Papers by Keyword: Diffusion Induced Stress

Abstract: The thermosonic bonding technique is a widely used method for Cu wire interconnections. However, issues arise due to volumetric changes in intermetallic compounds (IMCs) formed at the Cu-Al bonding interface, leading to voids in the Cu-Al IMC layer. This problem is exacerbated after annealing, such as in high-temperature Storage (HTS). In this study, a statistical modelling approach was employed to quantitatively analyse stress, studying the evolution and characteristics of the interfacial microstructure in the thermosonic Cu wire-Al bond pad system. Microstructural analysis focused on Cu-Al IMC crystallography and compositional classification. A stress model was proposed, considering both thermal misfit and diffusion-induced stresses. Results showed that interfacial stress generally increased with higher bonding temperatures. The influence of forming gas supply was relatively minor, with oxide layers minimally impeding Cu-Al interdiffusion during Cu-Al IMC formation. This stress modelling technique hold potential as a valuable failure analysis tool for implementing Cu wire in various industries.

Abstract: Traditional theories of interdiffusion in solids based on Fick’s first and second laws and Darken’s equations can not describe the relationship between the diffusion fluxes and the diffusion-induced stresses, because the subject matter of the traditional theories is the diffusing atom or atomic flux, not the volume unit within the interdiffusion field. For this reason, it is suggested that the concept of flow point in the interdiffusion field should be constructed to describe the diffusion-induced stresses and the phase growth.