IEC 62047-35:2019

IEC 62047-35 ®
Edition 1.0 2019-11
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Semiconductor devices – Micro-electromechanical devices –
Part 35: Test method of electrical characteristics under bending deformation
for flexible electromechanical devices

Dispositifs à semiconducteurs – Dispositifs microélectromécaniques –
Partie 35: Méthode d’essai des caractéristiques électriques sous déformation
par courbure de dispositifs électromécaniques souples

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IEC 62047-35 ®
Edition 1.0 2019-11
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Semiconductor devices – Micro-electromechanical devices –

Part 35: Test method of electrical characteristics under bending deformation

for flexible electromechanical devices

Dispositifs à semiconducteurs – Dispositifs microélectromécaniques –

Partie 35: Méthode d’essai des caractéristiques électriques sous déformation

par courbure de dispositifs électromécaniques souples

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 31.080.99 ISBN 978-2-8322-7636-5

– 2 – IEC 62047-35:2019 © IEC 2019
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
3.1 General . 7
3.2 Loading configurations . 7
3.3 Measure of loading levels . 8
4 Test piece . 8
4.1 General . 8
4.2 Shape of a test piece . 8
5 Test method . 9
5.1 Principle . 9
5.2 Test apparatus . 10
5.3 Procedure . 10
5.3.1 Testing conditions . 10
5.3.2 Selection of bending direction . 11
5.3.3 Determination of bending axes . 11
5.3.4 Measurement of test piece dimensions . 11
5.3.5 Measurement of folding distance . 12
5.3.6 Number of tests . 12
5.3.7 Instrumentation . 12
5.3.8 End of testing . 13
6 Test report . 13
6.1 General . 13
6.2 Bending direction(s) and in-plane locations of bending axes . 13
6.3 Dimensions of the test piece . 14
6.4 Performance degradation characteristics with the folding distance . 14
6.5 Distance at a defined operation limit . 15
6.6 Testing conditions . 15
Annex A (normative) Example of flexible MEMS device . 16
Annex B (informative) Controls for appropriate performance instrumentation and
setting of bending axis position . 18
B.1 Loading wall design with electric accessing cavity and fine adjustment
capability for bending axis location during the test . 18
B.2 Special arrangement of the target parts of device to obtain a number of
bending axis locations in a single testing . 19
Annex C (informative) Loading principle for extremely thin soft devices . 20
Annex D (informative) Issues related to local loading severity . 21
D.1 Possible inhomogeneity in local curvature and parameter of loading . 21
D.2 Possible variations of loading parameter . 21

Figure 1 – Schematic illustration of a flexible MEMS test piece . 9
Figure 2 – Principle of folding test . 10
Figure 3 – Selection of bending axis . 12
Figure 4 – Illustration of performance degradation in the test report . 14

Figure A.1 – Target part and loading configuration of test piece for organic thin-film
transistor device . 16
Figure A.2 – Device performance degradation behaviour and distances at defined

operation limits for an organic thin-film effect transistor . 17
Figure B.1 – Loading point adjustment mechanism . 18
Figure B.2 – Cascade arrangement of target parts for efficient testing . 19
Figure C.1 – Bending configuration . 20
Figure D.1 – Possibility of inhomogeneous local curvature distribution . 21

– 4 – IEC 62047-35:2019 © IEC 2019
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SEMICONDUCTOR DEVICES –
MICRO-ELECTROMECHANICAL DEVICES –
Part 35: Test method of electrical characteristics under bending
deformation for flexible electromechanical devices

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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indispensable for the correct application of this publication.
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patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 62047-35 has been prepared by subcommittee 47F: Micro-
electromechanical devices, of IEC technical committee 47: Semiconductor devices.
The text of this International Standard is based on the following documents:
FDIS Report on voting
47F/344/FDIS 47F/352/RVD
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.

A list of all parts in the IEC 62047 series, published under the general title Semiconductor
devices – Micro-electromechanical 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 "http://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 publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
– 6 – IEC 62047-35:2019 © IEC 2019
INTRODUCTION
In the recent trend toward ubiquitous sensor society and the world of internet of things,
demand and thus the market for softer electronic devices are quickly expanding. That is what
flexible micro-electromechanical devices are for, some of which are already released into the
market. Even a so-called foldable device is under development and will soon appear in the
market. However, to operate trillions of such devices for the comfort and safety of human
beings, the reliability of the individual devices is a critical concern. Especially in the case of
flexible devices, robustness against bending deformation is an important issue which is
shared among all the producers and users of such devices. In order to understand how safe a
situation is, critical conditions for possible dangers should be thoroughly determined so that
the potential risk can be for the first time managed. In this context, flexible devices should be
folded in two at least once so that every possible critical failure actually appears. This
standard procedure of testing is designed with the emphasis on such a point and with the
applicability not only to already emerging flexible devices but also to so-called foldable
devices which still function even when the device is folded.

SEMICONDUCTOR DEVICES –
MICRO-ELECTROMECHANICAL DEVICES –
Part 35: Test method of electrical characteristics under bending
deformation for flexible electromechanical devices

1 Scope
This part of IEC 62047 specifies the test method of electrical characteristics under bending
deformation for flexible electromechanical devices. These devices include passive micro
components and/or active micro components on the flexible film or embedded in the flexible
film. The desired in-plane dimensions of the device for the test method ranges typically from
1 mm to 300 mm and the thickness ranges from 10 µm to 1 mm, but these are not limiting
values. The test method is so designed as to bend devices in a quasi-static manner
monotonically up to the maximum possible curvature, i.e. until the device is completely folded,
so that the entire degradation behaviour of the electric property under bending deformation is
obtained. This document is essential to estimate the safety margin under a certain bending
deformation and indispensable for reliable design of the product employing these devices.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1 General
3.1.1
flexible micro-electromechanical system
flexible MEMS
device with structured semiconductor and/or mechanical components electrically connected to
each other, being assembled onto or embedded into flexible substrate and operated without
unacceptable loss of its functions under bending deformation
EXAMPLE Organic transistors, thermistors, smart diapers with wet sensors and smart epidermal patches for
health care, etc.
Note 1 to entry: This note applies to the French language only.
3.2 Loading configurations
3.2.1
bending axis
line on a device around which the device is bent with the minimum radius of curvature
Note 1 to entry: Due to the characteristics of this document, the bending axis can be and should be placed at
arbitrary positions in arbitrary directions in accordance with the requirements of the evaluation. The actual
positions and directions shall be intentionally determined according to the structures on the test piece.

– 8 – IEC 62047-35:2019 © IEC 2019
3.2.2
bending direction
direction in which the device is bent
3.3 Measure of loading levels
3.3.1
d
folding distance
distance between two loading walls, representing the load level applied to the device
Note 1 to entry: The degree of bending given to the device is here represented by the distance between two walls
approaching close to each other to bend the device, which is denoted as the folding distance.
Note 2 to entry: This measure may be optionally converted to the radius of curvature given around a bending axis
but it may not be uniform between the two walls especially when the rigidity distribution around the bending axis is
not homogeneous due to the heterogeneity of structures. More details are given in Annex D.
3.3.2
d
l
distance at defined operation limit
folding distance(s) corresponding to unacceptable deterioration(s) in the electrical
performance of the test piece
Note 1 to entry: More details can be found in Annex A.
4 Test piece
4.1 General
A flexible MEMS device, which is bent in use, can in principle be a test piece as it is and
subjected to the evaluation of this document. In principle, this test method is applicable
without restriction as to the size and shape of the devices. However, for ease of a load
application, it may be cut into a rectangular shape with target parts to be loaded at the center
as mentioned in 4.2. More methods for test piece preparation are suggested in Annex B.
4.2 Shape of a test piece
A rectangular shape of the test piece should be used for the ease of experiment as shown in
Figure 1. It may be necessary to cut out a part of the devices for the test, especially when the
target part to be tested, which determines its own functional feature, is not located in the
center of the device. In this case, the test piece shall be prepared in a rectangular form by
cutting a part out of the entire device with the target part located at the center of two parallel
edges which should also be parallel to the bending axis. This is because the point to be
loaded to the end is limited in this test method only along the bending axis likely coming out at
the center due to the loading scheme explained in 5.1.
In this document, the length l and the width w of test piece are the dimensions of the test
piece in the perpendicular and parallel direction to the bending axis, respectively. Because of
the structures assembled on or embedded in the flexible substrate, the thickness may not be
uniform over the entire device and hence depends on the location.
As a number of target parts can be arranged on a substrate, especially for testing purposes in
accordance with this document, some recommendations are given in Annex B.
NOTE The length and width can be interchangeable when the bending axis is rotated by 90°, which is
symbolically illustrated in Figure 3.

Key
1 target part 2 interconnects
3 electrodes 4 flexible substrate
5 bending axis 6 bending direction
7 length 8 width
9 thickness
Figure 1 – Schematic illustration of a flexible MEMS test piece
5 Test method
5.1 Principle
The principles of loading to the test piece are illustrated in Figure 2. The device shall be
inserted between two walls sliding closer to each other as illustrated in Figure 2 a). Then let
the distance between two walls, i.e. folding distance d, be gradually shortened as shown in
Figure 2 b) until finally touching each other with the folded test piece in between as in Figure
2 c). While the device is folded gradually tighter and tighter, its functions should be evaluated
to find which portion of the performance could be maintained while the folding distance is
applied.
– 10 – IEC 62047-35:2019 © IEC 2019

a) Initial stage b) Middle stage c) Final stage
Key
1 folding distance d
2 test piece
Figure 2 – Principle of folding test
5.2 Test apparatus
There is no special requirement for the configuration of the test apparatus in this document,
as long the device can be folded tighter and tighter until the end of the test. However, the
width and height of the walls shall be longer, preferably at least by 5 %, than the width and
half the length of the test piece, respectively, so that the whole test piece is firmly pressed by
the walls. The surface flatness and parallelism of the walls are carefully prepared so that they
do not to touch each other before the end of the test. The variance of the gap between the
walls shall be smaller than the thickness of the test piece. The surface roughness and
flatness of the walls are recommended to be less than 1/10 of the thickness of the test piece
so as not to distort the test piece by bumps of the wall except for the intended bending
deformation. Either wall or both walls are shifted by a motor drive system, or a manually-
actuated linear stage. A number of recommendations for the convenience of experiment can
be found in Annex B and Annex C.
The folding distance shall be measured to an accuracy of less than 5 % relative to the folding
distance itself. Therefore, it may be suggested to use a number of tools, for example a scale
for the millimeter range, a micrometer gauge for the submillimeter range, or a laser
displacement meter or microscopy for the micron and sub-micron range.
NOTE Not an absolute error for full range measurement but a relative error on the folding distance is of
importance to maintain the reproducibility in the bending deformation, especially around the end of the test,
because the nominal curvature can be approximated by 2/d under the bending deformation as shown in Figure 2b).
In addition, the value of d ranges from l, for example more than 100 mm, to 2t, for example values less than a
millimeter. The dimension with such a wide range is difficult to measure with an accuracy of less than 1 % by a
ready-made apparatus. That is why the accuracy of the folding distance is noted in terms of the relative value with
an accuracy of 5 % for the ease of experiment in this document.
5.3 Procedure
5.3.1 Testing conditions
Since the aim of this document is to see the deterioration behaviour of a device's performance
by bending to the end of possible curvature, it may not always be easy to find the testing
speed adequately corresponding to the conditions of the actual device operation. Therefore,
the evaluation of time-dependent deformation behaviour such as visco-elasticity is regarded
here as out of the scope, and thus the holding time between two loading steps before starting
the instrumentation as well as the loading speed itself are not specified here. It is here simply
suggested to keep the holding time for measurement the same for all the steps and be aware
of any drift after increasing the folding distance. The test speed and holding time determined
by the user shall be included in the test report, for example l per minute of the wall moving
speed and 1-min holding time per each measurement. Since substrates for flexible MEMS
may often be made of polymeric materials, the deformation behaviour should be in principle
more or less time-dependent. Non-elastic time-dependent behaviour should be mentioned in
the test report, if any is noticed.

Other conditions for testing, such as temperature and humidity, etc., shall be so far as
possible the same as those where the devices are operated in actual use.
NOTE 1 Since the aim of this document is to see the deterioration behaviour of the device's performance against
monotonic bending to the end of possible curvature, it may not be always easy to find testing conditions (especially
speed) which adequately correspond to those of the actual device operation. In such cases, the users are
responsible for determining the conditions and report them appropriately as mentioned in 6.6.
NOTE 2 When the length of the test piece l is 20 mm, the candidates for wall speed are 20 mm/min, 50 mm/min,
100 mm/min, 200 mm/min, etc. If a real-time monitoring system is available for measurement, the holding time can
possibly be zero.
5.3.2 Selection of bending direction
Set the test piece on the test apparatus, with the side to be loaded in a convex way facing
upward. Choice of this side, the bending direction in which the test piece is loaded, should
follow in principle the condition in which the device is actually bent during its service.
However, in order to explore possible failure modes, the two bending directions may be
examined regardless of how the device is actually used.
NOTE When a test piece as shown in Figure 1 is set on the test apparatus with the target part facing upward, the
test piece is loaded in a convex way and the target part is strained. On the other hand, for the test under the
opposite bending direction, the test piece is set with the target part facing downward and the target part is
compressed. In the test report, the curvilinear arrow is denoted in a concave form.
5.3.3 Determination of bending axes
Select a characteristic axis of individual devices to be tested. In addition, at least another
direction of 90° to this axis should also be tested as shown in Figure 3. The actual selection of
the directions is left to the suppliers and users. It is noted here that the actual bending axes
appearing at the end of the test may somehow not be exactly at the position expected, likely
because of a possible error in the test piece preparation and inhomogeneous stiffness
distribution over the device. Therefore, a fine adjustment of the bending axis location may be
necessary during the loading process. Possible methods for the precise control for this
adjustment are available in Annex B.
5.3.4 Measurement of test piece dimensions
The length and width of the test piece shall be measured and recorded for each test piece.
Measurement of the length of the device is critical because of the loading scheme explained
in 5.2. It shall be measured to an accuracy of 1 % relative to the length itself. Dimensions in
the direction parallel to the bending axis are not important but may also be measured in the
same way. Thickness may vary among different points over the test piece due to its
inhomogeneous structures. Therefore it shall also be measured at a number of typical points,
for example both the substrate part and the target part. A profilometer can measure the local
thickness of test piece with sufficient accuracy.
NOTE 1 As the preferable methods and accuracy in the measurement strongly depend on the individual devices,
nothing is normatively specified in this document. Instead, users of this procedure are responsible for choosing
adequate methods for their devices and reporting accuracy in the test report as described later.
NOTE 2 Since the distribution of thickness strongly depends on the structure of individual devices subjected to
the test, selection of measuring points is left to the users.
NOTE 3 It is optional to report the dimensions except for length because the width and the thickness are just a
supporting information for the design of the test apparatus for this document.

– 12 – IEC 62047-35:2019 © IEC 2019

a) 0° condition b) 90° condition

Key
1 target part 2 bending axis
3 bending direction 4 length
Figure 3 – Selection of bending axis
5.3.5 Measurement of folding distance
The distance between two walls is measured and recorded as the folding distance at each
measurement of the device performance. It shall be measured to an accuracy of 5 % relative
to the folding distance itself. Therefore, it may be suggested to use a scale for the millimeter
range, a micrometer gauge for the submillimeter range, or a laser displacement meter or
microscopy for the micron range.
5.3.6 Number of tests
A number of different positions shall be tested in the same way, i.e., a number of different
locations of the bending axes shall be loaded in this document. This is because the point of
the device to be loaded to the end is limited only along the bending axes, and because the
device may be bent at an arbitrary position in actual use. More details about the possible
issues and solutions to this problem are described in Annex B.
The number of test pieces to be tested is not specified in this document. However, as regards
the information on reproducibility, more than two specimens should be tested under the same
condition and the number shall be stated in the test report.
5.3.7 Instrumentation
Set the test piece on the apparatus and let the two walls come closer, step by step, to each
other. At each step, measure the folding distance d and the device performance (which are
the characteristic functions of the device) while loading. The test shall be continued until the
loading walls cannot be closer any more to each other. Finally, unload the folded test piece
and identify the exact location of the bending axis.

The device performance and its accuracy of measurement strongly depend on individual
devices. Therefore, nothing is normatively specified in this document. Instead, users of this
procedure should be responsible for adequate evaluation of the performance of their devices
and for reporting the accuracy of instrumentation in the test report as described in Clause 6.
5.3.8 End of testing
Stop the test when the walls will not come closer to each other anymore. It is not
recommended to stop the test before the folding distance reaches twice the maximum
thickness of the test piece.
Depending on the actuator system to drive the walls, the physical forces applied to the device
at this stage can change. Since this document is not for a compression test of folded devices,
testing should be stopped when an abrupt increase is detected by any means in the
resistance of walls against further driving.
NOTE The test piece can be bent as long as room remains on the concave side. Due to the thickness of the test
piece, however, the two loading walls cannot be closer to each other anymore beyond a certain point. This
situation is the end of the test. This is likely twice as long as the maximum thickness of the device but it also may
not always be exactly equal to it. Because the thickness may not be uniform for the case of structured devices as
explained in 4.2, room may still remain locally around the bending axis even when structures apart from the
bending axis touch each other so that the walls cannot be closer any more. In the meantime, when the point of
maximum thickness touches the other point with the thickness less than the maximum thickness, the distance at
the end of the test is obviously less than twice the maximum thickness.
6 Test report
6.1 General
The information in 6.2 to 6.6 shall be included in the test report of this document. The testing
conditions determined by users as mentioned in 5.3.1 shall be included as well.
6.2 Bending direction(s) and in-plane locations of bending axes
The bending direction(s) and detailed locations of the bending axes on the device shall be
reported, preferably with illustrations as shown in Figure 3 as an example. In case a test
piece was bent with more than one axis in a single test, it is highly recommended to dispose
of the result and try the test again with a shorter length of test piece (see Annex C).
The methods and accuracy of measurement for these parameters should be included in the
test report, though they are not normatively specified since they strongly depend on individual
devices.
– 14 – IEC 62047-35:2019 © IEC 2019

Key
1 distance at defined operation limit
Figure 4 – Illustration of performance degradation in the test report
6.3 Dimensions of the test piece
At least the length of the test piece shall be reported. However, other dimensions such as
width and thickness should be reported, if necessary.
NOTE Since a device is deformed by pushing its ends to come closer to each other for the case of the test shown
in Figure 2, the distance between the two ends, i.e., length, dominates its deformation against the folding distance
in the early stage of testing (Figure 2 a)). Therefore, length is the most essential parameter to be reported for each
test. In the meantime, although deformation is determined only by the folding distance and is independent of the
test piece dimensions in the middle stage (Figure 2 b)), the folding distance in the last stage (Figure 2 c)) is
intimately correlated with thickness distribution over the entire length and width of the test piece. Thus the width
and thickness are optionally reported in addition to length, in order to fully inform the geometrical characteristics of
the test piece.
6.4 Performance degradation characteristics with the folding distance
Supply in a graphical manner the relationship between the device performance plotted along
the ordinate and the folding distance d along the abscissa. Examples are shown in Figure 4.
The parameters along the ordinate can be selected in an arbitrary manner depending on the
device function to be examined, i.e. voltage, current or resistance. On the contrary, attention
should be paid to the parameter to indicate the folding distance along the abscissa. The
parameters along the abscissa may optionally be either the absolute distance between two
walls which is the original meaning of the folding distance, the distance between two walls
normalized by the length of the test piece, or the average diameter of curvature calculated
with the assumption of uniform bending deformation between the two walls. How the loading
parameter along the abscissa is defined shall be clearly stated in the report. The meanings of
these variations of the loading parameters are discussed further in Annex D.

6.5 Distance at a defined operation limit
If a sudden decrease of the device performance is noticeable and (or) the device performance
decreases beyond unacceptable levels (see item 1 of Figure 4) at certain points of loading,
the existence of these distances shall be reported in a separate comment to inform the users
and producers of the risk of the operation.
NOTE Since the degrees of sudden changes and unacceptable levels strongly depend on the individual cases of
the devices and their purposes of operation, a definition on what the operation limits are is left to the users'
subjective decision.
6.6 Testing conditions
The holding time between two loading steps before starting the instrumentation as well as the
loading speed itself are determined by the user and included in a test report, for example
10 mm/min of the wall moving speed and 1-min holding time for each measurement. Other
conditions for testing, such as temperature and humidity, etc., shall be also reported.
Since substrates for flexible MEMS are often made of polymeric materials, the deformation
behaviour should be in principle more or less time-dependent. Non-elastic time-dependent
behaviour should be mentioned in the test report, if any.

– 16 – IEC 62047-35:2019 © IEC 2019
Annex A
(normative)
Example of flexible MEMS device
Flexible MEMS devices may be composed of a number of characteristic structures with their
own functional features assembled together onto flexible substrates. For example, as shown
in Figure A.1, a flexible organic field effect transistor is composed of source, drain and gate
structures with silver-printed electrodes connecting them together. Such blocks of
components with their own functional features are here called target parts, whose
performance is subjected to evaluation in this document. Definitions of specific target parts
are not strictly determined nor limited by size, materials, features, but flexibly defined
depending on individual devices.
When flexible MEMS devices are subjected to bending deformation in a monotonically
increasing manner, sudden decreases of performance are occasionally observed as indicated
in Figure A.2 (item 2). This is likely due to a sudden fracture with local stress reaching critical
condition for the structural materials or their interfaces, which is often fatal to further
continuous service operation of devices. On the other hand, performance deterioration
beyond a certain level as also indicated in Figure A.2 (item 1) may occasionally not be
acceptable for a certain purpose of usage even if no sudden change is observed until then.
Both of these situations are indeed critical for device integrity. Since the degree of sudden
changes and unacceptable levels strongly depends on the individual cases of the devices and
their purposes of operation, nothing is normatively defined in this document to determine the
conditions for criticalness. Such a definition on what operation limits are is left to the users'
subjective decision. However, it is normatively required to report the folding distance at which
such limits are noticed as distances at defined operation limit. Examples are given in Figure
A.2.
a) Perspective view b) A-A' cross sectional view

Key
1 organic semiconductor 2 source electrode
3 gate electrode 4 drain electrode
5 bending axis 6 bending direction
7 insulation layer 8 smoothing layer
9 flexible substrate 10 target part
11 thickness
Figure A.1 – Target part and loading configuration of test piece for
organic thin-film transistor device

Key
1 distance at defined operation limit (20 % performance loss)
2 distance at defined operation limit (sudden change)
Figure A.2 – Device performance degradation behaviour and distances at defined
operation limits for an organic thin-film effect transistor

– 18 – IEC 62047-35:2019 © IEC 2019
Annex B
(informative)
Controls for appropriate performance instrumentation
and setting of bending axis position
B.1 Loading wall design with electric accessing cavity and fine adjustment
capability for bending axis location during the test
In order to keep measuring the performance appropriately to the end of the loading, electrical
contact should remain in the same situation while the device is being loaded with two walls.
For such a requirement, the walls may be shaped as illustrated in Figure B.1, where trenches
are dug out on the lower part of the walls to prevent the electrical contact from being pressed
by the walls. With this kind of modif
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