Ditto what Shay said.

In the first etch-rates paper I listed a variety of reasons for etch-rate
*variation*. One is a galvanic effect when two metal are on contact with
each other and also with the etchant. The less electronegative metal
(aluminum in this case) gives up electrons more easily and will probably
etch much faster when in contact with copper than aluminum sitting on an
insulator.

   --Kirt Williams

-----Original Message-----
From: mems-talk-bounces+kirt_williams=sbcglobal.net@memsnet.org
[mailto:mems-talk-bounces+kirt_williams=sbcglobal.net@memsnet.org] On Behalf
Of Shay
Sent: Wednesday, June 15, 2011 6:47 AM
To: 'General MEMS discussion'
Subject: Re: [mems-talk] aluminum etchant vs. copper vs. aluminum

Hi,

You should be careful with etch rates of structures. Two materials that are
in contact behave very different in etching environment because of the
different electro chemical potential.

I suggest that you run a test on a real small area. Also, try using copper
etchant. The FeCl stuff. It might work better.

Shay