Method of manufacturing a die designed to duplicate a video frequency signal recording

Claim 1

In a method of fabricating a die for duplicating a video frequency signal recording: (1) manufacturing a master impression consisting of a substrate covered with a layer of positive photosensitive material having a thickness on the order of 3000 to 4000 A; said layer presenting a multiplicity of cavities forming a spiral track in said photosensitive layer, by a process comprising the following steps: (a) exposing said photosensitive layer using a fine laser beam focussed on the layer and modulated by the signal which is to be recorded, said laser beam and said photosensitive layer moving in relation to each other so as to produce a signal latent impression forming a spiral track onto the substrate; (b) developing said layer of photosensitive material, to lay bare small portions of said substrate along said spiral track; and (2) manufacturing a die which is a counterpart of the recording and presents a multiplicity of metal projections adhering to said bare portions of the substrate, the heights of said projections being equal to the depths of the cavities of said master impression, by a process comprising the following steps: (c) depositing a metal layer on said developed layer and on said bare portions of substrate, the thickness of said metal layer being substantially equal to the thickness of the initial photosensitive material; and (d) eliminating the non-exposed photosensitive material thereby carrying away the portions of the metal layer overlying the non-exposed photosensitive material by an agent which dissovles said non-exposed photosensitive material but not said metal, to form said metal projections.