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May 2001

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Subject:
From:
Brian Ellis <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 17 May 2001 11:22:11 +0300
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Rick

The activity of typical water-soluble fluxes is approximately 1,000 to
10,000 times higher than that of typical "no-clean" fluxes. Of course,
like all generalisations, you will find exceptions to this statement.
After soldering, the ratio of the activity of the residues will have
dropped by an order of magnitude, because the hydrohalide activators in
the W/S will have largely decomposed at soldering temperature, while the
comparatively poor sublimability (if there is such a word!) of the
dibasic carboxylic acid activators in the N/C (usually) will mean that a
large proportion will remain.

The high activity of W/S means that it can be used for solder wetting
almost any reasonable and solderable surface, even if fairly heavily
oxidised. The low activity of the N/C means that it will allow
solder-wetting of only clean, very solderable, surfaces which are not
heavily oxidised. In other words, not only does W/S promote fast, wide
and reliable wetting, it offers a much wider process window which
pardons many errors, whereas N/C offers a very narrow process window
with little margin for error. Anyone who has worked with both will know
that the retouch rate (expensive) with N/C is often as much as an order
of magnitude higher than with W/S, all other things being equal and
optimised.

Of course, the down side of W/S is that you MUST clean and you must
clean demonstrably well (although it is not difficult). I also say that
the down side of N/C is that you should not clean, under most
circumstances, because the flux is not formulated to be cleaned and
cleaning may actually reduce the reliability under some of these
circumstances.

I suggest you may care to buy wour QA manager any of the usual books on
soldering, such as Klein Wassink, Manko, Strauss etc. or that he simply
speaks to your paste vendor's technical guys.

You think right.

Brian

Rick Thompson wrote:
>
> I've been having an ongoing discussion with our QA Manager regarding the
> wetting capabilities of No-clean versus Water-soluble solder pastes.  He
> believes that no-clean wets better, I think the opposite. This is in an air
> reflow environment. I'm curious as to what some of you might have to offer
> on the subject?
>
> Thanks in advance,
>
> Rick Thompson
> Ventura Electronics Assembly
> 2655 Park Center Dr.
> Simi Valley, CA 93065
>
> +1 (805) 584-9858   x-304  voice
> +1 (805) 584-1529 fax
> [log in to unmask]
>
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