I swore I'd never waste another minute making my own PCBs, but this seemed like such a good idea. Namely, spray a bare copper-clad board with paint, lacquer, or what-not, use a laser engraver to etch away all but the areas you want protected, then etch the board in the usual way. It eliminates the intermediate photo-tools and should provide micron-perfect resolution. Boy, was I in for a lesson!
First of all, not every spray-on aspiring resist etches away with a laser. When most are vaporized by the CO2
laser, the fumes redeposit on the newly-exposed copper, rendering it impervious to the etch bath. This rogue's gallery of resist pretenders includes black spray paint, aerosol lacquer, clear acrylic coating, and sprayed silicone conformal coating. This problem arose engraving top-down or bottom-up, air curtain on or off. Furniture wax had the opposite problem: the etchant attacked it immediately. The only coating I found that worked was MINWAX Fast-Drying Polyurethane (Clear Gloss) finish. It removed easily at a low-power setting and maximum speed, and its vapors left no residue.
As to etchant, I tried both ferric chloride (messy!) and HCl+H2
(muratic acid and hydrogen peroxide). I had better results with the latter, although it took forever
to etch a board with 3% H2
. Moreover, I had to increase my minimum trace width to 0.020" just to keep traces intact. But I was finally able to produce appears to be a workable board:
It's a 74HCT595+transistor drive+RGB LED illuminator for a project I'm working on. We'll see if it works. But first I have to clean, drill, paste, and solder it (and strengthen a couple over-etched traces).
Ugh! I could have had cheap, factory-produced boards in hand
in the time it took to do this. I swear I'll never waste another minute making my own PCBs! Anyone who thinks it's a good idea is just nuts!
Perfection is achieved not when there is nothing more to add, but when there is nothing left to take away. -Antoine de Saint-Exupery