From my company's experience a humid condition and sulfur (H@S, SO4-) in
the atmosphere can accelerate the process. Sulfurous gasses can be found
in the far east (China, India, and others) from coal fired power
generating plants, oil refineries, oil pumps stations and from
vulcanization of rubber). We have found that in the far east the air
conditioning of the building is turned off at nights and weekends.  We
have found evidence of condensation on vias from the humid atmosphere
being taken in by the cooling fans while the metal is still cold enough
to produce local saturation and condensation.  We are working with our
customers to have the air conditioning on all the time, or at least
dehumidify the incoming air to the point that water will not condense on
the PWBs' vias at their "cool" temperature.
mark

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Victor Hernandez
Sent: Tuesday, November 06, 2012 7:56 AM
To: [log in to unmask]
Subject: Re: [TN] Limits on flux residue

Folks,

   A ticking time bomb for leakage and/or perhaps corrosion!   How can
you determine/predict when the two events will occur?   What the worst
case environment that will active either attribute?

Victor,

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Tuesday, November 06, 2012 8:15 AM
To: [log in to unmask]
Subject: Re: [TN] Limits on flux residue

Dave, I could not agree with you more. Excellent posting, and excellent
philosophy.

Too many times I hear someone say "who cares, its no-clean, perfectly
safe" only to find the hard way that is not true.
Not only that, but most no-clean fluxes are very effective when applied
as a very, very thin sheen or veneer (less than 1 mil thick) over the
BGA pads. You DON'T need gobs, more flux does not mean better wetting.
Too much also means a better chance that not all of it will be
heat-activated.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Tuesday, November 06, 2012 7:27 AM
To: [log in to unmask]
Subject: Re: [TN] Limits on flux residue

Hi Wayne - no, the JSTD-001 committee has not addressed that aspect of
No Clean processing because there are a number of product use
environment influences and process parameters that come into play on
what is acceptable and unacceptable. Your description would lead me to
believe that someone has taken extreme liberty in calling something a
"no clean" 
process. One of the things that we have found most interesting in the
implementation of a no clean process for a couple of our products is
that many folks believe "no clean" is a sloppy process and you can leave
flux residue anywhere on the assembly in uncontrolled quantities. But
the reality is that "no clean" solder processing requires very careful
control of what/how much/where you allow flux residues to exist. In my
view, a "no clean" process actually is a much tighter controlled process
than a process that utilizes cleaning to insure that product
functionality is not impacted.

Dave Hillman
Rockwell Collins
[log in to unmask]



From:   "Thayer, Wayne - IS" <[log in to unmask]>
To:     <[log in to unmask]>
Date:   11/05/2012 05:52 PM
Subject:        [TN] Limits on flux residue
Sent by:        TechNet <[log in to unmask]>



Is there a spec somewhere which limits the amount of residue allowed for
no clean processing?  I just saw a board where a BGA was about 70%
"underfilled" by flux residue.  No, this was not a flux/underfill
product! 
 A quick look at JSTD-001 Section 8 didn't seem to have specific
guidance on this condition.

Wayne Thayer

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