Optimization of preparation process for successful electron backscatter diffraction of multilayer specimens: Application to lead-free solder joints

Electron backscatter diffraction (EBSD) is a powerful technique that provides a wide range of analytical data such as crystallographic orientation, phase identification, and grain size information. The quality of the diffraction pattern, which influences the quality of the indexing, depends mainly upon the achievement of a very flat and fully distortion-free sample surface. Many studies have reported specimen preparation guidelines for EBSD for a variety of materials such as metals and ceramics. However, limited studies have been documented in literature for optimized preparation of multilayer specimens. In this study, a series of mechanical polishing procedures have been developed which are adequate for producing damage-free surfaces in multiple-layer specimens for EBSD. The proposed method was used to prepare Sn-3.5% Ag/Cu-substrate solder joints, an example of a specimen which consists of multiple materials with a wide range of stiffness and wear resistance properties, and has produced the best possible surfaces. The results suggested the addition of a vibratory polishing step is critical in order to produce high quality EBSD patterns for the microstructure of Sn-3.5 Ag/Cu solder system. A poor pattern quality occurred, particularly in Cu and tin regions, when the vibratory polishing step was skipped. This study also investigated the effect of the processing parameters of the EBSD software on the EBSD results extracted for the multiple-layer specimen under investigation. It was found that the step size and the minimum number of detected bands are important parameters. It has been found that at least six detected bands are necessary for accurate mapping and quality imaging. At this optimum value, the indexing rate was the highest in all phases and the phase identification was the most accurate.