Ivo,
1.  In dealing with solder paste, you must first ask yourself why are you 
cleaning?  If you are using
a non-corrosive rosin flux per ANSI-J-STD-001, the residues are benign.  In 
addition, the amount of
residues on a board from solder paste reflow are considerably lower than the 
residues from wave
soldering.

2.  Low solids fluxes can leave visible residues.  Many of them have some 
rosin or resin in the formulation
to encapsulate residues.  These may be visible under the microscope but many 
of them are non-corrosive.

3.  If you are cleaning because you need to contact points for electrical 
test, your flux and cleaning choice
can be water soluble paste/aqueous cleaning, rosin or resin-based paste with 
semiaqueous cleaning,
or with aqueous detergent cleaning.

I hope that provides an additional perspective for your planning.


 ----------
>From: fo_elmo
>To: Technet
>Subject: Cleaning with Water and IPA for Surface Mount ?!
>Date: Monday, February 05, 1996 11:37AM
>
>TO:  W.G. KENYON and others ...
>
>Thanks for your quick reply !
>
>You're right, it should be :
>"At our new SMA facility we now use solder pastes WHICH show
>flux-residue after reflowing."
>
>At this moment, cleaning of the SMT P.C.B.'s is done
>with a special cleaning product in a Systronic machine.
>THIS IS NOT AN IN-LINE MACHINE. IT IS USED BY THE THROUGH HOLE
>PRODUCTION AS WELL. PERHAPS THAT IS A PROBLEM TOO.
>
>My questions are :
>
>1) can anybody give me an advise on which type of solderpaste
>   (SEE ALSO QUESTION 2) I should consider testing.
>NOT WITHOUT MORE INFORMATION- SEE BELOW
>
>2) is cleaning with water or IPA (or mixed) a good option for SMT
>   related products and who has experience with it ?
>ALCOHOL BY ITSELF CANNOT CARRY ENOUGH ROSIN FLUX RESIDUE, YOU
>WILL HAVE TO CHANGE IT OUT FREQUENTLY AND YOU MAY (ALMOST
>CERTAIN) TO HAVE "WHITE RESIDUE" PROBLEMS.  SAME FOR MIXED IPA
>AND WATER.
>IF YOU USE WATER SOLUBLE PASTE (FLUX) THEN THE QUESTION IS ONE OF
>PRODUCTION VOLUME. HIGH PRESSURE WATER SPRAY MACHINES CAN CLEAN
>EFFECTIVELY IN THE 0.005 INCH STAND-OFF RANGE WITHOUT ANY
>PROBLEM, HAVE BEEN REPORTED TO CLEAN AS LOW AS 0.002 INCH.
>HOWEVER, YOU WOULD HAVE TO HAVE ENOUGH PRODUCTIO VOLUME TO
>JUSTIFY SUCH AN INLINE CLEANER, WHICH IS NOT TYPICAL OF EUROPEAN
>PRODUCTION.  ALSO, IF YOU HAVE HIGH VOLUME, THEN THE SOLDER PASTE
>STENCIL LIFE IS NOT AS IMPORTANT, SINCE IT IS BEING REPLENISHED
>REGULARLY. LOW OR INTERMITTENT VOLUME USERS ARE OFTEN BETTER OFF
>WITH ROSIN BASED PASTES, WHICH DO HAVE A LONGER LIFE ON STENCIL.
>
>I hope your answers can help me in selecting the right
>solder-paste(s).
>THE ABOVE MAY NOT GIVE YOU A QUICK ANSWER, BUT MAY HELP TO SET
>YOUR PRIORITIES IN THE EVALUATION PROCESS.
>
>Your have an ineteresting point here. Production volume, i mean.
>Our volume is low. Much costumers are producers of "specials".
>We try to be "flexible", thus meaning low production volumes.
>The switch to higher production series, because of our automated SMA
>process, is difficult to make. Back to the subject ...
>
>What you stated about stencil life is affecting my decision. We now have
>a manual stencil printer, but want to buy an in-line machine.
>(NO COMMERCIALS PLEASE). When our equipment and organisation is ready
>for it, we want to change to higher volumes. At the moment we're in
>the "grey area" of changing process, organisation and materials.
>
>I think i will go and think it all over, thanks for your useful remarks !
>
>Ivo de Rooij
>Process Engineer/Operator Surface Mount Assembly
>Fokker Elmo BV
>
>-- Houdt Fokker in de lucht -- (Keep Fokker in the air) --
>
>