Thanks Dave,
those elements (EDAX) is exactly what we found, that's why I suspect human debris. Old NASA (think it was) reports show that spittle can be disatrous for hermetic packages. All people ought to use masks, from wafer manufacturing to final inspection of the hybrids. We don't. Maybe time to rethink...
Ingemar Hernefjord

-----Original Message-----
From: David Fish [mailto:[log in to unmask]]
Sent: den 11 februari 2003 15:01
To: TechNet E-Mail Forum.; Ingemar Hernefjord (EMW)
Subject: Re: [TN] Back to 97, silver migration


Ingemar

In response to one element of your question:

Saliva is made 99.5 percent of water and 0.5 percent of dissolved inorganic
compounds. One third of the 0.5 percent are dissolved metal-ions such as
Ca2+, Na+, K+, Cl- and PO43-. The remaining two thirds are organic
substances, among which long and complicated molecules-proteins-dominate.
These proteins tend to affect the viscosity of the saliva: the less the
total amount of water, the higher the concentration of proteins. Thus, if
there is a deficiency of water in the body, the saliva becomes 'thicker'.

Dave Fish

----- Original Message -----
From: "Ingemar Hernefjord (EMW)" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, February 10, 2003 9:56 AM
Subject: [TN] Back to 97, silver migration


> Hi Techies,
>
> anyone who remember the mails that come after my lines?
> If the guys at that time (97) aren't retired and are golfing and surfing
> in Florida, I would like to chat about the headline issue, because we have
seen some odd things likely. My worry is about human debris (spittle) and
epoxy bleeding. What does saliva contain, and what's in the silver epoxy
bleeding remnants? Silver migration took place between Au/Ag thickfilm
conductors and also across MIS chips. In the later case, Ag migrated from
the silver epoxy, across the MIS chip and climbed up on the gold bond wire.
Yes,really weird.
>
> I'm not so interested in 'qualified' guessings as in experiences from
people around the TN. We have had a lot of guessings ourselves, but need
corrective actions asap.
>
> I could of cause call Mike Fenner, but he is only 0.1% of TN, so there is
a chance that someone more are familiar with the sweet problem.
>
> Wonder what will migrate out of this?
>
> Ingemar Hernefjord
>
> Ericsson  Microwave Systems
>
> PS. Unfortunately, I don't know who 'Steve' was. Can't be Steve
Gregory,because he knows all secrets  himself, and is teaching others.
>
> ------------------------------------------------------------------
>
> teve wrote:
> >
> > All,
> >
> > Background;
> >
> > I'm being consumed by a hybrid failure suffered by one of my
> > subcontractors. The cause of failure is silver bridging two gold
> > conductors metallized on an alumina substrate. In DC mode, one conductor
> > is at -5.5V, the other at +28V. The conductor spacing is ~146 microns.
> >
> > The silver is from an epoxy die attach on the +28V conductor. The silver
> > bridging the conductors is a combination of deposited (workmanship) and
> > dendrite (electrochemical) formation. The deposited silver is half on
> > the -5.5V wire-bond land and half bridging the alumina. Dendrites form
> > the rest of the bridge across the alumina. Dendrites are also observed
> > *IN* the silver epoxy die attach.
> >
> > Now for the question;
> >
> > 1)Understanding the conditions necessary for silver (electrochemical)
> > migration, how could silver dendrites form *IN* the silver epoxy? There
> > shouldn't be any potential difference *IN* silver epoxy.
> >
> > 2)How could the +28V silver migrate out of the epoxy die attach across
> > the +28V gold metallization then across the alumina? The silver die
> > attach was completely within the +28V gold metallization. Again, no
> > potential difference to "steer" migration. Oddly, an identical config in
> > the same hybrid did have +28V silver epoxy squeeze out into the alumina
> > bridging 1/3 the way to -5.5V. No silver migration observed there.
> >
> > If any one can help, I can be reached @ steve.r.anderson @ trw.com
> > (remove the spaces before & after the @).
> >
> > I can post optical & SEM/EDX images to our ftp site but they will be
> > removed after 24 hrs.
>
> Steve
>
>
>
> ------------------------------------------------------------------
>
> Silver is one of the few metals that will form "single crystal"
> wire-like filaments when subjected to stress.  In fact, in the
> literature, it was reported back in the '30 forming filaments on the
> same conductor/plated surface.  I suspect the epoxy is expanding due to
> thermal stress which stresses the silver and then the silver forms the
> filaments.
>
> Silver has always been a reliability concern inelectronic assemblies.
>
> Hope this helps.
>
> Ralph
> --
> Ralph Hersey
>
> Ralph Hersey & Associates
> 3885 Mills Way
> Livermore, CA 94550-3319
> PHN: 510.454.9805
> FAX: 510.454.9805
> e-mail: [log in to unmask]
>
> ----------------------------------------------------------------------
>
> Hi Steve,
>
> you`re describing interesting phenomena. Unfortunally I don`t have a
> global answer but one (perhaps weird) idea relating to your first
> question, how migration can take place in the silver epoxy. Let try me
> to explain my thoughts:
>
> At first, conduction in silver filled epoxies is in principal done by
> random contacts between the randomly placed silver particles. Lets
> assume there are two adjacent conducting paths formed by particles
> contacting each another, but not particles of the other path (the two
> pathes are isolated from each other). One path is at +28 V, the other
> one (probably short and located at the edge of the conductive glue) is
> isolated. Now lets assume migration starts and dendrites grow from the
> -5.5 V side towards the +28V side. Where will they reach the +28V side?
> Perhaps by chance at first at the isolated path. This path then drops
> down to -5.5V and you`ve got two very close conducting paths in the
> epoxy with a potential difference of 33.5 V. Now one has: silver, high
> field strength, some ionic impurities (which are resulting from the
> chemicals used in the manufacturing of the epoxy), obviously moisture -
> migration starts.
>
> As I understand from your mail, you got a chip land covered with silver
> filled die attach epoxy and some bondpads very close (146 micrometers
> seems to be unusual close to me). The epoxy is sometimes squeezed out
> over the chip land, thus reducing the distance furthermore. The first
> idea to reduce migration issues is to get bigger distances.
>
> If, as you wrote, migration under identical build up conditions in some
> cases took place and in others didn´t, I would look carefully on
> moisture issues which will be probably different in these cases.
>
> By the way, if you can post pictures to your ftp-side, you should also
> be able to include them in emails. But to not upset some technetters by
> getting megabyte big mails, if you like, you could send them directly to
> me. I would be interested in receiving them.
>
> Greetings,
>
> Ulrich Korndörfer
>
>
> ----------------------------------------------------------------------
>
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