Elastomer Overview and Applicability

The development of the elastomer in keyboards is the basis for many of the most important aspects of keyboard design. Elastomer is found in both the visible and inner world of data entry devices in use daily. (To know what we mean by "visible" and "inner world", reference the two technology illustrations on this page).

Oftentimes individuals encounter elastomeric buttons by direct fingertip contact. For instance, the keypad might be on a home audio system, washing machine or cell phone. More often than not it is behind or underneath plastic keytops that you make indirect contact with elastomer — to initiate the tactile response, backlighting and electronic feedback to your key selection. Examine cell phones that are offered to the consumer and you will see this variation allowed in keypad design. The development of elastomer and the carbon contact interface with the PCB was a major element in removing cumbersome mechanical switch mechanisms in the design of keypads and data entry machines.

In order to appreciate this, it will be necessary to understand how elastomers are produced and what type of design considerations are made in the process of development. Following, are a few important terms to facilitate insight:

Durometer: Originally the name of the machine that is used to test the hardness of rubber, durometer here it will refer to the specific hardness of the silicone rubber used in elastomers. Derived from the Latin durus (meaning hard) — a difference in durometer doesn’t imply that a different material is being used; rather it is the same material with the attribute of its mass having a softer or harder consistency in its final form. This important attribute is part of the necessary element to achieving tactile feel.

Boot: Sometimes also referred to as the ‘web” this is the second overall factor in achieving tactile feel in elastomer design. Boot design provides several elements: the length of travel allowed before the boot enters its area of ‘snap’ or tactile feedback, the type of snap feedback required, and the amount of spring back return that the key possesses as it returns to its original configuration and height. At Advanced Input Systems, boot tactile feel is a measured element in all elastomerics.

Carrier: Also referred to as the ‘base material’, the carrier is the surface material that becomes the platform that keys rest on. More though than just a platform that interconnects with the keys, it interfaces with printed circuit boards, bezels and next assembly customer parts— thus it carries many important factors to complete the keyboard. A number of other elements become crucial as the final design is brought to fruition, including: thickness, venting for proper key actuation, attachment points for mating to PCB’s or bezels, ribbing for sealing, wrap around cut outs for sealing, alignment features, durometer, color, transparency, and over-molding requirements.