• A PCB substrate must have good dielectric performance. That is, it
must insulate the conductive layers from one another by blocking
electrical conductivity, to minimize electrical signal loss, crosstalk
between conductive layers and noise.
• Technically, that translates into a low dielectric constant (Dk ≤3.7)
and a low dissipation factor (Df ≤0.005).
• The higher the Dk, the lower the speed of the electrical signal. Df is a
measure of the loss in dielectric property, in this case, the insulative
capability of the PCB’s composite substrate.
• Because signal loss and noise are exacerbated by heat, substrates
must contribute to thermal management as well.
• The majority of PCBs are made with E-glass/epoxy prepregs -- the
PCB industry's traditional workhorse material, designated "FR-4," is
an E-glass/epoxy material -- although other reinforcing fibers,
including aramid and quartz, are sometimes used for specialty
• Resin alternatives include vinyl ester and polyester, for commodity
boards, and cyanate ester, polyimide and bismaleimide triazine (BT)
for more demanding, elevated-temperature applications.
• The coefficient of thermal expansion (CTE) of silicon memory chips
is 2.5 /°C
• CTE of a fiberglass laminate can range from 14 /°C to 24 /°C.
• An advantage of aramid as an alternative laminate substrate is its low
negative CTE, which reduces thermal stress, as well as its low
dielectric constant of 4, compared to 6.2 for E-glass.
2. Electromagnetic shielding
• Electromagnetic shielding principle
The effect of electromagnetic shielding is to reduce the
electromagnetic field effect in a certain area (not including these
sources) generated by some radiation sources, and to effectively
control the harm caused by electromagnetic radiation from one area
RISK FROM EM RADIATION
• If human beings are exposed to the EM waves, the network of veins in
high risk organs such as eyes might be affected. This is due to heat
build-up in the eyes by the EM waves which could not be easily
• In order to avoid these hazards to human beings and to protect the
sensitive circuits from undesired EM radiation, EMI shielding is
Fig 3: Electromagnetic shielding mechanism
Fig 4: Components of an electromagnetic wave
• The principle of action is the use of low-resistance conductor material,
because the conductor material has a reflection and guiding effect on
electromagnetic energy flow and within the conductor material.
• It create the current and magnetic polarization which is opposite with the
source of electromagnetic field, thereby reduce the effect of radiation
source in electromagnetic field, normally it represented by shielding
• The shielding effectiveness refers to the ratio of the incident or reflection
electromagnetic waves without shielding to the reflection or transmission
of electromagnetic wave under shielding at the same location, that is,
shielding material to the attenuation value of electromagnetic signal, the
unit is (dB).
Conductive mechanism of composite
• With the increase of the concentration of conductive filler, the conductivity of the
polymer increases slowly. When the concentration reaches a certain value, the
conductivity increases sharply, the polymer becomes a conductor, and the filler
concentration continues to increase but electro conductivity has not changed much.
• The conductivity filler concentration at which the conductivity changed abruptly is
called the 'diafiltration threshold'. So its conductive mechanism has two main theories:
one is the conductive channel theory; the other is the tunnel effect theory.
• The conductive channel mechanism plays a major role in the high concentration of
conductive filler, which means that when the content of the conductive filler reaches the
'diafiltration threshold', the conductive particles contact each other to form an infinite
network. The formation of conductive channels, carriers can freely move within the
system. Thereby making the composite conductive.
• The tunneling effect plays a major role in the low packing concentration, which means
that there is a certain spacing between the conductive particles. Electrons in the thermal
vibration under the action of migration form a conductive network. So that the
composite polymer becomes conductive.
Fig 5: Conductive path formed in a conductive polymer
• The low frequency signals can be arrested by means of reflection
whereas high frequency signals should be arrested by means of
absorption which needs much attention.
• Much research has been conducted to develop high frequency EM
absorbers by means of coating fillers with magnetic materials or
incorporation of magnetic materials in the polymer matrix.
• Materials with high absorption co-efficient could impart shielding
effectiveness of 80 dB for the frequency of 18 GHz electronic systems has
increased enormously in all the engineering and technology fields. The
advances in electronics reduces the component size and placing more
number of electrical parts in limited space reduces the system size and
increases the mobility.
• Placing more number of components in a very confined space builds the
problem of keeping the electromagnetic interference (EMI) of these
systems from interfering with other systems through radiation.
• Carbon-Carbon composites have good shield effectiveness of 124 dB in low
frequency range of 0.3Mhz to 1.2 Ghz, the dominant mode being
3. Electrical switching and insulation
Properties that composite materials have include :
• Dielectric strength
• High thermal conductivity
• Low electrical conductivity for insulation
• Electromagnetic interference (EMI) shielding effectiveness
• Heat resistance
• Track resistance
• Low coefficient of thermal expansion
• Durability to withstand repeated use without a decrease in performance
• Moisture resistance for safety and durability
• Sound baffling for quieter operation
• Paper-Phenolic Materials
Norplex-Micarta offers a variety of paper phenolic sheets. This cost-effective
line of products consists of multiple plies of various papers impregnated with
phenolic resins and laminated under heat and pressure to produce a thermoset
composite. Both papers and resins can be modified to change the finished
properties of the final laminate.
These products offer thermal, mechanical isolation, and thermal and electrical
insulation properties that meet or exceed those of most thermoplastic
materials. The properties and cost-effectiveness of these products often make
them the insulators of choice in low-voltage, dry-service electrical equipment.
• RTB326 - Epoxy Cotton/Linen Tube
Grade RTB326 is a tube made from a fine cotton fabric and an epoxy resin
system. It has low moisture absorption and excellent dimensional stability and
chemical resistance. Typical uses include bearing retainers and parts that
require excellent machining characteristics.
• NP509 - Melamine Glass Sheet
Woven glass fabric, melamine resin laminate. NP509 is very hard, flame
resistant, machining grade with excellent electrical properties in high
humidity conditions. NP509 has high physical strength and excellent arc
resistance. Meets MIL-I-24768/1 type GME, MIL-I-24768/8 type GMG and IEC
60893-3-3-MF GC 201.
• Paper-Epoxy Materials
These products consist of multiple plies of various papers impregnated with
specialty epoxy resin systems and laminated under heat and pressure to
produce a thermoset composite. Both papers and resins can be modified to
change the finished properties of the final product, and once cured, they will
not melt like most thermoplastics.
Thermoset epoxy composites are ideal for applications ranging from small
switch parts to insulating high voltage tap chargers in power transformers,
and other applications requiring electrical insulation properties.
P95 consists of woven glass fabric with polyimide resin. The product is
engineered to maintain excellent physical properties at 240°C, making it
suitable for high temperature applications. It offers a low coefficient of
thermal expansion, as well as high mechanical strength and consistent quality.
It can be used for structural components, thermal insulators, PCB manufacture
and assembly, and high temperature gaskets in petrochemical plants and other
applications requiring excellent compressive strength, low moisture
absorption, and excellent chemical resistance.
Applications in the Electrical Industry
• The unique properties of thermoset composites make the materials ideally suited to the
rigors of use in the electrical industry.
• Phenolic-matrix and melamine composites are used in many electronics including printed
circuit boards, gears, and insulators. Insulation, circuit boards, and components requiring
a high resistance to heat will often be made from a silicone-based composite.
Additional applications include:
• Control system components
• Circuit breakers
• Arc chutes
• Arc shields
• Terminal blocks and boards
• Substation equipment
• Microwave antennas
• Standoff insulators
• Pole line hardware
• Printed wiring boards
• Server rooms
• Metering devices
• Lighting components
4. Wearable electronics
• Graphene/CNT polymer composites are widely being used to make
• Silver nanofillers in elastomer composite used in wearables.
Fig 10: Textile integrated with electronics
Fig 11: Graphene/polymer composite in textile batteries
Fig 12: graphene/polymer composite in wearable SWNT
5. Electronic sensors
• Carbon black polymer odour and flavour sensors for detecting
vapours. Used for environmental monitoring to check air quality,
crime prevention such as bomb detection, quality control.
Reinforcing phase: Dispersed carbon black particles
(conc. 2 to 8% by wt.)
Reinforcing medium : Polymers ( usually
Fig 13: Electonic vapour sensor
Fig 15: Working of Li ion battery
7. Satellite electronics mounted on composite
Fig 16: electronics in satellite
8. Lightning harvester
• GC ltd. plans to adapt the high strength-to-weight characteristics of
Graphene based composite technology to manufacture ultra-long
cables - of circa 8 miles in length. These ultra-long cables would have
a highly-conductive coating of graphene - effectively making them
lightning rods which can reach up into the clouds !!
• Clouds contain a massive amount of energy, in the form of static
electricity, or the difference in voltage between the bottom of a cloud
and the ground. Lightning occurs when this voltage difference builds
up to such an extent that electricity leaps across this gap.
• GC ltd. believes it could also collect electrical energy from clouds. The
highly-conductive graphene coating on a GC composite cable (held
aloft by weather balloons) would be, by far, the path of least
resistance for electricity to travel along. As Electricity flows - even the
extremely large bursts from lightning strikes - would travel down the
graphene-coated cable into a super-capacitor array, which could
then release electricity into the power grid in a controlled way.
• Preliminary estimates indicate that if this design were to work, GC
Lightning Harvesters could be deployed at a lower cost than with
nearly every other form of electrical power generation - and, crucially,
it would be based on an infinitely renewable energy source, i.e.
Apparemment, vous utilisez un bloqueur de publicités qui est en cours d'exécution. En ajoutant SlideShare à la liste blanche de votre bloqueur de publicités, vous soutenez notre communauté de créateurs de contenu.
Vous détestez les publicités?
Nous avons mis à jour notre politique de confidentialité.
Nous avons mis à jour notre politique de confidentialité pour nous conformer à l'évolution des réglementations mondiales en matière de confidentialité et pour vous informer de la manière dont nous utilisons vos données de façon limitée.
Vous pouvez consulter les détails ci-dessous. En cliquant sur Accepter, vous acceptez la politique de confidentialité mise à jour.