>        Historically, if a high solids rosin flux is not cleaned from a
>printed wiring assembly within one hour of
>        mass soldering,

(not unusual
>for traditional high solid RMAs to meet environmental/SIR type testing);

On some newer "low
>residue" fluxes however, we find that little/no cleaning may be required
>to reach an acceptable cleanliness level (hence our interest in low
>residue fluxes).
>

>===============================
>Jim Maguire
>Senior Principal Engineer
>Boeing Information Space & Defense Systems
>PO Box 3999  M/S 3W-97
>Seattle, WA  98124-2499
>Phone (253)657-9063     Fax (253)657-8903
>Pager (206)982-3737
>Email:  [log in to unmask]
>================================
>

I find the whole area of SIR levels/solids content/activity levels interesting.
It has been reported that as you say High solids rosin fluxes can pass SIR
tests. Rosin is also supposed to be quite inert, and Indium claim that their
old RMA pastes can be used as a high solids no clean.
I like the idea of high solids content. I believe it's "swings and
roundabouts" if you have a low solids content flux, you loose something,
those solids are doing a job, i.e. protecting the solder spheres in the
paste from oxidation in a convection oven where masses of hot air are
passing by. There are probably other interesting aspects to higher solids
content.
There is only one real driver for low solids content and that is management
and non-technical types don't like the look of solids on an assembly. It
looks bad! It might be totally harmless, but that's never the issue with
this industry. It's driven by buzz words and marketing implications. So the
big paste suppliers push low solids because thats what people who don't
really know will buy.
Regards

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