Recently I got into PCB making. Some people use laser toner and iron method, I use photo resist film and UV lamp. But no matter what method you use, there is one common step - etching. You drop your PCB into chemical solution and it eats extra copper, leaving only the parts you need intact.
Key to successful etching is uniformity. Each part of your board needs to be equally exposed to chemicals - otherwise, some won't be ready, while others will be already destroyed.
Of course, you can watch entire process and correct it, yet it is boring.
There are commercial solutions - for example, this etching tank from Vellemann does great job but costs whopping £75.00 and needs 1.5L of liquid. That's a no-go for a typical hobbyist. We need something small, practical and cheap.
Here, I present you with a etching tank that fits 100x150mm boards and takes only 90ml of liquid. Since it connects to air pump, it allows to etch large PCB in just 4 minutes.
Step 1: Laser-cut the 2mm Acrylic Sheet and Assemble
You will need the following:
- about 30cm of thin silicone tube for aquariums (d=6mm),
- used aquarium air pump,
- a needle,
- few M3x16 bolts and nuts
- some acrylic glue (I used solvent with some discarded acrylic pieces dissolved in it)
- and access to acrylic laser cutter.
I ordered 2mm acrylic sheet cut in a local advertising firm that does outdoor signs. Total cost, including material, was less than $10.
Warning - acrylic is usually cut with the protective film still on. You will need to get rid of that before gluing.
The layouts in AutoCAD DWG and DXF formats are on GitHub.
After you'd get the parts, assemble them without gluing - just with M3 bolts. Don't tighten them - they are needed to align the acrylic "sandwich", not to hold it. Then use the needle to lead round the shape of the middle section on the outer layers. These marks will help you to apply glue only where needed.
Step 2: Gluing It All Together
Take the outer layer and insert M3 bolts with washers in it. Apply glue and install the second layer of the "sandwich". Let it dry and install the third layer.
Then insert the silicone tube. Make sure that the other end of it is shut closed (cut a tiny piece of tube and cram it into the end). Fix the tube with extra glue.
Once it holds, use the needle to make a series of holes in it. Place them 2mm apart.
Finally, attach the last layer of the "sandwich" and add legs to hold the tank vertically
There is also a lid that also gets assembled from 4 layers of acrylic. Assemble it as well - you will need one to prevent splashes.
Note: don't overtighten the bolts, since that will cause the thin acrylic to crack! Remember, bolts are for aligning the layers of the "sandwich" and it is glue that holds them together, not bolts.
Step 3: Testing It
After the glue sets, fill the tank with water and check that it doesn't leak. Attach air pump and see how the air bubbles make the water mix.
Fill the tank with etching solution, for example, with ferric chloride or a mix of hydrogen peroxide + citric acid + kitchen salt. You'd need just 90ml (half a cup!) of that. Hang up the PCB on a string in the middle of the tank and close the lid. Turn up the air pump and see through the glass how your board gets uniformly etched.
I hope this little device will help you make great looking PCBs with perfect and thin connectors in shorter time and with less effort. Good luck!