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Thread: Here's how I make ferric chloride etchant

  1. #1
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    Lightbulb Here's how I make ferric chloride etchant

    Hey guys, thanks for helping to answer my questions in the past. Here's something some of you may find interesting, it's an experimental result of me being poor and being tired of buying more expensive small bottles of ferric chloride etchant from Radio Shack every time I wanted to etch another board.

    How I Make Ferric Chloride Etchant

    Ingredients that I use...

    • Gallon bottle of muriatic acid (bought at local hardware store (Lowes) for a few dollars)
    • Half-gallon of 40-volume hydrogen peroxide (bought at local beauty supply store (Sally Beauty Supply) for under ten dollars)
    • Steel Wool 6-Pack #4/0 Steel Wool Pads (bought at WalMart for under 3 dollars, can get at Lowes for under 4 dollars) Do NOT use the soapy cleaning pads found in the kitchen area, use the shop pads found in the hardware section of the store!
    • Baking soda (Sodium bicarbonate, already had it in the kitchen)


    Hardware that I use...

    • Clean plastic one-gallon milk jug with lid
    • Clean plastic juice jug with lid (46 to 64 ounce size) or 32-ounce Gatorade bottle with lid
    • Silicone airline tubing for fish tank (about three dollars at pet supply shop)
    • Nitrile gloves (bought at hardware store for under 4 dollars, they're reusable)
    • Drill with 1/4" drillbit (or a drillbit slightly smaller than the diameter of the silicone airline tubing)


    Getting the ferric chloride labratory ready!

    1. Get your jugs, silicone tubing, and drill ready!
    2. Go outside and away from anything you don't want to get stained and discolored. Don't do any of this stuff indoors, because the fumes are harmful to your health and will corrode any exposed metal in your house (loose change, light fixtures, faucets, picture frames, circuit boards, etc). The fumes are harmful, but the spouse can be deadly if any important or expensive metallic objects in the house get irrepairably rusted. Also, ferric chloride will stain concrete rusty-red and will not wash off so stay away from sidewalks, the driveway, and the porch.
    3. For the milk jug, drill one hole in the middle of the lid for some silicone tubing.
    4. For the juice jug, drill two holes in the lid for some silicone tubing.
    5. Cut a three-foot piece of silicone tubing and push one end into the hole in the milk jug lid. When you're done, the silicone tubing will protrude only about a half-inch into the milk jug and it should fit tightly in the hole. If the silicone tube won't fit in the hole at all, find a slightly bigger drillbit and drill the hole a little wider. If the silicone tube fits loosely in the hole, find another milk jug lid and use a smaller drillbit to drill the tube hole. The tube needs to fit tightly!
    6. For the end of the silicone tubing that's sticking out of the milk jug, stick it in one of the holes in the juice jug lid. Push the tubing down the hole until it goes all the way to the bottom of the jug. When you're done, the silicone tubing should be touching the bottom of the juice jug.
    7. Cut a 12-inch piece of silicone tubing and stick it in the other hole in the juice jug. It should protrude about a half inch into the milk jug when you're done.


    Now we have a milk jug with a tube connecting it to a juice jug. The juice jug also has another short tube simply stickoug out of it and not connecting to anything. The lab equipment is now done, so you can put the drill away and get the chemicals ready. If you're not already outside, go outside! The chemicals are corrosive and the vapor and fumes are harmful, and the end result (ferric chloride) will permanently stain concrete/stone/wood! OK, on to post number two...

  2. #2
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    Default Re: Here's how I make ferric chloride etchant

    Get ready to make ferrous chloride! What, ferrous chloride!? Isn't that iron II chloride? That's not etchant! Patience my friend, this is a two-part process...

    The purpose of the two bottles (milk jug and juice jug) are as a reaction chamber and a chemical filter. The milk jug is where the chemical reactions are going to take place, and those reactions are going to produce dangerous and corrosive fumes. The juice jug is going to be a budget chemical filter, where hydrogen chloride gas and other corrosive fumes produced in the reaction chamber will be mostly neutralized. Ideally the only gaseous byproduct should be hydrogen gas, but since we're doing this in the cheap there's probably going to be some passage of other chemical vapors despite the chemical filter. Hydrogen gas is extremely flammable and will ignite explosively, so do not smoke or use any fire or flame around the ferric chloride generator while it's in use!

    Now, let's get back to business!

    1. Get the nitrile gloves, muriatic acid, and steel wool pads ready!
    2. Put on the nitrile gloves. We're going to be using strong chemicals and don't want to get any on your hands.
    3. Fill the juice/Gatorade jug about 2/3 full with cold water.
    4. Add about 1/4 cup (two ounces) of baking soda to the water in the juice jug, and stir it until it's mostly or completely dissolved.
    5. Put the lid on the juice jug. The silicone tubing from the milk jug should be protruding all the way into the water in the juice jug and resting at the bottom of the container. The second short extra piece of silicone tubing should be barely sticking in the lid and not touch the water at all.
    6. Fill the milk jug about 1/3 full with muriatic acid. You may see fumes as you pour the acid, especially if you live in a humid climate. Don't breathe the fumes, it's so strong that it will reflexively cause you to exhale and possibly spill the acid you're trying to pour into the milk jug. Be careful!
    7. Drop in two steel wool pads into the milk jug.
    8. Quickly put the lid back on the milk jug, and make sure the lid is tight on the juice jug too.


    Alright, now we have a milk jug with muriatic acid and steel wool pads in it. We also have a juice jug with water and baking soda in it. The muriatic acid should be reacting with the steel wool pads and producing gas, which you should see bubbling out of the end of the tube that's immersed in the baking soda water in the juice jug. The gas will percolate through the baking soda water and neutralize most of the hydrogen chloride gas that's expelled through the acid/steel reaction, and a somewhat salty smelling gas will come out of the short pipe that's sticking out of the juice jug. Keep all fire and flame away from the gas venting out of the juice jug. It's mostly hydrogen gas!

    Let this steel wool/muriatic acid reaction go for about a half-hour. Check back from time to time to see if gas is still bubbling into the baking soda water... If there's no more bubbling, look inside the milk jug and see if all of the steel wool has been dissolved. You may see some steel wool fibers floating on top of the muriatic acid (looks like hair floating in the acid), this is OK. When it's all dissolved (except for the 'hairs' floating on top), drop in another steel wool pad and close the milk jug lid. You should soon see the milk jug tube start bubbling through the baking soda water again in the juice jug. Let it go for another half-hour or so... Keep adding steel wool pads and letting the reaction happen until you see some steel wool pad in the milk jug after two hours of reaction time. Step one is done! On to step two, which is in post number three...

  3. #3
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    Default Re: Here's how I make ferric chloride etchant

    If you were to examine what's in the milk jug, you'd see a milky whitish-greenish 'stuff' settled at the bottom of a clear liquid. You'd also see the small chunk of steel wool pad left over from the previous step. You're now saying to yourself, "This isn't ferric chloride at all! Ferric chloride is a clear dark amber liquid, and this is an opaque white mess!" Well, you're right. We now have ferrous chloride, but we're about to turn it into ferric chloride!

    Step Two - FINALLY Making Ferric Chloride!

    Adding hydrogen peroxide to a solution of hydrochloric acid and ferrous chloride is DANGEROUS. It a very energetic exothermic reaction as the remaining hydrochloric acid is broken down and the resulting chlorine gas is immediately reacted with the ferrous chloride solution to create ferric chloride... Lots of bubbles and foam, and lots of heat is released. Follow the below instructions carefully or you could have a serious accident! When we're done, the milky white sludgy stuff you see now will be miraculously turned into clear dark amber ferric chloride etchant!

    1. Get the hydrogen peroxide and the nitrile gloves ready!
    2. Put on your nitrile gloves again. You're going to be messing around with REALLY corrosive stuff now!
    3. Take the lid off the milk jug, it's not going to be put on anymore so set it and the juice jug aside.
    4. The milk jug should have the previously mentioned mix of a milky white precipitate (ferrous chloride) and the chunk of undissolved steel wool. Do not take out the chunk of steel wool, leave it in the milk jug!
    5. SLOWLY add about 1/8 cup (one ounce) of hydrogen peroxide to the contents of the milk jug. The hydrogen peroxide will immediately and vigorously react with the ferrous chloride solution, which may splatter out of the opening of the milk jug. Make sure you keep the milk jug pointed away from you or anyone around you, the splatter is very caustic and will burn your skin! Do NOT attempt to put the lid back on the milk jug, because it may explode with the rapid buildup of pressure given off by the hydrogen peroxide reaction!
    6. After adding the hydrogen peroxide, wait until all the bubbling stops. Notice the change in color? That's right, it's turning into ferric chloride!
    7. When all of the bubbling stops, SLOWLY add another 1/8 cup of hydrogen peroxide and let it bubble furiously until all the bubbling stops.
    8. Feel the milk jug... Does it feel too hot to touch? If so, let it cool down before continuing.


    You should be noticing that the milky white stuff is turning into a dark amber mixture. You'll also notice that the chunk of steel wool is either dissolving or is completely gone. The hydrogen peroxide is breaking the chlorine away from the remaining hydrogen chloride gas dissolved in the ferrous chloride mixture, and the free chlorine atoms are reacting with the ferrous chloride molecules and are turning into ferric chloride! And the extra steel wool is reacting with the ferric chloride to revert to ferrous chloride, which in turn reacts with the extra chlorine gas to turn back into ferric chloride... Confused yet? I am!

    Each time you add a little bit of hydrogen peroxide, the reaction is immediate with a furious bubbling action followed by the bubbles completely going away. However, there will be a point where you'll add hydrogen peroxide and the familiar furious bubbling will be followed by an effervescent liquid... I'm getting ahead of myself, so let's continue with a few more steps:

    1. Continue to add a little bit of hydrogen peroxide and wait for the bubbles to go away. If the bubbles go away and the liquid in the milk jug is not bubbly at all, repeat the 'add more hydrogen peroxide' step.
    2. After you add enough hydrogen peroxide, the liquid in the milk jug will become effervescent. It will bubble like soda pop or beer, with bubbles slowly fizzling out of the mixture.
    3. Pull the silicone tube out of the milk jug lid, so that you end up with a milk jug lid with a hole in it.
    4. Add 1/8 cup more hydrogen peroxide, put on the milk jug lid, and leave the mixture alone.


    After a day or so, the remaining hydrogen peroxide will bubble out of the ferric chloride mixture and you will end up with something that looks like flat cola. It's very dark amber, clear, and is no longer effervescent. You will need to make a 'guesstimate ' to see if your new etchant is ready for work, and the way I do it is pretty simple: It's a color test! I simply take a drop of fresh commercial etchant (store-bought that hasn't been used yet) and compare it to a drop of my homemade etchant... If the Radio Shack etchant is much darker than my etchant, then my etchant isn't going to be strong enough to effectively etch circuit boards. To make my homemade etchant stronger, I do this:

    1. If the etchant failed the 'color test' and isn't strong enough, add two or three steel wool pads to the contents of the milk jug.
    2. Let this reaction go for an hour or so until the steel wool pads are gone.
    3. When the reaction is done, look at the contents of the milk jug. Is it still amber colored, or is it a liquid with milky white-ish stuff in it? If it's still amber colored, add another steel wool pad and let it dissolve for an hour or so. If it's milky white-ish, continue to the next step!
    4. When the contents of the milk jug is milky again, add hydrogen peroxide the same way you did in the previous steps until the mixture is dark amber and effervescent. Add another 1/8 cup of hydrogen peroxide, put the lid on the milk jug, and let it set until the effervescence goes away.


    I had to concentrate my etchant once after manufacture before it was strong enough to effectively etch circuit boards, but it now works GREAT! It's pretty nice to be able to pour out a gallon of etchant into an etch container and not worry about my circuit boards getting over-etched or badly under-cut the way they did when etched in a small container full of expensive overused etchant. I also don't have to worry about the resist ink getting eaten off my circuit boards the way it did with a mixture of hydrochloric acid and hydrogen peroxide.

    That's about it. It sounds like a lot of work, but if you put these steps in action you'll soon realize it's actually not that much work at all. And it's fun! It was fun, until my wife found the large rust-colored stain on the back porch...

  4. #4
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    Default Re: Here's how I make ferric chloride etchant

    Pine Fire, This is brilliant!
    However It could even be better if it had a few photos and/or drawings. Any chance to editing some into you text?

    the How-to move sounds like a good suggestion.

    Whilst I am willing to give it ago, I wonder how people can really get themselves into trouble by assuming they know what they are doing.
    Also better warn children not to do this with out asking their parents too.

    Cheers
    Matt
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  5. #5
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    Default Re: Here's how I make ferric chloride etchant

    I'm not sure that I see the point in this, since a number of people are using the precursor chemicals (muriatic acid and peroxide) for etching without all this extra work. And from the threads on this site they seem perfectly happy with it.
    Phil

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    Default Re: Here's how I make ferric chloride etchant

    Thanks Matt! As they say, lack of funds is the mother of invention... Er, is that how the saying goes? Anyway, I'll post pictures when I get the time (hopefully soon), I'm in the process of moving across the state so most of my chemistry equipment is packed away.

    I hope what I've italicized and put in bold is enough to keep most people out of trouble, but I don't really know how to write this article from the eyes of somebody who's never even mixed vinegar and baking soda. I've worked with chemicals for decades, so I'm used to handling and properly disposing of them. The safety measures I use are implemented out of habit; pretty much the same as climbing in a car and putting on a seatbelt without thinking about it. I just hope people read this article in its entirety before attempting to make ferric chloride, because the chemicals involved in its manufacture are indeed very dangerous. Skipping a step or rushing through any part can mean the difference between anything from a botched end product or a large dead spot in the lawn, or even chemical burns or permanent blindness.

  7. #7
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    Default Re: Here's how I make ferric chloride etchant

    I know this seems like a lot of work, Phil, but I also use Diazo Photo Emulsion (screen-printing emulsion) for photo-sensitizing blank copper boards. Muriatic acid/hydrogen peroxide etchant eats off this photo emulsion as quickly as the bare copper, so my boards become fiberglass coasters instead of circuit boards. Ferric chloride is less reactive to the photo emulsion, so the board gets properly etched before the emulsion starts to come off the board... I never had any luck with the toner transfer method, but I imagine it's a lot more durable than this photo emulsion stuff.

  8. #8
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    Default Re: Here's how I make ferric chloride etchant

    Do you find that purchased pre-sensitized boards (e.g. MG Chemicals boards) have the same issue with the alternate etch chemicals? Just wondering if it's just a resist makeup or thickness issue? I'm pretty happy with the outcome using these with FeCh but not so much with the price of the boards (about 2-3x a blank copper clad board).

    Can you go over the details of your resist application also - perhaps in another thread?

    Thanks!
    Brian
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  9. #9
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    Default Re: Here's how I make ferric chloride etchant

    OK Brian, I can do that tomorrow. My wife and two-year-old are home now so I don't have much time to write another article today. Uh oh, I think I hear my wife now... 'Are you still on that computer? Come out here and socialize!' Whoops, gotta go!

  10. #10
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    Default Re: Here's how I make ferric chloride etchant

    Mate, the biggest investment you will ever make is the relationship with your wife and kids. Don't ever apologise to go and spend time with them, enjoy it.

    Cheers
    matt
    (I invest in 6 children!)
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