Printed Wiring Assemblies (PWAs)
Staking failure on tantalum capacitor

This solid tantalum capacitor was staked to its circuit board, but after numerous flight missions it broke loose from its staking, the lead suffered a fatigue fracture, the capacitor failed, and the loose part did other damage to the board assembly.

There are many possible failure mechanisms that could have cause this type of failure. The amount of staking material could have been insufficient for the size of the part. With a sleeved part of this type staking material is required on the ends of the part in addition to the sides. The part or board may not have been properly cleaned prior to the application of the staking material and or the staking material may not have been mixed properly

Reference :
NASA-STD-8739.1, Requirements for Staking and Conformal Coating