Homebrew PCBs

Hi there,

I've finally found some time to check the acid cupric chloride etch
solution I started preparing back in July.

What I have is about 750ml consisting of:
  200ml 9% "food grade" hydrogen peroxide
  approx. 550ml "5 to 10%" hydrochloric acid (Cementone brick cleaner)


As a result of leaving the solution to stand in a dark concertina bottle
for a few months, it's now a delightful bright, transparent emerald
green. Going by [3], the Cu(I) concentration is somewhere between zero
and 0.5g/l.


After a series of mishaps with suppliers ("oh it'll be alright in a
jiffy bag", and it inevitably arrives smashed to bits) I popped down to
the local car parts shop and bought a car battery hydrometer. 1.100 to
1.300 range, not perfect, but not terrible.

I've measured the specific gravity of the etching solution at between
1.150 and 1.175. That's lower than it should be, but perhaps not as bad
as it could have been (I was expecting much worse). Seychell [1]
suggests a specific gravity between 1.220 and 1.380; Kasten [2] suggests
a starting s.g. of 1.170.

After a false start or two, I *think* I got the hang of the titration
process, and came up with a value of.. um... 0.5 mol/l. That would be...
less than half the minimum recommended by Seychell [1].

So my question is, what should my priority be? Do I try and fix the acid
level first by adding HCl, or do I throw in some copper and try to fix
the density (specific gravity)?

If I assume the etchant volume is currently 750ml, and I use the 35% HCl
I have on hand, per [1]:

  volume to add = Vt * (Cf - Ci) / (Cacid - Cf)

Aim - 2.75M (right in the middle of the 2.5~3M range Seychell [1] suggests):
  = 750 ml * (2.75M - 0.5M) / (11.1M - 2.0M)
  = 202 ml

That sounds like it'll leave me with quite a bit of etchant to dispose
of (too much to put in the tank or the storage bottle). To make matters
worse, that'll dilute the etchant still further when the s.g. is already
quite low to start with.

If I revise down to an aim of 2.0M:

Aim - 2.0 M
  = 750 ml * (2.0M - 0.5M) / (11.1M - 2.0M)
  = 124ml

Or 1.5M:
  = 750 ml * (1.5M - 0.5M) / (11.1M - 1.5M)
  = 78ml

Or even 1.0M:
  = 750 ml * (1.0M - 0.5M) / (11.1M - 1.0M)
  = 37ml

Which is still high but perhaps not insurmountable?


Should I concentrate on increasing the SG first, or should I work on
fixing the acid concentration?

Thanks,
Phil.


References --

[1] Seychell, Adam. (2005) Etching with
Air Regenerated Acid Cupric Chloride. Web:
http://members.optusnet.com.au/eseychell/PCB/etching_CuCl/index.html

[2] Kasten, Stephen D. (1983) "Electronic Prototype Construction".
Indianapolis: Sams.

[3]
http://members.optusnet.com.au/eseychell/PCB/etching_CuCl/cucl_colors2.jpg

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

I had exactly the same situation a couple months ago with the exception that I had left the solution in a gallon milk jug for about 2 years.

Anyway, the way I got it back to functional was to place it in my etching tank with air and heater on (about 40 degrees C) and suspending a large piece of bare copper wire (10 or 12 gauge) and letting it sit for 4-5 days. At this point the copper wire was dissolved and the color was back to a deep green. I can now etch a double-sided 3"x4", 1 oz. copper pcb in less than 15 minutes.

Hope this helps Good luck!

Do you have access to higher concentration H2O2?
If so you can leave the SG low, and let it build during regular etching.

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.

ST

On Sat, Nov 9, 2013 at 5:49 PM, Philip Pemberton <ygroups@...> wrote:
> Hi there,
>
> I've finally found some time to check the acid cupric chloride etch
> solution I started preparing back in July.
>
> What I have is about 750ml consisting of:
>   200ml 9% "food grade" hydrogen peroxide
>   approx. 550ml "5 to 10%" hydrochloric acid (Cementone brick cleaner)
>
>
> As a result of leaving the solution to stand in a dark concertina bottle
> for a few months, it's now a delightful bright, transparent emerald
> green. Going by [3], the Cu(I) concentration is somewhere between zero
> and 0.5g/l.
>
>
> After a series of mishaps with suppliers ("oh it'll be alright in a
> jiffy bag", and it inevitably arrives smashed to bits) I popped down to
> the local car parts shop and bought a car battery hydrometer. 1.100 to
> 1.300 range, not perfect, but not terrible.
>
> I've measured the specific gravity of the etching solution at between
> 1.150 and 1.175. That's lower than it should be, but perhaps not as bad
> as it could have been (I was expecting much worse). Seychell [1]
> suggests a specific gravity between 1.220 and 1.380; Kasten [2] suggests
> a starting s.g. of 1.170.
>
> After a false start or two, I *think* I got the hang of the titration
> process, and came up with a value of.. um... 0.5 mol/l. That would be...
> less than half the minimum recommended by Seychell [1].
>
> So my question is, what should my priority be? Do I try and fix the acid
> level first by adding HCl, or do I throw in some copper and try to fix
> the density (specific gravity)?
>
> If I assume the etchant volume is currently 750ml, and I use the 35% HCl
> I have on hand, per [1]:
>
>   volume to add = Vt * (Cf - Ci) / (Cacid - Cf)
>
> Aim - 2.75M (right in the middle of the 2.5~3M range Seychell [1] suggests):
>   = 750 ml * (2.75M - 0.5M) / (11.1M - 2.0M)
>   = 202 ml
>
> That sounds like it'll leave me with quite a bit of etchant to dispose
> of (too much to put in the tank or the storage bottle). To make matters
> worse, that'll dilute the etchant still further when the s.g. is already
> quite low to start with.
>
> If I revise down to an aim of 2.0M:
>
> Aim - 2.0 M
>   = 750 ml * (2.0M - 0.5M) / (11.1M - 2.0M)
>   = 124ml
>
> Or 1.5M:
>   = 750 ml * (1.5M - 0.5M) / (11.1M - 1.5M)
>   = 78ml
>
> Or even 1.0M:
>   = 750 ml * (1.0M - 0.5M) / (11.1M - 1.0M)
>   = 37ml
>
> Which is still high but perhaps not insurmountable?
>
>
> Should I concentrate on increasing the SG first, or should I work on
> fixing the acid concentration?
>
> Thanks,
> Phil.
>
>
> References --
>
> [1] Seychell, Adam. (2005) Etching with
> Air Regenerated Acid Cupric Chloride. Web:
> http://members.optusnet.com.au/eseychell/PCB/etching_CuCl/index.html
>
> [2] Kasten, Stephen D. (1983) "Electronic Prototype Construction".
> Indianapolis: Sams.
>
> [3]
> http://members.optusnet.com.au/eseychell/PCB/etching_CuCl/cucl_colors2.jpg
>
> --
> Phil.
> ygroups@...
> http://www.philpem.me.uk/
>
>
> ------------------------------------
>
> Be sure to visit the group home and check for new Links, Files, and Photos:
> http://groups.yahoo.com/group/Homebrew_PCBsYahoo Groups Links
>
>
>

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/

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/