Wire bonding problems can come from many sources.  First, you must the be
certain of the type materials you are bonding.  Au/Ge/Ni ohmic contacts very
hard compared to gold.  Make sure you have at least 200nm of pure gold deposited
over these contacts.
Second, gold bonding wire doped with silicon has a definite shelf life.  It
becomes brittle with time and difficult to bond. How old is your wire?   Do you
keep your wire in a controlled atmosphere when not in use?   Are your surfaces
clean from organic
contamination?   Always plasma clean your devics if possible.  Finally, have
your wire bonder serviced by a qualified service representative.

Bob Cole
The Aerospace Corporation