IEC PAS 62435:2005

PUBLICLY
IEC
AVAILABLE
PAS 62435
SPECIFICATION
First edition
Pre-Standard
2005-09
Electronic components –
Long-duration storage of electronic
components –
Guidance for implementation
Reference number
IEC/PAS 62435:2005(E)
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PUBLICLY
IEC
AVAILABLE
PAS 62435
SPECIFICATION
First edition
Pre-Standard
2005-09
Electronic components –
Long-duration storage of electronic
components –
Guidance for implementation
 IEC 2005  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
PRICE CODE
Commission Electrotechnique Internationale
U
International Electrotechnical Commission
Международная Электротехническая Комиссия
For price, see current catalogue

– 2 – PAS 62435 © IEC:2005 (E)

CONTENTS
FOREWORD.4
INTRODUCTION.5
1 Scope .6
2 Normative references .6
3 Storage decision criteria .6
3.1 Advantages .7
3.1.1 Technical simplicity – Rapidity.7
3.1.2 Solution durability .7
3.1.3 Preventive storage .7
3.2 Hazards – Drawbacks .7
3.2.1 Generic aging hazard.7
3.2.2 Poor stock dimensioning .7
3.2.3 Incorrect control of reliability during storage .8
3.2.4 Freezing equipment functionalities .8
3.3 Storage cost .8
3.4 Decision criteria.8
4 Purchasing – Procurement.9
4.1 List of components .9
4.2 Quantity of components to be stored .9
4.2.1 Production stock .9
4.2.2 Field service stock .9
4.3 When is it worth keeping in stock? .10
4.4 Procurement recommendations.10
5 Technical validation of the components.10
5.1 Purpose .10
5.2 Relevant field .10
5.3 Test selection criteria .11
5.4 Measurements and tests.11
5.4.1 Sampling .11
5.4.2 Visual examination, sealing, solderability.11
5.4.3 Compliance with the electrical specifications .12
5.4.4 Assessment of the supplied batch reliability.13
5.4.5 Manufacturing control check (technological analysis) .15
5.5 Sanction.15
6 Conditioning and storage .15
6.1 Type of environment .15
6.2 Elementary storage unit .16
6.3 Stock management .16
6.4 Redundancy .16
6.5 Identification – Traceability .16
6.6 Initial packaging .16
6.7 Stabilization bake .17
6.8 Storage conditions.17
6.8.1 Storage area.17
6.8.2 Temperature .17

PAS 62435 © IEC:2005 (E) – 3 –

6.8.3 Temperature variations .17
6.8.4 Relative humidity – Chemical attacks – Contamination.17
6.8.5 Pressure.17
6.8.6 Electrostatic discharges .17
6.8.7 Vibration – Mechanical impacts .18
6.8.8 Electromagnetic field – Radiation .18
6.8.9 Light .18
6.9 Maintaining storage conditions.18
7 Periodic check of the components.18
7.1 Objectives .18
7.2 Periodicity .19
7.3 Tests during periodic check .19
8 Destocking .19
8.1 Precautions .19
8.1.1 Electrostatic discharges .19
8.1.2 Mechanical impacts.19
8.2 Inspection .19
9 Feedback .20

Annex A (informative) Example of a component list .21
Annex B (informative) Examples of periodic and/or destocking tests (1/3) .23
Annex C (informative) Parameters influencing the final price of the component storage .25
Annex D (informative) Parameters influencing the quantity of components to be stored .26
Annex E (normative) Failure mechanisms: Encapsulated and non-encapsulated active
components.27
Annex F (normative) Failure mechanisms: GaAs components.29

– 4 – PAS 62435 © IEC:2005 (E)

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTRONIC COMPONENTS –
Long-duration storage of electronic components –
Guidance for implementation
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
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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.
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declared to be in conformity with an IEC Publication.
6) All users should ensure that they have the latest edition of this publication.
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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.
A PAS is a technical specification not fulfilling the requirements for a standard but made
available to the public.
IEC-PAS 62435 has been processed by IEC technical committee 47: Semiconductor devices.
The text of this PAS is based on the This PAS was approved for
following document: publication by the P-members of the
committee concerned as indicated in
the following document
Draft PAS Report on voting
47/1792/NP 47/1826/RVN
Following publication of this PAS, which is a pre-standard publication, the technical committee or
subcommittee concerned will transform it into an International Standard.
This PAS shall remain valid for an initial maximum period of three years starting from
2005-09. The validity may be extended for a single three-year period, following which it shall be
revised to become another type of normative document or shall be withdrawn.

PAS 62435 © IEC:2005 (E) – 5 –

INTRODUCTION
This PAS applies to the long-duration storage of electronic components.
Although it has always existed to some extent, obsolescence of electronic components and
particularly of integrated circuits, has become increasingly intense over the last few years.
Indeed, with the existing technological boom, the commercial life of a component has become
very short compared with the life of industrial equipment such as that encountered in the
aeronautical field, the railway industry or the energy sector.
The many solutions enabling obsolescence to be resolved are now identified. However, selecting
one of these solutions must be preceded by a case-by-case technical and economic feasibility
study, depending on whether storage is envisaged for field service or production, for example:
– remedial storage as soon as components are no longer marketed;
– preventive storage anticipating declaration of obsolescence.
Taking into account the expected life of some installations, sometimes covering several decades,
the qualification times, and the unavailability costs, which can also be very high, the solution to
be adopted to resolve obsolescence must often be rapidly implemented. This is why the solution
retained in most cases consists in systematically storing components which are in the process of
becoming obsolescent.
The technical risks of this solution are, a priori, fairly low. However, it requires perfect mastery of
the implemented process and especially of the storage environment, although this mastery
becomes critical when it comes to long-term storage.
All handling, protection, storage and test operations must be performed according to the state of
the art.
The application of the approach proposed in this document in no way guarantees that the stored
components are in perfect operating condition at the end of this storage. It only comprises a
means of minimizing potential and probable degradation factors.

– 6 – PAS 62435 © IEC:2005 (E)

ELECTRONIC COMPONENTS –
Long-duration storage of electronic components –
Guidance for implementation
1 Scope
This Publicly Available Specification (PAS) is, first of all, a practical guide to methods of long-
duration storage (more than five years) which summarizes the existing practices in the industry.
Unless otherwise specified, the approach, as well as the methods presented, apply to all families
of electronic components, such as
¾ passive components, including quartz crystals, connectors and relays. However,
components with "manufacturer's" specifications showing an expiry date or specific storage
conditions are excluded from this document (for example, primary cells, storage cells, etc.);
¾ encapsulated or non-encapsulated active components of a silicon [Si] or gallium arsenide
[GaAs] technology;
¾ micro-electronic assemblies.
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 60068-2-17:1994, Basic environmental test procedures – Part 2: Tests – Test Q: Sealing

IEC 60068-2-20:1979, Environmental testing – Part 2: Tests – Test T: Soldering

IEC 60410:1973, Sampling plans and procedures for inspection by attributes

IEC 61340-5-1:1998, Electrostatics – Part 5-1: Protection of electronic devices from electrostatic
phenomena – General requirements

IEC 61340-5-2:1999, Electrostatics – Part 5-2: Protection of electronic devices from electrostatic
phenomena – User guide
IEC 61945, Integrated circuits – Manufacturing line approval – Methodology for technology and
failure analysis
IEC 62380: Reliability data handbook – Universal model for reliability prediction of electronics
components, PCBs and equipment

EN 190 000:1995, Generic specification – Integrated monolithic circuits

3 Storage decision criteria
Any creation of an electronic component inventory should be carried out
•  on the one hand, after having compared with the following additional solutions:
¾ modification to the printed board by adding a "backpack" macro-component;

PAS 62435 © IEC:2005 (E) – 7 –

¾ development of a specific ASIC;
¾ production relaunched at a manufacturer specialized in the resumption of
obsolete technological processes and components;
¾ complete revision of the board or the equipment;

•   on the other hand, by taking into account the following aspects.

3.1 Advantages
3.1.1 Technical simplicity – Rapidity
When the various steps of the storage process are finalized and validated, the creation of a
stock is a simpler, faster and technically less hazardous solution than developing or modifying
electronic boards.
Storage can also be a temporary solution enabling equipment maintenance during modification
or development of electronic boards.
3.1.2 Solution durability
Any equipment changes based on the use of new electronic components will be faced,
eventually, with the obsolescence of these new components. Storage can resolve obsolescence
problems until the end of the operating life of the equipment.
3.1.3 Preventive storage
Preventive storage (i.e., before the component becomes obsolete) presents several additional
advantages compared with remedial storage (i.e., when the component has already become
obsolete), for example, when
− the component price has not become prohibitive as in the case of specific obsolete
components which have become very rare;

− the quality level is ensured if the component can be purchased direct from the manufacturer
or approved distributor. When a component has been obsolete for a long time, it can only be
found at specialists in purchasing, storage and resale of obsolete components ("brokers"). In
this case, no component reliability guarantee will apply.

3.2 Hazards – Drawbacks
3.2.1 Generic aging hazard
Stock dimensioning is based on the assumption of a constant component failure rate. The
problem of generic aging of the components ("bath-tub curve") cannot be easily taken into
account and quantified. However, the existing electronic components seem to have extremely
long lives provided that they are manufactured with all quality guarantees and that they are used
in accordance with their specifications.
3.2.2 Poor stock dimensioning
The calculation of the volume of components to be stored may be based on feedback (opera-
tional failure rate) and/or on theoretical models (predictive failure rate). Calculation using feed-
back is only valid if the sample is big enough (significant population of components installed,
operation for several years, high number of failures evidenced). Predictive calculations do not
generally take into account the extrinsic parameters of the components (defects caused by
printed-board handling and repair, systematic replacement of the components (including
functional components) during repairs, improper use of the components, etc.). Therefore, the
stock volume may be improperly assessed.

– 8 – PAS 62435 © IEC:2005 (E)

Underestimating the stock may lead to a lack of components to repair printed boards, which will
ruin the stock strategy. Overestimating it will lead to the purchasing and conditioning of compo-
nents which will not be used, including to significant additional costs.
3.2.3 Incorrect control of reliability during storage
Storage conditions shall be precisely defined and controlled, in order to guarantee the reliability
of the components stored (see Clause 5). In addition, it is important to check the quality of the
components to be stored (see Clause 4). This may lead to the setting-up of fairly heavy and
costly infrastructure and procedures.
Checking component quality may be an efficient means of reducing the risk of improper reliability
control during storage. This can be done either by performing periodic sampling in order to carry
out tests on the components (see Clause 6) or by checking that the components taken from the
stock and used on the electronic boards operate correctly (provided that the consumption of the
components in stock is sufficiently regular).
3.2.4 Freezing equipment functionalities
Storing components to ensure equipment maintenance over a long time implies that the
equipment functionalities be frozen. A long-duration storage solution is therefore not very
compatible with the desire to upgrade equipment and functionalities.
3.3 Storage cost
In order to assess the cost of a storage solution, various items should be taken into account,
such as:
– component purchasing;
– validation/test of purchased component batches;
– conditioning and de-conditioning;
– stock management;
– maintenance of installations dedicated to storage by means of manufacturing tests and/or
repair;
– staff ensuring storage, maintenance operations, etc.;
– financial cost of tied-up stocks.
3.4 Decision criteria
The following criteria should be taken into account:
– planned storage time;
– stock dimensioning;
– dimensioning reliability index;
– life of test means;
– life of manufacturing means and/or printed boards;
– competence traceability and related documentation;
– industrial consequences of under-dimensioning or a component failure at the end of storage;
– confidence level in the knowledge of potential component failure mechanisms;
– cost compared with other solutions.

PAS 62435 © IEC:2005 (E) – 9 –

4 Purchasing – Procurement
4.1 List of components
A detailed list of the components used shall be established. It should include the designations,
specifications, manufacturers and the corresponding trade references.
This list shall be related with the various lists of electronic boards (by means of either a
procurement code, or a generic designation).
The purpose of this list is to
– define all components of a market or a series of equipment;
– allow component approval at the beginning of their design stage;
– allow field service procurement
An example of this list is given in Annex A.
This list shall, as far as possible, mention the probable life of each component over a 10-year
period.
4.2 Quantity of components to be stored
There are two types of requirements:
• production stock;
• field service stock.
Special attention shall be paid to
– specific components;
– single-source components;
– components becoming obsolete before the end of production.
Care will also be taken to make sure that the stored quantities take into account parts used for
tests considered as destructive.

4.2.1 Production stock
This stock shall guarantee productions in progress and future productions (to relaunch the
market).
4.2.2 Field service stock
This stock shall enable components to be kept operational during the whole life of the equipment
and systems (for example, 25, 30, even 40 years for military, railroad or nuclear power plant
equipment).
A stock of the various component types shall be made up from the parts lists, the bills of material
and feedback (observed failure rate).
ASSESSMENT EXAMPLE: These batches of parts, calculated according to the following formula,
should not be less than 3 % of the total number of components installed (the higher of the two
values) on the relevant equipment:

N × h × λ × A
N
o =
– 10 – PAS 62435 © IEC:2005 (E)

where
N is the stock quantity;
o
N is the number of components in service;
h is the number of operating hours per year;
A is the number of years during which the requirement for these components must be
guaranteed;
λ  is the operational failure rate of the component, if known. Otherwise, the predictive failure
rate is used. It is given either in a reliability data handbook (IEC 62380) or by the
manufacturer.
4.3 When is it worth keeping in stock?
Depending on the component type
– the procurement of specific components should be launched at the latest at the same
time as the last component production batch;
– if it is a single-source component, the order shall be launched in the time prescribed by
the manufacturer.
4.4 Procurement recommendations
Every component batch should be clearly identified.
No batch should have date-codes older than two years at time of delivery.
Batches (compliance certificate, electrical test results, etc.) shall be accompanied by all the
documents enabling the traceability of the components to be ensured.
Components shall be delivered, if required, in packages guaranteeing ESD protection and
protection against humidity.
Packages will be correctly identified (date-code, manufacturer, component reference).
5 Technical validation of the components
5.1 Purpose
The purpose of the technical validation of the components with a view to their storage is to
detect a priori the batches which do not offer proper reliability and life guarantees.
5.2 Relevant field
All electronic components (“active” as well as “passive”) are concerned.
However, active semiconductor components are the most affected by the obsolescence issue.
This is why, in the following subclauses, we will only deal with active component validation
methods.
The methods to be applied for passive components, save a few adaptations specific to their
technologies, are directly applicable.

PAS 62435 © IEC:2005 (E) – 11 –

5.3 Test selection criteria
The first thing to be taken into account to select the tests to be implemented for storing compo-
nents is to have these components previously qualified, depending on the profile of their expec-
ted mission.
In addition, in the case of multiple-source components, the selection of the sources shall have
been validated by a method capable of evidencing "false" second sources.
The selection of the required tests and measurements will depend on the storage strategy
adopted. It can cover a range from a minimal utilization with no tests to a maximal utilization,
where all tests described in this chapter would be performed.
As a whole, the technical validation of the components requires the following items to be
checked:
a) compliance with the visual inspection criteria;
b) solderability checking;
c) sealing/hermeticity checking (for components with hermetic packages);
d) compliance with the electrical specifications in the temperature range;
e) checking of manufacturing control (technological analysis);
f) checking of the supplied batch reliability.
The criteria for sanctions and the number of tested components may vary depending on the
requirements and level of reliability, as well as the data collected from the manufacturer. At the
end of the technical validation, a status is established for this batch in order to decide on its
storage capability.
5.4 Measurements and tests
5.4.1 Sampling
Generally, the measurements of the component electrical parameters are performed on 100 % of
the batch. However, if a batch is too large and, depending on the storage strategy adopted, the
measurements can be made by sampling.
The sampling plan shall, in this case, adhere to the rules defined in the standards (for example,
IEC 60410).
The technological analysis must be made on a sufficient number of components in order to check
compliance with the characteristics required. Generally, three to 10 components are submitted to
the analysis.
For reliability tests, except for the package sealing test, all other tests are destructive tests.
The number of parts to be tested will either be fixed or a sample, but, to be representative, there
should not be less than 20 parts.
5.4.2 Visual examination, sealing, solderability
The purpose of these examinations is to check the integrity of the packages and the component
mounting problems. The test methods used are described in the European or American
standards.
– 12 – PAS 62435 © IEC:2005 (E)

It is worth mentioning, in particular:
– IEC 60068-2-17 for sealing;
– IEC 60068-2-20 for solderability;
EN 190 000, Annex A, for visual examination.

5.4.3 Compliance with the electrical specifications
5.4.3.1 Measurement of electrical parameters

a) Measurement of static parameters
Static parameters determine the component inter-changeability in particular by measuring the
...