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Sponge + Ferric Chloride Method -- Etch PCBs in One Minute!

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In this Instructable, I will show you how to etch a circuit board with about a tablespoon of ferric chloride etching solution and a 2 inch square sponge. You will be amazed as the exposed copper on the PCB disappears before your eyes, and your board is completely etched in a minute or less!

I found a passing mention of this technique of using a sponge with a small amount of ferric chloride on the Pulsar web site, and I was very skeptical that it could possibly work. So naturally, I tried it.

Whenever I have made circuit boards in the past, I did it just like most of us do. I put the ferric chloride into a small tub, dropped the masked circuit board into the solution, and rocked it back and forth for a long time. Even with fresh, strong ferric chloride solution, it would usually take at least 10 minutes for the copper to be removed. As the solution grew weaker, the etch would take longer and longer.

A few months ago, I discovered the 1-part pool acid (muriatic acid) to 2 parts hydrogen peroxide method of etching a circuit board. You will find lots of wonderful Instructables on this method. That method works great, and it made me mad that I spent so much money and effort with ferric chloride over the years when I already had all the chemicals I needed right at home to use this method. The down sides of the acid and hydrogen peroxide solution are that the muriatic acid can cause skin burns and is a little dangerous and damages things that it contacts. Also, I found the etching solution to be quite aggressive which was great for fast etching, but I ended up with severe undercutting and partial obliteration of the traces, and the solution tended to be more corrosive to the resist materials I used, and partially dissolved the mask away during the etch.

This weekend I tried this sponge and ferric chloride method to etch 3 Arduino shield boards I am prototyping for our RFID-enabled member access system at TechShop (TechShop is the 15,000 square foot membership-based DIY workshop with locations in Menlo Park CA, Portland OR and Durham NC). I was so impressed with the success of this technique that I decided to write it up as an Instructable.

The method I will now show you gives you the advantages of all the other methods, and none of the downsides. Specifically:

o You get a fast etch (much faster than either method I know of),
o You use a tablespoon of solution, so disposal problems are eliminated
o A small bottle of ferric chloride will last for hundreds of boards
o No tank or tub is needed, no heating or agitation
o Undercutting is practically non-existent, and the resist stays in place
o There is no need to try to reduce the amount of copper being etched
o The etch is so fast that it is actually exciting to watch and show your friends!

Let's get to it, shall we?
 
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BillK25 days ago

I've etched by immersion and generally it takes 12-15 minutes to etch the boards I use. I tried using the sponge method today and after 8 minutes I still have a copper clad board (less copper to be sure, but still continuity all around the surface. Did I miss something? I know etching is noticeably faster is the Ferric Chloride is heated which I didn't do here...

maxchu7652 months ago

Where did you get that copper clad pcb? I really like the clear-ish base layer and the contrast with the copper. I looked for it and can't seem to find it. All the boards I have found have a yellow base layer.

Thanks

TechShopJim (author)  maxchu7652 months ago

Hi maxchu765...

I got that at a local scrap metal supplier called Alan Steel here in the San Francisco Bay Area. What an awesome place that is!!! They have huge piles of these large PCB sheets (maybe 12" x 18") for $1 per sheet. It is double-sided so you can either use that to your advantage, or just use some extra ferric chloride or other etchant to remove the unused copper from the back side. These PCBs have the clear epoxy core as you are asking for, and they are really thin and lightweight and great for tiny projects that need to be light.

Unfortunately, Alan Steel doesn't do mail order or online ordering...just local.

Thanks!
sbergstc3 months ago

Thanks for the tut... You mentioned in one of the comments that you're now using a vinyl cutter to create the resist and I was thinking about the same thing for an etching project, but I want a very deep etch and wondered if you have any experience with how long the vinyl can be submerged in the ferric chloride.

To get the deep etched result I want, I have used a sharpie and suspended the copper pipe in a FC bath over a hot plate (to warm the FC and speed up the process) and it took 1.5 hours. For the most part the sharpie marker stayed on the metal, but I could tell it was not going to last much longer so I took out my pipe. The etch was OK, but not as deep as I wanted to see so I was thinking the vinyl method might give a clearer result. Plus the vinyl would wrap very nicely around the pipe.

Thanks for your response,

Sharon

TechShopJim (author)  sbergstc3 months ago

I think the vinyl will stay on as long as you need it, since the adhesive is not water-based.

Good luck!
jensenr304 months ago

do you know how thick your copper boards are?

I just tried to etch my first board and it took me an hour and about 8 oz of ferric chloride to get the board finally etched.

I put the copper clad board into a plastic container, poured in ferric chloride, and then jostled the container for about and hour, wiping it down a sponge periodically.

I think my copper board might have been too thick because it seems like I have way too much "spent" copper chloride.

What is your opinion on all of this?

thanks.

jensen.

TechShopJim (author)  jensenr304 months ago

My PCBs were 1/2-oz copper.

You don;t need to submerge your PCB in the FC. You only need to wet your sponge and continuously rub the PCB with the sponge. Resist the urge to submerge it in the FC!!!

ok xD I will try this again soon without submerging the board in Ferric Chloride.

Thanks for the quick response!

Jensen

cvan44 months ago

The board that I want to make is mostly copper, and not much traces, because I'm using it as a contact switch. I was wondering if I should use a Q-Tip instead of a sponge. I'll have to try this on a smaller less expensive board first.

TechShopJim (author)  cvan44 months ago

You could definitely use a q-tip (cotton swap for those not in certain countries) for localized etching. I would create artwork to separate that section from the rest of the board.

Good luck!
wbc7896 months ago

Thanks for the tutorial. We tried this using an iron and glossy photo paper and we had a very hard time getting our lines to stick to the copper. We cleaned the boards thoroughly and turned the iron up high (It actually seemed to be melting the paper slightly).We are doing this for a school project and would really prefer not to have to purchase a laminator to do this. Are there any other tricks to getting your design to stick well, such as a specific type of paper? We were wondering if the paper used to transfer images on to t-shirts would work well.

TechShopJim (author)  wbc7896 months ago

Hi WBC789...

I don't know about t-shirt transfer paper...I would doubt it would work for this application.

The type of laser printer you use really matters a lot. I used an old HP 1100 until it died. I tried a Brother and it failed completely...no toner would transfer at all. So I am going to go back to a current-model HP laser printer and see if it works.

The only paper I have found that really works great is some that I purchased that has a dextrin coating called Pulsar:

http://www.digikey.com/product-detail/en/50-1101/182-1003-ND/3386

I just found this article on how to make your own dextrin-coated paper:

http://paulwanamaker.wordpress.com/how-to-make-dextrin-coated-paper-for-the-toner-transfer-method-of-making-pcbs/

The great thing about dextrin-coated paper is that it accepts the toner quite well, and transfers the toner through the laminating process nicely, but when you put it in water, the paper comes right off leaving the toner behind on your bare PCB. With other types of paper, you have to scrub the paper off until the fibers come loose from the PCB.

By the way, Harbor Freight sells a 9" hot laminator for $30...I'm not sure if it would be hot enough for this type of work, but you could try it and take it back if it doesn't work. Here is the link:

http://www.harborfreight.com/9-inch-hot-laminator-92499.html

Good luck!
samzimmer6 months ago

Very nice tutorial. It says to simply rinse out the sponge containing the ferric chloride. Is there any danger rinsing it down a metal sink, or should it be squeezed out into a chemical waste bin?

TechShopJim (author)  samzimmer6 months ago

Hi samzimmer...

The issue with the used ferric chloride has been beaten to death already. Please read the previous comments.
rpotts27 months ago
just so you know you CAN use vinegar. the problem is, it is SO much weaker that by the time you have gotten your basic etch finished, half your traces are undercutted from being in solution so long. I just did this last night for the heck of it. quick cheap lesson. ill try the sponge method next. what am I looking WRT fumes by using a sponge. still need super ventilation? its winter now where I am.
hanlin_y1 year ago
I find that it etches a lot quicker in front of a heat lamp. The warmer it is, the faster it etches and less scrubbing is needed.
TechShopJim (author)  hanlin_y1 year ago
Yes, that is true with the ferric chloride immersion etching method as well...if you heat the solution up, even up to near boiling temperature, it really makes it etch faster.

Maybe you could put the ferric chloride on the sponge and then microwave it to heat it up. Be careful and don't burn yourself, and use your "NOT FOR FOOD" microwave oven for this. Doesn't every maker have one of those in their garages or sheds? ;)
kayush1 year ago
I have a doubt. My etching went perfectly! Well, the color and texture looks exactly like the photograph as far as my eyes work

But, just to make sure, the etching is properly done, I tested if the etched surface is still conducting and as it turns out, it is. As conducting as a copper itself. Well, I went on to test the conductivity of Ferric Chloride itself which is actually very close to a metal. Now, I think some of Ferric Chloride might have stuck on the surface which is conducting the thing.

How do I resolve this problem? How do I clean the PCB if the problem is what I think it is?
TechShopJim (author)  kayush1 year ago
Hi Kayush...

Ferric chloride is water soluble, so you should be able to give your etched board a rinse and it should be down to the bare copper and fiberglass substrate.

That's interesting that you discovered that ferric chloride is electrically conductive. I wonder if it is conductive when it is new and fresh, or it is conductive because of the copper that it consumed. I know that copper oxide is highly conductive, and I'm using that phenomenon for a different project to teach electronics to kids, but that's another Instructable. ;)

Thanks!
I'm going to try this, however I'm not finding any software to use to make or create patterns. I heard of Eagle but something along the lines of an app would be perfect. I try to use tablets for most of my work. Any suggestions would be appreciated. Wonderful Instructable, favorited and ill pass it along to family and friends.
Also, I used the pcb board from RadioShack. It does not list any specifications for copper thickness, just the size of the pcb board itself. Is this product going to present problems or in your opinion, would it be sufficient
Mudbud1 year ago
Well, I tried it with a sharpie and it was erased.... lol..
nice work sir,,,,i also use the same ferric chloride ...but in powder form....could you point out how much powder will create a solution strong enough to etch copper?? how much powder should i add to i litre of water
TechShopJim (author)  sbdash113911 year ago
I don;t know...I have never used the ferric chloride powder...only liquid. Sorry!
1 liter f water sorry for that typing error
for smaller circuits that are very simple it would be convenient to use a permanent marker available in india for 0.5 us dollars.....for larger ckts one needs to use a ckt outline printed on a photopaper available for 0.13 us dollars .....however the photo paperswork only on inkjet printers..laser printers burn them....be careful...a hand drill as the one shown may be tiring but if you are not in a hurry then it is great to use one ,,,use 0.5 mm 1mm and 1.5 mm drill bits so that they tolerate little bending, wooden board at the bottom is a must unless you want the drill bits to drill your floors, table tops.....this etchant method using sponge for etching is great
TechShopJim (author)  sbdash113911 year ago
Yes, definitely. I have used various inks in the past with success. Now I use a laser cutter or vinyl cutter to create my resist.
would this work for etching brass, too? If so, how thick do you think it could manage?
TechShopJim (author)  mushroom glue1 year ago
If it is thin brass, then probably so. If it is thick, then it would take a long time. Check out my other Instructable on electro-etching thick brass plates.
cold.geek5 years ago
You've just rinsed copper chloride out of the sponge and down the sink, which means you've not eliminated the disposal problem but you've ignored it. The main issue in the disposal problem isn't because of the the large amount of Ferric chloride that doesn't react with the copper, but the small amount of it that does.
So what is the best way to dispose of the resulting solution? I'm sure it varies from place to place, but is there a site where one can look these things up?
This is what the MSDS sheet says about disposal:

"Disposal Considerations

Whatever cannot be saved for recovery or recycling should be managed in an appropriate and approved waste facility. Although not a listed RCRA hazardous waste, this material may exhibit one or more characteristics of a hazardous waste and require appropriate analysis to determine specific disposal requirements. Processing, use or contamination of this product may change the waste management options. State and local disposal regulations may differ from federal disposal regulations. Dispose of container and unused contents in accordance with federal, state and local requirements. "

Its not much help, but I would take it to a landfill on one of their hazmat days, although its not illegal to dump it.
you can mix the etchant(+ pieces of used sponge) with a baking soda solution-any concentration 3-5% will do.You end up with a mixture of undefined iron hydroxides and table salt solution.Should be less aggressive than FeCl3 and possible to flush down the drain.
According to what you have just said, the dissolved copper (which is the problem after all) is nowhere to be seen after the baking soda reaction. Hmmm ......
JTomM129 hinge3 years ago
Sounds like a good compromise . . .

That said don't forget you are using a tiny fraction of the FeCl3 solution that the "traditional" method calls for per. PCB (and I bet lots of that solution goes guess where?). Also, the small amount of solution that is used using this method gets diluted many times over will probably not effect house pipes to any measurable degree. Just flush with lots of rinse water after each session.
If Ford can continue to make cars, I think the earth won't mind a bit of used and diluted ferric chloride.  Am I the only one here who feels this way?
Arex_x rykonen4 years ago
No.
You should always be careful about what you put down the drain. But ...well , I don`t know really.
I see what you`re saying , about this being a small source of copper into the nature. And I think it is.
But it could have been interesting to do some math on it, sometime : )
....and down the drain it goes!

thats what i think when i pour stuff (harmful) down the drain
just like the 5 microscope coverslips I broke in science a month ago. It ended up clogging the drain.
tgrundle hintss3 years ago
I think some of you may be missing another important point here (even a year and a half later). This stuff attacks copper and the plastic the circuit board is made of. No mater if you have a newer or older home this stuff could attack your pipes. I don't think anyone wants to waste several days digging up and replacing pipe when we could be etching circuit boards!!! :)
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