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etching printed circuit boards

A

Allan Adler

Jan 1, 1970
0
One of the problems with making your own printed circuit boards is the
difficulty of legally disposing of spent etchant. That might be easy in
some places, expensive or impossible in others.

It occurred to me that there might be less problematic alternatives for
dealing with printed circuit boards. For example, a few decades ago when
I wanted to try to synthesize copper acetate for myself, I dropped pennies
in vinegar and left them alone for a few weeks and copper acetate crystals
grew on the pennies. (I know that pennies are not pure copper, so this might
not have been pure copper acetate). The pennies never dissolved completely,
but I was after crystals and didn't worry about completely digesting the
pennies.

I was able hasten the process considerably by connecting the leads of a
battery to a cupful of vinegar with copper wire. In fact, the wire dissolved
completely. It produced a rich blue solution from which I obtained
broccoli-like dendritic growth, but it would probably have just as
well grown nice crystals under other conditions.

So, I was wondering what exactly would be wrong with dropping the printed
circuit boards in vinegar (or perhaps somewhat more concentrated acetic acid)
and trying to etch them that way. When you are done, you can just use the
resulting solution to grow nice copper acetate crystals. The battery idea
is also appealing, but it suffers from the obvious defect that once the
copper near the electrode is gone, the rest of the copper is no longer
connected to the battery. Maybe someone knows a clever way around that
inconvenience.

Alternatively, consider the problem of disposing of actual spent ferric
chloride or spent ammonium perchlorate. Some locales have no provision
for disposing of such chemicals at special waste sites, which are dedicated
to lists of specifically approved substances such as paint thinners, motor
fuel, used tires, etc. Instead, one has to contract with a company specializing
in toxic waste to get rid of it. That sounds like an expensive proposition and
they might simply refuse to deal with an individual and the tiny quantities
of spent etchant they generate.

Is there any reason why one can't simply try to use the spent etchant to
grow large single crystals and add them to one's crystal collection? In
fact, amateurs who etch their own printed circuit boards can have contests
for the largest and most perfect single crystals, or the most interesting
dendritic growth.

Ignorantly,
Allan Adler
[email protected]

****************************************************************************
* *
* Disclaimer: I am a guest and *not* a member of the MIT Artificial *
* Intelligence Lab. My actions and comments do not reflect *
* in any way on MIT. Moreover, I am nowhere near the Boston *
* metropolitan area. *
* *
****************************************************************************
 
G

Garrett Mace

Jan 1, 1970
0
I was able hasten the process considerably by connecting the leads of a
battery to a cupful of vinegar with copper wire. In fact, the wire dissolved
completely. It produced a rich blue solution from which I obtained
broccoli-like dendritic growth, but it would probably have just as
well grown nice crystals under other conditions.

So, I was wondering what exactly would be wrong with dropping the printed
circuit boards in vinegar (or perhaps somewhat more concentrated acetic acid)
and trying to etch them that way. When you are done, you can just use the
resulting solution to grow nice copper acetate crystals. The battery idea
is also appealing, but it suffers from the obvious defect that once the
copper near the electrode is gone, the rest of the copper is no longer
connected to the battery. Maybe someone knows a clever way around that
inconvenience.


Electro-etching is one way decent amounts of copper can be removed from a
board. Usually it's followed up by regular etchant to clean up the last
bits. This method allows you to use less etchant because you remove most of
the copper first, and don't wear out the etchant as quickly. I haven't tried
it.
 
H

Harry Conover

Jan 1, 1970
0
Allan Adler said:
One of the problems with making your own printed circuit boards is the
difficulty of legally disposing of spent etchant. That might be easy in
some places, expensive or impossible in others.

It occurred to me that there might be less problematic alternatives for
dealing with printed circuit boards. For example, a few decades ago when
I wanted to try to synthesize copper acetate for myself, I dropped pennies
in vinegar and left them alone for a few weeks and copper acetate crystals
grew on the pennies. (I know that pennies are not pure copper, so this might
not have been pure copper acetate). The pennies never dissolved completely,
but I was after crystals and didn't worry about completely digesting the
pennies.

I was able hasten the process considerably by connecting the leads of a
battery to a cupful of vinegar with copper wire. In fact, the wire dissolved
completely. It produced a rich blue solution from which I obtained
broccoli-like dendritic growth, but it would probably have just as
well grown nice crystals under other conditions.

So, I was wondering what exactly would be wrong with dropping the printed
circuit boards in vinegar (or perhaps somewhat more concentrated acetic acid)
and trying to etch them that way. When you are done, you can just use the
resulting solution to grow nice copper acetate crystals. The battery idea
is also appealing, but it suffers from the obvious defect that once the
copper near the electrode is gone, the rest of the copper is no longer
connected to the battery. Maybe someone knows a clever way around that
inconvenience.

Alternatively, consider the problem of disposing of actual spent ferric
chloride or spent ammonium perchlorate. Some locales have no provision
for disposing of such chemicals at special waste sites, which are dedicated
to lists of specifically approved substances such as paint thinners, motor
fuel, used tires, etc. Instead, one has to contract with a company specializing
in toxic waste to get rid of it. That sounds like an expensive proposition and
they might simply refuse to deal with an individual and the tiny quantities
of spent etchant they generate.

Is there any reason why one can't simply try to use the spent etchant to
grow large single crystals and add them to one's crystal collection? In
fact, amateurs who etch their own printed circuit boards can have contests
for the largest and most perfect single crystals, or the most interesting
dendritic growth.

Allan, while I applaud your rather extreme level of environmentally
related political correctness, I really think you should get a closer
grip on reality and realize that the copper laden waste residue
created by amateur PC board etching wouldn't even create a glitch in a
graph of the copper salt residue released into the waste water
treatment systems by millions of copper pipe plumbed homes.

That said, you are correct in believing that you can electroplate or
precipitate crystals or salts from spent etchant. Large PC shops have
been since the early 1980s required to do just this, however the costs
involved in this copper reclamation process have driven most of the
industry into the use of additive copper PC fabrication processes
rather than etching away the majority of surface area on a copper foil
laminated panel.

The pollution produced by simply dumping small quantities of home
produced spent etchant into a municipal waste water collection system
is arguably no worse than that released into the same systems by
millions of home darkrooms and drugstore sited photo processors.
Simply neutralize the etchant by adding some lye or ammonia to it (in
well ventilated conditions) prior to pouring it down the drain.

Important note: Never dump spent etchant into a domestic system that
feeds into a residential septic tank for reasons that should be
obvious.

Harry C.

p.s., Allan, stay away from using a solder plated resist on your PC
boards, because lead salts present a far more serious disposal problem
than does copper.
 
M

Muhammar

Jan 1, 1970
0
Copper does not dissolve in vinegar. Zinc does. Since you had some
"insoluble stuff" left from dissolving pennies, you managed to get
some dirty zinc acetate and separate all copper (3% of it, used for
coating).

If you want to dispose spent etchant solution in a cheap and
enviro-friendly way, you can mix it into concrete slush and leting it
harden. While you are pouring your concrete mix, you can also include
your mother-in law for more satisfying monolith.
 
G

Garrett Mace

Jan 1, 1970
0
Jamie said:
Yup, i know the problem.
i my self don't have very much trouble in disposing of the
etching due to a local dump that handles those kinds of
problems.
i did how ever develop 2 different X,Y,Z scanning tables.
one is a sprayer that uses Blue Dye and sprays the protective
coating onto the clad..
the other is a EDM (electro discharge Machine) that actually
is using a plasma removable approach with the Clad submerged in
a oil that is very easy cleaning afterwards. i use a small little
fluid pump to circulate and filter the oil..
both work, i would rather use the EDM over my Blue Dye sprayer due
to the mess it some times makes..
P.S.
currently i am having noise emission problems with EDM but working
on it..
:)


I am interested in this, might be a neat way to convert my mini CNC mill to
a quicker PCB maker. How fine of a cut do you get? What's the electrode made
out of, and the best angle for the point? Best working voltages and oils?
Any faster than milling?
 
G

Garrett Mace

Jan 1, 1970
0
I am interested in this, might be a neat way to convert my mini CNC mill to
a quicker PCB maker. How fine of a cut do you get? What's the electrode made
out of, and the best angle for the point? Best working voltages and oils?
Any faster than milling?


My experiment with a 24V supply, piece of copper-clad, blob of motor oil,
and fine drill bit was rough but successful enough to warrant further
investigation and experimentation. I'll go look for more information on EDM
and see if I can convert my little mill to use this. I'll most likely use
point-to-point outline removing (G code) instead of the scanning method you
outlined below. I wonder what it will take to monitor the electrode current
and modify TurboCNC to adjust Z accordingly...really this looks like a great
application of hobby EDM, removing a foil of copper is going to be much
faster than cutting a hunk of steel. The only thing I'm doing right now is
wondering why I didn't think of it before, just last week I was discussing
how to use continuity on copperclad to zero a Z axis very accurately. Never
occurred to me to just increase the testing voltage and put a little acrylic
tank on the mill.
 
M

Mohammed Farooq

Jan 1, 1970
0
Allan Adler said:
I'm still trying to understand how copper gets etched and am still
confused. I don't think it would take much to lift that confusion.
What I've been doing is looking in the CRC Handbook for electrochemical
potentials. For example, whereas Steve Turner writes that Cu(II) oxidizes
Cu to Cu(I), I find in the CRC book that
Cu(I) + e -> Cu with E0=0.52 V and Cu -> Cu(II) + 2e with E0=-0.64,
so that indeed Cu(II) + Cu -> 2 Cu(I) with E0 = 0.68 V. So far, I haven't
found any way to use that. Just working on my own, using the formulas in
the CRC book, I've done the following:
Water always has some hydroxide ions in it. The CRC book says that
Cu(OH)2 + 2e -> Cu + 2OH- with E0=-0.222 V and that
2 Cu(OH)2 -> 2e -> Cu2O + 2OH- + H2O with E0=-0.80 V, so I conclude that
2 Cu + 4OH- -> Cu2O + 2OH- +H2O + 2e with E0=0.364 V.

The electrode potentials given in CRC are for the standard conditions
.. If you are considering water as a source of hydroxide ions which is
approximately about 10^-7 mole/liter in water at 25 C, , you will need
Nernst equation to get the correct electrode potential for the
conditions you are applying and then check the possibility of the
reaction between copper and hydroxide ions.
Though the reaction under standard conditions seems to be
thermodynamically possible, but I never heard of copper being attacked
by common alkalis except ammonia, which perhaps dissolves copper by
the forming a blue complex rather than forming a oxide.
 
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