Reliability Behavior of Surface Mount Devices Assembled with Bismuth Bearing Low-Melt Solder Pastes

As the electronics industry continues to evolve in complexity, a concerted effort has developed to implement lower melting point solders. While several exist, one of the most popular has been the SnBi eutectic alloy. Although the process procedures required to create such assemblies is straight-forward, the reliability performance of the bismuth bearing alloys is not well documented and requires significant study before the materials can be adopted by the industry. This concern is compounded by the fact that the microstructural characteristics of the bismuth-based alloys are highly dependent upon processing parameters such as time and temperature when assembled in a “mixed” alloy system (i.e. combined with Tin-Silver-Copper) and it is theorized that such microstructural variability may result in significant thermo-mechanical reliability variations. Accordingly, BGA and LGA components were assembled using SnBi paste and subjected to thermo-mechanical cycling. Upon failure, the package reliability and interconnect failure mechanisms were studied.