Preparation and connectivity of sintering paste containing copper particles covered by nano-silver

A kind of sintering paste mixed of nano-silver and copper particles covered by nano-silver was made, by which oxygen-free copper pad with 99.99% purity were connected at low temperature. Firstly, nano-silver particles whose average diameter were 20-35 nm were synthesized by liquid chemical reduction method. Meanwhile the copper particles covered by nano-silver were prepared by the method of chemical plating. Afterwards, these two kinds of particles were mixed by mechanical method to prepare sintering paste, by which oxygen free copper plate with 99.99% purity were joined under the condition of 10 MPa, 200℃ for 30 min. Finally, the microstructure of sintering section was observed by the scanning electron microscope(SEM). The results showed that the connection interface was sintered compactly, and certain porosities existed throughout the joint organization. The everge shear strength of the joints was about 20 MPa.