I have Ionograph from the time before changing to "No Clean" process and
since 1992 we were switched to "no clean" to eliminate the usage of CFC's
and other cleaning solvents.
My advise after 11 years of "no clean" is, if you can change to "no clean",
Do it. All the cleaning issues such as flux under BGA's, and flux
absolution in coils, transformers and flux penetration into open components
such switches is history.
I do not understand why in USA the cleaning process is still dominant.
Best Regards
Reuven
David Douthit
<[log in to unmask] To: [log in to unmask]
> cc:
Sent by: TechNet Subject: Re: [TN] Ionograph
<[log in to unmask]
>
09/09/2003 03:22
Please respond
to "TechNet
E-Mail Forum.";
Please respond
to David Douthit
Ramon,
Now you've done it! You are asking, "How clean is clean?".
As Mr. Doug (where's my Mountain Dew) Paul would say, "It depends!"
Where is the product used?
How long is the warranty?
What is the product used for?
What are the expected environmental conditions?
What are the contractual requirements?
How much liability exposure is there?
There are major differences between a CD player or PC
and a Tactical Weapons System. Each needs to be evaluated on its own
merits.
There are many stories about contamination problems but the vast majority
are proprietary. After all they cost that company a lot of money and
why should they help "solve" their competitors problems.
I'm sorry but there is no simple single answer.
David A. Douthit
Manager
LoCan LLC
"Dehoyos, Ramon" wrote:
>
> David:
> Our boards are cleaned three times which gives us less
than
> 0.3 micro grams per cm sq, so we do not have a problem in this respect. I
am
> only trying to understand more about flux and other residues from other
> people's perspective. I have talked with people that have specialized in
> cleaning for years and say that any thing under 1.8 micro grams per cm sq
is
> good. I am sure there are examples such as the ones below of leaking caps
> and using no clean flux. But ff the flux residue at the top limit of 1.56
> micro grams per sp in of NaCl is a problem there shoud be a lot more
> instances at every company, specially with BGAs which are very difficult
to
> clean. Any thoughts?
> Regards,
> Ramon
>
>
> > -----Original Message-----
> > From: David Douthit [SMTP:[log in to unmask]]
> > Sent: Monday, September 08, 2003 4:05 PM
> > To: [log in to unmask]
> > Subject: Re: [TN] Ionograph
> >
> > Ramon,
> >
> > The answer is YES!!!
> >
> > Go to http://residues.com as a starting point.
> > Virtually all the labs can give you wonderful stories about
> > contamination induced failures.
> >
> > David A. Douthit
> > Manager
> > LoCan LLC
> >
> > ================================
> >
> > "Dehoyos, Ramon" wrote:
> >
> > > Brian:
> > > My appologies for stretching this subject since I know very
> > little
> > > beyond empirical experience. I was talking about different types of
> > boards
> > > including boards that performed in the giga frequency. At one time we
> > were
> > > producing about 20K boards per month and several thousands were of
the
> > high
> > > frequency application type.
> > > Are there any reports or articles that indicate field
failures
> > > from boards not being properly cleaned?
> > > Beat Regards,
> > > Ramon
> > >
> > > > -----Original Message-----
> > > > From: Brian Ellis [SMTP:[log in to unmask]]
> > > > Sent: Monday, September 08, 2003 10:19 AM
> > > > To: [log in to unmask]
> > > > Subject: Re: [TN] Ionograph
> > > >
> > > > It can depend on the application. Obviously, high-impedance, high
> > > > frequency applications, used as portable equipment with a high
> > > > reliability required, cannot be considered in the same breath as
the
> > PC
> > > > driving the screen you use to read this.
> > > >
> > > > However, be aware that salt is not usually the problem but solder
flux
> > > > residues and general handling contamination. This is why the
correct
> > way
> > > > of expressing the unit is n µg/cm2 eq. NaCl, the "eq." meaning the
> > > > electrical equivalent, not that there is actually NaCl present.
> > > >
> > > > Brian
> > > >
> > > > Dehoyos, Ramon wrote:
> > > > > Brian:
> > > > > Besides biomedical electronics in which boards need
to
> > be
> > > > > super clean, it has been my experience that any thing under 10
> > micro
> > > > grams
> > > > > of NaCl per square inch is passable. So far I have not heard of a
> > case,
> > > > > while tallking to my co-workers in several companies, where there
> > has
> > > > been
> > > > > any problems releted to salt contamination. Could you expand on
this
> > > > matter.
> > > > > Regards,
> > > > > Ramon
> > > > >
> > > > >
> > > > >>-----Original Message-----
> > > > >>From: Brian Ellis [SMTP:[log in to unmask]]
> > > > >>Sent: Saturday, September 06, 2003 3:29 AM
> > > > >>To: [log in to unmask]
> > > > >>Subject: Re: [TN] Ionograph
> > > > >>
> > > > >>IMHO, to say 1.56 ug/cm2 eq NaCl or any other figure is useless
> > without
> > > > >>qualification. Would it be reasonable to use this figure on both
a
> > > > >>through-hole circuit with conductor spacings of 0.5 mm and no
> > > > >>significant traps under components and a high density
interconnect
> > > > >>structure with shadowing components and gaps under them equal to
the
> > > > >>copper thickness? Of course not, it is ridiculous. The figure
quoted
> > was
> > > > >>derived from conditions in the first case, in the 1970s, before
SMDs
> > > > >>were current. IMHO, the figure, for equal reliability, must be
> > > > >>proportional to the maximum voltage gradient. In the first case,
we
> > are
> > > > >>talking of e.g. DILs working at 5 V, so we have a voltage
gradient
> > of 10
> > > > >>V/mm. I agree my example is perhaps extreme, so let's say 50
V/mm,
> > for
> > > > >>the sake of a more practical argument. Your HDIS may be using
> > > > >>semiconductors working at 3.0 V with minimum track/pad spacings
of
> > 25
> > > > >>µm, ie a voltage gradient of 120 V/mm (roughly the maximum
advisable
> > > > >>with FR-4, before dissociation starts), so if 50 V/mm and 1.56
> > µg/cm2
> > > > >>are OK, then you would want 1.56 * 50/120 = 0.65 µg/cm2, assuming
> > equal
> > > > >>accessibility of cleaning fluids under the components. As this is
> > not
> > > > >>the case, I suggest we have to weight the figure to compensate. I
> > > > >>propose a factor of 3 (from experience, we know that a tight SMA
is
> > 3
> > > > >>times more difficult to clean to an identical level than a 1970s
> > style
> > > > >>assembly). It would therefore seem that 0.2 to 0.25 µg/cm2 eq.
NaCl
> > > > >>would seem the most judicious figure to get an identical level of
> > > > >>reliability, all other things being equal. Empirically, this
> > argument
> > > > >>would extend to ~0.5 µg/cm2 eq. NaCl for a tightish non-HDIS SMA.
> > > > >>
> > > > >>That having been said, these arguments apply only to cases before
> > > > >>conformal coating is applied (MIL-P-28809n is specific on this
> > point) to
> > > > >>avoid vesication and to apply the same arguments to circuits
without
> > > > >>coating is totally unreasonable, because the conditions of
operation
> > are
> > > > >>totally different. Specifications have never considered this and
are
> > > > >>therefore useless. IMHO, the only thing to do is to determine
your
> > > > >>figure empirically. Unfortunately, this cannot be done overnight
and
> > > > >>requires great knowledge of how your products are going to be
used
> > and
> > > > >>under what climatic conditions. You can try accelerated tests but
> > they
> > > > >>are difficult, even impossible, to correlate with real-life
> > conditions,
> > > > >>but they may give you a starting point. If products coming back
for
> > > > >>subsequent repair show any signs of environmental damage, then
you
> > have
> > > > >>to tighten the figure. If they come back in a pristine condition
or
> > > > >>don't come back at all, then you may be able to relax your figure
> > > > >>slightly.
> > > > >>
> > > > >>Again, IMHO, no one here can advise you, without knowing a lot
more
> > > > >>about your products, the required reliability over a length of
time
> > and
> > > > >>the conditions of assembly, cleaning and use with a specific
figure.
> > It
> > > > >>may be that your 20 µg/cm2 is OK for you (although I very much
doubt
> > it,
> > > > >>as this figure is outside my knowledge of acceptable figures -
and I
> > am
> > > > >>one of the pioneers of ionic contamination testing, having worked
> > for
> > > > >>over three decades on this and related subjects).
> > > > >>
> > > > >>Please do not assume any figure is correct for you, without
> > > > verification.
> > > > >>
> > > > >>Brian
> > > > >>
> > > > >>Angela Gregor wrote:
> > > > >>
> > > > >>>First I wanted to thank you all for the gasket information you
> > gave.
> > > > >>>Evidently this forum is very much respected because I didn't get
> > any
> > > > >>>arguments from anyone here. Here's another one. At our company
we
> > are
> > > > >>>currently using Ionograph 500m version 3.02 to test our
assembled
> > > > boards
> > > > >>>after wash. Our pass/fail limit is 20 micro grams of sodium per
> > square
> > > > >>>centimeters. I'm not sure our calculation is correct, and I was
> > > > >>
> > > > >>wondering
> > > > >>
> > > > >>>what other companies pass/fail limits are for comparisons. I
called
> > > > >>
> > > > >>about
> > > > >>
> > > > >>>three places in my area and got three different answers. If this
> > helps
> > > > >>
> > > > >>most
> > > > >>
> > > > >>>of our boards are double sided. I would appreciate any
feed-back.
> > > > Thanks
> > > > >>
> > > > >>in
> > > > >>
> > > > >>>advance.
> > > > >>>
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