Post on 15-Feb-2022
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Reliability and fitness for purpose testing of flexible
and wearable electronics
Dr Adam Lewis
adam.lewis@npl.co.uk
Electronic and Magnetic Materials 20/03/2018
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Performance and Lifetime of Printed SemiconductorsPresented by Dr Sebastian Wood
Tuesday 15 May 2018 (14:30 hrs UK time)
Printed semiconducting materials have great potential for a range of electronic applications, particularly
where large active areas or flexible/stretchable devices are required. This class of materials is expanding
rapidly, with specific interest currently in organic semiconductors and hybrid organic-inorganic lead-halide
perovskites. As these materials begin to see commercial uptake, their short operational lifetime has become a
critical limitation. NPL has developed a suite of tools for monitoring and understanding the degradation
mechanisms affecting these devices in order to guide their ongoing development
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simple Webinar Guidelines
The majority of webinars run for between 60–90 minutes, with a Q&A session. The webinars are limited to 100
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Reliability and fitness for purpose testing of flexible
and wearable electronics
Dr Adam Lewis
adam.lewis@npl.co.uk
Electronic and Magnetic Materials 20/03/2018
Book your NPL webinars online at http://www.npl.co.uk/science-technology/electronics-interconnection/webinars/
Outline
▪ Brief introduction to NPL
▪ What do we mean by ‘flexibles’ and ‘wearables’?
• Examples
• Material sets and components
▪ Failure modes
▪ Harsh environments
▪ Test methods and standards
▪ Metrology for large area electronics
▪ CORNET project
▪ Conclusions
5
Brief Introduction
National Physical
Laboratory
▪ World leading national measurement
institute founded in 1900
▪ Over 600+ specialists in
measurement science
▪ State-of-the-art standards facilities
Electronic and Magnetic
Materials Group
▪ Printed electronics, sensors and
metrology for wearables
▪ Embedded electronics
▪ High temperature interconnects
▪ Tin whisker mitigation
▪ Coating/SIR/Condensation testing
▪ Electronics recycling
▪ Organic photovoltaics
▪ Magnetic materials characterisation
6
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What do we mean by ‘flexible’ and
‘wearables’?
▪ Merging of textiles or flexible
substrates and electronics
• This could include
implantable devices
▪ Not a conventional PCB
made into a discrete
wearable device, e.g.
external heartrate monitor,
fitness watch
• These can be tested using
conventional test methods
Wearables/
Flexibles
Flexible substrates
Textiles and fabrics
Flexible interconnects
Hybrid flexi-ridged
Protective coatings
7
Wearable electronics
▪ Fully printed electronics
• Very limited functionality
• Smart labels/greeting cards
▪ Hybrid electronics
• Conventional packages,
conductive adhesive, printed
tracking
• Tactile feedback monitoring
– example
8
Sensor: printed or discrete (+ conductive adhesive)
Interconnection: printed/woven strand
Data processing/communication: PCB + conductive adhesive
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Examples of Printed, Flexible and
Wearable Electronics
9https://www.oled-info.com/new-audi-a8-sports-oled-rearlights
http://www.heliatek.com/en/applications/pilot-projects
https://flisom.com/products/
https://www.digitaltrends.com/cars/toyota-prius-prime-solar-roof/
Automotive
Aerospace
Energy
Examples of Printed, Flexible and
Wearable Electronics
10https://www.labelandnarrowweb.com/issues/2016-08-01/view_narrow-web-europe/french-labels-rising-gently/
https://cartamundi.com/en/press/cartamundi-imec-holst-centre-win-best-product-award-printed-electronics/
https://iecetech.org/issue/2017-01/New-edition-of-Standard-for-OLED-displays
https://www.yaabot.com/31512/smart-clothing-health-care/
Health monitoringConsumer electronicsSmart packaging
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Materials sets
▪ Substrates
PET , PEN, Textiles (woven, printed) …
▪ Adhesives (epoxy, acrylics)
mostly silver based
▪ Some solders
Low temp (SnBismth)
▪ Printed active devices (not typically moisture tolerant)
11
Low temperature
Failure modes: conductive
adhesive/tracking failure
▪ Increase in W of interconnect
Conductive particle oxidation
Ag oxides conducting
Polymer matrix swelling (moisture)
Breaking contact of conductive
particles
Bond-line failure
Resin to filler adhesion failure
Polymer relaxation (above Tg)
Component
PCB
Oxides Interfaces
Conduction paths
12
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Failure modes: conductive
adhesive/tracking failure
▪ Reduction in mechanical strength
• adhesive/component interface adhesion
• adhesive/substrate interface adhesion
• bulk material failure
▪ Component or substrate interconnect
failure
• Fracture or delamination
• Can be caused by bending/flexing
13
Failure modes: metal migration
▪ Dendritic growth from metals (typically
silver) under bias and in the presence of
moisture, causing low surface insulation
resistance
• Metal fillers are encapsulated in resin and
thus not in direct contact with moisture
• NPL has encountered issues with surface
insulation resistance testing of Ag
tracking materials
• Lifetime improved by printing dielectric
over the top
http://nepp.nasa.gov/whisker./dendrite/Ag_dendrite-02.jpg
14
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Harsh environments for
wearables
▪ Temperature
Often high temperatures are used as an acceleration factor for
conventional electronics – generally not suitable for wearables due
to low melting points etc.
▪ Humidity/moisture
▪ Chemical (sweat, detergent, shampoo …)
▪ Mechanical (stretch, bend, flex, …)
Typical daily
usage.
Washing
machine.
A combination of chemical contamination + moisture + bias voltage will
lead to electrochemical failures protective coatings15
Protection
▪ Coatings – conventional coatings, nano-coatings, etc.
• Most testing is done on new coatings
• Knowledge gap – how good are coatings that have
been in the field for x years?
• Evaluation methods:
• Repeat SIR/mechanical/other tests as performed on
new coating
• Chemical analysis – FTIR and other spectroscopic
analysis
16
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TEST METHODS
17
Test methods for wearables
▪ Peel test
▪ Shear test
▪ Bend/flex testing
▪ Stretch rig
▪ Pneumatic
adhesion tester
▪ Washing machine
trials
Standards
IPC-9204: Guideline on Flexibility and Stretchability Testing for Printed Electronics
IEC TC 119 – Printed Electronics
IEC TC 124 – Wearable Electronics Devices and Technologies 18
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Accelerated ageing regimes
▪ Damp heat ageing Causes joint resistance rises due
to oxidation of PCB, component
and conductive particle surfaces
Bond-line failures due to loss of
adhesion.
▪ Thermal cycling For low TCE components, during
thermal cycling, the mismatch to
PCB causes strain in joints,
resulting in crack initiation usually
along joint interfaces, causing
joint resistance increases and
failure.
19
SOIC/Material A
40C
85C
125C
40C
/93%
RH
85C
/85%
RH
125C
/93%
RH
-20C
/+80C
-55C
/+125C
0
20
40
60
80
100
% F
ailu
res(
>100%
Resis
tan
ce In
cre
ase)
Peel/tape test, shear test
▪ Peel/Tape TestTape adhered to printed ink on
surface and peeled off
Gives information about
adhesion strength
▪ Test shear strengthProbe moved across surface
Force require to shear
component measured
20
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Pneumatic adhesion tester
▪ Test to measure bonding of
tracking to substrate
▪ Attachment of 1cm stud to
printed ink
▪ Pressurised collar used to
“lift” stub from surface
▪ Issues with finding adhesive
for stub
21
Printed track
area
Stub
Adhesive
Substrate
SIR testing of wearables
▪ SIR testing involves
bias, moisture and
contaminants (flux)
▪ should this
contaminant be:
• synthetic sweat
• detergents
• shampoo
▪ AutoSIR
22
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Failure modes: cracking due to
bending
▪ Stress caused by bending
can cause cracks to from
across tracks:
• increased resistance
• open circuits.
23
Fabric, flexible and stretchable
sensors: stretch test
24
Rig designed to stretch
fabric and measure
resistance throughout
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Fabric, flexible and stretchable
sensors: stretch test
25
Fabric, flexible and stretchable
sensors: strain test
26
Rig designed to apply
pressure to fabrics and
measure resistance
throughout
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On-going stretch and flex testing
▪ Modified Instron Electropuls E3000
with electrical contacts
1. Measure resistance as function of
tensile extension (can be
monotonic or cyclically)
2. Novel bend test where clamp is
able to move to give control of
bend location and apply pressure
over bend rather than at clamp
location27
http://www.renewableenergyfocus.com/view/44227/developing-the-next-generation-of-flexible-solar-panels/
METROLOGY FOR LARGE
AREA ELECTRONICS
28
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Metrology during printing
Large Area Metrology
▪ Batch checking
▪ Optical inspection
• Track width, length, thickness
• Defects
▪ Functional analysis
• Sheet resistivity
• Contact (e.g. bed of nails)
• Non-contact
• PV efficiency
29
Printing technologies
Wide Range
▪ Screen printing
▪ Roll-to-roll processes
▪ Flexographic printing
▪ Gravure printing
▪ Offset lithography
▪ Inkjet printing
▪ Aerosol printing
Roar R Søndergaard et al. Roll-to-roll fabrication of polymer solar cells Mater. Today Jan-Feb 2012 Vol. 15 No. 1-2
(DOI: 10.1016/S1369-7021(12)70019-6)
30
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Non-contact electrical resistivity
measurements
Measurement principle
▪ Measurement of
coil inductance
▪ Simple model
Coil design
𝐹𝑆𝑅 =1
2𝜋 𝐿𝐶
𝑍 ≅ 𝑗𝜔𝐿 + 𝑅 𝑍 ≅1
𝑗𝜔𝐶
ω: angular frequency
δ: skin depth
µ: magnetic permeability
σ: conductivity
f: frequency
𝛿 ≈1
𝜋𝑓𝜇0𝜇𝑟𝜎
31
Non-contact electrical resistivity
measurements
Samples Typical sensor response
32A. Lewis et al. 2017 Flex. Print. Electron. 2 044001
https://doi.org/10.1088/2058-8585/aa9875
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Effect of frequency on measured
response
Skin-depth theory Sensors over frequency range
33
Non-contact electrical resistivity
measurements
In-situ roll-to-roll metrology
34
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Multiscale Modelling and Characterization to Optimize the
Manufacturing Processes of Organic Electronics Materials and
Devices (CORNET)
This project has received funding from the European Union’s HORIZON 2020 research and
innovation programme under Grant Agreement No 760949.
CORNET consortium
Part no. Participant Organisation Name Short Name Country Nature
1 Aristotle University of Thessaloniki AUTh Greece HE
2 University of Surrey USUR UK HE
3 University of Ioannina UOI Greece HE
4 Centre National de la Recherche Scientifique CNRS France RES
5 Fluxim Fluxim Switzerland SME
6 Aixtron AIXTRON Germany IND
7 National Physical Laboratory NPL UK RES
8 Organic Electronic Technologies P.C. OET Greece SME
9 Centro Riserche Fiat CRF Italy RES
10 Granta Design Granta UK SME
11 Hellenic Organic & Printed Electronics Association HOPE-A Greece OTH
This project has received funding from the European Union’s HORIZON 2020 research and
innovation programme under Grant Agreement No 760949.
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CORNET objectives1. Develop an Effective Open Innovation Environment (OIE) Connecting World-class Industrial, Academic & Research experts in Manufacturing, Multiscale Characterization & Modelling, for Optimization of OE Materials, Materials’ Behaviour & Process Optimization and for Reliable Database, Citable Protocols & Contribution to Standards (TRL4)
2. Multiscale Characterization & Modelling to Optimize OE Materials’ & Devices’ Fabricationand Validation of Materials’ Models for Faster Development Cycle and Time-to-market. (TRL4)
3. Optimization of the Fabrication of OPV, PPV & OLED Devices by R2R Printing and OVPDManufacturing Processes (TRL5)
4. Efficient Large scale Fabrication of Tailored (OPV, PPV, OLED) Nano-devices by R2R Printingand OVPD Processes and Demonstration to Industrial Applications (TRL6)
This project has received funding from the European Union’s HORIZON 2020 research and innovation programme
under Grant Agreement No 760949.
This project has received funding from the European Union’s HORIZON 2020 research and innovation programme
under Grant Agreement No 760949.
http://www.cornet-project.eu
CORNET website
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Conclusions
▪ Materials used are typically not suitable to high
temperature and hence we cannot use significantly higher
temperatures to accelerate failure mechanisms
▪ Harsh environments for wearable electronics are different
to conventional electronics
introduces new failure mechanisms
particularly harsh with regards in electrochemical and
mechanical aspects
▪ New test methods need to be developed. These will need
to be combinatorial to mimic realistic end usage.
testing of protective coatings is important for reliability39
Questions
The National Physical Laboratory is operated by NPL Management Ltd, a wholly-
owned company of the Department for Business, Energy and Industrial Strategy
(BEIS).
Adam Lewis
adam.lewis@npl.co.uk
40
▪ Acknowledgements:Martin Wickham, Kate Clayton,
Ling Zou, Laura Kent, Fernando
Castro, Tony Samano, Owen
Thomas
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Performance and Lifetime of Printed SemiconductorsPresented by Dr Sebastian Wood
Tuesday 15 May 2018 (14:30 hrs UK time)
Printed semiconducting materials have great potential for a range of electronic applications, particularly
where large active areas or flexible/stretchable devices are required. This class of materials is expanding
rapidly, with specific interest currently in organic semiconductors and hybrid organic-inorganic lead-halide
perovskites. As these materials begin to see commercial uptake, their short operational lifetime has become a
critical limitation. NPL has developed a suite of tools for monitoring and understanding the degradation
mechanisms affecting these devices in order to guide their ongoing development
In preparation for the event and to ensure you are equipped to gain the maximum benefit, please read our
simple Webinar Guidelines
The majority of webinars run for between 60–90 minutes, with a Q&A session. The webinars are limited to 100
delegates/companies. A copy of each of the slides presented and links to NPL reports will be provided after
the webinar
Book your place online at http://www.npl.co.uk/science-technology/electronics-interconnection/webinars/