I've been etching my own prototype boards for many years in a glass tray, using a griddle to heat the solution. The large horizontal area of the solution resulted in lots of fumes that were hard to avoid breathing. The boards etched unevenly (due to hotspots of the griddle) and required a lot of hand agitation (and breathing the awful acid fumes).
I decided to make a vertical etching tray with self-contained heating (aquarium heater) and agitation (aquarium aerator). As I prefer using HCl/Peroxide solution for etching, the air bubbles replenish the solution in addition to agitating it while etching. And the small surface area makes it easy to evacuate the air above it to outside.
- Small footprint, perfect for the hobbyist with a small workshop
- Fast, even etching due to better heating and agitation
- Less fumes due to smaller area during storage
- Easier to vent due to small opening on top
- Looks and sounds really cool
Safety - READ THIS AND BE SAFE
Working with toxic chemicals requires care. Always use proper precautions. Make sure the container cannot be tipped over by securing it to a wall or a properly built base. Always use appropriate ventilation equipment and do not breathe fumes from the etching solution. Use nitrile gloves rated for your chemistry.
Keep the work area dry, especially around electric outlets and extension cords. Keep the air pump and tubing in a safe dry place, preferably above the water level to avoid any possibility of siphoning the caustic solution out of the tank!
Use common sense, and remember that accidents are painful, expensive and generally preventable.
Cost and complexity
This is an easy build. It should cost well under $50 to procure the parts. It took me about an hour to put it together.
Step 1: Procure Parts
Find a suitable container
I found a perfect glass container at the local Safeway flower area. It is a flower vase, about 11" by 2", deep enough for my small boards. Look for a flat container to avoid having to fill it with gallons of etching solution.
-Pick a glass aquarium heater that fits into your vase. It should be immersed almost completely.
-Get a small air pump for aerating aquariums. A really small one will do.
-Make sure you have enough transparent tubing for your setup.
Also, get some scrap plexy (1/8" -1/4") to make a lid.
Step 2: Mount the Heater
In my design the heater is hanging from 2 C-shaped pieces of plexi that form a part of the lid for my tank. If you find it too elaborate, feel free to improvise. The idea is to keep the heater stationary at one side of the container.
My heater has a rubbery top with grooves in it. The c-shapes fit right into the grooves from either side. The bottom one just fits into the opening of the tank; the top one is bigger and forms a cap.
Note: I left a small hole to feed the air tube into the tank.
Step 3: Make the Cap
I made a cap from 2 pieces of plexi. As in the last step, the smaller piece just fits the tank, and the larger forms the stopper over the top of the tank. Use any appropriate glue to attach the pieces.
Note: Do not create an airtight seal! When air is injected from the bubbler, it has to go somewhere. Make sure it can leave the tank and direct it to your air handling system so you don't have to breathe it.
Step 4: Fabricate the Bubbler
Feel free to improvise here. The idea is to blow a curtain of bubbles, from the bottom across the entire space as evenly as possible. Try it with water first!
I found that plastic drinking straws mate with the flexible tubing perfectly. I fabricated a plexi box with lots of holes. A straw delivers air into a hole sized appropriately. The box is angled to provide an oscillating bubbling across the bottom.
Check that the straw is etchant-resistant (by dipping one into your solution for a couple of hours).
Another way to do this (not shown) is to use a straw with a flexible section. Attach the tube to the short section, bend it to form an L shape. Cap the straw with something (hot glue, clay) and poke small holes in it. Find a way to keep it on the bottom.
Step 5: Assemble and Check Your Work
Insert the heater. Insert the bubbler tube (the hole in the plexi heater cap will hold it down). Fill with water and cap for testing.
Find a way to keep your container stable. You can build a wooden base with a slit wide enough to hold your tank steady, or strap it to something. You do not want to knock it over when it's full!
Plug in the heater and the bubbler and try it out.