Characterization and reliability of electrolytic capacitors exposed to halogenated solvents

To determine the effect of exposure to halogenated solvents on electrolytic-capacitor lifetime, populations of these capacitors were exposed to accelerated testing. It is shown that halogenated solvents cause electrolytic capacitors to fail open at the anode. The electrolytic corrosion, which dissolves the passivating oxide layer on the anodically biased aluminum and exposes a clean aluminum surface, is the rate limiting step in the failures. Halogenated solvents then readily react with the aluminum surface and erode the electrode until the solvent is consumed. The increase in pressure inside the capacitor can cause the capacitor to vent, further accelerating failure. Accelerated life testing of one of the capacitor types considered suggests that it may fail at normal operating conditions in 2-3 years. Monitoring of capacitor characteristics during the accelerated life test shows that changes in these characteristic parameters cannot be used to predict failure.< >