Effect of Intermetallic Growth on Durability of High Temperature Solders (SnAg, SAC305, SAC+Mn, SnAg+Cu Nano) in Thermal and Vibration Environments
Crandall, Michael Adam
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The RoHS ban of lead from electronics has pushed the industry to find lead free alternatives. In high temperature environments, high lead solders have typically been used. A suitable lead free replacement alloy is required. In this study quad flat packages (QFP) and 2512 chip resistors soldered with commercially available Sn3.5Ag and SAC305, and experimental SAC+Mn and SnAg+Cu Nano alloys on ENIG finished copper were subjected to three tests. Isothermal aging at 185°C for up to 1000 hours and at 200°C for up to 500 hours were performed to measure the interfacial intermetallic thickness, assess intermetallic compounds, and view the microstructure. A durability assessment was performed featuring thermal cycling ranges of -40 to 185°C and -40 to 200°C intermixed with 50G vibration cycling to determine the most durable solder alloy. Failure analysis was performed to understand the durability results. Finally, shear testing was performed to determine a correlation between shear strength and durability. The results show SAC305 is the most reliable solder under these conditions.