Driving force for enhancing the cold silver sinter joining using time domain-dependent Ag–Au epitaxy and interfacial stress

We reveal the mechanism of the cold silver sinter joining process using time-dependent characteristics of Ag–Au interactions grown in the highly (111) orientation. In the initial (∼15 min) state at 175 °C, the Ag–Au inter-diffusion layers developed strongly in the (001) direction, and with increasing time (∼60 min), they switched epitaxial growth in the (111) orientation. The die-bonding strength was significantly improved from 14.9 MPa to 37.8 MPa when the sintering time increased from 15 min to 60 min. The gradual Ag–Au epitaxial growth behavior with a higher stacking-fault energy (SFE) at 175 °C was the dominant factor linearly increasing the cold silver sinter joining strength and ultimately maximizing energy absorption leading to fracture. The surface finish of Au, which can contribute to the time-dependent growth of Ag–Au inter-diffusion layers, underwent a dramatic transformation from a Cube texture to a γ-fiber texture over time. This change was attributed to the micro/nanoscale shear deformation, and reduction of the twin boundary fraction. This study unveiled the in-depth fundamental mechanism for strengthening and pressureless cold sinter joining of Ag–Au epitaxial layers by comprehensively considering this texture behavior, changes in X-ray residual stress, and mechanical properties.