Since the spray painted copper clad board is not a Proofgrade material (meaning Glowforge knows about it), we'll need to enter in the settings. Since copper reflects the laser, I kept the laser at the lowest setting of 1%. I tried various speeds, but found a speed of 200 gave good results. You may need to vary the speed depending on your paint, how much was applied, etc. The important setting here is the lines per inch. Higher is better, but will obviously take longer. 'mil's are a common unit of measurement for PCB trace widths for us non-metric users. PCB trace widths are a setting when you do your PCB design, and are commonly around 10mils wide. A mil is 1/1000'th of an inch. So to get 1mil resolution, you need the glowforge to use at least 1000lpi. In my design, I used 14mil traces, so the 675lpi setting should be fine.
After engraving, the paint should be removed from the board, exposing the copper that will be removed later. There can be a bit of ash or a film still on the copper. Washing that off with plain water can speed the etching process.
Next is etching. I used Ferric Chloride, which is commonly used for etching DIY PCBs. You shouldn't touch ferric chloride, so I placed it into an old rubber maid container (so I can put the lid on it and keep it for the next project), and used tweezers to manipulate the board while it was in solution. Agitating the solution while the board is in it can help the process. It took my board about 20mins in the solution until all the exposed copper had been removed. You can remove the board and rinse it off to get a better look at any stage of the process, and put it back into the solution.
Keep in mind the point of the ferric chloride is to dissolve copper. What else is made of copper? Probably your plumbing! So don't pour it down the drain when you're finished with it!
Now all that's left is soldering!
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