With the anticipated growth in the electric vehicle market, advances in power electronics used in electric drivetrain, battery charging systems, etc. are delivering higher power densities, and with them, associated thermal challenges for operation in relatively closed vehicular systems. As such, the framework of reliability qualifications of electronic devices need to be reconsidered as system needs have moved beyond typical consumer electronic device needs, such as laptops or entertainment devices, where safe operation and longevity is essential to electric vehicle market viability. This work provides an overview of the reliability challenges associated with the operating environments and characteristics of power inverters in electric vehicles, particularly with respect to thermomechanical stresses. When considering the acceleration models presumed by the AEC Q100 specification for automotive electronics qualification, it is shown that inconsistencies in acceleration model form result in lack of clarity of how grades are chosen for different vehicle applications. Furthermore, the differences in vehicle drive cycles among user types show that service vehicles may have the most challenge to reliable operation, particularly in cold weather climates.
As an alternative metric for determining reliability in cyclic stresses, a novel test methodology for correlating solder fatigue life (and other thermomechanical failure modes) is proposed. The mechanical test for electronic packages is capable to disentangle the effects of temperature and design from the thermal cycling reliability such that the fundamental physics of failure can be extracted in a systematic fashion, and thereby develop better physics-based reliability acceleration models. Moreover, this novel approach enables the determination of independent stress to failure metrics that can translate risk across design and operating conditions for different system layouts without the need for multiple qualification tests.