Design and fabrication of an underwater digital signal processor multichip module on low temperature cofired ceramic

Abstract

An Underwater Digital Signal Processor (UDSP) multichip module (MCM) was designed and fabricated according to specifications outlined by the Naval Surface Warfare Center (NSWC), Dahlgren Division. Specifications indicated that low temperature cofired ceramic (L TCC) technology be used to fabricate the MCM with surface dimensions of 2"x2". The top surface of the module was to be designed to enclose mounted components and bare dice, and the bottom surface was to be equipped with a 144 pin grid array (PGA). The LTCC technology selected for this application incorporated DuPont's 951 Green Tape™ and compatible materials and pastes. A mixed metal system using inner silver system and outer surface gold system was used. Harris Corporation's FINESSE MCMTM, a computer-aided design (CAD) tool, was used to design the surface components and produce the circuit layout. FREESTYLE MCM™, an autorouter, was used to accomplish the routing of the signal layers. The design information provided by FINESSE MCM™ and FREESTYLE MCM™ was utilized to produce the artwork necessary for fabrication. Fabrication of the module was accomplished in part using thick film processes to produce the conducting areas on each layer. The layers were stacked in a press, laminated, and fired. Conducting areas were screen printed on the top surface of the module for wire bonding and on the bottom surface of the module for pin attachment.

The main objectives of this thesis work were to convert silicon UDSP MCM to ceramic using LTCC, learn a new tool in CAD design that incorporates an autorouter, apply the tool to design a MCM-C module, and to develop criteria to evaluate the MCM. Future research work includes conducting line continuity testing, materials evaluation to determine reactions at interfaces and via filling, and resistance and electrical crosstalk measurements on the module.