Sorry, you have misunderstood what I was trying to say. The premisse is 
that a minimal quantity of flux is applied ONLY to the joint and is dry. 
Any spread outside the joint area will be heated and will certainly be 
of insufficient quantity to spread several millimetres, as you suggest.

Brian

On 23/04/2012 17:52, Stadem, Richard D. wrote:
> [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.]
>
> Sorry, I do not agree. Any flux residue more than .150" away will not be heated at all from the touch of a solder iron at the joint. Flux residues that are part of a hot air reflow process are the only ones that will be inerted by heat.
>
> Anytime benchtop flux is applied for a touchup or rework application with solder irons, it should be cleaned.
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Ellis
> Sent: Monday, April 23, 2012 9:28 AM
> To: [log in to unmask]
> Subject: Re: [TN] No-Clean Flux
>
> 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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