Phase transformation behavior of Al-Au-Cu intermetallic compounds under ultra-fast micro resistance bonding process

Abstract Micro resistance bonding is an essential method to bond micro metal wire and pad for the manufacturing of ever-miniaturized electronic components. However, the bonding quality is unstable due to the limited understanding of the interfacial phases. Nano-scale interfacial details of micro resistance bonding Al wire to an Au/Cu pad were investigated by transmission electron microscope (TEM). Metallurgical bonding joints with sufficient interfacial reaction are formed in the Al-Au-Cu system. Under the effect of Joule heat, the center temperature of the bonding structure quickly rose to 868 °C, and the Al element at the interface melted rapidly and reacted with the Au, Cu element forming (Au, Cu)8Al3, (Au, Cu) Al2 and (Cu, Au)3Al8 phases. Moreover, due to the ultrafast cooling speed (1.7 × 104 °C/s), (Cu, Au)3Al8 phase would pre-transform into unstable (Cu, Au)9Al4 (γ phase) phase with body-centred tetragonal (BCT) structure and then form into symmetrical twin structure.