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Reply To: | TechNet Mail Forum. |
Date: | Sat, 8 Nov 1997 18:05:57 +0900 |
Content-Type: | text/plain |
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Metal migration is occasionally occurred when surface is exposed to
moisture and/or the substrate has high moisture absorption ratio. In fact,
with out moisture, the electrochemistry can not be processed. Therefore,
try to have a sort of passivation layer on the substrate to minimize
moisture attack.
Hope this will help.
Myung C. Chu, Ph. D.
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At 09:48 97-11-07 -0800, you 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.
>
CSS Asia Co., Ltd.
Tel: 82-2-523-8810
Fax: 82-2-523-1483
E-Mail: [log in to unmask]
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