Non-Dewetting Cu@Ag Bimodal Nanoparticle Paste and Low-Temperature Pressureless Sintering for Electronic Packaging

The surging power density and thermal demands of advanced electronic devices necessitate conductive pastes that can undergo pressureless sintering at low temperatures while maintaining reliable performance under high-temperature operating conditions─requirements that conventional Sn-based solders can no longer meet. Cu@Ag core–shell nanoparticles offer a compelling alternative by integrating the cost-effectiveness and low electrochemical migration of Cu with the oxidation resistance of Ag. However, thermal dewetting of the Ag shell during heating significantly compromises the joint integrity and reliability. Here, we report a surface modification strategy that effectively suppresses the surface energy of Cu@Ag nanoparticles, enabling exceptional structural stability up to 250 °C without Ag shell dewetting. By incorporating surface-modified Ag nanoparticles, we formulate a bimodal conductive paste that achieves pressureless sintering at low temperatures and delivers a maximum shear strength of 20.18 MPa, which is on par with or even better than the shear strength of Cu@Ag nanoparticles sintered under a protective gas atmosphere in similar recent work. After 96 h of thermal aging, the shear strength further increased to 30.13 MPa. We performed fracture surface analysis on joints with different shear strengths and proposed a mechanism for the shear resistance of Cu@Ag paste joints at varying sintering levels. This work offers a practical and scalable approach for developing high-performance, low-cost conductive pastes and paves the way for the broader adoption of Cu@Ag-based pastes and adhesives in advanced electronic packaging.