additional protection against oxidation is achieved by overprinting with carbon.
There are various techniques such as: B. metallic snap disks , which are mounted under the foil, or the so-called polydome technology, the whole consists of only one embossed foil. There are other techniques, such as without embossing and without metal domes.
The design of the buttons is usually printed on the back using the screen printing process .
Areas of application
The membrane keypad is mainly used where its dirt and water resistance or easy cleanability are required or indispensable, or where a compact design or inexpensive manufacture for only occasional use is desired. They can be found for controlling machines in industry or as a keyboard in industrial PCs as well as in medical devices , disinfectable applications and electrical household appliances, but also in peripheral devices for computers, remote controls and mobile phones .
With the classic, inexpensive design of the membrane keyboard (structure see schematic drawing above), the membrane will inevitably break at some point due to wear and tear or mechanical stress. The upper film breaks at the point above the edge hole of the middle film, where its mechanical stress is greatest due to the pressure. It can be delayed by plasticizers (which gradually outgas ) and careful operation, but not prevented completely.