Don
Methylene chloride or dichloromethane (DCM) may be LISTED as a
carcinogen by some idiotic organisations but large scale toxicological
and epidemiological tests with cohort groups totalling over 10,000
persons who have been industrially exposed to PROVE that it is NOT
carcinogenic to humans. This gross error was brought about because
testing on rodents did show slight carcinogenicity at very high exposure
levels but these rodents have a metabolic path that simply is not
present in humans. The European Centre for Toxicology and Ecotoxicology
(ECETOC) have published very serious studies on all the available data
for DCM, TCE and PCE, written and peer reviewed by the best brains in
the business. My interpretation of one of their findings is: if every
single adult in the USA were exposed to DCM at 50 ppm for 8 hours/day, 5
days/week between the ages of 20 and 65, there would (statistically) be
1 death due to DCM-related cancer up to the age of 85 every 200 years. I
can quote many references to support this, if required. I can also quote
more detailed facts and figures. I should mention that I have no
interest in chlorinated solvents; in fact, I avoid them where possible,
but it isn't always possible, because they are very useful molecules.
This is not to say that DCM is not toxic. It is. Unfortunately, even if
it does not cause cancer, it has an insidious effect on the human body
at high exposure levels, with a threshold starting about 250 ppm. One of
the metabolic breakdown products of DCM is carbon monoxide. This
combines with the haemoglobin in the blood to form carboxyhaemoglobin
(COHb). This is relatively persistent (several weeks) and COHb molecules
are Hb molecules that cannot transport oxygen to the various organs.
This can cause suffocation. It accumulates to an equilibrium level, in
relation to the exposure level, over a matter of weeks. I know of no
case resulting in death, but there are cases on record where the
patients had to be hospitalised for a few weeks with combined oxygen
therapy and blood exchange. Of course, these patients had been exposed
to really massive, consistent, levels.
All halogenated solvents must be treated with respect with minimal
exposure levels, but it really gets my back up when political bodies who
should know better make sweeping statements resulting in unnecessary
restrictions and which cannot be scientifically supported:
carcinogenicity of DCM is only one, have a thought about lead in solder
for another.
Brian
Don Vischulis wrote:
> I believe that the methylene chloride cure test was originally used for one
> and two part screened masks. It was later modified for use with dry film
> masks. I don't know the origin of the "acetone test", but my guess is that
> somebody decided to use acetone instead of methylene chloride because
> methylene chloride is listed as a carcinogen. I know that methylene
> chloride is not acceptable for use with UV cure and several LPI masks.
>
> Anyone else?
>
> Don Vischulis
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]]On Behalf Of Bev Christian
> Sent: Tuesday, October 29, 2002 1:19 PM
> To: [log in to unmask]
> Subject: Re: [TN] Acetone Test for Solder Mask
>
>
> Carrie,
> I don't know about acetone, but the test you are talking about sounds like
> IPC-TM-650 Test Methods Manual,number 2.3.23, "Cure (Permanency) Thermally
> Cured Solder Mask", where they talk about using methylene chloride.
>
> Perhaps your test is out of the old, what was it, SM840? Anyone else?
>
> regards,
> Bev Christian
> Research in Motion
>
> -----Original Message-----
> From: Morse, Carrie [mailto:[log in to unmask]]
> Sent: October 29, 2002 2:08 PM
> To: [log in to unmask]
> Subject: [TN] Acetone Test for Solder Mask
>
>
> We are currently doing an "Acetone Test" on our incoming PWB's to test for
> solder mask cure.
> Our test entails saturating a swab with acetone and rubbing it on the mask.
>
> Does anyone know where this test comes from? Is it a documented IPC test?
>
> Also, if we do see any residue (i.e.: green or blue discoloration on the
> swab), what does this
> tell us and how much is enough to deem the test "failed"?
>
> -Carrie
>
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