ESS and HASS: Concerns with the Practices and Standards

University of Maryland
Copyright © 2016 CALCE
1
Center for Advanced Life Cycle Engineering
Innovation Award Winner
ESS and HASS: Concerns with the
Practices and Standards
Diganta Das, PhD (diganta@umd.edu)
CALCE Webinar
January 26, 2016
www.calce.umd.edu

2
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.

3
CALCE Mission and Thrust Areas
Provide 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 Assurance
Supply 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

4
Instructor Biography
Dr. 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.

5
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.

6
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

8
Root Cause Analysis of Failures
Screening In Product Development
Qualification
Test for Design
Verification
Qualification
Test for Process
Verification
Design
Product
Establish
Manufacturing
Process
Manufacture Ship
Quality
Assurance
Tests and Screens

9
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

10
• 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

11
The “Idealized” Bathtub Curve
(Screen to Reduce Failures)
Time
HazardRate
Screen out early life
failures and reduce
“random” failures

12
Background
Probability density function
 <1
 =1
 > 1
Infant mortality
Time

13
Probabilitydensity
2
s
2
L
SL
SM
 


Load-Strength Interference
Strength 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 

14
Load (L) Strength (S)
Probabilitydensity
Load-Strength Interference
(result from screen)
SL 

15
Time
Failure occurrences in
defective subpopulations
Numberoffailures
(probabilitydensity)
Useful
life
Screen
Candidate For “Wear-out” Screening

16
Summary of HALT, HASS and ESS
Typical Test Profile Defects being
Addressed
Development Phase
being Applied
Stress Level
HALT In Sequence:
• Cold Step Stress
• Hot Step Stress
• Rapid Thermal Transition
• Vibration Step Stress
• Combined Environment
Defects due to
Design
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
Design
Establish
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

18
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.

19
• 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

20
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.

21
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/
Goals
Estimate Initial
Defect Density
Estimate
Screening
Strength
Refine
Estimates
Monitor and
Control
Implement
Product
Reliability
Verification
Test (PVRT)

22
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

23
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, DIN
and 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

24
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

25
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
projection
Baseline DIN, SS and
Dremaining for
monitor and control
Need for corrective
actions/
reimplementation of
ESS

26
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

27
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

29
Example of Defect Density Vectors (in PPM)
in MIL-HDBK 344A

30
Evolution of Microelectronics in 30 years
1980s Today
Finest 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

31
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

33
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 performed
Functional only 0.5 – 0.8
Functional and parametric 0.8 – 1
Environmental Conditions during test
Testing 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 another
0.8 – 1
DE=Product of values for factors being considered for DE

34
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 screen
k: stress precipitation constant
PE=1-exp(-kt)

35
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)

36
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.

37
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.

38
• 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

39
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.

40
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

41
Comparison of the Two Criteria
MIL-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.

42
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.

43
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

44
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.

45
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

46
Delivery of Defect versus Test as Web Site

47

48

49
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

50
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

51
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

52
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

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