John

This is the paper that I was referring to.

The people at Bell Laboratories Murray Hill studied silver migration for
years, because of the capacitor problem. I am not sure where they eventually
published the work, but they found there is an inventory threshold at about
40 micro inches (thick) below which silver does not migrate or at least the
rate is miniscule.

Best regards

Lee

J. Lee Parker, Ph.D.
JLP Consultants LLC
804 779 3389

----- Original Message -----
From: "John Barnes" <[log in to unmask]>
To: "(Leadfree Electronics Assembly Forum)" <[log in to unmask]>; "Lee parker"
<[log in to unmask]>
Sent: Sunday, August 20, 2006 2:18 PM
Subject: Re: [LF] Silver Migration


> Lee, Harvey,
> Checking my bibliography on lead-free electronics at
>    http://www.dbicorporation.com/rohsbib.htm
> the only item that I can find by Wenger and Furrow is
>
> Wenger, George M., and Furrow, Robert G., "Immersion Silver Surface
> Finish: Usage Requirement Test Results &  Production Experience,"
> Proceedings of the AESF SUR/FIN 2000, Chicago, IL, June 26-29, 2000, pp.
> xx-xx.
>
> Is this the one that you were referring to?  (I won't have access to the
> paper itself until I get home, in about a week.)
>
> I hit 9 engineering/science libraries in Missouri, Kansas, Colorado,
> Utah, and Oregon during my drive from Lexington, Kentucky out to
> Portland, Oregon for the IEEE EMC Symposium.  So far on this trip I've
> found about 30 additional papers, going back to 1869, that were on my
> want list at
>    http://www.dbicorporation.com/rohswant.htm
> I intend to hit the libraries at another 7 engineering schools on the
> drive back home.
>
> At the University of Colorado - Boulder I ran across:
>
>    Ditz, M. J., "Determination of the Moisture Threshold for Silver
>    Migration,"  Proceedings of the 20th International Symposium for
>    Testing and Failure Analysis, Los Angeles, CA, Nov. 13-18, 1994, pp.
>    181-187.
>
> This paper says that approximately 40% relative humidity (RH) is
> required for silver migration to occur.  They used chip capacitors
> attached to a hybrid with silver epoxy for their tests.  The gaps
> between exposed silver particles in adjacent joints were in the micron
> range.  With 50V bias at 50C, they saw one failure withing 48 hours at
> 43% RH.  At 40% RH they saw no failures in an additional 640 hours,
> whereupon they terminated the test.
>
> I hope that this helps!
>
> John Barnes KS4GL, PE, NCE, NCT, ESDC Eng, ESDC Tech, PSE, SM IEEE
> dBi Corporation
> http://www.dbicorporation.com/
>
>

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