Contact module

A contact module or contact assembly is a unit within metal contact switches which contains the switch contacts and usually the solder terminals. With Alps SKCL/SKCM series switches, they are inexplicably termed "switchplates", a term also seen used to refer to the mounting plate within a keyboard.

Description

The contact module is a plastic assembly that contains and supports the electrical contacts. Such a module can be inserted and removed from the switch. Without such a module, the bare contacts are supported purely by the switch shell. After removing a contact module, the contacts are still fully supported.

Switches that use contact modules include:

• Alps SKCC series
• Alps SKCL/SKCM series
• Alps SKCP series
• Mitsumi standard mechanical
• Omron B3G-S series
• Omron Alps-style switch

Alps

The Alps contact module design appears to have originated in Alps SKCC series, and was adopted wholesale into the Alps SKCL/SKCM series switches with no discernable alteration. Alps keyboard switches with this type of contact module have model numbers beginning SKC, where "C" appears to denote this contact arrangement. Alps SKCP series uses largely the same design as SKCC, SKCL and SKCM, but the contact module is laid flat across the bottom of the switch and the shapes of the parts are adapted slightly to suit the switch.

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 contacts, using and grooves in the upper shell for support. Simplified Alps switches are fairly easy to reassemble, but with many clones switches, forcing the thick contacts down the fine grooves in the upper shell is fiddly and taxing.

Alps SKCC/SKCL/SKCM switchplate
Long grey switchplate from an early Alps SKCL/SKCM series switch

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

Long switchplates

The original switchplate in Alps switches was the full internal height of the switch. These are termed "long switchplates". In early SKCC and SKCL/SKCM switches, the supporting block was coloured black. Subsequently this changed to pale grey, and finally colourless. Long switchplates can be fully disassembled and reassembled, although after the melted heads of posts that hold it together are snapped off, it will not hold itself together once removed from the switch, and it will need to be glued.

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  Black switchplate from an SKCC switch, together with the slider and return spring

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  Rear view of the switchplate

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  Full disassembly: top view of parts (rear to front)

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  Full disassembly: bottom view of parts (front to rear)

Short switchplates

Around 1988, the switchplate height was reduced, and the internal contact 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 sits above the bottom of the switch. Short switchplates were used with all of SKCC, SKCL and SKCM series switches.

Full disassembly of a short switchplate is essentially impossible, as the foil contact membrane is crimped into one of the terminals and cannot be removed with tearing it.

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  Short and long switchplates

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  Long and short switchplate front mounting blocks

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  Front view

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  Rear view

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  Rear contact/terminal removed to reveal the separator and foil membrane

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  Foil membrane comparison from short (left) and long (right) switchplates

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  Foil membrane is fragile; note the different foil colours

Alps plate spring

A very similar design was used in the Alps SKCP series "plate spring" switches, modified to lie flat across the bottom of the switch.

Omron

B3G-S series

Omron B3G-S series contact modules have an actuator leaf almost identical to Alps Electric's design, but the internals are completely different, with simple metal leaf contacts. As with Alps switchplates, these contact modules are secured with heat staking and will not hold together once disassembled.

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  Omron B3G-S series contact module

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  Contact module opened up

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  Contact module opened up