Jeffrey Gough from Warranty Void if Removed wanted to develop a method of printing circuit boards which was better than the current ways that a home hobbyist has available to them. He mentions the various current methods that are commonly used which are permanent marker, toner transfer, photolithography, isolation milling, UV photoplotting, laser engraving and inkjet. For his method he reverse engineered how an inkjet printer cartridge worked and made an adapter so that he could spray micro drops of molten wax out of the nozzle. The wax is sprayed onto a copper clad board, as soon as it hits the board the wax solidifies. The board with the printed wax resist is now placed in a warm etchant tank to etch away the non wax protected areas. I was thinking about what keeps the wax from melting in the warm etchant and it seems like an audience member was thinking the same thing. The answer was simple, the etchant solution is kept at a temperature slightly lower than the melting temperature of the wax.
Jeffery got the idea of printing the resist using wax after he attempted to print resist onto a flexible PCB using a thermal wax printer. I didn’t know there was such a thing but the wax transfer rolls are actually quite inexpensive. I don’t think Jeffery mentioned why he made his own instead of continuing to use the commercial printer, I am guessing the printer had a curvy paper path which allows printing onto only flexible PCBs. I wonder if it would be possible to convert a normal wax printer into one that could handle normal thickness copper clad boards, have a straight though path so that stiff boards could be sent straight though and have a method of indexing to some registration holes so that good double sided boards could be produced?
I guess even after these boards are done some drilling for vias would still be needed even if all of the parts that were used were surface mount but being able to print the resist out quickly and easily would be a great convenience.
Via: Dangerous Prototypes