# The Saltwater etch process

This is a one-off process to produce one printed circuit board by removing unwanted copper by electrolysis in a saltwater solution.

I shall illustrate the process by etching and building a board for 18-pin PIC (for the PC16F54, but any 18 pin PIC will fit in it) in the figure. It has to plug into my breadboard and accept the programming signals from my PIC programmer (just go to http://geocities.com/it2n/circuits.html and look at it).

To avoid battling with signal conflicts, the two programming pins shall not be brought to the breadboard. To play around with the clock frequency, the crystal shall be made pluggable. The Master clear signal will not be brought out.

These decisions mean a board with two .1" pitch connectors, one with 13 connections and the other with five connections, one pin spaced apart from the rest.

This is a tutorial intended for the absolute beginner, and almost every step shall be illustrated. I've even included a video of the etching process.
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## Step 1: Decide how large the board has to be

From the diagram, the side that plugs into the breadboard has 13 connections, and the holes in the bb are spaced 0.1 inch apart. So we need at least 1.3 inches to accommodate 13 pins.

Say one and a half inches, a nice figure. Take a piece of copper clad board larger than 1.5 inches a side. Draw a line at one and a half inches.

## Step 2: Score a line on the copper

Hold your ruler or straightedge firmly down on the board. Hold a knife lightly and draw across the line many times.

After some time, there will be a gouge on the copper, dividing it into two.

If you bear down with the knife, chances are that it might wander and cut the board deeply where you do not want it cut - and you will be looking ruefully down on your ruined PCB stock. Be patient. Being patient has its own virtues, as life will invariably teach you.
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rotor8 years ago
Thanks very much for getting around to doing this.

Btw, this is my favorite part:

Or the way I do it - use a 12V, 15A supply together with a car headlamp for indication. Small shorts that used to be there get vapourised, and if that lamp lights up, boy, that really IS a short circuit.

I actually loled.
greatnameless15 years ago
Just a question... wouldn't it be easier to just print a design and iron it on instead of hand drawing?
5 years ago
Sure. But what if you don't have a printer? Or a plastic sheet that you can use to do the transfer? Doing it with a marker uses a tool that everyone is sure to have, and it gives people learning about this for the first time a better feeling for what they're doing. For the author: I like your "lotto-card" procedure. It feels like it'll produce much better results than trying to draw the traces with the marker directly.
6 months ago

You could of course draw the resist on in the pattern of the circuit, and touch up around fine connections (such as the IC pins) by scraping away excess mask with a pin tip (or the awl tool commonly part of soldering tool sets).

I'm all for doing things on the cheap (I etch my own PCBs because I don't want to wait for a service to do it, and don't want to pay for fast shipping), but at the point you're doing circuit design work and have ICs and components to solder, surely a secondhand laser printer isn't a big outlay. The saved time alone, not to mention savings in material use (copper PCB material for instance) will make it a quick payoff.

splud6 months ago

I have a wife, but I don't use her nail polish - I have several bottles of clear acrylic for coating windings, and a few older bottles of garish nail polishes I picked up for tamper seals and makeshift threadlock.

mbainrot3 years ago
I am attempting this now.

It should be noted that you need a substantial load when using an switch mode power supply otherwise it may not switch on
mbluett7 years ago
"One final necessary step is to paint over a line connecting all pads" What line is being painted over? This is not clear. An arrow pointing to the line in the picture would help. "In my board, the pads are all connected along the left and bottom edges." I cannot discern anything connecting the pads along the left and bottom edges. Again arrows pointing this out would help.
neelandan (author)  mbluett7 years ago
You will note (if you look carefully) that the lines scratched on the paint do not reach the edge, but stop rather short. Wherever the line is drawn, the copper gets etched away. Thus the pads remain connected along the bottom and left hand edges in this layout.
4 years ago
why is this necessary that they be connected on the edges, what is you have isolated connection, will it still work?
3 years ago
if any of the pads aren't connected, they won't have electricity running to them, thus they won't necessarily etch all the lines you need to etch. does that answer your question?
neelandan (author)  mbluett7 years ago
The offending text has been re-worded.
macumbista6 years ago
OK, so the "Sodium chloride in Dihydrogen Monoxide" solution is harmless. What about the copper that gets absorbed into it? Is the waste product of this process chemically inert (i.e. salt, water and copper sludge)? If it is, I'd be very happy to use this over Ferric Chloride and other actually nasty stuff. If not, how to make the copper inert in the solution so I can flush it down the sink without poisoning the environment?
6 years ago
The Electrolysis process is chemically simple. NaCl (salt) is a strong electrolyte and therefore "transfers charge".
This is really just a "redox" (oxidation/reduction) reaction.
What happends is, The Chlorine ions (Cl-) migrate to the cathode where they loose electrons and bind to make Cl2(g). This gas is toxic even in small amounts, you should read MSDS for Cl2(g). (Just type Cg2(g) into google). You should therefore perform this in a well ventilated area (or not at all).
The Copper at the cathode (the cathode is the PCB board) looses electrons and dissolves in the solution. If there is excess water a complex-ion will form Cu[(H2O)6]2+ (Octahedral aqueous copper complex with a charge of +2), but this complex will be in some equilibria with the Cl- ions. If The Cl- ions are in excess (which would probably not happen in a aqueous solution) a yellow complex Cu(Cl4)2- would form (in equilibrium with CuCl2 which is quite soluble in water).
Some Hydrogen gas could form at the anode due to the self-ionization of water H20 <---> H+ + OH- (this equilibrium lies far to the left). H+ ions would migrate to the anode, pick up electrons and leave the solution as H2(g).
When two H+ ions leave the solution as H2(g) after reduction, two water molecules will dissociate to form 2H+ + 2OH-. The OH- ions combine with Cu2+ ions to form Cu(OH)2(s) which is insoluble so it will precipitate as a green-looking solid.
So, What you have in your solution is
a) Cu(OH)2 (s) (amount is proportional to the amount of hydrogen displaced, which is proportional to the amount of Cu(s) etched away).
b) Cu[(H2O)6]2+ (amount depending on the amount of Cl- to cause...)
c) CuCl2 +2Cl- <--> CuCl3(-) <--> CuCl4(2-)
d) Some Na+ ions and water
What will leave the solution?
H2(g) and Cl2(g)

So, now you know. And what you should do if you want to know if you can flush the solution down the drain is read the MSDS for Cu(OH)2, and Copper-solutions. Although I can tell you, we don't like solutions of heavy-metals flushed down the drain. You should dispose of this properly.

I suggest you find another electrolyte to avoid the Cl2(g). I don't have many ideas tough since my access to acids and metal-nitrates and such is not limited :-).

Hope this helps
Greetings from Iceland.

5 years ago
If I'm reading that right that suggests that this produces chlorine gas, which I was told was fairly deadly in small amounts.
4 years ago
but there is so little gas produced you may not even get one bubble of chlorine gas and if you do it will diffuse in the air.
4 years ago
What about using a baking soda (sodium bicarbonate, NaHCO3) solution as an electrolyte, Mr. Science Man? ;)

To the author: I have long considered using both this etch resist application process and reverse electroplating for PCB fabrication, but you actually did them... at the same time... and you wrote instructions for us! Good show!

I plan to adapt this process to the use of my CNC router with some kind of spring-loaded scratching implement and of Peroxide+Muriatic Acid as the etchant (assuming I can find an etch resist that is safe from its ravages... I'm thinking wax).
5 years ago
I did a quick search.. Cl2 and H2 tend to explode when combined o_o
No biggie if you do this out in the open but if you put a lid on it to erm fend of the fumes or something you might be actually doing more bad than good.

Can't see any problems however if you just do this outside =)
chaydgb4 years ago
Superb! A refreshing change from the usual "You will require: An industrial laser cutter, an enormous budget, twenty arduino boards". Personally I photoetch my boards, but should I ever find myself in a situation where I'd not have access to my kit, I'll remember this 'ible! Thanks.
soapmaker724 years ago
Firstly, A primer on NaCl (applies to all alkali metal halides) free chlorine gas can only be evolved in quantity given three conditions are met.

1. High salt concentration in solution
2.  A pH of 7 or lower( acidity promotes this)
3. An anode(+) that is CHEMICALLY INERT to chloride or chlorine

Notice that NONE of these conditions are met in this case.  The salt is in lower concentration.  The pH will probably increase if anything(go more alkaline).  And last but not least the copper is not inert and hence it is etched.

Secondly,  Disposal of copper waste is not an issue.  The oxides/hydroxides can be dissolved in diluted muriatic acid, vinegar, or battery acid and an aluminum wire is added until a clear solution is obtained.  This can be decanted down the drain as it simular to deodorant (aluminum chloride) or baking alum(aluminum sulfate).  The pinkish copper grains can be mixed with saw dust, oats, flour or any organic that chars black and borax and melted with a propane flame to get copper metal for later use.
rotf1014 years ago
Thanks so much for the instructable! I used the same saltwater etching process to etch a nameplate in aluminum. It turned out great!
eclarep5 years ago
Hey, girls make circuit boards too!
Malcolm Jackson5 years ago
Many thanks for all this.  You have got me really motivated and I will be having a go asap.  Great stuff.
Dude... that's the worst soldering I've seen in a long while, even worse than my very first soldered joint... and it was a cold one, damn! you need a) better tip b) more power c) practice the tin feeding and timing, you're not doing it properly. always lift on the same direction and feed enough to solder A and B, if not you have the potential of soldering X as well and with your thin traces that's very possible.
mbluett7 years ago
For the chemically illiterate your mention of DHMO being hazardous is inappropriate. It's not even funny!

DHMO = H20 = water
5 years ago
*Anything* is deadly under the right conditions. Helium has no toxicity at all, but if you breathe pure helium you won't last long. The DHMO joke is very old, but there are some seriously toxic compounds that your body requires or produces. One of these days, I'm going to write an essay called "The Poisons You Can't Live Without." Start with the hydrochloric acid in your stomach,
5 years ago
Some of the most toxic elements (Chromium, for one) are deadly in even small doses but essential in tiny, tiny doses. This is true for hundreds of other compounds, elements, substances, etc. What I want to know is who figured out that sucking on dynamite is good for you! (GTN (glycerol trinitrate) aka nitroglycerine is found in explosives, however is used in hundreds of medications to reduce blood pressure, and used as a reliever for angina sufferers.) Helium can also be very useful - BOC produce a gas known as HeliOx (He & O2 in a 8:2 ratio) used in hospitals (mainly intensive care) for asthma sufferers, as the 80% helium content makes the gas a lot more 'slippery' than air. This results in it being much more breathable; easier to get the oxygen in, and since it still has a 20% oxygen content no ill effects are had. Apart from sounding like a castrated mouse due to the higher resonance caused by inhaling helium.
7 years ago
Actually it's very funny. The page is a satire of irrational environmentalism and of people who are afraid of all "chemicals." I like the statement that "DHMO has been found in high levels in many lakes and streams in the US."
neelandan (author)  mbluett7 years ago
... and I might humbly add that that website is really preposterous! ( http://dhmo.org )
berin7 years ago
Time to educate you moron's on this, this is not some great easy quick method for producing a PCB board. This produced chlorine as a bi product, 5min of run time can produce a deadly lethal amount amount of Cl or also known as Chlorine. What you produce in a small VAT in this example is almost 2x what your YMCA uses to keep there entire POOL clean. AGAIN THIS IS A DANGERUS AND DEADLY EXPERIMENT. DO NOT TRY IT!!! besides putting this down the drain will kill a septic system AND will really really piss off your local wast water treatment plant to the point that they WILL investigate were the source of Chlorine is coming from. DANGER!!!!!
6 years ago
Er, isn't it going to produce copper chloride if you're dissolving copper in salt water?
5 years ago
Yes, at a high enough amperage this process will produce Cupric Chloride. Not the nicest of chemicals, but as long as you're not etching a full-size motherboard you should be fine. -recon506
5 years ago
i have just noticed something... doesnt cupric chloride etch pcbs??? if so, you could get a blank board and make some cool cupric chloride to etch your boards couldnt you? any suggestions please.. :) James
5 years ago
What if I do this outside, and dilute it before it goes down the drain? As well my water is almost completely distilled with just a bit of sodium because it comes from an underground source below my farm. Besides you can always use something other than salt, that will do the same job just as well.
5 years ago
... Any Cl gas that evolves, easily dissolves into solution (as gas). Cl gas and H2 gas that does escape are not deadly in such tiny concentrations. At most the Cl would be an irritant in an 3 x 3 meter room. It is all about the concentration. The waste water will never even know about the chlorine content... Any Cl gas would probably react with something and the Cl ions are so common in water (you get the same Cl ions from road salt). However, The EPA and your local DNR both care about copper ions being released into the ground water supply.
6 years ago
Could you give more info/ sources please? I'm not saying you're wrong, but if it's true it's something I'd like to know more about. In what way does it harm a septic system? I've worked on them and installed several, and except for something harming the pump with prolonged exposure (similar to using lye cleaners very often) I can't see how the chlorine would hurt a drain system. How does the concentration of chlorine in this solution compare to that of common bleach?
7 years ago
At first glance i see no Cl being produced Cl is normally only produced by electrolysis in normal saltwater when you have more than a Concentration 4M. otherwise gas is 1/3's O2 and 2/3's H do you have the reaction to help explain to me how Cl is produced ( perhaps when you do electrolysis you us too much salt)
7 years ago
oh had a look over people doing electrolysis Don't make a saturated salt solution and you should do fine, So a Maximum of 100g per L should be fine for no cl being produced
7 years ago
had a look at some electrolysis information and i believe: The Cu anode produces Cu 2+ ions which would like to bond with Cl- anyway (the fore no free cl gas is made) however its probably likely that the NaCl will only act as an electrolyte and CuO will be the only by product. Any gas produced if the Solution is under 4 mol will be the reduction of air. ( gas will be produced at both electrodes if you use more volts than you need even if the anode is inert, the gas produced will depend on the concentration as stated above) All reactions pretty much stop when electrolysis stops, You should to even be able to ingest some of this mixture and come out alright. Heres some more info.
7 years ago
I'm not a chemist, but it seems to me that the chlorine is instantly combining with the copper, forming copper chloride, which is the yellow stuff you see in the solution. So my guess is that it's probably not producing very much chlorine in the end. Like I said though, I'm not a chemist. Great instructable by the way; I think I'll try it the next time I use a SMT chip.
7 years ago
What about using sodium carbonate? I don't know if the salt here really does anything but increase conductivity...
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