Impact of Aging and Board Design Features on the Mechanical Shock Reliability of SAC305 Solder Interconnects

Abstract:  

The reliability of solder joints is a critical factor in the performance of electronic assemblies used in consumer, automotive, aerospace, and defense applications. Electronic devices continue to become smaller and more complex while operating under increasingly harsh conditions. Therefore, it is essential to understand the factors that influence solder joint reliability. This research investigates the effects of solder alloy composition, surface finish, aging conditions, and printed circuit board (PCB) design parameters on the drop shock reliability of electronic assemblies. SAC305 ball grid array assemblies with immersion tin (ImSn) and electroless nickel immersion gold (ENIG) finishes were evaluated following aging at 125 °C for up to 60 days. Aging significantly reduced reliability through intermetallic compound (IMC) growth and Ag3Sn coarsening, with ImSn assemblies outperforming ENIG due to the absence of brittle Ni-containing IMCs. In addition, the effects of PCB thickness, component type, and copper pad design were investigated using SAC305 joints with organic solderability preservative (OSP) finishes. Increased PCB thickness and the presence of solder mask openings improved reliability by reducing board flexure and stress concentrations. The influence of short-term preconditioning on SAC305, Innolot, and SnPb solder joints with OSP and ENIG finishes was also examined. Preconditioning stabilized joint microstructures and reduced failure variability, while OSP consistently provided superior performance to ENIG. Among the alloys studied, Innolot exhibited the highest drop shock reliability, whereas SnPb demonstrated the most consistent failure behavior.

Bio:

George T. Flowers is the Arnold Distinguished Professor and Chair in the Department of Mechanical Engineering at Auburn University. He was an Assistant Professor with the Department of Mechanical Engineering at the University of South Florida from 1988 to 1990. He joined the faculty of the Department of Mechanical Engineering at Auburn University in 1990. Dr. Flowers has also held visiting positions at NASA Marshall Space Flight Center and the Air Force Research Laboratory at Wright Patterson AFB and at Kirtland AFB. He has been an active member of IEEE, ASME, and AIAA for over 30 years. He is an ASME fellow and an AIAA Associate Fellow. He was the Conference Co-Chair for the 2009 ASME International Design Engineering Technical Conferences and Computers in Engineering Conference and Conference Chair for the 2021 IEEE Holm Conference on Electrical Contacts. He has served as chair of the ASME Technical Committee on Vibration and Sound, chair of the IEEE Holm Conference Technical Program Committee, and is currently a guest associate editor for the IEEE Transactions on Components and Manufacturing Packaging Technology. His scholarly research is in the general area of vibration, dynamics, and control, with an emphasis on electronic packaging particularly regarding electrical contacts. He has published over 200+ refereed research articles. He has had a long-term affiliation with the Auburn University Center for Advanced Vehicle and Extreme Environment Electronics (CAVE3), which has been a key sponsor for much of his electronic packaging research.