Evolution mechanism of interfacial multi-layer intermetallic compounds and failure behavior in the Al–Au wire bonding

Evolution mechanism of interfacial multi-layer intermetallic compounds (IMCs) and their impact on failure behavior in Al–Au wire bonding after thermal storage and thermal cycle process are investigated. Microstructural analysis shows that multi-layer IMCs form between the Al wire and barrier layer. After thermal storage and thermal cycle process, the Au₈Al₃ layer transforms into AuAl₂, and Au pad transforms to a thicker layer containing Au₂Al and AuAl. Thermodynamic analysis indicates that Au₈Al₃, Au₂Al, AuAl, and AuAl₂ have increasing stability. Small-size, equiaxed AuAl₂ grains form due to high stored energy, while large-size, columnar Au₂Al and AuAl grains result from slower reaction rate and limited recrystallization. The stack-like formation of AuAl₂ grains is attributed to the balance between driving force and interfacial energy resistance. During thermal storage, thicker IMC layers cause cracking between IMC layers and Au pad, and micro voids form near the IMC layers/barrier layer interface due to Kirkendall effect. Thermal stress results show that plastic deformation of the Al layer slightly affects the thermal stress in other layers during the thermal cycle process. The cyclic stress at the interface with initial cracks ranges from −157 MPa to 114 MPa, facilitating crack propagation. Additionally, micro void grows under cyclic thermal input, weakening interface adhesion. Therefore, bond strength decreases and frequency of bonding lift-off with cracking along the IMC layers/barrier layer interface increases after thermal storage and thermal cycle process. These results provide the guidance for regulating the interfacial IMCs and predicting the thermal stress in Al–Au wire bonding.