CHOOSING THERMAL CYCLIC SCREENING REQUIREMENTS TO ACHIEVE DESIRED TEST EFFECTIVENESS

摘要

Thermal cycling is routinely used to screen spacecraft and launch vehicle electronic assemblies. The utility of thermal cycling in precipitating infancy failures and improving the reliability of electronic assemblies is broadly accepted. However, there is not a broad consensus on the number of thermal cycles and the temperature extremes required to adequately screen electronic assemblies. A larger number of cycles at a wide thermal range would tend to be more effective in detecting latent defects, but will incur a larger cost and may significantly reduce the remaining useful life of the unit. The relation between thermal cycling failure rate and number of thermal cycles in electronic assemblies is investigated. Test histories of hundreds of assemblies are studied to extract where test failures occurred in the thermal cycling program. Statistical methods to derive a relationship between failure rate and number of thermal cycles are examined. A methodology to calculate the test effectiveness achieved as a function of number of testing cycles at a specific thermal range is provided. This methodology is applied to failure data gathered from spacecraft test programs. A larger set of failure data is required to draw substantial conclusions from this study. Simulations indicate that useful results might be obtained if a somewhat larger data set was available.