In a message dated 03/20/2000 11:29:04 AM US Eastern Standard Time, CSLPAT
writes:

>
>  Does anyone have experience with IPC-TM-650 method 2.3.38?  This test is
> specified as a manual way to detect surface organics.  Our first attempt
> found that even the untested solution left a visual residue.  The
> acetonitrile is the grade specified, but we are unsure of what is expected.

> We do not have easy access to analysis equipment to determine the source of
> the residue.
>
>  Dave Kell
>

Dave.
This test is a "quick and dirty" (pardon the pun) test for surface organics,
but is largely a meaningless test (in my opinion).  For those not familiar
with the test, HPLC grade acetonitrile (a known carcinogen) is dripped onto a
test substrate (e.g. circuit board) and the runoff collected on a glass
microscope plate.  The solution is allowed to dry.  If you have visible
residue, then you have a "contaminant".  As you have found out, even the
virgin HPLC grade acetonitrile leaves a faint residue.

This test suffers the same problem that all extraction-based test have.
First, the soil you are interested in must be soluble in the extract
solution.  If it won't dissolve in acetonitrile, you won't see it.  Second,
it must be soluble in the amount of time you allow for the extraction.
Running a solution over the board surface gives you only a few seconds of
contact time.  Third, the soil must be soluble at the temperature you choose.
 If the soil does not solubilize easily with room temperature acetonitrile,
you won't see the residue.

Now you run into the problem of test interpretation.  So you get a visible
residue on the glass slide.  So what?!  Is it a good residue or a bad
residue.  You have no way of knowing.  You might use the visible residue
together with the FTIR method found in test method 2.3.39, which is a more
analytical method.  You might be able to determine what organic compound is
present, but you are still left with the question of whether it is a good
residue or a bad residue.  I would suggest that you pick up a copy of IPC
J-Handbook-001 and read section 8.  It goes over the various residue
detection methods and what they mean.  Many test labs offer FTIR analysis.  I
can suggest a few if you are interested.

About the only use I can see for method 2.3.38 is as a process control.  If
you were able to do this test repeatably in the past with no appreciable
visible residue, and now are finding visible residue, something changed and
you better investigate.

What ever possessed you to try this test?  Is there a larger problem that you
are investigating, such as conformal coating not sticking?  Why are you
looking for organics?

Doug Pauls
Technical Director
Contamination Studies Laboratories

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