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

Two new technologies are described to manufacture bare circuit boards. Both methods are dry processes and are additive by nature. The above technologies have advantages over the current methods used to produce circuit boards and will alleviate the total dependency on wet chemical processing by the industry. The first technology is a process whereby circuit runs are written directly on to the substrate from a CAD/CAM database. There is no need for artwork to be generated so that flexibility is increased at the design stage. A circuit board is manufactured by coating it with a film of heat actuable adhesive to a substrate and depositing on the film a layer of conductive powder. The powder and film are then fused by the heat provided by laser radiation to define the circuitry. The excess unfused powder is then removed and the substrate fired to achieve final curing and bonding of the conductive runs to the substrate. The second technology is directed towards higher volume production and requires the use of a master pattern. The fundamental principles involved are well understood in the photocopying field. The technology has exciting potential for circuit board production due to the high reproduction rates which are possible. The master pattern consists of a conductive base upon which there is a pattern layer. A coating can be applied to the conductive particles to enable them to accept an electrostatic charge. The master pattern is also easily created by direct laser writing as described previously. 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 ink 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 on to the substrate to accurately define the circuitry. The particles are then fixed by heating which also dissipates the electrostatic charges. Multiple layer circuit boards can be built up by depositing complete layers of non-conductive material.