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High Temperature - High Voltage Solid Electrolytic Capacitors
Keywords: tantalum, electrolytic, capacitor
High Temperature – High Voltage Solid Electrolytic Tantalum Capacitors Y. Freeman and P. Lessner KEMET Electronics Corporation yurifreeman@kemet.com Increasing operating temperatures of the electronic devices to 200oC and higher is desirable for applications such as downhole drilling, power electronics, automotive under the hood, military and avionic devices. The advantages of Tantalum (Ta) capacitors such as record high volumetric efficiency and capacitance stability vs. temperature and bias are significant for these applications. Solid Electrolytic Tantalum capacitors with Ta anode, Ta2O5 dielectric, and MnO2 cathode, which undergo multiple heat treatments at about 280oC during pyrolytic deposition of the manganese dioxide, are suitable for these high temperature applications. Recently KEMET Electronics released the first surface mount non-hermetic Solid Electrolytic Ta capacitors with operating temperatures up to 230oC. Manufacturing of these capacitors includes advanced flawless technology (F-Tech) and unique simulated breakdown screening (SBDS). F-Tech suppresses activated by temperature degradation processes in the Ta2O5 dielectric and adjacent areas of the anode and cathode, which cause the capacitance loss, increase in the dc leakage (DCL) and equivalent series resistance (ESR), and eventually failures of Ta capacitors. SBDS allows screening of potentially unreliable capacitors with hidden defects in the dielectric that are not detectable by the existing screening techniques based on the DCL testing. Additionally, the traditional silver paste in the external metallization layer was replaced with plated nickel with low diffusion activity, which eliminated failures related to the metal migration from the external metallization layer through the external cathode layer toward the dielectric on the anode surface. With all the improvements, the operating voltages at 230oC in Ta capacitors were limited to about 10 V. Higher voltage Ta capacitors made with this technology didn’t pass the Life test at 230oC. This paper is dedicated to the further increase in the operating voltages and temperatures in Solid Electrolytic Tantalum capacitors. Comparison of the dielectric properties in the lower voltage and higher voltage Ta capacitors was performed at different stages of their manufacturing and high temperature testing. The major difference between the lower voltage and higher voltage capacitors was found at the electrochemical nickel plating when reverse voltage (“-“ on Ta anode) was applied to the dielectric. The electrochemical nickel plating caused no damage to the thinner dielectrics in the lower voltage Ta capacitors. After the final aging at normal polarity (“+” on Ta anode), DCL in these capacitors was well below the limit and didn’t change significantly during the high temperature testing. In contrast to that, reverse voltage at electrochemical nickel-plating induced defects in the thicker dielectric of the higher voltage Ta capacitors. These defects caused either over-the-limit DCL at the final aging or DCL increase and failures at the early stages of the high temperature testing. The nature of the defects in the Ta2O5 dielectric induced by the reverse voltage, technological means to address the issue, and the results of the testing of the Solid Electrolytic Ta capacitors at record high temperatures and voltages will be presented in this paper.
Dr. Yuri Freeman, Fellow - Vice President
KEMET Electronics Corporation
Simpsonville, , South Carolina
USA


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