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Lead-free Solder Durability in Wide Temperature Range Thermal-Vibration Environments
Keywords: Lead-free Solder, Reliability, High Temperature
The RoHS ban of lead from electronics has pushed the industry to find lead free alternatives. This is true even for high temperature environments, where high lead solders have typically been used. In this study quad flat packages (QFP) and 2512 chip resistors were reflowed with commercially available Sn3.5Ag and SAC305, and experimental SAC+Mn and SnAg+Cu Nano alloys on ENIG finished polyimide printed circuit boards. The experimental alloys were chosen because of previously published results showing reduced intermetallic formation in solders containing these elements. Isothermal aging at 200C for up to 500 hours was performed to measure the interfacial intermetallic thickness, and characterize intermetallic compounds. A durability assessment was then performed featuring thermal cycling from -40 to 200C intermixed with 50G vibration cycling to determine the most durable solder alloy in a combined temperature cycling and vibration environment. Failure analysis was performed to understand the durability results. The results indicated that SAC305, SnAg, and SAC+Mn were all highly reliable solders but their relative reliability depended on whether the components had copper or nickel leads.
Patrick McCluskey, Associate Professor
University of Maryland
College Park, MD

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