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Step 19Etching the board
To etch the board, you make up a saturated solution of salt water, make the board positive and immerse it into the solution together with a negative electrode.
A 12 volt supply capable of supplying about 500 milliamperes is sufficient. Wire it in series with a filament lamp, say 12V, 6W, for an indication of the current.
It would take about five minutes for the etching process to be completed. You will be able to watch its process by the light shining through the gaps that open up as the copper gets eaten away.
Bubbles of hydrogen will be seen rising from the negative electrode. If they are rising from the copper, you have connected up the supply backwards and your wire is being eaten up.
To make up the salt solution, you take some water and dissolve as much salt as possible, thus making up a saturated solution. You add a little salt, shake it and watch the salt disappear as it goes into solution. Then you add some more, and it too disappears.
After some of this the salt will stop dissolving however much you shake and mix it, and at this point you have the saturated salt solution you need.
This is a saturated solution of Sodium chloride in Dihydrogen Monoxide. See http://www.dhmo.org for more information in handling this potentially hazardous substance.
A 12 volt supply capable of supplying about 500 milliamperes is sufficient. Wire it in series with a filament lamp, say 12V, 6W, for an indication of the current.
It would take about five minutes for the etching process to be completed. You will be able to watch its process by the light shining through the gaps that open up as the copper gets eaten away.
Bubbles of hydrogen will be seen rising from the negative electrode. If they are rising from the copper, you have connected up the supply backwards and your wire is being eaten up.
To make up the salt solution, you take some water and dissolve as much salt as possible, thus making up a saturated solution. You add a little salt, shake it and watch the salt disappear as it goes into solution. Then you add some more, and it too disappears.
After some of this the salt will stop dissolving however much you shake and mix it, and at this point you have the saturated salt solution you need.
This is a saturated solution of Sodium chloride in Dihydrogen Monoxide. See http://www.dhmo.org for more information in handling this potentially hazardous substance.
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It should be noted that you need a substantial load when using an switch mode power supply otherwise it may not switch on
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.
Benedikt Ómarsson, B.Sc
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).
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 =)
DHMO = H20 = water