My new favorite etchant

Technology
My new favorite etchant

cupricChloride_cc.jpg
From the MAKE Flickr pool

I love etching my own PCBs. It’s a great way to incorporate some of art-school skills with my love for DIY electronics. Up until now, I’d always used traditional ferric chloride to etch my boards, though I’d heard many sing the praises of an alternative etchant easily made from common ingredients. Tired of mail-ordering ferric and dealing with proper disposal, I decided to give cupric chloride a try.

Following Open Circuits’ recipe, I picked up some muriatic acid from the local hardware store and a bottle of hydrogen peroxide 3% from the pharmacy. After setting up next to my big window fan, I slowly added 16oz of the muriatic to an equal amount hydrogen peroxide, resulting in a clear solution. Shortly after immersing my masked PCB and agitating a bit, the etchant turned a brilliant green hue as it began work on the exposed copper. Several minutes of gentle sloshing left me with a perfectly etched board – plus a etchant that can will last me a very long time. For me, that’s the real ‘selling point’ of cupric chloride – by oxygenating (air-bubbling) or adding some more H2O2 to the solution, I’ll be able to refresh this batch once it’s spent – awesome. I’m left wondering why I hadn’t tried this sooner!

34 thoughts on “My new favorite etchant

  1. Andy L says:

    Just don’t get it mixed up with Ecto-Cooler.

    1. Alan Ball says:

      I’ve been doing this for a while, one bottle lasts you pretty much forever :D.

  2. justDIY says:

    I’ve never gotten the regeneration process to work, despite LONG (days worth) periods of vigorous aeration. After etching a few boards very quickly, the solution would eventually turn a dark green and refuse to etch anything. Even with gentle heating and generous patience, tiny boards would not etch. Aerating the solution for two days changed the color from green to blue, yet it still does not etch.

    Although not environmentally friendly, I’ve taken to creating micro-batches, usually a cap full or two of each chemical, just enough to slosh around on the pcb in the smallest container I can find. After one or two pcb, I neutralize with sodium bicarbonate and flush it down the drain with lots of water.

    1. vivi says:

      I think I can give you an explanation. The dark green color in your case comes from the CuCl (brown) mixed with the CuCl2 (blue-green). When you aerate the solution, the following reaction takes place :
      2CuCl + 2HCl + 1/2 02 -> 2*CuCl2 + H20

      You can see that HCl gets consumed, so you need to add more HCl as you aerate your solution.

      You describe that your solution gets blue, which means that the CuCl has disappeared. However, it also means that the concentration of CuCL2 is low. In high concentrations, CuCl2 is emerald green. To be able to etch, you need quite a high concentration of CuCl2, I’ve got no exact number, but it’s in the order of several hundred grams per liter. You’d need to etch a lot of boards to get this. That’s why the first time you prepare the solution, you need to get a bunch of old copper wire, bits of unsoldered PCB, and dissolve everything in the solution. If you only use air for regeneration it will probably take several days. Much less with H202. When you get a nice intense emerald green color, your solution is ready. Remember to add HCl in sufficient quantities as per the equation above.

      About your “micro batch” idea, remember that the pollutants are the Cu ions. If you etch one board you’ll always get the same quantity of Cu ions, even if the quantity of etchant is small.

      1. Bob Ziggo says:

        The initial mix is somewhat wrong. The actual etching is done by cupric acid, which is formed when the hydrochloric acid reacts with the copper. You need less hydrogen peroxide than mentioned above. In fact, you don’t really need it at all.

        See a very detailed description at: http://members.optusnet.com.au/eseychell/PCB/etching_CuCl/index.html

        I’ve been etching with the same solution for about 8 years now. When it gets to dark I just aerate (with a fish tank bubble stone) for an hour or so. When the amount of fluid gets low, I add hydrochloric acid. That’s all and it works great for etching PCB’s.

  3. Dan says:

    it turns light blue from reacting with the chlorine in your tap water. Sorry guys, this is pretty much one time use. Especially when all of the copper ions bind to their chemicals of choice and inactivate them

    1. ether says:

      So, one should use distilled water then?

    2. vivi says:

      Actually Chlorine is a good way to regenerate the solution. Most people however prefer to use Hydrochloric acid, as it is safer. It has the inconvenient of diluting the solution a bit each time.

      I don’t know what you mean by “chemicals of choice” (pollutants in the tap water ? very minute quantities), but CuCl2 binds with Cu to give 2*CuCl. Add some more Cl and you get 2*CuCl2. You’ve created more etchant.

  4. Collin Cunningham says:

    hmmm … I did assume the refresh process would work without any firsthand evidence. I’ll keep using this batch and eventually try it myself – I”l be sure to post my results.

    1. Alan Parekh says:

      I have seen this stuff being used all over the place. The only stuff I have used is the ferric chloride. It works but is expensive.

      I am going to use this method I am making some boards!

  5. cnco says:

    I too have had trouble with the regeneration process. Other than that, this stuff works great and is easier to get the ferric chloride since you can just run down the the corner hardware and drug stores to get the ingredients (though I think Radio Shack may have started to carry the ferric chloride again).

    I’m not overjoyed about the idea of tossing this stuff down the drain. Anyone know how to properly dispose of this stuff in NYC? Other than the East River, that is.

    1. Anonymous says:

      You can precipitate the copper out by adding NaOH or lye. All that’s left in solution is salt NaOH, and solid CuO.

  6. alandove says:

    Precipitating the copper with NaOH would certainly be better than tossing the whole mess down the drain. Instead, or in addition, you could use a classic lab technique for getting rid of hydrophilic hazmats: stir it into a small amount of concrete mix, let it cure, then dispose in the regular solid waste stream. This entombs the toxins (in this case copper) in a matrix that effectively lasts forever in a landfill.

  7. Anonymous says:

    Hi all,
    I have to admit that I have never etched before nor do I have much of a background in chemistry. One of my deterrents in etching is that the fumes can be dangerous. Is this method of etching safe? Are there any things I have to be careful of? Thank you.

  8. Anonymous says:

    Hi all,
    I have to admit that I have never etched before nor do I have much of a background in chemistry. One of my deterrents in etching is that the fumes can be dangerous. Is this method of etching safe? Are there any things I have to be careful of? Thank you.

  9. Salt Water Cleanse says:

    I’m not finished read this yet, but it’s so fabulous ‘n I’ll back again when I was finished my job :D

  10. Johny Radio says:

    Have you tried vinegar, hydrogen peroxide, and salt?

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