Silicon switch mat

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Section through a button on a silicone keypad

A silicone keypad is the central component in many keyboards , which determines the feel , the optical and tactile impression and, via the integrated contact pill, also the electrical behavior.

Function and structure

Inside view of a silicone switch mat with carbon contact pills

A dome or cone is formed from the basic material silicone rubber , which merges into a cylinder in the central axis. The outer end of the cylinder represents the point of application of the actuation or the key cap. The inner end of the cylinder consists of a contact pill or a snap disk and represents the electrical contact element on a circuit board, which are bridged by the contact pill / snap disk. Usually several buttons are implemented together in a silicone keypad, but there are also buttons that can be equipped individually based on a silicone keypad, in which the connecting wires are arranged in the housing so that they are bridged by the contact pill.

The shape of the dome or the webs and the material properties of the base material can be used to set the feel and color of the keys over a wide range. The electrical properties of the button can be determined by choosing the contact pill:

  • Carbon-filled or -coated: cheap, contact resistance 10 to 200  Ω , small currents
  • Supra Conductive Pill (SC pill): Specially modified nickel grid, filled with silicone, contact resistance less than 1 Ω, relatively inexpensive, current-carrying capacity of up to 0.3  A.
  • Gold platelets or foil: relatively expensive, sensitive to contamination, very low contact resistance, current-carrying capacity of up to several amperes
  • Snap disk: relatively expensive, audible contact, low contact resistance

Since hard plastic keycaps can also be laminated directly onto the actuation cylinder, it is possible to provide the operator of the key with a hard surface which, via the design of the key (lacquered, lasered symbol, etc.), also has search and function lighting can be equipped.

use

Remote control mat

Almost all mobile devices with movable keys ( cell phones , digital cameras , remote controls, etc.) use silicone keypad to design the keys and key fields. They were used on computers in the 1980s and were nicknamed the chewing gum keyboard .

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