Conference 7.286::digital

    
    Contact Leo Lambert at GIAMEM::LAMBERT. Leo is Digital's expert on
    soldering, has worked in this area for many years and can probably give
    you the best info on low CFC soldering. 
    
    Roger

Just to point out what may not be obvious...

Soldering itself does not involve CFC's, but the removal of traditional
solder flux (rosin) residues from circuit boards does. 

    Thanks folks, I am in touch with the appropriate person now! I realize
    that soldering itself involves no CFC's, the solvents which were (are)
    used to clean up afterwards, however, are a different story. So thanks
    for the information and mail messages!
    
    Tim
    

For those of us not technically into how are products are manufactured,
would it be appropriate to follow-up on this subject a little bit here?

I recently heard on a news report that it was found that plain lemon
juice is as effective a flux remover as freon solvent. Has DEC done any
studies to verify this? Do we attempt to make use of more environmentally
sound materials, such as this, when possible? What type of criteria do
we use to determine the feasibility/applicability of such alternatives
in our processes?

Thanks,
-Jack

    DEC mfg. has been using water soluble soldering flux for some time.
    It washes off cleanly in plain water. Lemon juice, being mainly water,
    would perform similarly I suppose. The acidic content in lemon juice
    would seem a rather poor substance to be placing on the PCB lands
    however. 
    
    Unfortunately, certain surface mount components require a non-water
    soluble flux be used in order to get proper wetting (solder flow)
    between the component and the board. These boards then require cleaning
    with CFC. This problem is still being worked, without resolution,
    as far as I know.
    
    Another possible solution is to use an available flux which has a lower
    residue content and doesn't require as much, or any, washing to look
    good.
    However this process is at present un acceptable to certain Japanese
    customers, actually the DEC-Japan predelivery inspection people,
    making our boards unacceptable by them unless they have had the full
    CFC wash.
    
    So, there is still much political/environmental wrangling going on over
    this issue and I've heard of no final solution that's acceptable to
    all.
    
    Terry

	Digital Augusta developed a water-based process for cleaning 
	solder flux and other residues from electronic components.
	I wrote up the characterization and user documentation for
	it.  I believe I have copies of the documents available,
	if you need more data, contact me or folks up at Augusta
	(I can't do better than that because I have no idea who 
	is still up there.)

	I'm sure the EHS people will know about this process as we
	released it to the world on Earth Day 1990.  It works and
	is (was then) world-class state-of-the-art.

	Michael McGovern
	Technical Senior Writer, CUIP
	MRO1-3/T2
	DTN 297-9884

re .5:

Does this mean that flux is removed only for cosmetic reasons?

    
    RE: .7
    
    No, over time it can degrade circuit connections and cause failures.
    

I am a member of the Corporate No-Clean Team (team leader:  Pete Lison/TME), 
and I have some information on this subject.  

It is my understanding that the vast majority of our module cleaning operations
use saponified aqueous cleaners to remove residual flux.  Residual flux can 
limit the operational life of modules by accelerating corrosion mechanisms 
which act between adjacent conductors.  In addition, probe testing is very 
difficult on pads which have this sticky residue.  While our cleaners do not
involve the use of ozone-damaging chemicals, they do create problems with 
respect to water treatment.  Also, the entire cleaning process really does not 
add value to the finished product.

I haven't read anything specific about lemon juice, but there is an entire class 
of cleaners known as "terpenes".  They come from citrus fruits and woods, so
they're organic, plentiful, non-toxic, and have a host of other good attributes.
It's not nearly as simple as dumping them into the aqueous cleaner, though. An
entirely different process known as "semi-aqueous" cleaning is used.  There
are two loops in this process:  the modules go through a terpene loop where the
residual fluxes are removed from the modules, then they go through an aqueous
loop where the terpenes are washed from the board.  This really saves a lot of
the waste water treatment, as terpenes are a lot easier to clean from the water
than residual flux.  There are drawbacks, though.  It requires much more capital
equipment (fairly significant cost), and I've heard that terpenes have a low 
flash point (posing a potential safety hazard).  

No-Clean materials (also called Low Residue Fluxes) are a different story.  
There has been a lot of work on these materials within the industry in the past
couple of years, and there are some good products that we'll be implementing.
These materials contain a large amount of volatiles which evaporate during the 
high temperature reflow operation.  They leave a small, hard (non-tacky) 
residue.  We've done a lot of testing during the past year and identified 
several materials which are non-corrosive and solder just as well as our 
conventional materials.  Implementation has begun, and it's estimated that 
successful completion of this project will result in multi-million dollar
cost savings (cleaning is expensive!)

Greg Bartlett
TDA/Materials Science and Engineering

    re .9
    
    >>they leave a small hard non-tacky residue<<
    
    This is what causes us problems with the DEC-Japan inspection folks.
    
    They won't accept modules with that residue.
    
    At ABO Mfg. we're still using CFC to clean modules in those cases where
    soldering requirements demand non-aqueous flux. I don't know what
    the % of total modules shipped this represents, but in our dept. (
    field return repair) we would be forced to ship quite a few
    flux-encrusted modules if it weren't for CFC cleaning.
    
    And this does not address the situation where a field repair has been 
    attempted using non-aqueous flux, which is usually not cleaned at all
    until we receive the module. We then clean it with CFC, do the required
    repair, and clean again appropriately depending on the type of flux
    dictated by the components involved.
    
    Terry

re: .5 through .10

Thanks to all of you for the information. I always like to be able to learn
something about aspects of our business which I have no connection with.
I appreciate the enlightenment.

-Jack, software recluse

    The 17 Feb 1992 issue of Aviation Week and Space technology has an
    article on pg.45 which states: "Hughes Aircraft Co. has achieved a
    manufacturing breakthrough with a new solder flux that could
    eliminate.. CFCs.. in electronic manufacturing."   It goes on to
    discuss a water soluable flux with a citric acid base called HF1189
    that Hughes will use instead of rosin in existing wave solder
    machines..
    
    -Andy

    
    Even if there is an elimination of CFC's and a citric acid base is
    used,  there is still the residue that must be captured. It must still
    be controlled and carefully disposed and documented. Its stuff you
    can't just rinse down the drain.
    
    hy

re: .13

So - the flux is also a hazardous material?

-Jack

Re. 10 (Terry)

Thanks for the information as to what you folks are doing in ABO.  Part of the 
problem with this project that each module assy plant is doing something 
different, and change will have to be slow.

Excellent point with the issue of "customer satisfaction" with respect to 
residual flux.  Even though there is considerable data to show that certain
materials may be left on the boards with no degradation in life there will be
stubborn people/companies.  We've asked other companies how they've handled
this issue, and they've said that they simply compiled all of their 
reliability data and showed it to their customers.  Maybe we should talk about
doing this with your customer.  

Greg B.

Re: .14

The flux may not be the problem but the resultant wash, due to acidic
presence, may be tainted with tin and lead (of which the solder is made).

Lee

    re .15
    
    To get the latest straight scoop on CFC/flux/solder issues at ABO
    contact Anne Chiasson, process engineer at: ELMAGO::ACHIASSON.
    
    Terry