I agree 100% with Doug. The important point is to ensure that the 
carboxylic acids are sublimed. This starts to happen at temperatures 
around 180°C but it takes time as well as temperature. It is therefore 
essential to limit the quantity to the minimum necessary to do the job 
and confine to the joint area. What is positive is that soldering irons 
operate at a higher temperature than wave or reflow, so that residues 
that spread outside the joint area will probably be heated sufficiently 
to ensure sufficient sublimation. Another important point is to ensure 
that all the alcohol has evaporated before starting the retouch, so that 
the latent heat of evaporation would otherwise cool down the flux and 
allow it to spread before sublimation takes place. This requires the 
operator to wait a few minutes between dosing the flux and picking up 
the soldering iron. It is common to have a row of fluxed assemblies and, 
as one is added at one end, a circuit is picked up at the other end for 
soldering. I don't know whether it is still available, but a flux with a 
crimson dye showed where unheated flux was applied and was quite common 
in days of yore. The dye sublimated with the activators.

Brian

On 23/04/2012 16:42, Woolley, Mark D. (Mark) wrote:
> I have an issue with one of the assembly houses we use.  They are using
> a No-clean flux that contains adipit and succinic acids (per the MSDS)
> in an alcohol base.
>
> Is it allowed to leave flux on the PWB that HAS NOT BEEN DEACTIVATED BY
> HIGH TEMPERATURES OF SOLDERING?
>
> I am not talking about the flux used in the solder paste or wave
> soldered flus.  I am talking about the flux used at rework and touch-up
> of the PWB.
>
>
>
> I havce seen papers detailing corrosion on PWBs using "no-clean" fluxes
> and I have seen it on some of our products.  This usually pccurs near
> the periphery of the PWB where the wave solder flux is protected by the
> pallet used to pass the PWB through the solder wave.
>
>
>
> Any opinions and references will be appreciated.  I can give the
> manufacturer and flux type to individuals, but don't want to put it in a
> global email.
>
>
>
> Thanks
>
> mark
>
>
>
>
>
> mark
>
> Mark Woolley |PTRL Laboratory | Avaya | 1300 West 120th Ave |
> Westminster, CO 80234  USA |
>
> Voice (Lab): (303) 538-2166 | email: [log in to unmask] |
>
>
>
>
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