Keyboard technology

Lore & Background

The article describes several distinct keyboard technologies. Membrane keyboards, a common design, consist of three layers: top and bottom layers with electrical traces and a middle spacer; pressing the top layer bridges the contacts. Two subtypes are full-travel rubber dome over membrane, where a rubber dome acts as a return spring and force transfer surface, and flat-panel membrane, often used in appliances and harsh environments. Scissor-switch keyboards are a compact variant of rubber dome over membrane, using a scissors mechanism and commonly found on notebooks.

Metal contact switches use discrete modules per key, with a housing, spring, and slider; contacts are held apart at rest and pressed together for actuation. Cherry is a major producer of such switches, with a color-coding system imitated by others. These keyboards are often called 'mechanical keyboards,' though no universally agreed-upon definition exists. Hot-swappable keyboards allow switch replacement without soldering, using sockets on the PCB.

Reed switches operate magnetically, with a slider pushing a magnet near a sealed glass capsule containing metal contacts. Capacitive keyboards change capacitance when a key is pressed, using a foam and foil element over capacitor pads on a PCB; this technology does not rely on current flow through metal contacts and requires no debouncing. IBM's Model F used buckling spring over capacitive PCB, while the later Model M used the same spring with membrane sensing.

Reader's Guide

Keyboard technology is significant because it directly affects the user experience, durability, and cost of input devices. The article notes that rubber dome over membrane keyboards became very popular with computer manufacturers seeking to reduce costs as PC prices declined. Scissor-switch keyboards, while slightly more expensive, are quieter and require less force, making them suitable for slim notebooks. Flat-panel membrane keyboards are valued in harsh environments for their water or leak-proofing capabilities, though they have been supplanted in personal computers by more responsive designs.

Metal contact switches, commonly called mechanical keyboards, saw renewed use by gamers and professionals since the mid-2000s. Hot-swappable keyboards lower the barrier for users to change switches without soldering tools or knowledge. Capacitive technology offers advantages such as adjustable actuation point per key and no need for debouncing. Reed switches are considered separate from other metal contact switches due to their magnetic operation. The variety of technologies reflects ongoing efforts to balance tactile feedback, reliability, cost, and form factor across different applications.

Did You Know?

• The reed switch mechanism was originally invented in 1936 by W B Ellwood at Bell Telephone Laboratories.
• Cherry's color-coding system for switches has been imitated by other manufacturers such as Gateron and Kailh.
• IBM's Model F keyboard used a buckling spring over a capacitive PCB, while the later Model M used the same spring with membrane sensing.
• Hot-swappable keyboards allow switches to be replaced without soldering, using sockets on the PCB.