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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:
Mon, 18 Dec 2006 07:55:24 -0800
Content-Type:
text/plain
Parts/Attachments:
text/plain (101 lines)
I'm no materials guy and I don't know if all inks are created equal in the
extent they bind up silver but in the experience I had it was the silver
that caused switch failure.

Hey, if I was an expert at anything why would I be a QE? Where else is a
recovering VW mechanic supposed to go looking for work? ;^)

Have you looked at an undisturbed suspect under high magnification? You see
any dendrites or resisdue of growth that's been powdered by key action?

I'd encourage you to set up a sample in a humidity chamber with keypad
voltage applied and watch what happens (visually and to
isolation/resistance between sides of the key switch).

dw

At 05:17 PM 12/17/2006, carl wrote:
>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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