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As teed up in Part 1 of this series, a plausible theory of tin whisker growth can be postulated through deliberating the combination and confluence 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 processes, 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 movement is not easy to predict. Thus, grain boundary (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 characterization.
It often takes advanced equipment and analyses to identify g.b. and its movement. To uncover texture and grain boundary crystallography and to identify phases, electron backscatter diffraction (EBSD) and energy dispersive Xray spectroscopy (EDS) are the useful analytical tools. Transmission electron microscopy (TEM) and electron probe are the tools to reveal dislocation structures and grain boundary sergeant structures. Additionally, a scanning electron microscope-focused ion beam (SEM-FIB) system enables the analyses of atomic layers in nanoscale. Complementarily, these analyses pave the groundwork for the engineering of grain and interphase boundaries.
If you missed Part 1, click here.
Editor's Note: This article originally appeared in the July 2015 issue of SMT Magazine.