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!
>>>>>
>>>>>
>>>>>
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