ESS and HASS: Concerns with the Practices and Standards

University of MarylandCopyright © 2016 CALCE

1Center for Advanced Life Cycle EngineeringInnovation Award Winner

ESS and HASS: Concerns with the Practices and Standards

Diganta Das, PhD ([email protected])CALCE WebinarJanuary 26, 2016

www.calce.umd.edu



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.



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



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.



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.



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



• 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



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



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



• 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



The “Idealized” Bathtub Curve(Screen to Reduce Failures)

Time

Haz

ard

Rat

e Screen out early life failures and reduce “random” failures



BackgroundProbability density function

<1

=1

> 1

Infant mortality

Time



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



Load (L) Strength (S)

Prob

abili

ty d

ensi

ty

Load-Strength Interference(result from screen)

SL



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



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



• 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



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.



• 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



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.



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)



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



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



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



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



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



Example of System Complexity Matrix in MIL-HDBK 344A



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



Example of Defect Density Vectors (in PPM) in MIL-HDBK 344A



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



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



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



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



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)



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)



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.



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.



• 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



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.



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



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.



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.



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



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.



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



Delivery of Defect versus Test as Web Site



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



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



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



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

ESS and HASS: Concerns with the Practices and Standards

Engineering

Transcript of ESS and HASS: Concerns with the Practices and Standards