I think one should be less alarmist about the products resulting from
the incineration of FR-4. What do you mean by dioxin? Strictly speaking,
dioxin is formed by two benzene rings joined by, as the name implies, by
two oxygen atoms. None of the three unsaturated cyclic compounds is a
very dangerous or persistent chemical. However, the name dioxin has been
loosely applied to a dioxin derivative,
2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD)which has been blamed
for all sorts of ills, including the poisoning of the new Ukrainian
president. This is a very persistent chemical but is dangerous only in
relatively high doses. The only usual symptom of exposure is chloracne.
It is very undesirable, though, due to its long residence time. Since
the Seveso disaster, its toxicity and epidemiology has become well
known. There are a number of isomers of 2,3,7,8-TCDD but these do not
have the persistence of 2,3,7,8, nor do the analogue substances
containing fewer chlorine atoms.
It is conceivable to have a bromine analogue,
2,3,7,8-tetrabromodibenzo-p-dioxin. It is possible that this may be
slightly more toxic than 2,3,7,8-TCDD, because the looser covalent bonds
to the bromine may be the cause of a more rapid metabolisation. However,
by the same token, it would have a much lower persistence in nature.
Is it possible for 2,3,7,8-TBDD (or -TCDD) to be formed during
incineration? Let's discount the TCDD (the substance usually loosely
called 'dioxin') straight away: all the chlorine atoms in FR-4 resins
are ionically bonded. Let's examine how heat affects TBBPA in
cross-linked resins. The substance is stable until it reaches
temperatures exceeding 350°C. Decomposition occurs by the release of
bromine gas (which is what gives the flame-retardant properties). At
higher temperatures, a whole host of other reactions may occur and most
of the remaining bromine would be driven off as hydrogen bromide and
bromomethanes, which would rapidly decompose to hydrogen bromide and
carbonyl bromide (all nasty compounds, but easily removed by scrubbing).
It is true that TBBPA has two benzene rings, but they are separated by a
methyl group and there is insufficient oxygen in the resin to make it
likely that they would would form a dioxin bond together, let alone for
a 2,3,7,8-TBDD molecule to form. I therefore believe it to be a myth
that incinerating FR-4 will form dioxin and, if perchance it did, it
would neither be a dangerous one nor in any significant quantity. In
other words, the danger is within the emotive frame of the word 'dioxin'
and not in the incineration.
Brian
Thomi wrote:
> Please keep in mind that "RoHS compliant" is not synonym with "Halogen
> free".
> The already RoHS compliant available FR4 materials (nowadays standard
> materials) and polymer package compounds contain chemically bound TBBA
> (tetrabrombisphenol A) flame retardants, which are not forbidden by RoHS.
> Halogen free is way beyond RoHS scope, but (of course) better in terms of
> "green electronics" due to the fact that they do not form dioxines during
> carcination, and are better suited for recycling.
>
> Schön' Gruß
> Thomas Ahrens, Boostedt
>
> ----- Original Message -----
> From: "Lee Parker" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Tuesday, January 11, 2005 5:29 PM
> Subject: Re: [LF] Halogen free alert
>
>
>
>>Ofer
>>
>>Isola has a very good web page on their materials showing their degree
>>of compliance.
>>
>>While you are at it, you may also want to contact the soldermask
>>suppliers. I understand not all soldermask are compliant.
>>
>>Lee
>>
>>-----Original Message-----
>>From: Leadfree [mailto:[log in to unmask]] On Behalf Of Ofer Cohen
>>Sent: Tuesday, January 11, 2005 3:56 AM
>>To: [log in to unmask]
>>Subject: [LF] Halogen free alert
>>
>>Hi all,
>>Finally we've received a customer's requirement for halogen-Free
>>product. I've already looked at the PCB laminates issue. Does anyone
>>have any clue about the components availability? Any general idea for
>>the price tag?
>>
>>Regards
>>Ofer Cohen
>>Manager
>>Quality Assurance, Reliability and Production Technologies
>>SEABRIDGE Ltd. - A Siemens Company
>>
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