Brian
I am surprised by your hashness in your last few e-mails. It resonates to
me similar to the response much of the public gives "irradiated" vegetable
produce in which they believe it makes it radioactive (it does not). It is
emotional and without understanding.
For the record, I have recently been asking a different PWB group as to why
bother with getting lead(Pb)-free solders. But that is not what I am
discussing here:
One cannot label Pb as just one other metal and that health advocates will
regulate them all out of existence. There are different toxicities of
different atomic elements and molecules on a case by case basis. Pb is one
element known to particularly harmful in small doses over a long period of
time. There are others, for example cadmium(Cd) or Hg, but other metals are
not (e.g., iron or gold). Organometallic compounds need to be evaluated on
a case by case basis as well. Unfortunately, we (industry and government)
don't have the resourses to test each one, so one draws on general chemical
understanding and classifications to ascertain which molecules are expected
to be harmful. My guess is that tin by itself is not harmful in small
quantities, but their organometallics associates may be more of a threat
based on chemical structures and electronic similarities. A good example is
nickel carbonate (I think it is nerve gas) which has a very simple
structure. Pure Ni is not harmful in small quantities, but obviously this
organometallic comparison is. On the other hand, the organometallic
compounds we ingest daily within vitamin tablets (you have to get Fe in some
form your body can absorb) are obviously safe up to the point of liver
poisoning (i.e., overdosing).
Because of my newness to this forum, I am assuming ITRI has the task of
leading (pun intended) the no-lead development in the PWB industry. I
question it's importance. I even question it's objectivity (because that's
what I always do in my work). But I have no doubt they are trying to
evaluate solders without excess craziness as you suggest...
And yes, if the medical community said 5 g of Sn is ok in some form (tried
on animals, etc.), I'd eat it without worry...with chocolate on top, of
course!!!
Carey
-----Original Message-----
From: Brian Ellis <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: Monday, November 08, 1999 6:54 AM
Subject: Re: [LF] Long-term solutions
>Kay
>
>Obviously, you have to protect tin, that is what you are paid for.
>However, would you **willingly** ingest just 5 g of any tin compound,
>organic or inorganic?
>
>I repeat, no-one knows what reactions may occur in a landfill, simply
>because no-one knows what is in water that reaches tin. It MAY be
>perfectly benign, it MAY not. Furthermore, on the average PCB, apart
>from oxidised tin, there are a neat variety of organic acids readily
>available to reduce it!
>
>Going back to the start of this thread: it is my honest belief, ITRI
>notwithstanding, that the presence of all anthropo-sourced metals,
>beyond trace quantities, is undesirable in the environment. Sooner or
>later, as more knowledge is gained, they will probably all be restricted
>therefore they must be recycled to the maximum, tin and lead both. If
>they are recycled, why ban them?
>
>Of course, I understand that the ITRI would prefer otherwise a) because
>they receive their funding from tin production and b) because they would
>prefer that solder contains 95%+ Sn, rather than 63%. I have no vested
>interest in what I say, other than hoping electronics production may
>continue as economically and as easily as possible.
>
>Best regards
>
>Brian
>
>Kay Nimmo wrote:
>>
>> Dear Brian
>>
>> I would just like to clear up some of the points you make on toxicity of
tin. It is inaccurate to say that many tin compounds are toxic as
distinction should always be made between organo-tin compounds and all other
forms of tin. It is also inaccurate to generalise and claim all organotins
are toxic. The toxicity is not specifically related to the tin, but to the
nature and number of the organo- groups attached. See the paragraph below.
>>
>> As far as the comment on cans is concerned the lacquer coating is in fact
there to prevent corrosion. In some cases a lacquer coating is deliberately
not used in order for the tin to dissolve to a small extent in the acid food
juice and stabilise colour and (apparently) taste. Take a look at your cans
of tomatoes/beans etc and you will find that they are unlacquered, or only
partially lacquered.
>>
>> The effect of distribution of tin metal in the environment has been well
examined. In particular, the US Fish and Wildlife service made an extensive
study on tin toxicity during approval of tin as lead-free shot. Data on the
behaviour of tin in soils, water, wildlife, livestock and man was examined
with tin succesfully passing this stage of the approval process.
>>
>> Kay
>> ITRI
>>
>> Organotins: toxicity is related to the precise nature of the
organo-moiety. Essentially, there are four basic types: mono- (with one
organic group attached to the tin), di- (with two), tri- (three) and tetra-
(four). As a generalisation, toxicity is greater for tetra- and tri- types
than for di-, which in turn is greater than for mono-. However, within each
type, it is the nature of the organo- groups attached to the tin that is
important. With regard to mammalian toxicity, methyl- and ethyl- groups
generally give the highest toxicity, whereas larger alkyl groups (e.g
butyl-, octyl-) are less toxic to mammals, but are often more toxic to other
species. For example, tributyltin compounds (e.g. TBTO) are particularly
toxic to marine organisms, and are therefore used in antifouling paints to
prevent barnacle growth on boat hulls. This is the application that TBTO was
developed for. However, it is important to note that most of the di- and
mono- organotin compounds used commerci!
>!
>!
>ally
>> (e.g. in PVC stabilisers, catalysts, tin oxide film precursors) are of
low toxicity, and some are approved for food contact applications (as in PVC
packaging). The main message is that it is wrong to generalise and say that
all organotins (or, indeed, all tin compounds) are toxic.
>>
>> -----Original Message-----
>> From: Brian Ellis [SMTP:[log in to unmask]]
>> Sent: 05 November 1999 10:35
>> To: [log in to unmask]
>> Subject: Re: [LF] Long-term solutions
>>
>> I agree, but tin is also a severe issue which has not been sufficiently
>> addressed. Many tin compounds are toxic (some organotin compounds are
>> used as wood preservatives, fungicides, algicides etc.). Who knows what
>> reactions may occur in a landfill? Anyway, tin is (or at least was) not
>> federally regulated in waste water in the USA, although I believe some
>> States may cap it at 5 - 10 ppm. However, in Europe, the levels are set,
>> mostly at 1 - 5 ppm (copper at 0,5 - 2 ppm in many countries as a
>> comparison). I won't discuss Malaysia's limit at 0,1 ppm, because this
>> is a special case. Anyway, tin is considered about half as toxic as
>> copper, so don't consider it as being exempt from all future regulation.
>> Note that many tin-plate cans for acid foods are now polymer-coated as
>> additional protection against the ingestion of tin salts.
>>
>> I think the crux of the matter is that ALL metals can be shown to be
>> toxic in some form or another. Lead is just a technocrat's buzz-word and
>> should not be treated differently from any other metal. When these guys
>> cotton on to these facts, all metals will be banned, as will also
>> bromo-bisphenols used for fire-retarding PCB laminates. There is only
>> one logical solution: obligatory recycling of all metals. The sooner
>> this fact is realised, the better: then we can get on with our business
>> of soldering boards with tin/lead solders to our heart's content. AND I
>> say this as one much and actively concerned with the protection of our
>> environment.
>>
>> Brian
>>
>> "Bernier, Dennis" wrote:
>> >
>> > Though I am not an advocate of rapid changeover to lead-free solder
alloys
>> > without more reliability testing, I can see the lead-free alloys might
be a
>> > future environmental problem. However, the amount of silver and copper
>> > combined in the solder will only be about 10% of the amount of lead in
>> > Sn63Pb37 solder alloy used now. This will be a very small amount of
metal
>> > contamination due to the solder in the electronic product. It seems
then
>> > the copper may become the issue because there will be 20-50 times as
much
>> > copper in the assembly than silver.
>> >
>> > -----Original Message-----
>> > From: Carol Handwerker [mailto:[log in to unmask]]
>> > Sent: Wednesday, November 03, 1999 5:56 AM
>> > To: [log in to unmask]
>> > Subject: Re: [LF] Long-term solutions
>> >
>> > In the Assembly Processing group working on the Lead-Free Solder
Roadmap at
>> > the IPC meeting, the highest priority item from the group was to ensure
>> > that the new alloys are viable in the long term from a toxicology and
>> > environmental life cycle point of view. Having to change alloys again
in
>> > three years would be a waste of resources if we can formulate a proper
>> > solution now.
>> >
>> > At 07:06 PM 11/02/1999 -0800, you wrote:
>> > >All,
>> > >
>> > >As I read the debates ongoing, it strikes me that there are 2 major
focus
>> > >areas right now:
>> > >
>> > >1) Technical solutions to Pb-free solders
>> > >2) Is the decision environmentally correct?
>> > >
>> > >Are we missing a 3rd item?
>> > >
>> > >Regardless of what solder we end up with, how does the industry
position a
>> > >long term, environmentally sound policy that will forestall future
green
>> > >initiatives from causing such upsets?
>> > >
>> > >The history of Pb is rife with abuses -- Workers not following safe
>> > >practices, employers not requiring or implementing safe practices,
emission
>> > >controls not being in place on smelters, .... This is in addition to
Pb
>> > >being used without a full understanding of the toxicology and exposure
>> > risks
>> > >(Paint, gasoline, plumbing The point is, past uses (and abuses) and
>> > >handling of Pb has created the situation we are in now.
>> > >
>> > >I have not seen/heard any discussion on establishing practices and
>> > protocols
>> > >that will foster responsible use of any solder -- Both safe working
>> > >practices on the production end, and End of Life management. Should
this be
>> > >part of the overall strategy, or a recommended best known method? How
does
>> > >this link into product takeback requirements that are gaining
popularity in
>> > >the EU and Japan?
>> > >
>> > >Regards,
>> > >Paul Wermer
>> > >(Whose opinions are his own and do not necessarily reflect those of
his
>> > >employer)
>> > >
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>> > Carol A. Handwerker
>> > Chief, Metallurgy Division
>> > NIST
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>> > Fax:(301) 975-4553
>> > e-mail:[log in to unmask]
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