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/