PCB etch tank

So I've got hold of some of the things I need, aquarium heater, bubbler and check valves, the chemicals are on there way and should be here soon, I'm looking forward to testing some things out. The immediate problem, being a student, I am somewhat poor and I have slightly broken my aquarium heater (more on that later in this post) so things progress slowly (I also have exams and should be focussing on them, but I'm not, because I like electronics more and I'm dedicated to my hobby...)

Here are a few pictures of the the parts:

From PCB etch tank

From PCB etch tank

I got the heater today, I thought "Great, this is exactly what I want" I even managed to slice the limit stopping you from turning the knob too far so I could reach higher temperatures (read: ~40 °C)

N.B. *Sigh* just looked at the cupric chloride guide:

Temperature (°C)

0

40

HCl fuming increases. Etch speed increases. (see note 1)

Looks like I might not even need that heater... I think for the sake of simplicity and cost I shall eliminate it. Good, I feel like I have less things to limit my design now.

Coming back from my tangent, I had modded it and let it sit at ~45°C for a bit and went out for a run leaving it on, I came back to find it no longer working. I took it apart and found that the framework it was all attached to had melted and had pushed the magnet out stopping the lever from making contact with the contact. (best described with a picture)

From PCB etch tank

The lever on the bottom touches a contact when the blue knob is turned (this is how you set the temperature). When the temperature has reached a certain point, the lever expands and the magnet can no longer hold it touching the contact so it returns to the position in the picture breaking the circuit, I tried to remold the magnet hold and to some extent I had some sucess, I put it back in it's glass tube and turn it back on. *BANG* I have a nice set of sun spots and the breakers go; the heating element had shorted.

Before:

From PCB etch tank

After:

From PCB etch tank

I took it all apart and tested all the components then fixed the heating element (shortening it due to a part blowing off it. I assumed the bulb had gone so took it out and replaced it with a jumper, it didn't work. After 30 minutes of troubleshooting I thought to check the fuse (I should have done this first) and low behold it had blown. After reassembling it this time I got a lovely red glow from the element so I'm assuming this is due to the loss of part of the element and the element's resistance has gone down.

From PCB etch tank

Because the circuit is setup as a potential divider the bulb was dimmer due to the lower resistance of the element & thus lower current through the bulb. The bulb is attached to a ~120k resistor which I think I'll replace with a lower value one to divert more current to the bulb and hopefully remedy the over powered element issue.

From PCB etch tank

My apologies if this is a little incoherent, It's getting a bit late here. Time for experiment 18 I think, I fancy some electronics to calm me down after such an eventful evening!

Custom etch tank: The start.

I've decided to have a bash at making an etch tank as I like making PCBs, however at the moment I've got no way to heat my etchant up and the whole affair is looking like a rather sorry state. After reading this instructable, I decided to build my own, I really like the etch tank design but would like to redesign it myself, purely for the practice in CAD and in-depth knowledge it will provide. I've bought an aquarium pump and heater to use in it and I will be using cupric chloride to etch.

I've found a wonderful website with a list of several materials and their resistances to specified chemicals, it's really invaluable to picking materials to use.

So far I have chosen a few materials:

Etch tank - Acrylic

Tubing - Ideally polypropylene (but I will settle for PVC) 1/4" ID (same as aquarium pump)

Fittings - Ideally polypropylene, but if PVC one are available I'd settle for them, they're expensive and hard to find.

It's a rather pitiful list but it's all I've decided on for the moment. I'm looking at buying chemicals, shipping is painfully expensive and I haven't really calculated how much I need to get, so that's on my to do list. It looks like higher concentration solutions of hydrogen peroxide cost the same as the lower concentration ones, obviously I'll go for the higher concentration as It's less to store, shipping will be cheaper and It's easy to dilute it.

I also need to get some methylene chloride for solvent welding acrylic, it's pretty cheap here, but I might buy it from ebay depending on delivery prices, this seller has most/all of the chemicals I need. Scratch that, the first seller mostly what I want at lower prices, excellent!

Hydrogen peroxide is the only thing that isn't stocked there, I thought I'd figure out how much I need, at 35% it's pretty concentrated, I used this handy calculator to find the concentration in mol/dm^3, so 500ml at 35% can be diluted to give 5 litres of 1.16mol/dm^3 looking at the equation on the cupric chloride link:

2H⁺ + Cu¹⁺ + O_{aq} → Cu²⁺ + H₂O

This looks like it's probably going to be more than sufficient. Actually looking at the page again, it just occurred to me, I don't even need hydrogen peroxide after producing the etchant as I can regenerate the solution using air, I'm going to just get 250ml...

The acid gets used up so I'm buying a litre of that, the common mix to produce the starter etchant seems to be:

1 part HCl (35%)

2 parts H2O2 (3%)

UPDATE:
Just bought:

1 Litre HCl

1 Litre Acetone

1 Litre methylene chloride

1 kg NaOH (just in case I want to do titration and analyze my etchant)

£9.50 for delivery

£11.50 for the chemicals

Now I can whip up some etchant, have a play around with it and see whether the check valves I've bought are or are not made from polycarbonate... hopefully they'll be OK.

On a side note: I've picked up a laser printer (from freecycle!) which I may play around modding to print on circuit boards. However, it looks like a fairly complicated endeavour which currently I'm not sure I need to embark on, one for the future perhaps.