US Patent 7235752 Illuminating membrane switch and illuminating keypad using the same

An illuminating membrane switch includes an upper membrane sheet and a lower membrane sheet. The lower membrane sheet includes an electroluminescent device and a plurality of lower lead wires disposed on the illuminating surface of the electroluminescent device. An insulating spacer layer is further disposed on the illuminating surface of the electroluminescent device, and separates the upper lead wires of the upper membrane sheet from the lower lead wire. When a pressing force acting on the illuminating membrane is sufficient, the upper lead wire and the lower lead wire at the pressing position can contact each other through the opening of the insulating spacer layer so as to form a closed circuit. The keyboard can light up the symbols on the surfaces of key caps by light emitted from the illuminating membrane for a user to identify the function or alphabetic input of each key cap, and detect any input from a keystroke.