1. Introduction
Semiconductor industry is beginning to question the viability of System-On-Chip (SOC) approach due to its low-yield and high-cost problem. Recently, 3D packaging via System-On-Package (SOP) [1], [2], [3] has been proposed as an alternative solution to meet the rigorous requirements of today's mixed signal system integration.
A special issue on SOP (vol. 27, issue 2, May 2004) provides a comprehensive survey of the state-of-the-art in SOP technology.
The SOP is about 3D integration of multiple functions in a miniaturized package achieved by thin film embedding. The 3D SOP concept optimizes ICs for transistors and the package for integration of digital, RF, optical, sensor and others. It accomplishes this by both build-up SOP, similar to IC fabrication, and by stacked SOP, similar to parallel board fabrication. The uniqueness of 3D SOP is in the highly integrated or embedded RF, optical or digital functional blocks, and sensors, in contrast to stacked ICs and stacked package as illustrated in Figure 1.