This paper describes a failure analysis that effectively combined multiple analytic techniques to find the cause of I/O leakage in a flawed chip produced for an OEM (Original Equipment Manufacturer) product. Internal probing was initially used for defect isolation and a Tungsten (W) stud open circuit flaw was isolated by electrical characterization with internal probing. SEM (Scanning Electron Microscopy), TEM (Transmission Electron Microscopy, and FE-AES (Field Emission Auger Electron Spectroscopy) analysis with FIB (Focused Ion Beam) preparation were used for physical analysis. Cross-sectional SEM and TEM observations showed a gap with foreign material (FM) between the bottom of the metal line and the top of the W stud, possibly from the W CMP (chemical mechanical polish) process. FE-AES is effective for the analysis of light materials and their chemical composition, so a flat milling FIB process was used to prepare a cross-section for FE-AES analysis of the FM and the interfaces of the open defect. The spectra showed that the FM was traceable to the W CMP process. From these analytical results and problem reproduction experiments in the W CMP process on the manufacturing line, the failure mechanism was identified.