edfas.org ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 28 NO.4 8 analysis of advanced packaging devices. These structures contain deeply buried interconnects and interfaces—such as microbumps, RDLs, TSVs, and hybrid bonding interfaces—that are critical to device performance and reliability. The system enables efficient exposure and high-resolution inspection of these regions, allowing identification of defects such as voids, cracks, interfacial delamination, and metallurgical degradation, all of which directly impact electrical and mechanical integrity. Transmission electron microscopy (TEM) delivers nanoscale to atomic-scale insight into microstructural and chemical phenomena, such as intermetallic compound (IMC) formation, atomic diffusion, electromigration damage, crack initiation, and bonding quality.[17-22] It is essential for understanding long-term reliability risks under the sustained electrical and thermal loads typical of AI workloads. Figure 7 presents the characterization of a low-melting-point high-entropy alloy (HEA) solder, synthesized by melting equimolar amounts of In, Zn, Sn, and Bi into ingots, followed by deformation into 100 µm-thick solder foils.[22] IMC formation at the solder/Cu interface was investigated using the Thermo Scientific Helios 5 UC DualBeam system and the Thermo Scientific Talos F200X TEM. Microstructural and elemental analyses reveal the formation of a dual-layer IMC structure at the interface, consisting of Cu5Zn8 phases. TEM imaging shows that the IMC layer comprises two distinct sub-layers. Selected area diffraction patterns, compared with single-crystal spots and polycrystalline rings and referenced against the PDF database, confirm that both sub-layers correspond to Cu5Zn8. However, EDS point and line analyses indicate compositional differences: The sub-layer adjacent to the Cu substrate is composed of pure Cu5Zn8, whereas the sub-layer near the solder contains Cu5Zn8 mixed with Sn, Bi, and In. The activation energy for IMC formation was determined to be 35.67 ± 3.4 kJ/mol. These results demonstrate that TEM enables nanoscale phase identification, compositional mapping, and atomic-level structural analysis of IMC layers, providing critical insight into interfacial reactions and reliability mechanisms in HEA solder joints. Together, these destructive FA techniques transform abstract reliability concerns into concrete physical failure mechanisms that engineers can directly address. By enabling fast learning cycles, accelerated yield ramp, and robust reliability qualification, FIB/SEM and TEM play a critical role in ensuring that advanced AI systems meet the stringent requirements of hyperscale and data- center deployments. (a) (b) (c) (d) (e) (f) Fig. 6 High-resolution SEM images were captured after the Helios 5 Laser PFIB cross-sectioning process. (a) and (b) show the microbump array structure after the laser ablation process; (c) presents the Xe+ plasma polished cut face, revealing a clean and clear sandwiched Cu-Sn-Cu microbump and the stacked DRAM; (d) is a high-resolution SEM image of a single microbump; (e) and (f) are automatic metrological images used to measure each microbump offset, TSV width, and height.[16]
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