Today’s process technology requires ever-increasing number of metal layers to meet the power and layout needs of modern products. These advances have rendered many of the conventional fault isolation (FI) methods from the front side of the die obsolete. The flip-chip package not only brings about the need to localize defects at die level through the Si substrate, but also introduces the need to isolate new defects at the package level. Recently, an infrared (IR) emission microscope which utilizes the cryogenically cooled HgCdTe (MCT) imaging array having spectral response of 0.8μm- 2.5μm, for near IR emission detection was developed. This system supersedes the conventional CCD based emission microscope with a spectral response of 0.4 μm-1.1μm. Since spectral detection extends into the thermal spectral region, it also offers an added advantage of detecting thermal spots on the die and flip-chip package where liquid crystal hot spot detection method is not possible. This article is an account of the use of the Mercury-Cadmium- Telluride based IR detector for “real life” failures. The article will demonstrate key features of the system as well as several FI examples. Both emission and thermal detection modes will be discussed. The authors will present several problems, including melted die bumps and package copper trace shorts, that could not be detected through conventional failure analysis (FA) methods, such as liquid crystal or front side emission microscopy. The MCT detectors increased sensitivity and backside navigation capabilities coupled with backside die preparation has proven itself an indispensable FA tool in the high volume manufacturing environment.