J. Onuki et al., MICROSTRUCTURAL ANALYSIS OF THE BONDING INTERFACE BETWEEN THICK AL WIRE AND AL-1 MASS-PERCENT-SI ELECTRODE FILM, Materials transactions, JIM, 37(6), 1996, pp. 1324-1331
Enhancing reliability of thick Al wire bonds in high power transistor
modules is very important. In order to estimate bond reliability, micr
ostructural analyses of the bonding interface between Al wires and Al-
Si electrode films have been investigated. The bonding interface betwe
en Al wire and Al-Si electrode film were composed of three kinds of mi
crostructures, i.e. coincidence boundaries, layers of very fine grain
size, and layers with very high dislocation density. These boundaries
were assumed to be very strong and hence very stable in the reliabilit
y tests. After power cycle tests, the fine grain layers and the layers
with a very high dislocation density disappeared almost completely an
d form a good quality bonding interface. Very thin amorphous layers 10
-200 nm thick were found to be produced partly at the interface. This
may be formed through a process in which amorphous phases in the very
fine grain size layer were pushed out to the interface by grain growth
during the power cycle tests.