OK doc, I'll do as you say, but first, tell me what ions use to creep out of a typical silver epoxy (the gluemakers say there is soooo low ionic content that it's equal to nill)? If you don't dare because of the gluemaffia, tell me offline.
What mighty Ericsson?...Don't know him....oh, you mean the thin little guy with the too big costume...
Ingemar
-----Original Message-----
From: joyce [mailto:[log in to unmask]]
Sent: den 10 februari 2003 16:43
To: 'TechNet E-Mail Forum.'; 'Ingemar Hernefjord (EMW)'
Subject: RE: [TN] Back to 97, silver migration
Dig out original qual test performed by your material department
regarding the stuff and see if there is any infor... Make sure the
analysis was done based on the same cure parameter you used on the floor
(if you not cure the stuff, all the hell went loose...tough luck). I am
sure mighty Ericsson would keep all record and do the job properly at
old days. (the good old days...before someone get into Hell business
;-).
jk
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of Ingemar
>Hernefjord (EMW)
>Sent: Monday, February 10, 2003 10:33 AM
>To: [log in to unmask]
>Subject: Re: [TN] Back to 97, silver migration
>
>
>Joyce,
>
>what a rapid bounce! Two minutes after my 'send' there was
>click on my screen, and I saw your beautiful face, wow! Steve
>is not so sweet...
>
>Ionic extraction could be done, but it's not easy to remove
>the cured volumes, not bigger than what a fly leaves on your
>sandwich. The dispensed dots are some 50microns in diameter!
>We speak microelectronics.
>
>We could of cause dispense big silver epoxy volumes, cure and
>perform that analysis you mention, but it will be with a fresh
>epoxy tube, does not represent what was mounted years ago.
>What can be left after epoxy bleeding? I'm not so familiar
>with the stuff they put in.
>
>Ingemar
>
>
>-----Original Message-----
>From: joyce [mailto:[log in to unmask]]
>Sent: den 10 februari 2003 16:11
>To: 'TechNet E-Mail Forum.'; 'Ingemar Hernefjord (EMW)'
>Subject: RE: [TN] Back to 97, silver migration
>
>
>Inge,
>Can you do ionic extraction of your cured Ag epoxy? If it is
>higher than 40 microgram... Hmmm, what I can say...if it is
>40<x<100.... Not too bad, you should look other place. If it
>is more than 100 microgram...oh, boy, you have fun...(don't
>forget, you need add "+" and "-" together...Don't forget the
>organic complex either...hehehe). Now, let me ask you, did
>you cured stuff properly? (how many % cure? Within the 24 hr
>application of the stuff?). I am no Steve....Don't ask me more...
>
>jk
>
>>-----Original Message-----
>>From: TechNet [mailto:[log in to unmask]] On Behalf Of Ingemar
>Hernefjord
>>(EMW)
>>Sent: Monday, February 10, 2003 9:56 AM
>>To: [log in to unmask]
>>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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