Don't forget that many epoxies (etc.) contain chlorides, resulting from 
the pre-polymerisation reaction between epichlorohydrin and sodium 
hydroxide. It is easy to leach some of this out, especially if the 
subsequent cross-polymerisation is not stoichiometric.

Brian

On 09/10/2012 02:29, Phil Bavaro wrote:
> 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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