Simao Cardoso wrote:
>
> Nitric acid is an Oxidizing. The gas produced in the copper reaction is
> nitric oxide which is toxic. People shouldn't use it as copper etch has
> already discussed here long time ago by Adam Seychell, its hazard toxic
> and air pollutant.
> But in my quest for metallic resist compatible etchants i found one
> using nitric acid which i experimented. It's basically the same stuff as
> peroxide-sulfuric etchant, but using nitric acid as the oxidizer. Since
> i can't find here hydrogen peroxide in more than 9% solution, but i get
> nitric acid in 60% at less 1.70eur/liter, it seem a cheap etch with easy
> copper electrowinnig has i wanted. In peroxide-sulfuric the solution
> amount is always increasing, so you always need some disposal. But with
> nitric acid it consumes water, and the mixture of nitric sulfuric can
> regenerate one HNO3 molecule in each 3 spent while makes CuSO4, besides
> the air pollutant nitric oxide seems a nice etchant. I made various
> tests but, the nitric acid attacks the toner almost completely... I also
> etch a copper piece an got an enormous amount of CuS04 freezing it. The
> solution turn almost clear, so almost all copper is easily deposited.
> Only now i found a source of pure tin (in Australia) and i still have to
> try the phosphorous mixture with plated tin as resist.
>
A nice effort on finding a suitable etchant for metallic etch resist. I
tried persulfate but that attacked tin enough to make it unreliable.
From your description the nitric-sulfuric mix sounds like the best
hobby etchant compatible with pure tin metallic resist. The alkaline
ammonia chloride type works great on tin resists, not even affecting the
mirror shine tin surface. The downside is the need for regular ammonia
replenished due to NH3 loss. This etchant is regenerated with ammonium
chloride salt, concentrated aqua ammonia, water, and air. Alkaline
ammonia chloride etches relatively fast, up there with fresh FeCl3.
Have you tried etching a mix of concentrated HCl and HNO3, also known as
Aqua Regia ? That should give you a run for your money.