Wimps? My eye and Betty Martin! My all-time measured record heat index at 300 m altitude was 51.9°C on 28 August 2006 (my equipment is NOAA approved). You can reckon on about 1° higher in the plain. Summer hasn't really started yet as this month's highest heat index was a mere 43.7°C. I expect at least 5° higher between 15 July and 15 August. Wipe that Dewey sweat off your brow! Brian On 28.06.2013 16:33, Whittaker, Dewey (EHCOE) wrote: > Wimps! 48�C with no peaks; this is the valley. > > Dewey > > > > -----Original Message----- > From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge Hernefjord > Sent: Thursday, June 27, 2013 10:16 PM > To: [log in to unmask] > Subject: [TN] > > > > Brian, I guess then that you have hot dogs daily. > > > > Inge > > > > > > On 26 June 2013 08:18, Brian Ellis <[log in to unmask]<mailto:[log in to unmask]>> wrote: > > > >> Laura, > >> > >> Yes, I agree with you that once you take the temperature of FR-4 or > >> any other resin above the Tg, the opening of the structure becomes a > >> great issue in terms of absorbing/adsorbing contaminants. > >> > >> I don't want to appear more arrogant than I usually am but my > >> experience is that there is much misunderstanding both in terms of > >> what the resins are and how they behave. I believe there is a tendency > >> to forget that they are not electrically perfect and that they are > >> hygroscopic, with an electrical "memory", especially under voltage > >> stress of more than a few volts per millimetre. In these days of tiny > >> spacing, this becomes especially important. > >> > >> I also agree that there is much misunderstanding, even today, > >> regarding surface insulation resistance and the various forms of > >> electrochemical migration resistance. Unfortunately, this has become > >> enshrined because of the historical errors. > >> > >> Summer? Today we had a peak heat index of 41� C! > >> > >> Best regards > >> > >> Brian > >> > >> > >> On 24.06.2013 00:03, Laura J Turbini wrote: > >> > >>> Hi Brian, > >>> > >>> I personally believe that the glycols, and the bromideions diffuse > >>> into the epoxy during the soldering process. When the epoxy goes > >>> above its Tg it opens up its polymeric structure and allows the contaminants to enter. > >>> There is a good description of the epoxy backbone in a web site > >>> called Macrogallaria. > >>> http://www.pslc.ws/macrog/**level2.htm<http://www.pslc.ws/macrog/leve<http://www.pslc.ws/macrog/**level2.htm%3chttp:/www.pslc.ws/macrog/leve> > >>> l2.htm> You will note that there are a lot of places in the epoxy > >>> resin for hydrogen bonding to occur. In the late 90's we were > >>> analyzing a field failure due to CAF. The growth was around the 5th layer of a 10 layer board as I recall. When my student polished down to that layer, he was able to extract the ionic residues and found bromide, but no chloride. > >>> This board was processed with the high bromide HASL fluid. We have > >>> also published some work using different polyglycols in the flux, > >>> and we noted that the Cu and Cl ions in the matrix had a different > >>> morphology depending on the polyglycol used. > >>> > >>> I agree with you that the traditional test method described as > >>> Surface Insulation Resistance is in fact an electrochemical migration test. > >>> According to the IPC, Electrochemical migration (ECM) is defined as > >>> the growth of conductive metal filaments across a printed circuit > >>> board (PCB) in the presence of an electrolytic solution and a DC > >>> voltage bias. The low voltage test could also be described as ECM > >>> but it does more accurately show the insulation resistance at the > >>> given temperature and humidity conditions because dendritic growth > >>> would be rather slow under those conditions. > >>> > >>> I hope you are enjoying the summer. > >>> Regards, > >>> Laura > >>> > >>> > >>> > >>> -----Original Message----- > >>> From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Ellis > >>> Sent: June-21-13 7:28 AM > >>> To: [log in to unmask]<mailto:[log in to unmask]> > >>> Subject: [TN] > >>> > >>> Laura, > >>> > >>> Is is a long time since we had any conversation together or even > >>> crossed swords! But it's good to hear from you. > >>> > >>> I used the term 'chemi-physio-adsorption', which I coined for the > >>> occasion, to describe what I believe is the combination of why > >>> glycols tend to stick to epoxies. If the surface were glass smooth, I > >>> believe the only mechanism would be hydrogen bond adsorption. The > >>> broken surface of etched epoxy probably allows for considerable > >>> absorption, which of course is purely physical. The crunch lies in > >>> the fact that some of the adsorption occurs in the hollows, where > >>> removal is very much more difficult. Of course, acetonitrile is a > >>> very effective general-purpose solvent which can remove both hydrophilic and hydrophobic organics. > >>> Provided that the bond strength between the acetonitrile and a > >>> contaminant is stronger than the bond strength between the > >>> contaminant on the substrate, then the contaminant will be dissolved in the solvent. > >>> In the case of glycols, both OH and H bonds can form simultaneously > >>> with the solvent, so that it is not surprising that it can remove > >>> them, at least partially. > >>> > >>> Of course, being retired, I am totally out of touch with the latest > >>> developments. However, I'm a little surprised at your statement that > >>> bromide ions diffused into FR-4 as an affinity to the flame retardant > >>> bromine compounds. These are in no way ionic and, not only are the > >>> bromine atoms covalently bonded to the carbon, they are part of the > >>> cross-linking in the polymerisation of the resin. I would seriously > >>> suggest that the mechanism of migration of bromide ions is more > >>> likely to be due to an ion exchange mechanism with the residual > >>> sodium chloride molecules in the epoxy resin. This would also explain why chloride ions do not have any effect. > >>> > >>> I know you are the guru on the electrochemical migration and its > >>> effects on surface insulation resistance, but this is only one > >>> mechanism. In my opinion (not humble, of course), if you refer to the > >>> various publications on the subject I have made since about 1986, you > >>> will see that I make a very distinct differentiation between surface > >>> insulation resistance and electrochemical migration resistance; > >>> although many confuse the two, they are horses of different colours. > >>> The test that I was proposing in my earlier message was true surface > >>> insulation resistance and, for this reason, I stated that the test > >>> should be conducted without any bias voltage and with the > >>> measurements made at 5 V or less for as short a time as possible. > >>> This is to prevent any electrochemical migration from altering the > >>> results or, any dissociation of the sodium chloride molecules in the epoxy resin from doing the same. > >>> If you apply a bias voltage, there is migration of the sodium and > >>> chloride ions within the epoxy structure and this can seriously > >>> change the apparent surface insulation resistance independently from > >>> that due to the presence of a contaminant such as any form of surfactant. > >>> > >>> As you are probably aware, I pioneered the notion of such low > >>> voltage, unbiased, SIR tests when I developed the Insulohmeter IRMA. > >>> Much of the research into the effects due to contamination were done > >>> by myself, while the effects due to the structure of the epoxy was > >>> studied by a graduate student at the Swiss Federal Institute of > >>> Technology whose Master's degree dissertation was on this subject. > >>> Unfortunately, I cannot remember his name or details but I do > >>> remember that he worked under Prof Kausch who had the chair of > >>> polymers, at that time in the 1980s. As the guy had become so > >>> knowledgeable about the electrical characteristics of epoxy resins, I > >>> suggested to him that there must surely be many openings in the > >>> industry for a person with this experience; unfortunately, he chose > >>> to be attracted by American "big oil", rather than specialise in a > >>> very narrow field. I've never heard of him since! Incidentally, > >>> Kausch told me, after the adjudication of his dissertation (I was on > >>> the pane > >>> > >> l) that it was the best master's thesis he had ever had the pleasure > >> of reading! He bought me a dinner in recompense of having lent the > >> Department the Insulohmeter for three trimesters! > >> > >>> > >>> Of course that brings me to a remembrance of the dinner we had in > >>> Washington DC, together with Barbara K. I recall that we had some > >>> very interesting discussions in that Italian restaurant! > >>> > >>> Life goes on in sunny Cyprus, unfortunately with the physically > >>> degenerative effects of old age, about two weeks short of my 81st birthday! > >>> How is it with you in your colder climes? > >>> > >>> Best regards > >>> > >>> Brian > >>> > >>> On 21.06.2013 00:32, Laura J Turbini wrote: > >>> > >>>> Hi Brian, > >>>> You always add a little spice to the conversation including > >>>> references which only us "old timers" know. You are correct that > >>>> Zado's worked focused on PEG and polypropylene glycol. Today, there > >>>> are block copolymers such as polyethylene propylene glycol (PEPG), > >>>> and others that are used in HASL fluids. Jack Brous showed in > >>>> 1981-82 that the PEG absorbed into the epoxy (it was not a > >>>> chemi-physio-adsorption) and he was able to extract it from the > >>>> boards using acetonitrile. When he evaporated the acetonitrile solution and took an FTIR spectrum of the residues he found PEG. > >>>> > >>>> More recently, my former student, Dr. Antonio Caputo published a > >>>> paper which included extraction of PEG and PEPG from water soluble > >>>> fluxed FR-4 test coupons. Ref. A. Caputo, L.J. Turbini, D.D. > >>>> Perovic, (2009), "Conductive Anodic Filament (CAF) Formation Part I: > >>>> The Influence of Water Soluble Flux on its Formation", Journal of > >>>> Electronic Materials, Vol. 39, > >>>> 85-91 (2010). > >>>> > >>>> In another paper he also showed that if the HASL fluid contained a > >>>> high bromide content (~15%), the bromide ions also diffused into the > >>>> FR-4 (because for brominated epoxy - like dissolves like). > >>>> Chloride from the flux did not diffuse into the epoxy. ref A. Caputo, L.J. Turbini and D.D. > >>>> Perovic, "Characterization and Electrochemical Mechanism of > >>>> Bromide-Containing Conductive Anodic Filament (CAF) Failure," > >>>> Journal of Electronic Materials, Vol. 40, No. 9, 2011. > >>>> > >>>> You commented below - The only valid way of determining the presence > >>>> of hydrophilic surface phenomena is by non-biased, low voltage 50/90 > >>>> or 85/85 SIR qualification tests. What do you mean by non-biased, low voltage? > >>>> Aren't the two terms contradictory. > >>>> > >>>> The rate of electrochemical migration (dendrite or CAF growth) is > >>>> affected by the contamination present, but also by voltage, > >>>> temperature and humidity. Using low voltage testing would require a > >>>> longer time for the dendrite to form. There is a rule of thumb that > >>>> says that a chemical reaction doubles for each 10oC rise in > >>>> temperature. Thus, the use of a lower temperature would also require a longer time for dendrites to form. > >>>> Regarding humidity, FR-4 boards will easily have enough layers of > >>>> water molecules at 70% RH or higher, to allow the electrochemical > >>>> migration to occur. So whether it is 85% or 90%, the difference in > >>>> the rate of dendrite formation will be small. > >>>> > >>>> Regards, > >>>> Laura > >>>> > >>>> > >>>> > >>>> -----Original Message----- > >>>> From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Ellis > >>>> Sent: June-20-13 11:59 AM > >>>> To: [log in to unmask]<mailto:[log in to unmask]> > >>>> Subject: [TN] > >>>> > >>>> I'm afraid that some of what you say may be misleading. Frank Zado's > >>>> paper, at the Anaheim and Philadelphia Nepcon conferences in 1979, > >>>> explored mainly Carbowax (polyethylene glycol. PEG) of specific ranges of MW. > >>>> Although he did some tests with polypropylene and higher glycols, > >>>> these proved to be of much reduced effect. This was also specific to > >>>> wave soldering. Also the effect was not due to an epoxy-OH bond; it > >>>> was a hydrogen bond, exacerbated by the structural surface of the > >>>> epoxy, left by the copper treatment. It could be described as a chemi-physico-adsorption. > >>>> However, PEG fell largely into disuse in the 1980s, except for some > >>>> tin-lead reflow and HASL processes in the FAB side. Of course, it > >>>> was your famous OH group that potentially created any hydrophilic > >>>> characteristics at the other end of the molecule! > >>>> More particularly, as I have propounded many times since 1969 > >>>> (Inter-Nepcon), in my book and other publications, in lectures and > >>>> in my swansong paper in Circuit World, the water-break test is > >>>> absolutely meaningless, with easily produced false negatives and false positives. > >>>> IMO, anyone who uses it as determinant of any specific reliability > >>>> conditions needs his head examining. The only valid way of > >>>> determining the presence of hydrophilic surface phenomena is by > >>>> non-biased, low voltage 50/90 or 85/85 SIR qualification tests. The > >>>> oracle hath spoken! :) > >>>> > >>>> Brian > >>>> > >>>> On 20.06.2013 17:21, greg wrote: > >>>> > >>>>> It is true that WS flux should be removed in the cleaning process. > >>>>> > >>>>> However, many glycols actually bond to FR-4 epoxy through their -OH > >>>>> groups. Hence the surface after soldering and cleaning is > >>>>> hydrophillic. (Frank Zado showed this back in the early 80s.) > >>>>> > >>>>> An easy test is take a board that is clean but not WS soldered and > >>>>> drop DI water on it. It should bead up. > >>>>> > >>>>> If after WS soldering and cleaning a drop of DI spreads you have > >>>>> glycols bonded to the epoxy. > >>>>> > >>>>> Adding a no-clean (with dibasic acids) to a hydrophobic mix may be > >>>>> an iffy proposition. > >>>>> > >>>>> Better to use a Bellcore compliant flux for your final soldering. > >>>>> > >>>>> > >>>>> -------Original Message------- > >>>>>> From: Steven Kelly <[log in to unmask]<mailto:[log in to unmask]>> > >>>>>> To: [log in to unmask]<mailto:[log in to unmask]> > >>>>>> Subject: [TN] > >>>>>> Sent: 20 Jun '13 09:02 > >>>>>> > >>>>>> Thanks Dave - customer has not done any testing and for years > >>>>>> we have only used no-clean for both operations so now I have some > >>>>>> parts to be done one way and some another for Class 3 medical. Not > >>>>>> good in my 2 cent opinion. Regards Steve Kelly > >>>>>> > >>>>>> From: [log in to unmask]<mailto:[log in to unmask]> [mailto:ddhillma@** > >>>>>> rockwellcollins.com <[log in to unmask]<mailto:[log in to unmask]>>] > >>>>>> Sent: June-20-13 9:15 AM > >>>>>> To: TechNet E-Mail Forum; Steven Kelly > >>>>>> Cc: TechNet > >>>>>> Subject: Re: [TN] Mixing solders, > >>>>>> > >>>>>> Hi Steve - I'll have to pay Doug and use his tag line - "It > >>>>>> depends"! Anytime you mix two different flux systems, especially a > >>>>>> water soluble and a low residue (aka no clean), there may be an > >>>>>> issue of incompatibility that could result in a really hard > >>>>>> lacquer (best case) or a really cool corrosion cell (worst case). > >>>>>> My recommendation would be to advise the customer that the mixing > >>>>>> of the two flux systems would not be advised unless some testing > >>>>>> can be conducted to ensure no detrimental reactions would occur. A > >>>>>> second option would be to check with the flux supplier to see if > >>>>>> they have any compatibility data. If the fluxes come from two > >>>>>> different suppliers, don't waste your time asking that question as they won't have the answer. Good Luck. > >>>>>> > >>>>>> Dave Hillman > >>>>>> Rockwell Collins > >>>>>> [log in to unmask]<**mailto:ddhillma@**<mailto:[log in to unmask]**mailto:ddhillma@**> > >>>>>> rockwellcollins.com <[log in to unmask]<mailto:[log in to unmask]>>> > >>>>>> > >>>>>> > >>>>>> > >>>>>> From: Steven Kelly <[log in to unmask]<mailto:SKe** > >>>>>> [log in to unmask]<mailto:[log in to unmask]> <[log in to unmask]<mailto:[log in to unmask]>>>> > >>>>>> To: <[log in to unmask]<mailto:TechNe**[log in to unmask]<[log in to unmask]<mailto:[log in to unmask]:TechNe**[log in to unmask]@IPC.ORG>> > >>>>>>>> > >>>>>> Date: 06/20/2013 08:02 AM > >>>>>> Subject: [TN] Mixing solders, > >>>>>> Sent by: TechNet <[log in to unmask]<mailto:TechNe**[log in to unmask]<[log in to unmask]<mailto:[log in to unmask]:TechNe**[log in to unmask]@ipc.org>> > >>>>>>>> > >>>>>> ______________________________**__ > >>>>>> > >>>>>> > >>>>>> > >>>>>> Hi All, > >>>>>> I have been looking in the archives but can't seem to find > >>>>>> what I want an answer to . I have a customer who wants us to use > >>>>>> water soluble RoHS for the SMT process but wants no-clean RoHS for > >>>>>> the touch-up. Is this recommended? Regards Steve Kelly > >>>>>> > >>>>>> > >>>>>> If the recipient to whom this e-mail is sent has an NDA with > >>>>>> PFC Flexible Circuits Limited this e-mail is considered > >>>>>> confidential and is subject to any NDA agreements between the respective parties. > >>>>>> > >>>>>> See PFC on "How It's Made`` coming soon on the Discovery Channel! > >>>>>> > >>>>>> > >>>>>> > >>>>>> ______________________________**______________________________** > >>>>>> __________ > >>>>>> This email has been scanned by the Symantec Email > >>>>>> Security.cloud service. > >>>>>> For more information please contact helpdesk at x2960 or > >>>>>> [log in to unmask]<mailto:helpde**[log in to unmask]<mailto:[log in to unmask]:helpde**[log in to unmask]> <[log in to unmask]<mailto:[log in to unmask]>>> > >>>>>> > >>>>>> ______________________________**______________________________** > >>>>>> ________ > >>>>>> __ > >>>>>> > >>>>>> > >>>>>> > >>>>>> ______________________________**______________________________** > >>>>>> __________ > >>>>>> This email has been scanned by the Symantec Email > >>>>>> Security.cloud service. > >>>>>> For more information please contact helpdesk at x2960 or > >>>>>> [log in to unmask]<mailto:[log in to unmask]> > >>>>>> > >>>>>> ______________________________**______________________________** > >>>>>> ________ > >>>>>> __ > >>>>>> > >>>>>> > >>>>> ______________________________**______________________________** > >>>>> _________ > >>>>> _ This email has been scanned by the Symantec Email Security.cloud > >>>>> service. > >>>>> For more information please contact helpdesk at x2960 or > >>>>> [log in to unmask]<mailto:[log in to unmask]> > >>>>> ______________________________**______________________________** > >>>>> _________ > >>>>> _ > >>>>> > >>>>> > >>>> ______________________________**______________________________** > >>>> __________ > >>>> This email has been scanned by the Symantec Email Security.cloud service. > >>>> For more information please contact helpdesk at x2960 or > >>>> [log in to unmask]<mailto:[log in to unmask]> > >>>> ______________________________**______________________________** > >>>> __________ > >>>> > >>>> ______________________________**______________________________** > >>>> __________ > >>>> This email has been scanned by the Symantec Email Security.cloud service. > >>>> For more information please contact helpdesk at x2960 or > >>>> [log in to unmask]<mailto:[log in to unmask]> > >>>> ______________________________**______________________________** > >>>> __________ > >>>> > >>>> > >>> ______________________________**______________________________** > >>> __________ > >>> This email has been scanned by the Symantec Email Security.cloud service. > >>> For more information please contact helpdesk at x2960 or > >>> [log in to unmask]<mailto:[log in to unmask]> > >>> **______________________________**__________ > >>> > >>> ______________________________**______________________________** > >>> __________ > >>> This email has been scanned by the Symantec Email Security.cloud service. > >>> For more information please contact helpdesk at x2960 or > >>> [log in to unmask]<mailto:[log in to unmask]> > >>> ______________________________**______________________________** > >>> __________ > >>> > >>> > >> ______________________________**______________________________**______ > >> ____ This email has been scanned by the Symantec Email Security.cloud > >> service. > >> For more information please contact helpdesk at x2960 or > >> [log in to unmask]<mailto:[log in to unmask]> > >> **______________________________**__________ > >> > > > > ______________________________________________________________________ > > This email has been scanned by the Symantec Email Security.cloud service. > > For more information please contact helpdesk at x2960 or [log in to unmask]<mailto:[log in to unmask]> ______________________________________________________________________ > > ______________________________________________________________________ > This email has been scanned by the Symantec Email Security.cloud service. > For more information please contact helpdesk at x2960 or [log in to unmask] > ______________________________________________________________________ > ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. 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