Rene–I got the on using Ferric Nitrate with a rectifier
from orchid in Aug. 1998. It may be in the archives, but I’ll print
it here. Thank goodness I printed it out as my computer crashed
shortly after. It came from Anne Hollerbach (I’ll quote directly):
I use my anodizer to get a faster etch. This was an idea that
Charles Lewton-Brain discussed at a bench tips free-for-all at SNAG
’97. He suggested using electricity to speed up reactions, and this
really does work. I use a titanium cathode in my ferric nitrate bath,
and the piece to be etched is the anode. The amazing thing is how
little voltage it takes to make a huge differenc: I never go higher
than 20V, and usually work at 10V. For some of my applications, I
have been able to get an etch in 45 - 90 seconds that used to take
nearly 4 hours. And the quality is better because the resist isn’t
sitting in the bath all that time getting ratty around the edges.
Note: don’t do this with ferric chloride since the electricity will
break down the chemical and you will get chlorine gas which is toxic
By the way there is a happy medium to heating the ferric nitrate. If
it is warm-not hot-there doesn’t seem to be the fumes you describe and
it etches faster. I got a nice etch in an hour by using warm water to
mix the crystals and placing the pan on one of those microwave hot
plates. Basically, the hot plate is a piece of granite like material
on a plastic tray which you heat in the microwave for one minute.
It’s supposed to keep hot food hot, so I thought I’d try it this way.
Got it at the local dollar store!