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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