Design For Reliability

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Design For Reliability

  1. 1. Design for Reliability Hilaire Ananda Perera Define Measure Analyze Improve Control ES&S DFSS - Design For Reliability July 2002 Honeywell Toronto …………. …. 1 USE OR DISCLOSURE OF DATA CONTAINED ON THIS SHEET IS SUBJECT TO THE RESTRICTIONS ON THE TITLE PAGE OF THIS DOCUMENT
  2. 2. Contents • • • • • • • • • • • • • • • • • What is Reliability Designing for Reliability Design for Performance and Reliability Concurrently Reliability Design Tasks Derating Accelerated Life Testing (ALT) Reliability Estimation Significance of Weibull β values Gamma Function Assessment Prediction Models Stress/Strength Interference & Probabilistic Design Reliability Estimation with Safety Margin Mean and Variance for Any Distribution Binary Synthesis of Classical Equations Mean and Standard Deviation of an Algebraic Function Statistical Data from a Tolerance Statement False Alarm Probability Estimation ES&S DFSS - Design For Reliability July 2002 Honeywell Toronto …………. …. 2 USE OR DISCLOSURE OF DATA CONTAINED ON THIS SHEET IS SUBJECT TO THE RESTRICTIONS ON THE TITLE PAGE OF THIS DOCUMENT
  3. 3. Contents • • • • • • cntd. Screening Strength Estimation Adaptive Environmental Stress Screening How CDE Model Parameters Obtained Product Assurance Rolled Throughput Yield (RTY) The Challenge: DFR Physics of Failure Approach Types of Failure Mechanisms ES&S DFSS - Design For Reliability July 2002 Honeywell Toronto …………. …. 3 USE OR DISCLOSURE OF DATA CONTAINED ON THIS SHEET IS SUBJECT TO THE RESTRICTIONS ON THE TITLE PAGE OF THIS DOCUMENT
  4. 4. What is Reliability ? • Reliability is the likelihood(probability) that a product will – perform its intended function – within specified tolerances – under stated conditions – for a given period of time ES&S DFSS - Design For Reliability July 2002 Honeywell Toronto …………. …. 4 USE OR DISCLOSURE OF DATA CONTAINED ON THIS SHEET IS SUBJECT TO THE RESTRICTIONS ON THE TITLE PAGE OF THIS DOCUMENT
  5. 5. Designing for Reliability • Reliability part of the core design team • Reliability modeling guides design • Failure mechanisms designed-out • Super-accelerated life testing saves time • Lifetime is metric for design suitability • Longer lived products • Reduce manufacturing variability Iterative Approach to Reliability • Test and fix methodology • Modeling for performance • Single stress environmental testing • 1000 hrs or longer per test • Designing to specifications ES&S DFSS - Design For Reliability July 2002 Gap-Bridging Steps Cycle Time Reduction Designing for Reliability • Understand Failure Mechanisms • Share Internal Knowledge • Develop Reliability Databases • Deploy Super-accelerated Life Testing Honeywell Toronto …………. …. 5 USE OR DISCLOSURE OF DATA CONTAINED ON THIS SHEET IS SUBJECT TO THE RESTRICTIONS ON THE TITLE PAGE OF THIS DOCUMENT
  6. 6. Design for Performance and Reliability Concurrently Time & Money Saved Reliability Target Enhanced Design Redesign Design Time & $ Spending More Time in Design Speeds Time to Market ES&S DFSS - Design For Reliability July 2002 Honeywell Toronto …………. …. 6 USE OR DISCLOSURE OF DATA CONTAINED ON THIS SHEET IS SUBJECT TO THE RESTRICTIONS ON THE TITLE PAGE OF THIS DOCUMENT
  7. 7. Reliability Design Tasks Reliability Design Tasks should be performed as early as possible in the product development and iterated as necessary to effectively impact the product design, emphasizing the need for up-front reliability design Program Phase and Scope of Reliability Tasks Program Phase Concept and Planning • • • Design and Development • • • Production and Manufacturing • Purpose Study product feasibility Consider alternate solutions Understand design & operating environmemt Define approaches & solutions for producing a product Develop models or prototypes Validate through test, analysis or simulation Maintain inherent product reliability • • • • • • • • • ES&S DFSS - Design For Reliability July 2002 Scope of Task Trade-off analysis for critical items Customer needs refined Part selection alternatives evaluated Environmental aspects determined Integration of design & application guides Evaluation of design progress through analyses and/or tests Construction of product evaluation processes Implement process control and quality assurance procedures Operating & maintenance manuals refined Honeywell Toronto …………. …. 7 USE OR DISCLOSURE OF DATA CONTAINED ON THIS SHEET IS SUBJECT TO THE RESTRICTIONS ON THE TITLE PAGE OF THIS DOCUMENT
  8. 8. Derating Purpose: The purpose of Derating is to enhance the item inherent design reliability, increase safety margins and reduce repair and replacement costs. The enhancement is accomplished by compensating for many variables inherent in any design, some of which include: What % of the Maximum Allowed ? • Manufacturing Tolerances • Component Variation • Material Differences • Performance Anomalies • Parameter Drift Benefits: From an electronic component application, the benefits include lower failure rates through reduced stresses, less impact from material and manufacturing variability, proper circuit operation with part parameter changes and reduction in end of life failures. For mechanical and structural components, a reduction in stress or increase in strength means a greater factor of safety from catastrophic failure ES&S DFSS - Design For Reliability July 2002 Honeywell Toronto …………. …. 8 USE OR DISCLOSURE OF DATA CONTAINED ON THIS SHEET IS SUBJECT TO THE RESTRICTIONS ON THE TITLE PAGE OF THIS DOCUMENT
  9. 9. Accelerated Life Testing (ALT) Accelerated Life Testing involves measuring the performance of the product at accelerated load or stress conditions, in order to induce pattern failures quickly. The goal is to accelerate failure mechanisms and the accumulation damage, reducing the time-to-failure. Proper ALT requires that: • The failure mechanisms in the accelerated environment are the same as those observed under normal operating conditions; • Acceleration transforms are available to confidently extrapolate from the test life to the usage life of the product under actual operating conditions; • The failure probability density functions at normal operating levels and under accelerated conditions are consistent ES&S DFSS - Design For Reliability July 2002 Honeywell Toronto …………. …. 9 USE OR DISCLOSURE OF DATA CONTAINED ON THIS SHEET IS SUBJECT TO THE RESTRICTIONS ON THE TITLE PAGE OF THIS DOCUMENT
  10. 10. Reliability Estimation Reliability R(T) of a Device with a Mean Time (Hours) To Failure of “MTTF” for a specified Mission Time of “T” Hours using the Weibull reliability function is: β  R (T ) = e  T  1 − ⋅Γ  1+    MTTF  β   If β = 1; MTTF = 30000 Hrs and T = 2 Hrs Reliability = 0.99993. This means 99.99% of the missions will be completed successfully within 2 Hrs β is the Weibull Shape Parameter. For an Electronic Device, β = 1 (Exponential Distribution) in the Useful Life period. Γ represents the Gamma Function. Actual β values to determine Reliability can be derived using Time To Failure data of End-Units from the operating field ES&S DFSS - Design For Reliability July 2002 Honeywell Toronto …………. …. 10 USE OR DISCLOSURE OF DATA CONTAINED ON THIS SHEET IS SUBJECT TO THE RESTRICTIONS ON THE TITLE PAGE OF THIS DOCUMENT
  11. 11. Significance of Weibull β Values Value of β β<1 β=1 Product Characteristics Implies infant mortality. If product survives infant mortality, its resistance to failure improves with age Implies failures are random in occurrence. An old part is just as good (or bad) as a new part Implies early wearout If This Occurs, Suspect the Following • • • • • • • • • β>1&<4 • • β>4 Implies old age (rapid) wearout • • • ES&S DFSS - Design For Reliability July 2002 Inadequate environmental stress screening Quality problems in components Quality problems in manufacturing Rework/refurbishment problems Maintenance/human errors Failures are inherent, not induced Mixture of failure modes Electromigration Low cycle fatigue Corrosion or erosion failure modes Scheduled replacement may be cost effective Inherent material property limitations Gross manufacturing process problems Small variability in manufacturing or material Honeywell Toronto …………. …. 11 USE OR DISCLOSURE OF DATA CONTAINED ON THIS SHEET IS SUBJECT TO THE RESTRICTIONS ON THE TITLE PAGE OF THIS DOCUMENT
  12. 12. Gamma Function Assessment Enter the “z” Value Here This is the Calculated Gamma Value ES&S DFSS - Design For Reliability July 2002 Honeywell Toronto …………. …. 12 USE OR DISCLOSURE OF DATA CONTAINED ON THIS SHEET IS SUBJECT TO THE RESTRICTIONS ON THE TITLE PAGE OF THIS DOCUMENT
  13. 13. Prediction Models – IEEE 1413 Reliability Prediction Process Guide  Framework for Hardware & Software predictions at all levels – Telcordia TR-332 (previously known as Bellcore) – RDF 2000 (French) – MIL-HDBK-217F, N2  Piece-part reliability prediction, sum defect rates  No new technology or high complexity models - obsolete  Need to find a replacement . . . . . – RAC PRISM  Forces holistic consideration of factors influencing Reliability – Mission & Duty cycle – All processes – Devices ES&S DFSS - Design For Reliability July 2002 Honeywell Toronto …………. …. 13 USE OR DISCLOSURE OF DATA CONTAINED ON THIS SHEET IS SUBJECT TO THE RESTRICTIONS ON THE TITLE PAGE OF THIS DOCUMENT
  14. 14. Stress/Strength Interference & Probabilistic Design Reliability prediction using the Stress/Strength Interference and Probabilistic Design method: This method assumes that the material properties are time independent because of their slow change, and the components are not subjected to wear related failure modes. When components are subjected to reversing mechanical loads that exhibit a single failure mode, the reliability is designed-in by selecting the probability number representing the Safety Margin. For the use of this methodology, Binary Synthesis of the classical equations are needed. Safety Margin (SM) = Reliability (R) = 1 - ES&S DFSS - Design For Reliability July 2002 µS − µs σ S 2 + σ s2 1 2Π ∫ SM −t 2 2 µs = Mean Stress of the Stress function σs = Standard Deviation of the Stress µS = Mean Strength of material σS = Standard Deviation of the material Strength If SM = 3.5 Reliability = 0.9997 e dt −∞ Honeywell Toronto …………. …. 14 USE OR DISCLOSURE OF DATA CONTAINED ON THIS SHEET IS SUBJECT TO THE RESTRICTIONS ON THE TITLE PAGE OF THIS DOCUMENT
  15. 15. Reliability Estimation with Safety Margin To obtain Reliability, Go Here and Select Standard Normal Cumulative Distribution Enter “SM” Value to “Z” Reliability = 0.999767 ES&S DFSS - Design For Reliability July 2002 Honeywell Toronto …………. …. 15 USE OR DISCLOSURE OF DATA CONTAINED ON THIS SHEET IS SUBJECT TO THE RESTRICTIONS ON THE TITLE PAGE OF THIS DOCUMENT
  16. 16. Mean and Variance for any Distribution Let f(x) = Probability Density Function of the independent variable x If f(x) ≥ 0, for all x +∞ ∫ Mean = µ = xf ( x )dx −∞ Coefficient of Variation (CV) provides a relative measure of data dispersion compared to the Mean CV = +∞ σ µ ∫ 2 2 Variance = σ = ( x − µ ) f ( x )dx , where σ = Standard Deviation −∞ When “x = Time”, Lower boundary of the Integral will be 0 instead of -∞ This is the case for Reliability related functions ES&S DFSS - Design For Reliability July 2002 Honeywell Toronto …………. …. 16 USE OR DISCLOSURE OF DATA CONTAINED ON THIS SHEET IS SUBJECT TO THE RESTRICTIONS ON THE TITLE PAGE OF THIS DOCUMENT
  17. 17. Binary Synthesis of Classical Equations In a pressurized cylinder wall of “External Radius = a” and “Bore Radius = b”, the Failure Governing Stress Function (s) is the Circumferential (Hoop) Stress s =   a 2     + 1 b P.   2   a    − 1  b Where P = Internal Pressure For Reliability calculation using Safety Margin determine the Mean (µ) and the Standard Deviation (σ) of the variables “a”; “b”; “P” and calculate the µ & σ of the Stress Function (s) Note: The methodology for µ and σ calculation is in the slides named Mean and Standard Deviation of an Algebraic Function and Statistical Data from a Tolerance Statement ES&S DFSS - Design For Reliability July 2002 Honeywell Toronto …………. …. 17 USE OR DISCLOSURE OF DATA CONTAINED ON THIS SHEET IS SUBJECT TO THE RESTRICTIONS ON THE TITLE PAGE OF THIS DOCUMENT
  18. 18. Mean and Standard Deviation of an Algebraic Function Algebraic Function c c.x c.x + d c.x - d x+y x–y * x.y Mean Standard Deviation c c.µx c.µx + d c.µx - d µx + µy 0 c.σx c.σx c.σx µx - µy (µ µx . µy x * y µx µy n µxn * x * x 0.5 (σ (σ (0.5. 4.µ 2 x − 2.σ x 2 x ) 0.5 +σ y 2 0.5 2 +σ y 2 0.5 x x .σ y + µ y .σ x + σ x .σ y 2   1 µ  y 2 ) ) 2 (µ 2 2   µ x .σ y + µ y .σ x .  µ y2 +σ y2  ( n −1) n.µ x .σ x 2 2 2 − 0.5. 4.µ x − 2.σ x 2 x 2 2     2 ) 2 0.5 0.5 ) 0.5 c, d, n are constants * These are good approximations when the Coefficient of Variation (CV) is small. i.e. CV < 0.1 ES&S DFSS - Design For Reliability July 2002 Honeywell Toronto …………. …. 18 USE OR DISCLOSURE OF DATA CONTAINED ON THIS SHEET IS SUBJECT TO THE RESTRICTIONS ON THE TITLE PAGE OF THIS DOCUMENT
  19. 19. Statistical Data from a Tolerance Statement When the distributional Probability Density Function of a variable is Normal (or Gaussian) between the limits Low “a” and High “b” The Mean (µ) is approximately equal to a+b 2 The Standard Deviation (σ) is approximately equal to For a 10K Ohms Resistor with ±5% tolerance µ = 10K Ohms σ = 167 Ohms b−a 6 These simplified calculations are based on theoretical derivations and was justified by E. B. Haugen in University of Arizona, 1974 ES&S DFSS - Design For Reliability July 2002 Honeywell Toronto …………. …. 19 USE OR DISCLOSURE OF DATA CONTAINED ON THIS SHEET IS SUBJECT TO THE RESTRICTIONS ON THE TITLE PAGE OF THIS DOCUMENT
  20. 20. False Alarm Probability Estimation Voltage Divider Circuitry for Min_Limit & Max_Limit Tested Output Voltage = 12V +/- 180mV µ = 12 ; σ = 0.06 Resistor X VRef = 15V +/- 180 mV Resistor Y VTest = (Y/(X+Y))* VRef. µ = 15; σ = 0.06 Grnd False Alarms can happen due to Component Tolerances and Voltage Deviations Resistor Tolerance is +/- 10% Case 1: Min_Limit; X=100K Ohms; Y=302K Ohms µ (VTest) = 11.27 ; σ(VTest) = 0.064 Safety Margin (SM) = 8.343 Probability of Failure = 0.00E+00 Case 2: Max_Limit; X=100K Ohms; Y=541K Ohms µ (VTest) = 12.66 ; σ(VTest) = 0.079 Safety Margin (SM) = 6.679 Probability of Failure = 1.2084E-11 False Alarm Probability = 1.2084E-11 ES&S DFSS - Design For Reliability July 2002 Honeywell Toronto …………. …. 20 USE OR DISCLOSURE OF DATA CONTAINED ON THIS SHEET IS SUBJECT TO THE RESTRICTIONS ON THE TITLE PAGE OF THIS DOCUMENT
  21. 21. Screening Strength Estimation The Screening Strength of a given stress screen profile is defined as the probability that the stress screen will precipitate a latent defect into a detectable failure, given that a defect is present. Screening provide assurance on the Outgoing Reliability Screening Strength for Temperature Cycling (STn) is a function of Temperature Range =T; Temp. Rate of Change =R; Number of Cycles =n STn = 1 − e[−[0.0017⋅(T + 0.6) 0.6 ⋅ln(e + R ) ⋅n]] 3 Screening Strength for Random Vibration (SVt) is a function of G = gRMS; Vibration Duration = t SVt = 1 − e[−(0.0046⋅G 1.71 ⋅t )] Combined Screen Strength (SS) = 1 - (1-STn).(1-SVt) When T = 111oC; R = 5oC/Min n =16 Cyc; G = 2gRMS; t = 15 Min SS = 0.98432 The Screening Strength equations were developed by Hughes Aircraft Company, and modified by Rome Air Development Centre (RADC) based on the data from McDonnel Aircraft Co. and Grumman Aerospace Corporation ES&S DFSS - Design For Reliability July 2002 Honeywell Toronto …………. …. 21 USE OR DISCLOSURE OF DATA CONTAINED ON THIS SHEET IS SUBJECT TO THE RESTRICTIONS ON THE TITLE PAGE OF THIS DOCUMENT
  22. 22. Adaptive Environmental Stress Screening (ESS) The principle of adaptive screening is to adjust the screens on the basis of observed screening results, so that the screens are always most costeffective while meeting ESS program goals. Contract terms should be flexible enough to permit modifications of screening parameters when such modifications can be shown to be beneficial The Chance Defective Exponential (CDE) Model is the chosen prediction model for failure rate distribution analysis, as the constant failure rate portion could be extracted for Acceleration Factor calculation, the average rate of defect precipitation determined for Best Thermal Cycling Time and Failure Free Time calculation. CDE equation parameters are obtained using the SigmaPlot computer program P/N XXXX100-07 ESS Period: 01 Jan 99 - 31 Dec 99 0.04 Failure Rate (fr) 0.03 Fail/Hour Outgoing Defect Density = 5300 PPM Yield = 0.9947 4σ < Capability < 5σ Time To Remove 99.999% Defects = 32 Hrs Failure Free Time (99.99% Yield) at 90% LCL = 20Hrs 0.02 fr = 0.0031+ 0.0385*exp(-0.3669*t) 0.01 0.00 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 ESS Time (t) Hours CONDITION: Cumulative Thermal Energy due to previous runs And/Or NFF And/Or BIE Failure are also responsible for relevant failure precipitation ES&S DFSS - Design For Reliability July 2002 Honeywell Toronto …………. …. 22 USE OR DISCLOSURE OF DATA CONTAINED ON THIS SHEET IS SUBJECT TO THE RESTRICTIONS ON THE TITLE PAGE OF THIS DOCUMENT
  23. 23. How CDE Model Parameters Obtained Time To Failure Data Failure Rate Data ES&S DFSS - Design For Reliability July 2002 CDE Model Parameters Coefficient of Variation (CV) used as a gauge of the accuracy of the fitted curve parameters Honeywell Toronto …………. …. 23 USE OR DISCLOSURE OF DATA CONTAINED ON THIS SHEET IS SUBJECT TO THE RESTRICTIONS ON THE TITLE PAGE OF THIS DOCUMENT
  24. 24. Product Assurance Rolled Throughput Yield (RTY) RTY = Multiplication of the Yields at all steps in the Process Product Assurance (PA) Process R = Reliability Product Assurance (PA) Process S = Environmental Stress Screening Process S Process R If Temp. Range = 111oC If Mission Time = 2 Hrs If Temp. Rate of Change = 5oC/Min RTYPA = 98.43% Achieved MTBF = 30000 Hrs Performed Temp. Cycles = 16 DPMOPA = 7850 Yield = 0.99993 If Vibration Level = 2gRMS Sigma Level = 3.92 Performed Vibration = 15 Min Yield = 0.98432 DPMO = Defects (Failures) Per Million Opportunities Yield = e - TDU where TDU = Total Defects (Failures) Per Unit = Outgoing Defect (Failure) Density ES&S DFSS - Design For Reliability July 2002 Honeywell Toronto …………. …. 24 USE OR DISCLOSURE OF DATA CONTAINED ON THIS SHEET IS SUBJECT TO THE RESTRICTIONS ON THE TITLE PAGE OF THIS DOCUMENT
  25. 25. The Challenge DFR Physics of Failure Approach The Physics of Failure (PoF) approach to Design for Reliability is founded on the fact that the failure of electronics is governed by fundamental mechanical, electrical, thermal and chemical processes. By understanding the possible failure mechanism, design teams can identify and solve potential reliability problems before they arise. The PoF process can be extremely complex, and so requires the use of an expert system for its completion ES&S DFSS - Design For Reliability July 2002 Honeywell Toronto …………. …. 25 USE OR DISCLOSURE OF DATA CONTAINED ON THIS SHEET IS SUBJECT TO THE RESTRICTIONS ON THE TITLE PAGE OF THIS DOCUMENT
  26. 26. Types of Failure Mechanisms Overstress failure mechanisms occur when a stress excursion exceeds strength Wear-out failure mechanisms occur when accumulated damage exceeds endurance Mechanical • Fracture • Buckling • Yielding Mechanical • Fatigue • Creep • Corrosion Electrical • Fused or shorted wires • Electrostatic discharge • Electrical overstress Electrical • Leakage current • Metal migration • Threshold voltage shift Thermal • Melting Thermal • Elasticity degradation Physical/Chemical • Electron-hole pairs generation due to ionizing radiation Physical/Chemical • Interdiffusion • Depolymerization ES&S DFSS - Design For Reliability July 2002 Honeywell Toronto …………. …. 26 USE OR DISCLOSURE OF DATA CONTAINED ON THIS SHEET IS SUBJECT TO THE RESTRICTIONS ON THE TITLE PAGE OF THIS DOCUMENT

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