I have the following problem:

I have have an AlGaAs/GaAs chip (a.k.a. HEMT) with Au/Ge/Ni ohmics
and Au gates. The ohmics are covered by a thin layer of what seems
to be gold.
I am supposed to bond gold wires to the ohmics and the gates using
a wedge bonder.
The first time I tried, everything was fine.
The second time, with the same kind of chip and the same processing,
the gold wires do not stick to the ohmics, no matter how often I try.

Has anyone an idea of what is going on?


Olivio Chiatti
Royal Holloway University of London
o.chiatti@rhul.ac.uk