Abstract: A new type of 3D multichip module (3D-MCM) for wireless sensor networks is developed based on embedded FR-4 substrate,in which FCOB (flip-chip on board),COB (chip on board),BGA (ball grid array) technologies,and wire bonding and flip-chip interconnection technologies are combined.The PBGA device and bare die are hybrid-integrated on the embedded multi-layer FR-4 substrate.By solder ball placement and reflow,the BGA is formed at the bottom of the 3D-MCM.Solder balls with different melting points are used for initial and final vertical interconnections for the sake of compatability of all levels of interconnections of the BGA by reflow soldering.The application of embedded substrate solves the problem that the top surface of the wirebonded chip overtops the solder balls under the condition that the chip was assembled on the same side of the substrate as the BGA of the MCM.The thermal management is conducted and the thermal related reliability of the 3D-MCM is simulated and evaluated.This kind of packaging structure satisfies the electrical performance and thermal requirement,and meets the challenge of minimization,high reliability,and low cost of the package design for wireless network.

Key words: 3D-MCM, embedded substrate, combination of multiple interconnections, compatibility of solder melting, thermo-mechanical reliability