IEC 60539-2:2003

Directly heated negative temperature coefficient thermistors - Part 2: Sectional specification - Surface mount negative temperature coefficient thermistors

IEC 60539-2:2003 is applicable to surface mount directly heated negative temperature coefficient thermistors, typically made from transition metal oxide materials with semiconducting properties. These thermistors have metallized connecting pads or soldering strips and are intended to be mounted directly on to substrates for hybrid circuits or on to printed boards.

Thermistances à coefficient de température négatif à chauffage direct - Partie 2: Spécification intermédiaire - Thermistances à coefficient de température négatif pour montage en surface

La CEI 60539-2:2003 s'applique aux thermistances à coefficient de température négatif à chauffage direct pour montage en surface, typiquement constituées de matériaux faits d'oxyde de métal de transition dotés de propriétés semi-conductrices. Ces thermistances sont équipées de contacts de connexion métallisés ou de bandes de soudure et sont destinées à être montées directement sur des substrats pour circuits hybrides ou sur des cartes imprimées.

General Information

• Status: Published
• Publication Date: 18-Nov-2003
• ICS: 31.040.30 - Thermistors
• Technical Committee: TC 40 - Capacitors and resistors for electronic equipment
• Current Stage: DELPUB - Deleted Publication
• Start Date: 19-Jul-2019
• Completion Date: 31-Jul-2017

Relations

• Amended By: IEC 60539-2:2003/AMD1:2010 - Amendment 1 - Directly heated negative temperature coefficient thermistors - Part 2: Sectional specification - Surface mount negative temperature coefficient thermistors
• Effective Date: 05-Sep-2023
• Revised: IEC 60539-2:2019 - Directly heated negative temperature coefficient thermistors - Part 2: Sectional specification - Surface mount negative temperature coefficient thermistors
• Effective Date: 05-Sep-2023

Overview

IEC 60539-2:2003 is the sectional specification for surface mount directly heated negative temperature coefficient (NTC) thermistors. It complements the generic requirements in IEC 60539-1 and applies to SMD NTC thermistors typically manufactured from transition metal oxide semiconducting materials with metallized connecting pads or soldering strips. These components are intended for direct mounting on substrates for hybrid circuits or printed circuit boards (PCBs).

Keywords: IEC 60539-2:2003, surface mount NTC thermistors, SMD thermistors, directly heated NTC, printed circuit board mounting.

Key topics

The standard sets out technical and quality requirements, including:

• Scope and definitions specific to surface mount directly heated NTC thermistors.
• Detail specification requirements (outline drawings, dimensions, mounting, ratings and characteristics).
• Quality assessment procedures: primary manufacture, structurally similar components, qualification approval, fixed sample-size and lot-by-lot inspection.
• Test and measurement procedures, covering:
  • Electrical tests (zero‑power resistance, B‑value or resistance ratio, resistance/temperature characteristic).
  • Thermal tests (dissipation factor, thermal time constant).
  • Resistance to soldering heat and solderability tests for SMD applications.
  • Environmental tests: rapid change of temperature, thermal shock, damp heat (cyclic and steady state), endurance.
  • Mechanical and assembly-related tests: shear (adhesion), substrate bending, solvent resistance of components and marking.
• Marking and dimensional coding guidance for surface mount NTC thermistors.

These topics reference environmental test standards (IEC 60068 series) and sampling plans (IEC 60410).

Applications

IEC 60539-2:2003 is used where reliable, defined performance of surface mount NTC thermistors is required in electronic assemblies. Typical applications include:

• Temperature sensing and temperature compensation on printed circuit boards (PCBs).
• Inrush current limiting, circuit protection, and temperature monitoring in compact hybrid circuits and surface mount designs.
• Qualification of SMD thermistor components for automated assembly and reflow soldering processes.

Who should use this standard

• Component manufacturers developing or certifying surface mount NTC thermistors.
• Design and reliability engineers specifying thermistor performance and test requirements for PCBs and hybrid modules.
• Test laboratories and quality assurance teams performing qualification, lot inspection and environmental testing.
• Procurement and compliance personnel seeking to verify supplier conformance.

Related standards

• IEC 60539-1 (Generic specification for directly heated NTC thermistors)
• IEC 60068 series (environmental testing)
• IEC 60068-2-58 (solderability / resistance to soldering heat)
• IEC 60410 (sampling plans)

This standard ensures consistent performance, test methods and quality assessment for SMD NTC thermistors used in modern electronic assemblies.

Standards Content (Sample)

INTERNATIONAL IEC
STANDARD
60539-2
First edition
2003-11
Directly heated negative temperature
coefficient thermistors –
Part 2:
Sectional specification –
Surface mount negative temperature
coefficient thermistors
Reference number
Publication numbering
As from 1 January 1997 all IEC publications are issued with a designation in the

60000 series. For example, IEC 34-1 is now referred to as IEC 60034-1.

Consolidated editions
The IEC is now publishing consolidated versions of its publications. 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.
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INTERNATIONAL IEC
STANDARD
60539-2
First edition
2003-11
Directly heated negative temperature
coefficient thermistors –
Part 2:
Sectional specification –
Surface mount negative temperature
coefficient thermistors
 IEC 2003  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: [phone] Telefax: [phone] E-mail: [e-mail]  Web: www.iec.ch
PRICE CODE
Commission Electrotechnique Internationale
S
International Electrotechnical Commission
Международная Электротехническая Комиссия
For price, see current catalogue

– 2 – 60539-2  IEC:2003(E)
CONTENTS
FOREWORD . 4

1 General . 6

1.1 Scope . 6

1.2 Normative references . 6

1.3 Information to be given in a detail specification. 6

1.3.1 Outline drawing and dimensions . 7

1.3.2 Mounting. 7
1.3.3 Ratings and characteristics. 7
1.4 Terminology. 7
2 Preferred ratings and characteristics. 7
2.1 Tolerances on rated zero-power resistance . 7
2.2 Climatic categories . 7
3 Quality assessment procedures . 8
3.1 Primary stage of manufacture . 8
3.2 Structurally similar components . 8
3.3 Qualification approval procedures. 8
3.3.1 The manufacturer shall comply with 3.4 of IEC 60539-1. 8
3.4 Quality conformance inspection . 8
3.4.1 Qualification approval on the basis of the fixed sample size
procedure . 8
3.5 Quality conformance inspection .10
3.5.1 Formation of inspection lots .10
3.5.2 Test schedule .11
3.5.3 Delayed delivery .11
3.5.4 Assessment level.11
4 Test and measurement procedures .12
4.1 Mounting .12
4.2 Drying and recovery.12
4.2.1 Drying.12
4.2.2 Recovery .12
4.3 Visual examination and check of dimensions .12
4.3.1 Visual examination.12
4.3.2 Requirements .12
4.3.3 Marking.14
4.3.4 Dimensions.14
4.4 Electrical tests .14
4.4.1 Zero-power resistance .14
4.4.2 B-value or resistance ratio .14
4.4.3 Resistance/temperature characteristic .15
4.5 Thermal tests.15
4.5.1 Dissipation factor (δ).15
4.5.2 Thermal time constant by cooling after self-heating (τ ).15
c
60539-2  IEC:2003(E) – 3 –
4.6 Resistance to soldering heat .15

4.6.1 Initial measurement .15

4.6.2 Test conditions .15

4.6.3 Recovery .16

4.6.4 Final inspection, measurements and requirements .16

4.7 Solderability .16

4.7.1 Test conditions .16

4.7.2 Recovery .17

4.7.3 Final inspection, measurements and requirements .17

4.8 Rapid change of temperature .17

4.9 Thermal shock.17
4.10 Climatic sequence .18
4.10.1 Initial measurements .18
4.10.2 Dry heat .18
4.10.3 Damp heat (cyclic), first cycle.18
4.10.4 Cold .18
4.10.5 Damp heat (cyclic), remaining cycles.18
4.10.6 Final measurements .19
4.11 Damp heat, steady state.19
4.12 Endurance.19
4.12.1 Endurance at θ and P .19
3 max.
4.12.2 Endurance at upper category temperature .19
4.13 Shear (adhesion) test .20
4.14 Substrate bending test .20
4.15 Component solvent resistance.20
4.16 Solvent resistance of marking.20
Annex A (normative) Guide for the specification and coding of dimensions of surface
mount negative temperature coefficient thermistors .21
Table 1 – Upper and lower category temperatures and duration of the damp heat test.8
Table 2 – Fixed sample size test schedule for qualification approval of surface mount
negative temperature coefficient thermistors Assessment level EZ .10
Table 3 – Lot-by-lot inspection.11
Table 4 – Periodic test .12

Table 5 – Number of cycles .18
Table A.1 – Dimensions .21
Figure 1 – Fault: fissure or defect .13
Figure 2 – Fault: crack .13
Figure 3 – Separation or delamination .13
Figure 4 – Exposed electrodes.13
Figure 5 – Principal faces .14
Figure A.1 – Dimensioning of surface mount thermistors.21

– 4 – 60539-2  IEC:2003(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION

____________
DIRECTLY HEATED NEGATIVE TEMPERATURE

COEFFICIENT THERMISTORS –
Part 2: Sectional specification –

Surface mount negative temperature coefficient thermistors

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
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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.

International Standard IEC 60539-2 has been prepared by IEC technical committee 40:
Capacitors and resistors for electronic equipment.
The text of this standard is based on the following documents:
FDIS Report on voting
40/1346/FDIS 40/1368/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.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

60539-2  IEC:2003(E) – 5 –
The committee has decided that the contents of this publication will remain unchanged until
2008. At this date, the publication will be

• reconfirmed;
• withdrawn;
• replaced by a revised edition, or

• amended.
A bilingual edition of this document may be issued at a later date.

– 6 – 60539-2  IEC:2003(E)
DIRECTLY HEATED NEGATIVE TEMPERATURE

COEFFICIENT THERMISTORS –
Part 2: Sectional specification –

Surface mount negative temperature coefficient thermistors

1 General
1.1 Scope
This part of IEC 60539 is applicable to surface mount directly heated negative temperature
coefficient thermistors, typically made from transition metal oxide materials with
semiconducting properties. These thermistors have metallized connecting pads or soldering
strips and are intended to be mounted directly on to substrates for hybrid circuits or on to
printed boards.
1.2 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 60068-2-2:1974, Environmental testing – Part 2: Tests – Tests B: Dry heat
Amendment 1 (1993)
Amendment 2 (1994)
IEC 60068-2-14:1984, Environmental testing – Part 2: Tests – Test N: Change of temperature
Amendment 1 (1986)
IEC 60068-2-30:1980, Environmental testing – Part 2: Tests – Test Db and guidance: Damp
heat, cyclic (12 + 12-hour cycle)
Amendment 1 (1985)
IEC 60068-2-58:1999, 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 60068-2-78: Environmental testing – Part 2-78: Tests – Test Cab: Damp heat, steady

state
IEC 60410:1973, Sampling plans and procedures for inspection by attributes
IEC 60539-1:2002, Directly heated negative temperature coefficient thermistors – Part 1:
Generic specification
1.3 Information to be given in a detail specification
Detail specifications shall be derived from the relevant blank detail specification.
Detail specifications shall not specify requirements inferior to those of the generic, sectional
or blank detail specification. When more severe requirements are included, they shall be
listed in 1.9 of the detail specification and indicated in the test schedules, for example, by an
asterisk.
60539-2  IEC:2003(E) – 7 –
NOTE The information given in 1.3.1 may for convenience, be presented in tabular form.

The following information shall be given in each detail specification and the values quoted
shall preferably be selected from those given in the appropriate clause of this sectional
specification.
1.3.1 Outline drawing and dimensions

There shall be an illustration of the thermistor as an aid to easy recognition and for

comparison with others. Dimensions and their associated tolerances, which affect inter-

changeability and mounting, shall be given in the detail specification. All dimensions shall

preferably be stated in millimetres; however, when the original dimensions are given in

inches, the converted metric dimensions in millimetres shall be added.
Normally, the numerical values shall be given for the length, width and height of the body.
When necessary, for example when a number of items are covered by a detail specification,
the dimensions and their associated tolerances shall be placed in a table below the drawing.
When the configuration is other than described above, the detail specification shall state such
dimensional information as will adequately describe the thermistor.
1.3.2 Mounting
The detail specification shall give guidance on methods of mounting for normal use. Mounting
for test and measurement purposes (when required) shall be in accordance with 4.27 of
IEC 60539-1.
1.3.3 Ratings and characteristics
1.3.3.1 Particular characteristics
Additional characteristics may be listed when they are considered necessary to specify the
component adequately for design and application purposes.
1.3.3.2 Marking
See 2.4 of IEC 60539-1.
1.4 Terminology
See 2.2 of IEC 60539-1.
2 Preferred ratings and characteristics
2.1 Tolerances on rated zero-power resistance
Preferred values of tolerances on zero-power resistance are:
±1 %, ±2 %, ±3 %, ±5 %, ±10 %.
2.2 Climatic categories
The upper and lower category temperatures and the duration of the damp-heat steady-state
test shall be selected from Table 1.

– 8 – 60539-2  IEC:2003(E)
Table 1 – Upper and lower category temperatures and duration of the damp heat test

Lower category temperature
–55, –40, –25, –10, –5, +5
ºC
Upper category temperature
70, 85, 100, 105, 125, 150, 155

ºC
Damp heat, steady state
21, 42, 56
days
The detail specification shall prescribe the appropriate category.
3 Quality assessment procedures
3.1 Primary stage of manufacture
The primary stage of manufacture is defined as the initial mixing process of ingredients.
3.2 Structurally similar components
Surface mount thermistors may be grouped as structurally similar for the purpose of forming
inspection lots provided that the requirements of 3.1 of IEC 60539-1 are met, with the
following addition.
For the shear test and the substrate bending test, devices may be grouped if they have been
made on the same production line, have the same dimensions, internal structure and external
finish.
3.3 Qualification approval procedures
3.3.1 The manufacturer shall comply with 3.4 of IEC 60539-1.
3.4 Quality conformance inspection
Blank detail specifications associated with this specification shall prescribe the test schedule
for quality conformance inspection.
This schedule shall also specify the grouping, sampling and periodicity for the lot-by-lot and
periodic inspection.
Inspection levels and sampling plans shall be selected from those given in IEC 60410.
If required, more then one test schedule may be specified.
3.4.1 Qualification approval on the basis of the fixed sample size procedure
a) Sampling
The sample shall be representative of the range of thermistors for which approval is sought.
This may or may not be the complete range covered by the detail specification.
The sample shall consist of specimens having the lowest, highest and middle-rated zero-
power resistance of each case size.

60539-2  IEC:2003(E) – 9 –
Per value, three spare specimens are permitted and may be used as replacements for

specimens which are defective because of incidents not attributable to the manufacturer.

b) Tests
The complete series of tests specified in Table 2 are required for the approval of thermistors

covered by one detail specifica
...

IEC 60539-2 ®
Edition 1.0 2003-11
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Directly heated negative temperature coefficient thermistors –
Part 2: Sectional specification – Surface mount negative temperature coefficient
thermistors
Thermistances à coefficient de température négatif à chauffage direct –
Partie 2: Spécification intermédiaire – Thermistances à coefficient de
température négatif pour montage en surface

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IEC 60539-2 ®
Edition 1.0 2003-11
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Directly heated negative temperature coefficient thermistors –
Part 2: Sectional specification – Surface mount negative temperature coefficient
thermistors
Thermistances à coefficient de température négatif à chauffage direct –
Partie 2: Spécification intermédiaire – Thermistances à coefficient de
température négatif pour montage en surface

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
S
CODE PRIX
ICS 31.040.30 ISBN 978-2-88912-044-4
– 2 – 60539-2 © IEC:2003
CONTENTS
FOREWORD.4

1 General .6

1.1 Scope.6

1.2 Normative references .6

1.3 Information to be given in a detail specification .6

1.3.1 Outline drawing and dimensions .7

1.3.2 Mounting .7

1.3.3 Ratings and characteristics.7
1.4 Terminology .7
2 Preferred ratings and characteristics .7
2.1 Tolerances on rated zero-power resistance .7
2.2 Climatic categories.7
3 Quality assessment procedures.8
3.1 Primary stage of manufacture.8
3.2 Structurally similar components.8
3.3 Qualification approval procedures .8
3.3.1 The manufacturer shall comply with 3.4 of IEC 60539-1.8
3.4 Quality conformance inspection.8
3.4.1 Qualification approval on the basis of the fixed sample size
procedure .8
3.5 Quality conformance inspection.10
3.5.1 Formation of inspection lots.10
3.5.2 Test schedule .11
3.5.3 Delayed delivery.11
3.5.4 Assessment level.11
4 Test and measurement procedures.12
4.1 Mounting .12
4.2 Drying and recovery .12
4.2.1 Drying .12
4.2.2 Recovery .12
4.3 Visual examination and check of dimensions.12
4.3.1 Visual examination .12
4.3.2 Requirements .12

4.3.3 Marking .14
4.3.4 Dimensions .14
4.4 Electrical tests.14
4.4.1 Zero-power resistance .14
4.4.2 B-value or resistance ratio .14
4.4.3 Resistance/temperature characteristic .15
4.5 Thermal tests .15
4.5.1 Dissipation factor (δ).15
4.5.2 Thermal time constant by cooling after self-heating (τ ).15
c
4.6 Resistance to soldering heat .15
4.6.1 Initial measurement .15
4.6.2 Test conditions .15
4.6.3 Recovery .16

60539-2 © IEC:2003 – 3 –
4.6.4 Final inspection, measurements and requirements .16

4.7 Solderability .16

4.7.1 Test conditions .16

4.7.2 Recovery .17

4.7.3 Final inspection, measurements and requirements .17

4.8 Rapid change of temperature .17

4.9 Thermal shock.17

4.10 Climatic sequence .18

4.10.1 Initial measurements .18

4.10.2 Dry heat .18
4.10.3 Damp heat (cyclic), first cycle.18
4.10.4 Cold .18
4.10.5 Damp heat (cyclic), remaining cycles.18
4.10.6 Final measurements .19
4.11 Damp heat, steady state.19
4.12 Endurance.19
θ and P .19
4.12.1 Endurance at
3 max.
4.12.2 Endurance at upper category temperature .19
4.13 Shear (adhesion) test .20
4.14 Substrate bending test .20
4.15 Component solvent resistance.20
4.16 Solvent resistance of marking.20
Annex A (normative) Guide for the specification and coding of dimensions of surface
mount negative temperature coefficient thermistors .21
Figure 1 – Fault: fissure or defect .13
Figure 2 – Fault: crack .13
Figure 3 – Separation or delamination .13
Figure 4 – Exposed electrodes.13
Figure 5 – Principal faces .14
Figure A.1 – Dimensioning of surface mount thermistors.21
Table 1 – Upper and lower category temperatures and duration of the damp heat test.8
Table 2 – Fixed sample size test schedule for qualification approval of surface mount

negative temperature coefficient thermistors Assessment level EZ .10
Table 3 – Lot-by-lot inspection .11
Table 4 – Periodic test .12
Table 5 – Number of cycles .18
Table A.1 – Dimensions .21

– 4 – 60539-2 © IEC:2003
INTERNATIONAL ELECTROTECHNICAL COMMISSION

____________
DIRECTLY HEATED NEGATIVE TEMPERATURE

COEFFICIENT THERMISTORS –
Part 2: Sectional specification –

Surface mount negative temperature coefficient thermistors

FOREWORD
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patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60539-2 has been prepared by IEC technical committee 40:
Capacitors and resistors for electronic equipment.
This bilingual version, published in 2010-07, corresponds to the English version.
The text of this standard is based on the following documents:
FDIS Report on voting
40/1346/FDIS 40/1368/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.
The French version of this standard has not been voted upon.

60539-2 © IEC:2003 – 5 –
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

The committee has decided that the contents of this publication will remain unchanged until

the stability 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.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
– 6 – 60539-2 © IEC:2003
DIRECTLY HEATED NEGATIVE TEMPERATURE

COEFFICIENT THERMISTORS –
Part 2: Sectional specification –

Surface mount negative temperature coefficient thermistors

1 General
1.1 Scope
This part of IEC 60539 is applicable to surface mount directly heated negative temperature
coefficient thermistors, typically made from transition metal oxide materials with
semiconducting properties. These thermistors have metallized connecting pads or soldering
strips and are intended to be mounted directly on to substrates for hybrid circuits or on to
printed boards.
1.2 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 60068-2-2:1974, Environmental testing – Part 2: Tests – Tests B: Dry heat
Amendment 1 (1993)
Amendment 2 (1994)
IEC 60068-2-14:1984, Environmental testing – Part 2: Tests – Test N: Change of temperature
Amendment 1 (1986)
IEC 60068-2-30:1980, Environmental testing – Part 2: Tests – Test Db and guidance: Damp
heat, cyclic (12 + 12-hour cycle)
Amendment 1 (1985)
IEC 60068-2-58:1999, 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 60068-2-78: Environmental testing – Part 2-78: Tests – Test Cab: Damp heat, steady

state
IEC 60410:1973, Sampling plans and procedures for inspection by attributes
IEC 60539-1:2002, Directly heated negative temperature coefficient thermistors – Part 1:
Generic specification
1.3 Information to be given in a detail specification
Detail specifications shall be derived from the relevant blank detail specification.
Detail specifications shall not specify requirements inferior to those of the generic, sectional
or blank detail specification. When more severe requirements are included, they shall be
listed in 1.9 of the detail specification and indicated in the test schedules, for example, by an
asterisk.
60539-2 © IEC:2003 – 7 –
NOTE The information given in 1.3.1 may for convenience, be presented in tabular form.

The following information shall be given in each detail specification and the values quoted

shall preferably be selected from those given in the appropriate clause of this sectional
specification.
1.3.1 Outline drawing and dimensions

There shall be an illustration of the thermistor as an aid to easy recognition and for

comparison with others. Dimensions and their associated tolerances, which affect inter-

changeability and mounting, shall be given in the detail specification. All dimensions shall

preferably be stated in millimetres; however, when the original dimensions are given in

inches, the converted metric dimensions in millimetres shall be added.
Normally, the numerical values shall be given for the length, width and height of the body.
When necessary, for example when a number of items are covered by a detail specification,
the dimensions and their associated tolerances shall be placed in a table below the drawing.
When the configuration is other than described above, the detail specification shall state such
dimensional information as will adequately describe the thermistor.
1.3.2 Mounting
The detail specification shall give guidance on methods of mounting for normal use. Mounting
for test and measurement purposes (when required) shall be in accordance with 4.27 of
IEC 60539-1.
1.3.3 Ratings and characteristics
1.3.3.1 Particular characteristics
Additional characteristics may be listed when they are considered necessary to specify the
component adequately for design and application purposes.
1.3.3.2 Marking
See 2.4 of IEC 60539-1.
1.4 Terminology
See 2.2 of IEC 60539-1.
2 Preferred ratings and characteristics
2.1 Tolerances on rated zero-power resistance
Preferred values of tolerances on zero-power resistance are:
±1 %, ±2 %, ±3 %, ±5 %, ±10 %.
2.2 Climatic categories
The upper and lower category temperatures and the duration of the damp-heat steady-state
test shall be selected from Table 1.

– 8 – 60539-2 © IEC:2003
Table 1 – Upper and lower category temperatures and duration of the damp heat test

Lower category temperature
–55, –40, –25, –10, –5, +5
ºC
Upper category temperature
70, 85, 100, 105, 125, 150, 155

ºC
Damp heat, steady state
21, 42, 56
days
The detail specification shall prescribe the appropriate category.
3 Quality assessment procedures
3.1 Primary stage of manufacture
The primary stage of manufacture is defined as the initial mixing process of ingredients.
3.2 Structurally similar components
Surface mount thermistors may be grouped as structurally similar for the purpose of forming
inspection lots provided that the requirements of 3.1 of IEC 60539-1 are met, with the
following addition.
For the shear test and the substrate bending test, devices may be grouped if they have been
made on the same production line, have the same dimensions, internal structure and external
finish.
3.3 Qualification approval procedures
3.3.1 The manufacturer shall comply with 3.4 of IEC 60539-1.
3.4 Quality conformance inspection
Blank detail specifications associated with this specification shall prescribe the test schedule
for quality conformance inspection.
This schedule shall also specify the grouping, sampling and periodicity for the lot-by-lot and
periodic inspection.
Inspection levels and sampling plans shall be selected from those given in IEC 60410.
If required, more then one test schedule may be specified.
3.4.1 Qualification approval on the basis of the fixed sample size procedure
a) Sampling
The sample shall be representative of the range of thermistors for which approval is sought.
This may or may not be the complete range covered by the detail specification.
The sample shall consist of specimens having the lowest, highest and middle-rated zero-
power resistance of each case size.

60539-2 © IEC:2003 – 9 –
Per value, three spare specimens are permitted and may be used as replacements for

specimens which are defective because of incidents not attributable to the manufacturer.

b) Tests
The complete series of tests specified in Table 2 are required for the approval of thermistors
covered by one detail specification. The tests of each group shall be carried out in the order

given.
The whole sample shall be subjected to the tests of Group "0" and then divided for the other

groups.
Specimens found defective during the tests of Group "0" shall not be used for the other
groups.
"One defective" is counted when a thermistor has not satisfied the whole or a part of the tests
of a group.
Approval is granted when the number of non-conformances does not exceed the specified
number of permissible defects for each group or subgroup.
The conditions of test and performance requirements for the fixed sample size schedule shall
be identical to those described in the detail specification for quality conformance inspection.

– 10 – 60539-2 © IEC:2003
Table 2 – Fixed sample size test schedule for qualification approval of surface mount
negative temperature coefficient thermistors
Assessment level EZ
a) b)
Group Test Subclause Conditions of test and n c

requirements
No. of this
publication
0 Visual examination 4.3.1 See 4.3.1 to 4.3.2 90 0

Marking 4.3.3
Dimensions (gauging) 4.3.4 For requirements, see Table A.1

Zero-power resistance 4.4.1
1 Dimensions (detail) 4.3.4 For requirements, see Table A.1 10 0
B-value or resistance ratio 4.4.2 Choice to be made in the detail
specification
Resistance/temperature 4.4.3 Measuring temperatures to be
characteristic defined in the detail specification
Resistance to soldering heat – 4.6 See 4.6
dissolution of metallization
2 Solderability 4.7 See 4.7.1 to 4.7.3 10 0
Solvent resistance of marking 4.16
3 Resistance to soldering heat – 4.6 See 4.6.1 to 4.6.4 10 0
dewetting
4 Mounting 4.1 60 0
Visual examination 4.3.1
Zero-power resistance 4.4.1
4.1 Dissipation factor 4.5.1 10 0
Thermal time constant by cooling 4.5.2
after self-heating (τ )
c
4.2 Shear test 4.13 10 0
Rapid change of temperature 4.8
Climatic sequence 4.10
4.3 Damp heat, steady state 4.11 10 0
4.4 4.12.1 10 0
Endurance at θ and P
3 max
4.5 Endurance at upper category 4.12.2 10 0
temperature
5 Substrate bending test 4.14 10 0
a)
Number of specimens to be tested.
b)
Permissible numbers of non-conforming items.
3.5 Quality conformance inspection
3.5.1 Formation of inspection lots
a) Groups A and B inspection
These tests shall be carried out on a lot-by-lot basis.
A manufacturer may aggregate the current production into inspection lots subject to the
following safeguards:
a) the inspection lot shall consist of structurally similar thermistors (see 3.2);

60539-2 © IEC:2003 – 11 –
b) for Group A the sample tested shall consist of each of the values and each of the

dimensions contained in the inspection lot

– in relation to their number;

– with a minimum of five of any one value;

c) if there are less than five of any one value in the sample, the basis for the drawing of

samples shall be agreed upon between the manufacturer and the National Supervising

Inspectorate;
d) Group C inspection.
These tests shall be carried out on a periodic basis.

Samples shall be representative of the current production of the specified periods and shall
be divided into small, medium and large sizes. In order to cover the range of approvals in any
period, one rated zero-power resistance value shall be tested per group of sizes. In
subsequent periods, other sizes and rated zero-power values in production shall be tested
with the aim of covering the whole range.
3.5.2 Test schedule
The schedule for the lot-by-lot and periodic tests for quality conformance inspection is given
in Clause 2, Table 4 of the blank detail specification.
3.5.3 Delayed delivery
When, according to the procedures of 3.7 of IEC 60539-1, re-inspection has to be made,
solderability and zero-power resistance shall be checked as specified in Group A and Group B
inspection.
3.5.4 Assessment level
The assessment level(s) given in the blank detail specification shall preferably be selected
from Tables 3 and 4.
Table 3 – Lot-by-lot inspection
d)
EZ
Inspection subgroup
a) a) a)
IL n c
b)
A0
100 %
c)
A1
S – 4 0
c)
A2
II 0
c)
B1
S – 3 0
c)
B2
S – 2 0
a)
IL = inspection level;
n = sample size;
c = permissible number of non-conforming items.
b)
100 % testing shall be followed by re-inspection by sampling in order to
monitor outgoing quality level by non-conforming items per million (ppm).
The sampling level shall be established by the manufacturer. For the
calculation of ppm values, any parametric failure shall be counted as a
non-conforming item. In case one or more non-conforming items occur in
a sample, this lot shall be rejected.
c)
Number to be tested: sample size as directly allotted to the code letter for
IL in Table IIA of IEC 60410 (single sampling plan for normal inspection).
d)
The content of the inspection subgroup is described in Clause 2 of the
relevant blank detail specification.

– 12 – 60539-2 © IEC:2003
Table 4 – Periodic test
b)
EZ
Inspection subgroup
a) a) a)
p n c
C1 3 12 0
C2 3 12 0
C3.1 6 27 0
C3.2 6 15 0
C3.3 3 15 0
b)
C3.4 6 15 0
C4 6 9 0
a)
p = periodicity in months;
n = sample size;
c = permissible number of non-conforming items.
b)
The content of the inspection subgroup is described in Clause 2 of the
relevant blank detail specification.
4 Test and measurement procedures
4.1 Mounting
See 4.27 of IEC 60539-1.
4.2 Drying and recovery
4.2.1 Drying
Where drying is called for in this specification, the thermistor shall be conditioned as follows.
For 96 h ± 4 h in an oven at a temperature of 100 °C ± 5 °C, the thermistor shall then be
allowed to cool in a desiccator using a suitable desiccant, such as activated alumina or
silicagel, and shall be kept therein from the time of removal from the oven to the beginning of
the specified tests.
4.2.2 Recovery
Unless otherwise specified, recovery shall take place under the standard atmospheric
conditions for testing (see 4.2 of IEC 60539-1).

4.3 Visual examination and check of dimensions
4.3.1 Visual examination
Visual examination shall be carried out with suitable equipment with approximately 10×
magnification and lighting appropriate to the specimen under test and the quality level
required.
NOTE The operator should have facilities available for incident or transmitted illumination as well as an
appropriate measuring facility.
4.3.2 Requirements
Quantitative values for the requirements below may be given in the detail or in the
manufacturer’s specification.
The thermistor shall conform to the following requirements.

60539-2 © IEC:2003 – 13 –
4.3.2.1 Ceramic
a) Bulk type
1) It shall be free of fissures of coating glass longer than 25 % of dimension L (see
Annex A, Figure A.1) and defects of glass coating on each face greater than 10 %

of the area of that face (see Figure 1).

IEC  2543/03
NOTE Fissure on a corner and defect on one side.
Figure 1 – Fault: fissure or defect
2) It shall be free of cracks, except for small damage on the surface, which does not
impair the performance of the thermistor (see Figure 2).
IEC  2544/03
NOTE Crack on one side or extending from one face to another over a corner.
Figure 2 – Fault: crack
b) Layered type
1) It shall not exhibit visible separation or delamination between the layers of the
thermistor (see Figure 3).
Separation or delamination
Crack
IEC  2545/03
Figure 3 – Separation or delamination
2) It shall not exhibit exposed electrodes between the two terminations (see Figure 4).
Exposed electrodes
IEC  2546/03
Figure 4 – Exposed electrodes
– 14 – 60539-2 © IEC:2003
4.3.2.2 Metallization
a) It shall not exhibit any visible detachment of the metallized terminations nor any exposed

electrodes (see Figure 4).
b) The principal faces are those noted A, B and C (see Figure 5).

In the case of thermistors of square section, faces D and E are also considered principal.

The maximum area of gaps in metallization on each principal face shall not be greater than

15 % of the area of that face; these gaps shall not be concentrated in the same area. The

gaps in metallization shall not affect the two principal edges of each extremity of the block (or

four edges for square thermistors). Dissolution of the end-face plating (leaching) shall not
exceed 25 % of the length of the edge concerned.
A
E
B
C
Principal edges
D
IEC  2547/03
Figure 5 – Principal faces
4.3.3 Marking
If there is marking on the body, it shall be legible as determined by visual examination.
4.3.4 Dimensions
The dimensions indicated in the detail specification shall be checked and shall comply with
the values prescribed in Annex A.
4.4 Electrical tests
4.4.1 Zero-power resistance
See 4.5 of IEC 60539-1 with the following details.
The zero-power resistance shall be measured at the temperature given in the detail
specification and shall be within the limits specified in the detail specification, taking into
account the tolerance.
4.4.2 B-value or resistance ratio
See 4.6 of IEC 60539-1 with the following details:
– calculate the B-value or the resistance ratio using zero-power resistance values measured
at 25 °C and 85 °C, unless otherwise specified in the detail specification;
– the B-value or the resistance ratio shall be within the tolerance specified in the detail
specification.
60539-2 © IEC:2003 – 15 –
4.4.3 Resistance/temperature characteristic

See 4.9 of IEC 60539-1 with the following details:

– the measuring temperature shall be selected from those given in Table 1 of IEC 60539-1;

– the resistance/temperature characteristic shall be within the limits specified in the detail

specification.
4.5 Thermal tests
4.5.1 Dissipation factor (δ)
See 4.10 of IEC 60539-1 with the following details:
– thermistors shall be mounted according to 4.1;
– the zero-power resistance shall be measured at the temperature T , which is equivalent to
b
85 °C ± 0,1 °C unless otherwise prescribed in the detail specification;
– the dissipation factor shall be within the limits specified in the detail specification.
4.5.2 Thermal time constant by cooling after self-heating (τ )
c
See 4.12 of IEC 60539-1 with the following details:
– the thermistors shall be mounted according to 4.1;
– the thermal time constant by cooling after self-heating shall be within the limits prescribed
in the detail specification.
4.6 Resistance to soldering heat
See IEC 60068-2-58 with the following details.
4.6.1 Initial measurement
The zero-power resistance shall be measured according to 4.4.1.
4.6.2 Test conditions
4.6.2.1 Solder bath method
See IEC 60068-2-58, Clauses 5 and 6 with the following details, if not otherwise specified in
the detail specification:
– the specimen shall be preheated to a temperature of 110 °C to 140 °C and maintained for
30 s to 60 s;
– temperature: 260 °C ± 5 °C;
– duration of immersion: 10 s ± 1 s;
– depth of immersion: 10 mm;
– number of immersion: 1
4.6.2.2 Infrared and forced gas convection soldering system
See IEC 60068-2-58, Clauses 7 and 8 with the following details:
a) the solder paste shall be applied to the test substrate;
b) the thickness of the solder deposit shall be specified in the detail specification;
c) the terminations of the specimen shall be placed on solder paste;

– 16 – 60539-2 © IEC:2003
d) the specimen and test substrate shall be preheated to a temperature of (150 ± 10) °C and

maintained for 60 s to 120 s in an infrared and forced gas convection soldering system;

e) the temperature of the reflow system shall be quickly raised until the specimen has

reached (235 ± 5) °C and maintained at this temperature for (10 ± 1) s. Number of tests: 2;

f) the temperature profile shall be specified in the detail specification.

4.6.3 Recovery
The flux residues shall be removed with a suitable solvent.

4.6.4 Final inspection, measurements and requirements
After recovery, the surface mount thermistors shall be visually examined and measured and
shall meet the following requirements.
Visual examination shall be specified in the detail specification with the following details:
– under normal lighting and approximately 10× magnification, there shall be no signs of
damage such as cracks;
– dissolution of the end-face plating (leaching) shall not exceed 25 % of the length of the
edge concerned.
The zero-power resistance shall be measured according to 4.6.1 and the change shall not
exceed ±5 %.
4.7 Solderability
See IEC 60068-2-58 with the following details:
4.7.1 Test conditions
4.7.1.1 Solder bath method
See IEC 60068-2-58, Clauses 5 and 6 with the following details, if not otherwise specified in
the detail specification:
– the specimen shall be preheated to a temperature of 80 °C to 140 °C and maintained for
30 s to 60 s;
– temperature: 235 °C ± 5 °C;
– duration of immersion: 2 s ± 0,2 s;

– depth of immersion: 10 mm;
– number of immersion: 1
4.7.1.2 Infrared and forced gas convection soldering system
See IEC 60068-2-58, Clauses 7 and 8 with the following details:
a) the solder paste shall be applied to the test substrate;
b) the thickness of the solder deposit shall be specified in the detail specification;
c) the terminations of the specimen shall be placed on solder paste;
d) unless otherwise specified in the detail specification, the specimen and test substrate shall
be preheated to a temperature of (150 ± 10) °C and maintained for 60 s to 120 s in
infrared and forced gas convection soldering system;

60539-2 © IEC:2003 – 17 –
e) the temperature of reflow system shall be quickly raised until the specimen has reached

(215 ± 3) °C and maintained at this temperature for (10 ± 1) s;

f) the temperature profile shall be specified in the detail specification.

4.7.2 Recovery
The flux residues shall be removed with a suitable solvent.

4.7.3 Final inspection, measurements and requirements

See the detail specification with the following details:

– the surface mount thermistors shall be visually examined under normal lighting and
approximately 10× magnification and there shall be no signs of damage;
– both the end face and the contact areas shall be covered with a smooth and bright solder
coating with no more than a small amount of scattered imperfections such as pinholes or
un-wetted or de-wetted areas. These imperfections shall not be concentrated in one area.
4.8 Rapid change of temperature
See 4.16 of IEC 60539-1.
The thermistors shall be mounted according to 4.1.
The zero-power resistance shall be measured according to 4.4.1.
The test shall be carried out according to IEC 60068-2-14, Test Na with the following
conditions:
a) the lower temperature T shall be the lower category temperature;
A
b) the higher temperature T shall be the upper category temperature;
B
c) the number of cycles shall be 5;
d) the medium of the test chamber is air.
The thermistors shall be visually examined and the zero-power resistance shall be measured.
Under normal lighting and approximately 10× magnification, there shall be no signs of damage
such as cracks.
The zero-power resistance change shall not exceed ±5 %.

4.9 Thermal shock
See 4.21 of IEC 60539-1 with the following details:
– the thermistors shall be mounted according to 4.1;
– the zero-power resistance shall be measured according to 4.4.1.
The test shall be carried out according to IEC 60068-2-14, Test Nc with the following details:
a) the lower temperature T shall be the lower category temperature;
A
b) the higher temperature T shall be the upper category temperature;
B
c) the exposure time t shall be 30 min;
d) the number of cycles shall be 5;
e) the medium of the test bath shall be oil.

– 18 – 60539-2 © IEC:2003
The thermistors shall be visually examined and the zero-power resistance shall be measured.

Under normal lighting and approximately 10× magnification, there shall be no signs of damage

such as cracks.
The zero-power resistance change shall not exceed ±5 %.

4.10 Climatic sequence
See 4.22 of IEC 60539-1 with the following details:

– the thermistors shall be mounted according to 4.1;
– the tests and measurements shall be performed in the following order.
4.10.1 Initial measurements
The thermistors shall be dried using procedure I of 4.3.1 of IEC 60539-1.
The zero-power resistance shall be measured according to 4.4.1.
4.10.2 Dry heat
The thermistors shall be subjected to the test described in 4.24 of IEC 60539-1 for a duration
of 16 h.
4.10.3 Damp heat (cyclic), first cycle
The thermistors of categories –/–/56, –/–/42, –/–/21, –/–/10 and –/–/04 shall be subjected to
test Db of IEC 60068-2-30 for one cycle of 24 h.
After recovery the thermistors shall be subjected immediately to the cold test.
4.10.4 Cold
The thermistors shall be subjected to the test described in 4.23 of IEC 60539-1 for a duration
of 2 h.
4.10.5 Damp heat (cyclic), remaining
...

IEC 60539-2 ®
Edition 1.1 2010-11
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Directly heated negative temperature coefficient thermistors –
Part 2: Sectional specification – Surface mount negative temperature coefficient
thermistors
Thermistances à coefficient de température négatif à chauffage direct –
Partie 2: Spécification intermédiaire – Thermistances à coefficient de
température négatif pour montage en surface

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IEC 60539-2 ®
Edition 1.1 2010-11
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Directly heated negative temperature coefficient thermistors –
Part 2: Sectional specification – Surface mount negative temperature coefficient
thermistors
Thermistances à coefficient de température négatif à chauffage direct –
Partie 2: Spécification intermédiaire – Thermistances à coefficient de
température négatif pour montage en surface

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CH
CODE PRIX
ICS 31.040.30 ISBN 978-2-88912-248-6
– 2 – 60539-2 Ó IEC:2003+A1:2010

CONTENTS
FOREW ORD . 4

1 General . 6

1.1 Scope . 6

1.2 Normative references . 6

1.3 Information to be given in a detail specification . 7

1.3.1 Outline drawing and dimensions . 7

1.3.2 Mounting . 7

1.3.3 Ratings and characteristics . 7
1.4 Terminology . 7
2 Preferred ratings and characteristics . 7
2.1 Tolerances on rated zero-power resistance . 7
2.2 Climatic categories . 8
3 Quality assessment procedures . 8
3.1 Primary stage of manufacture . 8
3.2 Structurally similar components . 8
3.3 Qualification approval procedures . 8
3.3.1 The manufacturer shall comply with 3.4 of IEC 60539-1. . 8
3.4 Quality conformance inspection . 8
3.4.1 Qualification approval on the basis of the fixed sample size
p roced u re . 9
3.5 Quality conformance inspection . 10
3.5.1 Formation of inspection lots . 10
3.5.2 Test schedule . 11
3.5.3 Delayed delivery . 11
3.5.4 Assessment level . 11
4 Test and measurement procedures . 12
4.1 Mounting . 12
4.2 Drying and recovery . 12
4.2.1 Drying . 12
4.2.2 Recov ery . 12
4.3 Visual examination and check of dimensions. 12
4.3.1 Visual examination . 12
4.3.2 Requirements . 12

4.3.3 Marking . 14
4.3.4 Dimensions . 14
4.4 Electrical tests . 14
4.4.1 Zero-power resistance . 14
4.4.2 B-value or resistance ratio. 14
4.4.3 Resistance/temperature characteristic . 15
4.5 Thermal tests. 15
4.5.1 Dissipation factor (d) . 15
4.5.2 Thermal time constant by cooling after self-heating (t
) . 15
c
4.6 Resistance to soldering heat . 15
4.6.1 Initial measurement . 15
4.6.2 Test conditions . 15
4.6.3 Recov ery . 16

60539-2 Ó IEC:2003+A1:2010 – 3 –

4.6.4 Final inspection, measurements and requirements . 16

4.7 Solderability . 16

4.7.1 Test conditions . 16

4.7.2 Recov ery . 17

4.7.3 Final inspection, measurements and requirements . 17

4.8 Rapid change of temperature . 17

4.9 Thermal shock . 18

4.10 Climatic sequence . 18

4.10.1 Initial measurements . 18

4.10.2 Dry heat . 18

4.10.3 Damp heat (cyclic), first cycle . 18
4.10.4 Cold . 18
4.10.5 Damp heat (cyclic), remaining cycles . 18
4.10.6 Final measurements . 19
4.11 Damp heat, steady state . 19
4.12 Endurance . 19
4.12.1 Endurance at q and P . 19
3 max.
4.12.2 Endurance at upper category temperature . 20
4.13 Shear (adhesion) test . 20
4.14 Substrate bending test . 20
4.15 Component solvent resistance . 20
4.16 Solvent resistance of marking . 20
Annex A (normative) Guide for the specification and coding of dimensions of surface
mount negative temperature coefficient thermistors. 21

Figure 1 – Fault: fissure or defect . 13
Figure 2 – Fault: crack . 13
Figure 3 – Separation or delamination . 13
Figure 4 – Exposed electrodes . 13
Figure 5 – Principal faces . 14
Figure A.1 – Dimensioning of surface mount thermistors . 21

Table 1 – Upper and lower category temperatures and duration of the damp heat test . 8
Table 2 – Fixed sample size test schedule for qualification approval of surface mount

negative temperature coefficient thermistors Assessment level EZ . 10
Table 3 – Lot-by-lot inspection . 11
Table 4 – Periodic test . 12
Table 5 – Number of cycles . 19
Table A.1 – Dimensions . 21

– 4 – 60539-2 Ó IEC:2003+A1:2010

INTERNATIONAL ELECTROTECHNICAL COMMISSION

____________
DIRECTLY HEATED NEGATIVE TEMPERATURE

COEFFICIENT THERMISTORS –
Part 2: Sectional specification –

Surface mount negative temperature coefficient thermistors

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
misinterpretation by any end user.
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.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
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.

This consolidated version of IEC 60539-2 consists of the first edition (2003) [documents
40/1346/FDIS and 40/1368/RVD] and its amendment 1 (2010) [documents 40/2034/CDV
and 40/2051/RVC]. It bears the edition number 1.1.
The technical content is therefore identical to the base edition and its amendment and
has been prepared for user convenience. A vertical line in the margin shows where the
base publication has been modified by amendment 1. Additions and deletions are
displayed in red, with deletions being struck through.

60539-2 Ó IEC:2003+A1:2010 – 5 –

International Standard IEC 60539-2 has been prepared by IEC technical committee 40:
Capacitors and resistors for electronic equipment.

This bilingual version, published in 2010-07, corresponds to the English version.

The French version of this standard has not been voted upon.

This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

The committee has decided that the contents of the base publication and its amendments will

remain unchanged until the stability 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.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
– 6 – 60539-2 Ó IEC:2003+A1:2010

DIRECTLY HEATED NEGATIVE TEMPERATURE

COEFFICIENT THERMISTORS –
Part 2: Sectional specification –

Surface mount negative temperature coefficient thermistors

1 General
1.1 Scope
This part of IEC 60539 is applicable to surface mount directly heated negative temperature
coefficient thermistors, typically made from transition metal oxide materials with
semiconducting properties. These thermistors have metallized connecting pads or soldering
strips and are intended to be mounted directly on to substrates for hybrid circuits or on to
printed boards.
1.2 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 60068-2-2:1974, Environmental testing – Part 2: Tests – Tests B: Dry heat
Amendment 1 (1993)
Amendment 2 (1994)
IEC 60068-2-14:1984, Environmental testing – Part 2: Tests – Test N: Change of temperature
Amendment 1 (1986)
IEC 60068-2-30:1980, Environmental testing – Part 2: Tests – Test Db and guidance: Damp
heat, cyclic (12 + 12-hour cycle)
Amendment 1 (1985)
IEC 60068-2-58:1999 2004, 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 60068-2-78: Environmental testing – Part 2-78: Tests – Test Cab: Damp heat, steady

state
IEC 60410:1973, Sampling plans and procedures for inspection by attributes
IEC 60539-1:2002, Directly heated negative temperature coefficient thermistors – Part 1:
Generic specification
60539-2 Ó IEC:2003+A1:2010 – 7 –

1.3 Information to be given in a detail specification

Detail specifications shall be derived from the relevant blank detail specification.

Detail specifications shall not specify requirements inferior to those of the generic, sectional

or blank detail specification. When more severe requirements are included, they shall be

listed in 1.9 of the detail specification and indicated in the test schedules, for example, by an

asterisk.
NOTE The information given in 1.3.1 may for convenience, be presented in tabular form.

The following information shall be given in each detail specification and the values quoted

shall preferably be selected from those given in the appropriate clause of this sectional
specification.
1.3.1 Outline drawing and dimensions
There shall be an illustration of the thermistor as an aid to easy recognition and for
comparison with others. Dimensions and their associated tolerances, which affect inter-
changeability and mounting, shall be given in the detail specification. All dimensions shall
preferably be stated in millimetres; however, when the original dimensions are given in
inches, the converted metric dimensions in millimetres shall be added.
Normally, the numerical values shall be given for the length, width and height of the body.
When necessary, for example when a number of items are covered by a detail specification,
the dimensions and their associated tolerances shall be placed in a table below the drawing.
When the configuration is other than described above, the detail specification shall state such
dimensional information as will adequately describe the thermistor.
1.3.2 Mounting
The detail specification shall give guidance on methods of mounting for normal use. Mounting
for test and measurement purposes (when required) shall be in accordance with 4.27 of
IEC 60539-1.
1.3.3 Ratings and characteristics
1.3.3.1 Particular characteristics
Additional characteristics may be listed when they are considered necessary to specify the
component adequately for design and application purposes.

1.3.3.2 Marking
See 2.4 of IEC 60539-1.
1.4 Terminology
See 2.2 of IEC 60539-1.
2 Preferred ratings and characteristics
2.1 Tolerances on rated zero-power resistance
Preferred values of tolerances on zero-power resistance are:
±1 %, ±2 %, ±3 %, ±5 %, ±10 %.

– 8 – 60539-2 Ó IEC:2003+A1:2010

2.2 Climatic categories
The upper and lower category temperatures and the duration of the damp-heat steady-state

test shall be selected from Table 1.

Table 1 – Upper and lower category temperatures and duration of the damp heat test

Lower category temperature
–55, –40, –25, –10, –5, +5
ºC
Upper category temperature
70, 85, 100, 105, 125, 150, 155
ºC
Damp heat, steady state
21, 42, 56
days
The detail specification shall prescribe the appropriate category.
3 Quality assessment procedures
3.1 Primary stage of manufacture
The primary stage of manufacture is defined as the initial mixing process of ingredients.
3.2 Structurally similar components
Surface mount thermistors may be grouped as structurally similar for the purpose of forming
inspection lots provided that the requirements of 3.1 of IEC 60539-1 are met, with the
following addition.
For the shear test and the substrate bending test, devices may be grouped if they have been
made on the same production line, have the same dimensions, internal structure and external
finish.
3.3 Qualification approval procedures
3.3.1 The manufacturer shall comply with 3.4 of IEC 60539-1.
3.4 Quality conformance inspection
Blank detail specifications associated with this specification shall prescribe the test schedule

for quality conformance inspection.
This schedule shall also specify the grouping, sampling and periodicity for the lot-by-lot and
periodic inspection.
Inspection levels and sampling plans shall be selected from those given in IEC 60410.
If required, more then one test schedule may be specified.

60539-2 Ó IEC:2003+A1:2010 – 9 –

3.4.1 Qualification approval on the basis of the fixed sample size procedure

a) Sampling
The sample shall be representative of the range of thermistors for which approval is sought.

This may or may not be the complete range covered by the detail specification.

The sample shall consist of specimens having the lowest, highest and middle-rated zero-

power resistance of each case size.

Per value, three spare specimens are permitted and may be used as replacements for

specimens which are defective because of incidents not attributable to the manufacturer.
b) Tests
The complete series of tests specified in Table 2 are required for the approval of thermistors
covered by one detail specification. The tests of each group shall be carried out in the order
given.
The whole sample shall be subjected to the tests of Group "0" and then divided for the other
groups.
Specimens found defective during the tests of Group "0" shall not be used for the other
groups.
"One defective" is counted when a thermistor has not satisfied the whole or a part of the tests
of a group.
Approval is granted when the number of non-conformances does not exceed the specified
number of permissible defects for each group or subgroup.
The conditions of test and performance requirements for the fixed sample size schedule shall
be identical to those described in the detail specification for quality conformance inspection.

– 10 – 60539-2 Ó IEC:2003+A1:2010

Table 2 – Fixed sample size test schedule for qualification approval of surface mount

negative temperature coefficient thermistors

Assessment level EZ
a) b)
Group Test Subclause Conditions of test and n c

No. requirements
of this
publication
0 Visual examination 4.3.1 See 4.3.1 to 4.3.2 90 0

Marking 4.3.3
Dimensions (gauging) 4.3.4 For requirements, see Table A.1

Zero-power resistance 4.4.1
1 Dimensions (detail) 4.3.4 For requirements, see Table A.1 10 0
B-value or resistance ratio 4.4.2 Choice to be made in the detail
specification
Resistance/temperature 4.4.3 Measuring temperatures to be
characteristic defined in the detail specification
Resistance to soldering heat – 4.6 See 4.6
dissolution of metallization
2 Solderability 4.7 See 4.7.1 to 4.7.3 10 0
Solvent resistance of marking 4.16
3 Resistance to soldering heat – 4.6 See 4.6.1 to 4.6.4 10 0
dewetting
4 Mounting 4.1 60 0
Visual examination 4.3.1
Zero-power resistance 4.4.1
4.1 Dissipation factor 4.5.1 10 0
Thermal time constant by cooling 4.5.2
after self-heating (t )
c
4.2 Shear test 4.13 10 0
Rapid change of temperature 4.8
Climatic sequence 4.10
4.3 Damp heat, steady state 4.11 10 0
4.4 4.12.1 10 0
Endurance at q and P
3 max
4.5 Endurance at upper category 4.12.2 10 0
temperature
5 Substrate bending test 4.14 10 0
a)
Number of specimens to be tested.
b)
Permissible numbers of non-conforming items.

3.5 Quality conformance inspection
3.5.1 Formation of inspection lots
a) Groups A and B inspection
These tests shall be carried out on a lot-by-lot basis.
A manufacturer may aggregate the current production into inspection lots subject to the
following safeguards:
60539-2 Ó IEC:2003+A1:2010 – 11 –

a) the inspection lot shall consist of structurally similar thermistors (see 3.2);

b) for Group A the sample tested shall consist of each of the values and each of the

dimensions contained in the inspection lot

– in relation to their number;

– with a minimum of five of any one value;

c) if there are less than five of any one value in the sample, the basis for the drawing of

samples shall be agreed upon between the manufacturer and the National Supervising

Inspectorate;
d) Group C inspection.
These tests shall be carried out on a periodic basis.
Samples shall be representative of the current production of the specified periods and shall
be divided into small, medium and large sizes. In order to cover the range of approvals in any
period, one rated zero-power resistance value shall be tested per group of sizes. In
subsequent periods, other sizes and rated zero-power values in production shall be tested
with the aim of covering the whole range.
3.5.2 Test schedule
The schedule for the lot-by-lot and periodic tests for quality conformance inspection is given
in Clause 2, Table 4 of the blank detail specification.
3.5.3 Delayed delivery
When, according to the procedures of 3.7 of IEC 60539-1, re-inspection has to be made,
solderability and zero-power resistance shall be checked as specified in Group A and Group B
inspection.
3.5.4 Assessment level
The assessment level(s) given in the blank detail specification shall preferably be selected
from Tables 3 and 4.
Table 3 – Lot-by-lot inspection
d)
EZ
Inspection subgroup
a) a) a)
IL n c
b)
A0 100 %
c)
A1
S – 4 0
c)
A2
II 0
c)
B1
S – 3 0
c)
B2
S – 2 0
a)
IL = inspection level;
n = sample size;
c = permissible number of non-conforming items.
b)
100 % testing shall be followed by re-inspection by sampling in order to
monitor outgoing quality level by non-conforming items per million (ppm).
The sampling level shall be established by the manufacturer. For the
calculation of ppm values, any parametric failure shall be counted as a
non-conforming item. In case one or more non-conforming items occur in
a sample, this lot shall be rejected.
c)
Number to be tested: sample size as directly allotted to the code letter for
IL in Table IIA of IEC 60410 (single sampling plan for normal inspection).
d)
The content of the inspection subgroup is described in Clause 2 of the
relevant blank detail specification.

– 12 – 60539-2 Ó IEC:2003+A1:2010

Table 4 – Periodic test
b)
EZ
Inspection subgroup
a) a) a)
p n c
C1 3 12 0
C2 3 12 0
C3.1 6 27 0
C3.2 6 15 0
C3.3 3 15 0
b)
C3.4 6  15 0
C4 6 9 0
a)
p = periodicity in months;
n = sample size;
c = permissible number of non-conforming items.
b)
The content of the inspection subgroup is described in Clause 2 of the
relevant blank detail specification.

4 Test and measurement procedures
4.1 Mounting
See 4.27 of IEC 60539-1.
4.2 Drying and recovery
4.2.1 Drying
Where drying is called for in this specification, the thermistor shall be conditioned as follows.
For 96 h ± 4 h in an oven at a temperature of 100 °C ± 5 °C, the thermistor shall then be
allowed to cool in a desiccator using a suitable desiccant, such as activated alumina or
silicagel, and shall be kept therein from the time of removal from the oven to the beginning of
the specified tests.
4.2.2 Recovery
Unless otherwise specified, recovery shall take place under the standard atmospheric
conditions for testing (see 4.2 of IEC 60539-1).

4.3 Visual examination and check of dimensions
4.3.1 Visual examination
Visual examination shall be carried out with suitable equipment with approximately 10´
magnification and lighting appropriate to the specimen under test and the quality level
required.
NOTE The operator should have facilities available for incident or transmitted illumination as well as an
appropriate measuring facility.
4.3.2 Requirements
Quantitative values for the requirements below may be given in the detail or in the
manufacturer’s specification.
The thermistor shall conform to the following requirements.

60539-2 Ó IEC:2003+A1:2010 – 13 –

4.3.2.1 Ceramic
a) Bulk type
1) It shall be free of fissures of coating glass longer than 25 % of dimension L (see
Annex A, Figure A.1) and defects of glass coating on each face greater than 10 %

of the area of that face (see Figure 1).

IEC  2543/03
NOTE Fissure on a corner and defect on one side.
Figure 1 – Fault: fissure or defect
2) It shall be free of cracks, except for small damage on the surface, which does not
impair the performance of the thermistor (see Figure 2).

IEC  2544/03
NOTE Crack on one side or extending from one face to another over a corner.
Figure 2 – Fault: crack
b) Layered type
1) It shall not exhibit visible separation or delamination between the layers of the
thermistor (see Figure 3).
Separation or delamination
Crack
IEC  2545/03
Figure 3 – Separation or delamination
2) It shall not exhibit exposed electrodes between the two terminations (see Figure 4).

Exposed electrodes
IEC  2546/03
Figure 4 – Exposed electrodes
– 14 – 60539-2 Ó IEC:2003+A1:2010

4.3.2.2 Metallization
a) It shall not exhibit any visible detachment of the metallized terminations nor any exposed

electrodes (see Figure 4).
b) The principal faces are those noted A, B and C (see Figure 5).

In the case of thermistors of square section, faces D and E are also considered principal.

The maximum area of gaps in metallization on each principal face shall not be greater than

15 % of the area of that face; these gaps shall not be concentrated in the same area. The

gaps in metallization shall not affect the two principal edges of each extremity of the block (or

four edges for square thermistors). Dissolution of the end-face plating (leaching) shall not
exceed 25 % of the length of the edge concerned.
A
E
B
C
Principal edges
D
IEC  2547/03
Figure 5 – Principal faces
4.3.3 Marking
If there is marking on the body, it shall be legible as determined by visual examination.
4.3.4 Dimensions
The dimensions indicated in the detail specification shall be checked and shall comply with
the values prescribed in Annex A.
4.4 Electrical tests
4.4.1 Zero-power resistance
See 4.5 of IEC 60539-1 with the following details.
The zero-power resistance shall be measured at the temperature given in the detail
specification and shall be within the limits specified in the detail specification, taking into
account the tolerance.
4.4.2 B-value or resistance ratio
See 4.6 of IEC 60539-1 with the following details:
– calculate the B-value or the resistance ratio using zero-power resistance values measured
at 25 °C and 85 °C, unless otherwise specified in the detail specification;
– the B-value or the resistance ratio shall be within the tolerance specified in the detail
specification.
60539-2 Ó IEC:2003+A1:2010 – 15 –

4.4.3 Resistance/temperature characteristic

See 4.9 of IEC 60539-1 with the following details:

– the measuring temperature shall be selected from those given in Table 1 of IEC 60539-1;

– the resistance/temperature characteristic shall be within the limits specified in the detail

specification.
4.5 Thermal tests
4.5.1 Dissipation factor (d)
See 4.10 of IEC 60539-1 with the following details:
– thermistors shall be mounted according to 4.1;
– the zero-power resistance shall be measured at the temperature T , which is equivalent to
b
85 °C ± 0,1 °C unless otherwise prescribed in the detail specification;
– the dissipation factor shall be within the limits specified in the detail specification.
4.5.2 Thermal time constant by cooling after self-heating (t )
c
See 4.12 of IEC 60539-1 with the following details:
– the thermistors shall be mounted according to 4.1;
– the thermal time constant by cooling after self-heating shall be within the limits prescribed
in the detail specification.
4.6 Resistance to soldering heat
See IEC 60068-2-58 with the following details.
4.6.1 Initial measurement
The zero-power resistance shall be measured according to 4.4.1.
4.6.2 Test conditions
4.6.2.1 Solder bath method
See IEC 60068-2-58, Clauses 5 and 6 with the following details 6 and 8, if not otherwise
specified in the detail specification:

– the specimen shall be preheated to a temperature of 110 °C to 140 °C and maintained for
30 s to 60 s;
– temperature: 260 °C ± 5 °C;
– duration of immersion: 10 s ± 1 s;
– depth of immersion: 10 mm;
– number of immersion: 1
– 16 – 60539-2 Ó IEC:2003+A1:2010

4.6.2.2 Infrared and forced gas convection soldering system Reflow method

See IEC 60068-2-58, Clauses 7 and 8, with the following details: if not otherwise specified in

the detail specification.
a) the solder paste shall be applied to the test substrate;

b) the thickness of the solder deposit shall be specified in the detail specification;

c) the terminations of the specimen shall be placed on solder paste;

d) the specimen and test substrate shall be preheated to a temperature of (150 ± 10) °C and

maintained for 60 s to 120 s in an infrared and forced gas convection soldering system;

e) the temperature of the reflow system shall be quickly raised until the specimen has
reached (235 ± 5) °C and maintained at this temperature for (10 ± 1) s. Number of tests: 2;
f) the temperature profile shall be specified in the detail specification.
4.6.3 Recovery
The flux residues shall be removed with a suitable solvent.
4.6.4 Final inspection, measurements and requirements
After recovery, the surface mount thermistors shall be visually examined and measured and
shall meet the following requirements.
Visual examination shall be specified in the detail specification with the following details:
– under normal lighting and approximately 10´ magnification, there shall be no signs of
damage such as cracks;
– dissolution of the end-face plating (leaching) shall not exceed 25 % of the length of the
edge concerned.
The zero-power resistance shall be measured according to 4.6.1 and the change shall not
exceed ±5 %.
4.7 Solderability
See IEC 60068-2-58 with the following details:
4.7.1 Test conditions
4.7.1.1 Solder bath method
See IEC 60068-2-58, Clauses 5 and 6 with the following details, 6 and 8, if not otherwise
specified in the detail specification.
– the specimen shall be preheated to a temperature of 80 °C to 140 °C and maintained for
30 s to 60 s;
– temperature: 235 °C ± 5 °C;
– duration of immersion: 2 s ± 0,2 s;
– depth of immersion: 10 mm;
– number of immersion: 1
60539-2 Ó IEC:2003+A1:2010 – 17 –

4.7.1.2 Infrared and forced gas convection soldering system Reflow method

See IEC 60068-2-58, Clauses 7 and 8, with the following details: if not otherwise specified in

the detail specification.
a) the solder paste shall be applied to the test substrate;

b) the thickness of the solder deposit shall be specified in the detail specification;

c) the terminations of the specimen shall be placed on solder paste;

d) unless otherwise specified in the detail specification, the specimen and test substrate shall

be preheated to a temperature of (150 ± 10) °C and maintained for 60 s to 120 s in

infrared and forced gas convection soldering system;
e) the temperature of reflow system shall be quickly raised until the specimen has reached
(215 ± 3) °C and maintained at this temperature for (10 ± 1) s;
f) the temperature profile shall be specified in the detail specification.
4.7.2 Recovery
The flux residues shall be removed with a suitable solvent.
4.7.3 Final inspection, measurements and requirements
See the detail specification with the following details:
– the surface mount thermistors shall be visually examined under normal lighting and
approximately 10´ magnification and there shall be no signs of damage;
– both the end face and the contact areas shall be covered with a smooth and bright solder
coating with no more than a small amount of scattered imperfections such as pinholes or
un-wetted or de-wetted areas. These imperfections shall not be concentrated in one area.
4.8 Rapid change of temperature
See 4.16 of IEC 60539-1.
The thermistors shall be mounted according to 4.1.
The zero-power resistance shall be measured according to 4.4.1.
The test shall be carried out according to IEC 60068-2-14, Test Na with the following
conditions:
a) the lower temperature T shall be the lower category temperature;
A
b) the higher temperature T shall be the upper category temperature;
B
c) the number of cycles shall be 5;
d) the medium of the test chamber is air.
The thermistors shall be visually examined and the zero-power resistance shall be measured.
Under normal lighting and approximately 10´ magnification, there shall be no signs of damage
such as cracks.
The zero-power resistance change shall not exceed ±5 %.

– 18 – 60539-2 Ó IEC:2003+A1:2010

4.9 Thermal shock
See 4.21 of IEC 60539-1 with the following details:

– the thermistors shall be mounted according to 4.1;

– the zero-power resistance shall be measured according to 4.4.1.

The test shall be carried out according to IEC 60068-2-14, Test Nc with the following details:

a) the lower temperature T shall be the lower category temperature;
A
b) the higher temperature T shall be the upper category temperature;
B
c) the exposure time t shall be 30 min;
d) the number of cycles shall be 5;
e) the medium of the test bath shall be oil.
The thermistors shall be visually examined and the zero-power resistance shall be measured.
Under normal lighting and approximately 10´ magnification, there shall be no signs of damage
such as cracks.
The zero-power resistance change shall not exceed ±5 %.
4.10 Climatic sequence
See 4.22 of IEC 60539-1 with the following details:
– the thermistors shall be mounted according to 4.1;
– the tests and measurements shall be performed in the following order.
4.10.1 Initial measurements
The thermistors shall be dried using procedure I of 4.3.1 of IEC 60539-1.
The zero-power resistance shall be measured according to 4.4.1.
4.10.2 Dry heat
The thermistors shall be subjected to the tes
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