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. 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