Most organics like silver epoxy tend to die around 200deg C so I am
skeptical that using silver epoxy would work for an extended period. =20

I think you have to look closer at your metal surfaces. You are using an
extremely thin gold layer. Are you getting a weld to that layer? When
you run pull test or bond shear on the balls, you should see the
weldment of the bond. If not then I suspect your initial bonds are not
welding.=20

I think Pt is supposed to be a good stick layer for the gold and I do
not believe at 350 deg C you will see an diffusion of the two metals. I
am surprised you are not seeing any pull off of the gold leaving a Pt
surface underneath. You can improve the welding operation by adding
heat. Normally you would use 100 deg c with ultrasonic bonding. Thermo
compression bonding you would use 400 deg C. I would try increasing the
substrate temperature and see if this helps.

Have you done an edax or something to look at the surface metals on the
pad. Also have you made sure that all surfactants are removed after
dicing. A quick plasma surface conditioning can also help.


Regards,
=20
Steve Adamson
Market Manager - Hard Disk Drives=20
Asymtek
760-930-7274 office
760-802-1641 Cell
=20
=20

-----Original Message-----
From: mems-talk-bounces@memsnet.org
[mailto:mems-talk-bounces@memsnet.org] On Behalf Of David Nemeth
Sent: Tuesday, February 28, 2006 6:43 AM
To: sshanfield@draper.com; General MEMS discussion
Subject: RE: [mems-talk] Wire bonding problems

One possible solution would be to use a very small dab of silver
conductive epoxy after bonding.  Epotek makes such an epoxy, although it
is also available from a variety of other sources.


David Nemeth
Senior Engineer
Sophia Wireless, Inc.
14225-C Sullyfield Circle
Chantilly, VA 20151


-----Original Message-----
From: mems-talk-bounces@memsnet.org
[mailto:mems-talk-bounces@memsnet.org]On Behalf Of Stanley R. Shanfield
Sent: Monday, February 27, 2006 2:50 PM
To: mems-talk@memsnet.org; mems-talk-owner@memsnet.org
Subject: [mems-talk] Wire bonding problems


We are trying to manually wire bond to thin (~.2 micron) Pt/Au on glass.
Although we get good bonds on test wafers at the time the metal is
deposited, the bonding is very unreliable after it has gone through more
processing (i.e. at wire pull test, the wire falls off, leaving the pad
intact,& undamaged; or the pull strength is low <>
). The wafer sees anodic bonding conditions at one point in our process
sequence, and the sawing process can leave scratches on the pads (the
scratches do not penetrate the metal).

Going up in bonding energy, time and force is a concern, since the glass
sometimes forms fissures under the bonding area at more extreme bonding
conditions, and a subsequent wire pull creates a pull-out from the
glass. It does not seem to help anyway. These bonds have to survive a
~350C temperature excursion, so a pull-out is a concern.

Has anyone ever dealt with a problem like this? Any advice or
observations?