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Date: | Fri, 14 Dec 2012 07:29:40 -0600 |
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Hi Howard - Steve and Inge have provided you some good stuff so I can only
offer one additional detail. The reason for the 5000 ppm limit is that is
the' line in the sand' where you will get condensation inside a
hermetically sealed package as you go thru temperature swings. There are a
bunch of very fun mathematic equations which can be used to show that
below 5000 ppm you won't get condensation as you go thru the dew point.
With a reading of 5600, you may want to evaluate "are you good enough" in
terms of would water cause you issues in your product use environment.
Good Luck.
Dave Hillman
Rockwell Collins
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From: "Watson, Howard A" <[log in to unmask]>
To: <[log in to unmask]>
Date: 12/13/2012 05:25 PM
Subject: [TN] Component issue - epoxy die attach
Sent by: TechNet <[log in to unmask]>
Hello 'netters,
I debated posting this, as it seems to me to be an obscure problem, but
then, I'm always amazed at your knowledge base. I have a JFET 2N6550
component to be used for space application. Unfortunately, it is not
manufactured at JANS space quality, so we buy the commercial grade, plus
an option 2 screening, which upscreens the part to "like" JANTXV. I think
this is called re-branding. Then, we send it to a lab for further
upscreening to JANS. The problem is that the parts are failing the
moisture test of the residual gas analysis (RGA). I found out that epoxy
is used for the die attach, and likely the epoxy is outgasing during
subsequent baking as part of the testing. My first question is who knows
of a standard for die attach of this component type stating that epoxy is
forbidden for military and space use? The epoxy used by the manufacturer
is Ablestik p/n 84-1LMI; Material # 1119570. I just found out today that
they do have the capability of eutectic die attach, and I'm pursing this
option, expecting a huge expense and lead time.
Secondly, I had two independent labs perform the RGA. The first lab had
results averaging ~28,000 PPM. The second lab results averaged ~5600 PPM.
The standard is no more than 5000 PPM. They both performed the testing
to the same MIL-STD-750. I can't understand the wide range of results,
but my second question is who knows of any studies related to the negative
effects of excessive (>5000 PPM) moisture inside hermetically sealed
devices used in space? By the way, they all passed the seal tests.
Perhaps some of you are knowledgeable in this area. Thanks in advance for
your help.
Howard Watson
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