First of all, thanks for the replies concerning the various reasons you are
all constructing boards. I’m sure I’ll find the ongoing discussions
interesting in this group.
I suppose I’ll offer something to the group by making a submission on this
subject of Etchants. Since I don’t know what everyone is using for
etchants at home (and I’m not doing any type of this work at home myself),
I can offer what I know from the industry. My experience has been that the
three major etchant types used are:
1) Ammoniacal (Ammonium chloride)
2) Cupric Chloride
3) Ferric Chloride
Typically I find Ammonium Chloride and Cupric Chloride used for producing
circuit boards, and Ferric Chloride used in the chemical milling industry.
For home use, I would think that either Cupric Chloride or Ferric Chloride
would be preferred. Ammonium Chloride (as someone pointed out earlier)
produces quite an ammonia smell, which is much worse when the solution is
heated. However, if you are using tin / tin lead as an etch resist, then
Ammonical Chloride is “typically” required (this may not be the case in
home etching scenarios) since other etchants will etch away tin / tin lead
resist.
Cupric Chloride and Ferric Chloride share a few similarities. In the old
days, both were rejuvenated using the oxidizer “chlorine gas”, then later
people started using Hydrogen Peroxide, but now a-days people use Sodium
Chlorate (salt water, for example). This oxidizer can easily be made at
home by mixing a clean rock salt with water, allowing the water to absorb
as much salt as possible. Then the salt water (brine) is added to the
etchant to rejuvenate it. Note… this rejuvenation process is only for
Cupric Chloride or Ferric Chloride… not Ammonium Chloride. There is a
great deal of technical detail that can be discussed when adding an
oxidizer to the etchant (such as monitoring the oxidation reduction
potential), but I’m not sure if that is needed for this group. Let me
know if you would like that information and I’ll put something together,
or I’m sure this information could easily be found on the Internet.
Cupric Chloride and Ferric Chloride also need a certain amount of
Hydrochloric Acid, another item fairly easily obtained (Muratic Acid can be
used, and it is much easier to obtain). And of course, both Cupric and
Ferric will need a certain amount of Copper and Ferric Iron ions in
solution for the whole etching process to occur. Again, much detail is
available for these two components (monitoring the Hcl level with methods
such as titration or electronically, and monitoring the specific gravity of
copper / Iron levels… very easily done with a hydrometer).
Of the three, the Ferric Chloride is probably the easiest to dispose. I
have been told those years ago, some cities encouraged manufacturing plants
using Ferric Chloride to dump the solution down the drain when they wanted
to dispose of it. Apparently, it helped keep the city pipes clean! NOTE:
(here’s my disclaimer) I am in no way suggesting that you do this with
your ferric chloride etchant.
I’ll leave it there for now. I’ll just add that I remember many years
ago when I took an electronics class, I used Ferric Chloride as my etchant
(just poured it out of a gallon jug and “swished” my board around until
the exposed copper was gone. Worked pretty well for a single sided, single
layer board, but I also remember that board had line widths and spaces of
about a half inch.
Thanks for letting me contribute. Take care.
Marty
-----Original Message-----
From: wturchyn [mailto:
wturchyn@...]
Sent: Thursday, May 22, 2003 10:18 AM
To:
Homebrew_PCBs@yahoogroups.comSubject: [Homebrew_PCBs] Etchant options?
A previous poster made the following comment:
I did 'em myself using Radio Shack FeCl³. I tried Ammonium
Persulfate once, but NO WAY at home, ever again! Whew!
I had used messy ferric chloride when I made some hobby PCBs about 25
years ago, but I have seen other less-staining etchants are now
available, such as ammonium persulphate and sodium persulphate.
What are most people using at home, and what are the pros and
cons of the various etchants? Cost? Shelf life? Ease of use?
Safety? Cleanliness? Availability?
WT
Winnipeg, Canada
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