IEC 62715-6-22:2023

IEC 62715-6-22
®

Edition 1.0 2023-03
INTERNATIONAL
STANDARD

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inside
Flexible display devices –
Part 6-22: Crease and waviness measurement methods
IEC 62715-6-22:2023-03(en)

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IEC 62715-6-22

®


Edition 1.0 2023-03




INTERNATIONAL



STANDARD








colour

inside










Flexible display devices –

Part 6-22: Crease and waviness measurement methods


























INTERNATIONAL

ELECTROTECHNICAL


COMMISSION





ICS 31.120 ISBN 978-2-8322-6628-1




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® Registered trademark of the International Electrotechnical Commission

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CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms, definitions and abbreviated terms . 8
3.1 Terms and definitions . 8
3.2 Abbreviated terms . 8
4 Standard atmospheric conditions . 8
5 Preparation of specimen for measurement . 9
5.1 General . 9
5.2 Visual examination . 9
5.3 Specimen preparation . 9
5.4 Measurement location . 12
5.4.1 General . 12
5.4.2 Crease. 12
5.4.3 Waviness . 12
6 Measurement methods . 12
6.1 General . 12
6.2 Purpose . 13
6.3 Non-contact topography . 13
6.3.1 General . 13
6.3.2 Test apparatus . 13
6.3.3 Measurement procedure . 17
6.3.4 Data analysis and report . 17
6.4 Non-contact profilometry . 20
6.4.1 General . 20
6.4.2 Test apparatus . 21
6.4.3 Measurement procedure . 22
6.4.4 Data analysis and report . 23
6.5 Contact profilometry . 24
6.5.1 General . 24
6.5.2 Test apparatus . 24
6.5.3 Measurement procedures . 26
6.5.4 Data analysis and report . 26
Bibliography . 27

Figure 1 – Step 1: Preparing the components of the specimen . 10
Figure 2 – Step 2: Turning the back of the panel to face upward . 10
Figure 3 – Step 3: Turning over the base plate and attaching it to the back of the panel . 10
Figure 4 – Step 4: Turning over the base plate with the panel attached . 11
Figure 5 – Example of measuring area . 12
Figure 6 – Example of measurement system . 14
Figure 7 – Analysis flow chart for PMD . 14
Figure 8 – Surface normal vector N, sight ray of a camera p and reflected ray r . 15
Figure 9 – Osculating circle and curvature . 16

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IEC 62715-6-22:2023 © IEC 2023 – 3 –
Figure 10 – Example of data distribution in the crease measuring area . 17
Figure 11 – Example of data grouping on the vertical direction with folding axis . 18
th
Figure 12 – Example of the N profile data . 18
Figure 13 – Example of data distribution in the waviness measuring area . 19
Figure 14 – Concept of filtering profile . 20
Figure 15 – Schematic of the result of laser scanning . 21
Figure 16 – Schematic diagram of the laser scanning apparatus . 21
Figure 17 – Example of position 1 and position 2 in the crease measuring area . 23
Figure 18 – Schematic diagram of the contact profilometry apparatus . 24
Figure 19 – Schematic diagram of the motion of probe . 25

Table 1 – Example of specimen preparation condition . 11
Table 2 – Example of crease data report using the PMD method . 19
Table 3 – Example of reporting waviness data . 20
Table 4 – Example of laser scanning apparatus condition . 22
Table 5 – Example of reporting crease data by the laser scanning method . 24
Table 6 – Example of stylus condition . 25

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INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

FLEXIBLE DISPLAY DEVICES –

Part 6-22: Crease and waviness measurement methods

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,
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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.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
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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.
IEC 62715-6-22 has been prepared by IEC technical committee 110: Electronic displays. It is
an International Standard.
The text of this International Standard is based on the following documents:
Draft Report on voting
110/1491/FDIS 110/1503/RVD

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.
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.

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IEC 62715-6-22:2023 © IEC 2023 – 5 –
A list of all parts in the IEC 62715 series, published under the general title Flexible display
devices, 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,
• replaced by a revised edition, or
• amended.

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
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INTRODUCTION
The market for foldable display devices is growing rapidly, as shown in the new form factors for
portable devices. It is expected that various foldable display devices will be released in the near
future.
Typically, the cover for rigid displays is made of glass. A rigid glass cover protects the display
panel from external shock and produces a surface uniformity without visual distortion. In order
to utilize a foldable display, a thin and flexible cover is preferred rather than the thick general
rigid cover. Although cover materials like thin films or plastics can be flexible, their surface is
rougher and can crease more easily. Based on this expectation, there is an anticipation to
standardize the measurement of surface creasing and waviness due to folding in order to
evaluate the surface quality of foldable displays.
There is a wide variety of ways to analyse the surface of an object, and many of them are
1
already standardized, [1] to [9] . In this document, two of the non-contact methods and one
contact method using a probe are described, and the manner in which to report the values of
crease and waviness of foldable displays from the measured data is specified.


___________
1
 Numbers in square brackets refer to the Bibliography.

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IEC 62715-6-22:2023 © IEC 2023 – 7 –
FLEXIBLE DISPLAY DEVICES –

Part 6-22: Crease and waviness measurement methods



1 Scope
This part of IEC 62715 specifies the standard measurement conditions and methods for
determining the surface crease and waviness for the evaluation of foldable displays. The
measurement methods are used to specify the extent of geometrical distortions in foldable
display surfaces. This document applies to foldable display panels and modules (e.g. in-folding
and out-folding) with one axis.
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 60050-845, International Electrotechnical Vocabulary (IEV) – Part 845: Lighting (available
at )
IEC 62341-1-2, Organic light emitting diode (OLED) displays – Part 1-2: Terminology and letter
symbols
IEC 62341-6-2:2015, Organic light emitting diode (OLED) displays – Part 6-2: Measuring
methods of visual quality and ambient performance
IEC 62715-5-3, Flexible display devices – Part 5-3: Visual assessment of image quality and
defects
IEC 62715-6-1, Flexible display devices – Part 6-1: Mechanical test methods – Deformation
tests
ISO 4287, Geometrical Product Specifications (GPS) – Surface texture: Profile method – Terms,
definitions and surface texture parameters
ISO 16610-21, Geometrical product specifications (GPS) – Filtration – Part 21: Linear profile
filters: Gaussian filters
ASME B46.1-2019, Surface Texture (Surface Roughness, Waviness, and Lay)

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3 Terms, definitions and abbreviated terms
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 62341-1-2 and
IEC 60050-845 and 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
3.1.1
crease
permanent or temporary linear visual distortion or deformation in the screen due to folding
3.1.2
waviness
long wavelength variation in a surface away from its basic form
Note 1 to entry: Within small areas of the display, distortions can occur in what should be nominally straight features
in images, characters, and symbols. This measurement characterizes the deviations from straightness.
3.1.3
folding area
curved section of the panel due to folding
3.2 Abbreviated terms
For the purposes of this document, the following abbreviated terms apply.
CCD charge-coupled device
CMM coordinate measuring machine
CMOS complementary metal-oxide semiconductor
DUT devices under test
LIDAR light detection and ranging
PMD phase measuring deflectometry
PSD position sensitive detector
4 Standard atmospheric conditions
The standard atmospheric conditions specified in IEC 62715-6-1 shall apply as follows, unless
otherwise specifically agreed between customer and supplier:
• temperature: 25 °C ± 3 °C
• relative humidity: 25 % RH to 85 % RH
• atmospheric pressure: 86 kPa to 106 kPa
The temperature and humidity conditions shall be reported.

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IEC 62715-6-22:2023 © IEC 2023 – 9 –
5 Preparation of specimen for measurement
5.1 General
In this document, the measurement object is called specimen, and the specimen consists of
foldable panel, modules, adhesive, base plate and jig. The description of the specimen's
components and how to configure them is specified in 5.3. All measurements shall be performed
under non-operating conditions.
5.2 Visual examination
The foldable display panel is subjected to visual and dimensional checks under non-operating
conditions and a functional check under operating conditions specified as follows:
a) non-operating conditions: visual damage on the surface of the specimen shall be checked;
b) operating conditions: visual assessment shall be done by the methods specified in
IEC 62715-5-3.
Unless otherwise specified, visual examination shall be performed under the conditions and
methods specified in IEC 62341-6-2:2015, 5.2.2.1.
NOTE The purpose of 5.2 is to check the surface damage or failure of the DUT before performing the measurement.
5.3 Specimen preparation
The conditions for the preparation of the specimen (e.g. plate, jig, number of cyclic folding tests,
folding duration time) and its size shall be determined between the supplier and customer.
If a mechanical test (e.g. cyclic folding test) is performed in the process of preparing the
specimen, the mechanical test method and condition shall be determined between the supplier
and customer before the preparation of the specimen. This mechanical test specified in
IEC 62715-6-1 and the test method and condition shall be reported.
NOTE 1 If the mechanical test is not performed in the process of preparing the specimen, the corresponding content
in Table 1 will be empty.
The temperature, humidity, storage time prior to testing, and the delayed time between the
specimen preparation and measurement can affect the crease and waviness, so the specimen
preparation condition and delayed time shall be controlled and reported.
NOTE 2 If the foldable display panel is unfolded and the time is delayed, the measurement result of the crease and
waviness can be smaller or alleviated due to the resilience of the panel. Therefore, the delayed time will be reported
as illustrated in Table 1.
The order and process of preparing the specimen are described as illustrated in Figure 1,
Figure 2, Figure 3, and Figure 4.
a) Step 1: Preparing the components of the specimen: The foldable display panel should be
unfolded after a specific duration time under the conditions which are reported in Table 1.
The base plate shall be flat and bigger than the foldable display panel. The jig with a flat
surface should be fixed to the base plate and have an adhesive on the top attached to the
back of the panel. The panel holder is used to prepare the out-folding type panel. It is a tool
to maintain the flatness of the panel while the jig is attached to the back of the panel in
step 2 and step 3. The height of the panel holder should be high enough that the folding
area does not touch the ground when the out-folding type panel is placed on it.
NOTE 3 Once the jig and the panel are attached, the panel holder is no longer necessary.

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Figure 1 – Step 1: Preparing the components of the specimen
b) Step 2: Turning the back of the panel to face upward: The method and location of the
attachment should not affect the measurement. In order to eliminate the influence of tensile
tension that can occur in the process of attaching the panel to the jig, the foldable panel
shall be flipped so that the back of the panel faces upward. In other words, as shown in
Figure 2, the light emitting surface of the panel is placed downward.

Figure 2 – Step 2: Turning the back of the panel to face upward
c) Step 3: Turning over the base plate and attaching it to the back of the panel. The base plate
shall also be flipped so that the adhesive surface faces downward. Then, lower the base
plate from the top down and attach it to the back of the panel.

Figure 3 – Step 3: Turning over the base plate and attaching it to the back of the panel
d) Step 4: Turning over the base plate with the panel attached. When the base plate with the
foldable panel attached is turned over, the top of the panel to be measured faces upward
and the specimen preparation is complete, as shown in Figure 4.

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IEC 62715-6-22:2023 © IEC 2023 – 11 –

Figure 4 – Step 4: Turning over the base plate with the panel attached
The description of each element is as follows:
'a' length of jig: It should be longer than the width (length of y-axis) of the foldable display
panel;
'b' height of jig: It should be high enough that the folding area does not touch the base plate.
It can be affected by the folding radius.
'c' unattached area: It should include the folding axis. The minimum value of 'c' should be at
least 10 times the foldable panel's bending radius or higher.
NOTE 4 To measure the crease, a folding area is located in the unattached area 'c' and the measurement
location will include the unattached area 'c'. The folding area depends on the foldable panel's bending radius.
The minimum range of the folding area will be a value obtained by multiplying the bending radius by pi (π).
Therefore, to prevent the effects of the fixation of the adhesive on the crease measurement, the unattached area
will be at least 10 times the foldable panel's bending radius.
'd' width of jig: It should not intrude the folding area, and it should support the foldable display
panel to keep it flat.
The values of 'c' and 'd' shall be determined by the supplier and customer and reported.
The measurement object should be a specimen which consists of the foldable panel fixed on
the jig and base plate for reproducibility of the measurement. It is also a similar condition to the
foldable panel inserted in the foldable device. However, the attachment method which consists
of adhesive fixing while preparing specimen should not affect the measurement. To prevent the
forcible pulling of the panel, the process of attaching the panel to the jig with the panel turned
over is necessary. This is described in step 2 and step 3. The attachment method shall be
reported.
An example of reporting the items for specimen preparation described in 5.3 is shown in Table 1.
Table 1 – Example of specimen preparation condition
Foldable
Base plate Folded storage condition
panel
1. Before 2. Folded state storage
3. Unfolded
Unattached
Specimen
folding condition
area ('c')
no.
Attachment Bending
Mechanical
(≥ 10 times
method radius
test Storage Delayed
the bending
Temp. Humidity
(type/ time time
radius)
number)
Adhesive Cyclic 25 °C ±
No. 1 20 mm 85 % 24 h 15 min 2 R
tape folding/100 3 °C

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If a specimen is ready, particles should be removed from the surface before the measurement,
using an appropriate cleaning method for the specimens, for example compressed air, wiping
with isopropyl alcohol, using an anti-static gun, etc.
5.4 Measurement location
5.4.1 General
Crease and waviness measurements can be taken at several specified locations on the foldable
display panel surface. The height and width of the measuring area shall be determined by the
supplier and customer.
5.4.2 Crease
A folding area which is the curved section of the foldable display panel due to folding shall be
located in the measuring area. This folding area should be located at the centre of the crease
measuring area. Figure 5a) is an example of the crease measuring area in the foldable display
panel.
5.4.3 Waviness
The measuring area of waviness shall not include an unattached area ('c', having a value of
10 times the foldable panel's bending radius or higher, as described in 5.3). In other words, the
measuring area shall be designated from the point at which it is at least 5 times the foldable
panel's bending radius away from the folding axis. Figure 5b) is an example of the waviness
measuring area in the foldable display panel.

(a) Example of crease measuring area location (b) Example of waviness measuring area location

Figure 5 – Example of measuring area
6 Measurement methods
6.1 General
In this document, three types of methods are described for implementation:
a) a non-contact method in which a screen is used to measure the surface without contact;
b) a non-contact method using a laser;
c) a contact method in which a stylus contacts the surface for measurement.
The contact method can be used when the non-contact method cannot be performed (e.g., the
display surface becomes matte after applying an anti-glare film and the image is not reflected).

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IEC 62715-6-22:2023 © IEC 2023 – 13 –
However, the contact method is not recommended since this method can damage the foldable
display surface.
The non-contact topography (see 6.3) can be adopted to measure both crease and waviness.
The non-contact profilometry (see 6.4) and contact profilometry (see 6.5) methods can be
adopted to measure c
...