"why is there a drive for halogen free concurrently with the drive for
leadfree"?
The answer to this question is complex. First of all, some activist
ecolo-political organisations are constantly waging war on all
halocarbons, no matter their respective merits or effects on the
environment or on H&S. Secondly, some brominated fire retardants used in
the past for e.g., children's clothes have been proved to cause
developmental problems in the kids wearing them. This has given all
brominated fire retardants a bad name. Then, other brominated compounds
have been found to decompose into some really nasties, such as
tribromoacetic acid, which has retarded growth and yield of leguminous
plants, such as soya at ppt levels. In other words, bromocarbons have a
bad reputation. TBBPA, as far as is known, when crosslinked into epoxy
or polycarbonate resins, is relatively harmless.
I would take issue with DDave about ozone depletion. It is true that
many persistent bromocarbon gases and vapours are ozone-depleting and,
if they reach the ozone layer, are very damaging. However, the vapour
pressure of TBBPA is negligible and, once crosslinked, must be
considered as non-existent, so it is not considered as an ODC. It is not
included in the extensive lists of controlled substances in the Montreal
Protocol. Nor are any of the decomposition products, which all have a
short atmospheric residence time with hydrolysis within the troposphere
within hours of release. Of course, the major brominated by-product of
pyrolysis is hydrogen bromide, which has an ionic bond and rains out in
the atmosphere. Even if some reached the ozone layer, which is doubtful,
it would not undergo photolysis, releasing monoatomic bromine as a start
of the catalytic ozone-depletion mechanism, so it is considered as a
totally non-ozone-depleter. This is in contrast with n-propyl bromide
(1-bromopropane) used in our industry as a defluxing solvent, which is a
mild ozone-depleter and which hydrolyses relatively slowly, so that a
small percentage of the molecules may reach the ozone layer where there
is a fast transport mechanism, such as in the intertropical convergence
zone. Unfortunately, nPB has not been included in the Protocol, either,
because the mechanism of transport is so complex that it cannot be
accurately modelled, even with a supercomputer, as it is tightly bound
up with weather and the concentration of hydroxyl groups. I have been
working with this aspect of environmental science for nearly two decades
and have been tightly involved in the regulatory aspects of
ozone-depleting substances (especially solvents), so please consider me
as sufficiently authoritative to be able to pronounce validly on
ozone-depleting substances.
As TBBPA is tightly crosslinked into the epoxy structure, which is, of
course, thermosetting, recycling is virtually impossible. Re-use of FR-4
boards is best made by chopping them up and adding them to bitumen road
mix or concrete aggregates and similar applications. This is
environmentally harmless. To extract the chemicals back for recycling is
very difficult, expensive and requires an enormous amount of energy and
is therefore undesirable.
I have copied this message to the EnviroNet, should you wish to pursue
the environmental aspects.
Brian
Thomi wrote:
> Dear Brian,
>
> thank you for clarification! I apologize for spreading myths myself instead
> of asking proper questions. Your chemical explanation really stifles me,
> because now I have to ask myself "why is there a drive for halogen free
> concurrently with the drive for leadfree"? Excuse me if I let out this
> question here in the leadfree forum, but I feel now the discussion is once
> more on the edge of "is there any use behind this", after first politics
> drive us into economically (and ecologically) insane procedures, and now
> industry themself seems to do the same (maybe DDave knows a thread in
> halogen free where this has been discussed before?). Last question - how's
> it with recycling of FR4 do you see problems due to the TBBA content in the
> epoxy?
>
> Schön' Gruß
> Thomas Ahrens, Boostedt
>
> ----- Original Message -----
> From: "Brian Ellis" <[log in to unmask]>
> To: "(Leadfree Electronics Assembly Forum)" <[log in to unmask]>; "Thomi"
> <[log in to unmask]>
> Sent: Thursday, January 13, 2005 10:00 AM
> Subject: Re: [LF] Halogen free alert
>
>
>
>>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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