Rubber dome

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Rubber dome is a type of keyboard switching technology that is most commonly used on modern keyboards, using collapsible rubber domes to provide resistance and tactility to keys. The rubber dome replaces the helical spring found in other switch types, although some keyboards do use both, including Fujitsu Peerless and one Alps integrated dome variant.

Most rubber dome keyboards use a membrane contact sheet below the dome to provide electrical switching, but certain rubber dome switches, such as Topre switches, use capacitive switching, and a small number of boards used a PCB.

Contact mechanism

Membrane rubber domes from the AppleDesign Keyboard

Dome switch keyboards use several contact mechanisms:

Membrane

The "ceiling" of the dome presses two plastic membranes together to connect circuit traces; such keyboards require three membrane layers: upper and lower with exposed conductive traces, and a separator sheet to keep the conductor membranes separated until pairs of contacts are pressed together.

Membrane with carbon-coated domes

The ceiling of the dome is coated with carbon, and this conductive layer connects a pair of circuit traces together when it makes contact with the membrane or PCB.

Capacitive

Topre Realforce keyboards use the rubber dome solely as a spring, and switch actuation is performed using capacitance via a 5 cN spring compressed by the dome.

Discrete dome switches

The Alps integrated dome switch is a discrete, self-contained switch that uses a rubber dome with a conductive pad to connect two metal contacts at the bottom of the switch

Gallery

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  Membrane domes from the AppleDesign Keyboard

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  Membrane sheets and domes from the AppleDesign Keyboard

Varieties

Topre switch with the slider visible in black

Plain rubber dome

A stem is moulded into the keycap that pushes down on the dome; this is the most common variety

Domes with sliders

Similar to a microswitch mechanical, each switch contains its own slider that presses on the dome, onto which the keycap is mounted; on some keyboards the slider has a standard Cherry MX mount or Alps mount interface and the board will accept keycaps from mechanical keyboards and donate keycaps for mechanical boards. Dome switches with sliders are now uncommon, but this is the form taken by Topre switches

Scissors

Laptop keyboards introduced the use of scissor-like mechanisms to stabilise low travel switches that lack a shaft for the keycap to slide inside