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From:
"David D. Hillman" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Fri, 27 Apr 2012 07:45:29 -0500
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Hi Brian - wonderful details! Doug and Bill Kenyon pulled together a nice 
tutorial on the topic no clean and low residue - take a look in the IPC 
Cleaning Handbook ( IPC-CH-65B) which provides a lengthy description. As 
an electronic industry, we allowed our marketing departments to create 
some confusion. We should be describing this "set" of materials as low 
residue which provides the user a description of the flux characteristics. 
The term "no clean" is a manufacturing methodology. The flux chemistry 
suppliers can provide recommendations about their flux materials in terms 
of what the flux characteristics mean relating to cleaning but only the 
electronics producer can determine how a flux interacts with their product 
designs.

Dave Hillman
Rockwell Collins
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Brian Ellis <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]>
04/27/2012 01:54 AM
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Subject
Re: [TN] 4 Questions: No Clean vs flux Deactivation. Possible Hogwash ???






Mike

It seems that the threads here have got out of hand, but let me make one 
clarification. We seem to have some confusion in the minds of some of us 
as to what different flux types are and do. I offer below thoughts about 
a few of them:

1. Pure rosin: is rarely used in practice but is the prototypical 
"no-clean" flux. It is a mix of mainly tricyclic mono-carboxylic acids 
and is modified little by heating. It is non-conductive and 
non-corrosive before and after heating and does not sublimate. It is not 
easy to clean off.

2. Halide-activated rosin: is rosin with an addition of a small quantity 
of organic activators with a hydrochloride or hydrobromide group tagged 
on. The theory is that heat decomposes the activator completely and 
leaves pure rosin compounds; the practice is that some will always 
remain. Those with small quantities of activator (RMA) may be considered 
by some as "no-clean". In reality, the more active types (RA) are almost 
no worse. The activators may be different and frequently RA types were 
paradoxically safer and easier to clean to safe levels than RMA.

3. Organic acid-activated rosin: Originally developed in Germany to DIN 
standards with the designation F-SW 32, they had large quantities of 
generally alkane mono-carboxlic acids dissolved in the rosin. They did 
not decompose much in heating and the "stronger" types left potentially 
corrosive residues. They were absolute hell to clean and usually left 
the activators on the board as the rosin was removed. Later versions 
used smaller quantities of di- and tri-carboxylic acids but were little 
better. Uncleaned, the milder versions were reasonably safe for 
non-critical applications in reasonable environments but they were never 
as good as halide-activated ones.

All the above were used at 15-30% solids for wave soldering.

4. Low residue, no-clean flux: These were typically ~5% solids 
di-carboxylic acids for wave soldering with no rosin but small 
quantities of alkane derivatives (e.g. glycol ethers) as vehicles to 
blanket the solder joint in formation. These are the prototypical 
"no-clean" fluxes and theoretically most of the acids sublime at 
soldering temperature and the vehicles evaporate. As a rule, they are 
difficult to sheer hell to clean to safe levels and it is safer to not 
try to clean them.

5. Water-soluble fluxes: originally, these were organic halides in a 
glycol vehicle, typically 15-20% for wave soldering. These were the most 
active fluxes for electronics soldering and the residues were designed 
for easy cleaning in water. With the process properly controlled, thes 
gave the best soldering AND best cleaning, but woe betide he whose 
process was not properly controlled as improperly cleaned residues were 
conductive and corrosive. Later versions used other activators but were 
not as successful.

These 5 prototype fluxes have since been much modified (not always for 
the better!) but the principles generally remain similar. Border-lines 
have become less clear. So far, I have not mentioned pastes which have 
rheological and other additives and higher vehicles/lower solvents, all 
of which modify cleaning and "no-cleaning" behaviour.

What has always alarmed me - and still does - is that many solderers 
think they know better than the manufacturers how to handle their 
processes, often with inadequate cleaning equipment/products which often 
does a worse job than not cleaning at all or which are totally 
incompatible. When I was working, in a long-distant past life, I made 
expensive cleaning machines and ionic contamination testers. I had a 
pretty good idea of the physics/chemistry/metallurgy/cleaning of 
soldering processes and, without boasting, I wrote a book on all the 
problems around cleaning and contamination which was and is, even today, 
a best-seller. The whole subject is a Pandora's can of worms, if you 
allow me to mix my metaphors. If you have no or little knowledge of what 
you are doing, don't do it; follow makers' instructions to the letter 
and listen to the advice of guys like Doug Pauls, Terry Munson who, 
today, know more than I ever did. But we old-timers also know a wee 
bittie on the subject and we often have a wider experience, having grown 
up in the pioneering days, and we still see the same mistakes made today 
that we saw 50 years ago (I'll be 80 in a few weeks, DV)!

Hope this helps!

Brian

On 26/04/2012 21:51, Mike Fenner wrote:
> I started to answer your questions but the predicates and assumptions
> surrounding them are candidly a little wrong, [if all flux manufacturers
> make untrue claims about their no clean products then>90% of the world's
> electronics industry is in trouble. Clearly that is not the case. 
Equally
> candidly I don't have the time to write a treatise on flux chemistry.
> So here are some facts about fluxes which you can apply to your 
assumptions
> and questions. Hopefully this response will enhance your understanding.
>
> Fluxes have 3 functions
> De-oxidise surfaces to be soldered
> Keep them deoxidized at soldering temperatures
> Help the solder to spread and wet.
>
> So the flux has some mechanical functions as well as the simple chemical
> stuff you are addressing in your questions/statements
>
> After soldering to be considered safe flux residues have to be
> Non conductive
> Non corrosive
> Non hydroscopic
>
> There are various ways to do this, simple chemical means, like breaking 
down
> in to inert volatiles and disappearing up the chimney. Or mechanical,
> encapsulating active residues in an insulating mass. Or only being 
active
> when heated and so on. How significant the residues are depends very 
much on
> the application - plumbing fluxes don't need to be washed off pipes but 
will
> kill an electronics assembly.
>
> Alternatively the user can elect to clean the residues away.
>
>
> So if you apply the above to your questions and statements I think you 
will
> get some answers. The rest you will have to read on line or in a text 
book.
>
>
>
> Regards
>
> Mike
>
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert Kondner
> Sent: Thursday, April 26, 2012 3:44 PM
> To: [log in to unmask]
> Subject: [TN] 4 Questions: No Clean vs flux Deactivation. Possible 
Hogwash
> ???
>
> Hi,
>
> 4 Questions (Please respond by number and elaborate if possible.)
>
>   I have been listening to this thread about no clean fluxes and 
"Possible"
> problems with flux residues that have not been "De-Activated" through
> complete heating during a soldering process.
>
> First, I understand that a flux is "Activated", ie becomes chemically
> active, by heat. An example is ammonium chloride that when heated 
releases
> HCl (hydrochloric acid) which is a strong agent for cleaning a surface 
for
> good solderability. Below the temperature where a flux becomes 
"Activated"
> the flux in not active. IE: "All Cold Fluxes are De-Activated".
>
>   Question 1:  Are fluxes "Active" when they are cold?  Is a RMA active 
when
> it is cold?
>
>    If the above is true what is all the stuff about "Active Flux" 
remaining
> on a PCB surface? Hogwash?
>
>   Further, I know from experience that reflow temperatures that are too 
high
> or too long "Burn Off" the flux and provide very poor surface finishes. 
If
> so this implies a significant portion of un-used flux will remain on the 
PCB
> after the reflow cycle. Flux will not be "Activated" once the PCB cools 
but
> it will remain active during the liquid solder phases.
>
> Question 2:  Is it true that we want flux active throughout the entire
> liquid solder phase and does this imply there should be un-altered flux
> remaining on the PCB surface after the reflow period?  (Me Thinks Yes?)
>
>   A good example is an RMA flux. From experience I know RMA fluxes have 
a
> very wide processing window, You can "Touch Up" a joint covered with RMA
> without additional flux because of RMA robustness. It simply leaves a
> "Messy" board finish.
>
>   Also, it has been my understanding that leaving an RMA flux on a PCB 
was a
> "Cosmetic Issue" but I do find that hard to believe. There must be "Bad
> Stuff" in all that gunk left behind.  But wire solder and RMA flux has 
been
> used for decades and is considered "OK" to remain on a PCB, I think.
>
> Question 3:  Are any flux chemistries acceptable to be left on a PCB and 
not
> cleaned and would such PCBs pass an ionic contamination test?
>
> Question 4:  Do all the companies that make "No Clean" Flux lie when 
they
> call them "No-Clean"?
>
> Thanks,
> Bob K.
>
>
>> I have an issue with one of the assembly houses we use.� They are
>> using a No-clean flux that contains adipit and succinic acids (per the
>> MSDS) in an alcohol base.
>>
>> Is it allowed to leave flux on the PWB that HAS NOT BEEN DEACTIVATED
>> BY HIGH TEMPERATURES OF SOLDERING?
>>
>> I am not talking about the flux used in the solder paste or wave
>> soldered flus.� I am talking about the flux used at rework and
>> touch-up of the PWB.
>>
>>
>
>
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