Feature: Semiconductors
Know your safety application notes: failure rates
By Bryan Angelo Borres, Senior Product Applications Engineer, Analog Devices R
eliability predictions, typically in terms of failure in time (FIT), of a safety-related system’s components are crucial when complying with industrial functional safety standards, as they serve as inputs for the safety analysis that assesses whether the target safety
integrity level is achieved. Several databases exist to provide component failure rates that system integrators can use. This article discusses the three most common reliability prediction techniques for the failure rates of integrated circuits (ICs) and how Analog Devices’ safety application notes provide such failure rate information.
Why Are Reliability Predictions Needed? Failure rate or base failure rate refers to the number of failures per unit of time, typically in terms of failures in time (FITs) equivalent to one failure in a billion hours, which can be expected to occur for the product during its useful lifetime. Figure 1 shows the reliability bathtub curve model for failure of
electronic components that can be divided into three sections: early life or infant mortality failures, useful life or constant (random) failures, and wear-out failures. Tus, this article focuses on failure rates during the useful life of the component.
Safety Integrity Level Requirements with Respect to Probability of Dangerous Failure]
Note: Te PFD metric and PFH metric are equal when the demand
rate is once/year. Also, these failure rate requirements are for an entire safety function
and only a fraction of the above - for example, 1 per cent - will be available to an individual integrated circuit (IC).
How to Start Predicting Your System’s Reliability Several databases exist to provide failure rates that system integrators can use when designing a system. Among the available sources of failure rate data for electronic and non-electronic components are the IEC Technical Report 62380: 2004, Siemens Standard SN 29500, the ADI component mean time to fail (MTTF) data, field returns and expert judgment. Te ADI component MTTF data can be found at
analog.com under
the Reliability section. Under Reliability Data and Resources are the wafer fabrication data, assembly/package process data, Arrhenius/ FIT rate calculator, parts per million calculator, and the reliability handbook. Figure 2 shows what each resource subsection contains.
Figure 1: Reliability bathtub curve Knowing the failure rates of components in electronic systems is
essential in making reliability predictions to evaluate the overall system reliability. Reliability prediction involves specifying the reliability model, the failure modes to be assumed, the diagnostic intervals, and the diagnostic coverage. Tese predictions serve as the input to reliability modelling
techniques such as failure mode and effects analysis (FMEA), reliability block diagrams (RBDs), fault tree analysis (FTA), etc. In line with functional safety, the need to predict quantitative
reliability related to random hardware failures of a safety-related system against the safety integrity level (SIL) targets comes from the second part of the basic functional safety standard IEC 61508, which specifies the requirements for the hardware aspects of safety-related systems (SRS). Such SIL targets with respect to an SRS’s probability of dangerous failure are shown in Table 1.
28 June 2025
www.electronicsworld.co.uk
Figure 2: ADI reliability data and resources
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