After a lot of reading and inspiring from Instructables for two years now I decided to step ahead and do my first Instructable on two subjects I particularly like : PCB making & The scientific method.
Feel free to comment and criticize my work, I think scientific method is also about improving and discussing the best way to experiment :) !
English is not my native language so please excuse my hesitating grammar.
5/30 Edit : I would like to thank you all for supporting this Instructables in the Scientific Method contest =D See you for other experiments !

Most of us Instructables users etch PCBs occasionally if not on a daily basis. This process is not anodyne as it may have a great impact on the quality of the future circuit, the environment and, last but not least, on your wallet !

Ferric chloride is commonly used to etch PCBs as it is both reliable and efficient. However, it's a dangerous product which requires special care in handling. Recently, some alternatives have been found to accomplish the same task. Among them is an astonishing hydrogen peroxide, salt and vinegar mix which seems to be a “Mac Gyverish” way to print a circuit board.

Let's assess the “Mac Gyverish” hydrogen peroxide/vinegar/salt mix using the “tried and tested” ferric chloride solution as a control !

To etch a PCB one can either immerse the board into a bath of etchant (most common technique) or rub it with an impregnated sponge. I have tested both ways with each etchant so that makes a total of 4 experiments.

The techniques and etchants will be compared according to four criteria :

  • Time/Handling
  • Quality of resulting circuit
  • Cost
  • Environmental impact

Step 1: The theory behind pcb etching

A copper board is made of an epoxy resin board covered with a thin layer of copper. The etchant reacts with the layer of copper and dissolves it, except where a mask protects the copper. The epoxy is left intact as it does not interact.

Here are the two chemical reactions taking place : (1) is ferric chloride’s (aka Iron (III) chloride) and (2) is vinegar/hydrogen peroxide/salt mixture’s.

(1) FeCl3 + Cu --> FeCl2 + CuCl 
(2) H2O2 + 2(CH3COOH) + Cu  --> 2(CH3COO-) + Cu2+ + 2(H20)

The reactant is the result of the combination of acetic acid (which represents 80 grams per liter of white vinegar according to the bottle [which says 8° acidity]) and hydrogen peroxide (which is at 3% mass concentration).

We can calculate the optimal ratio of each component in order to get a maximum amount of it.

Hydrogen peroxide is 34 grams per mole and acetic acid is 60 grams per mole.

So, in a liter of vinegar there are 80 grams of acetic acid which represents 80/60 or 4/3 moles of acetic acid. In a liter of hydrogen peroxide, which approximately weighs a kilogram, we have 3% x 1000 grams = 30 grams, nearly a mole, of pure hydrogen peroxide.

Because the reaction uses twice the number of hydrogen peroxide molecules of acetic acid molecules we can say that we need to put roughly a 2/3 ratio of hydrogen peroxide/vinegar in volume to get things optimal.

Now you may be asking yourself “Why do we want to add salt to that ?”.

Well, one possible explanation (I'm not actually sure it is the right one) is that the reaction brings neutral Cu atoms of the board to Cu2+ ions in solution that would form copper acetate (it is the combination of one Cu2+ ion and two CH3COO- "acetate" ions). And, at one point the bath would reach an equilibrium (because there is as much Cu2+ forming from Cu than Cu2+ getting back at a solid Cu form).

Generally this happens before your board gets its beautiful tracks, which is quite sad. Table salt, or NaCl, brings chloride ions Cl- to which Cu2+ ions will bond to form cupric chloride or CuCl2 instead of being left in solution (those ions would endlessly come back and forth from Cu to Cu2+). You can see this during the reaction (if you leave the reaction with no salt it will turn blue which is the color of copper acetate and stop, whereas if you put salt it will turn green, the color of cupric chloride, and carry on).

2Cl- + Cu2+ --> CuCl2

By doing so, the equilibrium point is pushed forward and more copper can be dissolved, so that, if you are generous on salt (if you introduce table salt in excess) you may get your PCB in the end ! One tablespoon of salt on the board is generally sufficient.

Hypothesis : Given the concentrations of hydrogen peroxide and acetic acid in our "recipe" ferric chloride should be way more efficient. However the Salt/Vinegar/Hydrogen peroxide seems to be both less expensive and safer.

Now comes the fun part, let's put up the lab coat and etch PCBs !

Step 2: Setup & Experiment

The experiment aims at comparing, in a "normal" situation, what etching method is the most efficient (immersed or rubbed ? Ferric chloride or Hydrogen peroxide/Vinegar/Salt mix ?)

I printed and ironed a toner "barcode" with strips of decreasing width (5/4/3/2/1.7/1.4/1.1/0.7/0.4 millimeters) on four identical boards, those will show the resolution achieved by each method (I chose resolution as quality indicator).

In my lab (aka shed), each board is then immersed in a small bath (approx. 200mL at room temperature : 70°F) of etchant or rubbed with an impregnated sponge up to the point where I can’t see any unmasked copper left. The board is then rinsed and the circuit is wiped with acetone to remove the mask.

In this experiment :

  • Control variables (aka variables that do not change throughout the experiment) are lab temperature, size of copper board, masking technique, quantity of etchant in the bath/sponge.
  • Dependent variables (aka variables that may vary because of tested factors) are achieved resolution, duration of etching process, cost and environmental impact.
  • Independent variables (aka tested factors) are nature of etchant (Ferric chloride or Salt/Vinegar/Hydrogen peroxide) and etching technique (rubbed or immersed).

Step 3: The results

The experiment went very well even if got a little bit frustrated by my copper boards' poor quality and persistent toner ! ^^

Maximal resolution (0.4 millimeter) was obtained for each experiment which shows that the etchant/technique itself does not change the final quality of a regular PCB. I got some scratches on the rubbed PCBs because of the sponge (not very soft).

However the duration of etching process was not even : the shortest method is Ferric chloride rubbed (3 minutes) followed by Ferric chloride bath (10 minutes), Salt/Vinegar/Hydrogen Peroxide has the longest etching duration (11 minutes when rubbed and 20 when PCB is immersed).

Step 4: Cost and Environmental impact

Salt/Vinegar/Hydrogen peroxide mix is, by far, the cheapest etchant (Hydrogen peroxide 3% is 2$ for 16 oz, Vinegar is 2$ for a liter and salt is almost negligeable) with a price of less than 4$ per liter.

Ferric chloride costs around 10$ for 16 oz which is arround 20$ per liter, five times more than the first !

In terms of environmental impact "sponge technique" is, by far, the less dangerous for both etchants (and the most economic with only 10mL of etchant used). You only need to rinse your sponge once finished, a tablespoon of etchant is not harmful (I've asked local authorities).

Ferric chloride bath needs to be stored and brought where it can be treated. I'm not sure for Salt/Vinegar/Hydrogen peroxide mix as copper precipitates (the solution gets a pale blue tint only).

In terms of handling Salt/Vinegar/Hydrogen peroxide requires a small preparation before each etching session (the solution does not stay efficient very long) but it is safe whereas Ferric chloride is corrosive (wear gloves ;)).

Step 5: And the winner is...

Salt/Vinegar/Hydrogen peroxide (immersed) and Ferric chloride (rubbed) are 1st ex-aequo. The first has the advantage of being both readily available in the kitchen and quite safe whereas the second is both cheap and quick =D !

Then comes Salt/Vinegar/Hydrogen peroxide (rubbed) which has all the advantages above plus the fact of being extremely cheap and green, however you need to rub the sponge for 11 minutes which is not that funny (with all the risks of destroying your tracks if you rub too hard) !

Finally "old fashioned" Ferric chloride (immersed) comes last as it is relatively both expensive and difficult to dispose of (if you are responsible).

Step 6: Conclusion and possible improvements

The experiment in itself did not separate the two etchants which are almost as efficient for a regular hobbyist use. However factors such as cost, handling or environmental impact played a key role in putting the vinegar/salt/hydrogen peroxide mix forward. The setup and experiment are easy to make which is good for reproducibility. Don’t hesitate to cross check my results ;).

Though, as all experiments this one has limits. In fact I tested only two etchants whereas dozens exist and may be a middle ground such as Hydrochlorhydric acid + Hydrogen peroxide (which is more powerful than the Vinegar/Salt/Hydrogen peroxide mix) or Cupric chloride (whose effectiveness is comparable to the one of ferric chloride).

However Ferric chloride had the advantage of being the most common method for etching PCB so I thought it was the reference to which I had to compare other methods and Vinegar/Salt/Hydrogen peroxide was amazingly inoffensive and available at minimal cost. I was also skeptical about this “Mac Gyver” method : this experiment helped me to figure out that it is reliable =D !

One could also say that I only tested one temperature (21°C). Although this is true those chemicals’ reaction rate have the same dependence upon temperature. This means that if one method is relatively more efficient at 5°C, it will also be relatively more efficient at 40°C (but the reactions will take less time). The same goes about reaction rate in a bubbling tank or other setup improvements.

Please feel free to comment and help me improve this experiment with new factors and/or new methods ! =D

I had a great moment creating this first 'ible, I hope you liked it too ;)

Those great pages helped me making this 'ible :

Etch PCBs in One Minute !

Stephen Hobley's blog

I have to agree with the majority on this one... this is one of the most well written, informative, and practical 'ibles I've found on here. I had my PCB ready for etching, but had no enchant, so I searched "make ferric chloride"...brought me right to yours. I loved not only how easy this was, but your scientific research method of comparison, and how well informed you are on the chemistry involved. Thank you.
<p>This method IS NO GOOD IF YOU ARE LAYING OUT YOUR TRACES WITH PERMANENT MARKER ..you will watch , maybe hours, of work bubble away into blue goop in the bowl along with the copper...no good..you no like. I thought it would be nice if someone told you. </p>
<p>Tthanks for the heads up. I sometimes go over the traces with perm marker where the toner doesn't transfer properly.</p>
<p>I know you posted this about a year and a half ago, but WOW! I admire your interest in the &quot;scientific method&quot;, bro. I have been looking off and on now for about 7 years for a very good 'ible on this subject for a while now. I gave up for a couple of years, thinking there were going to be endless arguments over &quot;glossy photo paper!!&quot; or &quot;glossy magazine paper!!&quot; or &quot;Avery label backing!!&quot;.</p><p>I never thought I would see such a well thought out SCIENTIFICALLY VALID method (at least valid where I come from...hey, in my book, Mythbusters makes the cut too!) about etchants. I have toiled with some concoctions over the years...burned my self once, learned and carried on. I knew about the ferric chloride, and heard briefly about salt/peroxide/vinegar, but I tossed that idea out off hand because I couldn't imagine it would work better the ferric chloride, but there are some others I have used, with varying degrees of success. If you can find the right resist (toner doesn't seem to hold up for me) I find Sodium Hydroxide works really well on aluminum and copper too. But like I said, the toner just lifts off...it seems it can't handle the reaction ...or maybe because it's highly exo-thermic...or both....I dunno.</p><p>What I would like to follow up on is are there any other chemicals and metals that will hold up to the toner transfer method?</p><p>Great 'ible, Feynmaniac! Love the knowledge and the well documented experiments. Most people get overly excited about a technique, even when it is only marginal results...and the run with it...thumping their success stories as though they won the lottery. It's sad. I appreciate your time with this.</p>
<p>Another point to add. If you are using more concentrated vinegar (I got 25% ones from South Asian shops), you must add salt into the mixture to etch properly. I learned it the hard way... The etch was bubbling vigorously but the board doesn't seem to etch. Soon it gets too hot to handle and I have to chug it into the sink to stop the reaction. Now I have ugly brown stains on my table and the floor because of the copper...</p>
<p>Tried this today, didn't went very well :( Or i was impatient :)</p><p>The PCB was immersed at least 1h (agitated the container each 5min), i still saw copper, didn't saw any bubbles or anything, so i decided to remove-it and give up for today... then i washed the toner out to find out it was working! The traces where there already! PCB ruined...</p><p>I think my problem was i used &quot;cider vinegar&quot; witch is only 4% acid.. i will buy the normal one and try again someday!</p><p>I will add a picture of my failure :)</p><p>Very nice tutorial! Thanks! This was the reason i tried to make a PCB at all, since i don't have easy access to the other chemicals!</p>
<p>Tried this again today. It went better, but this time i had to use normal paper so it didn't went very well. But with some jumper wires to fix some traces it should do the job....</p><p>Maybe the 3st try is the one that will be perfect :)</p>
<p>Does anyone know if there's an alternative to hydrogen peroxide? It's heavily restricted in the EU because some idiots were using concentrated solutions to whiten their teeth.</p>
<p>Is that the reason?! I found it was being restricted in some countries and I'm really pissed off with the fact i cannot find hydrogen peroxide 110vol (33% concentration or so), but i couldn't know the reason about such restriction.I read the restrictions were due to the possible use of high concentrated hydrogen peroxide to make fuel.</p><p>Anyway if you look on the Internet, you can find some sites where it's explained the process to get high concentrates from common use 3% h.peroxide, basicly baking it in a kitchen oven in low temperature. And it works (it's said).</p><p>Honestly bleach is also dangerous and you can buy easily so I don't think the reason to restrict the hperoxide is by bleaching teeth. Surely something related to the paranoid about terrorists (and actually the terrorists dress smart and use ties).</p>
<p>Bravo sir! Now I can officially say that, besides the copper board itself. This PCB was manufactured entirely from things I already had in the house.. and this is my first PCB!</p>
Are you able to throw the used vinegar etchant down the Plughole????
<p>Extremely helpful instructable! Thanks a bunch!</p>
<p>I mixed the solution all up and dropped the boards in. All the boards did was make bubbles, make an underwater steam look, and rust (well at least look like rusting). The solution was not turning green. So I left it on for 2-4hours then I came back and my room stunk (Bedroom. Also I have to sleep in an hour). After that I checked if the boards were done and I wiped of the boards to reveal more copper underneath. Then my parents checked and said it was a lung irritant and i should sleep in the basement (I'm 13yrs old).</p>
<p>This has to be one of the best Instructables I've ever read! Not only is the 'ible itself, and its author, a total winner - The quality and content of the community feedback had me reading right through all 84 contributions on it.<br><br>There's obviously a lot more experimentation that can be done, but I don't think I'll ever buy ferric chloride again for the (fairly rare) occasions I make up a PCB - the half-used stuff just hangs around (and sometimes can't be found when I need it!) and then has to be disposed of, Is it too late to vote on this? :)</p>
<p>Congratulations on creating a wonderful instructable, and thank you for publishing this useful and important information! Even more impressive is that English is not your primary language, yet your grammar and diction is easily far superior to most of the people I know, who (attempt to) speak English as their primary language! Well done, Sir! I suspect we'll be seeing many more great things from you in the future, and I will most definitely keep a close eye on your further input! </p>
<p>So of course I wonder, can you extract the etched copper from the solution for later recycling or jewerly uses? Maybe through electrolysis?</p>
<p>You can. Just introduce another, more reactive metal... Like Aluminum. The reaction is 2Al + 3CuCl2 -&gt; 2AlCl3 + 3Cu thus you end with very pure copper-powder.</p><p>Seen here</p><p><iframe allowfullscreen="" frameborder="0" height="281" src="//www.youtube.com/embed/gqSXWbS6gzo" width="500"></iframe>Or you can electrolyse it. Seen here:<br><iframe allowfullscreen="" frameborder="0" height="281" src="//www.youtube.com/embed/gpr3DutYnS0" width="500"></iframe></p>
<p>Chemistry is so powerful. Especially when you know how to use it! Great comment.</p>
<p>I'm pretty sure you can recycle it for electrolysis. If you want you can check out this instructable : <a href="http://www.instructables.com/id/High-Quality-Copper-Plating/" rel="nofollow">http://www.instructables.com/id/High-Quality-Coppe...</a> </p><p>But for this electroplating you use copper acetate which means you'll have to avoid putting salt into the etching bath and adapt the mixture (you can stick to this instructable and simply put your board instead of copper scrubbers).</p>
<p>I understand the hydrogen peroxide and vinegar are a 2:3 ratio, but how much salt should I add to get the etchant correct?</p>
anyone can dispose of ferric chloride if they remove the copper from the solution. once the copper is removed, it can be purified and reused to make other compounds.
<p>is any of these solutions reusable ?</p>
every etchant based on CuCl2 is reusable. It may need oxygen if it turns dark green, more acid if it turns brown.<br>oxygen: bubble air in it with a cheap aquarium pump an a bubblestone.<br>acid: add more of your vinegar / HCl.
Can I use your research for my science fair project later in the year<br>
<p>what if i add a few drops of hcl in it</p>
<p>hey its not working jst wrkd fr the first time and irrespective of adding more of vinegar, h2o2&amp;saltsalt</p>
<p>I like the way you approached the subject with rigorous attention to detail and a scientific frame of mind. A few comments if I may:</p><p>1) The number on the vinegar bottle I think is in degrees Baume (density) rather than % concentration. I am not sure how this converts with acetic acid. For instance 20 degrees Baume HCl is about 35% concentrated.</p><p>2) The fact that you got better results with wiping than immersion demonstrates an important principle with all etching baths: There has to be agitation of the etchant. I run an aquarium pump through mine to create bubbles.</p><p>3) Ferric Chloride works better at higher temperature - I run mine close to 40 degrees C.</p><p>4) In terms of economics one has to point out that Ferric Chloride can be re-used - many times!</p><p>5) Environmental effects of disposal are determined by the copper ion content: For some reason even the small concentrations such as in your little set-up would be frowned upon. Ferric chloride by itself consists of chemicals which are naturally occurring in soil. OTOH if you want to get rid of roots in your garden or septic tank what do they sell you? Copper sulphate! Go figure.</p><p>6) Finally, having said all that about FeCl3, I have more or less stopped using it in favour of electro-etching with copper sulphate as electrolyte. However, for the occasional PCB that may way too much hassle.</p>
<p>With rock salt as a close second for the roots,but no doubt the Copper sulphate works better,and is longer lasting in this old plumbers opinion.</p>
<p>Many many valid points- and a very helpful article overall! Disposal of dissolved copper is always tricky; the electrochemical properties of copper make it a very good accumulator of other metals within a system that we otherwise don't want accumulating, such as Zinc or Magnesium. Caution is never overdone in the lab or workshop! I'd love to put some of these ideas to the test myself :)</p>
<p>Can the dissolved copper be used for copper plating steel/iron/ferrous materials?</p><p>That way it's kind of reclaimed and made into something 'useful'</p>
<p>Nice instructable mate</p>
<p>Thank you =)</p>
<p>Well done you... This makes it super simple to make a decision (choice) ... Thank you.</p>
<p>I thought it was a way to get an &quot;objective&quot; answer to this question of pcb etchant. It really seems to split people ^^ </p><p>Thank you =)</p>
<p>Great Instructable! I'm just trying to make sure I got the solution proportions right for the hydrogen peroxide/vinegar/salt. Twothirds liter of hydrogen peroxide with one liter of vinegar and 1 TBSP salt? I got a little lost in the chemical formulas (which I am very glad you figured out and explained, but I'm just an end user, not a scientist!). I want to try etching some copper sheet for jewelry, not PCB boards. I plan on trying a Sharpie marker as the mask, since I know that works for PCB etchant on copper sheets.<br>Thanks for the idea to try. I rarely do metal etching since the disposal of the etchant intimidates me, but this would be great!</p>
<p>It won't work well. The hydrogen peroxide/vinegar/salt mix will dissolve the sharpie ink. It will be better for you to use the electroetching method (http://www.instructables.com/id/How-To-Electro-Etch-a-Solid-Metal-Plaque/?ALLSTEPS)</p>
<p>Thanks for suggesting an alternative.</p>
<p>After staining more things than I care to count with ferric chloride I started using Sodium Persulphate. It requires a water bath to be quick, but this is fairly straightforward (just place the etch container in a bowl of very hot water). It's non-staining and the byproduct is copper sulphate solution. The main advantage is that it requires no agitation, the copper simply dissolves into the solution so you can easily check if it's done and there's no gunk to continually scrape off the boards. It's reasonably cheap, a small bag can be bought for &pound;5/$5 on eBay and it lasts for a long time if you make up the solution as you go.</p>
Don't fool yourself that persulfate is safe. I once spilled some on a blue bathroom rug. It left the fiber bleached yellowish white in no time.
Hmm wasn't aware of that, though wikipedia says it's essentially a bleach. May be just the thing to get rid of Ferric Chloride stains on my lab coat!<br><br>Also wasn't aware that it's used in hair bleaching products. Maybe a cheap source?
<p>I know that when using Hydrochloric Acid with Hydrogen Peroxide that using an air bubbler replenishes the oxygen and accelerates the action. I suspect that it would help with this Vinegar/Salt/H2O2 procedure also if doing a large board for example, or just to speed up the process.</p>
<p>I think that would make a great experiment =) </p>
<p>This is fascinating... Thanks for taking the time to explain the process. </p><p>I don't know if I &quot;invented&quot; the process... but adding the salt seemed to do the trick for me, and created a bit of a debate when I published my findings.</p><p>I get quite a bit of email still from people who can't get the mixture to etch, so this will be a great resource to point them to.</p>
<p>Thank you for sharing this process. Without your blog I think I would never have imagined that this mix could work given the concentration of acetic acid in vinegar ! =)</p><p>I'm glad my main source actually likes this 'ible =) !</p>
<p>Along this line is lowes muratic acid and hydrogen peroxide. Very low cost, foam brush used for board but no salt???</p>
<p>Muriatic acid is another name for hydrochloric acid, and is usually sold as a pool cleaner. I've found and purchased a 900ml bottle of a higher concentration on Amazon for just this purpose, but haven't tested it yet.</p>
<p>I think (I'm not sure) that HCl (muriatic acid) + Hydrogen peroxide does not need salt (NaCl) because it already has the chloride ions we are looking for to form cuppric chloride (CuCl2) :)</p><p>However I think this reaction creates toxic fumes, plus I feel more confident with a vinegar bottle than with a strong acid one ^^ ! </p>
<p>Interesting result. I have experiment with both method, but with some what different result. What I find is it is very hard to get consistent result with peroxide/vinegar/salt. Sometimes it will etch quickly and sometimes not (or not at all), which is most of the time. Also it is not Sharpie friendly, ie. it dissolve the ink, which is not good if you make any correction on your board. Although clear varnish will work, but it is less convenience. The long etch time leads to under cutting of tracks and pitting on large copper area which is not good. Compare this with Ferric chloride, my initial impression was this is bad stuff; it stain everything, hard to dispose of and expensive. But then I came across this, the Edinburgh Etch:</p><p><a href="http://www.nontoxicprint.com/etchcopperandbrass.htm" rel="nofollow">http://www.nontoxicprint.com/etchcopperandbrass.ht...</a></p><p>By adding Citric Acid (lemon juice if you like) to the Ferric chloride, it improve the efficiency and the longevity of your etchant, ie. number of time you can use it. if you use Ferric chloride before, you know the more you use it the less effective it is as it form a layer of sediment at the bottom of the bottle, the citric acid remove this. Also, I find the temperature does matter. I usually have the Ferric chloride sitting in a warm water bath and it etch fast! normally 25-30C is good enough.</p><p>I don't do a lot of PCB, but the time I do, I like it to work first time, so I need something that will have a long shelf life and consistent in result. The Edinburgh Etch does give me that. BTW, proper way to neutralise and dispose of Ferric chloride is also well known; Calcium Bicarbonate or baking power. I do consider </p><p>peroxide/vinegar/salt as my secondary method, as say, you can get the stuff any where and it is not toxic.</p><p>Anyway, well done as I was waiting for someone to do a more qualitative work on peroxide/vinegar/salt method.</p><p>Keep up the good work!</p>
<p>I did not refer to this in my experiment but it&rsquo;s true that efficiency really depends upon your Vinegar/Hydrogen Peroxide. Once I used what remained of an old vinegar bottle and I can tell you the result was quite sad ^^</p><p><br>However did you try to sprinkle some salt over your board while in the bath ? :)</p>
<p>I did, but the result again vary so much (from adding a tea spoon to half a bag) that it is hard to get consistent result, ie. a consistent repeatable recipe.</p>

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Bio: I'm a 19 years old physics undergraduate who spends his time making experiments and asking questions. Otherwise I play the bass guitar and the ... More »
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