Halogen-free cables pose electrical, mechanical, and performance challenges

Albert Tsang, Dell -November 19, 2012

Halogens, specifically chlorine and bromine, are suspected of posing serious dangers to human health and the environment when used as a brominated flame retardant (BFR) or in polyvinyl chloride (PVC). As a precautionary measure, many electronics manufacturers have adopted proactive policies to phase out the use of BFRs and PVC.

During the past several years, the electronics industry has been searching to identify PVC-free replacements for its cables and wires that are capable of meeting both stringent performance and safety requirements. A robust and cost-effective drop-in PVC-free replacement has yet to be identified.

To speed the process along, the High Density Packaging User Group (HDP User Group) consortium launched a project that brought together various parts of the supply chain during a three-year period - managing to work around intense intellectual property concerns - to search for halogen-free materials to replace PVC.

As part of this project, the electrical, mechanical, and performance characteristics of more than 50 halogen-free compounds were thoroughly investigated. Of these, 40 halogen-free compounds were successfully manufactured into cables. While these cables may or may not satisfy all baseline requirements, the consortium’s results are an encouraging step toward designing halogen-free, flame-retardant compounds.

Environmental impetus behind halogen-free cables
Environmental regulations such as the European Union’s Restriction of Hazardous Substances Directive (RoHS) and Waste Electrical and Electronic Equipment Directive (WEEE) mandate that certain chemicals used by the industry that are deemed as “hazardous” must be either phased out or restricted.

Halogens are among the chemicals identified as being potentially dangerous. The danger of using BFRs and PVC in electronics centers primarily on its end-of-life (EOL) disposal and the combustion byproducts that are released when using improper incineration methods.

A highly controlled incineration process must be used (>800°C) to prevent the creation of furans or dioxins, because incomplete combustion of halogens can create dioxin. Dioxins are highly toxic and of especially high concern during the uncontrolled burns typically used in developing countries—where much of this type of electrical waste is sent—to extract the precious metals used in cables.

Halogens are also suspected of being bioaccumulants, toxic and carcinogenic with chronic exposure, and environmentally persistent.

Why is halogen use so prevalent?
One of the key challenges the electronics industry faces is that because PVC is inherently flame retardant and works so well in terms of chemical and electrical performance, it can also be easily compounded to create other properties required for a wide variety of cable constructions, and it’s widely used in many products (See Figure 1).

For example, BRF and PVC are used in electronics products, including, but not limited to: internal cables, external wires and power cords; any electrical part with plastic encapsulation, mold compounds, and substrate materials; connectors; plastic bumpers and shock absorbers; keyboards, mice, webcams, and speakers; capacitors; heat sinks; PCB laminates; printer fuser assembly; flexible plastic parts; hard plastic parts; and labels, films, and insulation tapes.

The combination of physical performance, fire safety, transmission characteristics, processability, color, appearance, touch, feel, flexibility, and cost are all extremely difficult to balance to achieve halogen-free materials designed to replace PVC.

Halogen-free compounds are based on a variety of resin systems that can be flammable and generate smoke. To suppress these characteristics, they must be highly filled with bulky flame retardants and smoke suppressants to meet safety performance requirements. This translates into much more expensive cables that are more difficult to process—particularly into odd geometries frequently used for electronics, such as flat ribbon cables, or small or mini wires.

Technical challenges vary not only by product type, but also by material chemistry. Compounders use various ingredients that present unique technical challenges that must be well understood prior to selection to ensure the materials can meet wire and cable requirements, including future regulatory mandates.

While there are commercially available PVC-free alternatives at this time, they either have performance degradation issues or their cost is simply too prohibitive to be considered in high-volume production environments. Supply chain capacity is also a concern with halogen-free materials.

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