Brilliant, Greg, Just the sort of answer I'm looking for. I'll need to check to see if the resistivity options on the Zero Ion machine we have to play with will allow me to choose my own level, or if I'm stuck with the 60MOhms or 150MOhms it offers as standard. Can you help tell me how I would temperature-compensate the probe and why this is important? It sounds like you have to fool the machine into believing something that isn't, so I'ld like to understand the theory behind the adjustment. Also "guage R&R"? Need some help on what this reference means, as I haven't met it yet. I've seen for myself the amazingly rapid influence that atmospheric Carbon Dioxide has on the test solution, even at 150MOhm, so I can well imagine what it would do at 450MOhms+. We'll take precautions against it when we need to (i.e. to combat too many indications of boards not passing the test). Peter. "Miller, Greg @ DISPLAYS" <greg.miller 15/04/2003 08:33 PM To: "TechNet E-Mail Forum." <[log in to unmask]>, DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group@ST Domain cc: Subject: RE: [TN] ICT machines and high cleanliness requirements Having worked with both static and dynamic ionic contamination testers for a number of years in many different applications, the only way you can measure less than 1 micro gram equivalent (total) is to use a low volume (1 gallon max), dynamic tester with a starting cleanliness level of at least 450 meg ohm. The resistivity probe must be temperature compensated from 22 to 38 C. My experience in using the Ionograph 500 M SP shows that a level of 0.2 micrograms total can be measured, but you need to perform your own studies using a precision pipette. Guage R & R is a must at these levels. Unfortunately, when an alcohol/water solution is 400+ meg ohms or cleaner, carbon dioxide will influence the reading. As CO2 dissolves, derivatives of carbonic acid form and ionize in solution. If you want to see for your self, open the lid and gently blow (quick puff) on the solution and watch the resistivity drop. Perhaps testing under nitrogen will help. Greg Miller -----Original Message----- From: [log in to unmask] [mailto:[log in to unmask]] Sent: Tuesday, April 15, 2003 5:39 AM To: [log in to unmask] Subject: Re: [TN] ICT machines and high cleanliness requirements Brian, Very many thanks for replying to my post. Part of your answer begs another question - if conductivity is linear and can accurately reflect contamination levels down to virtually zero, why are all the Ionic Cleanliness Test machines designed to measure resistivity and not conductivity? I don't know how to set about coverting a machine to read conductivity of a liquid instead of resistivity. Is there an easy way to do it, or has no-one tried? I wouldn't want to just use a formula to convert the resistivity reading into a conductivity value, since I don't trust the resistivity readings at low contamination levels in the first place. There would be no point, as the results wouldn't be so linear. Sorry, I'm going to cross-examine further - using a 50:50 water:alcohol mix will certainly help dissolve more of the non-water-soluble residues and thereby release more ionic contamination into the test solution to be measured. That would prove that you have a dirtier board than you previously thought, and prove that cleanliness measurement is a relative thing, not an absolute. It does not, however, improve the linearity or correlation of the readings the machine gives against the amount of contamination in the test solution - the higher amount of contamination might just take the readings into a region of the correlation curve where they coincide better, but that's all. I agree with your other comments about minimising atmospheric CO2 absorbtion and restricting test-run times to 15 mins max (...?), although I was finding that at least one of the machines was reading low at the low contamination level end of my testing - bad enough if there had been no CO2 influences on the results, almost worse if there were such influences, since the departure from accurate figures would have been even worse. I should have the courage of my convictions - it had penetrated me reasoning that static technology ought to be better for measuring low contamination levels than dynamic. However, we have a dynamic machine in our hands for playing with, and a good price is being asked if we want to buy it. The man holding the budget is keen, even if he doesn't seem to understand the subtle minutiae of the measurement process and its pitfalls. We're 99% of the way to clinching the deal already, but I'm still not convinced that it can measure that well without a lot of work to correlate the readings with actual contamination levels - i.e. so an operator can look up the machine reading on a chart and get a "true" contamination figure. I would still like to know, though, if there is work being done to produce machines that are 'comfortable' with measuring low contamination levels to replace those that are operating right on their limits (or beyond) to measure low levels. Saying a machine is quite capable of reading 0.2ug NaCl eq-cm^-2, without taking the board area into account makes such a claim meaningless. Many a machine will return such a cleanliness level reading if you have a large enough board area to extract lots of contamination from. The real question is "What is the smallest gross weight of contamination that a machine can accurately measure, before it is divided by the board area?" If it can measure accurately all the way to zero ug (either by measuring resistivity or by measuring conductivity, that's the machine for me! Anybody have one at a reasonable price? Thanks again. Peter Brian Ellis <[log in to unmask]> 15/04/2003 03:20 PM To: "TechNet E-Mail Forum." <[log in to unmask]>, DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group@ST Domain cc: Subject: Re: [TN] ICT machines and high cleanliness requirements Peter As the original designer of the Contaminometer, but no longer involved with it, in any way, I guess that I'm as qualified as any to respond to you. You are partially right, but not entirely. First of all, it must be said that the 1.56 ug/cm2 eq. NaCl or, better, ug.cm^-2 eq. NaCl(which is the correct way of expressing the units cf. ISO 2000) dates from an interpretation of Hobson's original tests, way back in 1969. Please don't tell me that modern electronics are the same as they were 34 years ago. This figure is as antiquated as the dinosaur and has no meaning today. The voltage gradients on our substrates have increased by at least an order of magnitude, actually to the limit of acceptable with HDIS, even for low voltage operation. I therefore concur that 0.2 ug/cm2 eq. NaCl would seem reasonable for modern electronics with conductor spacings of less than 0.2 mm, **provided** that it is measured reasonably accurately and for hi-rel end-products. So, how can this be done? First of all, you need to maximise the sensitivity. The first and obvious way is to use the UK Mod standard solution of 50% v/v IPA and not the US MIL standard of 75%, which is a relic of Hobson's work which had an integration time of 1 min, because it was sprayed on from a wash bottle, and not immersed with longer integration times. The 50% solution gives twice the sensitivity of the 75% solution. Secondly, contamination in these equipments is directly and linearly proportional to the delta conductivity, so is inversely and non-linearly proportional to the delta resistivity. Unfortunately, for fine measurements, because resistivity meters have a range, you are working at the cramped end of the scale. It is therefore more accurate to use conductivity with its linear scale. Then the board size enters into play. If you are stuck with a small board and a large tank, you simply measure on a plurality of boards. For example, if you have a tank size of, e.g., 250 x 350 mm, you can put in 8 boards 100 x 100 mm at a time, to obtain maximum sensitivity. Of course, your answer will be an average of the eight, but this is not a disadvantage. Then there is the reduction of errors. These can come from many sources. A bad one comes from CO2 absorption. This can be reduced by presenting a minimal surface area of solution at the air interface (rectangular, rather than funnel-shaped, tanks) and further reduced by software compensation of the absorption, as well as keeping the lid on during the test, with a minimal air volume over the solution. Another point is to keep the test down to under, say, 15 minutes, so that what you measure is the dissolved contamination and not leachates from the substrate or the instrument constructional materials. For the same reason, you should use solution at low temperatures (20-25 deg C). At higher temperatures, the heterogeneous structure of the polymeric surfaces tend to open and provoke more leaching from the substrate. I won't enter into the so-called "static" and "dynamic" methods. Our old CM-5 and MCM-2 models could use either. Each had advantages and disadvantages but, overall, the "static" method is the better, especially for low contamination levels. (I put the words between inverted commas, "", because they are very misleading misnomers.) If you observe all these points, it is possible to have a reasonable accuracy at 0.2 ug/cm2 eq. NaCl. For the anecdote, I used to manufacture the Microcontaminometer MCM-1 and MCM-2, which had a sensitivity that it could measure down to better than 0.05 ug eq. NaCl absolute. This would have measured better than 0.01 ug/cm2 eq. NaCl on a 100 x 100 mm board (it had an interchangeable tank for a 4" hybrid substrate). I believe Multicore stopped the MCM-2 in 1993. It was partially replaced by the CM-20, but I don't know what happened to that. I can only answer for the CM-1 to CM-5 and MCM-1 to MCM-2 series, which were the ones I designed. Anyway, what you wish to do is possible, provided you have the right instrument and know how to use it correctly. Brian [log in to unmask] wrote: > Morning, All > > I was interested to see the cleanliness level of <0.2ug NaCl eq/cm^2 that > is being adopted by many manufacturers, actually being stated in a data > booklet published by Concoat Systems. Having done a bit of poking around > into the world of cleanliness testing, I have a question for discussion if > you're up for it: > > Most ionic cleanliness testers are still marketed as measuring cleanliness > to the level specified in the MIL and IPC specs (1.56ug NaCl eq/cm^2). Fair > enough. Having looked quite closely into such machines as the Ionograph, > Concoat's own CM11 Contaminometer, Omegameters and the Zero Ion, which > seems to be teacher's pet in the IPC books (TR-583, anyway). I find that > none of the machines reads at all reliably at levels as clean as 0.2ug, > very especially whan the boards are small. Does anyone know, and is willing > to discuss, what work is therefore being done to improve ICT machines in > terms of the following: > a) using the test solution at much higher starting resistivity (e.g. > >>200MOhm-cm +), assuming that at this level of resitivity, small amounts of > > contamination will have a greater impact on the drop in resistivity when > added (?) > b) how the test solution is presented to the resistivity probe for > measurement of these slight amounts of contamination. This is of especial > concern since small amounts of contamination don't affect the resistivity > of the test solution very much at current values (150MOhm-cm or so), which > thus remains relatively close to its starting value. If the test solution > is not homgeneous and the measuring portion of the probe is not in contact > with all the test solution that passes it, solution of a higher or lower > resistivity will not be measured and included in the machine's reading. > c) the capability of the probes to accurately measure these relatively very > small differences in high resistvity values. > d) the capability of the filters to clean the test solution without adding > further contanination back in. > > Suppose you have a board that only measures 4cm x 4cm, and it has to be > 0.2ug NaCl eq/cm^2 clean. This means that the max amount of salt-equivalent > contamination allowable is only 6.4ug. To measure this board alone is > impossible - no machine is remotely capable of accuratey measuring a > contamination level this low - so a batch of these little boards would have > to be tested all together and the reading taken across the combined board > area. After being divided by the number of boards, you are left with an > average reading only. This is maybe OK if you have a lot of boards to test, > but not so OK if you're repairing only one or two of them and want them > clean again to original requirement. > > What is on the cards for future Ionic Contamination Testing equipment? > > Peter > > [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 > ----------------------------------------------------- > > > [This e-mail is confidential and may also be privileged. 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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 ----------------------------------------------------- [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 -----------------------------------------------------