Halogen-Free has recently been hot topic in the electronics industry due to increasing concern over environmental issues. A voluntary initiative has been undertaken by the electronics industry, known as the “Halogen-free Initiative.” This self imposed initiative bans the use of halogenated materials in the manufacture of electronic equipment. Certain types of halogenated materials have a detrimental effect on the environment as well as being toxic to humans and animals. The types of materials covered are mechanical plastic parts (thermoplastics), cables, printed circuit boards, electronic components, connectors, films, adhesives, tapes and vibration dampening parts.

What are Halogens?

The halogens or halogen elements are a series of nonmetal elements from Group 17 (also called as Group-VIIA) of the periodic table, comprising Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I), and Astatine (At). Iodine and astatine complete the group, but are not the subjects of primary consideration for electronics manufacturers.

The term “halogen” means “salt-former” and compounds containing halogens are called “salts”.

Halogens are highly reactive, and as such can be harmful or lethal to biological organisms in sufficient quantities.

What are Halides?

Elemental halogens have seven valence electrons and are very reactive. In their quest to obtain an eighth electron, halogens can be very strong oxidizing compounds. Once a halogen does obtain that eighth electron, it picks up a net negative charge and becomes a halide. Having the net negative charge makes the halide compound ionic. A common example is table salt: Na+Cl-. Some readers also may be familiar with the similar term halite, spelled with a “t” as opposed to a “d.” Halite is the mineral form of NaCl that’s known as rock salt. It’s regularly used in winter climates to melt snow and ice from walkways and roadways.

Where and why are Halogens used?

In broad terms, halogens are associated with PWBs and components, while halides are associated with soldering operations. There are exceptions. For the most part, halogenated compounds are found in PCBs, solder masks, mold compounds, connectors, cable insulation and wiring conduit. They are used because they offer flame (fire) retardant properties to flammable plastics. The common halogens give off halides with elevated temperatures, decomposing and releasing halogenated compounds in order to extinguish fires. These are toxic and corrosive when decomposing. However, they are benign when at ambient temperatures.

As an example, Fluorine derived FEP (Fluorinated Ethylene Propylene) or Teflon provides extremely high heat resistance when used in the insulation of plenum rated communications cabling, which limits its combustion in a fire and provides excellent fire safety performance. Teflon in other forms is also used in many other consumer and industrial products.

Take as a second example Chlorine, which is a component of PVC (Polyvinyl Chloride). According to the Vinyl Institute, “Vinyl is the second largest selling plastic and the most versatile one. Vinyl’s low cost, versatility and performance make it the material of choice for dozens of industries such as health care, communications, aerospace, automotive, retailing, textiles and construction.” The chlorine in vinyl is derived from common salt and water, a readily available, inexpensive commodity allowing PVC to be produced at a lower cost compared to alternative materials.

The abundance of raw material components, relatively low material cost and desirable product properties are the key reasons many halogenated compounds are the materials of choice today. In many applications a halogenated material can provide the required product performance at a lower overall cost than halogen-free materials.

What is Halogen-Free?

In general as the term implies “halogen-free” means the product material that does not contain any compounds derived from halogen elements.

With regard to fire safety, the term “halogen-free” refers only to the toxicity of the smoke generated during combustion of a material. By its nature a halogen-free product will not release significant levels of toxic or corrosive gases when it is ignited.

“Halogen-free” does not alone indicate that a product enhances safety, health or is better environmentally for a given application.

Why Halogen-Free and Halide-Free?

If incinerated under certain conditions, they can form dioxins, which are known carcinogens. In structural fires, they can emit toxic gases that prevent victims from escaping (and rescuers from entering) burning areas. In a computer room, a fire in one machine can release acidic fumes that produce catastrophic failures in nearby machines. These combustion-related implications sound horrible, and there are plenty of other sound reasons to eliminate halogenated materials. Often, however, it’s the halogenated compounds that permit higher temperature operation and prevent fires in the first place, and elimination or substitution is not a simple process. Just like leaded solder alloys, there are no drop-in replacements for many halogenated products.

The amount of toxicity and smoke generation can also be specification factors for a particular material or product. These two factors are of greatest concern in environments where people will be within enclosed spaces where movement away from a fire source may be restricted. Examples of such environments are transportation applications such as in mass transit vehicles, in offshore oil and gas drilling rigs, and in shipbuilding. In addition to other factors, reducing the level of toxicity of any smoke generated during a fire in these environments is a key specification factor and safety requirement.

Some halogenated compounds have already been replaced with halogen-free products; others are slated for removal and replacement over the next several years. Bear in mind not all halogenated compounds are toxic. Consider table salt: Ingestion of excessive quantities may not be advisable, but it is certainly not considered a toxic substance.

How do we define halogen-free and halide-free?

Both halogens and halides can be found in trace amounts as impurities in many materials. Therefore, upper limits for the presence of these materials have been set by the following organizations:

How do we test for halogens and halides?

Halides can be detected using simple spot tests as described in J-STD-004A. They can be quantified using ion chromatography (IC). But halogens themselves are a little more difficult to test for. IC cannot distinguish them unless they are first ionized; the test preparation procedure itself can influence the results. Combustion IC is generally considered a reliable technique that ionizes the halogenated compounds through a combustion process. Another routine analytical technique that can detect halogens (and many other elements) down to the parts-per-billion level is inductively coupled plasma (ICP) spectroscopy. However, neither of these techniques can distinguish between an ionic halide and a non-ionic halogen.

What applications need halogen free products now and in the future?

In applications such as data centers and phone switching stations, and other areas where large concentrations of electronics exist, there is concern that th
e smoke from even a small fire could travel to other areas and damage or affect the performance of nearby equipment.

The mechanism of how this damage may occur and the extent of the damage possible from corrosive smoke are not entirely clear. However, companies can reduce the potential risk by specifying halogen-free products as part of a fire damage prevention strategy.

With regard to fire safety, the term “halogen-free” refers only to the toxicity of the smoke generated during combustion of a material. By its nature a halogen-free product will not release significant levels of toxic or corrosive gases when it is ignited.