IEC 60738-1:1998

INTERNATIONAL
IEC
STANDARD
60738-1
QC 440000
Second edition
1998-11
Thermistors –
Directly heated positive step-function
temperature coefficient –
Part 1:
Generic specification
Thermistances à basculement à coefficient de température
positif à chauffage direct –
Partie 1:
Spécification générique
Reference number
Numbering
As from 1 January 1997 all IEC publications are issued with a designation in the
60000 series.
Consolidated publications
Consolidated versions of some IEC publications including amendments are

available. For example, edition numbers 1.0, 1.1 and 1.2 refer, respectively, to the
base publication, the base publication incorporating amendment 1 and the base

publication incorporating amendments 1 and 2.

Validity of this publication
The technical content of IEC publications is kept under constant review by the IEC,
thus ensuring that the content reflects current technology.
Information relating to the date of the reconfirmation of the publication is available
in the IEC catalogue.
Information on the subjects under consideration and work in progress undertaken by
the technical committee which has prepared this publication, as well as the list of
publications issued, is to be found at the following IEC sources:
• IEC web site*
• Catalogue of IEC publications
Published yearly with regular updates
(On-line catalogue)*
• IEC Bulletin
Available both at the IEC web site* and as a printed periodical
Terminology, graphical and letter symbols
For general terminology, readers are referred to IEC 60050: International Electro-
technical Vocabulary (IEV).
For graphical symbols, and letter symbols and signs approved by the IEC for
general use, readers are referred to publications IEC 60027: Letter symbols to be
used in electrical technology, IEC 60417: Graphical symbols for use on equipment.
Index, survey and compilation of the single sheets and IEC 60617: Graphical symbols
for diagrams.
* See web site address on title page.

INTERNATIONAL
IEC
STANDARD
60738-1
QC 440000
Second edition
1998-11
Thermistors –
Directly heated positive step-function
temperature coefficient –
Part 1:
Generic specification
Thermistances à basculement à coefficient de température
positif à chauffage direct –
Partie 1:
Spécification générique
 IEC 1998  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 Geneva, Switzerland
Telefax: +41 22 919 0300 e-mail: inmail@iec.ch IEC web site http://www.iec.ch
Commission Electrotechnique Internationale
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International Electrotechnical Commission
For price, see current catalogue

– 2 – 60738-1 © IEC:1998(E)
CONTENTS
Page
FOREWORD. 4

Clause
1 General. 5

1.1 Scope. 5
1.2 Normative references. 5
2 Technical data. 6
2.1 Units and symbols. 6
2.2 Definitions. 6
2.3 Preferred values. 13
2.4 Marking. 14
3 Quality assessment procedures. 14
3.1 General. 14
3.2 Primary stage of manufacture. 15
3.3 Subcontracting. 15
3.4 Structurally similar components. 15
3.5 Qualification approval procedures . 15
3.6 Rework and repair. 24
3.7 Release for delivery . 24
3.8 Certified test records of released lots . 24
3.9 Delayed delivery. 24
3.10 Alternative test methods. 24
3.11 Manufacture outside the geographical limits of IECQ NSIs. 25
3.12 Unchecked parameters. 25
4 Test and measurement procedures . 25
4.1 General. 25
4.2 Standard conditions for testing . 25
4.3 Drying and recovery . 26
4.4 Visual examination and check of dimensions . 26

4.5 Zero-power resistance. 27
4.6 Temperature coefficient of resistance. 27
4.7 Insulation resistance (for insulated types only). 28
4.8 Voltage proof (for insulated types only). 29
4.9 Resistance/temperature characteristic. 29
δ
4.10 Dissipation factor at U ( ) . 29
max.
4.11 Response time by ambient temperature change (t ) . 30
a
4.12 Response time by power change (t ) . 31
p
4.13 Thermal time constant by ambient temperature change (τ ) . 32
a
4.14 Thermal time constant by cooling (τ ) . 32
c
4.15 Robustness of terminations . 34

60738-1 © IEC:1998(E) – 3 –
Clause Page
4.16 Soldering. 35

4.17 Rapid change of temperature . 35

4.18 Vibration. 35

4.19 Bump. 36

4.20 Shock. 36

4.21 Climatic sequence. 37

4.22 Damp heat, steady state. 38

4.23 Endurance. 38
4.24 Tripping current and tripping time . 41
4.25 Non-tripping current. 42
4.26 Residual current. 42
4.27 Surface temperature. 42
4.28 Inrush current. 43
4.29 Mounting (for surface mount thermistors only) . 44
4.30 Shear (adhesion) test. 45
4.31 Substrate bending test . 45
Annex A (normative) Interpretation of sampling plans and procedures as described
in IEC 60410 for use within the IEC quality assessment system
for electronic components (IECQ) . 46
Annex B (informative) Mounting for electrical measurements (except surface
mount types) . 47
Annex C (informative) Mounting for temperature measurements . 49

– 4 – 60738-1 © IEC:1998(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION

__________
THERMISTORS –
DIRECTLY HEATED POSITIVE STEP-FUNCTION

TEMPERATURE COEFFICIENT –
Part 1: Generic specification
FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of the 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, the IEC publishes International Standards. 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. The 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 the 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 National Committees.
3) The documents produced have the form of recommendations for international use and are published in the form
of standards, technical reports or guides and they are accepted by the National Committees in that sense.
4) In order to promote international unification, IEC National Committees undertake to apply IEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with one of its standards.
6) Attention is drawn to the possibility that some of the elements of this International Standard may be the subject
of patent rights. The IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60738-1 has been prepared IEC technical committee 40: Capacitors
and resistors for electronic equipment.
This second edition cancels and replaces the first edition published in 1982 and constitutes a
technical revision.
The text of this standard is based on the following documents:

FDIS Report on voting
40/1080/FDIS 40/1096/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.
Annex A forms an integral part of this standard.
Annexes B and C are for information only.
The QC number that appears on the front cover of this publication is the specification number
in the IEC Quality Assessment System for Electronic Components (IECQ).

60738-1 © IEC:1998(E) – 5 –
THERMISTORS –
DIRECTLY HEATED POSITIVE STEP-FUNCTION

TEMPERATURE COEFFICIENT –
Part 1: Generic specification
1 General
1.1 Scope
This International Standard prescribes terms and methods of test for positive step-function
temperature coefficient thermistors, insulated and non-insulated types, typically made from
ferro-electric semi-conductor materials.
It establishes standard terms, inspection procedures and methods of test for use in detail
specifications for Qualification Approval and for Quality Assessment Systems for electronic
components.
1.2 Normative references
The following normative documents contain provisions which, through reference in this text,
constitute provisions of this International Standard. At the time of publication, the editions
indicated were valid. All normative documents are subject to revision, and parties to
agreements based on this International Standard are encouraged to investigate the possibility
of applying the most recent editions of the normative documents indicated below. Members of
IEC and ISO maintain registers of currently valid International Standards.
In the case of IEC 60068 publications, the referenced edition shall be used, regardless of any
subsequent new edition(s) and amendment(s).
IEC 60027-1:1992, Letter symbols to be used in electrical technology – Part 1: General
IEC 60050: International Electrotechnical Vocabulary
IEC 60062:1992, Marking codes for resistors and capacitors
IEC 60068-1:1988, Environmental testing – Part 1: General and guidance
IEC 60068-2-1:1990, Environmental testing – Part 2: Tests – Tests A: Cold
IEC 60068-2-2:1974, Environmental testing – Part 2: Tes
...