Degradation Analysis of Several Performance Characteristics of Capacitors Under Elevated Thermal and Electrical Stress

Capacitors are electronic components with a wide field of technical applications. Their functionality has to be assured throughout the intended product lifetime. While in operation, the performance characteristics of capacitors slowly degrade. Ultimately, one or more of these characteristics reaches a threshold at which they are considered failed. Thus, modeling degradation is a key factor in assessing capacitor reliability. While most existing studies addressing capacitor degradation consider long runtimes and few stressors, this paper considers test performed under different temperature, humidity, voltage and excitation frequency (and thus, the number of voltage pulses). To reproduce realistic operation, repeated charging and discharging under PWM excitation is considered. Superimposed stress via controlled operation above the partial discharge inception voltage is included, as this is rarely explored. In the performed tests, the degradation of several performance characteristics was repeatedly measured. Based on the data, different degradation models are developed and compared. The influence of the considered stress factors on the degradation is estimated and statistically assessed. Unlike existing studies, where fixed performance thresholds are used to reduce the data to soft failure times, this paper focuses on the load dependency of the degradation path itself to allow variable failure thresholds.

Keywords: Metallized film capacitor, Degradation test, Accelerated degradation testing, Lifetime models, Design of experiments, Statistical evaluation.