The Bathtub Curve & the Impact of Age on Electronics
- Nexeya Canada
- Mar 17, 2021
- 3 min read
Electronic component and circuit failures follow a trend, commonly referred to the bathtub curve. Divided into three sections the bathtub curb describes the hazard function and how failures are experienced;
the first part is a decreasing failure rate, known as early failures (infant mortality),
the second phase is a constant failure rate, known as random failures,
the third part is an increasing failure rate, known as wear-out failures.
Failure rates tend to be higher at the offset but decrease rapidly as defective components are identified and repaired or replaced. These early failures are typically the result of production / manufacturing defects (out of spec), handling, installation, perhaps more seriously design or component selection. The vast majority of these defects are found and addressed during the production process and final acceptance testing of the manufacturing cycle.
Once the initial phase ‘shake out’ passes, the failure rate is typically low and constant as modern components are extremely robust and reliable.
In the later part of the product life the failure rate increases, as age and wear begin to take a significant toll on component performance and reliability. In this phase of the life cycle an increased failure rate may be attributed to latent defects. Latent defects do not impact the product functionality however they are a permanent defect to the component and a catastrophic failure can occur (unexpectedly) at any time. An example of latent defect is components that have been subjected to an ESD event. The component may continue to function however the component is compromised.
Another example of an input that contributes to the failure of electronics is environmental strain; it can significantly reduce an electronic lifespan. As much as extreme temperatures impact component reliability, temperature fluctuations have a significant negative impact on product functionality. The impact is caused primarily due to the expansion and contraction of the printed circuit board under the temperature cycling.
Hand in hand with the impact of temperature is the influence of moisture, which can cause rust, oxidation, and corrosion. These impacts contribute to intermittent issues, until permanent failures result.
Temperature and moisture are, to some degree, controlled by fans, keeping air circuiting through a system helps keep temperature in the appropriate range. The challenge with fans is that as much as they circulate fresher air, they also can introduce dust and debris. This dust and debris can build up on the electronic components causing overheating and other failures. Filter management is key to ensure fans support reliability and not introduce other failures.
The common thread of the impact of these inputs is the age of the components.
Age has a detrimental impact on the functionality of electronic components; time, functional cycling, temperature cycling all have an impact on reliability. Though uptime and reliability are critical in electronic products, failures do occur and it is not always easy, or simple, to trace the exact cause of an electronic component failure.
The good news is that when a defective component is found it can be replaced at a fraction of the price of a newly manufactured printed circuit board.
Though we benefit greatly from the ability to repair products that are in the second phase of the bathtub curve, when the components begin to enter phase three of their life cycle repairing components can quickly become an expensive and cyclical exercise.
It is important to remember that when components on a PCB are replaced, due to failure, the other (working components) still have the cumulative impact of functional cycling, thermal stressing, electrical overstress, the impact of electrostatic discharge and electro-magnetic interference. In essence, the latent defects we talked about earlier are lying under the surface of these ‘functioning’ components, waiting to appear.
As the product enters the third phase of the bathtub curve you may find yourself constantly experiencing more frequent failures, intermittent events and more frequent downtime.
The solution to phase three type failures is replacement of the aging product with a new one, a product that has not experienced functional and thermal cycling, EOS, ESD or EMI, and their cumulative effects.