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8 SMT Magazine • July 2015 by Dr. jennie S. Hwang CEo, H-TECHnologiES group SMT PROSPECTS & PERSPECTIVES The Theory Behind Tin Whisker Phenomena, Part 2 Column As teed up in Part 1 of this series, a plausible theory of tin whisker growth can be postulated through deliberating the combination and con- fluence of several key metallurgical processes. These key processes include: • Grain boundary movement and grain growth • Energy dynamic of free surface • Solubility and grain growth in response to external temperature • Role of recrystallization • Lattice vs. grain boundary diffusion • Crystal structure and defects • Reaction and dynamic of intermetallic compounds In response to external factors, these pro- cesses, operating sequentially and in parallel, drive intrinsic structural changes leading to the conditions that nurture whisker growth. Grain Boundary Movement and Growth Grain growth cannot occur without the movement of grain boundaries, but its move- ment is not easy to predict. Thus, grain bound- ary (g.b.) is a critical, yet elusive character to the behavior of materials. Adding to the elusiveness of g.b., the provenance of the material history needs to be established before embarking on a detailed mechanical and microstructural char- acterization. It often takes advanced equipment and analyses to identify g.b. and its movement. To uncover texture and grain boundary crystallog- raphy and to identify phases, electron backscat- ter diffraction (EBSD) and energy dispersive X- ray spectroscopy (EDS) are the useful analytical tools. Transmission electron microscopy (TEM) and electron probe are the tools to reveal dislo- cation structures and grain boundary sergeant structures. Additionally, a scanning electron microscope-focused ion beam (SEM-FIB) sys-

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