Check extractable ionics of the Ag epoxy for randomly selected 5 to 10 tubes. Ionics can come from vendor wash SS container, or Ag flake producer using some chemical to prevent them stick together. Not everybody can make electronic grade good silver epoxy. The chap charge a few extra pennies usually do have a Good reason or two to do so.
--------------------------
Sent using BlackBerry
----- Original Message -----
From: Graham Naisbitt [mailto:[log in to unmask]]
Sent: Thursday, July 08, 2010 10:09 AM
To: [log in to unmask] <[log in to unmask]>
Subject: Re: [TN] Underfill as a Remedy for Electro Migration?
Leif-Erik
In either option it will be important for you to consider outgassing issues IF your application is bound for space....
Ag + H2O + Electricity = electromigration? I am guessing there might be some ionics also involved? Maybe a conformal coating would help more, but cleaning might be a better route?
Just please keep-in-mind that a coating, even an underfill, seals in as well as out and you might actually exacerbate the problem rather than overcome it.
Regards
Graham Naisbitt - KBO
Email: [log in to unmask]
Phone: +44 (0)12 5252 1500
Web: www.gen3systems.com
On 7 Jul 2010, at 23:11, Leif Laerum wrote:
> Technetters,
>
> We have identified electromigration as the root cause of some field failures we have been seeing. During the troubleshooting we came across the following NASA paper. All of the details of this paper fits our situation perfectly. We use the same package as described.
>
> http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/40854/1/08-23.pdf
>
> The executive summary is that the silver in the epoxy used to attach as die attach migrated to create a short. The migration was triggered by humidity.
>
> The paper suggests using underfill or conformal coating to remedy the problem. Currently we do not use either in our process. I have some questions regarding these:
>
> - What are the pros and cons using either of these for this particular purpose? IMO underfill seems the best solution for us.
> - Does anyone have any experience as to whether this is a good solution? I am not quite understanding the "chemistry" here.
> - Does anyone have a recommendation as to what type of underfill would work well for this application?
>
> Thank you for your input.
>
>
>
> --
> Leif Erik Laerum
>
>
>
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