Etching: sodium persulfate vs ammonium persulfate??

Terry King

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Oct 29, 2002, 9:40:08 PM10/29/02

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Somewhere in the 10 years since I last etched a board,
Kepro has switched to Sodium Persulphate, with some
catalyst.

Does anyone know what the tradeoffs are between
sodium persulfate vs ammonium persulfate?

I see ammonium persulphate (which I used to favor)
sold as an etchant by some suppliers. Isthere
some reason for the switch??

--
Regards, Terry King ...In The Woods In Vermont
tk...@waitsriver.k12.vt.us

Bob Wilson

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Oct 29, 2002, 11:06:57 PM10/29/02

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In article <MPG.1829108f5...@news.k12.vt.us>,
tk...@waitsriver.k12.vt.us says...

>
>Somewhere in the 10 years since I last etched a board,
>Kepro has switched to Sodium Persulphate, with some
>catalyst.
>
>Does anyone know what the tradeoffs are between
>sodium persulfate vs ammonium persulfate?
>
>I see ammonium persulphate (which I used to favor)
>sold as an etchant by some suppliers. Isthere
>some reason for the switch??

They are both similar; and both relatively mediocre etchants. Sodium
persulphate is often suggested because no ammonium ions end up in the
wastewater. It is only a sewage treatment issue.

With either, don't forget the small amount of Mercuric Chloride that acts as
a catalyst to get the fresh solution started.

Bob.

Andrew Tweddle

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Nov 17, 2002, 12:18:54 AM11/17/02

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Smell.
The Ammonium ion in aq soln carrys away the copper very effectively.
Sulphate ion is not as effective as chloride ion at etching copper at
the same temperature. As a trade off for kitchen sink use. ie. using an
elevated temperature to move the reaction rate along and relatively
safe, and non smelly compared to ammonium copper chloride which works
brilliantly but requires fume hoods, it isn't a bad one.

Wafer

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Nov 23, 2002, 5:38:42 PM11/23/02

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From my research, sodium persulfate seems a better choice if you want
shelf life. It seems that ammonium persulfate recrystalizes when it
cools down, and becomes useless. However, sodium persulfate can be used
at room temp or heated, and can even be reused again until it's used up.

Uwe Zimmermann

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Nov 23, 2002, 6:30:32 PM11/23/02

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Wafer wrote:
>
> Andrew Tweddle wrote:
> > Terry King wrote:
> >
> >>Somewhere in the 10 years since I last etched a board,
> >>Kepro has switched to Sodium Persulphate, with some
> >>catalyst.
> >>
> >>Does anyone know what the tradeoffs are between
> >>sodium persulfate vs ammonium persulfate?

> > Smell.

> > The Ammonium ion in aq soln carrys away the copper very effectively.
> > Sulphate ion is not as effective as chloride ion at etching copper at
> > the same temperature. As a trade off for kitchen sink use. ie. using an
> > elevated temperature to move the reaction rate along and relatively
> > safe, and non smelly compared to ammonium copper chloride which works
> > brilliantly but requires fume hoods, it isn't a bad one.
>
> From my research, sodium persulfate seems a better choice if you want
> shelf life. It seems that ammonium persulfate recrystalizes when it
> cools down, and becomes useless. However, sodium persulfate can be used
> at room temp or heated, and can even be reused again until it's used up.

sodium persuphate is also less aggressive to cloths, skin and alike...

http://physchem.ox.ac.uk/MSDS/AM/ammonium_persulfate.html
http://www.mgchemicals.com/msds/410.html

http://physchem.ox.ac.uk/MSDS/SO/sodium_persulfate.html
http://www.mgchemicals.com/msds/4101.html

Uwe

Terry King

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Nov 24, 2002, 10:16:12 PM11/24/02

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Thanks for this and other info discussed. What I needed to know!

> sodium persuphate is also less aggressive to cloths, skin and alike...
>
> http://physchem.ox.ac.uk/MSDS/AM/ammonium_persulfate.html
> http://www.mgchemicals.com/msds/410.html
>
> http://physchem.ox.ac.uk/MSDS/SO/sodium_persulfate.html
> http://www.mgchemicals.com/msds/4101.html

--

Bob Wilson

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Nov 24, 2002, 11:57:43 PM11/24/02

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In article <3DE00F98...@imit.kth.se>, u...@imit.kth.se says...

Aggressiveness to clothes isn't so much the problem, as making a bloody mess
out of them! Ferric chloride tends to produce insoluable brown hydroxides on
exposure to air. At one point, it seemed that half the clothes I owned had
brown stains on them! Ammonium persulphate does not. All its reaction
products are soluable and stable.

Be aware that one should use a very small amount of mercuric chloride as a
sort-of catalyst when using ammonium persuplhate. Full details are givem in
Clyde Coombs' very well known book "Printed Circuits Handbook", among other
places. Failure to do this results in slow etching times.

Generally ammonuim persuplhate has about half the copper capacity of ferric
chloride, has a greater tendency to undercut, and is rather unstable (it can
decompose very rapidly in the presence of some impurities. Still, it can be
useful if one can accept these rather serious disadvantages.

Bob.

John Woodgate

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Nov 25, 2002, 2:04:05 AM11/25/02

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I read in sci.electronics.design that Bob Wilson <rfwi...@intergate.nos
pam.bc.ca> wrote (in <uu3be7h...@corp.supernews.com>) about
'Etching: sodium persulfate vs ammonium persulfate??', on Mon, 25 Nov
2002:

>At one point, it seemed that half the clothes I owned had
>brown stains on them!

A course of anxiolytics might help. (;-)
--
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
Interested in professional sound reinforcement and distribution? Then go to
http://www.isce.org.uk
PLEASE do NOT copy news posts to me by E-MAIL!

Bob Wilson

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Nov 25, 2002, 10:54:29 PM11/25/02

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In article <ieU9xmAl...@jmwa.demon.co.uk>,
j...@jmwa.demon.contraspam.yuk says...

Bob Wilson

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Nov 25, 2002, 10:55:36 PM11/25/02

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In article <ieU9xmAl...@jmwa.demon.co.uk>,
j...@jmwa.demon.contraspam.yuk says...
>

>I read in sci.electronics.design that Bob Wilson <rfwi...@intergate.nos
>pam.bc.ca> wrote (in <uu3be7h...@corp.supernews.com>) about
>'Etching: sodium persulfate vs ammonium persulfate??', on Mon, 25 Nov
>2002:
>>At one point, it seemed that half the clothes I owned had
>>brown stains on them!
>
>A course of anxiolytics might help. (;-)

Ooops just sent a reply without any reply! Anyway, what I meant to say
was.... Not THOSE kind of brown stains!

Bob.

Parmin

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Nov 26, 2002, 1:46:24 AM11/26/02

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rfwi...@intergate.nospam.bc.ca (Bob Wilson) sat on the toilet, drank
beer and burped out news:uu5s5ok...@corp.supernews.com:

Which kind?

Par.