Brittle-to-ductile transition of Au₂Al and AuAl₂ intermetallic compounds in wire bonding

Au–Al intermetallic compounds (IMCs) were conventionally regarded as damage sources within wire bonding interfaces. Among the Au–Al IMCs system, Au₂Al and AuAl₂ IMCs were commonly observed after long-term service. Here, the intrinsic mechanical properties of Au₂Al and AuAl₂ IMCs were investigated by in-situ bending tests. The results clearly revealed that the transition from brittle to ductile facture behavior was determined by the atomic ratio of Au and Al elements, while Al-rich Au–Al IMC exhibits higher bending strength than that of Au-rich Au–Al IMC. The Al-rich Au–Al IMC such as AuAl₂ indeed showed brittle fracture behavior, in which cracks propagated through the grain boundaries. In contrast, the Au-rich Au–Al IMC such as Au₂Al appeared to be quite ductile and crack resistant, and its plastic deformation was undertaken by slip bands. This work suggested that not all Au–Al IMCs cause brittleness and lead to damages, only Al-rich IMCs should be avoided at wire bonding interfaces.