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PCBA Hardware Component different failure types - How to rate detection?


Starting to get Involved
Hello all,

Let's say that a PCBA uses a specific Resistor in it.

We identified in the FMEA two different failure modes:

- Resistance too low: This is a design issue in which we wrongly calculate the Resistance value of the component
- Short circuit due to silver migration: This is a common failure of a component. Note that in this case the Resistance value was perfectly designed, but the component failed regardless of the defined initial value.

In the first case, Resistance too low, I can rate a low Occurrence value on the fact that we have used this PCBA design multiple times, that we have successfully dimensioned this specific Resistor several times, that we have good calculation sheet to determine its value.
I can also rate a low Detection value based on the fact that we have standard and effective testing method to verify whether the right Resistance value was selected.

In the second case, however, I can rate the occurrence value based on the standard FIT value given for this component based on its environment.

The question is: how do I rate detection for this second form of failure mode?

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