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Where are membrane keyboards used today?
Mashine building Control technology Measuring technology Medical technology Communication electronics
What advantages does a membrane keyboard have, compared to other keyboard technologies?
Completely sealed front making it water and dust proof (IP65) Durable even against many chemicals such as oils, detergents, alcohol, fuels, bleaches, and the like. Open to all kinds of graphical designs Variable geometry Low price per switching element A very low profile is possible The integration of pockets for customer specific legends, LEDs, and LCD-displays is possible.
The mechanical structure of membrane keyboards:

Flat input keyboard	Structure as flexible pcb with adhesive film on the rear

Membrane-covered short travel-keyboard	Structure with a closed design foil on aluminum sheet metal over high-quality short-travel keys on a circuit board.
Membrane keyboard with a rigid PCB	Structure with closed design foil directly on the circuit board with integrated switching elements as well as the controller
Membrane-covered short-travel keyboards are structured torsionally stiff due to the front plate. The short-travel keys are very durable and offer a precise switching of the keys. Different grid dimensions and overall heights are possible, depending on the selection of the keys. Illuminated keys are also available. As a side effect the front plate, e.g. aluminum sheet metal serves as an electromagnetic screen.
The following is the basic structure of a flexible membrane keyboard

The foil is built up of several layers. The base is the switching comb foil (Schaltkamm-Folie). The snapping disk (Schnappscheibe) closes the electrical contact on the switching comb foil. The snapping disk is kept in place by a spacer (Spacer) and the fixing foil (Fixier Folie). All is covered by the membrane (Decor-Folie) which in this case has a dome embossing.
The connector - the interface to the controller
Direct connection	Here the foil is plugged directly into a socket on the PCB of the controller. The somewhat stronger connector is sealed at the contacts with carbon lacquer and is therefore more resistant. Additionally the contact silver remains bonded to the conductive strip (no silver migration).
Indirect connection	Here a socket is crimped onto the end of the connector strip leaving the keyboard. The appropriate counterpart is placed on the PCB of the controller.





The feel of the keys - emossing and the snapping disk
To better find the correct position on the keyboard and to ensure a tactile feedback, the membrane can be embossed and placed over snapping disks.
Types of embossing:

Key embossing	Raised embossing of the entire keytop.

Rim embossing	Rim embossing stresses the foil due to the many radii. Instead of this emboss a relief should be printed onto the surface of the membrane.

Dome embossing	The advantage of the dome embossing is that the keyboard can be easily cleaned, since there are no angles, where dirt can cling to.

Relief embossing	Only the rim of the key is embossed like a relief
This type of embossing shortens the lifetime of the keyboard as well, though about 1 million keystrokes are still possible.
The height of the embossing is possible up to 1.5 times the thickness of the topfoil. Only dome embosses can be higher due to the low edge radius.
Snapping disk:
It is possible to integrate a snapping disc into the switch to obtain a good tactile feedback.

Feedback and tactility
The following is a diagram that shows the typical force vs. the distance when pressing and releasing the key. This diagram describes a soft impact of the key.

Integration of displays and pockets for customer specific lettering:
Displays:	Displays can be integrated under the topfoil, which dooes not need to be cut out. This window can be coloured or left clear and it can be matte or reflecting.
Pockets for customer specific lettering:	The lettering can be changed by inserting a strip into the pocket. The keyboard can be thus changed to other languages or the customers name can be inserted (OEM)
	The strips can be inserted from the front, the side or the rear of the keyboard.

Electrical connection:
Interconnecting the individual keys takes place as matrix or as network with a common control line. Sometimes there are also combinations of both. Miniature LEDs can be integrated into the foil in this way. Those for this it is necessary to lead the lines out seperately.
The matrix connection:

The advantage of the matrix connection is theat many keys are possible with a minimal amount of outgoing leads.
The matrix needs an inelligence in form of a controller.
The common control line:

Very few keys are possible, as there are too many outgoing leads. A controller is not needed.
Amount of leads = Amount of keys + 1
As you can see, the membrane keyboard is a very complex matter. This page can only give an overview of basic possibilities.
Customer specific production of membrane keyboards:
Do youhave a project and don't know where to have your membrane keyboard developed and manufactured ? We will put our many years of know-how to work for you so that we can contribute our part to the success of your project. Beside the keyboards has we also have keyboard controllers in our program, so that you can get everything from one hand. That saves time and money.
Which information do we need for the development of a membrane keyboard?
Please click here, to download the questionaire.
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Membrane Keyboards

Description