I would agree that the most likely situation is cracked oxide or a punch through
caused by excessive bond force and /or time.

Can you look at the bonds with a 100x scope and see any cracking ?
Are the Wedges excessively  deformed ?
How have you done your set up of the bonder ?
Any Trial pieces before using your prime material ?

Ken


-----Original Message-----
>From: Shay Kaplan 
>Sent: Mar 22, 2010 12:13 PM
>To: 'General MEMS discussion' 
>Subject: Re: [mems-talk] wire bonder ruined my device
>
>If the bond force is too high you might have cracked the oxide below the pads.
>
>Shay