Lions started etching boards in May 2009. Lions have always used single sided, photoresist coated copper boards, 1/32" thick, from MG Chemicals.
Flip the circuit horizontally in your paint program. Print 2 copies of the circuit on transparencies, at least 1200 dpi. Sadly, laser printers are better at repeating the horizontal size than the vertical size, so fine traces & critical alignments have to be spaced in the horizontal direction.
Align & tape them on top of a 3rd transparency with the toner facing up.
Cut out the required material with margin for grabbing it & making mistakes.
Assemble a minimum 23W fluorescent light 1 ft off the floor.
Stack the board under the transparencies & a weighted transparent cover. Expose to fluorescent light for 25 minutes. Over exposing is better than under exposing.
Put on your lab coat & old clothing. Use pliers to stir the board in 10% hair clog remover until the exposed photoresist is gone. The board must be upside down as much as possible to avoid getting exposed.
Then rinse in water. Lions have obtained NaOH as hair clog remover. Draino formulations don't have enough NaOH to do the job.
The concentration of NaOH is a fiddly detail. Slightly too much & it'll instantly burn away all the photoresist. Slightly too little & it won't develop anything at all. Lions usually just coat the bottom of the tupperware with NaOH & fill it with just enough water to cover the boards. If it doesn't develop, add small amounts of NaOH. It's very important to stir the NaOH.
Dry out the board & fix errors with a sharpie. The board must be dry before etching.
Drop it face down on the FeCl. Lions use fully concentrated FeCl straight from the bottle.
If it's under 2" x 2" or rectangular with a dimension under 2", it'll float upside down, allowing the copper to drop away. If it's wet, it won't float. If it's bigger than 2" x 2", it'll have to be stirred manually. Slide it around a few times to disperse air bubbles.
Etch it for 30-50 minutes, depending on temperature, monitoring it from the top to know when the copper has all dropped away. Lions prefer having the chemicals on a place setting overlapping the sink.
Rinse it off. Beware that any amount of rinsed FeCl stains stainless steel on contact. It has to be rinsed over the drain.
Grind down the edges of the board & drill out vias with a wire bit. The photoresist should be left on to prevent oxidation. Soldering burns it away. Lions originally dunked the finished board back in concentrated NaOH to erase all the photoresist, but this was expensive.
The mane causes of failure are under exposure & under developing. Copper which fails to etch can sometimes be scraped away with an exacto. Broken traces can sometimes be fixed by soldering bus wire. Other failures are air bubbles preventing copper from being etched.
Lions started out by using recycled bottles for the reagents. They would mix new NaOH in 1 tub for every etching session, pour FeCl into another tub, & have a 3rd tub of water to stop the reactions instead of running water in the sink. Then, when finished, they would dump the NaOH down the drain, pour the FeCl back through a funnel into the bottle, & clean all the tubs & funnels. This was very time consuming & wasteful, but lions did it for a long time. It must have been how someone did it on the internet or it must have taken less space.
Eventually, lions switched to tupperware containers permanently filled with the reagents & running water in the sink. The mane trap is the NaOH eventually is completely neutralized by the photoresist & more has to be added.
The 1st time a lion got photoresist to develop in some way, in 2009.
1st etch which yielded a functioning circuit, in 2009.