Design

Nomenclature

The Alps SKCL/SKCM series has gone by many names, therefore leading to a misunderstanding of the series. The Alps  1993/1994 catalog refers to linear switches as "CL series" and "CM series" for other switches, assuming tactile and clicky variants. The Alps catalog used the terms "SKCL/SKCM series" ("SKCL／SKCMシリーズ"), suggesting that Alps changed the series name in the mid-90s.

Based on the known nomenclature, SK refers to "Single Key" where the keyboard module is referred to as "KF". The meaning of KF has yet to be determined and can be found on Alps-produced modules for typewriters or other keyboards that don't use an Alps-produced case.

Evolution 

SKCM/SKCL was a new series to meet the specifications of the newly introduced DIN standard. Alps' current lineup of switches at the time was too tall to comply with the new standard(SKCC). The "switchplate" design was still used as the contact assembly within the new SKCM/SKCL series. The switchplate was mounted lower in the bottom housing of the switch bottom housing. The redesign from SKCC to SKCM/SKCL allowed the operation of the switch to be the same while reducing the overheight of the keyboard profile.  With the additional redesign of the top housing, the new SKCM/SKCL series also allowed LEDs to be inserted within the top housing instead of being on two springs that switches in the SKCC series relied on. 

Generations

First Generation

1983-1984 Asymmetrical top housing and slider with the bottom housing containing a long pole. 

Second Generation

1984–1989; original colours, no top branding, long switchplates, and dry lubricant applied to the sliders in at least some instances. Later on in this generation, the switch plate colour, which was originally Black, was switched to Grey and later to White. 

Third Generation

1989–1993; replacement colours, top branding, short switchplates, and potentially a change in slider plastic to remove the need for dry lubricant.

The 1989–1990 overhaul also saw the introduction of top branding on switches using the newer Alps logo and SKCL switches changed over to the shorter tabs between the slits when the shells were retooled (noticeable in comparison between typical SKCL Green and typical SKCL Yellow). Additional changes were made to the switchplate found in SKCM/SKCL switches. At first, long white switchplates were found, until later it was changed to shorter white switchplates, and the switch bottom housing now included standoff poles under the switchplate.

Fourth Generation

1993–1996; removal of slits (bamboo generation).

Bottom Housing

The bottom housing contains four wings(butterflies) which push against the keyboard plate. The four wings can easily break when too much pressure is applied unevenly upon removing the key switch from the keyboard plate.

The bottom housing is made out of a PBT plastic blend that is outlined within the English patent: https://patents.google.com/patent/US4642433A/en

Slider 

The slider is the moving part between the keycap and the return spring. The slider colour helps to identify the type of switch along with the top housing. Prototype sliders were asymmetrical, but later SKCM/SKCL were horizontally symmetrical; however, in most cases, the slider cannot be inserted in any orientation. Tactile, clicky, and later linear have a notch cutout on the bottom of one side of the slider. This notch allows room for the return spring when the slider interacts with the switchplate. Therefore, the notch in the slider must always face the switchplate to operate correctly. The side with the notch in the slider is also more rounded at the bottom to reduce contact bounce when interacting with the fingers(metal arms) of the switch plate.

Some exceptions to the rule come in the form of:

• SKCMAA(SKCM Brown)

• SKCLAA(SKCL Green)

Both of these switches contain notches on the bottom of the slider on both sides.

Leaf spring

The Alps SKCM switches were likely the first to use a folded leaf spring to provide tactile feedback and or audible feedback once a switch has been actuated. The first tactile switch, as outlined above, was SKCMAA(SKCM Brown) followed by SKCMAC(SKCM Blue). Afterwards, Alps created additional tactile leaves found in switches like SKCMAF(SKCM Cream) and SKCMAQ(SKCM White). 

The folded tactile leaf is similar to clicky leaves however, it includes an additional metal tab at the top of the click leaf to prevent the tactile leaf from moving forward and clicking. This additional tab likes to deform over numerous uses of the switch. This can be remedied through either bending the tab back or putting a piece of paper behind the tactile leaf. This method is called "paper mod" and will add additional tactility to the switch.

Alps Logo

Alps SKCM/SKCL switches were originally branded only on the bottom housing. Later on in 1989, Alps also added the word "ALPS" in capital letters to the top housing of each switch. Sometimes, either both logos on both housing or only one can be located on a switch at one time.

Alps SKCM/SKCL Models 

Early Models

The early models of SKCM/SKCL models are found in keyboards that were made in Japan. Some keyboards that were exported to the USA were also found to be made in Japan and contained early switches. Some of these keyboards, including very early Texas Instruments low-profile keyboards, contain early SKCM Brown switches(SKCM Brown Prototype). The model number assigned to the switches can be found on the plate where the switches are located in. The sticker on the plate that contains the "ALPS P/N" also refers to the main type of switch that can be found within the module. 

ie, KCMAA002 equals SKCMAA. This code refers to the Tactile SKCM Prototype Brown(Green) or the later SKCM Brown.

The same identification principle can be applied to SKCL switches as well. If the "ALPS P/N" contains "KCLAA003," then this refers to either Prototype SKCL Green or the later SKCL Green. 

Later Models

Further models have been identified thanks to a posting on eBay that contained an assortment of SKCM/SKCL switches and their associated SK Model Name. The booklet was called "LOW-PROFILE KEYBOARD SWITCHES". Numerous switches in the table further below have their SK Model Name derived from the booklet. Additionally, there was a 1993/1994 booklet that was also uploaded to Deskthority that contained more model names of switches from later on in the SKCM/SKCL production. 

Apple Models

These switches were made exclusively for Apple for their machines. No documentation has been found so far of their model names besides the ones already listed in the Alps catalogs. Further information about the switches names are required.

Goldstar Models

Goldstar is a Korean manufacturer that manufactured different coloured Alps SKCM/SKCL switches. Alps still held all the rights to the switches however, they contracted Goldstar to make switches as well. Partial names have been derived from the keyboards that the switches have been found in. The "E" in the naming is assumed to mean "External" as External production. However, this has yet to be proven and is only an assumption. Further information is required.

Additionally, on the PCB, the PCB Code also contains the last letter of "K" which is assumed to stand for Korea.

Documentation:
Alps 1993/1994 Catalog
SKCM Brown Prototype