Shortest possible answer
Don't do it.
Shortish answer.
The above plus
The solderpaste is a lot less expensive than what you are making (<1% of BOM
cost typically) so why bother?
Medium answer.
The above plus.
The paste will not be restored to as supplied condition. Possibly it won't
be restored to a usable condition, but if it were it would only be an
illusion and only for a very short time.
Better to address the problem by avoidance: control rate of issue to
machine, do not use recycle old paste. In other words all the things that
your paste supplier/best practice has been telling you.
Long answer.
The above plus
IF you were to do this the likely result: poor wetting, tack life, tack
strength out the window, component lifting blocked stencils etc.
There are any number of reasons why you should not do this. Just starting
with the thinning aspect which is presumably what you are trying to fix.
Wave solder fluxes are not just thin versions of solder pastes, they are
different animals altogether. The flux residues (after soldering) may meet
the same specifications, but that doesn't means they are the same to start.
Wave solder fluxes are based on low boiling/high volatility alcohols,
usually IPA. Solderpastes are not.
Liquid fluxes of the RMA type have at most 15% - maybe for an old fashioned
type - 25% solids. If measured the same way the solids in the "flux" part of
solderpaste are nearer 60%. Except you would have to say non volatiles.
There are no rheology builders in liquid fluxes and so on.
IPA is hydroscopic and will tend to suck in water from air. This will set
off the flux activators and they will start chewing on the powder, the
result is likely to be an increase in viscosity which is the exact opposite
of your intention. At the same the flux will now be messed up and...
I could go on , but that should be enough for now!
Hope this helps.
Regards
Mike Fenner
Indium Corporation
T: + 44 1908 580 400
M: + 44 7810 526 317
F: + 44 1908 580 411
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dacia Schoolfield
Sent: 23 March 2006 17:15
To: [log in to unmask]
Subject: [TN] Solder Paste Question
Gurus of the manufacturing industry -
What is your take on adding RMA flux to solder paste - either new paste or
used paste? Is there a difference in results when adding flux to leaded
versus non-leaded paste?
For those of you who do add additional flux to paste, what types of controls
do you have in place to ensure the paste itself is still viable?
I understand this is an extremely general question, and am looking for
general answers.... or, if anyone has recommendations as far as research, I
would gladly accept all input.
I appreciate your thoughts.
Dacia
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