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EBSD Analysis—A New Materials Analysis Tool |
In recent years, Electron Back Scatter Diffraction (EBSD) has gained popularity as a material analysis tool in the electronics industry. The principle behind it involves positioning an electron beam at a 70° angle to the surface of a sample. Then, when the electron beam hits the sample, elastic scattering results in backscattered electrons, which, along with the crystal structure of the surface, generate a diffraction signal and forms a Kikuchi pattern. The complex Kikuchi pattern can then be analyzed via specialized computer software. This software uses EBSD diffraction patterns in order to systematically gather and analyze a range of information about material crystals.
EBSD has strict requirements when it comes to sample surfaces. The surface of the test piece must be flat. Traditional test piece preparation methods, such as chemical mechanical polishing, electrolytic polishing, and ion beam milling, cause surface stress and oxide layers, etc. that all affect the resolution of images. The advantage of EBSD is that it combines a Focused Ion Beam (FIB) microscope’s observation abilities and dual beam capabilities which can be carried out surface polishing on the area being viewed simultaneously. This enables the accurate and efficient analysis of materials’ crystal structure properties.
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In the packaging and PCB industries, EBSD is an emerging but already widely used analytical method. It is used to study the microstructure and crystalline orientation of materials. |
It is able to observe a wide range of grain structures and morphologies, and can be used to determine grain sizes, high angle grain boundaries, low angle grain boundaries, twin boundaries, special grain boundaries, crystal orientations, textures and more.
Figures 1 to 3 show the analysis of the grain structures in the X, Y and Z directions of a copper foil cross section using an Inverse Pole Figure Map (IPF Map). The grain structure shown in the figures is a polycrystalline structure (with uneven grain sizes) with directionality. One of the advantages of EBSD is that it can use colors to intuitively distinguish between individual grains and the crystal orientation of each grain in the X, Y, and Z directions. Take the Y direction growth of the copper foil, for example, where the majority of the grains are green. This means that this direction is dominated by the 101 crystal orientation.
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Figure 1. IPF Map‖X |
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Figure 2. IPF Map‖Y |
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Figure 3. IPF Map‖Z |
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Figure 4 is a graph of grain size statistics. In this way, grain size distributions and average grain sizes can be effectively and quickly presented. When it comes to the counting and calculation of grain sizes, no other technology even comes close. |
 Figure 4. Grain Size Statistics |
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Generally, the physical and mechanical properties of polycrystalline materials are greatly affected by the material’s crystal orientation. Therefore, crystal orientation has always been a topic of extensive discussion in material research and process improvement. |
EBSD is capable of correlating the crystal orientation and aggregate organization of polygrain materials to create intuitive statistical representations of the materials’ textures. Figure 5 shows the overall crystalline orientation of a material using an Inverse Pole Figure (IPF). There is a clear 101 orientation in the Y direction. This result is consistent with the results shown in Figures 1 to 3.
Figure 5. Inverse Pole Figure |
In Figures 6 to 8, the Texture Component method is used to show the distribution and quantity statistics of 001, 101 and 111 grains in the Y direction within a positive and negative angle of 20°. The closer the color is to dark red, the smaller the difference in orientation from that of the 001, 101 and 111 respectively. The crystal orientation of the material can be clearly indicated using the above Inverse Pole Figure and the Texture Component function. It is then possible to study how certain textures can affect certain characteristics of a material. For example, in the crystal structure of copper FCC, 101 is the most densely packed orientation.
Therefore, in the FCC crystal structure, the movement of electrons along the 101 direction should be the fastest, making it better for conductivity. Based on the above example, compared to the X and Z directions, the Y direction has a more obvious 101 oriented texture. Therefore, it can be deduced that the conductive properties of the Y direction should be better than that of the other two.
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Figure 6. Texture Component – Distribution and Quantity Statistics of the 001 Orientation in the Grains Parallel to the Y Direction and Within a Positive and Negative Angle of 20° |
Figure 7. Texture Component – Distribution and Quantity Statistics of the 101 Orientation in the Grains Parallel to the Y Direction and Within a Positive and Negative Angle of 20° |
Figure 8. Texture Component – Distribution and Quantity Statistics of the 111 Orientation in the Grains Parallel to the Y Direction and Within a Positive and Negative Angle of 20° |
All material microstructure analysis equipment can observe grain boundaries. However, except in the case of some Twin Boundaries, there are very few intuitive ways to determine the qualitative and quantitative information on the various types of boundaries. EBSD analysis can make up for this deficiency. As mentioned above, EBSD generates images by comparing a sample’s Kikuchi pattern with a database. It is therefore possible to observe when the electron beam scan reaches a grain boundary or another type of boundary, such as a difference in crystal orientations on either side of a boundary, poor crystallinity at a boundary, special crystal orientation relationships on both sides of a boundary or other special characteristics. This enables EBSD to outline various grain boundary topographies and characteristics as well as the angle differences between the two sides of a boundary.
Figure 9 uses different colors to define and quantify high angle grain boundaries and low angle grain boundaries. The black lines indicate high angle grain boundaries. The green lines indicate low angle grain boundaries. Note that this angle range can also be customized. Figure 10 shows the use of EBSD to characterize and quantify annealed twin grain boundaries of low stack energy copper foil materials.
Figure 9. High Angle and Low Angle Grain Boundary Distribution and Statistics |
Figure 10. Twin Boundary Distribution and Statistics |
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Some of the more in-depth areas of materials science research requires the exploration of the properties of the Coincidence Site Lattice (CSL) boundary, which can also be analyzed via EBSD. Special grain boundary energies, impurity segregation behaviors, and mobility are all important considerations when it comes to Coincidence Site Lattices. |
The precipitation process of some precipitants and the ease of movement of boundaries can be estimated using the distribution of the Coincidence Site Lattice boundary. It is then possible to estimate the nucleation and growth of the precipitants, segregation behavior, and where the phase changes in re-crystallization may tend to occur. Figure 11 shows that different Σ boundaries can be fully presented and quantified via EBSD technology. This will no doubt be invaluable to more in-depth materials science research.
Figure 11. Distribution and Statistics of Coincidence Site Lattice Boundaries |
Has the analysis in this article given you a better understanding of EBSD analysis? EBSD uses a different aspect of material analysis to uncover heretofore unknown secrets about various materials. With its help, you can accurately and effectively solve numerous material microstructure problems!
