The authors describe a multichip module (MCM) technology for making broadband digital switching modules. A copper/polyimide thin-film multilayer substrate is developed to achieve high-speed digital transmission. The substrate is formed on an aluminum nitride ceramic (AlN) wafer with good thermal characteristics. The meshed strip-line structure is used to control the characteristic impedance for 50- Omega signal lines, and the thin-film termination resistors are made of NiCr to prevent reflections. With this technology, the authors experimentally fabricated a broadband digital switching module, which is constructed from switching ICs in bare dies, clock distributing ICs in flat lead packages, and chip/micro-chip capacitors. In this module, differential digital transmission lines are adopted for high-speed signals to reduce the crosstalk noise effect. Heat generated from the module, which has a total of 25 W of power dissipation, is efficiently conducted through the AlN wafer. This module can operate many 2-Gbit/s high-speed channels. A novel multichip module technology for high-performance systems was successfully developed.
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