membrane switches are flexible keyboards, the surface of which consists of polyester films. The membrane keyboard is embossed and mostly thermally deformed. In addition, the keyboards are versatile and permanently usable.
Capacitive keyboards are not membrane keyboards. With the capacitive keyboards there is no tactile feedback, but with the membrane keyboard it does.
In simple terms, a membrane switches consists of 5 basic parts:
- Decorative film
- upper and lower switching foil
- Spacer film
- Adhesive film
The individual layers are placed on top of each other. The top layer is the decorative film. This film is usually made of polycarbonate or polyester. This ensures protection against write-offs. Depending on the use of the keyboard, the decorative film can be made from a UV-resistant polyester. In addition, the decorative film can be coated with an antibacterial coating, this is especially necessary in the medical field.
The functional elements such as switching points and conductor tracks are located on the lower switching film. In contrast to this, the contact areas with the switching points are located on the upper switching film, which are exactly opposite to the lower films. Most of the switching foils are also made of polyester. In some more complex circuits, the lower switching film is made of Polimid.
The spacer foil serves as an insulator and separates the upper and the lower switching foil. The spacer film can also serve as a fixing film.
Areas of application
Membrane keyboards are mainly used where water and dirt resistance and easy cleaning are necessary. Membrane keyboards are also often used for devices with a compact design or only occasional use. Membrane keyboards are often used or used in the following industries and devices:
- Remote controls
- Mobile phones
- Industry, e.g. B. for the operation and control of machines
- Electric household appliances
- Medical industry, for example Medical PCs
- Industrial PCs
- Devices and applications that must be easy to disinfect
Advantages of membrane keyboards
Membrane keyboards offer many advantages
- are very light and light in weight
- easy cleaning and disinfection
- long life span
- water resistant and dustproof
A cheap membrane keyboard can break the membrane due to mechanical stress and wear, faster than high-priced and high-quality keyboards. The top film breaks over the edge hole of the middle film. The top film is most likely to break because it is subjected to the most pressure due to the mechanical stress.
Illuminated membrane keyboards
In simple terms, an illuminated membrane keyboard using SideLED technology consists of:
- Decorative film
- Scattering element
- Optional light barrier
- Holding film
- Adhesive on the back if necessary
All layers are glued together. With a circumferential adhesive surface of at least 5 mm, the illuminated membrane keypad is even protected according to IP 65 dust and splash water. IP protection up to IP69K can be guaranteed for special design measures.
Special SideLEDs are used for LED technology. These LEDs emit the light from the side into a diffusing element and do not have to be mounted at a distance. therefore take up less space.
This means that less space is required and keyboard layouts from 2.2 mm thick are possible.
An optional light barrier between the individual buttons even allows the separate lighting of each individual button. The use of bicolor or RGB LEDs also enables an almost unlimited choice of colors. Since the assembly must be carried out on a printed circuit board, its unused back can be used to populate series resistors and driver ICs or even the entire customer-specific circuit electronics.
The LED technology, combined with a special keyboard structure, enables illuminated membrane keyboards, which are only slightly thicker than the common lighting using EL light film (electroluminescent film). A long service life, bright and homogeneous key lighting, as well as the possibility of individual key control open up completely new areas of application for the membrane keyboard.
A common method for illuminating membrane keyboards was previously the use of EL foils. Due to the flat design, the low power consumption and a very homogeneous light emission, the EL film is basically predestined for this purpose. On the other hand, the relatively short service life - depending on the control voltage, the half-life is <10,000 hours -, a rather moderate brightness and the need for a special control voltage (110 VAC, 400 Hz) of this technology set narrow limits. Color changes or single key lighting are also not possible with this technology.
Illumination with short-stroke keys
Short-travel keyswitches with illuminated LED caps are a frequently used alternative. However, this solution requires a complex and space-intensive structure, consisting of a printed circuit board with buttons and a support for the front film mounted at a precisely defined distance. This method poses a challenge, in particular the precision of the assembly of the front plate with the printed circuit board, which is necessary for proper functioning.
Advantages of SideLED technology
- super flat cold light source
- Homogeneous lighting of key areas, symbols and frames
- Single and multi-colored side LEDs for an unlimited choice of colors
- Key lighting with color change possible
- Brightness adjustable within wide limits
- Lighting built on circuit board, rear side can be used for customer-specific assembly
- Optional light barrier between lighting units
- Hoffmann +Krippner
- Hoffmann +Krippner develops and produces tailor-made solutions from the membrane keyboard to the modern touch system.
- Richard Wöhr
- In addition to membrane keyboards, Wöhr also manufactures front foils and front panels.
- N&H Technology
- At N&H, customers can configure the membrane keyboards according to their needs.
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