Multiscale characterization of the joint bonded by Cu@Ag core@shell nanoparticles

Abstract

The bimetallic Cu@Ag nanoparticle (NP)-based Cu–Cu bonding method is reported to be plausible in electronic packaging, whereas the microstructure and elemental distribution of the joint, which determine the bonding quality, were not well investigated yet. In this work, comprehensive characterization techniques are used to demonstrate the microstructure and elemental information of the joint. Microstructure analysis exhibits a eutectic structure with a low porosity of 2.5%, which is achieved by NP sintering. Twin structures in both the Cu-rich and Ag-rich phases are confirmed, where (111) is the twin mirror plane. Particularly, atom probe tomography analysis accurately demonstrates that the concentration of Cu in the Ag-rich phase is 1.51% and vice versa, 0.45%; this indicates sufficient atom exchange for achieving high-quality bonding. This investigation improves the understanding of the elemental behavior during the core@shell NP bonding process and provides important information for pushing this bonding method toward practical application.