The American Society for Testing and Materials (ASTM) defines a membrane keypad as “a momentary switch device in which at least one contact is on, or made of, a flexible substrate.”
Therefore, the simplest membrane switch can be a two-layer construction. However, other multi-layered complicated assemblies are also possible. Irrespective of the type of construction, a membrane switch being a momentary switch must contain a static layer and a membrane layer. Other optional layers may have different functions, such as shielding, decoration, adhesive, backlighting, tactile response, and rigid support. For reliability and ease of use, membrane switches need at least five layers:
Graphic Layer: This layer contains the decoration of the membrane switch. Usually, this is a thin, polyester or polycarbonate film, screen printed with the desired graphic. Other methods of switch assembly decoration use elastomers, which form an attractive and functional alternative and give the switch a three-dimensional look and feel.
Membrane Layer: This is a thin and pliable layer, with at least one pole of the switch. In some designs, this layer may also carry a conductive shorting pad. Usually, this flexible layer is made of metal, polyester, elastomer, or polyimide. This layer may terminate into an edge connector.
Tactile Layer: This layer is required in tactile membrane switches and provides a feedback to the operator when the switch has operated. Although some manufacturers resort to a separate layer to provide the tactile feedback, others integrate this functionality with the graphic layer. For instance, an embossed polyester dome overlay forms the graphic layer as well as the tactile layer. Another way of achieving this dual function on the membrane layer is by forming a poly dome, metal dome, a polyester dome, elastomer, or a dome embossed in the graphic layer. In the absence of the tactile layer, the switch is a non-tactile membrane switch.
Static Layer: As the name suggests, this layer does not move, and has at least one pole of the switch, or a pair of conducting pads. This layer is usually made from a variety of materials such as a printed circuit board, polyimide, ITO, transparent conductor, or polyester. This layer may terminate into an edge connector.
Rigid Layer: This layer provided mechanical rigidity to the membrane switch, such as by laminating the static layer to it, in case it is made of a flexible material. The rigid layer may be made of fiberglass, glass, plastic, steel, aluminum, or other rigid materials. Some users may opt to provide their own rigid layer, and purchase the membrane switch without one. In such cases, the static layer becomes truly static only when it is attached permanently to the instrument panel.
No design files? No problem – Synergy Electronics can take your current keypad sample and reverse engineer it with final modifications to update and modernize your keypad at no extra charge.
Synergy Electronics offer membrane switches with a multitude of different standard Pantone colors and transparency levels. For instance, an electronic device for use in low light levels may need backlight to illuminate its switches. Instrument designers have several options for this. They may use LED backlights, optical fibers, or electroluminescent lamps for providing the backlight. Membrane switch design is highly adaptable, and Synergy Electronics can adapt membrane switches to any type of backlight specified by the designer, for further information please email your enquiry to firstname.lastname@example.org.
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