Sponge method for etching PCBs?

Discussion in 'General Electronics Chat' started by spinnaker, Oct 29, 2010.

  1. spinnaker

    Thread Starter AAC Fanatic!

    Oct 29, 2009
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    When I make PCBs I place the PCB in an etchant bath and agitate the bath.

    I saw a video on line for making PCBs and in the video they poured just a small amount of etchant over the PCB and rubbed the board with a sponge.

    Has anyone used this method? Does it work?

    Seems there would be a lot less waste using this method.
     
  2. thatoneguy

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    Feb 19, 2009
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    If you don't mind a rather large mess form the spray when sponge 'flicks' the edge of the board, it's not bad. Don't use in a sink, etc. Basically do outside.

    The Friction + Agitation does go a bit faster, at the same time, when working on larger projects, areas/shorts can be overlooked easily. The latter is why I still soak mine with Ferric Chloride. The Peroxide based etchants just aren't as good, or when they are, it is only for a small time window before it needs diluting again.

    Fastest: Friction + Agitation in a spray etchant tank, the professional level stuff costs quite a bit though, but it works very fast by heating up the etchant, then sprays it against the board at a high pressure in a fan shape (like a car wash).
     
  3. nerdegutta

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    Dec 15, 2009
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    I'm using Natriumpersufalt. I have it in a plastic container, and the container in a pot/souce pan on the stove, under the ventilation fan, in the kitchen. So I heat it up to around 40-50 degrees Celsius. The time it takes to etch, is depending on how many times I've used the etchant, and the heat.

    (BTW: My girlfriend is very patient with me, when I turn the kitchen into a etching laboratory.)
     
  4. jpanhalt

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    Jan 18, 2008
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    I use mainly full immersion too. A sponge is helpful if you have a stubborn spot that is etching more slowly than the rest of the board, and you don't want to risk over etching the whole board. Remember, the etching process actually involves oxidation of the copper. Thus, agitation and rubbing a thin layer in air increases the speed.

    Some people swear by the sponge method. You can get fine detail, and it is used by artists doing copper etching for that reason.

    John
     
  5. Wendy

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    Mar 24, 2008
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    Never done it, might try it sometime. The problem I perceive is most of my etch resist is fairly fragile, it isn't meant to stay after all.
     
  6. jpanhalt

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    I use the photoresist method. It is quite tough. John

    Edit: There is also what is called the Edinburgh etching recipe. It contains citric acid, which apparently complexes with the metal oxides, reduces sludge formation, and speeds up the process. See: http://www.nontoxicprint.com/etchcopperandbrass.htm

    I tried it for a few boards, but switched to cupric chloride before I had formed any strong opinions about it. If you are into experimentation, though, it is worth a try.
     
    Last edited: Oct 30, 2010
  7. shortbus

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    Sep 30, 2009
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    I've only etched one board but I used ferric chloride and while board was in the bath I slowly wiped it with a disposable foam paint brush. It worked great!
     
  8. Wendy

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    Whatcha maken?
     
  9. bertus

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    Apr 5, 2008
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    Hello,

    A soft brush or a soft sponge can be used for speeding up the etching.
    I have used some tissue paper instread of the sponge.
    It is cheap and disposable.
    Always use protective gloves when using the sponge.
    Also take good care of the correct disposal of the used etchant and the used sponge or brush.

    Bertus
     
  10. MrChips

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    Oct 2, 2009
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    In english, that would be sodium persulphate (or persulfate). Do you add sulfuric or sulphuric acid (H2SO4) or hydrochloric acid (HCl) ? What do you do with the used solution? Have you tried rejuvenating it with more acid and hydrogen peroxide (H2O2)?
     
  11. nerdegutta

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    I'm only dissolving it in water. When it's used a few times, I store it in plastic bottles. After awhile it crystallize on the bottom. When I have a few bottles, I deliver them to a disposal center, and say what it is. The guys working there don't have a clue of what I'm talking about, so they tell me to put it near the lead acid car batteries.

    I have occasionally mixed in more, but most often I make a new solution.
     
  12. MrChips

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    Oct 2, 2009
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    I use ammonium persulfate with hydrochloric acid added, heated to about 80C. When the solution starts to slow down, I add more HCL and H2O2. I just keep on getting more and more etchant.

     
    Last edited: Dec 3, 2011
  13. nerdegutta

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    Dec 15, 2009
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    I'm expanding my horizon, and have started to use Ferric Chloride. I recon that it works even thou it's not heated to 40-50°C.

    The construction of an agitating device is starting to form in my head...

    How do you get rid of your etchant?
     
  14. MrChips

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    Oct 2, 2009
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    Also try using copper fill or pour in the layout. You can save a lot on etchant.
     
  15. nerdegutta

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    Yes, I know. I do it sometimes.
     
  16. Wendy

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    Mar 24, 2008
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    I use around a cup and a half, total, sometimes less. I use a sponge to wipe the board while etching to move it along, it is quite fast (about 3 minutes), but the board is lightly immersed. I throw the sponge part (I cut it off a larger mass) away in the trash, and and dispose of the etchant in the grass.

    The receipt is very cheap, 1 part muriatic acid and 2 parts hydrogen peroxide. Both are both very inexpensive chemicals. I'm still using the 1st gallon of muriatic acid I bought after 10 boards, with the 1 gallon container less than ½ used. The mixture self heats quite warm when you mix them, always pour acid into the H2O2, it can splash around otherwise.

    I'm still tweaking my process, next batch of boards I make is going to have baking soda in the rinse to neutralize the acid. I'm going to try acrylic clear Krylon spray paint as a non conformal coating to see how well it works, someone recommended it on another site.

    I'm also trying baking soda to see if I can keep the fumes under control while storing it.
     
    Last edited: Dec 3, 2011
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