Kumar Upadhyayula and Abhijit Dasgupta
CALCE Electronic Products and Systems Consortium
University of Maryland
College Park, MD 20742
This paper provides the first study where significant interactions between combined thermal cycling and vibration loads are experimentally observed to result in slower damage accumulation in solder joints as compared to damage accumulation due to vibration load alone. The reverse may occur for some other load conditions. The popular Palmgren-Miner's hypothesis that superposes damage due to each load in a linear fashion cannot explain the observed trend because interactions between applied loads are ignored in linear damage superposition scheme. Obtaining a meaningful acceleration transform (acceleration transform correlates the accelerated life test results to field life predictions) hinges upon being able to capture the interactive effects between applied loads in the failure models. The paper also outlines physics of failure (PoF) based modeling approaches that adequately quantify the complex interactions between temperature and vibration loads using an incremental damage superposition approach (IDSA). The first modeling approach (macroscale IDSA) is formulated at the macroscale without any attention to microstructural phenomena and phenomenologically captures the dominant failure drivers. The second modeling approach (microscale IDSA) is formulated at the microscale and incorporates the underlying physical mechanisms and microstructural parameters that drive the failure process. Both macroscale and microscale damage models are applied to predict the durability of surface mount interconnect architectures (84 pin plastic leaded chip carrier). The prediction trends are found to be in good agreement with the experimental results confirming that the dominant damage contributors have been successfully captured in the IDSA model. This study provides a systematic way of quantifying complex interactions between thermal cycling and vibration loads on durability of electronic assemblies. Further, by incorporating the influences of microstructure on damage predictions, this study has also provided a new modeling approach to extrapolate accelerated test results to field life conditions irrespective of their significantly different microstructural states.
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