The ASTM defines membrane switches as momentary switch devices in which at least one contact is on, or made of, a flexible substrate.
In other words, membrane switches are electrical switches used for turning circuits on and off. They are not to be confused with mechanical switches, which are composed of plastic parts and copper instead of a circuit and a substrate.
A fairly new technology, membrane switches require fewer materials for fabrication than other types of more resource-intensive and complicated interface equipment, like mechanically operated keyboards. As such, they are highly cost-effective, and have customers in many industries, including aerospace, medical manufacturing, gaming and recreation, electronics, and security. Read More…
Exhaustively, membrane switches have three main components. These are the aforementioned printed electrical circuit board, an electrically insulating spacer, and a top button layer that usually features a graphic overlay.
The circuit board is the component upon which the circuit pattern, using electrically conductive silver-based ink, is printed. This board is made of a thin polymer film, most likely ITO or PET.
The insulating spacer is actually an adhesive bonded to the circuit board and patterned with cutouts where the electronic switches emerge. The top button layer features the membrane switch button, which may be tactile or non-tactile. Tactile switches are made up of small metal domes held in place between the layers by polyester adhesive film. The domes, when pushed down adequately, give way and produce a response that confirms that the keystroke has been registered. This response either comes in the form of an auditory signal, the feeling of a dome being depressed, or both. Non-tactile switches, on the other hand, rely on silver-based conductive ink, printed on the back of the graphic overlay, to make electrical connections.
This graphic overlay can be made in a variety of different ways. Visible from the surface of the membrane switch, it is usually embossed or printed. It may be screen-printed with different colors and text. It may be covered with acetate film patterned with buttons via photochemical processing. It can, for the sake of application requirements, be equipped with various levels of heat resistance, impact resistance, abrasion resistance, or corrosion resistance.
Membrane switches may be categorized as user-equipment interface utilities, which are utilities that allow users to successfully communicate their commands to electronic devices. Utilities of this type range in design from complex membrane keyboards used with computers to straightforward tactile switches used to control lighting. Membrane switches tend to be valued over the others, though, because of their affordability, layered design, and versatility.
Typically, they have at least four layers, starting with, on top, a graphic interface and a printed circuit or a flex circuit made of polyimide material and copper. Usually, these layers are brought and held together with pressure-sensitive adhesives. Because of the way in which they are layered, they have no spaces through which contaminants can spill. This is important, because it means rubber and plastic keypads are less likely to suffer damage caused by dirt accumulation or accidental spills. By combining keypads with metal and plastic domes, layering can go so far as to create an enhanced keystroke experience.
Frequently, membrane switches are accompanied by backlighting. If this is the case, the light is emitted via one of three methods: light emitting diodes (LED), optical fiber, or electroluminescent lamps (EL).
LEDs may be installed on a separate LED layer or they may be surface mounted to the circuit layer itself. Because LEDs create bright spots, they are recommended only as indicator lights, not as overall panel lighting.
Optical fiber, on the other hand, which is affected by neither extreme temperatures nor humidity and has between 10,000 and 100,000 hours of light to offer, is better suited to panel lighting.
Finally, EL lamps are less expensive and have more design flexibility than optical fiber, but they are not good for long term use, as once they reach their half-life (between 3,000 and 8,000 hours), their brightness begins to fade rapidly.
Some of the oldest membrane switch applications include microwave oven panels, television remote controls, and air conditioning control panels. As membrane technology advances, membrane switches gain more and more applications. They are found in cellphones, children’s toys, handheld medical devices, x-ray machines, lift bed controls, ATM machines, calculators, and even home appliances. Today, some of their most important applications reside with keypad performance.
Membrane keypads do a number of things, including ensuring the proper function of building security systems, keeping sensitive information defended, and making sure industrial and manufacturing equipment runs safely and correctly.
For the most trustworthy membrane keypads, manufacturers must make sure that each element remain uncontaminated during the assembly process. For this reason, manufacturers are encouraged to fabricate them inside cleanrooms.
In addition, membrane switches often team up with other interface utilities and systems, like lighting, keyboards, and touchscreens, to tackle other applications. Space-saving, durable, attractive, sealable, and easy to clean, membrane switches are the way of the future.