There are lots of plans for PCB etchant tanks out there, and this one is no different really. I'm providing it here because it was easy, cheap, and turned out to be exactly what I needed.
Most of the pieces of this project can be purchased at your local pet store. For mine I used a 1.7 gallon plastic tank I purchased at PetSmart for about $20, though I have seen similar tanks at WalMart for under $10. It was worth the extra ten dollars for this tank for a couple of features that worked to my advantage, namely the hinged lid and curved front surface (both of which I'll discuss later on).
Step 1: Parts
The parts you will need are:
- A small plastic fish tank. Anything less than two gallon should work. Keep in mind that if you go too big then it will take a lot of echant to fill the tank, but if you go too small you will be unable to etch larger boards. The 1.7 gallon tank I used will etch boards up to 4 X 8 inches.
- A 4 to 6 inch bubble stone. Etchant works best if it is aerated and the bubble stone creates a curtain of bubbles in the tank. Note that the bubble stone shown in the picture is actually a twelve inch stone, but that in the build I changed it to a six inch one with a nice plastic base that made mounting it easier. Also, I discovered that my twelve inch tank would not hold a twelve inch bubble stone.
- Plastic tubing to connect an air pump to the bubble stone.
- An aquarium pump. You don't need a very large one. The one shown here is designed for 1 to 5 gallon tank.
- A backflow preventer. This little device keeps the etchant from crawling back down the ait tube and damaging the aquarium pump.
- Plastic canvas with the largest weave you can find.
- Plastic zip ties. You'll need six small ones and two fairly large ones.
The tools you will need are:
- A hot glue gun
- wire cutters to trim the zip ties (or the scissors will usually work for this too if you are careful).
Step 2: Installing the Bubbler
Aerated etchant is happy echant. I saw a description somewhere that explained that by aerating your tank you actually cause the copper residue from previously etched boards to magically come out of solution and somehow (also magically) evaporate off. Please don't kill me if I got this wrong, I didn't really pay close attention in science class when I was younger.
Start by hot gluing the bubble stone to the bottom center of the tank. The one I used had a nice flat plastic base on it, which made mounting easy. You could also use silicone to stick the bubbler down if you like. Super glue does not work well to bond these two types of plastic together, sorry.
Step 3: Installing the Tubing
The tubing is fairly easy to install. Simply connect the tubing to the nipple on the bubble stone and route it out through one of the holes at the top back of the tank. I highly recommend hot gluing the line to the back of the tank to keep it from floating up and into the way when you go to use it.
You'll also want to install a back flow preventer in the line between the bubbler and the pump. Fluid pressure tends to try to push some of the liquid in the tank back down the line when the pump is switched off and if the echant acid were able to make it all the way back down the line and into the pump you'd likely be out the next day buying a new pump (echant does eat metal after all).
Bubble stones work best if you soak them for an hour or two before you use them. This opens up the pores in the stones and makes it bubble more evenly. Regardless of what it says on the box, DO NOT soak the stone in water; water and acid aren't very friendly mates. Instead you can soak the bubble stone in hydrogen peroxide for the same effect. I'd do this after you get everything assembled, but if you just want to get it done and test out your bubbler (and who wouldn't) then go ahead and rummage through the medicine cabinet and pour away.
Step 4: Building the Card Holder
Obviously we need a place to put the card we plan to etch. For this we'll build a card pocket that will eventually hold our card suspended in the middle of the tank.
Step 1: Cut a piece of plastic canvas to size. Cut it the overall width you want and twice the height. I cut mine eight inches wide by ten inches high, which gave me a finished card holder size of five by eight. This will hold a four by eight card with enough wiggle room to make it easier to insert the card. The idea of this holder is to hold the card firmly in place while still allowing echant to circulate around it and you to see the card to know when it's time to take it out of the acid bath. Look for plastic canvas with really big holes to make these two tasks easier.
Step 2: Fold the the plastic canvas in half like a taco shell, but DO NOT crease the bottom. The bend in the bottom will help to hold the sleeve open enough to make it easy to slip the card in and out and for acid to circulate.
Step 3: Tie the two halves together on both sides of the plastic canvas with zip ties to form a pocket at the bottom. Go ahead and pull these nice and tight and clip the tails off. I just left the tails on mine in the picture for illustration. You want to leave the rest of the sides open so you can get the card in and out of the sleeve.
Step 4: Tie the tops of the pocket together but leave larger loops in the ties (see the last picture). You'll end up with a sort of narrow basket.
Once you have everything assembled clip the tails off of the zip ties. I also put dabs of hot glue on the ends of my top two ties just to insure they stay put and don't somehow mysteriously tighten up on me later.
Step 5: Mounting the Card Holder
As I mentioned in the introduction I found a nice aquarium with a hinged lid, which makes it simple to remove the card from the acid bath; I just open the lid and the card comes up to meet me. I also got lucky in that the lid already had pre-cut vent slots in it that i could use to tie the card pocket to the lid. You might have to drill a hole or two to mount your pocket, or buy the same tank I did and leave the drill out of this.
To mount the pocket just feed larger zip ties through the aquarium lid and connect them to the smaller loops at the top of the pocket as shown in the pictures. The pocket should hang down in the center of the tank and end up suspended just above the bubbler when you close the lid, as shown in the last picture.
I also mentioned in the introduction that the tank I chose had a curved front face. This is important for two reasons:
First, since my tank face curves inward it reduces the volume of acid needed to fill the tank (in other words this would have probably been a two gallon tank versus a 1.7 gallon one without the curved face).
More importantly, the curved face tends to magnify the contents of the tank a bit. Aquarium manufacturers do this to make it easier to see your fish, of course. You can kind of see this in the last picture, but wait until you see what it looks like with the etchant in the tank.
Step 6: Conclusion
And here's the finished etchant tank. Just fill it with your favorite metal devouring acid and enjoy! The clear acids like hydrocloric are probably best because you can better see what's going on, because they are a little less caustic than commercial board etchant, and because they are cheaper. Most recommend a mixture of one part hydrocloric, or muratic, acid to two parts hydrogen peroxide.
Other discussions I've seen also recommend heating the tank for better performance. I didn't install one, but you can find aquarium heaters fairly cheaply. Just make sure it's glass and plastic with no exposed metal parts, otherwise things might get a little interesting. Hmmm, do electricity and acid mix well?
As for other disclaimers:
- You are not supposed to store the acid in the tank because it tends to evaporate and fill the room with semi-toxic fumes, so keep the chemical bottles to store the acid when you are done. Otherwise, I suppose you could fashion a plastic cover for the tank to not have to dump the tank after each use.
- Use the tank in a well ventilated area.
- Use caution when opening the lid to avoid splashing acid onto/into body parts you might want to use later, especially the eyes. Have I mentioned yet that eye protection might be a good thing?
- Definitely don't put fish in the tank ever again.
- This tank is not intended for any other use than as stated in this instruction . . .
. . . yada, yada, yada.