Ok, so we’ve got a masked board ready to etch.
Let’s get out our chemicals and make some etchant!
My first boards I used 1:1 vinegar and hydrogen peroxide with a pinch of salt. It works. But it’s slow. I then switched to 1:1 HCL and H2O2 which worked much better…and after doing some more research I settled on 1:2 HCL:H2O2 which is what I now use.
Remember - always add acid to water - or in this case H2O2.
To start - fill your bigger container with water and toss it in the microwave for about 2 minutes. This will be a water bath we’ll float our etching tank in to heat it and help it work quicker.
Then take the shot glass and measure 2 shots (about 3oz) of H2O2 into the bottom of your smaller disposable tray. Now it’s time to glove up and measure out 1 shot (1.5oz) of HCL and add it to the H2O2. Finally float this little tray in the big tray of warmed water:
And in goes your board!
After a few seconds you’ll probably (hopefully) notice some of the exposed copper starting to darken:
At this point I start gently wiping the board with another foam brush (not the same one from before!) You can just let the board sit…but it will take longer. Instead I keep wiping it to remove the dissolved copper and expose fresh. If you let it just sit it will quickly darken more and more - as copper dissolves into the solution it actually makes it strong and more efficient at etching:
You’ll also note the solution start to turn green as the copper dissolves into it.
After just a few minutes of this with gentle wiping all exposed copper will be dissolved:
If you had more exposed copper your solution will be more green. Usually it gets almost as dark as simple green - this board just didn’t have a whole lot of exposed copper to etch.
Once all of the exposed copper is etched pull your board out and rinse it clean with fresh water. Note - do not do this in a stainless steel sink - this etchant is strong stuff and will attack the sink.
Heck - I made the mistake of just storing my jug of HCL in my outside SS sink 2 years ago when I noticed the jug was starting to crack. Big mistake:
Looks like I get to replace the sink when I redo my countertops now 
And yes…that’s a 2 year old gallon jug of HCL which is cracked and leaking. I need to move it into a better container ASAP.
Speaking of containers. What to do with the etchant when you’re done?
Well…you can store and re-use it if you plan on doing more boards. Just keep it in an airtight plastic bottle and you should be good. If it starts to get weaker you can either bubble some air through it with an aquarium pump or add another shot of H2O2 and perk it back up. If you’re particularly analytical you can measure the specific gravity and do some titrations and determine just how much more copper to dissolve in it and oxygen to add…but…we’re hobbyists and this is a pretty forgiving process so unless you enjoy that kind of thing you don’t have to do that.
When you are ready to get rid of it…you have a few options. The solution is cupric chloride…which is many areas is sold in solid form as a root destroyer for drains. So…just dumping it down the drain with some water isn’t as bad of an option as you may initially think. Still - it’s not the best habit to get into tossing chemicals down the drain.
One solution is to add plaster of paris and turn it into a solid which you can then toss in the trash. I haven’t tried this option because I live in the desert so evaporation is an easy solution for me. I just set the tray out side with a screen over it to keep critters out and in about two days I’m left with just some green crystals. These can either be tossed into a campfire (preferably one you’re NOT cooking over) to make some pretty colored flames…or tossed in the trash.
So - with the board out of the etch and washed off it should now look like this:
We’re almost there! Next we need to get that mask off to expose our copper.
For this you’re going to re-use your developer from when you made the mask. Toss the tray with it in it into your microwave and give it 2 minutes. That should get it good and really hot. Then add 1 heaping tsp of additional washing soda so you’ve got a really strong and hot solution. Then dunk the board in.
You can wipe it at this point to help speed this up…but it’s still going to be one of the slowest parts of the process. I usually just walk away for 10-15 minutes. Then come back and give it a brush…it may be all the mask came off at this point. If it didn’t then I usually nuke the solution for another minute after brushing off as much loose mask as possible then put it back in. I’ve had some boards strip clean in 10 minutes and others still have some mask clinging to them after 45.
You can also use acetone to remove the mask…but I’ve found that’s trickier and still takes a good soak and I don’t have any trays I can fill with acetone (acetone will destroy most plastics) and who really wants a tray of acetone sitting out stinking up the kitchen anyway. If the mask seems particularly tough then while re-heating the developer I will sometimes give the mask a gentle scrub with a blue scotch brite pad and a bit of acetone to help weaken it and help the developer finish it off.
Once the mask is stripped you’ve got a board!
Now is the time to bust out your magnifier and continuity meter and check out your work. Make sure all the traces that should connect have continuity and none of them short to ground or each other. If it’s not perfect you may be able to save it. If there are shorts you can get out a razor blade and cut through them. If there are breaks you can use a little bit of cut off component lead and solder it across to repair it.
My first few boards I had to do quite a bit of that. Since I got the printing process dialed in to make a good negative and got my exposure dialed in I haven’t had to deal with it and just get boards that work…assuming the circuit itself is designed correctly 
If you’re doing a SMD board you’re now done. Go solder down your devices and enjoy. If you’re building through hole…then there’s one more step. Drilling.
Drilling sucks. It’s my least favorite part of the process. It’s fiddly and if you mess up it can be hard to repair the mistake. So let’s take our time and go slow here. First off…one more thing you need that I forgot to add to the list:
PCB drills. These are really easy to break…but thankfully they’re also cheap. I got 5 sets of 10 sizes for $18 off Amazon: https://www.amazon.com/gp/product/B07S636JHY/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 You can also get them off aliexpress, banggood, ebay and other places for equally low prices.
For most components you’ll want the 0.8mm drill which is the one with the orange ring in that photo. Some things are spec’d for 0.7mm but unless they have really small pads I usually just drill them as 0.8 anyway. You’re going to want to start with the smallest size and work up - you can always make holes bigger but its incredibly difficult to make them smaller. On things like IC’s, headers, and IDC sockets it can help to use a larger 0.9 or 1mm bit so there’s extra wiggle room. (plus some of them have wider pins that call for a larger hole.)
I’ve used three different methods to drill
- By hand. A pin vise makes this a lot easier but I couldn’t find mine so my first board I did the absolute hardest way possible. I just held the drill bit in my fingers and did it by hand. I used one hand to steady the board and hold the bit in place putting gentle pressure it the back of the bit, and with the other hand I grabbed the ring on the bit and twirled it back and forth between my fingers. This actually works. On the plus side it’s the easiest way to be super accurate with your hole positioning. On the downside…it’s slow…your fingers will get sore…and the fiberglass dust is itchy.
Note - Any of these methods will create fiberglass dust. Which is BAD stuff. You do NOT want to get it in your lungs. You could drill under water to keep down the dust - but that raises it’s own set of issues. Thankfully we probably all have facemasks available now. But I use an actual respirator because I have one and would rather be safe than sorry. Usually a decent respirator with replaceable filters is pretty cheap. I paid $17 for mine and love it. I use it while doing yard work to keep the dust out of my mouth and nose, I use it when woodworking or painting, I use it when working with my 3D resin printers…it’s comfortable and has interchangeable filters so I can use a particle filters in the yard and woodshoop and switch to charcoal vapor filters when working with chemicals. Unfortunately right now due to COVID they’re more expensive and harder to find
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Drill press. I have a “small” benchtop drill press. I used this for my next few boards. It works…but it’s not ideal. Even on it’s fastest speed it’s not really fast enough for these little bits. It’s accurate…but at these sizes not quite as accurate as I’d like. It’s also loud and sits at a height that’s too low to use while standing but too high to use comfortably while sitting. It works…but I wanted something better.
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DIY micro drill press. So I bought a cheap micro drill motor off Amazon (https://www.amazon.com/gp/product/B06XGQ24PS/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1) (yes, my mailman is getting really tired of my Amazon habit) and 3D printed a drill press around it:
It’s not bad. But it’s also not great. I’m working on improving it. The original design is here: https://www.thingiverse.com/thing:1444938
My upgrades are here: https://www.thingiverse.com/thing:4633213 I basically redrew almost the whole thing. I added bearings on the shaft, made it a few mm taller to fit the smooth shafts I found on (you guessed it) Amazon, added some extra bolts to keep the top on better, added threads to the handle so you just screw the rod in, snugged up some of the clearances, added a hook on the side to hold the chuck key…little things. I still need to redo the motor mount and bearing carrrier. The motor mount because it’s kind of a pain to install and just threads into the plastic of the bearing carrier (I want to add some nut traps) and the bearing carrier because the bearings fit too loose and cause some slop - which is my biggest complaint about it as that makes it hard to get accurate holes.
Anyway…with either drill press a lighted magnifier REALLY helps:
If you do your own design in kicad (or work from an existing kicad design) you can choose “small drill marks” when generating the negative. The nice thing about those is they act kind of like a center punch mark to help center the drill. Just go slow and as the tip of the bit meets the board it will pull the board into position…then hold the board well and pull the bit in.
When you’re done a bit of backlight will help you check for missing holes:
Well, in theory it will. I still missed two holes that I didn’t notice until I went to install the components in them. Can you spot them?
Now…you’ve got a usable board! Break out the soldering iron and:
If it’s a proven board design you should be in business.
If it’s your own design…and it doesn’t work…now comes the fun part 
A few cuts with an xacto and a few bits of 30awg wire can work wonders for fixing circuit design errors:
Oh - and that messy area just under where I did the re-work? That one trace was just a little iffy so I chose to reinforce it with some component lead…but I got a bit of solder on the ground plane. Doesn’t hurt anything but does make it a bit messy looking.
Two big things to watch out for assembling these self-etched boards:
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You don’t have a solder mask (you can though…I’ll do a post on that later) so be careful of creating solder bridges…it’s a lot easier than it is with a solder masked board.
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You don’t have a silkscreen. So you have to be a lot more careful placing components. There’s a nice plugin for Kicad that will generate an interactive BOM that helps a lot:
When you select a row from the BOM on the left it will highlight the components on the board layout. You can then check them off to track your assembly process. Very nice and super helpful when you don’t have a silkscreen to help you along!
But…you could have a silkscreen. I’ll follow up later with a few options on that.
For now I need to get back to work. So updates later tonight on how to do silkscreen and solder mask. Details on how to build the exposure rig, how to get good negative prints, and how to dial in your exposure coming soon!