Testing The Efficiency Of PCB Etchants

etchIn the interest of the scientific method [Feynmaniac] (great name, btw) over on Instructables has posted a little experiment on something we all, no doubt, care about: putting PCB traces in copper clad boards with the most common etchants out there.

The experiment used the ‘ol standard, ferric chloride, and the safe, inexpensive newcomer, vinegar, hydrogen peroxide, and table salt. Finding the most efficient mixture of ferric chloride is easy: just use what’s in the bottle. The vinegar and H2O2 requires some stoichiometry, though, and [Feynmaniac] calculated that with an 8% acetic acid solution and the most commonly available 3% peroxide solution, a 2:3 ratio of peroxide to vinegar is the best. Salt to taste, or until everything turns green.

Four copper clad boards were used for the test, masked off in a ‘barcode’ pattern. Two methods of applying the etchant were used: either rubbing the etchant on with a sponge, or immersing the boards in a bath of the etchant being tested.

In terms of speed, ferric chloride was by far the fastest, with 3 minutes until the board was etched using the rubbing method, or 10 minutes when simply immersed. Vinegar/peroxide took longer with 11 minutes rubbed, and 20 minutes immersed. No differences in the quality of the etch were noticed.

While ferric chloride was by far the fastest etchant, it does have the downside of being environmentally unfriendly and fairly expensive. The vinegar and peroxide etchant is safe, cheap, and can be found in any grocery store on the planet.

This experiment didn’t test other common etchants like HCl and H202, or cupric chloride (which is is the byproduct of HCl and H202). Still, it’s a good confirmation that the vinegar and peroxide method actually works, in case you were wondering.

73 thoughts on “Testing The Efficiency Of PCB Etchants

    1. PLEASE, just throw in some balls of aluminum foil in order to precipitate out the copper from the waste solution….. This isn’t hard people. And you can see the color change to know that it has worked. The aluminum salts are far less environmentally harmful, even if there is only a quite small amount of dissolved copper to begin with. You can even get fancy and add baking soda to this mix in order to precipitate out aluminum hydroxide if you don’t want to pour the soluble Al down the drain.

      The entire conversation of how it’s too little copper to matter makes me think about when people pour gasoline on anthills or dump their used motor oil in a hole in the yard because “it’s only drops in a bucket after all”

      I will agree that it may not be possible to quantify how much/whether damage is being dealt environmentally by this small amount of copper. It’s also difficult to discern why aquatic invertebrates are important in the ecosystem. BUT, it’s easy to eliminate this copper by simply tossing in a ball or two of aluminum foil which most everyone already has in their kitchen.

      1. Also, if hackaday would post it, I will make a quick 1 minute youtube tutorial demonstrating this technique and explaining it’s operation and purpose for hobby circuit board makers. Just say the word :D

        1. I am sure such a video would be quite useful, gain a lot of popularity on youtube and would be picked up by hackaday sooner or later. What I am trying to say is: go for it and do the world a favor.

          1. Salts are ionic compounds, creating a solution liberates the ions from the lattice, so you basically already have the ions.
            The oxidation state that defines how a compound will react doesn’t change so we’re talking about Cu(II) ions in a lattice as well as in solution. Copper(II) sulfate readily dissolves, providing large amounts of Cu(II) ions.
            The trick is to minimize the rate at which ions could leach out of contaminated waste. This can be done by changing the oxidation state (electrochemical deposition of elemetal copper or precipitation of insoluble compounds such as copper sulfide).

            To summarize:
            – don’t spill hazardous substances (ideally collect and dispose of properly)
            – if you’re going to make a mess, contain it (make hazardous substances insoluble)

        1. that unfortunately still seems to be common practice. Nevertheless environmental awareness – as inefficient as it may appear on the small scale – must not be ridiculed by the mistakes we haven’t yet learned to avoid.

  1. Something you need to be mindful if with either method is how to dispose of the waste. Both etching solutions will finish with copper in it, which is toxic. Dumping it down the sink is a Bad Thing. I am not sure what the best method is to dispose of this. In the past I have dropped it off at the fire station’s toxic materials drop off (labelled) but I don’t think this sort of thing exists everywhere. This is a big reason why I don’t etch my own boards anymore… Although the price if seeed et al sure helps too, as long as I am not in a hurry.

    1. The amount of copper the average hobbyist would drop down the sink is a rounding error in countries where all house piping is made of copper and has slowly corroded away from the inside over the years. Not to mention that down the sink does not straight away imply into the ocean. The dissolved metals that end up at a typical sewage treatment plant is easily dealt with compared to the sewage treatment of a typical industrial site.

      1. You can also precipitate it out and be left with a lot less waste, eg react with sodium bicarbonate (baking soda) to make copper carbonate which is insoluble in water.

    2. Ditto this. The vinegar/peroxide solution reacts with copper metal to yield copper (II) acetate. It makes pretty crystals, but it’s toxic to fish, invertebrates, and certain fungi. Definitely not something to pour down the drain. That said, it’s less nasty than FeCl and the associated copper compounds from that reaction.

      More generally: copper compounds happen whenever you etch a board. There’s no way around that. Most of them are quite harmful to fish and wildlife, and shouldn’t go down the drain.

      1. I have been told to mix the FC copper solution with LOTS AND LOTS of cheap washing powder which neutralises the solution and makes it safe to dispose of at sites, makes it safer to handle.

        I usually buy the cheap supermarket own brand at £1.90 for 2.2kg(ish). It usually takes 2 of these for a full etch tanks worth.

        The council staff at the tip are happier this way!

  2. BTW, Hydrogen peroxide is readily available at beauty supply stores (like the Sally chain) in strengths up to 30% for not a whole lot more than the 3%. I know nothing about the suitability for board etching, but usually stronger means faster.

    1. I use the 30% peroxide. It etches FAST. Too fast sometimes. It’s also exothermic. It get really hot, very quickly. Using a sponge works well to keep the heat down. 1/4 to 1/2 cup of it will heat up while etching so much that you can’t put your (gloved) hand into it. (I wonder if it could start boiling – so be careful with it) Sometimes I water it down a bit, otherwise I use a sponge, or only mix up small qualities. Just enough to cover the board. Something like 1/4″ of enchant on the bottom of a recycled tall cottage cheese container. You can etch 10 sq in of board in under a min depending on how much copper there is to remove. Sometimes it’s as fast as 20-30 seconds..

      1. Be careful with higher concentrations of H2O2. It dissolves flesh as easy as it dissolves copper.
        Just ask the German ME-163 pilots that dissolved in their seats due to fuel leaks.

        1. Here’s a question… Where do you even *get* higher concentrations of H2O2? The drug store stuff is 3%, and the stuff you get from a beauty supply store is still less than 10%.

          It needs to be above 67% to be rocket fuel.

          1. Yeah, that’s the ~= 10% stuff I mentioned. Despite what it says on the bottle, there’s no way it’s 30% H2O2. A quick googling suggests “30 volume” is 9% H2O2. There’s supposedly “40 Volume” which is 12%.

          2. My bad. It doesn’t say what percentage it is on the bottle – I assumed it was 30% – it may not be. Anyways, it’s PLENTY strong for etching – if not dangerous.

          3. You’d need to distill it yourself.

            Strong concentrations of H2O2 have been outlawed for sale to private persons due to terrorist scares.

            And 67% is in itself a dangerous concentration level for H2O2.
            “handling with care” is a gross understatement.

          4. Try a hydroponics supply shop. I get 29% from a local one.

            It doesn’t dissolve flesh. It does bleach it and make small bubbles of oxygen in the skin of your hands which itches like nothing else. It will also react with lots of things very energetically and bleach carpet/clothes.

  3. I wish they would have tested HCl and H202 as that is where I can see myself going. I’ve had FeCl crap out on me too much once it gets copper loaded. Although I hear it can be regenerated somewhat with some sulfuric acid added to it.

  4. I’ve been using ammonia persulfate
    – 10 – 20 mins depending on how strong you make it.
    – Temperature should be around 60 – 70 degress C.

    It’s cleaner than ferric… it does take a while, but no rubbing required.. agitate it to make it go faster. :-)

  5. >While ferric chloride was by far the fastest etchant, it does have the downside of being environmentally unfriendly and fairly expensive.

    I have said it before and now again, please show your references to the “environmentally unfriendly” part of ferric chloride.

    Mine is here:
    >In industrial application, iron(III) chloride is used in sewage treatment and drinking water production.

    So if it is so bad, why are they used for those particular applications? As an editor, you should be ashamed of passing off unverified info.

    The copper compounds are what is toxic to the environment and you’ll have it may it be with the table salt or whatever unless you neutralize it to form insoluble compound.

  6. I want to try etching my own boards and the peroxide and vinegar method seems like a good place to start. Is there a similar, easily available masking material?

      1. If you’re going to use toner transfer method be sure to purchase some toner reactive foil (TRF) as well. While I’ve used vinegar/H2O2/salt with great success, my boards always suffered from pitting (to the point where I had breaks in narrower traces) with toner alone.

    1. You can mask copper foil with a Sharpie pen and that will resist etching solutions. I have also used acrylic craft paint to hand draw boards too. On sale acrylic craft paint can be dirt cheap. Go after a holiday when craft stores are blowing out all of those left over holiday colors they still have in stock. Then they sell ounce bottles for like a quarter. An ounce of craft paint can paint a lot of circuit traces.

      The classic is stealing your girlfriend’s fingernail polish if you have a girlfriend. Or I suppose if you paint your own nails. If you want a more automated masking process then you have to go to the toner transfer method, or if you want top quality results photo resist. But photo resist can be expensive, and somewhat complicated.

      Radio Shack used to sell rub on transfer patterns to make circuit boards with. That is what I used for the first boards I ever made. Here is a picture of a package of them


      1. this is not exactly correct. iv’e used a sharpie to fix up transfer errors and the vinegar/peroxide/salt mixture just ate right through it. what you need is a lacquer pen.

        1. I also use permanent markers to make tiny corrections and sometimes to mask parts of copper that I didn’t want to waste toner/resist on. It never really fully works for me either. I have a theory that maybe it takes a longer time than is commonly believed for the marker ink to fully set, maybe some mild oven treatment could harden it?

          1. I have a CG/Thorsen “resist” marker that I got 20yrs ago. I use it to touch up toner masks. It looks just like a “sharpie” but smells different. It smells more like a “Marks-a-lot” or other artist type marker. I don’t know if it is the chemical or the pigment in it, but it makes a more opaque line than a sharpie. Still not as good as the toner, but does work. Writes just as good as it did 20yrs ago which amazes me.

          2. you need to use the industrial super permanent sharpie marker the regular ones will not work, I have also had good luck using the fabric markers labeled RUB-A-DUB

        2. I’ve only ever etched with Ferric Chloride and a Sharpie works with it. But it has to be a fresh Sharpie, not one that is laying down faded, half ass ink. If you can see through ink so can your etching solution.

    2. I have had some great results with using adhesive vinyl as a mask material. Just use an exacto and go to town. If you have a cutting plotter, you can reliably create 10 mil traces.

      Here is a pretty decent instructable detailing the process: http://www.instructables.com/id/Fast-and-Easy-PCB-Prototyping-with-Vinyl/

      Oh, and as a tip, don’t bother buying the expensive vinyl. Just get contact paper used to line kitchen shelves. It’s $2-3 a roll, and it’ll last you forever.

  7. Maybe it’s just too simple to mention, but I’ve been able to make a lot of copper disappear off boards simply by running a low voltage current through it in a saltwater bath. Basically electroplating in reverse.

  8. I am watching closely as the minds of many exceed my own and there is a desire to do these with the least impact on the environment. Where is a good competent chemist when one is needed? An authority. Someone to direct us to the solution. Man, I make a lot of boards….

  9. i use the salt, peroxide, and vinegar solution because 2 of those can be bought with food stamps. leaving me to buy a $3 bottle of peroxide every time i want to etch something.

    last time i did the immersion method, it took about an hour to etch a batch of 6 double sided pcbs that i had all layed out together. granted i had a lot of copper to etch. i was having problems with my etchant getting saturated with copper and had to keep adding peroxide which seemed to speed things along when things seemed to stall.

  10. I use sodium persulfate and I’m very satisfied with the results. It takes longer than ferric chloride, but it’s much less «dirty» and cheap enough. The remainder is сopper(II) sulfate.

  11. just my 0.04:
    1. You can do electrolysis and save come FeCl and reduce time, I have tried this method, but the hassle is not worth it.
    2. The cost/etch is the same whether you rub it or immerse it, the same amount of etchant is required for the same amount of copper…. unless you are stupid and throw it away after one use.
    3. FeCl is so expensive in the US. I can buy 1 liter 38% for like 2-3 euro from local producer or 500g of pure cloride for like 5-7euro from larger distributors.
    4. Maybe a more realistic pattern should have been used for the tests, the results look quite bad to me…

  12. Frankly, drop the FeCl stuff guys. Way too slow, way too messy and unpractical (you can’t easily see through it so you don’t know if the etch is complete or not).
    I use sulfuric acid and 30% vol H202. The H202 was the most complicated ingredient to get, as you don’t see it very often in those ‘home improvement’ stores.
    Anyway, 30% vol is way too concentrated, if I use a 40/60 mix with HSO4 and H2O2, a board is etched in around 5 seconds! Also it’s quite exothermic so the mix starts to fume acid fumes.
    I did some mixes with 10/90 H2SO4 and 3% H2O2 and the speed was very correct (2-3 minutes I think).
    seems also be more environmentally friendly…

    1. I’ve gotten good etches using FeCl in under 2 minutes. How fast do you need a board done? Do you have a hot date or something? Then again I know what I’m doing, and that might be a factor.

  13. I often hear people saying “ditch that nasty ferric chloride” and recommending HCl/H2O2 but completely ignoring how nasty this etchant is too.

    Ferric Chloride may stain if you spill it, but those HCl fumes sound far more unpleasant. In the workshop where I do my etching I have a fair bit of expensive equipment – a lathe, CNC mill, laser cutter, oscilloscope, etc. I don’t want these corroding away. I’m sure HCl fumes won’t do me much good either.

    I must admit I haven’t tried HCl/H2O2 for these reasons, but I don’t find ferric chloride that bad. Of the two etchants I’d rather risk some stains – and when I have been careless I seem to have got away with this anyway. The stains washed off my hands easily and the stainless steel sink survived. One T-shirt looks a bit worse now. However, nothing has rusted to junk.

    1. One remainder – FeCl will eat steel/iron for breakfast, you have to watch where you spill it ;-)
      Also, if you are running bubbles through the solution, it will create an aerosol, which can go places…

      As for HCl/H202 etching – outside or in a fume hood, anything else will lead to damage of surroundings (that includes plants as well)…on the other hand the used solution can be used to make CuCl, which can be reclaimed indefinitely…

    2. If you’re using FeCl right it’ll fume too. You really should heat it up until it does fume for it to etch well. Happens at about 105F What I hate the most about FeCl is when it gets loaded with copper then it is done, and must be disposed of. Although I have heard of people regenerating FeCl with sulfuric acid to some extent. I don’t know about it personally though, as I’ve never tried that myself. But to get the best FeCl etch heat the bath, and pump air through it, then the stuff rips.

    3. HCL/H202 works amazingly well, it’s worth doing the etching outdoors.

      Typically 3-4 minutes for a board/batch and if you keep agitating it will work very evenly. It is a bit on the harsh side if your mask isn’t good though.

  14. I use HCl (sold as Muriatic Acid in most hardware shop) with peroxyde. Hairdresser have 6% peroxyde, but when you consider the price and the availability, is not worth the trouble. I use a ratio of 1 part of HCl for 2-3 parts of peroxyde.
    I always do my etching on the kitchen oven, with the fan at its max speed.
    A 3in x 4in PCB will take 2-3 minutes depending on the surface to remove.

  15. Nice to see the vinegar/salt/peroxide method getting some love. I think it’s underappreciated.

    I’d have liked to see the author test a third method- immersed PCB with regular wiping off with a foam brush. This is what I do, and it speeds the process considerably. With the vinegar method, a precipitate forms on the surface of the copper, and that acts to protect it from further etching. Wiping this off to expose new copper every minute or so really helps.

    Regarding disposal, there’s a thread about this on the comments of my article on etching. Therein, some chemists and other experts weigh in, and it’s interesting.


  16. The rubbing method albeit interesting could be dangerous when using those transfer sheets with pads,vias, symbols etc. They’re rare today but still very useful when one needs DIP traces and other well known pin placements.

    1. I’ve used dry transfers. They would scratch off if you got it with something about as hard as a fingernail. I’m not sure if a wet sponge would do it though. Don’t do the sponge method anyways. That is for saps. Rock a bye boardy is a chump move too. Bubbling is the best way to go for an amateur. Setting up an etchant sprayer is too hard for the improvement over a bubbler. I’ve finished bubble etches in under 2 minutes. How much time could a sprayer possibly save over that? A minute? Bubble etches are crisp too. No undercutting, jagged edges, etc.

      My favorite bubbler is a 12V tire inflation air compressor rigged up to a spray can cap. It puts out just the right pulsating flow. Some folks use fish tank aerators and they’re probably too steady. A spastic 12V tire compressor just has a certain action to it that lends itself perfectly to etch aerating IMO. Scour thrift stores and flea markets and find the lousiest 12V tire compressor that you can get. It’ll be great! Mine has a plastic body and rubber suction cup feet. It is the cheapest of the cheap.

      At one point it even broke down on me throwing its pot metal connecting rod. That did not deter me though as I had a pail of bent nails on hand to make a new one for it out of. It’s a runner!

  17. Hi, am from Germany,
    We have bought Dual jet etching machine from Etchcut, India, So far we have not faced this problem from last 7 years, they are using some patented technology in design, we easily cut high precision components in stainless steel

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