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In this series of articles, I will cover practical topics related to validating products for release into the marketplace. They will include such things as how to create a test profile from field data, how to accelerate that test while maintaining the integrity of the test (i.e., maintaining field correlation), how and when to best utilize qualitative test acceleration methods, and recommended strategies for demonstrating reliability. Additionally, I will offer some discussion related to the necessary disciplines of design and product validation, which I call Validation Rigor. For each I will pull from many years of lessons learned while exercising these tools directly and while leading the reliability and validation function for a large company.
If I must date myself, I cut my teeth as a product development engineer in the automotive industry in the bad old days when warranty terms were shockingly poor. Let’s examine this through the lens of my first new car which I purchased in 1984. Why was my warranty coverage so bad, what drove the significant improvements seen in the industry since that time, and how do we now validate our products to keep it that way?
The Arrhenius Equation is widely used and accepted by reliability and validation engineers from many industries to develop accelerated life tests (ALT) for thermal aging environments.
The general form of the equation describes the reaction rate of a process as a function of temperature (K), the Boltzmann constant (8.617E-5 eV/K) and two empirical factors. It can be written as:
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An example of an automotive validation test reliability target is R97C50. In this case, the objective of the validation effort would be to demonstrate at one life on test, with 50% confidence, that the product has a reliability of 97% or better.
Does this mean that a field failure rate of 3% can be expected?
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As you begin design validation (DV) and product validation (PV) testing you are entering the more formal phase of a test program. Usually, you are working to internal and/or customer test specs with timelines that are critical and little margin for error. If you’ve conducted adequate design verification testing and given your parts a chance to fail on test exposures that are similar to those your product will see in the field, you have reason to expect to be successful in validation [see previous article outlining accelerated test methods: Expect to Pass Validation].
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Product Validation Testing is a critical and expensive endeavor. The part build process must align with the latest prototype process (for Design Validation (DV)) or production process (for Product Validation (PV)) and be fully documented for posterity. Depending on the product and application, the validation test plan consists of a battery of tests, some of which are lengthy – often six months or more. Because of this, DV and PV test plans are invariably on the critical path for a customer program. Test failures that require fixing the design and repeating DV or PV jeopardize project timing and company profits. Further, they jeopardize the customer program along with your company’s reputation.
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