Abstract :
The purpose of this study is to understand
the morphological changes that occur during annealing
of Al–Au wire-bonds, by analyzing the interface region
of annealed model wire-bonded samples between 5N
(99.999%) Au wires and Al pads. Due to the small
length scale of the intermetallic region at the interface
of the bond, the analysis was done using scanning/
transmission electron microscopy combined with
energy dispersive spectroscopy. Samples were prepared
using a dual-beam focused ion beam system.
Microstructural characterization showed that during
annealing, a Au-rich intermetallic region was formed
under the bond and at the periphery of the bond. Two
types of failures occurred during annealing: crack formation
at the bond periphery due to an increase in
volume during intermetallic growth and the formation
of stresses; and oxidation of the AlAu4 phase adjacent
to the Au ball, which resulted in the formation of
continuous cracks between the Au ball and the intermetallic
region. The characteristic void-line found inside
the intermetallic region played no part in failure
that occurred during exposure to elevated temperatures.
