I doubt it has mercury. But why don’t you just get rid of it? Do you have electronic recycling in your area?
Get rid of an XT keyboard? That is collective
Well, I measured these films with a continuity meter. The surface of the film that touches the pads on the PCB is non-conductive! The metal must be from the back side (the one of the plastic buttons of the keys). They seem to be capacitive indeed and the film forms the dielectric. I read about capacitive keys here
https://en.wikipedia.org/wiki/Keyboard_technology
They do not say anything about toxicity...
Wikipedia states
"The movable part ends with a flat foam element about the size of an
aspirin tablet, finished with aluminum foil. Opposite the switch is a PCB with the capacitor pads. When the key is pressed, the foil tightly clings to the surface of the PCB, forming a
daisy chain of two capacitors between
contact pads and itself separated with thin soldermask, and thus "shorting" the
contact pads with an easily detectable drop of
capacitive reactance between them. Usually this permits a pulse or pulse train to be sensed. Because the switch doesn't have an actual electrical contact, there is no debouncing necessary. The keys do not need to be fully pressed to be actuated, which enables some people to type faster."
So they say it is aluminum foil.
I have never seem aluminum to be "evaporated" like this
In my case there is no "thin dielectric" over the pads. The dielectric is this film on the moving side of the keys.