1
What are halogens and halides?
At their most basic level, halogens are the electronegative
elements in column 17 of the periodic table, including
fluorine (F), chlorine, (Cl), bromine (Br), iodine (I) and
astatine (At). In electronics
applications, iodine and
astatine are rarely if ever
used. A halide is a chemical
compound that contains a
halogen. A host of halides
are essential to human life,
including a wide variety of
salts and acids. Chlorine is
used to keep drinking water
safe. Halides are present
abundantly throughout
nature in minerals, animals
and plants.
Where are halogens found in an electronics
assembly?
Chlorine, as found in circuit boards, is primarily in the form
of residual materials left over from production of non-
brominated epoxy resins used to assemble circuit boards.
It is difficult to remove all the chlorinated compounds
produced in epoxy resin and minor quantities of sodium
chloride and other chlorides can be found. Concentrations
are typically below 100ppm.
Bromine in electronics is most commonly bound to
brominated flame retardants (BFRs). Brominated flame
retardants have been in common and effective usage
for the last few decades to combat fire risk and property
damage. Brominated flame retardant use is not limited
to electronics. It is also in common usage in furniture,
construction materials and textiles.
Other sources of halogens in circuit boards include
fiberglass sizing, epoxy curing agents and accelerators,
resin wetting and de-foaming agents, flux residues, and
contamination from handling. In the broader category of
“electronics,” many plastics, papers, coatings, sealants,
lubricants, and adhesives are added to the list of sources.
Why are halogens of concern?
There are both known and suspected risks associated
with halogens in electronics. Hundreds of studies have
been performed to determine the immediate and long-
term effects of various halogenated compounds in both
laboratory and outdoor environments. Both the groups
supporting a ban on halogens and the groups opposing a
ban reference specific studies as proof that their point of
view is correct.
The most widely publicized
risk is associated with
byproducts of uncontrolled
disposal by incineration,
which produces dioxins and
furans. Modern incineration
technology, in comparison
to uncontrolled burning,
has virtually eliminated
concerns over dioxin and
furan production from
waste disposal in modern facilities. Given the global waste
disposal economy, proponents of halogen elimination
point to the fact that it is impossible to predict where or
how an electronic product will be disposed of.
Halides and Halogens. What do I need to know?
John Vivari, Nordson EFD
Abstract
With halogen-containing substances in the public eye due to scrutiny by the European Union and a variety of non-
governmental organizations (NGOs) as possible additions to the list of substances banned from electronics, we at EFD
have received numerous inquiries from customers asking how this subject will affect them and their processes. Having just
overcome the hurdle of RoHS (Restriction of Hazardous Substances), they want to know what halogens and halides are,
and what changes they should be prepared for if required to stop using them.
Halide-free materials are not new. Some segments of the electronics industry have been sensitive to halides and their
significance for decades. This paper will give the reader a working knowledge of halogens and halides. Armed with this
education, the reader will be able to make informed decisions when required to use halogen-free materials, either because
regulations dictate it or social pressure makes acceptance preferable to resistance.
Key Words: halide, halogen, bromine, chlorine, flame retardant, RoHS
Figure 1: Columns 14 through 18 of the
periodic table of elements
Figure 2: Burning E-waste to reclaim
precious metals
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Dioxins
Dioxins are naturally occurring materials. Everybody
has some dioxins in them. They enter the body primarily
through food.
Common usage of the term “dioxin” refers to halogenated
dibenzo compounds including polychlorinated dibenzo-
dioxins (PCDDs), polychlorinated dibenzo-furans
(PCDFs) polybrominated dibenzo-dioxins (PBDDs) and
polybrominated dibenzo-furans (PBDFs). There are 210
known dioxin and furan family compounds. Of those
210, 7 dioxins and 10 furans are tracked by the US
Environmental Protection Agency for computation of total
dioxin contribution to the environment.
Sources of dioxin include a wide variety of combustion
and chemical processing methods, along with natural
sources such as forest fires. In 2008, the EPA estimated
dioxin and furan production from human associated
sources in the United States was roughly equivalent to the
estimated dioxin and furan production from documented
wild fires in the United States over the same period.
Both dibenzo-dioxins and dibenzo-furans have 8 bond
sites that chlorine and bromine can attach. The number
and position of attached chlorine or bromine atoms
determines whether the dioxin has any toxic properties.
Dioxins that enter the body are poorly metabolized and
accumulate in fatty tissue and the liver. The most toxic
dioxin is 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD).
There is no known safe exposure level to TCDD. Several
dibenzo-dioxins are established carcinogens and dibenzo-
furan testing classifies furans as predictably carcinogenic.
Brominated Flame Retardants (BFRs)
Brominated flame retardants come in many compositions.
The only property some have in common is a single
bromine atom. Surveys of water samples, animals and
humans have found the presence of BFRs. Some BFRs
are persistent in the environment. Some BFRs do bio-
accumulate, but are also rapidly eliminated so that a
substantial, extended duration source of exposure is
required for adverse effects to be realized. Grouping all
BFRs together is no more appropriate than grouping
all 210 dioxins and furans. A collection of studies over
10 years was assessed by the European Union in 2007.
The conclusion was that the continued use of DecaBDE
and TBBPA, which represent over 95% of BFR use in
electronics, do not pose human or environmental risks.
Despite the European
studies, there remains
a constituency lobbying
against those BFRs that are
persistent; there is concern
over the long-term impacts
on humans and animals.
Testing of particular BFRs
in pure form in laboratory
environments has produced
measureable effects given prolonged exposure of
sufficiently high dosage. Testing of other BFRs suggest
that some are benign. Assessment of the effects on
humans and creatures in the wild is less well understood.
Individual BFRs, such as polybrominated biphenyls (PBBs)
that have established toxic properties are either no longer
manufactured or in the process of discontinuation.
How will halogen-free materials be different?
The “Green” social movement has created an environment
in which it can be to the financial advantage of a company
to be halogen-free as a demonstration of corporate
responsibility. It is left to the technologists to figure out
how to supply safe, high-quality products that meet
corporate environmental goals. Research into halogen-
free materials for circuit board manufacture started in the
1990’s in Europe as companies began to address halogen
concerns. Depending on what materials you are using,
there may be no difference in your process because you
may already be “halide free.”
The governing document defining “halide free” in Europe is
IEC 61249-2 Specification for Non-Halogenated Epoxide/
Woven E-glass Laminates for Defined Flammability. This
specification defines both the term non-halogenated and
flammability performance requirements. The definition
of non-halogenated in this document is 1500ppm with
a maximum chlorine content of 900ppm and maximum
bromine content of 900ppm.
IPC-J-STD-004a defines halide-free fluxes as a flux
containing <500ppm chlorine (bromine and fluorine
converted to chlorine equivalent by molecular weight.)
The primary replacements for BFRs are phosphorous-
based materials. These materials are typically more
hydrophilic, so moisture sensitivity ratings are lower. In
most cases, significantly more halogen-free material is
required by mass to achieve the same level of flammability
resistance. Side effects include shorter shelf life, greater
Figure 2: 2,3,7,8 tetrachlorodibenzo-p-dioxin (TCDD)
Figure 4: 2,3,7,8 tetrachlorodibenzo-p-furan (TCDF)
Figure 3: E-Waste
3
PCB stiffness and lower coefficient of thermal expansion
(CTE). Of potential benefit, some halogen-free laminate
systems have greater thermal stability than traditional
FR-4. Phosphorous-based chemistries are currently
more costly and the majority are supplied out of Europe
and Asia. The process window for successful board
manufacture is smaller than with FR-4, requiring close
cooperation between material vendors and board
fabricators.
Halide-free fluxes are typically less active than their
halogenated predecessors. A consequence is that many
do not wet as well and have a smaller profile process
window. Component lead solderability has a greater
effect on joint quality. In addition to changes in the reflow
process, migration to halide-free reflow may necessitate
other material changes to accommodate the limitations of
halide- free flux chemistry.
Conclusion
The decision to produce a halogen-free electronics
product is not based on existing regulation. Those
halogenated compounds that have established risks
have been removed from the market. The key drivers
for the major multinational players with halogen-free
implementation plans are a combination of public
perception of environmental sensitivity and a choice on
the side of caution to avoid the cost of a last- minute shift
in the face of possible future legislation.
Currently available halogen-free materials are not identical
in performance to their halogenated counterparts and
require more attention to detail to accommodate the
smaller process windows associated with them. Their
long-term performance is less well understood.
Development of halogen-free materials continues to
advance. As the desirable properties of halogen-free
materials increase relative to their undesirable properties,
their acceptance will increase. Whole new avenues of
research into inherently flame- resistant materials promise
profound changes in how flammability risk is balanced
against environmental concerns. Until those potentials are
realized, it is left to technologists to make the best of what
they are given to work with.
References:
U.S. EPA (Environmental Protection Agency). (2006)
An inventory of sources and environmental releases of
dioxin-like compounds in the United States for the years
1987, 1995, and 2000. National Center for Environmental
Assessment, Washington, DC; EPA/600/P-03/002F.
Available from: National Technical Information Service,
Springfield, VA, and online at http://epa.gov/ncea.
IPC-WP/TR-584A.: ipc.org, Print. (2007)
Birnbaum, Linda S., and Daniele F. Staskal. “Brominated
Flame Retardants: Cause for Concern?” Environmental
Health Perspectives 112.1 (2004): 9-17. Web. 2 Sep. 2009.
Dioxin Facts - Dioxins, Furans, TCDD, PCBs Chlorine
Chemistry Division of the American Chem, 2009. Web. 15
Aug. 2009 .
“Fire Information - Wild Land Fire Statistics.” National
Interagency Fire Center N.p., 2008. Web. 11 Sep. 2009
.
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