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December 2006

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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:
Fri, 15 Dec 2006 18:42:31 -0800
Content-Type:
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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
>1800 NW 169th Place, Suite B-100
>Beaverton, OR  97006
>Phone (503)-617-7447 extension 20
>
>
>
>-----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
>
>In a message dated 12/13/2006 2:01:54 P.M. Eastern Standard Time, 
>[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
>VP, Business Development
>T: (800) 560-9457
>F:  (800) 878-5566 (y servicio de mensaje espaņol)
>E:  [log in to unmask]
>W:_  www.CircuitConnectUSA.com_ (http://www.CircuitConnectUSA.com)
>
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