In exida’s Component Reliability Database (CRD), every component includes a Useful Life expressed in years and/or cycles.

Understanding Useful Life

This post, drawing from exida's whitepaper [1] on how environmental factors impact component reliability, shows how Useful Life, like failure rates, is affected by factors such as temperature and vibration. Useful Life is explained along with the need for this metric. This post also discusses how exida's CRD and OEMx tool help engineers use Useful Life data to improve product reliability. What is the Useful Life of a component?

In the aforementioned whitepaper [1], we looked at the environmental impact on failure rates and how this has been incorporated into exida’s FMEDAx tool. As mentioned in that whitepaper, the Useful Life is another important factor when considering the reliability of a component. Useful Life approximates the time period before a component’s failure rate begins to significantly increase. Failure rate numbers used for functional safety verification are no longer valid after the Useful Life period. This time period is distinguishable from the initial period of a component’s life where weak units from a production population fail early (“Infant Mortality”, Region A in Figure 1) and the end of a component’s life where the strength of the component declines and the failure rate increases significantly (“Wear-Out”, Region C in Figure 1).

What is the Useful Life metric used for?

Per IEC 61058, the “useful lifetime” must be made available, specifically in the Safety Manual of the product (IEC 61508-2, 7.4.9.4.f / 7.4.9.6). End-users / integrators can then use this information to plan restoration and replacement requirements for a safe system. Failing to account for Useful Life will compromise safety.

As indicated in the environmental impacts whitepaper, we carefully assess how environmental parameters affect a product’s failure rate in an FMEDA. Because FMEDA failure rates are only valid within a product’s Useful Life - which is just as dependent on environmental factors as the failure rate - defining Useful Life accurately is critical for a product and its components.

For some types of components, Useful Life is understood to the point that there are well-established formulae derived from knowledge of the component’s physical properties and test data. However, for many components published Useful Life is generic, offering no clear formulas for engineers to estimate it accurately for their unique application without considerable research.

How does exida calculate the Useful Life?

In exida’s Component Reliability Database (CRD), every component includes a Useful Life expressed in years and/or cycles. When conducting an FMEDA of a system or subsystem, the Useful Life of all components included in the analysis is compared, and the shortest is identified as the Useful Life of the device under analysis. Just like the FMEDA will reveal the component contributing the most dangerous failures to the design, it will also highlight the component with the shortest Useful Life. This allows the design engineers to identify potential weaknesses and subsequent opportunities for improvement of the design.

For example, aluminum electrolytic capacitors have limited lifespans due to well-documented failure modes (e.g., electrolyte drying up, leakage, increased ESR over time). Some sources, such as this paper published by Würth Elektronik [2], identify formulas for such components, utilizing the manufacturer-rated endurance of the capacitor at a specified voltage and specified temperature, as well as the application temperature (i.e., component ambient temperature within the application).

The following figure depicts an Electrolytic Aluminum Aqueous Capacitor from the CRD, used in a low ripple application rated for 10,000 hours at 105°C. The 16 years of Useful Life calculated is based on exida Industrial Profile 1, which assumes a climate-controlled environment (daily temperature swing of 5°C), and an average internal ambient temperature of 60°C.

Compare this to exida Industrial Profile 3, which assumes an average internal ambient temperature of 45°C and daily temperature swing of 25°C. The resulting Useful Life is 22 years.

Modification of the Options will also impact the Useful Life calculation. Note the following Figure, in which the electrolytic capacitor component in Profile 3 (Figure 3) has the Rated Temperature lowered to 85°C. This lowers the Useful Life to 6 years.

This data was recently used during a design analysis to identify the weakness of using electrolytic capacitors in a power supply circuit that might see high ripple current (and therefore experience higher internal product temperature). The original product life was estimated to be in excess of 20 years. After properly accounting for the application temperature the capacitor useful life was predicted to be 6 years, which would also make the product life six years. This was unacceptable to the manufacturer so additional analysis was done on the application environment. Namely, the manufacturer was able to provide test data showing a lower average internal ambient temperature than the assumed profile. exida was able to apply the lower temperature to the useful life calculation, ultimately resulting in an acceptable useful life (16 years).

Until recently, some components in the CRD (e.g., Capacitors) had options for characterizing the application, such as “General Purpose” and “Open Mode”, that would impact the Useful Life. However, the Useful Life was largely based on input from industry experts and generic component life data, and the parameters of the environmental profile were not adequately considered. With a strong background in analyzing and certifying products (representing over 400 billion unit operating hours), exida engineers have improved Useful Life calculations in the CRD through review of publications like the Würth Elektronik paper and in-depth discussions amongst subject matter experts. These significant updates are available for non-electrolytic and electrolytic (solid and non-solid) components in OEMx 2.5.5 and beyond.

For more information on this topic, see exida whitepaper on capacitor useful life. Additionally, be on the lookout for continued improvements to Useful Life in the exida CRD.

References

[1] Motto, Valerie. Environmental Impact on Failure Rates. exida, 2025. https://www.exida.com/resources/Whitepapers/environmental-impact-on-failure-rates

[2] Expected Lifetime Calculation of Electrolytic Capacitors. Würth Elektronik, 2023. https://www.we-online.com/components/media/o171047v410%20WE-eiSos_Tutorial_Expected_Lifetime_Capacitors.pdf