How does the metal dome work?

As previously said metal dome is the contact medium between the pcb and the graphics overlay or a silicone rubber keyboard. But how does it work, especially how would it play the conductivity role on this?

Firstly the metal dome has to be positioning perfectly to the conduct pad of the pcb/fpc/membrane pet printed circuit layer, by mounting(DIP) to the though holes on the circuit trace, or sticking to the mylar pet layer(it's called metal dome array or metal dome sheet for the full part). no matter which solution, the bottom part of the dome will contact directly to the pcb(close circuit), and the top part of the dome will be open to the contact pad.

When the end user operates the control panel by pressind down the button, the dome roof will go down to contact the central area of the pad, then it becomes another close circuit, now the full system is close circuit and the circuit will transfer between the bottom and the top of the dome.

What is the difference of poly dome? Poly dome is thermal forming with heat press tool to be a dome shape, the basic material is pet resin, which has no electricity conductivity on itself. On its rear side(closing to the conduct pad) there is printed conductity ink, normally the ink is made of silver paste, one the top of this silver paste it's carbon powder for prevent purpose. Poly dome has the same struture than a metal dome array, so it works exactly the same way as a metal dome array.