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etching printed circuit boards

Discussion in 'Misc Electronics' started by Allan Adler, Feb 11, 2004.

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  1. Allan Adler

    Allan Adler Guest

    One of the problems with making your own printed circuit boards is the
    difficulty of legally disposing of spent etchant. That might be easy in
    some places, expensive or impossible in others.

    It occurred to me that there might be less problematic alternatives for
    dealing with printed circuit boards. For example, a few decades ago when
    I wanted to try to synthesize copper acetate for myself, I dropped pennies
    in vinegar and left them alone for a few weeks and copper acetate crystals
    grew on the pennies. (I know that pennies are not pure copper, so this might
    not have been pure copper acetate). The pennies never dissolved completely,
    but I was after crystals and didn't worry about completely digesting the
    pennies.

    I was able hasten the process considerably by connecting the leads of a
    battery to a cupful of vinegar with copper wire. In fact, the wire dissolved
    completely. It produced a rich blue solution from which I obtained
    broccoli-like dendritic growth, but it would probably have just as
    well grown nice crystals under other conditions.

    So, I was wondering what exactly would be wrong with dropping the printed
    circuit boards in vinegar (or perhaps somewhat more concentrated acetic acid)
    and trying to etch them that way. When you are done, you can just use the
    resulting solution to grow nice copper acetate crystals. The battery idea
    is also appealing, but it suffers from the obvious defect that once the
    copper near the electrode is gone, the rest of the copper is no longer
    connected to the battery. Maybe someone knows a clever way around that
    inconvenience.

    Alternatively, consider the problem of disposing of actual spent ferric
    chloride or spent ammonium perchlorate. Some locales have no provision
    for disposing of such chemicals at special waste sites, which are dedicated
    to lists of specifically approved substances such as paint thinners, motor
    fuel, used tires, etc. Instead, one has to contract with a company specializing
    in toxic waste to get rid of it. That sounds like an expensive proposition and
    they might simply refuse to deal with an individual and the tiny quantities
    of spent etchant they generate.

    Is there any reason why one can't simply try to use the spent etchant to
    grow large single crystals and add them to one's crystal collection? In
    fact, amateurs who etch their own printed circuit boards can have contests
    for the largest and most perfect single crystals, or the most interesting
    dendritic growth.

    Ignorantly,
    Allan Adler


    ****************************************************************************
    * *
    * Disclaimer: I am a guest and *not* a member of the MIT Artificial *
    * Intelligence Lab. My actions and comments do not reflect *
    * in any way on MIT. Moreover, I am nowhere near the Boston *
    * metropolitan area. *
    * *
    ****************************************************************************
     
  2. Garrett Mace

    Garrett Mace Guest


    Electro-etching is one way decent amounts of copper can be removed from a
    board. Usually it's followed up by regular etchant to clean up the last
    bits. This method allows you to use less etchant because you remove most of
    the copper first, and don't wear out the etchant as quickly. I haven't tried
    it.
     
  3. Allan, while I applaud your rather extreme level of environmentally
    related political correctness, I really think you should get a closer
    grip on reality and realize that the copper laden waste residue
    created by amateur PC board etching wouldn't even create a glitch in a
    graph of the copper salt residue released into the waste water
    treatment systems by millions of copper pipe plumbed homes.

    That said, you are correct in believing that you can electroplate or
    precipitate crystals or salts from spent etchant. Large PC shops have
    been since the early 1980s required to do just this, however the costs
    involved in this copper reclamation process have driven most of the
    industry into the use of additive copper PC fabrication processes
    rather than etching away the majority of surface area on a copper foil
    laminated panel.

    The pollution produced by simply dumping small quantities of home
    produced spent etchant into a municipal waste water collection system
    is arguably no worse than that released into the same systems by
    millions of home darkrooms and drugstore sited photo processors.
    Simply neutralize the etchant by adding some lye or ammonia to it (in
    well ventilated conditions) prior to pouring it down the drain.

    Important note: Never dump spent etchant into a domestic system that
    feeds into a residential septic tank for reasons that should be
    obvious.

    Harry C.

    p.s., Allan, stay away from using a solder plated resist on your PC
    boards, because lead salts present a far more serious disposal problem
    than does copper.
     
  4. Muhammar

    Muhammar Guest

    Copper does not dissolve in vinegar. Zinc does. Since you had some
    "insoluble stuff" left from dissolving pennies, you managed to get
    some dirty zinc acetate and separate all copper (3% of it, used for
    coating).

    If you want to dispose spent etchant solution in a cheap and
    enviro-friendly way, you can mix it into concrete slush and leting it
    harden. While you are pouring your concrete mix, you can also include
    your mother-in law for more satisfying monolith.
     
  5. Garrett Mace

    Garrett Mace Guest


    I am interested in this, might be a neat way to convert my mini CNC mill to
    a quicker PCB maker. How fine of a cut do you get? What's the electrode made
    out of, and the best angle for the point? Best working voltages and oils?
    Any faster than milling?
     
  6. Garrett Mace

    Garrett Mace Guest


    My experiment with a 24V supply, piece of copper-clad, blob of motor oil,
    and fine drill bit was rough but successful enough to warrant further
    investigation and experimentation. I'll go look for more information on EDM
    and see if I can convert my little mill to use this. I'll most likely use
    point-to-point outline removing (G code) instead of the scanning method you
    outlined below. I wonder what it will take to monitor the electrode current
    and modify TurboCNC to adjust Z accordingly...really this looks like a great
    application of hobby EDM, removing a foil of copper is going to be much
    faster than cutting a hunk of steel. The only thing I'm doing right now is
    wondering why I didn't think of it before, just last week I was discussing
    how to use continuity on copperclad to zero a Z axis very accurately. Never
    occurred to me to just increase the testing voltage and put a little acrylic
    tank on the mill.
     
  7. The electrode potentials given in CRC are for the standard conditions
    .. If you are considering water as a source of hydroxide ions which is
    approximately about 10^-7 mole/liter in water at 25 C, , you will need
    Nernst equation to get the correct electrode potential for the
    conditions you are applying and then check the possibility of the
    reaction between copper and hydroxide ions.
    Though the reaction under standard conditions seems to be
    thermodynamically possible, but I never heard of copper being attacked
    by common alkalis except ammonia, which perhaps dissolves copper by
    the forming a blue complex rather than forming a oxide.
     
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