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July 2009

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From:
"Thayer, Wayne - IIW" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Thayer, Wayne - IIW
Date:
Wed, 15 Jul 2009 14:07:33 -0400
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1. I believe EpoTek, manufacturer of the ubiquitous H20E, has done a bunch of studies of electromigration of silver epoxies.  I would check out their website and call them up.  What killed conductive epoxy for a Pb-free attach technology wasn't electromigration, it was that it won't reliably connect to tin metallization.
2. If you coat with silcone gel, then you will be fine.  I believe there is silver epoxy in under hood apps which is coated with this stuff.  But, of course, silicone gel is a very nasty contaminant/particle getter.  We call it "snot" here.

Wayne Thayer

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of John Burke
Sent: Wednesday, July 15, 2009 1:50 PM
To: [log in to unmask]
Subject: Re: [TN] Silver epoxy

Exposed PWB

John Burke
(408) 515 4992
-----Original Message-----
From: Steven Creswick [mailto:[log in to unmask]]
Sent: Wednesday, July 15, 2009 10:29 AM
To: 'TechNet E-Mail Forum'; John Burke
Subject: RE: [TN] Silver epoxy

John,

We did do not experience electro-migration problems in a hybrid or multi-chip module so long as long-term hermeticity was maintained - to keep the moisture out.

From my perspective, PEMs - plastic encapsulated modules do not possess long-term hermeticity characteristics [am sure to ignite a firestorm with that], but they certainly do well in the short-term, and under reasonable environmental challenges.  They delay the ingress of moisture - do they delay it long enough for your application is the question.  Optically clear molding compounds tend to be worse because - 1) there are no expansion modifiers present [dah!, it's clear], 2) they just don't have the ruggedness of the filled versions ...

Therefore, whatever you do to delay the ingress will be to your benefit.
Paralyene, some of the new hydrophobic plasma coatings, careful selection and processing [storage, handling, molding and post-cure] of the mold compounds, plating on the lead-frame or PWB.

Depends on your requirements....  just a matter of time & voltage, it would seem.


You did not really say whether your application was over-molded, exposed PWB, etc...

Steve



-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of John Burke
Sent: Wednesday, July 15, 2009 1:09 PM
To: [log in to unmask]
Subject: [TN] Silver epoxy



Many years back (too many) I was working on silver epoxy connected hybrids for high reliability applications.



I seem to recall that silver migration is a definite issue. Does anyone have any rules for mitigating this risk such as design clearances between pads etc?



Best regards,





John Burke

Director of Operations





http://www.optichron.com

4221 Technology Drive

Fremont, CA 94538



Cell (408) 515 4992

Desk (510) 249 5233

Main (510) 249 5200




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