Failure analysis in capacitors

Multilayer capacitors are made by a complex process that allows local inhomogeneities to occur. Such localized deviations from the norm are potential failure sites. Measurements of capacitance and loss tangent at fixed frequencies do not show any differences that would suggest the presence of structural variations. One measurement that does show pronounced unit-to-unit differences is the capacitance vs. frequency plot in the frequency region below and above self-resonance. Unit-to-unit variations were found when dc bias voltages were applied. In particular, secondary resonances, indicative of the presence of structural inhomogeneities were found to occur at frequencies near to the self-resonance frequency.