Pump motor to circulate Ferric Chloride etchant?

xanatos · 2013-02-04 10:24

Anybody know of a good small volume little pump that has NO metal part contact in the liquid paths, that would be suitable for pumping Ferric Chloride etchant - a recirculator to offload the tedious task of rocking my etch tank for 15 minutes per board...

Thanks!

Dave

erco · 2013-02-04 10:34

A peristaltic pump might work if the flowrate is high enough for your needs. Nothing touches the fluid but surgical tubing or silicon tubing.

http://en.wikipedia.org/wiki/Peristaltic_pump

http://www.ebay.com/itm/Aquarium-Peristaltic-dosing-pump-Head-Marine-Magic-/281056002421?pt=LH_DefaultDomain_0&hash=item41703e4175

erco · 2013-02-04 10:36

Here's a magnetic coupled pump, but stainless & brass: http://www.ebay.com/itm/Refurbish-Speck-MY2-8000-magnetic-coupled-pump-GERMANY-/250778497839?pt=BI_Pumps&hash=item3a6390332f

You might find an all-plastic unit.

Beau Schwabe · 2013-02-04 10:41

Even vinyl tubing is no match for Ferric Chloride over a short time ... aka "liquid rust"

I have had best results with an upright bubbler to agitate the Ferric Chloride, rather than try to pump it. This way a simple air pump attached to an expendable/replaceable piece of vinyl tuning.

PJAllen · 2013-02-04 10:58

Make something that will rock your etch tank.
Use a hinge for a pivot, a cam mounted on a slow-turning motor beneath raises and lowers the tank (sort of like a wave machine.)

Lawson · 2013-02-04 11:10

or use a magnetic stirrer?

Lawson

Leon · 2013-02-04 11:35

I etch my boards with ferric chloride in a small container placed in a larger container with very hot water in it, by rocking it continuously. It takes under 5 minutes.

Morris · 2013-02-04 14:14

I use a lab rocker, but I only have access to this very overpriced (>$500) machine due to my affiliation (and occasional duties) at a local research department. If you don't feel like improvising such a thing, an aquarium air pump might be your thing. It's much easier to pump air, after all, than it is to pump corrosive etchant.

jrjr. · 2013-02-04 16:06

I had a nice setup for that long ago, a windshield wiper pump (on one end) on a hinge base (the other end).

You can use glass pyrex baking dishes on it of suitable size. Heat lamp hung above it.

Variable 12 volt supply running at ~ 4 V.

Be careful of the fumes, it rusts (or corrodes) anything near it severely, bolts, nuts, cabinets, the dog.

Some kind of venting is needed, dryer vent tubing (not aluminum) with plastic fan etc;

A few nylon screws keeps the board out of the 'mud' (you'll see).

Air sparging does work.

jack

xanatos · 2013-02-04 16:58

Thanks guys. I've been etching since I was a kid - that was a LONG time ago... and I've never, ever, bothered to do anything but a cold etch and rocking the tray. But then again, I rarely had to make more than one PC board a month, if that. Now I'm making 5 or so a month, and I've decided to finally do something about the process.

I considered air sparging but in order to etch some of the boards it seems like I'd need a LOT more etchant to have a board vertical, unless I found a very tall and thin, but wide-enough, clear plastic tank... :-) Right now I just cover the board in a tray only about an inch wider than the board on all sides, and to a depth of about 3/8" - if that - so I don't use much etchant...

Which I guess brings up another question I should have asked 30 years ago - how much copper do you REALLY get out of a given quantity of etchant? If I etch a 4" x 6" board as described above, cold, rocked, it takes about 15 minutes for the first board. If I reuse the same etchant for a second board, it can take almost half an hour, so I rarely reuse etchant, preferring instead to use fresh etch for each board. Is there some trick to keeping the etchant functional for longer?

Lastly - if I do choose to heat the etchant, what do you folks find to be a good temp?

Thanks for the thoughts...

Dave

xanatos · 2013-02-04 17:04

jrjr. wrote: »

Be careful of the fumes, it rusts (or corrodes) anything near it severely, bolts, nuts, cabinets, the dog.

Beau Schwabe (Parallax) wrote: »

Even vinyl tubing is no match for Ferric Chloride over a short time ... aka "liquid rust"

I spilled a tub full of the stuff on a beige suit I once owned. While wearing it I might add. Anyway, by the time I got home, I rinsed the hell out of it with a hose, then threw it in the wash. The material had already decomposed significantly - you could feel the difference. So I put it in the give-away pile with a frown...

Two weeks later I went to bag up the give away collection. The material had almost completely disintegrated everywhere the etchant had spilled.

Fortunately the leg fared better! :-) 20 years and not even a stain! :-)

Dave

ElectricAye · 2013-02-04 18:28

erco wrote: »

A peristaltic pump might work...

Here's a fairly decent resource for chemical and material compatibility:

http://www.coleparmer.com/Chemical-Resistance

garyg · 2013-02-04 19:59

If you decide to use the peristaltic pump technique I believe it could work quite well except for the fact that
the pump itself is hard on the tubing.
When the tubing fails, the pump needs to be in a tub or something to contain the mess.
Years ago, I used paristaltic pumps to move adhesive.
I've spent many hours cleaning up adhesive messes.
My peristaltic pumps were moving adhesive from a 300 gallon tank. Failures of tubing were very intense.

frank freedman · 2013-02-04 22:03

I have seen kits that don't pump or rock. Instead, they put an airstone like that in a fish tank and an aquarium air pump to create constant flow across the board by having the bubbles move the chemical across the board surface. The board is placed vertically. The claim also is that the solution is more uniform due to continuous circulation. Sometimes a low end version of this shows up at Fry's.

Leon · 2013-02-05 02:26

xanatos wrote: »

Thanks guys. I've been etching since I was a kid - that was a LONG time ago... and I've never, ever, bothered to do anything but a cold etch and rocking the tray. But then again, I rarely had to make more than one PC board a month, if that. Now I'm making 5 or so a month, and I've decided to finally do something about the process.

Lastly - if I do choose to heat the etchant, what do you folks find to be a good temp?

Thanks for the thoughts...

Dave

As I said, I put the etching container in a larger container with some very hot (just boiled) water in it. Etching just takes a couple of minutes with continuous agitation

I find that that the etchant lasts indefinitely, if I add a little hydrochloric acid when sludge forms.

RDL2004 · 2013-02-05 05:02

I think the rocking method with temperature control is best. It shouldn't be too hard to come up with some sort of mechanism to do it automatically. If you should decide to try the airstone/bubbling method, be sure to keep the tank tightly sealed. The bubbles can create an incredible amount of tiny aerosol particles which will end up everywhere if not contained. The entire room the etching container is in (and possibly farther) will be covered with corrosive material and you probably won't notice it until too late.

tonyp12 · 2013-02-05 09:11

Though the "used" ..... , attaching the arm to the container or attaching a long plastic piece to the arm to reach down in to container.
http://www.allelectronics.com/make-a-store/item/VB-2/PERSONAL-MASSAGER-USED/1.html

erco · 2013-02-05 09:31

Beau Schwabe (Parallax) wrote: »

Even vinyl tubing is no match for Ferric Chloride over a short time ... aka "liquid rust"QUOTE]

How about silicone tubing?

Or along the lines of tonyp12's suggestion, rig up an overhead low-RPM motor turning a polyethylene paddlewheel or propeller to drop down into the fluid and agitate it.

kwinn · 2013-02-05 09:53

I have tried pretty much every method mentioned so far in this post and am now using a rectangular glass vase as the etching tank, an aquarium heater (the type in a glass tube) to heat the etchant, and a small 30rpm gear motor to rock the tank. It holds a bit more etchant than other tanks but works well for me. I can hang 4 or 5 boards in one direction, or 8 to 10 the other way.

AJ-9000 · 2013-02-06 18:32

Is the Webster S series, model S1 pump (1/15 hp 10+ GPM all plastic pump) what your looking for ?
http://www.haywardcontrolsonline.com/pdf/d_series_product_brochure.pdf

Phil Pilgrim (PhiPi) · 2013-02-06 18:57

jrjr. wrote:

Be careful of the fumes, it rusts (or corrodes) anything near it severely, bolts, nuts, cabinets, the dog.

Ditto that. I have shop tools that bear rust just from being in proximity to (i.e. in the same room as) the FeCl₂. (Unlike dogs, however, cats seem immune to oxidation.)

BTW, this is a good argument against an aeration pump, which is what I used, as it tends the aerosolize the etchant.

-Phil

xanatos · 2013-02-09 12:55

Thanks for the ideas and links - there's some good stuff. My mechanic gave me an all plastic windshield washer pump/motor... I'm going to try that and see how long it takes for that to fall apart! :-) In the interim, I need a pump to remove all the snow from my property... :-)

D

xanatos · 2013-02-09 12:57

Phil Pilgrim (PhiPi) wrote: »

...it tends the aerosolize the etchant.

-Phil

I'm sure that's a great tonic for the respiratory system... yikes.

ElectricAye · 2013-02-09 13:30

xanatos wrote: »

I'm sure that's a great tonic for the respiratory system... yikes.

Hey, and it's high in iron, too! Beats Geritol any day.

Mark_T · 2013-02-09 14:13

Since its an ionic fluid I wonder if its possible to directly pump the etchant by passing a current through it in a magnetic field?
Or would the iron ions be too magnetic? Could the copper be recovered at the same time? Could electrolysis be used to speed up
etching?

xanatos · 2013-02-09 14:22

I've wondered about copper recovery before. Interesting idea. As for passing the current - I'm thinking electrode selection would be interesting - something that wouldn't get eaten... Platinum? :-)

D

Pump motor to circulate Ferric Chloride etchant?

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