I think Brian is the real source of knowledge here. Iono chrom or SIR or
ROSE or whatever you name the common two methods have some disadvantage:
takes time. Furthermore, if you solve some concentration of Na ions (used
as base reference) from some part of the board, what do you get out of that?
And the ug levels are arbitrarily set, more or less. We prefer a more
practical way, not superseding the two above, but most of the time good
enough for daily checking. The first one is simply illumination with purple
light, inspection done under stereo microscope in total darkness. Organic
veils and particles like glue residues, flux, fingerprints, fat and other
unwanted debris lights up even being as small as micron sized. It takes
just minutes to overlook a board. Another method is to provoke possible
dangerous debris, whatever ion kind, simply by biasing a board in a humidity
box and at elevated temperature, followed by visual inspection. This kind of
test reveals real contaminations that could be a serious issue when operated
by the customer. Even the tinest little migration can be seen with a good
set of microscopes and with variable beam colour. Neither of the described
methods can be refered to any standards or other papers, and neither can be
put in the hands of whom else. However, if you are happy enough to have a
sharpeyed and experienced analyst at hand, you can do some very handy, fast
and cheap inspections on sample basis. I don't say that the described
methods are better nor that they correspond to ROSE/SIR, they just let you
see the issues with your own eyes instead of scratching head about
micrograms of this and that.
Gaggyman or Metusalem or Professor Calcule (they have many names on me, the
striplings at my work)
/Inge
----- Original Message -----
From: "Graham Collins" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, October 30, 2009 3:19 PM
Subject: Re: [TN] Cleanliness
Hi Blair
There are always other options! What's your budget??? I'm sure Bev and
Inge could give you analysis down to the last molecule...
ROSE is a good process monitoring tool. IMHO, its biggest weakness is
that it does not tell you what type of ionic contamination you've got -
which is an important distinction.
My preference is to use ion chromatography testing to determine what's
on the assembly in what quantity. When you are content with those
results, a ROSE test on the same product made the same way will give you
a benchmark.
regards,
- Graham
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Blair Hogg
Sent: Friday, October 30, 2009 10:40 AM
To: [log in to unmask]
Subject: [TN] Cleanliness
A ROSE by any other name would smell as sweet, right SIR?
Happy Friday, Technetters! As you may have guessed, I've spent a bit of
time
over the last few days looking over cleanliness testing specs, searching
through the archives and what not to get more information on the
different
types of testing. Now it is time to visit the well of knowledge and see
if the
Technet gurus can help me along the road to cleanliness enlightenment.
>From what I understand, the ROSE test measure the change in resisitivity
/
conductivity of a test solvent solution (75% IPA / 25% DI Water) that is
rinsed over a board / assembly. This will detect contaminants and
provide a
relative level of the contamination. However, it will only detect those
contaminants that are ionic in nature or will affect the resistivity (is
that
redundant?). The results are near immediate.
The SIR test measures the insulation resisitance change that occurs when
an
assembly is exposed to humidity and voltage, and thus has the capability
of
detcting the presence of contaminants that may not be ionic, but can
cause
corrision and / or dendrites to grow. The drawback is that the samples
must
be exposed to controlled humidity / temperature for a priod of time.
Does that sound right? Am I missing anything?
Are there any other options?
Thanks,
Blair
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