Original Date: 11/01/2004
Revision Date: 01/18/2007
Best Practice : Physics-of-Failure Strategies for Accelerated Stress Testing: Product Qualification
The Center for Advance Life-Cycle Engineering has established systematic procedures to combine Physics-of- Failure modeling with accelerated stress testing to qualify new designs and processes for a given life cycle. Proper Physics-of-Failure-based use of accelerated stress tests within cost and time budgets can achieve quality and stress margins that are far better than those achieved using traditional design-build-test-fix approaches.
Accelerated qualification is a key method for risk assessment in the electronics industry. However, qualification of devices, packages, and systems has consisted of decades-old military and commercial standards. Qualification is typically conducted late in product development, often after the design is frozen, putting a burden on product time to market. Furthermore, the old “one size fits all” standard tests do not address the actual failure mechanisms occurring in the application environment. As new reliability assessment and qualification techniques are being introduced, questioned, evaluated, and reinvented for today’s marketplace, it is necessary to have a thorough understanding of the potential failure mechanisms, not only to prevent them under life-cycle stresses but to precipitate them effectively during accelerated testing.
The Center for Advanced Life-Cycle Engineering (CALCE) has demonstrated a thorough understanding of the failure mechanisms with its Physics-of-Failure- (PoF)-based reliability prediction methodologies. CALCE determined the need for a method to relate the results of accelerated wearout tests to in-service reliability. CALCE researchers realize that successful answers to these issues can and will result in dramatic breakthroughs in reducing product development cycle time and increasing confidence in the product’s life cycle. Researchers realize that development budgets are shrinking and there is a push to enhance test time compression. This has served to develop the most cost effective and scientific way to conduct accelerated wearout testing for electronic packages. CALCE researchers agree that PoF principles hold the greatest promise for evaluating accelerated life tests under adverse environments.
CALCE’s PoF approach to accelerated wearout testing follows a five-step process, starting with INPUTS of the product configuration (program objectives, product architecture, material properties) and life-cycle loads (operational use environment). In Step 1, PoF-based virtual qualification is used to identify the potential failure sites, damage mechanisms, and failure modes under the life-cycle loads. Computer models identify the intrinsic design limits of the product and rank the potential failures. Step 2 involves the design of an accelerated test plan to target the design weaknesses. Step 3 involves characterization of test loads specimens so the PoF model can be verified and calibrated, as well as development of an accelerated stress profile which does not violate any overstress limits. Step 4 involves accelerated life test on selected sample lots. Failure mechanisms are verified using failure analysis to ensure validity. Step 5 repeats the virtual qualification (VQ) assessment, but in an accelerated environment to identify the acceleration factors for the selected accelerated test program. The OUTPUT of this five- step process is a PoF assessment of durability of the product in the life-cycle environment, calibrated with accelerated test data.
CALCE has successfully demonstrated a systematic process for integrating PoF strategies for accelerated stress testing. The application of enhanced stresses ruggedizes the design and manufacturing process of electronics packages through systematic step-stress testing, and increases the stress margins by corrective action (reliability enhancement testing) and by conducting compressed/accelerated life tests in the laboratory to verify in-service reliability (qualification testing). When done early in the development phase, such PoF modeling and tailored accelerated testing can enhance process and design maturity and enable early introduction of mature products with robust design margins.
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