Rubber Dome

Rubber Domes are also known as rubber dome switches & silicone Domes. It is made of silicone rubber material and is small and flexible. Rubber dome is a switching technology of membrane keyboard.

Generally, rubber domes molded with conductive carbon pill, or need conductive printing after molded.

This means that the rubber dome acts as a switch inside the membrane keyboard, providing resistance and tactile feedback.

When you press the key, the conductive carbon pill or conductive printing touches the circuit board, completes the circuit, then the membrane keyboard works.When the key is released, the rubber dome bounces back to its original shape and returns to its original resting state.

The rubber domes collapse under pressure, often abruptly rather than gradually.This sudden crash provides tactile feedback.

Rubber dome act as a return spring for each key.

Most membrane keyboards made today use rubber domes.Most laptops and some desktop keyboards use discrete rubber domes, while more traditional style desktop keyboards typically use a rubber dome sheet.

Rubber dome advantages

-It's cheap.Compared with metal dome, the price of rubber dome will be much cheaper.

-Less noise when typing.

-Have a fairly good tactile feedback.Rubber dome keyboards has a softer and more comfortable tactile feel than mechanical keyboards

-Resist leakage and corrosion because the rubber dome layer covers the critical substrate.

Rubber dome disadvantages:

-The main disadvantage of rubber dome keyboards is that the behaviour of silicone rubber changes with age, which limits the lifetime of the keyboard.

-Rubber domes also will harden with age and require more and more force to press the keys;Very old keyboards may require excessive force to operate.

-Something unusual is that the rubber domes have become very weak.

-Another problem is that replacing rubber domes is much more difficult than replacing coil springs.If the membrane keyboard use discrete rubber domes, they only need to replace the bad rubber dome.But if the membrane keyboard use a whole piece of rubber dome sheet, they need to replace the whole piece, which is costly.

Rubber dome design guide

A single rubber dome as a return spring and actuator. It can be a discrete rubber dome or a continuous rubber dome sheet.

Like standard silicone keypad design structure, most rubber domes are designed with conductive contact and key webbing.As a return spring and actuator for the membrane keyboard, the actuation force of the rubber dome is crucial.

Generally speaking, membrane keypad is typed usually.So the actuation force of the membrane keyboard should be low.About 40-90g, with a tolerance of about 10g.

For the rubber dome we have done, the actuation force is 65g+/-5g.In order to achieve so low actuation force, we need to choose high-quality mold steel material, and high-tensile, good resilience silicone rubber material.

Different design of rubber dome:

The exact tactile feedback of the keyboard depends in part on the profile of the rubber domes. In Electronic Engineers Master 1985–86 Volume 2 (page B·1734), Moxness illustrated five different profiles of rubber dome, along with the force curve that each one would produce:

Rubber dome manufacturing process