Denny,
There has never been a case of lead fumes in any normal soldering
process - the temperatures are too low. In my lead pollution
presentation I have added in a slide that compares the vapor pressure of
mercury to that of lead. The difference is quite stark. There is no
currently available reasonable method that I know of to detect the
infinitesimal amount of elemental vaporized lead over a soldering iron
or solder pot set at any temperature that would ever be seen by a
circuit pack during manufacturing or rework.
It is a different story regarding lead oxide negligently drossed off of
a wave solder pot.
Bev
RIM
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Joe Fjelstad
Sent: Tuesday, February 17, 2009 12:25 PM
To: [log in to unmask]
Subject: Re: [TN] Leadfree has gone too far.
Hi Denny
We need Cr3 in our diets as an aid in glucose metabolism, the same
case,
cannot be made for lead. As for the lead industry lack or response, with
lead
in solder representing less than 0.5% of all lead used annually, there
was not
enough there to for them to worry about, on the other hand the increased
use
of tin was very beneficial to that industry and would provide ample
incentive
to have lead in solder blackballed, whether or not they actually ever
did
so is known only for certain by the leaders of tin industry. ( with
the word
leaders obviously pronounced "leeders" not "leders"... ;-)
Cheers,
Joe
In a message dated 2/17/2009 8:30:57 A.M. Pacific Standard Time, DDFRITZ
writes:
My ancient chemical engineering degree stirs me to comment on this
thread
(always dangerous)
The main culprit in lead uptake by all animals is the chemistry of the
lead.
Oxidized state lead - lead oxide left from burning leaded gasoline, or
lead
chromate from the various yellow, orange and red lead pigments in
paints is
very easy for the blood to pick up. Tetraethyl lead for leaded gas is
horribly toxic to all animals because it is so very easy to absorb
(remember
washing grease off your hands with gasoline before about 1970?). That
ionized lead
is still out there in the paint chips or soil surface layer, as Joe
points
out.
Elemental lead is pretty innocuous to animals (carrying a bullet from
the
war, etc.) except for one nice way to create ionic lead in the body -
the
stomach acid that works on elemental lead when eaten. That is not very
fast, but
it is steady - in the case where the lead remains in the stomach -
ducks
whose gizzards grind shot or sinkers against sand and gravel in
digestion,
someone's cow where the weight stayed at the bottom of one of the four
stomachs,
or sadly, some super cheap lead trinkets that lodged in small child
stomachs
or intestines. Don't forget the cheap yellow and orange paint on toys
- we
covered that before.
I think years ago on TechNet, we discussed how much lead is absorbed
from
lead solder assembly - I can't remember a single case of significant
lead fumes
- am I wrong? Sanity says to ventilate - the flux smell can get to
you. I
hear about lead exposure from "roasting circuit boards on an open fire"
in
third world countries. How much of that is no hand washing instead of
breathing? How much from using the same pot for stir fry as for
roasting boards?
How did we get the environmentalists to limit chrome controls to Chrome
+6?
A better marketing job by the "Chrome Industry Council"?. Lawmakers
still
wanted their shiny cars and plumbing fixtures? The stainless steel
folks
drove some sanity? Guess there is no "Lead Industry Council" to stand
up for
their product.
My simple answer would be to restrict lead where it is ionic (done now
through these bans), AND elemental lead where it can easily be ingested
- shotgun
shot, sadly for me fishing sinkers, and anything say smaller than 2
ounces.
And, in my opinion, lead in solder for circuit boards is safe - who
eats
them? I think IPC helped get circuit boards in toys exempted from this
legislation, right?
What da ya think?
Denny Fritz
-----Original Message-----
From: Joe Fjelstad <[log in to unmask]>
To: [log in to unmask]
Sent: Tue, 17 Feb 2009 10:49 am
Subject: Re: [TN] Leadfree has gone too far.
Unfortunately, the road to perdition is paved with good intentions and
it's
sad to say, but common sense is not so common anymore. I am confident
that
there are many folks out there paving the road who are applauding this
news.
So it goes...
Joe
PS Steve's observations are on target. The lead acetate (aka lead
sugar) in
paint is what make eating paint chips attractive to children. The
elimination
of lead from gasoline and paint were two of the best solutions to
reducing
lead in the environment. Others have followed wanting to build on that
legacy
using assertion without proof and conjecture rather that science or
data.
For
the record, the discovery of the fall out from lead in gasoline came
when
there was a study done to see if there was risk from using tin-lead
solder
for
canned food lids which was shown to account for a smaller percentage
than
expected. The "no effect" limit for lead consumption is 3 mg per
person per
week according to "Encyclopaedia of Environmental Agricultural
Pollution
and
Its Control" By G.R. Chhatwal. in Chapter 21 "The Impact of Inorganic
Spoil
Pollutants on Consumers" (but it was not recommended ;-)
He also pointed out lead paint licking by animals as one of the prime
sources and reported in the book that higher calcium intake
significantly
reduced
lead uptake/absorption. Interestingly, most of the lead comes from the
soil
attached to the roots eaten by grazing animals. Given the fact that a
micro
thin layer of lead has been deposited all over the land over for the
half
century that leaded gasoline was most common, it reinforces the
validity of
the
ban (though it is still in use for some aviation fuel and in some less
developed countries I believe)
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