TECHNET Archives

December 2006

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
Reply To:
Date:
Mon, 18 Dec 2006 10:18:44 -0800
Content-Type:
text/plain
Parts/Attachments:
text/plain (136 lines)
I have a new keypad set up with a bias voltage (5V) and a series resistor
(20k) in a big plastic bag with a cup of water.  I know this is not test-lab
quality, but it should let me know if I have a problem.  So far (4 days), no
problem . . .

The previous (bad) units would "grow" shorts when biased at 5V with a 20k
resistor.  When the resistor was changed to 2k, the shorts would disappear.
I think they must have been very thin and the 2.5mA current blew them open.

Thanks,
Carl


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dwight Mattix
Sent: Monday, December 18, 2006 7:55 AM
To: [log in to unmask]
Subject: Re: [TN] Membrane keypad failures

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

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e To
unsubscribe, send a message to [log in to unmask] with following text in the
BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or
(re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet
NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send
e-mail to [log in to unmask]: SET Technet Digest Search the archives of
previous posts at: http://listserv.ipc.org/archives Please visit IPC web
site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100
ext.2815
-----------------------------------------------------

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------

ATOM RSS1 RSS2