IEC TR 62380:2004

TECHNICAL IEC
REPORT TR 62380
First edition
2004-08
Reliability data handbook –
Universal model for reliability prediction
of electronics components, PCBs
and equipment
Reference number
IEC/TR 62380:2004(E)
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TECHNICAL IEC
REPORT TR 62380
First edition
2004-08
Reliability data handbook –
Universal model for reliability prediction
of electronics components, PCBs
and equipment
:
” IEC 2004  Copyright - all rights reserved
No part of this publication may be reproduced or utilized in any form or by any means, electronic or
mechanical, including photocopying and microfilm, without permission in writing from the publisher.
International Electrotechnical Commission, 3, rue de Varembé, PO Box 131, CH-1211 Geneva 20, Switzerland
Telephone: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmail@iec.ch Web: www.iec.ch
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XC
International Electrotechnical Commission
ɆɟɠɞɭɧɚɪɨɞɧɚɹɗɥɟɤɬɪɨɬɟɯɧɢɱɟɫɤɚɹɄɨɦɢɫɫɢɹ
For price, see current catalogue

– 2 – TR 62380 ” IEC:2004(E)
CONTENTS
FOREWORD .5

INTRODUCTION . 7

1 Scope . 8

2 Normative references. 8

3 Terms and definitions. 9

4 Conditions of use . 10

4.1 Introductory remarks . 10
4.2 Assumptions adopted for TR 62380 . 11
4.3 Influencing factors. 13
4.4 How to use the data . 14
4.5 Uses and aims of a reliability prediction. 15
5 Environment influence. 16
5.1 General remarks . 16
5.2 Environment types defined . 16
5.3 Electrical environment conditions . 20
5.4 Validity model according to environment. 20
5.5 Components choice. 20
5.6 Learning during the deployment phase of new equipment . 21
5.7 Mission profile. 22
5.8 Mission profile examples . 23
6 Equipped printed circuit boards and hybrid circuits (IEC 60326) . 25
6.1 Failure rate calculation of an equipped printed circuit board . 25
6.2 Hybrid circuits . 26
7 Integrated circuits . 27
7.1 Validity domain . 27
7.2 Junction temperature evaluation of an integrated circuit . 27
7.3 The reliability model . 30
8 Diodes and thyristors, transistors, optocouplers (IEC 60747-xx) . 36
8.1 Evaluating the junction temperature of diodes and transistors . 36
8.2 Low power diodes . 38
8.3 Power diodes . 40

8.4 Low power transistors . 42
8.5 Power transistors . 44
8.6 Optocouplers . 46
9 Optoelectronics. 49
9.1 Light emitting diodes diode modules (IEC 60747-12-2, IEC 62007). 49
9.2 Laser diodes modules - Failure rate. 52
9.3 Photodiodes and receiver modules for telecommunications (IEC 60747-12). 53
9.4 Passive optic components . 54
9.5 Miscellaneous optic components . 54
10 Capacitors and thermistors (ntc). 55
10.1 Fixed plastic, paper, dielectric capacitors - Radio interference suppression
capacitors (plastic, paper) . 55

TR 62380 ” IEC:2004(E) – 3 –
10.2 Fixed ceramic dielectric capacitors – Defined temperature coefficient – Class I

(IEC 60384) . 56

10.3 Fixed ceramic dielectric capacitors – Non defined temperature coefficient – Class

II – Radio interference suppression capacitors (Ceramic, class II) . 57

10.4 Tantalum capacitors, solid electrolyte (IEC 60384). 58

10.5 Aluminum, non-solid electrolyte capacitors - Life expectancy . 59

10.6 Aluminum electrolytic capacitor, solid electrolyte . 61

10.7 Aluminum electrolytic capacitor, polymer electrolyte (IEC 60384) . 62

10.8 Variable ceramic capacitors, disks (Dielectric ceramic) (IEC 60384) . 63

10.9 Thermistors with negative temperature coefficient (NTC) (IEC 60539) . 64

11 Resistors and potentiometers (IEC 60115). 65
11.1 Fixed, low dissipation film resistors – High stability (rs), general purpose (rc),
“minimelf” . 65
11.2 Hot molded carbon composition, fixed resistors (IEC 60115) . 66
11.3 Fixed, high dissipation film resistors (IEC 60115). 67
11.4 Low dissipation wirewound resistors (IEC 60115). 68
11.5 High dissipation wirewound resistors (IEC 60115). 69
11.6 Fixed, low dissipation surface mounting resistors and resistive array (IEC 60115) 70
11.7 Non wirewound cermet potentiometer (one or several turn) (IEC 60393). 71
12 Inductors and transformers (IEC 61248) . 73
13 Microwave passive components, piezoelectric components and surface acoustic wave
filters (IEC 61261, IEC 61019, IEC 60368). 74
13.1 Microwave passive components . 74
13.2 Piezoelectric components. 74
13.3 Surface acoustic wave filters . 74
14 Relays . 75
14.1 Evaluating voltage and current (vt, it) in transient conditions . 75
14.2 Mercury wetted reed relays, low power (IEC 60255). 78
14.3 Dry reed relays (IEC 60255) . 80
14.4 Electromechanical relays, miniature or card – European type, thermal relays
(power up to 500 W) (IEC 60255) . 82
14.5 Industrial relays, high voltage vacuum relays, power mercury wetted relays (IEC
60255) . 84
15 Switches and keyboards (IEC 60948) . 86
16 Connectors . 87
16.1 Circular, rectangular. 87

16.2 Coaxial connectors. 87
16.3 Connectors for PCBs and related sockets . 87
17 Displays, solid state lamps . 88
17.1 Displays (IEC 61747) . 88
17.2 Solid state lamps (IEC 60747) . 88
18 Protection devices (IEC 60099, IEC 60269, IEC 60738, IEC 61051) . 89
18.1 Thermistors (PTC). 89
18.2 Varistors . 89
18.3 Fuses . 89
18.4 Arrestors. 89
19 Energy devices, thermal management devices, disk drive . 90
19.1 Primary batteries. 90
19.2 Secondary batteries . 90

– 4 – TR 62380 ” IEC:2004(E)
19.3 Fans . 90

19.4 Thermoelectric coolers . 90

19.5 Disk drive . 90

19.6 Converters (IEC 60146). 90

Table 1 – Mission profiles for spatial. 10

Table 2 – Mission profiles for military. 10

Table 3 – Description and typical applications of the commonest types of environment . 17

Table 4 – Mechanical conditions according to the environment: characteristic shocks and

vibrations. . 18

Table 5 – Mechanically active substances. 19
Table 6 – Chemically active substances. 19
Table 7 – Typical conditions for each environment type according to Table 3 (mechanically
and chemically active substances and climatic conditions) . 19
Table 8 – Table of climates. 23
Table 9 – Mission profiles for Telecom. 23
Table 10 – Mission profiles for military and civil avionics . 24
Table 11 – Mission profiles for automotive . 24
Table 12 – Thermal resistance as a function of package type, the pin number and airflow
factor . 28
Table 13 – Typical values of the air flow speed V, and the air flow factor K. 29
Table 14 – Thermal expansion coefficients D and D . 32
S C
Table 15 – Failure distribution (for non interfaces integrated circuits) . 32
Table 16 – Values of O and O for integrated circuits families . 33
1 2
Table 17a – O values for integrated circuits as a function of S (pin number of the package) 34
Table 17b – O values for surface mounted integrated circuits packages as a function of D
(package diagonal). 35
Table 18 – Values of O and junction resistances for active discrete components . 37
B
................... 21
Figure 1 – Time dependant failure rate of a new electronic printed circuit board
Figure 1 – Time-dependant failure rate of a new electronic printed circuit board . 21
Figure 2 – Equivalent diagram representing the circuit of a relay contact . 75

Figure 3 – Positions of capacitors in the real circuit diagram for which the values must be
counted in C. 75
Figure 4 – Regions adopted for the purposes of Figures 5, 6 and 7 . 76
V I
t t
Figure 5 – Evaluating the ratios and according to RR R , C, L, and C , L
V I 12 p p
( R in k:, C, C in nF ; L , L in mH). 76
p p
V I
t t
Figure 6 – Evaluating ratios and when L and C are not known . 77
V I
V I
t t
Figure 7 – Default values of and when nothing is known about the electrical
V I
circuit of the contact . 77

TR 62380 ” IEC:2004(E) – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION

____________
RELIABILITY DATA HANDBOOK –
UNIVERSAL MODEL FOR RELIABILITY PREDICTION

OF ELECTRONICS COMPONENTS, PCBs AND EQUIPMENT

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
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this preparatory work. International, governmental and non-governmental organizations liaising with the IEC also
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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
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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.
The main task of IEC technical committees is to prepare International Standards. However, a
technical committee may propose the publication of a technical report when it has collected data of

a different kind from that which is normally published as an International Standard, for example
"state of the art".
IEC 62380, which is a technical report, has been prepared by IEC technical committee 47:
Semiconductor devices.
The text of this standard is based on the following documents:
Enquiry draft Report on voting
47/1705/DTR 47/1722A/RVC
Full information on the voting for the approval of this standard can be found in the report on voting
indicated in the above table.
– 6 – TR 62380 ” IEC:2004(E)
This technical report does not follow the rules for structuring international standards as given in

Part 2 of the ISO/IEC Directives.

NOTE This technical report has been reproduced without significant modification to its original content or drafting.

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.
TR 62380 ” IEC:2004(E) – 7 –
INTRODUCTION
This reliability calculation guide for electronic and optical card, is an important progress compared

to older guides. Calculation models take directly into account the influence of the environment. The

thermal cycling seen by cards, function of mission profiles undergone by the equipment, replace

environment factor which is difficult to evaluate. These models can handle permanent working,

on/off cycling and dormant applications. On the other hand, failure rate related to the component
soldering, is henceforth-included in component failure rate.

– 8 – TR 62380 ” IEC:2004(E)
RELIABILITY DATA HANDBOOK –
UNIVERSAL MODEL FOR RELIABILITY PREDICTION

OF ELECTRONICS COMPONENTS, PCBs AND EQUIPMENT

1 Scope
This technical report provides elements to calculate failure rate of mounted electronic components.

It makes equipment reliability optimization studies easier to carry out, thanks to the introduction of

influence factors.
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 60086 (all parts), Primary batteries
IEC 60099 (all parts), Surge arresters
IEC 60115 (all parts), Fixed arrestors for use in electronic equipment
IEC 60146, (all parts), Semiconductor convertors – General requirements and line commutated
convertors
IEC 60255 ((all parts), Electrical relays
IEC 60269 (all parts), Low-voltage fuses
IEC 61951 (all parts), Secondary cells and batteries containing alkaline or other non-alkaline
electrolytes – Portable sealed rechargeable single cells
IEC 60326 (all parts), Printed boards
IEC 60368 (all parts), Piezoelectric filtgers of assessed quality
IEC 60384 (all parts), Fixed capacitors for use in electronic equipment

IEC 60393 (all parts), Potentiometers for use in electronic equipment
IEC 60535, Jet fans and regulators
IEC 60539 (all parts), Directly heated negative temperature coefficient thermistors
IEC 60721-3 (all Parts 3), Classification of environmental conditions – Part 3: Classification of
groups of environmental parameters and their severities
IEC 60738 (all parts), Thermistors - Directly heated positive step-function temperature coefficient
IEC 60747 (all parts) Semiconductor devices - Discrete devices
IEC 60747-12 (all Parts 12) Semiconductor devices - Part 12: Optoelectronic devices

TR 62380 ” IEC:2004(E) – 9 –
IEC 60747-12-2, Semiconductor devices – Part 12: Optoelectronic devices – Section 2: Blank detail

specification for laser diode modules with pigtail for fibre optic systems and sub-systems

IEC 60748 (all parts) Semiconductor devices – Integrated circuits

IEC 60879, Performance and construction of electric circulating fans and regulators

IEC 60948, Numeric keyboard for home electronic systems (HES)

IEC 61019 (all parts), Surface acoustic wave (SAW) resonators

IEC 61051 (all parts), Varistors for use in electronic equipment
IEC 61248 (all parts), Transformers and inductors for use in electronic and telecommunication
equipment
IEC 61747 (all parts), Liquid crystal and solid-state display devices
IEC 61261 (all parts), Piezoelectric ceramic filters for use in electronic equipment – A specification
in the IEC quality assessment system for electronic components (IECQ)
IEC 61951 (all parts), Secondary cells and batteries containing alkaline or other non-acid
electrolytes
IEC 61951-1, Secondary cells and batteries containing alkaline or other non-acid electrolytes –
Portable sealed rechargeable single cells
IEC 61951-2, Secondary cells and batteries containing alkaline or other non-acid electrolytes –
Nickel-metal hydride
IEC 62007 (all parts), Semiconductor optoelectronic devices for fibre optic system applications
IEC 62255 (all parts), Multicore and symmetrical pair/quad cables for broadband digital
communications (high bit rate digital access telecommunication networks) - Outside plant cables
ETS 300 019, Environmental engineering (EE); Environmental conditions and environmental tests
for telecommunications equipment
ISO 9000:2000, Quality management systems – Fundamentals and vocabulary

UTE C 96-024:1990, Modèles thermiques simplifiés des circuits intégrés monolithiques
3 Terms and definitions
For the purposes of this technical report, the following definitions apply.
3.1
spatial
Mission profiles corresponding to the MIL-HDBK-217F "Space; flight" environment.
NOTE Only one working phase is taken into account during each orbital revolution (LEO), or earth revolution (GEO).

– 10 – TR 62380 ” IEC:2004(E)
Table 1 – Mission profiles for spatial

(t )
ac 1 W W W n 'T
1 on off 1 1
Application types
°C
cycles/year °C/orbit
'Tjc
Low earth orbit (LEO) with On/Off cycling 40 0,15 0,15 0,85 5256
+7
Low earth orbit (LEO) permanent working 40 1 1 0 5256 3
Geostationary earth orbit (GEO) permanent working 40 1 1 0 365 8

3.2
military
Mission profiles corresponding to the MIL-HDBK-217F "Ground; mobile" environment.
NOTE Two working phases are taken into account:
Phase 1: 36 annual switch on
Phase 2: 365 days of dormant mode
Table 2 – Mission profiles for military
(t )
ac 1 W W W n 'T n 'T
1 on off 1 1 2 2
Application type
°C
cycles/year °C/cycle cycles/year °C/cycle
'Tj
Portable Radio 26 0,01 0,01 0,99 36 365 8
+15
4 Conditions of use
4.1 Introductory remarks
4.1.1 Theory of reliability predictions
Calculation of a reliability prediction for non-redundant equipment is the very first step in any
complete reliability study concerning that equipment, and indeed, of any study of the reliability,
availability, or safety of a system.
Reliability predictions are based on numerous assumptions, all of which need to be verified (choice
of component family, for example).
A reliability study of an item entails not only verifying these assumptions, but also optimizing its
reliability (qualification of components and mounting processes, minimizing risk of external failure,
etc).
A reliability prediction is essential, but no more so than research into the best possible reliability for
least cost.
This handbook provides all the information needed to calculate electronic component and equipped
printed circuit board failure rates: failures rates delivered include the influence of component
mouting processes.
4.1.2 Structure of the handbook
The handbook is specifically designed as an aid to research into how to maximize equipment
reliability, and to assist in the design of the equipment, by introducing various influencing factors
(see also 4.3). In order to meet this objective, it is important that any reliability prediction should
begin with the start of design (and then be finalised in accordance with 4.5.4). Similarly, the choice
of values for the influencing factors should not be automatic.

TR 62380 ” IEC:2004(E) – 11 –
4.1.3 Data source
The reliability data contained in the handbook is taken mainly from field data concerning electronic

equipment operating in four kinds of environment:

a) «Ground; stationary; weather protected» (in other words: equipment for stationary use on the

ground in weather protected locations, operating permanently or otherwise).

This applies mainly to telecommunications equipment and computer hardware.

b) «Ground; stationary; non weather protected» (in other words: equipment for stationary use on

the ground in non-weather protected locations).

This relates mainly to public payphones and GSM relays.
c) «Airborne, Inhabited, Cargo» (in other words: equipment used in a plane, benign conditions).
This relates to on board calculators civilian planes.
d) «Ground; non stationary; moderate» (in other words: equipment for non-stationary use on the
ground in moderate conditions of use).
This concerns mainly on board automotive calculators and military mobile radio.
By processing the raw data (statistical processes, results based on geographic distribution,
according to equipment type, etc.), it has been possible to include various influencing factors and
eliminate the main aberrant values. Other influencing factors are derived from the experience of
experts (failure analyses, construction analyses, results of endurance tests).
The values adopted are those considered most probable at the present time (1992-2001).
This databook does not give any part count values, because mission profiles are needed in order to
have credible values.
4.2 Assumptions adopted for TR 62380
4.2.1 Nature of data
4.2.1.1 Reliability data
The reliability data in this handbook comprises failure rates and, for some (very few) component
families, life expectancy.
Failure rates are assumed to be constant either for an unlimited period of operation (general case)

or for limited periods: in these particular cases the laws governing failure rates versus time have not
been adopted in the interests of simplicity.
Apart from a few exceptions (see section 4.2.1.3), the wear-out period is never reached by
electronic components; in the same way it is accepted, again apart from some exceptions (see
section 4.2.1.2), that the added risks of failure during the first few months of operation can be
disregarded.
4.2.1.2 The infant mortality period
In practice, except for a few component families, the increased risk of failure during the first months
of operation can be disregarded, because of the diversity of reasons for variations or uncertainty in
the failure rate. This superficially simplistic hypothesis is in fact very realistic. It is confirmed by field
data concerning the operation of equipment designed very carefully, with well chosen components
(based on compatibility with use) and produced by a well controlled production system, as is
generally the case for the components covered by this handbook.

– 12 – TR 62380 ” IEC:2004(E)
4.2.1.3 Wear-out period
For the vast majority of components, the -wear-out period (during which failures take on a

systematic character) is far removed from the periods of use (which range from 3 to 20 years).

There are, however, two cases in which the occurrence of wear-out failures should be taken into

account (the failure rate of which increases with time):

a) For some families, if due care is not taken, the wear-out mechanisms may give rise to

systematic failures after too short a period of time; metallization electromigration in active

components, for example.
This risk needs to be eliminated by a good product design, and it is important to ensure this by
qualification testing. In other words, it should not be taken into account for a prediction, and
should be eliminated by qualification testing and by technical evaluation, which are, therefore,
of critical importance.
b) For some (few) component families, the wear-out period is relatively short. For these families,
this handbook explains how to express the period for which the failure rate can be considered
constant. This life expectancy is subject to influencing factors.
Such families include relays, aluminium capacitors (with non-solid electrolyte), laser diodes,
optocouplers, power transistors in cyclic operation, connectors and switches and keyboards.
For these component families, it is important to ensure that the life expectancy given by the
handbook is consistent with the intended use. If not, room for manoeuvring is fairly restricted:
you can reduce the stresses, change the component family (or sub-family: for aluminium
capacitors with non-solid electrolyte, there are several types characterized by different
qualification tests).
Provision can also be made for preventive maintenance.
NOTE: As before, and in the interests of simplicity, this handbook does not give the wear-out failure mathematical model
(for which the failure rate increases over time), but a period during which the rate can be considered constant (in some
cases the period at 10% of the cumulative failure rate).
4.2.2 Nature of failures
4.2.2.1 Intrinsic failures
The data in this handbook covers intrinsic failures (apart from the few exceptions given in 4.2.2.2).
In practice (see section 4.1.3), the raw reliability data has been processed to eliminate non-intrinsic
component failures.
4.2.2.2 Special case of non-intrinsic residual failures due to electrical overloads
There is, necessarily, a small proportion of non-intrinsic failures in the data, because it is
impossible to detect all the non-intrinsic failures when they are residual.
Take, for example, the reliability of the components used in equipment located “at the heart” of a
system, which is significantly better than that of the components located at the periphery (in other
words connected to the external environment). It is understood that this is due to residual
overloads, since the equipment is assumed adequately protected.
For the purpose of this handbook, we have therefore included an utilisation factor to take into
account nonintrinsic residual failures due to the electrical environment for active components.

TR 62380 ” IEC:2004(E) – 13 –
4.2.2.3 Other non-intrinsic failures

The other non-intrinsic failures (due to errors of design, choice, uses) are excluded from this

handbook.
Errors of this kind should be avoided; hence they are not taken into for predictions. As a matter of

fact, they are very largely independent of component family.

However, for some particular objectives, such as calculation of stocks of spare parts, it may be

useful to include the risks of non-intrinsic residual failures due to design errors: some indications

are given in section 4.4.3.
4.2.3 Large-scale integrated circuit, production date influence
Since the 90's, the reliability growth of components no longer occur, as in the70's and the 80's;
thanks to fields failures returns data collections. This is particularly true for integrated circuits, and
can be attributed to: generalization of nitride based passivations, generalization of dry etching and
better planarization controls. However, the integration density for integrated circuits continues to
grow at the same rate as in the past, at a constant reliability figure. For this reason, and in order to
takes into account the Moore law, it is necessary to know the manufacturing year to calculate the
failure rate of integrated circuits.
4.3 Influencing factors
4.3.1 Component failure rate
The component failure rate depends on a number of operational and environmental factors. This is
why, for each component family, the handbook gives a base failure rate value (normally a value
which corresponds to the commonest internal temperature taken as a reference) multiplied by a
number of influencing factors. This simplified, empirical expression takes account of the more
significant influencing factors when it comes to conditions of use.
The main factors adopted are as follows:
a) Factors giving the influence of temperature (S , S )
t w
It is now widely accepted that temperature has a moderate effect on component reliability. The
effect is significant for some families (active components and aluminum capacitors with non-solid
electrolyte). The models adopted are those which give the effect of temperature on the
predominating failure mechanisms (which are not normally the “wear-out” mechanisms).
For semiconductors, an Arrhenius equation has been applied with activation energy of 0.3 to 0.4
electron volts.
For passive components, an Arrhenius equation has been applied with an activation energy of 0.15
to 0.4 electron volts.
Factor S for potentiometers gives the influence of load resistance on the temperature rise.
w
In the case of power dissipating components, the thermal resistance (semiconductors) or the
equation giving the internal temperature as a function of ambient temperature (resistors) has been
given.
b) Factors giving the influence of special stresses:
Utilization factor S for thyristors, Zener diodes (operating permanently powered or otherwise).
u
Factor S for Aluminum liquid electrolyte capacitors giving the effect of current pulses.
A
– 14 – TR 62380 ” IEC:2004(E)
Factor S for relays (operating cycle rate).
Y
Factor S for connectors (current intensity).
i
c) Factors giving the influence of applied voltage (S ).
s
The influence of applied voltage is taken into account for transistors and optocouplers (voltage

applied between input and output).

4.3.2 Life expectancy
Life expectancy, when limited, is also influenced by certain factors (optocoupler operating current;
temperature of aluminum capacitors with non-solid electrolyte; contact current for relays).
Life expectancy can be expressed as a number of cycles (power transistors, switches).
4.4 How to use the data
4.4.1 Calculation method
Given that the component failure rates are assumed constant, the failure rate of a non-redundant
equipment can be obtained by adding together the failure rates of its individual components. In this
handbook, the failure rates given for components include the effects of the mounting on a printed
circuit board, the failure rate of the naked PCB or hybrid has to be added.
Clause 6 of this handbook explains the method to be used to calculate the failure rate of a printed
circuit board or a hybrid.
4.4.2 Reliability prediction results
The results of a reliability prediction are many and various, and not limited to failure rate: the
following information is also obtained:
- Failure rate (of component or equipment).
- Choice of technical construction for some components (choice of component family).
- Choice of conditions of use.
4.4.3 Failure rate
The failure rate can be used directly if the aim is to identify a reference base. Such is the case for
many objectives described in 4.5.
However, if the aim is to obtain an accurate estimate of stocks of spare parts, the result should be
uprated to take account of non-intrinsic failures:
- unconfirmed failure phenomena (equipment, subsystem, identified as defective and found to be
OK on repair);
- incorrect component usage, wrong choice of components for the first months of use of
equipment of new design (period of improving reliability);
- incorrect maintenance, inappropriate use, human error, environmental attack;
- production process learning factor (component mounting process, etc).

TR 62380 ” IEC:2004(E) – 15 –
The appropriate uprating factors cannot be given in this handbook: they depend on the prior

experience of a company and how new the equipment production process is (for example, for
unconfirmed failures, the uprating factor ranges from 10% to over 100%, depending on newness).

4.4.4 In cases where conditions are not yet known default conditions can be assumed.

According to 4.5.1, reliability prediction calculations should begin as early as possible, at the start

of the equipment design phase, even if not all the applicable conditions can yet be known: in this

case default values can be used provisionally, to help determine those conditions which are as yet

unknown. These default values will then be gradually discarded as the definitive conditions are

identified.
This method is far preferable to the simplified calculation method (for which all the values are
replaced by default values, including those, which are already known).
The calculations must therefore be prepared in such a way as to enable values to be modified
easily.
4.5 Uses and aims of a reliability prediction
4.5.1 Reliability prediction as an aid to equipment design
The most beneficial use of a reliability prediction is as an aid to equipment designers, In this case,
the help is based on determination of the stresses and factors influencing the reliability of each
component (temperature, input voltage, technical construction of the components, etc.). Predictions
based on this handbook will lead the originators of a new design to choose the best conditions and
the best component families, and to draw up component qualification or evaluation programmes.
If this important objective is to be met, it is essential for the reliability prediction to be begun at the
very start of design, by the design originators, and then revised as required. The work should be
carried out in close collaboration with the company's component quality experts.
4.5.2 Reliability prediction to assess the potential of new equipment
The predicted reliability can be compared with the reliability objectives or stated requirements.
4.5.3 Predicted reliability values as a basis for contractual reliability values
The contractual value of a failure rate must be determined on the basis of the predicted value; these
two values will not necessarily be equal: a number of contractual values may be assumed
depending on observation period or certain data may be modified provided it is justified. However,
in all cases, the predicted value should be taken as the base.

4.5.4 Where used in conjunction with other characteristics of a project (electrical characteristics,
weight, etc.), the results of a reliability prediction can be used to compare different project
solutions, such as when evaluating proposals from tenderers. Comparisons of this kind are possibl
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