3D packaging via System-On-Package (SOP) is a viable alternative to System-On-Chip (SOC) to meet the rigorous requirements of today's mixed signal system integration. In this article, we present the first physical layout algorithm for 3D SOP that performs thermal-aware 3D placement and crosstalkaware 3D global routing. Existing approaches consider thermal distribution and crosstalk issues as an afterthought, which may require expensive cooling scheme and additional routing layers. Our goal is to overcome this problem with our thermal and crosstalk-aware 3D layout tools. The traditional design objectives such as performance, area, wirelength, and via costs are considered simultaneously to ensure high quality results. Related experimental results demonstrate the effectiveness of our approach. 1 A special issue on SOP (vol. 27, issue 2, May 2004) provides a comprehensive survey of the state-of-the-art in SOP technology. SOC complete system on one chip MCM interconnects components SIP stacked chips or packages SOP optimizes btw chip/package