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Each new generation of avionics is driven by the same requirements provide a tenfold improvement in performance density, halve the cost, and double the reliability. In the past, avionics designers have been able to meet these requirements through advances in device technology and faster clocking. Further advances in performance density will require accompanying improvements in interconnection, packaging, and thermal management. Multichip modules, 3-D interconnections, conformal packaging, and liquid cooling could provide these needed improvements, but their reliability and compatibility with other avionics components is largely unknown. AT&T has initiated a program to prototype and evaluate these and other promising interconnection and packaging approaches for avionics applications. This paper describes some of the prototypes and presents some preliminary test results. of the more promising techniques for implementing these THE INTERCONNECTION PROBLEM Every ten years avionics engineers are tasked to build the "next-generation'' processing system. The requirements are always the same increase the performance density by tenfold, halve the cost, and double the reliability. In the past, this challenge has been met primarily through finer device lithography, faster intrinsic speeds, fewer components, and lower switching/storage energies. While device technology is projected to continue its dramatic advancement, further improvements in performance density will require reductions in the communications between components. At high clock frequencies (>40 MHz), chipto-chip signal propagation can require a significant fraction of a clock cycle. If a communication cannot be completed within the allotted cycle time, wait states must be introduced and system performance drops. This problem occurs at every interconnection level in the system, since faster devices and modules require faster communications at the board, backplane, and system level. There are thrce basic approaches to reducing communication delays: (1) move the devices closer together, (2) eliminate a level of packaging, and (3) improve the dielectric constant and signal integrity of the interconnection media. Multichip modules and 3-D interconnections are two "This paper is a declared work of the U.S. Government and is not subject to copyright protection in the United States" 421 approaches, but they introduce unique thermal management and protective packaging problems. The heat dissipated by a device increases with clock frequency, while moving devices closer further increases the heat density. When a level of packaging is eliminated, a level of protection is also eliminated and must be provided for at the next packaging level. Techniques such as liquid cooling and conformal encapsulation are possible solutions to these problems, provided they are compatible with other components and their processes and do not introduce any new problems of their own. AT&T Federal Systems has formed a small group to investigate these new technologies and determine their reliability and compatibility for use in advanced avionics systems. The following sections outline some of efforts and test results. |
