Sealed terminals are a feature or option of a number of switch families. The purpose is not known. RAFI note the following in the Electromechanical Components 2001 catalogue:
Following momentary/latching keyswitches can be flow-soldered:
- Momentary/latching keyswitches with sealed bottom and sealed terminals:
- Momentary keyswitches RS 74 M with increased ESD-strength
- Keylock, code and rotary switches
- All momentary/latching keyswitches RS 76 C (Hall-IC)
The sealant is a firm but not strong substance, typically red in colour. Depending on the switch, scraping it with a sharp implement can cause it to flake (RS 74 M) or scratch, but it can be scratch-resistant.
With Alps SKCC series and General Instrument Series S950, the base of the switch contains a recess surrounding the terminals that appears to be placed there to contain the sealant. RS 74 M sealed switches have small recesses around the legs to hold the sealant, instead of the typical large holes through which the legs pass.
US patent 4760225 filed by Alps Electric (in relation to Alps common mount low profile) is titled "Push button switch having a frame member for preventing solder penetration of switch contacts", which ties in with the possibility that the increased level of manufacturing automation required some means of preventing the solder entering the switch during wave soldering.
With SMK J-M0404 series switches, the sealant secures the terminals sufficiently that they can be reinserted into the upper shell with ease, making light work of the typically fraught process of trying to reassemble an SMK switch. The widespread occurrence of this sealant in easy-to-assemble switches suggests that is is not a manufacturing aid, however.