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May 2008

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Subject:
From:
Guy Ramsey <[log in to unmask]>
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Date:
Thu, 22 May 2008 07:55:59 -0400
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I am seeing a reoccurring theme here. 

HFC, HCFC, HFE manufacturers are making claims about their solvents, out of
the can. But, over time these chemicals breakdown. As they break the
attributes of the resulting chemicals are not desirable. 

The makers of these chemicals don't tell us about that part of the product
life cycle. We need to get that information elsewhere.

Is this to much of a simplification? 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Ellis
Sent: Thursday, May 22, 2008 7:46 AM
To: [log in to unmask]
Subject: Re: [TN] Are these substances OK for use in electronics

OK, the HFCs are severe greenhouse gases, with GWPs of 300-1500 (CO2=1) and
are controlled substances under the Kyoto Protocol. They are not aggressive
cleaning solvents and, by themselves, are not good flux removers. They are
almost non-toxic. They should not be used near soldering equipment as
pyrolytic decomposition may occur at >200°C and the resultant by-products
are VERY toxic (carbonyl fluoride and hydrogen fluoride).

The trans-DCE is quite similar to trichloroethylene and is fairly toxic: 
it is added to make the mix a better solvent for oils and greases. This was
used in preference to other chlorocarbon solvents because it is the only one
for which OSHA do not have an official PEL, as epidemiological studies on
its toxicity have not been conducted: it is therefore in that legal limbo
where manufacturers can suggest their own exposure limits which may or may
not be safe. Because it is a lot cheaper than HFCs, it tends to pull the
price of the blend down. It is hardly ozone-depleting and is not a
controlled substance. It attacks many plastics.

The methanol is added to widen the dissolution spectrum and to improve the
dissolution of rosin and some organic ionic materials. It is highly toxic
and damages the central nervous system and the damage is cumulative. It is
very easily absorbed through the skin, as well as by respiration (hopefully
not to be ingested!). Of course it is flammable.

The nitromethane is a stabiliser to prevent the trans-DCE from hydrolysing
into hydrochloric acid. Normally, it would be present in very small
quantities. It is violently flammable and toxic, but this is not your worry.

The use of spray cans to achieve good cleaning is very difficult. 
Normally, you will have to hold the board at about 45° from the horizontal
(coincidentally, about 45° to the vertical, as well!!!!) and spray the area
to be cleaned very liberally, until the liquid well and truly starts to
stream off the edge of the board. Pause a few tens of seconds and repeat n
times (n >5), until the desired level of cleanliness is achieved. Never
allow the solvent to dry on the board, as this will just spread the residues
where they will cause more harm than if you had not tried to clean in the
first place. Spray cans, used properly, are an expensive cleaning method.

Brian

Ioan Tempea wrote:
> Dear Technos,
> 
>  
> 
> I've got one for the chemists: a customer of ours requests us to clean 
> their boards with 2 spray canned products. Here's the stuff that's 
> inside of them:
> 
> 1,1,1,2,3,4,4,5,5,5-Decafluoropentane
> 
> Trans,1,2-Dichloroethylene
> 
> Methanol
> 
> Nitromethane
> 
> 1,1,1,2-Tetrafluoroethane
> 
>  
> 
> Are they safe for the product? What about the production personnel and 
> the environment?
> 
>  
> 
> Thanks,
> 
>  
> 
> Ioan
> 
> 
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