# My new etching tank

#### cmartinez

Joined Jan 17, 2007
7,099
In a previous post, I showed off my etching tank as part of my PCB making process.

But here's the thing: I HAVE JUST HAD IT! with the stupid thing...

My original design was made out of three layers of 1/4" thick tempered glass:

Initially, I thought that my headache was going to be finding an appropriate valve to drain the thing when the FeCl3 lost its potency after processing several PCBs... and it took me a while, but I did find it and it performed quite well.

BUT... my personal pain in the backside turned out to be the thing that I least expected to be an issue (isn't that usually the case?) I used silicone to seal the tank's edges. And after many leaks, fails and catastrophic events that did considerable corrosion damage to the tooling stored in my shop, I finally realized that FeCl3 actually attacks and eats through silicone sealant!

I tried many other sealants after that. Among them there were acrylic-based, polyurethane, and some other stuff that I can't remember. But the result was always the same: after a few days of laying in the tank, the etching solution ate through the sealant and made a mess on my work bench and on the floor. That event happened to me more than once. Trust me, finding a nasty surprise awaiting you inside your workshop after enjoying a normally nice weekend is not the ideal way of starting your mondays.

Here's another downer: I spent a few bucks buying silicon hose at Amazon, only to find out that the frigging etchant also attacks the stupid thing!

On the positive side, I had learned that the only materials I've seen that are (apparently) immune to the etchant are:
• Acrylic
• PVC
• Teflon
• BUNA-N (Nitrile)
(That last material I tested myself, placing a small o-ring in a glass covered with etchant for a few days, and seeing how the thing was unaffected.)

So here's my latest design and construction of my etching tank:

The materials I used are:
• a sheet 3/8" clear acrylic
• another sheet of 1/4" clear acrylic
• clear 1/4" PVC hose
• 1/4" diameter o-ring material (actual diameter is 0.275")
• A few 1/2"-13-UNC Hex PVC screws
• One NPT 3/8" PVC valve
• A 2-209 o-ring (11/16" I.D. 1/8" thick) to guarantee a perfect seal between the valve and the back plate.
• An aquarium double-outlet air pump.
• 1/2" PVC hose for the drain valve's output
• One plastic bucket to receive the used etchant

The front and back plates of the tank were cut in my CNC router, and afterwards several 1/2" threads were tapped in the back piece's perimeter. The front plate was similarly cut, with an equal amount of slightly larger holes (17/32") in the front plate. A NPT 3/8" thread was also tapped in the back plate, to attach the PVC drain valve.
I also cut the "U" shaped acrylic separator for the tank in the CNC router with the same holes in it, but using 1/4" thick acrylic instead.

The three layers were then assembled and bolted together. The 1/4" o-ring material and the 1/4" pvc hose were also placed between the front and back plates. I drilled six small holes (using a needle) in the PVC hose prior to assembling the thing. This is so as to have a more or less uniform bubble curtain inside the tank after the aquarium pump is turned on. But after testing it, I realized I could've gotten away with maybe up to 12 holes instead of just six.

I then replaced my old tank with my new one on my heating fixture and, voilá! ... the thing worked beautifully!

Another advantage of this new tank is that I made it smaller, so it stores considerably less etchant, and therefore its temperature raises much faster than with the previous tank.

I'm just crossing my fingers now and hope that none of the materials I used is affected (on the short term at least) by the FeCl3

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#### cmartinez

Joined Jan 17, 2007
7,099
Here are the AutoCAD 2010 drawings of my design, in case anyone here ever feels like replicating my creation.

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#### nerdegutta

Joined Dec 15, 2009
2,676
Great! Thanks for sharing. Several years ago, I made an agitator. With no possibility to heat the FeCl. Now I put this setup on my to-do list.

#### cmartinez

Joined Jan 17, 2007
7,099
Great! Thanks for sharing. Several years ago, I made an agitator. With no possibility to heat the FeCl. Now I put this setup on my to-do list.

Heating the etchant (recommended temp is 50°C) makes all the difference. You go from a +25 min process to one lasting only about 7 minutes!

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#### #12

Joined Nov 30, 2010
18,210
I had learned that the only materials I've seen that are (apparently) immune to the etchant are:
• Acrylic
• PVC
• Teflon
• BUNA-N (Nitrile)
Aha! That's why I got away with using a Teflon coated baking pan!

I'm afraid to set it up as something, "permanent". Everybody should know a Teflon cooking pan has a very thin coating, but it worked for 3 boards.

#### cmartinez

Joined Jan 17, 2007
7,099
Aha! That's why I got away with using a Teflon coated baking pan!

I'm afraid to set it up as something, "permanent". Everybody should know a Teflon cooking pan has a very thin coating, but it worked for 3 boards.
Mhhh.... if you used a chinese teflon coated pan, then it was around = $1.00 dlls per board.... BUT if you used a Cuisinart teflon coated pan you ended up paying >=$19.00 dlls per board...
Perhaps we should take this conversation to the Economics Forum instead... wait... there is NO Economics Forum in this place!

#### #12

Joined Nov 30, 2010
18,210
if you used a Cuisinart teflon coated pan you ended up paying >= \$19.00 dlls per board...
Who said I threw the pan in the trash? I still have it! Besides that, I found it for free when I moved into this house. If it ever starts fizzing and bubbling, I will know it's shot, but that hasn't happened yet.

Even if it does die, it will continue being the place where I store my etching supplies.

#### cmartinez

Joined Jan 17, 2007
7,099
Hey... I forgot to include the pic of the plastic bucket I use to receive the discarded etchant:

#### cmartinez

Joined Jan 17, 2007
7,099
I still have it!
ugghhh... please don't ever invite me over for breakfast ... let's go to an iHop instead, or something...

#### Lestraveled

Joined May 19, 2014
1,946
C
That is a beautiful piece of work. You are a fine craftsman.

#### cmartinez

Joined Jan 17, 2007
7,099
C
That is a beautiful piece of work. You are a fine craftsman.
That's it??? No medal awarded???

Seriously now. Thanks, man. Coming from you that's a great compliment.

#### GopherT

Joined Nov 23, 2012
8,012
And a few more:
@Wendy, @GopherT (I'd love to hear your opinion on proper sealants), @OBW0549, @JohnCase and @MITCH electronics
To etch my boards, I pour about 10 - 20 ml of water into a plastic tray that I saved from the last time I bought cold cuts. Then i add 30 to 50 ml of concentrated ferric chloride solution to the dish. I grab a makeup removing sponge from a bag that I stole from my wife. Then I put on some rubber gloves and I gently wipe the solution around the board one direction - then another - then another. After about 8 - 10 minutes I am through the copper (usually starts in the center) and then I just focus on the edges until clear. Usually done and cleaned up in about 15 minutes. I pour the extra solution over some news paper in the bottom of a five gallon plastic bucket and let it dry.

I clean my wash tub a couple of times per year with iron out.

I am not sure how well it works with the toner transfer method but it works great with photo method.

I have no idea which sealant to use.

#### Wendy

Joined Mar 24, 2008
22,165
I don't know which sealant to use either. I would probably try RTV (silicon rubber or silicon calk).

#### sirch2

Joined Jan 21, 2013
1,026
Great job, thanks for posting. It's something I've been considering making for years but time making a tank is time I'm not doing something else.

Just one question, do you do double sided boards in it? I ask because I note you have it mounted on a slope.

#### OBW0549

Joined Mar 2, 2015
3,551
Beautiful work, there!

#### cmartinez

Joined Jan 17, 2007
7,099
I don't know which sealant to use either. I would probably try RTV (silicon rubber or silicon calk).
I tried both... neither worked

#### cmartinez

Joined Jan 17, 2007
7,099
... do you do double sided boards in it? I ask because I note you have it mounted on a slope.
Yes, the tank is tilted for three reasons: it makes it easier to pour the etchant in it, the printed side of the board is always facing up (and therefore is exposed the most to the FeCl3), and also that side is always kept away from touching the glass, thereby minimizing the (extremely unlikely) possibility of scratching the print.
I've never done two sided boards. I tried once, but I found it extremely difficult to align both prints properly. I simply use jumpers instead. That was years ago. But now that I know much more about the process, I might give it a try one more time, see how it works out.

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#### sirch2

Joined Jan 21, 2013
1,026
I agree that alignment is a major pain however the few times I have done it I put extra pads in opposite corners of the layout, stuck one side of the layout to the PCB, drilled the smallest hole possible (0.3mm in my case) through the centre of the alignment pads, put needles though the holes and then aligned the layout for the other side on the needles. It wasn't spot on but it was good enough for things like 0.1" pitch PCB headers.