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12 SMT007 MAGAZINE I FEBRUARY 2019 Part 5 of the series will address the most in- teresting, yet intricate, aspect of the subject— plausible underlying operating mechanisms among the four elements (Sn, Ag, Cu, Bi) in a SnAgCuBi system. I will provide some illustra- tions on relative elemental dosages in relation to relevant properties and performance. In an Sn-based system, the starting point is to con- sider the metallurgical interactions of three ele- ments—Ag, Cu, and Bi—with Sn as the matrix. How do these three elements affect physical and mechanical properties individually and collectively as well as the importance of the specific dosage of each element in the system to the resulting properties and performance of a specific alloy composition? First, to be in line with SnPb eutectic reflow peak temperature (SnPb eutectic continues to be a viable reference point), the target is to The Role of Bismuth (Bi) in Electronics, Part 5 make the melting temperature as close to that of SnPb eutectic as feasible since the required reflow process peak temperature is directly de- termined by the alloy's melting temperature. And the reflow temperature is crucial to the integrity of the circuit boards produced, pri- marily to avoid encountering the risks of any detectable or undetectable thermal damages while not to marginalize the required process window. Accordingly, a challenging goal has been to lower the melting temperature of the lead-free Sn-based alloy without entering into the ter- ritory of low-temperature alloys (e.g., melting temperature below 175°C). Thus, research, de- velopment, and manufacturability efforts have been so directed in our studies. Also, in this writing, for practicality, the liquidus tempera- ture of a non-eutectic alloy composition is ex- SMT Prospects & Perspectives by Dr. Jennie S. Hwang, CEO, H-TECHNOLOGIES GROUP

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