I think the discussion we had in the J-STD-001 Handbook on this subject
does a good job of capturing the intent of this section:
8.1.3 Post-Soldering Cleaning
(Requirement from 001b)
WHEN CLEANING IS REQUIRED, FLUX RESIDUE SHALL BE REMOVED AS SOON
AS POSSIBLE, PREFERABLY WITHIN
ONE HOUR AFTER SOLDERING. SOME FLUXES OR PROCESSES MAY REQUIRE
MORE IMMEDIATE ACTION TO
FACILITATE ADEQUATE REMOVAL. MECHANICAL MEANS SUCH AS AGITATION,
SPRAYING, BRUSHING, ETC., OR
VAPOR DEGREASING AND OTHER METHODS OF APPLICATION MAY BE USED IN
CONJUNCTION WITH THE
CLEANING MEDIUM. THE TIME BETWEEN SOLDERING AND COMPLETION OF
CLEANING MAY BE EXTENDED FOR
HAND SOLDERING OPERATIONS, PROVIDED INTERIM CLEANING IS
PERFORMED AND COMPLETE CLEANING IS
PERFORMED PRIOR TO THE END OF THE PRODUCTION SHIFT.
(Rationale)
Historically, if a high solids rosin flux is not cleaned from a
printed wiring assembly within one hour of
mass soldering, the rosin will polymerize, making it nearly
impossible to remove or dissolve without
destroying the assembly. This can be true to some extent in
modern fluxes, as well, hence the one-hour
reference. Highly aggressive fluxes, due to their acidic nature,
need to be removed more rapidly to limit
the attack of metallic surfaces. The method of cleaning solution
delivery, or other mechanical aids to
cleaning, is left up to the manufacturer. Due to typical
logistics of assembly, it may be difficult to do all
the hand soldering operations and clean within an hour.
Typically, the hand soldering cored wire fluxes
are not as immediately harmful (as the wave solder fluxes), so a
longer period is allowed, but some
measures must be taken to limit the harmful effects of the flux.
An example is isopropanol cleaning of
RMA fluxes during hand solder, with a more global cleaning by
the end of the production shift. The
sooner the time to cleaning, the better.
Overall, I believe the idea in the 001B wording was (sorry to disagree
with Mel) with the extent of cleaning of the PWA. In other words, if
you figure to meet your end item requirement for cleanliness for a flux
you have to do IPA bench cleaning followed by batch aqueous (not unusual
for traditional high solid RMAs to meet environmental/SIR type testing);
then you were to complete all the steps necessary to achieve this
cleanliness level on the same shift. It should be noted that for
technolgies such as SMT, no clean, etc. it has been well documented that
simply passing a Resistance of Solvent Extract (ROSE) test (e.g.
Omegameter) is NOT an adequate measure of the "cleanliness" of the
assembly. ROSE was meant as a process control method (Doug Pauls can go
into MUCH more detail on this if you like).
The reason was that many of us have had the experience of the "2nd shift
guy forgot", "I was out sick and they didn't clean them" or "the
planning wasn't updated" when we "string out" the required steps across
mulitple days/shifts in the factory.
Is bench cleaning "good enough", well if it meets your end item
cleanliness level (however you measure/determine it) then yes it is. As
an example though, we find that for SMDs hand soldered with RMAs, we can
meet Omegameter (13 micrograms NaCl equivalent/in^2) after just IPA
bench cleaning but we fail environmental/SIR testing and so we aren't
"done" till we go through a follow-on cleaning. On some newer "low
residue" fluxes however, we find that little/no cleaning may be required
to reach an acceptable cleanliness level (hence our interest in low
residue fluxes).
How do you know when is "enough"? Well, the testing methodology shown
in Appendix D of the 001B is a good place to start and I would also
suggest IPC-RT-467 which details the background / supporting data for
this appendix.
===============================
Jim Maguire
Senior Principal Engineer
Boeing Information Space & Defense Systems
PO Box 3999 M/S 3W-97
Seattle, WA 98124-2499
Phone (253)657-9063 Fax (253)657-8903
Pager (206)982-3737
Email: [log in to unmask]
================================
> ----------
> From: Kenny Bloomquist[SMTP:[log in to unmask]]
> Reply To: TechNet E-Mail Forum.;Kenny Bloomquist
> Sent: Wednesday, March 25, 1998 1:03 PM
> To: [log in to unmask]
> Subject: [TN] Completly Clean
>
> There has been a great deal of discussion in our company about in
> process
> cleaning. Paragraph 8.1.3 of ANSI J-STD-001 states that "The time
> between
> soldering and completion of cleaning may be extended for hand
> soldering
> operations provided interim cleaning is performed and COMPLETE
> CLEANING is
> performed prior to the end of the production shift." Where we have
> trouble
> is whit the term "complete cleaning". Assuming that the assembly will
> see
> further cleaning processes and cleanliness testing prior to conformal
> coating, does that mean good bench cleaning practices and inspection
> for
> flux residue is good enough or does it required batch or in-line
> cleaning?
> If it does then how clean is clean? If so does this cleaning require
> testing to prove that it is "completely clean"?
>
> I love stuff like this, it's so green and purple.
>
> Thanks in advance for all responses.
>
> Kenny Bloomquist
>
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