In a message dated 10/18/2000 5:34:21 PM US Eastern Standard Time,
[log in to unmask] writes:
> Recalling the rule we learned early on in Chemistry, that "like dissolves
> like", I would venture a guess that non-aqueous cleaning is not going to be
> real effective at removing no-clean flux residues.
>
I agree with Rudy although the degree of flux removal does depend on the
chemistry of the flux residues involved. I have seen our clients perform
cleaning on assemblies processed with low solids fluxes. Some do it to
remove the higher degree of solder balls that seem to come with no-clean
technology. Others clean because their clients are still of the old school
where visible flux is bad. Many times, the thought processes behind the
production decisions stagger me. If you are going to clean, for whatever
reason, you are better off to use a more aggressive flux and eliminate some
of the solderability problems of a low activity flux.
I have seen some clients try to clean a low solids flux residue with
solvents, only to find that the flux residue stays and absorbs the solvent.
When that solvent was chlorinated (e.g. trike), you had a sponge full of
chloride on the board. Can you say "green and fuzzy" boards? If you are
going to combine ANY kind of cleaning operation on a flux designed for no
cleaning, then your HAVE to study the materials compatibility.
For the most part, the clients we have who clean a low solids flux residue,
do so using a saponified aqueous process. The saponifier chosen (not all
created equally) needs to be able to adequately remove the soils involved. I
have seen some clients try to do saponified cleaning of no clean residues
using either a marginal saponifier chemistry, or a saponifier concentration
that is too weak, or one that is not refreshed as often as it needs to be, or
a process that is too fast. The result of any of these is that the cleaning
energy goes to dissolve the top "shell" of the flux, leaving a soft mass of
flux/saponifier still on the assembly. As this mass is usually conductive,
bad things happen. If you are looking for a saponifier to try with no
cleans, I have seen good results with Kyzen Aquanox and Lonox formulations,
and Envirosense Envirogold 816 is my personal favorite. Contact me off line
if you want to more on these materials.
Doug Pauls
CSL
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