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March 2014 • SMT Magazine 29 feaTure bled with alternative low/no silver solder paste is recommended. SmT references 1. J. Smetana, R. Coyle, P. Read, T. Ko- shmeider, D. Love, M. Kolenik and J. Nguyen, "Thermal Cycling Reliability Screening of Mul- tiple Pb-Free Solder Ball Alloys," Proceedings of IPC APEX EXPO conference, 2010. 2. G. Henshall, et al., "INEMI Pb-Free Alloy Characterization Project Report: Part I-Program Goals, Experimental Structure, Alloy Character- ization and Test Protocols for Accelerated Ther- mal Cycling," Proceedings of SMTAI, 2012. 3. K. Sweatman, et al., "iNEMI Pb-Free Alloy Characterization Project Report: Part III—Ther- mal Fatigue Results for Low Ag Alloys," Proceed- ings of SMTAI, 2012. 4. Jennifer Nguyen, David Geiger and Dong- kai Shangguan, "Evaluation of Lead-Free Solder Paste Materials for PCBA," Proceedings of IPC APEX EXPO conference, 2011. NOTE: This article was published in the 2013 IPC APEX EXPO technical conference proceedings. FEaSIBILITY OF LOW/NO SILvEr aLLOY SOLDEr PaSTE maTErIaLS continues figure 15: visual images of solder joints reflowed with different lead-free alloys using low lead-free profile. 15a) Solder paste was melted for SaC305 alloy. 15b and 15c) Cold solder was observed for SaC0307 and Sn100C using a low lead-free profile. Jennifer nguyen is manager of worldwide assembly and test technology at Flextronics. ranilo aranda is a process engineering manager at Flextronics. David geiger is director of assembly and test technology at Flextronics. Murad Kurwa is vice president of engineering for the advanced engineering group at Flextronics. Wearable body sensors and robotic skin must ferry information along flexible routes. electron- ics that bend and stretch have become possible, but similar work in the field of optics has lagged behind. Particularly difficult to engineer have been optics that stretch when someone wearing body sensors bends or twists. belgian researchers report progress with an optical circuit that uses both bendable and stretchable interconnections made of a rubbery material called poly-dimethylsiloxane. "To our knowledge, this is the first truly bendable, stretchable optical link with these miniature dimensions," said lead author Jeroen Missinne of ghent university and imec, a nano- electronics research center in belgium. Circuits with stretchable optical Interconnections