Reliability Demonstration testing (RDT) is an efficient way to test whether the product will attain a specified reliability for a given life. This life is typically the products required useful life, it’s MTBF, or even warranty length.
Reliability Demonstration Tests can utilize HALT & ALT data to provide useful life data. Whilst HALT is a product improvement process, RDT is an excellent tool for extracting statistically representative life data through the use of acceleration factors. Acceleration factors can be determined in a variety of ways, each using mathematical formulas based on the stress applied. Some of the acceration stresses include:
- Steady state elevated temperature.
- Temperature cycling.
- Power cycling.
- Temperature and humidity, or pressure.
- Electrical Stress.
Reliability Demonstration Test Sequence
The following steps are conducted to complete a successful RDT.
- Test is planned, what are the goals?
- Time frame to conduct testing?
- Sample availability?
- Acceleration model is chosen.
- Distribution is typically tied to acceleration model.
- Accept and Reject boundaries are created and plotted.
- Stress level chosen:
- Ideally HALT has been conducted if using temperature as accelerating stress.
- Functional test plan created.
- RDT is conducted, units checked for operation periodically.
- Graph created showing daily progress.
- Report generated at completion of testing to show accept or reject result.
The value is in the data
Conducting a Reliability Demonstration Test will provide you with invaluable data about your products ability to survive it’s intended use environment. It will allow you to set goals for product improvement, set warranty periods and to determine trigger points for production screening and returns.
When to conduct an RDT
RDT is ideally performed when the product development is stable, with all design flaws removed. For most companies RDT is performed at either the Pilot Production phase, or first mass production as a final qualification before initiating full blown production.
Applying HALT results to an RDT
HALT is an excellent means to understanding your product’s response to stress. In addition, after improvements have been made we will have defined the operating limits of the product, and be able to use these to set an appropriate level of stress during the RDT.
As an example, if the upper operating limit (OUL) is found to be 120C then we would apply statistical calculations to arrive at the RDT stress intensity of approximately 80C. Using the acceleration factor calculations, and coupling this with a sample size of 5-10 units we would be able to demonstrate and MTBF of 65,000Hrs within 2 weeks.
Determining MTBF from HALT
Many of our customers would like to be able to perform HALT and, using the results attained, arrive at an estimated life time. At this moment there are no proven mathematical models for illustrating product life from HALT.
Reliability Demonstration Tests allow for the determination of life by using acceleration factors, and increased stress levels. Conducting HALT will allow you to remove any weak points in the design, improve your operating llimits – and therefore decrease the duration required to demonstrate a given MTBF using a process such as RDT.