ANALYSIS OF RELIABILITY AND CONDUCTION MECHANISMS IN EMBEDDED PLANAR CAPACITORS
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An embedded planar capacitor is a thin laminate embedded in a multilayered printed wiring board (PWB) that functions both as a power-ground plane and as a parallel plate capacitor. The capacitor laminate consists of a dielectric material (epoxy-BaTiO3 composite dielectric is widely used) sandwiched between two Cu layers. These capacitors have gained importance with an increase in the operating frequency and a decrease in the supply voltage in electronic circuits since it can lead to PWB miniaturization. Further, the use of embedded planar capacitor leads to better electrical performance of the PWB. Although embedded planar capacitors have various advantages there are some issues such as lack of reliability information and a high leakage current in the epoxy-BaTiO3 composite dielectric. This dissertation aims in investigating these issues that needs to be investigated for wide scale commercialization of these capacitors.
The reliability of embedded planar capacitors is critical since these capacitors are not reworkable and its failure can lead to PWB failure. In this work the reliability of an embedded planar capacitor (with epoxy-BaTiO3 composite dielectric) is investigated under environmental stress conditions in the presence of an applied bias. Temperature-humidity-bias (THB) tests and highly accelerated life test (HALT) was performed at multiple stress levels to investigate the reliability under these conditions. The failure modes and mechanisms during THB and HALT are investigated. Further, during HALT the life time is also modeled using the Prokopowicz model and regression of the in-situ capacitor data.
The loading of BaTiO3 in the epoxy-BaTiO3 composite dielectric should be as high as possible (until the theoretical maximum packing density is achieved) to maximize the effective dielectric constant of the composite. But as the loading of BaTiO3 in the composite dielectric increases, the undesirable leakage current also increases. The mechanism of current conduction in this composite dielectric is investigated in this work. The effect of various factors such as BaTiO3 loading, BaTiO3 particle diameter, temperature, and voltage on the resulting leakage current has been modeled. Measurements of leakage current were performed on embedded capacitors with varying BaTiO3 loading and varying particle diameters over a range of temperature and voltage. The consistence of the leakage current data with standard conduction models is compared to investigate the conduction mechanism.