A Failure Analysis on Leakage of Ceramic Capacitor

Failure analysis is a comprehensive process which needs to apply kinds of physical and chemistry methods to find out the mechanism. You must learn as more background information as you can, only then could you choose the applicable methods to study the failure sample avoiding disturbance aroused by analysis methods. In this paper, a print circuit board assembly of TV sets which were exported to South America will be analyzed. There was a leakage found on the ceramic capacitor through a series of tests. When the failed ceramic capacitor was soldered once again by manual welding, the leakage of electricity became disappeared. Given this novel phenomena, the failed ceramic capacitor should be dismantled through mechanical method instead of using heat gun, because the phenomena might be affected by the heat. The electrical measurement result showed that isolated ceramic capacitor still manifest leakage. Then Energy Disperse Spectroscope analysis was applied to identify if there was migration or conductive contamination on the surface between two electrodes of the ceramic capacitor, no abnormity was found. After ultrasonic cleaning was performed to clear the surface trash of the capacitor, the electrical test result showed the ceramic capacitor still failed. But the ceramic capacitor became normal when it experienced bake. The all test results above led to that there might be defect in the ceramic capacitor. So the further analysis used the destructive method-cross section - to investigate the defects in the ceramic capacitor. Finally, the defects were found through abrasion of cross section, there was dielectric void and electrode tumor between electrode layers in the ceramic capacitor which was the essential reason to cause leakage, especially when the ceramic capacitor worked under hot and humid environment just as the climate of South America. The voids and electrode tumors dramatically decrease the insulation space between contiguous electrode layers. When the ceramic capacitor worked in heat and moist environment, water vapor could be trapped in the voids, and impurity ions could migrate by water vapor under bias voltage which gave rise to leakage. Put the baked capacitor into temperature/humidity test chamber, then performance electrical test on the capacitor after 96 hours. The result of verification test showed the leakage phenomena reappeared which proved the conclusion above was valid.