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edfas.org ELECTRONIC DEV ICE FA I LURE ANALYSIS | VOLUME 23 NO . 4 16 MIP process was then used to remove the remaining overmold with 12 etch and clean cycles, taking approximately 11 hours. After the overmold was removed, the top surface of the interposer was perfectly preserved including the passivation over the metal (Fig. 4). Some of the soldermask on the top surface of the laminate was also removed, but the area of attack was reduced by the raster pattern used and physical masking. The perimeter chain was now visible for further fail isolation. LARGE SAMPLE DEFECT ISOLATION WITH EBAC To find the exact location of the open in the perimeter via chain, EBAC analysis pro- vides an excellent option. [6] It was decided to leave the existing passivation on top of the metal to ensure any defect present would be preserved. It was also preferable to not cut the sample to a smaller size, causing stresses in themodule that could change the defect, create defects, or crack the interposer. These limitations eliminated the option to use a typical SEM nanoprobe system. Instead, wires were soldered to the ball grid arrays underneath the module which were connected to the perimeter chain (Fig. 5a). The sample was then loaded into a large chamber environmental SEM, and the wire ends fed to an EBAC amplifier through an existing probing platform. The module could then easily be scanned over a large area to detect the location of the defect. Figure 5b shows the resulting EBAC signal, isolating the perimeter via chain fail down to one link. The sample was then resized and sectioned in a tri-beamFIB using a Ga beam, then imaged with a He beam. The fabrication processing defect was clearly visible (Fig. 5c). CONCLUSION As the semiconductor industry moves toward more 2.5D and 3D advanced packaging, and the use of over- mold to stabilize and protect the elements of the package proliferates, the challenges to perform failure analysis on those systems increases. The ability to remove the overmold nondestructively and isolate failswhile keeping themodule intact is critical to the success of failure analy- sis. Removing the overmold without disassembling the modules is difficult to dowith traditional acid based or O 2 plasma or RIE processing. The availability of microwave induced plasma spot etching has helped to meet many of those challenges. Subsequent analysis using EBAC and other beam-based techniques require innovative ways to collect signals. In this analysis a large chamber environmental SEM was used, and the ball grid arrays were directly wired to the EBAC amplifier, which enabled localization of the failure. ACKNOWLEDGMENT The authors would like to acknowledge J. Myers and R. Russotti for the FIB analysis shown. References 1. C. Ferrandon, et al.: “InnovativeWafer-level Encapsulation&Underfill Material for Silicon Interposer Application,” Proc. 63rd IEE Electronic Components and Technology Conference, 2013, p. 761-767. 2. K. Distelhurst, D. Hunt, and D. Bader: “Isolating an Open in 2.5 D µBump & Chip Bump Chains using SDR, EBAC and Capacitive Measurements,” Proc. 45th International Symposium for Testing and Failure Analysis, 2019, p. 393. 3. X. Ma, D.G. Yang, and G.Q. Zhang: “Decapsulation Methods for Cu Interconnection Packages,” 13th International Conference on Electronic Packaging Technology & High Density Packaging, 2012, p. 1387-1391. 4. L. Heusinger-Jonda, J. Tang, and K. Beenakker: “Enabling True Root Cause Failure Analysis Using an Atmospheric Oxygen-only Plasma for Decapsulation of Advanced Packages,” Electronic Device Failure Analysis, 2021, 23 (1), p. 4-10. 5. K. Distelhurst, et al.: “Benefits of Using aCF4-FreeMicrowave Induced Plasma (MIP) Spot Etch Process to Remove Underfill and Analyze 2.5 D Modules,” Proc. 46th International Symposium for Testing and Failure Analysis, 2020, p. 226-232. 6. S. Wei, et al.: “Optimization and Application of Electron Beam Absorbed Current Technique,” IEEE 22nd International Symposium on the Physical and Failure Analysis of Integrated Circuits, 2015, p. 250-254. (a) (b) (c) Fig. 5 (a) Diagram of module prepared for electron beam absorbed current (EBAC) analysis. (b) EBAC signal shows precise location of open via chain link. (c) A He beam image of a Ga beam focused ion beam section showing the defect found at the isolated via chain link.