Low-temperature Cu-to-Cu electrode bonding by sintering Cu core-Ag shell nanoparticle paste

Metal-to-metal bonding is critical in modern electronics technology such as 3D-IC packaging and automotive electronics. In this study, we applied Cu core-Ag shell nanoparticle paste (CANP) for bonding Cu electrodes and developed the CANP sintering conditions. The electrical conductivity of the CANP films sintered at 400 °C without pressure was 3.3–4.0 × 10⁴ S/cm. Compact Cu-CANP-Cu joints could be fabricated by sintering the CANP at 350–400 °C under the bonding pressure of 1.0 or 1.7 MPa. Thermal conductivity and shear strength of the CANP joints increased with sintering temperature and bonding pressure, which is attributed to the enhanced interconnection of nanoparticles as shown by the scanning electron microscopy of the cross-section and the fractured surface of the CANP joints. The Cu-CANP-Cu joints had thermal conductivity up to 31.2 W/mK and shear strength up to 10.9 MPa when the CANP was sintered at 400 °C under 1.7 MPa. This work provides a pathway for a cost-effective and reliable sintering-bonding method for electronics packaging applications.