No surprises there, you're using H202 up to 10x stronger than most people.
Another guy using 30%:
http://milwaukeemakerspace.org/2012/04/pcb-with-lasered-paint-resist-and-fast-sponge-etching/ --- In Homebrew_PCBs@yahoogroups.com, Slavko Kocjancic <eslavko@...> wrote:
>
> I use 1:1:1 and with near Nill agitation and without heating I the pcb
> is etched in les than 2 minutes.
> I use HCL 29%, H2O2 31%, and 100% H2O
>
> Dne 10.7.2012 17:53, pie Peter:
> > Never tried acid etching myself. This might be worth noting:
> > If your PCB is lying flat in the bottom of the etch container, the disloved copper will leave a film on your PCB. This effectively acts as a barrier between the PCB and etchant. The answer is to agitate the PCB or as mentioned, use something like a paint brush. Also mentioned is highter temperatures which usually speeds up chemical reactions - sometimes to a mad gallop. :-)
> >
> > Peter
> > Shetland Islands.
> >
> > [Non-text portions of this message have been removed]
> >
>