Failure Mechanisms in Embedded Planar Capacitors during High Temperature Operating Life (HTOL) Testing

High temperature operating life (HTOL) testing was performed on embedded planar capacitors (with epoxyBaTiO3 composite dielectric) by subjecting these devices to highly accelerated temperature and voltage aging conditions. The objective of HTOL testing was to precipitate avalanche breakdown failures as a result of defects in the composite dielectric. These defects include porosity, voids, and agglomeration of BaTiO3 in the epoxy matrix and are introduced during the manufacturing process. Since these tests were conducted under highly accelerated conditions, the failure mechanisms observed may not occur under the normal operating conditions of this device. However, the results of HTOL can be used in qualification of embedded planar capacitors and to further improve manufacturing processes to reduce the number of these defects. During HTOL testing, the failure modes observed were a gradual decrease in the capacitance and a sharp decrease in the value of insulation resistance. The sharp decrease in the value of insulation resistance after some time was expected to be governed by the avalanche breakdown (ABD) of the dielectric. The ABD failures were modeled using the Prokopowicz model. The effect of the area of the capacitor and dielectric thickness on the time-to-failure as a result of ABD was also investigated. A novel failure analysis technique was developed that can be used to locate the failure site of avalanche breakdown and understand the failure mechanism in this material. This technique can also be applied to some other dielectric materials as well. It was also observed that before ABD failures the dielectric material started to show signs of degradation. These degradations were detectable using AC measurements (measurement of dissipation factor) but were not observed in DC measurements (measurement of insulation resistance).