Membrane switches typically include two opposing surfaces, each of which include circuits thereon which, when engaged, complete the desired electrical circuit. Membrane switches normally employ a pair of stacked flexible membranes having opposed contacts printed on their facing surfaces. Each of the membranes has electrical contacts printed on their opposing faces at button locations that are brought into electrical conduction when the membrane is flexed, and held apart by the natural elasticity of the membrane and a spacer layer when the front membrane is released. A spacer layer separates the membranes, except at a region about the contacts, allowing pressure from a finger or the like to deform one of the membranes so that its contact touches the contact of the other membrane closing an electrical switch. The spacer layer may be an adhesive layer or a plastic film carrying adhesive on both of its surfaces, and thus serve to laminate the two ciruit-carrying panels together, or a plastic film without adhesive. The spacer layer has an opening therethrough exposed over each pair of first and second electrode members. The upper membrane layer is mounted on the insulative spacer layer. To maintain the two opposing surfaces apart and the circuit in an open state, some type of insulating layer or spacer is disposed between the two substrates. Because the switching action of a membrane switch involves repeated pressing, the base films used therefor must be flexible and resistant to deformation. Base films used for conventional membrane switches have generally been polyethylene terephthalate (PET) films because of their deformation resistance, adhesion with electrodes, bonding with printing pastes, and other properties. However, membrane switches and remote control switches are becoming more common in the operating panels of automobile-related parts (car audio systems, car air conditioners, car navigation systems and the like). Base films of membrane switches have therefore been required to have deformation resistance at high temperatures that cannot be withstood by PET films.

A membrane switch typically includes an array of switches such that the electrically conductive material forms a plurality of pairs of first and second electrode members. Each pair of the first and second electrode members is used to complete separate conductive paths. The array of pairs is disposed in two dimensional array across the upper face of the lower membrane layer. In general, membrane switches comprise a circuit or matrix layout embedded in a plastic film. Most membrane switches are made with a plurality of switch cells arranged in rows and columns. The columns and rows of the matrix layout must exit the membrane from the same location so that the output signals generated by activation of the switches can be easily taken from the membrane switch to a processing device. Switches, generally comprising domes, are located at specific locations in the plastic film. The matrix layout comprises a plurality of lines arranged in columns and rows upon the membrane. The switches are located at the intersection of a column and row line in the matrix layout such that when the switches are activated, the two lines in the matrix layout become electrically connected, decreasing the resistance between the two lines and thereby indicating that the corresponding switch has been activated. Domed switches can be activated by pressing down on the switch to electrically connect a row line with a column line. Individual switches can be provided so that the activating force brings the electrical contacts which complete the electrical circuit into communication and thus actuates or closes the switch, providing an electrical signal for use by other circuitry. Alternatively, the switch units can be configured so the electrical circuit normally is completed, and the communication of the contacts is not disrupted until a force is applied to separate the contacts. Combinations of normally open and normally closed switches can be provided in a single membrane switch to best accommodate the requirements of the circuitry supplied by the signals from the switch elements. Membrane switches also are known that include an amalgam of switch types, each of which may comprise two or more switches that are ganged together at a switch site, so that multiple switch signals are sent to the target circuitry when a force is mechanically applied to only one key.

Membrane switches typically include a circuit board having spaced electrical contacts fixed on its upper surface, an overlaying spacer with an aperture aligned with the contacts, and a resilient membrane overlaying the spacer. The circuit board can be either rigid or flexible, depending on the application. The circuits include conductive contacts defining switch cells and conductive tracks leading from each cell to an edge of the films for connection to external circuitry. The electrical contact on the underside of the membrane is normally spaced a predetermined distance above the circuit board contacts, whereby a normally open switch is provided. A downward force applied to the membrane lowers the membrane contact into electrical contact with the spaced circuit board contacts, to short the latter together and thereby close the normally open switch. A typical membrane switch includes a tail portion integral with and extending outwardly from the edge of one or both of the conductor-carrying layers, on which tail or tails the individual conductor leads are carried for connection to external circuitry. In order to make the connection to external circuitry, it is the usual practice to attach an electrical connector to each of the conductive leads at or near the outward end of the tail. Membrane switches provide electrical contacts closing when a front flexible membrane is compressed by a finger touch or the like against a rear surface, typically a second membrane. In order for a membrane switch to serve most effectively as an interface device with a human operator, it is designed that the user be able to sense with a finger when sufficient activating force has been applied to close or open an individual switch. Membrane dome switches typically comprise a conductive dome-shaped spring disk retained in a sandwich array between an underlying circuit layer having a conductive circuit pattern formed thereon, and an overlying shield layer. Fingertip pressure applied to predetermined points or regions of the shield layer is effective to deform the spring disk in a manner contacting the circuit layer, thereby achieving momentary closure of a circuit path for purposes of operating the electronic device.

Membrane switches have been primarily of the resistance type in which two conductive zones or contacts are closed and electric current flows through them in proportion to the voltage applied across them. A more recent development in membrane switches is the capacitance type of membrane switch which operates upon the change in capacitance between spaced conductive zones. Membrane switches are made either as a laminated construction or a folded construction. The membrane switch with a laminated structure is composed of a pair of electrode sheets having electrodes formed respectively on opposite surfaces of a pair of sheetlike base materials disposed oppositely, the electrodes constituting a contact portion, and of a sheetlike spacer interposed therebetween. In a laminated construction, two plastic film layers that are to carry conductive patterns are made from separate or independent panels cut to the desired configuration. A conductive pattern is applied to a surface of each panel, the two panels are then properly registered relative to one another and laminated together to form a completed switch with a spacer layer positioned between the two panels. In order to allow the upper and lower electrodes to come into contact with each other by an appropriate pressing force, the contact portion of the membrane switch is configured in such a manner that a hole of a predetermined size is drilled in the spacer, and the upper and lower electrodes come into contact with each other through this hole. In a folded construction, a single sheet of plastic film is die-cut to form the two panels that are to carry conductive patterns in a configuration in which the panels are joined together along a fold line. A conductive pattern including contact zones is applied to a surface of one panel and another conductive pattern with contact zones is applied to what will be the facing surface of the other panel with the sheet in a flat condition. Thereafter, one contact-carrying panel is folded along the fold line so as to overlie the other contact-carrying panel, after which the two panels are joined together with a spacer layer of adhesive or die-cut film having adhesive on its opposed surfaces. Most commercial membrane switches are made in laminated constructions.

Touch sensitive membrane switches have been incorporated into many electronic devices to enable operators to provide instructions to the device by selecting a corresponding horizontal and vertical coordinate location on the membrane switch. Membrane switches enjoy widespread use because they are inexpensive to manufacture, are easily custom configured, and are fairly reliable.  The advantages of a membrane switch includes the ability to seal the switching apparatus behind the membrane and the ability to utilize compact switching components such as printed circuits and switches formed of conductive layers formed on the circuit boards. Membrane switches have the considerable design flexibility in terms of panel layout, including the key size and shape and graphic labels. Membrane switches are particularly well-suited for use in certain environments wherein it is desired to seal an electronic system against moisture, dust etc. Membrane switches presently find widespread use in installations in which a sealed or protected switch or operating panel is desirable. For example, they are employed in equipment which requires manual data entry such as computer keyboards, terminals, cash registers and the like. Also, membrane switches are widely used as a control or instrument panel for appliances such as washers and microwave ovens, industrial controls, copy machines, and the like, in which finger touch micro-motion actuation is a useful feature. A membrane switch is generally utilized for an application wherein a light force is applied to an indicator to make an electrical contact which in turn controls certain selected electrical circuitry. Membrane switches have recently come into wide use for the keypads of cellular phones or portable personal computers. The range of applications for membrane switches is ever increasing, as is the need for producing low cost membrane switches.