I have been asked to investigate two failures of 10u 25v  solid tantalum capacitors.

They are rectangular plastic/resin encapsulated, sintered tantalum/ manganese
dioxide/ graphite-silver types.
These items are "cremated" beyond investigation!

  I am lead to believe (hmm!) all correct operating conditions have been met/not
exceeded i.e. excessive voltage, ripple and reverse voltage.
The capacitors  have seen service for at least 5 years in a very humid environment.
I am not aware if they are from the same batch. One was fitted across a +15v rail
in one unit and the other was fitted across a -15 rail in another unit.

Question? Does anyone know of an ageing condition, or what the effects of humidity
are that can lead to failure of these capacitors?

Alan Peters
Failure Analysis Engineer
Materials & Components Labs

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