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74 SMT007 MAGAZINE I JULY 2019 sumption is significantly reduced during the reflow process (Figure 34). These low-temper- ature solders are estimated to save 20–25% in (reflow) energy cost over SAC-305. It is also estimated that using these low-tem- perature solders would also reduce the CO 2 emissions by 1.1 metric tons per week [1] . This is roughly equivalent to 10 average gasoline vehicles (driven in the U.S.) per year. Conclusions Preliminary results investigating the low-tem- perature paste alloys against the Sn3Ag0.5Cu paste alloy look promising. Limited internal testing to date, combined with limited external testing data, indicates that these newer, doped, lower-temperature solders perform as well or better than Sn3AgCu (SAC305). Further testing and evaluation is needed and is underway. We are proceeding with drop/ shock and higher strain rate monotonic bend testing, which is where we expect to see a dif- ferentiation between the doped and non-doped solders under investigation. Future Work If the materials continue to make it past the tests previously mentioned, additional qualifi- cation testing will include SIR, cleanliness, and application-specific scenarios, such as large BGA assembly, high-mix assembly, paste-in- hole assembly, and rework. Finally, to fully understand the manufactur- ing process window for reflow, a DOE will be conducted to define the range of peak tem- peratures and their effect on mixed alloy reli- ability across a multitude of alloys (i.e., when used to attach SAC-305 or low silver containing SAC125 BGAs. SMT007 References 1. S. Sahasrabudhe, S. Mokler, M. Renavikar, S. Sane, K. Byrd, E. Brigham, O. Jin, Pubudu, Goonetilleke, N. Badwe, S. Parupalli, "Low-Temperature Solder: A Breakthrough Technology for Surface-Mounted Devices," IEEE 68 th Elec- tronic Components and Technology Conference, 2018. 2. R. Aspandiar, "Characterization of Mixed Alloy SAC- BiSn BGA Solder Joints: Part II of Report on iNEMI Project on Process Development of Bi-Sn-Based Low-Temperature Solder Pastes," Pan Pacific SMTA. This paper was first presented at the IPC APEX EXPO 2019 Technical Conference and published in the 2019 Technical Conference Proceedings. Howard "Rusty" Osgood is manager, assembly and test technology, in the Advanced Manufacturing Engineering Group at Flex Inc. David Geiger is the senior director of AME assembly and test technology. Christian Biederman is an engineering technologist in the Advanced Manufacturing Engineering Group. Jon Bernal is an engineering technologist in the Advanced Manufacturing Engineering Group. Robert Pennings and Jie Jiang are no longer with the company. Figure 34: Comparison of the typical reflow profiles for both SAC-305 (red) and the low-temperature solder (green) [1] .

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