System-Level Reliability Qualification of Complex Electronic Systems

Qualifying functional complex electronic systems and products for reliable performance under a given life cycle history is a difficult task, because of the complex competing aggregation of potential failure sites and failure modes. The current approach, driven by industry specifications and standards, is to conduct standardized tests that are intended to represent a compressed version of representative life cycles. The problem is that there is no clear articulation of what failure mechanisms are being targeted. Consequently, it is not clear what the acceleration factor is likely to be. Especially, as technologies and materials undergo changes, new failure mechanisms may emerge and acceleration factors for old obsolete test conditions may no longer be adequate for expected life cycle conditions. In this study, a systematic and system level approach is used to qualify the interconnects of a new electronic system by using a rapid-assessment method based on the physics of failure approach. The rapid-assessment approach is based on a combination of experimentation and simulation which is focused on identifying and ranking potential modes and mechanisms. The system analyzed in this case is an electronic control box used on a rotating non-stationary platform for a medical instrument. The box contains three PWBs stacked on top of each other and secured using stand-off fasteners and rotates in a gantry up to 220rpm. Dynamic mode shapes are found using finite element simulation, which informs ideal places for instrumentation during experiments to measure the life cycle stress conditions. Quasi-static bending, vibration, and thermal life-cycle conditions are collected with on-board strain gages, accelerometers and thermocouples. The results of these measurements are used as inputs for rapid-assessment simulations, to directly estimate durability and life. All PWAs are found to meet durability goals, although the smallest PWA on top of the stack is found to have the smallest durability margins, and further study is recommended. Tailored accelerated stress testing is recommended in future to verify the predicted durability margins for the entire product.