Role Of The Physics-of-Failure (PoF) Approach
PoF is an approach to aid in the design, manufacture, and application of a p...
Purposes of Reliability Assessment
The two primary purposes for quantitative reliability assessment of systems are to :

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Role of The Physics-of-Failure (PoF) Approach

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Comparison of Empirical and Physics-of-Failure based reliability prediction/assessment methods

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Role of The Physics-of-Failure (PoF) Approach

  1. 1. Role Of The Physics-of-Failure (PoF) Approach PoF is an approach to aid in the design, manufacture, and application of a product by assessing the possible failure mechanisms due to expected life-cycle stresses. PoF is used for reliability assessment, not reliability prediction. Reliability assessment involves the evaluation of the package’s potential to survive for the mission life in the application environment. Relevant attributes for this assessment include dominant failure mechanisms, the stress drivers for failure, and a pareto ranking of the time-to-failure due to the dominant failure mechanisms. How do microelectronic device failures manifest themselves ? Failures can be broadly categorised by the nature of the loads mechanical, thermal, electrical, radiation, or chemical that trigger or accelerate the mechanism. The PoF approach aids in determining potential causes, locating failures, and developing effective tests and screens. This approach supports good engineering judgement in evaluating the impact of stresses on the product or its elements PoF Process Inputs Outputs Operational Ranked list of Loads expected failure including power Life Cycle Sensitivity Analysis mechanisms dissipation, voltage, Stress and sites current, and frequency Evaluate sensitivity Profiles of the product life to the application - Environmental Stress Analysis Stress-margins Evaluate the Loads Thermal safe operating region on products including Thermo- for the desired life temperature, relative mechanical cycle profile humidity, pressure, Radiation Design - shock and their cyclic Hygro- trade-offs Evaluate potential ranges, rate of change mechanical screening and and time Electromagnetic accelerated test The life cycle includes Vibration shock transportation, storage, conditions Diffusion Screening handling and conditions application environments Reliability Assessment Accelerated Products Determine appropriate test conditions materials, geometry, failure mechanism models architecture and and calculate time-to-failure defectives for each failure mechanism Ref: CALC E EPRC Hilaire Perera, hilaireperera@rogers.com Long Term Quality Assurance (LTQA)
  2. 2. Purposes of Reliability Assessment The two primary purposes for quantitative reliability assessment of systems are to : 1) Assess the capability of the parts and design to operate reliably in a given application (robustness, durability) 2) Estimate the number of field failures or the probability of mission success Purpose # 1 does not require statistically based data or models, but rather, component part-selection/qualification and design techniques. It is for this purpose that the Physics- of-Failure (PoF) approaches have merit. Purpose # 2 requires empirical data, and models (MIL-HDBK-217, etc) derived from those data. This because component field-failures are predominantly caused by component and manufacturing defects which can be quantified only through the statistical analysis of empirical data. PoF approaches address only wearout phenomena, which from the industry viewpoint, constitute an irrelevant portion of all electronic component failures Comparison of Empirical and PoF Prediction/Assessment Methods Empirically based models: PRISM; Physics-of-Failure MIL-HDBK-217; CNET, Bellcore, British Telecom; etc • • Reflects actual field failure rates and Models specific failure mechanisms defect densities • Valuable for estimating end-of-life for • Can be a good indicator of actual field- known failure mechanisms reliability • Highly complex and costly to apply • Difficult to collect good quality field • data Cannot be used to: 1) estimate field reliability • 2) model defect-driven failure Difficult to keep up-to-date mechanisms • Difficult to distinguish correlated • variables (e.g., quality and Not practical to use for the reliability environment) assessment of an entire system Hilaire Perera, hilaireperera@rogers.com Long Term Quality Assurance (LTQA)

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