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Subject:
From:
Brian Ellis <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Sat, 13 May 2000 09:14:05 +0300
Content-Type:
text/plain
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text/plain (78 lines)
Scott

Chlorides -and their relatives, bromides - can come from many sources,
let's group them together under halides. Many fluxes, including HASL, as
well as soldering, contain halides, as do some etching and plating
solutions. Even your FR-4 substrate contains halides, including small
quantities of sodium chloride, in some cases. The only way of tracing
the source is by systematic analyses. That having been said, if you have
poorly selected the soldering flux/paste and, if relevant, the cleaning
process, this would seem a likely starting place to look.

>From your description, it seems likely your halides are inorganic. As
such, they are readily ionised and a cheap way of doing the tracing is
with an ionic contamination tester (e.g. Contaminometer, Omega Meter,
etc...).

Let it be said that halide activated fluxes/pastes are generally easier
to use than those with weakly ionisable acid activators, so you may be
looking at a trade-off between the ease of the soldering process against
reliability, especially if you are not subsequently cleaning. If you are
cleaning after soldering, almost certainly - if there is no possibility
of subsequent contamination - your cleaning process would merit a close
examination. Post-contamination sources may include sea spray or road
spray from salted roads etc.

We need to know more before being more positive - or hire a consultant.

Hope this helps

Brian

"Scott B. Westheimer" wrote:

> I was wondering if any one has encountered chloride contamination on
> the surface of a loaded PCB. I had an interesting conversation with
> one of our customers yesterday that informed me that they had a
> problem with loaded boards in the field failing. During their
> investigation they disassembled the boards and tested they and found
> no shorts or failures. They then re-populated the boards and tested
> again. Once again no failure. They then placed the boards in a
> temperature/humidity chamber and cycled them. During this test the
> boards shorted and failure. Analysis of the surface was performed and
> chloride was one of the material found. The theory is that during
> accelerated aging the chloride is causing the parts to fail and they
> believe that the chloride is coming out of the S/M. Has anyone
> encountered a similar problem?  I have look at the S/M and do not find
> any mention of it containing chloride. Can the S/M be absorbing
> chloride during wave solder from the flux? Interesting. Scott
> Westheimer

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