My experience with cleaning "no-cleans" has not been good. HFCs, HCFCs, and
HFEs are not very good solvents, though they are compatible with many
materials used in electronic manufacturing. No-clean fluxes are not easy to
clean the result is often white residue. This problem will be compounded
because the board sees two heat cycles. If you want to get the stuff off you
will probably have to clean between cycles.
My gut says that the materials and process you described will require a
co-solvent with vapor phase rinse. This is not a difficult process to
set-up, but it does take some care and experimentation.
That said, if you have to clean, then why not open your process window by
using a more agressive but cleanable flux.
Guy Ramsey
American Competitiveness Institute
Senior Lab Technician / Instructor
610 362-1200 ext 107
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Furrow, Robert Gordon
(Bob)
Sent: Wednesday, October 18, 2000 3:57 PM
To: [log in to unmask]
Subject: [TN] Cleaning Help Needed
Hi TechNetters,
I need some help regarding possible course of action and also possibly local
contact for cleaning.
We use a BellCore compliant solderpaste on our product which we do not
clean. Flux residues have been tested and passed for SIR and
Electromigration (as well as other tests). This flux was chosen over another
candidate because although it basically performed equivalently during
surface mount, at In-Circuit Test with via in pad product it was superior.
This of course means a softer more penetrable residue. Unfortunately, it
also means a more visible residue on and around the solder joints. This is
particularly true of bottomside since after the bottomside is reflowed, the
board is flipped over and the topside is reflowed. This extra heat results
in the flux residues on the bottomside flowing further out onto the
soldermask and are very evident. This had been considered a cosmetic issue
and a direct result of the improved pin testability.
We now have some boards in prototype where under system test conditions
(slightly elevated temperature and high humidity), there is a failure,
possibly due to impedance variations. The test/design group feels that the
flux residues could be causing this failure. I have been asked to clean a
few of the boards to confirm. I don't want to hand clean as I am concerned
all I will really accomplish is spreading the residues around. I can't go
through my normal semi-aqueous cleaner as there are now power modules on the
board that would be impractical to remove entrapped liquid inside. It is
preferred not to remove any parts so that we have the exact same boards only
with no flux residues. Would a vapor phase cleaner work in this application
since the solvent should evaporate relatively quickly. There are press fit
connectors on the board also so I can't have anything too aggressive. I am
looking to do just a few boards to be able to conclusively show if it is
caused by flux residue or not. Does anyone have a better idea? Does anyone
have a cleaning system available to do a few 14 inch by 14 inch circuit
packs on a quick turn basis? I would prefer a local solution so I can get
this done tomorrow. I am in North Andover, MA. If you have comments please
respond via the TechNet. If you are able to meet my cleaning needs, please
contact me by my email below.
Thanks,
Robert Furrow
SMT Process Engineer
Lucent Technologies
978-960-3224 [log in to unmask]
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