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November 2005

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Subject:
From:
"Stadem, Richard" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard
Date:
Tue, 29 Nov 2005 12:44:38 -0600
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I like those words used together; reliability and due diligence. 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dwight Mattix
Sent: Tuesday, November 29, 2005 12:27 PM
To: [log in to unmask]
Subject: Re: [TN] Humidity and enclosed RF board

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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