To show my gratitude to all those who answered my query, here
is a compilation of the answers I received.

My original question was:
>
> Dear MEMS experts,
>
> I would like to get some advice about Au wire bonding, as I am new to
>  the field of packaging.
>
> I wish to bond to Al pads on my chip, sputter-deposited onto PZT films
> (1 micron thick).  I have tried this, but have so far failed: either
> the first ball bonding does not stick to my Al film, or this film
> sticks to the Au wire and lifts off from the PZT film surface.  I have
> tested different power and time settings, but again, all in vain.
>
> I am using 1000A thick Al pads, and I am slightly reluctant to use a
> thicker film, since the whole structure is already rather stressed.
>
> Any comments, suggestions, and information, like the conventional film
> thickness range and materials used for top metallisation, are most
> welcome. I thank you all for your time.
>
> Marvin

HERE ARE THE ANSWERS...


From: Michael Young   Save Address  Block Sender
Reply-To: acsensor@acsensor.com
To: Marvin Zai , mems-cc@ISI.EDU
Subject: Re: Help needed for    -     Au wire bonding
Date: Thu, 18 Feb 1999 22:26:48 -0800


1000A Al is way too thin for good thermosonic bonding.  You may want to
try thermocompression bonding.  Also, you may want to deposit an
adhesion layer prior to Al deposition, such as TiW.

Call me if you need more help.

Michael Young
ACSI
949-4538988
http://www.acsensor.com




From: kyuhos@samsung.co.kr  Save Address  Block Sender
To: marvinzai@hotmail.com
Subject: (´äÀå)Help_needed_for____-_____Au_wire_bonding
Date: Fri, 19 Feb 1999 15:54:25 +0900


Dear Marvin

I'd like recommand that it would be better to increase the Al
thickness(about
8000A).
and the temperature of wire bonder's hot plate will be 120 to 150 degree
C.

hope to good result and your response, thank you a lot.





From: C S Premachandran   Save Address  Block Sender
To: 'Marvin Zai' ,
"'mems-cc@ISI.EDU'"
Subject: RE: Help needed for    -     Au wire bonding
Date: Fri, 19 Feb 1999 15:05:52 +0800


I feel your Al metal adhesion is not so good otherwise it would not have
come out from PZT. If  you can improve the adhesion I think you can work
it
out. Also try to measure the Al thickness variation , it may not be
1micron
across the bond pad.

Prem



The problem is probably not the thickness of the Al layer, but the
energy
absorbing PZT layer.
If you can, use a structured layer of PZT and do your bond pads in a
different
area.


Torsten
torsten.eggers@uni-bremen.de



Marvin,

Your best course of action is to "let the experts do it".  Contact at
least
two wirebonder manufacturers and send them samples to try.  They may
even do
it for free. If the experts can't do it, then you will need to change
your
surface topology.  Run the aluminum off the PZT, and on to a more stable
surface such as your substrate. If this is not possible, perhaps a
designed
experiment should be performed.  I can help with this if you need it.

Good luck and best regards,

Mike Mattes
 MicroMechatronics
MicroMech1@aol.com




You might talk with a wire bonder manufacturer such as Kulicke and Soffa
in
Horsham PA, even if you don't use their bonder at this point.  They have
been
doing wire bonding equipment since the 1960's, so they know quite abit
about
the subject.

John West
Microcosm Technologies
www.memcad.com
johnwest@memcad.com




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