IEC 61189-2-805:2024

IEC 61189-2-805 ®
Edition 1.0 2024-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Test methods for electrical materials, printed boards and other interconnection
structures and assemblies –
Part 2-805: X/Y CTE test for thin base materials by TMA

Méthodes d’essai pour les matériaux électriques, les cartes imprimées et autres
structures d’interconnexion et ensembles –
Partie 2-805: Essai à faible CDT X/Y par TMA pour matériaux de base minces
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IEC 61189-2-805 ®
Edition 1.0 2024-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Test methods for electrical materials, printed boards and other interconnection

structures and assemblies –
Part 2-805: X/Y CTE test for thin base materials by TMA

Méthodes d’essai pour les matériaux électriques, les cartes imprimées et autres

structures d’interconnexion et ensembles –

Partie 2-805: Essai à faible CDT X/Y par TMA pour matériaux de base minces

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 31.180  ISBN 978-2-8322-8700-2

– 2 – IEC 61189-2-805:2024 © IEC 2024
CONTENTS
FOREWORD . 3
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Test specimens . 5
4.1 Preparation . 5
4.2 Number . 5
4.3 Form . 5
4.4 Conditioning . 6
5 Apparatus and materials . 6
6 Procedure . 6
7 Evaluation . 7
7.1 General . 7
7.2 Calculation of coefficient of thermal expansion curve . 8
7.3 Calculation of instantaneous coefficient of thermal expansion curve
(optional) . 9
8 Report . 9
Bibliography . 10

Figure 1 – TMA expansion curves: first heat cycles and second heat cycles . 6
Figure 2 – TMA expansion curve . 7
Figure 3 – TMA expansion curve and instantaneous CTE curve . 8

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
TEST METHODS FOR ELECTRICAL MATERIALS, PRINTED BOARDS AND
OTHER INTERCONNECTION STRUCTURES AND ASSEMBLIES –

Part 2-805: X/Y CTE test for thin base materials by TMA

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
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Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.
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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.
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shall not be held responsible for identifying any or all such patent rights.
IEC 61189-2-805 has been prepared IEC technical committee 91: Electronics assembly
technology. It is an International Standard.
The text of this International Standard is based on the following documents:
Draft Report on voting
91/1755/CDV 91/1782/RVC
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.

– 4 – IEC 61189-2-805:2024 © IEC 2024
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/standardsdev/publications.
A list of all parts in the IEC 61189 series, published under the general title Test methods for
electrical materials, printed boards and other interconnection structures and assemblies, can
be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn, or
• revised.
IMPORTANT – The "colour inside" logo on the cover page of this document 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.

TEST METHODS FOR ELECTRICAL MATERIALS, PRINTED BOARDS AND
OTHER INTERCONNECTION STRUCTURES AND ASSEMBLIES –

Part 2-805: X/Y CTE test for thin base materials by TMA

1 Scope
This part of IEC 61189 defines the method to be followed for the determination of the X/Y
coefficient of thermal expansion of thin electrical insulating materials via the use of a
thermomechanical analyser (TMA). This method is applicable to materials that are solid for the
entire range of temperature used, and that retain sufficient rigidity over the temperature range
so that so that irreversible indentation of the specimen by the sensing probe does not occur.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
4 Test specimens
4.1 Preparation
The test specimen shall be between 0,01 mm and 0,5 mm thick. The effective length of the
sample clamped in the fixture shall be 8 mm and the recommended length of the sample is
60 mm, The sample width shall be 4 mm.
NOTE The test results will vary based upon the layup used, the resin to glass ratio and the ultimate cure of the
laminated stack.
4.2 Number
One specimen shall be prepared unless noted otherwise for each direction X and Y.
4.3 Form
The test specimen shall be cut to the specified size using appropriate procedures and
equipment to minimize thermal shock and mechanical stress. The edges shall be smooth and
without tears.
– 6 – IEC 61189-2-805:2024 © IEC 2024
4.4 Conditioning
The specimens shall be preconditioned by baking for one hour ± 15 minutes.
After removal from the oven, the specimens shall be allowed to cool to room temperature in a
desiccator or drying cabinet capable of maintaining an atmosphere less than 30 % RH at 23 °C.
5 Apparatus and materials
a) Thermomechanical analyzer (TMA) capable of detecting dimensional change to within
± 0,002 50 mm margin over the specified temperature range. It is desirable to have a TMA
comprised of a data acquisition and analysis system as well as the thermal cell. The TMA
shall have an environmental chamber capable of holding pure flush gas and an ultimate
temperature of 350 °C.
b) Drying chamber air circulating oven capable of maintaining 105 ± 2 °C.
c) Desiccator of low humidity drying cabinet capable of maintaining less than 30 % relative
humidity at 23 °C.
d) Specimen preparation: Etching system capable of complete removal of the metallic cladding.
6 Procedure
a) Metal-clad samples shall be tested without the cladding. Etch and dry the samples using
appropriate procedures and equipment.
b) Calibrate of the TMA instrument should be carried out according to the manufacturer’s
instructions.
c) Remove the specimen from the desiccator and place the specimen using the thin film fixture
clamp of the TMA stage. The first test should be with the sample oriented in the "X" direction.

Figure 1 – TMA expansion curves: first heat cycles and second heat cycles
d) Apply 0,03 N of tension force and enclose the specimen.
e) Start a pure gas purge at the rate of 30 ml/min to 150 ml/min to the environmental chamber.
f) Start the temperature ramp (or scan) from room temperature or other specified temperature.

g) Depending on the sample preparation, two heating cycles may be required to obtain
accurate CTE information. If the samples show unexpected shrinkage (see Figure 1), the
two heat test method is required. If two heating cycles are needed, perform procedure h) i)
and j), if just scan once, perform procedure j). The heating rate shall be conducted at 10 °C/
minute for both cycles.
h) The temperature excursion of the first scan shall be until a temperature of 20 °C above the
glass transition temperature (Tg) is observed. Hold the temperature for a minimum of
5 minutes or until the thermal relaxation has stopped. Avoid holding the temperature for too
long so as to avoid degradation of the specimen.
i) Cool the specimen to the initial temperature at 5 °C/min to 10 °C/min.
j) Repeat the procedure for the second heat cycle. The second heat cycle should end at the
temperature as specified.
7 Evaluation
7.1 General
The TMA expansion curve should resemble the plot shown in Figure 2.

Figure 2 – TMA expansion curve
An ideal TMA curve has a linear section below the Tg and a linear section above the Tg. The
software of the TMA may provide a more normalized result by averaging the data.
Examine all the specimens for signs of excessive loads, distortions, tears and other defects. If
any defects or specimen irregularities are found, discard the specimen and start over.
The analysis shall be repeated on the Y specimen. In most modern TMA instruments, the
calculations are handled by the system software.

– 8 – IEC 61189-2-805:2024 © IEC 2024

Figure 3 – TMA expansion curve and instantaneous CTE curve
7.2 Calculation of coefficient of thermal expansion curve
The average coefficient of thermal expansion α over the temperature interval of interest is
calculated as follows:
a) CTE below glass transition
CC− 10
( )
BA
α =
BA−
( )
LT( −T )
0 BA
For most materials, this will be the range of 7 ppm to 50 ppm (reinforced) or 30 ppm to
150 ppm (unreinforced)
b) CTE above glass transition
(CC− )10
DC
α =
(DC− )
LT −T
( )
0 DC
For most materials, this will be the range of 50 ppm to 100 ppm (reinforced) or 150 ppm to
500 ppm (unreinforced). Any reinforced materials, where the reinforcement has negative
CTE, will shrink rather than expand when heated above Tg of the resin.
T = temperature at point A in Figure 2;
A
T = temperature at point B in Figure 2;
B
T = tempera
...