We are faced with designing extremely high performing packages with mixed technology content such as high speed digital, analog, and RF. At the same time, the density requirements are forcing us to use 3D packaging technologies. Prototypes really are a relic of the past when it comes to packaging design. Early planning and evaluation, parasitic extraction simulation, and verification become more and more critical. In this article we will look at how to design modern 3D packages with mixed technology content with emphasis on chip-package-board co-design and package substrate design.