Materials Issues
The RoHS Directive prohibits the presence of lead, mercury, cadmium, hexavalent chromium and
certain brominated flame retardants (BFRs) in most EEE put on the market in the EU after July
1, 2006. There are exemptions to these restrictions where alternatives are unavailable,
impractical or unacceptable with current technology.
Maximum concentration values (MCV)
Because lead, cadmium, mercury and hexavalent chromium are found naturally in the environment,
they are often present in trace amounts as contaminants in many alloys and other substances,
even though they were not deliberately added. Therefore, the RoHS Directive allows a maximum
concentration value (MCV) up to 0.1% by weight (1000 ppm) of lead, mercury and hexavalent
chromium, and up to 0.01% by weight (100 ppm) of cadmium.
There has been much discussion about how the MCV will be applied to a finished product. The
EU Technical Adaptation Committee (TAC) has recommended that the MCV will be applied at the
material level, rather than at the product, board or even component level. It is being
interpreted as homogeneous material that cannot be mechanically disjointed into different
materials. For example, considering a component, there would be many homogenous materials
and the MCV would apply to the percentage of restricted substances present in, for instance,
the plastic molding, the metal leadframe, or the wire bonding individually as opposed to the
percentage present in the component as a whole. The TAC is expected to issue a final
recommendation by the end of the year, 2004. TAC recommendations are not binding; final
determination rests with the EU Commission.
The TAC is an EU forum comprised of representatives from each of the 25 member states charged
with determining the meaning and application of interpretive issues associated with the WEEE
and the RoHS Directives.
Lead
The most significant consequence of the RoHS Directive for the electronics industry is the
elimination of lead banning or limiting the use of Hazardous Materials in Electronic Assemblies
is bringing about a major change in the printed circuit board (PCB) assembly industry. The
elimination of lead (Pb) in these assemblies raises many issues and challenges for companies
in the supply chain. Understanding how these changes impact the reliability and the total cost
of ownership are key to the successful implementation of a Pb free product.
Hexavalent Chromium
Hexavalent chromium (CrVI) is used in many industry sectors for a variety of applications
including leather tanning; pigments in paints, dyes, inks and plastics; and wood preserving.
In the electronics industry, CrVI as an anti-corrosion treatment. Given its widespread use and
utility, there will always be a strong voice in support of its continued use.
Nevertheless, the human health threats of hexavalent chromium are well known and widely accepted,
and there is increasing pressure to eliminate its use altogether. Hexavalent chromium is a known
human carcinogen and is extremely corrosive to human tissue. Prolonged inhalation exposure can
damage mucous membranes of the nasal passages and respiratory tract. There are widespread efforts
to restrict, control or eliminate the use of hexavalent chromium.
If the RoHS Directive is any indication of the future of hexavalent chromium, it is quite
possible that its use will be phased out completely in all except for a limited number of
applications.
Cadmium
Cadmium has a variety of uses in electronic and electrical equipment, including, colorants and
pigments, stabilizer in PVC plastic, contact buttons in relays (silver-cadmium oxide), plating
for corrosion resistance, low temperature solders (tin-lead-cadmium). Alternatives exist, but
they generally do not have the same thermal stability, low electrical resistivity and excellent
solderability properties as cadmium.
The primary use of cadmium by the EEE industry is in nickel-cadmium batteries, although these
are rapidly being replaced by lithium-ion and nickel metal hydride batteries.
Mercury
Mercury is widely known as a serious neurotoxicant and poses a significant material replacement
challenge to the EEE industry. It is used in various lighting applications, such as in cold
cathode fluorescent lamps for flat panel displays and laptop screens, to transform UV energy
into visible light. Considerable research has been invested to find viable alternatives to Hg
in these and other applications, but none have proven technically or economically feasible.
Therefore, the RoHS Directive currently exempts Hg from lighting applications. However, the
EEE industry continues to research viable alternatives for these applications.
Brominated Flame Retardants
Flame retardants are used by the EEE industry to prevent or delay the spread of fire in plastics.
They are very inexpensive and highly effective. However, Polybrominated biphenyls (PBB) and
polybrominated diphenyl ethers (PBDE) are targeted by the RoHS directive because of concerns
over their persistence in the environment and potential toxicity to humans. PBBs have been
phased out of use and are not used by the EEE industry. There are three primary congeners of
PBDEs: penta-, octa-, and deca-brominated diphenyl ether. The penta and octa forms of PBDEs
are understood to be toxic and the EEE industry has agreed to voluntarily phase out its use of
the penta and octa forms. However, there is inconclusive evidence regarding the risk of the
deca form; studies indicate that deca-BDE poses an insignificant risk of toxicity to humans or
the environment, provided it remains in the deca form. However, it is unclear whether it tends
to break down into the penta or octa forms once it enters the environment. The EU will decide
soon whether to exempt deca-BDE from the RoHS Directive. In the meantime, the industry is
conducting voluntary risk reduction and monitoring strategies.
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