Thick-Film Fine Pattern Formation by a Photolithographic Process

A printing process is generally used for pattern formation of · thick films. With this method, however, it is difficult to achieve high yield production rates for pattern widths which are less than 200 mum. To obtain finer patterns, a hybrid technique of thick-film technology has been developed. A photolithographic technique, using a water-soluble negative photoresist, has realized fine pattern widths down to 50 m. The technique involves the following processes. 1) A thick film paste is first printed on the entire substrate surface. 2) A water-soluble negative photoresist mixture of PVA-diazo compound is coated on the dried thick film and is exposed through a photomusk. 3) The unexposed areas of the photoresist are washed away with water. 4) An organic solvent which dissolves dried thick films is then sprayed over the exposed thick film, and the desired thick film pattern is obtained. 5) Finally, the substrate is fired at a predetermined temperature with the resist still on the substrate surface. Commonly available conductive, resistive, and insulating pastes can be used with this technique. Special paste such as photosensitive paste is not required. A few examples utilizing the technique described above will be described.