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August 2014 • The PCB Magazine 15 mated wire "stitching" (one well-known trade name is "Multiwire") and variations on the sub- tractive techniques. The simplest, and to some, the most obvious early solution involved depositing a conductive material where it was needed: to connect the elements of a circuit into some useful assembly. The various alternative methods of depositing conductive materials on an insulator eventu- ally yielded what is believed to be the first high- volume production examples of printed circuits during World War II. An alternative method generally credited to Paul Eisler involved depositing a chemically re- sistant ink (resist) on a copper-foil-clad insulat- ing sheet in a pattern that would eventually con- nect component parts as wires would have in the past. Thus prepared, the sheet was immersed in a solution that dissolves copper etchant, leaving the protected copper in place. The resist could then be removed with solvent, component leads inserted in holes drilled "in board" and then sol- dered to the copper conductors. 1950–2000: Printed Electronics— the Path not Taken Improvements in the placement of the re- sist, methods developed to electrically con- nect electrical conductors on stacks of layered circuits (multilayers), meant that printed elec- tronics (i.e., depositing an electrically conduc- tive paste on an insulating substrate) could not economically meet the speed, miniaturized fea- tures, and precise size and positioning required in the rapidly developing electronics industry, given the technologies of the day. Thus, for the second half of the 20 th century, printed electronics was a minor player in the PRINTED ELECTRONICS 2014: WORLD STANDARDIzATION EFFORT continues figure 2: subtractive process multilayer printed wiring board production sequence.