## 5 Conclusions  
State-of-the-art non-destructive defect localization technology, magnetic field imaging and high-resolution three-dimensional X-RAY microscopy were utilized to localize the open defect in a 3D package with a TSV daisy chain in this paper. Open defects were intentionally induced by running a thermal cycle experiment from \(-55\)\({}^{\circ}\)C to 125 \({}^{\circ}\)C for 1000 cycles. For magnetic field imaging, in order to locate a possible open failure location, it is very important to identify the circuit involved. The AC and RF scans of the reference sample helped us to understand the way that the current is supposed to propagate in the sample when there is no failure. RF signals may show intensity attenuation as they propagate along the circuit and couple to other circuits that are not part of the circuit under study. In this particular case, there were a lot of different branches that proved very difficult to isolate and complicated identification of the circuit. Therefore, a two-probe RF method in magnetic field imaging was performed to resolve isolation of the defect difficulties resulting from many different branches of TSV daisy chains. Moreover, a linear decay method was used to target sub-micron resolution at a long working distance. For three-dimensional X-RAY microscopy, to achieve sub-micron resolution, a high-resolution 3D X-ray microscopy with a two-stage magnification structure was used for scanning. In order to further improve the resolution, multiple partition scans are required, followed by image reconstruction and observation, which requires a long test time. The defect location identified by magnetic field imaging was consistent with that identified by three-dimensional X-ray microscopy. Additionally, the physical failure analysis revealed the presence of a crack in the Top_M1. From the results presented in this paper, it can be concluded that by specific methods, both magnetic field imaging and high-resolution three-dimensional X-RAY imaging can achieve sub-micron resolution in defect location at long working distances without decapsulation  
Figure 16: Morphology under SEM.  
Figure 17: Crack defect under SEM.  
or cutting samples. Both technologies are promising for future 3D-architecture-related quality assessment and failure analysis.  
Conceptualization, Y.C. and P.L.; methodology, H.-Z.H.; validation, P.Z. and X.L.; formal analysis, P.Z.; investigation, Y.C.; data curation, Y.C.; writing--original draft preparation, Y.C.; writing--review and editing, H.-Z.H.; funding acquisition, P.L. All authors have read and agreed to the published version of the manuscript.  
This research was funded in part by the Key Realm R&D Program of Guangdong Province under Grant 2018B010142001, in part by the Key Realm R&D Program of Guangdong Province under Grant 2019B010143002 and in part by the Key Realm R&D Program of Guangdong Province under Grant 2019B010145001.  
Not applicable.  
The data supporting this study can be accessed by contacting with the first author via: [EMAIL_ADDRESS].  
The authors would like to acknowledge the technical support from Neocera.  
The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.