Hi Jan,

How many points are you giving for techniques that worked, but never became popular to begin with?

I saw a demo once of a PWB prototyping machine that dispensed conductive paste enveloped in an insulating paste. Think of tooth paste coming out of a tube with a conductive core coaxial to an insulating outer layer. The machine then placed the paste "traces," extruding a bit of extra conductor at the ends to form "pads." Multiple layers weren't needed because, like wire wrap, the "traces" could just be laid across each other. If memory serves, the paste traces then had to be oven cured before assembly. The unwieldy nature of the process notwithstanding, there were other reasons that it never caught on. I seem to recall complaints about the geometry of the prototype traces were just too dissimilar from normal etched traces to be an adequate model for high speed/digital circuits. But mainly the pitch of electronics rapidly exceeded the limit of the technology. Past a certain pitch, the paste just became a mess.

Anther technique that I read about was plating. It was intended as a production technique, not a prototyping technique, so I never saw it first hand. Instead of etching away unwanted copper, traces were formed by plating up where they were desired. I'm not certain, but I believe the idea was to eliminate much of the hazardous material associated with the etching process. In any case and as my memory goes, it took far too much time to produce a board and never caught on.

Joe