Contact module

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Revision as of 00:46, 4 April 2018 by Daniel beardsmore (talk | contribs) (Daniel beardsmore moved page Switchplate to Contact module: WTF is a switchplate anyway?)
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the term "switchplate" is strange and misleading and may need deprecating; even if we keep it, the scope of the term is not understood: does it for example cover NEC oval contact cartridges? It also gets used to refer to the mounting plate in keyboards, which works against keeping it. Possible alternatives are "contact module" and "contact assembly".

A switchplate or switch plate is the keyboard community term for a fully self-contained contact assembly in metal leaf contact switches.


The switchplate is a plastic assembly that contains and supports the electrical contact plates and the actuator leaf. After removing the top of the switch, the contact assembly is still fully supported.

The Alps switchplate design appears to have originated in the Alps SKCC series switch, and was adopted wholesale into the Alps SKCL/SKCM series switches with no discernable alteration. The Alps design comprises a complex sandwich of metal and plastic layers, hence the term "complicated" when referring to Alps switches. Alps SKBL/SKBM series (simplified Alps) and Alps clones replaced this whole assembly with bare switch terminals, using various slots and grooves in the upper shell for support. Simplified Alps switches are fairly easy to reassemble, but with many clones switches, forcing the thick contact plates down the fine grooves in the upper shell is fiddly and taxing.

Alps internals--CM, complicated, grey switchplate.svg

Grey full-height switchplate from an early Alps SKCL/SKCM series switch

Alps clone internals--CP, both, APC older.svg

Simplified clone switch
Simplified contact mechanism in an early Tai-Hao APC series; the front contact plate is still the full width of the switch


Switches that use switchplates include:


Alps SKCC series

Alps SKCC series switches used both long black, and long grey, switchplates.

Alps plate spring

A very similar design was used in the Alps plate spring switch, modified to lie flat across the bottom of the switch.[1]

Alps SKCL/SKCM series

SKCL inherited the switchplate from SKCC; both SKCC and early SKCL/SKCM use the exact same design (including both black and grey examples for both series):

Long switchplates

Complicated Alps switches initially used long black switchplates. The colour changed twice, first to grey, and then to translucent white. These three variants appear to have maintained the same internal construction.

Short switchplates

Around 1988, the switchplate height was reduced, and the internal construction was altered. The large foil membrane was reduced to a smaller strip, and instead of being a loose fit, it was crimped into two holes in the front terminal. The switch shell gained two small posts on the inside to support the switchplate which now sat a short distance above the bottom of the switch.

Full disassembly of a short switchplate is extremely difficult, as the foil membrane is fragile and likely to tear if an attempt is made to remove it from the terminal.

Omron B3G-S series

Omron B3G-S series switchplates have an actuator leaf almost identical to Alps Electric's design, but the internals are completely different, with simple metal leaf contacts. Additionally, the switchplate is sealed and cannot be safely disassembled.