Doug: You right... I think I was unclear in my discussion, as what you said agreed with what I MEANT to write.. we are in accord...at least in our thinking.
The reason why I wrote what I did is that I suspect that most folks do not realize that the units are Sodium Chloride EQUIVALENTS in conductivity, and think it really is Sodium Chloride....
Rudy Sedlak
"Douglas O. Pauls" <[log in to unmask]> wrote: Rudy,
I must disagree with you. My first job was at the Naval Avionics Center,
working with the late Bill Hobson and Bob Denoon, who is fortunately still
around.
Their initial work, the basis for all present day ROSE tests, the basis for
the Omegameters, etc., was to wash a solution of isopropanol and water over
a test board, examining the change in resistivity as materials moved into
solution from the rosin fluxes they were examining. They needed to
baseline the change in resistivity of the solution. As a basis for
comparison, they used the resistivity drop that occurred from a set amount
of an easily ionizable salt, in this case sodium chloride. That is why the
ROSE units are always given in sodium chloride EQUIVALENTS per unit area.
It would take that much sodium chloride to product an equivalent drop in
solution resistivity. The ROSE test has NEVER been related to the amount
of sodium chloride on a board, or the amount of sodium, or the amount of
chloride.
I have some of Jack Brous' old papers, as well as some I wrote, on the
topic, if anyone is interested. Perhaps I can send over to Steve. Both
Hobson and Denoon were horrified and amused at what the industry did with
their process control test.
Doug Pauls
R Sedlak
O.COM> To
Sent by: TechNet [log in to unmask]
cc
Subject
02/20/2006 03:46 Re: [TN] NaCl Contamination levels
PM on Plated Metal Parts
Please respond to
TechNet E-Mail
Forum
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to
R Sedlak
O.COM>
Joseph:
Just because it seems a good idea, I thought I might give some discussion
and background on this subject.
The "Sodium Chloride" concept was chosen as perhaps the worst possible
scenario. The Sodium Chloride is measured by the conductivity of warm
stagnant wash water, and virtually any soluble salt will increase the
conductivity, and thus register as "Sodium Chloride". In fact, it is
highly unlikely that these values are in fact Sodium Chloride, principally
because real Sodium Chloride is so soluble, and thus readily rinsed in
process rinses, from surfaces.
What the test is probably measuring are heavy metal salts, and
particularly, (perhaps this is now, or going to be, history) they were/are
likely Lead salts. This is because many/most Lead salts are particularly
slow to dissolve, and thus do not rinse readily, but will dissolve and
stand up to be measured, in the "Sodium Chloride" test.
Chloride is a strong corrosion accelerator, and one of the worst things to
have on an electrical device, but most of the moieties measured as Sodium
Chloride are not nearly as dangerous.
FYI..
Rudy Sedlak
RD Chemical Company
"Joseph H. Smith" wrote: Fellow technetters,
I realize that there is an expected specification levels for the NaCl
contamination of PCB's. Pardon me if I may be asking a dumb question, but
does plated metal such as housings and the like be under the same
specification limits for NaCl? Are there guidelines or documentation
within the industry which state this value? These are metals that may come
in close proximity to the PCB but necessarily mounted on the PCB.
Andrew Kettlewell
Sr Process Engineer
Sypris Electronics
Tampa, Fl
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