Use carbon pills to integrated with rubber keypad during moulding process.There are 2 kinds of carbon pills,1 with textured surface,is preferable and mostly used for wear resistant and long lasting life;the other with smooth surface.
2)Carbon ink printing
This is a even lower cost solution but often leads to low grade keypad,Most Chinese remote controll in domestic market adopted it.
Generally you cannot tell the difference of a carbon ink printed carbon conductor keypad and smooth surfaced carbon pill keypad.However,the carbon layer thickness of ink printed one is surely smaller.
During printing,factory need a fixing tooling with keypad feet profile too;
As most know,keypad moulding need 2 sets of moulding,1 for rubber forming and the other for carbon pill fixing.