Direct writing of carbon interconnections.

The in situ formation of conductive carbon lines on polymeric substrates was demonstrated by "writing" with CO(2) and Nd:YAG lasers. The effect of material composition, power density, energy density, and wavelength on the electrical resistance and morphology of the carbon lines was investigated. After a minimum energy density of 400 Joules/cm(2) is achieved, the electrical resistance of carbon lines was found to be a function of energy density input, independent of wavelength. A prototype telephone keypad was written on a FR-2 substrate with a linear resistance of 16 Ohms/cm and to which electrical contacts were successfully made using a conductive epoxy. The feasibility of applying the laser writing process to printed wiring boards and other interconnection medium is discussed.