###### Abstract  
With the development of 3D integrated packaging technology, failure analysis is facing more and more challenges. Defect localization in a 3D package is a key step of failure analysis. The complex structure and materials of 3D package devices demand non-destructive defect localization technology for full packages. Magnetic field imaging and three-dimensional X-ray technology are not affected by package material or form. They are effective methods to realize defect localization on 3D packages. In this paper, magnetic field imaging and high-resolution three-dimensional X-ray microscopy were used to localize the open defect in a 3D package with a TSV daisy chain. 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. Additionally, a linear decay method was used to target sub-micron resolution at a long working distance. Multiple partition scans from a high-resolution 3D X-ray microscopy with a two-stage magnification structure were used to achieve sub-micron resolution. The open location identified by magnetic field imaging was consistent with that identified by a three-dimensional X-ray microscope. The opening was located on the top metal in the proximity of the fifth via. Physical failure analysis revealed the presence of a crack in the top metal at the opening location. magnetic field imaging (MFI); 3D X-ray; failure analysis; defect localization; TSV; non-destructive +
Footnote †: journal: Applied Sciences  
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Footnote 0: _Applied Sciences_  
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Footnote 0: _Applied Sciences_  
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Applied Sciences_  
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detection is not affected by package materials or package forms [15]. Magnetic fields can be detected after passing through multiple layers of metal, chip or packaging materials. Therefore, sample preparation is not necessary when undergoing defect localization by magnetic field imaging technology, such as decapsulation, depassivation layer, etc. There are two major implementations for MFI: Magnetic Current Imaging (MCI) [16], for locating shorts and leakage, and Space Domain Reflectometry (SDR) [17], for locating open defects. Either Superconducting Quantum Interference Device (SQUID) or Giant Magneto Resistive (GMR) sensors can be used for magnetic field imaging. The magnetic field sensitivity and spatial resolution of the two sensors are different. SQUID is the most sensitive magnetic sensor [18], and it can detect the weak current of fully package devices at a working distance of several hundred microns, but its spatial resolution is low. The magnetic field sensitivity of the GMR sensor is low, but the spatial resolution is high [19]. Generally, the SQUID sensor is first used for overall scanning to obtain the approximate location of defects, and the GMR sensor is used for detailed scanning to obtain high-resolution (sub-micron) imaging. In SDR application, the SQUID sensor can detect an RF (\(\sim\)40 MHz) current forming a standing wave when the trace is open [20]. Possible limitations for the SQUID sensor are mainly lack of resolution. Signals in close proximity may not show up as a result of the cancellation effect when signals run in different directions or the two signals are merged together into a single one when they travel in the same direction. Signals in close proximity may also be artificially separated as a result of the inversion algorithm resolution limitation. X-ray CT (Computed Tomography) is currently the most advanced X-ray detection technology, with 3D imaging capabilities; thus, it is also called 3D X-ray technology [21]. By eliminating the impact of object overlap on detection, the details of the target of interest can be seen visually from the three-dimensional image made by the 3D X-ray, and a large amount of information of covered defects can be accurately obtained, including structure, size, location and other characteristics [22].