A novel methodology for vibration induced fatigue life assessment of BGA devices in avionics systems of satellite launch vehicles

Abstract

A new PCB strain-based methodology for BGA fatigue damage assessment, during system level vibration analysis, is established. The Stress-Life curve for solder joints (Sn37Pb), extracted by FE modelling from peer-reviewed data, is utilized as the damage thresholds instead of traditionally used empirical criteria. To eliminate the modelling effort and resource intensive computations associated with solder joint stress calculations, a correlation between the PCB strain and device solder joint stress is established. Harmonic vibration analysis of PCBs with 3 different sizes, 2 boundary conditions, and different device locations are utilized for this purpose. A novel device and PCB model simplification technique, which does not affect PCB strain results, is also proposed. The methodology is demonstrated for fatigue life assessment of BGA device in a launch vehicle avionics package, under random vibration environment. Subsequently, design improvement to meet the fatigue life requirement is also suggested. Fatigue life is calculated using three different stress cycles estimation models namely Dirlik, Single Moment, and Steinberg's 3-band method, and Single Moment method is found to be most appropriate.