I do not have any experience of bonding pads over Su8 but I have done a
lot of bonding to pads on polymer films.

Area: most bond pads are 100 microns square. Wires are typically 25
microns in diameter and you are going to squash the wire about 2 to 3
times the diameter of the wire. It depends on the type of bonding you
are doing Ball Bonding or wedge Bonding. You can get thinner wire, say
20 microns and use a smaller pad of 50 or 75 microns if you are space
limited. Of course as the area of your pad gets less you will have a
lower strength to the substrate.=20

With good clean gold surfaces you can lower the energy significantly to
minimize cracking of the underlying film. Similarly you can raise the
temperature to lower the amount of Ultrasonic Energy required. I am
assuming you will have a chrome or ti stick layer on the device.=20

What can happen is you make a good bond to the pad but pull the pad off
the device. You need good adhesion of the polymer layer. Minimize damage
at the bonding process but there is going to be a minimum amount of
energy you will have to use and some of it is going to get absorbed by
the polymer layer.=20


Regards,
=20
Steve Adamson
Market Manager, Asymtek
IMAPS President Elect 2007
=20
760-930-7274 Office
760-802-1641 Cell
ADAMSON14645 Skype

-----Original Message-----
From: Yue Mun Pun, Jeffrey
Sent: Friday, May 11, 2007 6:30 AM
To: mems-talk@memsnet.org
Subject: [mems-talk] Bonding gold wires to gold electrode

Hi,
I need to bond gold wires to gold electrode.  Typically, how thick
should the gold electrode be and what should the surface area of the
electrode be for a good bond? =20
Also, will there be any impact if the gold electrode is sitting on a
film of SU-8, for if ultrasound is used in the bonding process, I'm
afraid that the underlying SU-8 might crack due to the high energy of
the ultrasound.