Cleaning copper boards with oxalic acid?

Discussion in 'General Electronics Chat' started by spinnaker, Dec 5, 2011.

  1. spinnaker

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    So I decided to give the advice on this site a try and clean my PCB with oxalic acid, I chose Bar Keepers fiend since that is what I had. My question is how to know when it is clean.

    No matter how much I scrub I get black that comes up on the paper towels I am using. I assume this is the oxalic acid reacting with the copper or is it still oxidation residue?

    BTW I also get debris coming off the board using the scotch brite pad. Is this also copper?

    How do you know when the board is really clean?
     
  2. thatoneguy

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    I use a grey ScotchBrite pad and rub until shiny, then spray it with isopropyl alcohol, wipe off with clean, lint-free towel, and do the transfer (laminator method here).

    Maybe you are supposed to rinse after the first application of the acid? I've never required it when using ScotchBrite grey pads. They are a bit more aggressive than the green, but don't leave (major) scratch marks.
     
  3. MrChips

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    Just use a plain household powdered scouring cleanser such as Old Dutch or Vim. Use the power dry on J-cloth and add just a few drops of water to moisten the powder. Scrub the board hard until it shines copper bright. Requires lots of elbow grease. Wash with lots of water. Final rinse with acetone.

    [​IMG]
     
  4. thatoneguy

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    That's essentially what BarKeeper's Friend is. He's trying to get it all off.

    Maybe the Acetone rinse is what he needs? It also helps clean up the board after etching. I use the Acetone to get the majority of toner off, then the grey scotch pad again for a nice clean board.
     
  5. Wendy

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    I use nothing but scotchbrite myself, and wear gloves to keep the finger oil off.
     
  6. nerdegutta

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    When I'm doing the toner-transfer, I rub the board with this:

    [​IMG]

    And then wipe it with a coffee machine filter soaked in Acetone. I use gloves with the Acetone.
     
  7. Wendy

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    The rough site is a form of scotchbrite. I suspect if you were to look on the package of an unopened sponge you would find the name attached.
     
  8. strantor

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    I used to clean pennies with that stuff. same thing. always black, even when its clean. might be oxidation. not sure.
     
  9. spinnaker

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    Yeah that is what I am trying to figure out. Is it really clean or still oxidized?
     
  10. thatoneguy

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    If you let it dry overnight, it's probably slightly oxidized again. Copper starts oxidizing immediately after it is cleaned, like aluminum, but quite as fast. You have an hour or so.

    Use the scotchbrite pad on it, wipe down with alcohol or acetone to remove all oils, let dry.

    Warm board up (this will aid in drying), when board is warm, apply transfer and laminate or iron until it is "stuck" everywhere. You'll see the dark spots start to "bleed through" when it is transferred well.
     
  11. spinnaker

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    Not letting it dry overnight. It;s still wet. As much as I rub it black still comes off on the paper towel.
     
  12. strantor

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    i think its a chemical reaction. maybe causes rapid oxidation. try a different cleaner.
     
  13. thatoneguy

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    Possibly true. Maybe he's down to 3/8 oz. copper board now. :D
     
  14. spinnaker

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    Just less copper to etch. :)

    Which brings up a good question. If all I am dealing with is low current, am I better off with the lightest weight copper I can find? Which etches better lighter or heavier copper?
     
  15. thatoneguy

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    Integrated over-current protection, entire board is a fuse.
     
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