Acoustic Phenomena in Damaged Ceramic Capacitors

Multilayer ceramic capacitors are prone to mechanical defects and damage because of the fragility of the ceramic dielectric. Because these faults are often not recognized by visual or electrical inspection, a nondestructive fast way of detecting these defects would be very useful. Ceramic capacitors are known to generate acoustic emissions, caused by mechanical vibration of the capacitor body. Physical defects alter the mechanical properties of the capacitor, which, in turn, affect the acoustic signature of the capacitor. In this paper, acoustic information is acquired directly from both pristine and damaged capacitors. An experiment was conducted where capacitors were driven with a voltage chirp over a wide range of frequencies, and subsequent acoustic emissions were measured with a piezoelectric point contact sensor. Test boards were bent to cause flex cracks to the soldered capacitors, which were measured acoustically before and after bending. A comparison of these measurements showed that printed circuit board bending causes characteristic changes to the capacitor acoustic response, which can be correlated with the resulted damage.