I worked a few summers ago at an aerospace contractor doing alot of SMT
work. If I needed to touch something up, I used 3-Propanol to thin out the
flux and sometimes the paste. For really fine work, I would thin the flux
with the propanol, but mix it in with a little solder paste. The heating
action is imparted better on the solder balls of the paste, almost negating
what would be a sort of surface tension. I've never heard of the ultra-sonic
method but I'm guessing it could work in the short term.

Matt Bajor

On Thu, Jun 12, 2008 at 4:11 AM, Alan B. Pearce <A.B.Pearce@rl.ac.uk> wrote:

> >I throw my completed and tested new boards straight into the
> >ultrasonic bath, with plain water. I usually leave then there for 30
> >seconds.
> >
> >It removes any and all flux, even the flux left residue underneath the
> >chips (on smt packages). It works great to remove the flus, even if
> >the flux is not the water soluble type.
> >
> >It sure beats the heck out of drowning the board with toxic and
> >expensive flux remover::>
>
> However ultrasonic baths are also a known destroyer of chips. What appears
> to happen is that the ultrasonic vibration seems to shake bond wires off
> chips.
>
> I know that ultrasonic cleaning is banned for anything we fly in space
> because of known problems induced by ultrasonic cleaning.
>
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