Matthew,
Ouch! Beverly Crusher?! Last time I looked I was male. I have answered
your questions below after each question.
> -----Original Message-----
> From: Matthew Park [SMTP:[log in to unmask]]
> Sent: Wednesday, March 10, 1999 3:45 PM
> To: [log in to unmask]; Christian, Bev [BVW:9810-M:EXCH]
> Subject: RE: [TN] Fluxless Soldering
>
> Dr. Beverly Crusher,
>
> Could you tell us a little bit more about your experience with
> PADS? Sure
>
> We, I or many of manufacturing guys/gals are morons
> about chemical terminology.
> What's this oxy-business? How does PADS' process turn tin suface to
> oxyflu?
You are not moronic, you're just like me and my knowledge of ancient
Greek history, you don't use it, you lose it.
>
A solder surface becomes unsolderable for one of three main reasons:
oxide formation, intermetallic formation or organic and/or salt
contamination. The latter is relatively rare compared to the first two.
PADS will only work on the first one of these. If your boards/parts are so
old that the intermetallic has grown all the way through you are out of
luck. Tin, like most metals will "rust", oxidize. Unlike rust which is
red, most surface metal oxides are white so in very thin layers these oxides
appear to be colorless but they are still there. An oxidized tin surface
will form tin(II) oxide (SnO) as the tin is first oxidized to the +2
oxidation state and then will form tin(IV) oxide (SnO2) as it is changed to
the +4 oxidation state. This is how the oxygen gets on the surface of the
tin. We won't go into things like the possibility of hydrated oxides,
nitrates and sulfate formation.
In the PADS process SF6 is ripped apart by the energy put into the
gas by a microwave source. There will be unreacted SF6 and what we refer to
as a plasma, an ionized gas consisting of free electrons , free uncharged
atoms and molecular fragments and ions that consist of one or more atoms
still hooked together. As the vacuum pump pulls this mess out of the range
of the microwaves most of the material will reform SF6 or perhaps react with
the walls of the tube. One species that remains around longer than other
unstable species is the free fluorine atom. Now it gets speculative. Do
these atoms react directly with the tin oxide surface to form, say, SnOF2
(thus the term oxyfluoride)? or does the fluorine atom find a friendly
hydrogen atom and form HF (Hydrofluoric acid) which might weakly bond with
the oxide surface? I don't know.
> What is your experience with PADS?
We have run a considerable number of trials with this technology.
> Does it change the chemical property of tin surface to a molecular
> structure to inhibit corrosion?
It is not that the surface is changed to resist further corrosion as
it is more or less changed so that the surface is its own flux. The
Microelectronics Center of North Carolina and the US Army have neat slow
motion film showing the treated surface layer of oxide breaking up in
"continents" and then "islands" and then disappearing as the solder under
the surface layer melts and then shows through as a clean surface ready to
bond.
> How thin is this coating?
Angstroms thick (molecular layer(s) thick).
> How long is the coating good?
In a vacuum or nitrogen about two weeks. In an air conditioned
plant, about a week.
> Any special process requirement for implementing the fluxless soldering in
> production?
Sure, the PADS process is a batch process because of the vacuum
requirement. Your EHS people will probably go squirrelly if you tell them
you are using a chemical that generates free fluorine, never mind we are
talking low concentrations in a vacuum.
> How practical is it for the future replacement of
> no-clean and water-soluble processes?
Personally I think not very likely, as it does not deal well with
parts and boards that have sat around long enough to form some tin(IV)
oxide. It works well on new parts and boards that only have a normal thin
coat of tin(II) oxide. Also, if you were to use this to any great extent
could you sleep at nights knowing that you might be contributing to global
warming (if there is such a thing, but that's another set of e-mails)?
> Well, whatever info I have is good for marketing guys, and is too
> good to be true for mfg engineers. Throw away all existing
> known processes and go, go for the fluxless soldering?
No, not yet.
> Wait a
> minute, I tested a similar thing with an electrically conductive
> epoxy for the future replacement of solderpaste. It turned out it
> was too good to be true for SMT manufacturing.
You betcha.
> I'm keeping
> these technologically advanced marketing secrets handy in case
> our senior management has a future vision of us to become a
> world-class manufacturer.
My point was that there is such a thing as fluxless soldering. It
is certainly not there yet for most of us but does meet requirements of some
very special circumstances. I am also hoping that I can spark some thought
on the subject so one of you might actually come up with a system that will
work, will make you a million and eliminate flux. Although now that we have
really good VOC free fluxes and wave soldering is dying, I don't know if
fluxless soldering is going to be needed for that long anyway. But this
stuff sure is fun!
> Well there's no chance of that
> happening, our mfg operation is being marketed out, phased
> out, or booted out. Whichever way is convenient for my employer.
>
> Hope oxyflu is not one of those Asian flu.
>
> Sign out
> Matthew.
>
>
> >>> "Bev Christian" <[log in to unmask]> March 10,
> 1999 10:43 am >>>
> Technetters,
> A PADS unit can be purchased from Integrated Electronic
> Innovations in North
> Carolina (919-461-3773). I know a couple of other big
> companies have also
> played with this system besides us. PADS is especially useful if
> you
> positively cannot have any organic residues around, like say for
> an optical
> system.
>
> I wouldn't say it turns the surface oxide resistant but rather
> solder-philic. Somehow it transforms tin(II) oxide to either a tin
> oxyfluoride or perhaps there is a formation of a hydrogen bonded
> adduct
> between the surface oxide and hydrogen fluoride produced in the
> process.
> (Don't worry, from a corrosion point of view, the "coating" is so
> thin it is
> Bellcore compliant.)
>
> Of course there are always down sides to everything, right, even
> marriage?
> :) The system uses sulfur hexafluoride, which like CFCs, are
> relatively
> safe for humans but terrible environmentally. Now there is no
> chlorine so
> there is no threat to the ozone layer, but SF6 is one heck of a
> good global
> warmer. With CO2 having a global warming value of 1 SF6 has
> a value over
> 3000! The other thing is that it won't do much for tin(IV) oxide, so
> if you
> have old parts and boards you are out of luck.
>
> There are also other systems that are sometimes lumped in
> with fluxless
> soldering, like the SEHO formic acid vapor system of the early
> 90's, special
> very hot systems where reducing gases have been tried, and
> even the ROSA
> system that uses a vanadium based aqueous reducing solution.
> Of course we
> could start arguing semantics here, but that is not what I am
> trying to
> start. The point is there have been/are fluxless units, but I doubt
> that is
> what your marketing guy was after. These systems are not well
> known.
>
> regards,
> Bev Christian
> Nortel Networks
>
> > -----Original Message-----
> > From: Matthew Park [SMTP:[log in to unmask]]
> > Sent: Wednesday, March 10, 1999 1:09 PM
> > To: [log in to unmask]
> > Subject: Re: [TN] Fluxless Soldering
> >
> > Richard,
> >
> > This time, I guess, your design engineering manager is right.
> There is a
> > fluxless soldering process available. If I remember correctly,
> one process
> > I am aware is called *PADS* (Plasma Assisted Dry
> Soldering???). Wow... a
> > fancy jargon isn*t it? In this process, components or
> assembled boards
> > are exposed in a PADS treatment within a vacuum chamber.
> This treatment
> > turns soldering surface to oxide-resistant by modifying
> soldering surface
> > layer. From there, you can store components or assembled
> boards for a
> > specified period prior to wavesoldering, reflow or
> handsoldering. You
> > don*t need to apply flux to allow wetting, thus no cleaning is
> required.
> >
> > This process is ok for a lab application or a small production
> run. I
> > don*t have the info handy, but I am sure I have it filed away in
> my filing
> > cabinets. I can dig out something for you if you need to look
> further.
> >
> > Regards
> > Matthew
> > Norsat International Inc.
> >
> >
> >
> > >>> Richard Hamilton <[log in to unmask]> March
> 10, 1999 8:46 am >>>
> > Hello fellow TechNetters,
> >
> > Well, we were asked a question by the design engineering
> manager yesterday
> > if we had considered a fluxless soldering process. We are
> aware of a
> > process
> > called Solid Solder Deposit (SSD), but not a fluxless process
> by name.
> >
> > After the manager read us the email he got from one of the
> marketing
> > types,
> > I tend to believe that he was referring to no-clean process
> because of a
> > reference in his note about cleaning boards at a previous
> manufacturer
> > (TI).
> > My guess (oh how I hate to guess/assume) is that this
> marketing type has
> > just mixed up a couple of buzz-words together,.....kinda like
> 'military
> > intelligence'. I mean look at it, 'no-clean flux', I can see how a
> sales
> > person would want to shorten that to 'no-flux'. Now as usual, it
> is up to
> > us
> > manufacturing people to invent the process that has been sold
> to the
> > customer!!
> >
> > And as a side note: Steve -
> >
> > Your comments on machine maintenance are RIGHT ON!! You
> couldn't be more
> > correct. Sometimes I cringe at the way some machines are
> treated, and the
> > surprise that goes on when it does drop out!
> >
> > Thanks all.
> >
> > Richard Hamilton
> > Clemar Mfg. / Rain Bird
> > [log in to unmask]
> >
> >
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