MTBF Estimate
Mean Time Between Failures (MTBF)
Mean time between failures (MTBF) is a methodology used to estimate the number of failures expected in the life of a repairable product. The analysis examines the rate of random failures, excluding systematic defects caused by faulty designs, software errors, manufacturing defects, or wear and tear at the end of product life.
This method takes into account a given environment during the calculations.
The MTBF figure can be of significant value to a potential customer at the time of a transaction. Without this data, the product could be rejected.
MeanTime To Failure (MTTF)
Mean Time to Failure is a reliability prediction method for nonrepairable parts. The average time to the first expected failure of a part is estimated using this calculation. MTTF is a statistic that estimates the average value over a long period of time across multiple units.
Mean Time To Repair (MTTR)
MTTR is the average time needed to fix a defective product by replacing a damaged part. Thus, the MTTR of a product could be considered as the average time required to evaluate a failure and then replace the corresponding defective components.
Prediction Methods
MILHDBK217, Electronic Equipment Reliability Prediction. This reliability prediction method is widely used in the military and commercial fields. This method of empirical forecasting is widely acknowledged worldwide.
Telcordia SR332, the Telcordia SR332 standard assumes a series model for electronic components addressing failure rates at both the infant mortality stage and the steady state stage with Methods I, II, and III.
Failure Rate (F.R.)
The failure rate is a function that describes the number of defects that can be expected over a given period. Failure rates are not constant throughout the life cycle of electronic equipment. This function is part of the MTBF analysis and follows a bathtub curve divided into three time periods:
Infant Mortality: F.R. is high but decreases rapidly.
The calculation methods assume that this period corresponds to the first year of operation.
Steadystate: Failures occur at a constant rate (steadystate failure rate).
MILHDBK 217F assumes that F.R. is always a constant. On the other hand, the
Telcordia SR332 standard provides that this is the period after the first year of
operation (8,760 to 10,000 hours).
Wearout: The failure rate increases rapidly. Wear and tear does not occur during the
lifespan of an electronic device, which is approximately 20 years. Telcordia SR332
does not take this period into account.
Factors impacting F.R.

Operational requirements

Electrical stress

Temperature

Environment

Quality of components
Essential data to evaluate the MTBF

List of parts (BOM)

Calculation method

Privileged environment

Temperature difference
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