# Silicone rubber keypad / Elastomeric Keypads



## niks neims (Sep 21, 2017)

Is there ever silver in this type of keypads:

https://en.wikipedia.org/wiki/Silicone_rubber_keypad

wikipedia lists carbon and it looks like carbon, but the reason why I am asking is that I stumbled upon this post while lurking ScrapMetalForum:

https://www.scrapmetalforum.com/general-electronics-recycling/7921-old-lcd-displays.html
(i hope it is not against the rules to post it here)



> On the third photo, of the keyboard, those big grey/black spots are silver.
> Scrape em off & dissolve em in nitric acid till it turns blue & then precipitate the silver out with some copper



Sadly those photos seem to no longer be displaying but I will attach some of my own, from Mitel superset 4### series that look very similar. problem is - i tried to test (dissolve) those spots in nitric with absolutely no effect... are they carbon?


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## g_axelsson (Sep 21, 2017)

Looking at your pictures, black is carbon and the only silver I can see is in the flat conductor going up to the display.

As I read the comments on scrap metal forum it was the rubber buttons that is used to close the circuit across the black carbon contacts. Most commonly used is black carbon infused rubber buttons under the keys but there might exist ones based on silver too. Nothing I can remember seeing though.

A similar silver source might be conductive rubber ribbons that is used to connect the glass surface to a circuit board for smaller LCD-displays. I have saved up a couple but haven't tested them yet so the jury is still out on that one. If there is some silver there, it is probably only in quite small amounts.

Göran


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