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December 1999

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Subject:
From:
Brian Ellis <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 1 Dec 1999 09:41:45 +0200
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Alberto

There is no "better" process. It depends on what you are trying to do. If you must clean,
for whatever reason, then **carefully** selected water soluble chemistry with
**carefully** selected equipment is the most economical way to go. If you do not have to
clean, it is more economical to use a "no-clean" process. However, because you have no
cleaning equipment, no water treatment, no waste water treatment, no space taken by
cleaning equipment, no cleaning chemicals to buy, no energy for cleaning, etc. don't think
that it is all financial gain by not cleaning. The much narrower operating window with
"no-clean" techniques are also very expensive (higher operator skills required, more
retouches, higher solderability requirements, cleaner bare boards and components etc.). It
is rare for the overall financial gain of a well-run "no-clean" process to be better than
10% of a relatively poorly run water-soluble one and, on rare occasions, it may even be
more expensive! In both cases, you should KNOW exactly what you are doing.

Some "no-clean" processes are more equal than others. The exact figures I have forgotten,
but a few years ago a large company qualified about 50 liquid "no-clean" fluxes in terms
of the subsequent reliability of consumer telecommunications equipment, compared with
their then current RMA flux and CFC-113 azeotrope cleaning. The results were:
0 gave no problems
3 were acceptable, of which 1 was their existing RMA flux not cleaned
about 40-odd were unacceptable for diverse reasons
about 5 were downright corrosive (of which one was possibly the most sold "no-clean" flux
at that time -- and also the one with the widest operating window, the two being
inter-related).

Finally, no "no-clean" process eliminates cleaning. At the best, it should displace it
backwards to the PCB and component suppliers, who often do not take care of their
responsibilities. Even today, many supplied boards and components are heavily contaminated
when they reach the goods-in department of your factory. This contamination may affect
your soldering process but, more important, it will upset the careful formulation of your
"no-clean" residues which may become much more harmful than the maker intended, as a
result. If you wish reliability without cleaning, then you MUST ensure that all your
supplies are clean on arrival and that they are not contaminated by your
storage/assembly/handling processes before soldering. This requires much more expensive
attention than being slightly more careless and subsequently cleaning.

Its your choice, but I have said for many years that if you can get away with not
cleaning, then don't! See
http://www.protonique.com/psagraph/files/whycl.htm
for further arguments.

Brian

Alberto Callo wrote:

> So what process is better?  No-clean, water soluble, etc?
>
> Brian Ellis wrote:
> >
> > Dave
> >
> > As a pedant, I may go along with you on this, at least partially. I have used the
> > term "no-clean" (always in inverted commas) for both material and process. "Low
> > residue" is not necessarily the same, though. Many people use RMA with 25% or more
> > solids as a "no-clean" and certainly the DIN F-SW32 fluxes, generally 15-30% solids,
> >
> > must be "no-clean" because you cannot clean them for love nor money. And no solder
> > paste can be classed as low solids, as 50% or thereabouts of the stuff (by volume)
> > is low-volatility chemistry. OK, the residues may be neatly transparent and matt, so
> >
> > you have difficulty seeing the residues but they are there.
> >
> > My personal definition of a "no-clean" flux/paste is one where the residues do not
> > have to be removed for selected and qualified applications. A "no-clean" process is
> > one where the post-soldering residues are not removed.
> >
> > Again, as a pedant, I think your message has revealed a requirement for a new
> > terminology but, where there is already a firmly entrenched one, neither you nor I
> > will ever budge it.
> >
> > Best regards
> >
> > Brian
> >
> > [log in to unmask] wrote:
> >
> > > Hi TechNet! Just to add a bit of wordsmithing to Brian's internet references.
> > > The electronics community has created itself a technical "cultural" bias which
> > > is going to take some time to undo. We have interchangeably used "no clean" to
> > > describe both the material and process aspects of a product (e.g. flux). We
> > > should be using the term "low residue" to describe the material characteristics
> > > of a flux - how much flux residue is left on a printed assembly after soldering
> > > processing. We should be using the term "no clean" to describe the process
> > > characteristics of a flux - is it removable  or non-removeable after solder
> > > processing. The use of the term "no clean" for both the material and process
> > > aspects is very confusing to the folks on the factory floor because they can
> > > unintentionally misinterpret the product labeling as permission to no longer
> > > clean an assembly which may not be the case. I also know very few process
> > > engineers who are keen on having someone unfamiliar with their soldering process
> > > to suggest that a "no clean" flux is ok.  The description of "using a low
> > > residue flux in a no clean process mode" leaves little room for
> > > misinterpretation. Ok, enough soapboxing.
> > >
> > > Dave Hillman
> > > Rockwell Collins
> > > [log in to unmask]
> > >
> > > Brian Ellis <[log in to unmask]> on 11/27/99 02:21:23 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] Wave Soldering
> > >
> > > The United Nations Environment Programme Solvents Technical Options
> > > Committee gives an excellent explanation, with the advantages and
> > > disadvantages of each, in Chapter 2 of their 1998 Report to the Parties to
> > > the Montreal Protocol. This 200 + page report can be downloaded (free) in
> > > PDF format from the non-commercial committee site at
> > > http://www.protonique.com/unepstoc
> > > or you may purchase the printed document from
> > > http://www.unep.org/ozone
> > >
> > > Brian
> > >
> > > Alberto Callo wrote:
> > >
> > > > Hi,
> > > >
> > > > I wonder if anyone can explain the difference between NO CLEAN and Water
> > > > Soluble wave solder methods.
> > > >
> >
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