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Design Considerations for Reliable High Temperature Performance of Wet Electrolytic Tantalum Capacitors
Keywords: tantalum, capacitor , reliability
Wet electrolytic tantalum (Ta) capacitors have historically been utilized in a variety of applications with harsh ambient conditions. Thermal, mechanical and electrical stresses, though, pose significant challenges to reliable performance of these capacitors in such environments. A major hurdle to overcome due to thermal stress is internal pressure of the capacitor. Despite being favored for high electrical conductivity, aqueous electrolytes are burdened by their inherently high vapor pressures at elevated temperature. Thermal stress also fatigues materials over time, potentially disrupting the mechanical integrity of the capacitors. Due to the sheer mass of one vital component, the Ta anode, mechanical stresses, resulting from shock and vibration for example, can jeopardize the internal mechanical integrity of the capacitors. The density of Ta cannot be avoided, as Ta is specifically selected for the dielectric properties of its oxide. During operation, as the capacitor is not ideal, some electrical current flows through the capacitor. This current, in aqueous electrolyte, can generate hydrogen gas within the capacitor, further exacerbating the internal pressure issue and potentially embrittling Ta components, including the Ta case. So, one option is to throw our hands up in exasperation, and curse the gods for these unyielding physical and chemical properties that seemingly thwart high temperature operation of wet Ta capacitors at every turn. A better option, though, is to thoroughly understand each obstacle, as well as their interactions, and address them accordingly. This paper will elaborate on these impediments; it will also present results of high temperature wet Ta capacitors, including initial results of 230C testing, manufactured with proper attention to these concerns.
Jeremy Ladd,
Evans Capacitor Company
East Providence, RI
USA


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