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

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

About: I'm the Founder and Chairman of TechShop.

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?

Step 1: What You Will Need

You don't need a lot of supplies for this Instructable, just the following:

o Ferric chloride (available at Radio Shack, 16 oz bottle for $10, part number 276-1535)
o Sponge (2" x 2" square, cut from any sponge, or paper towel will work too)
o Rubber Gloves (you don't want to stain your hands)
o Copper Circuit Board (one or two sided)
o Cup of water (to drop the etched board into to stop the etching)

Step 2: Clean the Copper and Apply the Resist for the Circuit Pattern

There are lots of Instructables about how to apply the circuit pattern onto your copper, including peel and press, photo paper, tape, photo-sensitive emulsions, and even Sharpie pen. I will not touch on that part of the process here, but the method I prefer to use is laser printing onto a piece of Pulsar's dextrin paper and using one of their $70 personal laminators to apply the toner to the board. Then you rinse the paper and PCB under water and the paper slides right off, leaving the toner stuck fast to the board.

The key to any method of applying the resist is to make sure your copper circuit board is absolutely clean. I use a Scotch Brite pad and some dish detergent to scrub the copper clean, as shown in the first photo. Then I blot it with paper towel and let it completely dry. Never touch the cleaned copper, because oil from your fingers will cause the resist to not adhere to the copper, and the resist will come off during the etching process.

If you want to play with this Instructable right now and you don't want to make an actual circuit, just use a Sharpie pen to draw a little squiggle onto your cleaned copper circuit board.

In this case, I laser printed the Instructables robot onto Pulsar paper and applied it to the clean copper board with a laminator. Hey, it came out pretty good!

Step 3: Etch the Board (Instant Gratification!)

Put on your rubber gloves.

Open the bottle of ferric chloride and put the sponge over the opening, and tip the bottle to let about a tablespoon or so of solution saturate into the sponge.

Now with the circuit board in the palm of one hand, simply wipe the solution-saturated sponge over the surface of the board over and over. Don't scrub, just keep wiping it all over. In just a few seconds of wiping, you will see the copper start to disappear!

You will find that unlike the submersion etching method, the copper in the center of the board etches away first, so you might want to try to focus on the edges as you wipe.

In less than a minute of continuous gentle wiping, your board will be fully etched before your eyes!

Drop the etched circuit board into the bowl of water to stop the etching action.

If you are etching multiple boards, you can rinse out the sponge, squeeze out most of the water, then re-apply ferric chloride solution if desired, but I have found that I can etch two 2" x 3" boards with one application.

Step 4: Clean Up (Not Much to Do)

The clean up really is just a matter of rinsing out the sponge, throwing away the rubber gloves (or rinsing them off for reuse), and cleaning any spilled drops of ferric chloride from the work surface.

You can reuse the sponge over and over, so rinse it and let it dry, and keep it with your bottle of ferric chloride.

Step 5: Finished Product, and Your Results

Here's the finished product. Not too bad for 5 minutes from start to end!

I hope you will agree that this method is faster, cheaper, and more exciting to watch than other etching methods you may have used in the past. I'll bet you'll never use the ferric chloride tub or tank immersion method again.

I'm not sure if this low-volume wiping method will work with the muriatic acid and hydrogen peroxide etchant, but it is worth a try.

Some information I read indicated that adding a small amount of citric acid to the ferric chloride will make it an even more effective etchant for use with the sponge or immersion methods. You can find citric acid powder at beer and wine making shops, and even on eBay.

Go ahead and try this sponge method, and let me know in the Comments section if this will become your new method for etching circuits like it did for me.

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276 Comments

Brilliant! Just done my first ever etch after 'putting it off' because of the doubts raised by articles mentioning temperature, solution, paper type etc etc.

Just normal laser paper & printer and Ferric Chloride. Brilliant.....thank you. :-)

I tried this method using vinegar and hydrogen peroxide as the etchant. The problems that I encountered were mostly answered here, but for some reason I did not see them.

The first problem I encountered was when I tried to get the transfer of toner onto the copper clad. The iron-on method at the heat suggested by those using it didn't transfer anywhere near completely. I tried again with magazine paper which worked much better. But I still had to thicken up some of the lines and make the areas around the holes larger. I did that using permanent marker. I found a really fine line marker by the same maker of the other permanent markers. Still when I went to etch, the marker wore off and the etching process went on and on. But I get ahead of myself - the first try actually did absolutely nothing. I waited and gently rubbed, but nothing happened. So being a reasonably smart guy, I decided that the vinegar I had was probably too old, so I stopped and went for some new stuff. That worked much better, but the marker wore off as I said.

Thinking that I might have rubbed too hard, I remarked all of the etched off traces and tried again. Judging from the amount of solution I was using, my copper clad is too thick OMG - they are 1 oz boards. Well, that's ok, I'll try again with the remarked board and use a pan rather than a sponge.

I did and things seemed to go along quite well. I kept the board agitating to keep the bubbles from forming - I got kind of a foam over the top, so I cleaned that off and turned the board over. Every 15 minutes or so, when the activity seemed to stop, I removed the board, dumped the old material into a container and put fresh etching solution in the tray. However, again I get ahead of myself. I noticed during the second try that the marker was coming off again. It appeared that the toner was holding up ok, but the marker was not.

So I decided to remark the board a third time and try once more with the same result - so I let it finish. I refreshed the solution a fourth time and it took the last of the copper off with a woosh! The toner covered areas were ok , but they were not continuous so I decided to hand wire this prototype and see if it works while I determined what went wrong.

I was able to wire the board and nearly got it working, still having trouble with floating inputs. And I decided a couple of 'pull-down' resistors were needed and I found an error in the logic, so not all was lost. Also the holes for the power connectors were in the wrong places, so I'll have to redo them as well.

For the next board, I plan to use the sponge method again with vinegar and hydrogen peroxide to see if I can succeed in making good traces. The board is quite large 4.5" x 6.0" and two sides which I am doing at the same time. I am debating whether to drill the 550 holes first again. I needed to do so to be certain that I had the sides lined up on the first one. Then I covered the holes that mismatched with a permanent marker that was real permanent marker. I put the thick end of the marker into the hole and left a good sized circle around the hole, thinking it would partially etch off. It did for a few of them, but not all - so I ended up separating the copper using an exacto knife.

BTW to drill the holes I used a standard bench press, cranked the speed to its maximum (3000 rpm) and mounted a portable fluorescent light with a lens to help me locate the holes. The only problem I had was that many of the holes had no copper around them because of the poor transfer. (I know - I should have not tried without a good transfer. But I needed to get a usable board right away. I did get some good out of it because I found some errors, etc.) Anyway, I was able to make reasonably good guesses at where the holes should be and it worked fairly well.

I used the 1/8" shank carbide tipped drills available from Amazon. I busted one of them because I got too tired and forgot to let the press up before moving the board - snap! I used a 0.9 mm for the most of the holes and 1.1 for the holes that needed to be larger (I have a 50 pin DIP for I/O). I bought a bunch of 0.9 mm drills (not carbide) to try as well. i think I will put a small drill chuck into the chuck on the press to see how that works.

I used a piece of plastic cardboard with a shop paper towel on top to keep the drill bit from getting broken. The shop towel did wrap a couple of times so I think something like Styrofoam might work better. The plastic corrugated board works quite well on top of the press plate but it needs something softer on top of it to accept the drill without going sideways and breaking the bit. I was going to use a Dremel tool but decided against it.

Well sorry about the long post.

Do you know if anyone has tried PCB etching with Armour Etch? (The stuff that crafters use to etch glass) I googled for it and didn't find any, but maybe someone more switched in to the DIY PCB scene might have seen something on a BBS somewhere?

1 reply


Hi GToal...

Armour Etch is made from Barium Sulfate, Sulfuric Acid, Sodium Bifluoride, and Ammonium Bifluoride. It used to be made from hydrofluoric acid, which will etch glass very well, but that type of acid is very dangerous because it has a strong affinity for calcium and goes through your skin and after your bones to get it. Nasty stuff! (https://en.wikipedia.org/wiki/Hydrofluoric_acid)

You might try doing a google search for 'etch' and 'copper' and each of the chemicals above individually to see if they will etch or react with copper. I'm really not sure if any of them would be effective etchants.

Consider just getting some ferric chloride PCB etch in liquid or powdered form, or making your own etchant with common pool acid (hydrochloric or "muriatic" acid) and drugstore-variety 3% hydrogen peroxide. The latter actually works very well.

Good luck!


2016

I did my first PCB Oct. 9th using this technique w/ ferric chloride. Then I coated the copper with TInnit dissolved in water. It turned out great.
Then I realized I forgot to print the pads on this thru-hole board. So I did it again, after rerouting the tracks.
I also got this technique from pulsar fx. I didn't find your write-up here until Oct. 30th.

1 reply

P.S. If you etch w/ ferric chloride, don't forget to wear clothes too ugly to shop in at Walmart, work atop newspapers atop plastic sheeting, and wear chemical safety goggles.

Thanks very much it was very useful!

Too uneven - killed my traces.

This was with a MG Chemicals 1 oz copper photo resist board. Some areas with minimal resist did not get etched away, while some of the traces now have breaks in them. Back to the slow & reliable way...

Your method is not as fast as you have claimed! I have myself tried it multiple times and found to be a time consuming one.

1 reply


Hi TryxCorp...

Some people initially had problems, but they usually were caused by several issues:

o Ferric chloride was spent or weak,
o Using etchant other than ferric chloride,
o PCB copper was very thick (1/2 oz is recommended),
o Resist on PCB was too weak and rubbed off during etching (this won't prevent etching, but can result in a failed etching job),
o PCB copper had an unseen layer of polymer or other coating preventing the etchant from attacking it (scrub the copper with a ScotchBrite pad and put a drop of ferric chloride on the copper to see if it discolors...if it doesn't, then there is still a layer of resist)

Please read up through the comments and see if anyone else had the same issues you did. Maybe you can find a solution from what they did.

I assure you this works amazingly well. Don't give up yet!

I have the powdered FeCl3, how should I mix it to get the same results??

1 reply

the powdered FeCl3 SHOULD have introductions on the back to dilute it with distilled water. I use just enough water with mine to make it a higher concentrate for the wiping method. I have since switched to the Muratic acid/HCL solution with better results in emersion. (I haven't tried the wipe method)

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...

1 reply

Wiping isn't as fast as the author suggested. I have had the same experience as you did, multiple times.

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

2 replies


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!

Hmm, I paid $2 each. 'Personalized' pricing, perhaps. Still an order of magnitude cheaper than what I see on Ebay, though.

To anybody considering picking some up: the sheets stocked by the front desk are a little beat up. There are cleaner ones on the other side of the warehouse, covered in cardboard. Those are a little heavier (270 grams for a 20"x12" sheet, instead of 230 grams), but don't have a label. The plastic (it says "glass-resin") core in either one is pretty flimsy (though it says the core is 42 mils thick). The copper is 1 oz.

hi,, what a nice one.. ahmmm,, does it still works if i use photo paper???? please answer.. thank you..

You probably shouldn't wash that sponge in the sink as the environment hazard from the process is the copper, not the ferric chloride, and washing the sponge means that you are still pouring the same amount of copper down the drain. You should collect the sponges and dump them in a hazardous materials dump. Advantage is that it's smaller amounts compressible solid waste so it's easier to handle.

I would recommend that you add the Edinburgh Etch method as well and possibly try the cleaner option altogether of etching inside a zip lock bag using a cheap soft rubber roller as follows:

No gloves or sponge needed. Materials needed: two Ziploc bags (preferably the "Easy Zipper" type), piece of sand paper (about 220 grit) and a hand-held brayer. Simply put one Ziploc bag inside the other (for leak-proof security). Take your board and while holding it on a 45º angle, run it over the sandpaper on all edges and both sides if a double-sided board. The objective here is to round-off sharp copper edges to further prevent any leakage through the bags. Now insert your board (single or double-sided) followed by pouring in an ounce or two of Ferric Chloride. Close each bag letting as much air out as possible. Using a standard 4" SOFT RUBBER brayer (not the hard rubber type), roll it over the board with good pressure, back and forth. This roller idea to squish-out the etchant sitting on top of the board. If the board is double-sided, flip the bag over about every 30 seconds. Key to this technique is to be consisant in the rolling with moderate pressure to squish-out the etchant. This method is just a tad slower than the physical wiping of the board, but it is still much faster than any of the conventionl etching tanks on the market!