I finally built a simple bubble etching tank; I’ve seen people with them all over the place in the past, but I just haven’t had the desire to put one together until today. In the past, I’ve been etching my PCBs by just filling a pyrex tray with etchant, dropping the masked board in and manually agitating with a foam brush.
This new piece of equipment has these advantages:
- Less etchant required; the vertical tank takes up less volume and thus it is more space efficient.
- Air agitation; the bubbles oxidize the etchant, which allows it to more effectively etch away copper. It also creates turbulence in the liquid that helps etch very small areas.
- Less manual interaction; the acid in the etchant is toxic stuff, and I really need to be more careful than I have been in the past.
The tank is made from some pieces of spare acrylic sheet I had, which are put together with acrylic cement and the outsides of the joints are reinforced with hot glue (just in case). I had an old aquarium air pump around and carefully hot-glued the end of the tube across the bottom of the tank through some holes drilled into the edges; I then carefully poked holes into the tube using some very small-diameter drill bits. Of course, I tested it with water before trying it with the cupric chloride etchant seen in the photos.
I found that there were a lot of droplets splashing out of the tank, so I made a small lid with a spare IC storage tube. The whole construction took a total of two hours.
UPDATE: I put together a small, adjustable acrylic rig to top the tank and hold the part being etched in place.
The green top is a piece of junk acrylic sheet that I found and drilled a series of holes into. The sticks are 1/8″ squared acrylic rods pieced into an edge and covered in double-sided tape (for some extra tackiness); the ends that meet the green top piece are sanded down to round pegs that compression-fit into the holes, which allows the spacing to be adjusted for any size board that may fit in the tank. Small holes are drilled in the pegs so that small screws can be set as an added safety measure should the weight of the board cause the peg to slip, but I’ve found that it isn’t really necessary (maybe for larger boards). In fact, the actual problem is that even the thicker (3.175mm) boards I am etching for my microwave antenna array project are able to fall off the holding rods and down to the bottom of the tank if I am not careful.
So far, the whole setup seems to work well for both developing photoresist (why didn’t I think of that initially?!) and etching boards. The only complaint I have right now is the uneven bubble cover; if the board is not moved around occasionally, the parts in the path of the heavier bubble streams etch faster than the less-covered areas. Etch times for cupric chloride etchant seem to be about 15 minutes for 1/2-oz copper and up to 90 minutes for 2-oz copper (ugh).