Reliability assessment of components, integrated circuits, and microassemblies is clearly identified as a major factor in the on-going development of microelectronics. Since the last decade, the 3-D packaging and interconnections have emerged, and integrated packages have been developed. System-in-package (SIP) has become the principal support for integrated systems. Numerous problems are linked to their decreasing dimensions, the increasing numbers of interfaces (multichips stacked one on top of another), and plastic packages that must tolerate higher temperatures (RoHS). How is the reliability of such components assessed? What are the tools to investigate failure mechanisms in these new packages? This article gives some solutions mixing acoustic analysis, x-ray microscopy, electrical testing, and the use of specific tests points (sensors) placed in the package.