It is known that flux removal decreases with time as it hardens,
sometimes even turning white  (moisture) . It is so difficult to remove
partially due to its diffusion into the components. If it is so hard to
remove, wouldn't the equipment used to measure the salt content have the
same difficulty in extracting enough flux to get an accurate reading the
longer the flux is on the board.  Appreciate any light shone on this matter.
        Regards,
        Ramon


> -----Original Message-----
> From: Brian Ellis [SMTP:[log in to unmask]]
> Sent: Monday, May 26, 2003 2:13 AM
> To:   [log in to unmask]
> Subject:      Re: [TN] ROSE for Flip Chip
>
> Peter
>
> To some extent I agree with you, but not entirely.
>
> Using the pasted area is no better than using the board area. The paste
> is deposited on metal. The danger lies on substrate and the paste
> chemistry spreads over the substrate during preheat and reflow.
>
> I agree that most current models of equipment do not meet the
> requirements of cutting-edge industry. This is why I hatched the
> Microcontaminometer in 1983, culminating in the MCM-2 in the late 1980s,
> which was able to go down to 50 ng of absolute sodium chloride with a
> 50% solution (in other words over 4 orders of magnitude more sensitive
> than your instrument). The conductivity measuring system was able to
> measure 1.5 parts per billion (ppb) of salt in the solution! Multicore,
> in their wisdom, decided to abandon this model after they took over the
> range. They did make a vague effort in the late 1990s to resuscitate the
> idea with the CM-20, I believe, but I don't think that got much beyond
> the pre-production stage (I don't know for sure, as there were a lot of
> communication difficulties). Maybe Graham Naisbitt of Concoat can tell
> you what the current situation is, as I understand they are the present
> successors to the Contaminometer legacy (I have absolutely no interest
> in it, either technical or financial).
>
> I agree that to calibrate and drive these ultra-sensitive instruments is
> not great fun, unless you are a masochist, but they were able to produce
> the desired results accurately, with care and, above all, knowledge. I
> had several customers for them within the great names of the Swiss watch
> industry (including Swatch!), the hybrid circuit industry and component
> manufacturers and they were all able to use them without problems, even
> if it required a day's training.
>
> I see, in my book pp 316-320, I was suggesting that 0.5 ug/cm2 eq. NaCl
>   was necessary, even then (written 1983-5, published 1986, for hybrid
> and SM circuits). So, what you are saying has a 20 year history, already!
>
> Hope this helps.
>
> Brian
>
>
>
> [log in to unmask] wrote:
> > Ah, Glen!
> >
> > I've been battling this one for far too long now myself, and one of the
> > questions I posed was just the one you are posing here - is it imore
> > realistic to calculate the solder paste area, since this is where all
> the
> > flux contamination wil be concentrated, or go with the spec requirements
> > which gives a cleanliness requirement calculated from 2x entire board
> area?
> >
> > I have my own opinion which I'll explain in a moment, but let's look at
> > history first. The cleanliness figures in the IPC and MIL specs are now
> > over 30 years old and date from the days when components were all PTH
> and
> > wave soldered. With wave soldering, the entire board area is fluxed, and
> > with the technology of those days, trace weights, widths and spacings
> were
> > much greater than they are today. Hence the cleanliness level required
> was
> > not as stringent as it needs to be today. The cleanliness level, taken
> over
> > the entire board area made sense then, but has not been updated since to
> > account for the much finer traces, closer spacing and SMT technology of
> > today. SMT technology, of course, largely uses Convection Reflow
> soldering
> > techniques in which solder paste (flux) is deposited only in localised
> > areas.
> >
> > Doug Pauls from Rockwell Colins will probably give you a very
> knowledgeable
> > answer to your question, but my opinion is this:
> >
> > a) if you want your boards to meet IPC or MIL spec, it can be easily
> done
> > using the current ROSE test equipment, which also has changed very
> littlle
> > in principle in 30 years. Take whatever reading you get from the machine
> at
> > face value, divide it by the total board area and you have the
> appropriate
> > figure against which to judge if you've passed or failed.  However ...
> > b) Industry concensus seems to have it that a much tighter cleanliness
> > figure is now required than in days of yore - 0.2ug NaCl eq cm^-2
> instead
> > of 1.56ug is the figure that's been bandied about, based, I believe, on
> SIR
> > and Ion Chromatography results for modern boards. It's a figure I prefer
> to
> > believe than the IPC spec  figure.
> > c) Using the solder pasted area as the divisor for the cleanliness
> result
> > makes the test much harder to pass, but will give you (to my mind) a
> more
> > realistic idea of how clean the fluxed areas are. I think, too, that the
> > real truth about overall board cleanliness will lie somewhere in between
> > the two areas, though where I cannot say for sure but probably nearer to
> > the pasted area than the overall board area.
> > d) as boards get smaller and clealiness level requirements become
> tighter,
> > we run into problems with the ROSE testers, which are still happily
> > claiming compliance with the IPC and MIL Specs and tend to assume a
> board
> > area that may be much larger than you normally deal with. The problems
> are
> > those of working at the extreme limits of the machines' capabilities.
> Sure,
> > you can continue to do what you do now, which is to test a number of
> boards
> > at the same time to, as you say, give the machine something to measure,
> but
> > I believe it's time that the ROSE tester manufacturers looked to
> updating
> > their technology.
> > I've been giving Mike Konrad at Aqueous Technologies a hard time,
> demanding
> > "official" figures for how well their Zero Ion reads at low levels of
> > contamination, because from tests I have carried out, machines tend to
> > start reading inaccurately when total contamination weights drop much
> below
> > 1000ug NaCl eq. I have boards that measure just over 9" x 6" and have a
> > target cleanliness figure of 0.2ug NaCl eq cm^-2. This means that the
> > maximum permissible contamination weight must not exceed 143ug per
> board.
> > The ROSE test tank I have is large enough to allow two boards to be
> tested
> > at one time, which means that the machine has to be capable of reading
> > accurately 286ug NaCl eq (board area is irrelevant as it's just a
> divisor
> > that you programme into the machine yourself - it doesn't affect the
> > machines ability (or otherwise) to detect and measure the contamination
> > level. 286ug is well below the level at which the machines seem to read
> > accurately, or consistently. The variance at these levels is also great,
> > and if my tests are accurate, makes the measurement at these
> concentrations
> > meaningless.
> >
> > As more people move to "no-clean" technology, the only folks left using
> > ROSE testers will be the Class 3 board builders who continue to use
> > water-soluble fluxes. Maybe that market is not big enough to justify
> > re-evaluating the capabilities of the testers, in which case ways round
> the
> > capability problem have to be found.
> >
> > Glen, whether you choose to use overall board area or pasted area for
> your
> > cleanliness calculation is up to you. If you want a better idea about
> the
> > board cleanliness, use pasted area, but if you want the boards to pass
> test
> > for shipment, use overall area adn no-one can legitimately criticise
> you.
> >
> > Hope some of the other gurus will give me a debate on ROSE tester
> > capability.
> >
> > Peter.
> >
> >
> >
> > Glenn Pelkey <[log in to unmask]>  23/05/2003 09:59 PM
> > Sent by: TechNet <[log in to unmask]>
> >
> > Please respond to "TechNet E-Mail Forum."; Please respond to
> glenn.r.pelkey
> >
> >               To:  [log in to unmask]
> >               cc:  (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
> >               Subject: [TN] ROSE for Flip Chip
> >
> >
> >
> >
> >
> >
> >
> >
> > Hi Technetters,
> >
> >
> >         My buddy and I have a disagreement on using Resistivity of
> Solvent
> > Extract (ROSE) for measuring cleanliness on a Flip Chip board.  So,
> we're
> > throwing it to league of experts on this forum for feedback
> >
> >
> >         Here's the story:  The board and assembly are very simple.  One
> > flip chip die at about 0.002 square inches and one board about 0.490
> square
> > inches.  Flux is applied only to the flip chip die, reflowed, and DI
> inline
> > washed.
> >
> >
> >         Here's the disagreement:  I say use 2X the surface area of the
> die
> > for the calculation.  My good friend says use 2X the board surface.  Of
> > course, you can see one number is much higher than the other in ug/sq
> inch
> > NaCl equiv.  My logic for using only the die area is to understand the
> > process cleanliness at that location only, but I recognize the entire
> board
> > surface could be cross contaminated in some manner.  We also loaded the
> > machine with 32 of these units to get something measurable.  When we
> only
> > put 4 in, nothing showed up, but the smallest entry for surface area is
> 0.1
> > square inches.
> >
> >
> > Thanks for your input!
> >
> >
> > Glenn
> >
> >
> > ---------------------------------------------------
> > Technet Mail List provided as a free service by IPC using LISTSERV 1.8e
> > To unsubscribe, send a message to [log in to unmask] with following text
> in
> > the BODY (NOT the subject field): SIGNOFF Technet
> > To temporarily halt or (re-start) delivery of Technet send e-mail to
> > [log in to unmask]: SET Technet NOMAIL or (MAIL)
> > To receive ONE mailing per day of all the posts: send e-mail to
> > [log in to unmask]: SET Technet Digest
> > Search the archives of previous posts at:
> http://listserv.ipc.org/archives
> > Please visit IPC web site http://www.ipc.org/html/forum.htm for
> additional
> > information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700
> > ext.5315
> > -----------------------------------------------------
> >
> >
> >
> >
> >
> >
> >
> > [This e-mail is confidential and may also be privileged. If you are not
> the
> > intended recipient, please delete it and notify us immediately; you
> should
> > not copy or use it for any purpose, nor disclose its contents to any
> other
> > person. Thank you.]
> >
> > ---------------------------------------------------
> > Technet Mail List provided as a free service by IPC using LISTSERV 1.8e
> > To unsubscribe, send a message to [log in to unmask] with following text
> in
> > the BODY (NOT the subject field): SIGNOFF Technet
> > To temporarily halt or (re-start) delivery of Technet send e-mail to
> [log in to unmask]: SET Technet NOMAIL or (MAIL)
> > To receive ONE mailing per day of all the posts: send e-mail to
> [log in to unmask]: SET Technet Digest
> > Search the archives of previous posts at:
> http://listserv.ipc.org/archives
> > Please visit IPC web site http://www.ipc.org/html/forum.htm for
> additional
> > information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700
> ext.5315
> > -----------------------------------------------------
> >
> >
>
> ---------------------------------------------------
> Technet Mail List provided as a free service by IPC using LISTSERV 1.8e
> To unsubscribe, send a message to [log in to unmask] with following text in
> the BODY (NOT the subject field): SIGNOFF Technet
> To temporarily halt or (re-start) delivery of Technet send e-mail to
> [log in to unmask]: SET Technet NOMAIL or (MAIL)
> To receive ONE mailing per day of all the posts: send e-mail to
> [log in to unmask]: SET Technet Digest
> Search the archives of previous posts at: http://listserv.ipc.org/archives
> Please visit IPC web site http://www.ipc.org/html/forum.htm for additional
> information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700
> ext.5315
> -----------------------------------------------------

---------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/html/forum.htm for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
-----------------------------------------------------