Chiatti,
        The second try may have had either a light oxide, yes gold can oxidize
lightly or some organic contaminant.  In any case the easy answer is to plasma
clean in an inert gas atmosphere typically Argon.  Think of the Argon plasma as
the worlds lightest sand blaster.  It is using an active hot argon ion as the
cleaner.  This will bombard the surface remove trace levels off the surface say
100 angstroms and give more surface area for the bond to work on.  let me know
if you have access to a plasma cleaner I can probably walk you through process
parameters that will work.  Bill Moffat

-----Original Message-----
From: Chiatti O [mailto:O.Chiatti@rhul.ac.uk]
Sent: Monday, October 21, 2002 7:25 AM
To: 'mems-talk@memsnet.org '
Subject: [mems-talk] Gold bonding problem


I have the following problem:

I have have an AlGaAs/GaAs chip (a.k.a. HEMT) with Au/Ge/Ni ohmics
and Au gates. The ohmics are covered by a thin layer of what seems
to be gold.
I am supposed to bond gold wires to the ohmics and the gates using
a wedge bonder.
The first time I tried, everything was fine.
The second time, with the same kind of chip and the same processing,
the gold wires do not stick to the ohmics, no matter how often I try.

Has anyone an idea of what is going on?


Olivio Chiatti
Royal Holloway University of London
o.chiatti@rhul.ac.uk

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