8/17/2019 Conductive plastics for electrical and electronic applications.pdf
1/4
38 REINFORCEDplastics September 2005
Plastics are by nature very good
insulators. This inherent electrical
insulation causes the plastic to
tend to hold electrostatic charges and to
allow electromagnetic/radio frequency
interference (EMI/RFI) to pass through.
Recently, plastic has become the material
of choice for internals in electronic com-
ponents such as computers and other
consumer products, replacing metals, as
they offer greater design flexibility,
lighter weight, colorability and cost-
effectiveness. Thus, the challenge is to
convert inherently insulating thermo-
plastic materials to a product that would
provide antistatic or electrostatic
dissipative or EMI/RFI shielding or a
combination of these properties.
Managing heat is crucial to main-
taining the reliability and extending the
life of electronics. A wide range of
choice of cooling solutions is available
for shunting away excess component
heat, including fans, metallic or ceramic
heat sinks, pipes and spreaders. With
increasing demand for miniaturisation
of electronic devices such as laptops,
PDAs and other hand-held devices,
designers are now focusing on innova-
tive thermal management solutions
using design flexible, lightweight therm-
ally conducting plastics.
The Electronic Industries Associa-
tion (EIA) Standard 541 classifies con-
ductive plastics with respect to their
ability to protect against either electro-
static discharge (ESD) or electromagnet-
ic interference/ radio frequency inter-
ference (EMI/RFI). Materials with a
measured surface resistivity between
105-1012 ohms/sq. provides adequate
ESD performance, with lower conduc-
tivity products acting as antistatic prod-
ucts. Plastics with surface resistivity of
8/17/2019 Conductive plastics for electrical and electronic applications.pdf
2/4
39September 2005 REINFORCEDplastics
have also been used. Recently, more
emphasis has been on the use of carbon
nanofibres, where with small loading
high conductivities can be achieved sus-
taining plastic-like properties.
Although a wide variety of conduc-
tive fillers are available, the choice of filler depends on the end-user specifica-
tions in the target application. In some
antistatic applications, manufacturers
are looking for clear plastics, and thus
the additive or filler used should match
the refractive index of the polymer
matrix. In applications such as com-
puter chip and hard drive carrier trays,
the original equipment manufacturer
(OEM) is looking for conductive plastics
with low ionic concentrations. There-
fore, fillers used should not have leach-able ionics and other impurities at min-
imum levels. Lastly, both conductivity
and processability of these plastics
depend on the manufacturing process –
type of extruder used, screw configura-
tion, shear and temperatures employed.
The information presented here will
be focused on the use different surface-
active chemical agents, fillers such as
carbon fibres, carbon powders, carbon
nanotubes and combination of these
fillers to impart conductivity in plastics
especially in electrical and electronic
applications. Using mixed filler systems,
and utilising their interactions/syner-
gism, we were able to tailor the plastic
components to meet specific surface
resistivity range and processing require-
ments for different applications.
Antistatic plasticsStatic electricity is a common phen-
omenon that all of us have experienced –
clinging of hair when brushed and an
electrical shock obtained by touching a
doorknob or metal part. Static electricity
on a surface is generated due to the
build-up of charge. This could happen
either by a triboelectric effect – rubbing
sliding, or separating of nonconductiv
materials, or by an electrostatic field, cre
ated when one charged body induce
charge on a nearby second body. There
are many common processes wher
effective static charge dissipation is criti
cal to the device’s useful functions. On
example is the copying process. If the
components in the copier are not prop
erly grounded to dissipate charge, pape
jamming occurs. Plastics with antistati
properties are becoming increasingly
popular in applications such as printe
and copier components, vacuum cleane
dirt collecting cups, electrostati
painters, air cleaners, computer internal
and ink-jet printer penholders. Good
antistatic plastics should have highe
static decay rates. Antistatic plastics ar
widely used in media drives and in stor
age devices since these need rapid dissi
pation of surface charges generated dur
ing their operation (Figure 2).
Incorporation of antistatic agent
such as poly(amid-ether-ester) type poly
mers or organic alkyl sulfonates to th
plastics is one method of achieving th
required static dissipative properties
These types of polymers act as surface
active agents and impart a sligh
conductivity that is necessary for plastic
Conductive plastics for electrical and electronic applications
Figure 2. Antistatic plastics are widely used in applications where dissipation of static charge is needed, such as media drive cartridges. ( Picture courtesy of Plasmon.)
Figure 3. Effect of different types of fillers (at 10% loading) on PC-ABS resin. Metallic fillers or metal coated fibres provide higher conductivities with lower filler loadings.
8/17/2019 Conductive plastics for electrical and electronic applications.pdf
3/4
40 REINFORCEDplastics September 2005
to perform as antistatic agents. We have
found that the combination of these
types of chemical agents with carbon
fibres may provide a synergetic effect on
electrostatic decay characteristics.
Electrostatic dischargeElectrostatic discharge is a transfer of electrostatic charges between bodies at
different potentials caused by direct con-
tact induced by an electrostatic field.
Electrostatic dissipation has become an
important issue within the electronics
industry, especially in electronic compo-
nents such as data storage devices, chip
carriers and computer internals.
Different levels of surface and bulk
connectivity can be achieved with vari-
ous types of conductive fillers. Anincrease in conductive additive corre-
lates with a decrease in electrical resistiv-
ity and a critical threshold of fillers is
needed for complete and adequate dis-
charge. Volume resistivities obtained
using some commonly used fillers are
shown in Figure 3.
The changes seen in the resistivity
depend on the conductivity (type) of the
filler used, the degree of dispersion and
distribution, and the polymer system.
The most common fillers used in plastics
to impart electrical conductivity are
carbon powders and carbon fibres.
Although carbon powder products pro-
vide an inexpensive solution, for elec-
tronic applications these products are
not always attractive since they tend to
slough and deposit carbon on compo-
nents in contact with the plastic. As a
result, carbon fibres are widely used inconductive plastics, especially in electri-
cal and electronic applications. Carbon
fibres from different suppliers have diff-
erent characteristics due the sizing and
coupling agents used during their manu-
facture. As such, the plastic obtained
with same loading of carbon fibres from
different suppliers shows different con-
ductivity properties. Therefore, the selec-
tion of conductive filler type, processing
conditions and resin system used play an
important role in achieving the desiredsurface resistance values.
Conductive plastics are widely used
in electronic packaging applications,
such as chip trays and conductive carrier
tapes where IC chips are transported
from manufacturers to assembly plants.
These products require good control of
electrostatic dissipative properties cou-
pled with tighter dimensional tolerances
in pockets where chips are placed.
(Figure 4).
Recently nano-carbon fibres have
become popular since they allow higher
conductivities to be obtained even with
smaller loadings. For example 3% multi-
walled nanotube (MWNT) filled poly-
carbonate products exhibit the same
conductivity as 15% carbon fibre filledproducts (Figure 5), and with single
walled nanotubes (SWNT), the required
loading is less than 1%.
More and more conductive plastics
with MWNTs are now used in electri-
cal/electronic applications since they are
good electrical conductors with lower
filler loading. Furthermore, they do not
slough as carbon powder containing
products do. Although SWNTs give high-
er conductivities than MWNTs, this tech-
nology is still in early stage due to the
challenges in processing of these fibres.
The SWNT has strong van-der-Waal
forces and tends to form ropes. De-rop-
ing and good dispersion of individual
tubes in the plastic matrix are critical for
effective conductivities with SWNTs.
EMI shieldingElectromagnetic interference (EMI)
shielding is another property of import-
ance in many applications. Electronic
devices operating normally in their
intended environment, without con-
ducting or radiating excessive amounts
of electromagnetic energy, or not being
susceptible to such energy from internal
or external sources, are in the state of
electromagnetic compatibility (EMC).
EMI is radiated or conducted energy that
adversely affects a circuit’s performance,
and thus disrupts a device’s EMC. Many
types of electronic circuits radiate or are
Conductive plastics for electrical and electronic applications
Figure 4. Conductive chip trays use conductiveplastics with conductivity as specified by JEDEC standards. Chip trays need to berigid with no warpage after baking at set temperatures, usually at 150°C.
Figure 5. Effect of different types of conductive fibres in polycarbonate. Carbon nanotubes such as multi-walled nanotubes (MWNT) and single-walled nanotubes provided higher conductivities thancarbon fibres.
8/17/2019 Conductive plastics for electrical and electronic applications.pdf
4/4
4September 2005 REINFORCEDplastics
susceptible to EMI and must be shieldedto ensure proper performance.
EMI shielding using plastics can be
accomplished by using high-aspect ratio
conductive fillers such as carbon and
stainless steel fibres. Shielding is provided
by a conductive medium that reflects,
absorbs or transmits the electromagnetic
radiation to the ground. Shielding effec-
tiveness is determined by the extent to
which the intensity of an electromagnet-
ic signal is reduced by the introduction of
a shielding medium. To obtain good
shielding effectiveness, a higher filler
loading and good dispersion in the
plastics are required.
For EMI shielding plastics, metal-
coated fillers such as nickel-coated
carbon fibre or stainless steel fibres are
widely used. In order to effectively shield
electromagnetic waves the fillers used
should be able to reflect the radiation
from the plastic matrix. For these appli-
cations long carbon fibres that can form
an effective network in the polymermatrix are a better choice than short
fibres, as seen in Figure 6.
Thermally conductive plasticsWith electronic devices gaining power
with faster chips, speedy media drives
and hard disks, design engineers have
really started to feel the heat generated
in these systems. Thermal management
was once accomplished with a few well-
placed fans, vents and aluminium heat
sinks. But today’s small, hot electronicscan benefit from new ways to keep cool
like using thermally conductive plastics.
Whereas unfilled thermoplastics have a
thermal conductivity of around 0.2 W/
mK (Watts/meter-°Kelvin), most therm-
ally conductive plastic compounds typi-
cally have 10-50 times higher conduct-
ivity (1-10 W/mK). Similar to electrically
conductive plastics, thermal conduct-
ivity in plastics can be accomplished by
adding different thermally conductive
fillers. The most common fillers are
alumina-type ceramic fillers since they
are less expensive and impart isotropic
thermal conductivity (Figure 7).
Much higher thermal conductivity
can be achieved using speciality graphite
fibres made from petroleum pitch. Unlike
polyacrylonitrile (PAN)-based carbon
fibres, pitch-based carbon fibres have low
electrical conductivity but high thermal
conductivity due to their wavy radial
structure, and have conductivity values
of 500-1000 W/mK. By comparison,
structural-grade carbon fibres based on
PAN have conductivities less than 10 W/
mK. Other commonly used fillers include
boron nitride and aluminium nitride,
which are electrically insulative ceramic
fillers with a thermal conductivity of 60-
80 W/mK for boron nitride and 300 W/
mK for aluminium nitride powders.
Thermally conductive plastics are get-
ting increasingly popular in hard disk
drive internal components (Figure 8), lap
top computers, and other electrica
devices where placing cooling fans i
becoming impractical. These types oplastics are also used in larger device
such as computer base stations as hea
sinks to protect electronic components.
ChallengesPlastic composites play an importan
role in the electrical and electroni
industry for their optimum performance
as described here by controlling both
electrical and thermal conductivity. A
this industry grows, designers face mor
challenging requirements. These can
only be met through innovation of new
polymers and fillers systems and ways o
effectively combining these to obtain
maximum benefit.
Conductive plastics for electrical and electronic applications
Figure 6. The shielding effectiveness of PCwith different amounts of carbon fibres.Plastic pellets made from short carbon fibrehave random orientation of fibres, whereas long fibre pellets have fibres oriented on thefull pellet length. When parts are moulded,long carbon fibre products thus give enhanced shielding effectiveness.
Figure 7. Alumina (Al 2 O 3 ) filled PPS composites.
Higher filler loading is needed for effectivethermal conductivity with these types of ceramic fillers.
Figure 8. The spindle motor of a hard disk drive uses ceramic filler filled plastics to dissipate heat.
Dr Jay Amarasekera, GE Advanced Mat-
erials/LNP, 475 Creamery Way, Exton,
PA 19341, USA; e-mail: jay.amarasek-
This article was presented at the RP Asia
2005 conference in Bangkok, Thailand,
on 25-26 August ( www.
rpasia.com ). The pro-
ceedings from this con-
ference are available to
purchase; e-mail rp@
elsevier.com for details.
mailto:[email protected]:[email protected]://www.rpasia.com/http://www.rpasia.com/http://www.rpasia.com/mailto:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]://www.rpasia.com/http://www.rpasia.com/Top Related