Al wire bonding is been done very successfully on ENIG.
ENIG is electroless Nickle (7 - 10% Phosphorous) and immesion Gold. The gold
thickness in this type of finish is 2 - 4 microinches (very thin).
The bonding occurs between the Al wire and the underlying Nickel.
ENIG is not an ideal surface for Au wire bonding, as the gold thickness is
inadequate to ensure 100% successful bonds.

George Milad
HDI Consulting
Chairman IPC Plating Committee
(703) 860-6162 Office
(516) 901-3874 Cell