Homebrew PCBs

I think I'm finally getting somewhere!

This evening I drained 400ml of the etchant from the tank and added the
same volume of 35% HCl, mixing well. This increased the acid strength to
around 3 Mol, and turned the etchant from blue to emerald green.

And when I say emerald green, I mean bright, vivid, "Emerald City from
the Wizard of Oz isn't this green" green.

Tank state is currently:
  Acid molarity -- Between 2.9 and 3 moles per litre. Higher than I
wanted (I was aiming for 2.25) so it would seem my HCl is stronger than
the label indicates, or (more likely) I added too much.

  Specific gravity -- 1.160. Fairly low, but not too low for the etchant
to etch a board in a reasonable time (around 12 minutes per Seychell's
test data).

I've added 40g of loosely bundled copper wire (UK mains earth cable) and
turned the air on. I'm going to leave that etching away for a few hours
and see what I end up with.


And now a free bit of advice -- clean your glassware, and keep dirty
glassware well away from the work area!
I had a few ml of CuCl2 etchant in a measuring jug and accidentally
spilled about 50ml of HCl into it. It immediately changed colour to
yellow-green and started fuming. Thankfully there wasn't much of it to
fume and adding the contents of my bottle of deionised water stopped it
in its tracks.

If you're adding strong HCl to an etch bath, use a clean funnel and make
sure the end of the funnel is below the liquid!

This should give you an idea of how HCl concentration affects the colour
of the CuCl etch bath:
  http://en.wikipedia.org/wiki/File:CuCl2_equilibrium.JPG
What you want is something like the middle test tube.


Now I just need to neutralise the ~500ml of waste etchant...


Cheers,
Phil.



On 09/11/13 18:38, Philip Pemberton wrote:
> On 09/11/13 17:17, Stefan Trethan wrote:
>> Do you have access to higher concentration H2O2?
>> If so you can leave the SG low, and let it build during regular etching.
> 
> I've got a bottle of 35% on hand.
> 
> I also noticed that my etch tank isn't 1 litre -- it's 2.25l. Which
> means I don't have 750ml of etchant -- I have TWO LITRES.
> 
> So the acid concentration calculations look even worse now. To get the
> acid concentration to 2.75 Molar, I'd have to drain off around 400ml of
> solution and neutralise it, then add roughly the same amount of 35% HCl...
> 
> My current plan of action looks something like this:
> 
>   * Drain off 400ml etchant. Neutralise and dispose of -- per
> <http://chemistry.stackexchange.com/questions/872/copper-chloride-neutralizing-and-disposal>:
>     * Add Aluminium foil - result: AlCl_3 in solution, Cu metal
>       (also see <https://www.flinnsci.com/media/622135/95000.pdf>)
>       *** VERY exothermic reaction ***
>     * Add sodium carbonate - CuCO_3 in water or precipitated
>     * Add sodium hydroxide - CuOH?
> 
>   * Add HCl to increase the acid level
>   * Add copper metal (wire)
> 
> It looks like my best bet might be to fix the acid concentration
> (increase to at least 1.0 Molar, maybe 1.5 Molar) then throw in some
> copper, leave it in the etch tank with air on and readjust s.g. and HCl
> concentration after the copper is gone.
> 
> Which leaves one remaining question -- how much copper do I need to add?
> 
> 
>> If you don't have concentrated H2O2 you may want to increase the SG
>> and put the oxygen in from the air.
>>
>> You'll notice a lack of HCl when adding H2O2 does not help, and the
>> surface of the copper turns blue.
> 
> I don't think there's a problem with the oxidation state of the copper
> chloride -- that is to say, based on solution colour, I definitely have
> Cu(II)Cl (cupric chloride, green/blue) not Cu(I)Cl (cuprous chloride,
> olive green).
> 
> Although to be absolutely honest the solution seems to be edging towards
> blue -- going by the photos on Wikipedia
> (<http://en.wikipedia.org/wiki/Cupric_chloride>, under "properties and
> reactions"), that might suggest that the acid level is indeed quite low.
> It certainly turns blue when diluted (e.g. when washing out the glassware).
> 


-- 
Phil.
ygroups@...
http://www.philpem.me.uk/