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 -----------------------------------------------------