High bonding strength of silver sintered joints on non-precious metal surfaces by pressure sintering under air atmosphere using micro-silver sinter paste

Abstract

Owing to its superb properties such as high melting temperature, high thermal and electrical conductivity, silver sintering is considered as a promising die attach technology in recent years for high power electronics packaging with demanding requirements such as high power density, high current capacity and high operating temperature. Our previous studies have demonstrated the feasibility of semiconductor devices attachment on silver, gold and copper surfaces by silver sintering. Eliminating precious metal finishing on substrate would represent significant compatibility to present supply chain and lower the entry barrier to adopt silver sinter solution. In this paper, we extended our study to semiconductor devices attachment on non-precious metal surfaces by pressure sintering process in air atmosphere. We attached Ag metallized Si dies on direct copper bonding substrates with nickel plated and without plating as well as on aluminum plate by silver sintering process at $250^{\circ}\mathrm{C}$ with a pressure of 10 MPa for 3 min using a newly developed silver sinter paste. We demonstrate that it is feasible to create high bonding strength of silver sintered joint on Ni, Al and Cu surfaces with an average die shear strength above 15 N/mm$^{2}$. The die shear failure mode shows that cohesive break in the sintered layer was obtained for all the samples. SEM-EDX results further confirmed that silver sintered joint was formed on Ni, Al and Cu surfaces with an interdiffusion between Ag and Ni, Ag and Al as well as Ag and Cu. SAM was performed on the samples after pressure sintering and the SAM images clearly illustrate that void, drying channel and delamination in the silver sintered layer were not observed.