The growth in mobile device market and the increasing demands for higher level systems integration is driving significant advancements in packaging technologies. Next generation semiconductor devices demand redistribution layers that are shrinking to accommodate multiple chips on a single package. In this paper, we present the application of Picosecond Ultrasonics (PULSE™) in combination with high resolution reflectometer to provide a comprehensive in-line metrology for full process characterization of the redistribution layer. This first principles technique provides gage capable measurements for production monitoring and is capable of providing measurements on various types of structures such as dense lines, pads, and bumps. Accuracy of the measurements have been validated using cross-sectional scanning electron microscopy.