"The Handbook of Metal Etchants" is a good place to go for metal etches.
Theres is an Iodidee/Ammoniumum Idodide etch that attacks gold and is
realtivaly benign.    It does not leave the gold surface looking good, so
it's only useful if you're etching all the gold away.
I have seen weird effects with this etch when using it on a stack of metal.
In particular, it doesn't notrmally attack nickel, but if the nickel has
gold on top of it, it is very aggressively attacked.

For thin layers, an argon plasma etch or ion gun is the cleanest and easiest
way to go.

David Nemeth
Senior Engineer
Sophia Wireless, Inc.
14225-C Sullyfield Circle
Chantilly, VA 20151

From: Nik Dee
Subject: [mems-talk] Gold etching (Nik Dee)

Hi guys, I have been using HCl (hydrochloric) and NaCl (nitric) acid to etch
the
gold away. I recently realised that if there is copper in the sample the
acid
attacks the copper and has no affect on the gold surface anymore. Does
anybody
know any etching recipe that i can remove the gold without affecting the
copper?