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
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>>>>>> Security.cloud service.
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>>>>>> For more information please contact helpdesk at x2960 or
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>>>>>> [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]>>>
>
>>>>>>
>
>>>>>> ______________________________**______________________________**
>
>>>>>> ________
>
>>>>>> __
>
>>>>>>
>
>>>>>>
>
>>>>>>
>
>>>>>> ______________________________**______________________________**
>
>>>>>> __________
>
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>>>>>> Security.cloud service.
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>>>>>>
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>>>>>> ______________________________**______________________________**
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>>>>>>
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>>>>>>
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>>>>> ______________________________**______________________________**
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>>>>> _ This email has been scanned by the Symantec Email Security.cloud
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>>>>> ______________________________**______________________________**
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>>>>> _
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>>>>>
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>>>>>
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>>>> ______________________________**______________________________**
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>>>> __________
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>>>> For more information please contact helpdesk at x2960 or
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>>>>
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