Good morning Phil,
So your candidate process passes ROSE and passes SIR, but "fails" an IC
test. If you use the IPC-9202 criteria, your candidate process "passes".
That is because 9202 is based on SIR as the metric to pass. IC is taken
to benchmark what you have in terms of ionic residues. 9202 does not give
a pass or fail for IC data, so this must be from other studies.
Your testing of controls has shown you what your overall problem is. Your
incoming boards, bought as a commodity item, are not clean. So, either
your pre-cleaning process was not effective, or the chloride residues of
interest are soaked into the assembly and do not come out except in IC
extraction. If you still have some of the as-received boards, take one
and pass it through reflow with no other application of flux or cleaning.
If you see a big jump in residues, you have a problem with the solder
mask.
You ask what you should get, ionic-wise, from a standard water soluble
process. There is no such thing. All fluxes will have their own
interactions with the substrates or materials of construction, which is
why in 9202, if you are qualifying a manufacturing process, the B52 is
made from your intended material set from your intended fabricators. That
way, if you saw the same thing with your polyimide substrate and your
chosen mask and surface finish, then you have a problem with your fab
source, not your process.
Since your process is just over the 0.9 limit you indicate, you can expect
for it to be lower with polyimide, since that has a lower chloride
content.
Doug Pauls
From: Phil Bavaro <[log in to unmask]>
To: <[log in to unmask]>
Date: 10/08/2012 06:31 PM
Subject: [TN] ION CHROMATOGRAPHY - EXCESS CHLORIDE CONTENT
Sent by: TechNet <[log in to unmask]>
We have some results that have left me puzzled. We are processing the
IPC B-52 test PWAs using water soluble paste/flux and we can pass the
ROSE test (of course) and the SIR test, but fail the IC test for
excessive choride anion content.
Here is what baffles me.....our control sample is similar and worse than
the test samples.
There seems to be some documentation that the chloride ion might be
related to mishandling and/or soldermask not being properly cured but I
don't have any experience with this test result so I am not sure how to
respond to that (hopefully Terry will chime in on this). We processed
all the samples using the proper gloves and bags and doubt that we
contaminated them.
We are trying to meet the requirement of 0.9 micro-gm/cm-cm maximum and
our failing control sample is 3.36, one test sample is 4.67, and the
other two samples are running at .91 and .90. What value for chloride
anion content does a normal WS process yield? Are these numbers way out
of range for normal test results or is chloride always a pesky result?
I am looking for the answer to the question "is this really a problem?"
The control sample was washed but did not have any paste applied to it
at all. The test samples were run through the full assembly reflow
process then cleaned and Rose tested before shipment to the lab.
All the rest of the results for the IC test are passing so I don't know
quite how to proceed from here.
My current plan is to run another set of tests with more than one
control sample, and then to simulate various phases of clean (IOW barely
cleaned, half cleaned, and then a couple of fully cleaned samples). As
I am not really familiar with IC test results, I want to see the what
the constituents of the "dirt" really look like from an IC test
perspective as well as repeat the previous test results.
One item I have noted is that we did not have our chosen board supplier
build these boards but instead bought these off the shelf from one of
the dummy component suppliers. But the thought was that as long as they
were cleaned using our normal process, they should be acceptable.
These particular test samples use FR4 and not the high Tg polyimide that
most of our PWBs are built from.
Any comments on this would be appreciated.
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