Screen Printing - April/May 2018 - 20

Dupont Advanced
Materials showcased
various examples of
smart clothing uses for
its intexar technology at
the 4th Wearable Expo in
tokyo in January [left].
Each intexar heat unit
[right] is light, stretchable, and creates warmth
when integrated into
outdoor clothing and
powered. (Courtesy
of DuPont Advanced
Materials.)

The Three CaTegories of e-TexTile r&D
in 2018, the smart clothing/e-textiles
industry seems to be stratified in three
main tiers, based on the complexity of
the technology.
Low CompLexity/SimpLe DeviCeS:
patCheS anD appLiqueS
these devices have single-layer circuits
with simple +/- connectivity or electrolytic/electrochemical operations. they
have simple designs and fairly low
critical tolerances in terms of deposition thickness or trace width. in many
cases, they are deposition only, with
basic shapes and sometimes no traces.
the circuits are typically not printed
directly on a garment. instead, they are
printed on a cloth or nonwoven elastomer, or printed as a patch or attachable
part. the complexity with these types of
projects is less about the printing and
more about how the components will be
designed and converted into a functioning, marketable product.
meDium CompLexity/printeD
CirCuit traCe patternS: wearabLeS with Smart propertieS
in these devices, complete circuits are
printed on the cloth, but the cloth is not
yet part of the circuit.
Some involve multiple layering
(either through printing or stack-up
construction) and contact pads, and
require moderate precision in the
traces. the substrate is very critical
because it has a bearing on the
precision of the traces. the printed
stack-ups use printed dielectrics and
conductives. the flexibility of the final

screenprinting

product is pivotal to the design.
Lifespan, washability, and connections
are also critical factors.
high preCiSion/aDvanCeD DeSign:
Smart textiLeS
this category includes fabrics that have
been woven with conductive threads or
threads with chemically reactive or light/
energy reactive (solar) coatings. these
products can actually be classified as
"smart textiles" and not simple wearable electronic devices. they are
process-intensive, custom substrates
with tight tolerances. these substrates
provide in-thread or in-cloth connectivity for devices before a circuit is ever
printed. the cloth is part of the device.
in some cases, these are multilayer
fabrics. the threads at different levels
have different functions and potentials.
Some threads are simply conductive,
some are capacitive, some are heatsensitive, and some are electrolytically
reactive. Some smart textiles can block
electromagnetic signals (Faraday cage),
enhance electromagnetic signals
(antenna), transmit electromagnetic
signals (rFiD), or change potential
under heat and pressure.
Before the cloth is woven, conductive
threads can be made by filling the
polymers with metal before the polymers
are spun into filaments. Other processes
used to make conductive threads include:
electroless plating of various metal types,
chemical vapor deposition, or chemical
etching and deposition processes.
in some cases, whole woven cloth
made of dissimilar threads can be

ray greenwooD
electroless plated. A specific angstrom/
micron thickness of metal is plated within
a given plating dosage period. So, in one
process step, you might get a uniformly
woven cloth made with several different
types of thread with very different
resistances or levels of connectivity.
Some threads may have no plating at all.
interspersing threads with no connectivity between connective threads can
create a spacer layer, just like that on a
membrane switch circuit.
Manufactured smart textiles represent
a whole new arena of substrates. printing
conductive circuits on cloth woven with
conductive threads delivers a much
wider range of possible applications.
plating and chemical or vapor deposition
processes are commonly used in
manufacturing rigid circuit boards and
semiconductors. they have high
overhead costs because they require
chemical networks or clean rooms.
the r&D expenses related to
advanced design applications are high,
so researchers are targeting applications where a high cost per unit is
tolerated. this includes military/
aerospace products, medical diagnostic
devices, and automotive or industrial
process controls.
Hundreds of organizations are
working on high precision/advanced
applications of e-textiles. But few are
talking publicly about it.
ray greenwood is a high-precision screen
printing and production technology consultant
within the industrial, medical, and printed electronics imaging industry. His primary focus is
in high-precision industrial screen printing.

Table of Contents for the Digital Edition of Screen Printing - April/May 2018