May
18, 1998 Design News
COVER STORY/PLASTICS
Plastics spark electronics designs
Benefits include fewer parts,
more design freedom, longer life, less cost
Gary Chamberlain, Senior Editor
Faster. Smaller. Cheaper. More Powerful.Sound
familiar? It should, at least if you work in the world
of electronics.
Nearly every day, it seems, some electrical/electronics
firm announces a new device that will "revolutionize"
the industry--smaller, has twice the capacity of its
predecessor, and doesn't cost as much. How do they do
it? In today's fast-paced electronics world, plastics,
especially the engineered variety, help make these seemingly
impossible designs come true. Here's why.
Engineered plastics can serve as a dielectric/insulator
or as a mechanical support. They have adequate dielectric
strength to resist the electric field between two conductors,
and good surface resistivity to prevent leakage of current
across the surface of the connector. Moreover, the materials
have good arc resistance to prevent damage in case of
accidental arcing, as well as good mechanical properties
to permit accurate alignment of the connected elements.
And that's just for starters.
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Demand for engineered plastics in the electrical/electronics
marketplace will expand from 251 million lbs in
1985 to 768 million lbs in the year 2001. Here?s
how those resins will be used at the turn of the
century.
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Because of this versatility, it's little wonder that
plastics used in electrical devices will increase in
both dollar volume and types of applications they serve.
For instance, sales of these materials will spiral from
$251 million in 1987 to an estimated $768 million in
2001. Poundage is expected to increase accordingly--from
250 million to 767 million lbs over the same time period.
Those predictions come from plastics industry observer
The Freedonia Group (Cleveland).
Information storage devices provide the best growth
opportunities for engineered plastics, say Freedonia
analysts. In this area alone, resins use will reach
117 million lbs in the year 2001. Heading the list:
the proliferation of computers and audio devices, plus
a burgeoning demand for compact discs and newly introduced
digital versatile discs (DVDs). Wire and cable resin
demand also will expand to 75 million lbs, primarily
as a jacketing material to enhance thermal and flame-resistant
properties, Freedonia predicts.
Connectors, switches, and related electrical and electronic
components will continue to benefit from engineered
plastics. In this segment of the industry, plastics
use will grow to more than 400 million lbs by 2001.
Energizing this growth will be the improved performance
of these materials (primarily high-temperature resistance
and dimensional stability) that will enable manufacturers
to lower costs through parts consolidation.
Moreover, Freedonia reports, business equipment demand
for plastics will expand to more than 170 million lbs
in 2001, due mainly to new and growing needs for computer,
printer, facsimile-machine, and other housings. Other
leading benefactors include: video display terminals,
machine covers (for noise reduction and protection),
keyboards and keys, paper trays, and other exterior
components.
Let's take a closer look at how these engineered plastics
are making their mark in the electronic/electrical marketplace:
Conductives catch on. One area where
engineered plastics have made big gains is in the conductive
polymers arena. This stems from the need to prevent
costly electrostatic discharge damage or to provide
shielding from electromagnetic or radio frequency interference
(EMI/RFI). Demand here will reach 290 million lbs by
the year 2000, based mainly upon the impressive growth
in high-speed electronic devices.
Denser packing of electronic devices also creates higher
levels of electronic noise, requiring a greater degree
of protection from EMI/RFI emissions. Only increased
use of fiber-optic cables and sensors, which are neither
affected by nor cause electromagnetic interference,
will slow this growth, the Freedonia analysts predict.
Plastic housings provide a good example of how plastics
solve the EMI/RFI problem. For instance, 3M, when developing
its new model 721 continuous wrist strap monitor, needed
a housing material that was static-dissipative and had
a high impact resistance. The monitor alerts a user
in a manufacturing environment that resistance to ground
has increased above a preset value.
3M (St. Paul, MN) tested a number of materials before
choosing Stat-Loyr A, an ABS composite, from LNP Engineering
Plastics (Exton, PA). "We chose the material because
it is inherently dissipative," says Brian Cox,
product design technologist at 3M. "It's an essential
requirement for our molded electronic packaging equipment
in order to ensure minimum failure of sensitive electronic
components."
Likewise, Axiohm Transaction Solutions (Riverton, WY)
needed a wear-resistant, anti-static compound for the
black inner frame of its new point-of-sale thermal printer.
The frame houses a roll of thermal paper and a motor
to enable the printer to silently roll out miles of
customer transaction receipts.
The desired material had to meet three requirements.
First, it had to minimize friction and wear where the
gear shafts and rollers interact. Second, it had to
exhibit conductive properties to eliminate static and
ensure smooth paper feed through the printhead. Finally,
it had to resist high temperatures from a continually
running motor.
RTP Co. (Winona, MN) met all three demands with a single
impact-modified polycarbonate compound. The material
exhibits unnotched impact strength of 35 ft lbs/inch
at 1/8 inch (1,869J/m), volume resistivity of 102-104
ohm-cm, and a heat deflection temperature of 270F at
264 psi (132C at 1,820 kPa).
"We tried two custom formulas before we achieved
the right combination of performance features,"
reports John Bertalan, senior mechanical engineer at
Axiohm. "The inner frame holds the key to reliable
operation of these printers; no one can afford to have
them shut down. RTP really focused on the project and
solved the problem in a short time."
Most families now have at least one cellular telephone
at their service (see sidebar). So when Motorola's Cellular
Subscriber Sector put out the call for a durable, attractive
material for the front and rear housings of its next-generation,
palm-sized cellular telephone, Bayer Corp.'s Polymers
Div. (Pittsburgh) answered with a new grade of Makrolonr
polycarbonate (PC) resin.
Before making the final decision, however, Motorola
subjected a number of materials to reliability testing
that measured the effect of temperature and other environmental
factors. It found the Makrolon DP1-1456, an opaque,
impact-modified PC, combined good processibility and
impact strength.
"The cell-phone industry wants to go smaller and
lighter," says Howard Dunlap, telecommunications
market manager at Bayer. "Makrolon can fill wall
housings from about 0.025 inch thick, helping Motorola
to produce a durable, high-tier phone."
In addition, Motorola selected Bayer's Bayfolr CR polycarbonate
film for the phone's key set. The thermoplastic polyester
and PC blend resists chemicals, making it well suited
for membrane-switch overlays.
Processing prowess. When it comes
to processing electrical/electronic components, plastics
play an equally critical role. A slight variation from
the specifications during a production run can cost
a semiconductor maker millions of dollars in material
waste, downtime, and lost sales.
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Passengers at the Minneapolis-St. Paul airport
should feel safer now that AlliedSignal?s
Precision Runway Monitor for parallel runway approaches
automatically ?patrols? plane locations.
Microwave laminates from Rogers played a critical
role in the development of the system?s antenna.
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With this in mind, EGC Corp. (Houston) recently launched
a material designed specifically for the semiconductor
industry. The new polyimide, called Xytrexr 574 HP,
should serve as an alternative to other polyimides typically
used in semiconductor processing equipment, according
to Steve Kealler, EGC's semiconductor products manager.
"Our new material has excellent resistance to
mechanical abuse and permanent deformation," Kealler
explains. "It can withstand abrasion without requiring
additives that could contaminate the process environment."
Xytrex resists temperatures up to 550F (288C) in a
wide range of applications. "It has tensile strength
of 20,000 psi compared to 12,500 psi for a typical polyimide,"
Kealler notes. "At 500F (260C), it has tensile
strength of 10,150 psi compared to 6,000 psi for a standard-grade
polyimide."
In addition, Xytrex can withstand most chemical fluids
and gases commonly found in or near semiconductor process
vessels, such as epitaxial reactors, photoresist developers,
dry etchers, and ion implanters. It is compatible with
most solvents, etchants, electronic chemicals, vacuum
fluids, and hydraulic oils.
To ensure that components in its vacuum handling system
pose no risk of contamination, H-Square Corp. (Sunnyvale,
CA) turned to a polyetheretherketone (PEEK) polymer
for the system's vacuum tips. These are the components
that remove wafers for test purposes (or from non-wo
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