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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Signing UpStep 1: Decide how large the board has to be
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.































































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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
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.
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