Agitating PCB etchant

Discussion in 'General Electronics Chat' started by Wendy, May 25, 2009.

  1. Wendy

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    Mar 24, 2008
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    At this point I'm talking hypothetically, else I would be posting this in the projects forum. I've been thinking how to slowly rock the etchant solution in the bowl/pan back and forth, say around 5 seconds per cycle. It needs to be gentle, since I really don't want to make a mess.

    The base arrangement might be something like this, using a piece of wire as a fulcrum.

    [​IMG]

    Two separate methods suggest themselves, each with their own problems and solutions. One is a couple of magnets and electromagnets, to cause it to rock. Breadboarding a power oscillator is a snap, but the hardware is awkward.

    The other is a drill motor set for slow speed and an offset cam, made out of wire or wood. I can even put a wheel on it. Mounting the motor is a minor hassle, but it is heavy enough to stay put I'm thinking.

    I thought of sparge, but that can be very messy, and I don't want to mess to much with these chemicals.

    Anyone else do something similar?
     
  2. beenthere

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    The alternative for agitating the solution is to have a plastic pipe with holes glued to the bottom of the tank. An aquarium air pump blows air through the pipe, which has holes drilled into it to allow bubbles to come out. The board is held almost vertically in the tank, so the emerging bubbles flow up over the surface to etch. The idea is that each bubble agitates the solution as it passes over the PCB.
     
  3. Wendy

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    Which is the definition of sparge. :D I tend to lay the boards flat in the solution, the pan is shallow.

    I used to service a professional etchant machine, complete with heater and sprayers, with the board layed sideways. It used FeCl and titanium parts inside a PVC box. The shop was happy with it, but I hated it myself. It was for prototypes.

    One of the things I might do in time is get one of the flat rubber heaters and put it under the pan to warm the liquid, a little heat does tend to help. If I can find where I buried it that is. I helped a friend a long time ago with something similar, it was a 120VAC unit, we built a box and put a dimmer in it.

    If I need to do two sided boards I think a little blob of clay on each corner will expose the board enough to be handy.
     
  4. beenthere

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    I've got a Kepro BT-202 spray etcher, which is great for prototypes and small production runs.
     
  5. Wendy

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    Do you use FeCl or something else? I just bought a gallon of Muriatic Acid to experiment with.
     
  6. Bernard

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    I had 4 RPM motor, so used an escentric mounted ball-bearing to ride on the end of a 12X 18 in board, pivited at 2/3 of its length. Rocking was gentle enough that there was no splash. Ttravel about + & - 1/2 in. " Was etching numbers on two Pelorus's for National Geographis Soc. Both lost in a flood in Mexico.
     
  7. Wendy

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    Where did you get the motor?
     
  8. jpanhalt

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    Here are some of my thoughts and experiments to date:

    1) For sparging (sometimes called bubbling), I got a "Bubble Wall" from the local pet shop. The website is: www.pennplax.com I have used them with both ferric chloride and cupric chloride etchants. Being plastic, they are non-reactive and easy to clean. The inside does not become contaminated. They do not cause "a lot" of splashing (sometimes called fomites :D). For air pump, I use the "Aquatic Gardens 1500" . In reality, I do not use the sparging for agitation, but rather to regenerate the etchant. I cover the flask with a few layers of paper towel and there is no soak through to the top layer.

    2) I made some glass trivets from 1/8" (3 mm) pyrex rod and a MAPP-air torch.

    [​IMG]

    Had to use glass, as the SG of etchants is about 1.3 and plastic floats. Set the board on the trivets.

    3) Try etching upside down, i.e., copper facing down for one sided boards.

    4) I use a magnetic stirrer and teflon magnet. Non-heated stirrers are fairly cheap; good heated ones run about $100 on ebay.

    5) I have thought about using a tall narrow etching chamber, like is used to thin-layer chromatography. Basically, you take a glass brick and have the top cut off. That would allow sparging without much splash.

    6) Finally, I have thought about using an in-line or submersible pump for re-circulation of the etchant. HF has a Chicago Electric pump #45305 rated at 145 gal/hour. It is quite cheap and that flow rate is really not that much and is easily throttled. I use one on my pedestal grinder when I need to wet grind something.

    John
     
  9. Wendy

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    Most etchants are pretty corrosive (make that extremely corrosive), you'll need a pump rated for acidic chemicals (they exist, but are expensive) for spaying. Nice job on the glassware. Bubbling doesn't take anything that special of course.

    I can see the advantages of mounting the PCB sideways. but it does take a deep tank, and lots of etchant. With that scheme sparging does become a lot more practical though.

    Basically I'm looking for a countertop method, so I'm being cautious.
     
  10. beenthere

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    If careful. I suppose you could place the PCB in a plastic zip-seal bag along with etchant and manually agitate the bag. I would want to do it over a plastic laundry tub, though.
     
  11. jpanhalt

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    Most of the common plastics are pretty stable to acid, so long as it is not as strongly oxidizing as nitric, concentrated sulfuric, or sulfuric+chromic. In other words, they stand up to acid, but like all organics, they can be charred. That holds for Teflon, LPE, HDPE, PP, PS, and even ABS. Nylon is relatively stable, but you probably won't find that is used much. Any metal must be avoided -- there are a few exotic exceptions. For our level of use, and for the cost of that in-line/submersible pump, I think it is worth a try, if you are inclined to go in that direction.

    John
     
  12. Wendy

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    Yuck. I've always stood over it and aggitated it by hand myself. I also have a glass casserole disk that is designated for nothing else, though lately I've been buying disposable tupperware.

    One of the reasons I'm thinking of the hydrogene peroxide/hydrocloric acid etchant is it is much more friendly ecologically speaking. No clue if it will work, but it comes highly recommended.

    http://www.k7qo.net/lab.pdf
    See Chapter 5

    Since the process takes a long duration I'm wanting a little automation. Which is why I started this. Still hypothetical at this point though. Really.
     
  13. THE_RB

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    Bill, I built an almost exact version of what you are after but for a separate purpose mxing viscous fluids. I used a microwave oven turntable motor, these are compact, run direct from mains at a few mA, won't burn out it stalled, and run about 5rpm typically.

    I just made a crude metal cam and attached to the end of the motor shaft, then mounted on a simple bracket under one end of the fluids tray which was pivoted in the middle. My cam had 2 "bumps" so it rocked the tray gently every few seconds.
     
  14. KL7AJ

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    The traditonal "auto-slosh" just used a clock motor with a little cam arrangement under one end of the tray. The older ARRL Handbooks always had a project description of this.


    Eric
     
  15. SgtWookie

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    If you're going to try the H2O2/muriatic route, you'll get much faster results if you continually wipe the board surfaces with a soft paper towel. You'll need heavy-duty rubber gloves though, as you wouldn't want that stuff on your skin.

    I tried the H2O2/muriatic with just agitation, but it doesn't work nearly as fast as if you're wiping the board surfaces.

    Oh, and don't try using anything made of nylon with H2O2/muriatic; it dissolves. I ruined a board when I tried to use a couple of zip-ties as spacers; the zip-ties turned into a goo that stuck all over the partially-etched bottom of the board. Makes for an interesting coaster, though. :rolleyes:
     
  16. Wendy

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    Nylon disolves? That's unexpected. Wonder what tupperware is made from (I'll have to look)?

    Sparge may be the way to go on this, but I'll fight it. If I do go sparge I'll want a flat beaker to put the board in sideways.
     
  17. jpanhalt

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    You can think of nylon as being a little like silk or protein in tendons. It is a polyamide. It can be dissolved or destroyed with strong acids, as you have in the peroxide methods, but it is relatively stable to ferric chloride. Here is an interactive chart for checking chemical compatibility.

    Plastics that have a waxy feel, such as polypropylene, LPE, etc. (e.g.,Tupperware) are generally pretty stable to acids and bases as noted above. However, plastics also may have plasticisers added to tailor their properties, and a chemical that affects the plasticiser will change those properties. For example, a plastic may seem fine at first but become brittle or craze as the exposure time increases.

    John
     
  18. Wendy

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    Nice thing about tupperware though, is you can throw it away. I still keep that old dish just in case, so far glass rules all in terms of reliability.

    I've seen people refer to FeCl as toxic, which isn't my impression. It is technically a salt, and breaks down into two of the more common minerals used for organics out there. I wouldn't want to pour it down my copper plumbing however, for obvious reasons. That is everyone elses take on this?

    If anyone knows a good source of motors or gearboxes (or both) cheap please let me know.
     
  19. jpanhalt

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    I agree about the low toxicity of ferric chloride from a practical standpoint and when it is used with common sense. As an etchant, it is one of the standards to which others are compared. It is fast and gives relatively little undercutting.

    Ferric chloride has three major risks: 1) It's quite corrosive and stains skin and fabric; 2) With heat and water, it releases HCl, which is not much of a problem in the amounts we use and at temperatures <60°C; and 3) Toxicity from iron overload.

    Iron absorption from our food is not actively controlled. The amount one absorbs is determined by the amount ingests. Our normal diets contain 10 to 15 mg of iron per day from which we absorb about 1 to 2 mg/day. We typically lose about 1-2 mg/day too, mostly as sluffed cells. Females need more iron, particularly during pregnancy. It seems strange from an evolutionary standpoint that absorption and excretion of something as essential and potentially toxic as iron is not actively controlled.

    The dose for acute toxicity of iron is usually given as 20 mg/kg body weight. If one assumes a typical etchant has 400g FeCl3/L (400 mg/mL), then one can see that acute iron toxicity would require ingestion of several mL's. A simple splash won't do it. That much ferric chloride would probably cause gastric irritation and vomiting by itself. Long-term toxicity is another matter, but would still require significant amounts over a long period.

    John
     
    Last edited: May 27, 2009
  20. KL7AJ

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    From the Opus of Amateur Radio Knowledge and Lore:

    The typical ham shack has numerous poisons of varying intensity. We mentioned coffee. We also have soldering fumes, something that has drawn a lot of attention in recent years. It’s probably a good idea to use some ventilation while soldering, although it really spoils the ambience. This is one of those gut-wrenching judgment calls. A good deal of my personality, for better or worse, is a direct result of having inhaled solder fumes for several decades. Far be it from me to deprive any young ham of such an enriching experience. But I suppose, again, I am obligated to point this out. Solder contains lead, and molten solder emits lead in a vapor state, which can be inhaled, thereby causing the sundry deleterious things that lead is supposed to do. Some people are allergic to rosin flux, since it is an organic compound, closely related to some human-type amino acids and such. Burning rosin flux is believed by some to be potentially carcinogenic. We occasionally use corrosive compounds, like circuit-board etching solutions. Use rubber gloves and chemical goggles when etching circuit boards. Dispose of the used chemicals in the proper fashion, which means, don’t flush it down the sink. Save it in a proper plastic bottle, sneak it over to your neighbor’s garage, where, upon its discovery, they can flush it down their sink. No. Just kidding. Scratch that from the record. Forget I ever said that.
    Instead, check with your local official bureaucratic entity for proper means of disposing these sorts of things. Every city has a proper, official means for doing this, but it can vary from place to place.
    Hams use a lot of alcohol. For cleaning things, that is. Alcohol is flammable, and denatured alcohol is quite toxic. Avoid using it for cleaning your hands and such.
    If you’re into homebrewing, (ham radio equipment, that is, not alcohol) you will most likely want to paint your masterpieces. This is a task you DEFINITELY want to do outdoors. Spray enamels and other paints are HIGHLY toxic. As are solvents like Xylene, Toluene, and most other “enes.” Be sure your item is fully dried before you bring it indoors. The rule is——if you can smell it, you’re inhaling toxic fumes. And there are toxic fumes you can’t smell, as well. Many hams spend a lot of time in the basement, which is where they have their ham shacks. Be sure to have carbon monoxide detectors down there, because things that make CO, like crotchety old furnaces, are also frequently located in basements, and you can be poisoned to death in the very same house where the XYL (ham lingo for wife) is upstairs sitting——um——er——ahh——“buoyant, unapprised, and blissful”——watching Sponge Bob on the telly, with no ill effects whatsoever.
     
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