High-Voltage Capacitor Failure on a Downhole Oilfield PCB

This article explains how the failure of a high-voltage capacitor led to the discovery of an unusual defect. Testing showed that the capacitor shorted due to silver migration, which investigators believe was facilitated by voids in the dielectric that had been present from the time of manufacture. Through some combination of time, electric potential, trapped humidity, and elevated operating temperature, plate material migrated into the voids, creating a short path that led to the failure. Using acoustic images as a guide, the failed capacitor was cross-sectioned, allowing investigators to examine the voids more closely and thereby confirm their theory.