Inge,
Thanks for the reply. Your information is very helpful, and perhaps I should have also consulted with my buddy Sherlock! Yes, different samples were sent to the 2 labs, since basically it is a destructive test - I think they pierce the can to extract the gases?.  Additionally, these components are > 1 year old, though they have been in my possession for a couple months. The RGA was done just recently.

Thanks,

Howard  Watson


From: Inge Hernefjord [mailto:[log in to unmask]]
Sent: Thursday, December 13, 2012 6:04 PM
To: TechNet E-Mail Forum; Watson, Howard A
Subject: Re: [TN] Component issue - epoxy die attach

Hi Watson..where is Sherlock Holmes as you need contact TN?

There is a lot to comment.     If we start with the second question, I assume you did NOT send one and the same test objects to the two labs. If you did, which is highly unusual, no wonder that you got so different results, because during the first RGA, vacuum is used, which gives free passage for the residual gas(es) to escape. If you then do the RGA -test with an other lab, you will of course read a lower value. If you did NOT use same test samples, it's still not remarkable that you got different values, because you don't get perfect components even if they had <<5,000 ppm. The reason is this: The sealing is done in a 20 ppm O2 environment, and do you perform RGA immediately after sealing, you measure on fresh packages filled with dry Nitrogen (or an inert gas). If one or two of the packages have a leak, there  will be an exchange of the inner and outer gas pressure i.e. water vapor will flow through the  leak and worse it will be, depending on how many days, weeks, pass between the two RGAs. Understood?

The other half of Q2 was, whether >>  5,000 ppm is negative for the component functions. Depends on the chips own protection (oxides, polymers.), but the answer is 'yes' in general terms. Examples: 1) NiCr etching 2) Bond pad corrosion  3)Metal migration  4) whisker formation 5) Dendrites 6) Lekage currents 7) parameter instability.

I  have some experience from this area and i have lots of saved reports. Before we continoue, I tell you that this is a labyrinth of opinions and interpretations of test methods, discussions of gas molecule's free medium way transportation through orifices, Hydrogen molecules that penetrates right through metal cans etc.

Will be back with more stuff..

Inge

On 14 December 2012 00:23, Watson, Howard A <[log in to unmask]<mailto:[log in to unmask]>> wrote:
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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