Original Date: 11/01/2004
Revision Date: 01/18/2007
Best Practice : Virtual Qualification (Simulation-Assisted Reliability Assessment)
The Center for Advanced Life-Cycle Engineering has developed a simulation-assisted reliability assessment process for electronic hardware. This process includes the use of unique software (e.g.,the Center for Advanced Life-Cycle Engineering-developed Printed Wiring Assembly) used for reliability assessment of electronic hardware. One function of the Virtual Qualification process is to establish correlations between qualification tests and anticipated field conditions.
Reliability prediction modeling has been underway for decades. The traditional method of predicting reliability was to follow the Military Handbook for Reliability Prediction of Electronic Equipment (MIL-Hdbk-217) that used prediction methods that lead to reliability being directly correlated to temperature. Failure rates were a function of device quantity, characteristics, and temperature – not the underlying physical mechanisms that produced the failures. With constant changes that microcircuits were undergoing, the virtual elimination of ceramic, and the growing quality aspects of plastic parts, the world was being driven away from MIL-Hdbk-217 as a reliability prediction method. This has given rise to the Center for Advanced Life-Cycle Engineering (CALCE) physics-of- failure (PoF) approach to reliability assessment, which includes Virtual Qualification (VQ) and physical verification.
Because of the time involved in building a prototype, VQ offers the ability to assess a design prior to physical construction. VQ is a simulation-based process that models the product design and its anticipated life-cycle lead history to assess if the anticipated reliability is achievable. This approach has been successfully applied on avionics, automotive, and military electronic hardware, and has been shown to reduce the life-cycle cost and reliability risks of a product. VQ relies on the ability of the practitioner to adequately model the product and its anticipated life-cycle loads and to evaluate potential failure sites based on the anticipated life-cycle loads. Failure models derived and documented from test and physical analysis are used to conduct the failure assessment.
Figure 2-3 depicts the four main tasks into which the VQ process is divided. First, the anticipated design is captured. This provides relevant detail of the product configuration and layout, including physical dimensions and material properties, to create computer models for the life assessment. Second, the life-cycle loading characteristics are identified and modeled to represent the anticipated environmental loads that the design will experience through its life-cycle. Third, the load transformation relates the response of the system to the environmental and operational loads. Last, a failure risk assessment pulls all of these aspects together by evaluating failure models with data from design capture, life-cycle loads, and load transformation. The output of VQ is an assessment of the product’s life expectancy and a ranking of the potential failure sites under life-cycle load combinations. The VQ process can be closely tied to physical testing.
CALCE’s approach to VQ and CALCE-developed software have been applied to a variety of electronic hardware. In one application, three circuit card assemblies from an airborne radio system were examined and found to be unable to meet desired life-cycle requirements. The total time to construct and perform the initial simulation on the three circuit cards was approximately six weeks. An application on an automotive module produced results that improved thermal and structural performance, which translated into increased product life. Comparisons between the VQ method and the traditional design-build-test-fix method showed a 16% reduction in development time and an 83% reduction in test issues.
Figure 2-3. Virtual Qualification Process
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