Abstract:
Several types of molded chip, CRW09-style tantalum capacitors were subjected to environmental stresses, including various humidity testing (20 °C/100% RH, 85 °C/85% RH, 121 °C/100% RH, and 135 °C/85% RH) and high temperature air and vacuum bakes. Variations of the AC (frequency dependencies of C and ESR) and DC (polarization currents) characteristics during these tests, as well as the kinetics of the parametric changes, have been analyzed. To estimate times of moisture ingression into the parts, coefficients of moisture diffusion and sorption have been measured for two types of epoxy molding compounds in temperature range from 30 °C to 170 °C. A sleeping cell model has been suggested to explain parametric changes in tantalum capacitors caused by environmental conditions. Moisture-related degradation of materials used in tantalum capacitors, failure mechanisms, and the effectiveness of the existing moisture resistance qualification testing are discussed.
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