Multi-chip modules: a comparative study-phase I: system design and substrate selection

Harris Corporation has undertaken a multichip module (MCM) project that will develop a four-channel digital RF receiver as a very dense, lightweight system. A single-channel system has been implemented with its supporting logic chips in a 6"×7" PCB (printed circuit board). The four-channel module was fabricated on a 2.5"×2.5" substrate that will be assembled in a 2.75"×2.75" metal package with 200 leads. The module contains a total of 41 chips, twelve being VLSI. To test currently available substrate technologies, the substrate was fabricated in two different varieties: a low-temperature cofired ceramic, the DuPont Green Tape, and a high-density copper/polyimide. Bonding to the top level of the system was done by both TAB (tape automated bonding) and gold wire bonding. An important feature of this MCM is that it exploits design-for-testability concepts which allow defective die or interconnects to be easily identified, thus facilitating module rework. This approach does not require boundary scan to be incorporated into chip design, or test registers to be added to the module