BRIAN,
are they going to take them back after use? (like the leadfree group
proposed for the lead containing solder). Does EU got a task group study
this? wow! I thought just the fire insurance goes up as side effect (as the
otherside argue about the health insurance goes down)...
jk
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]]On Behalf Of b_ellis
>Sent: Wednesday, August 14, 2002 2:16 AM
>To: [log in to unmask]
>Subject: Re: [TN] Bromine
>
>
>Joyce,
>
>Not to mention that the new stuffs (nitrogen- and phosphorus- organics)
>may leach just as much ... or more!
>
>Brian
>
>joyce wrote:
>>
>> Dave,
>> agree with you on the toxins... the engineering method is to
>determine what
>> is probability of burning at what temp. produce what kind of
>result. Most
>> of the Flame retardant product is UL 94-0 rating... as long as
>you replace
>> something with the same performance: corrosion, UL, material
>compatibility
>> etc.etc. and low cost...I am sure everybody would be happy.
>However, few of
>> the traps some of us went into are the "flashy" stuff, promise a lot,
>> implemented at the product level without sufficient test in real
>life data.
>> To replace a deficient product with an "unknown" is very scary. Costly
>> lesson to learn.
>> ...my 2.cents.
>> jk
>>
>> >-----Original Message-----
>> >From: TechNet [mailto:[log in to unmask]]On Behalf Of David Fish
>> >Sent: Tuesday, August 13, 2002 1:05 PM
>> >To: [log in to unmask]
>> >Subject: Re: [TN] Bromine
>> >
>> >
>> >Brian
>> >
>> >Bromine always seemed like such a 'nice' chemical, didn't it?
>> >
>> >Let me take you in a different direction. Brominated flame retardant
>> >incineration produces toxins:
>> >* polybrominated biphenyl ether (PBBE)
>> >* polybrominated biphenyl oxide (PBBO)
>> >
>> >Dave Fish
>> >
>> >----- Original Message -----
>> >From: "b_ellis" <[log in to unmask]>
>> >To: <[log in to unmask]>
>> >Sent: Tuesday, August 13, 2002 5:14 AM
>> >Subject: [TN] Bromine
>> >
>> >
>> >> Yet once again, bromine has raised its head in a couple of recent
>> >> threads on this list. I'm beginning to question whether
>brominated fire
>> >> retardants are as bad as they are made out to be or whether they are
>> >> just painted bad. Unfortunately, my knowledge of polymer chemistry is
>> >> insufficient to form a judgement. Here is what I'm thinking:
>> >>
>> >> The basic manufacture of epoxy resins is in two stages, the
>> >> prepolymerisation and the crosslinking. I won't go into more than the
>> >> basics, as I know that the subject is very complex. The epoxy group is
>> >> provided by epichlorohydrin which is reacted with bisphenol A (BPA) in
>> >> the presence of an alkali (NaOH), the latter serving to
>react with the
>> >> liberated chlorine atom to form NaCl, during the
>prepolymerisation. Most
>> >> of the latter is removed for electrical grade resins, but some remains
>> >> (hence the high dielectric constant and poor power factors).
>> >>
>> >> The epoxy groups are subsequently reacted with cross linking
>agents for
>> >> the final polymerisation (curing) of the resin. Theoretically, if all
>> >> the components are stoichiometric, the resultant cured resin is
>> >> perfectly homogeneous with uniformly-sized molecules. In
>practice, this
>> >> is never perfect.
>> >>
>> >> The bromine comes in with FR-4 by using tetrabromobisphenol A
>(TBBPA) in
>> >> place of some of the BPA. This has the characteristic of releasing HBr
>> >> and Br2 when heated to combustion temperature, this, being heavy,
>> >> blankets the burning resin and excludes oxygen, thereby extinguishing
>> >> the flame. TBBPA is identical to BPA other than that 4 of the H atoms
>> >> are replaced by Br atoms, which are therefore covalently bonded to two
>> >> of the non-cyclic carbon atoms. There is therefore no question of any
>> >> ionic bromide being present in FR-4. Why then do bromide ions
>leach out
>> >> of FR-4, as has been proved time and time again? (Let's
>discount bromide
>> >> activated fluxes from this equation.)
>> >>
>> >> I have several thoughts on the matter:
>> >> a) could it be that the TBBPA is supplied with excess free Br atoms or
>> >> with brominated impurities that are less stable?
>> >> b) could it be that pressing temperatures already start a breakdown of
>> >> the TBBPA, allowing free HBr to float around the resin
>matrix? (This may
>> >> explain why FR-4 is marginally poorer electrically than G-10)
>> >> c) could it be that the NaOH is capturing some Br from the
>TBBPA during
>> >> prepolymerisation?
>> >> d) could it be that the TBBPA is astoichiometrically in excess,
>> >> providing an easily attacked molecule?
>> >> e) could it be that there are no free bromide ions at all, until our
>> >> extraction fluid hydrolyses some organobromine compound? (If
>this is so,
>> >> then our ion extraction/ion chromatography tests become less
>meaningful,
>> >> as providing a means of a reaction!)
>> >>
>> >> I think we need the thoughts of a specialist polymer chemist
>to obtain a
>> >> much better understanding of what is happening and its
>influence on the
>> >> reliability of our FR-4 substrated assemblies.
>> >>
>> >> Anyone any ideas????
>> >>
>> >> Brian
>> >>
>> >>
>>
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