Thick film on metal encoder element

Abstract

A switching element, specifically an encoder element, is fabricated by forming a conductive track on an insulative substrate, and then screen printing an insulative layer on the track in a predetermined pattern that forms a contact array that comprises a plurality of conductive contacts separated by nonconductive areas. The substrate may be a polymeric resin, and the track comprises (a) a copper base layer formed on a surface of the substrate in the configuration of the track, (b) a first metal-plated layer, preferably of nickel, on the base layer, and (c) a second metal-plated layer, preferably of gold, on the first metal-plated layer. The insulative layer is formed of a thick film dielectric material comprising a difunctional monomer (e.g., diallyl isophthalate), a glycol ether ester (e.g., ethylene glycol monobutyl ether acetate), an inorganic filler (e.g., BaSO,), and an acetate surface modifier (e.g., an ethyl acrylate/ethylhexylacrylate copolymer). The screen-printed dielectric material on the conductive track results in an array of contacts separated by nonconductive areas that extend no more than about 30 microns above the surface of the contacts. An encoder element so fabricated includes first and second concentric annular contact arrays formed that concentrically surround a central collector contact.