Packages with the Modified Daisy-chain (MDC) die have been used increasingly to accelerate reliability stress testing of IC packaging during package development, qualification, and evaluation and reliability monitor programs . Utilizing this approach in essence eliminates chip circuit failure mechanisms. Unlike packages with active die, in packages with the MDC die, when short occurred between two daisy-chain pairs of I/Os, there are four possibilities that can attribute to each pin of the two daisy-chain pairs. That makes the isolation of short failure difficult. Time Domain Reflectometry (TDR) is a well-described technique to characterize package discontinuity (open or short failure). By using a bare package substrate and a reference device, an analyst can characterize the discontinuity and localize it: within the package, the die-package interconnects, or on the die . Scanning SQUID (Superconducting Quantum Interference Device) Microscopy, known as SSM, is a non-destructive technique that detects magnetic fields generated by current. The magnetic field, when converted to current density via Fast Fourier Transform (FFT), is particularly useful to detect shorts and high resistance (HR) defects . In this paper, a new methodology that combines Resistance Analysis, TDR Isolation and SSM Identification for electrical debugging short in packages with the MDC die will be presented. Case studies will also be discussed.