Time-domain based characterization methods, mainly time-domain reflectometry (TDR) and time-domain transmissometry (TDT), have been used to locate faults in twisted cables, telegraph lines, and connectors in the electrical and telecommunication industry. This article provides a brief review of conventional TDR and its application limitations to advanced packages in semiconductor industry. The article introduces electro optical terahertz pulse reflectometry (EOTPR) and discusses how its improvements of using high frequency impulse signal addressed application challenges and quickly made it a well-adopted tool in the industry. The third part of this article introduces a new method which combines impulse signal and the TDT concept, and discusses a combo TDR and TDT method. Cases studies and application notes are shared and discussed for each technique. Application benefits and limitations of these techniques (TDR, EOTPR, and combo TDR/TDT) are summarized and compared.