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The superposition of thermal cycling and vibration loading has been experimentally observed to slow down fatigue damage accumulation rates in solder joints as compared to damage accumulation due to vibration load alone. The reverse may occur for some other load combinations. The popular Palmgren-Miner's hypothesis, which linearly superposes the separate damage caused by each load, is not suitable for explaining the observed trend because interactions between the thermal and vibration loads are ignored in linear damage superposition schemes. Obtaining a meaningful acceleration transform (acceleration transform correlates the accelerated life test results to field life expectations) therefore hinges on the ability to capture the interactive effects between applied loads in the failure models. A modeling approach based on physics of failure (PoF) is presented that adequately quantifies 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 it 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 a selected surface mount interconnect architecture (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 durabilit y of electronic assemblies. Furthermore, by incorporating the influences of microstructure on damage predictions, this study has also provided a new modeling approach to explicitly account for different microstructural states when extrapolating accelerated test results to field life conditions.
Combined Temperature and Vibration Accelerated Life Tests
The Macroscopic Incremental Damage Superposition Approach Macro-IDSA)
The Micromechanistic Incremental Damage Superposition Approach (Micro-IDSA)