PCB etchants

[Nigel Eddis]

I keep reading on various websites that 'Persulphate' is a better etchant
than Ferric Chloride from Radio Shack, but I don't know how strong to mix
it and cannot seem to find any actual formulae.

I have, as it happens, plenty of both Ammonium and Potassium Persulphate,
and have tried mixing what I thought was a strongish solution of each,
but it seems very slow compared to Ferric Chloride. I did heat it, and
agitated the dish constantly, and the Potassium salt did go a bit blue,
but slow...slow...slow! I also tried adding a small amount of Mercuric
Chloride, which I understand is supposed to be the approved catalyst, but
nothing much happened except that the copper became plated with mercury.

Can anybody offer any advice about this? (And which is better, the
Ammonium or Potassium salt?)

Thanks
Nigel Eddis
NYC

 

[Dominic-Luc Webb]

On Sun, 23 Jan 2005, it was written:

I keep reading on various websites that 'Persulphate' is a better etchant
than Ferric Chloride from Radio Shack, but I don't know how strong to mix
it and cannot seem to find any actual formulae.

I have, as it happens, plenty of both Ammonium and Potassium Persulphate,
and have tried mixing what I thought was a strongish solution of each,
but it seems very slow compared to Ferric Chloride. I did heat it, and
agitated the dish constantly, and the Potassium salt did go a bit blue,
but slow...slow...slow!

Yes, if you are still in here to read this, the ammonium persulphate can
be a bit slow, but it is much more gentle on the circuit pattern,
including lines drawn by "permanent" markers. Outgassing is also less
problematic. Reaction is concentration dependent. For a small double
sided board around 4x3 cm, I use around a heaping teaspoon and heat to
about 70 C. I just wait it out, as I am not usually in a big hurry and
am more concerned about a quality etch, and also environmental/health
issues in using some of the alternatives.

Dominic

 

[Bob Masta]

On Wed, 2 Feb 2005 18:40:39 +0100, Dominic-Luc Webb <dlwebb@canit.se>
wrote:

On Sun, 23 Jan 2005, it was written:

I keep reading on various websites that 'Persulphate' is a better etchant
than Ferric Chloride from Radio Shack, but I don't know how strong to mix
it and cannot seem to find any actual formulae.

I have, as it happens, plenty of both Ammonium and Potassium Persulphate,
and have tried mixing what I thought was a strongish solution of each,
but it seems very slow compared to Ferric Chloride. I did heat it, and
agitated the dish constantly, and the Potassium salt did go a bit blue,
but slow...slow...slow!


Yes, if you are still in here to read this, the ammonium persulphate can
be a bit slow, but it is much more gentle on the circuit pattern,
including lines drawn by "permanent" markers. Outgassing is also less
problematic. Reaction is concentration dependent. For a small double
sided board around 4x3 cm, I use around a heaping teaspoon and heat to
about 70 C. I just wait it out, as I am not usually in a big hurry and
am more concerned about a quality etch, and also environmental/health
issues in using some of the alternatives.

Dominic

Hmmm. At the lab where I used to work we tried
ammonium persulfate exactly one time... it completely
dissolved the "permanent" felt-tip lines, whereas with
ferric chloride we rarely had problems. We just used
the ammonium persulfate right out of the bottle (from
Radio Shack, I think... many years ago), so maybe it
needed dilution first?

Amazingly, we did find that most pre-mixed ferric chloride is too
*concentrated* to etch properly, so slow that it appears
to be exhausted on its first use. Dilution down to
1.30 specific gravity fixes it right up.

Best regards.


Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com

 

[Skaface]

Bob Masta wrote:

On Wed, 2 Feb 2005 18:40:39 +0100, Dominic-Luc Webb <dlwebb@canit.se
wrote:


On Sun, 23 Jan 2005, it was written:


I keep reading on various websites that 'Persulphate' is a better etchant
than Ferric Chloride from Radio Shack, but I don't know how strong to mix
it and cannot seem to find any actual formulae.

I have, as it happens, plenty of both Ammonium and Potassium Persulphate,
and have tried mixing what I thought was a strongish solution of each,
but it seems very slow compared to Ferric Chloride. I did heat it, and
agitated the dish constantly, and the Potassium salt did go a bit blue,
but slow...slow...slow!


Yes, if you are still in here to read this, the ammonium persulphate can
be a bit slow, but it is much more gentle on the circuit pattern,
including lines drawn by "permanent" markers. Outgassing is also less
problematic. Reaction is concentration dependent. For a small double
sided board around 4x3 cm, I use around a heaping teaspoon and heat to
about 70 C. I just wait it out, as I am not usually in a big hurry and
am more concerned about a quality etch, and also environmental/health
issues in using some of the alternatives.

Dominic



Hmmm. At the lab where I used to work we tried
ammonium persulfate exactly one time... it completely
dissolved the "permanent" felt-tip lines, whereas with
ferric chloride we rarely had problems. We just used
the ammonium persulfate right out of the bottle (from
Radio Shack, I think... many years ago), so maybe it
needed dilution first?

Amazingly, we did find that most pre-mixed ferric chloride is too
*concentrated* to etch properly, so slow that it appears
to be exhausted on its first use. Dilution down to
1.30 specific gravity fixes it right up.

Best regards.


Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com

I use ammonium persulphate here for my home projects, I use those iron
on laser printer masks. It will even etch out surface mount IC pads
perfectly. Usually takes about 3-5 minutes to fully etch the board,
however i usually make the mix a bit weaker as to save money.
The directions on this stuff that i have are to mix 400 grams of
ammonium persulphate in one to one-and-a-half litres of water heated to
about 60 to 70 degrees C