My bubble etch tank arrives. The kit consists of the tank, some clips for the PCB and heater (not shown), a fish tank pump and fish tank heater.
First a quick test with water. The tank really needs to be filled to the top, the water is only just at the "minimum" height required on the heater and it's touching the bottom!
After calculating the volume of water in the tank, I worked out how much copper I needed from Adam Seychell's page here: http://members.optusnet.com.au/~eseychell/PCB/etching_CuCl/index.html It's quite a bit! This copper was harvested from some old coax TV cable that I had no purpose for. The shielding wire is very fine, the core is much thicker.
Following the method layed out on Adam's site, here's the copper packed into the tank, with the hydrogen chloride (10% of filnal volume) added to the bottom of the tank. The acid was clear, after a few seconds it had already gone a bit coloured.
After a day or so a small amount of oxidisation started to appear on the copper.
The amount of oxidisation grew as the days past.
As the oxidisation built up the surface of the acid started to turn dark brown.
After about a week (if I remember correctly) there was quite a bit of oxidisation. Time for stage 2.
Here's the tank filled up with the remaining acid and water. At this point the fish tank pump was turned on.
Soon the solution turned clear again. Notice the green pool forming under the tank, this was from the liquid splashed up by the bubbling, which collected on the improvised cover and dribbled down the side of the tank. Thankfully I had put the tank in a plastic tray in case this happened.
After checking it each day for a while, with nothing much seeming to happen, I was beginning it get worried. That was until I walking in one morning to discover all the fine copper had gone and the solution was darkening again!
After a few more days the solution went very dark brown. So dark you couldn't see a torch through it. I could just make out some of the copper touching the side of the tank.
After another week (I think) the last traces of the copper pressing against the walls of the tank disappeared and the liquid in the tank started to turn green.
Ready to etch I guess.
Using "PCB" (http://pcb.gpleda.org) I created a test pattern to try out the etch tank. Since the press n' peel comes in US letter size sheets I exported the design as an encapsulated postscript file; imported it into OpenOffice Draw and laid multiple copies out onto a sheet.
I only want to do one at a time, so I marked out a panel from the sheet of sigle sided copper PCB (bought from Maplin) and cut it out. I tried doing this with a junior hacksaw, I'm going to have to find something a bit better, because it kept straying away from my cut lines. A proper hacksaw was a bit better, but not as accurate as I'd like.
The press n' peel was also cut down.
The PCB was pre-heated (ironing on "wool" setting through a folded piece of printer paper). The press n' peel was then ironed onto the board for a minute or so (again using the paper to make ironing a little easier).
After cooling under a cold tap the press n' peel was peeled off.
The mask wasn't perfect, but not bad for a first go. I think I'm running low on toner in my laser printer which probably doesn't help.
Here's the clip and wire provided in the kit.
PCB in tank, heated to 35 deg C and left to bubble for just over 8 mins.
Voila! Just need to remove the the etch resist.
After quite a scrub with a polish block under running water, I've got pretty much all of the etch resist off. Next time I think I'll try a solvent of some description, too much like hard work. :-)