Did you try Potassium cyanide (I know it etches Au, Ag, and Cu)? Although I wasn't aware that the KI:I:H2O (did you try it in a 2:1:10 ratio?) etchant would have an affect on Al. The only other gold etchant I'm aware of is Aqua Regia and that will definitely etch your Al also... There is a table of etchants located at http://grover.mirc.gatech.edu/processing/etchants.pdf Good Luck Regards, Dave Lewis Sensor R&D Lake Shore Cryotronics Dave.Lewis@Lakeshore.com -----Original Message----- From: mems-talk-bounces@memsnet.org [mailto:mems-talk-bounces@memsnet.org] On Behalf Of Lisa Gades Sent: Monday, February 15, 2010 3:59 PM To: mems-talk@memsnet.org Subject: [mems-talk] Wet-chemical etching of Au without etching Al Hello, We have a process in which 20nm Au were deposited as a sacrificial layer on Al. We need to remove the Au in a later step. We have found that iodine-based Au etchant undercuts the Al. We are looking for a process that will selectively etch the Au without etching the Al. Thank you, Lisa Gades