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/
Jan.vanfleteren@elis.ugent.be
Contents
• Introduction – options for comfortable
electronics
• Stretchable Mould Interconnect (SMI)
technologies
• Reliability / technology improvement
• Textile integration and washability
• Applications
• Conclusions and outlook
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
Jan Vanfleteren
COLAE Seminar
Gent, April 25, 2012
© imec/restricted 2012
3
Introduction
• Wearable and implantable systems require
lightweight, comfortable, conformable versions of
electronics and sensor systems  conventional large
rigid PCB’s are not acceptable
(Philips)
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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.
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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
Together with
KULeuven
components, folded flex)
• Possible embedding in 3D shaped
biocompatible material
(Oticon)
Implantable pressure sensor
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Introduction – options for comfortable electronics
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
UTCP
T. Torfs, FS2,
App. Sess. 3
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Introduction – options for comfortable electronics
Option#2 : non-flat
substrates
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)
Jan Vanfleteren
COLAE Seminar
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Introduction – options for comfortable electronics
Option#2 : non-flat substrates
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
Jan Vanfleteren
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Introduction – options for comfortable electronics
Unobtrusive
circuits
Flat substrates :
small area
UTCP
Flex
Non-flat
substrates
SMI
Small area
Stretch
Large area
Stretch
Flex
(Use as functional islands in stretchable circuits)
Jan Vanfleteren
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Contents
• Introduction – options for comfortable
electronics
• Stretchable Mould Interconnect (SMI)
technologies
• Reliability / technology improvement
• Textile integration and washability
• Applications
• Conclusions and outlook
Jan Vanfleteren
COLAE Seminar
Gent, April 25, 2012
© imec/restricted 2012
11
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
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Introduction - Stretchable wiring options
• 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
Our choice
But : metals not intrinsically stretchable ??
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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)
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Stretchable wiring – out of plane deformation of
metal interconnects
• Lacour et al. (Princeton),
IEEE Proceedings, August
2005)
•
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2D metallic springs – in plane deformation of
metallic 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)
–
“multitrack” “horseshoe” shaped conductors
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2D metallic springs – in plane deformation of
metallic interconnects
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-toreel capabilities)
“MID” = Moulded
Interconnection
Device
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CMST’s MID based processes overview
Acronym
Full Name
SMI
Stretchable Mould Interconnect
SCB
Stretchable Copper Board
Technology ID
SMI-1
SMI-2
SMI-3
SCB-1
Properties
Circuit fabrication and component
assembly on sacrificial flex or rigid
substrate; stretchability introduced at
the end of the process
Start from elastic substrate;
circuit fabrication and component
assembly on this substrate
Name
Plated conductor technology
Peelable substrate technology
Laser structured conductor technology
Stretchable substrate technology
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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
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SMI-1 : plated conductor technology
(a)
Flexible base material
components
Meander shaped wiring
(b)
Local stiffener
Underfill, adhesive
(c)
Elastic carrier
(d)
(e)
(f)
• (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
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SMI-1 : plated conductor technology
•
(a)
Flexible base material
components
Meander shaped wiring
(b)
Local stiffener
Underfill, adhesive
(c)
•
•
Elastic carrier
(d)
•
(e)
(f)
•
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
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Stretchable materials selection
Dowcorning
type
Way of
application
Sylgard 184
Sylgard 186
Silastic
MDX-4210
Spinning
Casting
Moulding
# components
Remarks
Cure
Elongation
(%)
Young’s
Modulus
(MPa)
Viscosity
(Pa.s)
2
Used in literature
as a stretchable
dielectric
15’ @150°C
160
1,9
3,9
Designed for
MEDICAL
device
encapsulation
15’ @100°C
470
base/curing agent
10:1
WL-5150
Spinning
1
WL-5351
JCR6224
Printing
1
Photopatternable
Store @ -15°C
BLACK
Store @ -20°C
60
Extra
products
needed
* Dowcorning
360 medical fluid
=>lower
viscosity
Lowtemperaturecurable
60’ @150°C
37,6
160
0,45
7,4
370
0,1
3,0
270
• Suppliers of silicone materials : DOW Corning, Nusil
• From stretchability point of view : Sylgard and Silastic are
the most interesting DOW Corning materials
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Moulding technology for polymer substrates
a
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
b
c
d
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Mould Design
The areas where the
components are, are
thicker to make them
locally less
stretchable.
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Use of solder mask for component assembly
1,5 mm
Component
Solder or ICA
Solder Mask (not removed)
0,5 mm
•
•
Plated stretchable
interconnection
Silicone
component assembly compatible / identical
to standard flex circuit assembly
low level stress at component assembly
sites
8 lead SMD packaged temperature sensor
assembled using adhesives and embedded in
PDMS (Dow Corning Silastic)
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SMI-1 Demonstrators
Operating blue LED under 35%
stretching
Stretch test of operating elastic
circuit
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SMI-1 Demonstrators
Stretchable thermometer
Real-time temperature measurement
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SMI-1 : plated conductor technology
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
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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)
copper
wax
carrier
PDMS, PU
component
Lamination
Lithography + wet etch
Assembly
Embedding I
Peeling
Embedding II
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SMI-2 demonstrators
• Inductive link (with
KULeuven/ESAT/MICAS)
• 70micron Cu to ensure
sufficient high Q-factor
• Water-proof operation (>
2 months)
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SMI-3 : Laser structured conductor technology
Standard flex
PI + Cu
copper
PI
wax
ceramic
silicone
Laser cutting
Removal of
residues
component
• Very fast
prototyping
technology
• Cu on polyimide
carrier  high
reliability
• Industrialization of
residue removal
step ? Seems
difficult
Assembly +
Molding I
Molding II
After laser cutting
After residue removal
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SMI-3 demonstrators
• 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)
Stretchable watch (master thesis T. Vervust)
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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)
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SCB-1 : Stretchable substrate technology
(a)
(b)
(c)
(d)
(e)
(f)
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
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COLAE Seminar
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SCB-1 demonstrators
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
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Comparison of the process flows
Technology
SMI-1
SMI-2
SMI-3
SCB-1
Technology
SMI-1
SMI-2
SMI-3
SCB-1
Name
Plated conductor
technology
Peelable substrate
technology
Laser structured
conductor technology
Stretchable substrate
technology
Name
Plated conductor
technology
Peelable substrate
technology
Laser structured
conductor technology
Stretchable substrate
technology
Lab
throughput
speed
Potential indutrial
throughput speed
Conductor
thickness
(micron)
Min. conductor
pitch (micron)
slow (plating)
slow (plating)
4 to 7
30
fast
fast
17, 35, 70
100
very fast
slow (laser
structuring)
9, 12, 17, 35…
50
fast
fast
17, 35, 70
100
Potential
indutrial
throughput
speed
Test before
embedding
Rework before
embedding
Rework after
embedding
slow (plating)
not possible
not possible
not possible
fast
possible
possible
not possible
slow (laser
structuring)
possible
possible
not possible
fast
possible
possible, but
more difficult
not possible
Jan Vanfleteren
COLAE Seminar
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Comparison of the process flows (2)
Technology
Name
SMI-1
Plated conductor
technology
SMI-2
SMI-3
SCB-1
Peelable substrate
technology
Laser structured
conductor technology
Stretchable substrate
technology
Special features / issues
very fine pitch possible
battery integration difficult
lots of waste (Cu substrate back-etch)
need for high-T temporary bonding adhesive to avoid
process instability during solder assembly
Cu meanders still on PI carrier; high reliability expected
limited 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)
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Contents
• Introduction – options for comfortable
electronics
• Stretchable Mould Interconnect (SMI)
technologies
• Reliability / technology improvement
• Textile integration and washability
• Applications
• Conclusions and outlook
Jan Vanfleteren
COLAE Seminar
Gent, April 25, 2012
© imec/restricted 2012
38
Reliability tests : uniaxial stretching
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 test vehicle (with
or without interposer)
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1-time stretchability
W : track
width
3
L : track
period
0
3 type of “horseshoes” :
H = 0 => H0
H = 30deg => H30
H = 45deg => H45
R = 900 µm
SMI-3 technology
W <= R/10
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Elongation
Reliability tests : Cyclic uniaxial stretching
20%
cycle
10s Time
• 3000 cycles until conductor break
for
Ω
–
–
–
–
–
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
Instron 5543
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Reliability tests : Cyclic uniaxial stretching
•
•
•
•
Cyclic uniaxial stretch tests on SMI-2 samples
Meander radius = 700m, metal track width = 100m
Period of stretch & release cycle = 2s
Monitoring of electrical continuity of stretchable interconnection lines
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Measurements
End of life
SMI-3 (Cu on
PI)
Ag filled PDMS
shunt
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Reliability tests : Cyclic uniaxial stretching
Lifetime of a stretchable interconnect
Ongoing experiment
Interconnect lifetime (# cycles)
1000000
100000
10000
1000
y = 2E+06x-3.061
100
1
•
•
•
•
10
% strain 100
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
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Reliability : failure modes and solutions
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
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Reliability enhancement : Multitrack design
“Twirl” shape
Reliability enhancement by providing bridges
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Reliability enhancement : Multitrack design
Non-lethal break
20% deformation
60% deformation
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Reliability enhancement : component and
meander support for SMI-2
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.
metal
metal
Polyimide supporting the component island
protecting the straight tracks and soldered
joints
B
Polyimide supporting the stretchable copper
conductors
support
metal
support
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Reliability enhancement : component and
meander support for SMI-2
Temporary support
during process
Strong and flexible
Polymer
Flexible support
for functional
Islands and
meanders
Temporary adhesive
during process.
Melts when heated.
Standard
PCB
process
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Reliability enhancement : component and
meander support for SMI-2
Flexible functional
island
Rigid carrier
Stretchable
interconnection
Wax Adhesive layer
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Reliability enhancement : component and
meander support for SMI-2
Completely embedded
in stretchable material
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Reliability enhancement : rigid-flex-stretch
transition improvements
– 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
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Reliability enhancement : rigid-flex-stretch
transition improvements
– Molding improvement:
– Gradual transition (fillet) between thicker and thinner parts
Less local stress concentration at interface
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Reliability enhancement : rigid-flex-stretch
transition improvements
Interposer integrated
Single layer:
multilayer interposer can be mounted
Rigid-flex-stretch transition
Molding improved
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Reliability enhancement : rigid-flex-stretch
transition improvements
4 samples TM1-v1
5 samples TM1-v2
# Cycles to failure
• cyclic strain of
10% @ 1% strain
rate
• supported
component islands
• non-supported
meanders
Large spread
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Reliability enhancement : rigid-flex-stretch
transition improvements
• Failure mechanisms : breaking of supporting PI layer, Cu plastic
deformation
• Combination meander narrowing / thickness transition to be
optimised
Failure modes :
Position on crossection:
Meanders (m):
M T W
B
Interposer connection:
- Base (B):
- Thin buckle (T)
- Wide buckle (W)
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Polyimide as mechanical meander support
Photodefinable polyimide significantly improves lifetime
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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)
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Meander circuit design
Theoretical stretchability
in meander direction
Theoretical stretchability
perpendicular to meander
direction
• Meanders designed as
“horseshoes” =
connected circular
segments
• Best stress distribution
along the line
• Theoretical stretchability
determined by α
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Meander circuit design
W : track
width
L : track
period
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
Jan Vanfleteren
COLAE Seminar
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60
Contents
• Introduction – options for comfortable
electronics
• Stretchable Mould Interconnect (SMI)
technologies
• Reliability / technology improvement
• Textile integration and washability
• Applications
• Conclusions and outlook
Jan Vanfleteren
COLAE Seminar
Gent, April 25, 2012
© imec/restricted 2012
61
Textile integration
Interconnection: Principle
Copper pad, free of silicone
Stretchable test sample
with interconnection pads
Interconnect different stretchable modules
with: stitched conductor, embroidered wire,
conductive ribbon,…
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Textile integration: procedure
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Textile integration:
Screenprinting PDMS gluing layer
PDMS type Viscosity (centipoise)
9601
280000
9600
184
186
490000
4575
66700
Dow Corning 9600 textile glue
Screenprinting done @ Centexbel
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Textile integration:
Screenprinting PDMS gluing layer
Silicone
Viscosity
(centipoise)
186
9601
66700
280000
No silicone on backside
Lamination of silicone sheet (186) on textile via silicone layer of 9601
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Textile integration: Demonstrators
7x8 led matrix on a T-shirt
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Technology extensions – textile integration
Molding allows creation of breathable zones (textile integration)
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Textile integration: Interconnection
Stitched conductive yarn (done @ Centexbel Verviers)
Stitched conductive yarn : Shieldex (PA + Ag)
Stitched contactpad
Sealed with silicone
(Mechanical and water
protection)
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Textile integration: Interconnection
Soldered electric wire
Soldered
Electric wires
Sealed with silicone
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Textile integration: Interconnection
Soldering + sealing
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Textile integration: Interconnection
Finished samples
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Textile integration : washability
Complete
embedding creates
potential for
washability
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JL-73
Textile integration : washability
Purpose: Reliability of solder contacts of SMD components on flexible islands
Mechanical test: washing
10cm
- 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
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JL-74
Textile integration : washability
Sample details: package types & measurement points
Reference sample
Optimized sample
FR4 stiffeners underneath
TSSOP and QFN
components
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JL-75
Textile integration : washability
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
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JL-76
Textile integration : washability
1) Chain status after 25 cycles (woven, in bag) – reference sample:
2) Chain status after 25 cycles (woven, no bag) – reference sample:
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JL-77
Textile integration : washability
Failure analysis of reference sample:
Crack in solder & copper
Delamination
Failure on TSSOP leads
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JL-78
Textile integration : washability
1) Chain status after 25 cycles (woven, in bag) - Optimized design:
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JL-79
Textile integration : washability
1) Woven, in bag
Both for optimized design
Better with protective bag !
2) Woven, no bag
-
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JL-80
Textile integration : washability
1) Woven, in bag
Both for optimized design
3) Woven, in bag
Reproducible
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JL-81
Textile integration : washability
Failure analysis of optimized design:
Corners of flex sticking out of PDMS encapsulation
Cracks in flex of resistor chains
Folding of flex (dummy IC islands)
- Partner restricted
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JL-82
Textile integration : washability
1) Chain status after 25 cycles (knitted, in bag) - Optimized design:
No measurements at t=0
 early failures might be
due to assembly
No failures after 25 washing cycles !
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JL-83
Textile integration : washability
1) Chain status after 25 cycles (knitted, not in bag) - Optimized design:
No failures after 25 washing cycles !
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Contents
• Introduction – options for comfortable
electronics
• Stretchable Mould Interconnect (SMI)
technologies
• Reliability / technology improvement
• Textile integration and washability
• Applications
• Conclusions and outlook
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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
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Stretchable electronics applications
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)
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Stretchable electronics applications
Philips EC-STELLA demonstrator: fitness monitor
Smooth
flex-stretch transition
Flexible islands for
interposers
PI + copper
Soldermask applied
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Stretchable electronics applications
Philips Activity Monitor
Functional boards mounted on flexible islands
Functionality of circuit tested before molding
Developed in EU Project Stella
Molded demonstrator using Sylgard 186 PDMS
Fully Functional demo, The system includes a
wireless link, a rechargeable battery circuit and
accelerometers for activity detection.
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Stretchable electronics applications
Verhaert EC-STELLA demonstrator: baby monitor
Smooth
flex-stretch transition
Temporary flex connector
Polyimide
Copper
Soldermask
Flexible island
Smooth
flex-stretch transition
Respiration sensor connections
Buzzer connections
Embedded in Sylgard 186 by casting
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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
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SMI Demonstrators
Party Shirt (5x10 full color led matrix)
Including wireless communication
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SMI Demonstrators
Party Shirt (5x10 full color led matrix)
Fully integrated in T-shirt
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Contents
• Introduction – options for comfortable
electronics
• Stretchable Mould Interconnect (SMI)
technologies
• Reliability / technology improvement
• Textile integration and washability
• Applications
• Conclusions and outlook
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Conclusions and outlook
• 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
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Conclusions and outlook
• 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
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Acknowledgements
•
•
•
•
•
•
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)
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Recent publications
•
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),
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Thank you for your attention
Questions ?
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