Ceramic capacitor insulation resistance failures accelerated by low voltage

Ceramic capacitors failed insulation resistance at less than 1/10 th their rated voltage despite the fact that they had been subjected to "voltage conditioning" at twice the rated voltage for 100 h. Many failures recovered as the voltage was increased. Using special sectioning procedures, the failures were isolated to single ceramic plates; however, extensive analysis did not initially determine the cause of failure. Finally, the ceramic was ground from all four sides and an unexpected discovery was made: the plates could be peeled apart intact. This allowed dissection of the capacitor structure, completely exposing the shorted plates. Using the absorbed-current mode of the SEM, it was determined that the only leakage was through very small voids in the ceramic. Peeling the plates apart also provided the ability to see delaminations and other defects in three dimensions and to examine the electrodes and plate surfaces in minute detail. Based on this and related experiences, it is concluded that ceramic capacitors that fail at low voltage and recover or partially recover as the voltage is increased are fairly prevalent. Screening results indicate the need for special screening for ceramic capacitors intended for low-voltage applications.