Dichromic process for preparation of conductive circuit

Claim 1

A process for the preparation of a conductive circuit which comprises (a) applying to a substrate two photohardenable layers, the upper photohardenable layer being sensitive to ultraviolet radiation and relatively insensitive to visible radiation and being hardenable and nontacky when exposed to short wavelength ultraviolet actinic radiation but unhardenable when exposed to longer wavelength visible radiation, and the lower photohardenable layer being tacky and hardenable when exposed to the longer wavelength visible actinic radiation; (b) exposing the photohardenable layers to radiation containing ultraviolet and visible radiation through a dichromic phototool containing one or more areas characteristic of a circuit pattern which transmit visible radiation and masks out ultraviolet radiation whereby the lower photohardenable layer becomes hardened but remains tacky and the upper photohardenable layer remains unhardened, one or more clear areas which transmit visible and ultraviolet radiation whereby the upper and lower photohardenable layers become hardened, and areas characteristic of vias of the circuit pattern which mask out all said radiation; (c) removing with a solvent the unhardened areas of the upper photohardenable layer to uncover the exposed tacky areas of the lower photohardenable layer corresponding to the circuit pattern and removing unhardened areas of the unexposed lower photohardenable layer forming holes corresponding to the vias; (d) applying finely divided metal, alloy or plating catalyst material to the uncovered tacky circuit areas and edges of the via holes of the lower photohardenable layer; and (e) plating the metallized or catalyzed image to form an electrically conductive circuit.