Physics of Failure (PoF) Overview
A PoF approach to reliability utilizes knowledge of life-cycle loads and product architecture (geometry and material properties) to identify potential failure mechanisms and prevent operational failures through robust design, validation and manufacturing practices. PoF based methodologies have been successfully implemented in consumer, avionics and medical industries resulting in:
- Reduced time to market
- Product cost reductions
- Improved product reliability
A PoF based approach yields the following benefits:
- Proactively designs reliability into the product development process by providing a logical and methodical engineering basis for predicting product life under actual use conditions
- Minimizes product risks by proactively quantifying its reliability and ensuring the product performs as intended in its use environment for its entire warranty period. Field reliability and quality is increased
- Reduces development times and cost by minimizing failures prior to test and reducing product validation test-fix-retest cycle costs
- Develops and quantifies an internal knowledge-base of product performance
A PoF methodology involves quantitative modeling of the expected root-cause failure mechanisms, based on quantitative estimates of product loads, stresses and relevant material behavior as captured by the PoF model. Quantitative modeling is typically carried out for both test and actual use loads. The output of such analyses is an estimate of acceleration factor which when multiplied by the accelerated wearout test data, results in estimating product life under use case conditions. PoF failure models are useful for conducting trend analysis, for design trade-offs, and for estimating acceleration factors and offer the unique ability to virtually qualify an electronic product.
The PoF approach minimizes product reliability risks through a systematic investigation and quantification of the dominant failure mechanisms. Knowledge of the product failure mechanisms also permit the development of a cost and time efficient accelerated test program by appropriate selection of test stresses (e.g., temperature, relative humidity, vibration, temperature cycling) and the levels of those stresses so as to cause wearout failures in the shortest test duration without changing the failure mechanism.
Steps in the PoF approach can be summarized as follows:
- Identify use environment and product hardware configuration:
- Review field history data and similar product performance
- If a new product category, evaluate comparable products
- Design & conduct a suite of accelerated stress tests on a representative design:
- Failure-limited step-stress tests, to identify overstress limits
- Failure-limited long-term accelerated stress tests, to identify durability
- Identify failure modes and perform root-cause assessment of failure mechanism(s):
- Identify failure modes and mechanisms through failure analysis
- PoF model constants at field & test conditions
- Conduct stress analysis for field and test environments:
- Modeling and simulation (FEA, etc)
- Experiments
- Statistical tools (Weibull) for confidence limits
- Input stress levels into PoF model(s) to estimate product durability
The information generated from this work is used to:
- Identify the product stress limits and weak links
- Proactively incorporate design mitigation solutions for current and next generation of products
- Identify focused accelerated product life tests
- Evaluate long term durability of the product
A PoF based methodology differs significantly from a "standards based"
reliability methodology. In the latter, products are subjected to a set of "one size
fits all" set of tests prescribed by military and commercial standards.
Each approach has its advantages and limitations and at CES we combine the best
of both approaches to provide a unique solution to your product reliability needs.
