Homebrew PCBs

Hi Adam -

Though I mention 5 pounds of copper in the related post, in fact I
used less. It was about 4 pounds, plus a bit more from an extra test
wire I hung over the side and a 3" x 5" piece if PCB I used to confirm
etching. My original etchant consisted of 4 litres of 31.5% (20
Beaume) HCl and 8 litres of distilled water. (I thought I was making
10% HCl but I think I needed a different formula). Later I added 500
ml of 3% hydrogen peroxide. Later yet I added about a cup of distilled
water. And later again I gradually added approximately 3 litres of
31.5% HCl. And, since the tank lid was off until the weekend, some of
the etchant may have evaporated - enought to rust some tools, anyway!

I think I need to study up on "stoichiometry". My highschool chemistry
was over 30 years ago, and I have forgotten all I ever knew, which
probably wasn't all that much.

I understand that your calculations below were in reply to my earlier
post. Maybe the above will make it easier for you to approximate any
adjustment I should now be making to the etchant. As I said in a
recent post, the ph has changed from 2 to 3 in the last day or so.

Grant

--- In Homebrew_PCBs@yahoogroups.com, Adam Seychell
<adam_seychell@y...> wrote:
> I'm glad to see its finally working.
> As I learned on the weekend, the bubbles is what makes the 
> process move forward. It was a bad idea to initially let the 
> copper stay in a stagnant solution. The correct method is to add 
> all the acid and copper together in one hit and bubble it like 
> crazy. Then wait until it turns to a transparent deep green. At 
> 150g/L of copper (SG 1.3) you won't see through more than 1cm 
> without a bright backlight. A drop on white surface shows up nice 
> bright green.
> 
> Thanks for this link, http://www.pacificsun.ca/~robert/pcb/cucl.htm
> 
> I like his idea of HCl titrations using a eyedropper and counting 
> the drops. Just look for the formation of insoluble Cu hydroxide, 
> which will turn the solution cloudy. The eye dropper method is 
> good enough for determining the acid content of this etchant. An 
> indicator will make it easier. I'll post more analysis details 
> another time.
> 
> The HCl can be very low 0.1M and still etch perfectly ok. At very 
> high say 3M then it will create more fuming. The HCl should never 
> be zero because air regeneration cannot happen and your solution 
> will quickly build up insoluble copper(I) film over the copper 
> and inhibit etching.
> One thing I noticed in the article is that he uses much lower 
> copper content (100g/L of CuO) or 80g/L of copper. I'm sure at 
> 140g/l copper you get over double the speed, I'll have to check 
> that again.
> 
> Grant, you mention 5.0 pounds of copper (2.3kg). if you desire 
> 140g/L of dissolved copper then you looking at 16 liters of 
> etchant !. Thats a lot of etchant :) Worry about disposal another 
> day.
> 
> The HCl will needed to react with all this copper and have some 
> left over for about a 1M of free HCl then you'll need;
> 
> Moles of copper = 2300grams / 63.5  = 36 moles
> 
> Cu + 2HCl -> CuCl2
> 
> So you need twice as many moles of HCl than moles of Cu, or 72 
> moles. You also need another 16 liters * 1 Mole/liter = 16 moles 
> of HCl. Total moles of HCl = 72+16 = 88.
> 
> according to.
> 
> http://www.starch.dk/isi/tables/hcl.htm
> 
> and the fact that molecular weight of HCl = 36.g grams/mole
> then
> 30%wt HCl = 345g/l = 345/36.5 = 9.5 Moles/Liter.
> 
> then to calculate the volume HCl needed to get 88 moles
> 
> Total volume of 30% HCl = 88/9.5 = 9.3 liters.
> 
> I hope I'm making some sense here.
> 
> Adam
> 
> 
> 
> 
> 
> grantfair2001 wrote:
> > I am happy to say that I can now see unmistakeable signs of progress
> > with my etchant. I now have about 17 litres of it, in a 34 litre
> > Coleman cooler, gugrgling away on the floor next to my laundry tubs.
> > 
> > The air bubbler I made is the type described at Think & Tinker:
> > 
> >
http://www.thinktink.com/stack/volumes/voliii/equipmnt/bubltank/bubltank.htm
> > 
> > I am using air from the exhaust output of a small vacuum pump.
> > Sometime recently, the bubbler started putting out more air, so almost
> > all the surface of the etchant is constantly bubbling vigorously. I
> > don't know whether the sparger moved, or the pump, which has carbon
> > vanes, suddenly decided to put more air out. The pump has been running
> > continuously for several days with only slight heat to the touch for
> > the motor case. The pump casing seems even less warm than the motor
> > casing.
> > 
> > Anyway, I can see two changes tonight (in addition to the more
> > vigorous air bubbling). 
> > 
> > The etchant is an even deeper brown color than it has been for a few
> > days. It is so dark I can hardly see the wire under the etchant
> > surface. And all the remaining wire is clearly decreasing in diameter.
> > (I hung one piece of copper wire over the edge of the tank about 4
> > days ago. The etched part is 1/2 the diameter or less than the
> > unetched end). Also, at the start, the whole mass of copper wire was a
> > large jumble, with some wire under etchant and some above it. Clearly
> > the etchant is working, because the level of wire above the surface
> > has substantially decreased. 
> > 
> > It is great to see this working, after the slow start I had, and all
> > my worrying and wondering. I hope I will be able to start etching
> > boards within a week or so. Yahoo!
> > 
> > I do like this process because: 
> > 
> > 1) it is non-polluting
> > 
> > 2) replenishing HCl is cheap and easy to do
> > 
> > 3) a Coleman cooler, 8 litres of HCl, and 5 pounds of copper wire,
> > along with a bubbler are all it took me to get started, (along with a
> > hell of a lot of advice)
> > 
> > 4) this list is a great source of information and encouragement
> > (thanks Adam, and everyone else who helped!)
> > 
> > 5) cheap and dirty chemical analysis is possible - see:
> > 
> > http://www.pacificsun.ca/~robert/pcb/pcb.htm
> > 
> > for related work by Donald Aitken and Robert Grauman
> > 
> > Grant
> > 
> > 
> > 
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> > 
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