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ANSI/VITA 51.1: A Standard for Adjusting MIL-HDBK-217F Reliability Predictions
Reliability prediction is a method of estimating the probability of failure and the mean time between failures (MTBF) of a system or a component based on various factors, such as environmental conditions, stress levels, quality levels, and part characteristics. Reliability prediction can be used to compare different design alternatives, identify weak points, allocate reliability goals, and assess compliance with reliability requirements.
One of the most widely used reliability prediction models is MIL-HDBK-217F Notice 2, which was developed by the US Department of Defense in 1995. MIL-HDBK-217F provides failure rate models for various types of electronic components, such as microcircuits, discrete semiconductors, passives, connectors, soldered assemblies, electro-optical/mechanical devices, and others. However, MIL-HDBK-217F has some limitations and drawbacks, such as being outdated, overly conservative, inconsistent, and not applicable to some modern technologies.
To address these issues, ANSI/VITA 51.1 was developed by the VITA Standards Organization (VSO) in 2008 and reaffirmed in 2013. ANSI/VITA 51.1 is a subsidiary specification that provides standard defaults and methods to adjust the models in MIL-HDBK-217F Notice 2. ANSI/VITA 51.1 is not a revision of MIL-HDBK-217F Notice 2 but a standardization of the inputs to the MIL-HDBK-217F Notice 2 calculations to give more consistent and realistic results.
ansi vita 51 1 pdf reliability prediction pdf
ANSI/VITA 51.1 covers the following aspects of reliability prediction:
Quality factor: ANSI/VITA 51.1 defines a quality factor (Q) for each component type based on its qualification level and screening level. The quality factor is used to adjust the base failure rate of the component according to its quality level.
Environment factor: ANSI/VITA 51.1 provides a table of environment factors (E) for each component type based on its application environment. The environment factor is used to adjust the base failure rate of the component according to its operating environment.
Temperature factor: ANSI/VITA 51.1 provides a formula for calculating the temperature factor (T) for each component type based on its junction temperature and activation energy. The temperature factor is used to adjust the base failure rate of the component according to its temperature stress.
Stress factor: ANSI/VITA 51.1 provides a formula for calculating the stress factor (S) for each component type based on its applied voltage or current and rated voltage or current. The stress factor is used to adjust the base failure rate of the component according to its electrical stress.
Learning factor: ANSI/VITA 51.1 provides a formula for calculating the learning factor (L) for each component type based on its years in production and learning rate. The learning factor is used to adjust the base failure rate of the component according to its maturity level.
Application factor: ANSI/VITA 51.1 provides a table of application factors (A) for each component type based on its application category. The application factor is used to adjust the base failure rate of the component according to its functional complexity.
The adjusted failure rate (Î) of a component is calculated by multiplying the base failure rate (Îb) by all the adjustment factors (Q, E, T, S, L, A). The adjusted failure rate of a system is calculated by summing up the adjusted failure rates of all its components.
ANSI/VITA 51.1 can be downloaded as a PDF file from this link.[^1^] More information about reliability prediction methods and models can be found at this website.[^2^] 0efd9a6b88