SIST EN 61163-1:2008

SLOVENSKI STANDARD
01-februar-2008
Presejalno preskušanje glede zanesljivosti - 1. del: Popravljivi sestavi, izdelani v
lotih (IEC 61163-1:2006)
Reliability stress screening - Part 1: Repairable assemblies manufactured in lots (IEC
61163-1:2006)
Zuverlässigkeitsvorbehandlung durch Beanspruchung - Teil 1: Instandsetzbare
Baugruppen, losweise gefertigt (IEC 61163-1:2006)
Déverminage sous contraintes - Partie 1: Assemblages réparables fabriqués en lots (IEC
61163-1:2006)
Ta slovenski standard je istoveten z: EN 61163-1:2006
ICS:
03.120.01
21.020
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN 61163-1
NORME EUROPÉENNE
December 2006
EUROPÄISCHE NORM
ICS 03.120.01; 03.120.30; 21.020

English version
Reliability stress screening
Part 1: Repairable assemblies manufactured in lots
(IEC 61163-1:2006)
Déverminage sous contraintes Zuverlässigkeitsvorbehandlung
Partie 1: Assemblages réparables durch Beanspruchung
fabriqués en lots Teil 1: Instandsetzbare Baugruppen,
(CEI 61163-1:2006) losweise gefertigt
(IEC 61163-1:2006)
This European Standard was approved by CENELEC on 2006-11-01. CENELEC members are bound to comply
with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard
the status of a national standard without any alteration.

Up-to-date lists and bibliographical references concerning such national standards may be obtained on
application to the Central Secretariat or to any CENELEC member.

This European Standard exists in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CENELEC member into its own language and notified
to the Central Secretariat has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Cyprus, the Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Central Secretariat: rue de Stassart 35, B - 1050 Brussels

© 2006 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 61163-1:2006 E
Foreword
The text of document 56/1102/FDIS, future edition 2 of IEC 61163-1, prepared by IEC TC 56,
Dependability, was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as
EN 61163-1 on 2006-11-01.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2007-08-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2009-11-01
Annex ZA has been added by CENELEC.
__________
Endorsement notice
The text of the International Standard IEC 61163-1:2006 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standards indicated:
IEC 60068 NOTE  Harmonized as EN 60068 (series) (not modified).
IEC 61014 NOTE  Harmonized as EN 61014:2003 (not modified).
__________
- 3 - EN 61163-1:2006
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications

The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.

NOTE  When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD
applies.
Publication Year Title EN/HD Year

1)
IEC 60050-191 - International Electrotechnical Vocabulary - -
(IEV)
Chapter 191: Dependability and quality of
service
1) 2)
IEC 60068-2-2 - Environmental testing EN 60068-2-2 1993
Part 2: Tests - Tests B: Dry heat

1) 2)
IEC 60068-2-6 - Environmental testing EN 60068-2-6 1995
Part 2: Tests - Test Fc: Vibration (sinusoidal)

1) 2)
IEC 60068-2-14 - Environmental testing EN 60068-2-14 1999
Part 2: Tests - Test N: Change of temperature

1) 2)
IEC 60068-2-29 - Environmental testing EN 60068-2-29 1993
Part 2: Tests - Test Eb and guidance: Bump

1) 2)
IEC 60068-2-30 - Environmental testing EN 60068-2-30 2005
Part 2-30: Tests - Test Db: Damp heat, cyclic
(12 h + 12 h cycle)
1) 2)
IEC 60068-2-64 - Environmental testing EN 60068-2-64 1994
Part 2: Test methods - Test Fh: Vibration,
broad-band random (digital control) and
guidance
1) 2)
IEC 60068-2-78 - Environmental testing EN 60068-2-78 2001
Part 2-78: Tests - Test Cab: Damp heat,
steady state
1) 2)
IEC 60300-2 - Dependability management EN 60300-2 2004
Part 2: Guidelines for dependability
management
1) 2)
IEC 61165 - Application of Markov techniques EN 61165 2006

1)
IEC 61649 - Goodness-of-fit tests, confidence intervals - -
and lower confidence limits for Weibull
distributed data
1)
ISO 2041 - Vibration and shock - Vocabulary - -

1)
Undated reference.
2)
Valid edition at date of issue.

NORME CEI
INTERNATIONALE
IEC
61163-1
INTERNATIONAL
Deuxième édition
STANDARD
Second edition
2006-06
Déverminage sous contraintes –
Partie 1:
Assemblages réparables fabriqués en lots

Reliability stress screening –
Part 1:
Repairable assemblies manufactured in lots

 IEC 2006 Droits de reproduction réservés  Copyright - all rights reserved
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МеждународнаяЭлектротехническаяКомиссия
Pour prix, voir catalogue en vigueur
For price, see current catalogue

61163-1  IEC:2006 – 3 –
CONTENTS
FOREWORD.9
INTRODUCTION.13
1 Scope.19
2 Normative references .19
3 Terms and definitions .23
4 Symbols .27
5 General description .27
5.1 The reliability stress screening principle .27
5.2 Failure categories.31
5.3 Time of occurrence of failures .33
6 Planning .33
6.1 Stress conditioning.33
6.2 Evaluation of the failure-free period T .37
M
6.3 Time graphs for determination of the failure-free period .41
7 Pilot-production screening .51
7.1 General .51
7.2 Collection of information.51
7.3 Evaluation of information.51
7.4 Re-evaluating the failure-free period T .53
M
8 Mature production screening .55
8.1 General .55
8.2 Collection of information.55
8.3 Evaluation of information.55
8.4 Dealing with discrepancies .55
8.5 Eliminating reliability stress screening .59
Annex A (informative) Stress conditions – General information .61
Annex B (informative) Stress conditions – Temperature .67
Annex C (informative) Stress conditions – Vibration and bump .75
Annex D (informative) Stress conditions – Humidity .87
Annex E (informative) Stress conditions – Operational stress .93
Annex F (informative) Voltage stress .97
Annex G (informative) Highly accelerated stress screening.99
Annex H (informative) Bimodal distributions – Weibull plotting and analysis.101
Annex I (informative) Evaluation of the failure-free period and the average screening
duration.113
Annex J (informative) Worked example .133
Bibliography.161

61163-1  IEC:2006 – 5 –
Figure 1 – Conceptual difference between reliability screening and growth .15
Figure 2 – Typical flow for the design and modifications of reliability stress screening
processes for repairable assemblies .17
Figure 3 – Typical flow of hardware assemblies from the component manufacturer to
the end user .21
Figure 4 – Reliability stress screening of repairable assemblies.29
Figure 5 – Dependency of categories of failures .33
Figure 6 – Elements of stress conditioning.33
Figure 7 – Assembly showing screening duration.37
Figure 8 – Time graphs for the determination of the failure free period .43
Figure 9 – Example of an experimentally determined Weibull curve that is levelling off
at p % failures.53
1,5
t
 
-
 
 
Figure H.1 – The S-curve for a bimodal Weibull distribution mixed by F (t) = 1− e
1,5
 t 
 
-
 
60 000
 
and F (t) = 1− e in the proportions 15 % and 85 %, respectively .103
Figure H.2 – Estimation of p, β and η for the purpose of reliability screening
1 1
optimization .105
Figure H.3 – The c.d.f. curves for bimodal exponential distribution.109
Figure H.4 – The hazard rate function for bimodal exponential distribution.111
Figure I.1 – The basic system .113
Figure I.2 – An assembly surviving the screening period T with n remaining
RE
M
weak components .117
Figure I.3 – Possible states when a component fails during the stress screening .117
Figure I.4 – Assembly states after failure and repair .117
Figure I.5 – Time graph for evaluation of the failure-free screening period .121
Figures I.6a and I.6b – Average screening duration versus the normalized failure-free
T
M
period – p = 0,000 5 and p = 0,001 .125
c c
m
F1
Figures I.6c and I.6d – Average screening duration versus the normalized failure-free
T
M
period  – p = 0,002 and p = 0,005 .127
c c
m
F1
Figures I.6e and I.6f – Average screening duration versus the normalized failure-free
T
M
period – p = 0,015 and p = 0,02 .129
c c
m
F1
Figures I.6g and I.6h – Average screening duration versus the normalized failure-free
T
M
period – p = 0,03 and p = 0,04.131
c c
m
F1
Figure J.1 – Derivation of the failure-free period T .139
M
Figure J.2 – Derivation of the average screening duration.143
Figure J.3 – Weibull plot of the observed and predicted failure pattern for the pilot
production PBAs .149

61163-1  IEC:2006 – 7 –
Figure J.4 – Weibull plot of relevant failures and predicted S-curve for the pilot
production screening .153
Figure J.5 – Time graph (corrected) for determination of the failure-free period .155
Figure J.6 – Time graph (corrected) for evaluation of the screening duration .157

Table A.1 – Stress types – Indication of cost of application.63
Table J.1 – Relation between sensitivity of flaws and stresses.137
Table J.2 – Observed failure ranks and times to first failure for the pilot production .145
Table J.3 – Revised rank values .151

61163-1  IEC:2006 – 9 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
___________
RELIABILITY STRESS SCREENING –

Part 1: Repairable assemblies manufactured in lots

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61163-1 has been prepared by IEC technical committee 56:
Dependability.
This second edition cancels and replaces the first edition published in 1995.
The main changes with respect to the previous edition are as follows:
– alignment of terminology on Weibull distribution with the future (second) edition of
IEC 61649 (currently a Committee Draft);
– inclusion of a procedure for starting an RSS process without previous information;
– inclusion of highly accelerated stress screening; and
– inclusion of combinations of stresses.

61163-1  IEC:2006 – 11 –
The text of this standard is based on the following documents:
FDIS Report on voting
56/1102/FDIS 56/1118/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in
the data related to the specific publication. At this date, the publication will be
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.
61163-1  IEC:2006 – 13 –
INTRODUCTION
Quality control and good design are prerequisites for reliability. However, in cases where an
assembly has an unacceptably low reliability in the early failure period, a reliability screening
process may be necessary.
An unacceptably low reliability level can be different from one customer to another, or can be
based on general market requirements.
Reliability stress screening (RSS) and reliability growth programmes both aim at
improvements in the reliability found by the user. However, the two methods are different in
principle:
– a reliability growth programme is a development activity, the purpose of which is to
improve the inherent reliability performance of the assemblies by effecting changes to the
design (see IEC 61014 and IEC 61164);
– the purpose of reliability stress screening is to detect and remove flaws; it is part of the
production process, and should not be relied upon to reveal inadequacies in design.
Furthermore, the two methods affect the reliability performance differently. This is illustrated
in Figure 1. In principle, a reliability screening programme "cuts away" the early failure period
(or part thereof), while a reliability growth programme reduces the overall failure rate level. A
reliability growth programme may affect the need for a reliability screening programme if the
flaws are of such a nature that they can be prevented from being present at all.
The user of this standard should be aware that reliability stress screening does not improve
the intrinsic reliability of the assemblies under consideration and, where possible, should be
made unnecessary by reliability growth programmes and/or quality control.
In this standard the term “Item” is used when it is not necessary to distinguish between
components, assemblies and system(s).
The specific purpose of carrying out a reliability screening process is to detect and remove
flaws in hardware assemblies before they reach the customer, or are assembled into higher-
level products. This means that, in principle, every hardware assembly under consideration
should be included when a reliability screening process is introduced into a production
process.
Reliability screening may cover hardware assemblies of different types and at different levels
of the manufacturing process. This standard covers composite items – assemblies which are
intended to be repaired. Once the allowable fraction of weak assemblies has been specified,
the methods in this standard lead to the most economical screening process for assemblies
that are manufactured in lots. This is because not all types of assemblies need to be
subjected to a reliability screening process. Only the types of assemblies likely to contain
flaws should be included. Furthermore, the extent (stress conditions, duration, etc.) to which
these selected assembly types will be subjected to screening needs to be minimized.
In reliability stress screening the flaws are precipitated into failures by exposure of the
assemblies to a suitable stress, for example environmental stress, operational stress, or a
combination of these. Reliability stress screening is often called environmental stress
screening (ESS).
61163-1  IEC:2006 – 15 –
If rogue components are known about and proved to originate in the component
manufacturing process, it is much more effective to use screening e.g. burn-in of the rogue
components in question instead of the assembly. However screening a component cannot
remove flaws introduced in the assembly process (e.g. soldering, handling (ESD) etc.).
The typical steps in a reliability stress screening process are illustrated in Figure 2.
Failure rate
Equipment version A
Failure pattern before
reliability improvements
are introduced
0 Time to first failure
Reliability screening IEC 61163 series Reliability growth IEC 61014
Applicable to hardware and
software containing
Applicable to hardware
systematic weaknesses
containing flaws
Failure rate Failure rate Equipment version B
Equipment version A
Failure pattern after
Failure pattern before
reliability screening
reliability improvements
are introduced
Remaining failures are caused
Remaining failures are
by remaining flaws and
caused by residual weakness
systematic weaknesses
(including flaws)
Part "cut" away
Overall level reduced
by reliability
by reliability growth
screening
0 Time to first failure 0 Time to first failure

IEC  1026/06
NOTE This standard addresses reliability screening only. For reliability growth see IEC 61014 and IEC 61164.
Figure 1 – Conceptual difference between reliability screening and growth

61163-1  IEC:2006 – 17 –
Start
Perform the reliability stress
Specify the maximum
screening, collect and analyse
allowable fraction of weak
the failure information
assemblies
generated 1)
J.2 step 1
6.3, 7, 8 and J.3
Evaluate the actual
fraction of weak
Design of modify (if necessary)
assemblies
the reliability stress
J.2 step 2
screening
6.2 and J.2 step 3 to step 5
Is the actual fraction
Reliability stress
No
of weak assemblies
screening is necessary
equal to or lower than the
J.2 step 2
specified value?
Yes
Reliability stress
srceening is not
necessary
8.5 and J.2 step 2
Stop
IEC  1027/06
1)
The result of the analysis of the failure causes may be used in a reliability growth and quality control
programme.
Figure 2 – Typical flow for the design and modifications of reliability stress screening
processes for repairable assemblies

61163-1  IEC:2006 – 19 –
RELIABILITY STRESS SCREENING –

Part 1: Repairable assemblies manufactured in lots

1 Scope
This part of IEC 61163 describes particular methods to apply and optimize reliability stress
screening processes for lots of repairable hardware assemblies, in cases where the
assemblies have an unacceptably low reliability in the early failure period, and when other
methods, such as reliability growth programmes and quality control techniques, are not
applicable. The reasons for using reliability stress screening may be time constraints and/or
the very nature of the deficiencies that the reliability stress screening is designed to catch.
The processes apply to any stage of a series production of repairable assemblies (see
Figure 3). The methods for setting up a process can be used during production planning,
during pilot-production, as well as during well-established running production.
A prerequisite for the application of the methods is that a certain level of flaws remaining in
the outgoing assembly can be specified.
The processes described are general processes for reliability stress screening in cases where
no specific process is described in a product standard. They are also intended for use by IEC
committees in connection with preparation of product standards. A reliability stress screening
process can form part of an overall reliability programme (see IEC 60300-2).
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 60050(191): International Electrotechnical Vocabulary (IEV) – Chapter 191: Dependability
and quality of service
IEC 60068-2-2: Environmental testing – Part 2-2: Tests – Test B: Dry heat
IEC 60068-2-6: Environmental testing – Part 2-6: Tests – Test Fc: Vibration (sinusoidal)
IEC 60068-2-14: Environmental testing – Part 2-14: Tests – Test N: Change of temperature
IEC 60068-2-29: Environmental testing – Part 2-29: Tests – Test Eb and guidance: Bump
IEC 60068-2-30: Environmental testing – Part 2-30: Tests – Test Db: Damp heat, cyclic
(12 h + 12 h cycle)
IEC 60068-2-64: Environmental testing – Part 2-64: Test methods – Test Fh: Vibration, broad-
band random (digital control) and guidance
IEC 60068-2-78: Environmental testing – Part 2-78: Tests – Test Cab: Damp heat, steady
state
61163-1  IEC:2006 – 21 –
IEC 60300-2: Dependability management – Part 2: Guidelines for dependability management
IEC 61165: Application of Markov techniques
IEC 61649, Goodness-of-fit tests, confidence intervals and lower confidence limits for Weibull
distributed data
ISO 2041, Vibration and shock – Vocabulary
Possible applications of reliability stress screening process for repairable items as indicated by the arrows below.
Component manufacturer
System manufacturer
Material Component Component Subsystem System System
level level level level level level
IEC  1028/06
NOTE Screening may be made on subsystems (left black circle and open circle) or on system level (right black
circle).
Figure 3 – Typical flow of hardware assemblies from the component manufacturer
to the end user
61163-1  IEC:2006 – 23 –
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
NOTE 1 Unless otherwise stated, general reliability terms used in this standard conform to IEC 60050(191).
NOTE 2 Terms of particular importance for reliability stress screening of repairable assemblies are quoted with
the IEC 60050(191) reference number stated in square brackets. Where certain notes do not apply, the term
“modified” has been used. All comments on an IEV term, relevant to reliability stress screening, are stated as
"additional notes".
NOTE 3 Other terms defined in this clause are specific to reliability stress screening.
3.1
reliability improvement
process undertaken with the deliberate intention of improving the reliability performance by
eliminating causes of systematic failures and/or by reducing the probability of occurrence of
other failures
[IEV 191-17-05]
ADDITIONAL NOTE Reliability stress screening reduces the probability of occurrence of other failures. The
systematic failures are principally catered for by a reliability growth programme, but some may appear during
reliability screening.
3.2
reliability screening
process of detection of flaws and removal or repair of weak assemblies for the purpose of
reaching rapidly the reliability level expected during the useful life
NOTE 1 IEV 191-17-02 defines the term "burn-in". This term, however, is used by many manufacturers to
describe a so-called "soak test", which is only one of many possible ways of screening. Furthermore, "burn-in" may
include ageing, the purpose of which is to stabilize parameters, and in many cases where no failures occur.
NOTE 2 IEV 191-14-09 defines the term "screening test". This term, however, is defined too broadly to be
applicable in the present context, because it encompasses screening for any type of non-conformities.
Furthermore, reliability screening is a process, not a test.
3.3
reliability stress screening
reliability screening process using environmental and/or operational stresses as means of
detecting flaws by precipitating them as detectable failures
NOTE Reliability stress screening is designed with the intention of precipitating flaws into detectable failures. An
ageing process designed with the intention of stabilizing parameters is not a reliability screening process, and
therefore, lies outside the scope of this standard.
3.4
item
any part, component, device, subsystem, functional unit, equipment or system that can be
individually considered
NOTE 1 An item may consist of hardware, software or both, and may also, in particular cases, include people.
NOTE 2 In French the term "entité" is preferred to the term "dispositif" due to its more general meaning. The term
"dispositif" is also the common equivalent for the English term "device".
NOTE 3 In French the term "individu" is used mainly in statistics.
NOTE 4 A number of items, for example a population of items or a sample, may itself be considered as an item.
[IEV 191-01-01]
ADDITIONAL NOTE 1 In this standard the term “item” is used when there is no need to distinguish between
components, assemblies and system(s)

61163-1  IEC:2006 – 25 –
ADDITIONAL NOTE 2 In the context of reliability screening, only the hardware part of an item is relevant. Current
examples are electronic components, assemblies, equipment, and hardware parts of systems.
3.5
assembly
any composite item which is intended to be repaired
3.6
weak assembly
assembly which has a high probability of failing early in life, due to a flaw
3.7
component
any single item which is not intended to be repaired
3.8
component class
group of components characterized by having one or more of the following features in
common
– technology;
– type;
– manufacturer;
– batch
3.9
rogue component class
component class, which is likely to contain components with inherent and/or induced flaws
NOTE The lifetime distribution of a rogue component class can, for the purpose of reliability stress screening, be
approximated with a bimodal distribution. This means that the individual component may be either weak or strong.
3.10
relevant failure
failure that should be included in interpreting test, or operational results, or in calculating the
value of a reliability performance measure
NOTE The criteria for inclusion should be stated.
[IEV 191-04-13]
ADDITIONAL NOTE The criterion for inclusion here is that the failure is caused by either an induced or an
inherent flaw.
3.11
weakness
any imperfection (known or unknown) in an assembly, capable of causing one or more
weakness failures
NOTE Each type of weakness is assumed to be statistically independent of all other such types.
3.12
weakness failure
failure due to weakness in the assembly itself when subjected to stress within the stated
capability of the assembly
NOTE A weakness may be either inherent or induced.
[IEV 191-04-06, modified]
61163-1  IEC:2006 – 27 –
3.13
flaw
weakness in hardware which gives rise to early weakness failures
NOTE A flaw is localized to a component, or to an interaction between components, with characteristics close to
the margins of the design requirements.
3.14
inherent flaw
flaw in an assembly related to its technology and manufacturing process
3.15
induced flaw
flaw in an assembly related to assembling, testing, handling, or other manipulation of the
assembly after it has been manufactured
NOTE The induction may take place at the component manufacturer's plant, during transportation or at the
system manufacturer's plant.
3.16
early failure period
that early period, if any, in the life of an item, beginning at a given instant of time and during
which the instantaneous failure intensity for a repaired item, or the instantaneous failure rate
for a non-repaired item, is considerably higher than that of the subsequent period
[IEV 191-10-07, modified]
ADDITIONAL NOTE The early failure period is the period where the weak assemblies fail.
4 Symbols
For the purposes of this standard, the following symbols apply.
m the mean time to failure for the weak components in the rogue component
F1
classes lumped together
m the mean time to first failure for the weak assemblies among the assemblies
Fs
under consideration
N the sum of the numbers of components in the rogue component classes
p the acceptable fraction of weak assemblies remaining after reliability stress
B
screening
p the fraction of weak components in the rogue component classes lumped
c
together
p the fraction of weak assemblies before reliability stress screening
s
T average duration of reliability screening per assembly
B
T the failure-free period an assembly has to survive before submission to the next
M
production step or to the customer
5 General description
5.1 The reliability stress screening principle
The general principle of reliability stress screening is shown on the flow diagram in Figure 4.
According to this principle, an assembly shall survive a so-called "failure-free period", T ,
M
before it is released to the next step of production, or to the customer. Other screening
principles may be possible, but are not covered by this standard.

61163-1  IEC:2006 – 29 –
Start
Testing
Repair
No
Yes
Yes
Function No
Scrapping?
Ok?
Monitoring
type?
A B C
Stop
First partial
stress
conditioning
Stress
conditioning
First
and
testing
continuous
monitoring
No
Function
In case
OK?
the monitoring
Stress
Yes system reveals a
conditioning
failure the item is
Second partial
taken out for repair
stress
1)
conditioning
Second
testing
Yes
Failure?
No
Function
Ok?
No
Yes
Final
Testing
testing
No No
Function
Function
Ok?
Ok?
Yes
Yes
Release Release
Release
IEC  1029/06
1)
Sometimes it may not be practical to remove and repair the failed assemblies before the end of the period T
M
(see 6.1.3).
Figure 4 – Reliability stress screening of repairable assemblies

61163-1  IEC:2006 – 31 –
The flow diagram shows three alternatives in connection with stress conditioning:
– alternative A shows two function checks, one before and one after the stress conditioning;
– alternative B shows performance monitoring at discrete points in time with time intervals,
preferably selected according to a logarithmic scale, so that the closest monitoring takes
place at the beginning of the stress conditioning;
– alternative C shows continuous monitoring during the entire stress conditioning. This
alternative is preferable, especially for complex products, because of:
• time and cost saving;
• detection of intermittent failures and of failures present only during the action of the
stress;
• avoidance of stressing after a failure.
Performance monitoring is of particular importance during pilot-production reliability stress
screening. During reliability stress screening of mature production the performance monitoring
under stress conditioning may be deleted, according to the circumstances. However, the two
function checks, one before and one after the stress conditioning period, can never be
omitted. It is essential that assemblies are not put directly under stress conditioning without
the initial function check.
The extent and the details of the functional checking before, during and after the stress
conditioning depend strongly on the nature and intended function of the assemblies in
question. This standard contains no guidance in that respect. The procedures described
hereafter, however, presume that the function checks are efficient in evidencing failures.
The further details of the screening procedures depend on the time phase from product
design to mature production. Three stages are considered:
– planning of reliability stress screening;
– pilot-production reliability stress screening;
– mature production reliability stress screening.
5.2 Failure categories
Assemblies that fail during a reliability stress screening shall be carefully examined in order to
establish the failure modes, mechanisms, and/or causes.
For the purpose of defining corrective actions, the failure shall be classified according to the
following three categories, based on an assessment of the above-mentioned examination
result:
a) inadequate product design;
b) inherent flaws;
c) induced flaws.
Referring to Figure 5, the classification may differ depending on whether the assessment
takes place at the component manufacturer’s or at the assembly manufacturer’s.
Inadequate component design and flaws induced into the component by the component
manufacturer become inherent flaws for the assembly manufacturer.

61163-1  IEC:2006 – 33 –
In most cases, only the induced and inherent flaws can be weeded out by the screening
process. However, in some cases a screening process may be applied to cater for marginal
design problems, and/or for processes, which are difficult to control.

IEC  1030/06
Figure 5 – Dependency of categories of failures
5.3 Time of occurrence of failures
The time of occurrence of failures shall be recorded and evaluated. This is a vital part of the
reliability stress screening process, making it possible to monitor it permanently in order to
ensure that the failure data used for the design of the process are still relevant.
6 Planning
6.1 Stress conditioning
6.1.1 General
Stress conditioning is composed of the screening duration and the stress conditions as
illustrated in Figure 6. Stress conditions are defined in terms of levels, cycles and type.
Stress conditioning
Stress conditions
Stress conditions
(6.1.3)
(6.1.2)
Stress levels and
Stress types
cycles
IEC  1031/06
Figure 6 – Elements of stress conditioning
6.1.2 Stress conditions
Preferably, the stress conditions should be tailored for the assemblies under consideration.
They shall aim at excitation of flaw-related failure mechanisms likely to create failures in the
field, without altering the characteristics of sound assemblies or sound parts of an assembly.

61163-1  IEC:2006 – 35 –
The procedure for the choice of stress condition is as follows:
a) consider the expected field conditions, i.e. the operational and environmental stresses in
the field, and list as far as possible the weaknesses likely to give early failures under
these conditions, taking into account the design and the manufacturing process of the
assembly. The weaknesses considered should not only include previously seen failures
but also failure modes that, from an engineering point of view, are possible.
b) group the weaknesses listed into the following three groups:
1) weaknesses that can be removed cost-effectively by design or process modifications.
Reliability stress screening should not be applied to remove weaknesses of this kind.
2) weaknesses that can be removed cost-effectively by some kind of inspection or
process control during production. These should not be taken care of by reliability
stress screening. Visual inspection, process control or reliability indicator screening
should be used.
3) the remaining weaknesses constitute the flaws that can be removed by reliability stress
screening.
NOTE In cases 1 and 2 screening can be used until the changes are implemented and effective.
c) consider the flaws and evaluate the environmental and/or operational stresses which are
most likely to develop these flaws into failures. Guidance concerning the effect of different
stress conditions can be found in Annexes B to G.
d) select among the stresses identified the most efficient stress condition/conditions,
including their sequence and/or combinations. The stresses selected may not be directly
related to the field conditions. Guidance concerning preferred stress conditions and their
efficiency can be found in Annex A.
e) for
...