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Multilayer boards development. The American Tinkertoy and Micromodule programmes had shown that layers of etched circuits could be built up to provide a complete unit, and high densities could be achieved. The Hazeltine Corporation in America perfected a technique in which three or more layers with coincident holes were bonded together with insulating sheets and the layers connected through by using the existing plated‐through hole technique. Their ‘Multiplanar’ process was disclosed in 1961, and is the only accepted method of making multilayer boards today, and the one on which all existing specifications are based.

he development of printed circuit technology is almost inseparable from the development of materials. Copper clad laminates could be said to have started with the discovery of phenolic resins by Dr Leo Baekeland in 1909. He found that by using catalysts he could control the speed and extent of the reaction of phenol with formaldehyde, suspending the reaction at any time to add reinforcements. Using resins in a liquid form he was able to combine them with wood cloth, paper or fibre to build an insulating material.

This study reviews the development of printed circuit technology from its origins before the Second World War until the present day. Various inventions appeared before the war for producing circuits on a flat surface, but it was not until Dr Paul Eisler had the idea of utilising the long established arts of the printing industry that viable methods of production were established. Stimulated by the release of an American official secret of the use of a printed circuit in a proximity fuse, and the first Technical Symposium in 1947, government and industries researched into the best ways of producing planar circuits. Dr Eisler's etched foil method emerged as the most practical technique. The first decade of the technology was spent learning and refining print and etch techniques, during which time printed circuits gradually became accepted by the consumer industry, as well as by industry and government bodies. Most of the major advances were made during the second decade, such as plated‐through hole, multilayer and additive processes. Since then manufacturing technique has been consolidated and refined, affected by the continuing demands of the electronics industry for increasing miniaturisation and packaging densities.