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Global clocks are a dedicated network of interconnect specifically designed to reach all clock inputs to the various resources in an FPGA. These networks are designed to have low skew and low duty cycle distortion, low power, and improved jitter tolerance. They are also designed to support very high frequency signals. Faults in global clocks are very hard to isolate because it runs across the die. Furthermore, temperature-dependent clock failures make it more complex to analyze because of intermittency. Conventional failure analysis techniques such as OBIRCH/TIVA and photon emission analysis cannot be used to localize the failure because of the low power nature of global clocks. In this investigation, a combination of temperature-dependent probeless fault isolation and pattern analysis has been utilized in the analysis of global clock failures. We will illustrate how information from conventional techniques and new innovative techniques can lead to successful root cause analysis of the failure mechanism. It is for this purpose that the detailed electrical fault isolation in combination with pattern analysis was used during the characterization of failure mechanism in this study. Other techniques utilized were frontside parallel lapping and FIB cross-sectioning FA techniques to physically expose the defect in the failing region.