-Case studies were conducted using a stochastic model to predict the life cycle cost impact associated with the application of Prognostic Health Management (PHM) to helicopter avionics. The life cycle costs of systems that assumed unscheduled maintenance and fixed-interval scheduled maintenance were compared to the costs of precursor-to-failure and life consumption monitoring PHM approaches, and the optimal safety margins and prognostic distances were determined.

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In this paper, the vibration durability of SnAgCu (SAC) solders is compared to that of SnPb solder, using selected surface mount technology (SMT) interconnects. A time-domain approach, reported in the literature [1], was adopted for this study. Vibration durability tests under random excitation (between 10 Hz & 500 Hz) were conducted for both SAC and SnPb SMT boards. The test assembly consists of daisy-chained components, to facilitate real-time failure monitoring. Step-stress tests were conducted by increasing the RMS excitation levels from 7G to 14G in out of plane direction. The test was continued until most of the components on the board failed. In general, the SAC solders were found to have lower fatigue durability than the SnPb solder, under the vibration excitation levels applied in this study. This result is consistent with results in the literature from mechanical cycling studies, repetitive mechanical shock studies [2] and vibration studies [3] [4]. Destructive failure analysis (cross-sectioning, polishing and microscopy) was used to confirm that the failure was by solder fatigue. Durability model constants were estimated for a generalized Coffin-Manson strain-life fatigue model [5], for both SnPb and SAC solders