Silicone Rubber Keypad Experience? 1

[BobM2]

I'd like to use a silicone rubber keypad for our products. However, my experience with membrane switches hasn't been good. I find that many, over time, have trouble making electrical contact. I'm guessing a film develops on the PCB. Is the contact technology better these days? What would I need to specify for the board and the conductive pill to make sure I have a long-lasting contact? Any good web resources?

 

[logbook]

When we did work on this (10,000+ units shipped and working)we put carbon loaded ink on the pcb tracks so there was a "carbon to carbon" contact rather than "carbon to copper" or "carbon to gold" or "carbon to tin-lead". Use a pcb vendor with experience of these carbon ink patterns. The resistance is much higher than you would expect for an ordinary switch; say hundreds of ohms worst case. Nevertheless it is easy to detect the difference between hundreds of ohms and tens of megohms.