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PCB etchants

Discussion in 'Electronic Basics' started by Nigel Eddis, Jan 23, 2005.

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  1. Nigel Eddis

    Nigel Eddis Guest

    I keep reading on various websites that 'Persulphate' is a better etchant
    than Ferric Chloride from Radio Shack, but I don't know how strong to mix
    it and cannot seem to find any actual formulae.

    I have, as it happens, plenty of both Ammonium and Potassium Persulphate,
    and have tried mixing what I thought was a strongish solution of each,
    but it seems very slow compared to Ferric Chloride. I did heat it, and
    agitated the dish constantly, and the Potassium salt did go a bit blue,
    but slow...slow...slow! I also tried adding a small amount of Mercuric
    Chloride, which I understand is supposed to be the approved catalyst, but
    nothing much happened except that the copper became plated with mercury.

    Can anybody offer any advice about this? (And which is better, the
    Ammonium or Potassium salt?)

    Nigel Eddis

  2. Yes, if you are still in here to read this, the ammonium persulphate can
    be a bit slow, but it is much more gentle on the circuit pattern,
    including lines drawn by "permanent" markers. Outgassing is also less
    problematic. Reaction is concentration dependent. For a small double
    sided board around 4x3 cm, I use around a heaping teaspoon and heat to
    about 70 C. I just wait it out, as I am not usually in a big hurry and
    am more concerned about a quality etch, and also environmental/health
    issues in using some of the alternatives.

  3. Bob Masta

    Bob Masta Guest

    Hmmm. At the lab where I used to work we tried
    ammonium persulfate exactly one time... it completely
    dissolved the "permanent" felt-tip lines, whereas with
    ferric chloride we rarely had problems. We just used
    the ammonium persulfate right out of the bottle (from
    Radio Shack, I think... many years ago), so maybe it
    needed dilution first?

    Amazingly, we did find that most pre-mixed ferric chloride is too
    *concentrated* to etch properly, so slow that it appears
    to be exhausted on its first use. Dilution down to
    1.30 specific gravity fixes it right up.

    Best regards.

    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
  4. Skaface

    Skaface Guest

    I use ammonium persulphate here for my home projects, I use those iron
    on laser printer masks. It will even etch out surface mount IC pads
    perfectly. Usually takes about 3-5 minutes to fully etch the board,
    however i usually make the mix a bit weaker as to save money.
    The directions on this stuff that i have are to mix 400 grams of
    ammonium persulphate in one to one-and-a-half litres of water heated to
    about 60 to 70 degrees C
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