There was a thread on here about using ultrasonics to assist etching, but it went off topic and fizzled out. So I decided that the only way to find out if it worked was to give it a go.
I decided not to confuse things with the quality of the board exposure (I use presensitised boards) so my test boards were just 1.5cm square pieces of uncoated copper clad. I can't find the thickness of the copper (Maplin ref HX00A), but it's a comparative test so I don't suppose it matters.
I mixed up some fresh ferric chloride (with a dash of citric acid) and tried the following:
- Just a bit of sloshing in a small plastic container
- Placing the container in an ultrasonic cleaning bath (James 7050 50W) full of water.
- Using a small ziplock bag of etchant in the same bath in case the container absorbed too much of the ultrasonic
- Attaching the board to the end of a small cheap AAA battery powered electric toothbrush.
I kept the temperature around 42C. I had a thermometer, but it wasn't an accurately temperature controlled experiment.
The results:
Sloshing - half of the copper had gone around 12 minutes, all at 13:30.
Ultrasonic in container - pretty much the same
Ultrasonic in ziplock - looked like it was doing better with patterns of bubbles on the board, but pretty much the same.
Toothbrush - half by 5:00 and all by 8:00
So there you have it. The Ultrasonic bath is pretty much a waste of time. Also it's small and as the bath is stainless steel it needs to be protected from the etchant with an inner container. That reduces the working size further.
The toothbrush (Oral B pulsar - 2 for about £7) worked surprisingly well. I suspect it wouldn't make as much difference on a larger board. The small board on the end of the brush meant it could vibrate it easily. To be honest it's a good way to hold the board anyway. I cut of the bristles and drilled a hole for a cable tie.
If it had been a success my next step would have been to see how the resist stood up to ultrasonics, but there seems little point.