As the electronics industry strives to higher frequency processing in integrated circuits and denser packing arrangements on printed circuit boards, lower Equivalent Series Resistance (ESR) is crucial. The carbon and silver layers in polymer tantalum capacitors have an integral role in achieving low ESR. As a consequence, greater emphasis on the raw material selection used in the formulation of these is required. With the carbon layer a thin and consistent thickness is essential, as the current path is through the z-axis. The silver layer must exhibit excellent electrical conductivity and good interfacial wetting as well as good corner and edge coverage. It is important to ensure that good adhesion between the layers is achieved and that delamination does not occur during processing. This paper outlines some of the important characteristics of the carbon and silver inks necessary to achieve low ESR with polymer tantalum capacitors. The importance of polymer electrolyte compatibility with the carbon and silver layers will be discussed. Resin selection in the carbon is critical to the optimisation of the ESR and the ESR shift of the tantalum capacitor when exposed to high temperatures during fabrication and surface mounting. Experimental data will be presented to show how the carbon to resin ratio and total solids content in the carbon ink will affect ESR. In addition, the relationship between the particle size distribution and morphology of the silver powder starting material, and the resultant silver flake will be addressed.
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