An acid resistant ink was printed onto the copper foil side of the board that was etched to remove the exposed copper leaving the "printed wire" behind. The plate was used to create a printing plate for an offset printing press. A drawing was made of the wiring pattern and then photographed onto a zinc plate. The patented process involved using a base material like melamine to which a layer of copper foil had been securely laminated. In 1956 the US Patent Office issued a patent for the "Process of Assembling Electrical Circuits" that was sought by a small group of scientists represented by the US Army. Copper had replaced brass as the metal of choice because of its ability to carry electrical current, relatively low cost and ease of manufacturing. That allowed circuits on both sides of the board to be connected electrically. Eventually processes were developed that would plate copper onto the walls of the drilled holes.
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