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November 2005

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Subject:
From:
Dwight Mattix <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Dwight Mattix <[log in to unmask]>
Date:
Tue, 29 Nov 2005 10:26:51 -0800
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At 09:34 AM 11/29/2005, Eric CHRISTISON wrote:
>Agree with Richard about the environment. Letting the enclosure breathe is
>also a good plan; how many mobile phones fail due to humidity related
>failures?

The answer is a very large number -- if the pwb and assembly are not
clean.  In layman's terms think of it like the fire triangle -- remove one
leg and the fire goes out.  If you can't remove potential or humidity then
ensure an ionic clean assembly and avoid surface finishes prone to
dendretic grow (e.g. silver in carbon ink, traditional immersion tin
finishes) and the electromigration problem should be thwarted.

Back in the 90's I dealt w/ big electro-migration problems (talking massive
recall) in wireless local loop phones.  They weren't even mobile
phones.  In that case they were installed in a condensing
residential/office environments (India in monsoon season).  The root cause
fix in that particular case was in the cleanliness of the bare pwb.

To the original question:
Test and verify.  Do your reliability due diligence -- sacrifice some
hardware to science.

my $.02
dw

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