Mohammed A. Alam, Michael H. Azarian, and Michael G. Pecht
Center for Advanced Life Cycle Engineering (CALCE), University of Maryland, College Park, MD 20742, USA
Embedded planar capacitors are thin laminates embedded inside a multilayered printed wiring board (PWB) that serve both as a power/ground plane and as a parallel plate capacitor. These capacitors are typically used in decoupling operations and are found to reduce the number of surface mount capacitors enabling PWB miniaturization. The physical dimensions of the embedded planar capacitor such as area and dielectric thickness depend on the requirements of a particular application. In this paper the effect of these physical dimensions on the reliability of embedded planar capacitors is investigated during highly accelerated life testing (HALT).
HALT (at 125oC and 285 V) was conducted on embedded planar capacitors with two different areas and two different dielectric thicknesses. The dielectric was a nanocomposite of epoxy and barium titanate (BaTiO3), which is widely used as a dielectric material for embedded capacitors. Under these conditions, the failure modes observed were a gradual decrease in capacitance and a sudden increase in the value of leakage current. The decrease in capacitance with time followed the traditional aging curve of pure BaTiO3. The sudden increase in the leakage current implied avalanche breakdown and was expected due to defects in the dielectric. The effect of area and dielectric thickness on time-to-failure as a result of the above failure modes is presented in this paper. Finally, recommendations are provided for selecting the physical dimensions of embedded planar capacitors that can be helpful to designers of circuits using these capacitors.
Keywords : Embedded planar capacitors, Polymer-ceramic composites, Reliability, Highly accelerated life test
Complete article available to CALCE consortium members.