Fantastic Plastic, Part 2: Electric Action
Plastic's role in the realm of electronics need not be limited to insulating conductive metals. New technologies are emerging that give the material a larger role, with the emergence of substances like intelligent semi-responsive polymers, flexible electronics, thin-film transistors and electroactive polymers that can change shape on the application of voltage.
Feb 3, 2011 5:00 AM PT
Part 1 of this series explored the markets and industries surrounding polymers in computing.
Plastics, those ubiquitous malleable synthetic polymers so essential to the needs of virtually the entire spectrum of global business, have become the pulsing heart of the high-tech world.
The universal insulator for the electrical and electronics industries, plastic materials can also be semi-insulating, semiconducting, and even fully electrically conducting. Leading edge examples include:
- Electroactive polymers (EAPs) change shape on the application of voltage.
- "Intelligent," stimuli-responsive polymers can create an electrical circuit and act as electrodynamic sensors to detect and measure ambient conditions or work as actuators to produce required outputs.
- Flexible electronics (also known as "flex circuits") technology can be used for assembling electronic circuits by mounting electronic devices on flexible plastic substrates.
- Thin film transistors (TFTs) made from polythiophene, an organic semiconductor, are attractive candidates for sensor arrays because they can be easily arrayed with deposition methods like inkjet printing, and they have a rich chemistry that can exploited to tune their sensor behavior.
- Polymer LEDs (sometimes called "light-emitting polymers" or "polyLEDs") technology utilizes polymers as the semiconductor material in LEDs (light-emitting diodes).
The Many Sides of Poly
Polymers, the largest revenue segment of the chemical industry at about 33 percent of the basic chemicals dollar value (according to BCC Research), includes all categories of plastics and man-made fibers. The largest-volume polymer product, polyethylene (PE), is used mainly in packaging films and other markets within the US$379 billion (in shipments) U.S. plastics industry. Conductive polymers and plastics are increasingly desired for a growing number of sophisticated end-uses.
Polymethyl methacrylate (PMMA), a transparent thermoplastic familiar to hockey fans as shatter-resistant Plexiglas barriers surrounding ice rinks, is also a nanotechnology tool used in the semiconductor industry as a resist in the electron beam lithography process.
Polyphenylene vinylene (PPV) is the only conducting polymer that has so far been successfully processed into a highly ordered crystalline thin film, which makes it a candidate in many electronic applications such as LEDs and photovoltaic devices.
Polyaniline is among a family of conductive polymers with properties similar to some metals. A unique type of polymer because it is a semiconductor, polyaniline can be used in applications ranging from intelligent windows to computer chips.
Demand for polymers and conductive polymers in the electronics industry is on track to grow from an estimated $1.9 billion in 2010 to about $5.9 billion in 2015, reports BCC Research. Most of the projected growth is attributable to conductive polymers.
But the seemingly limitless variety, range and abundance of these miracle materials disguises a potential problem.
"Global chemical companies are no longer developing new polymers -- we are seeing new polymer alloys and new additives to existing resins, but few, if any, new polymers," said Chuck Brewer III, CEO of C. Brewer Company, a precision plastic injection molding firm based in Anaheim, Calif.
"The new frontier is for processors to pioneer techniques that challenge current practices and the perceived processing limitations of polymers," Brewer told TechNewsWorld. "Those who have embraced the challenge are providing small but significant incremental advances."
Wolfgang Clemens is head of application for PolyIC GmbH & Co. The German developer of polymer electronics technology was set up in 2003 as a joint venture between Leonhard Kurz (hot stamping and coating) and Siemens (electronics) for the development and production of printed polymer electronics.
"The single most important technical issue regarding polymers is the availability of conducting and semiconducting materials that have good enough properties like mobility or conductivity, are easy to process, are stable and aren't too expensive," Clemens told TechNewsWorld.
Thermosets and Thermoplastics
The basic division of polymers into "thermoplastics" and "thermosets" helps define their areas of application.
Thermoplastics are a type of plastic made from polymer resins that become a homogenized liquid when heated and hard when cooled. They can be melted to a liquid, made soft and deformable, molded and shaped when heated, and cooled to a solid. Examples are polystyrene and polyethylene.
Thermosets, which take a hardened form after they've been heated and allowed to cool, cannot be melted down and reformed. Thermosets can be solids like the molding compounds used in semiconductors and integrated circuits (ICs). Phenol-formaldehyde resin is an example.
"Most polymers used in electronics are thermosetting polymers, that is they undergo a chemical reaction to form a highly crosslinked network that is stable-it doesn't change shape when heated to high temperatures," said Jeffrey T. Gotro, Ph.D., president of InnoCentrix , a California-based consulting firm serving the polymer industry.
"With the elimination of lead as a solder in electronics, the new lead-free solders melt at much higher temperatures," Gotro told TechNewsWorld. "Additionally, polymers used in electronics are subjected to other harsh operating conditions like temperature/humidity aging and accelerated life testing to ensure they are reliable in consumer applications."
Electronic packaging refers to enclosures and protective features built into both end products and components.
"The package is the bridge linking two critical but divergent industries -- semiconductors and printed circuit boards (PCBs)," wrote Ken Gilleo in a 2006 paper "Thermoplastic Electronic Packaging: Low Cost -- High Versatility." Gilleo, a materials scientist/chemist, electronic packaging/assembly expert and general technologist, is principal of ET-Trends, a research firm based in Warwick, RI.
The electronic package is the physical scale translator that makes ultrafine chip features compatible with any interconnecting substrate, according to Gilleo. Essential requirements include providing the electrical interconnect structure between tiny, extremely dense semiconductors and large-scale, lower density PCBs.
"Encapsulation" is an electronic packaging technique widely used to protect semiconductor components from moisture and mechanical damage, and to serve as a mechanical structure holding the lead frame and the chip together. The process consists of immersing a part or assembly in a liquid resin, and then curing it. Encapsulation can be done in a pre-molded potting shell, or directly in a mold.
Thermoset epoxies, discovered in 1927 and used for nearly 50 years as encapsulants for electronics, remain the workhorse material for most electronic packages. Plastic packaging primarily based on thermoset materials accounts for perhaps 95 percent of the world electronic packaging market because of low cost, versatility and easier automation.
But thermosets, once polymerized, cannot be melted for reuse and so become scrap. Also, epoxy molding compounds are generally classified as hazardous waste, which makes disposal increasingly difficult.
In contrast, modern halogen-free thermoplastics can provide excellent thermomechanical properties and fabrication with highly automated high-efficiency high-volume processes.
"Thermoplastics attributes include low moisture uptake, fast processing and the highest stability in the world of polymers," stated Gilleo's report. "Thermoplastics can be cheaper, more environmentally friendly, reusable, recyclable, and boast near-hermetic properties far superior to non-hermetic epoxies."
Electroactive Polymers (EAPs)
The increasing need for greater sophistication in the automation industry and in electronics protection is driving the market for low-cost, light-weight, and low driving voltage materials. Advances in electronics and polymers manufacturing technology have given rise to the concept of electroactive polymers.
The EAPs market is segmented into conductive plastics (materials capable of conducting modest amounts of electrical current); inherently conductive polymers (ICPs), which have electrical conductivity properties similar to inorganic semiconductors and so are able to discharge static before charges reach unsafe levels; and inherently dissipative polymers (IDPs), which are widely used as permanent antistatic additives in plastic parts and packaging where they prevent electrostatic discharge and dust attraction.
In general, there are two categories of applications for conducting polymers. Static applications rely upon the intrinsic conductivity of the materials, combined with their ease of processing and material properties common to polymeric materials. Dynamic applications utilize changes in the conductive and optical properties resulting either from application of electric potentials or from environmental stimuli.
Printed and Flexible Electronics
Printed electronics is an emerging industry that takes advantage of printing technologies to manufacture electronics with a wide variety of form factors, including thin, flexible plastic substrates. The method typically uses common printing equipment and technologies such as screen printing, flexography, gravure, offset lithography and inkjet. Electrically functional electronic or optical inks are deposited on the substrate, creating active or passive devices, such as thin film transistors or resistors.
Flexible electronics, also known as "flex circuits," is a technology for assembling electronic circuits by mounting electronic devices on flexible plastic substrates like polyimide, transparent conductive polyester, or polyether ether ketone (PEEK), a colorless organic polymer thermoplastic used in engineering applications.
In 2010, IDTechEx, a global custom consulting, research and advisory services firm based in Cambridge, Mass., issued a report "Printed, Organic & Flexible Electronics Forecasts, Players & Opportunities 2010-2020," by authors Raghu Das and Peter Harrop
IDTechEx estimated the 2010 market for printed and thin film electronics at $1.92 billion. Forty-three percent of that amount was predominately organic electronics such as OLED display modules. Of the total market in 2010, 35 percent was printed. In the years to come, photovoltaics, OLED and e-paper displays will initially grow rapidly, followed by thin film transistor circuits, sensors and batteries. By 2020, the market will be worth $55.1 billion, with 71 percent printed and 60 percent on flexible substrates.
According to the report, more than 3,000 organizations are pursuing printed, organic and flexible electronics, including companies in the printing, electronics, materials and packaging fields. While some of these technologies are currently in use, with substantial growth in thin film photovoltaics, for example, others such as thin film transistors, developed by over 500 organizations, are only now becoming commercially available.
"The benefits of these new electronics are numerous, ranging from lower cost, improved performance, flexibility, transparency, reliability, better environmental credentials and much more," wrote Das and Harrop. "Many of the applications will be newly created, and where existing electronic and electrical products are impacted, the extent will be varied."
But the technology future of polymers involves an important human factor, according to Stephen Cheng, dean of the College of Polymer Science & Polymer Engineering at the University of Akron.
"The most important technical issue regarding polymers is almost non-technical, or semi-technical -- it is necessary for polymer scientists and engineers to reach out to highly technological people and find polymer applications in other fields, like communications," Cheng told TechNewsWorld. "This is an interdisciplinary approach, and it is the key to success in the 21st century."