Growth behaviour of gold-aluminum intermetallic phases (IMP) in temperature aged ball bonds observed by electron backscatter diffraction

Gold wire bonding on aluminum pads plays still an important role in microelectronic packaging. The lifetime of these bonds is mostly determined by the intermetallic phases (IMP) at the gold/aluminum interface. To investigate the phase growth after the wire bonding process, bond samples were produced. Several samples have been exposed to elevated temperatures to initiate further phase growth. To obtain different reaction stages of the intermetallic compound formation, the samples have been annealed for different defined times in a furnace. As an alternative to common methods like transmission electron microscopy (TEM), the electron backscatter diffraction (EBSD) technique has been applied for phase identification in the Au/Al system. After optimization of the cross-section preparation as well as the internal parameters of the EBSD software, EBSD phase and orientation mappings of bond interfaces have been conducted. It has been shown that the different IMPs are reliably distinguishable by their crystallographic structure. In addition, the transformation of the phase regions within the interconnect at different reaction stages could be determined.