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Ergonomic Product Categories > Keyswitches > Membrane Keyswitches
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Membrane Keyboards - (i.e. Keyboards with Membrane Keyswitches)

What is a Membrane Keyboard (i.e. a Keyboard with Membrane Keyswitches)?

The majority of computer keyboards currently in production use a rubber dome membrane keyswitch (which is actually usually made of silicon, but is referred to as rubber).  There are three physical elements in a membrane keyswitch mechanism which are simple and inexpensive to manufacture, making them popular for most mass market keyboards. 

The first is the keycap which is object which the user touches with their fingertip. The keycap typically has a plunger (or stem) which extends below the keycap and serves two purposes.  The primary function is to compress the rubber dome when the keycap is pressed downward.  The secondary purpose is to maintain the position of the key by restricting twisting or tilting of the vertical movement vector over the key travel distance.

The second component is the rubber dome which is where the feel of the keyboard and force curve of the keyswitch is derived.  The third component is a three-layer membrane sheet which covers the entire base of the keyboard, which is responsible for capturing the physical action and sending a signal to the computer. 

When the user presses the keycap the full key travel distance, a dimple at the top of the dome pushes the top membrane layer through a hole in the middle layer to contact the bottom layer.  This closes the circuit which actuates the keystroke, and the keyboard will then send the character information to the computer. The middle layer of the membrane keeps the top and bottom layers from contacting each other except when a switch is depressed completely.  Differences in the shape and thickness of the domes determine the travel, resistance, and tactile feedback of the switches.  However, the keystrokes are only generated when the key is fully depressed.

What are the Characteristics of Dome Membrane Keyboards?

Key Travel Distance: Membrane keyswitches are usually 'full-travel' i.e. the key will move down between 3.5 - 4.0 mm before 'bottoming out', and the elasticity of the membrane returns the keycap and associated plunger to their default 'up' position.  However, the key travel can be as short as 2.5 mm.

Noise Level: Membrane keyswitches are the quietest switches due to the lack of any hard objects striking one another without cushioning.

Durability: Most standard membrane keyswitches are rated at 1 million keystrokes, however some manufacturers use superior materials and have ratings of as high as 10 million keystrokes.  Regardless of the rating, over time some domes will become inelastic and others will become overly elastic due to debris buildup, compression fatigue, manufacturing imperfections and even ultraviolet radiation (which can 'vulcanize' rubber).  This results in a variance in the amount of force to type on different keys on a single keyboard.  As such even though a keyboard may have a rating of 10 million keystrokes, the force curve and tactility of the domes can be affected within the first year of use.

Key Activation Force: The 'factory' actuation force varies widely, and can be as low as 25 grams or as high as 150 grams.  Most membrane keyswitches are rated between 60 and 80 grams. 

Tactility ('Feel'): Most membrane keyswitches are not tactile and tend to have a 'mushy' feel due to the cushioning that is a inherent in their design.  However, they can be engineered to provide a degree of tactility, but it is not possible to have the crisp distinct key action or feel which scissor-switch or mechanical keyswitches can provide.

NOTE: Dome membrane keyswitches should be distinguished from flat-panel membrane keyswitches which have no dome at all (like what is often encountered on a microwave) and have no significant movement (i.e. key travel) whatsoever. These are occasionally found on some specialty computer keyboards such as travel keyboards and industrial keyboards.

What is a Conductive Rubber Keyboard?

Conductive rubber keyboards are a distinct subset of rubber dome membrane keyboards. While the mechanical portion of the switch can be identical to a membrane keyboard (either simple rubber dome or scissors switch), the electrical portion only uses a single layer. The 'pill' portion of the rubber dome is a specially designed rubber which conducts electricity, so that when the switch bottoms out, the pill directly shorts out two different circuits to cause a switch action. Conductive rubber computer keyboards are rare, in part because they are somewhat more expensive to manufacture than membrane keyboards. However, one advantage of conductive rubber keyboards is they can easily be repaired in the field by cleaning or replacing the rubber and the conductive layer. In contrast, a membrane keyboard must be manufactured and assembled in a clean-room environment, so that it is not generally effective to try to clean or repair such a keyboard.



Last edited December 9th, 2013

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