High Temperature Shear Strength of Cu-Sn Transient Liquid Phase Sintered Interconnects

In this paper, we assess the high temperature shear strength of interconnects formed by sinter pastes via a Transient Liquid Phase Sintering (TLPS) process. The joints assessed in this study were formed by the transient liquid phase sintering of Sn and Cu. The shear strength of Cu dies sintered to Cu substrates with Cu-Sn sinter pastes was assessed at temperatures of 200°C and compared to that of specimens attached with Sn3.5Ag solder. In contrast to the shear strength of the sintered specimens, the shear strength of the soldered specimens drops below 10MPa under these conditions. High temperature creep tests were performed at the same temperature level for the soldered and sintered specimens. It was found that the Sn3.5Ag interconnects show extensive creep with short time-to-failure. The joints of sintered specimens did not undergo considerable deformation due to creep. Microstructural analyses have been performed on interconnects formed between Cu dies and Cu substrates and Si diodes on Direct Bond Copper (DBC) substrates. The joint microstructure consists of a matrix of Cu-Sn intermetallic compounds (IMCs) either with or without additional Cu particles dispersed in the matrix. It is demonstrated that the paste-based TLPS interconnects assessed combine short durations for process completion with both high shear strength and high resistance to creep under elevated temperature conditions. This, in combination with high thermal conductivity, shows that transient liquid phase sinter pastes have the potential to be an excellent high temperature and high power interconnect technology.