CALCE Electronic Products and Systems Consortium
IEEE Standard 1332-1998 [IEEE 1998] requires that, "The [equipment] supplier shall determine the customer's requirements and product needs," and that, "The [equipment] supplier, working with the customer, shall include the activities necessary to ensure that the customer's requirements and product needs are fully understood and defined, so that a comprehensive design specification can be generated." Among the design specifications, thermal environment is an input parameter for a variety of design, manufacturing and test functions.
The thermal environment influences parts selection, reliability assessments, manufacturing processes, and qualification procedures, and indirectly influences system architecture, maintenance plans, warranties and life cycle costs. Traditionally, the reduction in operating temperature was taken as the primary means to improve reliability and performance. An indication of the importance attached to temperature reduction is demonstrated by the willingness to accept heavy complex avionics cooling systems by the aircraft industry. However, studies of the various thermally influenced reliability failure mechanisms have suggested that steady state temperature itself may not be as important as the spatial and temporal gradients of temperature [Lall, Pecht, and Hakim 1997]. Thus, environmental specifications should include thermal parameters such as temperature cycling, ramp rates and thermal gradients.
Thermal analysis of electronic products and systems during design is an iterative process. The limitations of the thermal analysis process must be understood for its effective utilization as a design tool. It is most important to understand the influence and sensitivity of the final temperature results on actual performance and reliability of the parts and systems. If one attempts to identify the effects of this variation without considering the failure mechanism and/or performance metric, the results will likely be erroneous.
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