edfas.org ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 28 NO. 2 32 INTRODUCTION As semiconductor device complexity increases, the ability to isolate electrical defects at the silicon level becomes paramount for ensuring long-term product reliability. This article presents a technical evaluation of a universal serial bus (USB2) interface failure within a platform controller hub (PCH) following a system-level electrostatic discharge (ESD) event. By distinguishing between electrical overstress (EOS) and ESD mechanisms and employing a structured fault analysis and fault isolation (FAFI) workflow—ranging from parametric characterization to laser-based isolation and physical failure analysis (PFA)— the author demonstrates the isolation of a resistive short on the silicon. This case study underscores the necessity of high-precision isolation in correlating system-level zapping events with sub-micron silicon defects. In modern computing architectures, such as the 14 nm Intel 10th generation processors, functional integration is increasingly bifurcated. The architecture typically splits functionality between a compute die responsible for logic processing and a PCH chiplet. The PCH serves as the “southbridge” for critical high-speed interfaces, including SATA, PCIe, and USB, making it a focal point for architectural vulnerability analysis. Among these interfaces, the USB2 protocol utilizes a tiered star topology capable of addressing 127 devices across a seven-layer system. Communication is managed via bidirectional control pipes and unidirectional data pipes (interrupt and bulk). Physically, the interface relies on a differential signaling pair (D+ and D–) operating at 3.3 V, employing non-return-to-zero (NRZ) coding with bit stuffing. However, these external-facing lines are inherently susceptible to transient electrical events, specifically EOS and ESD. FROM SYSTEM ZAP TO SILICON IMPROVEMENT: ADVANCED FAULT ISOLATION OF USB2 ELECTROSTATIC DISCHARGE FAILURES Omkar Rajesh Kachare Intel Corp., Hillsboro, Oregon omkar.kachare@intel.com The development of robust semiconductor devices requires a profound understanding of the electrical phenomena that lead to premature failure. For the failure analysis engineer, the “detective work” begins with correctly classifying the stress mechanism to drive the appropriate isolation strategy. DISTINGUISHING EOS FROM ESD While often grouped under the broader umbrella of “overstress,” EOS and ESD represent opposite ends of the voltage, current, and time spectrum. A methodological approach to FAFI must begin with the precise classification of these mechanisms. EOS: The Thermal Runaway. EOS is characterized by thermal damage occurring when a device operates outside its specified voltage or current limits. Technically, this damage results from Joule heating, where resistive heating in low-resistance paths creates localized hot-spots. These events are typically low-voltage, high- current phenomena with durations exceeding 1 millisec- ond (>1 ms) (Fig. 1). The duration is a critical differentiator. To utilize a common industry analogy, EOS is akin to an “open faucet.” Even if the flow is moderate, the continuous energy dissipation allows for massive thermal runaway, often leading to melted internal connections, high VCC leakage, and shorted I/O pins. Root cause diagnostics for EOS typically involve analyzing powered handling (hot-plugging), unpowered handling, or switching applications involving electromagnetic pulse exposure. ESD. In contrast, ESD is a high-voltage (>500 V), lowenergy event occurring over an extremely short duration (<1 µs). ESD is described as “adiabatic,” meaning the timescale of the event is significantly faster than the thermal diffusion time of the silicon. This results in instantaneous EDFAAO (2026) 2:32-40 1537-0755/$19.00 ©ASM International®
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