IEC 60738-1:2022

Thermistors - Directly heated positive temperature coefficient - Part 1: Generic specification

IEC 60738-1:2022 describes 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.
This edition includes the following significant technical changes with respect to the previous edition:
a) Restructured completely to comply with ISO/IEC Directives; categorization and reorganization of test methods into these categories;
b) Some wordings, figures and references have been revised.

Thermistances - Coefficient de température positif à chauffage direct - Partie 1: Spécification générique

L’IEC 60738-1:2022 décrit des termes et des méthodes d’essai pour les thermistances à basculement à coefficient de température positif, de type isolées ou non isolées, normalement fabriquées à partir de matériaux semiconducteurs ferroélectriques.
Elle établit des termes normaux, des procédures de contrôle et des méthodes d’essai destinés aux spécifications particulières pour l’homologation et pour les systèmes d’assurance de la qualité des composants électroniques.
Cette édition inclut les modifications techniques majeures suivantes par rapport à l’édition précédente:
a) restructuration complète pour être conforme aux Directives ISO/IEC; catégorisation et réorganisation des méthodes d’essai dans ces catégories,
b) révision de certaines formulations, figures et références.

General Information

• Status: Published
• Publication Date: 13-Oct-2022
• ICS: 31.040.30 - Thermistors
• Technical Committee: TC 40 - Capacitors and resistors for electronic equipment
• Drafting Committee: MT 60738-1 - TC 40/MT 60738-1
• Current Stage: PPUB - Publication issued
• Start Date: 28-Oct-2022
• Completion Date: 14-Oct-2022

Relations

• Revises: IEC 60738-1:2006 - Thermistors - Directly heated positive temperature coefficient - Part 1: Generic specification
• Effective Date: 05-Sep-2023
• Revises: IEC 60738-1:2006/AMD1:2009 - Amendment 1 - Thermistors - Directly heated positive temperature coefficient - Part 1: Generic specification
• Effective Date: 05-Sep-2023

Standards Content (Sample)

IEC 60738-1
®

Edition 4.0 2022-10
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside


Thermistors – Directly heated positive temperature coefficient –
Part 1: Generic specification

Thermistances – Coefficient de température positif à chauffage direct –
Partie 1: Spécification générique

IEC 60738-1:2022-10(en-fr)

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IEC 60738-1

®


Edition 4.0 2022-10




INTERNATIONAL



STANDARD




NORME


INTERNATIONALE
colour

inside










Thermistors – Directly heated positive temperature coefficient –

Part 1: Generic specification



Thermistances – Coefficient de température positif à chauffage direct –

Partie 1: Spécification générique
















INTERNATIONAL

ELECTROTECHNICAL

COMMISSION


COMMISSION

ELECTROTECHNIQUE


INTERNATIONALE




ICS 31.040.30 ISBN 978-2-8322-5731-9




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® Registered trademark of the International Electrotechnical Commission
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– 2 – IEC 60738-1:2022 © IEC 2022
CONTENTS
FOREWORD . 7
1 Scope . 9
2 Normative references . 9
3 Terms and definitions . 10
4 General requirements . 19
4.1 Units and symbols. 19
4.2 Preferred values . 20
4.2.1 Climatic categories . 20
4.2.2 Spacings . 20
4.3 Marking . 20
4.3.1 General . 20
4.3.2 Coding . 21
5 General provisions for measurements and test method . 21
5.1 General . 21
5.2 Standard conditions for testing . 21
5.2.1 Standard atmospheric conditions for testing . 21
5.2.2 Error of measurement . 21
5.3 Drying and recovery . 21
5.3.1 Drying . 21
5.3.2 Recovery . 22
5.3.3 Shock test severities . 22
5.3.4 Vibration severities . 22
5.4 Mounting (for surface mount thermistors only) . 22
5.4.1 General . 22
5.4.2 Printed wiring board and land pattern . 23
5.4.3 Wave soldering method . 23
5.4.4 Reflow soldering method . 23
6 Electrical tests and measurements . 24
6.1 Zero-power resistance . 24
6.1.1 General . 24
6.1.2 Measurement procedures . 24
6.1.3 Requirements . 25
6.2 Temperature coefficient of resistance . 25
6.2.1 General . 25
6.2.2 Requirements . 25
6.3 Insulation resistance (for insulated types only) . 25
6.3.1 General . 25
6.3.2 Test methods . 25
6.3.3 Applied voltage . 26
6.3.4 Requirements . 26
6.4 Voltage proof (for insulated types only) . 26
6.4.1 General . 26
6.4.2 Test methods . 26
6.4.3 Test voltage . 26
6.4.4 Requirements . 26
6.5 Resistance/temperature characteristic . 26

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IEC 60738-1:2022 © IEC 2022 – 3 –
6.5.1 Test methods . 26
6.5.2 Requirements . 27
6.6 Dissipation factor at U (δ) . 27
max
6.6.1 General . 27
6.6.2 Preconditioning . 27
6.6.3 Test circuit . 27
6.6.4 Test methods . 27
6.6.5 Requirements . 28
6.7 Response time by ambient temperature change (t ) . 28
a
6.7.1 General . 28
6.7.2 Preconditioning . 28
6.7.3 Test procedures . 28
6.7.4 Measurement procedures . 29
6.7.5 Requirements . 29
6.8 Response time by power change (t ) . 29
p
6.8.1 Mounting . 29
6.8.2 Test methods . 29
6.9 Thermal time constant by ambient temperature change (τ ) . 30
a
6.10 Thermal time constant by cooling (τ ) . 30
c
6.10.1 Mounting . 30
6.10.2 Test methods . 30
6.10.3 Requirements . 32
6.11 Tripping current and tripping time. 32
6.12 Non-tripping current . 32
6.13 Residual current. 32
6.14 Surface temperature . 33
6.15 Inrush current . 34
6.15.1 Measuring circuit . 34
6.15.2 Measuring method . 34
6.16 Energy by discharge . 35
6.16.1 Measuring circuit . 35
6.16.2 Measuring method . 35
7 Mechanical test and measurements . 36
7.1 Visual examination and check of dimensions . 36
7.1.1 Visual examination . 36
7.1.2 Marking . 36
7.1.3 Dimensions (gauging) . 36
7.1.4 Dimensions (detail) . 36
7.2 Robustness of terminations . 36
7.2.1 General . 36
7.2.2 Test Ua – Tensile . 36
1
7.2.3 Test Ub – Bending . 37
7.2.4 Test Uc – Torsion . 37
7.2.5 Visual examination . 37
7.2.6 Final measurements and requirements . 37
7.3 Vibration . 37
7.4 Shock . 38
7.5 Shear (adhesion) test . 38

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7.5.1 Test conditions . 38
7.5.2 Test methods . 38
7.5.3 Requirements . 38
7.6 Substrate bending test . 38
7.6.1 Mounting . 38
7.6.2 Initial measurements . 39
7.6.3 Test procedures . 39
7.6.4 Measurements . 39
7.6.5 Requirements . 39
7.6.6 Final inspection and requirements . 39
8 Environmental and climatic tests . 39
8.1 Rapid change of temperature . 39
8.2 Climatic sequence. 39
8.2.1 General . 39
8.2.2 Initial measurements . 39
8.2.3 Dry heat . 40
8.2.4 Damp heat (cyclic), first cycle . 40
8.2.5 Cold. 40
8.2.6 Low air pressure . 40
8.2.7 Damp heat (cyclic), remaining cycles . 40
8.2.8 Final measurements . 40
8.3 Damp heat, steady state . 41
8.4 Endurance . 41
8.4.1 Endurance at room temperature (cycling) . 41
8.4.2 Endurance at upper category temperature . 42
8.4.3 Endurance at maximum operating temperature and maximum voltage . 43
8.4.4 Cold environment electrical cycling . 44
8.4.5 Thermal runaway . 45
9 Test related to component assembly . 45
9.1 Solderability . 45
9.1.1 General . 45
9.1.2 Thermistors with leads . 45
9.1.3 Surface mount thermistors . 46
9.2 Resistance to soldering heat . 46
9.2.1 General . 46
9.2.2 Test conditions . 46
9.2.3 The period of recovery . 47
9.2.4 Requirements for except surface mount thermistors . 47
9.2.5 Requirements for surface mount thermistors . 47
10 Quality assessment procedures . 47
Annex A (informative) Mounting for electrical measurements . 48
A.1 Mounting for thermistors without wire terminations . 48
A.2 Mounting for thermistors with wire terminations . 48
A.3 Mounting for surface mount thermistors . 49
Annex B (informative) Mounting for temperature measurements . 51
Annex Q (normative) Quality assessment procedures . 52
Q.1 General . 52
Q.2 Applicability of qualification approval . 52

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IEC 60738-1:2022 © IEC 2022 – 5 –
Q.3 Primary stage of manufacture . 52
Q.4 Subcontracting . 52
Q.5 Structurally similar components . 52
Q.5.1 General . 52
Q.5.2 For electrical tests . 53
Q.5.3 For environmental tests . 53
Q.5.4 For visual inspection . 53
Q.5.5 For endurance tests . 53
Q.6 Qualification approval procedures . 53
Q.6.1 Eligibility for qualification approval . 53
Q.6.2 Application for qualification approval . 53
Q.6.3 Test procedure for qualification approval . 53
Q.6.4 Qualification approval based on the fixed sample size procedure. 54
Q.6.5 Granting of qualification approval . 59
Q.6.6 Maintenance of qualification approval . 59
Q.6.7 Quality conformance inspection . 60
Q.7 Rework and repair. 61
Q.7.1 Rework . 61
Q.7.2 Repair . 61
Q.8 Release for delivery . 61
Q.8.1 General . 61
Q.8.2 Release for delivery under qualification approval before the completion
of group B tests . 62
Q.9 Certified test records of released lots . 62
Q.10 Delayed delivery . 62
Q.11 Alternative test methods . 62
Q.12 Manufacture outside the geographical limits . 62
Q.13 Unchecked parameters . 62
Annex X (informative) Cross-references to IEC 60738-1:2009 . 63
Bibliography . 65

Figure 1 – Typical resistance-temperature characteristic and definitions for PTC
thermistors (at zero power) . 12
Figure 2 – Typical R-TNF characteristic for PTC thermistors in sensor applications . 13
Figure 3 – Typical current/voltage characteristic for PTC thermistors . 14
Figure 4 – I against t at U . 17
in dc
Figure 5 – I against t at U . 17
in RMS
Figure 6 – Dissipation factor test circuit . 28
Figure 7 – Temperature gradient . 29
Figure 8 – Circuit for measurement of thermal time constant by cooling . 30
Figure 9 – Circuit for surface temperature measurement . 33
Figure 10 – Measuring circuit . 34
Figure 11 – Measuring circuit . 35
Figure 12 – Circuit for endurance at maximum operating temperature and maximum
voltage . 44
Figure A.1 – Example of a preferred mounting method for thermistors without wire
terminations . 48

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– 6 – IEC 60738-1:2022 © IEC 2022
Figure A.2 – Example of a preferred mounting method for thermistors with wire
terminations . 49
Figure A.3 – Example of a preferred mounting method for surface mount thermistors . 50
Figure B.1 – Example of a preferred mounting method for temperature measurement
on cylindrical heating elements . 51

Table 1 – Creepage distances and clearances . 20
Table 2 – Test severities of vibration . 22
Table 3 – Tensile force . 37
Table 4 – Number of cycles per climatic category . 40
Table A.1 – Recommended land dimensions . 50
Table Q.1 – Fixed sample size test schedule
...