Correlative X-Ray Microcomputed Laminography and Electron Microscopy for Failure Analysis in Loaded SiC MOSFETs

Power electronic systems based on silicon carbide (SiC) MOSFETs are essential components in electric mobility applications, where devices are exposed to extreme voltage spikes, high current densities, and thermal cycling [1-2]. Overvoltage events can induce localized semiconductor breakdown, leading to crack formation and catastrophic failure [3]. Due to encapsulation and multilayer PCB integration, these failure mechanisms are difficult to access using purely destructive methods. While conventional X-ray microcomputed tomography (µCT) enables non-destructive three-dimensional inspection, its sensitivity to very thin cracks in flat, extended assemblies remains limited. The present study demonstrates a multimodal failure analysis approach combining laboratory X-ray µCT, propagation-based phase-contrast laminography, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX) to investigate overvoltage-induced damage in a loaded SiC MOSFET. A PCB-based technical demonstrator containing a 0.4 mm thick SiC MOSFET was subjected to controlled electrical overvoltage (>1,200 V), resulting in semiconductor breakdown. The complete PCB assembly had a thickness of approximately 3 mm. Initial overview scans were performed using laboratory µCT (Procon Alpha system) at 220 kV and 140 µA, with a voxel size of 30 µm and 1,440 projections over 360°. High-resolution X-ray computed laminography was subsequently performed using an RX Solutions EasyTom system equipped with a 160 kV nanofocus tube and a Varian flat panel detector (1920 × 1536 pixels). Scans were acquired at 100 kV and 59 µA with an effective lateral voxel size of 5 µm. A tilted acquisition geometry with large propagation distance (FOD ≈ 29.45 mm; FDD ≈ 650.32 mm) was employed to enable propagation-based phase contrast imaging [3-4]. Following non-destructive X-ray imaging, the MOSFET was mechanically exposed and analyzed using a JEOL JSM-7100F field-emission SEM. EDX analysis was performed at 25 kV accelerating voltage at 350× magnification. Quantification was conducted using eZAF correction. Spectra were acquired from the damaged region as well as from surrounding solder-rich zones for comparison. The optical image of the exposed MOSFET reveals a local damage zone with visible discoloration (Fig. 1a). Conventional µCT provided three-dimensional context and revealed macroscopic features such as solder voids but did not reliably resolve fine crack structures. High-resolution laminography revealed a network of intersecting crack-like features within the semiconductor die (Fig. 1b). These features exhibit strong edge enhancement and high local signal intensity, characteristic of propagation-based phase contrast. The crack topology includes radial propagation from a central breakdown region with multiple branching interfaces. SEM imaging confirmed the presence of intersecting microcracks and branching fracture patterns across the silicon surface (Fig. 2a). The morphology and orientation of cracks correlate closely with the laminographic findings. EDX quantification showed an elevated Si concentration that confirms that the analyzed region is predominantly semiconductor material (Fig. 2b). Importantly, no enrichment of high-density solder constituents such as Ag or significant Sn clusters in the crack interfaces. The elemental maps demonstrate that the crack network is located within silicon-dominated material rather than within high-density solder accumulations. This finding excludes absorption contrast from solder as the origin of the high laminographic signal. The strong signal observed at crack interfaces in laminography is therefore attributed to X-ray refraction at sharp density discontinuities, rather than to high-atomic-number inclusions. Due to the crack morphology, propagation-based phase contrast produces sufficient edge enhancement to enable reliable visualization. The close agreement between laminography, SEM morphology, and EDX spectra strongly suggest that the detected features correspond to semiconductor fractures. This study demonstrates the diagnostic power of combining non-destructive phase-contrast X-ray laminography with high-resolution microscopy and compositional analysis. The multimodal approach provides both structural context and chemical validation, enabling robust discrimination between true semiconductor cracking and artifacts caused by solder or metallic debris [6]. a) Photograph of the electrically loaded MOSFET before encapsulation removal. The local damage region is visible in the upper right corner of the MOSFET. b) X-ray computed laminography slice (voxel size 5 µm) showing crack network in the SiC MOSFET die. a) SEM micrograph of crack region. b) Representative EDX spectrum and elemental map of crack region (25 kV).