> Membrane Keypad Structure:
1) 4 layers structure: Graphic overlay + Spacer + Circuit(can be PET circuit or FPC circuit) + Back Adhesive
2) 6 layers structure: Graphic overlay + Spacer: Dome Retainer + Spacer + Circuit(can be PET circuit or FPC
    circuit) + Back Adhesive;
3) Other Structure
     3.1) Overlay + Rubber Adhesive + Rubber Keypad + Rubber Adhesive + Retainer + Spacer + Circuit + Back
            Adhesive;
     3.2) Overlay + Spacer + Retainer + PCB Circuit;

And also there are many other kinds of structures for the interface keypads structure. It based on customer's real needs and we can design the suitable and economical structure for our customer's final application.