Mr. Stewart,

In my experience, it is very difficult to consistently attach gold  bonds
to a gold film 0.07 um (3 microinches) thick.  Nickel tends to diffuse
through a gold layer this thin, oxidizing at the surface.  Aluminum wedge
bonding seems to be more forgiving.

I believe that 0.5 um (20 microinches) pure (soft) gold is near the minimum
thickness that I would use for thermosonic gold bonding.

I think that the 5 um (200 microinches) of nickel is what the U.S. military
specified as a diffusion barrier for reliability purposes.  I am not sure
about the reliability issues, but one can gold wire bond to 2.5 um (100
microinches) or less.

A reference text would be:

Reliability and Yield Problems of Wire Bonding in Microelectronics by
George Harman.

Dave Anderson

***************************************************************************
* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
***************************************************************************
* To unsubscribe from this list at any time, send a message to:           *
* [log in to unmask] with <subject: unsubscribe> and no text.        *
***************************************************************************
* If you are having a problem with the IPC TechNet forum please contact   *
* Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask]      *
***************************************************************************