Reliability Assessment of Lead-Free Universal Solder for Direct Bonding in Power Electronics Packaging

A novel, lead-free universal (rare earth) solder is investigated for high temperature power electronics packaging. The material is Sn-3.5Ag-0.5Cu solder with small additions of a rare earth element exhibiting superb bonding properties. It is capable of direct, reliable bonding of dissimilar materials without the use of flux and eliminates the need for multilayer metallization which is typically required to aid in wetting. The problem of surface oxidation is done away with because of the strong thermodynamic affinity of the rare earth metal in the solder to oxygen. [1] This paper offers a first investigation of the thermal performance and reliability of this universal solder joint for power switching applications.