Leakproof vertical etching tank - Page 1
Forum section: electronics / general

author: KL27x
author_rank: Super Contributor
timestamp: September 06, 2015, 09:18:36 pm
content: My second solvent-welded plexi etch tank died after 5 years. A few weeks ago, I decided to replace it for the last time.3 plates of plexiglass, silicone, and a plywood brace. All held in tension withnylon bolts!http://vid18.photobucket.com/albums/b103/klee27x/Vertical%20Etch%20tank_zpsi8pv5943.mp4It's way too early to tell if it's leakproof, but it rips apart for a rebuild in 5 minutes.Additional details:I use a regular "bubble wand" across the bottom. It's been at the bottom of a tank of cupric for 6 years and has never needed cleaning or replacement... because I use compressed air to run the agitation/aeration. When you get up to around 20-30 psi, an aged air wand just gives finer bubbles than before.Also, it looks like there might be some sediment in the tank, blowing around, but when the solution settles for a day, it clears right up. I think there's so much fine aeration that under operation, a copper oxide precipitates out of solution? I've seen an inch of white precipitate at the bottom of the tank, before, and it was still etching?

author: Macbeth
author_rank: Super Contributor
timestamp: September 06, 2015, 09:49:06 pm
content: I think everyone should enjoy the pleasure of etching their own boards. Everyone like me that is, with old bottles of Ferric Chloride, developer, stock of single sided PCBs, UV lamps, trays, kitchen sink, pillar drill, tiny drill bits that dull or snap instantly, laser printer, OHP film, etc. Not to mention all the tinning and stuff like that. Forget soldermask, vias, and silkscreens.Once I am done with all my old stock I never want to go back.Everyone else should use KiCad (Official tool of eevblog? - I think I saw a tweet) and send the Gerbers off to someone like dirtypcb instead.

author: KL27x
author_rank: Super Contributor
timestamp: September 06, 2015, 10:13:15 pm
content: It took me 5 years to learn how to use Eagle.I order boards from several places. In the tens, in the hundreds. I have hundreds of flex boards being manufactured as we speak!But sometimes, I still need to etch something. Last board I etched was the smallest PCB I ever made. Two components and about 0.083 square inches. >300 boards on a 6" x 8" single-sided 0.007" FR-4 panel, designed to be cut with scissors with no kerf. Check how much that will cost from China. Except you can't, because no one fabs PCB on 0.007" FR-4. They can't do it, because it curls. I can, because of something called carpet tape.So you're onto flex and flex costs, and they are high, even if you have zero drill holes, let alone thru holes, and you don't need a soldermask or silkscreen, anyhow.This pcb wasn't so much to correct a mistake, but to add some additional functionality to an existing board (professionally manufactured), with a corresponding firmware update.Ditch the ferric and the tray and the sponge.I leave my tank outside, in the elements, filled and ready to go 24/7, year round. When I need to etch a board, I toner transfer it with a laminator. Scrub board, pre-etch, rinse in water, dry with heat gun, transfer in laminator while hitting with said heat gun, use dextrin paper (I use Pulsar). It works 99% first time, and for smaller pcb's 100% of the time (you might lose one or two on the edge, once in a blue moon - IF you transfer all the way to the very edge of the copper clad; Otherwise, pretty much 100% yield in the last 40-50 boards I have done). Clip into my board holder, drop in tank, and plug in the air. The work takes 15-20 minutes and I don't stain so much as a fingernail.

author: chickenHeadKnob
author_rank: Super Contributor
timestamp: September 07, 2015, 12:11:03 am
content: Quote from: KL27x on September 06, 2015, 09:18:36 pmInteresting, do you know why your glued tanks failed? I assume they were glued with a solvent slurry based on one of the chloromethanes (mono,di,tri), because that would be my preferred method for constructing build-ups of plexi. I also assume you meant compression when you wrote tension. If tension how does that work?Thanks

author: KL27x
author_rank: Super Contributor
timestamp: September 07, 2015, 12:45:12 am
content: My last tank was made with IP #4, and I think MEK is, indeed, the main ingredient.The reason it failed was partly because it was made with only 1/8" plexi (with doubled joints and some additional bracing). I think outdoor temp swings and direct sunlight added to the challenge. It sprung a tiny leak some weeks after first filling it, although slow enough that it never dripped. It grew copper salt crystals in a couple of spots, which are annoying because I had to take stain precautions for when it rained.The reason it died is because I decided to fix the leak by lining it with a low viscosity epoxy. It fixed the leak, alright. For about 2 weeks.Well, years later, due to constant exposure to UV and acid, the epoxy lining started peeling and interfering with the function of the tank. Trying to repair a permanently welded tank that is 3/4" wide is really only practical if you have an endoscopy suite.Yes, I meant compression. I let the silicone cure free-standing to give it some tangible thickness, so there's some compression in the silicone gasket, once assembled and torqued. I gave it not much torque, at all, but it adds up over the course of 23 bolts. I got the idea after watching someone reassemble a differential gear box on Youtube.I suppose I would have had better success using thicker plexi, to begin with. I think using only 3 pieces of plexi instead of 5, and making the seams very thick, that solvent welding could work out great. But just in case, this method makes the tank completely serviceable for the cost of a box of bolts and a bit of interior volume.

author: artag
author_rank: Super Contributor
timestamp: September 07, 2015, 06:46:36 pm
content: Won't nylon bolts eventually crack when held under tension ? They'll also absorb water.

author: KL27x
author_rank: Super Contributor
timestamp: September 07, 2015, 09:12:53 pm
content: QuoteI'm not sure what good a bolt and a nut are, if they can't hold tension.Quote?? Sure, when it is windy and it rains. Besides, I would think that nylon bolts are made specifically for corrosive (e.g. wet) environments. I am way more worried about what the elements will do to the plywood brace.I let the silicone gasket cure thick as possible so that it could take up slack in case of internal stresses/swelling/torqueing/handling. So far, so good.