Note: This is the first article of a three-part series covering plastics in electrical and electronic (E/E) device (1) trends, (2) material/process advances and (3) applications.


Manufacturers in the various electrical/electronic (E/E) sectors can choose from an enormous and versatile range of plastics to meet every requirement. Depending on the electronic component or device, designers choose plastics for their rigidity or flexibility, toughness/durability, resistance to low or high voltage and their electrical insulation or conductive qualities. Ease of fabrication into complex shapes can also be a requirement for E/E applications.

Depending on their targeted application or operating environment, the plastic material's mechanical properties, temperature/chemical resistance and flame-retardant properties must also be considered. The ongoing miniaturization of circuit boards and components such as computer chips increasingly relies on high-performance plastics to provide tough, dimensionally stable parts, often with thin walls that can withstand both the stress of assembly and the strain of use.

As a result of these many property requirements, the E/E sector is a significant consumer of engineering and high-performance specialty polymers.

The electrical/electronic market is the world's third-largest plastics market after packaging and building and construction. Plastics have been a basic material for housing electronics, insulating components from all types of interference and protecting both parts and users.

Plastics Institute of America
Electrical/electronic plastics market usage by material type.

Thermoplastics, particularly engineering plastics, dominate the plastics E/E market sector. Without plastics, most electronic products would not be practical or economical. Applications range from miniature connectors to housings for large electronic devices. The electronics market requires materials and parts for new products to be evaluated against UL (Underwriters Laboratories) requirements

If not inherently flame-resistant, plastic material for electronics applications must be offered in flame-resistant formulations. In Europe, the Restriction of Hazardous Substances (RoHS) and Waste Electrical and Electronic Equipment (WEEE) directives also mandate that flame resistance be achieved without the use of halogenated components.

An important UL requirement is limiting temperature index (LTI), which specifies the maximum continuous use/operating temperature for a material. Derived from long-term oven aging tests, LTI is the maximum temperature that causes a 50 percent decay in the studied properties over the "very long term." While a UL listing for flame resistance for a qualified product is relatively quick and inexpensive to get, the LTI rating typically takes at least one year to obtain.

Important plastics properties for electronics are readily summarized. Apart from mechanical properties, the material's electrical behavior is a decisive factor in using plastics for electronic applications, with key starting point test guidelines as follows:

  • Insulation properties: Often of primary importance — most plastics are good to excellent insulators with specific resistance around 1013 Ohm-meters
  • Dielectric strength: Of special importance for plastics in high-tension applications, such as automotive ignition systems
    • Typical dielectric strength values are approximately 30,000 volts/meter
    • For nylons, it may drop by 10-20 percent due to absorption of humidity
    • With static charges, surface resistivity is the determining factor
  • Tracking resistance
  • Arcing resistance
  • Dielectric properties
  • Glow-wire test: Provides information about whether an object such as an overheating conductor could be a fire hazard in an electrical device
  • Flame retardants: Used to slow down combustion or prevent it altogether as nearly all plastics are inherently flammable, an important consideration in electronics
  • Flow characteristics: Important in miniaturization

Plastics Institute of America
Flame-retardant compound technology drivers.


Let's now review some key trends in flame retardant plastics compounds. New developments in flame-retardant compounds are being driven by:

Environmentally responsible solutions

Increasingly halogen-free flame retardants (HFFR) are replacing conventional halogenated flame retardants in the E/E sector in response to regulations, consumer environmental awareness and corporate sustainability objectives. Government regulations and directives, as well as consumer demand for more environmentally-friendly materials have directed the plastics and flame retardant industries to seek alternatives to the halogenated additives generally used for flame retardancy, especially in electrical and electronic applications.

The European Parliament has adopted amendments to the RoHS Directive coined RoHS2. RoHS1 currently bans the use of certain hazardous substances in electrical and electronic equipment including two categories of brominated flame retardants polybrominated biphenyl (PBB) and polybrominated diphenyl ethers (PBDE).

While the recast directive (RoHS2) does not expand the substances list subject to the directive's restrictions, and does not list substances for possible future addition, a nonbinding recital directs the European Commission to study four additional substances: brominated flame retardant hexabromocyclododecane (HBCDD) and three phthalate plasticizers bis (2-ethylhexyl) phthalate (DEHP), butyl benzyl phthalate (BBP) and dibutylphthalate (DBP)].

Cost

Novel phosphorus-organic FR and mixtures of HFFR have been developed and introduced for various materials in E/E applications in response to drastically increased costs of brominated flame retardants.

Polymer/processing compatibility

Many new HFFR are reactive systems that become part of the polymer network, or represent salts or polymer species in the form of additive flame retardants. Through reaction, or additive low volatility, flame retardant migration and subsequent loss of flame retardancy are prevented.

Meanwhile, these additives have a sufficient thermal stability to be easily incorporated in polymers being processed.

Thinner walls/lighter weight

The demand for more compact, lighter-weight LED lighting, as well as consumer electronics, automobiles and medical devices that call for thinner wall design is also driving development of improved flame retardant materials.

Two advantages in phosphorus-containing FR development are enhanced hydrolysis stability (mainly arylphosphates) and lower-loading requirements of nitrogen-containing phosphorus compounds (i.e., phosphamides, phosphacenes) due to potential synergistic effects. This trend is applicable to both polymer enclosures and glass fiber-reinforced materials.

Pinfa-NA, the North American sister organization of the Phosphorus, Inorganic and Nitrogen Flame Retardants Association (Pinfa) was formed recently by leaders in the flame retardant industry that focus on nonhalogen solutions and materials. The group's primary focus is to:

  • Advance environmentally-friendly nonhalogenated flame-retardant solutions in North America.
  • Bring together manufacturers and users of major flame-retardant technologies.
  • Support fire safety through innovative, reliable and sustainable fire performance solutions, using products based on halogen-free phosphorus, nitrogen and inorganic compound (metal ions, hydroxides).