Doug Pauls describes himself as an "Old War Horse".
That's pretty depressing as I know I have quite a few years on him!
When it comes to fluxes and flux residues and how they might impact
on electro-chemical reliability - you really should test to find out
if your production process will be give you acceptable or
unacceptable reliability. The latest IPC-TM-650 2.6.3.7 method will
help...
Kindest regards,
Graham
[log in to unmask]
On 30 May 2007, at 15:53, Douglas O. Pauls wrote:
> Wee Mei,
> It would not be accurate to say that flux residue is never a good
> thing to
> leave behind on an assembly. We make military product and in select
> cases, we leave flux residue intact. But, we know exactly what the
> residue is, we know its characteristics in the end use environment,
> have a
> ton of test data behind us, and have many measures in place to
> control the
> manufacturing process surrounding those flux residues. The military
> position on RMA fluxes and cleaning are largely due to inertia or old
> school mind sets. On the other hand, military programs often have
> to take
> low bids and have been severely bit many times from assemblers who
> do NOT
> know what they are doing, or where "cost" is the only driver.
>
> There is no such thing as a good flux or a bad flux. No flux is
> "safe".
> Many of the horror stories that we old war horses can (and do) tell
> can
> usually be traced back to one root cause - a failure to understand
> precisely the materials of manufacture and how the end use environment
> effects the residues on the assemblies. Or the corollary cause -
> cost is
> the only consideration. I would say that someone like Bill Kenyon
> could
> take Superior 30 flux and make a reliable heart pacemaker. But for
> the
> rest of the world, nooooooo way.
>
> Military programs today, at least the ones that I deal with, are
> more open
> to something other than RMA fluxes (which technically have not been
> around
> since 1995), IF you have the test data and demonstrated expertise
> to back
> it up. We use low residue fluxes with aqueous cleanings. There are
> programs doing true no-clean (not here though). There are programs
> doing
> water soluble flux. Granted, it often takes a tremendous amount of
> effort
> to educate a customer with an RMA mind set, but it can be done.
>
> Doug Pauls
> Rockwell Collins
>
>
>
> Lum Wee Mei <[log in to unmask]>
> Sent by: TechNet <[log in to unmask]>
> 05/30/2007 07:57 AM
> Please respond to
> TechNet E-Mail Forum <[log in to unmask]>; Please respond to
> Lum Wee Mei <[log in to unmask]>
>
>
> To
> [log in to unmask]
> cc
>
> Subject
> Re: [TN] Flux residue, burnt flux
>
>
>
>
>
>
> Hello,
>
> From what have discussed, I gathered that flux residue is never a good
> thing to leave behind on the PCBA. Regardless whether it is water
> soluble,
> no clean or RMA flux, the chemical compounds in the flux residue
> can react
> with whatever present in its surrounding over period of time and
> "mutate".
> This mutated power is so powerful that it "eats" away connector
> housing,
> give rise to dendrites and cause short, etc.
>
> Is that the reason why military products only use RMA flux with IPA or
> Ensolve or other cleaning agent and never no clean and water
> soluble flux?
>
> Thanks and regards,
>
> Wee Mei
>
> ----------------------------------------------------------------------
> ---------------------------
>
> I have seen many, many cases of electrical failure due to flux being
> left on the board, including no-clean, water soluble, and RMA.
> I have had to perform as an industry consultant for several companies
> that had field returns and cancelled contracts due to flux issues
> causing performance problems (crosstalk, etc.)
>
> The worst one I ever had to deal with was many years ago (mid-'80s)
> when
> a contract manufacturer used a no-clean flux to add (build-around) a
> printer connector on a computer motherboard. They liberally spread the
> flux over the SMT pads and hand-soldered the connector in place. They
> did not realize that the field returns they were getting shortly
> afterwards were due to the use of the no-clean flux.
> The chemicals in the no-clean flux attacked the connector housing
> material, turning it into a grey powder. Some of the motherboards came
> back with no connector body left, only the connector leads soldered to
> the pads, and a grey powder where the body used to be. This company
> brought me in to find out why the connectors were deteriorating. Upon
> reviewing the original process travelers, I found that the build-
> around
> was approved without qualifying the hand-soldering of the connectors,
> whereas they had been reflow soldered with water-soluble flux prior to
> that.
> This company was forced to take back more than 100,000 computer
> motherboards, remove the connector, remove all traces of the no-clean
> flux, assemble a new connector using water-soluble flux, wash the
> boards, re-test the boards, and replace them into the computers,
> all on
> their own nickel. They nearly went bankrupt.
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Kathy Kuhlow
> Sent: Tuesday, May 29, 2007 1:52 PM
> To: [log in to unmask]
> Subject: Re: [TN] Flux residue, burnt flux
>
> Inge,
>
> When NAFTA first came into play, the company I worked for ran to the
> border for cheaper products to be built. We built industrial computing
> products at the time so it needed to be pretty durable. We ended up
> within 9 months scrapping everything built south of the border due to
> two reasons. One was a dendrite growth on all of the gold (simm
> sockets
> mainly) due to water quality (said it was DI but apparently our
> definitions of DI differed a bit). The second reason was flux under
> the
> older 386 and 486 chip sets.
> There was flux underneath that never was cleaned up. We found that the
> flux was eating through the traces underneath the chips. I suspect it
> was due to a solder issue and the boards were flooded for rework but
> insufficiently cleaned up. About 2000 boards were scrapped because it
> was impossible to determine the extent of both problems. Left south of
> the border shortly after that and only used them for cables
> afterwards.
>
> Kat
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Hernefjord Ingemar
> Sent: Wednesday, May 23, 2007 3:11 AM
> To: [log in to unmask]
> Subject: Re: [TN] Flux residue, burnt flux
>
> What I say now may cause some to think that I'm member of Ku-Flux-
> Klan,
> which is not the case. So, we follow the general habit of removing
> 'all'
> flux residues. However, I can't deny, that I think this flux removal
> hysteria is little exaggerated. I've been in the business for so
> long a
> time, and I have not seen many reported failures that have been caused
> by flux residues. In theory, flux residues have many ingredients that
> can cause corrosion, leakage current, decreased insulation etc, but it
> seems as that does not happen in reality. 100% cleanliness is
> satifying
> and beautiful, but costs a lot to obtain.
> Just a thought. Would be very interesting if anyone could describe a
> case with flux residues causing massive failures.
> Inge
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Ellis
> Sent: den 23 maj 2007 09:38
> To: [log in to unmask]
> Subject: Re: [TN] Flux residue, burnt flux
>
> I'm sure that an eminent co-contributor to this forum will tell
> you, "it
> depends". If the flux is truly burnt, i.e., black, this indicates
> pyrolysis, which is a fancy word meaning decomposed by heat. Pyrolysis
> indicates that the residues have split apart into numerous compounds,
> leaving carbon-rich stuff. Elemental carbon can be an electrical
> conductor; do you want conducting particles in your assembly? They may
> appear fixed in place now, but will they remain so during the life of
> the equipment?
>
> More important, WHY are they there? It may be because the operators
> don't keep the bits of their irons clean. Do they wipe them on a wet
> sponge before each joint is made? It may be that the time/temperature
> conditions of the joint being made are far from optimal. It may be
> lack
> of adequate training of the operators. I can't tell. Whatever,
> prevention is better than cure; a lttle research into the causes may
> give you the answer.
>
> As to flux flow, maybe your solder wire simply has too much flux. Some
> manufacturers allow you to choose the percentage. Yes, it is easier to
> solder with an excess. It's a compromise.
>
> What you have not told us is the essential information: what kind of
> assemblies are you making. You can obviously be more tolerant of
> imperfections if you are making toys than if you are making inertial
> guidance or satellite systems. Probably you are somewhere between thes
> extremes. "It depends"!
>
> Brian
>
> Sue Powers-hartman wrote:
>> We fight a constant battle with operators leaving burnt flux in
>> joints. Maybe only a small speck, but drives the inspectors nuts.
>> The
>
>> way I read JStd-001D, if they can not see it at referee inspection
> power, they have to accept it.
>> How dangerous is this burnt flux to the PWB? If it's not seen at
>> inspection power and left on the board, what happens. Also, what
> about no clean flux?
>> Our solder training video says that if no clean flux runs out to far
>> and is not heat activated, it can cause problems. Operators watch
>> this
>
>> video, but somehow do not get this. They say that it's no clean, they
> can leave it all on.
>> I keep saying that this can be a problem, and then they ask me, how
>> far out can the flux be away from the joint before it's unacceptable.
>>
>> Wow, I'm glad I found this forum, I have so many questions to ask you
> guys.
>> Anyway, thanks for the help on this subject.
>>
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