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1996

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Thu, 11 Apr 1996 17:31:48 -0400
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Mr. de Rooij,

I must ask why you feel that any residue is not acceptable.  In my
experience, that stance is most often driven by fear (it's new), tradition
(we've always cleaned), or by customers who fear.  In many cases, low solids
flux residues are primarily weak organic acids and are benign on an assembly
surface.  The layer of flux residue can provide a sort of protection, similar
to conformal coating.  If the no-clean flux is not designed for cleaning, you
may have a difficult job removing the flux.

That being said, we have worked with customers who, for one reason or
another, clean a no-clean flux, usually for cosmetic reasons.  I would not
recommend a chlorinated solvent, nor a semi-aqueous material.  You should
look for a saponifier that runs in the 140-145F temp range with a good
surfactant constituent.  The saponifier attacks the weak organic acids while
the surfactant breaks down the water tension, allowing the saponifier to get
into low standoff areas.  In any case, do not use tap water, which will give
you nothing but grief.  Use at least RO water, and DI water is preferred.

Two saponifier packages that we have seen work very well with low solids flux
residues are Kyzen Aquanox SSA and Envirosense Envirogold 816.  The SSA runs
at a 25-30% solution, the 816 runs in a 5-10% solution.  Both are also very
good at cleaning chlorides, which may remain from the board fabrication
process.  I know of several companies using these products successfully.
 Both formulations were originally designed for RMA flux residues, but work
well for most fluxes we have examined.

Hope this was of some help.

Doug Pauls
CSL
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