Plastics spark electronics designs

May 18, 1998

14 Min Read
Plastics spark electronics designs

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.

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-Loy(reg) 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 Makrolon(reg) 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 Bayfol(reg) 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.

With this in mind, EGC Corp. (Houston) recently launched a material designed specifically for the semiconductor industry. The new polyimide, called Xytrex(reg) 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-working machines) and manually sort them.

"We chose PEEK polymer because it is an inherently pure material with few trace elements," says Bud Barclay, vice president of sales and marketing for H-Square. "By using the polymer for the tips, we minimized the risk of contamination." Victrex (West Chester, PA) supplied the PEEK polymer.

H-Square selected PEEK for yet another reason--the material's continuous service temperature of 500F (260C). "Because silicon wafers are often processed in a high-temperature environment, handling equipment has to withstand extreme temperatures," says Barclay.

For this project, the tips are made from a carbon-fiber-reinforced PEEK. "We needed the addition of the carbon fiber to protect the wafer against ESD," Barclay adds. "A minute amount of static electricity can damage a silicon wafer."

In yet another wafer application, IPEC Planar (Phoenix, AZ) turned to retaining rings made of a chemically resistant polyphenylene sulfide (PPS) to extend service life, add dimensional stability, and produce a low-cost wafer. The company's new Avanti 672 polishing unit comes with two or four polish-head configurations. It can polish up to 100 wafers per hr.

The polisher uses three retaining rings made of Techtron PPS plate supplied by DSM Engineering Plastics Products (Reading, PA). The rings make up part of the integrated wafer carrier heads for the polishing cycle and post-polishing cycles.

A key benefit of the Techtron PPS plate is its ability to be machined to the very close tolerance (±0.001 inch/inch) required for the rings. This enables the heads to securely hold the wafer to maintain process polishing stability. Dimensional stability is enhanced by the low moisture absorption and low coefficient of linear thermal expansion of the PPS.

During polishing, Techtron resists the abrasive and chemically reactive polishing silica slurry needed to produce the wafers. It also wards off the deionized water or dilute citric acid and ammonium hydroxide solutions used in the cleaning stage.

IPEC expects the rings to last up to 5,000 wafer polishing cycles. That's about two to five times longer than traditional materials previously used in such applications.

Air superiority. Polymers came into play in yet another critical application--a new air-traffic control system designed by AlliedSignal.

Currently, the Precision Runway Monitor (PRM) is the world's only operational electronically scanned radar system for parallel runway approaches. Simply put, the system functions as a secondary radar for high-traffic airports to provide more accurate monitoring of plane locations. It uses an electronically scanned phased array antenna system, which has some distinct advantages over traditional mechanically scanning antennas.

For instance, there are no moving parts. Also the scanning takes place electronically so it can be done more rapidly. As AlliedSignal puts it: "The PRM is a complete stand-alone air-traffic control system using an electronically scanned monopulse secondary surveillance radar system for increased airport capacity and enhanced safety, especially during bad weather conditions."

A significant part of the system's magic resides in the antenna. To maintain the needed accuracy--particularly as the thermal environment changes--AlliedSignal engineers made extensive use of RT/duroid(reg) 6002 microwave laminate supplied by Rogers Microwave Materials Div. (Chandler, AZ). The PTFE/ceramic-based material has excellent dielectric constant thermal stability, and a coefficient of thermal expansion equal to that of copper.

More specifically, the RF power dividers, the Butler Matrices, and the RF phase shifters incorporate the microwave laminate material. The material's low-loss, well controlled dielectric remains very stable over a large temperature range.

"These features give RT/duroid 6002 unprecedented system stability," says Gregory W. Bull, key program manager-microwave products at Rogers. "After all, you wouldn't want to bump into the plane next to you or miss the runway a bit just because it is a little cold outside, would you?"

The first production system operates at the Minneapolis-St. Paul airport--a good proving ground for cold-weather performance. To date, AlliedSignal has built five systems for the FAA. The other four will reside at New York's John F. Kennedy, and at the St. Louis, Philadelphia, and Atlanta airports.

Keeping pace with progress. Like their electrical/electronic counterparts, plastics suppliers must move quickly to keep up with the demands placed upon them in this dynamic marketplace. Some other examples illustrate that they are meeting the challenge.

For instance, the familiar metal dog tag worn by members of the U.S. armed forces may soon give way to a rugged plastic tag containing medical records on a memory chip. Data-Disk Technology Inc. (Sterling, VA) developed the record carrier, called the Medi-Tag(reg), with an assist from DuPont Engineering Plastics (Wilmington, DE).

The tag has a rugged outer shell of DuPont Zytel(reg) nylon, while inside there's a flash memory chip surface-mounted on an integrated circuit board. The chip's memory can include an individual's complete medical history, x-rays, allergies to medications, dental records, etc. With the tag, medical personnel can read and update the record by inserting it into a slot in a standard PCMCIA reader attached to a personal computer.

"The reliable, long-term protection provided by Xytel is crucial to the tag's reliability as a permanent record," says Tom Clark, Data-Disk president. Relying on encapsulation molding techniques developed by DuPont, Data-Disk achieves a complete, hermetically sealed shell to block penetration by dust and fluids. In addition, the glass-reinforced nylon 612 polymer protects against impact damage, mechanical loads, abrasion, and chemical attack by skin oils.

Clark reports that the tag has performed well in tests conducted by DOD's Telemedicine Technology Area Directorate. "It's a leading candidate for a $40 million contract involving field testing of a personal information carrier by the armed forces in 1998-1999," Clark says.

Metallocene-based polymers also are coming on strong for packaging applications in computer and other electronic components (see Design News, 2/19/96, p. 15). Witness metallocene-catalyzed propylene polymers (mPP) produced by Exxon Chemical (Houston, TX).

"Test results indicate that our Achieve(reg) mPP offers the extreme cleanliness and minimal outgassing critical in packaging for electronic components," says Chris Davey, polypropylene rigid packaging market development representative. "The material measures below the lower detection limit for chlorine compared to 20-ppm chlorine for a conventional polypropylene. This means that it provides a non-corrosive environment essential in packaging applications for computer electronics and other sensitive components."

Achieve also shows better results in regard to oligomer levels when compared to conventional polypropylene. Conventional polypropylene generates a total oligomer level of more than 500 ppm, according to Davey, while Achieve polymers showed a total level of less than 100 ppm. "This indicates that Achieve mPP polymers are super-clean and provide products with significantly less potential to produce haze on sensitive electronic components," he notes.

When it comes to conformal coatings, Nordson Corp. (Amherst, OH) has introduced a coating system it claims can deliver productivity and material savings of more than 50% over traditional dip and spray systems for circuit-board applications. The new Century system robotically applies acrylics, silicones, epoxies, and urethanes that conform to the external shape of the article being encapsulated "only on specified areas of a circuit board," Nordson reports.

The system can accommodate many types of boards, making it suitable for low- to medium-volume, high-mix operations. In contrast to many traditional dip and air-spray coating systems, Century eliminates VOC emissions, Nordson says. Any solvents are contained in the coating chamber, and a ventilation port for connection to exhaust ducting precludes the need for special hoods.

As for prototyping electronic components, check out a new polyurethane material from Ciba Specialty Chemical Corp. (East Lansing, MI) that can produce new "Parts in Minutes." In fact, that's what the company calls its UL 94 V-O-rated transparent material.

The flame-retardant system gels in 60 sec, permitting the demolding of cast parts in less than 30 min. The cured material has a Shore 81D harness, compressive strength of 20,000 psi, and a heat-deflection temperature of 208F. "It's well suited for medical equipment, computer housings, appliances, and other electronic-product prototypes," says Ciba's Bill Geresy.

Such materials and applications only begin to hint at what the future holds in store. As electrical/electronics companies continue to introduce new products at a record pace, it seems likely that plastics producers will follow suit. That's good news for design engineers, who will have more smaller, faster, less costly components to choose from, made from materials that last longer, can withstand more abuse, and give engineers more design flexibility.

What this means to you

- Plastics continue to enhance new electrical/electronic applications.

- Expanded use of these materials permit smaller, faster, and less-costly components.

- Plastic suppliers will tweak a material to meet nearly any specification.

- Increased numbers of materials entering the marketplace give engineers greater design flexibility.

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