CONDUCTIVE CONNECTIONS AND SWITCHES
Membrane keyboard is usually composed of two polyester films to which silver conductive connections and connective surfaces are placed through the method of screenprinting. A self-adhesive foil of suitable thickness (spacer foil) with cuttings where connective surfaces are separates both key poles and forms a firm foil composite. The cuttings enable an electrical contact between both poles of a key.
The upper layer of the composite is equipped with foil which is the carrier of distinct information for each key. We name it »graphic foil« because it has to do with graphic procedures of printing colours. It is important that the colours (symbols and signs) are printed on the bottom side of the graphic foil – on the side which is fixed to the basic composite. This procedure prevents the user from coming in touch with the printed colour which enables durability of the printed information.
An appropriate quality of a graphic foil also enables the use of membrane keyboards in extremely demanding environments (the presence of dust, chemicals and high humidity) especially where maintenance and cleaning is needed. This is of extreme importance in the case of medical devices where the membrane keyboard has become almost irreplaceable.
The bottom side of the basic composite is equipped with assembling adhesive the purpose of which is to fix the keyboard to the complete keyboard area. This is why the use of membrane keyboards assures high IP standards.
The insertion of tactile elements in the basic composite creates the physical feeling - so called 'click' effect - when pressing the key which is synchronized with the electrical function of a key. It is an important feature of the membrane keyboard because it abolishes the need for additional signalization (sound, light). Some kind of signalization is necessary in the case of a keyboard without the feeling of switch because it informs the user that the key when pressed did its task. The feeling can be created with metal tactile elements (metal domes) or an appropriate embossing of the graphic foil (poly-dome). The presence of the tactile feeling provides for the basic division of membrane keybords: keybords with and without a 'click'.