edfas.org 33 ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 28 NO. 1 ISTFA 2025 OPTICAL FAULT ISOLATION, TEST, AND DIAGNOSTICS USER GROUP Chair/Co-Chairs: Dan Bockelman, Dan Bodoh, and Munindhran Nagaswara Rao dan.bockelman@intel.com, dan.bodoh@nxp.com, munindhran.rao@cirrus.com The ISTFA 2025 Optical Fault Isolation (OFI), Test, and Diagnostics User Group, attended by 75 participants, convened on November 20 to discuss the evolving landscape of failure analysis. William Lo of Nvidia delivered opening remarks, outlining the FA roadmap and emphasizing the strategic shift toward “test and diagnostics.” This approach advocates for integrating testability features—like IEEE fault models and probing-friendly architectures—earlier in the design cycle. Lo also highlighted the increasing intersection of FA with photonics and quantum computing. The discussion centered on several critical themes. Dynamic lock-in thermography (LIT) usage with automated test equipment (ATE) was a major topic, focusing on high-wavelength thermography, heat spreading behavior, and the effectiveness of ATE-driven patterns in activating latent defects. Practical insights were shared regarding ELITE setups and thermal modeling approaches, while questions about RF-based LIT sparked interest for future exploration. Security challenges in debugging and failure analysis were another focal point. Participants examined the complexity of disabling zero-trust firmware during FA without compromising system integrity. Strategies such as controlled override paths, decode-cell modifications, and collaboration between security and design-for-test teams were debated, underscoring the tension between robust security and diagnostic accessibility. Visible light probing (VLP) discussions centered on wavelength selection, comparing 785 nm and 1064 nm options. Engineers noted that device stack composition, thinning requirements, and thermal constraints often dictate the choice, with pulsed probing and localized thinning strategies emerging as potential solutions. Similarly, soft defect localization (SDL) was addressed, with emphasis on improving test system responsiveness, advancing LSM hardware, and leveraging JTAG readouts for quantitative measurements. Emission microscopy comparisons between InGaAs and mercury cadmium telluride (MCT) detectors revealed that while MCT offers broader spectral coverage—extending to approximately 2500 nm—and superior imaging for backside power delivery architectures, it introduces cost and optical complexity. Backside power delivery (BPD) itself was recognized as a disruptive technology, forcing a reevaluation of traditional isolation methods and driving innovation in sample preparation and signal routing. Finally, thermoreflectance (TR) was highlighted as a complementary thermal-optical technique, particularly valuable for advanced packaging environments where spatial resolution is critical. Surface coatings were noted as a means to enhance TR performance on low-reflectivity substrates. The meeting highlighted that FA techniques continue to evolve for modern nodes and packaging technologies. Moving forward, success will hinge on adopting new optical probing methods, leveraging extended-spectrum detectors, and rethinking sample preparation workflows to keep pace with backside power delivery and heterogeneous integration. “STRATEGIES SUCH AS CONTROLLED OVERRIDE PATHS, DECODE-CELL MODIFICATIONS, AND COLLABORATION BETWEEN SECURITY AND DESIGN-FOR-TEST TEAMS WERE DEBATED, UNDERSCORING THE TENSION BETWEEN ROBUST SECURITY AND DIAGNOSTIC ACCESSIBILITY.”
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