Ask Hackaday: What’s Your Etchant?

Although the typical cliché for a mad scientist usually involves Bunsen burners, beakers, and retorts, most of us (with some exceptions, of course) aren’t really chemists. However, there are some electronic endeavors that require a bit of knowledge about chemistry or related fields like metallurgy. No place is this more apparent than producing your own PCBs. Unless you use a mill, you are probably using a chemical bath of some sort to strip copper from your boards.

The standard go-to solution is ferric chloride. It isn’t too tricky to use, but it does work better hot and with aeration, although neither are absolutely necessary. However, it does tend to stain just about everything it touches. In liquid form, it is more expensive to ship, although you can get it in dry form. Another common etchant is ammonium or sodium persulphate.

pcbyThere’s also a variety of homemade etchants using things like muriatic acid and vinegar. Most of these use peroxide as an oxidizer. There’s lots of information about things like this on the Internet. However, like everything on the Internet, you can find good information and bad information.

When [w_k_fay] ran out of PCB etchant, he decided to make his own to replace it. He complained that he found a lot of vague and conflicting information on the Internet.  He read that the vinegar solution was too slow and the cupric acid needs a heated tank, a way to oxygenate the solution, and strict pH controls. However, he did have successful experiments with the hydrochloric acid and peroxide. He also used the same materials (along with some others) to make ferric chloride successfully.

pcbxEven then, it is a good example of conflicting information on the Internet. While  [w_k_fay] says his vinegar solution didn’t do much, we’ve seen examples where it seems quite effective. Bad information could be especially dangerous with this sort of thing. In [w_k_fay’s]  case, he is careful to work outdoors and used protective gear, but you don’t always see discussions of that on web sites. The acid and peroxide will fume, and that can corrode metal. [w_k_fay] read somewhere that the solution would break down after a few days, but one of our editors has been using the same batch for the last five years. Go figure.

A common theme in etchants is to use hydrogen peroxide as an oxidant. The problem is, what you get in the drug store isn’t all that strong. In general, the higher the concentration of peroxide the stronger the solution. You can freeze 3% peroxide to increase the concentration or go to a beauty supply store and by peroxide at higher concentrations, but it will cost more. Of course, if you’re diluting the acid with water anyway, the peroxide concentration may be moot.

Speaking of cost, some of these solutions are cheap, but it isn’t like premade etching solution is that expensive either. However, sometimes the commercial chemicals are hard to source locally, so that may be more of an inducement to homebrew.

So the question for all Hackaday readers is a simple one: what do you use to etch your boards? A commercial solution? Something homebrew? A CNC machine? (Well, that doesn’t really count for the purpose of this question, but we’ll take the answer anyway.) We suppose plasma etching doesn’t count, either, but it would be interesting to know if anyone’s doing that. Leave a comment with what you are using and why.

Just to remind you, copper etching isn’t just for electronics. That’ll give you something to do with your etchant when you decide to just start sending your boards out.

87 thoughts on “Ask Hackaday: What’s Your Etchant?

    1. I used to use Ferric Chloride but it’s no longer available because the government is worried about terrorists making bombs. Mind you, I can readily buy everything nessisary to make one of the nastiest explosive from a hardware store, no questions asked.

      I can’t use Hydrogen Peroxide either for much the same reason. Hair dressers can still buy it though because being a terrorist and a hair dresser are mutually exclusive – some how.

      So now I use Ammonium Per-sulphate which needs to be heated to 70 degrees Celsius.

      Here’s my process –
      ) I put some 10mm plastic spacers into an electric frying pan that is turned off
      ) and then place a square Pyrex bowl on top the spacers.
      ) place boiling water into the frying pan but not enough to float the Pyrex dish
      ) place about 1/4″ (6mm) of boiling water into the Pyrex dish
      ) Place a temp sensor into the water in the Pyrex dish
      ) The cooler frying pan and Pyrex dish will cause the water temps to fall
      ) Wait till the temp of both waters reach 70 degrees Celsius
      ) Now turn on the frying pan and observe or mark both ends of the hysteresis on the temp control
      ) Move the temp probe from the bowl to the frying pan
      ) Safety mask is then put on (organic compounds filter and not just a particulate), safety goggles and gloves
      ) Add a small amount of Ammonium Per-Sulphate. It will release a white gas, stir it in with a disposable plastic spoon
      ) If it’s etching far too slow after a wile then add a little more. I use about two teaspoons but at the correct temp it will etch even if slowly. I also print minimum-etch boards.
      ) continue monitoring and adjusting the temp of the water in the frying pan till cooked!

      I am not sure of how the waste should be disposed of so I pore it into a full laundry tub of water, stir and then drain.

      Am I doing anything wrong?

      1. Make your own etchant. At the hardware store buy a 1l bottle of 37% hydrochloric acid, usually sold as cement stain remover or pool pH regulator. Strip half a kilo of copper wires to the bare copper. Put the copper and the acid into the same container so that part of the copper is exposed to air. Attach a fishtank air pump, bubble air into the acid. Every 24 hours shake the bottle.
        After about a week all the copper will have dissolved. The solution will be brown at first. Keep bubbling air till it turns grass green. You just made CuCl2 etchant. Use like FeCl3 etchant. Every couple dozen boards add some more acid and run the airpump for a few days to regenerate the etchant, it’s useable almost indefinitely.

        1. I can’t even get HCl same reasons as above. I am wondering if crystallized citric acid in aqueous solution will work, in theory it will(Cu-citrate) but wondering if anyone has tried. I send out or use perf board now.

        2. I use muriatic acid instead of hydrochloric acid, which I get from any pool supply store. I also use peroxide initially to kick off the reactions. Still don’t quite have the ratios balanced so etching takes a little longer than I would like, but each time I add a little more acid and oxygenate as much as possible. Should get to faster etch times soon. Still not too long and I love the fact it never needs to be replaced like FeCl. Much easier to dispose of when necessary too.

          1. FTR, Muriatic acid *IS* HCl. It is available in varying concentrations, generally referred to in degrees Baume. 20 degrees Baume is 31.45% HCl (sometimes just called 32 HCl) – the rest of the jug is H20.

            I used to use FeCl – I have a couple of bottles, one of which is (I’m not kidding) 30+ year old from when I started etching PCBs (back when it was rub-on masks and resist pens). Availability/added shipping costs/disposal prompted me to switch to HCl as a base. It’s effective, doesn’t take too long, is less toxic, is readily available and WAY cheaper. Oh, and unlike FeCl, you can recondition the Cupric Chloride

            The fumes do need to be contended with though, and when storing the fluid, a glass or plastic container with a plastic lid (not metal) should be used. Label it for what it is and as CORROSIVE.

            Another plus to Cupric Chloride – being able to see your PCB through the solution while immersed. I’ll use a bright LED flashlight to shine through (I generally stick to single sided PCBs for home etch as it’s trivial to set up), and you can easily see when it’s nearing done.

            I laser print my designs on proper transfer paper (no photo paper or advertising glossies). I print one run on plain paper, then cut and carfully tape (on the feed leading edge only) a suitable size of the transfer paper over that and send the page through the printer a second time, which conserves the transfer paper.

            After etch and rinse, I tin plate with Stannous Chloride + Thiourea + Sulfamic Acid (all purchased as dry ingredients and mixed at an 0.5g : 2.0g : 3.0g ratio, as measured in a precision scale and stored in little plastic containers awaiting my need to use a “dose”. In dry form, they’ll last a long while, as compared to a packaged tinning solution (or once you’ve dissolved them into 100mL of distilled water). I pre-heat the water in a beaker in a microwave in the shop (I’ll heat water there, but not some solution that might outgas).

            For solutions which work best when kept heated (and when dealing with small enough PCBs), those single mug heater coasters (akin to the base plate of consumer coffee pot warmers) are handy: just set your jar on top and let it heat away.

      2. I’m curious why ferric chloride would be regulated over fears that terrorists would use it. Would it be used as a sort of chemical weapon or is the potential due to some other explosive reaction?
        Other than generating hydrogen which is far cheaper and easier using other chemicals, I am unaware of any (reasonable) potential explosive danger.

        1. I am completely unaware of a weaponry use for Ferric Chloride but that does *not* distress me because I am equally unaware of any politician that introduces legislation for *rationalised* reasons.

  1. When I was young “hardware hacker” (early 90s in Russia) I used mix of “cupric sulfate” (медный купорос) and “sodium chloride” (соль) with warm water – it took about a day to etch a board (on heating radiator), but I was happy anyway :)

      1. Me too comrade!
        With the right proportion I was getting the best result – 8 minutes.
        Also the board must float on top of the warm mixture.
        If the proportion salt and copper chloride is wrong, it takes much longer.

        We had some hi power radio transmitter equipment in the shop and we put the container with the PCB on top of it. It adds heat plus vibration. Make sure PCB is still floating on top of liquid.

        If the mixture turns light blue, the proportion did not work. The color must be dark green.
        I do not remember the right proportion. My chemistry teacher helped me back in USSR. :)

        8 минут мой рекорд!

    1. I was using vinegar, salt and hydrogen peroxide, but I couldn’t get it to work very well. It was taking a day to do its job and often it was also removing some of the traces (or making them very thin).
      Then I found out about the copper sulfate (or bluestone, as I knew it). Mixing 1 part copper sulfate with 3 parts salt (or enough for the solution to turn bright green), I was able to etch perfectly in less than an hour, with no additional heating.

  2. Not that I would ever choose to etch a board with it, but the most terrifying and aggressive etchant I have ever used was comprised of the following: HF, Nitric, Sulfuric, Hydrochloric and Phosphoric acids. I will say that, if you wanted to etch a PCB with it, it would do it in about 3 seconds, assuming the FR4 survived, and assuming you could find a mask that would survive. More to the point of the question – I find that HCl and H2O2 is still the most mundane and reliable method, plus the materials are cheap and that helps.

    1. What for did you use this devil’s brew? Really toxic, strongly acidic and strongly oxidizing. Not that this is a guarantee to dissolve everything, think of silver in aqua regia.
      I just used 200ml HCl (conc. 37%), 30ml H2O2 (30%) and H2O up to 1 liter. Worked very well and we had the stuff at home for the pool care.

      1. There are certain things in this world that don’t like to be etched by anything short of an O2 plasma ash. I work with some of those things daily. In the absence of the option of plasma ashing, the above brew is an acceptable substitute for some things. I work in the semiconductor industry.

    2. We used to use hot NaOH to strip an IC down to the leadframe. We also used HF to eat glass, of course. And there was some nasty cyanide etch I was always afraid of to strip the gold coating off parts that had been in the SEM. They told us that dropping that etch in water would have released a big load of cyanide gas. Never tried that although I did get a snoot full of fuming nitric fumes when moving a beaker between vent hoods one time.

  3. I bought a 1 litre bottle of ferric chloride at my local Radio Shack when I was 14. I am 40 now, and I’m still using it. Granted, I took a 20+ year hiatus from etching boards, but it still works great, except for staining every damn thing. It outlasted Radio Shack Canada and the margarine tub I put my first pour in, which started to turn to dust about five years ago.

    1. With a cheap(ish) setup (~$100) you can go from CAD design to working board in 45 minutes. I do all SMD too to avoid having to drill holes. Use lots of 0 ohm jumpers, but they are like $5 for 1000.

    2. On the same thread, mine is a professional-grade etchant as well, whichever one is used by OSHPark… I use a professional-grade solder-mask and silkscreen as well, and it works reasonably well down to around .04mm pitch. The best part is I don’t have to handle volatile chemicals or own a laminator. The cost is quite reasonable, although the process takes a few days rather than a few minutes. :)

    3. My etchant is aliexpress.com. Cleaner, easier, more precise, better soldering and faster PCB design. ;) And I took it to yet another level and created a TV-set using Sharp etchant and a computer using DELL etchant (inside is a CPU that I made using Intel etchant). :)

  4. A long time ago, I draw my first pcb with the tar extracted from 4.5 V batteries (diluted in benzene) applied with a drawing pen and then etched them the pcb (diluted) nitric acid… Quite nasty chemicals, but since I was in a scientific section, I was not too afraid :-)

      1. you should go to jail. Or even better to a place that is so polluted because of people like you that it’s impossible to survive there. If you don’t know how to dispose your chemicals correctly just call the town hall or your local authority whatever. In my country you can get rid of almost everything for free at the local recycling centre. If this is too much trouble for you don’t use or even buy those chemicals.

          1. The problem is the copper dissolved in the solution. You might be able to neutralize/transform the actual etchant in (at least in small quantities) harmless stuff, but the copper will still be there.

    1. Or, google for your local dumping options. Someone in Switzerland once complained about this. 30 seconds at google and yep. Household chemical waste there takes it, too! For free! Here in Baltimore County, USA, can just hand it to a guy at the dump and they just know what to do with it, for free!

      1. I can vouch for Washington DC and Germany as well. Firehouses in DC know what to do with toxics, and in Germany you go to the normal recycling (Wertstoffhof). Munich has a mobile dangerous chemicals and batteries wagon, but I’ve never managed to get the timing right.

        The copper isn’t good for water, water plants, or fish. The drains, especially where they’re prone to flooding and overflow, are probably not a good place.

        Of course, I’m saying this now after years of just pouring darkroom chemicals down the sink in my youth. Sorry, future generations! I’m trying to be better now.

    2. “…is there a way to regenerate it like cuprous chloride?”

      First, a superior etchant based upon ferric chloride made by adding a small amount of citric acid (Edinburgh etchant).
      Citric acid powder is cheap and easy to obtain as it’s used by home brewers.

      http://www.lawrence.co.uk/shop/etch.pdf

      On the regeneration of ferric chloride etchants without the hazard of toxic fumes:

      https://www.google.com/patents/US5227010

      That patent deals with regeneration via a particular method of injecting pure oxygen, but it also says this:

      “In addition, there have been certain suggestions to regenerate ferric chloride solutions by aerating or oxygenating. However, the suggested procedures tend to be relatively slow and do not adequately keep up with the rate of formation of ferrous ion during high volume etching procedures.”

      Note that for low volume hobbyist use rather than in an industrial continuous etching process the rate of formation of ferrous ion during the etching process may not exceed the ability of aeration to keep up and even if it did the etchant can be aerated before, during, and after the etch to compensate.

      1. Edinburgh Etchant is the way to go for me. I have another trick I use to reduce the amount of etchant used for each board and insure a fresh quick etch each time. I make sure my board corners and edges are rounded over slightly so they are not sharp then I place them in a ZipLock Freezer bag

        The next step is to add a small amount of Edinburgh etch (enough to cover the board when it is lying flat) and Zip it up. I also have an old crock pot filled with water heated up on Low. I place the bag in the heated water bath and gently agitate. The bag can be removed from the bath to inspect as needed without spillage. I can see the condition of the etch through the transparent bag and can stop the process when done.

        When done, unzip the bag and pour the exhausted etch into a container for hazardous waste disposal, rinse the board (still in the bag) in water and bobs your uncle. There is no open FeCl containers so there is little chance of staining of clothes and surfaces.

        I have never had a leak using this method, but if there is one, chances are it will be the crock pot water where it will be apparent and diluted by a large quantity of water.

  5. Always used ferric chloride, I intended to try some of the homebrew solutions but right around that time small run PC boards started getting cheap, and my designs started to become too complicated for home use.

    One day I intend to make more homebrew boards, using those foil patterns from electronics magazines I’d read years ago. At the time, I had no way to transfer them to a circuit board, so I always built everything point-to-point on perfboard.

  6. My etchant of choice copper chloride + hydrochloric acid

    I made the copper chloride myself using hydrochloric acid from patio cleaner, hydrogen peroxide and copper from some old wire. It is ideal for my infrequent use because it gains strength in storage and can be regenerated by bubbling air through it.

    1. You can skip the peroxide if you are patient, by the way. Leave some of the copper exposed to air and bubble air into the acid with a fishtank pump. Shake the container with your acid+copper mix once a day. It will take a week to fully convert the copper into CuCl2, but it will be more concentrated because adding peroxide might speed up the reaction but also dilutes it quite a bit. So… just hydrochloric acid, copper, air, and time….

  7. I’ve used the vinegar/H2O2/salt solution with good luck. Make sure you use fresh H2O2 and don’t skimp on the salt. I’ve also found that using a small watercolor brush to periodically remove the precipitate that builds up on the copper helps.

  8. HCl from a commercial toilet cleaner (approx 30% concentration) with Hydrogen Peroxide from a chemist or beauty shop (the strongest they have) – works wonders in very little time! I throw away everything once i’m done etching, Ferric Chloride used to be too messy and not easy to dispose of.

        1. You, Sir, ought to be ashamed of yourself for downplaying so recklessly the dangers of dihydrogen monoxide and the harm and damage caused by it to thousands of human beings on our planet every year, especially young children. You’re probably one of those paid shills of the chemical industry, at least judging by your shameless attempt at greenwashing this highly hazardous chemical. So let’s leave your unsubstantiated greenwashing propaganda aside for a moment and have a look at the actual scientific facts:
          * While some people in this discussion thread mentioned the dangers of Hypochloric Acid and Fluoric Acid, especially when inhaled – which is all correct – the fact is that the yearly number of injuries and actual deaths by inhalation of these substances is several orders of magnitudes lower than the yearly number of deaths by inhalation of dihydrogen monoxide. We’re talking about hundreds of thousands of deaths worldwide every year, many of which among children.
          * dihydrogen monoxide also causes thousands of deaths directly and indirectly in other ways. For example, it modifies the tribological properties of car tyres, causing them to lose grip and thus leading to accidents.
          * and many more dangers (see ref page linked below)
          * You can ask any scientific expert in the matter, and they will confirm these facts. Actually, I do incourage you to go to the next university and ask a chemistry professor. These dangers are all well known and scientifically proven, but the lobby of the chemical industry (which uses it e.g. as a solvent for toxical chemicals and other applications) and food industry (which uses it as a cheap commoditiy chemical for many reciepies) is so powerful that no attempt to ban DHMO has succeeded so far. In fact, the chemical is nowadays found even in most beverages, among other reasons because of its lower price compared to alternatives.
          But there are alternatives, even fully organic: For example, I recommend beverages replacing (at least partially) dihydrogen monoxide with C2H5OH or CH3CH2OH. It’s fully biologically produced, gluten-free and has many advantages. Of course, that comes at the cost of a higher price, but it’s worth it.
          So for a better world, let’s ban dihydrogen monoxide.

          Ref: For more detailed information about the dangers of dihydrogen monoxide and the scientific facts about it, have a look here: http://www.dhmo.org/facts.html

          1. My friend Brittany Benzaia, who developed a very efficient air conditioner that uses R718 (dihydrogen monoxide), poured a few gallons of R718 all over herself to prove how safe it is. Try that with whatever other refrigerant you use for HVAC. :)

  9. So many people here use HCl. I’ve tried it once with H2O2, and it etched reasonably quickly but produced a cloud of fearcely AWFUL smell. What’s up with that? Did I do something wrong?

    1. Too much/strong H2O2. The more or stronger H2O2 you add, the more vigorous the reaction will be. Less H2O2 slower more controlled reaction. Also of course if the HCl is too strong it will be fuming on it’s own, dilute the HCl until it is not fuming.

  10. My first etching experience was with ferric chroride.. that experience was enough for me to swear never to touch the stuff again.. messy, smelly etc.. after that I used to mix up a solution of 40% hydrogen peroxide, Hydrochloric acid and water.. cant remember the exact ratios *( I wrote a small ratio calculator app in delphi for that).. And that worked fantastically… I did however have one bad experience with that mix (My stupidity or still being partially asleep’s fault, not the mix)
    my sister (with whom I shared a house) complained about the 2 2 liter bottles of etchant that I stored in a cupboard in the kitchen, and asked that I dispose of them early one morning.. me not being very awake at the time hit on the bright idea of neutralising the acidic solution by adding something very basic so as to make disposal easier.. the only basic chemical I could find was caustic soda (sodium hydroxide).. long story short, I did not bother to measure out anything, just chucked the caustic soda and etchant into a largish plastic bucket and shortly thereafter my kitchen was filled with hydrogen chloride gas.. The look I got from the neighbor walking his dog when he saw me standing outside waiting for the fumes to dissapate and I told him what it was, not burning toast as he had assumed, was priceless :)

  11. I’ve always used Sodium persulfate (I think that’s the correct English name for it). It’s sold in orange plastic bags as etchant here in Sweden. It works very quickly, doesn’t smell and is easy to use.

    I usually boil some water, poor a bit of it in an old ice cream container (this becomes my heat source), stack another container in that, add as much SP as I think I need (maybe a tablespoon) and about 3-4dl of water. Dump the board in, agitate it and it’s done in 2-3 minutes depending on size and amount of copper to remove.

  12. 10% HCL + 30% H2O2 bought in the hardware store and drugstore store respectively. I don’t dilute it since HCL is already a diluted solution of 10%. 200ml HCL + 30ml H2O2, but less H2O2 can also work. I put hot water from the tap in a tub at about 60 degrees C, and the acid in a smaller container placed in the tub to warm up the solution. It speeds the etching up by about 3x, usually in 3-5mins. When done I store the acid in a used plastic bottle with screw on cap, but with the cap half undone so that the oxygene can escape. After a few days the cap can be screwed on fast.
    When reusing it, I drop in 10ml of H2O2 to reactivate it. Once the HCL is replaced by copper you can continue indefinitely. You can replace H2O2 with a fish tank bubbler but I’m too lazy to do that.
    When I want to dispose the acid I bring it to the local electronics shop where it is disposed of responsibly or I can bring it in to the municipal garbage collection point in the chemicals section. Labeling what’s in the container is a must. I’ve also tried recovering the copper using electrolysis but that took all night and still didn’t get all of it out. I’ve also seen people use sodium or calcium to neutralize the acid.
    I don’t ever touch the stuff, nor do I get anything covered by the stuff because of the tub, and I use an insulated single core electrical wire of about 50-70cm length (twisted a few turns to fasten it) put though a hole I drill in the pcb and hold that at a distance of about 30cm.
    I usually stand at the kitchen table with a window open for ventilation. When I feel the sting of fumes in my nose I step away or try to stand in the breeze from the window. I also keep a container with clean tap water ready to dip the pcb in when done, in order to get most of the acid off before washing it under the tap. Only then I touch the pcb to get the wire off.
    The acid is just strong enough to see some gentle bubbles coming from the pcb after a minute or so. If its more reactive than that, the acid is too strong. If the whole container turns bubbly and the level raises it’s way too strong. At some point if it gets stronger the acid also heats up, making it react even stronger and you’ve got a run away process that’s getting dangerous.
    I usually agitate the pcb by moving it back and forth and up and down with the wire. The edges are removed before the center so that’s the place where I look to see if the etching is in progress. Once the corners are etched, usually means the process is about half way.

  13. I did a couple of boards with vinegar and hydrogen peroxide, but gave up on that. I then made my own ferric chloride with hydrochloric acid and iron oxide (basically rust, but the dark rather than orange stuff). With use that basically turned into the copper chloride etchant that is mentioned in the article. I don’t heat it or anything, and it works fine but takes a while.

    For boards, I buy pre-coated photoresist board, and expose it with a home-made exposure unit (UV LED strips). Or I draw the mask on bare copper boards by hand with a Sharpie marker, for simple boards.

  14. Safety glasses, kitchen, rubber gloves, open door. Ammonium persulfate. Done. Or dirtypcbs.com. Depends what and how fast I want it. Dremel with drill press attachment for holes. CNC for cutting the boards. Eucalyptus oil to clean off the toner. Then either PCB laquerer or UV paint if I CBF.

  15. Copper(II) chloride. It’s great stuff! It’s actually not as fussy as the OP suggests. I find it to be a good etchant. Hydrochloric acid with hydrogen peroxide will etch very quickly – about two minutes. Copper(II) chloride takes a bit longer – maybe around half an hour to an hour – because copper(II) chloride is a weaker oxidizer than hydrogen peroxide.

    The fastest way to get going is to add hydrogen peroxide and a few metres of (stripped and cut) stranded copper wire to hydrochloric acid. The hydrogen peroxide will oxidize the copper, and the hydrochloric acid will react with the copper oxide to give copper(II) chloride. The copper should dissolve quickly to produce a green solution. The hydrogen peroxide will fairly promptly react with the hydrochloric acid, so you’ll soon have only the Copper(II) chloride and hydrochloric acid to do your etching.

    Once the copper(II) chloride has been used too much, it’ll turn a muddy brown. This is because the copper(II) chloride reacts with copper to form copper(I) chloride. When this happens, the etchant can be “regenerated” one of two ways:
    – Adding a small amount of hydrogen peroxide will quickly oxidise the copper(I) chloride back to copper(II) chloride and your solution will turn a lovely green again.
    – Leave the solution in a tub open to air for a day or two. The copper(I) chloride will react with oxygen in the air with the same result, albeit slower.

    The hydrogen peroxide is optional, however, because in addition to being able to regenerate your etchant without it, you can bootstrap the process to obtain copper(II) chloride in the first place. Oxidise some of the copper by heating it. Place this in hydrochloric acid. Your solution will turn a pale green. Now you can dissolve more (unoxidised) copper, and oxidize the resulting cuprous acid until all the copper is dissolved.

    Eventually you’ll run out of hydrochloric acid, and will have to top this up too. As a result, your etchant will (very slowly, depending on how much you etch) “grow”. For the most part, you shouldn’t have to dispose of your etchant (unlike ferric chloride) because it’s so easy to recycle back to usable etchant, but eventually you’ll have more than you need. I guess once this happens you can either dispose of the excess as you would ferric chloride, or far better: just give the excess to a friend whose new to PCB etching.

  16. A little conclusion: Seems all etching methods come with the same backpack: Chemicals, mixing ratios, fumes, gloves, savety glasses, stains, spills, smells, toxic waste. Oh and the trace mask needs to get onto the PCB somehow, so I add foils, UV exposer or direct-toner-transfer press etc. to the story.
    The article said CNC-milling PCBs counts as well, so here I am. I don’t say milling PCBs is better. Especially when you don’t have neither CNC mill nor etching gear, etching is the cheaper start. But when you have a mill, milling is fast, especially for small projects. A bit less precise however than etching, I admit. But the machine also drills the holes and can cut the PCB into any shape after.

    1. A tip for milling, If you have a beefy enough solder station, try pre tinning the copper clad prior to milling. That vastly improves the milling property compared to pure copper.

      1. Interesting! Good to know too. I’m betting that the solder works in two ways: 1, it acts as a lubricant, and two, it penetrates into and alloys with the copper, making it softer for a part of the depth between the surface and the FR4. I also wonder if the heat may anneal the coper a little bit, making it softer. Does anyone here know if any or all of what I’ve said is correct?

        1. I cannot try the tin-plating idea, unfortunately. But I hope it doesn’t make the copper softer; copper already tends to “smear” and be more pushed away by the milling cutter than cut away. I could imagine that the tin-layer gives the copper a bit of stability and prevents it from folding away (so that the cut chips go away and not just fold over).

      2. My speculation from what I can see is that it is the forming of a harder/brittle “alloy” that the bit can bite into and chip instead of surfing on top of the smearing copper. I also believe I can go more shallow and cut away the metal only. Without plating it’s like I have to force the bit through the copper and down into the substrate to cut away the copper properly.

    2. I want to add that there should not be a layer of tin on the board. Excess tin should be wiped of leaving just a flat surface.

      Something I haven’t got around trying yet is to go really fast and see if it possible to cut through the harder top layer only and surf on the underlaying copper and etch it afterwards. If it works it should make it possible to have thinner clearance and extend the life of the bits.

  17. Sodiumhydroxide (HaOH) to develop the precoated boards after UV exposure (transparent films). And then heated Sodiumpersulfate (Na2S2O8) aka Disoduimperoxidisulfate to etch the boards.
    (Using one of the etching stations from MEGA UK to heat and bubble the acid).
    Works pretty well and is not too messy. It just does not get used that much anymore since 4 layers and pretty fine pitch SMDs (<0.5mm) are usually the standard for the design complexity these days. Most boards get ordered in from professional board houses now…

  18. Cat piss removed a large patch of copper off a PCI card in one ofy computers awhile back, so I am curious if ussing “piss & vinegsr” would work as an etchant, if only for the lulz. ;-)

  19. Ferric chloride eventually ends up as copper chloride when its spent, so u dont have to do much to get copper chloride (the iron precipitates out). Off course u can make it with acid and copper. Once made u can bubble ozone through it (6x more soluble than oxygen). Ozone bubblers are supplied for aquariums etc.

    1. Saw a youtube-clip trying this idea once. It actually worked(‘ish), but keeping the “non”-traces connected to the current source is hard when they are eaten away in the process. You will end up with remaining copper everywhere, where the current stopped dragging the copper ions into the water.

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