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 PCB bending causes
characteristic changes to the capacitor acoustic response, which can be
correlated with the resulted damage.