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PCB Photoresist Chemical

Discussion in 'Electronic Basics' started by Animesh Maurya, Feb 12, 2004.

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  1. Hi everybody,

    Sorry, although this is not anyhow related with electronics,
    but I think you people can me.

    Can anybody exactly mention which chemical is used to photoresist PCB.

    Thank you,

    Animesh Maurya
  2. Robert Baer

    Robert Baer Guest

    In the "good old daze" of hand-layouts ("taping"), Kodak Photo Resist
    (KPR) was commonly used, along with KMER.
    However, an el-cheapo way is to use egg-white sensitized with
    Potassiun DiChromate.
    Exposure to UV in either case polymerized the material, allowing the
    solvent to wash away the un-exposed material.
    For the sensitized egg-white, warm water is the developer, and one can
    do some careful baking to achieve a more robust covering.
    Be careful with that chemical; water becomes more corrosive as the
    purity increases (no joke).
    Ordinary water is bad enough on mountains!
  3. I read in that Robert Baer
    When do you collect your Nobel Prize for that discovery? (;-)
  4. Adam S.

    Adam S. Guest

    Corrosive to what ?, sodium metal?
  5. Leon Heller

    Leon Heller Guest

    Lead springs to mind - lead pipes are more dangerous with soft water.

  6. cpemma

    cpemma Guest

    But traces of chloride ion make water much more corrosive on damn near every
    other metal.
  7. Well, this is one of those Usenet 'true, but...' things. Lead chloride
    is soluble in water, so traces of lead chloride get into water that is
    virtually free of carbonate ions - 'soft' water. 'Hard' water, with
    carbonate, forms an insoluble coating on the inside of lead pipes - you
    can see a sort of fawn coloration.
  8. Mark Zenier

    Mark Zenier Guest

    Last I checked, the dominant resist is a dry film that is heat
    laminated on the board. Dupont "Riston", or something
    like that. Maybe there's a MSDS (chemical safety form) on the
    web for it that would tell the active ingredients.

    There are a zillion types of photoresist, etchant, and plating
    solutions. Try Coomb's "Printed Circuits Handbook".

    Mark Zenier Washington State resident
  9. Robert Baer

    Robert Baer Guest

    Plastics, glasses, metals, minerals, other liquids and gasses,
    anything - except nothing (ie a vacuum).
    Water is a *polar* molecule and that dipole moment is not exactly weak
    in the chemical scheme of things.
    If you get into serious work requiring pure water measured in the
    megohms, you will find that the purest available water does not last
    very long - as it dissolves the container and becomes less pure,
    eventually becoming in equlibrium with the container material.
  10. They don't call it the "universal Solvent" for nothing.

    Glenn Ashmore

    I'm building a 45' cutter in strip/composite. Watch my progress (or lack
    there of) at:
    Shameless Commercial Division:
  11. Pity you can't train them to solve PCB-copper only.

  12. Sam B.

    Sam B. Guest

    If you are looking for photo-resist, Think and Tinker has some dry
    film. I've used it and it works very well down to 5mil traces, if
    you know what you are doing.

  13. Thanks, Robert for the info.

    In addition to KPR, I would also like to try out egg-white one.

    Can you please put detailed preparation of it. What should be the
    ratio of egg-white and Potassium Dichromate?

    Thanks again,

    Animesh Maurya
  14. Robert Baer

    Robert Baer Guest

    Cannot say, i only heard about that, and seen an equivalent using a
    variant of Elmer's glue.
    I do not think you need very much, as potassium dichromate is a rather
    powerful oxidizer.
    Try adding just enough to get a pink mixture.
    Powedered egg-white is easily available and seems a lot less expensive
    than using whole eggs for the source.
  15. Robert Baer

    Robert Baer Guest

    Riston has been a commonly used resist for ages.
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