Homebrew PCBs

There is a special type of material that is used on PCB's for membrane-switch 
contacts.  I believe it's carbon, and usually laid out in some "interlocking" 
fashion to ensure contact/bridging when the membrane touches it.  Seems to be 
made directly on the PCB.  Anyone know what this is, and how it's made?

No, I don't need any, but would like to know what it is exactly and how it's 
done.

I'm sure I have something with it here, and will take a pic when I find it.

Cheers,
-Neil.

In a message dated 5/23/2003 3:21:22 AM Central Standard Time, 
cobra_neil@... writes:

> There is a special type of material that is used on PCB's for 
> membrane-switch 
> contacts.

Neil:  The only such stuff I am aware of is "conductive rubber" which the 
membrane presses onto GOLD-plated contacts on the PCB.  These are usually several 
interwoven "fingers" so that even a small % of contact by the rubber 
"plunger" causes a "make".  


[Non-text portions of this message have been removed]

----- Original Message ----- 

  From: JanRwl@... 
  To: Homebrew_PCBs@yahoogroups.com 
  Sent: Friday, May 23, 2003 6:33 PM
  Subject: Re: [Homebrew_PCBs] Membrane-switch material/process on PCB's


  In a message dated 5/23/2003 3:21:22 AM Central Standard Time, 
  cobra_neil@... writes:

  > There is a special type of material that is used on PCB's for 
  > membrane-switch 
  > contacts.

  Neil:  The only such stuff I am aware of is "conductive rubber" which the 
  membrane presses onto GOLD-plated contacts on the PCB.  These are usually several 
  interwoven "fingers" so that even a small % of contact by the rubber 
  "plunger" causes a "make".  

  I've also seen screen printed conductive ink on the pcb. The gold plating with conductive rubber seems to be a better solution, but perhaps someone else can expand the discussion. Maybe its a cost issue?
  Ron

[Non-text portions of this message have been removed]

I've seen very simple ultra-low profile switches 
on some PCB's.
The mechanism seems to be a flexible concave piece
of metal which, when pushed down, "pops" into the 
depressed state, but has enough springiness to
pop back up when released. The buttons are usually
taped to the board with a strip of adhesive tape.