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

<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>You can get 3% hydrogen peroxide from amazon in Germany. So I assume, in EU it is not a big deal.</p>
<p>You can buy up to 12% in the EU and anything over that is restricted. I purchased 30% a while back but when I returned for more I found that only up to 12% was available to the general population in the UK. I now get 9% so I do not have to mess around watering down with distilled water.</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>Its restricted in the EU because it is an ingredient in diacetyl peroxide which is a form of explosive that is difficult to detect. I suspect that this is in reaction to the bombings.</p>
<p>I also encourage you to never try making diacetyl peroxide. It is very dangerous, very illegal, and very unstable. Think nitroglycerin and you'll have the right idea.</p>
<p>how to make tri-nitro glycerol. VERY CAREFULLY!</p>
<p>i do not think i would recommend, having hydrogen peroxide over 19 volume. </p><p>hydrogen peroxide over 29%, can explode on contact with any combustibles. and contact with flammables, would be even more disastrous.</p><p>this stuff over 30% can, self ignite explosively with any combustible material. even working with it, on a wood table is dangerous.</p><p>it can also form, metallic and organic peroxide salts that are highly explosive and highly sensitive. </p><p>this is the kind of stuff, you do not want to keep in storage. if you must use it, only order enough for immediate use.</p><p>and this concentration will do more, than bleach hair or teeth. hydrogen peroxide, at this concentration is highly toxic.</p><p>it kills living tissue, on contact. and internally it, will kill you. this is what does the killing, in radio-active contamination. the radio-ionization of water, produces toxic hydrogen peroxide in the body besides cooking you from the inside.</p>
<p>maybe try something like sodium peroxide Na2O2? i, would suggest trying a very small test batch first. or if it, would remove the protective coating on copper clad board.</p><p>it is some pretty strong stuff, in pure or technical form. this and vinegar, may not go too well together. but it is a very strong oxidizer, so much caution is needed as with concentrated hydrogen peroxide. organic peroxides, may pose even a greater danger.</p><p>and i do not think i would recommend sodium perborate, since borates can form some pretty nasty super-catalytic toxins.</p>
<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>Sorry , you must be doing something wrong. or perhaps making of marker. I used the solution today and etched a sample board, because i make pcb with markers and i read your comment. I forgot / lazy to go check and when after 8 hours i check , not even a hint of marker dissolved also my solution is very clear no blue or green hint.</p>
<p>Its all depends on the marker you use. Normal alcohol perm. marker does not cut it. The vinegar and hydrogen peroxide will lift it. Paint base one is ok. Also, since it took longer to etch, you get &quot;undercut&quot; on tracks. While FeCl is messy, it does it quick (need a 50C heated bath) and if you add Citrus Acid to it, it will not create settlement and stays as a liquid. I found vinegar and hydrogen peroxide a bit of hit'n'miss, more miss than hit! You can't quite get the mix right and it take ages to etch, hence &quot;undercut&quot; on tracks.</p>
<p>Thankyou for sharing info, didnt knew about paint/alcohal ink.</p><p>I have managed to work with toner transfer &gt; hot salt water electrolysis with 12v battery &gt; vinegar/peroxide to remove remaining copper dust. </p>
<p>Here are my new observations</p><p>1. either <br>its ,more diluted vinegar or hydrogen per oxide. the process is NOT 10 -<br> 20 minutes long, but takes hours. <br>Poor method for my usage.</p><p>2. Better: use electrolysis in salt water solution. BUT it leaves dust like structure behind, perhaps not fully etched. </p><p>3.<br> BEST OF BOTH WORLDS. I used electrolysis to remove access copper from <br>pcb than used vinegar method (1) to remove the little dust like <br>structures. </p><p>Worked like charm.</p>
<p>I read an article about a Brit that paints his traces with a tar paint that holds up to a hydrochloric acid etchant.</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>The vinegar and hydrogen peroxide worked for me! I had a good PCB in 15 minutes. Works like a charm. If it doesn't work for you, go back and read the instructable. :D</p>
<p>I believe you may have the proportions represented incorrectly. The balanced equation for the reaction is:</p><p>4(CH3C00H) + 2(H2O2) + Cu2 = 2(Cu(CH3COO)2 + 4(H2O)</p><p>This means that we consume twice as much acetic acid as we do peroxide. You have written it the other way around in your text.</p><p>I have not (yet) tried this method myself, but if you have written it backwards that could explain why so many people did not have much success with the approach.</p>
<p>Hi!</p><p>I am coming for a different lobby. I made a very nice knife out of bronze. I tried several way to etch a few words into that knife. First I cut out the words from a Sticker and sticked it on so that the letters a bare. My question is the mixture I need to make now.</p><p>I have 30% Hydrogenperoxide, 5% Vinegar and Salt. Which ratio would be a save one to try?</p><p>What do you do with te remaining fluid?</p>
<p>I am currently trying this out. Its outside and bubbling away. But it is taking quite a long time. Still the bath is turning green. I am taking that as a good sign.</p>
<p>I've used <br>20% vinegar with <br>Hydrogen Peroxide 3%<br>Salt 2-3 spuns.<br>outside, with temperature 10C<br><br>How knows how to dispose solution?<br>Thank you for tutorial.</p>
<p>The sunlight probably sped up your etching solution. For more info, look up the Photo-electric effect.</p>
<p>I think it was problem of cold weather, because it was dark outside at this time. But I've notest, if I apply salt it speeds up process and if I put it warm tank, it goes even faster.</p>
<p>Hot vinegar is unbelievably reactive. With careful planning I have dissolved 1/4 of copper in about an hour. Not terribly useful unless you need copper acetate (which I did), but... it kind of gives a new appreciation for how misrepresented chemicals are in society.</p>
<p>is it matter if vinegar is 5% or 20%. Proportion remains the same?</p>
<p>No, if the concentration is different, then you need to use less of it, or you need more peroxide. 20% has 4x the number of moles per liter than the 5% stuff.</p>
<p>Thank you, I wanted to try it during next time. Now I'm more confident to do it. Thank you.</p>
<p>Amazon carries 4 Liter bottles of MG Chemical Ferric Chloride for 32$ shipped.</p>
<p>even cheaper to buy, the ferric chloride in bulk solid form. seen it, as low as $5 a pound on eBay. just like dehydrated H2O crystals, just have to add water.</p>
<p>and unlike h2o crystals, ferric chloride solids exist.</p>
<p>well actually H2O crystals and solids, do exist below 32*F at a bar 30&quot; or less. but i still only use and reuse ammonium persulfate, as a copper clad etchant.</p>
<p>are we talking water ice or &quot;dehydrated water, just add water.&quot;?</p>
<p>That's a great price, however I chose Radioshack's as a reference as I thought it would be the &quot;regular price&quot;, even if bulk prices exist and are lower :)</p>
<p>1 Liter is $11.66 at Amazon.com and shipping is always a great price or free if you're a prime member.</p>
<p>The source I found for 30% Hydrogen Peroxide was the local Beauty Shop supplier. I live in the USA so at least for now it is easy to buy.</p><p>I do have a question: What would the proper ratio be for h2o2 to vinegar?</p><p>In the past I have used 30% h2o2 and Muriatic Acid (HCl). 3 to 1. This worked well and if I put the tray in a hot water bath it worked even better. I never knew if this was the proper ratio or not but it did work.</p><p>I would like to try the vinegar instead of the muriatic acid and try adding the salt.</p><p>Thanks You for this Write up. Good Job!</p>
<p>Has anyone tried this by using a stainless electrode and reverse electroplating the copper off the board with an old computer power supply?</p>
<p>Thanks for the Run through on this... I will be using the Ferric Chloride solution - I picked up a bottle today at Radio Shack. I think the sponge version is the way I will be going...</p><p>Tim</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>Sounds like you had way too much of the peroxide. Copper hydroxide (which is what forms from reacting copper with peroxide) has that patina smell. It isn't dangerous, but it can be annoying. It is about as dangerous as breathing the air around a freshly cleaned bathroom. Be sure to wear gloves when handling copper salt byproducts. Some forms of copper can be absorbed through the skin and lead to metal poisoning.</p>
<p>well that depends on whether the reaction, was violent enough to cause a chemical fog/mist. which could be dangerous, without knowing the fog/mist composition.</p><p>but i think we need to address, the need for adequate ventilation. since we could be producing, hydrogen and oxygen gasses also. since there was and unexpected reaction, in this case.</p><p>and it, only takes, 2% hydrogen mixture in air to be explosive. hydrogen has the lowest explosive limit and the highest upper explosive limit mixture of any other element or chemical.</p><p>of course i am assuming, the smell is the same you get when you produce hydrogen with aluminum and sodium hydroxide without a cold trap and a drier. </p><p>as the violence he described, is way to violent for the specified formula in the instruction.</p>
<p>sounds almost like, you did not add the vinegar. and the free iron ions, reacted with the peroxide resulting in rust and iron hydroxide.</p>
<p>Be careful with googling. Don't forget to check safety recommendation working with acids before getting hands on the lab. Most of amateur tutorials explains how to do something but they doesn't say about safety and material disposal.</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>chloral mannate, works for at least five years. and if you want to get rid of all plants, for the next 20 years use motor oil.</p>
<p>Baume is used to measure the volume of gas, dissolved in solution at a specific temperate normally room temperature. like with ammonia, hydrochloric, or hydrofluoric acid gas. HCl and HFl are gasses, not a liquid or solid. glacial acetic acid, is a solid at room temperature. so it's solution in water, would be parts per volume or parts by weight. and i believe most vinegar, is measured in volume.</p><p>and all acid based etchants, perform better at a higher temperature. and by constantly moving, fresh etchant over the surface. if you leave the etchant, undisturbed it will form pools of copper etchant salts around the etching thus prohibiting any further etching. because you have used up the ferric chloride other etchant in the immediate area. </p><p>and most plumbers i know, recommend chloral mannate for root removal. since copper sulfate or other copper compounds really screws up, water treatment plants. and copper compounds, are bactericides, fungicides, pesticides, and toxic to humans. and can attract rodents, that need copper in their diet. it is why rats, mice, rabbits, and other rodents, chew on electrical wires.</p><p>i do not use, electro-etching since it can cause undercutting on thin traces. typically i can etch a one ounce copper board, with ammonium persulfate in 30 seconds or less. depending on the strength of the solution, and the temperature in either my bubble etcher or spray etcher. and can do more than one double sided board at a time in my bubble etcher. the spray etcher, is limited to one double sided board at a time.</p><p>and when my solution, gets weak i use electroplating to restore it to remove the copper and restore the ammonium persulfate. and ammonium persulfate, and other persulfates, are used as a bleach, disinfectant, and cleaner in toilet bowl products. yes! it, will bleach your clothes, wood, carpet, and other organic stuff, so wear white clothes or lab coat.</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>You're using hydrogen peroxide and the rinsing in acetone!!!</p><p>I'm not a chemist, but read here recently - mixing the two, even in tiny quantities can BLOW YOU UP! </p><p>If there is any hydrogen peroxide on the board when you wipe with acetone, you are mixing them.</p><p>After googling it (I'm probably now on the&quot; no fly list), I wouldn't get them anywhere NEAR each other.</p>
<p>Quite interesting article. My approach has been to use Muriatic acid - used as swimming pool or concrete cleaner from Lowes in their paint department. Mix in hydrogen peroxide about 2 part to 3 of acid and it will etch a board in about 15 to 20 minutes. This is also quite cost effective but the vinegar idea is very interesting too. BTW use ketchup to clean the surface of the board before starting and rinse well.</p><p>I want to look into that ammonium persulfate etchant idea. Wonder where to get it?</p><p>I want to look into Alpersulfate but wonder where it cn be had</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.

About This Instructable




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 »
More by Feynmaniac:Is the best PCB etchant in every kitchen ? 
Add instructable to: