I was unhappy with the depth of my brass etching. Calculations
suggested that I should be getting about 0.020" depth for the given
current and time but I was getting about 0.006". I thought that the
explanation was that the current was wasted on gas production at the
anode (whatever the gas may be).

I was not sure what the problem was. I found a pot of my old
electrolyte (bought from a commercial vendor) and tried it. I quickly
found two things;

1) At current density over 0.1A/cm2 there was gas production on anode
and if one went even higher there was gas production on the cathode as
well.

2) At the beginning of the process there are some weird things
happening. My power source delivers constant current and to do so the
voltage fluctuates wildly (up to 20 V) and at one point there was an
oscillatory type of effect where the voltage dropped, gradually
increased and dropped again at about 1 of these events every two
seconds.

Anyway I managed to etch a piece of brass and separately a piece of
copper with an area of 100mm2 to the depth of 0.009" which was
consistent with calculated prediction.

Today I tried my new electrolyte (CuSO4, H2SO4 in H2O) on a piece of
brass with an area of about 450 mm2 (I had an accident with the
resist). At the start of the process I set the current at 0.45A and
got it with hardly any voltage at all. At 8 minutes the instability
started as above, then it settled with the current steady and voltage
of 10V. After 90 minutes the instability reappeared but was less
dramatic, the voltage oscillating between 2 and 4 volts keeping the
current steady.

There was no detectable gas production throughout.

I went for total 2 hours. The result is he

http://www.flickr.com/photos/2768312...in/photostream

I cannot even begin to guess why the current blew a hole where it did
while only removing between 0.0065" and 0.0075" elsewhere.

The cathode, BTW, showed a pretty even deposit of copper throughout.

Michael Koblic,
Campbell River, BC

On 2012-07-31, wrote:
I was unhappy with the depth of my brass etching. Calculations
suggested that I should be getting about 0.020" depth for the given
current and time but I was getting about 0.006". I thought that the

[ ... ]

1) At current density over 0.1A/cm2 there was gas production on anode
and if one went even higher there was gas production on the cathode as
well.

[ ... ]

Today I tried my new electrolyte (CuSO4, H2SO4 in H2O) on a piece of

[ ... ]

There was no detectable gas production throughout.

I went for total 2 hours. The result is he

http://www.flickr.com/photos/2768312...in/photostream

I cannot even begin to guess why the current blew a hole where it did
while only removing between 0.0065" and 0.0075" elsewhere.

A question occurs to me. Was the area with the hole at the
bottom, top, or a side in the etchant?

Also -- was there anything stirring the etchant during the
etching? I would suggest that you get a magnetic stirrer (with the
magnet in a Teflon coating so it does not get etched), which might help
reduce the buildup of either coatings, or perhaps a very fine gas layer,
not enough to bubble free, but enough to protect part of the surface
part of the time. The oscillation of the voltage might be explained by
a buildup of a fine insulating layer of gas bubbles, which eventually
pop as the area being etched drops, allowing the voltage to swing low
again as more area is being etched. Since you have a constant current
supply, I would expect the voltage to be proportional to the inverse of
the area being actively etched at a given moment. And the current,
while constant at the power supply, will be varying with the exposed
area actually being etched.

While I've not used the mag stirrer during electro-etching, I
have used it for chemical etching of printed circuit boards, and it
makes a big difference there.

Just some thoughts,
DoN.

--
Remove oil spill source from e-mail
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

"DoN. Nichols" wrote in message
...
On 2012-07-31, wrote:
I was unhappy with the depth of my brass etching. Calculations
suggested that I should be getting about 0.020" depth for the given
current and time but I was getting about 0.006". I thought that the

[ ... ]

1) At current density over 0.1A/cm2 there was gas production on anode
and if one went even higher there was gas production on the cathode as
well.

[ ... ]

Today I tried my new electrolyte (CuSO4, H2SO4 in H2O) on a piece of

[ ... ]

There was no detectable gas production throughout.

I went for total 2 hours. The result is he

http://www.flickr.com/photos/2768312...in/photostream

I cannot even begin to guess why the current blew a hole where it did
while only removing between 0.0065" and 0.0075" elsewhere.

A question occurs to me. Was the area with the hole at the
bottom, top, or a side in the etchant?

Also -- was there anything stirring the etchant during the
etching? I would suggest that you get a magnetic stirrer (with the
magnet in a Teflon coating so it does not get etched), which might help
reduce the buildup of either coatings, or perhaps a very fine gas layer,
not enough to bubble free, but enough to protect part of the surface
part of the time. The oscillation of the voltage might be explained by
a buildup of a fine insulating layer of gas bubbles, which eventually
pop as the area being etched drops, allowing the voltage to swing low
again as more area is being etched. Since you have a constant current
supply, I would expect the voltage to be proportional to the inverse of
the area being actively etched at a given moment. And the current,
while constant at the power supply, will be varying with the exposed
area actually being etched.

While I've not used the mag stirrer during electro-etching, I
have used it for chemical etching of printed circuit boards, and it
makes a big difference there.

Just some thoughts,
DoN.

--
Remove oil spill source from e-mail
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. |
http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---



What Don said, plus perhaps try air agitation. I etch PCBs and us a length
of stainless tube with small 1mm holes drilled along its length. Etching is
much faster and MUCH more even with vigorous agitation.

wrote:

I was unhappy with the depth of my brass etching.

I etch brass shim stock with ferric chloride to make stencils for
solder paste for PC boards. My spray etcher has a heater in it, and
I get the etchant up to about 35 - 40 C. The spray system is a typical
pump (Little Giant-style with stainless or maybe titanium impeller and
shaft) and the wand is PVC tubing with holes drilled in it. A fiberglass
window screen is used as a diffuser to break up the jets. I get complete
etch-through of .003" shim stock in about 3 minutes. No electrochemistry
involved here, just etchant and agitation.

Your results look like the effect of no agitation and gas bubble buildup
blocking the electrolyte.

Jon

On Tue, 31 Jul 2012 14:42:25 -0500, Jon Elson
wrote:

wrote:

I was unhappy with the depth of my brass etching.

I etch brass shim stock with ferric chloride to make stencils for
solder paste for PC boards. My spray etcher has a heater in it, and
I get the etchant up to about 35 - 40 C. The spray system is a typical
pump (Little Giant-style with stainless or maybe titanium impeller and
shaft) and the wand is PVC tubing with holes drilled in it. A fiberglass
window screen is used as a diffuser to break up the jets. I get complete
etch-through of .003" shim stock in about 3 minutes. No electrochemistry
involved here, just etchant and agitation.

Your results look like the effect of no agitation and gas bubble buildup
blocking the electrolyte.

I used Ferric Chloride for years but gave it up because I could get
better results with electricity. I used to heat it to about the same
temp and agitate manually.

Anyway, I think I know the answer to my original problem. It has to do
with the way I put the resist on. I am hoping to find the time to do a
couple of confirmatory tests tomorrow.

Michael Koblic,
Campbell River, BC

On Wed, 01 Aug 2012 17:27:02 -0700, wrote:

On Tue, 31 Jul 2012 14:42:25 -0500, Jon Elson
wrote:

wrote:

I was unhappy with the depth of my brass etching.

I etch brass shim stock with ferric chloride to make stencils for
solder paste for PC boards. My spray etcher has a heater in it, and
I get the etchant up to about 35 - 40 C. The spray system is a typical
pump (Little Giant-style with stainless or maybe titanium impeller and
shaft) and the wand is PVC tubing with holes drilled in it. A fiberglass
window screen is used as a diffuser to break up the jets. I get complete
etch-through of .003" shim stock in about 3 minutes. No electrochemistry
involved here, just etchant and agitation.

Your results look like the effect of no agitation and gas bubble buildup
blocking the electrolyte.

I used Ferric Chloride for years but gave it up because I could get
better results with electricity. I used to heat it to about the same
temp and agitate manually.

Anyway, I think I know the answer to my original problem. It has to do
with the way I put the resist on. I am hoping to find the time to do a
couple of confirmatory tests tomorrow.


Well, so much for that theory!

I put on the resist differently this time and run the test again with
mechanical agitation of the electrolyte. The result is he

http://www.flickr.com/photos/2768312...in/photostream

(and the next picture) - i.e. exactly the same!

Even with magnification one could see no bubbles during the process
but there was a lot of black crap that covered the etched areas as the
voltage rose to keep the current constant. With agitation this got
worse briefly and then it disappeared.

The finished area looks better but there is still a depth gradient
from the bottom of the area to the top - 0.009" to 0.008" (the
starting thickness was 0.018"). This of course ignores the hole!
Actually, this depth of etch is consistent with the calculated results

I do not understand why the current is drawn preferentially to this
edge of the area. Why not to all the other boundaries? One can see on
the back picture that it is beginning to work on one of the vertical
boundaries but nothing like the top one.

I also run another test to see if the stencils I use leave any
appreciable glue behind that might hinder etching. I took 0.003" off a
0.005" piece using 3A current for 1/2 hour (the area was appx 1900
mm2). There was no evidence of the glue being a problem. There was
much preferential etching at the edges, some of these worn completely
away, but that I understand and have seen before.

I have generated more questions than I answered. All I know is that
agitation is good and that no gas is produced on anode below the
current density of 0.15A/cm2.

Michael Koblic,
Campbell River, BC

wrote:

I have generated more questions than I answered. All I know is that
agitation is good and that no gas is produced on anode below the
current density of 0.15A/cm2.

I don't know much about etching, but I have
done a lot of black and white film processing.
In that case, consistent, repeatable agitation
is critical because the solution in immediate
contact with the work decomposes rapidly and
agitation provides a method for getting fresh
solution against the metal. There's also a
relationship between the degree of agitation
and the amount of undercutting you get at the
resist edge.