Diagnosing the root cause of a failure is particularly challenging if the symptom of the failure is not consistently observable. This article focuses on Laser Assisted Device Alteration/Soft Defect Localization (LADA/SDL), a global fault isolation technique, for detecting such failures. The discussion begins with a section describing the three steps in LADA/SDL analysis setup: create the test loop with the fail flag and loop trigger, select the laser dwell time, and select the shmoo bias point. An overview of LADA/SDL workflow is then presented followed by a brief section on time-resolved LADA. The closing pages of the article consider in detail SDL laser interaction physics and LADA laser interaction physics.