Membrane switches or membrane touch switches are printed electronic circuits acting as momentary electrical on/off switches for activating or deactivating circuits. When arranged in an array, they are collectively also known as a membrane keyboard. These switches are normally of the open type, requiring a push to close them, and immediately open when the pressure is released. That means the switch requires to be pressed, either with a finger or with an actuator, to make its two poles make contact and close the low-voltage, low-current switch. As soon as the pressure is released, the spring action of the membrane makes the poles separate immediately, and the switch returns to its original open state.
The membrane switch is most often screen printed onto a heat-stabilized polyester film base or substrate using conductive inks, typically of silver, carbon, and/or graphite. An overlay acting as the graphic interface is applied to the outer surface of the switch. The word membrane comes from the use of thin, pliable materials for the substrates. Sometimes, the substrates are also known as graphic overlay films.
Most membrane switches form an interactive part of devices and act as user interface, operator interface, or man-machine interface. They supplement other user interfaces such as slide, rocker, toggle, push-button switches, and display based touch screens. As with other switches and interfaces, the ultimate purpose of using a membrane switch is to facilitate an interface between the operator and the machine, enabling the operator to control or communicate with an equipment, machinery, or instrument.
A variety of industries use membrane touch switches. These include consumer appliances, aerospace and medical applications, industrial control systems, computer keyboards, touch-sensitive toys, cellphones, and many more. Used mostly with microprocessor-based control systems, and with the advantage of being more durable compared to other types of switches, membrane switches are being increasingly used in manufacturing and engineering industries. Additionally, membrane switches enhance the aesthetics of the human-machine interface.
As the membrane switch technology offers a sealed switch, it has become a reliable front panel solution for equipment requiring frequent cleaning or facing environmental concerns. Several industries prefer the use of membrane switches because of their reliability, and the ability to offer tremendous flexibility in aesthetics.
As a broad classification, there are two types of membrane switches—tactile and non-tactile types—based on the type of feedback the switches offer to their operators. While tactile membrane switches operate with a snap action that lets the operator notice immediately the switch has operated, the non-tactile membrane switch has a softer action, and offers no indication of the action of the switch. In most cases, placing an LED near the non-tactile membrane switch and linking it to glow along with the switch operation provides the necessary feedback.
Although this requires additional components, circuitry, and expense, non-tactile membrane switches find more favor in the industry because they require less force to operate, are sturdier, and more reliable than their tactile brethren are. In place of optical feedback, audible feedback may also be considered, commensurate with the electronic design of the equipment. It is also possible to use a mix of tactile and non-tactile membrane switches in the same panel.
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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.
The road from initial design to manufacture is a bumpy one at the best of times. It only takes a slip at an early stage, and budgets and timelines can spiral dangerously out of control. One part of the process that needs to go smoothly, and with no surprises, is the creation of Printed Circuit Board (PCB) prototypes.
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