Printed Circuits—Origins and Development

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.