IEC TS 62788-8-1:2024
(Main)Measurement procedures for materials used in photovoltaic modules - Part 8-1: Electrically conductive adhesive (ECA) - Measurement of material properties
Measurement procedures for materials used in photovoltaic modules - Part 8-1: Electrically conductive adhesive (ECA) - Measurement of material properties
IEC TS 62788-8-1:2024 defines test methods and datasheet reporting requirements for key characteristics of ECA used in photovoltaic modules, involving mechanical characteristics, adhesive characteristics, electrical characteristics, thermal characteristics, etc.
The object of this document is to offer a standard test procedure to ECA manufacturers for product design, production and quality control, and to PV module manufacturers for the purpose of material screening, material inspection, process control, and failure analysis.
This document is intended to be applied to ECA used in solar PV modules. For non-conductive adhesives or tapes used in PV modules, the applicable test methods except for electrical characteristics in this document may be used.
General Information
Standards Content (Sample)
IEC TS 62788-8-1 ®
Edition 1.0 2024-06
TECHNICAL
SPECIFICATION
Measurement procedures for materials used in photovoltaic modules –
Part 8-1: Electrically conductive adhesive (ECA) – Measurement of material
properties
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IEC TS 62788-8-1 ®
Edition 1.0 2024-06
TECHNICAL
SPECIFICATION
Measurement procedures for materials used in photovoltaic modules –
Part 8-1: Electrically conductive adhesive (ECA) – Measurement of material
properties
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 27.160 ISBN 978-2-8322-8735-4
– 2 – IEC TS 62788-8-1:2024 © IEC 2024
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 8
4 Test procedures . 12
4.1 General . 12
4.2 General characteristics . 12
4.2.1 Visual inspection . 12
4.2.2 Density . 12
4.2.3 Viscosity . 13
4.2.4 Thixotropic index . 14
4.2.5 Fineness . 15
4.3 Mechanical characteristics . 16
4.3.1 Tensile strength / elongation at break . 16
4.3.2 Storage normal modulus and loss normal modulus . 19
4.4 Adhesive characteristics . 21
4.4.1 Lap shear strength . 21
4.4.2 Peel strength . 23
4.5 Electrical characteristics . 25
4.5.1 Volume resistivity . 25
4.5.2 Contact resistivity . 28
4.6 Thermal characteristics . 32
4.6.1 Coefficient of thermal expansion (CTE). 32
4.6.2 Solids content . 34
4.7 Conditions of use . 35
4.7.1 General . 35
4.7.2 Shelf life . 35
4.7.3 Pot life . 36
5 Uniform characterization form (UCF) . 37
5.1 Purpose . 37
5.2 Details of the UCF . 37
5.3 Reporting requirements . 38
6 Data sheet . 38
6.1 Purpose . 38
6.2 Details of the data sheet . 38
6.3 Reporting requirements . 39
7 Product identification sheet (label) . 39
Annex A (normative) Sampling for lap shear strength test . 40
A.1 Sampling for on-line test . 40
A.2 Sampling for off-line test . 41
Annex B (normative) Sampling for volume resistivity test . 42
Annex C (normative) Sampling of contact resistivity between silver electrode and ECA . 44
Annex D (normative) Sampling of contact resistivity between PV ribbon and ECA . 46
Annex E (informative) Estimate of deviation and elimination of outliers . 49
E.1 General . 49
E.2 Estimate of deviation . 49
E.3 Z score . 49
E.4 Outliers elimination . 49
Bibliography . 51
Figure 1 – Shape of dumb-bell test specimen (ISO 37:2017) . 16
Figure 2 – Die for dumb-bell test specimen . 16
Figure 3 – Schematic diagram of tensile strength and elongation at break test . 18
Figure 4 – Schematic diagram of modulus specimen installation . 20
Figure 5 – Schematic diagram of lap shear strength test . 22
Figure 6 – Schematic diagram of peel strength test (180° peel) . 24
Figure 7 – Schematic diagram of volume resistivity test tooling . 26
Figure 8 – Schematic diagram of volume resistivity test . 27
Figure 9 – Schematic diagram of contact resistivity test between ECA and silver
electrode . 30
Figure 10 – Schematic diagram of contact resistivity test between ECA and PV ribbon . 31
Figure 11 – LR scatter plot and linear fit curve . 31
Figure 12 – Schematic diagram of ECA life time at various stages . 35
Figure A.1 – Schematic sampling diagram of lap shear strength test (on-line) . 40
Figure A.2 – Picture of ECA on the top of the electrode of a solar cell . 40
Figure A.3 – Picture of a final specimen slice cut from the bonded assembly . 41
Figure A.4 – Schematic sampling diagram of lap shear strength test (off-line) . 41
Figure B.1 – Schematic sampling diagram of volume resistivity test . 42
Figure B.2 – Picture of a volume resistivity test specimen after curing . 43
Figure C.1 – Schematic sampling diagram of ECA and silver electrode contact
resistivity test . 44
Figure C.2 – Schematic of an EVA and electrode contact resistivity test specimen . 45
Figure D.1 – Schematic sampling diagram of ECA and PV ribbon contact resistivity test . 47
Figure D.2 – Schematic of an ECA and PV ribbon contact resistivity test specimen . 48
Table 1 – Dimensions of dies for dumb-bell test specimens . 17
Table 2 – Uniform characterization form (UCF) for an ECA . 37
Table 3 – Minimum required characteristics for the datasheet . 39
Table E.1 – Contact resistance between ECA and silver electrode . 49
Table E.2 – Contact resistance between ECA and silver electrode with z scores . 50
– 4 – IEC TS 62788-8-1:2024 © IEC 2024
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
MEASUREMENT PROCEDURES FOR MATERIALS USED
IN PHOTOVOLTAIC MODULES –
Part 8-1: Electrically conductive adhesive (ECA) –
Measurement of material properties
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
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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9) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
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shall not be held responsible for identifying any or all such patent rights.
IEC TS 62788-8-1 has been prepared by IEC technical committee 82: Solar photovoltaic energy
systems. It is a Technical Specification.
The text of this Technical Specification is based on the following documents:
Draft Report on voting
82/2200/DTS 82/2241/RVDTS
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 Technical Specification is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
A list of all parts in the IEC 62788 series, published under the general title Measurement
procedures for materials used in photovoltaic modules, 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.
– 6 – IEC TS 62788-8-1:2024 © IEC 2024
INTRODUCTION
Electrically conductive adhesive (ECA) is a material composed of conductive fillers blended
with an organic adhesive polymer matrix. Already widely used as an interconnect material in
electronic packaging and interconnection technologies for electronic devices, ECA is beginning
to replace metallic solders as an innovative interconnection method in recent designs of
photovoltaic (PV) modules. In a typical shingled PV module, solar cells are cut into strips and
these solar cell strips overlap each other. ECA is applied in between the top electrode of one
cell strip and the bottom electrode of the adjacent cell strip to form the electric interconnection.
In some back-contact PV module designs, ECA allows the interconnection of solar cells’ rear
busbars to a conductive backsheet. In some PV modules where the solar cells are sensitive to
high soldering temperatures, ECA is used to connect PV ribbons to the electrodes of the solar
cells. The solar cell interconnections based on ECA can effectively reduce mechanical stress,
shading loss and interconnect ohmic loss, and have been profiled as a promising alternative to
traditional soldering process.
ECA can be used for wiring and surface assembly in PV modules. Initial performance and
environmental endurance in application are highly dependent on its inherent material
characteristics. For instance, adhesive properties are the primary requirement for ECA. Good
adhesion between ECA and the adherends enables the structural integrity and long-term
durability of the bonded joint over its service lifetime. Furthermore, the electrical performances
of ECA, including volume resistance and contact resistance, are essential for the output
performance and field durability of PV modules. Other characteristics such as viscosity,
fineness, and conditions of use have a significant impact on the process conditions in
manufacturing.
It is impractical to perform all the tests on ECA at the PV module level. Evaluation of the inherent
material characteristics of ECA is highly desirable for pre-qualification of materials. This
document defines test methods for key characteristics of ECA intended for use in photovoltaic
modules.
The material property tests in this document cover general characteristics, mechanical
characteristics, adhesion characteristics, electrical characteristics, thermal characteristics and
the conditions of use.
MEASUREMENT PROCEDURES FOR MATERIALS USED
IN PHOTOVOLTAIC MODULES –
Part 8-1: Electrically conductive adhesive (ECA) –
Measurement of material properties
1 Scope
This document defines test methods and datasheet reporting requirements for key
characteristics of ECA used in photovoltaic modules, involving mechanical characteristics,
adhesive characteristics, electrical characteristics, thermal characteristics, etc.
The object of this document is to offer a standard test procedure to ECA manufacturers for
product design, production and quality control, and to PV module manufacturers for the purpose
of material screening, material inspection, process control, and failure analysis.
This document is intended to be applied to ECA used in solar PV modules.
For non-conductive adhesives or tapes used in PV modules, the applicable test methods except
for electrical characteristics in this document may be used.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60068-1, Environmental testing – Part 1: General and guidance
IEC TS 61836, Solar photovoltaic energy systems – Terms, definitions and symbols
IEC TS 62788-2, Measurement procedures for materials used in photovoltaic modules – Part 2:
Polymeric materials – Frontsheets and backsheets
ISO/IEC Guide 98-3:2008, Uncertainty of measurement – Part 3: Guide to the expression of
uncertainty in measurement (GUM:1995)
ISO 37:2017, Rubber, vulcanized or thermoplastic – Determination of tensile stress-strain
properties
ISO 291, Plastics – Standard atmospheres for conditioning and testing
ISO 1524:2020, Paints, varnishes and printing inks – Determination of fineness of grind
ISO 2393, Rubber test mixes – Preparation mixing and vulcanization – Equipment and
procedures
ISO 2811-1, Paints and varnishes – Determination of density – Part 1: Pycnometer method
ISO 4587, Adhesives – Determination of tensile lap-shear strength of rigid–to–rigid bonded
assemblies
– 8 – IEC TS 62788-8-1:2024 © IEC 2024
ISO 4664-1:2022, Rubber, vulcanized or thermoplastic – Determination of dynamic properties
– Part 1: General guidance
ISO 5893, Rubber and plastics test equipment – Tensile, flexural and compression types
(constant rate of traverse) – Specification
ISO 7500-2, Metallic materials – Verification of static uniaxial testing machines – Part 2:
Tension creep testing machines – Verification of the applied force
ISO 7886-1, Sterile hypodermic syringes for single use – Part 1: Syringes for manual use
ISO 8510-2, Adhesives – Peel test for a flexible-bonded-to-rigid test specimen assembly –
Part 2: 180 degree peel
ISO 10365, Adhesives – Designation of main failure patterns
ISO 11358-1, Plastics – Thermogravimetry (TG) of polymers – Part 1: General principles
ISO 11358-2, Plastics – Thermogravimetry (TG) of polymers – Part 2: Determination of
activation energy
ISO 11359-1, Plastics – Thermomechanical analysis (TMA) – Part 1: General principles
ISO 11359-2:2021, Plastics – Thermomechanical analysis (TMA) – Part 2: Determination of
coefficient of linear thermal expansion and glass transition temperature
ISO 16525-1:2014, Adhesives – Test methods for isotropic electrically conductive adhesives –
Part 1: General test methods
ISO 16525-2:2014, Adhesives – Test methods for isotropic electrically conductive adhesives –
Part 2: Determination of electrical characteristics for use in electronic assemblies
ISO 17212, Structural adhesives – Guidelines for surface preparation of metals and plastics
prior to adhesive bonding
ISO 23529:2016, Rubber – General procedures for preparing and conditioning test pieces for
physical test methods
ASTM D1337-10, Standard practice for storage life of adhesives by viscosity and bond strength
ASTM D4287-00, Standard Test Method for High – Shear Viscosity Using a Cone/Plate
Viscometer
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC TS 61836, together
with the following apply.
ISO and IEC maintain terminology 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
3.1
contact resistivity
electrical resistance that is generated on the contact surface between the isotropic electrically
conductive adhesive and the adherend
2.
Note 1 to entry: It is expressed in Ω·mm
Note 2 to entry: Contact resistivity is the resistance times the contact area.
[SOURCE: ISO 16525-2:2014, 3.3, modified – deleted and interfacial.]
3.2
coefficient of linear thermal expansion
-1
K
reversible increase in length of a material per unit length per degree change in temperature
[SOURCE: ISO 11359-2:1999, 3.2]
3.3
electrically conductive adhesive
adhesive consisting of conductive fillers that provide electrical conduction and resin that serves
for adhesion
Note 1 to entry: The resin can either be thermoplastic or cross-linked.
[SOURCE: ISO 16525-1:2014, 3.1, modified – deleted isotropic, added note.]
3.4
elongation at break
E
b
tensile strain in the test length at breaking point
[SOURCE: ISO 37:2017, 3.5]
3.5
four-probe method
method for measuring resistance that consists of two terminals for current application and two
terminals for voltage measurement
[SOURCE: ISO 16525-2:2014, 3.4]
3.6
fineness
reading obtained on a standard gauge under specified conditions of test, indicating the depth
of the groove(s) of the gauge at which discrete solid particles in the product are readily
discernible
Note 1 to entry: It is expressed in µm.
[SOURCE: ISO 1524:2020, 3.1, modified – fineness of grind was changed to fineness.]
3.7
lap shear strength
force per unit surface area necessary to bring an adhesive joint to the point of failure by means
of stress applied in the longitudinal mode, parallel to the plane of the bond-line
[SOURCE: EN 923:2015, 2.7.18]
– 10 – IEC TS 62788-8-1:2024 © IEC 2024
3.8
loss normal modulus
loss Young’s modulus
E′′
component of the applied normal stress, which is 90 degree out of phase with the normal strain,
divided by the strain
Note 1 to entry: It is expressed in Pa.
[SOURCE: ISO 4664-1:2022, 3.2.7]
3.9
peel strength
force per unit width necessary to bring an adhesive joint to the point of failure or to maintain a
rate of failure by means of a stress applied in the peeling mode
[SOURCE: EN 923:2015, 2.7.16]
3.10
pot life
maximum period of time during which the properties of ECA in working conditions could maintain
within the specified tolerances
[SOURCE: EN 923:2015, 2.4.24]
3.11
shelf life
time of storage under stated conditions during which an adhesive can be expected to retain its
working properties
[SOURCE: EN 923:2015, 2.4.33]
3.12
shingled PV module
solar cell module comprising solar cell strips arranged in a shingled manner
3.13
solids content
percentage by mass of non-volatile matter in a product determined under specified test
conditions
[SOURCE: EN 923:2015, 2.4.3]
3.14
elastic normal modulus
storage normal modulus
elastic Young’s modulus
E′
component of the applied normal stress, which is in phase with the normal strain, divided by
the strain
Note 1 to entry: It is expressed in Pa.
[SOURCE: ISO 4664-1:2022, 3.2.6]
3.15
tensile strength
maximum tensile stress recorded in extending the test piece to breaking point
[SOURCE: ISO 37:2017, 3.3]
3.16
test length of a dumb-bell
initial distance between reference points within the length of the narrow portion of a dumb-bell
test piece used to measure elongation
[SOURCE: ISO 37:2017, 3.10]
3.17
thixotropic index
ratio of viscosities measured at two shear rates
[SOURCE: ASTM D2556-14:2018, 3.2.2]
3.18
viscosity
property of resistance to steady flow exhibited within the body of the material
Note 1 to entry: It is expressed in mPa·s.
[SOURCE: ASTM D4092-07:2013, 3]
3.19
volume resistivity
electrical resistance of the isotropic electrically conductive adhesive for a given cross-sectional
area or given length
Note 1 to entry: It is expressed in Ω·mm.
Note 2 to entry: Volume resistivity is the volume resistance times the cross-sectional area divided by the length of
the sample.
[SOURCE: ISO 16525-2:2014, 3.2]
– 12 – IEC TS 62788-8-1:2024 © IEC 2024
4 Test procedures
4.1 General
Tests shall be carried out under standard atmospheric conditions as described in IEC 60068-1.
ECA is usually stored at a low temperature, and it shall be returned to the experimental ambient
temperature before test.
Specimens shall be pre-conditioned under 23 °C ± 2 °C and 50 % ± 10 % RH for at least 4 h,
as specified/recommended in ISO 291.
4.2 General characteristics
4.2.1 Visual inspection
4.2.1.1 Purpose
To identify and document visual defects in an ECA.
4.2.1.2 Sampling
ECA is normally supplied in tubular or canned containers. To obtain uniform specimens which
are adequately representative of the ECA being sampled, the following procedures shall be
applied:
a) For tubular package, the ECA shall be squeezed on a substrate with flat and smooth surface.
b) For canned packaging, open and stir well before visual inspection.
4.2.1.3 Procedure
Inspect the specimens under an illumination of not less than 1 000 lux at a 15 cm to 30 cm
viewing distance for the following:
a) colour inhomogeneity;
b) impurities;
c) bubbles;
d) any other phenomenon.
4.2.1.4 Reporting requirements
Report the following information:
a) Note and report the presence or absence of any phenomenon described in the procedure.
b) A photograph is recommended for documentation.
4.2.2 Density
4.2.2.1 Purpose
This test is performed to characterize the density of an ECA.
The density of an ECA can be measured according to ISO 2811-1. The test method consumes
a lot of samples and is not suitable for the daily inspection. In this subclause, a test method
using a small volume measuring tool, such as a syringe, is described.
4.2.2.2 Apparatus
A syringe with a nominal capacity of less than 5 ml, in accordance with ISO 7886-1.
An analytical balance, accurate to ± 1 mg.
4.2.2.3 Procedure
a) Weigh the empty syringe and record the reading as m .
b) Fill the syringe with a suitable amount of ECA from a tubular package. Or draw a suitable
amount of ECA into the syringe from a canned package. Ensure no bubbles exist at the
interface between the ECA and syringe. If there exist bubbles, push the plunger to push
some ECA and all bubbles out. Record the volume reading on the syringe where the plunger
is located as V.
c) Weigh the same syringe filled with ECA and record the reading as m .
d) Calculate the net weight m of the ECA specimen: m = m – m .
2 1
e) Calculate the density ρ, in grams per cubic centimetre.
f) For each ECA sample, at least three specimens shall be prepared and tested.
4.2.2.4 Result
The density of an ECA specimen can be calculated from Formula (1).
m
ρ= (1)
V
where
ρ is the density of ECA specimen (g/cm );
m is the weight of ECA specimen (g);
V is the volume of ECA specimen (ml).
4.2.2.5 Reporting requirements
Report the following information:
a) test equipment information;
b) test condition;
c) specimen quantity;
d) the density of each specimen and the mean value.
4.2.3 Viscosity
4.2.3.1 Purpose
This test is used to measure the viscosity of an ECA. Viscosity affects the production process,
and can also be used as an index to evaluate the stability of an ECA during storage and
application.
– 14 – IEC TS 62788-8-1:2024 © IEC 2024
4.2.3.2 Apparatus
The test apparatus shall conform to ASTM D4287-00.
A cone/plate type viscometer, with a viscosity test range from 1 000 mPa·s. to 1 000 000 mPa·s,
and viscosity test accuracy of at least 1,0 %. A speed of 0,5 rpm to 5 rpm is recommended for
viscosity test of conventional silicone based ECA with a viscosity range of 10 000 mPa·s to
100 000 mPa·s, and the rotor type should be selected according to the device type.
A constant-temperature bath, capable of maintaining a temperature from 5 °C to 80 °C with an
accuracy of 0,1 °C.
NOTE cP = 1 mPa·s.
ECA is a non-Newtonian liquid whose shear stress is not linearly related to shear rate, so the
data under different shear rates are not comparable. The ECA supplier and the user need to
reach an agreement on what kind of equipment and parameters should be used for the test.
4.2.3.3 Procedure
a) Turn on the viscometer and constant-temperature bath, and set the bath temperature to the
test temperature, which is recommended to be 25 °C.
b) Install an appropriate type of rotor and specimen cup. Adjust the rotor position to make sure
the distance between the rotor and the bottom of specimen cup equal to the clearance
recommended by the viscometer manufacturer.
c) Remove the specimen cup, transfer 0,5 ml to 2 ml ECA into the centre of the specimen cup,
and make sure no bubbles exist.
d) Install and fasten the specimen cup.
e) Set the rotor speed (ղ), time length and the data logging mode. It is recommended to use
the single-point data logging mode.
f) Test and record the data.
g) For each ECA sample, at least three specimens shall be prepared and tested.
Set an appropriate time length so that the output viscosity value tends to be stable and meets
the requirements of the date logging mode. Choose an appropriate rotor and set a proper rotor
speed so that the viscosity reading is between 10 % and 90 % of the full scale.
4.2.3.4 Reporting requirements
Report the following information:
a) test equipment information;
b) test condition: rotor type and size, speed, time length, temperature;
c) specimen quantity;
d) the viscosity of each specimen and the mean value.
4.2.4 Thixotropic index
4.2.4.1 Purpose
This subclause defines the method for measuring the thixotropic index of an ECA. The
thixotropic index has a profound impact on the printability of an ECA.
4.2.4.2 Apparatus
Refer to 4.2.3.2.
4.2.4.3 Procedure
a) Test the viscosity value at rotational speed ղ for a specimen.
b) After the test, let the specimen stand for 10 min before another viscosity test.
c) At the same setting, test the viscosity value again at rotational speed 10 ղ for the same
specimen.
d) For each ECA sample, at least three specimens shall be prepared and tested.
4.2.4.4 Result
The thixotropic index of an ECA specimen can be calculated from Formula (2).
viscosity @η rpm
TI=
(2)
vicosity @1 0η rpm
where
TI is the thixotropic index.
4.2.4.5 Reporting requirements
Report the following information:
a) test equipment information;
b) test condition: rotor type and size, speed, time length, temperature;
c) specimen quantity;
d) the thixotropic index of each specimen and the mean value.
4.2.5 Fineness
4.2.5.1 Purpose
The fineness of the ECA describes the size distribution of the discrete electrically conductive
particles in the resin filler. This subclause specifies a method for determining the fineness of
ECA filler with a suitable gauge.
4.2.5.2 Apparatus
Test apparatus shall meet the requirements in ISO 1524:2020.
The fineness plate shall be made of hardened steel blocks with a suitable dimension,
e.g. 175 mm in length, 65 mm in width and 13 mm in thickness.
The scraper shall be made of a single or double blade steel sheet with a recommended
dimension of 90 mm in length, 40 mm in width and 6 mm in thickness.
4.2.5.3 Procedure
Test procedure shall meet the requirements in ISO 1524:2020.
For each ECA sample, at least three specimens shall be prepared and tested.
– 16 – IEC TS 62788-8-1:2024 © IEC 2024
4.2.5.4 Reporting requirements
Record and report the following information:
a) the type of fineness plate;
b) test condition;
c) specimen quantity;
d) the fineness of each specimen and the mean value.
4.3 Mechanical characteristics
4.3.1 Tensile strength / elongation at break
4.3.1.1 Purpose
This subclause is to determine the tensile properties of an ECA.
4.3.1.2 Sampling
Prepare cured ECA films in thickness of 2 mm ± 0,1 mm without bubbles, according to ISO 2393.
Then prepare test specimens according to ISO 37:2017, which recommends specimen type 2
(see Figure 1). The test length of the specimen shall be 20,0 mm ± 0,5 mm.
The dimensions of a dumb-bell specimen shall meet the requirements given by the responding
die (see Figure 2 and Table 1).
For each ECA sample, at least three specimens shall be prepared and tested.
The test length shall not exceed the length of the narrow portion of the test piece.
Figure 1 – Shape of dumb-bell test specimen (ISO 37:2017)
Figure 2 – Die for dumb-bell test specimen
Table 1 – Dimensions of dies for dumb-bell test specimens
Dimension
Type 2
mm
A Overall length (minimum) 75
B Width of ends 12,5 ± 1,0
C Length of narrow portion 25 ± 1,0
D Width of narrow portion 4,0 ± 0,1
E Transition radius outside 8,0 ± 0,5
F Transition radius inside 12,5 ± 1,0
4.3.1.3 Apparatus
Test apparatus shall provide the following conditions:
a) Type 2 dumb-bell test specimens in compliance with ISO 37:2017 are recommended.
b) The thickness gauge shall meet the requirements specified in method A of ISO 23529:2016.
c) Tensile testing machine shall meet the requirements of ISO 7500-2 with accuracy of class 1.
d) The extensometer shall have an accuracy in compliance with Class D of ISO 5893.If using
a non-contact extensometer, mark the dumb-bell test pieces with two reference marks to
define the test length using a suitable marker.
4.3.1.4 Procedure
In the following, a test procedure using a contact extensometer is described. For non-contact
extensometers, a similar procedure can be used according to ISO 37:2017.
a) Measure the width and thickness at the centre and at each end of the test length in
millimetres with precision of 0,1 mm. Use the median value of the three measurements to
calculate the area of the cross-section. In any one dumb-bell, none of the three thickness
measurements of the narrow portion shall differ by more than 2 % from the median
thickness. The width of the test specimen shall be taken as the distance between the cutting
edges of the die in the narrow part.
b) Insert the test specimen into the tensile-testing machine, ensuring that the specimen is
gripped symmetrically so that the tension is distributed uniformly over the cross-section. It
is strongly recommended that the load cell be reset to zero before each test. If necessary,
apply a prestress of 0,1 MPa so that the test piece is not bent when the initial test length is
measured. Grippers shall have an inner surface that stably holds the material without
piercing and causing any other mechanical damage.
c) Clamp the extensometer on the specimen with 20 mm distance (see Figure 3). There shall
be no sign of distortion or damage to the test specimen.
d) Start the machine and monitor the change in length and force until the test part (see 20 mm
part in Figure 3) breaks.
e) The speed of the moving grip shall be 100 mm/min ± 10 mm/min.
f) The data shall be discarded and the test shall be repeated if the specimen breaks outside
the test length or if there is any slippage between the extensometer grip and the test
specimen that significantly affects the test results.
g) At least three specimens shall be tested.
– 18 – IEC TS 62788-8-1:2024 © IEC 2024
Dimensions in millimetre
Key
1 ECA specimen
2 grip
3 extensometer
Figure 3 – Schematic diagram of tensile strength and elongation at break test
4.3.1.5 Result
The tensile strength can be calculated from Formula (3).
The elongation at break can be calculated from Formula (4).
F
σ= (3)
W× t
LL−
t 0
ε ×100 %
(4)
L
where
σ is the tensile strength (MPa);
F is the force recorded at break (N);
W is the width of the narrow part of the specimen (mm);
t is the thickness of the test piece over the test length (mm);
ε is the elongation at break (%);
L is the initial test length (mm);
L is the test length at break (mm).
t
=
4.3.1.6 Reporting requirements
Record and report the following information:
a) test equipment information;
b) specimen information: curing condition, dimension, shape and quantity;
c) test condition;
d) tensile strength and elongation at break of each specimen and the median value.
4.3.2 Storage normal modulus and loss normal modulus
4.3.2.1 Purpose
This test is to quantify the storage normal modulus, loss normal modulus and loss factor (tanδ)
of ECA. Mechanical modulus directly affects the mechanical coupling between components,
including the stress and strain within the module. Results of the test offer great help in the
thermal mechanical analysis of PV modules, especially at the interconnection positions, where
ECA is the bonding material.
A dynamic test shall be performed to determine the normal modulus of ECA according to
ISO 4664-1:2022. In the test, a dynamic force (e.g. a sinusoidal force) is applied to the
specimen, and the displacement is measured. ECA is a viscoelastic material, i.e. it shows both
an elastic response and a viscous drag when strained. Storage normal E’ is the stiffness of the
viscoelastic material and proportional to the elastically stored energy while loss normal modulus
E’’ is proportional to the dissipated energy during the test. Loss factor tanδ is an indication of
the ratio between E’’ and E’. E’, E’’ and tanδ can be calculated from Formulas (5), (6) and (7).
These properties depend on excitation frequency and temperature. The maximum of the loss
factor (tanδ), is a good indicator to identify glass transition when the material behaviour changes
from energy-elastic to entropy-elastic.
4.3.2.2 Sampling
Prepare cured ECA films in thickness of 1 mm to 3 mm without bubbles first according to
ISO 2393. Cut the ECA film to make test specimen with dimensions about (30 mm to 60 mm) ×
(3 mm to 12 mm).
The specimen length between two clamps is defined as effective length and shall be controlled
within 15 mm to 20 mm.
Sandpapers could be used to smooth the specimen.
For each ECA sample, at least three specimens shall be prepared and tested.
4.3.2.3 Apparatus
A dynamic mechanical thermal analyser (DMA) according to ISO 4664-1:2022.
4.3.2.4 Procedure
The test shall be performed according to ISO 4664-1:2022 with small-sized test apparatus and
tensile mode selected.
a) Measure the width and thickness at the centre and at each end of the test length in
millimetres wit
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