IEC 60539-1:2022

IEC 60539-1 ®
Edition 4.0 2022-12
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Directly heated negative temperature coefficient thermistors –
Part 1: Generic specification
Thermistances à coefficient de température négatif à chauffage direct –
Partie 1: Spécification générique

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IEC 60539-1 ®
Edition 4.0 2022-12
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Directly heated negative temperature coefficient thermistors –

Part 1: Generic specification
Thermistances à coefficient de température négatif à chauffage direct –

Partie 1: Spécification générique

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 31.040.30 ISBN 978-2-8322-6192-7

– 2 – IEC 60539-1:2022 © IEC 2022
CONTENTS
FOREWORD . 8
1 Scope . 10
2 Normative references . 10
3 Terms and definitions . 11
4 General items . 21
4.1 Units and symbols. 21
4.2 Preferred values and appropriate category . 21
4.2.1 General . 21
4.2.2 Appropriate category . 21
4.3 Marking . 21
4.3.1 General . 21
4.3.2 Marking for small size types such as surface mount NTC thermistors . 22
4.3.3 Coding . 22
4.4 Quality assessment procedures . 22
5 General provisions for measurements and test methods . 22
5.1 General . 22
5.2 Standard atmospheric conditions for testing . 22
5.3 Drying and recovery . 23
5.3.1 Drying . 23
5.3.2 Recovery . 23
5.4 Mounting (for surface mount thermistors only) . 23
5.4.1 General . 23
5.4.2 Printed wiring board and land pattern . 23
5.4.3 Mounting on board . 23
6 Electrical tests and measurements . 25
6.1 Zero-power resistance . 25
6.1.1 General . 25
6.1.2 Measurement procedures . 25
6.1.3 Requirements . 25
6.2 B-value or resistance ratio . 25
6.2.1 General . 25
6.2.2 Requirements . 25
6.3 Insulation resistance (for insulated types only) . 26
6.3.1 General . 26
6.3.2 Test methods . 26
6.3.3 Applied voltage . 29
6.3.4 Requirements . 29
6.4 Voltage proof (for insulated types only) . 29
6.4.1 General . 29
6.4.2 Test voltage . 29
6.4.3 Requirements . 29
6.5 Resistance/temperature characteristic . 29
6.5.1 General . 29
6.5.2 Test methods . 29
6.5.3 Requirements . 29
6.6 Dissipation factor (δ) . 30

6.6.1 General . 30
6.6.2 Initial measurements . 30
6.6.3 Test methods . 30
6.6.4 Requirements . 31
6.7 Thermal time constant by ambient temperature change (τ ) . 31
a
6.7.1 The hot to cold thermal time constant for ambient temperature change . 31
6.7.2 The cold to hot thermal time constant for ambient temperature change . 32
6.7.3 Final measurements and requirements . 32
6.7.4 Requirements . 33
6.8 Thermal time constant by cooling after self-heating (τ ) . 33
c
6.8.1 General . 33
6.8.2 Initial measurements . 33
6.8.3 Preconditioning . 33
6.8.4 Test method . 34
6.8.5 Final measurements and requirements . 34
7 Mechanical test and measurements . 34
7.1 Visual examination and check of dimensions . 34
7.1.1 Visual examination . 34
7.1.2 Dimensions . 35
7.2 Robustness of terminations (not applicable to surface mount thermistors) . 35
7.2.1 General . 35
7.2.2 Initial measurements . 35
7.2.3 Test methods . 35
7.2.4 Test Ua – Tensile . 35
7.2.5 Test Ub – Bending (half the number of terminations) . 36
7.2.6 Test Uc – Torsion (remaining terminations). 36
7.2.7 Final measurements and requirements . 36
7.3 Vibration . 36
7.3.1 General . 36
7.3.2 Initial measurements . 36
7.3.3 Test procedures . 36
7.3.4 Final inspection, measurements and requirements. 37
7.4 Shock . 37
7.4.1 General . 37
7.4.2 Initial measurements . 37
7.4.3 Mounting . 37
7.4.4 Test procedures . 37
7.4.5 Final inspection, measurements and requirements. 37
7.5 Free fall . 37
7.5.1 General . 37
7.5.2 Initial measurements . 37
7.5.3 Test procedures . 38
7.5.4 Final inspection, measurements and requirements. 38
7.6 Shear (adhesion) test (for surface mount NTC thermistors only) . 38
7.6.1 General . 38
7.6.2 Initial measurements . 38
7.6.3 Test conditions . 38
7.6.4 Final inspection, measurements and requirements. 38

– 4 – IEC 60539-1:2022 © IEC 2022
7.7 Substrate bending test (for surface mount NTC thermistors only) . 38
7.7.1 General . 38
7.7.2 Initial measurements . 38
7.7.3 Test procedures . 38
7.7.4 Final inspection, measurements and requirements. 39
8 Environmental and climatic tests . 39
8.1 Rapid change of temperature . 39
8.1.1 General . 39
8.1.2 Initial measurements . 39
8.1.3 Test procedures . 39
8.1.4 Final inspection, measurements and requirements. 39
8.2 Thermal shock . 40
8.2.1 General . 40
8.2.2 Initial measurements . 40
8.2.3 Test procedures . 40
8.2.4 Final inspection, measurements and requirements. 40
8.3 Cold . 40
8.3.1 General . 40
8.3.2 Initial measurements . 40
8.3.3 Test procedures . 40
8.3.4 Final inspection, measurements and requirements. 41
8.4 Dry heat . 41
8.4.1 General . 41
8.4.2 Initial measurements . 41
8.4.3 Test procedures . 41
8.4.4 Final inspection, measurements and requirements. 41
8.5 Damp heat, steady state . 42
8.5.1 General . 42
8.5.2 Initial measurements . 42
8.5.3 Test procedures . 42
8.5.4 Recovery . 42
8.5.5 Final inspection, measurements and requirements. 42
8.6 Endurance . 42
8.6.1 General . 42
8.6.2 Endurance at room temperature with applied continuous maximum
current (I ) (for inrush current-limiting thermistors only) . 43
max25
8.6.3 Endurance at room temperature with applied cyclic maximum current
(I ) (for inrush current-limiting thermistors only) . 44
max25
8.6.4 Endurance at T and P (for other than inrush current-limiting
3 max
thermistors only) . 45
8.6.5 Endurance at upper category temperature . 46
8.6.6 Maximum permissible capacitance (for inrush current-limiting
thermistors only) . 47
8.7 Salt mist . 49
8.7.1 General . 49
8.7.2 Initial measurements . 49
8.7.3 Test conditions . 49
8.7.4 Final inspection, measurements and requirements. 49
8.8 Sealing . 49

8.9 Composite temperature/humidity cycle . 49
8.9.1 General . 49
8.9.2 Initial measurements . 49
8.9.3 Test conditions . 50
8.9.4 Final inspection, measurements and requirements. 50
9 Tests related to component assembly . 50
9.1 Resistance to soldering heat . 50
9.1.1 General . 50
9.1.2 Preconditioning . 50
9.1.3 Initial measurements . 50
9.1.4 Test procedure . 50
9.1.5 Recovery . 50
9.1.6 Final inspection, measurement and requirements . 51
9.2 Solderability . 51
9.2.1 General . 51
9.2.2 Initial measurements . 51
9.2.3 Test procedure . 51
9.2.4 Final inspection, measurements and requirements. 51
9.3 Component solvent resistance . 52
9.3.1 General . 52
9.3.2 Initial measurements . 52
9.3.3 Test conditions . 52
9.3.4 Requirements . 52
9.4 Solvent resistance of marking . 52
9.4.1 General . 52
9.4.2 Initial measurements . 52
9.4.3 Test conditions . 52
9.4.4 Requirements . 52
Annex A (normative) Rules for the preparation of detail specifications for directly
heated NTC thermistors for electronic equipment for use within quality assessment
systems . 53
A.1 Drafting . 53
A.2 Reference standard . 53
A.3 Circulation . 53
Annex B (informative) Typical examples of mountings for measurements of directly
heated thermistors . 54
Annex Q (informative) Quality assessment procedures . 56
Q.1 General . 56
Q.1.1 Scope of this annex . 56
Q.1.2 Quality assessment definitions . 57
Q.1.3 Rework . 57
Q.1.4 Alternative test methods . 57
Q.1.5 Certified test records of released lots . 58
Q.1.6 Unchecked parameters . 58
Q.1.7 Delayed delivery . 58
Q.1.8 Repair . 58
Q.1.9 Registration of approvals . 58
Q.1.10 Manufacture outside the geographical limits . 59
Q.2 Qualification approval (QA) procedures . 59

– 6 – IEC 60539-1:2022 © IEC 2022
Q.2.1 Eligibility for qualification approval . 59
Q.2.2 Application for qualification approval . 59
Q.2.3 Subcontracting . 59
Q.2.4 Test procedure for the initial product qualification approval. 59
Q.2.5 Granting of qualification approval . 59
Q.2.6 Maintenance of qualification approval . 59
Q.2.7 Quality conformance inspection . 60
Q.3 Capability approval (CA) procedures . 60
Q.3.1 General . 60
Q.3.2 Eligibility for capability approval . 60
Q.3.3 Application for capability approval . 60
Q.3.4 Subcontracting . 61
Q.3.5 Description of the capability . 61
Q.3.6 Demonstration and verification of capability . 61
Q.3.7 Granting of capability approval . 61
Q.3.8 Maintenance of capability approval . 61
Q.3.9 Quality conformance inspection . 61
Q.4 Technology approval (TA) procedure . 62
Q.4.1 General . 62
Q.4.2 Eligibility for technology approval . 62
Q.4.3 Application of technology approval . 62
Q.4.4 Subcontracting . 62
Q.4.5 Description of technology . 62
Q.4.6 Demonstration and verification of the technology . 62
Q.4.7 Granting of technology approval . 62
Q.4.8 Maintenance of technology approval . 62
Q.4.9 Quality conformance inspection . 63
Q.5 Interpretation of sampling plans and procedures as described in IEC 60410
for use within quality assessment systems . 63
Q.6 Rules for the preparation of detail specifications for NTC thermistors for
electronic equipment for use within quality assessment systems . 63
Q.6.1 Drafting . 63
Q.6.2 Reference standard . 63
Q.7 Layout of the first page of a PCP/CQC specification . 64
Q.8 Requirements for capability approval test report . 65
Q.8.1 General . 65
Q.8.2 Requirements . 65
Q.8.3 Summary of test information (for each CQC) . 65
Q.8.4 Measurement record . 65
Q.9 Guidance for the extension of endurance tests on fixed thermistor . 65
Q.9.1 Overview . 65
Q.9.2 Guidelines . 66
Annex X (informative) Cross-references to IEC 60539-1:2016 . 67
Bibliography . 69

Figure 1 – Typical resistance-temperature characteristic for NTC thermistors . 14
Figure 2 – Decreased power dissipation curve . 16
Figure 3 – Maximum current derating . 18
Figure 4 – Basic circuit for zero-power resistance measurement . 25

Figure 5 – Example of Method 1 for testing the insulation resistance . 26
Figure 6 – Example of Method 2 for testing the insulation resistance (1) . 27
Figure 7 – Example of Method 2 for testing the insulation resistance (2) . 27
Figure 8 – Example of Method 3 for testing the insulation resistance . 28
Figure 9 – Example of Method 4 for testing the insulation resistance . 28
Figure 10 – Example of test chamber . 30
Figure 11 – Dissipation factor measuring circuit . 31
Figure 12 – Thermal time constant measuring circuit . 34
Figure 13 – Endurance at room temperature with I evaluating circuit . 43
max25
Figure 14 – Endurance at room temperature with I evaluating circuit . 44
max25
Figure 15 – Maximum permissible capacitance test circuit (Method 1) . 48
Figure 16 – Maximum permissible capacitance test circuit (Method 2) . 48
Figure B.1 – Mounting for measurements of surface mount thermistors . 55

Table 1 – Lower and upper category temperatures and duration of the damp heat,
steady state test . 21
Table 2 – Tensile force . 36
Table B.1 – Recommended land dimensions . 54

– 8 – IEC 60539-1:2022 © IEC 2022
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
DIRECTLY HEATED NEGATIVE TEMPERATURE
COEFFICIENT THERMISTORS –
Part 1: Generic specification
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
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preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with
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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
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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
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any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
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services carried out by independent certification bodies.
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.
IEC 60539-1 has been prepared by IEC technical committee 40: Capacitors and resistors for
electronic equipment. It is an International Standard.
This fourth edition cancels and replaces the third edition published in 2016. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) Restructured completely to comply to ISO/IEC directives; categorization and reorganization
of test methods into these categories;
b) Annex X added for comparison to the previous edition;
c) Some wordings, figures and references have been revised.

The text of this International Standard is based on the following documents:
Draft Report on voting
40/2975/FDIS 40/3016/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
A list of all parts in the IEC 60539-1 series, published under the general title Directly heated
negative temperature coefficient thermistors, can be found on the IEC website.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
– 10 – IEC 60539-1:2022 © IEC 2022
DIRECTLY HEATED NEGATIVE TEMPERATURE
COEFFICIENT THERMISTORS –
Part 1: Generic specification
1 Scope
This part of IEC 60539 is applicable to directly heated negative temperature coefficient
thermistors, typically made from transition metal oxide materials with semiconducting properties.
It establishes standard terms, inspection procedures and methods of test for use in sectional
and detail specifications of electronic components for quality assessment or any other purpose.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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 60062, Marking codes for resistors and capacitors
IEC 60068-1:2013, Environmental testing – Part 1: General and guidance
IEC 60068-2-1, Environmental testing – Part 2-1: Tests – Tests A: Cold
IEC 60068-2-2, Environmental testing – Part 2-2: Tests – Tests B: Dry heat
IEC 60068-2-6, Environmental testing – Part 2-6: Tests – Test Fc: Vibration (sinusoidal)
IEC 60068-2-11, Environmental testing – Part 2-11: Tests – Test Ka: Salt mist
IEC 60068-2-14, Environmental testing – Part 2-14: Tests – Test N: Change of temperature
IEC 60068-2-17, Basic environmental testing procedures – Part 2-17: Tests – Test Q: Sealing
IEC 60068-2-20, Environmental testing – Part 2-20: Tests – Test Ta and Tb: Test methods for
solderability and resistance to soldering heat of devices with leads
IEC 60068-2-21:2021, Environmental testing – Part 2-21: Tests – Test U: Robustness of
terminations and integral mounting devices
IEC 60068-2-27:2008, Environmental testing – Part 2-27: Tests – Test Ea and guidance: Shock
IEC 60068-2-31, Environmental testing – Part 2-31: Tests – Test Ec: Rough handling shocks,
primarily for equipment-type specimens
IEC 60068-2-38, Environmental testing – Part 2-38: Tests – Test Z/AD: Composite
temperature/humidity cyclic test

IEC 60068-2-45:1980, Basis Environmental testing procedures – Part 2-45: Tests – Test XA
and guidance: Immersion in cleaning solvents
IEC 60068-2-45:1980/AMD1:1993
IEC 60068-2-52, Environmental testing – Part 2-52: Tests – Test Kb: Salt mist, cyclic (sodium
chloride solution)
IEC 60068-2-58, Environmental testing – Part 2-58: Tests – Test Td: Test methods for
solderability, resistance to dissolution of metallization and to soldering heat of surface mounting
devices (SMD)
IEC 60068-2-69, Environmental testing – Part 2-69: Tests – Test Te/Tc: Solderability testing of
electronic components and printed boards by the wetting balance (force measurement) method
IEC 60068-2-78, Environmental testing – Part 2-78: Tests – Test Cab: Damp heat, steady state
IEC 60294, Measurement of the dimensions of a cylindrical component with axial terminations
IEC 61193-2, Quality assessment systems – Part 2: Selection and use of sampling plans for
inspection of electronic components and packages
IEC 60717, Method for the determination of the space required by capacitors and resistors with
unidirectional terminations
IEC 61249-2-7, Materials for printed boards and other interconnecting struct
...