Organic RDL interposer is used in a 2.5D package structure to enable high interconnectivity density with 2um/2um line width/spacing. The presentation includes RDL design implementation with Allegro Package Designer (APD+) and physical verification with Pegasus DRC. System integration with Orbit IO, substrate design with APD+ are also neccesary for a complete package product design cycle.In order to optimize performance of 2.5D package, simulations of electrical, mechanical stress and thermal can also be conducted. Co-design of silicon, interposer and substrate is critical to meet requirements while minimizing cost. An example from HBM2e to CPU interconnect is demonstrated that finer trace width, samller spacing and smaller via pad can reduce the layer count.