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
>
>
>