Two novel additive processes to manufacture circuit boards: direct laser writing and direct electrostatic transfer and deposition

Two technologies are described to manufacture bare circuit boards. Both methods are dry processes and are additive by nature. The first technology is a process whereby circuit lines are written directly onto the substrate from a CAD/CAM database. There is no need for artwork to be generated with its inherent limitations. A circuit board is manufactured by applying a film of heat-sensitive adhesive to a substrate and depositing on the film a layer of conductive powder. The powder and film are then activated by laser radiation to define the circuitry. The excess powder is then removed and the substrate fired to cure or bond the powder to the substrate. The second technology is directed toward higher-volume production and requires the use of a master pattern. The fundamental principles involved are well understood in the photocopying field. The master pattern consists of a conductive base on which there is a pattern layer. The master pattern is also easily created by direct laser writing. The pattern layer receives an electrostatic charge. The master pattern is contacted by a developer containing a conductive material in the form of a powder or link and which transfers the conductive material to the pattern by electrostatic force. A substrate is then brought to a position closely adjacent to the master pattern and electrostatic force is used to deposit the particles from the pattern onto the substrate to accurately define the circuitry. The particles are then fixed by heating.<
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