stretchable electronics for smart textiles -...

Stretchable Electronics for

Smart Textiles

J. Vanfleteren

IMEC – UGent/CMST Technology Park Building 914-A,

B-9052 Gent-Zwijnaarde, BELGIUM http://tfcg.elis.ugent.be/ or http://www.cmst.be/

[email protected]

http://tfcg.elis.ugent.be/

http://www.cmst.be/

mailto:[email protected]

Jan Vanfleteren COLAE Seminar

Gent, April 25, 2012 © imec/restricted 2012 2

Contents

• Introduction – options for comfortable electronics

• Stretchable Mould Interconnect (SMI) technologies

• Reliability / technology improvement

• Textile integration and washability

• Applications

• Conclusions and outlook



Contents





• Applications



Gent, April 25, 2012 © imec/restricted 2012



Introduction

• Wearable and implantable systems require lightweight, comfortable, conformable versions of electronics and sensor systems conventional large

rigid PCB’s are not acceptable

(Philips)





Introduction

2 facts to take into account for development of wearable and implantable circuits :

• Fact #1 : In industrial environment : electronic circuits are produced and assembled on flat substrates (rigid or flex)

• Fact #2 : Demand for complex systems requires the use of COTS (components-off-the-shelf) like commercial IC’s : microcontrollers, memory, display drivers, radio chips, etc.





Introduction – options for comfortable electronics

Option#1 : Small area flat substrates

Requires :

• Miniaturisation & high density integration

• Use of 3rd dimension of the substrate (multilayer, embedded & stacked components, folded flex)

• Possible embedding in 3D shaped biocompatible material

(Oticon)

Implantable pressure sensor

Together with KULeuven






Option#2 : non-flat substrates

Case#2a : application allows/requires compact, non-flat assemblies : • from flat to cylindrical or conical shape : possible to use flexible circuits • 3D integration for surface minimization

T. Torfs, FS2, App. Sess. 3

UTCP







Case#2a : application allows/requires compact, non-flat assemblies :

• from flat to any other shape (e.g. spherical : stretchable circuits necessary; e.g. spherical camera sensor, (J. Rogers group, Beckman Institute, U. Illinois)







Case#2b : application requires large area, distributed electronics, e.g. displays & signage, sensor arrays

• at least flex cylindrical or conical shape

• preferably stretchable circuit arbitrary shape

Stretchable circuit = (compact) rigid/flex functional islands with stretchable interconnects






Small area

Flex

Stretch

Large area

Flex

Stretch

Non-flat substrates

Flat substrates : small area

Unobtrusive circuits

(Use as functional islands in stretchable circuits)

UTCP SMI

Stretch_SD.avi





Contents





• Applications




Stretchable electronics

• Start from conventionally packaged sensors and electronic components, not available in flexible / elastic format circuits with advanced functionality possible

• Individual components or rigid/flexible component islands connected by stretchable wiring





• Conductive polymers : conductivity 3 orders of magnitude lower than metallic conductors – Intrinsic conductive polymers (PEDOT, PANI, Polypyrrole,…) – Stretchable insulating polymers with conductive fillers (e.g. Ag

filled silicones)

• Nanotechnology based materials : e.g. Metal Rubber™ of Nanosonic Inc. (www.nanosonic.com) : – Self-assembled nanocomposite material – Electrical resistance 5x10-6 Ω·cm

(Cu : 1.7 x 10-6 Ω·cm) – Max. elongation : 200% – Still extremely expensive

• Metallic conductors – Highest conductivity – Lowest cost – Standard use in PCB industry

Introduction - Stretchable wiring options

Our choice

But : metals not intrinsically stretchable ??

http://www.nanosonic.com/



Stretchable wiring – out of plane deformation of

metal interconnects

• Deposition of Cr/Au conductors on pre-stretched Silicone

(S. Lacour, Princeton University, New Jersey, USA)





• Lacour et al. (Princeton), IEEE Proceedings, August 2005)

•

Stretchable wiring – out of plane deformation of

metal interconnects



• Stretchability, while maintaining sufficient conductivity, obtained by meander-shaped fine-line metallic conductors - “2D springs”

• Mechanical Modelling : Stress under deformation (stretching) dependent on : – Wave shape (moderate) – Wave amplitude

(moderate) – Line width (drastic)

2D metallic springs – in plane deformation of

metallic interconnects

“multitrack” “horseshoe” shaped conductors



Overmoulding of pattern

plated Au tortuous wires

(Source : D. Gray et al.,

Johns Hopkins University,

Baltimore, MD, USA)

expensive process (evaporated silver sacrificial layer, batch processing (no reel-to-reel capabilities)

“MID” = Moulded

Interconnection

Device

2D metallic springs – in plane deformation of

metallic interconnects



CMST’s MID based processes overview

Technology ID Name

SMI-1 Plated conductor technology

SMI-2 Peelable substrate technology

SMI-3 Laser structured conductor technology

SCB-1 Stretchable substrate technology

Acronym Full Name Properties

SMI Stretchable Mould Interconnect

Circuit fabrication and component

assembly on sacrificial flex or rigid

substrate; stretchability introduced at

the end of the process

SCB Stretchable Copper Board

Start from elastic substrate;

circuit fabrication and component

assembly on this substrate



CMST’s MID (Mould Interconnect Device) processes

overview

Common technology properties :

• Key features : – Meander shaped interconnections

– Moulding technology

– Stress relief (rigid/flex/stretch transistions)

• Processes close to industrial printed circuit manufacturing use conventional leadfree solder

assembly process (250-260 degC)

• Completely embedded circuits – Washability

– Implantability



• (a) pattern plating of meander shaped metal wiring on metallic sacrificial substrate (e.g. Au plating on Cu foil)

• (b) mount components

• (c) mold/cast stretchable substrate material (silicone / poly-urethane)

• (d) remove sacrificial substrate (wet etch)

• (e) optionally mount additional components

• (f) apply second layer of stretchable material for complete embedding

SMI-1 : plated conductor technology

components

Underfill, adhesive Local stiffener

(a)

(b)

(c)

(d)

(e)

(f)

(a)

(b)

(c)

(d)

(e)

(f)

Elastic carrier

Flexible base material Meander shaped wiring



• All processing (including component assembly (b)) is done on non-stretchable substrate, similar to flex assembly

• completely embedded circuits possible (immersion in liquids, implantation)

• potential to produce non-planar (e.g. cylindric) circuits (by bending Cu foil + components before moulding)

• Process applicable for

• Any platable metal stack (Au, Ni/Cu/Ni/Au, Pt,..)

• Any liquid, curable stretchable materials (silicones (Dow Corning), polyurethanes,...)

• Back-etch of Cu sheet not environmentally friendly

components

Underfill, adhesive Local stiffener

(a)

(b)

(c)

(d)

(e)

(f)

(a)

(b)

(c)

(d)

(e)

(f)

Elastic carrier

Flexible base material Meander shaped wiring




Casting

Moulding

Sylgard 186

Stretchable materials selection

• Suppliers of silicone materials : DOW Corning, Nusil

• From stretchability point of view : Sylgard and Silastic are the most interesting DOW Corning materials

2703,060’ @150°CBLACK

Store @ -20°C1PrintingJCR6224

0,13707,4WL-5351

0,4516037,6Low-

temperature-

curable

Photopatternable

Store @ -15°C1Spinning

WL-5150

* Dowcorning

360 medical fluid

=>lower

viscosity

60470 15’ @100°C

Designed for

MEDICAL

device

encapsulation

Silastic

MDX-4210

3,91,916015’ @150°C

Used in literature

as a stretchable

dielectric2

base/curing agent

10:1

Spinning

Sylgard 184

Extra

products

needed

Viscosity

(Pa.s)

Young’s

Modulus

(MPa)

Elongation

(%)

CureRemarks# componentsWay of

application

Dowcorning

type

2703,060’ @150°CBLACK

Store @ -20°C1PrintingJCR6224

0,13707,4WL-5351

0,4516037,6Low-

temperature-

curable

Photopatternable

Store @ -15°C1Spinning

WL-5150

* Dowcorning

360 medical fluid

=>lower

viscosity

60470 15’ @100°C

Designed for

MEDICAL

device

encapsulation

Silastic

MDX-4210

3,91,916015’ @150°C

Used in literature

as a stretchable

dielectric2

base/curing agent

10:1

Spinning

Sylgard 184

Extra

products

needed

Viscosity

(Pa.s)

Young’s

Modulus

(MPa)

Elongation

(%)

CureRemarks# componentsWay of

application

Dowcorning

type



a) Injection of polymer to embed the first face

of system on cupper foil

b) Etching of the cupper substrate

c) Injection of the bottom layer of polymer

d) Unmolding the stretchable system

a

b

c

d

Moulding technology for polymer substrates



Mould Design

The areas where the

components are, are

thicker to make them

locally less

stretchable.





Use of solder mask for component assembly

• component assembly compatible / identical to standard flex circuit assembly

• low level stress at component assembly sites

0,5 mm

Component

Solder or ICA

Solder Mask (not removed)

Plated stretchable

interconnectionSilicone

1,5 mm

0,5 mm

Component

Solder or ICA


Plated stretchable


1,5 mmComponent

Solder or ICA


Plated stretchable


1,5 mm

8 lead SMD packaged temperature sensor assembled using adhesives and embedded in

PDMS (Dow Corning Silastic)





Operating blue LED under 35%

stretching

Stretch test of operating elastic

circuit

SMI-1 Demonstrators





Stretchable thermometer

Real-time temperature measurement

SMI-1 Demonstrators



Drawbacks of SMI-1 :

• Etching of (thick) uniform Cu sacrificial substrate

• Shorts between component pads when mounting components : – Impossible to assemble charged battery

– Impossible to check circuit functionality and to perform repair






SMI-2 : Peelable Substrate Technology

• Elimination of conducting sacrificial substrate : use polyimide (PI) flex or FR4 type carrier subsrate instead of metal foil

• No more plating of the conductors standard PCB Cu

• Process close to PCB manufacturing and component assembly practices (use of lead-free solder)

• Need for high-T temporary bonding adhesive (withstanding 250degC solder process)

Lamination

Lithography + wet etch

Embedding I

Peeling

Embedding II

Assembly

copper

wax

carrier

PDMS, PU component





SMI-2 demonstrators

• Inductive link (with KULeuven/ESAT/MICAS)

• 70micron Cu to ensure sufficient high Q-factor

• Water-proof operation (> 2 months)





Standard flex

PI + Cu

Laser cutting

Assembly +

Molding I

Molding II

Removal of

residues

copper

PI

wax

ceramic

silicone

component

• Very fast prototyping technology

• Cu on polyimide carrier high

reliability

• Industrialization of residue removal step ? Seems difficult

SMI-3 : Laser structured conductor technology

After laser cutting After residue removal





SMI-3 demonstrators

Stretchable watch (master thesis T. Vervust)

• Normally processed single-sided flex with laser cut stretchable interconnects

• Fully functional stretchable wrist watch inlcuding

• TI Microcontroller

• Rigid 4 x 7 segment TN LCD

• Pushbuttons

• Battery

• Passive components

• Lifetime : 1 year (battery)





SMI-3 demonstrators

2nd Approach :

• “perforated flex” : “stretchabilisation” of standard flexible circuit

• No real stretchable interconnects

• Less deformable, more reliable than 1st approach

• 7 x 8 LED matrix, driven by single chip

(charlieplexing)





SCB-1 : Stretchable substrate technology

copper

photoresist Silicone

component

• Rough copper base substrate (18 μm thick) (a)

• Spinning silicone (as thin as few 10s of microns) (b)

• Patterning the Cu (c)(d)

• Component assembly (now on stretchable substrate) (e)

• Conventional PCB manufacturing and component assembly flow

• use of high T stretchable material necessary to allow use of vapour phase reflow and SAC solder (260° C max.) for component assembly

(a)

(b)

(c)

(d)

(e)

(f)





Copper TW-TW

Spinned silicone Polyimide foil (no adhesion to cured silicone)

Patterned meanders and functional island in copper (Ni/Au plating)

Soldered components Final system

SCB-1 demonstrators





Comparison of the process flows

Technology Name

Lab

throughput

speed

Potential indutrial

throughput speed

Conductor

thickness

(micron)

Min. conductor

pitch (micron)

SMI-1Plated conductor

technologyslow (plating) slow (plating) 4 to 7 30

SMI-2Peelable substrate

technologyfast fast 17, 35, 70 100

SMI-3Laser structured

conductor technologyvery fast

slow (laser

structuring)9, 12, 17, 35… 50

SCB-1Stretchable substrate

technologyfast fast 17, 35, 70 100

Technology Name

Potential

indutrial

throughput

speed

Test before

embedding

Rework before

embedding

Rework after

embedding


technologyslow (plating) not possible not possible not possible


technologyfast possible possible not possible


conductor technology

slow (laser

structuring)possible possible not possible


technologyfast possible

possible, but

more difficultnot possible





Comparison of the process flows (2)

Technology Name Special features / issues


technology

very fine pitch possible

battery integration difficult

lots of waste (Cu substrate back-etch)


technology

need for high-T temporary bonding adhesive to avoid

process instability during solder assembly


conductor technologyCu meanders still on PI carrier; high reliability expected


technologylimited to high-T elastic carrier materials

Favourite technology, in terms of the state of technology development and potential industrialisation :

SMI-2 : Peelable substrate technology (SMI-3 (“perforated flex”) also used for fast prototyping)





Contents





• Applications






2 types of « stretchability » tests :

• 1-time stretchability (stretch until failure, i.e. loss of electrical connection)

• Cyclic stretching (more relevant for actual use)

Relevant cases :

• Reliability of stretchable interconnects

• Reliability of transition component / component island to stretchable interconnect

Measurements

• Electrical resistance

Reliability tests : uniaxial stretching

Reliability test vehicle (with or without interposer)





R = 900 µm

SMI-3 technology

W <= R/10

H = 0 => H0

H = 30deg => H30

H = 45deg => H45

3 type of “horseshoes” :

1-time stretchability

0

3

L : track

period

W : track

width





Reliability tests : Cyclic uniaxial stretching

Elo

ngation

Time 10s

20%

cycle

Ω

Instron 5543

• 3000 cycles until conductor break for – SMI-3 technology (laser cut Cu on PI)

– Track width W = 100µm

– Meander length L = 800µm

– Horseshoe angle = 30

– 20% elongation

• SMI-2 (pure Cu) behave worse


Gent, April 25, 2012 © imec/restricted 2012 42 42

• Cyclic uniaxial stretch tests on SMI-2 samples • Meander radius = 700m, metal track width = 100m • Period of stretch & release cycle = 2s • Monitoring of electrical continuity of stretchable interconnection lines


Movie.avi



Measurements

SMI-3 (Cu on PI) Ag filled PDMS shunt

End of life



y = 2E+06x-3.061

100

1000

10000

100000

1000000

1 10 100

Inte

rco

nn

ect lif

etim

e (

# c

ycle

s)

% strain

Lifetime of a stretchable interconnect

Ongoing experiment

• Lifetime decreases with % strain to the power 3 • At 10% strain : lifetime of 2500 cycles • At 2.5% : 500 000 cycles exceeded, test still ongoing • At lower strains (< 5%) : lifetime exceeds this law




1) Crack formation and propagation

avoid plastic deformation

by use of other metals

optimize meander design,

based on FEM modeling

reduce crack propagation

with PI support

2) Buckling :

reduce width of meander track (planned)

Support meander with PI

Reliability : failure modes and solutions





Reliability enhancement : Multitrack design

“Twirl” shape

Reliability enhancement by providing bridges





20% deformation 60% deformation

Non-lethal break

Reliability enhancement : Multitrack design



Straight tracks on component island: when stretched, a lot of stress is induced in the copper wiring, which breaks. Components on pads of stretch interconnects: when stretched, a lot of stress is on the solder joints and pads, which break.

Polyimide supporting the component island protecting the straight tracks and soldered joints

Polyimide supporting the stretchable copper conductors

metal

metal

B

support

support

metal

Reliability enhancement : component and

meander support for SMI-2



Standard

PCB

process

Temporary support

during process

Temporary adhesive

during process.

Melts when heated.

Strong and flexible

Polymer

Flexible support

for functional

Islands and

meanders





Flexible functional

island

Stretchable

interconnection

Rigid carrier Wax Adhesive layer





Completely embedded

in stretchable material





– Flexible supporting islands:

– Better transition between rigid interposers

and stretch connections

– Better transition between SMD components

and stretch connections

– Better transition from flex to stretch:

patterning supporting polyimide and copper

– Stretchable conductors:

– Support of stretchable conductors by

polyimide

Reliability enhancement : rigid-flex-stretch

transition improvements



– Molding improvement:

– Gradual transition (fillet) between thicker and thinner parts

Less local stress concentration at interface





Interposer integrated Rigid-flex-stretch transition

Molding improved Single layer:

multilayer interposer can be mounted





4 samples TM1-v1 5 samples TM1-v2

• cyclic strain of

10% @ 1% strain

rate

• supported

component islands

• non-supported

meanders

# Cycles to failure

Large spread





Failure modes : Meanders (m):

Interposer connection: - Base (B): - Thin buckle (T) - Wide buckle (W)

M T W B

Position on crossection:

• Failure mechanisms : breaking of supporting PI layer, Cu plastic

deformation

• Combination meander narrowing / thickness transition to be

optimised





Polyimide as mechanical meander support

Photodefinable polyimide significantly improves lifetime





Thin-film based SMI with double-sided PI meander

support

Cyclic strain : 10%

Strain rate : 10%/s

Lifetime > 500’000 cycles (4 tracks, 2 with PI and 50nm TiW/200nm Au same pattern, 2 with wider PI support)





Meander circuit design

• Meanders designed as “horseshoes” = connected circular segments

• Best stress distribution along the line

• Theoretical stretchability determined by α

Theoretical stretchability

in meander direction

Theoretical stretchability

perpendicular to meander

direction





Meander circuit design

Preliminary design rules :

• W/R < 0.1

• Practical stretchability 0.1*theoretical stretchability (H=0…45deg)

• W : determined by technology, determines also minimum R

• Application determines required practical stretchability, this determines horseshoe angle

L : track

period

W : track

width





Contents





• Applications




Interconnection: Principle

Stretchable test sample

with interconnection pads

Copper pad, free of silicone

Interconnect different stretchable modules

with: stitched conductor, embroidered wire,

conductive ribbon,…

Textile integration



Textile integration: procedure

63



Textile integration: Screenprinting PDMS gluing layer

9601

Viscosity (centipoise)

9600

186

280000

490000

66700

4575 184

Screenprinting done @ Centexbel

PDMS type Dow Corning 9600 textile glue

64



Lamination of silicone sheet (186) on textile via silicone layer of 9601

No silicone on backside

Viscosity

(centipoise)

186

9601

66700

280000

Silicone

Textile integration: Screenprinting PDMS gluing layer

65



7x8 led matrix on a T-shirt

Textile integration: Demonstrators

66



Molding allows creation of breathable zones (textile integration)

Technology extensions – textile integration



Stitched conductive yarn : Shieldex (PA + Ag)

Stitched contactpad

Sealed with silicone

(Mechanical and water

protection)

Stitched conductive yarn (done @ Centexbel Verviers)

Textile integration: Interconnection

68



Sealed with silicone

Soldered electric wire

Electric wires

Soldered


69



Soldering + sealing


70



Finished samples


71





Textile integration : washability

Complete

embedding creates

potential for

washability

JL-73



- On flexible substrate (lasercut) - Daisy chain of 0 Ohm resistors: 0603 and 0402 package - Dummy IC’s with daisy chain: TSSOP 28 and QFN 32 - Contact pads P1 to P43 to detect broken contacts in the chain - Contact pads are accessible for measurement trough openings in silicone

10cm

Purpose: Reliability of solder contacts of SMD components on flexible islands Mechanical test: washing


73

JL-74



Sample details: package types & measurement points

FR4 stiffeners underneath TSSOP and QFN

components

Reference sample Optimized sample


74

JL-75



Testsamples and test overview

=

For every test, 6 samples (5 optimized + 1 reference sample) Test effect of using protective bag during washing

Test reproducability of results


75

JL-76



1) Chain status after 25 cycles (woven, in bag) – reference sample:

2) Chain status after 25 cycles (woven, no bag) – reference sample:


76

JL-77



Crack in solder & copper Delamination

Failure on TSSOP leads

Failure analysis of reference sample:


JL-78



1) Chain status after 25 cycles (woven, in bag) - Optimized design:


78

JL-79



1) Woven, in bag

2) Woven, no bag

-

Both for optimized design Better with protective bag !


79

JL-80



1) Woven, in bag

3) Woven, in bag

Reproducible

Both for optimized design


80

JL-81



Cracks in flex of resistor chains

Failure analysis of optimized design:

Folding of flex (dummy IC islands)

Corners of flex sticking out of PDMS encapsulation

- Partner restricted PTW OCT. 2011 - HUMAN++


81

JL-82



1) Chain status after 25 cycles (knitted, in bag) - Optimized design:


No failures after 25 washing cycles !

No measurements at t=0 early failures might be

due to assembly

82

JL-83



1) Chain status after 25 cycles (knitted, not in bag) - Optimized design:


No failures after 25 washing cycles !

83





Contents





• Applications






Stretchable electronics applications

Stretchable electronics useful only if

• Application requires large surface with electronic components or modules, distributed over the area

or

• Circuit is too large and must be partitioned in single flex/rigid modules which are then connected with stretchable interconnects






Examples :

• Lighting, and especially LEDs – Wearable signage : leisure (party shirt), safety (signage in jackets for

road workers, bikers,…), advertising (the modern sandwich man),

– advanced lighting : atmospheric lighting in interior (upholstery, curtains, walls, etc.)

• Large area arrays with distributed sensors – Pressure sensors in mattress

• Body area sensor networks, and especially movement sensors – Fall detection

– orientation tracking, body posture tracking for : gaming & entertainment (advanced Wii), music & dance performances, revalidation, sports, medical applications (epileptic seizure detection)



PI + copper Soldermask applied PI + copper Soldermask applied

Philips EC-STELLA demonstrator: fitness monitor

Flexible islands for interposers

Smooth

flex-stretch transition




Functional boards mounted on flexible islands

Functionality of circuit tested before molding Molded demonstrator using Sylgard 186 PDMS

Fully Functional demo, The system includes a

wireless link, a rechargeable battery circuit and

accelerometers for activity detection.


Philips Activity Monitor

Developed in EU Project Stella

http://www.stella-project.de/



Embedded in Sylgard 186 by casting

Respiration sensor connections

Buzzer connections

Temporary flex connector Polyimide

Copper

Soldermask

Flexible island

Smooth

flex-stretch transition

Smooth

flex-stretch transition Verhaert EC-STELLA demonstrator: baby monitor




SMI Demonstrators

Verhaert Baby breathing demonstrator The demonstrator contains 79 components, 2 rubbery rulers and a buzzer.

The rubbery rulers are integrated in the moulded device acting as sensors for the breathing detection.

Developed in EU Project Stella

90

http://www.stella-project.de/



Party Shirt (5x10 full color led matrix)

SMI Demonstrators

Including wireless communication

91



Party Shirt (5x10 full color led matrix)

SMI Demonstrators

Fully integrated in T-shirt

92





Contents





• Applications




Conclusions and outlook

94

• Stretchable circuits were developed, based on meander shaped high-conductance Cu interconnects and liquid injection moulding technology

• The technology is to a large extent compatible with standard PCB circuit fabrication and assembly technology

• The feasibility of stretchable circuitry was proven by mechanical reliability tests and functional demonstrators

• Textile integration is feasible; washability up to 25 cycles proven for test samples on knitted substrates



• Industrialisation of the technology requires a chain of companies with various competences :

• Printed Circuit Board Manufacturers

• Electronic assembly companies

• Polymer processing specialists (moulding, …)

• Textile integrators (confection)

• End users

• Technology has reached the level of maturity to start building this chain

Conclusions and outlook



• EC-IST-FP6-IP-”STELLA” (STretchable ELectronics for Large Area applications) (contract nr. 028026) (http://www.stella-project.eu/)

• EC-IST-FP7-CA-”Systex” (co-ordination action on intelligent textile systems (since 05/2008) (http://www.systex.org/)

• Flemish IWT-SBO-”BioFlex” : Biocompatible Flexible and Stretchable Electronics circuits (http://tfcg.elis.ugent.be/projects/bioflex/)

• Belgian TAP2-”SWEET” : Stretchable and Washable Electronics for Embedding in Textiles (http://tfcg.elis.ugent.be/projects/sweet/)

• EC-IST-FP7-IP-Place-It – “Platform for Large Area Conformable Electronics by InTegration” (since 02/10) (http://www.place-it-project.eu/)

• EC-IST-FP7-IP-PASTA – “Integrating Platform for Advanced Smart Textile Applications” (starting 10/2010)

Acknowledgements

http://www.stella-project.eu/



http://www.systex.org/

http://tfcg.elis.ugent.be/projects/bioflex/

http://tfcg.elis.ugent.be/projects/sweet/

http://www.place-it-project.eu/







• J. Fjelstad et al. “Stretchable Circuits”, in “Flexible Circuit Technology”, 4th edition, BR Publishing, Seaside, USA, Chapter 13, pp. 478-513, November 2011.

• J. Vanfleteren et al., “Printed circuit board technology inspired stretchable circuits” MRS Bulletin, Vol.37, pp.254-260 , March 2012.

• T. Vervust et al., “Integration of stretchable and washable electronic modules for smart textile applications”, J. Textile Institute, 05 Mar 2012, 12 pages.

• Y.-Y. Hsu et al., "The effects of encapsulation on deformation behavior and failure mechanisms of stretchable interconnects", Thin Solid Films, Vol. 519, No. 7, pp. 2225-2234, Jan. 2011.

• R. Verplancke et al. “Thin-film stretchable electronics Technology based on meandering interconnections: fabrication and mechanical performance”, J. Micromech. Microeng., Vol.22, No1, published online December 8, 2011.

• Y.-Y. Hsu at al., “Polyimide-Enhanced Stretchable Interconnects: Design, Fabrication, and Characterization”, IEEE Trans. Electr. Dev., Vol. 58, No. 8, pp. 2680-2688, August 2011.

• Patents / patent applications : #US 7,487,587 B2 (February 10, 2009), #EP 1 746 869 B1 (July 27, 2011), #US 2009 0107704 A1 (April 30, 2009), #WO 2010/086416 A1 (August 5, 2010), #WO 2010/086033 A1 (August 5, 2010), #WO 2010/086034 A1 (August 5, 2010),

Recent publications





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