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Are we over designing for solder joint reliability? Field vs. accelerated conditions, realistic vs. specified requirements

The recent trend towards miniaturization is requiring engineers to look for packages which are near chip size and have finer pitch I/Os with small solder joints. Although the reliability of solder joints may not meet the field life requirements in some cases the engineer may have to select a package that is not optimum for electrical and thermal performance, may not meet size and density requirements or does not meet price targets. Faced with such a situation, an engineer is forced to ask whether the reliability requirements are realistic and if the system is being over designed to meet those requirements? This paper seeks to answer these questions. An industry survey of reliability requirements for various applications is presented, showing inconsistencies within industry groups. Various thermal cycle field conditions are discussed and a validated life prediction approach is used to determine the acceleration factors from field to accelerated test conditions. A comparison is made between realistic and specified reliability requirements for various applications to determine if the systems are being over designed. Acceleration factors for different test conditions are also presented to help sort out the published data on solder joint reliability.