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12 SMT007 MAGAZINE I JULY 2018 One straightforward remedy to alleviate the loosely defined brittleness of SAC305 was to reduce the Ag content, which consequently has led to the introduction of low-Ag SAC alloy compositions (e.g., SAC0308 containing 0.3wt%Ag, 0.8%Cu) to the industry. Appar- ently, the reduced metal cost of the low-Ag compositions also offers an upside. However, with the reduction of Ag content, the mechan- ical properties of resulting solder joints (the yield strength, tensile strength and creep resis- tance) are expected to decrease. In the ranges of Ag and Cu contents of this discussion, the fatigue resistance, which often involves more complex mechanisms, is also expected to decrease with the reduction of Ag content. Testing measurements coincide well with the expectations. For the effect of Ag content (at a range of 0.5–1.5 wt% Cu), tests showed that yield strength and tensile strength increase SMT Prospects & Perspectives by Dr. Jennie S. Hwang, CEO, H-TECHNOLOGIES GROUP Part 3 of this series focuses on how Bi plays a role to the answers of these two questions: Why isn't SAC able to be a universal intercon- necting material for electronic circuits, and why does a quaternary alloy system offer a more wholesome approach? (Note: a quater- nary system referred herein does not include SAC compositions incorporated with one or more doping elements.) Overall, SAC305 has performed to expecta- tions—delivered satisfactory solder intercon- nections for most (but not all) applications under most service conditions. Nonetheless, some performance deficiencies have manifested as anticipated. Specific deficiencies include the undesirable brittleness (loosely defined) rela - tive to SnPb counterpart and the potential occurrence of solder joint surface cracks and other production-related defects and issues (e.g., head-on-pillow, pad-cratering). The Role of Bismuth (Bi) in Electronics, Part 3

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