250°C !  Only the flux directly in contact with the soldering tools would
see that temperature. Heck our wave temp isn't 250°C. So, what is the
physical change? Are you saying then: Low-residue fluxes may not require
cleaning because the low level of activators remaining are trapped in a
residue that may contain them safely, in some end use environments?

> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Ellis
> Sent: Friday, May 07, 2004 3:57 AM
> To: [log in to unmask]
> Subject: Re: [TN] OA / RMA
>
> Yes, that is partly the theory, but what of the practice?
> Actually, the change is physical, rather than chemical: at
> soldering temperature, say ~250°C, most (but never all) of
> the activators sublimate into a vapour phase (incidentally,
> as do the organic hydrochlorides in WS flux). But sublimation
> is certainly nowhere near complete at lower temperatures.
> What of the flux that penetrates through the holes and up the
> leads, then spreads out somewhat over the top side of the
> board? Does that reach a quasi-complete sublimation
> temperature? No! Then, as the board moves through the
> sublimated vapour, can you guarantee that none of this vapour
> will not condense on cooler components? No, I thought not.
> Then, if some flux or vapour is trapped under a component
> with low clearance, what action is there to ensure that it is
> evacuated? Then there is the possibility of hydrogen bonding
> between activator molecules and the surface of the epoxy
> substrate. If this occurs, then the bond will be stronger
> than the forces causing sublimation.
>
> Take any board soldered with such fluxes and make an extract
> from it and analyse the extract: you will find considerable
> quantities of activators present (the quantity will diminish
> with time, as the sublimation process will continue slowly,
> even at room temperature).
>
> Can these quantities be dangerous? Yes, sometimes. There is a
> well-known but undocumented (for obvious reasons) case of a
> European telecoms manufacturer making street-box multiplexer
> assemblies on large four-layer boards, in the late 1980s.
> After a few months, some boards started to trickle back with
> corrosion and malfunctioning. Then the flood started. Under
> the conditions of street boxes, the flux residues started
> reacting. Incidentally, this manufacturer happened to be
> using the same "no-clean" flux as the anecdote I recounted in
> the previous post. This error cost the manufacturer something
> in the seven figures.
> As it happens, I was slightly involved because he changed to
> WS and I supplied the ionic contamination tester for his
> subsequent process control. OK, this was possibly an extreme
> example of the manufacturer not properly qualifying his
> process and materials (I can assure you he did it well,
> second time round, even introducing conformal coating for
> street box electronics which are, of course, subject to
> condensation conditions, on occasion).
>
> Another case I was involved with was a manufacturer of high
> power electronics, running on 380 V 3 phase circuits with
> currents in the hundreds of amps. He had been using a
> "no-clean" flux (known make) for over 2 years, without
> problems. He then decided to contract the assembly/soldering
> to an outside company, also using a "no-clean"
> (unknown make) flux. The results were catastrophic (and
> spectacular). I was asked to find out why, in the first batch
> produced outside, whole conductors on 105 µm thick copper,
> several millimetres wide, between the power in connectors and
> the fuses, had literally volatilised, while the fuses were
> intact, after a few days in real service. It transpired that
> flux residues under and around the massive fuse-holders had
> started to conduct, heated up, sublimated and condensed on
> the top of the fuse-holders, where the clearance between them
> was too small, causing a flash-over. This illustrates that
> not all "no-clean" fluxes and their residues are created
> equal, even if some are more equal than others!
>
> Brian
>
> Blair K. Hogg wrote:
>
> > Brian,
> >
> > Interesting story. However, isn't the principle behind NC
> flux that the flux changes chemically with the heat of
> soldering and then becomes non-corrsive?
> >
> > Blair
> >
> >
> >>>>[log in to unmask] 05/04/04 11:08AM >>>
> >
> > Phil
> >
> > In all the many tens of installations I have done, never
> once have I
> > used any parts that contact the flux that were not in PVC, PP or
> > titanium (notably fingers), other than the sintered plastic foaming
> > "stone". Big mistake to use brass or stainless steel, both of which
> > are attacked like gangbusters by the flux. I agree that a PVC air
> > knife is very useful for adjusting the quantity of flux,
> before the pre-heat.
> >
> > Actually, the worst case of corrosion I have seen of a soldering
> > machine was not with a WS flux but with a "no-clean" of a
> particular
> > brand made in N. Europe. I was visiting a factory which had
> been using
> > it for several years for telecoms equipment. I "naively" asked the
> > engineer whether he was not worried about his boards corroding in
> > service. He replied that the flux in question was non-corrosive,
> > bringing forth the manufacturer's data sheet as "proof". I
> then asked
> > him, equally naively, how he explained that every bit of iron/steel
> > was practically rusted through in a 50 cm radius round his
> fluxer. He
> > had a good look, turned pale and said, "Mon Dieu!"!!! :-( I
> then asked
> > him what qualification tests he had done and he replied that their
> > sole criterion was the "no-clean" flux that soldered best.
> It simply
> > hadn't occurred to him that high-activity = high risks. I
> knew what to
> > expect because I had seen other cases with that one,
> particular, flux.
> > I just checked and this same flux is still manufactured!
> >
> > Brian
> >
> > Phil Nutting wrote:
> >
> >
> >>Ramon,
> >>
> >>Brass fittings in the Flux tank were eaten through, rivets
> on the fluxer assembly were dissolved to the point where they
> fell out, the stainless steel enclosure of the flux reservoir
> and fluxer now look rusty and the excess flux dripping off
> boards into the pre-heat elements have caused flash over arcs
> that trip circuit breakers.
> >>
> >>The solutions to date have been to change the brass
> fittings to stainless steel, the rivets have not been
> replaced, the stainless enclosures are cleaned more
> frequently and the air knife has been adjusted for air
> velocity and angle to reduce the amount of excess flux.
> >>
> >>These items sound like we have a lot a trouble with OA (or
> WS), but it yields better boards as Brian Ellis has outlined.
>  I'll take the problems to get better yield.
> >>
> >>Phil
> >>
> >>-----Original Message-----
> >>From: Dehoyos, Ramon [mailto:[log in to unmask]]
> >>Sent: Tuesday, May 04, 2004 8:27 AM
> >>To: Phil Nutting; [log in to unmask]
> >>Subject: RE: [TN] OA / RMA
> >>
> >>
> >>
> >>        Thanks Phil:
> >>        What parts of the machine have been eaten or
> corroded and what steps have you made to slow down the corrosion?
> >>        Regards,
> >>        Ramon
> >>
> >>
> >>
> >>>-----Original Message-----
> >>>From: Phil Nutting [SMTP:[log in to unmask]]
> >>>Sent: Monday, May 03, 2004 2:25 PM
> >>>To:   [log in to unmask]
> >>>Subject:      Re: [TN] OA / RMA
> >>>
> >>>Ramon,
> >>>
> >>>About 3 years ago we switched from a no clean flux to an
> OA flux.  This change was driven by a change in board washing
> equipment.  We had been using a Terpene & Alcohol based batch
> system that no one liked and switched to a closed loop DI
> batch cleaner.
> >>>The plus side has been better solder joints out of the
> wave and cleaner looking boards after cleaning.
> >>>The minus side has been that the OA flux really eats up
> everything in sight in the wave soldering machine.  We have
> accepted this as a cost of business when using the OA flux.
> >>>
> >>>The good out-weighs the bad.
> >>>
> >>>Phil
> >>>
> >>>-----Original Message-----
> >>>From: TechNet [mailto:[log in to unmask]]On Behalf Of Dehoyos, Ramon
> >>>Sent: Monday, May 03, 2004 2:19 PM
> >>>To: [log in to unmask]
> >>>Subject: [TN] OA / RMA
> >>>
> >>>
> >>>               Hi Technetters:
> >>>               Has anybody done a comparison study of
> RMA/OA fluxes for wavesolder?  Or any personal experiences in
> this regard will be appreciated..
> >>>               Thanks in Advance
> >>>               Ramon
> >>>
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