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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