ESS and HASS: Concerns with the Practices and Standards
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Transcript of ESS and HASS: Concerns with the Practices and Standards
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ESS and HASS: Concerns with the Practices and Standards
Diganta Das, PhD ([email protected])CALCE WebinarJanuary 26, 2016
www.calce.umd.edu
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CALCE Introduction• The Center for Advanced Life Cycle Engineering (CALCE) formally
started as an NSF Center of Excellence in systems reliability. • One of the world’s most advanced and comprehensive testing and
failure analysis laboratories• Funded by over 150 of the world’s leading companies and agencies• Supported by over 100 faculty, visiting scientists, research assistants• Received 2009 NSF Innovation Award and NDIA Systems
Engineering Excellence Award.• Received IEEE Standards
Education Award in 2013.• Received University of
Maryland Corporate Connector Award in 2014.
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CALCE Mission and Thrust AreasProvide a knowledge and resource base to support the development and
sustainment of competitive electronic products
Life Cycle Risk, Cost Analysis and Management
Accelerated Testing, Screening and
Quality AssuranceSupply Chain Assessment
and Management
Physics of Failure, Failure Mechanisms and
Material BehaviorDesign for Reliability and
Virtual Qualification
Diagnostic and Prognostic Health
Management
Strategies for Risk Assessment, Mitigation and Management
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Instructor BiographyDr. Diganta Das (Ph.D., Mechanical Engineering, University of Maryland, College Park, B.Tech, Manufacturing Science and Engineering, Indian Institute of Technology) is a member of the research staff at the Center for Advanced Life Cycle Engineering. His expertise is in reliability, environmental and operational ratings of electronic parts, uprating, electronic part reprocessing, counterfeit electronics, technology trends in the electronic parts and parts selection and management methodologies. In addition, Dr. Das is involved in prognostics based risk mitigation of electronics.Dr. Das has published more than 75 articles on these subjects, and presented his research at international conferences and workshops. He had been the technical editor for two IEEE standards and is currently vice chair of the standards group of IEEE Reliability Society. He is a sub group leader for the SAE G-19 counterfeit detection standards group. He is an Associate Editor of the journal Microelectronics Reliability. He is a Six Sigma Black Belt and a member of IEEE, IMAPS and SMTA.
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Abstract
Environmental Stress Screening (ESS) and its accelerated version Highly Accelerated Stress Screening (HASS) are used in some industries for detecting and minimizing defects in the production stream. This Webinar will discuss the standards that are being used in the Industry and show the steps that are the standards catalog as requirements for proper implementation of these screening techniques. It will discuss the level of use the various steps in the industry and how they relate to and differ from the standards based on feedback received by CALCE in a survey. We will also trace back the sources of some of the quantitative assessments used in the standards and identify the features that are in need of update based on current technology developments. The webinar will close with development process of a defects versus tests matrix that can be used for identifying the effective tests in ESS and HASS.
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Outline
• Introduction to screening• What is HALT, ESS and HASS?• Standards used for implementation of ESS and HASS
in industry• Steps in use of ESS standard• Some concerns with use of the standards• Defects based selection of test methods
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• Screening is a process of separation of products with defects from those without defects.
• Screening need not involve load (stress) conditions. Visual inspection can also be a screen.
• The purpose of “stress” screening such as environmental stress screening (ESS) or highly accelerated stress screening (HASS) is to precipitate failures in weak or defective populations using some load (stress) condition(s) without reducing the required useful life of the product.
Screening
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Root Cause Analysis of Failures
Screening In Product Development
Qualification Test for Design
Verification
Qualification Test for Process
Verification
Design Product
Establish Manufacturing
ProcessManufacture Ship
Quality Assurance
Tests and Screens
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Identify potential defects (and the associated failure modes, failure mechanisms, failure sites, and failure-causing conditions) and other
customer-return-causing conditions. Use virtual qualifications, accelerated life testing and customer inputs in the assessment.
Define the set of screens and screen parameters to precipitate (uncover)
defects. Verify with sample screening and error seeding.
Determine where in the manufacturing process flow to apply the screen(s).
Collect and analyze data (use cause and effect diagrams and Pareto plots to facilitate product improvement).
Consider cost factors
Implement 100%.
Conduct trial runs, defect (failure) analysis, and proof-of-screen.
Screening Methodology
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• Overstress failure: a failure which arises as a result of a single load (stress) condition. Examples of load conditions that can cause overstress failures are shock, temperature extremes, and electrical overstress.
• Wearout failure: a failure which arises as a result of cumulative load (stress) conditions. Examples of load conditions that cause cumulative damage are temperature cycling, wear, and material ageing.
Overstress and Wearout Failures
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The “Idealized” Bathtub Curve(Screen to Reduce Failures)
Time
Haz
ard
Rat
e Screen out early life failures and reduce “random” failures
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BackgroundProbability density function
<1
=1
> 1
Infant mortality
Time
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Prob
abili
ty d
ensi
ty
2s
2L
SLSM
Load-Strength InterferenceStrength distributions can be determined by applying a load and assessing the strength for a population of product. Usually it is only necessary to determine the “weak” population or the “weak” tail of the strength distribution.
Load (L) Strength (S)SL
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Load (L) Strength (S)
Prob
abili
ty d
ensi
ty
Load-Strength Interference(result from screen)
SL
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Time
Failure occurrences in defective subpopulations
Num
ber
of fa
ilure
s(p
roba
bilit
y de
nsity
)
Useful life
Screen
Candidate For “Wear-out” Screening
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Summary of HALT, HASS and ESSTypical Test Profile Defects being
AddressedDevelopment Phase
being AppliedStress Level
HALT In Sequence: • Cold Step Stress• Hot Step Stress• Rapid Thermal Transition• Vibration Step Stress• Combined Environment
Defects due toDesign Limitations
Design Phase Highest
HASS In Combination:• Rapid Thermal Transition• Vibration Step Stress
Defects due to Process Variations
End of Manufacturing Phase
High
ESS In Sequence:• Random Vibration• Thermal Cycling
Defects due to Process Variations
Most Cost Effective Stage(s) of Manufacturing Phase
Moderate
DesignEstablish
Manufacturing Process
Manufacture Ship to Customer
HALT ESS, HASS
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• Company internal standards are specified to be used in most responses in HALT and HASS respectively.
• A small number of responses have indicated ‘no specific standard is followed’ and the use of ‘IPC 9592/9592A’ and ‘IESR-RP-PR-003’
Standard(s) being Followed in HALT, HASS and ESS
Examples of standards listed in the question
Choice of Standards in HALT and HASS
IEST-RP-PR003: Standard for HALT and HASS
MIL-STD-2164/ MIL-HDBK 2164A: Environmental Stress Screening Process for Electronic Equipment
MIL-HDBK 344A/ DOD-HDBK 344: Environmental Stress Screening(ESS) of Electronic Equipment
IPC 9592/ IPC 9592A: Requirement for Power Conversion Devices for the Computer and Telecommunication Industries
NAVYMAT P-9492/ NAVMAT P-4855-1A: Navy Manufacturing Screening Program for Electronic Equipment
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Chinese ESS Standards
• Standards published by China on ESS are evaluated: Chinese ESS Standards, GJB-1032 and GJBZ 34 are found to have significant similarities with MIL-HDBK-2164A and MIL-HDBK-344 respectively
• No Chinese HALT or HASS standards are found. • As many products are manufactured or assembled in
China – we might see applications of Chinese standards by manufacturers and laboratories there.
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• Use of MIL-HDBK 344A/DOD-HDBK 344A are most prevalent• Sources of basis of company internal standards are often reported to
be MIL-HDBK 344A and MIL-HDBK-2164A
Choice of Standards in ESS
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Differences Between Two Popular Standards
• MIL-HDBK-344A:Environmental Stress Screening for Electronic Equipment (1993)– Describes a quantitative approach for monitoring and
controlling ESS
• MIL-HDBK-2164A: Environmental Stress Screening Process for Electronic Equipment (1996)– Describes implementation details of ESS. For example,
chamber requirements, stress profile individualization.– MIL-STD-2164 was first published in 1985 and was
converted to MIL-HDBK-2164A in 1996.
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Steps in ESS Implementation as per MIL-HDBK 344A
• Six main steps involved in quantitative approach in MIL-HDBK344A• Purpose: Monitor and control ESS process statistically.
Establish Objectives/
GoalsEstimate Initial Defect Density
Estimate Screening Strength
Refine Estimates
Monitor and Control
Implement Product
Reliability Verification Test (PVRT)
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Inputs to the Steps of MIL-HDBK 344A (1)
Reliability Goal
1. Establish Objectives/Goals
System Complexity
Matrix
Defect Density Vector at
Baseline Stress
2. Estimate Defect Density
Precipitation Efficiency (PE)
Detection Efficiency (DE)
3. Estimate Screening Strength
Stress Adjustment Factor (SAF) from step 2
Field Precipitation Rate (k) from step 3
Estimated Remaining and Initial Defect
Densities (Dremaining and DIN) from step 1 and 2
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Inputs to the Steps of MIL-HDBK 344A (2)
Fallout Data as plot of
cumulative failure vs screen
duration
4. Refine Estimates of
Defect Density and Screening
Strength
Values for Dremaining, DINand SS from
continuously monitored fallout data
Regression line from best fit of actual data
and expected statistical variations
5. Monitor and Control
First Pass PRVT Yield
6. Product Reliability
Verification Test
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Outputs from the Steps of MIL-HDBK 344A (1)
1. Establish Objectives/Goals
2. Estimating Defect Density
2. Estimating Screening Strength
Remaining Defect Density Goal (Dremaining)
Initial Remaining Defect Density
(DIN)
Stress Adjustment
Factor (SAF)
Required Screening
Strength (SS)
Initial ESS Profile for the required SS
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Outputs from the Steps of MIL-HDBK 344A (2)
4. Refining Estimates of
Defect Density and Screening
Strength
5. Monitor and Control
6. Product Reliability
Verification Test
Dremaining, DIN and SS from fallout data
Trend of Dremaining,DIN and SS for future planning
SPC Charts and PARETO Charts
Minimum ESS for field reliability
projectionBaseline DIN, SS and
Dremaining for monitor and control
Need for corrective actions/
reimplementation of ESS
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Defect Density Estimation in MIL-HDBK 344A
• Initial Defect Density (DIN) of a system is estimated using the following relationship in MIL-HDBK 344A
• System Complexity Matrix defined in MIL-STD 2000 is computed for a system by the quantity and quality of the parts and interconnections being used.
• Defect Density Vectors are the estimated initial defect density values at anticipated stress level of parts and interconnections used in a system.
• Defect Density values of different parts for various environments from field data are included in this handbook.
[1] U.S Department of Defense, Environmental Stress Screening (ESS) of Electronic Equipment, MIL-HDBK-344A, 1993.
Initial Defect Density =System Complexity Matrix*Defect Density Vectors
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Example of System Complexity Matrix in MIL-HDBK 344A
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Example of Defect Density of Devices in Various Environments (in PPM) in MIL-HDBK 344A
• 12 alike tables for different devices are included in the handbook for defect density estimation
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Example of Defect Density Vectors (in PPM) in MIL-HDBK 344A
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Evolution of Microelectronics in 30 years
1980s TodayFinest Microelectronic Feature Size [7, 8, 11]
1 μm 22-35nm
Microprocessor Clock Speed [9] 25 MHz
3.5-4.2 GHz
Size of Available Commercial Memory [10]
1MB 256GB
[7] P O'Connor. Future trends in microelectronics - impact on detector readout. SNIC Symposium, Stanford, California, pages 1-6, Jan 2006. [8] J. Lau, C. P. Wong, J. L. Price, and W. Nakayama. Electronic Packaging Design, Materials, Process: McGraw-Hill, 1998.[9] Microprocessor Timeline [Online]. Available at :https://www.raptureready.com/time/rap31d.html (Retrieved from web on Jan 24, 2016), 2015[10] Cost of Semiconductor RAM Over 50 Years: 1970 to 2020 [Online]. Available: http://www.crescentmeadow.com/document_imaging/pdf/22045p.pdf (Retrieved from web on Jan 24, 2016), [11] Nanotechnology: A Brief Overview [Online]. Available: http://barrett-group.mcgill.ca/tutorials/nanotechnology/nano03.htm (Retrieved from web on Jan 24, 2016),
128MB 128GB
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Limitations of Defect Density Estimation in MIL-HDBK 344A
• The method of counting number of parts/ leads/ interconnections over the system for complexity is not considered a valid method any longer.
• Limited data on factory defect rates and field failure rates for parts of various quality grades [12] was used in research conducted by Hughes Aircraft Company [2] to derive the defect density values for several part types, which is not universally applicable to all products.
• The defect densities given for different quality of parts/ interconnects is developed over 20 years ago with, which can be totally invalid with the improvement in quality of parts and assembly technologies.
[12] Institute of Environmental Sciences, Environmental Stress Screening Guidelines, 940 East Northwest Highway, Mount Prospect, IL 60056, 1984.[2] U.S. Air Force, Environmental Stress Screening, RADC-TR-86-149, 1986
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Validity of Screening Strength Calculation in MIL-HDBK 344A
• Screening Strength (SS) is defined as the probability that a specific screen will precipitate a latent defect to a patent defect and detect it by test, given that a latent defect susceptible to the screen is present.
• SS equation is given by the multiplication of Precipitation Efficiency (PE) and Detection Efficiency (DE):
[1] U.S Department of Defense, Environmental Stress Screening (ESS) of Electronic Equipment, MIL-HDBK-344A, 1993.
SS PE * DE
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Screening Strength Calculation: MIL-HDBK 344A• Detection Efficiency (DE) is defined as a measure of the capability
of detecting a patent defect. • The estimation of DE is given as functions of type of testing,
environmental conditions, and defect isolation abilities and these values are assigned as per the table below:
Type of testing performedFunctional only 0.5 – 0.8Functional and parametric 0.8 – 1
Environmental Conditions during testTesting performed under ambient conditions only 0.2 – 0.6 Testing performed concurrently with stress 1
Ability to observe, isolate, and remove a defect without introducing another0.8 – 1
DE=Product of values for factors being considered for DE
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Screening Strength Calculation: MIL-HDBK 344A
• Precipitation Efficiency (PE) is defined as a measure of the capability of a screen to precipitate latent defects to patent defects.
• The estimation of PE is given as by
t: duration of screenk: stress precipitation constant
PE=1-exp(-kt)
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k Values for Different Stresses Included in MIL-HDBK 344A
For Temperature Cycling: k=0.0017 (∆T+0.6)0.6[ln(RATE+2.718)]3
For Constant Temperature: k=0.0017t(∆T+0.6)0.6
For Random Vibration: k=0.0046G1.71
For Swept Sine Vibration: k=0.000727G0.863
For Fixed Sine Vibration: k =0.00047G0.49
(Formulae from RADC-TR-86-149 [2])
[2] U.S. Air Force, Environmental Stress Screening, RADC-TR-86-149, 1986.
PE=1-exp(-kt)
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Limitations of Screening Strength Estimation in MIL-HDBK 344A
• The precipitation efficiency model did not take any parameter of the product into account.
• For detection efficiency, the way to select a value within the range given for each factor is not provided.
• K values of only few stresses are included for precipitation efficiency in the standard. They included temperature cycling, constant temperature, random vibration, swept sine vibration, fixed sine vibration.
• The difference of precipitation efficiency of random vibrations between a repetitive shock shaker and a electrodynamic shaker, which is shown to have different effects [2] [6], is not differentiated in the standard.
[2] U.S. Air Force, Environmental Stress Screening, RADC-TR-86-149, 1986[6] IEST, HALT and HASS, IEST-RP-PR003.1, 2012.
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Limitations of Screening Strength Estimation in MIL-HDBK 344A
• Mathematical expressions for Precipitation Efficiency are derived by Hughes Aircraft Company in 1982 [3] by data collected by Mcdonnel Aircraft Company in 1980 [4] and by Grumman Aerospace Corporation in 1973 [5] respectively. – Not universally applicable since the coefficients in these models are
from regression analysis of specific screened results of selected products
– With several decades of changes in technology in the electronics industry, these models and model coefficients are completely out of date.
[3] Saari, A.E., Schafer. R. E., and VanDenBerg, S.J., “Stress Screening of Electronic Hardware”, Hughes Aircraft Company, Ground Systems Group, Fullerton, CA., RADC-TR-82-87, May 1982.
[4] Anderson, J.R., “Environmental Burn-in Effectiveness”, McDonnell Aircraft Company, St. Louis, NO., Report No. AFWAL TR-80-3086, August 1980.
[5] Kube, F., Hlrschberger, G., “An Investigation to Determine Effective Equipment Environmental Acceptance Test Methods”, Grunman Aerospace Corporation, Report No., ADR14-04-73.2, April 1973.
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• Simulation of relevant defects and failure mechanisms
• Step stress and analysis (overstress)
• Cumulative stress and analysis (wearout)
• Error seeding (especially useful if there is a “remote” potential for defects in products with high reliability requirements) and analysis
• Feedback from test and field (failure analysis)
Techniques to Establish Screen Intensity
Comment: A combination of these methods may be necessary
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Thermal Stability Criteria for ESS
• Thermal stability criteria are used for describing how a unit being exposed to a specified temperature is considered thermally stable.
• Different thermal stability criteria in two popular ESS handbooks, that are not exclusive for certain products, are included for comparison:
• MIL-HDBK-344A – The component in the unit under test which has the longest thermal lag
should not have a temperature change more than 2oC/hour [1]. (whole assembly should reach the specified temperature)
• MIL-HDBK-2164A– Average of times required for 2/3 of thermocouples reaching within 10oC
of the temperature set point, where thermocouples are attached to representable locations for thermal analysis within the equipment [13].
[1] U.S Department of Defense, Environmental Stress Screening (ESS) of Electronic Equipment, MIL-HDBK-344A, 1993.[13] U.S Department of Defense, Environmental Stress Screening (ESS) Process For Electronic Equipment, MIL-HDBK-2164A, 1996.
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Illustration of a Thermally Stable Board Based on Different Thermal Stability Criteria
Component with the longest thermal lag in the unit Locations of interests
Based on MIL-HDBK 344A Based on MIL-HDBK 2164A• When the component longest thermal lag is stabilized at the desired temperature, the
whole unit should also reach that temperature.• A unit is considered thermally stable when 2/3 of locations of interests have reached
within 10oC
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Comparison of the Two CriteriaMIL-HDBK 344A
(with more stringent criteria)• Defects that are sensitive to
thermal cycling/ dwell can be ‘searched for’ within the unit whether it is a suspected location or not
• Useful life for some parts can be over consumed while waiting for other parts to reach the thermal extremes
• Time and cost associated with the longer dwell time can be higher.
MIL-HDBK 2164A(with less stringent criteria)
• The time and cost needed for ESS is likely to be less because locations of interests are considered for thermal stability
• Defects at unexpected locations are less likely to be uncovered
• More preparation has to be performed to evaluate the sensitivity of defects at different locations for representable locations be selected
Conclusion: Depending on the goal of ESS, one can select a handbook/ standard with desirable thermal stability criteria and an applicable scope. Mix and matching content of different standards for particular purposes is not recommended.
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Thermal Stability Criteria for HALT and HASS
Although the standards published on HALT and HASS are not widely used according to the survey result. Examples of different thermal stability criteria for HALT and HASS can be found these standards.• IEST-RP-PR003.1
- Thermal stability is achieved when the point of maximum thermal mass on the UUT is within 2oC of the desired temperature, with a rate of change of less than 2oC/hour [6].
• IPC-9592A- Determined by thermocouples – depends on size and weight of the
UUT [14].
[6] IEST, HALT and HASS, IEST-RP-PR003.1, 2012.[14] IPC, Requirements for Power Conversion Devices for the Computer and Telecommunications Industries, IPC-9592A, 2010.
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Defects of Most Concern in Surveys
Connectors Board Layers Board
Metallizations Plated Through
Holes (PTHs)
Solder Joints Passive Parts Integrated Circuits
• The top four defects of concern for detection are consistent in all the test: solder joints, connectors, ICs, and passive parts
• Other defects of concern specified by responses include bus bars, IGBT modules, current sensors in the HASS survey, overall structural integrity in the HALT survey and defective insulation materials in the ESS survey.
A selection was given as below but the respondents could add others
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Focus on Defect Types instead of Failure Modes
• Same defects can result in different failure modes depending on the environment they are being exposed to.
• Eliminating one defect during design or manufacturing phase can prevent multiple possible failure mechanisms/modes in the field
• Therefore, we are interested in defect types that are of concern for detection by companies
• Defect versus Stress Database is being developed to provide the most possible and efficient way to precipitate common defect types.
• However, while the database is being prepared, we also have looked into and have noted the possible failure modes of defects under different environments.
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Failures in HALT, HASS and ESS• Failure modes being uncovered in HALT, HASS and ESS are
expected to be different due to the different stress conditions.• Since defect types were of interests, the variation in failure modes
in HALT, HASS and ESS from this company’s experience did not reveal in the survey result.
• Some of the suggested failure modes can be expressed as defect types:– Loss of communication and excessive voltage drop as component/IC defects– CTE mismatch between plastic & metal as overall structural integrity
• Conclusion: While acknowledging the circuit design failures during HALT, defects-driven failures is still the primary focus of this project because of the highly product-dependent circuit designs and potential problems, and limitations in circuit design corrections
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Delivery of Defect versus Test as Web Site
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Delivery of Defect versus Test as Web Site
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Delivery of Defect versus Test as Web Site
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Points to Remember• If Proof of Screen is used to confirm ESS or HASS profile is
not destructive, this can represent a risk if piece part suppliers are changed, manufacturing processes are changed, or even when piece part suppliers change internal components, processes, or manufacturing locations.
• HASA (Highly Accelerated Stress Audit) in conjunction with non-HASS ESS as a possible strategy to gain the benefits of HASS to detect systemic changes in infant mortality risk in products without exposing 100% of product to potentially destructive HASS (due to changes in product noted above) over time since the last proof of screen activity.
Thanks to Ted Schnetker Ph.D. - United Technologies Corporation
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Points to Remember• There is value in examining the defects found in testing not
only to adjust ESS/HASS, but to also evaluate the possibility of additional process controls or design/ supplier changes to reduce the PPM of infant mortality defects entering the manufacturing process.
• In theory with sufficient process and materials control and design margin, HASS / ESS can be minimized or even eliminated.
Thanks to Ted Schnetker Ph.D. - United Technologies Corporation
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What Have we Covered?• Defects Density Estimations
– System complexity method not appropriate– Defect density estimates out of date
• Screening Strength Calculation in MI-HDBK 344A– Mathematical expressions for precipitation efficiency is derived 20 years ago from
company internal data for selected products
• Alternative Thermal Stability Criteria– Standards with different thermal stability criteria for HALT, HASS and ESS are available
for selection based on the goals of the processes– Pros and Cons for more and less stringent criteria are analyzed– Mix and match of contents from different standards for particular purposes such as cost
and time reduction is not recommended.
• Defects Based Selection of Tests– Defect types can result in different failure modes in the field. – Eliminate a defect can prevent multiple failure modes/ mechanisms
• Points to Remember from Ted Schnetker, UTC
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What do We Offer at CALCE?
• Simulation of effects of stress on electronics hardware
• Development and review of test plans• Training on accelerated testing• Analysis of test data• Failure and degradation analysis