Good morning Cedric,
If you are using flux from the same manufacturer, eg. a Kester paste with
a Kester cored wire, then your flux manufacturer can probably provide you
SIR or similar data on the interaction of the two flux residues. If,
however, you are dealing with a flux from Vendor A and a cored wire from
Vendor B, you may have to generate that yourself as any incompatiblities
will always be the fault of the "other guy's" residues. But, it never
hurts to ask the vendors. They do a fair amount of testing in house on
their products and how they react with their competitors materials. Karen
Tellefsen has some neat stories of such.
What kinds of issues can happen? Well, with low solids fluxes (I hate the
term no-clean), the residues from the fluxes are designed to be benign
after reflow, with the assumption that they get fully up to temperature
and are processed within vendors recommendations. If you start mixing in
flux residues from another chemistry, then those assumptions are violated
and the mixed residue system can have unpredictable properties. They may
absorb water, not come to full hardness, soften and flow, discolor or
corrode metal (discolor more likely), turn white and cause your customers
to loose their minds, etc.
I will give an example that Hillman and I published somewhere years ago.
We had a manual rework situation. A cored wire from Vendor A, fully
qualified and used on almost all products, was being used to solder a
large component. The flux in the cored wire would not do the job alone.
So a tacky flux (paste flux) from Vendor B, was added as a soldering aid.
The tacky flux was also fully qualified. The tacky flux was a low residue
and had been designed by its vendor to be relatively soft for 24 hours to
allow for better probe penetration during in-circuit testing (bed of
nails). When the tacky flux residues mixed with the cored wire flux
residues, we got a mix of residues for this particular application that
was a problem. The combined residues never hardened and so remained soft
and tacky. Since we could not guarantee the reliability of such a residue
mix, we developed a special cleaning process to remove it. We did later
do some SIR work that showed the combination to be undesirable.
Doug Pauls
Cedric ORAIN <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
09/14/2011 02:10 AM
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[TN] Flux Compatibility
Good morning dear Technetters,
I'm asked by one of my customer if I checked the compatibility between in
one hand the no-clean flux from the SMD paste and the other hand the resin
flux from the wires.
The answser was no !
Could you advise which kind of issue could occur if any ?
Thanks for your help,
Regards,
Cedric
www.inovelec-groupe.com
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