Good morning all,
The answer, of course, is It Depends. I tell ya, that Brian Ellis is
positively clairvoyant....
In a former life, I worked with many manufacturers going through the pain
and agony of converting to a low residue flux in a no-clean assembly
operation. I did see some fairly significant recalls for such fluxes and
processes. In some cases, it meant potential disbarment from existing and
future contracts, or at least severely damaging the relationship between
manufacturer and customer.
All of these failures had a general root cause of the manufacturers not
fully understanding the materials they were dealing with, accepting
everything the salesman told them at face value (never a good practice),
and generating their own erroneous concepts, like "it's no-clean, it must
be safe everywhere". Low solids fluxes, in order to become "safe" or
"benign", must receive a minimum amount of heat.
The way that I describe low solids fluxes (I never call them no-clean
fluxes) to our operators is that low solids fluxes are a lot like Dr.
Jekyll and Mr. Hyde, or as is more often the case, Dr. Pauls and Mr.
Hillman. You need a minimum amount of heat to turn the nasty corrosive
Mr. Hillman residues to the kind and benevolent Dr. Pauls residues.
Failure to provide that heat and you have an undesirable situation. We
train our operators to use no more flux than they absolutely have to. I
have found that using a "bulls-eye" target to be a good teaching tool.
Your soldering iron is the center of the bullseye and everything around it
gets activated. The outer ring is where it is unactivated. The rings in
between are a combination of the two and do really odd things to circuit
performance.
As for the burnt residues, how detrimental they are depends on the circuit
and the risk that this carbonized residue will migrate somewhere. If they
do not easily come away from the surface of the solder joint, it is
unlikely it will cause problems, unless you have an assembly that is very
sensitive to particulates, like optics or gyros. If the particles are so
small that you have to inspect at high magnification, it is even less
likely to be an issue. I would still consider it a process indicator and
would want to figure out why it is happening.
Doug Pauls
Brian Ellis <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
05/23/2007 07:34 AM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Brian Ellis <[log in to unmask]>
To
[log in to unmask]
cc
Subject
Re: [TN] Flux residue, burnt flux
Inge
I know of no cases of massive consumer recalls for flux-related issues,
but they probably exist. I have never worked much with consumer
electronics. I know of one case of a telecomms manufacturer who had
corrosion problems due to the use of an insufficiently qualified
"no-clean" flux causing corrosion in street boxes. His unique customer
(a government telecomms monopoly) rejected a whole batch of 1500
multilayer boards costing well into the 4 figures each. I was not
personally involved in this case, but I knew the production manager of
the company quite well and he told me about it. He said that he had been
foolish and he had tested over 10 "no-clean" fluxes and had chosen the
one that offered the best soldering quality (of course, the most
active), not even thinking of the consequences. Fortunately, there were
only about 100 of the returned assemblies that were not recoverable by
cleaning and coating. One lesson learnt!
As for the proportions of cleaned:not cleaned, I don't know. Sitting in
front of a screen on a remote Med island is not conducive to getting
accurate up-to-date info. I can say that "no-clean" hit a peak of about
75% 10 years ago and, since then has had the figure slowly eroded away.
If I were to hazard a guess today, I would say 50-60%. Reason: smaller
spacings.
Brian
Hernefjord Ingemar wrote:
> Thanks, Brian,
>
> those were indeed worst case stories. However, limited to one customer
and one place. Some boards are produced in numbers of millions, for
instance electronics for cars. Or PWBs for microwave ovens, or parabol
antenna cards etc. I have never heard about recalling thousands of boards
because of flux residues. I would like to know how many boards are made
yearly with flux removal vs. non removal. Maybe flux removal is still
dominating?
> Inge
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Ellis
> Sent: den 23 maj 2007 11:07
> To: [log in to unmask]
> Subject: Re: [TN] Flux residue, burnt flux
>
> I have seen many cases of massive failures due to flux residues. The
most spectacular was in the late 1970s. I had a client making NC machine
tools and he used boards made by a very large German company. These were
soldered with a DIN 8511 (?) F-SW32 flux, which many Germans considered as
"no-clean" as they were halogen-free (and they were hell to clean,
anyway). They were rosin fluxes, typically 15-25%, activated with alkane
carboxylic acids. The theory was that the rosin held the activators
harmless in its matrix. The practice was far different. I had a look at
some circuits that had been in service for a year or two. The copper had
all but disappeared on several of them. I was asked to find out why, as
this was the first time this problem was recorded and it was not just one
circuit but many. I visited my client's client and found the machine in
question was installed in a large workshop where there also a number of
honing machines using a water soluble cutting oil. The
visibility in the shop was about 20 m, as there was a mist of this
cutting oil. I needed no further knowledge; the circuits were operating in
an aqueous aerosol and this was reacting with the flux residues to produce
a nice acid solution. The rest is history. I recommended my client that he
clean-air-purged the NC electronics cabinet and replaced all the existing
circuits and this cured the problem.
>
> Another spectacular case, about 10 or 12 years ago. A client, making
very high-power electronics, asked me for advice. He had a number of
failures from a recent batch of units that he had been making for a number
of years. Tracks connected to three-phase 400 V power had sinply and
suddenly volatilised, even though they were about 7 mm wide in 105 µm
copper, between the input connector and the 100 A fuse holders, a distance
of about 5 or 6 cm, all three of them. To cut a long story short, no-clean
wave-soldering flux residues had their activators sublimate as the
conductors warmed up and they condensed on the top edge of the
fuse-holders. These were, unfortunately, spaced by only about 3 or 4 mm
and, after some time, a short-circuit occurred sufficient to start an arc
between two phases and one of the tracks overheated to explosively
splutter molten copper around like there was no tomorrrow, causing the
other two tracks to volatilise in turn. It transpired there had recentl
y been a change in the formulation of the flux that was used, which was
why it had never happened before. I recommended that they used a W/S flux
with cleaning and they redesigned the PCB for more spacing between the
fuse holders. No further problems, AFAIK.
>
> Many other cases of leeser massiveness.
>
> Brian
>
> Hernefjord Ingemar wrote:
>> 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.
>>>
>>> ---------------------------------------------------
>>> Technet Mail List provided as a service by IPC using LISTSERV 15.0 To
>>> unsubscribe, send a message to [log in to unmask] with following text
>>> in
>>> the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt
>>> or (re-start) delivery of Technet send e-mail to [log in to unmask]:
>>> SET
>>> Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the
>>> posts: send e-mail to [log in to unmask]: SET Technet Digest Search the
>>> archives of previous posts at: http://listserv.ipc.org/archives
>>> Please
>>> visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16
>>> for additional information, or contact Keach Sasamori at
>>> [log in to unmask] or 847-615-7100 ext.2815
>>> -----------------------------------------------------
>>>
>> ---------------------------------------------------
>> Technet Mail List provided as a service by IPC using LISTSERV 15.0 To
>> unsubscribe, send a message to [log in to unmask] with following text in
>> the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt
>> or
>> (re-start) delivery of Technet send e-mail to [log in to unmask]: SET
>> Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the
>> posts: send e-mail to [log in to unmask]: SET Technet Digest Search the
>> archives of previous posts at: http://listserv.ipc.org/archives Please
>> visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16
>> for additional information, or contact Keach Sasamori at
>> [log in to unmask] or 847-615-7100 ext.2815
>> -----------------------------------------------------
>>
>> ---------------------------------------------------
>> Technet Mail List provided as a service by IPC using LISTSERV 15.0 To
>> unsubscribe, send a message to [log in to unmask] with following text in
>> the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt
>> or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET
>> Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the
>> posts: send e-mail to [log in to unmask]: SET Technet Digest Search the
>> archives of previous posts at: http://listserv.ipc.org/archives Please
>> visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16
>> for additional information, or contact Keach Sasamori at
>> [log in to unmask] or 847-615-7100 ext.2815
>> -----------------------------------------------------
>>
>
> ---------------------------------------------------
> Technet Mail List provided as a service by IPC using LISTSERV 15.0 To
unsubscribe, send a message to [log in to unmask] with following text in the
BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or
(re-start) delivery of Technet send e-mail to [log in to unmask]: SET
Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts:
send e-mail to [log in to unmask]: SET Technet Digest Search the archives of
previous posts at: http://listserv.ipc.org/archives Please visit IPC web
site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100
ext.2815
> -----------------------------------------------------
>
> ---------------------------------------------------
> Technet Mail List provided as a service by IPC using LISTSERV 15.0
> To unsubscribe, send a message to [log in to unmask] with following text
in
> the BODY (NOT the subject field): SIGNOFF Technet
> To temporarily halt or (re-start) delivery of Technet send e-mail to
[log in to unmask]: SET Technet NOMAIL or (MAIL)
> To receive ONE mailing per day of all the posts: send e-mail to
[log in to unmask]: SET Technet Digest
> Search the archives of previous posts at:
http://listserv.ipc.org/archives
> Please visit IPC web site
http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100
ext.2815
> -----------------------------------------------------
>
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to
[log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to
[log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16
for additional information, or contact Keach Sasamori at [log in to unmask] or
847-615-7100 ext.2815
-----------------------------------------------------
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------
|
