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10 SMT007 MAGAZINE I APRIL 2023 In my column series on "The Role of Bismuth (Bi) in Electronics," I have addressed the properties, safety, resources of elemental bismuth (Bi), the effects of Bi in SnPb, and the effects of Bi on the properties and performance of solder interconnections when Bi is not a constituent element in lead-free solder alloys. The intricate interactions of the four elements—Sn, Ag, Cu, Bi—in a Sn-based lead- free SnAgCuBi or SnAgCuBi+ systems ("+" denotes other doping elements incorporated in the system) were also previously highlighted. Additionally, the plausible underlying operating mechanisms and resulting mechanical behavior of a lead-free alloy containing these commonly and likely-used elements were outlined. This installation focuses on a case study illustrating a problematic phenomenon called fillet-lifting, what lessons have been learned, and how these findings have helped and will continue to help develop new lead-free alloys. The fillet-lifting phenomenon has "inspired" fruitful thoughts and deeper examinations in the role of Bi in a Sn-based alloy system. This understanding has substantially helped shorten the development time to reach viable alloy formulae that can deliver the desired performance under thermal fatigue environments that microelectronic/electronic products inevitably encounter. Background A decade before the Restriction of Hazardous Substances Directive (RoHS) was proposed in The Role of Bismuth (Bi) in Electronics, Part 7: A Case Study in Fillet-lifting SMT Prospects and Perspectives by Dr. Jennie S. Hwang, CEO, H-TECHNOLOGIES GROUP

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