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December 2006

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Sun, 17 Dec 2006 17:17:46 -0800
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The ink is a heavy silver-fill with resistively less than 0.01 per square
when dried.  Is this something that I should worry about?  If so, where can
I find more information on the "migration risk" and how much to worry?

Thanks,
Carl


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dwight Mattix
Sent: Friday, December 15, 2006 6:43 PM
To: [log in to unmask]
Subject: Re: [TN] Membrane keypad failures

Is there any silver content in the conductive ink? If below 100 ohms/sq then
it probably has it intentionally and is a migration risk.

There the risk of unintended silver in carbon ink as well.  Long ago and far
away i lived through an ugly humidity keypad field issue on a test
deployment of wireless local loop phones in India.  Finally discovered we
were getting carbon ink that had residues of silver from previous mixes.
You throw that silver into the mix with a phone operating with an
continuously biased keypad, in a condensing monsoon environment in
Bangalore, and voila!  First failures came inside 30 days of fielding.

Thank goodness for Bangalore traffic -- the test system installers were
lucky to get around the city and install more than a couple phones/day.
Most of the hardware was still on the shelf and we were able to recall and
send reworked units to India and outfit a test system in Myanmar with
properly reworked and re-qual'd units in the nick of time.

The rework evolution and requal effort was a whole 'nother story involving
walnut shells, lemon pledge and BB's -- takes at least 3 beers to tell it
properly.  Still have that qual plan around here somewhere...

cheers,
dw


At 03:25 PM 12/15/2006, Carl VanWormer wrote:
>
>The dielectric is Electordag 452SS UV Curable Dielectric Coating.  The
>manufacturer says they coat with 2 layers to reduce the chances of a
>pinhole opening allowing a short circuit.  Is this a possible clue of
>something to chase for my humidity related shorts?
>
>Carl Van Wormer
>Cipher Systems
>
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert Lazzara
>Sent: Thursday, December 14, 2006 6:08 AM
>To: [log in to unmask]
>Subject: Re: [TN] Membrane keypad failures
>
>[log in to unmask] writes:
>
>have two  membrane keypads that have shown intermittent "short circuit"
>failures.
>Hello, Carl:
>
>OK, you've probably already looked for residual conductive ink between
>conductors, but look closer for dust. Over-cured thick film conductive
>polymers lose ductility and become [relatively] brittle. The
>"...wiggling,  banging..."
>you described could produce enough conductive particulate between  the
>circuits to yield an intermittent high-resistance short.
>
>I'm also wondering about your dielectric: What is the dielectric
>material (e.g., is it solder mask)?
>
>
>ROBERT LAZZARA

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