A disastrous case study
The morning of January 28th, 1986 was especially cold as the Challenger space shuttle began its launch. It was cold enough to fatally increase the failure risk of the fateful O-rings that were used in critical joints of the solid rocket motor.
While that morning had slowly thawed to about -1°C, most of the 24 previous launches had been between 18 and 25°C with the lowest temperature launch being at 12°C. Without previous experience to rely on, the decision to launch hinged on the reliability analysis of the O rings, which had been incorrectly assumed for such low temperatures. The pre-launch analysis was based on their available reliability data which was later found to be inadequate and erroneous. Correct reliability testing would later show a strong correlation between low temperature and O-ring failure.
The consequences of neglecting thorough reliability testing were disastrous that morning, resulting in a 32-month hiatus of the space program and the Roger’s commission to investigate the accident.
Introduction to Reliability
Although not all applications of Photonic Integrated Chips (PICs) and the devices that incorporate them are a matter of international news, thorough knowledge of their reliability remains important. In-field failures of PICs still regularly result in warranty costs, loss of brand reputation, liability issues, and safety issues.
To avoid these situations, it is crucial for the chips to maintain a standard level of functionality for their entire intended deployment within their intended-use environment and operation.
Reliability Testing
Eventually, all devices fail when they reach the limits of their basic durability. This type of failure is known as wear-out failure. The durability limitations of the device are based on failure mechanisms: changes at an atomic and molecular level that result in a deterioration of a device’s materials and parts. Failure mechanisms are brought about by the application of environmental and/or operational stress(es).
»Accelerated testing: One common method for investigating such failures is accelerated testing, where relevant high stresses are applied to the device. Statistical methods are then used to determine the associated lifetime distributions. A lifetime distribution illustrates how failures occur across a large population of devices, under stress levels that would be present in normal use. To achieve this, accelerated testing involves the application of high stress conditions over a shorter period of time designed to mimic the effects of lower stress applied over a number of years. These two timeframes are related by a multiplication factor called the acceleration factor. Although advanced, there is extensive literature and software available dedicated to this type of reliability analysis.
One drawback of this kind of testing is that in order to have a realistic view of device performance a large number of devices (a statistically significant proportion of devices in the run) are required to be tested to failure.
»Standard methods: Other useful reliability testing may be done through the use of standardized test methods. These are broadly defined test procedures used to apply stress in a controlled way to test the resistance of the devices to harsh short-term stress conditions.
The specific test conditions and level of reliability are determined by the individual requirements of each project, since the tests methods are designed for a wide range of devices. These test methods are standardized by organizational bodies and designed for the applications of the industries that they regulate. These standards are also known as IEC, MIL-883F, JEDEC, Telecordia-GR-468 CORE, JEITA, AEC-Q100 etc. In short, standardized tests show whether the devices can withstand intense stress conditions and are useful for qualifying devices instead of thoroughly investigating their stress limits.
To recap, reliability tests on PICs are used to investigate their lifetime and failure modes as well as to verify their resilience to harsh conditions.
How to benefit from reliability testing of PICs
Reliability testing can be done through all development stages of a PIC device, the design phase, development stages, and the trial run before mass production. The most effective of which is when reliability testing is used to inform future reliability design considerations. For example, lifetimes can be determined for worse case outdoor applications.
This informs and allows for the design of reliable devices for environments from tropical areas (high humidity) to arctic conditions (thermal cycling between indoor and outdoor use). Additionally, high temperature lifetimes may be determined and used in consideration of cooling solutions which can improve cost and environmental impact. Additionally still, humidity may be accelerated to determine the possibility of using the more cost-effective solution of non-hermetic packaging etc.
To reiterate, the most productive approach to reliability testing is a Designing For Reliability (DFR) approach. An attitude of continuous improvements and ongoing reliability sampling and testing is key to this approach. Overall, assessing the reliability requirements of a project before starting is the most effective way to reduce in-field failures down the line. It is better to be proactive than reactive when it comes to failures!
VLC Photonics: Leading the way in PIC Reliability Testing
At VLC Photonics, we understand the critical role that reliability testing plays in ensuring the success of PICs across various industries for a variety of applications. We offer a range of reliability testing services, supported by the recent investment in two climatic chambers that have the capabilities to conform to standardized tests including IEC, MIL883-F, JEDEC, AC, JEITA.
Our testing capabilities include:
- • High-Temperature Storage: Assessing device stability at elevated temperatures while all reactions are being accelerated.
- • Low-Temperature Storage: Testing for mechanical failures in extreme cold.
- • Thermal Cycling: Simulating mechanical strain caused by differences of CTE during extreme temperature fluctuations- extreme in time and magnitude of fluctuations
- • Moisture Resistance Testing: Evaluating corrosion, moisture absorption, and de-lamination under high humidity conditions.
Conclusion
Reliability testing is a vital component of PIC design and production. By identifying potential failure mechanisms through calculating lifetime distributions and defect rates through standardized tests, VLC Photonics can offer insights into designing for reliability as well as producing devices that are resilient to harsh conditions.
At VLC Photonics, we are committed to providing our clients with the facilities and expertise that can satisfy their reliability needs. Whether you’re developing a new PIC or refining an existing design, reliability testing is a cost-effective solution for preventing costly in-field failures of PIC devices.
Now read PIC Testing House: Why is it key to test with one?
References:
Doganaksoy, N., Meeker, W., & Hahn, G. (2021). Achieving Product Reliability A Key to Business Success. CRC Press.
Waldron, Finbarr. (2024, June 6th). Introduction to Reliability Testing. [Power Point slides]. Tyndall National Institute. Photonhub Reliability Lecture 06-06-2024.pdf
Herrick, Robert. (2020, March 11). Reliability Qualification and Failure Mechanisms for Semiconductor Lasers and Fiber Optic Transceivers. [Power Point slides]. Intel Corporation. Intel Optoelectronics Reliability Tutorial OFC 2020.pdf
Hoefler, G. E., Muthiah, R. C., Salvatore, R. A., De Dobbelaere, P., & Herrick, R. W. (2023). 13 – Reliability of Photonic-Integrated Circuits for data center and high-performance computing applications. In M. Glick, L. Liao, & K. Schmidtke (Eds.), Integrated Photonics for Data Communication Applications (pp. 439–470). doi:10.1016/B978-0-323-91224-2.00010-2
Herrick, Robert. (2021). Reliability engineering in optoelectronic devices and fiber optic transceivers. 10.1016/B978-0-12-819254-2.00003-5.
Renesa. (2017). Semiconductor Reliability Handbook Rev.2.50. Renesas Electronics Corporation
