Method of forming conductive tracks
A patterned electrical conductor having improved conductivity and controllably high resolution track and gap widths is obtained by exposing, to a desired conductive pattern, a pressure-sensitive or photosensitive element comprising a support and a pressure-sensitive or photosensitive material coated thereon being sensitive to the exposure (e.g. the wavelength of exposing radiation) and capable of providing a latent image upon exposure, and then developing the exposed element to form a developed element having a metal (e.g. silver) image thereon and then electroless plating and/or electroplating the metal image with a second metal (e.g. silver) whilst subjecting the developed element to ultrasonic agitation.
1. A process for preparing a patterned electrical conductor comprising a conductive track pattern on a support, said process comprising the steps of
providing a pressure-sensitive or photosensitive element comprising
a support substrate; and
a pressure-sensitive or photosensitive material coated onto said support, said pressure-sensitive or photosensitive material being capable of providing a latent image upon exposure to pressure or sensitising radiation and comprising a pressure-sensitive or photosensitive metal salt dispersed in a binder;
exposing said pressure-sensitive or photosensitive element to pressure or sensitising radiation according to a desired conductive track pattern to form a latent image on said element;
subjecting said latent image to a conventional-development step to form said developed element having an image formed by a first metal corresponding to said desired conductive track pattern, together with non-imaged areas; and
electroless plating and/or electroplating said metal image with a plating of a second metal to improve the conductivity of said metal image, wherein during said electroless plating and/or electroplating step(s) said developed element is subjected to ultrasonic agitation.
2. The process of claim 1 , wherein said development step comprises a wash-off process, whereby said binder is substantially removed from said non-imaged areas of said developed element.
3. The process of claim 1 , wherein said development step comprises a hot fix step, whereby said binder is substantially removed from said non-imaged areas of said developed element.
4. The process of claim 1 , wherein said binder in said pressure-sensitive or photosensitive material is susceptible to decomposition and/or dissolution upon treatment with a solution comprising an enzyme and the process further comprises treating said developed element, prior to and/or during said plating step(s), with said enzyme capable of decomposing and/or dissolving said binder.
5. The process of claim 1 , wherein said photosensitive material comprises a silver halide emulsion in gelatin and said first metal is silver.
6. The process of claim 5 , wherein said silver halide is present in an amount of at least 1 g/m 2 .
7. The process of claim 1 , wherein said second metal is selected from silver, gold, zinc, lead copper or nickel.
8. The process of claim 7 , wherein said second metal is silver.
9. The process of claim 8 , wherein said electroplating step comprises applying a voltage across the developed metal image in the presence of a solution of a silver thiosulfate complex.
10. The process of claim 9 , wherein said silver thiosulfate solution is present in a concentration of from 0.01 to 0.1 molar.
11. The process of claim 1 , wherein said metal image formed by said first metal is capable of conducting when a voltage is applied across it, prior to any plating step.