When looking in the Relex PRISM Handbook and the five terms that make up a 217Plus/PRISM failure rate calculation. The failure rate is also expressed as the sum of Operating Portions and Non-operating Portions. The Non-operating Portion has only one term the one with Pi-DCN (DutyCycle for non-operation) as a factor. The other 4 terms are the Operating Functions. Is this distinction between Operating and Non-operating terms correct?

Of the 4 Operating terms, two do not have a DutyCycle factor: the Lambda-EOS and Lambda-SJ. L-EOS is for electrical overstress and L-SJ is for solder joint fatigue.

If I were to make 217Plus/PRISM Dormancy calculation, DutyCycle of zero, I would expect that the Lambda EOS term should go to zero since the equipment is off, no power. The L-SJ would be a factor if there is a temperature variation and cycling, otherwise for no change in temperature the term should also be zero. Would this interpretation of terms going to zero be correct?

Quanterion Solutions Incorporated Staff answered 16 years ago

When looking in the Relex PRISM Handbook and the five terms that make up a 217Plus/PRISM failure rate calculation. The failure rate is also expressed as the sum of Operating Portions and Non-operating Portions. The Non-operating Portion has only one term the one with Pi-DCN (DutyCycle for non-operation) as a factor. The other 4 terms are the Operating Functions. Is this distinction between Operating and Non-operating terms correct?

[COLOR=”Blue”]This interpretation is not entirely correct. The four terms other than the non-operating failure rate term are not specifically related to the operating failure rate.[/COLOR]

Of the 4 Operating terms, two do not have a DutyCycle factor: the Lambda-EOS and Lambda-SJ. L-EOS is for electrical overstress and L-SJ is for solder joint fatigue.

[COLOR=”Blue”]Pi-DC is a multiplying factor only for the operating failure rate term, since it is the only term that explicitly relates to the steady state operating periods of the device. For example, the temperature cycling term predicts the failure rate from the transition of temperature, and therefore the relevant accelerants of this term are the frequency and magnitude of the transitions. The amount of time the device dwells at each temperature is not relevant to this term. The same argument applies to the solder joint term, in which case failures due to solder joints are accelerated only by temperature transitions.[/COLOR]

If I were to make 217Plus/PRISM Dormancy calculation, DutyCycle of zero, I would expect that the Lambda EOS term should go to zero since the equipment is off, no power. The L-SJ would be a factor if there is a temperature variation and cycling, otherwise for no change in temperature the term should also be zero. Would this interpretation of terms going to zero be correct?

[COLOR=”Blue”]The lambda EOS term does not go to zero as the duty cycle goes to zero since the majority of EOS events are not a function of the device being operated, rather EOS transients are generally externally applied events. Therefore, this term related to