Tactile membrane switches incorporate a metal dome or a polydome into the membrane assembly to achieve a desired tactile response. By using different materials and sizes for these domes, you can vary the actuation force required to activate the switch. An additional adhesive layer – called the dome retainer – is placed just under the graphic overlay to hold the dome in place.
Metal domes come in a large variety of shapes and sizes, with actuation forces between 180 to 700 grams. 340 grams is the most common.
Metal domes are typically stainless steel, and are nickel-, silver-, or gold-plated. The selected plating depends on the conductivity requirements of the switch, chosen based on electrical resistance. Nickel is the standard, while gold drives down the resistance. Most screen-printed silver circuits are paired with metal plated domes. Gold plating is typically reserved for copper flex or PCBA-based designs.
Another factor that can determine the plating choice is the need to match the material of the underlying circuit. For instance, gold on gold is a common approach to optimize electrical performance.
Softer and quieter than metal domes, plastic polydomes are another option for engineers to create a desired tactile experience.
To make a polydome, a layer of polyester is screen printed with silver “shorting” pad, and then it is thermo-formed into a dome. This also allows you to create multiple buttons across a single panel, and it is a very cost-effective technique for high-volume switches (after the cost of the initial tooling).
Different actuation forces can be achieved by changing the diameter and height of the polydome to meet your requirements.