IEC 60539-1:2008

Directly heated negative temperature coefficient thermistors - Part 1: Generic specification

IEC 60539-1:2008 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.

Thermistances à coefficient de température négatif à chauffage direct - Partie 1: Spécification générique

La CEI 60539-1:2008 s'applique aux thermistances à coefficient de température négatif à chauffage direct, typiquement constitués de matériaux faits d'oxyde de métal de transition dotés de propriétés semi-conductrices. Elle définit les termes normalisés, les procédures d'inspection et les méthodes d'essai utilisés dans les spécifications intermédiaires et particulières des composants électroniques dans le cadre de l'assurance qualité, ainsi qu'à d'autres fins.

General Information

• Status: Published
• Publication Date: 12-Feb-2008
• ICS: 31.040.30 - Thermistors
• Technical Committee: TC 40 - Capacitors and resistors for electronic equipment
• Drafting Committee: MT 60539-1 - TC 40/MT 60539-1
• Current Stage: DELPUB - Deleted Publication
• Start Date: 27-Apr-2016
• Completion Date: 26-Oct-2025

Relations

• Revised: IEC 60539-1:2016 - Directly heated negative temperature coefficient thermistors - Part 1: Generic specification
• Effective Date: 05-Sep-2023
• Revises: IEC 60539-1:2002 - Directly heated negative temperature coefficient thermistors - Part 1: Generic specification
• Effective Date: 05-Sep-2023

Overview

IEC 60539-1:2008 - "Directly heated negative temperature coefficient thermistors - Part 1: Generic specification" - is the international generic specification for directly heated NTC thermistors. It covers thermistors typically made from transition metal oxide semiconducting materials and establishes standard terms, inspection procedures and methods of test for use in sectional and detail specifications and in quality assessment of electronic components.

This Part 1 provides the generic framework for manufacturers, test laboratories and purchasers; Part 2 of IEC 60539 addresses sectional requirements for surface-mount NTC thermistors.

Key topics and technical requirements

The standard defines technical data, measurement methods and quality assessment procedures, including (but not limited to):

• Terms, units and symbols relevant to directly heated NTC thermistors
• Resistance–temperature characteristic and methods to determine zero‑power resistance and B‑value/resistance ratios
• Dissipation factor (δ) and thermal time constant (τ) measurement procedures
• Insulation resistance and voltage proof tests for insulated types
• Environmental and mechanical tests referenced to IEC 60068 series, such as:
  • Resistance to soldering heat, solderability, rapid change of temperature, thermal shock
  • Vibration, shock, bump and free-fall tests
  • Damp heat (steady state), salt mist and solvent resistance
• Endurance and long-term stability test methods
• Quality assessment procedures: primary manufacture, qualification approval, conformance inspection, sampling and certified test records

Diagrams, typical test circuits and mounting examples support standardized measurement and reporting.

Practical applications

IEC 60539-1 is used to ensure consistent performance, reliability and interchangeability of directly heated NTC thermistors across applications such as:

• Temperature sensing and measurement (thermometry, HVAC)
• Inrush current limiters and power protection circuits
• Thermal compensation in electronic circuits and sensors
• Consumer electronics, automotive electronics and industrial controls where predictable NTC behavior and environmental robustness are required

By following the standard, manufacturers and engineers can specify component requirements, perform reproducible testing, and reduce risk in product design and procurement.

Who should use this standard

• Component manufacturers (design, production and quality teams)
• Test laboratories and certification bodies (including IECQ users)
• Electronic product designers and reliability engineers
• Procurement and quality-assurance professionals specifying NTC thermistors

Related standards

• IEC 60539-2 (Sectional specification: surface-mount NTC thermistors)
• IEC 60068 series (environmental testing)
• IEC 60027-1, IEC 60050 (terminology and symbols), IEC 60062 (marking codes)

Keywords: IEC 60539-1:2008, NTC thermistors, directly heated thermistors, test procedures, quality assessment, resistance–temperature characteristic, dissipation factor, thermal time constant.

Standards Content (Sample)

IEC 60539-1
Edition 2.0 2008-02
INTERNATIONAL
STANDARD
QC 430 000
Directly heated negative temperature coefficient thermistors –
Part 1: Generic specification
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IEC 60539-1
Edition 2.0 2008-02
INTERNATIONAL
STANDARD
QC 430 000
Directly heated negative temperature coefficient thermistors –
Part 1: Generic specification
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
X
ICS 31.040.30 ISBN 2-8318-9584-7

– 2 – 60539-1 © IEC:2008(E)
CONTENTS
FOREWORD.4

1 General .6
1.1 Scope.6
1.2 Normative references .6
2 Technical data.8
2.1 Units, symbols and terminology .8
2.2 Terms and definitions .8
2.3 Preferred values.16
2.4 Marking .16
3 Quality assessment procedures.17
3.1 General .17
3.2 Primary stage of manufacture.17
3.3 Structurally similar components.17
3.4 Qualification approval procedures .18
3.5 Quality conformance inspection.18
3.6 Certified test records of released lots .18
3.7 Delayed delivery.19
3.8 Release for delivery under qualification approval before the completion of
group B tests.19
3.9 Alternative test methods .19
3.10 Unchecked parameters.19
4 Test and measurement procedures.19
4.1 General .19
4.2 Standard atmospheric conditions for testing .19
4.3 Drying and recovery .20
4.4 Mounting (for surface mount thermistors only) .20
4.5 Visual examination and check of dimensions.21
4.6 Zero-power resistance.22
4.7 B-value or resistance ratio.22
4.8 Insulation resistance (for insulated types only) .23
4.9 Voltage proof (for insulated types only) .26
4.10 Resistance/temperature characteristic.26
4.11 Dissipation factor (δ) .26
4.12 Thermal time constant by ambient temperature change (τ ) .28
a
4.13 Thermal time constant by cooling after self-heating (τ ) .28
c
4.14 Robustness of terminations (not applicable to surface mount thermistors) .29
4.15 Resistance to soldering heat .30
4.16 Solderability .31
4.17 Rapid change of temperature .32
4.18 Vibration.32
4.19 Bump .33
4.20 Shock.33
4.21 Free fall (if specified in the detail specification) .33

60539-1 © IEC:2008(E) – 3 –
4.22 Thermal shock (if specified in the detail specification) .34
4.23 Cold (if required by the sectional specification) .34
4.24 Dry heat (if required by the sectional specification) .34
4.25 Damp heat, steady state.35
4.26 Endurance.35
4.27 Shear (adhesion) test .40
4.28 Substrate bending test .40
4.29 Component solvent resistance.41
4.30 Solvent resistance of marking.41
4.31 Salt mist (if required by the sectional specification) .41
4.32 Sealing (if required by the sectional specification) .41
4.33 Composite temperature/humidity cycle (if required by the sectional
specification).41

Annex A (normative) Interpretation of sampling plans and procedures as described in
IEC 60410 for use within the IEC quality assessment system for electronic
components (IECQ) .43
Annex B (normative) Rules for the preparation of detail specifications for capacitors
and resistors for electronic equipment .44
Annex C (informative) Typical examples of mountings for measurements of directly
heated thermistors .45

Figure 1 – Typical resistance-temperature characteristic for NTC thermistors .10
Figure 2 – Decreased power dissipation curve .12
Figure 3 – Maximum current derating.14
Figure 4 – Zero-power resistance measuring basic circuit .22
Figure 5 – Test method 1 .23
Figure 6 – Test method 2 .24
Figure 7 – Test method 2 .24
Figure 8 – Test method 3 .25
Figure 9 – Test method 4 .25
Figure 10 – Example of test chamber.27
Figure 11 – Dissipation factor measuring circuit.27
Figure 12 – Thermal time constant measuring circuit .29
Figure 13 – Endurance at room temperature with I evaluating circuit.36
max.25
Figure 14 – Maximum permissible capacitance test circuit (method 1) .39
Figure 15 – Maximum permissible capacitance test circuit (method 2) .39
Figure C.1 – Mounting for measurements of surface mount thermistors .45

Table 1 – Upper and lower category temperatures and duration of the damp heat test.16
Table 2 – Tensile force .30

– 4 – 60539-1 © IEC:2008(E)
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 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
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between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
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5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
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6) All users should ensure that they have the latest edition of this publication.
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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 60539-1 has been prepared by IEC technical committee 40:
Capacitors and resistors for electronic equipment.
This second edition cancels and replaces the first edition published in 2002 and constitutes a
minor revision related to tables, figures and references.
The text of this standard is based on the following documents:
FDIS Report on voting
40/1878A/FDIS 40/1895/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.

60539-1 © IEC:2008(E) – 5 –
The QC number that appears on the front cover of the publication is the specification number
in the IEC Quality Assessment System for Electronic Components (IECQ).
IEC 60539 consists of the following parts, under the general title Directly heated negative
temperature coefficient thermistors:
Part 1: Generic specification
Part 2: Sectional specification: Surface mount negative temperature coefficient thermistors
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result 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.
A bilingual version of this publication may be issued at a later date.

– 6 – 60539-1 © IEC:2008(E)
DIRECTLY HEATED NEGATIVE TEMPERATURE COEFFICIENT
THERMISTORS –
Part 1: Generic specification
1 General
1.1 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.
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 60027-1, Letter symbols to be used in electrical technology – Part 1: General
IEC 60050, International Electrotechnical Vocabulary (IEV)
IEC 60062, Marking codes for resistors and capacitors
IEC 60068-1:1988, Environmental testing – Part 1: General and guidance
Amendment 1 (1992)
IEC 60068-2-1:2007, Environmental testing – Part 2-1: Tests – Tests A: Cold
IEC 60068-2-2:2007, Environmental testing – Part 2-2: Tests – Tests B: Dry heat
IEC 60068-2-6:1995, Environmental testing – Part 2-6: Tests – Test Fc: Vibration (sinusoidal)
IEC 60068-2-11:1981, Environmental testing – Part 2-11: Tests – Test Ka: Salt mist
IEC 60068-2-14:1984, Environmental testing – Part 2-14: Tests – Test N: Change of
temperature
Amendment 1 (1986)
IEC 60068-2-17:1994, Environmental testing – Part 2-17: Tests – Test Q: Sealing
IEC 60068-2-20:1979, Environmental testing – Part 2-20: Tests – Test T: Soldering
Amendment 2 (1987)
IEC 60068-2-21:2006, Environmental testing – Part 2-21: Tests – Test U: Robustness of
terminations and integral mounting devices

60539-1 © IEC:2008(E) – 7 –
IEC 60068-2-27:1987, Environmental testing – Part 2-27: Tests – Test Ea and guidance:
Shock
IEC 60068-2-29:1987, Environmental testing – Part 2-29: Tests – Test Eb and guidance:
Bump
IEC 60068-2-32:1975, Environmental testing – Part 2-32: Tests – Test Ed: Free fall
Amendment 2 (1990)
IEC 60068-2-38:1974, Environmental testing – Part 2-38: Tests – Test Z/AD: Composite
temperature/humidity cyclic test
IEC 60068-2-45:1980, Environmental testing – Part 2-45: Tests – Test XA and guidance:
Immersion in cleaning solvents
Amendment 1 (1993)
IEC 60068-2-52:1996, Environmental testing – Part 2-52: Tests – Test Kb: Salt mist, cyclic
(sodium chloride solution)
IEC 60068-2-54:2006, Environmental testing – Part 2-54: Tests – Test Ta: Solderability
testing of electronic components by the wetting balance method
IEC 60068-2-58:2004, 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 60068-2-69:2007, Environmental testing – Part 2-69: Tests – Test Te: Solderability
testing of electronic components for surface mounting devices (SMD) by the wetting balance
method
IEC 60068-2-78:2001, Environmental testing – Part 2-78: Tests – Test Cab: Damp heat,
steady state
IEC 60294, Measurement of the dimensions of a cylindrical component having two axial
terminations
IEC 60410, Sampling plans and procedures for inspection by attributes
IEC 60617, Graphical symbols for diagrams
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 structures – Part 2-7:
Reinforced base materials clad and unclad – Epoxide woven E-glass laminated sheet of
defined flammability (vertical burning test), copper-clad
IECQ 001002-3, IEC Quality Assessment System for Electronic Components (IECQ) – Rules
of procedure – Part 3: Approval procedures
ISO 1000, SI units and recommendations for the use of their multiples and of certain other
units
– 8 – 60539-1 © IEC:2008(E)
2 Technical data
2.1 Units, symbols and terminology
Units, graphical symbols, letter symbols and terminology should, whenever possible, be taken
from the following publications:
– IEC 60027-1
– IEC 60050
– IEC 60617
– ISO 1000
When further items are required, they should be derived in accordance with the principles of
the publications listed above.
2.2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.2.1
type
products having similar design features manufactured by the same techniques and falling
within the manufacturer's usual range of ratings for these products
NOTE 1 Mounting accessories are ignored, provided they have no significant effect on the test results.
NOTE 2 Ratings cover the combination of
– electrical ratings;
– sizes;
– climatic category.
NOTE 3 The limits of the range of ratings should be given in the detail specification.
2.2.2
style
variation within a type having specific nominal dimensions and characteristics
2.2.3
thermistor
thermally sensitive semiconducting resistor whose primary function is to exhibit an important
change in electrical resistance with a change in body temperature
2.2.4
negative temperature coefficient thermistor (NTC)
thermistor in which the resistance decreases with increasing temperature
2.2.5
directly heated negative temperature coefficient thermistor
thermistor which obtains its resistance variation by the changes of physical conditions such as
current through it, ambient temperature, humidity, wind velocity, gas, etc.
2.2.6
indirectly heated negative temperature coefficient thermistor
thermistor which obtains its resistance variation primarily by the change of temperature of the
thermistor, due to the change of a current through a separate heater which is in close contact
with, but electrically insulated from, the thermistor element
NOTE The temperature of the thermistor can also be changed by the changes of physical conditions such as
current through the thermistor element itself, ambient temperature, humidity, wind velocity, gas, etc.

60539-1 © IEC:2008(E) – 9 –
2.2.7
positive temperature coefficient (PTC) thermistor (for information only)
thermistor in which the resistance increases with increasing temperature
2.2.8
thermistor with wire terminations
thermistor provided with wire terminations
2.2.9
thermistor without wire terminations
thermistor provided only with two metallized faces, to be used as electrical contacts
2.2.10
insulated thermistor
thermistor coated with materials such as resin, glass or ceramic, capable of meeting the
requirements of the insulation resistance and voltage proof tests when specified in the test
schedule
2.2.11
non-insulated thermistor
thermistor with or without coating materials for surfacing of elements but not intended to meet
the requirements of the insulation resistance and voltage proof tests when specified in the
test schedule
2.2.12
surface mount thermistor
thermistor whose small dimensions and nature or shape of terminations make them suitable
for use in hybrid circuits and on printed board
2.2.13
assembled thermistor (probe)
thermistor encapsulated in different materials such as tubes, plastic and metal housing and/or
assembled with cables and/or connectors
2.2.14
thermistor for sensing
thermistor which responds to temperature changes and therefore is used for temperature
sensing and control
2.2.15
inrush current limiting thermistor
thermistor which limits the inrush current just after switching on the power
2.2.16
residual resistance (only for inrush current-limiting thermistors)
value of the d.c. resistance of a thermistor when its thermal stability is reached with the
maximum current passing
2.2.17
maximum permissible capacitance (only for inrush current-limiting thermistors)
maximum permissible capacitance value of a capacitor which can be connected to a
thermistor under loading
2.2.18
zero-power resistance, R
T
value of the d.c. resistance of a thermistor, when measured at a specified temperature, under
such conditions that the change in resistance due to the internal generation of heat is
negligible with respect to the total error of measurement

– 10 – 60539-1 © IEC:2008(E)
2.2.19
rated zero-power resistance
nominal value at the standard reference temperature of 25 °C, unless otherwise specified
2.2.20
resistance-temperature characteristic
relationship between the zero-power resistance and the body temperature of a thermistor
The resistance law follows approximately the formula:
⎛ ⎞
1 1
B⎜ − ⎟
⎜ ⎟
R = R ×e
T T
a
⎝ a ⎠
where
R is the zero-power resistance in ohms (Ω) at absolute temperature T in kelvins (K);
R is the zero-power resistance in ohms (Ω) at absolute temperature T in kelvins (K);

a a
B is the thermal sensitivity index (see 2.2.22).
NOTE This formula is only applicable for representing the resistance variation over a restricted temperature
range. For more precise representation of the R/T-curve, a resistance/temperature relation should be specified in
tabulated form in the detail specification.

Ig R
R
a
R
R
b
T T T T  (K)
a b
IEC  019/08
Figure 1 – Typical resistance-temperature characteristic for NTC thermistors
2.2.21
resistance ratio
ratio of the zero-power resistance of a thermistor measured at the reference temperature of
25 °C to that measured at 85 °C, or at such other pairs of temperatures as may be prescribed
in the detail specification
2.2.22
B-value
index of the thermal sensitivity expressed by the formula:
B = [(T × T )/(T – T )] × ln(R /R )
a b b a a b
or
B = 2,303 × [(T × T )/(T – T )] × log(R /R )
a b b a a b
where
B is a constant in kelvins (K);
R is the zero-power resistance in ohms (Ω) at temperature T in kelvins (K);
a a
60539-1 © IEC:2008(E) – 11 –
R is the zero-power resistance in ohms (Ω) at temperature T in kelvins (K);
b b
*
T = 298,15 K ;
a
*
T = 358,15 K .
b
* The values given above for T and T are the preferred values and are equivalent to +25 °C and +85 °C
a b
respectively.
NOTE Where the detail specification prescribes that the B-value should be measured at other temperatures, the
specified values (in kelvins) shall be used for T and T in the calculation in place of the preferred values and the
a b
B-value may be expressed by “B ”.
a/b
2.2.23
zero-power temperature coefficient of resistance, α
T
ratio at a specified temperature (T) of the rate of change of zero-power resistance with
temperature to the zero-power resistance of the thermistor, expressed by the formula:
α = (1/R ) × (dR /dT) × 100
T T T
The value α can be approximately calculated by the formula:
T
α = (–B/T ) × 100
T
where
α is the zero-power temperature coefficient of resistance in %/K;

T
R is the zero-power resistance in ohms at temperature T in kelvins (K);

T
B is the index of the thermal sensitivity in kelvins (K).
2.2.24
category temperature range
range of ambient temperatures for which the thermistor has been designed to operate
continuously at zero-power, defined by the temperature limits of the appropriate category
2.2.25
upper category temperature, θ
max
maximum ambient temperature for which a thermistor has been designed to operate
continuously at zero-power
2.2.26
lower category temperature, θ
min
minimum ambient temperature for which a thermistor has been designed to operate
continuously at zero-power
2.2.27
storage temperature range
range of ambient temperatures for which a thermistor can be stored continuously under no-
load condition
2.2.28
decreased power dissipation curve (not for inrush current-limiting thermistors)
relation between the ambient temperature and the maximum power dissipation P , which is
maxθ
usually expressed as curve a or, alternatively, as curve b in Figure 2

– 12 – 60539-1 © IEC:2008(E)
P
maxθ
P
max
θ
R
θ
θ θ θ   θ θ θ θ
R
min 1 2 3 4 max
Curve a
Pmax
θ
P
maxθ
R
θ
θ θ = θ θ θ
R
2 3
4 max.
Curve b
IEC  020/08
Figure 2 – Decreased power dissipation curve
2.2.29
θ (P )
maximum power dissipation at rated ambient temperature

R maxθR
maximum value of the power dissipation which can be continuously applied to the thermistor
at the rated ambient temperature θ .
R
NOTE See curve a, θ2 ≤ θR ≤θ3 or curve b, θ2 ≤ θR = θ3 in Figure 2.
The rated ambient temperature θ is the ambient temperature specified in the detail
R
specification and is usually 25 °C.
2.2.30
maximum power dissipation at ambient temperature θ (P )

maxθ
maximum value of the power dissipation which can be continuously applied to the thermistor
at an ambient temperature θ
Curve a
The maximum power dissipation rises at a temperature θ linearly to a temperature θ .
1 2
Between temperature θ and θ the power dissipation is constant. When the temperature

2 3
exceeds θ , the power dissipation must be decreased linearly to zero at a temperature θ
3 4
The maximum power dissipation at ambient temperature θ in general is calculated as follows:
P = I × U
maxθ maxθ
where U is the voltage across the thermistor (for I see 2.2.32).
,
maxθ
The maximum power dissipation can be expressed by the following formula:

60539-1 © IEC:2008(E) – 13 –
θ − θ
θ ≤ θ ≤θ P = P ×
:
max.θ max.θ
1 2
R
θ − θ
2 1
θ − θ
θ ≤ θ ≤θ P = P ×
:
max.θ max .θ
3 4
R
θ − θ
4 3
where
θ is the rated ambient temperature in Celsius (°C);
R
θ is the temperature in Celsius (°C) specified in the detail specification below which zero-

power shall be applied. θ is equal to the lower category temperature θ (°C) or
min.
higher;
θ is the lowest temperature at which P can be applied. θ = 0 °C, unless otherwise
2 max.θ 2
specified in the detail specification;
θ is the maximum temperature at which P can be applied. θ = 55 °C, unless

3 max.θ 3
otherwise specified in the detail specification;
θ is the temperature in Celsius (°C) specified in the detail specification, above which zero-
power shall be applied. θ is equal to, or lower than, the upper category temperature
θ (°C).
max
Curve b
The maximum power dissipation is constant between temperature θ and θ . θ = 0 °C, unless
2 R 2
otherwise specified in the detail specification. When the temperature exceeds θ , the power
R
dissipation must be decreased linearly to zero at a temperature θ .
The maximum power dissipation at ambient temperature θ in general is calculated as follows:
P = I × U
maxθ maxθ
where U is the voltage across the thermistor (for I , see 2.2.32).
max.θ
The maximum power dissipation can be expressed by the following formula:
θ −θ
θ ≤ θ ≤θ P = P ×
: maxθ maxθ
R 4
R
θ −θ
4 R
where
θ is the rated ambient temperature in Celsius ( °C). θ = 25 °C, unless otherwise specified
R R
in the detail specification;
θ is the temperature in Celsius (°C) specified in the detail specification, above which zero-
power shall be applied. θ is equal to, or lower than the upper category temperature
θ (°C).
max
2.2.31
maximum current at ambient temperature of 25 °C (I ) (for inrush current-limiting
max25
thermistors)
maximum value of current (d.c. or r.m.s. values for sine-shaped a.c.) which can be conti-
nuously applied to the thermistor at an ambient temperature of 25 °C.
NOTE 1 See curve c, θ ≤ 25 °C ≤ θ or curve d, θ ≤ θ = θ in Figure 3.

2 3 2 R 3
NOTE 2 The maximum power dissipation at ambient temperature of 25 °C (P ) is calculated by P = I
max25
max25 max25
× U, where U is the voltage drop across the thermistor.

– 14 – 60539-1 © IEC:2008(E)
I
maxθ
I
max25
θ
θ θ θ θ θ θ θ
R
min 1 2 3 4 max.
Curve c
I
max
θ
I
max25
θ
θ θ = θ θ
R 3 θ
2 4 max.
Curve d
IEC  021/08
Figure 3 – Maximum current derating
2.2.32
maximum current at ambient temperature θ (I )

maxθ
maximum value of the current which can pass continuously through the thermistor at an
ambient temperature θ
Curve c
The maximum current rises at a temperature θ linearly to a temperature θ . Between
1 2
temperature θ and θ the current is constant. When the temperature exceeds θ , the current

2 3 3
must be decreased linearly to zero at a temperature θ .
The maximum current can be expressed by the following formulae:
θ −θ
θ ≤ θ ≤θ I = I ×
:
maxθ max25
1 2
θ −θ
2 1
θ ≤ θ ≤θ
:
3 4
where
θ is the ambient temperature in Celsius ( °C);
θ is the temperature in Celsius (°C) specified in the detail specification, which is equal to the

lower category temperature θ (°C) or higher;
min
θ is the ambient temperature at 0 °C, unless otherwise specified in the relevant detail
specification;
θ is the ambient temperature at 55 °C, unless otherwise specified in the relevant detail
specification;
θ is the temperature in Celsius (°C) specified in the detail specification, which is equal to the
upper category temperature θ (°C) or lower.

max
60539-1 © IEC:2008(E) – 15 –
Curve d
The maximum current is constant between temperature θ and θ . θ = 0 °C, unless otherwise
2 R 2
specified in the detail specification. When the temperature exceeds θ , the current must be
R
decreased linearly to zero at a temperature θ .
The maximum current can be expressed by the following formulae:
θ − θ
θ ≤ θ ≤θ  I = I ×
:
R 4 maxθ max25
θ − θ
4 R
where
θ is the rated ambient temperature specified in the detail specification. θ = 25 °C, unless

R R
otherwise specified in the detail specification;
θ is the temperature in Celsius (°C) specified in the detail specification, which is equal to the

upper category temperature θ (°C) or lower.

max
2.2.33
δ
dissipation factor,
power dissipation required for a thermistor to raise its temperature by 1 K and which is
generally the ratio of the power dissipation change to the resulting thermistor body
temperature change at a specified ambient temperature
2.2.34
response time
time (in s) required for a thermistor to change its temperature between two defined conditions
when subjected to a change in ambient temperature, power or a combination of temperature
and power
NOTE Because of the impracticability to measure response time direct, two methods are defined to measure the
thermal time constant direct.
2.2.34.1
thermal time constant by ambient temperature change, τ
a
time (in s) required for a thermistor to respond to 63,2 % of an external step change in
ambient temperature in a defined medium
NOTE Step change and medium are specified in the detail specification.
2.2.34.2
thermal time constant by cooling after self-heating, τ
c
time (in s) required for a thermistor to cool by 63,2 % of its temperature excess induced by
self-heating, in a defined medium
NOTE The medium is specified in the detail specification.
2.2.35
heat capacity, C
th
energy (in joules) the thermistor needs to raise 1 K in temperature. It is completely
determined by the component design
NOTE The heat capacity is calculated by the following formula: C = δ × τ or C = δ × τ
.
th c th a
2.2.36
voltage-current characteristic
relationship between the voltage (d.c., a.c. r.m.s.) across the thermistor and the applied
steady-state current when the thermistor reaches a thermal equilibrium condition in still air or
in the still medium specified in the detail specification, at 25 °C or at the temperature
specified in the detail specification

– 16 – 60539-1 © IEC:2008(E)
2.2.37
maximum operating power for limited self-heating, P (only for thermistors for sensing)
ΔT
maximum value of the power dissipation (I × U ) based on the consideration of the sensing
ΔT ΔT
error due to the internal generation of heat (self-heating) of the thermistor, which can be
continuously applied to the thermistor in its practical use.

Unless otherwise specified in the detail specification, ΔT is equal to 1 K. The relationship
among P , I and U is expressed by the following formulae:
ΔT ΔT ΔT
PΔT = δ ×ΔT
δ ×Δ T
IΔT =
RT
UΔT = RT×()δ ×Δ T
where,
P is the maximum operating power for limited self-heating;
ΔT
δ is the dissipation factor;
ΔT is the temperature rise of the thermistor due to its internal generation of heat;
I is the permissible operating current;

ΔT
U is the permissible operating voltage;

ΔT
R is the value of resistance at temperature T in kelvins (K).

T
2.3 Preferred values
Each sectional specification shall prescribe the preferred values appropriate to the subfamily.
2.3.1 Climatic categories
The thermistors covered by this standard are classified into climatic categories according to
the general rules given in Appendix A of IEC 60068-1.
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 -90, -80, -65, -55, -40, -25, -10, -5,
+5
ºC
Upper category temperature 30, 40, 55, 70, 85, 100, 105, 125,
150, 155, 175, 200, 250, 315, 400,
ºC
500, 630, 800, 1000
Damp heat, steady state 4, 21, 42, 56
days
The detail specification shall prescribe the appropriate category.
2.4 Marking
2.4.1 General
The following shall be clearly marked on the thermistor in the following order of precedence
as space permits:
60539-1 © IEC:2008(E) – 17 –
a) rated zero-power resistance;
b) manufacturer's name and/or trade mark;
c) date of manufacture;
d) tolerance on rated zero-power resistance;
e) the number of the detail specification and style.
The package containing the thermistor(s) shall be clearly marked with all the information
listed above.
Any additional marking shall be so applied that no confusion can arise.
2.4.2 Small size types such as surface mount thermistors are generally not marked on the
body. If some marking can be applied, they shall be clearly marked with as many as possible
of the above items as is considered useful. Any duplication of information in the marking on
the thermistor should be avoided.
2.4.3 Coding
Where coding for resistance value, tolerance or date is used, the method shall be one
selected from those given in IEC 60062.
3 Quality assessment procedures
3.1 General
When this standard and any related standards are used for the purpose of a full quality
assessment system such as the IEC Quality Assessment System for Electronic Components
(IECQ), compliance with 3.4 and 3.5 is required.
When such standards are used outside such quality assessment systems as the IECQ system
for purposes such as design proving or type testing, the procedures and requirements of 3.4.1
and 3.4.2b) may be used, but the tests and parts of tests shall be applied in the order given in
the test schedules.
3.2 Primary stage of manufacture
The primary stage of manufacture is defined as the initial mixing process of ingredients.
3.3 Structurally similar components
Thermistors may be grouped as structurally similar for the purpose of forming inspection lots
provided that the following requirements are met.
– They shall be produced by one manufacturer on one site using essentially the same
design, materials, processes and methods.
– The sample taken shall be determined from the total lot size of the grouped devices.
– Structurally similar devices should preferably be included in one detail specification but
the details of all claims to structural similarity shall be declared in the qualification
approval test reports.
3.3.1 For electrical tests, devices having the same electrical characteristics may be grouped
provided that the element determining the characteristics is similar for all the devices
concerned.
3.3.2 For environmental tests, devices having the same encapsulation, basic internal
structure and finishing processes, may be grouped.

– 18 – 60539-1 © IEC:2008(E)
3.3.3 For visual inspection (except marking), devices may be grouped if they have been
made on the same production line, have the same dimensions, encapsulation and external
finish.
This grouping may also be used for robustness of terminations and soldering tests where it is
convenient to group devices with different internal structures.
3.3.4 For endurance tests, thermistors may be grouped if they have been made on the same
production line using the same design and differing only in electrical characteristics. If it can
be shown that one type from the group is more heavily stressed than the others, then tests on
this type may be accepted for the remaining members of the group.
3.4 Qualification approval procedures
3.4.1 The manufacturer shall comply with
a) the general requirements of Clause 3 of IECQ 001002-3 governing qualification approval;
and
b) the requirements for the primary stage of manufacture (see 3.2).
3.4.2 In addition to the requirements of 3.4.1, the procedures a) or b) below shall apply.
a) The manufacturer shall produce test evidence of conformance to the specification
requirements on three lots taken in as short a time as possible for lot-by-lot inspection and
on one lot for periodic inspection.
Samples shall be taken from the lots in accordance with IEC 60410 (see Annex A). Normal
inspection shall be used, but, where the sample size would give acceptance on zero non-
conformances, additional specimens shall be taken to meet the sample size required to
give acceptance on one nonconforming item.
b) The manufacturer may, as an alternative to the procedure specified in 3.4.2a), produce
test evidence to show conformance to the specification requirements on one of the fixed
sample size test schedules given in the sectional specification.
The specimens taken to form the sample shall be selected at random from current
production or as agreed with the National Supervising Inspectorate.
For the two procedures the sample sizes and the permissible number of nonconformances
shall be of comparative order. The test conditions and requirements shall be the same.
3.4.3 Qualification approval obtained as part of a quality assessment system, shall be
maintained by regular demonstration of compliance with the requirements for quality
conformance (see 3.5). Otherwise, this qualification approval must be verified by the rules for
the maintenance of qualification approval given in 3.1.7 of IECQ 001002-3.
3.5 Quality conformance inspection
Blank detail specifications associated with the sectional specifications 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.
3.6 Certified
...

IEC 60539-1 ®
Edition 2.0 2008-02
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 2.0 2008-02
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
PRICE CODE
INTERNATIONALE
CODE PRIX X
ICS 31.040.30 ISBN 978-2-88912-902-7

– 2 – 60539-1  IEC:2008
CONTENTS
FOREWORD . 4

1 General . 6
1.1 Scope . 6
1.2 Normative references . 6
2 Technical data . 8
2.1 Units, symbols and terminology . 8
2.2 Terms and definitions . 8
2.3 Preferred values . 16
2.4 Marking . 16
3 Quality assessment procedures . 17
3.1 General . 17
3.2 Primary stage of manufacture . 17
3.3 Structurally similar components . 17
3.4 Qualification approval procedures . 18
3.5 Quality conformance inspection . 18
3.6 Certified test records of released lots . 18
3.7 Delayed delivery . 19
3.8 Release for delivery under qualification approval before the completion of
group B tests . 19
3.9 Alternative test methods . 19
3.10 Unchecked parameters . 19
4 Test and measurement procedures . 19
4.1 General . 19
4.2 Standard atmospheric conditions for testing . 19
4.3 Drying and recovery . 20
4.4 Mounting (for surface mount thermistors only) . 20
4.5 Visual examination and check of dimensions . 21
4.6 Zero-power resistance . 22
4.7 B-value or resistance ratio . 22
4.8 Insulation resistance (for insulated types only) . 23
4.9 Voltage proof (for insulated types only) . 26
4.10 Resistance/temperature characteristic . 26
4.11 Dissipation factor (δ) . 26
4.12 Thermal time constant by ambient temperature change (τ ) . 28
a
4.13 Thermal time constant by cooling after self-heating (τ ) . 28
c
4.14 Robustness of terminations (not applicable to surface mount thermistors) . 29
4.15 Resistance to soldering heat . 30
4.16 Solderability . 31
4.17 Rapid change of temperature . 32
4.18 Vibration. 32
4.19 Bump . 33
4.20 Shock . 33
4.21 Free fall (if specified in the detail specification) . 33
4.22 Thermal shock (if specified in the detail specification) . 34
4.23 Cold (if required by the sectional specification) . 34

60539-1  IEC:2008 – 3 –
4.24 Dry heat (if required by the sectional specification) . 34
4.25 Damp heat, steady state . 35
4.26 Endurance . 35
4.27 Shear (adhesion) test . 40
4.28 Substrate bending test . 40
4.29 Component solvent resistance . 41
4.30 Solvent resistance of marking . 41
4.31 Salt mist (if required by the sectional specification) . 41
4.32 Sealing (if required by the sectional specification) . 41
4.33 Composite temperature/humidity cycle (if required by the sectional
specification) . 41

Annex A (normative) Interpretation of sampling plans and procedures as described in
IEC 60410 for use within the IEC quality assessment system for electronic
components (IECQ) . 43
Annex B (normative) Rules for the preparation of detail specifications for capacitors
and resistors for electronic equipment . 44
Annex C (informative) Typical examples of mountings for measurements of directly
heated thermistors . 45

Figure 1 – Typical resistance-temperature characteristic for NTC thermistors . 10
Figure 2 – Decreased power dissipation curve . 12
Figure 3 – Maximum current derating . 14
Figure 4 – Zero-power resistance measuring basic circuit . 22
Figure 5 – Test method 1 . 23
Figure 6 – Test method 2 . 24
Figure 7 – Test method 2 . 24
Figure 8 – Test method 3 . 25
Figure 9 – Test method 4 . 25
Figure 10 – Example of test chamber . 27
Figure 11 – Dissipation factor measuring circuit . 27
Figure 12 – Thermal time constant measuring circuit . 29
Figure 13 – Endurance at room temperature with I evaluating circuit . 36
max25
Figure 14 – Maximum permissible capacitance test circuit (method 1) . 39
Figure 15 – Maximum permissible capacitance test circuit (method 2) . 39
Figure C.1 – Mounting for measurements of surface mount thermistors . 45

Table 1 – Upper and lower category temperatures and duration of the damp-heat test . 16
Table 2 – Tensile force . 30

– 4 – 60539-1  IEC:2008
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 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 provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
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.
International Standard IEC 60539-1 has been prepared by IEC technical committee 40:
Capacitors and resistors for electronic equipment.
This second edition cancels and replaces the first edition published in 2002 and constitutes a
minor revision related to tables, figures and references.
This bilingual version (2012-01) corresponds to the monolingual English version, published in
2008-02.
60539-1 © IEC:2008 – 5 –
The text of this standard is based on the following documents:
FDIS Report on voting
40/1878A/FDIS 40/1895/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.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
IEC 60539 consists of the following parts, under the general title Directly heated negative
temperature coefficient thermistors:
Part 1: Generic specification
Part 2: Sectional specification: Surface mount negative temperature coefficient thermistors
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result 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.
– 6 – 60539-1  IEC:2008
DIRECTLY HEATED NEGATIVE TEMPERATURE COEFFICIENT
THERMISTORS –
Part 1: Generic specification
1 General
1.1 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.
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 60027-1, Letter symbols to be used in electrical technology – Part 1: General
IEC 60050, International Electrotechnical Vocabulary (IEV)
IEC 60062, Marking codes for resistors and capacitors
IEC 60068-1:1988, Environmental testing – Part 1: General and guidance
Amendment 1 (1992)
IEC 60068-2-1:2007, Environmental testing – Part 2-1: Tests – Tests A: Cold
IEC 60068-2-2:2007, Environmental testing – Part 2-2: Tests – Tests B: Dry heat
IEC 60068-2-6:1995, Environmental testing – Part 2-6: Tests – Test Fc: Vibration (sinusoidal)
IEC 60068-2-11:1981, Environmental testing – Part 2-11: Tests – Test Ka: Salt mist
IEC 60068-2-14:1984, Environmental testing – Part 2-14: Tests – Test N: Change of
temperature
Amendment 1 (1986)
IEC 60068-2-17:1994, Environmental testing – Part 2-17: Tests – Test Q: Sealing
IEC 60068-2-20:1979, Environmental testing – Part 2-20: Tests – Test T: Soldering
Amendment 2 (1987)
IEC 60068-2-21:2006, Environmental testing – Part 2-21: Tests – Test U: Robustness of
terminations and integral mounting devices

60539-1  IEC:2008 – 7 –
IEC 60068-2-27:1987, Environmental testing – Part 2-27: Tests – Test Ea and guidance:
Shock
IEC 60068-2-29:1987, Environmental testing – Part 2-29: Tests – Test Eb and guidance:
Bump
IEC 60068-2-32:1975, Environmental testing – Part 2-32: Tests – Test Ed: Free fall
Amendment 2 (1990)
IEC 60068-2-38:1974, Environmental testing – Part 2-38: Tests – Test Z/AD: Composite
temperature/humidity cyclic test
IEC 60068-2-45:1980, Environmental testing – Part 2-45: Tests – Test XA and guidance:
Immersion in cleaning solvents
Amendment 1 (1993)
IEC 60068-2-52:1996, Environmental testing – Part 2-52: Tests – Test Kb: Salt mist, cyclic
(sodium chloride solution)
IEC 60068-2-54:2006, Environmental testing – Part 2-54: Tests – Test Ta: Solderability
testing of electronic components by the wetting balance method
IEC 60068-2-58:2004, 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 60068-2-69:2007, Environmental testing – Part 2-69: Tests – Test Te: Solderability
testing of electronic components for surface mounting devices (SMD) by the wetting balance
method
IEC 60068-2-78:2001, Environmental testing – Part 2-78: Tests – Test Cab: Damp heat,
steady state
IEC 60294, Measurement of the dimensions of a cylindrical component having two axial
terminations
IEC 60410, Sampling plans and procedures for inspection by attributes
IEC 60617, Graphical symbols for diagrams
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 structures – Part 2-7:
Reinforced base materials clad and unclad – Epoxide woven E-glass laminated sheet of
defined flammability (vertical burning test), copper-clad
IECQ 001002-3, IEC Quality Assessment System for Electronic Components (IECQ) – Rules
of procedure – Part 3: Approval procedures
ISO 1000, SI units and recommendations for the use of their multiples and of certain other
units
– 8 – 60539-1  IEC:2008
2 Technical data
2.1 Units, symbols and terminology
Units, graphical symbols, letter symbols and terminology should, whenever possible, be taken
from the following publications:
– IEC 60027-1
– IEC 60050
– IEC 60617
– ISO 1000
When further items are required, they should be derived in accordance with the principles of
the publications listed above.
2.2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.2.1
type
products having similar design features manufactured by the same techniques and falling
within the manufacturer's usual range of ratings for these products
NOTE 1 Mounting accessories are ignored, provided they have no significant effect on the test results.
NOTE 2 Ratings cover the combination of
– electrical ratings;
– sizes;
– climatic category.
NOTE 3 The limits of the range of ratings should be given in the detail specification.
2.2.2
style
variation within a type having specific nominal dimensions and characteristics
2.2.3
thermistor
thermally sensitive semiconducting resistor whose primary function is to exhibit an important
change in electrical resistance with a change in body temperature
2.2.4
negative temperature coefficient thermistor (NTC)
thermistor in which the resistance decreases with increasing temperature
2.2.5
directly heated negative temperature coefficient thermistor
thermistor which obtains its resistance variation by the changes of physical conditions such as
current through it, ambient temperature, humidity, wind velocity, gas, etc.
2.2.6
indirectly heated negative temperature coefficient thermistor
thermistor which obtains its resistance variation primarily by the change of temperature of the
thermistor, due to the change of a current through a separate heater which is in close contact
with, but electrically insulated from, the thermistor element
NOTE The temperature of the thermistor can also be changed by the changes of physical conditions such as
current through the thermistor element itself, ambient temperature, humidity, wind velocity, gas, etc.

60539-1  IEC:2008 – 9 –
2.2.7
positive temperature coefficient (PTC) thermistor (for information only)
thermistor in which the resistance increases with increasing temperature
2.2.8
thermistor with wire terminations
thermistor provided with wire terminations
2.2.9
thermistor without wire terminations
thermistor provided only with two metallized faces, to be used as electrical contacts
2.2.10
insulated thermistor
thermistor coated with materials such as resin, glass or ceramic, capable of meeting the
requirements of the insulation resistance and voltage proof tests when specified in the test
schedule
2.2.11
non-insulated thermistor
thermistor with or without coating materials for surfacing of elements but not intended to meet
the requirements of the insulation resistance and voltage proof tests when specified in the
test schedule
2.2.12
surface mount thermistor
thermistor whose small dimensions and nature or shape of terminations make them suitable
for use in hybrid circuits and on printed board
2.2.13
assembled thermistor (probe)
thermistor encapsulated in different materials such as tubes, plastic and metal housing and/or
assembled with cables and/or connectors
2.2.14
thermistor for sensing
thermistor which responds to temperature changes and therefore is used for temperature
sensing and control
2.2.15
inrush current limiting thermistor
thermistor which limits the inrush current just after switching on the power
2.2.16
residual resistance (only for inrush current-limiting thermistors)
value of the d.c. resistance of a thermistor when its thermal stability is reached with the
maximum current passing
2.2.17
maximum permissible capacitance (only for inrush current-limiting thermistors)
maximum permissible capacitance value of a capacitor which can be connected to a
thermistor under loading
2.2.18
zero-power resistance, R
T
value of the d.c. resistance of a thermistor, when measured at a specified temperature, under
such conditions that the change in resistance due to the internal generation of heat is
negligible with respect to the total error of measurement

– 10 – 60539-1  IEC:2008
2.2.19
rated zero-power resistance
nominal value at the standard reference temperature of 25 °C, unless otherwise specified
2.2.20
resistance-temperature characteristic
relationship between the zero-power resistance and the body temperature of a thermistor
The resistance law follows approximately the formula:
 1 1 
B − 
 
R=R ×e
T T
a
a
 
where
R is the zero-power resistance in ohms (Ω) at absolute temperature T in kelvins (K);
R is the zero-power resistance in ohms (Ω) at absolute temperature T in kelvins (K);

a a
B is the thermal sensitivity index (see 2.2.22).
NOTE This formula is only applicable for representing the resistance variation over a restricted temperature
range. For more precise representation of the R/T-curve, a resistance/temperature relation should be specified in
tabulated form in the detail specification.

Ig R
R
a
R
R
b
T T T T  (K)
a b
IEC  019/08
Figure 1 – Typical resistance-temperature characteristic for NTC thermistors
2.2.21
resistance ratio
ratio of the zero-power resistance of a thermistor measured at the reference temperature of
25 °C to that measured at 85 °C, or at such other pairs of temperatures as may be prescribed
in the detail specification
2.2.22
B-value
index of the thermal sensitivity expressed by the formula:
B = [(T × T )/(T – T )] × ln(R /R )
a b b a a b
or
B = 2,303 × [(T × T )/(T – T )] × log(R /R )
a b b a a b
where
B is a constant in kelvins (K);
R is the zero-power resistance in ohms (Ω) at temperature T in kelvins (K);
a a
60539-1  IEC:2008 – 11 –
R is the zero-power resistance in ohms (Ω) at temperature T in kelvins (K);
b b
*
T = 298,15 K ;
a
*
T = 358,15 K .
b
* The values given above for T and T are the preferred values and are equivalent to +25 °C and +85 °C
a b
respectively.
NOTE Where the detail specification prescribes that the B-value should be measured at other temperatures, the
specified values (in kelvins) shall be used for T and T in the calculation in place of the preferred values and the
a b
B-value may be expressed by “Ba/b”.
2.2.23
zero-power temperature coefficient of resistance, α
T
ratio at a specified temperature (T) of the rate of change of zero-power resistance with
temperature to the zero-power resistance of the thermistor, expressed by the formula:
α = (1/R ) × (dR /dT) × 100
T T T
The value α can be approximately calculated by the formula:
T
α = (–B/T ) × 100
T
where
α is the zero-power temperature coefficient of resistance in %/K;

T
R is the zero-power resistance in ohms at temperature T in kelvins (K);

T
B is the index of the thermal sensitivity in kelvins (K).
2.2.24
category temperature range
range of ambient temperatures for which the thermistor has been designed to operate
continuously at zero-power, defined by the temperature limits of the appropriate category
2.2.25
upper category temperature, θ
max
maximum ambient temperature for which a thermistor has been designed to operate
continuously at zero-power
2.2.26
lower category temperature, θ
min
minimum ambient temperature for which a thermistor has been designed to operate
continuously at zero-power
2.2.27
storage temperature range
range of ambient temperatures for which a thermistor can be stored continuously under no-
load condition
2.2.28
decreased power dissipation curve (not for inrush current-limiting thermistors)
relation between the ambient temperature and the maximum power dissipation P , which is
maxθ
usually expressed as curve a or, alternatively, as curve b in Figure 2

– 12 – 60539-1  IEC:2008
P
maxθ
P
max
θ
R
θ θ θ   θ θ
R θ θ θ
min 1 2 3 4 max
Curve a
P
maxθ
P
max
θ
R
θ
θ θ = θ θ
R θ
2 3
4 max.
Curve b
IEC  020/08
Figure 2 – Decreased power dissipation curve
2.2.29
maximum power dissipation at rated ambient temperature θ (P )

θ
R max R
maximum value of the power dissipation which can be continuously applied to the thermistor
at the rated ambient temperature θ .
R
NOTE See curve a, θ2 ≤ θR ≤θ3 or curve b, θ2 ≤ θR = θ3 in Figure 2.
The rated ambient temperature θ is the ambient temperature specified in the detail
R
specification and is usually 25 °C.
2.2.30
maximum power dissipation at ambient temperature θ (P )

maxθ
maximum value of the power dissipation which can be continuously applied to the thermistor
at an ambient temperature θ
Curve a
The maximum power dissipation rises at a temperature θ linearly to a temperature θ .
1 2
Between temperature θ and θ the power dissipation is constant. When the temperature

2 3
exceeds θ , the power dissipation must be decreased linearly to zero at a temperature θ
3 4
The maximum power dissipation at ambient temperature θ in general is calculated as follows:
P = I × U
maxθ maxθ
where U is the voltage across the thermistor (for I see 2.2.32).
,
maxθ
The maximum power dissipation can be expressed by the following formula:

60539-1  IEC:2008 – 13 –
θ − θ
θ ≤ θ ≤θ P = P ×
:
max.θ max.θ
1 2
R
θ − θ
2 1
θ − θ
θ ≤ θ ≤θ P = P ×
:
max .θ max .θ
3 4
R
θ − θ
4 3
where
θ is the rated ambient temperature in Celsius (°C);
R
θ is the temperature in Celsius (°C) specified in the detail specification below which zero-

power shall be applied. θ is equal to the lower category temperature θ (°C) or
min
.
higher;
θ is the lowest temperature at which P can be applied. θ = 0 °C, unless otherwise
2 max.θ 2
specified in the detail specification;
θ is the maximum temperature at which P can be applied. θ = 55 °C, unless

3 max.θ 3
otherwise specified in the detail specification;
θ is the temperature in Celsius (°C) specified in the detail specification, above which zero-
power shall be applied. θ is equal to, or lower than, the upper category temperature
θ (°C).
max
Curve b
The maximum power dissipation is constant between temperature θ and θ . θ = 0 °C, unless
2 R 2
otherwise specified in the detail specification. When the temperature exceeds θ , the power
R
dissipation must be decreased linearly to zero at a temperature θ .
The maximum power dissipation at ambient temperature θ in general is calculated as follows:
P = I × U
maxθ maxθ
where U is the voltage across the thermistor (for I , see 2.2.32).
max.θ
The maximum power dissipation can be expressed by the following formula:
θ −θ
θ ≤ θ ≤θ P = P ×
:
R 4 maxθ maxθ
R
θ −θ
4 R
where
is the rated ambient temperature in Celsius ( °C). θ = 25 °C, unless otherwise specified
θ
R R
in the detail specification;
θ is the temperature in Celsius (°C) specified in the detail specification, above which zero-
power shall be applied. θ is equal to, or lower than the upper category temperature
θ (°C).
max
2.2.31
maximum current at ambient temperature of 25 °C (I ) (for inrush current-limiting
max25
thermistors)
maximum value of current (d.c. or r.m.s. values for sine-shaped a.c.) which can be conti-
nuously applied to the thermistor at an ambient temperature of 25 °C.
NOTE 1 See curve c, θ ≤ 25 °C ≤ θ or curve d, θ ≤ θ = θ in Figure 3.

2 3 2 R 3
NOTE 2 The maximum power dissipation at ambient temperature of 25 °C (Pmax25) is calculated by P = I
max25 max25
× U, where U is the voltage drop across the thermistor.

– 14 – 60539-1  IEC:2008
I
max
θ
I
max25
θ θ θ θ
θR θ θ θ
min 1 2 3 4 .
max
Curve c
I
maxθ
I
max25
θ
θ θ = θ
R θ θ
2 max.
Curve d
IEC  021/08
Figure 3 – Maximum current derating
2.2.32
maximum current at ambient temperature θ (I )

maxθ
maximum value of the current which can pass continuously through the thermistor at an
ambient temperature θ
Curve c
The maximum current rises at a temperature θ linearly to a temperature θ . Between
1 2
temperature θ and θ the current is constant. When the temperature exceeds θ , the current

2 3 3
must be decreased linearly to zero at a temperature θ .
The maximum current can be expressed by the following formulae:
θ −θ
θ ≤ θ ≤θ I = I ×
:
1 2 maxθ max25
θ −θ
2 1
θ ≤ θ ≤θ
:
3 4
where
θ is the ambient temperature in Celsius ( °C);
θ is the temperature in Celsius (°C) specified in the detail specification, which is equal to the

lower category temperature θ (°C) or higher;
min
θ is the ambient temperature at 0 °C, unless otherwise specified in the relevant detail
specification;
θ is the ambient temperature at 55 °C, unless otherwise specified in the relevant detail
specification;
θ is the temperature in Celsius (°C) specified in the detail specification, which is equal to the
upper category temperature θ (°C) or lower.

max
60539-1  IEC:2008 – 15 –
Curve d
The maximum current is constant between temperature θ and θ . θ = 0 °C, unless otherwise
2 R 2
specified in the detail specification. When the temperature exceeds θ , the current must be
R
decreased linearly to zero at a temperature θ .
The maximum current can be expressed by the following formulae:
θ − θ
θ ≤ θ ≤θ  I = I ×
:
R 4 maxθ max25
θ − θ
4 R
where
θ is the rated ambient temperature specified in the detail specification. θ = 25 °C, unless

R R
otherwise specified in the detail specification;
θ is the temperature in Celsius (°C) specified in the detail specification, which is equal to the

upper category temperature θ (°C) or lower.

max
2.2.33
dissipation factor, δ
power dissipation required for a thermistor to raise its temperature by 1 K and which is
generally the ratio of the power dissipation change to the resulting thermistor body
temperature change at a specified ambient temperature
2.2.34
response time
time (in s) required for a thermistor to change its temperature between two defined conditions
when subjected to a change in ambient temperature, power or a combination of temperature
and power
NOTE Because of the impracticability to measure response time direct, two methods are defined to measure the
thermal time constant direct.
2.2.34.1
thermal time constant by ambient temperature change, τ
a
time (in s) required for a thermistor to respond to 63,2 % of an external step change in
ambient temperature in a defined medium
NOTE Step change and medium are specified in the detail specification.
2.2.34.2
thermal time constant by cooling after self-heating, τ
c
time (in s) required for a thermistor to cool by 63,2 % of its temperature excess induced by
self-heating, in a defined medium
NOTE The medium is specified in the detail specification.
2.2.35
heat capacity, C
th
energy (in joules) the thermistor needs to raise 1 K in temperature. It is completely
determined by the component design
NOTE The heat capacity is calculated by the following formula: C = δ × τ or C = δ × τ
.
th c th a
2.2.36
voltage-current characteristic
relationship between the voltage (d.c., a.c. r.m.s.) across the thermistor and the applied
steady-state current when the thermistor reaches a thermal equilibrium condition in still air or
in the still medium specified in the detail specification, at 25 °C or at the temperature
specified in the detail specification

– 16 – 60539-1  IEC:2008
2.2.37
maximum operating power for limited self-heating, P (only for thermistors for sensing)
ΔT
maximum value of the power dissipation (I × U ) based on the consideration of the sensing
∆T ∆T
error due to the internal generation of heat (self-heating) of the thermistor, which can be
continuously applied to the thermistor in its practical use.

Unless otherwise specified in the detail specification, ∆T is equal to 1 K. The relationship
among P , I and U is expressed by the following formulae:
∆T ∆T ∆T
P∆T = δ × ∆T
δ ×Δ T
I∆T =
RT
U∆T = RT × (δ ×Δ T )
where,
P is the maximum operating power for limited self-heating;
ΔT
δ is the dissipation factor;
ΔT is the temperature rise of the thermistor due to its internal generation of heat;
I is the permissible operating current;

ΔT
U is the permissible operating voltage;

ΔT
R is the value of resistance at temperature T in kelvins (K).

T
2.3 Preferred values
Each sectional specification shall prescribe the preferred values appropriate to the subfamily.
2.3.1 Climatic categories
The thermistors covered by this standard are classified into climatic categories according to
the general rules given in Appendix A of IEC 60068-1.
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 -90, -80, -65, -55, -40, -25, -10, -5,
+5
ºC
Upper category temperature 30, 40, 55, 70, 85, 100, 105, 125,
150, 155, 175, 200, 250, 315, 400,
ºC
500, 630, 800, 1000
Damp heat, steady state 4, 21, 42, 56
days
The detail specification shall prescribe the appropriate category.
2.4 Marking
2.4.1 General
The following shall be clearly marked on the thermistor in the following order of precedence
as space permits:
60539-1  IEC:2008 – 17 –
a) rated zero-power resistance;
b) manufacturer's name and/or trade mark;
c) date of manufacture;
d) tolerance on rated zero-power resistance;
e) the number of the detail specification and style.
The package containing the thermistor(s) shall be clearly marked with all the information
listed above.
Any additional marking shall be so applied that no confusion can arise.
2.4.2 Small size types such as surface mount thermistors are generally not marked on the
body. If some marking can be applied, they shall be clearly marked with as many as possible
of the above items as is considered useful. Any duplication of information in the marking on
the thermistor should be avoided.
2.4.3 Coding
Where coding for resistance value, tolerance or date is used, the method shall be one
selected from those given in IEC 60062.
3 Quality assessment procedures
3.1 General
When this standard and any related standards are used for the purpose of a full quality
assessment system such as the IEC Quality Assessment System for Electronic Components
(IECQ), compliance with 3.4 and 3.5 is required.
When such standards are used outside such quality assessment systems as the IECQ system
for purposes such as design proving or type testing, the procedures and requirements of 3.4.1
and 3.4.2b) may be used, but the tests and parts of tests shall be applied in the order given in
the test schedules.
3.2 Primary stage of manufacture
The primary stage of manufacture is defined as the initial mixing process of ingredients.
3.3 Structurally similar components
Thermistors may be grouped as structurally similar for the purpose of forming inspection lots
provided that the following requirements are met.
– They shall be produced by one manufacturer on one site using essentially the same
design, materials, processes and methods.
– The sample taken shall be determined from the total lot size of the grouped devices.
– Structurally similar devices should preferably be included in one detail specification but
the details of all claims to structural similarity shall be declared in the qualification
approval test reports.
3.3.1 For electrical tests, devices having the same electrical characteristics may be grouped
provided that the element determining the characteristics is similar for all the devices
concerned.
3.3.2 For environmental tests, devices having the same encapsulation, basic internal
structure and finishing processes, may be grouped.

– 18 – 60539-1  IEC:2008
3.3.3 For visual inspection (except marking), devices may be grouped i
...