AuSn BRAZING FOR HERMETIC SEAL RING ATTACHMENT TO POST-PROCESSED MCM-D's

摘要

Hermetic Packages are used to enhance reliability but represent a large cost adder to hybrid or MCM manufacturing process. One possible solution to minimize cost is to integrate the package and substrate function in MCM-D fabrication. Attachment of metallic seal ring after fabrication of a thin film/polyamide MCM-D can provide hermeticity, while the substrate provides both as the MCM substrate and package I/O functions. AuSn eutectic brazing represents a process where the melting point of the braze (280℃) is below the process temperature of the polyamide dielectric, and where solid state reactions can be used to produce a non-eutectic composition with a remelt temperature approaching 500℃.rnThe seal ring attachment process can be analyzed and optimized for induced mechanical stress using finite element analysis (FEM). However, a major failing of many analyses is the use of room-temperature mechanical properties and ignoring time dependent stress relaxation processes such as creep. In this work, the at-temperature properties of AuSn, and the major intermetallics of the Au-Sn system are analyzed for mechanical properties (elastic modulus, yield point, UTS and creep) and physical properties ( expansion coefficient, micro structure ). These results were integrated into an FE analysis to optimize the brazing process. Numerous experimental methods ( acoustic, dynamic mechanical analysis, uniaxial mechanical testing ) were used and cross correlated to obtain the mechanical properties, and the results will be reported.