Step 11: Notes on Etching
First, everyone should know is that if you go this route you need to use ferric chloride to etch the boards. I know it's nasty for the environment and a lot of people are trying not to use it, but the Mis Pro yellow ink will only work with ferric chloride as far as I know. You may ask how I figured this out and some of the images will show you how. I tried to etch my first set of boards in a mixture of hydrochloric acid and hydrogen peroxide, but the etching solution ate right through the Mis Pro ink and I ended up with those nice green boards of junk (oxidized copper) when I got frustrated and washed them off with water. Ferric chloride however does not eat away the Mis Pro ink and the etching will work as expected provided you follow the next suggestion.
Second, the thickness of the copper layer on your copper clad board is somewhat important. In the past I've used the old permanent marker drawing method and the toner transfer method of PCB etching on some copper clad that had a 2 ounce per square foot copper layer. This worked fine in the past as the permanent marker ink and the toner are a bit more robust and can withstand a longer etching process. The Mis Pro yellow ink however in my experience cannot withstand that same duration. This makes sense seeing as it wasn't necessarily designed for this purpose. The solution however is quite easy. If you choose a copper clad board with a thinner copper layer of 1 ounce per square foot the Mis Pro ink will survive the shorter etching process and give you a better PCB in the end. (If you're looking to buy PCB material check out eBay as it's a great source for bulk material at a good price. I buy from an eBay store run by the user abcfab and have gotten some good deals on some nice PCB material. The nice thing too is that you can contact him if you want a specific material (size, copper thickness, # of boards, etc.) and he'll work with you to get an order going.)
Lastly, my "Trace and Pad Test Board" was poorly designed. Yes that's a shot at myself, but I thought it was worth admitting. I realized during the etching process that there is way too much copper on that board that needs to be etched away. As such I thought about redesigning it with less open space, but then decided to stop trying to etch a nonuseable test board because I didn't want to waste more ferric chloride when I knew the process was working already. Also the Ethernet Arduino serves as much a better measure of printing and etching with this new printer modification as it will be a functional board that I can solder parts to and test traces on.
I know that those may seem like somewhat stupid or strict requirements, but they're things that worked for me and I figured I'd relay them to everyone. If you come out with results that aren't quite perfect just play with your printer settings and heat time as once I got those right things started to work a whole lot better and got some really nice results and a PCB which is ready for tinning and parts.