Al-clad Cu bond wires for power electronics packaging: Microstructure evolution, mechanical performance, and molecular dynamics simulation of diffusion behaviors

With the advancement of power electronics, aluminum-clad copper thick bonding wires have garnered attentions due to superior electrical and thermal properties, making them well-suited for high-temperature and highcurrent applications. However, the impact remains unveiled of whether the growth of intermetallic compounds (IMCs) at the bonding interface presents critical challenges to the reliability of wedge wire bonds. Therefore, it is necessary to investigate the evolution behavior of Cu/Al IMCs in Al-clad copper wires. In this study, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) were firstly employed to characterize the phase composition and growth behavior of Cu/Al intermetallic compounds (IMCs) at two distinct interfaces-the bonding interface and the core-shell interface-under various annealing conditions during high-temperature storage (HTS) tests, revealing a parabolic relationship between aging time and IMCs thickness. Subsequently, shear and pull tests of Al-clad copper bond wires were conducted to evaluate the bonding strength under different aging conditions, clarifying the correlation between various failure modes of the bonds and the evolution of IMCs at the bi-interfaces of this novel composite across different aging stages. Additionally, molecular dynamics (MD) simulations were employed to explore the diffusion behavior of Cu and Al atoms. It revealed that polycrystalline structures enhanced the mutual diffusion at the interface, with copper serving as the predominant element in the interdiffusion process. In conclusion, this study integrates experimental and numerical approaches to elucidate the growth mechanisms of Cu/Al intermetallic compounds and their effects on reliability, providing valuable guidance for optimizing the performance of composite bonding wires in high-temperature power device applications.