PCB bubble etch tank.
This project started out because of a need to etch circuit boards and a lack of success doing it the cheap ‘etchant in a tray’ method.
Heated bubble etch tanks were well over my budget and at five liters were also too large. As always eBay came to the rescue by providing three A4 (210 x 297) 6mm sheets of perspex and a 150 watt aquarium heater.
As you can see I divided up one sheet of perspex in to three sections. Two, two inch pieces for the sides of the tank and the remainder for the base. I used a hand held jigsaw to make the cuts, the secret is to use a very fine blade with lots of teeth and when cutting go slow and steady, don’t try to push to much.
Now the messy part starts. Glue the sides all together making sure every things clean and free of burrs first. I initially used normal silicone bathroom sealant but it wouldn’t hold the panels together (probably to smooth) so I had to clean everything up and start again. In the end I used aquarium sealant / glue, used for making fish tanks. Then clamp it all together (you might getaway with elastic bands) and leave it overnight to dry.
The etchant I use is sodium persulphate which works best when heated to between 40 to 50°C which is where the aquarium heater comes in. I had to modify the heater to reach the fish killing temperature needed as it only went up to about 35°. That was as simple as pulling of the temperature selector knob, unscrewing the holder underneath it and cutting off the plastic stop. I picked up a cheap aquarium thermometer (notice a theme here) that handily goes up to 50° so that I could fine tune the temperature.
Now to the bubbly part. I already had an aquarium air pump so I ran a length of pipe (I used medical oxygen hose as it’s a. what I had to hand and 2. allows the hose to be bent without blocking the flow.) to a piece of rigid plastic pipe. I used a hot needle to pierce holes in the pipe and held it down with some suction cups.
If you’re following along at home now is the time to fill it with water and give it a test run. For some reason after a while the bubbles were only coming out of half the pipe, but it’s still enough to keep the etchant moving around so it still does it’s job. (and anyway it was getting late and I was in a rush to etch a board) This is also a good time to adjust the heater to the required range.
Fill with etchant and your done! The capacity is approximately two and a half liters so I had to use five 100g packs of sodium persulphate.
Of coarse if you actually want to be able to use it, you’ll need some way of hanging the board in the etchant. As I only needed to etch a small board I put a couple of plastic cable ties on to a bamboo skewer and bent the bottoms up with the aid of a little heat.
And that’s all there is to it.
Epilogue
Don’t design and make all of this late at night because you’ll forget about silly little things like a lid. Sod it, cling film will do.
