AZ351 contains NaOH - a strong aluminum etchant. For my particular
application for other reasons, I use a thin Pd overcoating on top of the
aluminum and this retards the etch rate significantly. I have not,
however, done a matrix experiment with various developer/de-ion H20
solutions.

-----Original Message-----
From: Robert Black
Subject: RE: [mems-talk] 319 developer while protecting Al

The TMAH in the developer is what attacks the metal. Almost all developers
including the ones from AZ developers contain TMAH. TMAH is the active
ingredient; and most developers contain 3-4% TMAH.  I seem to remember pure
Al etches about 10 times faster than Al-Cu. That is one reason why pure Al
is not usually used for metal layers in semiconductors.