A tale of two methods

There was once the method of circuit fabrication, which took a piece of aluminium foil, stick it onto a piece of paper (for backing), print or draw on (with liquid paper) the circuit traces onto the foil, then dip it in concentrated saline and let it be the anode (did i get it right? hiyah the positive end of the power source lah) of the electrolysis of salt solution.


Supposedly, the chemistry goes like this: in the presence of chloride ions, the aluminium oxide layer that is so omnipresent on the aluminium surface will sorta dissolve. When the electrolysis occurs, the chloride ions are also discharged and highly oxidising chlorine gas is produced. Which attacks the raw aluminium metal whose protective oxide layer has been stripped. So the aluminium metal gets oxidised and forms aluminium chloride, which dissolves into aqueous solution.


This basically means that the parts of the aluinium that are exposed to the
saline solution will dissolve, leaving the parts protected by liquid paper. Which we can remove with alcohol and connect metal parts to.

Sounds perfect, but here's the snag(s):
1. because the whole sheet of aluminium is only linked to the power source at ONE particular point, what happens if etching occurs such that an "island" of aluminium is left behind? Since the aluminium is no longer connected to the voltage source, the electrolysis does not occur, so the aluminium isn't etched away, and remains behind. Leaving a really really messy (i call it 'noisy') circuit board. And it totally sucks if these things interfere with the operation of the circuit. But tests showed they didn't matter too much.

2. i totally chose to totally ignore the fact that aluminium cannot be soldered using the conventional tin/lead solder. All thanks to the irritating oxide layer present on all aluminium surfaces. And all previous attempts to temporarily eradicate the oxide layer for the solder to stick first, failed to work.

There exists solder that allows for soldering onto aluminium. It is no doubt expensive, and difficult to get.

Another alternative may be treatment by a chemical, called the tinning solution. okay maybe its called something else, nvm...anyway this is an organometallic compound, whose metallic component is, well, tin. Basically it liberates the metallic tin onto the metal surface. Since we can solder on
tin, we've solved the problem. Of course i do wonder if the tin sticks to the
aluminium in the first place! Such a solution is used in the conventional PCB
fabrication process, to coat with tin portions of copper onto which we want
to solder our electronic components. This is because tin makes a better medium to solder on, due to its lesses reactivity as compared with copper.

Once again, the hindrance to solderability is the bloody oxide layer!!!

As for Snag #1, we could conduct the electrolysis with a set of inert electrodes, and then place the aluminium to be etched really really really close to the anode...hoping that the chlorine produced would dissolve all the exposed aluminium nearby. Of couse chlorine is a very powerful oxidant, so how to find an 'inert' piece of metal 'impotent' enough to resist the temptation of losing its electrical virginity to chlorine? Can't possibly use mum's gold jewellery for this purpose can i?! (yes i was actually audacious enough to think of that.) Okay actually pencil lead can do the job (sentence added on 10th Sept)

The investigations into this method happened too long ago for me to recall if i've tried the remedy stated in the paragraph above. I must have made tons of notes on countless sheets of surplus "Industrial and Marine Electrical Contractor Tax Invoice" papers, but they are now nowhere to be found in my new home...and i've unfortunately forgotten the numerous minor details of my previous exploits. dank. (btw, 'dank' is the only word my schoolmate of 6 years considers 'clean' enough for usage as general expressor of anger/disappointment.)

Lone exploits sometimes get quite tiresome. You conceive it, you try it, you fail it, you try it again some other way, you get yourself out of your blind alleys and nasty snags, you kick yourself out of depression and disappointment, you debug everything yourself, you be the worst and harshest critic of yourself, you judge yourself, you screw yourself, until someday it (hopefully) works and you have something to be proud of.

IF that day EveR COMES.

Meanwhile, no one's gonna test your crazy ideas, so you've gotta test them yourself, and sometimes you've got so many tests which involve so much repetition that you get tired of doing them and too lazy to bash through that dense vegetation of drudgery to get to that lone tree on the empty patch.

**The Hand of Hang Jian's Rationality Department pulls him back from his
natural-inclination-driven digression**


Woo...okay (insert slightly dazed look containing a tinge of bewilderment)Anyway, i was thinking about this method which i had long abandoned, and compared it with the current one involving electroplating. The electroplating method creates really fragile circuit traces, but allows for soldering. The other method has rather robust circuit traces, but resists soldering. BOTH face the same problem of messy, noisy circuit patterns. (oh boy...circuit patterns...i do sound metaphysical to the electrically uninformed human don't i now?) Which i think i have solved by distributing my electrical contact points. BUT if the proposed solution to Snag #1 (see above) works? Then i have no more noisy circuit traces to worry about anymore!
(by the way, i will not extend the proposed solution to Snag #1 to copper clad boards, because they don't allow me to pass the circuit through a printer so i can only hand draw my circuit patterns...with liquid paper!!! no way...)

Which leads me to the question...Any other compelling reasons for using the electroplating method instead of the 'other' aluminium foil etching method?
Other than solderability? And supposing the noisy circuit pattern problem in this method was solved?

Reasons FOR the plating method
Environmentally friendlier because unlike etching, we don't need to dispose
of the plating solution.
Soldering is possible. Can't solder on aluminium without special solder which
is hard to find.


Reasons FOR the etching method
Don't need to hunt for zinc cation containing solutions...just add salt to
water
there's a good thickness to the circuit trace. Furthermore, the resistance of
aluminium is lower than that of zinc...(i think...you think, i thought, who
confirm? later...)
If the solution to Snag #1 works, we also don't have a problem with noise.

There is also a snag with the plating method regarding soldering. Due to the
tiny thickness of the plated metal, the circuit trace is extremely fragile. During soldering, the heat of the soldering iron will be passed from the circuit trace to the adhesive below it. The adhesive will melt under the heat, thus losing its tack. There is also cohesion between the circuit trace, the soldering iron, and the molten solder in between. When the soldering iron is lifted from the trace, this combination of factors causes the trace to dislodge from the substrate of the circuit board. This condition occurs in both the plating and etching methods.

The difference is made by the thickness of the trace. Aluminium foil is certainly thicker and more able to handle the physical strain due to the above situation than the plated trace. Nevertheless we do not discount the possibility that the aluminium foil trace may tear during soldering too. In response to the certainty of this occuring in the case of the plated circuit (as indicated to much disappointment by most recent tests...but also long anticipated AND ignored) 2 methods were developed to reduce the possibility of tearing.

They are, in short, to sink the heat rapidly, and to reinforce the traces by prudent and effective coating of the traces with quick-drying adhesive.

So i think the main issue wiith aluminium foil lies with its unsolderability.

Provided our solution to Snag #1 works...(okay i know the repeated reference to Snag #1 is getting irritating), unsolderability is a serious problem.
if we didn't use soldering, what could we use? a room temperature solution?

Powdered metal?

---Date line. the above was written on 9/9/05. the below is written today.---

Anyway, with reference to that issue of uneven etching of the aluminium foil in the 'other' method, a solution has just occured to me. It would be possible to press a matrix of pins onto the aluminium surface. These pins are all connected to the positive end of the power source. Which means that we now have multiple contact points on which we apply our positive potential. Which means most large islands created are probably in contact with one of these contact points and thus will eventually be etched away. Which leaves us with the very very tiny pieces of aluminium micro-islands that makes up the bulk of the noise. I can imagine using sharp pencils as positive electrodes, press them firmly on the micro islands such that electrical contact is made, and see them dissolving away. This was attempted before, but i think it somehow didn't work out...will investigate again. The micro-islands, as mentioned a couple of paragraphs ago, do not quite affect circuit operation...unless we've got really close circuit traces. The benign-ness of

these noisy things are based on the assumption (okay make that a fact) that most of the islands are electrically isolated from each other. But we should have a way to remove them if we need to. So i hope the proposed method works...though i think it did not. We'll see.

To do now:
1. make sheets of paper-backed aluminium foil
2. print copies of a test pattern onto the foil with my laser printer
3. try out the etching method again with the new recommendations