Research on Cu-Sn Interfacial Diffusion Behaviors of Ultrasonic-assisted Bonding by Molecular Dynamics Simulation

Ultrasonic-assisted bonding, as a prevalent three-dimensional integration method in integrated circuit packaging, achieves accelerated bonding time, reduced bonding temperature, enhanced bonding quality, and improved reliability through ultrasound-enhanced metal interface diffusion. However, the intense and rapid ultrasonic effects pose challenges for real-time process monitoring and direct observation of metal interface evolution, leading to incomplete understanding of ultrasonic mechanisms and compromised process stability. This study focus on the changes of copper-tin micro bumps during the bonding process and explores the atomic diffusion situation under ultrasonic effect. A molecular model of copper-tin micro bumps is established to investigate copper-tin interfacial evolution and intermetallic compound (IMC) layer growth under varied ultrasonic frequencies, amplitudes, and thermal gradients. Simulation results reveal that ultrasonic vibration significantly enhances copper-tin atomic interdiffusion, producing thicker IMC layers compared to non-ultrasonic processes. Through MD simulation analysis, optimal bonding parameters were identified as 500K bonding temperature, 32ps cycle, and 8Å amplitude, yielding IMC layers with best quality and diffusion degree. After reaching the melting point of tin, the temperature has no significant effect on the diffusion of copper tin atoms. It can be seen from the conclusion of the study that ultrasonic-assisted bonding has a positive effect in the field of flip chip bonding and provides a solution for solving the problems of three-dimensional integrated packaging.