>
Kathy and Stever wrote:

In a message dated 11/25/98 3:53:54 PM Pacific Standard Time,
> [log in to unmask] writes:
>
> << I am having a cleaning problem.
>
>  We use a liquid, water soluble touch-up flux to assemble a module.
When the
>  module is complete we run it through an in-line cleaning system.
>
>  When the modules are inspected there is still yellow crusty residue
left on
>  the module.  We have sent the modules out to a lab and their analysis
shows
>  that the crusty residue is a form of tin oxide.
>
>  We beleive this tin oxide is not soluble and can not be cleaned with
any
>  thing, and in order to eliminate this tin oxide residue we must
eliminate
>  oxygen in the assembly process and use Nitrogen (N2).
>
>  Does this sound correct?
>
>  Is their anyone out there who could help steer me in the right
direction?
>
>  Thanks for your help in advance!!
>
>  Kathy Palumbo
>
>  PS  Have a Happy and Safe Thanks Giving Holiday!!!
>   >>
>
> Kathy,
>
> Does this residue remain around the periphery of the solder joint?
Right
> around the outside edges? I may have seen this too and was told that
it could
> be Tin Carboxilates?!? (whatever that stuff is) Basically, I was told
that I
> probably was staying liquidous too long or too high in my peak
temperature
> during reflow. I was also told that wash temperatures that are on the
high
> side (120 degrees F. +) will exacerbate the problem. I re-profiled my
reflow
> oven and lowered the wash temperature down to 110 degrees and it went
away.
> It's not ionic, is it? Just looks like crap, huh? I don't know if it's
the
> same deal with you that I had, but it's something to eliminate....
>
> -Steve Gregory-

----------------------------------------------------------------------

We have seen this also, and some paniked and meant this stuff must be
removed. I consultated my Wassink (as usually) and came to the result it
can not be Tin Oxides, because these are very thin, at least after
normal soldering and normal oven atmosphere. In SEM it seems more likely
to be 'anomalous' solder grains that appear as 'contaminations' on the
otherwise nice solder joint. And as being so, they won't harm. Our
decision was: don't clean, don't try to remove, let it be. And we have
heard no complaint or any reported failure from anyone since then. I
hope we did not come on a false trace.

                                     //Ingemar Hernefjord

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