Questions concerning the MTBF specification for aluminum electrolytic capacitors are a common request Digi-Key receives from our customers. In short, aluminum electrolytic capacitors are not rated in terms of MTBF. These capacitors contain multiple materials, so they are rated in hours of expected life. Under different conditions the expected life of the part changes. As one example of this, Digi-Key supplier United Chemi-Con has the following to say about aluminum electrolytic capacitor MTBF.
“For designing the device with aluminum electrolytic capacitors, a failure rate and useful life are necessary to be considered for their reliability. The failure rate of aluminum electrolytic capacitors is approximated by the bathtub curve shown in below figure.”
MTBF, MTTF and FIT Data - Support