As a general rule, ionic contamination testing is done immediately after
cleaning (or not-cleaning!). If rosin has polymerised and/or hydrolysed,
I agree it is difficult to remove, although I don't understand your
"diffusion into the components".
Brian
Dehoyos, Ramon wrote:
> 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
> -----------------------------------------------------
>
>
---------------------------------------------------
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
-----------------------------------------------------
|
