Contents. Introduction Field Return Rate Estimation Process Used Parameters

Transcription

1 Contents Introduction Field Return Rate Estimation Process Used Parameters Parts Count Reliability Prediction Accelerated Stress Testing Maturity Level Field Return Rate Indicator Function Field Return Rate Estimation Summary Questions FRR Estimation Page 1

2 VESTEL ELECTRONICS Consumer Electronics Manufacturer TFT LCD TV Set Top Box Notebook 8 million TV sets per year FRR Estimation Page 2

3 Introduction LCD TV reliability has become a MAJOR concern for the manufacturers as TV prices have dropped quite dramatically The cost of warranty failure support has become a greater % of the profit margin In Europe, the average cost per failure including logistics cost is greater than $150 LCD TV designs are being upgraded continually to stay ahead of customer expectations. However, new product release is under continual focus to meet planned market release dates to get maximum sales profit. This makes achieving high levels of reliability even more critical FRR Estimation Page 3

4 Introduction Many companies use reliability prediction standards, but, most of such standards are stressbased (temperature, voltage, power dissipation etc.) models for predicting a component s failure rate In addition, accelerated stress testing is widely used to predict failure rate of the product. But, the main stress factors are temperature, humidity, voltage, temperature cycling and vibration FRR Estimation Page 4

5 Introduction However, these stress factors are not the only failure reasons in field for a component/product. We need a new parameter (maturity level) which can also express component/product failures in field caused by Electro Static Discharge Voltage Variation, Interruptions, Dips Lightning Surge Inrush Current while turning on Loose Plug Opening the product at low temperature FRR Estimation Page 5

6 Introduction In this presentation, we create an indicator for an electronic product which consists of 3 parameters Failure Rate which is based on predicting a Component s failure rate Failure Rate which is calculated from Accelerated Stress Testing Failure Rate which is calculated from Maturity Level of the product And, use this indicator to estimate field return rate Improve your design before mass production FRR Estimation Page 6

7 Field Return Rate Estimation Process PARTS COUNT RELIABILITY PREDICTION FAILURES LIFE DATA LIFE DATA ANALYSIS FIELD RETURN RATE INDICATOR RETURN RATE SAMPLES TESTS PROBLEMS BUG LIST MATURITY LEVEL SOFTWARE RELIABILITY FRR Estimation Page 7

8 Field Return Rate Indicator Parameters Failure Rate 1 (FR 1 ) - Calculated from Parts Count Reliability Prediction Method Failure Rate 2 (FR 2 ) - Calculated from Life Data Analysis Failure Rate 3 (FR 3 ) - Calculated from Maturity Level of the project FRR Estimation Page 8

9 FR 1 Parts Count Reliability Prediction Measure and determine the specifications of all components on the electronic cards Operating Temperature Operating Voltage Power Dissipation Component Type Number of Pins Connection Type Environment Quality FRR Estimation Page 9

10 FR 1 Parts Count Reliability Prediction Main Board p1 p2 p Serial Connected Reliability p1 p2 p Power Board... pn... pn Part Failure Rate (λ p ) Board Failure Rate Mainboard Reliability (R MB ) Powerboard Reliability (R PW ) System Reliability (R system ) = Base Failure Rate * Corrective Factors (MIL-217F) = Σ λ p = 1 - λ MB = 1 - λ PW = R MB * R PW System Failure Rate (λ system ) = 1 R system FR 1 = 3000*λ system System MTTF (MTTF system ) = 1/ λ system FRR Estimation Page 10

11 Accelerated Stress Test Temperature Humidity Voltage Thermal Cycling Vibration FR 2 Life Data Analysis Acceleration Factor Calculation Arrhenius Model Corrosion Modeling Corrosion Modeling with Voltage Applied Modified Coffin-Manson Method Basquin s Model FRR Estimation Page 11

12 FR 2 Life Data Analysis Arrhenius Model AF = exp[-(ea/k)(1/t 1 1/T 2 )] Where; Ea = activation energy (0,6 0,7 for TFT LCD TV) K = Boltzmann s constant= x 10-5 ev/k T 1 = Test Temp (ºK), T 2 = Usage Temp (ºK) FRR Estimation Page 12

13 Corrosion Model FR 2 Life Data Analysis AF = (RH test /RH use ) n exp[-(ea/k) (1/T 1-1/T 2 )] n is dependent on the failure mechanism. Values of 2 to 4 are common. RH test = Relative humidity during stress test. R use = Relative humidity during application. Ea = activation energy (0,6 0,7 for TFT LCD TV) K = Boltzmann s constant= x 10-5 ev/k T 1 = Test Temp (ºK), T 2 = Usage Temp (ºK) FRR Estimation Page 13

14 FR 2 Life Data Analysis Corrosion Model with Voltage Applied AF = (V test /V use ) N (RH test /RH use ) n exp [-(Ea/K) (1/T 1-1/T 2 )] V test = Test voltage, V use = Use voltage N is dependent on the technology (2 to 4 common, 3 typical). n is dependent on the failure mechanism. Values of 2 to 4 are common. RH test = Relative humidity during stress test. R use = Relative humidity during application. Ea = activation energy (0,6 0,7 for TFT LCD TV) K = Boltzmann s constant= x 10-5 ev/k T 1 = Test Temp (ºK), T 2 = Usage Temp (ºK) FRR Estimation Page 14

15 FR 2 Life Data Analysis Modified Coffin Manson Method AF = exp [(0.123 / K) (1/T u - 1/T s )] (ƒ u / ƒ s ) 0.3 ( T s / T u ) 1.9 T u = Maximum Solder Joint Temp while in use in Kelvin (+273) T s = Maximum Solder Joint Temp while in test in Kelvin (+273) K = Boltzmann's Constant ( ) ƒ u = Frequency of temperature cyclic changes in use ƒ s = Frequency of temperature cyclic changes during stress T u = Temperature change during normal operation in C T s = Temperature change during stress in C FRR Estimation Page 15

16 Basquin s Model FR 2 Life Data Analysis AF = (Grms test / Grms use ) n Where; Grms test is the test vibration level Grms use is the use vibration level n is dependent on material characteristic FRR Estimation Page 16

17 Plan accelerated stress testing Collect data Complete data Exact failure time of the sample Suspend data FR 2 Life Data Analysis Test time of each unfailed sample Try to continue testing until min. 40% of the sample size fails FRR Estimation Page 17

18 FR 2 Life Data Analysis Multiply failure time and test time by Acceleration Factor of the accelerated stress test to calculate simulated normal condition use time Analyze simulated use time with Weibull distribution to calculate Failure Rate for a specific time period (3000 hrs for first year) Now, we have FR 2 FRR Estimation Page 18

19 Test types Pass / Fail Tests FR 3 Maturity Level Minimum 5 samples are required Board Level Tests ELP Tests Minimum 20 samples are required Product Level Tests DVT Tests Minimum 20 samples are required FRR Estimation Page 19

20 FR 3 Maturity Level Pass/Fail Tests After Trial-1 Usually with small sample size 3 Sub-categories Electrical Environmental Mechanical International standards and company experinces are used Major design problems are determined FRR Estimation Page 20

21 FR 3 Maturity Level Pass/Fail Tests Test Category Test Name Electrical Environmental Mechanical Test Points Voltage Current Stress Test 100 Temperature Stress Test 100 Open/Short Circuit Test 100 ESD Test 100 Surge Test 25 Lightning Test 50 Voltage Dips, Interruption and Variation Test 50 Power Switch On/Off Test or Momentary Power Out Test 50 Inrush Test 75 Heat-Run Test 100 High Temperature Test 50 Low Temperature Test 50 High Humidity Life Test 50 Vibration Test 25 Wall Holder Strenth Test 25 Drop Test 50 Total 1000 FRR Estimation Page 21

22 FR 3 Maturity Level ELP Tests Early Life Period Tests Component quality problems Production Process Problems Solder-Joint problems Cracks Voids PCB problems Powered and Unpowered Tests Passive Loads are used while testing with energy FRR Estimation Page 22

23 FR 3 Maturity Level ELP Tests Test Category Test Name Test Points Thermal Cycling Test (Powered/Unpowered) 75 Environmental High Temperature High Humidity Test 50 Thermal Shock Test 50 Mechanical Random Vibration Test 50 Total 225 FRR Estimation Page 23

24 FR 3 Maturity Level DVT Tests Design Verification Tests Are not Pass/Fail tests, but feedback is given to design groups and modification is wanted Usually with large sample size Minor design problems Probability of failure Combined stress factors are used to accelerate failure mechanism FRR Estimation Page 24

25 FR 3 Maturity Level DVT Tests Test Category Test Name Test Points Electrical Powered / Unpowered Temperature Cycling Test 100 ESD Step Stress to Failure Test 50 Combined High Temperature High Humidity Test 50 Thermal Shock Test 75 Environmental Temperature Step Stress to Failure Test 50 Operational High / Low Temperature Humidity Test 50 High Humidity Storage Test 25 Temperature Cycle Test 50 Constructional Inspection Test 50 Mechanical Unpackaged Shock Test (Fragility Test) 50 Random Vibration Step Stress to Failure Test 25 Total 575 FRR Estimation Page 25

26 FR 3 Maturity Level Test Type Test Points Pass / Fail Tests 1000 Early Life Period Tests 225 Design Verification Tests 575 Total Test Points (TTP) 1800 FRR Estimation Page 26

27 Severities of the bugs / failures Showstopper 40 points High 8 points Medium 5 points Low 3 points Status Coefficients Open 3 points Closed 0 points Duplicate 0 points FR 3 Maturity Level FRR Estimation Page 27

28 Calculations Points Lost PL = Severity Point x Status Coefficient Total Points Lost TPL = Σ PL Maturity Level FR 3 Maturity Level ML = [(TTP TPL) / TTP] x 100 FR 3 = 1 ML or (TPL / TTP) x 100 FRR Estimation Page 28

29 FR 3 Maturity Level Percentage Lost according to Severities Showstopper 6.67% High 1.33% Medium 0.83% Low 0.5% FRR Estimation Page 29

30 Field Return Rate Indicator Function Field Return Rate Indicator (FRRI) is a function of FR 1, FR 2 and FR 3 FRRI = f(fr 1, FR 2, FR 3 ) FRRI = (FR 1 x FR 2 x FR 3 ) There is a relation between FRRI and RR FRRI ~ RR 3 Relation Between Projects (FRRI 1 /FRRI 2 ) ~ (RR 1 /RR 2 ) 3 FRR Estimation Page 30

31 Field Return Rate Estimation Calculate FRRI for all projects (old&new) Calculate FRRI ratios of all projects (old&new) (FRRI 1 /FRRI 2 ), (FRRI 1 /FRRI 3 ), (FRRI 2 /FRRI 3 ),... Determine RR for old projects Calculate RR ratios of old projects (RR 1 /RR 2 ) 3, (RR 1 /RR 3 ) 3, (RR 2 /RR 3 ) 3,... FRR Estimation Page 31

32 Draw a graphic Field Return Rate Estimation X-axis is the ratios of FRR Indicators Y-axis is the cubes of the ratios of Return Rates Set the points to the graphic Points; [(FRRI 1 /FRRI 2 ),(RR 1 /RR 2 ) 3 ],... Draw an estimated line which is the nearest to the points Create the equation of this estimated line Estimate the new project s return rate with respect to its FRR Indicator FRR Estimation Page 32

33 Field Return Rate Estimation - Example 3 old & 1 new project Estimate the new project s 1 year return rate before mass production Project FR1 1st year (%) FR2 1st year (%) Maturity Level (1-FR3 (%)) FRRI Field Return Rate 1st year (%) ???? FRR Estimation Page 33

34 Field Return Rate Estimation - Example Indicator Ratios Cubes of Return Rate Ratios FRRI1/FRRI RR1/RR2^ FRRI1/FRRI RR1/RR3^ FRRI2/FRRI RR2/RR3^ Cubes of Ratios of RR y = x Ratios of FRRI FRR Estimation Page 34

35 Field Return Rate Estimation - Example Indicator Ratios Cubes of Return Rate Ratios FRRI1/FRRI (RR1/RR4)^ FRRI2/FRRI (RR2/RR4)^ FRRI4/FRRI (RR4/RR3)^ Return Rate Ratios Return Rate Predicts 1st year (%) RR1/RR RR RR2/RR RR RR4/RR RR FRR Estimation Page 35

36 Field Return Rate Estimation - Example There are 3 predictions for the new projects 1st year return rate 1.78%, 2.08% and 2.14% We can say that new project s 1st year return rate will be between 1.78% and 2.14% We can say that new project s 1st year return rate will be average 2.00% FRR Estimation Page 36

37 Summary Prediction standards and known distribution models can predict return rate caused by only basic stress factors New parameter is needed to predict failure rates caused by different effects (Maturity Level) Combining 3 parameters makes the estimation more accurate New parameters can be added to the model (for ex. SW Reliability) FRR Estimation Page 37

38 References MIL-HDBK-217F Franck Bayle, Thales Division Aeronautique, Adamantios Mettas, ReliaSoft Corporation Acceleration Models in Reliability Prediction Standards: Justification and Improvements, 2010 ARS, Europe: Berlin, Germany Martin Shaw Reliability Solutions, LCD TV Reliability Testing: An Effective Approach, 2010 ARS, Europe: Berlin, Germany Tekcan, T.; Kirisken, B.;, "Reliability test procedures for achieving highly robust electronic products," Reliability and Maintainability Symposium (RAMS), 2010 Proceedings - Annual, vol., no., pp.1-6, Jan FRR Estimation Page 38

39 Questions Thank you for your attention. Do you have any questions? FRR Estimation Page 39