Sodium Persulphate does not etch unless it is heated. I have used the sponge with Ferric Chloride but most of the times I etch indoors without a hood it was too dangerous. If you try the sponge thing you have to use a hood.
I have not tried the sponge with Sodium Persulphate. I have not had and undercutting problems that I noticed.
--- On Fri, 6/26/09, jc805sb <jc805sb@...> wrote:
From: jc805sb <jc805sb@...>
Subject: [Homebrew_PCBs] Heating etchant: Re: “Dragon’s Blood” resin reduces undercut?
To: Homebrew_PCBs@yahoogroups.com
Date: Friday, June 26, 2009, 5:22 AM
--- In Homebrew_PCBs@ yahoogroups. com, Daniel Johnson <a3v03v0@... > wrote:
>
> I switched from ferric chloride to sodium persulphate (MG Chemicals). It is a much easier to handle are requires somewhat less care.Â
>
> I often etch single PCBs in a glass bread pan sitting on a foam rubber block while read mail. A slight rocking of the pan is enough to keep the etchant moving.  I heat the etchant to about 130 degrees prior to starting. Depending on how worn out the etchant is I may have to reheat.
>
> One of these day I should make a real etching tank.
>
> The heavier the copper is the more you will have undercutting. This post on Electrotech has some images of a PCB I was working on a while back. Compare the edges to what you are getting.
>
> http://www.electro- tech-online. com/chit- chat/86683- cricut-2. html#post674243
>
How are you heating the etchant?
Have you tried "sponging" the surface or not bothered with
trying it?
Also, do you keep your boards etching copper up, or copper down.
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