PCB etching tank bubbler - Page 1
Forum section: electronics / general

author: ftransform
author_rank: Frequent Contributor
timestamp: April 22, 2012, 10:39:37 pm
content: Hi, I thought that I should make a thread about this because other people might be interested and the shoutbox does not last forever.I am building my own PCB etching chamber made of a tall 21cup Tupperware container which is highly resistant to both NaOH 10% solution and FeCl3 solution @ 40 degrees Celsius (polypropylene) . In order to heat this I am going to use a glass aquarium heater (cylindrical style)In order to feed the air into the reactor I am going to use a piece of teflon tubing. However here is where my dilemma begins, how to diffuse the air?I have seen different solutions proposed on the internet which include-Using a standard aquarium bubble stone (I don't know the chemical composition of these). I have read conflicting reviews of this method as some people claim that the stone will deteriorate quickly in the etchant.-Drilling holes in whatever material in order to create a chemically resistant bubbler. This will work but I read that it is not the optimal solution as it is difficult to get uniformity and bubbles that emerge from drill holes are just generally too big.-Using a glass fritted diffuser. This in my mind is the best solution but it is expensive. It is easy to find a "disk" style fused silica diffuser fairly cheap but since this container is rectangular I would imagine a diffuser bar would be optimal. The only place where I could find diffuser bars made of fused silica ishttp://www.aquaticeco.com/subcategories/2219/Air-Diffusers-by-Sweetwater, but I am not too keen on paying 25$ for it. Another problem I forsee is that precipitate/gunk will form in the tank and clog up my diffuser... but I never worked with etchant before so I don't know. Unclogging fritted glass usually involves dipping it in strong hot caustic solution, which decreases life of the silica as it etches away some glass... I would like a 25$ investment to last a while.-Using a rubber hose type diffuser (I read that someone had success with this method) :http://www.ebay.com/itm/180682128524?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649But again I am unsure of the chemical resistance of the rubber hose.. god knows what such cheap shit is made of.Any tips?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: April 22, 2012, 11:08:59 pm
content: It isn't that critical - rigid plastic tube with ~1mm holes drilled with PCB drill is fine. Pit holes in side or bottom, not top to reduce clogging by sediment. They will still clog eventually so make it easy to remove the tube. .

author: ftransform
author_rank: Frequent Contributor
timestamp: April 23, 2012, 12:50:39 am
content: this is horribly anticlimactic

author: IanB
author_rank: Super Contributor
timestamp: April 23, 2012, 01:06:08 am
content: To avoid clogging, remove the bubbler after use and clean it by bubbling in distilled water before storage. Don't leave parts sitting in the tank of etchant between uses. Also, don't leave the etchant itself sitting in the tank between uses. Decant it back into its bottle through a filter funnel to remove sediment, stopper the bottle, and rinse out the the tank after emptying. In short, do the stuff you learned in chemistry lessons (or should have learned)

author: ftransform
author_rank: Frequent Contributor
timestamp: April 23, 2012, 02:37:25 am
content: BTW, i am not familiar with the etching process but one website mentioned that bubbles above a certain size are incapable of "aerating" the etchant... I could not really find more information about this.

author: Spawn
author_rank: Frequent Contributor
timestamp: April 23, 2012, 02:45:55 am
content: I have a similar project runninghier, with an aquarium bubble stone. Didn’t test with any etchant yet because I am busy with building up my bench when I have time.I made this video a while ago but never posted on the forum, it is just plain water. It is a 30 minutes run (time lapsed 4:41) to stabilize the temperature with a 300Watt aquarium heater.I got two other aquarium stones now, which I posted in the first post in above topic, those will make more bubble, actually more than needed but my pump is adjustable. When I got some time left I will take a video etching with this setup. Because it is first time in this tank I have to figure out right UV light time and such so I will make couple PCB’s before I get it right and if the bubble stones are good at last test they will be okay to use I think.Quote from: ftransform on April 23, 2012, 02:37:25 amI don’t think bubble size matters, I seen a lot different videos with different bubbles and they work quite well. I mean if you do really huge bubbles like 1cm diameter the etchant will fly out your tank anyways.

author: ftransform
author_rank: Frequent Contributor
timestamp: April 23, 2012, 08:02:25 am
content: I look forward to your experiments. It will be a bit before I get enough money to buy anything. Do you know the brand of your bubble stones in case they do work well?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: April 23, 2012, 08:35:56 am
content: Quote from: IanB on April 23, 2012, 01:06:08 amThat is a bit over the top - just clean it out when you replace used-up etchant. Don't see a need to use distilled water to flush.

author: Spawn
author_rank: Frequent Contributor
timestamp: April 23, 2012, 02:55:33 pm
content: Quote from: ftransform on April 23, 2012, 08:02:25 amThe bubble stone (the round one) in the video is from a pet shop in the neighborhood, the long ones are from eBay and no name ones, I think it is just pressed and colored sand with some kind a glue so time will learn if these fall apart after long usage. I think they won’t clog easily since the bubble will push out the copper rests but it is handy to wash them when you dry store the tank.As far for the testing, unfortunately I have only at nights time and I don’t wake up people by testing, I will have to make some time, but I think I could do some testing in next couple weeks.