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You wont find the term ‘homogeneous’ in the RoHS
Directive. In fact, it doesn’t appear in the related
WEEE Directive or even the ‘Guide to the implementation
of directives based on the new approach and the global approach’
(commonly referred to as the ‘blue book’). So
where did it come from?
The expression first appeared in a Commission stakeholder
document of December 2003. It was used in the context of proposing
maximum concentration values for RoHS restricted substances:
"A maximum concentration value of 0.1% by weight
in homogeneous materials for lead, mercury, hexavalent chromium,
polybrominated biphenyls (PBB) and polybrominated diphenyl
ethers (PBDE) and of 0.01% weight in homogeneous materials
for cadmium shall be tolerated. Homogeneous material means
a unit that can not be mechanically disjointed in single materials."
At the time, this document didn’t help a great deal,
as no one fully understood how to correctly interpret ‘homogeneous’
or ‘mechanically disjointed’. Lead (Pb) was restricted
to 0.1%, but 0.1% of what?
The latest interpretation of homogeneous from the UK government
and Commission suggests the term ‘homogeneous’
to be understood as "of uniform composition throughout".
So examples of "homogeneous materials" would be
individual types of plastics, ceramics, glass, metals, alloys,
paper, board, resins and coatings.
They go on to suggest the term “mechanically disjointed”
means that the materials can, at least in principle, be separated
by mechanical actions such as unscrewing, cutting, crushing,
grinding and abrasive processes.
So how do these expressions actually apply in the real world
of electronics?
Take an electrical cable, for example. It has a metal core,
a plastic insulation and perhaps tinned terminations. The
cable as a whole is not homogenous as it can obviously be
separated by some of the methods described above. The metal
core, even though it may be an alloy of more than one element,
is still considered homogeneous, as mechanical disjointing
cannot separate these alloys. The same applies to the plastic
insulation. So the metal conductor, the plastic insulation
and the solder used to tin the terminations are each homogeneous
elements and must all comply individually with the requirements
of the RoHS Directive. Moreover, if the conductor received
some form of passivation treatment, any residual passive film
would also need to comply.
Using this same methodology, a semiconductor is not homogeneous
as it consists of, amongst other things, die, die attach,
a lead frame and a housing. In essence, the legislation applies
to the lowest common denominator of an item of uniform composition.

Maximum
concentration values, or MCV’s, define the maximum amount
of the individual restricted substance that RoHS directive
will tolerate in each homogeneous material (see above). Whilst
the text of the legislation defines the six substances to
be restricted, it doesn’t actually specify what the
MCV’s might be. The Directive clearly requires you to
restrict (not remove) six substances - but to what level?
During August 2005, Commission
Decision 2005/618/EC was published which amended article
5.1(a) of the RoHS Directive. This decision states:
"For the purposes of Article 5(1)(a), a maximum
concentration value of 0,1 % by weight in homogeneous materials
for lead, mercury, hexavalent chromium, polybrominated biphenyls
(PBB) and polybrominated diphenyl ethers (PBDE) and of 0,01
% by weight in homogeneous materials for cadmium shall be
tolerated."

The term
‘put on the market’ has probably caused the most
confusion surrounding the legislation. The expression comes
from Article 4.1 of the RoHS Directive, which states:
"Member States shall ensure that, from 1 July 2006,
new
electrical and electronic equipment put on the market does
not contain lead, mercury, cadmium, hexavalent chromium, polybrominated
biphenyls (PBB) or polybrominated diphenyl ethers (PBDE).
National measures restricting or prohibiting the use of these
substances in electrical and electronic equipment which were
adopted in line with Community legislation before the adoption
of this Directive may be maintained until 1 July 2006."
The ‘market’ refers to the European single market.
However, as EU Directives apply to the European Economic Area
(EEA), Iceland, Liechtenstein and Norway also fall within
its scope.
So what does putting (or placing) a product on the market
actually entail? Guidance from the European Commission suggests
"... a product is placed on the Community market
when it is made available for the first time. This is considered
to take place when a product is transferred from the stage
of manufacture with the intention of distribution or use on
the Community market."
The term ‘transfer’ is key in interpreting this
expression. In essence, the transfer of a product takes place
when it passes from the manufacturer (or his representative)
to the importer, distributor or end user. There doesn’t
need to be a financial transaction for this to occur –
product that is donated or given away is still considered
to have been placed on the market.
A product is not considered
to have been placed on the market when it is transferred to
a manufacturer for further assembly, packaging or labelling,
is held by customs, is to be exported to a third country or
is to be displayed at trade fairs, exhibitions or demonstrations.
So, if a device enters the EU, but requires a little final
assembly or packaging then it has not yet been 'put on the
market'. In addition, product is not classed as been placed
on the market when it is
"... in the stocks of the manufacturer, or
the authorised representative established in the Community,
where the product is not yet made available ..."
Have you made the product available for sale? Could a customer
buy it? If not, then again, one could argue that it has not
been placed on the market.
Finally, RoHS does not apply exclusively to new products.
The definition above states that a product is placed on the
Community market when it is made available for the first time.
So a product originally sold outside of the EU, which subsequently
enters the market secondhand after the 1st July 2006 (whether
bought or free issued) would also fall within the scope of
the legislation, regardless of the fact it is 'used'.
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