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August 2017 • SMT Magazine 15 THE ROLE OF BISMUTH (BI) IN ELECTRONICS: A PRELUDE – Pb-containing – Pb-free • Bi-containing Pb-free solder alloys – Melting temperature range – Compositional control level – Physical, mechanical properties – BGA thermal fatigue performance • PCB through-hole fillet-lifting vs. Bi – Causes – Solutions • Low temperature BiPbSn phase – Presence or absence – Thermograms – Detectable or non-detectable effects – General guidelines • Design limits in Pb-free solder joints vs. solder joint reliability • Sn-based Bi-bearing solder vs. Bi-based solder – Differentiation – Physical properties – Mechanical properties – Service environments SMT References 1. Yves Palmieri, Bismuth Institute Informa- tion Center, Belgium. 2. Jennie S. Hwang, "Bismuth in Electronic Solders," Bulletin of Bismuth Institute Informa- tion Center, Belgium, #78, 2001. Dr. Jennie Hwang, an international businesswoman, international speaker, and business and technology advisor, is a pioneer and long-standing contributor to SMT manufacturing since its incep- tion as well as to the lead-free electronics imple- mentation. Among her many awards and honors, she is inducted to the International Hall of Fame- Women in Technology, elected to the Nation- al Academy of Engineering, named an R&D-Stars- to-Watch and YWCA Achievement Award. Hav- ing held senior executive positions with Lockheed Martin Corp., Sherwin Williams Co., SCM Corp, IEM Corp., she is currently CEO of H-Technologies Group providing business, technology and manu - facturing solutions. She serves as Chairman of As- sessment Board of DoD Army Research Laborato- ry, Commerce Department's Export Council, Na- tional Materials and Manufacturing Board, various national panels/committees, international leader- ship positions, and the board of Fortune-500 NYSE companies and civic and university boards. She is the author of 475+ publications and several books, and a speaker and author on trade, business, edu - cation, and social issues. Her formal education in- cludes four academic degrees as well as Harvard Business School Executive Program and Columbia University Corporate Governance Program. Further info: www.JennieHwang.com. A team of researchers at the Har- vard John A. Paulson School of En- gineering and Applied Sciences (SEAS) and the Wyss Institute for Biologically Inspired Engineering at Harvard University has created a highly sensitive soft capacitive sen- sor made of silicone and fabric that moves and flexes with the human body to unob- trusively and accurately detect movement. The team's technology consists of a thin sheet of silicone sandwiched between two layers of sil- ver-plated, conductive fabric, forming a capac- itive sensor. This type of sensor registers move- ment by measuring the change in capacitance of the electrical field between the two electrodes. The hybrid sensor's performance stems from its novel manufacturing process, in which the fabric is attached to both sides of the silicone core with an ad- ditional layer of liquid silicone that is subsequently cured. This method allows the silicone to fill some of the air gaps in the fabric, mechanical- ly locking it to the silicone and in- creasing the surface area available for distributing strain and storing electrical charge. This silicone- textile hybrid improves sensitivity to movement by capitalizing on the qualities of both mate- rials. Finally, thin, flexible wires are permanent- ly attached to the conductive fabric with thermal seam tape, allowing electrical information from the sensor to be transmitted to a circuit without a hard, bulky interface. Soft and Stretchy Fabric-Based Sensors for Wearable Robots