Depressing of CuCu bonding temperature by composting Cu nanoparticle paste with Ag nanoparticles

In this paper, we proposed a depressing bonding temperature method for Cu Cu bonding with nanoparticle paste. The paste was prepared by composting dominant Cu nanoparticles with Ag nanoparticles of lower sintering temperature , where the average nanoparticle size of Cu and Ag was 61.02 and 69.25 nm, respectively. The reliable bonding was successfully achieved at the temperature of 250 °C, the pressure of 1.12 MPa and the protection of Ar-H 2 gas mixture comparing with pure Cu nanoparticles paste. An optimal resistivity of sintered Cu-Ag composite nanoparticle paste can achieve 1.99 × 10 −7  Ω m with the 2:1 molar ratio of Cu to Ag, and the largest shear strength of the bonded Cu-Cu joint can reach 25.41 MPa. The underlying sintering mechanism of the composited nanoparticles was discussed. It suggests the compositing with Ag nanoparticles is a practical strategy towards lowering the bonding temperature for Cu-based interconnect. The experimental process can be easily implemented, the bonding temperature and the performance can satisfy the packaging requirements of current 3D-IC. The developed Cu-Ag composite nanoparticle paste is also promising for packaging of other thermal and force sensitive chips.